Abstract 12 - 7th AGC Geosciece in the Development of Natural Resources Sydney 1984 by GSAustralia

Geological Society of Australia

ABSTRACTS NUMBER 12

GEOSCIENCE IN THE DEVELOPMENT OF NATURAL RESOURCES Seventh Australian Geological Convention Sydney, 1984

Geological Society of Australia Abstracts NUMBER 12

G E O S C I E N C E IN THE DEVELOPMENT OF NATURAL R E S O U R C E S

Seventh Australian Geological Convention Sydney, 1984

Geological Society of Australia Incoi^>orated Office Bearers 1983-1984

President

M.J. Rickard

Vice-Presidents

R.D. Gee, J.B. Waterhouse

Hon• Secretary

P.A. Smith

Hon• Treasurer

P. Wellman

Hon• Administrative Officer

D.H. Probert

Seventh Australian Geological Convention, 1984 Organizing Committee

Convener

R.A. Binns

Secretary

G.F. Taylor

Assistant Secretary

K.M. Scott

Treasurer

R.H. Flood

A.S. Andrew

B. Marshall

R.A. Creelman

J. McAndrew

L.B. Gilligan

J.W. Pickett

P.B. Hostetler

G.D. Pooley

M.B. Katz

S.R. Sangameshwar

G.G. Lowder

S.E. Shaw

E.C. Leitch

M. Smyth

M. J. Lennox

F.L. Sutherland

N.L. Markham

D.J. Whitford

Published by the Geological Society of Australia Incorporated Challis House, 10 Martin Place, Sydney IFSN ISBN

0729-011X 0 909869 38 3

NEW ERA PRINTING COMPANY - 570-5288.

ACKNOWLEDGEMENTS The Organizing Committee of the Seventh Australian Geological Convention expresses its sincere thanks to the many persons, companies and other organizations who have assisted the organization and holding of the Convention. Particular appreciation is recorded of the assistance received from the following companies and organizations:

Aberfoyle Exploration Proprietary Limited Ampol Exploration Limited Ansett Airlines of Australia Australian Academy of Science The Broken Hill Proprietary Company Limited BP Minerals Australia Limited CRA Exploration Proprietary Limited CSIRO Institute of Energy and Earth Resources CSR Limited The Earth Resources Foundation within the University of Sydney Esso Australia Limited Freeport of Australia Incorporated Geological Society of Australia Incorporated and the Specialist Group in Economic Geology Geological Survey of New South Wales, Department of Mineral Resources Getty Oil Development Company Limited Macquarie University National Australia Bank New South Wales Institute of Technology Poseidon Limited Santos Limited The Shell Company of Australia Limited Southern Pacific Petroleum N.L. University of New South Wales University of Sydney Utah Development Company Western Mining Corporation Limited

Geological Society of Australia Abstract Series Number 12

C O N T E N T S

Convention Symposia

Specialist Group Symposia

Convention Workshops

Abstracts, alphabetically by author

Author index

571

CONVENTION SYMPOSIA CONVENTION KEYNOTE Monday 27 August Chairman: R.A. Binns 11.00 - 12.00

ADDRESS

Venue: Macquarie Theatre

W.S. FYFE Energy options and the environment NON-METALLIC

SYMPOSIUM Al

Convener: Poster Paper:

MINERALS

GEMSTONES Dr. B.J. Franklin T. COLDHAM, B.J. FRANKLIN and A.D. GILES •Inclusions in Australian sapphires.

Monday 27 August Session 2 11.00am - 12.40 pm Chairman: B.J. Franklin

Venue: E7B T5

11.00 - 11.40

T. COLDHAM KEYNOTE ADDRESS The Australian Sapphire Industry - "Selling wheat and not knowing the price of flour."

11.40 - 12.00

J.D HOLLIS Characterising zircon - corundum assemblages in eastern Australia.

12.00 - 12.20

S.R. LISHMUND and G.M. OAKES Sapphires and diamonds in NSW - are Tertiary diatremes and related pyroclastics the answer?

12.20 - 12.40

W.S. YIM, A.J.W. GLEADOW and J.C. VAN MOORT Origin of zircons and sapphires in stanniferous deepleads of northeast Tasmania.

Monday 27 August Session 3 1.40pm - 3.20pm Chairman: J.L. Gordon

Venue E7B T5

1.40 -

2.20

R. BRIGHTMAN Gemmological attributes of the common rock forming minerals.

2.20 -

2.40

D.J. FLINT, E.A. DUB0WSKI and J.G. 0LLIVER Nephrite jade near Cowell, South Australia.

2.40 -

3.00

P.J. DARRAGH and R.E.T. HILL The geology and geochemistry of an emerald deposit at Warda Warra near Yalgoo Western Australia.

3.00 -

3.20

L.C. BARNES South Australian opal fields - similar but different.

Monday 27 August Session 4 3.50pm - 5.30pm Chairman: J.L. Gordon 3.50 -

Venue: E7B T5

4.30

P.J. DARRAGH Instruments in gemmology.

4.30 -

4.50

J.G. OLLIVER and L.C. BARNES Government subsidised exploration for opal at Andamooka and Coober Pedy.

4.50 -

5.10

P.A. TEMBY, F.L. SUTHERLAND and J.D. HOLLIS Distribution and possible origin of diamonds in Eastern Australia.

SYMPOSIUM A3

INDUSTRIAL

MINERALS

Convener:

Mr. D. Nichol

Poster Papers:

M. CREECH Torrington topaz - its industrial potential.

Tuesday 28 August Session 1 8.30am - 10.30am Chairman: J.G. Olliver 8.30 -

8.50

INTRODUCTION

Venue: W5A T2

8.50 -

9.30

B.M. COOPE KEYNOTE ADDRESS Australia's role in world industrial minerals markets - player or spectator

9.30 -

9.50

E.P. AMBLER Serpentine for steel making in Australia.

9.50 - 10.10

B.G. LEES Processes responsible for the development of industrial silica resources in coastal sands, eastern Australia.

10.10 - 10.30

E. KREUTZER and D. NICH0L The geological distribution, mining and utilisation of industrial grade magnetite in eastern Australia.

Tuesday 28 August Session 2 11.00am - 12.40pm Chairman: K.R. Steggles

Venue: W5A T2

11.00 - 11.20

F.C. LOUGHNAN The nature and origin of kaolinite clayrocks.

11.20 - 11.40

A. DRIESSEN, D. NICH0L and R. TOWNER A perspective and historic review of industrial minerals in Australia.

11.40 - 12.00

S.R. PEC0VER Friable sandstones of the Sydney Basin - a major source of industrial and construction sand for the Sydney market.

12.00 - 12.20

J.E. SIEM0N and M.S. BIGGS Exploration techniques used in the evaluation of two limestone deposits in central Queensland.

12.20 - 12.40

L.C. BARNES and J.G. 0LLIVER Some industrial minerals of South Australia.

SYMPOSIUM A5

CONSTRUCTION MATERIALS, RESEARCH M A N A G E M E N T AND

ENVIRONMENTAL

GEOLOGY Convener:

Dr. I. Wallace

Tuesday 28 August Session 3 1.40pm - 3.20pm Chairman: E.J. Minty

Venue: W5A T2

1.40 -

2.00

R.W. CORKERY Quarry planning in the Bringelly Shale, Sydney.

2.00 -

2.20

J.M. HANN The commercial potential of marine sands.

2.20 -

2.40

M.N. HIERN Rehabilitation of Stonyfell Quarry near Adelaide South Australia.

2.40 -

3.00

I.E. STEWART Asbestos-bearing rocks in construction operations - potential hazards.

3.00 -

3.20

I.W. McHAFFIE Stone resources for the Melbourne metropolitan area.

Tuesday 28 August Session 4 3.50pm - 5.30pm Chairman: D.A. Nicholson

Venue: W5A T2

3.50 -

4.10

G. W. HOFMANN Geological investigation of construction material resources for planning purposes.

4.10 -

4.30

V. SMITH Difficulties in establishing quarrying operations under the New South Wales planning legislation.

4.30 -

4.50

I.' WALLACE How can government bodies set aside extractive resources for future development?

4.50 -

5.30

GENERAL DISCUSSION

WATER SYMPOSIUM

Convener:

HYDROGEOLOGY, EXPLORATION AND DEVELOPMENT OF RESOURCES

GROUNDWATER

Mr. W.H. Williamson

Thursday 30 August Session 1 8.30am - 10.30am Chairman: W.H. Williamson

Venue: E7B 100

8.30 -

9.10

M.A. HABERMEHL Hydrogeology and development of groundwater resources of the Great Artesian Basin.

9.10 -

9.30

L.W. DRURY and R.C. HARW00D Municipal water supplies along the N*S.W. coast, Australia.

9.30 - 9.50

N.Z. GERGES The Stuart Highway: environment.

9.50 - 10.30

a case study in groundwater supplies in an arid

D.R. WOOLI.EY and R.M. WILLIAMS The hydrogeological framework of the New South Wales section of the Murray Basin.

Thursday 30 August Session 2 11.00am - 12.40pm Chairman: D.R. Woolley

Venue: E7B 100

11.00 - 11.40

K.V. SHETTIGAR Electrical resistivity investigation of the Schofield high-level water body, Oahu, Hawaii.

11.40 - 12.00

R.M. WILLIAMS Hydrogeology and hydrochemistry of groundwater associated with the Young Granodiorite near Young, N.S.W.

SYMPOSIUM B4 Convener:

HYDROGEOCHEMISTRY Mrs. A.M. Giblin

Tuesday 28 August Session 1 8.30am - 10.30am Chairman: P.B. Hostetler

Venue: E7B T4

8.30 -

8.50

M.A. HABERMEHL Hydrochemistry of the Great Artesian Basin.

8.50 -

9.10

A.R. CHIVAS, I. BARNES, J. LUPT0N and K. COLLERSON Isotopic studies of south-east Australian C02~rich discharges : deep sources and shallow sources.

9.10 -

9.30

P.A. HUNT and A.M. GIBLIN Iron mobility and the geochemistry of groundwaters in the Hawkesbury Sandstone of the Sydney Basin.

9.30 - 10.30

H.D. HOLLAND KEYNOTE ADDRESS Paleosols and the evolution of atmosphere.

Tuesday 28 August Session 2 11.00am - 12.40pm Chairman: P.B. Hostetler

Venue: E7B T4

11.00 - 11.20

J.J. FARDY, T.M. FLORENCE and T.W. HAMILTON Direct hydrogeochemical prospecting for gold by surface waters analysis.

11.20 - 11.40

C.B. DISSANAYAKE The impact of the natural environment on human health in Sri Lanka.

11.40 - 12.00

C.R.M. BUTT and M.J. G0LE Use of helium for hydrogeochemical exploration for uranium.

12.00 - 12.20

B.L. DICKSON Interpretation of radium isotopic ratios in groundwaters.

SYMPOSIUM

MODIFICATION OF WATER QUALITY BY DEVELOPMENT ACTIVITIES MINING HYDROGEOLOGY

AND

Convener:

Dr. M.J. Knight

Poster Papers:

I.F. JOHNSON and K.G. McQUEEN Heavy metal distribution and behaviour in the Molonglo River system downstream from Captain*s Flat, New South Wales. P.C. SMITH and G. SCHRALE Aquifer contamination with cheese factory waste

Wednesday 29 August Session 1 8.30am - 10.30am Chairman: M.J. Knight

Venue: E7B T4

8.30 -

9,30

K. CARTWRIGHT KEYNOTE ADDRESS Hydrogeologic investigation of failures at hazardous waste disposal sites.

9.30 -

9.50

G. JACOBSON Pollution of shallow aquifers by urban development - case studies from Canberra.

9.50 - 10.10

A. SHUGG Groundwater pollution by dairy factory effluent at Allansford, Victoria.

10.10 - 10.30

DISCUSSION

Wednesday 29 August Session 2 11.00am - 12.40pm Chairman: D. Woolley

Venue: E7B T4

11.00 - 11.20

M.W. MARTIN and R.A. STOKES Hydrology of a reforestation experiment on a saline agricultural catchment.

11.20 - 11.40

S. HANCOCK, C.F. FORBES and R.E. BLACK The course of hydrology assessments for mining environmental impact studies.

11.40 - 12.00

R.K. HAZELDENE and W.J. McKAY Hydrogeological domains behind the east wall of the Woodlawn open cut and implications for slope stability.

12.00 - 12.20

C. H. KIDD Hydrogeological problems of mining under wetlands, Waitako Coalfield, New Zealand.

12.20 - 12.40

W.J. RUSSELL and S. NICH0L Development and management of geothermal water resources for spas and domestic heating in New Zealand. OIL AND GAS

SYMPOSIUM C2

PERMO-TRIASSIC OIL AND GAS

Convener:

Mr. C. Herbert

Poster Paper:

B.P.J. WILLIAMS and E.K. WILD Late Carboniferous - early Permian sandstone reservoir fades analysis in hydrocarbon exploration of the Gidgealpa Group, southern Cooper Basin, South Australia

Monday 27 August Session 2 11.00am - 12.40pm Chairman: L. Etheridge

Venue: E7B T2

11.00 - 11.20

T.G. RUSSELL Sealion: a Permian .gas play in the offshore Sydney Basin.

11.20 - 11.40

J4.R. BHATIA and P.H. COISY A reservoir geological model of the late Permian sands in the Petrel and Tern gas fields, offshore Bonaparte Basin.

11.40 - 12.00

P.W. VINCENT Review of the geology and hydrocarbon potential of the Gidgealpa Group in the northern Cooper Basin.

12.00 - 12.40

B.P.J. WILLIAMS Reservoir geometry and alluvial architecture of the Toolachee Formation, Moomba field, southern Cooper Basin.

SYMPOSIUM

Convener:

EVALUATION OF PETROLEUM PROVINCES AND

FIELDS

Dr. D.J. Forman

Wednesday 29 August Session 1 8.30am - 10.30am Chairman: D.J. Forman

Venue: E7B T2

8.30 -

9.10

F.S. JEFFRIES KEYNOTE ADDRESS Methods for estimating future discovery and supply of hydrocarbons.

9.10 -

9.30

W.V. PINCZEWSKI Evaluation of the potential for enhanced oil recovery in Australia.

9.30 -

9.50

T.G. POWELL The role of petroleum geochemical studies in resource evaluation.

9.50 - 10.10

M.F. MIDDLETON Hydrocarbon maturity of the southern continental margin of Western Australia.

10.10 - 10.30

M.J. GOLE, M.K.W. HART and C.R.M. BUTT Near-surface gas geochemistry over the Gingin and Bootine gas fields, Western Australia.

Wednesday 29 August Session 2 11.00am - 12.40pm Chairman: D.J. Formari

Venue: E7B f2

11.00 - 11.20

P.A. SYM0NDS Geology and hydrocarbon potential of Australia's legal continental shelf beyond the exclusive economic zone.

11.20 - 11.AO

H.R. KATZ Petroleum potential in the SW-Pacific island arcs.

11.40 - 12.00

G.R. H0LDGATE, G. MACKAY and G.C. SMITH Hydrocarbon potential of the Portland Trough area.

12.00-12.20

M.A. ETHERIDGE, J.C. BRANSON and P.G. STUART-SMITH Structural interpretation of extensional sedimentary basins and its relevance to hydrocarbon exploration - examples from the Bass Strait region.

12.20 - 12.40

J.B. WILLCOX 'Deepwater* Gippsland Basin.

SYMPOSIUM

Convener:

DEPOSITIONAL ENVIRONMENTS, MIGRATION AND

DIAGENESIS

Dr. D. Hobday

Thursday 30 August Session 1 8.30am - 10.30am Chairman: D. Hobday

Venue: E7B T2

8.30 -

9.30

W.L. FISHER KEYNOTE ADDRESS Oil exploration and exploitation:

9.30 -

9.50

J.W. HUNT and A.T. BRAKEL Sulfur in coal - implications for basin analysis in coal bearing sequences.

9.50 - 10.30

new trends and new geologic challenges.

T.G. POWELL Depositional and source controls on the composition of crude oils.

Thursday 30 August Session 2 11.00am - 12.40pm Chairman: D. Hobday

Venue: E7B T2

11.00 - 11.20

V.J. WALL and J.M. BODARD The role of fluid - rock interaction in sandstone diagenesis.

11.20 - 11.40

K.R. MARTIN Diagenesis of the Aldebaran Sandstone in the Yellowbank and Springvale gas fields, Denison Trough, Queensland.

11.40 - 12.00

J.M. BODARD and V.J. WALL Clay matrix diagenesis and the evolution of Gippsland Basin oil reservoirs.

12.00 - 12.20

B.G. STEVESON and D.I. GRAVEST0CK Stratigraphic, petrographic and petrophysical features of the Tirrawarra Sandstone in the Big Lake field.

12.20 - 12.40

SYMPOSIUM C7 : Convener:

I.D. PALMER The geology and stress state of the Mesaverde section in the Piceance Basin, Colorado, and its effect on hydraulic fracture stimulation.

LATE PROTEROZOIC AND EARLY PALAEOZOIC HYDROCARBONS Dr. M.R. Walter

Friday 31 August Session 1 8.30am - 10.30am Chairman: R.E. Summons

Venue: E7B T2

8.30 -

8.50

T.G. POWELL Geochemistry of lower Palaeozoic oils and source rocks, Ontario, Canada.

8.50 -

9.10

D.M. MCKIRDY, B.L. WATSON and B.A. M00NEY Optical and pyrolitic characterisation of pre-Devonian oil-prone kerogens.

9.10 -

9.30

R. ALEXANDER New methods for assessing maturity and palaeotemperatures.

9.30 -

9.50

M.R. WALTER Proterozoic and Palaeozoic stromatolitic carbonates as sources and reservoirs for petroleum.

9.50 - 10.10

10.10 - 10.30

R.V. BURNE and M.R. WALTER Stromatolite reefs and cyanobacterial mats of Hamelin Pool, W.A. significance for Proterozoic and younger petroleum plays. DISCUSSION

Friday 31 August Session 2 11.00am - 12.40pm Chairman: T.G. Powell 11.00 - 11.20

Venue: E7B T2

K.S. JACKSON, D.M. MCKIRDY and J.A. DECKELMAN Hydrocarbon generation in the Amadeus Basin, central Australia.

11.20 - 11.40

I.P. SWEET and K.A. PLUMB The McArthur Basin - a middle Proterozoic hydrocarbon province?

11.40 - 12.00

G. WESTE, R.E. SUMMONS, D.M. MCKIRDY, P.N. S0UTHGATE, R.L. HENRY and A.M. BREWER Cambrian palaeoenvironments and source rocks of the eastern Officer Basin.

12.00 - 12.40

DISCUSSION COAL AND OIL SHALE

SYMPOSIUM D1 :

COAL MEASURE SEDIMENTATION AND EVALUATION OF COAL DEPOSITS

Convener:

Mr. A. Crouch

Poster Papers:

C.R. WEBER, J. BECKETT, D.S. HAMILTON, M.B.L. HILL, I. McDONALD, R.S. M0FFITT and V.Z. TADR0S Identification of genetically based sedimentary fades in Permian drillcore in the Sydney - Gunnedah Basin

Thursday 30 August Session 1 8.30am - 10.30am Chairman: I. Blayden 8.30 -

8.50

P.L. EISLER SIROLOG borehole logging technology development and applications.

8.50 -

9.10

R. NOLAN Tasmanian coals - products of their environments.

9.10 -

9.30

A. CROUCH and 0. SHIELS Approaches to codes for the calculation of coal resources.

9.30 -

9.50

C.W. MALLETT, L. GRIMSTONE, J. GORMAN and J. WOODS The identification of fault zones in coal measures, Blackwater district, central Queensland.

9.50 - 10.30

Venue: E7B T3

R.A. RAHMANI KEYNOTE ADDRESS Coal seam geometry as a predictive tool to interpret depositional environments and paleogeography of associated clastic rocks.

Thursday 30 August Session 2 11.00am - 12.40pm Chairman: I. Blayden

Venue: E7B T3

11.00 - 11.20

C.R. WARD, J. COMINO and A. WALTHO Classification and systematic description of coal-bearing rocks in drill cores.

11.20 - 11.AO

C.W. MALLETT, L. GRIMSTONE, J. GORMAN and J. WOODS Deltaic depositional environments in the Rangal Coal Measures, Curragh mine, central Bowen Basin, Queensland.

11.40 - 12.00

J.W. HUNT Dull coal seams - their distribution and origin in the Permian basins.

12.00 - 12.20

D.S. HAMILTON Deltaic depositional systems, coal distribution and quality, and petroleum potential of the lower Black Jack Formation, Gunnedah Basin, New South Wales.

SYMPOSIUM D3 :

Convener:

GEOTECHNICAL AND ENVIRONMENTAL ASPECTS OF COAL EXPLORATION, MINE DEVELOPMENT AND REHABILITATION Mr. P. Goodwin

Wednesday 29 August Session 1 8.30am - 10.30am Chairman: P.J. Woottou

Venue: E7B 100

8.30 -

8.50

R.W. SEEDSMAN The behaviour of clay rich rocks during mining.

8.50 -

9.10

P.J. HATHERLY and G.E. HOLT In-seam seismic surveys in the Hunter Valley.

9.10 -

9.30

R.J. WILLIAMS, F. HUNGERF0RD, B.B. BEAMISH and B. McKAVANAGH Research in overcoming the problem of instantaneous outbursts of coal and gas at Collinsville.

9.30 -

9.50

L.K. RIX0N and J. SHEPHERD Mining induced fractures in coal.

9.50 - 10.10

I. J. STONE An empirical approach to assessing the in situ stress field and its role toward improving coal mine roof conditions.

10.10 - 10.30

DISCUSSION

SYMPOSIUM D4 Convener:

GEOLOGICAL ASPECTS OF COAL

UTILIZATION

Dr. C.R. Ward

Friday 31 August Session 1 8.30am - 10.30am Chairman: A. Crouch

Venue: E7B T3

8.30 -

8.50

R. GUYOT and H. READ Sampling and laboratory testing of coal.

8.50 -

9.10

N.V.P. KELVIN and J. BAKER Borecore testing for assessing key aspects of coal utilisation.

9.10 -

9.30

M.J. ROBINSON The quality aspects of coal utilised in the cement industry.

9.30-10.10

G.E. EDWARDS KEYNOTE ADDRESS New markets for Australian coal.

10.10 - 10.30

DISCUSSION

Friday 31 August Session 2 11.00am - 12.40pm Chairman: A. Crouch

Venue: E7B T3

11.00 - 11.20

N.J. RUSSELL Gelification of Victorian soft brown coal wood.

11.20 - 11.40

P.R. WARBROOKE Effect of dykes on coal structure and quality.

11.40 - 12.00

J.W. HUNT, A. ANDERSON, A.T. BRAKEL, A. MCMINN and M. SMYTH The Bayswater Seam and its equivalent s — origin, distribution, and utilisation in the Sydney and Gunnedah Basins.

12.00 - 12.40

DISCUSSION

SYMPOSIUM

Convener:

OIL

SHALE

DEPOSITS

Mr. A.W. Lindner

Monday 27 August Session 2 11.00am - 12.40pm Chairman: A.W. Lindner

Venue: E7B T3

12.00 - 12.20

R.V. BURNE Lake Eliza, South Australia, and Lake Tenggano, Rennell Island : two possible environments of oil-shale genesis.

12.20 - 12.40

J.G. THOMPSON The application of solid state Si and 1 3 C nuclear magnetic resonance (NMR) spectroscopy to the study of clay mineral-organic intercalates and their naturally occurring analogues.

Tuesday 28 August Session 1 8.30am - 10.30am Chairman: A.W. Lindner

Venue: E7B T3

8.30 - 8.50

D.L. GIBSON and C.J. B0REHAM Organic-rich Cambrian carbonates, Camooweal area, Georgina Basin.

8.50 - 9.10

D.A. MADRE The Alpha oil shale deposit - the resource and its potential.

9.10 - 9.30

S. 0ZIMIC and J.D. SAXBY Geology, geochemistry and geophysics of oil shale in the Toolebuc Formation.

9.30 - 10.30

H.J. WARD Oil shale occurrences in southwestern Australia.

9.50-10.30

M.D. PICARD

KEYNOTE ADDRESS

Geology of Green River Formation and oil-shale genesis in Uinta Basin, northeast Utah, U.S.A. Tuesday 28 August Session 2 11,00am - 12.40pm Chairman: A.C. Hutton

Venue: E7B T3

11.00 - 11.20

T.A. NOON Departmental stratigraphic drilling in Queensland Tertiary basins.

11.20 - 11.40

L. C0SHELL A proposed classification of ore types (facies) for the Rundle oil shale deposit.

11.40 - 12.00

D.A. HENSTRIDGE, J.F. IVANAC, A.W. LINDNER and T.R. O f bEA The geology of the Nagoorin oil shale deposit.

12.00 - 12.20

P.B. D1AUVERGNE Early Miocene oil shales of the Suttor Formation, Mt. Coolon district, eastern central Queensland.

12.20 - 12.40

C.J. JONES Oil shale : Georgina Basin, N.W. Queensland.

Wednesday 29 August Session 1 8.30am - 10.30am Chairman: D.A. Henstridge

Venue: E7B T3

8.30 -

KEYNOTE ADDRESS

9.10

J.S. TURNER

Oil shale - the quiet revolution.

9.10 -

9.30

J. MANDELSON Julia Creek shale oil : technical and economic advances.

9.30 -

9.50

P.J. REDANN The status of the Condor oil shale project.

9.50 - 10.10

M. GLIKS0N Transmission electron microscopy backed by C-isotope analysis - a powerful tool in resolving the nature and source of organic matter in oil shales.

10.10 -

R.T. MATHEWS and S.J. HAM Pyrolysis studies of some Queensland shales.

10.30

Wednesday 29 August Session 2 11.00am - 12.40pm Chairman: J.D. Saxby

Venue: E7B T3

11.00 - 11.20

A.C. HUTTON, J. KORTH, J.ELLIS, and P. CRISP Petrography of oil shales and geochemistry of shale oil, Duaringa.

11.20 - 11.40

L.S. DALE, J.J. FARDY, J.H. PATTERSON and A.R. RAMSDEN Ceochemical profile of the Toolebuc Formation at Julia Creek.

11.40 - 12.00

B.L. DICKSON and A.R. RAMSDEN Can the widespread gamma-ray anomaly of the Toolebuc Formation be used to determine its oil yield potential?

12.00 - 12.20

P.J. MATHEW, T.B. FOGG and J.G. MILES An oil shale borehole core density analyser.

12.20 - 12.40

B.D. SOWERBY and K.E. DAVIES On-line bulk analysis of Rundle oil shale.

METALLIC SYMPOSIUM El Convener:

REMOTE SENSING

MINERALS

IN MINERAL

EXPLORATION

Mr. R.D. Walker

Thursday 30 August Session 1 8.30am - 10.30am Chairman: G. Tassell

Venue: E7B T1

8.30 -

9.10

J.F. HUNTINGTON, A.A. GREEN, A.R. GABELL, C. HORSFALL and S. FRASER Implication of visible, near and short wavelength infrared and mid infrared remote sensing for exploration in Australia.

9.10 -

9.30

C.R. NASH, A.C. THERON, M.M. COUPARD and B.R. MINTY Systematic landsat interpretation, data integration and tectonic synthesis.

9.30 -

9.50

J.A. RICHARDS Microwave remote sensing - University of N.S.W. participation in the SIR-B experiment.

9.50 - 10.10

P. WILSON, I.J. TAPLEY and F.R. HONEY The golden handprint : a structural interpretation of the eastern goldfields, Western Australia, from N0AA-AVHRR imagery.

Thursday 30 August Session 2 11.00am - 12.40pm Chairman: C.R. Nash

Venue: E7B T1

11.00 - 11.20

M.C. AUBREY and G.W. TASSELL Computer assisted analysis of landsat and geological data - a new approach to regional exploration.

11.20 - 11.40

A.A. GREEN, M.D. CRAIG and J.F. HUNTINGTON Integrated analysis of image data for mineral exploration.

11.40 - 12.00

F.R. HONEY, J.L. DANIELS and P. WILSON Evaluation of imagery from the Carr Boyd minerals/CSIRO airborne multispectral scanner.

12.00 - 12.40

J.F. HUNTINGTON Panel discussion

SYMPOSIUM E2:

GEOCHEMICAL

EXPLORATION

FOR GOLD

Conveners:

Dr. P.M.D. Bradshaw and Dr. G.J.S. Govett

Poster Paper:

J.R. WILMSHURST and L.R. B0TT0MER Soil geochemical response In the Drake Field, N.S.W.

Tuesday 28 August Session 1 8.30 - 10.30 Chairman: P.M.D. Bradshaw

Venue: E7BT1

8.30 - 8.50

D. HALL, D. O'NEILL, P.D. KLIPFEL, G.L. DUNCAN and P.M. VANDERSPUY A soil-sampling orientation survey to determine the value of gold, silver, and base metals in delineating bedrock gold mineralization.

8.50 - 9.10

J.G. WEBSTER Gold and silver remobilization during the oxidation of sulphide-bearing carbonate ore.

9.10 - 9.30

C.S. RUGLESS An integrated geological and soil geochemical exploration programme for gold at Mt. McDonald, N.S.W.

9.30 - 9.50

A.W. MANN Lateritic weathering and its implications for geochemical exploration of nearsurface gold deposits.

9.50 - 10.10

M.B.M. H0CHMAN, D.W. RUSSELL, and J. VAN MOORT Preliminary use of thermoluminescence in gold exploration

10.10 - 10.30

DISCUSSION

Tuesday 28 August Session 2 11.00 - 12.40 pm Chairman: A.R. Collins 11.00 - 11.20

W.E. BAKER Gold in vegetation as a prospecting method in Tasmania

11.20 - 11.40

G.R. TAYLOR and E.C. COMSTI Hydrothermal fluids from the Hillgrove tungsten/gold/antimony deposits.

11.40 - 12.00

A.F. WILSON, M.J. THOMAS and J. FARDY Examples of the use of neutron activation analysis of gold in waters to identify gold prospects K. BURLINS0N Fluid inclusion decrepitation as a gold exploration technique in the Pine Creek area, N.T.

12.00 - 12.20

12.20 - 12.40 SYMPOSIUM E4 Convener:

DISCUSSION :

STRUCTURAL CONTROL OF ORE

DEPOSITS

Dr. T. Hopwood

Wednesday 29 August Session 1 8.30am - 10.30am Chairman: T. Hopwood

Venue: E7B T1

8.30 -

8.50

I.B. LAMBERT, J. KNUTS0N, T.H. DONNELLY and H. ETMINAN Copper metallogeny of the Adelaide Geosyncline - Stuart Shelf region.

8.50 -

9.10

J.D. JOHNSTON and V.J. WALL Why unconformity-related U

9.10 -

9.30

S.A. TOMICH The role of lineaments in the Yilgarn Block.

9.30 -

9.50

W.R. LEYH Shear zone and lineament control of mineralization, Broken Hill, New South Wales.

9.50 - 10.10

S.A. BOOTH Some aspects of ore control at the Zinc Corporation Ltd., New Broken Hill Consolidated Ltd., and Southern Cross Mines, Broken Hill, New South Wales.

10.10 - 10.30

D.M. RANSOM and F.L. HUNT A reinterpretation of the Ballarat East goldfield.

Wednesday 29 August Session 2 11.00am - 12.40pm Chairman: D.M. Ransom

Venue: E7B T1

deposits are unconformity related.

Venue: E7B T1

11.00 - 11.20

R.A. GLEN Structural control of copper-rich deposits at Cobar, N.S.W.

11.20 - 11.40

D.A.C. ARCHIBALD Ore/host rock relationships at the Elura Mine. Cobar. N.S.W.

11.40 - 12.00

A. TAUBE The Mount Morgan gold-copper mine and environment, Queensland: a volcanogenic massive sulphide deposit associated with possible volcanic cauldrpn structure.

12.00 - 12.20

R.L. McLEOD and A. TAUBE Penecontemporaneous faulting and volcanogenic massive sulphide deposits.

12.20 - 12.40

T. HOPWOOD Contrast in wall-rock textures and sedimentary host textures of some ore deposits.

SYMPOSIUM

M A G M A T I S M AND H Y D R O T H E R M A L

PROCESSES

IN O R E

FORMATION

Conveners:

Dr. P.M. Ashley and Dr. M. Solomon

Poster Papers:

P.B. ABEYSINGHE, A.J.R. WHITE, T.A.P. KWAK and R.C. PRICE Fractionation of the Burstall Granite and the source of uranium in the Mary Kathleen deposit. A.S. ANDREW and R.A. BINNS Petrographic, geocheraical and sulfur isotope studies on massive sulfide ores from Currawang East, New South Wales. Z.U. BAJWAH, R. OFFLER and P.K. SECCOMBE Hydrothermal and regional raetamorphic alteration at Big Cadia (Iron-Duke) deposit, Orange, N.S.W., Australia. B.L. GULSON and L.R. BOTTOMER Proterozoic source for granites and volcanics and source of Ag-Au mineralization in the Drake area, New England T.A.P. KWAK A model relating sulphide cassiterite to Sn-W magnetite skarn replacement deposits. M. MACLENNAN and M.S. BLOOM Geologic, paragenetic and fluid inclusion studies of gold-sulphide-sulphosalt veins, Cassilis, Victoria.

Monday 27 August Session 2 11.00am - 12.40pm Chairman: L.B. Gilligan

Venue: E7B T1

11.00-11.20

M. CREECH, S. SANGAMESHWAR and B. MARSHALL Torrington topaz and silexite geology.

11.20-11.40

C.L. STEGMAN Evolution of the Mole Granite and its Sn-W-3i-Mo basemetal mineralization northern N.S.W.

11.40 - 12.00

J.D. ADAM The Elsmore Granite and its bearing upon the origin of greisen and cassiterite mineralization.

12.00 - 12.20

A.S. ANDREW and C.A. HEINRICH Isotopic and fluid inclusion evidence for sources of mineralizing fluids at the Sundown tin prospect, S.E. Queensland.

12.20 - 12.40

C.A. HEINRICH and P.J. EADINGT0N Hydrothermal geochemistry of arsenic in relation to cassiterite - arsenopyrite - base metal sulfide mineralization in New England.

Monday 27 August Session 3 1.40pm - 3.20pm Chairman: R.W.T. Wilkins

Venue: E7B T1

1.40 -

2.00

P.L.F. COLLINS, M.A. ETHERIDGE, S. HALLEY, K.J. HELLSTEN, N.C. HIGGINS, M. SOLOMON and V.J. WALL The formation of the Aberfoyle and Lutwyche veins.

2.00 -

2.20

G.W. MORRISON The Renison mine sequence and its relationship to tin mineralization.

2.20 -

2.40

J.H. WRIGHT The significance of tourmaline breccias at Mt. Bischoff, Tasmania.

2.40 -

3.00

P.G. JACKSON and T.A.P. KWAK The evolution of the Cleveland greisen-vein-skarn system, a geological, fluid inclusion and thermodynamic study.

3.00 -

3.20

J. HAJITAHERI and M. SOLOMON Preliminary stable isotope studies of the Heemskirk Granite and its mineral deposits.

Monday 27 August Session 4 3.50pm - 5.30pm Chairman: J.L. Walshe

Venue: E7B T1

3.50 -

4.10

W.K. WITT Nature of fluids and some controls on fluid evolution associated with alkali metasomatism and greisenization of a tin-mineralized granite.

4.10 -

4.30

P.J. EADINGT0N and R.G. PATERSON Microdeformation and fluid inclusions and their significance in mineralized breccia columns in the Ardlethan tin mine, NSW.

4.30 -

4.50

T.A.P. KWAK and G.J. PLUMMER Chemical and physical variation of vein systems in some plutonic environments.

4.50 -

5.10

M.S. BLOOM and V.J• WALL Aqueous chemistry of tin at 300^C, with applications to tin transport and cassiterite deposition in alumino-silicate host rocks.

5.10 -

5.30

J.R. TAYLOR, V.J. WALL and M.S. BLOOM The mobilisation of tin from granitoid magmas.

Tuesday 28 August Session 1 8.30am - 10.30am Chairman: W.P. Laing

Venue: E7B T2

8.30 -

8.50

K.J. MOON and M. SOLOMON The nature of the ore fluids at the Sangdong scheelite deposit, Korea.

8.50 -

9.10

C.R. RAMSAY Recognition of mineralizing plutons in granitoid terrains : a case history in the Arabian Shield.

9.10 -

9.30

M.S. BLOOM Hydrothermal fluid compositions in molybdenum-mineralised granites: application of fluid/mineral equilibria.

9.30 -

9.50

B.W. NISBET An exploration model for tantalum pegmatites with an example from the Pilgangoora area, Pilbara, Western Australia.

9.50 - 10.10

T.A.P. KWAK, W.M. BROWN, P.B. ABEYSINGHE and T.T. HING High iron solubilites in natural hydrothermal systems: in some ore deposits.

10.10 - 10.30

D.A.F. HENDRY, A.R. CHIVAS, J.V.P. LONG and S.J.B. REED Chemical differences between minerals from mineralizing and barren intrusions from some North American porphyry copper deposits.

Tuesday 28 August Session 2 11.00 am - 12.40pm Chairman: I.R. Plimer

its relation to zoning

Venue: E7B T2

11.00 - 11.20

J.M. RODGERS and J.L. WALSHE Muscovite geothermometry.

11.20 - 11.40

J.L. WALSHE Progress in the development of the six component chlorite solid solution model and the search for uniqueness in chemical models of hydrothermal ore deposit formation.

11.40 - 12.00

R.W.T. WILKINS and A.H. EWALD The inference of boiling or mixing of fluids from fluid inclusion data.

12.00 - 12.20

A.J.B. THOMPSON and S.D. SCOTT Diffusion of Zn and Fe in sphalerite.

12.20 - 12.40

D.W. HAYNES and M.S. BLOOM Stratiform copper deposits hosted by low energy sediments - nature of metal transporting water and controls on metal ratios.

Wednesday 29 August Session 1 8.30am - 10.30am Chairman: M. Solomon

Venue: Macquarie Theatre

8.30 -

8.50

A.J.R. WHITE, J.R. HOLLOWAY and T.A.P. KWAK Proposed chemical trap for gold precipitation.

8.50 -

9.10

S.E. HO Nature of Archaean gold-bearing ore fluids: a fluid inclusion study of hydrothermal gold deposits, Western Australia.

9.10 -

9.30

F.B. NEALL and G.N. PHILLIPS Fluid-wallrock interaction around Archaean hydrothermal gold deposits: thermodynamic model.

9.30 - .9.50

I.B. LAMBERT, G.N. PHILLIPS, T.H. DONNELLY, D.I. GROVES and F. NEALL Sulfur isotope compositions of Archaean gold deposits: their significance for genesis, exploration and seobiochemical evolution models.

9.50 - 10.30

R.W. HENLEY KEYNOTE ADDRESS Structure of active geothermal systems and implications for the origins of some hydrothermal gold and base metal ore deposits.

Wednesday 29 August Session 2 11.00am - 12.40pm Chairman: R. R. Keays

Venue: Macquarie Theatre

11.00 - 11.20

I.R. PLIMER Two fundamental types of sediment-hosted exhalative Pb-Zn deposits.

11.20 - 11.AO

R.G. LOGAN and N. WILLIAMS Sedimentary controls on the hydrothermal system that formed the H.Y.C. deposit at McArthur River, Northern Territory.

11.40 - 12.00

M. NEUDERT Are the Mount Isa lead-zinc ores really syngenetic?

12.00 - 12.20

G.R. CARR and B.L. GULSON Multiple lead sources In the stratiform Lady Loretta Zn-Pb-Ag deposit, northwest Queensland.

12.20 - 12.40

K.G. McQUEEN Sulphidic sediments and base metal sulphide mineralisation in the Quidong Basin, southeastern New South Wale.s.

Thursday 30 August Session 1 8.30am - 10.30am Chairman: P.M. Ashley

Venue: Macquarie Theatre

8.30 -

8.50

R.E.T. HILL Some aspects of the metamofrphic and magmatic history of the Six Mile Well nickel deposit, W.A.

8.50 -

9.10

D.R. HUDSON Distribution of sperrylite, sudburyite and other platinum group minerals in the Kambalda nickel deposits, Western Australia.

9.10 -

9.30

P.R. HAMLYN and R.R. KEAYS Sulphur saturation, second-stage melts and the origin of magmatic PGE deposits.

9.30 -

9.50

R.R. KEAYS and P.R. HAMLYN Sulphide immiscibility and the genesis of hydrothermal ore deposits : the upper mantle connection.

9.50-10.30

B.J. SKINNER KEYHOTE ADDRESS Environments and process of ore deposition on the seafloor.

Thursday 30 August Session 2 11.00am - 12.40pm Chairman: J. Angus

Venue: Macquarie Theatre

11.00 - 11.20

H. ETMINAN, I.B. LAMBERT, I. BUCHHORN, C. CHAKU and G. MURPHY Mineralising and diagenetic processes in the Devonian reefs, Lennard Shelf, Western Australia.

11.20 - 11.40

T.G. POWELL and R.W. MACQUEEN Role of organic matter in precipitation of lead-zinc sulphides at Pine Point Canada.

11.40 - 12.00

W.P. LAING, S.S. SUN and R.W. NESBITT Acid volcanic precursor to Potosi Gneiss at Broken Hill and its implications for ore genesis.

12.00 - 12.20

L.J. LAWRENCE Ore remobilization at Broken Hill.

12.20 - 12.40

Z.U. BAJWAH, P.K. SECCOMBE and R. 0FFLER Paragenetic and geochemical studies of Big Cadia (Iron-Duke) deposit, Orange, N.S.W., Australia.

Friday 31 August Session 1 8.30am - 10.30am Chairman: J. Martyn

Venue: Macquarie Theatre

8.30 -

8.50

R.J. DUDLEY, P.M. ASHLEY, A.W. RYALL and E.R. MAY Scuddles: an Archaean-aged volcanogenic massive sulphide deposit, Golden Grove, Western Australia.

8.50 -

9.10

P.M. ASHLEY Wallrock alteration at the Scuddles volcanogenic massive sulphide deposit, Golden Grove district, Western Australia.

9.10 - 9.30

M. VAASJ0KI Geochronological and genetic implications of lead isotopic data from the Archaean massive sulfide deposits at Golden Grove, Teutonic Bore and Salt Creek, Western Australia.

9.30 -

9.50

D.J. WHITFORD and D.B. WALLACE The Mt Read Volcanics at Que River: primary geochemical affinities and REE geochemistry.

9.50-10.10

W. NASCHWITZ and J.C. VAN M00RT The primary halo at Rosebery.

10.10 - 10.30

D.A. P0LYA, M. SOLOMON, C.J. EASTOE and J.L. WALSHE The Murchison Gorge, Tasmania - a possible cross section through a massive sulphide circulation system.

Friday 31 August Session 2 11.00am - 12.40pm Chairman: V.J. Wall

Venue: Macquarie Theatre

11.00 - 11.20

R.A. BINNS and D.J. WHITFORD Problems in applying primary geochemical haloes to exploration for blind orebodies.

11.20 - 11.40

P. ABEYSINGHE, T.A.P. KWAK and A.J.R. WHITE The evolution and concentration of U and REE in the Mary Kathleen skarn, Queensland.

11.40 - 12.00

M.M. HEDGES, V.J. WALL and M.S. BLOOM Hydrothermal transport and deposition of uranium:

12.00 - 12.20

S. K0UL, V.J. WALL and J.D. JOHNSTON Fission-track studies of the East Alligator River uranium field (Northern Territory, Australia) and their implications.

12.20 - 12.40

A.E. WILLIAMS-JONES and M.J. SAWIUK Karpinka Lake, Saskatchewan, Canada: uranium deposit.

SYMPOSIUM E7

Convener:

GEOLOGICAL AND GEOTECHNICAL AND OPERATION

8.50

a rare example of a Proterozoic roll-type

STUDIES

IN MINE DESIGN,

DEVELOPMENT

Mr. J.R. Blair

Friday 31 August Session 1 8.30am - 10.30am Chairman: J.R. Blair 8.30 -

modelling and implications.

Venue: E7B T4

J.M. PEARSON Geotechnical aspects of stope design at the Elura mine, Cobar, NSW.

8.50 -

9.10

N.R.P. BACZYNSKI Probabilistic stability analysis of mine openings.

9.10 -

9.30

M.C. HANCOCK and Q.G. AMOS The Paddington gold project evaluation drilling and ore reserve estimation.

9.30 - 10.10

FILM PRESENTATION - FREEP0RT OF AUSTRALIA INC. Episode in Irian Jaya Mining challenge Films relate to the development of the Gunung Bijih (Ertsberg) copper mine in Irian Jaya.

Friday 31 August Session 2 11.00am - 12.40pm Chairman: J.R. Blair

Venue: E7B T4

11.00 - 11.20

B.K. MUTTON

11.20 - 11.40

S.A. BOOTH and I.D. BLUCHER Programme Logger: a computer based core logging facility developed at the Zinc Corporation Limited and New Broken Hill Consolidated Limited, Broken Hill, New South Wales.

Some aspects of geology for pre-production mining of the Hilton mine Mt. Isa.

GENERAL SYMPOSIUM G1

PETROLOGY, GEOCHEMISTRY

TOPICS AND VOLCANISM

Convener:

Dr. G.S. Gibbons

Poster Papers:

J.L. BAXTER, S.A. WILDE, R.T. PIDGEON and I.R. FLETCHER The Jack Hills metasedimentary belt: an extension of the early Archaean terrain in the Yilgarn Block, Western Australia. R. AHMAD Electron microprobe study of the distribution of trace elements in conodont apatite : intra elemental and secular variations.

Monday 27 August Session 2 11.00am - 12.40pm Chairman: G.S. Gibbons

Venue: E7B T4

11.00 - 11.20

R . L . OLIVER and D.G. BOYER Metamorphic pressures and temperatures evidenced by amphibolites of the Irindinna supracrustals, Harts Range.

11.20 - 11.40

W.J. COLLINS and A.J.R. WHITE Geochemical variation of granite suites within an Archaean batholith.

11.40 - 12.00

W.J. COLLINS and C.M. GRAY Rb-Sr isotopic studies of the Mount Edgar batholith.

Friday 31 August Session 1 8.30am - 10.30am Chairman: F.L. Sutherland

Venue: E7B 100

8.30 -

8.50

D.. HILYARD Wooltana metabasalt: late Proterozoic.continental tholeiitic rift sequence, Adelaide Geosyncline, South Australia.

8.50 -

9.10

D.J. MARTIN A suite of teschenitic intrusions from the coalfields of New South Wales.

9.10 -

9.30

W.E. CAMERON, D.A. WALKER and D.P. WINDRIM Boninite - tholeiite volcanism in the southwest Pacific.

9.30 -

9.50

M.D. BUCK Muswellbrook volcanic centre - a source for the Carboniferous ignimbrites in the upper Hunter Valley.

9.50 - 10.10

J. McPHIE Ignimbrite and ash-fall tuff from a large magnitude rhyolitic hydrovolcanic eruption: late Carboniferous Cana Creek Tuff, northeastern N.S.W.

10.10 - 10.30

K. ORTH, R.A.F. CAS and J.V. WRIGHT Facies associations in a probable ancient silicic volcanic caldera terrain lower Devonian Snowy River Volcanics of southeastern Australia.

Friday 31 August Session 2 11.00am - 12.40pm Chairman: F.L. Sutherland 11.00 - 11.20

SYMPOSIUM G2 : Convener:

Venue: E7B 100

L.R. RAYNOR Geology of Ruby Hill and other breccia-fill diatremes at Bingara, N.S.W.

WEATHERING, DIAGENESIS AND SEDIMENTARY STUDIES Dr. G.S. Gibbons

Thursday 30 August Session 1 8.30am - 10.30am Chairman: D.F. Branagan

Venue: E7B T4

8.30 -

8.50

J.F. BANFIELD and R.A. EGGLETON Aspects of granite weathering.

8.50 -

9.10

R.A. EGGLETON and K.L. SMITH Basalt weathering in eastern Australia

9.10 -

9.30

B. MURRELL The logical development of deeply weathered profiles

9.30 -

9.50

R.A. CALLEN Silicified concentric ridges of Stuart Creek, South Australia.

9.50 - 10.10

B.P. RUXTON The initiation of debris flows on steep mountain slopes in Hong Kong.

10.10 - 10.30

D.F. BRANAGAN, A.R. NORMAN and K.L. WILLIAMS St. Peters quarry - a man-made environment (film and discussion).

Thursday 30 August Session 2 11.00am - 12.40pm Chairman: S.R. Pecover

Venue: E7B T4

11.00 - 11.20

M.W. FENTON Geochemical characterisation of siliciclastic sedimentary rocks with examples from the lower Palaeozoic of Victoria.

11.20 - 11.40

G.S. GIBBONS Salts and sands:

crystallization processes in rock capillaries.

11.40 - 12.00

T.C. PARKS An electron-permeable pore fluid during burial metamorphlsm: implications.

12.00 - 12.20

evidence and

T.C. PARKS Which way did the fluids flow through the Fortescue metabasalts?

Friday 31 August Session 2 11.00am - 12.40pm Chairman: J.W. Pickett

11.20 - 11.40

Venue: E7B 100

A.R. CHIVAS. P'. DE DECKKER and J.M.G. SHELLEY Mg and contents of non-marine ostracods as a combined palaeothermometer and palaeosalinometer. A.R. CHIVAS, T. T0RGERSEN and H. P0LACH Growth rates of stromatolites from Shark Bay deduced by C-14 and Po-210 dating.

11.40 - 12.00 12.00 - 12.20

M.W. FENTON and C.J.L. WILSON Evidence for shallow water conditions during the upper Ordovician at Mallacoota, Victoria.

12.20 - 12.40

W.W.S. YIM Cainozoic geomorphological evolution and genesis of stanniferous placers in northeast Tasmania.

SYMPOSIUM G3 Conveners:

TERTIARY

GEOLOGY

Dr. A.N. Carter and Dr. G.S. Gibbons

Friday 31 August Session 3 1.40pm - 3.20pm Chairman: V. Palmieri

Venue: E7B 100

1.40 -

2.00

V. PALMIERI Late Miocene - early Pliocene biostratigraphy in four localities in the Australasian region.

2.00 -

2.20

S. SHAFIK Displaced Cretaceous nannofossils and middle Eocene marine sedimentation along the Australian western and southern margins.

2.20 -

2.40

A.N. CARTER Some aspects of eustasy in the Murray Basin.

2.40 -

3.00

C.J. JENKINS Terrigenous sedimentation along the eastern Australian slope and abyssal plain - a starved continental margin.

3.00 -

3.20

K . G . MCKENZIE Advances in Australian ostracode studies.

Friday 31 August Session 4 3.50pm - 5.30pm Chairman: G.M. Taylor

Venue: E7B 100

3.50 -

4.10

G. TAYLOR Uplift and the southeastern highlands of New South Wales - a review.

4.10 -

4.30

H.A. MARTIN The use of quantitative relationships in Tertiary stratigraphic palynology in the Murray Basin, New South Wales.

4.30 -

4.50

R.A. CALLEN The stratigraphy and age of the silcrete floras, Stuart Creek, South Australia.

Chairman: D. Denham

4.50 -

5.10

I. McDOUGALL, P. R0DDA, R.A. CASSIE, D.A. FALVEY, R. TODD and J.A. WILCOXON Isotopic ages, magnetostratigraphy and biostratigraphy from the early Pliocene Suva Marl, Fiji.

5.10 -

5.30

S. MANICKAM and H. OKADA Mineralogy and paleoenvironment of Quaternary sediments cored in the Kashima Sea off the east coast of central Honshu, Japan.

SPECIALIST GROUP SYMPOSIA

SYMPOSIUM SI (SGEG) Convener:

ORE DISCOVERY - THE INTERPLAY OF GEOSCIENCE AND INTERVENTION

DIVINE

Dr. N. Williams

Thursday 30 August Session 3 1.40pm - 3.20pm Chairman: N. Williams

Venue: Macquarie Theatre

1.40 -

2.00

A.H. VOISEY Evolving mineral exploration techniques and available facilities over fifty years - 1934 to 1984.

2.00 -

2.20

D.S. TYRWHITT The Telfer gold deposit, Western Australia.

2.20 -

2.40

M.C. HANCOCK and Q.G. AMOS The Paddington deposit, Western Australia - the rediscovery of an old gold mine.

2.40 -

3.00

W.E. MATTHEWS and P.D. TIMMS The Mungana Red Dome deposit.

3.00 -

3.20

G.I. WILSON, R.W. LEWIS and J. GALLO The Kidston gold mine, Queensland.

Thursday 30 August Session 4 3.50pm - 5.30pm Chairman: J.R. Ross

Venue: Macquarie Theatre

3.50 -

4.10

E.H. SKEY Dualism in the discovery of the Que River and Hellyer polymetallic sulphide deposits in western Tasmania.

4.10 -

4.30

J.S. HARTLEY Thalanga - exploration history.

4.30 -

4.50

K.J. HARVEY The discovery of the Balcooma massive sulphide deposit.

4.50 -

5.10

R.R. LARGE Developing genetic models for volcanogenic massive sulphide ores - do they contribute to exploration success?

5.10 -

5.30

DISCUSSION

Friday 31 August Session 3 1.40pm - 3.20pm Chairman: G.P. Moore

Venue: Macquarie Theatre

1.40 -

2.00

J.J. GRESHAM and G.D. LOFTUS-HILLS The discovery of the Kambalda nickel deposits - realisation of a prospector' and a geologist's dream.

2.00 -

2.20

J.R. LORD The discovery of the Frieda River porphyry copper deposit, Papua New Guinea

2.20 -

2.40

L.A. NEWNHAM Discovery history of Renison Bell tin deposits.

2.40 -

3.00

M. HATCHER The Greenbushes tin-tantalum-lithium deposit.

3.00 -

3.20

DISCUSSION

Friday 31 August Session 4 3.50pm - 5.30pm Chairman: J.R. Blair

Venue: Macquarie Theatre

3.50 -

4.30

W.J. ATKINSON, F.E. HUGHES and C.B. SMITH The discovery of the Argyle diamonds.

4.30 -

5.10

J.H. LALOR Olympic Dam, South Australia — the discovery history.

5.10 -

5.30

DISCUSSION

SYMPOSIUM S 2 : ( S G E G , SGGMP)

Convener:

GOLD

EASTERN

AUSTRALIA

Dr. G.G. Lowder

Monday 27 August Session 3 1.40pm - 3.20pm Chairman: G.G. Lowder

Venue: Macquarle Theatre

1.40-2.40

R. L. NIELSEN KEYNOTE ADDRESS Eplthermal precious metal deposits in volcanic rocks of the western USA geological setting and exploration models.

2.40 -

L.B. GILLIGAN Precious metal - antimony - arsenic metallization.and magmatism in central New England, New South Wales.

3.20

Monday 27 August Session 4 3.50pm - 5.30pm Chairman: L.R. Bottomer

Venue: Macquarie Theatre

3.50 -

4.10

K.G. McQUEEN, I.P. GORDON and T. POTTER Epigenetic gold mineralisation at Cowarra, southeastern New South Wales.

4.10 -

4.30

J.F. GILFILLAN and M.R.W. GARMAN The London Victoria gold prospect, Parkes,N.S.W.

4.30 -

5.10

R.R. KEAYS and T.H. DONNELLY Controls of gold mineralization in the Woods Point dyke swarm, Victoria.

Tuesday 28 August Session 3 1.40pm - 3.20pm Chairman: R.E. Keevers

Venue: E7B T1

1.40 -

2.20

A.F. WILSON and S.D. GOLDING The application of stable isotopes to the genesis of gold deposits in eastern Australia.

2.20 -

2.40

G.M. DERRICK Conception, development and results of gold exploration in jaspilite and related rocks near Cloncurry N.W. Queensland.

2.40 -

3.00

J.H.C. BAIN, I.W. WITHNALL and L.P. BLACK Some aspects of the geology and geochronology of gold mineralization in the Georgetown region, Queensland, Australia.

3.00 -

3.20

K.B. COOK and J.E. NETHERY The geology and mineralizing environment of the Kimberly Sue maar complex, Forsayth, Queensland.

Tuesday 28 August Session 4 3.50pm - 5.30pm Chairman: G.W. Morrison

Venue: E7B T1

3.50 -

4.10

E. M. BAKER A classification of gold bearing breccia pipes with reference to exploration.

4.10 -

4.50

H. MUSTARD Brecciation and mineralisation at the Kidston gold deposit, north Queensland.

4.50 -

5.30

DISCUSSION

SYMPOSIUM (SGGMP)

RECENT

ADVANCES

PETROLOGY

Convener:

Dr. D.C. Green

Poster Paper:

R;A. DAY Geochemical constraints on the evolution of magmas and mantle sources beneath south eastern Australia - evidence from Victorian Tertiary lava fields.

Monday 27 August Session 3 1.40pm - 3.20pm Chairman: D.H. Green

Venue: E7B T2

1.40 -

KEYNOTE SPEAKER

2.20

D.J. ELLIS

Geothermometry and geobaroraetry. 2.20 -

2.40

T.H. GREEN and N.J. PEARSON Stability of REE-acceptor minerals at high pressures and temperatures.

2.40 -

3.00

W.N. SAWKA and B.W. CHAPPELL Compositionally zoned plutons by double - diffusive sidewall fractionation processes. Evidence from the Palisade Crest Suite, central Sierra Nevada, California.

3.00 -

3.20

S.E. SHAW, V.R. TODD, J. COOPER and J.R. 0 f NEIL S-type granitoids in the Peninsula Ranges Batholith, southern California.

Monday 27 August Session 4 3.50pm - 5.50pm Chairman: R.C. Price

Venue: E7B T2

3.50 -

4.10

S. KUEHNER and D.H. GREEN Mafic dykes from the Vestfold Hills, Antarctica

4.10 -

4.30

J.M.T. DOWNS and V.J. WALL The origin of quartzo - feldspathic segregations in semi-pelitic host rocks, Broken Hill, N.S.W.

4.30 -

4.50

B.J. HENSEN and R.G. WARREN Fluid evolution in granulites from the Arunta Block, central Australia.

4.50 -

5.10

W.R. TAYLOR and S.F. FOLEY Application of FTIR spectroscopy to studies of magmatic volatile solubility mechanisms.

5.10 -

5.30

C.K. BAKER and C.F.K. DIESSEL Geothermometry in rocks of the Barrington Tops metamorphic aureole using phytoclast reflectance.

5.30 -

5.50

K.R. LUDWIG and J.A. COOPER Crockers Well and associated mineralization: and hosts.

Tuesday 28 August Session 3 1.40pm - 3.20pm Chairman: T.H. Green

U, Th, Pb geochronology of ore

Venue: E7B T2

1.40 -

2.00

I.E.M. SMITH and C.J.N. WILSON Processes in silicic magma chambers - evidence from rhyolite eruptives in the Taupo Volcanic Zone, New Zealand.

2.00 -

2.20

E.J. MIKUCKI and V.J. WALL The Mt. Macedon Dacite: origin and evolution of a weakly peraluminous magma of intermediate composition.

2.20 -

2.40

R.C. PRICE, R.W. JOHNSON, C.M. GRAY and F.A. FREY The geochemistry of phonolites and trachytes from the summit region of Mt. Kenya.

2.40 -

3.00

G.E. WHELLER and R. VARNE Evolution and petrogenesis of the Batur Volcano, Bali.

3.00 -

3.20

J.A. GAMBLE and P.A. MORRIS Cenozoic and Recent volcanism on the Campbell Plateau: geochemistry of volcanic rocks and an assessment of the sub-continental mantle.

Tuesday 28 August Session 4 3.50pm - 5.30pm Chairman: V.J. Wall

Venue: E7B T2

3.50 -

4.10

R.C. PRICE, M.R. SNEERINGER and F.A. FREY Geochemistry of basalts from the west Indian Ocean triple junction: evidence for primary magmas and magma mixing at an active ridge system.

4.10 -

4.30

R. VARNE Involvement of subcontinental mantle in arc petrogenesis: implications.

evidence and

4.30 -

4.50

W.D. BIRCH Late-stage crystallization trends in basic and alkaline volcanic rocks in Victoria.

4.50 -

5.10

F.L. SUTHERLAND and J.D. HOLLIS The composite lithosphere of eastern Australia - records from volcanic rocks.

5.10 -

5.30

G.W. EBERZ, I.A. NICHOLLS and V.J. WALL Mechanical interaction and mixing of magmas in a bimodal pluton, Swifts Creek area, Victoria.

SYMPOSIUM S4 (SGGMP) Convener:

MICRO-BEAM METHODS

Dr. R.A. Eggleton

Wednesday 29 August Session 1 8.30am - 10.30am Chairman: R.L. Stanton

Venue: W5A T2

8.30 -

8.50

R.L. STANTON Introduction

8.50 -

9.10

J.D. FITZ GERALD Electron beam methods in geosciences: TEM - the technique.

9.10 -

9.50

R.A. EGGLETON High resolution electron microscopy.

9.50 - 10.10

I.D.R. MACKINNON A geological perspective on analytical electron microscopy.

10.10 - 10.30

J.F. BANFIELD and R.A. EGGLETON The fixation of mobile R.E.E. during weathering by replacement of apatite.

Wednesday 29 August Session 2 11.00am - 12.40pm Chairman: R.L. Stanton

Venue: W5A T2

11.00 - 11.40

V.N.E. ROBINSON KEYNOTE ADDRESS Backscattered electron imaging as an aid to geological and mineralogical studies.

11.40 - 12.00

I.A. NICH0LLS Determination of rare-earth element partition coefficients for experimental calcic clinopyroxene-basaltic liquid pairs: interpretation and microprobe analysis of assemblages.

12.00 - 12.20

S.H. SIE An accelerator laboratory for the earth sciences.

12.20 - 12.40

S.H. SIE, C.G. RYAN and D.R. COUSENS The HIAF particle microprobe facility.

Friday 31 August Session 1 8.30am - 10.30am Chairman: J.F. Lovering

Venue: E7B T1

8.30 -

9.10

T.R. IRELAND Fundamentals of the ion microprobe.

9.10 -

9.50

I.S. WILLIAMS Geochemistry by ion microprobe.

9.50 - 10.10

R.W.T. WILKINS The Raman microprobe - a unique tool for inclusion research.

10.10 - 10.30

Y. BONE and B.J. GRIFFIN Qualitative analysis of the fluid in fluid inclusions, using the electron microprobe.

Friday 31 August Session 2 11.00am - 12.40pm Chairman: j.p. Lovering

: WINDOWS TO THE NEW MINERALOGY

Venue: E7B T1

11.00 - 11.20

J. OSTWALD Microbeam methods in manganese oxide mineralogy.

11.20 - 11.40

P.A. MORRIS EPMA analysis of ultramafic nodules from Oberon, NSW: thermobarometry.

mineral chemistry and

SYMPOSIUM S5

PERCEPTION, PEOPLE AND PRACTICE - EVOLUTION OF THE GEOSCIENCES

AUSTRALASIA Convener:

Dr. B.J. Cooper

Poster Paper:

D.F. Dr.BRANAGAN Odernheimer's map.

Thursday 30 August Session 3 1.40pm - 3.20pm Venue: E7B T2 Chairmen: D.F. Branagan and B.J. Cooper I.40 -

2.00

B.J. COOPER Australian geology:

2.00 -

2.20

D.W. CORBETT South Australian geology:

2.20-

2.40

D.F. BRANAGAN A.R.C. Selwyn, pioneer of the Australian geological profession.

2.40 -

3.00

W.A. MCGEE The gold mine at Kulumadau, Papua New Guinea, a cautionary tale.

3.00 -

3.20

E.B. JOYCE Development of geological concepts in the young volcanic province of Victoria, Australia.

Thursday 30 August Session 4 3.50pm - 5.30pm Chairmen: A.H. Voisey and B.J. Cooper

some lessons from history. the early years 1836-1860.

Venue: E7B T2

3.50 -

4.10

R.E. RELPH Early history of oil exploration in Australia.

4.10 -

4.30

A.A. DAY Was the Imperial Geophysical Experimental Survey (1928-1931) really necessary?

4.30 -

4.50

B.J. COOPER South Australian geology 1940-1970:

4.50 -

5.30

A.H. VOISEY Geologists from 1930-1980, some personalities and their contributions.

SYMPOSIUM S6 Convener:

a preliminary review.

METALLOGENY AND TECTONIC DEVELOPMENT OF EASTERN

AUSTRALIA

Dr. E. Scheibner

Tuesday 28 August Session 1 8.30am - 10.30am Chairman: N.L. Markham

Venue: E7B T5

8.30 -

9.00

P.L.F. COLLINS and E. WILLIAMS Metallogeny and tectonic development of the Tasman Fold Belt system in Tasmania.

9.00 -

9.20

A.J. PARKER Metallogeny and tectonic development of the Tasman Fold Belt in South Australia.

9.20 -

9.50

W.R.H. RAMSAY and A.H.M. VANDENBERG Metallogeny and tectonic development of the Tasman Fold Belt system in Victoria.

9.50 - 10.30

P. DEGELING, L.B. GILLIGAN, E. SCHEIBNER and D.W. SUPPEL Metallogeny and tectonic development of the Tasman Fold Belt system in New South Wales.

Tuesday 28 August Session 2 11.00am - 12.40pm Chairman: N.L. Markham

Venue: E7B T5

II.00 - 11.40

C.G. MURRAY Metallogeny and tectonic development of the Tasman Fold Belt system in Queensland.

11.40 - 12.00

C.R. NASH Tectonic evolution and metallogenesis, Rockhampton-Maryborough area, Queensland.

12.00 - 12.20

A.J. CRAWFORD Geochemistry of Cambrian volcanics in some dispersed fragments of east Gondawanaland foldbelts.

12.20 - 12.40

K.J. KEMEZYS Metallogeny and tectonic development of southeastern Australia.

Tuesday 28 August Session 3 1.40pm - 3.20pm Chairman: I.R. Plimer 1.40 -

2.00

K. DADD Volcanic stratigraphy and palaeogeography of the Eden-Comerong-Yalwal rift zone.

2.00 -

2.20

P. BAILLIE A Palaeozoic suspect terrane in southeastern Australia and north Victoria Land, Antarctica.

2.20 -

2.40

B.P.J. STEVENS The Proterozoic Willyama Supergroup, Broken Hill N.S.W. and the search for a tectonic model.

2.40 -

3.00

S.S. WEBSTER Geophysics of some granitoid related mineral deposits.

3.00 -

3.20

E.J. HEIDECKER and J.M.W. RYNN Geomorphology, seismology and mineral targets - an exploration approach through tectonic studies?

Tuesday 28 August Session 4 3.50pm - 5.30pm Chairman: S.S. Webster

Venue: E7B T5

3.50 -

4.10

A.M. BRAMALL and I.R. QURESHI A preliminary investigation of the gravity anomalies in the Gunnedah-Tamworth area.

4.10 -

4.30

R.S. STEPHENSON and K« LAMBECK Erosion-isostatic rebound models for uplift: Australia.

4.30 -

4.50

SYMPOSIUM

Convener:

an application to southeastern

J.W. CREASEY Brittle deformation associated with joints and ironstone veins in Triassic sandstones, Sydney Basin.

ENGINEERING

GEOLOGY

IN THE SERVICE OF MAN

Dr. M.J. Knight

Monday 27 August Session 3 1.40pm - 3.20pm Chairman: J. Brumley

Venue: E7B T3

1.40 -

2.40

D.H. BELL KEYNOTE ADDRESS Presentation of geological data for engineering purposes.

2.40 -

3,20

N.R.P. BACZYNSKI The computer slave in geomechanics.

Monday 27 August Session 4 3.50pm - 5.30pm Chairman: A. Power

Venue: E7B T3

3.50 -

4.20

A. SHAY AN and C.J. LANCUCKI Rapid decay of slate roofing tiles in service.

4.20 -

4.50

G.W. WON and R. H0DGINS Use of coal washery waste as a construction material.

4.50 -

5.20

W.F. COLE and C.J. LANCUCKI The formation of talc from mica effected by the breakdown of pyrrhotite.

Tuesday 28 August Session 3 1.40pm - 3.20pm Chairman: M.J. Knight

Venue: E7B T5

Venue: E7B T3

1.40 -

2.10

R.J. FROST Water resources management in mining-experiences of the BHP Company.

2.10 -

2.40

J. BRUMLEY Hydrogeology of the Latrobe Valley related to groundwater extraction at Morwell open cut, Victoria.

2.40 -

3.10

K . H . R . MOELLE and D . F . BRANAGAN Foundation damage in water-affected Permian rocks, Newcastle, N . S . W .

Tuesday 28 August Session 4 3.50pm - 5.30pm Chairman: D . H . Bell

Venue: E7B T3

3.50 -

4.20

R . JOHNSTON Geological disposal of nuclear fuel wastes: Canadian program.

4.20 -

4.50

N . M . GRAY Support of geological defects in tunnels in the Sydney area.

4.50 -

5.20

G . W . H0FMANN Landslide risk assessment for local authorities in Queensland.

SYMPOSIUM S9 : (ASSG) Convener:

engineered barriers in the

FLUVIO-DELTAIC SEDIMENTATION D r . P . J . Conaghan

Thursday August- 3.20pm Session 3 30 1.40pm Chairman: A . P . Belperio

Venue: E7B T1

B . R . RUST KEYNOTE ADDRESS Alluvial sedimentary m o d e l s .

1.40 -

2.20

2.20-

2.40

C . M c A . POWELL, P.J. CONAGHAN and E . I . PRENDERGAST Tectonostratigraphy of the Devonian-?Carboniferous Lambian foreland b a s i n .

2.40 -

3.00

C.L.A. KILLICK Palaeocurrents and provenance of conglomerates in the Lambie and Catombal Groups, central western New South W a l e s .

3.00 -

3.20

A . T . WELLS and P . E . O'BRIEN Styles of channel sedimentation in the Marburg Formation, northern ClarenceMoreton Basin, southeast Queensland.

Thursday 30 August Session 4 3.50pm - 5.30pm Chairman: I.H. Lavering

Venue: E7B T1

3.50 -

4.10

P . E . O'BRIEN and A . T . WELLS Processes on a Jurassic floodplain, the Marburg Formation In southeast Queensland.

4.10 -

4.30

K . L . MCDONNELL and P . J . CONAGHAN Late Permian to middle Triassic alluvial depositional environments of the Sydney Basin: coastal transect.

4.30 -

4.50

P . HARVORD, C . HERBERT, P . J . CONAGHAN, J . W . HUNT and K . ROYCE The Marrangaroo Conglomerate - its distribution and origin in the Sydney Basin.

4.50 -

5.10

N . SENAPATI and D . J . BOURKE The Mesozoic sequence of the north eastern Carpentaria Basin - a series of marine transgressions.

Friday 31 August Session 3 1.40pm - 3.20pm Chairman: R . A . F . Cas 1.40 -

2.20

Venue: E7B T1

J . M . COLEMAN KEYNOTE ADDRESS Modern delta processes and m o d e l s .

2.20 -

2.40

D . A . FEARY Proposal for a generalised facies model for clastic shorelines.

2.40 -

3.00

I.H. LAVERING Wave and river-dominated delta systems of the early Permian Wooramel G r o u p , Carnarvon Basin.

3.00 -

3.20

B . G . LEES Recent deltaic sedimentation in the southern Joseph Bonaparte G u l f , northern Australia.

Friday 31 August Session 4 3.50pm - 5.30pm Chairman: P» Moore 3.50 -

4.10

P.E. O'BRIEN Permian glaciolacustrine deltas in central Victoria.

4.10 -

4.30

P.A. SYM0NDS and P.J. DAVIES Fluvio-deltaic depositional systems and shelf development in the central Great Barrier Reef region.

4.30 -

5.10

P.J. C0NAGHAN Aapamire (string-bog) origin for stone-roll swarms and associated 'fluviodeltaic 1 coals in the late Permian Illawarra Coal Measures of the southern Sydney Basin: climatic, geomorphic and tectonic implications.

S Y M P O S I U M S10

LITHOSPHERIC

P R O C E S S E S A N D T H E F O R M A T I O N OF S E D I M E N T A R Y

BASINS

Convener:

D r . G.D. Karner

Poster Paper:

H.W. D0SS0, W.D. PARKINSON and W . NIENABER Analogue modelling of the electromagnetic response of Tasmania and southern Australia - preliminary results.

Monday 27 August Session 3 1.40pm - 3.20pm Chairman: K . Lambeck 1.40 -

2.20

2.20 -

2.40

2.40 -

3.00

3.00 -

3.20

Venue: E7B T4

M.F. MIDDLETON Lithospheric processes involved in the formation of the Canning Basin, Western Australia. D.M. FINLAYSON and C.D.N. COLLINS Seismic velocity structures of the lithosphere under the shelves and troughs of the central Eromanga Basin. M.A. ETHERIDGE, J.C. BRANSON, P.G. STUART-SMITH and A.S. SCHERL The geometry of extensional structures in the Bass Basin. G.D. KARNER, M . ETHERIDGE, J . BRANSON and A.S. SCHERL Sedimentary basin modelling: constraints from the Bass Basin.

Monday 27 August Session 4 3.50pm - 5.30pm Chairman: M.F. Middleton

Venue: E7B T4

3.50 -

4.10

J.C. BRANSON and D.A. FALVEY Seismic stratigraphy, basin structure and evolution of a passive continental margin - Otway basin southeast Australia.

4.10 -

4.50

H.W.S. MCQUEEN and K . LAMBECK Post-orogenic basin evolution models.

4.50 -

5.10

I.A. MUMME The role of geological faulting in south-east Australia, and its bearing on the seismicity of the region.

5.10 -

5.30

K . LAMBECK and C . PENNEY Deep crustal structure below central Australian basins.

Tuesday 28 August Session 3 1.40pm - 3.20pm Chairman: G.D. Karner

Venue: E7B T1

Venue: E7B T4

1.40 -

2.20

I.R. QURESHI Geophysical evidence for the rifting of the basement underlying the Sydney Basin.

2.20 -

2.40

R.M. CARTER and L . CARTER Submarine fans, channels and levees, Bounty Trough, southwest Pacific Basin.

2.40 -

3.00

P.J.J. KAMP The mid-Cenozoic extent, continuity and geotectonic development of a continental rift system through western New Zealand: implications for the age of Alpine Fault inception.

3.00 -

3.20

G . HOUSEMAN and P . ENGLAND Dynamical models of lithosphere extension and sedimentary basin formation.

Tuesday 28 August Session 4 3.50pm - 5.30pm Chairman: G.D. Karner

Venue: E7B T4

3.50 -

4.30

G.D. KARNER and J.K. WEISSEL Thermally induced uplift and lithospheric flexural readjustment of the eastern Australian highlands.

4.30 -

4.50

DISCUSSION

SYMPOSIUM

S1I

STRUCTURE, COMPOSITION

AND TECTONIC HISTORY OF THE

SUBCRUSTAL

LITHOSPHERE Convener:

Dr. B.J. Drummond

Thursday August - 3.20pm Session 330 1.40pm Chairman: S.Y. O'Reilly

Venue: E7B T3

1.40 -

2.20

D.H. GREEN KEYNOTE ADDRESS The Earth's lithosphere and low velocity zone.

2.20 -

2.40

K.J. MUIRHEAD The base of the lithosphere under Australia.

2.40 -

3.00

B.J. DRUMMOND Seismic velocities as an indicator of tectonic processes in the deep lithosphere under Australia.

3.00 -

3.20

D.M. FINLAYS0N Upper mantle velocities for the central and east Australian lithosphere and comments on Pn anisotropy.

Thursday 30 August Session 4 3.50pm - 5.30pm Chairman: D.H. Green

Venue: E7B T3

3.50 -

4.10

J.C. DOOLEY Velocity variations and isostatic compensation in the Australian region.

4.10 -

4.30

G. F. DAVIES Steady and transient thermal regimes of continental lithosphere.

4.30 -

4.50

D. C0NLEY Depth of the Curie Point beneath Australia.

4.50 -

5.10

P. WELLMAN and A.S. MURRAY Australian long-wavelength magnetic anomalies.

Friday 31 August Session 3 1.40pm - 3.20pm Chairman: B.J. Drummond

Venue: E7B T3

1.40 -

2.00

J.P. CULL Magnetotelluric soundings and anisotropy in electrical profiles of the lithosphere.

2.00 -

2.20

I. JACKSON, M.S. PATERSON, S.L. WEBB and H. NIESLER The use of petrophysical data in the interpretation of seismological models of the continental lithosphere.

2.20 -

2.40

M.S. PATERSON Extrapolation of laboratory rheological behaviour in tectonophysics.

2.40 -

3.00

D.J. ELLIS Metamorphism and metasomatism of the Archaean basement - the relationship between high grade gneiss terrains and intracratonic mobile zones from Enderby Land, Antarctica.

3.00 -

3.20

J. KNUTSON, S.Y. O'REILLY, M.B. DUGGAN and A.L. JAQUES The nature of the lower crust and upper mantle beneath eastern Australia as inferred from xenolith studies.

Friday 31 August Session 4 3.50pm - 5.30pm Chairman: I.N.S. Jackson 3.50 -

4.10

Venue: E7B T3

R.L. RUDNICK, S.R. TAYLOR and I. JACKSON Geochemistry and seismic velocities of the lower crust in northeast Queensland evidence from granulite facies nodules in Recent basalts.

4.10 -

A.30

S.Y. O'REILLY and W.L. GRIFFIN A xenolith-derived geotherm for southeastern Australia, and its geophysical implications.

4.30 -

4.50

W.F. MCDONOUGH and M.T. MCCULLOCH

4.50 -

5.10

D.R. NELSON, M.T. MCCULLOCH and A.L. JAQUES Nd-Sr isotope ratios in ultrapotassic rocks from S.E. Australia and their implications for the subcontinental lithosphere.

SYMPOSIUM

S12

Nd-Sr isotopic compositions of basalts from southeastern Australia: implications for mantle isotopic variation.

Convener:

THE

TECTONICS

AND RESOURCES

OF A C T I V E

MARGINS

Dr. H.L. Davies

Tuesday 28 August Session 1 8.30am - 10.30am Chairman: D.A. Falvey

Venue: E7B 100

8.30 -

8.50

C.T. KL00TWIJK The Himalayan arc: continental analog of oceanic subduction.

8.50 -

9.10

G. HOUSEMAN and P. ENGLAND Finite element models of continental collision - the distribution of strain and strain rate in central Asia.

9.10 -

9.50

E.A. SILVER

KEYNOTE ADDRESS

Modern tectonics of the western Indo-Pacific region as a model for the Mesozoic North American cordillera. 9.50 - 10.10

H. LETZ Seismicity of Irian Jaya 1900-1980.

10.10 - 10.30

E.A. BOWEN Structural elements and petroleum potential of the Papuan Basin, Papua New Guinea.

Tuesday 28 August Session 2 11.00am - 12.40pm Chairman: H.L. Davies

Venue: E7B 100

11.00 - 11.20

E.A. SILVER Multibeam study of the Flores and Wetar backarc thrusts, eastern Indonesia.

11.20 - 11.40

M.0. MICHAEL-LEIBA The Banda Sea earthquake of 24 November 1983: thrust faulting in the Benioff Zone.

evidence for intermediate depth

11.40 - 12.00

J. LOCK Solomon Sea structure from seismic reflection data.

12.00 - 12.20

J.G. VEDDER, D.L. TIFFIN and J.B. C0LWELL, and others Geology, tectonic evolution and petroleum potential of the central Solomons Basin: results of recent tripartite cruises.

12.20 - 12.40

R.C. PRICE, K.T.M. JOHNSON and J.M. SINT0N Geochemical affinity of volcanic rocks from the northern Melanesian borderland.

CONVENTION WORKSHOPS

WORKSHOP

W12

G E O S C I E N T I S T S AND G O V E R N M E N T - D E V E L O P M E N T G E O S C I E N C E POLICY

Convener:

OF A

RATIONALISED

K.R. Glasson

Wednesday 29 August Session 3 *1.30pm - 3.20pm Chairman: K.R. Glasson

Introduction and aims of workshop K.R. GLASSON Human resource survey M. SANT DISCUSSION Education and research policies J.F. L0VERING B.J. SKINNER DISCUSSION Environmental problems and geoscientists G.H. TAYLOR W.S. FYFE DISCUSSION

1.30 - 1.40 1.40 - 1.55 1.55 - 2.00 2.00 - 2.15 2.15 - 2.30 2.30 - 2.40 2.40 - 2.55 2.55 - 3.10 3.10 - 3.20

Wednesday 29 August Session 4 3.50 - 5.30pm Chairman: K.R. Glasson

4.45 - 5.05 5.05 - 5.30

Convener:

Venue: Macquarie Theatre

Resource development and geoscience policy J.N. ELLIST0N W.L. FISHER T.P. H0PW00D DISCUSSION Geoscience societies and government C.D. BRANCH Panel discussion C.D. BRANCH - Chairman

3.50 - 4.05 4.05 - 4.20 4.20 - 4.35 4.35 - 4.45

WORKSHOP

Venue: Macquarie Theatre

AGID-ILP WORKSHOP - G E O S C I E N C E S FOR D E V E L O P M E N T : D E V E L O P I N G C O U N T R I E S NEEDS AND THE A U S T R A L I A N ROLE AND THE PACIFIC

ASIA

Dr. M.B. Katz

Monday 27 August Session 3 1.40pm - 3.20pm Venue: E7B100 Chairmen: R.V. Burne and R.N. Richmond 1.40 -

2.00

R.W.R. RUTLAND KEYNOTE ADDRESS Some Australian experience in geoscientific cooperation with developing countries.

2.00 -

2.20

J.F. MCDIVITT KEYNOTE ADDRESS UN's role in the development of the geosciences in southeast Asia and the Pacific.

2.20 -

3.20

Speakers, panel discussion and Working Group on Offshore Mineral and Energy Resources

Monday 27 August Session 4 3.50pm - 5.30pm Venue: E7B 100 Chairmen: R.V. Burne and R.N. Richmond Offshore Mineral and Energy Resources 3.50 -

4.10

R.V. BURNE Petroleum and mineral resources of the southwest Pacific.

4.10 -

4.30

N.F. EX0N Manganese nodules, cobalt-rich crusts and hydrothermal metal deposits in the southwest Pacific.

4.30 -

4.50

E.J. LANGEVAD The development of deep sea mining in the international areas of the oceans.

4.50 -

5.10

B. HOCKING Chinese petroleum geology.

5.10 -

5.30

DISCUSSION

Tuesday 28 August Session 3 1.40pm - 3.20pm Chairmen: H.F. Doutch and R. Green

Venue: E7B 100

1.40 -

2.00

R.N. RICHMOND KEYNOTE ADDRESS South Pacific mineral potential, government policies and misplaced advice.

2.00 -

2.20

P. NUTALAYA KEYNOTE ADDRESS A G I D ^ programs in southeast Asia.

2.20 -

3.20

Speakers,'panel discussions and Working Group on Onshore Minerals and Energy Resources

Tuesday 28 August Session 4 3.50pm - 5.30pm Chairmen: H.F. Doutch and R. Green

Venue: E7B 100

Onshore Minerals and Energy Resources Poster Display:

H.F. DOUTCH Maps

3.50 -

4.10

P.F. HOWARD The UNESCO-IUGS phosphorite program - a model of successful scientific cooperation.

4.10 -

4.30

R. KENDARSI Coal, the challenge of the future for Indonesia.

4.30 -

4.50

D. TAYLOR The tin resources of southeast Asia.

4.50 -

5.30

DISCUSSION

Thursday 30 August Session 3 1.40pm - 3.20pm Venue: E7B 100 Chairmen: R.J. Blong and R.W. Johnson Geological Hazards 1.40 -

2.00

R.W. JOHNSON and R.J. BLONG Geological hazards : assessment, mitigation and disaster/emergency responses in the southwest Pacific/southeast Asia region.

2.00 -

3.20

Speakers, panel discussions and Working Group on Geological Hazards.

Thursday 30 August Session 4 3.50pm - 5.30pm Venue: E7B 100 Chairmen: P. Clutterbuck and G. Jacobson Engineering Geology and Groundwater

3.50 -

4.10

G. JACOBSON Engineering geology and hydrogeology as factors in development.

4.10 -

4.30

S.J. HANCOCK and W.H. MORTON Groundwater consultants1 experience in aid programs.

4.30 -

4.50

K. SHARP Aid program experience with engineering geology for major construction works.

4.50 -

5.10

J.R. MCALPINE and D.N. BODY Land use assessment for development:

5.10 -

5.30

DISCUSSION

the role of earth scientists.

THE EVOLUTION AND CONCENTRATION OF U AND REE IN THE MARY KATHLEEN SKARN, QUEENSLAND P. Abeysinghe, T.A.P. Kwak and A.J.R. White La Trobe University, Bundoora, Victoria The evolution of the Mary Kathleen U-REE deposit is very similar to other andradite-rich skarns, particularly Sn and W ones, except for the unusual minor element content. Uraniferous andradite rich garnet and pyroxene (stage one) skarn was successively overprinted by ferrohastingsite-epidote mineral (allanite)-apatite-sulphide-uraninite (stage 2) skarn and later more hydrous, phyllite (stage 3) alteration. There is a progressively changing evolution of mineral and fluid compositional characteristics from stage one to stage two skarn in both time and space relative to the Mary Kathleen shear, viewed as the main source of hydrothermal solutions. Garnet, which hosts nearly all the U-REE content in primary skarn has an average andradite composition of 867® nearest the shear to 64% furtherest away (230 metres). U and REE values in individual garnets are compositionably growth zoned but no clear trend was identified. In garnet U values vary from 5ppm to 24ppm (by fission track and probe analysis) while REE generally vary from 400ppm to 7600ppm (a probe analyses) with Ce>La>Nd>Y. Fluids, as determined by fluid inclusions, reflect a decreasing trend in temperatures from 775°C nearest the shear to 318°C furthest from the shear. The composition of the fluids changed from 72.7 to 34.6 weight per cent total dissolved salts over this interval. These, now largely "spent" or exhaust" solutions are rich in CaCl2 KC1, NaCl and U-REE salts (identified as daughter products in fluid inclusions). The likely reactions at this stage would be of the type: Fe-U-REE Chlorides + Si02 (primary solution) + CaC03(marble) • Ca-Fe-(U,REE) silicate (skarn) + CaCl2 + C02(exhaust solution) As suggested by textural, fluid inclusion, mineral composition and thermodynamic calculation studies, U and REE were leached from stage I skarn during retrograde stage II skarn genesis probably due to limited ( 2 0 7 o ) meteoric water mixing. Both temperatures were still high (approx. 450°C in apatite, ;approx. 500°C in ferrohastingsite) and salinities were considerable, (approx. 50wt. 7o total dissolved salts). Deposition of U as fine grains of uraninite and REE as solid solution in allanite occurred in late, permeable areas, such as fractures or fracture intersections.

fo2 was around 10~22 to 1 0 " ^ bars during stage I and has progressively dropped during stages II and III. The fs2 during stage two was around 10"^.4 t o 10~6.3 bars. During stage II, reactions of the following type occurred: U-REE garnet 4- CO2 +H2O = allanite + uraninite + calcite -I- silica 4- hematite + 02. Some uranium may well have been leached transported and redeposited outside the skarn, since the skarn generating system was complete. The unique compositional nature of the skarn is related to the unique nature of (orthomagmatic) mineralizing solutions derived from crystallization of the nearby Burstall granite and related rhyolite dykes. These contain a highly unusual early Ca-Fe amphibole phase and anomalously high U and REE whole rock contents. In this they resemble variants of A-type granites such as those of Gabbo Island. N.S.W.

FRACTIONATION OF THE BURSTALL GRANITE AND THE SOURCE OF URANIUM IN THE MART KATHLEEN DEPOSIT P.B. Abeysinghe, A.J.R. White, T.A.P. Kwak and R.C. Price La Trobe University, Bundoora, Victoria Granite-related hydrothermal uranium deposits occur within or near felsic U-rich granites OlOppm U) that have geochemical features indicative of feldspar fractionation (eg. Cuney 1978). The major elements of these granites are dominantly Si(>2, AI2O3, Na£0 and K2O and these show no appreciable variation with continued fractionation. This is reflected in the dominance of quartz, K-feldspar and albite in the granites and their more or less constant proportions during fractionation. However, minor elements that preferentially enter feldspars (e.g. Sr and Ba) show a progressive decrease concomitant with an increase of those elements that preferentially enter the melt phase. As quartz and feldspars are removed from the system there will also be a progressive increase of volatile content. This paper describes the fractionation of the Burstall Granite and related dykes that are considered to be the source of the uranium of the Mary Kathleen deposit (Whittle 1960: Derrick et al. 1977). The granite is felsic, K-feldspar-rich and contains ferro-hastingsite as the main mafic mineral with minor biotite (all altered) and accessory sphene, apatite, zircon and fluorite. The ferro-hastingsite is Cl-rich (about 27oCl) and persists even in highly fractionated rocks: rarely it is seen to replace early hedenbergite. Dykes are even more felsic and richer in K-feldspar, but still have accessory amphibole. New analytical data on 21 samples of granite and porphyritic microgranite (dykes) show a systematic decrease in Sr from near lOOppm, resulting from feldspar fractionation. Since Sr does not enter the biotite structure, alteration of the small amount of biotite in the Burstall samples does not affect the geochemical trends when Sr is used as the index of fractionation. With decreasing Sr there is an increase in Rb, K, Th and W and K/Rb, whereas Na20,Ba and the rare earth elements decrease. Nb, Zr, Pb and Ga show virtually no change with decreasing Sr. Log-log plots are essentially linear so that data can be projected back to unfractionated parent rocks OlOOppm Sr) and deductions made about the unfractionated granite type. When this is done the Burstall Granite and its related dykes are seen to be fractionated A-types (Collins et al. 1982). Fractionation results in an increase in U to levels OlOppm) such that uraninite becomes a primary phase: this is readily leached by hydrothermal solutions and is considered to be the source of uranium for the Mary Kathleen deposit. References Collins, W.J., Beams, S.D., White, A.J.R., andChappell, B.W., Contrib. Miner Petrol. 80^ 189-20. Cuney, M., 1978, Econ. Geol. 73^ 1567-1610. Derrick, G.M., 1977, BMR. Journ. Geol. Geophys. 2^ 123-130. Whittle, A.W.G., 1960, Neues Jahrbuch Miner. Abh., 94, 798-830.

1982,

THE ELSMORE GRANITE AND ITS BEARING UPON THE ORIGIN OF GREISEN AND CASSITERITE MINERALIZATION J.D. Adam Geology Department, University of Tasmania, Hobart The Elsmore Granite occurs within the.southern part of the New England Fold Belt, 10 km east of Inverell in N.S.W. It is a small pluton km 2 ) of highly felsic biotite-granite and possibly forms a cupola of the very much larger (-100 km 2 ) Gilgai Granite which is exposed 5 km to its south. Northeast-trending greisen veins composed of quartz, Fe-rich muscovite and accessory cassiterite, occur within the northern and eastern parts of the granite. Although typical of greisens fluorite, topaz and tourmaline are absent and sulphides rare within the greisen at Elsmore. Fluorite however is present within the unaltered granite. Granite in the northwestern part of the pluton is kaolinized to a nearly pure kaolinite-quartz rock. Greisen veins occurring outside this area are accompanied by incomplete but pervasive sericitization of the granite. Fluid inclusions within greisen veins homogenize principally at between 250 and 400°C and have salinities generally <3 ewt.%NaCl. A pressure estimate of approximately 200 bars was derived from fluid inclusion evidence. The chemistry and pattern of hydrothermal alteration can be explained in terms of experimentally and naturally observed phase relationships in the system Na20-K20-Al203-Si02-H20-Cl,1 together with theoretically calculated cooling rates of plutons cooled by the convection of groundwater.2 The occurrence of slickensides, shearing and localized linear zones of phenocryst alignment, suggest that a regional shear stress was important in producing sufficient permeability within the granite and its country rocks to enable the convection of groundwater to occur. The nature of greisenization at Elsmore suggests that greisen formation and associated cassiterite mineralization need not necessarily involve special circumstances of magma genesis. The probable mode of Sn transport in hydrothermal solution - wallrock systems is such that it can be concentrated from convecting hydrothermal solutions as they pass through a temperature and wallrock induced pH and f02 gradient.3 Therefore only circumstances of intrusive history and bulk composition are needed for the development of a hydrothermal system, with physical and chemical conditions that will produce greisen-type mineral assemblages and concentrate Sn in cassiterite as an accessory alteration phase. References 1

Burt, D.M., 1976, Econ. Geol., 71, 665-671. 2 Norton, D., & Knight, J., 1977, Am. Jour. Sci., _277, 937-981. 3 Eadington, P.J., $ Giblin, A., 1979, CSIRO Div. Mineralogy, Tech. Commun. 68.

ELECTRON MICROPROBE STUDY OF THE DISTRIBUTION OF TRACE ELEMENTS IN CONODONT APATITE : INTRA ELEMENTAL AND SECULAR VARIATIONS Raisuddin Ahmad Macquarie University, North Ryde A number of conodont elements of Ordovician to Permian ages from different geographical locations in the U.S.A. have been analyzed for eleven trace elements by Electron Microprobe. Line scans were also made in some conodont elements for many of those trace elements. Systematic temporal.variations exist in the concentration of Na, CI, Sr, Fef F, etc. Similar variations are also displayed by the Cl/Na and Sr/Fe ratios respectively. These temporal variations of individual trace elements and their ratios are tentatively attributed to possible changes in the chemistry of ancient oceans where the conodont elements were deposited. The line scans by Electron Microprobe do not show any significant variation in the distribution of S, Fe, Sr, CI, Na, etc. among the basal part, tip and rest of the areas in a particular conodont element and disprove the finding of such a variation by Pietzner et al. (1968) . However, the line scans show inter lamellar variations in the concentration of the above elements which could possibly be due to yearly or seasonal variations in the amount of uptake of these elements. Partial support for the present study was provided from the United States N.S.F. Grant - EAR 8115985 awarded to Dr. W.T. Holser, Geology Department, University of Oregon.

NEW METHODS FOR ASSESSING MATURITY AND PALAEOTEMPERATURES R. Alexander School of Applied Chemistry, Western Australian Institute of Technology, Bentley Recent developments in molecular geochemistry have provided reliable methods for assessing the thermal maturity of organic matter in sediments. Biological marker compounds, which are constituents of petroleum and most organic rich sediments, undergo epimerisation reactions which alter their molecular goemetry. The extent to which these reactions have progressed have been used to assess thermal maturity of sediments up to that usually associated with maximum oil generation.1>2 * Other processes such as the rearrangement of methylphenanthrenes39k and methylnaphthalenes5 have also been shown to progress in a uniform manner with increases in thermal maturity. Changes in isomer ratios of these aromatic compounds can provide information about the maturity of sediments from those which are immature through to those within the oil window and beyond. The relative response of different processes has been shown to be dependent upon temperature. These differences have been established for a sediment column where the present temperatures are assumed to be the maximum temperatures of the sediments. Determination of the relative extent to which these processes have occured in a second sediment column enables their palaeotemperatures to be inferred. This approach to estimating palaeotemperatures and palaeotemperature gradients of sediments will be illustrated with examples from the Carnarvon Basin.

References 1. Seifert, W.K., and Moldowan, J.M., 1978, Geochim. et Cosmochim. 77-95.

Acta, 42,

2. Mackenzie, A.S., Patience, R.L., Maxwell, J.R., Vandenbroucke, M., and Durand, B., 1980, Geochim. et Cosmochim. Acta, 44, 1709-1721. 3. Radke, M., Welte, D.H., and Willsch, H., 1982Geochim. et Cosmochim. Acta, 46, 1-10. 4. Radke, M., and Welte, D.H., 1983, In: M. Bjor^y et al.,Wiley, 504-512.

Advances in Organic Geochemistry, eds

5. Alexander, R.? Kagi, R.I., and Sheppard, P., 19«4, Nature, 308, 442-443.

SERPENTINE FOR STEEL MAKING IN AUSTRALIA • E. P. Ambler Hooker Industrial Sands & Minerals, Sydney In mid-1975 Australian Iron & Steel Pty* Ltd. (A,ItS,) Port Kembla, began investigations into the use of magnesium silicate in the steel making process. It was proposed to raise the MgO content of blast furnace slag by the addition of either finely crushed serpentine or dunnite to sinter. Sinter, at that time, consisted of a fused agglomeration of fine iron ore (82%), limestone (11%), coke fines (4%), mill scale and blast furnace flue dust (3% combined). Production of sinter is aimed at utilising iron ore dust, a by-product of crushing and screening, which cannot be charged directly into blast furnaces because of the fine particle size, A plant trial was proposed to determine the potential benefits of raising the MgO content of slag by between 1.3% and 6% by addition of serpentine to sinter. An alternative to this recommendation was the addition of lump dunnite directly into the blast furnace, however, such additions would have lowered the SiO content of the slag and this was considered undesirable. It was not until mid-1976 that the proposed trial was given approval and a source serpentine was chosen. Trial shipments totalling 12,000 tonnes of minus 5 mm serpentine were received from Japan between December, 1976 and May, 1977. This source was selected because of its history of supplying Japanese steel mills and the advantageous freight rate available to A,I.S. by utilising returning coal bulk carriers. The trial addition of serpentine to sinter at A*I.S. produced significant improvements in the quality of hot metal to the Basic Oxygen Steelmaking (BOS) furnace as a result of increased MgO in blast furnace slag. Reduced hot metal silicon resulted in higher productivity from the BOS as a consequence of reduced requirements for flux additions• Lower sulphur contents of hot metal and lower slag volumes were recorded. Further, as a consequence of these improvements the life of refractory furnace lining was projected to be extended. In short, the trial addition of serpentine to sinter produced significant technical and financial benefits for the steel making process. Routine addition of serpentine fines was begun in late 1978 after A.I.S. signed a two-year contract for supply with a Japanese company. Since December, 1979 A.I.S. has purchased approximately 475,000 tonnes of minus 5 mm serpentine from Japan.

Hooker Industrial Sands & Minerals, (H.I%S. & M.), a division of the Hooker Corporation Ltd., became aware in early 1979 of the A*I.S. serpentine imports and attempted to establish an indigenous alternative supply operation. Serpentine was located in the Orange area of central-western N.S.W. and processing carried out at the Division's Lithgow crushing plant. Several hundred tonnes were transported to Port Kembla, however, purchases were terminated when the serpentine was found to contain unacceptable levels of asbestos fibre. Whilst the Division was encouraged by A,I.S. to find an indigenous source, it was essential that the physical and chemical attributes be equivalent to the Japanese material, and that the mineral be nof a nonfibrous nature11. The search for an appropriate serpentinite shifted to the Coolac-Goobarragandra ultra-mafic belt in southern N.S.W. and an area was selected north of Coolac, The two year contract period between AtI.S* and the Japanese ended and a further three year contract signed before an evaluation could be commenced . With the end of the second contract period approaching, H.I.S. & M. reactivated its interest in serpentine in mid-1983. The Division concluded a private agreement to mine serpentine with landowners in the selected area and a fourteen hole percussion drilling programme was carried out in August September, 1983. Planning consent was granted by the Gundagai Shire Council and, after a detailed technical and financial evaluation, an order for 40,000 tonnes per annum was placed by A.I.S. in December, 1983. Site preparations began at the Somerset Serpentine Mine, 12 km north of Coolac, in late February and a primary impactor began crushing quarried serpentine in mid-March. The fine crushing plant began production of minus 5 mm serpentine early in the 1984-85 financial year.

PETROGRAPHIC, GEOCHEMICAL AND SULFUR ISOTOPE STUDIES ON MASSIVE SULFIDE ORES FROM CURRAWANG EAST, NEW SOUTH WALES A.S. Andrew and R.A. Binns CSIRO Division of Mineralogy, North Ryde The Currawang East deposit (Malone, 1982) is a concealed body of massive Fe-Zn-Pb-Cu sulfides discovered by St. Joe Australia Pty Ltd. about 10 km NNW of the Woodlawn mine. The deposit occurs within a subvertical sequence of pillow basalts. In plan and cross-section it appears conformable and in longitudinal section the body is lobate. Early exploration was based on a volcanic exhalative model by analogy with the mineralization in acid volcanic rocks at Woodlawn. However, the association Pb-rich sulfides with mafic lavas is unusual and the genesis of the mineralization at Currawang East is controversial. The mineralization ranges between two extreme types - pyritic and pyrrhotitic. Pyritic mineralization tends to be banded, richer in galena and deficient in chalcopyrite. Pyrrhotitic mineralization possesses patches of anastomosing ore rich in chalcopyrite and is poorer in galena. Pyrrhotitic mineralization dominates the deeper portion of the deposit, and pyritic mineralization the upper and fringe zones. Both mineralization types and transitional variants have recrystallized microstructures with pyrite and pyrrhotite in textural equilibrium. Banded structures in the mineralization are mostly deformational in origin: these and relationships with gangue minerals indicate deformation preceded recrystallization of the mineralization.

Sulfur isotope values of sulfides from Currawang East vary from -1.6 to 2.1 permil CDT. These values are similar to those reported by Burns & Smith (1976) at Currawang East and in the order of 7-8 permil more depleted in ^ S compared with values reported for Woodlawn. Within this small range there is no apparent relationship between 6 ^ S and mineralization type, structure or position within the deposit. The order of increasing ^ S enrichment in sulfide minerals (gn<cp<po<sp<py) suggests an approach to isotopic equilibrium. Apy-gn (3.0-3.4) and Asp-gn (2.2-2.3) suggest a temperature of 320 ± 40°C using the fractionation factors of Kajiwara & Krouse (1971). A temperature of 320 ± 40°C may be a reasonable estimate for the mineralization of Currawang East but this temperature may also reflect the conditions of greenschist facies metamorphism and recrystallization to which the ores were subjected. . Metamorphism may have caused reequilibration of sulfur isotope values resulting in changes to isotopic fractionation and calculated temperatures. If the temperature of mineralization were in the range 250-350°C then, the presence of reduced sulfur species, the absence of sulfates, and the narrow range of values suggests that sulfur in the fluid was predominantly as HS~ and 6^S(fluid) - 0. The different mineralization types (pyritic and pyrrhotitic) probably reflect variations in the amount of sulfur in the fluid (ZS) rather than variations in T, pH, f02 o r source of sulfur. The conclusion that 6 34 S(ES) - 0 suggests that the source of sulfur was magmatic, i.e. the sulfides are a direct product of a magmatic process, or that the mineralizing fluids have leached sulfur from an igneous source rock. This conclusion also distinguishes the Currawang East deposit from the Kuroko-style mineralization at Woodlawn. Alteration and fracturing surround the mineralization in a zone which extends upwards and along strike from the massive sulfides both in the footwall and in the hangingwall volcanics. Chlorite schists within and adjacent to the mineralization (generally < 50 m wide) represent the most intense alteration. Further from the mineralization the alteration grades through a zone of brecciation (approx. 100 m wide) into pillow basalts, reworked devitrified hyaloclastites and dolerite dykes. Alteration associated with mineralization has resulted in increases in Mg, Cu, Pb and Zn and decreases in Ca and Na. A zone of enrichment in K is present on the periphery of the mineralized zone. Al, Si and Fe show little mobility, in the mineralized zone pyrite (Fe and S) addition is associated with dilution of Al, Si, Ti, Zr and Y values. These alteration trends are found, and are of similar magnitude, in both the footwall and hangingwall to the mineralization. Sulfur isotope values of disseminated pyrite from wall rocks range from -5.6 to 3.6 permil. There appears to be a correlation between distance from the mineralization (degree of alteration), S content and S ^ S values. Towards the mineralized zone disseminated pyrite is enriched Q / Q/ in Deviations from the correlation of S j q S with distance are associated with zones of pyrite addition. The direction of change in values suggests the sulfur isotope "halo" is a result of mixing of enriched sulfur in the mineralizing fluid with sulfur already in the basalts from a prior alteration or metamorphism. This model suggests the mineralization at Currawang East is epigenetic in origin and the mineralizing fluids and sulfur are not related to the basalts now hosting mineralization. Geochemical exploration programs are initially based on commodity elements. At Currawang East these provide the least ambiguous but a restricted target. Haloes defined by CaO, MgO, Na2° and S ^ s are in the order of 200-300 metres in both the footwall and hangingwall.

References Burns, M.S. & Smith, J.W., 1976, Bull. Aust. Soc. Explor. Geophys., 7, 4344. ~ Kajiwara, Y., & Krouse, H.R., 1971, Canadian Jour. Earth Sci., 8, 13971408. Malone, E.J., 1982, Geol. Soc. Aust. Abst., 551-578.

ISOTOPIC AND FLUID INCLUSION EVIDENCE FOR SOURCES OF MINERALIZING FLUIDS AT THE SUNDOWN TIN PROSPECT, S.E. QUEENSLAND A.S. Andrew and C.A. Heinrich CSIRO Division of Mineralogy, North Ryde The Sundown tin prospect in SE Queensland, comprises several extensive lenses of multiple quartz-cassiterite veinlet mineralization within sediments (Texas Beds) intruded by the Stanthorpe Adamellite (Goode et al. 1982). The mineralization can be traced into granite and greisen at depth. Several generations of veining and alteration have been recognized in the hornfelses. Veins formed prior to mineralization, possibly by fluids derived from contact metamorphism of siltstones to biotite-rich hornfelses, are granoblastic quartz-biotite veins. These are cut by pyrrhotite-filled stringer and hairline veins, and the main mineralized veins which are characterized by their distinctive bleached alteration haloes. The latter veins contain coarse-grained muscovite, quartz, cassiterite and sulfides between sharply defined, usually subparallel vein walls. A symmetrical mineralogical zonation allows two vein mineral assemblages to be distinguished, which are interpreted as forming in two successive, but possibly overlapping, stages of hydrothermal mineralization. Assemblage I (cassiterite + muscovite + quartz + topaz + fluorite ± beryl + arsenopyrite) forms as the selvage in complex veins. Where any vein space remained between euhedral crystals of assemblage I, it was filled by assemblage II (chalcopyrite + pyrrhotite + sphalerite + minor chlorite and carbonate). Late carbonate hairline veins form a network cutting altered and unaltered hornfelses and all earlier veins. In contrast to mineralization in the hornfelses, veins in the underlying granitic rocks are wide with diffuse boundaries and contain quartz + muscovite + topaz + fluorite ± chlorite ± siderite. This greisen zone hosts most of the ore minerals as dispersed grains with a mineralogy similar to that of the metasiltstone-hosted veins but without mineralogical growth zoning. Fluid inclusion data are limited to the mineralized veins because the early quartz-biotite veins contain only secondary inclusions which are too small for detailed study. The data show that in assemblage I, simultaneous with (or immediately following) the formation of the muscovite selvage, quartz + cassiterite + arsenopyrite ± fluorite ± topaz crystallized from solutions of 370 ± 30°C and a salinity. of 5 ± 1 wt% NaCl-equivalent. Later, a fluid of lower temperature, 310 ± 20°C, and somewhat lower salinity, 2-4 wt% NaCl-equivalent, deposited the base metal rich assemblage II (chalcopyrite + sphalerite + pyrrhotite + chlorite). This fluid deposited no quartz, but generated secondary inclusions in quartz adjacent to overgrowing sulfides.

Quartz from a wolframite vein in the Red Rock Gorge, 5 km east of Sundown, contains fluid inclusion trails indicating entrapment of vapour and liquid from a boiling hydrothermal system between 350 and 400°C. Their composition places an upper limit of 1-3 km on the depth of mineralization. The same shallow depth can be assumed for the Sundown mineralization, in which case the homogenization temperatures given above are close to the actual fluid temperatures. Oxygen isotope values (6^®0) on samples from unaltered granite, greisen, and main-stage veins (Table 1) clearly show the predominance of a magmatic fluid in the first stages of the mineralizing processUsing temoeratures from fluid inclusion studies on the same samoles. the i8 calculated 6 0 value for the fluid in equilibrium with assemblage I at 370 ± 30°C is well constrained and similar to the calculated range for 6 1 8 0 values of fluid in equilibrium with igneous-textured quartz from the granite and greisen at > 500°C. Meteoric water is important in the alteration of the granite, where biotite exchanged more readily than quartz, and in unmineralized veins within the greisen. Isotope values from quartz and muscovite in close contact with assemblage II base metal sulfides is indistinguishable from the values in the veins containing only the earlier assemblage I. This.suggests that quartz and muscovite have not reequilibrated with the fluid that deposited assemblage II. Table 1.

Ranges for oxygen isotope values at Sundown

quartz granite greisen - igneous - vein assemblage I

fluid(T°C)

6 1 8 0 (permil SMOW) muscovite fluid(T°C)

9.6-10.5>7.3-8.2 (>500) 9.6 >7.3 (>500) 6.0 1.4 (370) 10.4-12.65.8-8.0 (370)

Fractionation factors:

biotite 0.5

8.3-8.7 6.4-6.8(370)

Matsuhisa et al. (1979), O'Neil & Taylor (1969). o/

Sulfur isotope values (6 S) for sulfides from main-stage veins show little scatter within the range -2.7 to -8.5 permil CDT. These values contrast with the strongly depleted 6 3 4 S value (-27.9) from disseminated pyrrhotite in Texas Bed distant from mineralization. These values suggest sulfur in the mineralizing fluid was derived by mixing from two sources: magmatic sulfur from the granite underlying mineralization (fi34S (ES) = -2 to -3 at > 300°C) and sulfur, ultimately biological in origin, from the barren meta-siltstones, now the host for mineralization. The sulfur isotope values from metasiltstone-hosted mineralization lie between these values but the magmatic component is dominant. Fluid inclusion coupled with stable isotope studies of the Sundown tin prospect show that at least the fluid responsible for cassiterite mineralization (assemblage I) was predominantly magmatic. An influx of depleted meteoric fluid has occurred in the granite but has not been recognized in the metasiltstone hosted vein mineralization. During the base metal (assemblage II) stage of vein mineralization the influence of meteoric fluids cannot be excluded because no quartz was deposited and preexisting quartz and muscovite, while containing secondary fluid inclusions from this stage, did not reequilibrate. Meteoric water may have been restricted to the granite because the wider alteration zones indicate that the permeability of the granite was higher than the hornfelses.

References Goode, A.D.T., Clarke, D.A., Watmuff, G. , Butler, I., and Steele, D., 1982, In Flood, P.G., Runnegar, B. (Eds.) New England Geology, p. 313-320. Matsuhisa, Y., Goldsmith, J.R., & Clayton, R.N., 1979, Geochim. Cosmochim. Acta 43> 1131-1140. 0fNeil, J.R. and Taylor, H.P., 1969, J. Geophys. Res. JM, 6012-6022.

ORE/HOST ROCK RELATIONSHIPS AT THE ELURA MINE, COBAR,

N.S.W.

D.A.C. Archibald Electrolytic Zinc Co. of A/Asia Ltd., Cobar The Elura Pb-Zn-Ag orebody is hosted by an unremarkable sequence of Lower Devonian distal turbidites. These have been metamorphosed to lower greenschist facies and folded along north-south axes, characterised by shallow plunges. The pipe-shaped ore mass is vertically emplaced within the sediments. It has an undefined depth in excess of 500 metres and an oval cross-section measuring approximately 100 x 200 metres in plan. The ore is dominantly pyritic with pyrrhotite, sphalerite, galena and a relatively minor silicate component. Margins of the orebody are extremely sharp. Close to the ore contacts the bedded sediments reorientate and steepen into crude concordance with the margins of the deposit. As a consequence the mineralisation is interpreted as occupying the core of an antiformal dome. A band of sediment separates the upper 250 metres of mineralization into a north and south ore mass. There is a regional sub-vertical cleavage which is co-planar with the axes of the folds in the host rock away from the deposit. Like the bedding close to the ore the strike of the cleavage has reorientated into concordance with the ore margins, whilst cleavage dip remains close to vertical. This implies that the ore was at least partially emplaced in its current location after the regional cleavage had developed. Two other observations add further support to this conclusion. The sediments within 25 metres of the ore margins are often buckled into small to medium size folds which plunge steeply and radially away from the orebody. Their specific location and orientation suggest an outward movement and compression of the sediment whilst the pipe-shaped orebody was emplaced. Quartz-carbonate and quartz-feldspar veins tend to be prolific in host rock within 15 metres of the ore margins. These features are commonly sub-horizontal indicating that the veining occurred during a period characterized by low vertical compressive stress. The close proximity of the quartz rich veins to the ore is consistent with a local vertical extension of the rock during upward (or downward) emplacement of the ore. Most of the veining took place subsequent to the development of the regional cleavage. However, there is also evidence for a much earlier start to ore emplacement at Elura. Up to 20 metres beyond the sharp ore contacts, the sediments contain sparse nodules and conformable bands of massive sulphide with similar mineralogy to the ore. Transposition of the sulphides in these nodules and bands can be extremely well developed. Nodules have extended vertically into alignment with the steep regional cleavage. The sulphide bands have transposed into vertically elongated pods parallel to cleavage. These pyritic bodies peripheral to the ore therefore clearly predate the cleavage development.

Structural evidence at the orebody margins suggests that pyritic mineralisation rich in base m e t a l had already started to accumulate in the vicinity of the orebody prior to the completion of regional deformation. On the other h a n d , the sulphides constituting the orebody itself were emplaced in their current position at a later stage post-dating the development of a regional structural fabric. The source of the m i n e r a l i s a t i o n , as elsewhere in the cobar field, remains enigmatic.

W A L L R O C K ALTERATION AT THE SCODDLES V O L C A N O G E N I C MASSIVE SULPHIDE D E P O S I T , GOLDEN GROVE D I S T R I C T , WESTERN A U S T R A L I A P.M. Ashley Esso M i n e r a l s , Sydney T h e Scuddles volcanogenic massive sulphide deposit contains stratiform and stratabound polymetallic • Zn-Cu-Pb-Ag-Au mineralisation enclosed in subaqueous felsic to intermediate ash flow tuffs and lavas, tuffaceous sediments, and sulphidic and siliceous exhalites (Dudley et a l . , 1 9 8 4 ) . and the precipitation of exhalites Hydrothermal alteration effects accompanying sulphide mineralisation have created extensive mineralogical and chemical changes to the primary volcaniclastic rocks, particularly in the mineralised horizon and the footwall. Despite these changes, particular stratigraghic units can be defined by preserved textural criteria and by absolute abundances and ratios of the "immobile" elements T i , V , Z r , Y and N b . Only where there has been major exhalite input have the "immobile" element systematics been significantly d i s t u r b e d . + chlorite + Alteration mineral assemblages comprise sericite carbonate ± quartz ± relic albite in the stratigraphic hangingwall (grading up-sequence into the effects of regional low-grade metamorphism), chlorite + quartz ± carbonate ± talc ± sulphides , ± sericite in the mineralised horizon (MH) and quartz + chlorite + sericite Chlorite-rich veins and stratiform ± carbonate ± pyrite in the footwall. beds occur in the M H and footwall. Sulphide mineralisation is markedly zoned within the M H . Massive Zn-rich mineralisation, dominated by pyrite + sphalerite (+ magnetite + pyrrhotite + galena + chalcopyrite) and characterised by a Fe Zn (Pb Ag Sn Cd Mn Cu Sb As Co) metal association occurs towards the upper interface of the MH; it is accompanied by a Fe Mg M n Ca gangue assemblage rich in chlorite, amphiboles, carbonates, talc and quartz and grades upwards into a prominent laminated exhalative Fe(Mn)-enriched quartz + magnetite (+ silicate + carbonate + sulphide) marker h o r i z o n . T h e Zn-rich mineralisation passes downwards through pyrite-rich massive sulphides or "combined" Cu Zn Fe sulphides into disseminated, stringer and semi-massive Cu mineralisation, dominated by chalcopyrite + pyrite (+ pyrrhotite + magnetite + sphalerite) and a Fe Cu (As Co Zn) metal association. Gangue is largely chlorite + quartz (± carbonate ± talc ± sericite), and reflects the zone of strongest Mgenrichment. T h e effects of subsequent metamorphism on the alteration mineral assemblage are restricted to the pervasive weak development of biotite and rare chloritoid throughout the sequence and to the restricted occurrences of Fe M g Mn and Ca Fe Mg Mn amphiboles around the top of the MH.

Chemical zoning across the stratigraphy at Scuddles is w e l l developed. The primary dispersion halo extends from 20-150m into the hanging-wall and probably several hundred metres into the footwall. The hanging-wall sequence is pervasively altered stratigraphically above the M H , where effects merge with those of regional metamorphism. H2O and CO2 have been added, whereas there have been subtle depletions of N a , Ca and S r . Immediately overlying the M H , hanging-wall rocks are enriched in F e , M n , base metals, As and F , with strong Na-depletion. Within the MH, strong enrichment of F e , base metals and associated chalcophile elements has occurred. Mn is enriched toward the upper interface, whilst moderate Mg(F) enrichment is evident in lower regions. N a , Ca and Sr are mostly strongly depleted and K is also generally depleted. The footwall sequence has a progressive increase in contents of F e , base metals, A s , M g , H 2 0 , CO2 (Mn, F ) towards' the M H . N a , Ca and Sr are strongly depleted, K is patchily depleted and SiC^ does not show any marked enrichment. The primary dispersion halo at Scuddles is evidently contiguous with that of the nearby (4 km to the south) Gossan Hill Cu-Zn deposit (Frater, 1983), forming portion of a stratabound alteration-mineralisation system at least 10 km in length. The entire alteration-mineralisation system is characterised by feldspar destruction and Na-Ca-Sr depletion. T h e major zones of mineralisation are viewed as localised volumes of strong Fe-Mgbase metal enrichment below and adjacent to the sites of subaqueous The mineralised volumes exhalation of hydrothermal metal-bearing fluids. may have flattened inverted conical shapes with bases representing the tops of the mineralised horizon, dominated by sulphidic exhalites. References Dudley, R . J . , Ashley, P . M . , Ryall, A . W . , & M a y , E . R . , 1 9 8 4 , 7th A u s t . Geol. Congr., a b s . Frater, K.M., 1983, Econ. Geol., 78,875-919.

THE DISCOVERY OF THE ARGYLE 1

2 W . J . Atkinson , F . E . Hughes 1

DIAMONDS

1 and C . B . Smith

C R A Exploration Pty. Limited, Perth C R A Exploration Pty. Limited, Melbourne

The Argyle discovery was not a chance find. It resulted from 10 years' systematic exploration of the Kimberley region using modern geological, mineralogical and geophysical techniques, and requiring expenditure of $10 million to the time of discovery. The Kimberley region was selected for diamond exploration by analogy with African ore deposit situations because it has the appropriate geological setting of an ancient craton stable since 1800 my a g e . The Argyle find was preceded by the discovery of 90 kimberlite and lamproi te pipes and dykes in three separate provinces. Many of these are diamondiferous and the Ellendale deposits in the West Kimberley, though sub-economic at today's diamond prices, may be worked in the future. In the West Kimberley the diamonds were found in primary source rocks now termed olivine lamproite, which differ in their mineralogy and chemistry from classical South African kimberlite. This created a new target for diamond exploration and led to the discovery of the Argyle A K 1 lamproite pipe in the East Kimberley.

Mining of alluvial diamonds at Argyle commenced in January, 1983 and production is now at a rate of 5 million carats per annum. Output should increase to 25 million carats per annum when the AK1 pipe comes into production in 1986, making this mine, and Australia, the world's largest producer of diamonds by volume. Divine intervention may have prevented "Russian Jack", and his co-prospectors of the Halls Creek gold rush days from finding it last century, but the Argyle discovery is essentially the product of persistent, meticulous work based on scientific principles.

COMPUTER ASSISTED ANALYSIS OF LANDSAT AND GEOLOGICAL DATA - A NEW APPROACH TO REGIONAL EXPLORATION M.C. Aubrey and G.W. Tassell Technical and Field Surveys, Crows Nest, NSW The paper describes the computer database system devised by Technical and Field Surveys, a computer assisted approach to Landsat lineament analysis and the integration of the two — illustrations are taken from actual case studies. Since most geological data is generally presented in plan form, the best database model is that of a'geographic information system' in which spatial co-ordinates are the common denominator. Access programs have been written to permit the selection of records based on attributes in any field and their display on screen or printer. Statistics can be compiled for the number of records containing specific attributes and for the generation of plot files, rose diagrams or attribute frequency diagrams. The system can be used as a decision-making tool in the evaluation of provinces or in regional investigation rather than just as a bibliographic index. If a particular exploration target is defined by commodity, host age, lithology and mode occurences, e.g. Cu(Mo) occuring in DevonianCarboniferous adamellite or granodiorite as disseminated sulphides, then a search of the Mineral Occurrence Database will show the distribution of this style of occurrence; the Exploration Database will outline the areas investigated for this type of target, which exploration techniques were favoured and what results were obtained and the Literature Database will identify geological studies in the selected environment. Landsat lineaments are interpreted by eye from prints, digitised and plotted by computer with appropriate frequency rose diagrams based on number, length and average length of lineaments. Contours of density of intersection of lineaments are automatically plotted for correlation with published maps and the company's geological database.

PROBABILISTIC STABILITY ANALYSIS OF MINE OPENINGS Norbert R.P. Baczynski Dames & Moore, Sydney Rock masses are rarely homogeneous with respect to their intact rock component properties or the spatial distribution of weakness planes within them. Uniform or homogeneous models are unlikely to realistically reflect their in-situ behaviour during mining. A statistical approach has been applied to site characterization and stability analysis of large, unsupported underground openings at the Mount Isa Mine in Queensland. Results suggest a good degree of correlation between model predictions and ground response in the past. Statistical models are an avenue for assessing the reliability of any stability predictions and constitute a sound and logical basis for evaluation of most, if not all, geotechnical problems. References Baczynski, N.R.P., 1980A, Proc. 3rd Aust. N.Z. Conf. Geomech., Wellington, N.Z. May 12-16, Vol 2, 137-143. Baczynski, N.R.P., 1980B, Rock Mass Characterization, PH.D Thesis, Univ. of Melbourne, 233p. Barton, N.R., Lein, R. & Lunde, J., 1974, Rock Mech., Vol. 6, 189-236. Bieniawutski, Z.T., 1976, Proc. Symp. Exploration for Rock Engineering, Johannesburg, Nov. 1-5, Vol. 1, 97-106. Desai, C.S. and Abel, J.F., 1972, Introduction to the Finite Element Method: A Numerical Method for Engineering Analysis, Van Nostraud Reinhold Company, 577p. Hansagi, 1. , 1974, Int. J. Rock Mech. Min. Sci. & Geomech. Abstr. , Vol 11, 379-388. Krumbein, W.C. & Graybill, F.A., 1965, An Introduction to Statistical Models in Geology, McGraw Hill Book Company, 475p. Larson, H.J., 1974, Introduction to Probability Theory and Statistical Inference, John Wiley & Sons Inc. 430p. Laubscher, D.H. & Taylor, H.W., 1976, Proc Symp. Exploration for Rock Engng. Johannesburg,'Nov 1-5, Vol 1, 119-128.

THE COMPUTER SLAVE IN GEOMECHANICS Norbert R.P. Baczynski Dames & Moore, Sydney Geomechanics efforts should be focused on engineering geological investigation, interpretation and model formulation rather than being distracted by routine processing and compilation of field and laboratory data. Recent developments in computer hardware and software have markedly advanced the state of computing technology. This situation presents an excellent opportunity for engineering geologists and geotechnical engineers to make full use of their mechanical slave. Various routine tasks are time consuming and are best suited to computer-aided processing. Several typical examples are cited. There is a need for a common approach to the development of geomechanics software tools and systems. This approach will minimise duplication of programming effort and will ensure that software is more readily portable between various computers. The man-machine interaction not only facilitates rapid data processing and analysis, but also dictates the type of data that requires to be measured in the field. 42

References Baczynski, N.R.P., 1980, Ph.D Thesis, Univ. of Melbourne, 233p. Baczynski, N.R.P., 1983, Aus.I.M.M. Conf. Computers in Mining, CIMf83, Brisbane, 23-25 May, 127-135.

A PALAEOZOIC SUSPECT TERRANE IN SOUTHEASTERN AUSTRALIA AND NORTH VICTORIA LAND, ANTARCTICA Peter Baillie Geological Survey of Tasmania, Hobart A number of attempts have been made to correlate pre-Late Carboniferous rock sequences in Tasmania with similar sequences in southeastern Australia and north Victoria Land, Antarctica. A new interpretation is given in which a major N-S trending lineament is recognised, separating areas of Precambrian/Cambrian basement with shallow-water Ordovician sedimentary rocks from deeper-w^ter Ordovician flysch deposits. Lateral offset of this lineament along two major faults adequately explains the present distribution of major rock types in the three areas and also resolves a number of problems previously encountered in correlation (fig. 1) The N-S lineament is expressed as the Stawell Fault in Victoria, the Tamar Fracture System in Tasmania, and the Leap Year Fault in north Victoria Land. It is proposed that strike-slip movement of several thousand kilometres brought the contrasting regions into juxtaposition.

Figure 1.

Reconstruction at time of docking.

SOME ASPECTS OF THE GEOLOGY AND GEOCHRONOLOGY OF GOLD MINERALIZATION IN THE GEORGETOWN REGION, QUEENSLAND, AUSTRALIA J.H.C. Bain1, I.W. Withnall2, L.P. Black1 'Bureau of Mineral Resources, Canberra ^Geological Survey of Queensland, Brisbane The Rb-Sr and K-Ar isotopic ages of hydrothermal minerals intimately associated with three gold deposits indicate that there were at least two extensive Palaeozoic gold mineralisation events in the Georgetown region. The first occurred in Siluro-Devonian time as indicated by the Mt Hogan (400 _+ 4 Ma) and Jubilee Plunger (407 +_ 6 Ma) deposits. The Mt Hogan deposit comprising shallowly dipping thin quartz veins with broad sericitic. alteration envelopes is hosted by Proterozoic granite whereas the Jubilee Plunger deposit occupies a steeply dipping complex fracture zone in SiluroDevonian granodiorite. Individual mineralised quartz-carbonate-sulphide veins have sericitic envelopes within a broad zone of kaolinised and sericitised granodiorite. Regional spatial relationships suggest that the majority of quartz vein deposits in the Etheridge Goldfield also formed at this time, and are used with reconnaissance fluid inclusion and <5^0 isotope data to develop a crude model for the formation of these deposits. It is suggested that the deposits are genetically related to the major 400 Ma I-type magmatic event that caused uplift and heating of the central part of the region, and that deposits as far afield as Cape York and Charters Towers may also be related to this event. The second event occurred during the late Palaeozoic, which was a period characterised throughout much of northeast Queensland by continental felsic volcanism, associated granitoid emplacement, volcanic subsidence, and a large number and variety of mineralisation events: especially multiple SnW events in the Herberton area. At least one period of gold mineralisation is represented by the epithermal, breccia-hosted Kidston deposit, which formed in mid-Carboniferous time (321 15 Ma) during the main phase of volcanisifi in the region. The multiplicity of SnW mineralisation events in the Herberton area during the Carboniferous suggests by analogy that gold deposits too may have a similar spectrum of ages and diversity of styles within the region.

HYDROTHERMAL AND REGIONAL METAMORPHIC ALTERATION AT BIG CADIA (IRON-DUKE) DEPOSIT, ORANGE, N. S .W., AUSTRALIA Z.U. Bajwah, R. Offler and P.K. Seccombe Geology Department, University of Newcastle, Newcastle Big Cadia (Iron Duke) is a stratiform deposit which occurs in the upper part of the Angullong Tuff, an Ordovician sequence of andesitic flows and volcanoclastic rocks. The deposit is composed of magnetite, hematite and minor pyrite and chalcopyrite.

During mineralisation, the volcanoclastic host rocks underwent intense hydrothermal alteration resulting in the development of zones of epidotization, chloritization and sericitization progressively away from the orebody. Obliteration of the original fabric and mineralogy occurs in the epidote and chlorite zones. Electron microprobe analyses show that the hydrothermal epidotes (Ps 22 _ 38 ; mean Ps 32 ) are more enriched in Fe than metamorphic epidotes (Ps 21 _ 29 ; mean Ps2tf); similarly chlorite formed during mineralisation (FeO = 25.32 - 40.15%) is more Fe-rich than metamorphic chlorite (FeO = 8.30 - 28.66%). Chemical analyses indicate that in general, the host rocks were depleted in Na20 and K 2 0 and enriched in FeO, CaO, MgO and H 2 0, in the epidote and chlorite zones. However, K 2 0 has been added in the sericite zone. The mineralogical and chemical composition of the metasomatic assemblages indicate that fluid chemistry and f02 have been the dominant factors during hydrothermal alteration. These minerals were formed over a temperature range of 200 to 300°C and log f02 -31 to 36.8 atmos. Subsequently, the deposit and the host rock underwent lower greenschist facies metamorphism at T -350°C and Pj<3Kb. However, the effects of this metamorphism were less in the orebody and the associated hydrothermal zones. Apart from F^ and T the main variables involved in the crystallisation of the metamorphic minerals appear to be fluid and whole rock chemistry and p

co2.

PARAGENETIC AND GEOCHEMICAL STUDIES OF BIG CADIA DEPOSIT, ORANGE, N.S.W. f AUSTRALIA

(IRON-DUKE)

Z.U. Bajwah, P.K. Seccombe and R. Offler Geology Department, University of Newcastle, Newcastle

The Big Cadia (Iron-Duke) ore body is a stratiform chalcopyrite-bearing magnetite deposit, hosted by andesitic flows and volcanoclastic rocks of Ordovician age, within a Paleozoic island arc environment of the Lachlan Fold Belt. The mineralisation consists of a lens of primary magnetite, hematite, pyrite and chalcopyrite. Three generations of magnetite and two generations of hematite have been recognised in the ore body. Due to regional metamorphism and deformation, magnetite has been extensively fractured, and hematite lamellae are fractured and folded. Pyrite shows varying degrees of cataclasis and an annealing recrystallisation fabric is well developed in chalcopyrite. The primary minerals have undergone extensive oxidation and weathering to produce goethite, chalcocite and bornite. Fifty samples of magnetite-hematite, pyrite and chalcopyrite were analysed for Co, Ni, Se, Cd, Mn, Pb, Ba, Zn and Cu. The mineralisation is characterized by generally high contents of all elements analysed. Pyrite shows the greatest enrichment in Co and Ni, followed by chalcopyrite then magnetite-hematite. Co and Ni ratios in the mineralisation are amongst the highest of all volcanic-hosted ore deposits compared in the study. Sulfur isotope ratios of sulfides show a narrow range of S3i*S (-3.5 to 4.0 zero per mil). Despite the proximity of this range to zero per mil a magmatic source of sulphur is not implied. Rather, the high oxidation state of the ore fluid suggests that sulfur has been derived from partially reduced Ordovician sea water. Calculated temperatures based on the sulfur isotope geothermometer for coexisting pyrite and chalcopyrite are erratic and range from 190° to 1065°C with a mean of 501°C.

Homogenisation temperatures from primary fluid inclusions (5-12ym) in hydrothermal calcite and quartz, range from 220° to 325°C. This temperature range is compatible with that determined from the chemistry of hydrothermal silicate minerals but is inconsistent with sulfur isotope geothermometry. Secondary fluid inclusions give a temperature range from 110° to 200°C.

GEOTHERMOMETRY IN ROCKS OF THE BARRINGTON TOPS ,MET AMORPHIC AUREOLE USING PHYTOCLAST REFLECTANCE C.K. Baker* and C.F.K. Diessel Geology Department, The University of Newcastle, Newcastle Levels of coalification and metamorphic grade have been established in Devonian to Carboniferous rocks of the Tamworth Trough, north west of Newcastle, N.S.W., within the contact metamorphic aureole of the Permian Barrington Tops Granodiorite. Conventional microscope-photometric methods have been employed for the determination of mean maximum reflectance values for dispersed vitrinite fragments (phytoclasts) found in clastic rock types. Maximum reflectance values (R max) range from less than 1% (bituminous coal rank) in areas unaffected by the intrusive, to these of metaanthracites and semi-crystalline graphite (R max > 10%) adjacent to the intrusive body. Contoured R max values are concentrically arranged around the granodiorite body. (Irregularities in the contour patterns have been attributed to faulting.) Similarly, a broadly concentric pattern of metamorphic mineral zones is observed: Zone 1, zeolite group minerals (including wairakite) ± prehnite, peripheral to the aureole; Zone 2, pumpellyite ± prehnite; Zone 3, epidote - chlorite ± biotite dt actinolite; Zone 4, biotite ± hornblende, adjacent to the intrusive. The width of the hornfelsic zone (less than 1km, comprising the higher grade portion of Zone 3 and Zone 4) is small compared with the full extent of the aureole. The prehnite isograd, for example, lies some 25 to 35km away from the intrusive body. Discrepancies which exist between mineral isograds and phytoclast isorank contours are attributable to a paucity of index mineral species. In areas where data density allows, construction of reflectance sections normal to the granodiorite contact reveals an exponential relationship between RQinax and lateral distance from the contact. When these results are plotted as log(R max) against normalized lateral distance (distance normalized between the 2% isoreflectance contour and the graphite-in isograd), linear plots with similar properties and high correlation coefficients are observed (r>0.92). It is concluded that these gradients approximate the cooling profile of the intrusive. Middleton (1982) has developed an empirically-derived temperature-time model for coalification from the results of Hood et al. (1975). Application of this model to coal rank studies in metamorphic terrains (Munsterland 1 borehole, North West Germany, Teichimiller et al., 1979; New Caledonian high pressure schists, Diessel et al., 1978) has resulted in a close correlation between observed and calculated reflectance profiles. Modelled values for geothermal gradient, burial time and rate are compatible with geological estimates. Observed reflectance gradients surrounding the Barrington Tops Granodiorite can be approximated using Middleton's (1982) model, assuming relatively short durations of heating. At distances greater than 10km from the intrusive, an apparent geothermal gradient of 4°C/lateral km is required to match the observed profile. Within 5 to 10km of the contact, a better^ correlation is found by increasing the apparent geothermal gradient to 14 C/lateral km and decreasing the duration of heating (< 10 million years). 46

Field evidence and comparison with other contact metamorphic aureoles suggests that the cooling mechanism for the Barrington Tops Granodiorite was either through heat loss by conduction or as a result of a closed convective system with an impermeable heat source (that is, the intrusive acted as a heat conductor only). Theoretical models presented by Norton and Knight (1977), Parmentier and Schedl (1981) and others shows that, in both cases where an igneous body is intruded into a sedimentary sequence with an existing geothermal gradient, the isotherms above the intrusive are closely spaced. However, peripheral to the body, isotherms begin to splay outwards and become widely spaced, resulting in low apparent lateral geothermal profiles. It is considered likely that lithostatic pressures would have varied little over much of the area (1 to 2 kb) . Therefore, values for AT/AP would have been consistently high. This is in accordance with the presence of wairakite and paucity of actinolite, features characteristic of metamorphic terrains which have been subjected to high real geothermal gradients. Parmentier and Schedl (1981) present the results of theoretical calculations relating the initial intrusion contact temperature, base level temperature and maximum country rock temperature attained, with the distance away from the intrusive and its geometry. Applying the geothermal gradients deduced from one phytoclast reflectance section normal to the Barrington Tops Granodiorite contact, the following intrusion geometry at outcrop seems likely: a slab-like body, 14km in width at a shallow depth below the intrusion top. This interpretation is supported by the occurrence of roof pendants and by the irregular outline of the granodiorite country rock contact. Temperatures deduced from metamorphic assemblages are comparable with those from phytoclast reflectance values, but are in general lower than that predicted from the coalification model. #The disappearance of Mg-pumpellyite estimated from experimental data (Schiffman and Liou, 1980) at 325 C at pressures less than 2 kb compares with 340 - 350 C deduced from phytoclast reflectance. The first appearance of biotite is assigned 375 C by Turner (1981) , and compares with approximately 400 C from the modelled reflectance values. References Diessel, C.F.K., Brothers, R.N., & Black, P.M., 1978, Contr. Mineral. Petrol., 68, 63-78. Middleton, M.F., 1987, Geophys. J. Roy. Astron. Soc., 68, 121-132. Norton, D.L., & Knight, J.E., 1977, Amer. J. Sci., 277, 937-981. Parmentier, E.M., & Schedl, A., 1981, J. Geol., 89, 1-22. Schiffman, P., & Liou, J.A., 1980, J. Petrol., 21, 441-474. Teichmiiller, M., Teichroiiller, R. , & Bartenstein, H. , 1979, Fortschr. Geol. Rheinld. u. Westf., 27, 137-170. Turner, F.J., 1981, "Metamorphic Petrology", 2nd edition, McGraw-Hill. *

Present address - Costain Australia Limited, Sydney.

A CLASSIFICATION OF GOLD BEARING BRECCIA PIPES WITH REFERENCE TO EXPLORATION E. Max Baker James Cook University, Townsville Examples, of gold bearing breccia pipes range from shallow level volcanic related features associated with typical epithermal style mineralization through to deeper level bodies associated with subvolcanic intrusions and associated porphyry-type mineralization. Generally the breccia pipes are only indirectly related to mineralization by way of providing a suitable structural environment to host bulk mineable low to medium grade mineralization. Similar albeit sub^economic vein and stockwork/disseminated mineralization not associated with brecciation often occurs elsewhere in the district. Hydrothermal eruption breccias are shallow level somewhat irregular breccia bodies generally less than several hundred metres in diameter and. vertical extent. They typically occur in geothermal areas and are associated with epithermal mineralization. Brecciation results from cyclic 'self-sealing' of hydrothermal conduits by deposition of silica and carbonate followed by explosive release of overpressured fluids. In addition to breccia pipe formation fluid overpressures result in stockwork and/or bonanza style mineralization in the hanging walls of fissures and beneath impermeable cap rock and sinter. Mineralisation within a hydrothermal eruption breccia is probably occurring at present beneath the Champagne Pool, Waiutapu, N.Z. where Au-Ag rich precipitates are forming in sinters surrounding the eruption crater. Maar volcanoes (diatremes), another example of shallow level breccia pipes, are formed by 'phreatomagmatic explosions' resulting from the interaction of an ascending magma body with water. These upward flaring pipe shaped bodies are generally an order of magnitude larger than hydrothermal eruption breccia which are frequently found within and adjacent to them. Subsidence of an unsupported vent wall of a maar volcano at Wau, P.N.G. has provided a structurally suitable site for gold mineralisation associated with hydrothermal eruption breccias. Commonly the vent breccia itself is impermeable to hydrothermal fluids and therefore unmineralised. The 'GW orebodies' at the Balatoc Plug, Philippines occurs at the intersection of individual veins and the breccia margin where permeability has been enhanced by slight movement of the breccia subsequent to brecciation during mineralisation. At Lepanto, Philippines hydrothermal fluids trapped beneath the impermeable vent breccia have produced a massive replacement quartz-alunite-enargite body. Mineralization is of typical epithermal style. Formation of deeper level sub-volcanic breccia pipes is associated with escape of a volatile-rich fluid phase comprised of fluids evolved from a crystallizing intrusive and/or magmatically heated connate waters. Unlike the shallow level breccia pipes which vent, these bodies are carrotshaped and in some cases appear to terminate upwards. They range in diameter from 50 m up to 1.5 km with vertical extents in excess of 1 km. Proposed mechanisms of breccia formation include collapse, chemical expansive or solution brecciation, fluidization and explosive escape of volatiles* No one process adequately explains all the features of any particular breccia pipe. It seems probably that a number of these processes, either simultaneously or in sequence, are responsible for producing the typical sub-volcanic breccia pipe. Mineralization is typically mesothermal consisting of open-space fill and sheeted veining in

the breccia pipe margins. Ortiz, New Mexico and the Chadbourne Mine, Quebec are probably examples of this style of association. Although such a classification of breccia bodies is somewhat general it provides a framework for exploration by which styles of gold mineralization can be related to types of breccia bodies. Hydrothermal eruption breccias and maar volcanoes are likely to host epithermal style mineralization and will be preserved only in areas of shallow to moderate erosion. Sub-volcanic breccia pipes are associated with porphyry-style mineralization and will only be exposed in areas of deeper erosion.

GOLD IH VEGETATION AS A PROSPECTING METHOD IN TASMANIA W.E. Baker Department of Mines, Hobart Reports on the gold content of plants present conflicting data and the most recent compilation of results is to be found in Brooks (1982). Studies of one genus in particular, namely the horsetail rush (Equisetum spp), have produced highly variable results with Babicka (1943) recording an incredible maximum content of 610 000 ng/g whilst Warren and Delavault (1950) found only 340 ng/g. More recently Boyle (1979) reported values of up to 8500 ng/g for the genus. In view of the literature record, the Tasmania Department of Mines decided to examine the gold content of local plant species in order to assess the potential of biogeochemical exploration for gold. A rapid technique involving wet oxidation of plant material, extraction of the gold as the aurichloride complex by Heptan-2-one and gold determination by carbon furnace atomic absorption was developed. This enabled the processing of 40 samples per day with a relative standard deviation of 26% at an absolute gold content of 0.2 ng. The method was applied over an old alluvial goldfield in the Lisle Valley in north-eastern Tasmania and over the Jane River goldfield area in western Tasmania. In the Lisle Valley background values were seldom greater than 100 ng/g ( in the ash) whilst anomalous values frequently exceeded 5000 ng/g. Where anomalous values occurred all plant genera were found to contain high gold-content, resulting in contracts ranging from 10 to in excess of 200. This differs from results recorded for Siberian plants by Kovalevsky (1978) which showed that only 10% of plants studied yielded information on gold in the substrate. In the Jane River area background gold values were generally greater than 200 ng/g whilst anomalous results rarely exceeded 2000 ng/g yielding a maximum contrast of only 10. Given the capricious nature of gold distribution it is likely that biogeochemical prospecting could prove useful in delineating target areas within prospective areas defined by other methods. The gold results obtained suggest that parts of the Lisle Valley are highly interesting targets whilst, on the basis of biochemistry, the Jane River is far less attractive. This view is currently under test since activity is increasing in the Lisle Valley with one Prospecting syndicate currently producing about 800 g of gold (25 ozs troy) per month and a much larger venture due to commence late in 1984. References Babicka, J., 1943, Mikrochim. acta, 31, 201-253. Boyle, R.W., 1979, Geol. Surv. Canada Bull., 280, 79-88. Brooks, R.R., 1982, J. Geochem. Explor., V7, 109-122. Kovalevsky, A.L., 1978, Dokl. akad. Nank. SSSR., 242, 430-433.

GEOSCIENTIFIC DEVELOPMENT NEEDS OF THE PHILIPPINES - HOW AUSTRALIA CAN BEST MEET THESE NEEDS Guillermo R. Balce Bureau of Mines and Geo-Sciences Geoscience is an emerging concern in the Philippines as it finds applications in all areas of development apart from its traditional role in mineral prospecting. In the government sector, specifically designated units in four government ministries, four authorities and three government corporations carry out geoscientific investigations separately. The National Committee on Geological Sciences (NCGS) provides for the systematic planning, deliberation, promotion and coordination of national geological programs. In the private sector, many outfits engaged in engineering geology, geotechnical engineering, groundwater geology, geothermal energy, and coal resources development have been established recently. This has compensated the inactivity in recent years of many mineral and oil exploration companies. In the academe, geoscience education and training continue to be pursued by three universities in Metro Manila. The National Institute of Geological Sciences in the University of the Philippines System is giving more thrust to its graduate program in geology. The institutional framework for geoscientific development appears to be fairly adequate. However, given the current pace of development, much has yet to be done to put it in the proper direction. With this premise in mind, the number and capability of manpower in the geosciences have to be raised to a higher level. The system of geoscience education is one factor which may preclude or advance this requirement, and it is for this reason that the geoscience curricula of the three institutions should be upgraded and standardized. At least, three more schools — one each for Northern Luzon, the Visayas, and Mindanao — should be encouraged to offer courses in geology. The inadequate laboratory facilities and dearth of training staff in these institutions are deterrents which must be given foremost attention. Specialization in the various fields of the geosciences should be enhanced by making available more opportunities for advanced training and graduate studies. Competent members of social and ethnic minorities should be encouraged to engage in the geosciences as this will expedite the gathering of geological information, particularly in Mindanao and other areas where tribal possessions are dominant. Training and research facilities/systems should be strengthened and enhanced. The Philippine Institute of Volcanology, Bureau of Energy Development, and Philippine Atmospheric, Geophysical, and Astronomical Services Administration, require the most modern facilities for research in their specific geoscience areas. A research laboratory for engineering geology and geotechnics ought to be initiated to ensure the proper growth of these fast-developing aspects of geoscience. The analytical and survey facilities of the Bureau of Mines and GeoSciences, including the new Petrological, Mineralogical and Geochronological Laboratory (PETROLAB), as well as the geophysical research vessel, RPS Explorer, require specialists and expert technicians to make them fully operational and properly maintained. The scenario of Philippine geoscientific development needs inevitably invites strong Australian cooperation. Assistance from Australia can be provided through: (1) provision of lecturers/trainors for the geoscience training institutions in the Philippines; (2) provision of experts to assist in the management and implementation of geoscientific programs; (3) education of Filipinos, in degree and non-degree training programs, in Australian institutions(4) joint undertaking by Australian and Filipino geoscientists; and (5) provision of equipment and funds. The mechanisms of the Australia-Philippines bilateral arrangements, the AustraliaASEAN cooperation agreements and arrangements through various multilateral organizations involving both countries can be effectively harnessed for these purposes. The Commonwealth Scientific and Industrial Research Organization, the Australian Development Assistance Bureau, the Bureau of Mineral Resources and the various Australian Universities are agencies that can facilitate effective technology transfer in geosciences between Australia and the Philippines.

ASPECTS OF GRANITE

WEATHERING

J.F. Banfield & R.A. Eggleton Department of Geology, Australian National University, Canberra Whole rock, mineral and clay chemistry, X R D , and electron microscopy have been used to examine the process of granite weathering. This process is considered in terms of mineral transformations and bulk changes within the weathering profile. Three profiles have been examined from southeastern N.S.W., two developed in I-type and one in S-type granite. The mineralogy of all three granites has been modified to some degree by hydrothermal alteration. Biotite in the I-type granites has been partially converted to chlorite, epidote and sphene, and amphibole has been altered to actinolite and mildly chloritized. In all three granites, plagioclase cores contain laths of sericite and aggregates of clinozoisite. K-feldspar has suffered relatively little alteration and has developed only a minor dusty brown appearance along exsolution lamellae and grain boundaries. Weathering of granite minerals appears to proceed initially by dissolution, often initiated at dislocations. T.E.M. observations indicate that etching is frequently accompanied by the development of a small quantity of amorphous material which is relatively rapidly recrystallized to form clays. These clays appear to inherit little orientational control from the parent phase. Both plagioclase and Kfeldspar exhibit this behavior. Halloysite is an abundant product of both these feldspars and can be observed to develop from apparently amorphous material via relatively unstructured spherical aggregates which enlarge to form layered balls or tubes. SEM observations demonstrate that these tubes coalesce to form platy kaolin. Curved, fan-shaped aggregates, and lenticular bundles of 12-16A material (possibly smectite) also develop. Later these appear to be aggregated and reorganized to form more ordered, regularly layered clay. Amphibole, like the feldspars, shows little evidence for development of alteration products directly from the parent structure. This phase weathers by the formation at pre-existing dislocations of remarkably evenly spaced, crystallographically controlled saw-tooth etches. In some areas, where dissolution channels become extremely closely spaced the orientation of adjacent clays parallels that of these etches. Most amphibole is degraded to areas of apparently amorphous material which recrystallizes into long strands of clay often only two or three unit cells in width. These aggregate into bunches which display increasing regularity and are finally recognisable as moderately well formed laths of clay. In thin section the amphibole is observed to weather by widening of cleavages and the development in these areas of orange-brown Fe rich, A1 poor vermiculite and smectite. The composition of the alteration products is variable and reflects the variation in the composition of the parent amphibole.

Of the major granite minerals, only biotite shows clear evidence that it weathers directly to vermiculite without an intervening amorphous stage. This conversion appears to proceed by two mechanisms and results in the development of a series of mixed layer phases before the biotite is replaced by vermiculite and kaolin. In the first of these mechanisms K + is removed and interlayer cations and water are introduced and swell the layer. The second mechanism appears to involve paired terminations of biotites sheets with a local volume loss of 30% associated with the conversion of 2 biotite layers to one vermiculite layer. Splits and gaps develop and coalesce throughout the structure to accommodate the volume changes associated with these mechanisms. Biotite is also altered by conversion of wide strips within the structure to a near-amorphous material which recrystallizes to curving bands of clay. Development of rectangular etches filled with amorphous material and newly crystallizing clays are also observed, and halloysite commonly develops in larger gaps between strips of altered biotite. Alteration of apatite proceeds firstly by dissolution. This is accompanied by loss of Ca and introduction of large quantities of LREE, Al, Ba, Fe and Pb to form a range of minerals including LREE-A1phosphates and LREE-phosphates. This process results in the fixation of phosphorus, and of LREE which are clearly added to the profile from outside the sampled area. (Up to 20X enrichments of LREE are observed). The source of these elements is presumably allanite which alters from the rim inwards to a red-brown phase. La is detectable in the unaltered allanite but not in the altered rim suggesting initial alteration of this phase produces the first REE fractionation in a series of fractionations associated with the apatite replacement. Whole rock chemistry is considered in terms of an isovolumetric 3 weathering model. When elemental abundances in gm/cm are plotted against bulk density many major and trace elements display linear or near linear trends. The most notable exceptions are Na and Ca which undergo a period of rapid loss reflecting the destruction of plagioclase. As is observed in many cases this deviation from an otherwise regular trend corresponds with a rapid oxidation of Fe and increase in abundance of bound HgO. It is considered that these trends in the bulk chemistry largely reflect the establishment and persistance of weathering reactions which proceed until the parent phases are consumed. Observations of mineralogical transformations and bulk chemical trends indicate a number of processes which appear to control the nature of granite weathering. Well before the development of soil characteristics weathering results in a decrese in rock density (and, hence a mass loss) of up to 50%. As many minerals appear to develop an amorphous precursor from which secondary products crystallize, it is proposed that bulk dissolution is an important early step. Secondly, where the chemistry of secondary phases indicates components not derived from the parent mineral it is apparent that in the weathering environment most elements have at least considerable local mobility. Thirdly, the physiochemical conditions within the profile control the nature of the alteration assemblage, and hence influence the degree of retention or loss of individual components.

THE FIXATION OF MOBILE R.E.E. DURING WEATHERING BT REPLACEMENT OF APATITE J.F. Banfield and R.A. Eggleton Department of Geology, Australian National University, Canberra A Scanning Electron Microsope (S.E.M.) examination of biotite from weathered Bemboka Granodiorite revealed the presence of a number of phases developed both in apatite etch pits and as rinds on relic apatite crystals. The aim of this study was to identify these phases and explain their origin. Prismatic and hexagonal pits range in size from a few microns to 100 microns. As new phases occupy a considerably smaller volume than the original apatite, techniques providing reasonably high magnification and allowing analysis of small areas were required for the study of this material. The S.E.M. was used primarily to locate areas of interest and to identify the range of distinctive morphologies developed by these phases. These included numerous fdonut1-shaped objects, ropes and chains of fdonuts', platelets, a variety of crystallites, and rinds on the apatite parent. Qualitative energy dispersive S.E.M. and quantitative wavelength dispersive CAMECA probe analyses indicated that this material was composed of L.R.E.E., Al, P with smaller quantities of Fe, Ba, Ca and heavier R.E.E.. Measurement of individual R.E.E. contents established the presence of three quite distinct fractionation patterns and revealed a large range in the proportions of major components. A combined S.E.M. and T.E.M., A.E.M., X.R.D. and light optics study was employed to establish the crystallinity, examine the structure, and identify the phases present. This approach revealed that both the 'donuts' and altered rims are composed essentially of radiating crystals of florencite (CeAl3(P04)2(0H)6). Two very distinct L.R.E.E. fractionation patterns occur in both these forms. Where the surface of this material is disrupted evidence is found for the presence of an Al enriched (presumably clay) coating. Data also indicates the coexistence of R.E.E. (primarily Nd, La) phase apparently devoid of Al and P. X-ray data, and the form of these crystals suggest this phase may be a carbonate similar to ancylite ((Sr, Ca)(La, Ce)(C03)20H.H20). The observed variation in chemistry is attributed to the variable proportions of these phases. Crystallites located in the S.E.M. were extracted and examined in the A.E.M.. Combined electron diffraction and qualitative chemical analyses indicated this mineral was rhabdophane (CeP04.H20). S.E.M. observations of unweathered through to strongly weathered samples indicate that in early stages fresh apatite is rapidly etched and chemically transformed by loss of Ca and introduction of Al, Ba, Pb, Fe and variable quantitites of the L.R.E.E.. Whole rock chemical data indicates that early in weathering large quantities of L.R.E.E. (up to 20 times original contents) are introduced and fixed. The source of these elements is not clear. It is assumed that they have migrated in from outside the sampled zone, possibly from higher in the profile, and were fixed so that changes in conditions and abundance of individual R.E.E. are preserved. These observations reflect the considerable mobility of R.E.E., and the ease with which these elements can be fractionated from one another in a weathering environment. 53

The development of donut-shaped R.E.E. phases after apatite has also been observed in one, and possibly two other weathered granites. The large migration and stabilization of R.E.E. is not observed in these cases, and dissolution of apatite is the most common feature noted. R.E.E. phases commonly form under supergene conditions and are frequently noted in soils. They have attracted particular attention as they represent a major sink for phosphorus in the surficial environment. It would appear that by using a variety of microbeam techniques many of the aspects of apatite weathering and replacement can be documented.

SOUTH AUSTRALIAN OPAL FIELDS - SIMILAR BUT DIFFERENT L.C. Barnes S.A. Department of Mines and Energy, Adelaide South Australia, the Opal State, produces about 75% of the world's precious opal. Current production comes from three unique centres, Andamooka, Coober Pedy, and Mintabie but small finds have been made at numerous locations scattered through the north of the State. Most deposits are hosted by marine shale and siltstone of Early Cretaceous Marree Subgroup which has been bleached and altered by Tertiary weathering. At Andamooka, Stuart Creek and Coober Pedy, precious opal is found at different relative positions in the weathering profile and opal formation is controlled by different structural and stratigraphic features. At Mintabie, Early Palaeozoic kaolinitic fluviatile sandstone hosts precious opal whereas at nearby Granite Downs, opal is found in weathered Early Proterozoic gneiss and granite. Mining methods are as diverse as the opal miners, but are partly determined by the different geological conditions on the three fields. Underground mining is preferred at Andamooka, mainly by individuals or pairs using simple mechanical equipment. Large boulders in the opal level preclude use of tunnelling machines, and limit use of blowers. Underground mining is also preferred at Coober Pedy but most miners work in teams of 2, 3 or 4 with a variety of equipment, principally tunnelling machines and blowers. Rising costs have curtailed the use of bulldozers but the presence of numerous bulldozer dumps has stimulated use of noodling machines. The much harder rock at Mintabie requires heavy earth moving equipment and liberal use of explosives both in open cuts and underground. Because of the random distribution of opal, from the surface down to at least 20 m, slow and careful open cut mining has been the most successful method. Opal abundance and quality varies between the three fields but no field can boast a unique opal type. Andamooka is characterised by high quality crystal opal, Coober Pedy is dominated by lower quality white and grey opal but top quality black and crystal opal are found and Mintabie boasts superb black and semi-black opal.

The potential of each field is unlimited but the beliefs and whims of the opal miners, and the control of the market by overseas buyers will dictate the future of the South Australian industry unless Government drastically change policies. Reference Barnes, L.C., and Townsend, I.J. f 1982. Opal, South Australia's Gemstone. Handbook No. 5. S. Aust. Dept. Mines and Energy.

SOME INDUSTRIAL MINERALS OF SOUTH AUSTRALIA

L.C. Barnes and J.G. Olliver South Australian Department of Mines and Energy, Adelaide South Australia has traditionally been the major supplier of industrial minerals to the Australian market, being the leading producer of salt, gypsum, talc, mica, barite, phosphate, and metallurgical and glass grade dolomite, and the sole supplier of sillimanite. Barite is widely distributed in rocks of all ages. Since early this century all of Australia's industrial grade barite requirements have come from a number of open infill fissure type deposits within the Adelaide Geosyncline. Deposits are localised in or near major faults, breccia zones or fdiapirsf in various Adelaidean sediments, mainly shale and siltstone of Umberatana and Wilpena Groups. Since 1940, the Oraparinna area in the central Flinders Ranges has been the major supplier. At Bunker Hill Mine, four high grade, white barite lodes up to 5 m wide have been worked by open cut and traditional underground methods. The mine has recently been redeveloped and reequipped. Less pure barite lodes nearby have been worked to supply oil drilling grade barite for Bass Strait and the Cooper Basin. Large lower grade barite deposits in the Olary Province comprise lenticular barite-quartz-magnetite beds within albitic schist of Willyama Complex of Early Proterozoic age. These deposits have been worked for oil drilling grade requirements and benefication is being investigated. In contrast, South Australia's talc deposits are restricted stratigraphically. In the Mount Lofty Ranges coarse grained, pale green talc, intimately associated with albite has formed by metamorphism and metasomatism of pelitic dolomite as lenses and pods within Stonyfell Quartzite and Woolshed Flat Shale. Gumeracha deposits have been worked since 1901 with most production being second and third grade talc. High purity white talc deposits at Mount Fitton in the northern Flinders Ranges are within Balcanoona Formation and have resulted from metamorphism of impure dolomite. Folding and faulting control location, orientation and dimension of ore bodies. Gypsum deposits are of Pleistocene or Holocene age. In many places around the coastline massive rock gypsum up to 10 m thick has formed in low lying salinas, topographically separated from, but hydrogeologically connected to the nearby ocean. Reserves at Lake MacDonnell and Streaky Bay are immense, but are limited at Stenhouse Bay and Kangaroo Island where mining will cease in the near future.

Near Blanchetown on the River Murray massive laminated rock gypsum up to 3.6 m thick near the top of Blanchetown Clay of Pleistocene age is being worked on an increasing scale for plaster and cement manufacture. On the eastern side of many inland playa lakes gypsum sand lunettes, derived from gypseous sediments within the playa, have been exploited as a source of industrial and agricultural grade gypsum. Exploration for industrial minerals is increasing, both for minerals currently being mined, particularly gypsum, and for a variety of other minerals not being mined in South Austalia at present. In this latter category celestite, palygorskite, wollastonite, feldspar, silica and fracturing sand offer some potential for future development.

THE JACK HILLS METASEDIMENTARY BELT: AN EXTENSION OF THE EARLY ARCHAEAN TERRAIN IN THE YIL6ARN B L O C K , WESTERN AUSTRALIA J . L . Baxter, S.A. Wilde, R . T . Pidgeon and I.R. Fletcher Western Australian Institute of Technology, Perth The Jack Hills Metasedimentary Belt (Elias, 1 9 8 3 ) is situated in the northern part of the Western Gneiss Terrain of the Archaean Yilgarn Block of Western Australia. The Belt consists of minor volcanics and substantial thicknesses of chert and banded iron formation interleaved with pelitic and psammitic metasediments. The predominance of sediments is analogous with the nearby Narryer Metamorphic Belt (Williams et al. , 1983) which is composed of psammitic metasedimentary rocks of early Archaean age (de Laeter et a l . , 1981; Froude et a l . , 1983). The paucity of volcanics the Jack Hills Metasedimentary Belt and the Narryer distinguishes Metamorphic Belt from typical greenstone belts in the Yilgarn Block. On the basis of detailed mapping carried out in 1983 the Jack Hills Metasedimentary Belt has been subdivided into three rock associations that are separated tectonically by shear zones. The southernmost association is composed of semi—pelitic schist interleaved with thin chert and ortho— quartzite. The central association is predominately orthoquartzite with T h e northern interlayered chert and locally developed volcanic rocks. association is essentially banded iron formation and ultramafic metavolcanic rocks. Ultramafic intrusives occur in a l l but the northern association. The belt is bounded to north and south by major shear zones which have strongly affected the adjacent orthogneisses. Deformation within the Belt is heterogeneous, with the boundaries between each of the rock associations and the gneisses being marked by high strain shear zones which are nearly parallel to the regional strike. two Locally developed shear zones also disrupt each association. At le§st # penetrative deformation events occur in the supracrustal rocks. i s indicated by a strongly developed mineral elongation lineation co—axial with recumbent isoclinal folds, while the shear zones and locally developed asymmetric folds are associated with D 2 . The J)^ event is not present in the granitic rocks suggesting their emplacement during or prior to D 2 A systematic study of metamorphism has not yet been carried out, but available information suggests variable conditions close to the greenschist-amphibolite facies boundary. Few rocks contain minerals or mineral assemblages that could be used to determine metamorphic conditions. Many of the sediments are extremely rich in iron, resulting in the growth of magnetite porphyroblasts during metamorphism.

The pelitic assemblage of quartz-biotite-chloritoid in the western part of the belt is indicative of upper greenschist facies conditions. However, the presence of grunerite in banded iron formations and hornblende with garnet in some amphibolites clearly indicate amphibolite facies metamorphism. This is further substantiated by the presence of andalusite with kyanite, recorded by Elias (1983). It seems possible that slightly higher metamorphic grades (both temperature and pressure) are associated with the shear zones. Near the southern margin of the belt, biotite has developed across the fabric of certain pelites, whereas hornblende shows a similar relation in metabasic rocks. This later static amphibolite facies event is perhaps a contact metamorphic effect related to granite emplacement. Preliminary geochronological data indicate an early Archaean history for the entire Jack Hills Metasedimentary Belt. A Sm-Nd model age (T^ HUR ) of 3.68 ± 0.05 Ga has been obtained for a felsic volcanic unit from the central association, and gneissic granitoids from the northern margin of the Belt give a U-Pb zircon age of 3.5 Ga. These dates are similar to those determined for gneisses from the Narryer Metamorphic Belt and at Errabiddy (de Laeter et al. , 1981; Fletcher et al. , 1983; I.S. Williams et al., 1983), indicating that remnants of this ancient terrain are widespread in the northern Yilgarn Block. Granite rocks from immediately south of the Jack Hills Belt have a zircon U-Pb age of c_ 2.6 Ga and the one sample so far analysed for Sm-Nd has a T c h u r of 2.59 ± 0.08 Ga. References de Laeter, J.R., Fletcher, I.R., Rosman, K.J.R., Williams, I.R., Gee, R.D. and Libby, W.G., 1981, Nature, 292, 322-324. Elias, M., 1983, Belele, Geol. Survey West. Australia Explan. Notes. Fletcher, I.R., Williams, S.J., Gee, R.D. and Rosman, K.J.R., 1983, J. Geol. Soc. Aust. 30, 167-174. Froude, D.O., Ireland, T.R., Kinny, P.D., Williams, I.S., Compston, W., Williams, I.R. and Myers, J.S., 1983, Nature, v. 304, p. 616-618. Williams, I.R., Walker, I.W., Hocking, R.M., and Williams, S.J., 1983, Byro, Geol. Survey West. Australia Explan. Notes. Williams, I.S., Page, R.W., Froude, D. , Foster, J.J., Compston, W., 1983, Geol. Soc. Australia 6th Geol. Convention, Canberra, p. 169-170.

PRESENTATION OF GEOLOGICAL DATA FOR ENGINEERING PURPOSES D.H. Bell University of Canterbury, Christchurch, New Zealand For the safe design and economic construction of geotechnical works it is essential that engineering geology data be provided at all stages from project inception to final commissioning, and that the engineering geologist involved is in a position to influence both the formulation and the execution of any site investigation programme. A "team" approach to such investigations is strongly advocated, with clearly-defined objectives that are constantly reviewed as site-specific geological and geotechnical data are obtained.

Engineering geological data must be presented in a format that is appropriate to the project stage, and use consistent and clearly-defined terminology. Clear separation of geological inference from site observations is essential, and optimum use should be made of graphic presentation techniques to show geological data in ways that can be understood by other professionals who are not geologists. Regular progress reporting is necessary during the project, and the routine evaluation and formal publication of relevant site data is strongly recommended following satisfactory completion. Examples are given of geological data presentation for engineering purposesj and include the following: 1.

a brief review of rock and soil terminology, with recommended descriptive procedures;

methods of plan and section compilation for various compact and corridor projects at different stages of this development;

logging techniques that are appropriate to drill holes, shallow excavations and underground exposures;

data presentation methods that may be appropriate for legal and contractual purposes.

The majority of examples provided relate to consultant situations in New Zealand, and include data from railway instability assessment, dam and canal construction, residential subdivision of land, and natural hazard evaluation.

A RESERVOIR GEOLOGICAL MODEL OF THE LATE PERMIAN SANDS IN THE PETREL AND TERN GAS FIELDS, OFFSHORE BONAPARTE BASIN M.R. Bhatia and P.H. Coisy Australian Aquitaine Petroleum Pty Ltd, North Sydney The Late Permian sandstones of the Hyland Bay Formation form one of the principal objectives in the search for hydrocarbons in the southeastern offshore Bonaparte Basin. These sandstones constitute the reservoirs of the Tern and Petrel Gas Fields. Gas has been produced on drill stem test from the Hay Member reservoir in the Petrel Field, while the overlying Tern Member reservoirs have been productive in the Tern Field. A Late Permian depositional model has been formulated based on sedimentary facies studies of cores and seismic stratigraphy. The producing reservoirs of the Petrel Field were deposited in various environments associated with a deltaic system. The log correlation and core studies suggest the progradation of a northwesterly trending delta, whereas the seismic facies studies are not as conclusive. The producing sands in the Tern Field were deposited in a shoreface environment of a barrier bar-lagoon system.

The resorvoir quality of the sands is controlled by facies dependent diagenesis. In the Petrel Field, sandstones deposited in the upper delta plain and along the shoreline are clean, medium to coarse grained and highly quartzose but have very low porosity and permeability due to extensive quartz overgrowth. However, sands deposited in the delta front and lower delta plain environments are medium to fine grained, argillaceous and have fair to good reservoir potential. In these sands, the dispersed clays formed coats and rims on quartz grains during early diagenesis and inhibited quartz overgrowth. In the Tern Field, sands of the upper shoreface have poor reservoir quality due to early calcite cementation. However, finer grained sandstones of the lower shoreface facies have good reservoir quality. The porosity in these sands is mainly primary and preserved due to high clay content. The processes of quartz and calcite cementation which drastically reduced the reservoir quality of the coarsegrained sands occurred early and were influenced by the texture of the sands and probably also by the chemical character of the formation waters. GEOSCIENCE TECHNICAL ASSISTANCE - DEVELOPING COUNTRIES 1

NEEDS

S.A. Bilgrami Resource Development Corporation, Karachi Earth Science aid to developing countries was discussed at the 24th International Geological Congress, Montreal, August 24-25, 1975. A number of problems were identified and suggestions given. An International Workshop on Earth Science Aid was held at Memorial University, St. Johns May 18-19, 1974. Here again a number of problems were identified and suggestions given. However, little change has since taken place either in attitude to geoscience aid or its substance. Better utilization of existing capability in the developing countries, financing of geoscience aid to poor LDC's, utilization of existing earth science data, better resource management, measures for environmental protection, multi-disciplinary approach to mineral development and application of the new concepts in geosciences to exploration and evaluation of mineral resources are the areas identified for closer attention of the aid giving agencies. The strategy outlined would have a very beneficial effect if it is implemented. PROBLEMS IN APPLYING PRIMARY GEOCHEMICAL HALOES TO EXPLORATION FOR BLIND OREBODIES R.A. Binns and D.J. Whitford CSIRO Division of Mineralogy, North Ryde, NSW Detection of primary geochemical haloes in rocks surrounding mineralization has been widely acclaimed as an exploration technique of particular relevance to the discovery of blind orebodies. Treatises on the subject, such as Beus and Grigorian (1977) and Govett (1983) refer to several theoretically attractive aspects of primary geochemical haloes, for example their lateral and vertical zonality, their wide extent relative to recognizable mineralogical alteration, and their preservation in weathered materials. Taken together with recent developments in analytical instrumentation and computerized data treatment, these features suggest a potential which is not reflected, however, in compilations of actual experience. Even between closely juxtaposed occurrences of equivalent ore types, the distribution of particular elements in wall rocks can display quite contrary patterns, and it is not possible at present to predict their behaviour with sufficient confidence to plan an exploration program covering more than the very local scale. 59

To overcome this situation, a formidable amount of research is needed, directed particularly towards improved understanding of fluid-rock interaction, and towards careful documentation and interpretation of numerous mineralized environments. In addition sampling strategy requires careful consideration, being a subject that appears to have received insufficient attention in many reported case studies and which may be responsible for a large measure of the apparent confusion referred to previously. By concentrating on collection and analysis of specific rock types, better understandings of haloes associated with wallrock alteration and their relation to mineralizing events should be achieveable, but in practical application the results may only be directly relevant where abundant drill core or excellent exposure is available. In the more common exploration situation for Australia where percussion chips or soil samples must be used, complications arising from weathering and also geochemical dispersal arising from minor outlying manifestations of ore will interfere with haloes arising directly from fluid-rock interaction. Care must then be taken that element abundance patterns are not simply reflecting structural characteristics of the mineralized environment. It is possible that judicious manipulation of chalcophile elements and lithophile elements associated with gangue constituents may resolve such problems. In that part of a new CSIRO project directed towards varied epigenetic ore types in relatively homogeneous host rocks from eastern Australia, we have demonstrated the feasibility of detecting haloes related to wallrock alteration. However differences in individual element abundances between sample sets representing 'background' and situations close to ore are commonly only slightly outside the variance within sample sets, even where there is careful petrographic control. Thus the haloes are mostly subtle, and require enhancement by multielement statistical approaches. There is considerable variability in the dimension of haloes. An additional problem becoming evident is that the haloes may reflect fluid-rock interactions not directly contemporary with ore deposition, thus their more appropriate application may be to locating plumbing systems, rather than orebodies. At present there are too few data to allow generalized correlations between haloes and ore types, or to distinguish 'barren' from 'fertile' alteration patterns. Primary dispersion haloes around Australian volcanogenic massive sulfide orebodies are also being examined. Their recognition is often difficult because of the superimposed effects of 'normal' submarine hydrothermal alteration, and in most cases, later regional metamorphism. The geochemical effects of all these processes are often similar, varying only in degree. Attempts to understand ore-related primary dispersion around volcanogenic deposits require knowledge of the primary geochemical affinities of the rocks subjected to alteration. In many deposits, even in the most altered rocks where all primary igneous textures have been obscured, elements such as Ti, Zr, V, Nb, and the HREE appear to have remained immobile, preserving primary ratios that identify the parent volcanic rocks. In some circumstances, sparingly mobile elements such as the LREE may be better primary dispersion indicators than very mobile elements, such as the alkalis and alkaline earths, that can be substantially modified during later metamorphism. Such modification is implied by Rb/Sr isotopic investigations. No general patterns have yet emerged in our studies of primary dispersion haloes in volcanogenic terrains. Differences between deposits presumably reflect variations in the chemical and physical properties of host rocks, the nature of the fluid, and effective fluid-rock ratios. Most of these parameters are very difficult to determine in deformed and metamorphosed terrains.

Despite these reservations the project is continuing. Besides expansion to additional case studies it is planned to incorporate isotopic ratio measurements and to examine the effects of weathering on haloes in fresh bedrock. Difficulty in obtaining suitable 'background' samples is a significant constraint for many potential case studies. References Beus, A.A., Grigorian, S.V., 1977, "Geochemical Exploration Methods for Mineral Deposits", Applied Publishing Ltd., Wilmette. Govett, G.J.S., 1983, "Rock Geochemistry in Mineral Exploration", Elsevier, Amsterdam.

LATE-STAGE CRYSTALLIZATION TRENDS IN BASIC AND ALKALINE VOLCANIC ROCKS IN VICTORIA W . D , Birch Museum of Victoria, Melbourne Late-stage, high-temperature assemblages in pegmatoidal veins and vesicles are relatively widespread in the Newer Volcanic rocks of Victoria. Although these are dominated by alkali olivine basalt and olivine tholeiite, salic differentiates and high-potassium lavas (including leucitites) are present in small amounts. Pegmatoidal rock types associated with alkali olivine basalt (Portland) olivine leucitite (Cosgrove) and analcime basalt (crinanite) (Lake Bullenmerri) have been studied. The pegmatoidal assemblages are dominated by clinopyroxene, with compositional trends from diopside-salite to aegirine o r , rarely, Ti-aegirine. Pyroxenes do not achieve this degree of enrichment in Na and T i in the host lavas. Feldspars range from andesine to anorthoclase/sanidine, with some crystals showing the full composition range. Feldspars in host basalts show a similar range, but commence from slightly more calcic compositions (labradorite). Feldspar compositional trends in the host lavas and their pegmatoids are clearly distinguished by higher Or components in the former. This appears to reflect higher temperatures of crystallization, rather than differing bulk rock composition. Iron titanium oxides (ilmenite and titanomagnetite) occur in all rock types, but with ilmenite more abundant in the lavas, and magnetite more common in the pegmatoids. Ilmenites show a systematic decrease in M g O content from host to pegmatoid. Titanomagnetites are generally exsolved to ulvospinel and titaniferous magnetite in the pegmatoidal rocks. Pegmatoidal rocks may be characterized by small amounts of alkali-rich amphiboles, aenigmatite and sodalite which crystallized interstitially from the last volatile-rich m e l t s . These phases are absent from the vesicle and open-fissure assemblages which are closely associated with the pegmatoidal v e i n s . This association probably arose from early release of volatiles from the erupted lavas having provided channelways through which the residual melt could m i g r a t e . The phases present and their textural relationships indicate that the pegmatoidal rock types crystallized from fractionated m e l t s , whose compositions were determined chiefly by crystallization trends of clinopyroxene, feldspars (and/or leucite, nepheline and analcime) and Fe-Ti oxide Accumulation of volatiles such as H 2 Q , F , C I , P w a s an important factor in facilitating rapid growth of large crystals. These crystallization trends reflect bulk rock compositions, which indicate that, in general, the pegmatoidal rocks are depleted in M g O , Cr and N i , and enriched in Na^O and TiO relative to the host lava. Other elements, such as K , Fe and Ca are less predictable in their fractionation behaviour.

Application of various geothermometers to the pegmatoidal and vesicle assemblages is limited by exsolution in most magnetites and by the sodic compositions of coexisting feldspars. However, an upper limit of between about 800 and 900 C may be placed on crystallization temperatures in these rocks by determinat ions on the Fe—Ti oxides in the olivine leucitite•

HTDROTHERMAL FLUID COMPOSITIONS IN MOLYBDENUM-MINERALISED GRANITES: AN APPLICATION OF FLUID/MINERAL EQUILIBRIA Mark S . Bloom Department of Earth Sciences, Monash University, Clayton Molybdenum mineralisation in granites typically occurs as early quartz1 biotite-K feldspar-molybdenite veins with fluid inclusion temperatures of 300 C to 500 C and hypersal ine brine compositions, and quartz-pyritemolybdenite veins with lower temperatures (250° to 300°C) and lower salinities (Bloom, 1981)• Oxygen and sulphur gas fugacities measured in solutions extracted from fluid inclusions (Smith et al., 1982) are in good agreement with fugacities calculated from observed sulphide-oxide mineral assemblages• Highly variable and complex compositional zoning characterises (K, N a ) feldspar, biotite, and muscovite ( - topaz) solid solutions in the vein assemblages from early F-rich biotite alteration (Bloom, 1984a). Although zoning within individual mineral grains is common, compositional trends in the averaged compositions can be correlated with distinctive fluid inclusion populations as well as with position in the vein emplacement sequence. The coincidence of mesoscopic vein assemblages with daughter mineral associations in fluid inclusions (Anthony et al., 1983) indicates that mineralisation occurred from solutions equilibrated with veinlet assemblages• Computations of fluid/mineral equilibria have been employed to predict compositions of the ore-forming solutions at steam saturation and 350°C + + ( B ^ o m , ^J84b) 1 Activities of the ionic components N a , K , Ca , Mg , Fe , Al , CI , F , S and H^SiO^, and their dependent species, are constrained by the presence of alkali feldspar , biotite , fluortopaz S , quartz, fluorite, halite, hematite and anhydrift in equilibrium with the solution. Redox equilibria and pH are externally imposed with log f 0 o and log f S 2 of -26 and -9 respectively, and pH of 5 (Smith et al., 1982). Molybdenite limits the activity of molybdenum in the fluid phase. Molal concentrations of dissolved components are calculated using the predictive algorithms of Helgeson et a l . (1981) for solutions of high ionic strength. The resulting solution compositions are hypersaline brines similar to those inferred from inclusion fluids and observed in the deepest levels of active geothermal systems.

Using thermochemical data for oxidised aqueous molybdenum species, the high temperature speciation of molybdenum and the solubility of molybdenite in these brines has been calculated (Figure 1). Significant amounts of molybdenum are transported as HMoO, and MoO^F and these complexes eacn or in combination can give rise to potential ore-forming concentrations (several hundred ppm) of molybdenum. Chloride and sulphide complexes are relatively unimportant in molybdenum transport under the conditions investigated. MoO^F becomes the predominant molybdenum complex in acid solutions and at the HF fugacities inferred from H^O/HF fugacity ratios calculated from F-rich biotite compositions (this study, and Gunow et al., 1980). Precipitation of molybdenite at the site of ore deposition could have been controlled primarily by physical temperature gradients, from precursor solutions to those considered here. Smith et al. (1980) suggested a similar temperature dependence of molybdenite solubility, and predicted that rising ore-forming solutions would deposit molybdenite in a narrow, confined zone as temperature decreased. The fluid/mineral equilibria also infer that controls on molybdenite deposition by reactions that involve fluorinebearing alteration phases and K1feldspar can also be extremely effective under isothermal conditions. Two such generalised equations are: 3KAlSi 3 0 8 + 4MO0 3 F~ + 8H 2 S° +

KAl 3 Si 3 Oio (F) 2 + 2KF° + 6Si0 2 + 4MoS2 + 10H 2 0 + 20 2

and KAlSi 3 0 8 + MO0 3 F~ + 3MgFJ + 2H 2 S° + H + ^ K M g 3 A l S i 3 O l 0 (F) 2 + MoS 2 + 5HF° •

The widespread occurrence of the K1feldspar-fluorphlogopite-muscovitequartz-molybdenite assemblage which coincides with the bulk of molybdenum mineralisation is thus explained in terms of reaction of the ore-forming fluid with the Kffeldspar component of the rock hosting mineralisation. References Anthony, E.Y., Reynolds, T.J. and Beane, R.E., 1983, Geol. Soc. America Abstracts with Programs, v.15, p.516. Bloom, M.S., 1981, Economic Geology, v.76, p.1906-1920. Bloom, M.S., 1984a, Canadian Jour. Earth Sciences (in press). Bloom, M.S., 1984b, Canadian Jour. Earth Sciences (in press). Gunow, A.J., Ludington, S. and Munoz, J.L., 1980, Economic Geology, v.75, p.1127-1137. Helgeson, H.C., Kirkham, D.H., and Flowers, G.C., 1981, Am. Jour. Science, v.281, p.1249-1516. Smith, R.W. and Norman, D.I., 1981, Geol. Soc. America, Abstracts with Programs, v.13, p.557.

AQUEOUS CHEMISTRY OF TIN AT 300°C, WITH APPLICATIONS TO TIN TRANSPORT AND CASSITERITE DEPOSITION IN ALUMINOSILICATE HOST ROCKS M.S. Bloom and V.J. Wall Department of Earth Sciences, Monash University, Clayton Numerous field-related and experimental studies have recognised a direct genetic relationship between primary tin concentrations and felsic igneous rocks. Observations from the quartz-cassiterite stage in a variety of tin-mineralised systems restrict the most critical stage of tin concentration to the evolution of a supercritical, hypersaline aqueous phase> and the onset of cassiterite deposition to decreasing temperature and acidity and increasing oxygen fugacity in the magmatic-hydrothermal solution. Mineralisation has also occurred in many deposits, however, more or less continuously from magmatic conditions down to, and in some deposits largely at, temperatures of 350°C or less from relatively dilute solutions. In this paper, we address the physical and chemical conditions that are conducive to the migration of tin in hydrothermal aqueous fluids to the sites of ore deposition, and what changes in these conditions can lead to economic accumulations of this metal. Acid to near-neutral pH's are characteristic of the ore-forming solutions at 300 C, as indicated by muscovite (_+ kaolinite) alteration in vein- and fracture-controlled quartz-cassiterite mineralisation and in chlorite (+ talc tremolite muscovite) alteration in cassiterite-sulphide deposits. Furthermore, the presence of fluoromuscovite, fluoroapatite, and fluorotopaz in alteration assemblages indicates high H^O/HF fugacity ratios. We have used electron microprobe analyses of hydrothermal alteration products, together with the appropriate activity-composition relations, to characterise the composition of the ore-forming solutions. log ppm So ru in I II E (0 Q Q• &

C\ l I t

I 0) A X o v/ £ CO

1*5 Dlfd \ D

CO i I in I A tM X O c o 0) v c X

-CM

These computations of fluid/mineral equilibria provide first approximations to tin concentrations and tin speciation in the hydrothermal fluids. In dilute solutions tin transport is effected by hydroxide and oxyhydroxide species of tin (IV) at oxygen fugacities greater than nickel-nickel oxide, or of tin (II) below this buffer. The neutral SnCl° complex becomes increasingly important in acid solutions at all oxygen fugacities considered, and in the nearneutral pH region as fO is decreased. Total dissolved tin in solutions of near-neutral pH increases from less than one ppm at an oxygen fugacity corresponding to the hematite-magnetite buffer, to greater than 50 ppm in solutions buffered by the presence of SnO-SnO . The dependence on fO and pH infers chat tin transport is most effective under reducing and distinctly acid conditions in chloride-rich electrolytes.

In fluids having high H O/HF fugacity ratios consistent with the fluorine-rich alteration assemblages, the Sn(OH) F complex dominates speciation for neutral solutions regardless of chloride concentration or oxygen fugacity. Under more acid conditions and lower f 0 2 > however , SnCl^ and Sn(OH) F° may eachj or in combination contribute to cassiterite solubility which may reach tin concentrations of several hundred ppm. In addition to temperature decrease, tin deposition may result from a variety of isothermal processes which promote destabilisation of the predominant aqueous complexes. Mixing or boiling of fluids can shift solution pH to near-neutral compositions, or partition fluorine into a vapour phase, with resultant solution compositions which coincide with the solubility minimum for cassiterite. Such processes are independent of the rock compositions hosting mineralisation. Water-rock interaction similarly drives solution chemistries toward neutral pH as a consequence of silicate hydrolysis reactions precipitating muscovite. This irreversible mass transfer may also bring about saturation with respect to one or more silicate alteration phases which partition fluorine from the fluid into the solid phase. A generalised reaction of a tin- and fluorinerich solution reacting with alkali feldspar in an alumino silicate host rock is + 3KAlSi 3 0g + 2 H + + 2Sn(OH) 3 F° == 2Sn0 2 + K A l 3 S i 3 0 1 Q ( F ) 2 + 6Si0 2 + 2K + 4 ^ 0

Examination of the above reaction indicates that cassiterite deposition attends formation of fluorine-rich muscovite, and that solution pH is driven toward neutrality with reaction progress. Another reaction involving the muscovite component of the host rock and replacement by more fluorine-rich alteration mica is K A l 3 S i 3 O 1 0 ( O H ) 2 + 2Sn(OH) 3 F° ==

2SnC>2 + K A l 3 S i 3 0 1 Q ( F ) 2 + 4 H 2 0

Wall-rock reactions which attend quartz-sericite alteration may thus result in cassiterite deposition, with initial tin concentrations in the fluid dependent on oxygen fugacity but mechanisms of precipitation dependent largely on shifts in solution composition as a result of isothermal processes of fluid/mineral equilibria.

CLAY MATRIX DIAGENESIS AND THE EVOLUTION OF GIPPSLAND BASIN OIL RESERVOIRS J.M. Bodard and V.J. Wall Department of Earth Sciences, Monash University, Clayton, Victoria Diagenetic ajustments causing the rejuvenation or enhancement of porosity and permeability play a major role in the evolution of many economic hydrocarbon deposits (eg. Bodard, Wall & Cas, 1984). The porosity resulting from the dissolution of both detrital and authigenie rock components, in particular, contributes to the nature and quality of siliciclastic reservoirs. In view of its effect on reservoir quality, we examine the diagenesis of the clay matrix component of mature quartz-rich arenites which make up the main oil-bearing strata in Kingfish, Halibut and Mackerel oil reservoirs, offshore Gippsland Basin, Victoria. Our major findings are: 1. The detrital matrix component of these sandstones has undergone extensive post-depositional modification involving mixed-layer clay-mica/expandite alteration, kaolinization, and/or dissolution. 2. Although medium to very coarse sandstones have a regular framework packing configuration, they exhibit patchy matrix/pore distribution with some pore boundaries cross-cutting matrix. Individual pores may have matrix-clotted portions which can appear gradationally less dense towards clean open parts. Metasomatic-like zonations may alfeo be evident along the fringes of residual matrix clots where abutting inter-framework porosity. Together these features constitute the prime evidence for matrix removal by dissolution, a process which adds significantly to post-depositional porosity and permeablility enhancement in the oil fields studied.

Rock component dissolution is not restricted to clay matrix alone, but includes framework and authi genie K-f eld spar, and such chemically less stable framework grains as low-grade metasedimentary, sedimentary, and rare volcanic rock fragments. Thus porosity, of hybrid primary and secondary origin, can be exceptional - up to 30 per cent with attendant permeabilities in excess of 1000 md's.

Poorly sorted to bimodal sandstones with significant initial matrix contents tend to best exhibit textural evidence of matrix removal. Framework dissolution in clean sandstones may also indicate some clay matrix dissolution therefrom.

The porosity contribution owing to matrix and framework dissolution, however, is not large (probably less than 5 per cent of total rock volume), but removal of fines in the process reduces the sediment surface area per unit volume, and consequently levels of irreducible water saturation markedly diminish. Permeability increases.

Some porosity reduction has resulted from minor kaolinite precipitation (during/after the stage of matrix dissolution), framework reorganisation and compaction, pressure solution, quartz overgrowth and cementation. The amount of secondary porosity resulting from matrix removal depends on initial matrix content, and the degree and extent of dissolution processes, whereas, the porosity now present also depends on the nature of subsequent porosity reducing diagenetic adjustments, as well as the porosity at time of deposition.

Oil emplacement probably followed closely or was associated with matrix and framework dissolution, insofar as residual bitumen pore lining mantle modified remnant matrix and adjacent clean detrital grain surfaces.

Dissolution evidently results from the ingress of more acid fluids (Wall & Bodard, 1984), probably related to the thermal maturation of organic material* The relative importance of organic acids in relevant solution processes is implied. Moreover, the significant aluminium transport required indicates a very large throughput of the f1uid s involved•

The diagenetic adjustments described above characterise a significant portion of the Latrobe Group in the southeastern part of the Gippsland Basin, wherein the major known oil fields are located. Clay matrix diagenesis may be an important post-depositional phenomenon in other hydrocarbon-prone sedimentary basins as well.

References Bodard, J.M., Wall, V.J., and Cas, R.A., 1984, A.P .E.A. Jour., v. 24, part 1, p. 314-335. Wall, V.J., and Bodard, J.M., 1984, The role of fluid - rock interaction in sandstone diagenesis. This volume.

QUALITATIVE ANALYSIS OF THE FLUID IN FLUID INCLUSIONS, USING THE ELECTRON MICKOPROBE Y. Bone1 and B.J. Griffin2 ^Geology Department, University of Adelaide, Adelaide ^Electron Optical Centre, University of Adelaide, Adelaide The nature of the fluids which were involved in the deposition of mineral deposits is one of the most important considerations in the exploration for and study of the deposits. During the last twenty years or so, the role of fluid inclusions as retained examples of these fluids has been recognised. The data obtained by microthermometric techniques led to the theoretical calculation of the composition of these fluids in terms of NaCl equivalent brines, by reference to existing chemical data. This was followed by recognition of depressed first melting temperatures as an indicator of the necessary presence of other components in the fluid. This has led more recently to the interpretation of many of these fluids as CaC^-rich brines. Analytical techniques exist for the extraction of the fluid from fluid inclusions, but these techniques are fraught with difficulties such as extremely small sample volumes and concomitant problem of contamination. Sophisticated and expensive techniques have been developed, e.g. laser probe; but these are available to only a few workers.

The analytical technique described here uses the now relatively common electron microprobe and associated energy dispersive X-ray analysis system (EDS). A standard doubly-polished fluid inclusion section is carbon coated and mounted in the normal way. Using optical microscopy a near-surface fluid inclusion is located under the electron beam and the beam current increased, generally to around 150-200 nanoamps. The use of a finely focussed beam results in localised heating of the specimen and may lead to decrepitation of the inclusion. One in twenty inclusions in material examined to date decrepitated. The evacuated chamber environment results in surface deposits of the solute together with daughter salt crystals in the vicinity of the inclusion site. This process may be observed through the optical microscope or on the display CRT of the electron microprobe. The surface deposits can be qualitatively analysed by firstly: collection of a spectrum from the host phase and then from the surface deposits. Subtraction, visually or through electronic hardware routines in the EDS system, of the host spectrum from each of the spectra from the surface deposits gives a qualitative analysis of the material and hence the fluid composition. This process of host spectrum subtraction is essential as, in nearly all cases, the electron beam penetrates the surface deposits and the collected spectrum is a record of both surface and host composition. Results may be either recorded photographically (figures 1-5) or relative peak heights may be recorded from each spectrum using conventional software. Although the technique is laborious and gives qualitative rather than quantitative results, it provides very specific information that is otherwise normally unattainable. A study of samples from the Rum Jungle deposits in the Pine Creek Geosyncline, N.T., using a JEOL 733 Superprobe and KEVEX EDS system in the Electron Optical Centre, University of Adelaide, has been very successful. Results show that the fluids involved in the Rum Jungle mineralisation consist not only of Na-Ca±Mg chloride brines (figures 2-5), but that carbonate and sulphate complexes are also involved (figures 1-3); in some cases probablv as the sole component (figure 1). Figures

Fig. 1

Fig. 2.

Analysis of 5 fluid inclusions from Rum Jungle, N.T. These two samples, C43 - Celia Dolomite quartz and E28 - Coomalie Dolomite magnesite, contained the same types of fluid inclusions and produced similar microthermometric data for each type. It was assumed that they represent the same fluids. (1) C43 (Si only element present for host): Mg only cation present. No anion - therefore probably a carbonate. (2) C43: Na, Mg, K and Ca all present. CI is a strong peak - indicating a saline brine. As there were no daughter minerals present in this fluid inclusion, the S line indicates a dissolved S species, probably sulphate. (3) E28 (Mg only element present for host): The CI indicated is not sufficient to account for the Ca+Fe indicated, especially as some of the background Mg could also be from the fluid. Therefore there is the probability of carbonate present. (4) E28: The Na and Ca alone, without considering any Mg, is far in excess of the available CI, so once again there is the probability of carbonate. (5) E28: In this case the CI and S lines indicate more than adequate amounts of these elements to accommodate all the Na and Ca shown. This supports the hypothe sis that Mg is a fluid component, masked by the background peak.

Fig. 3

Hm m

ma m

N I H ***** M lftl«ttfttUif

Fig. 5

Fig. 4

SOME ASPECTS OF ORE CONTROL AT THE ZINC CORPORATION LIMITED, NEW BROKEN HILL CONSOLIDATED LIMITED AND SOUTHERN CROSS MINES, BROKEN HILL, NEW SOUTH WALES S.A. Booth The Zinc Corporation, Limited, Broken Hill, N.S.W. Stratabound/stratiform and remobilised mineralisation are the two dominant styles of mineralisation which are recognised to constitute the Broken Hill ore deposit. The general stratigraphic succession of the ore deposit including the internal stratigraphy of the ore lenses and enveloping rocks is briefly presented. Major emphasis is placed on the role of remobilised mineralisation, that is, mineralisation of sufficient tenor to constitute ore. Although volumetrically less significant, remobilised mineralisation has in recent years been recognised as providing a significant contribution to known ore reserves. Additionally, this form of mineralisation may provide the best short term potential for adding to known ore reserves. Three styles of ore remobilisation are discussed. parameters for each style are considered.

Exploration

The first style is that mineralisation remobilised into the hinge of an F3 fold axis. The current mining strategy for the lower grade 'A' Lode at The Zinc Corporation, Limited (ZC) relies on incorporating this higher grade remobilised material into stope designs. Similarly, the thickening in the keel of fBf Lode is recognised as due to remobilisation of sulphides into a F3 fold hinge. The second style is best exhibited by the classical Lead Lode "droppers". These have long been known at the New Broken Hill Consolidated Limited (NBHC) mine and recent diamond drilling has delineated two Lead Lode dropper structures at the ZC mine. The characteristics of this style of mineralisation are:1.

They detach themselves from the main orebody within the axial plane of a fold, migrate into a limb position and occupy a distinct stratigraphic horizon. Here they become stratabound.

The fold producing the dropper does not need to be a major feature.

The droppers generally migrate to the eastern limb of an F3 fold.

The dropper neck or "lead-in" is usually thin and, in places tenuous. This may be on the scale of millimetres. When occupying a stratabound position the dropper rapidly thickens.

The droppers are enveloped by a sericite schist zone which is concordant with the dropper but discordant with the host lithologies.

Mineralogically, droppers tend to have a high grade margin with a, low grade core dominated by manganese silicates (rhodonite, manganoan hedenbergite, bustamite, knebelite). Pyrrhotite is locally abundant (+ 20%) and often massive. Arsenic levels are generally high due to coarse grained arsenopyrite and/or lollingite. Silver content is relatively high with respect to lead.

Although volumetrically insignificant, dropper style mineralisation, when occurring close to existing openings,is considered to represent a valid exploration target. The third style considered involves remobilisation of ore into a major sub-vertical, north-south trending shear zone. Remobilisation may extend up to two hundred metres within the shear, as in the eastern keel of Southern fAf Lode at the Southern Cross mine. This style of mineralisation may offer the best potential for significant additions to the ore reserves at ZC/NBHC. Some exploration parameters are as follows:Style 1: (a) Definition of F3 folds through detailed structural and stratigraphic analysis. (b) When low grade mineralisation is intersected in the limb of a fold, to trace it into the hinge zone. Style 2: (a) Recognition of discordant schist zones, especially where they occur in axial planes of folds. (b) Follow-up, by drilling, narrow intersections of mineralisation within the pelitic metasediments below Nos. 2 and 3 Lens. This may or may not be in conjunction with point (a), above. (c) The development of dropper style mineralisation may be associated with a series of cross folds, trending WNW-ESE. The periodicity of these cross folds may decrease northward.

Style 3:

Structural considerations assume major importance, generally overprinting stratigraphic features.

In addition the following parameters are common to all:1.

A detailed knowledge of the prevailing stratigraphic and structural regimes, and

Drilling density must be high to adequately test a target.

P R O G R A M M E LOGGER: A COMPUTER BASED CORE LOGGING FACILITY DEVELOPED AT THE ZINC CORPORATION LIMITED AND NEW BROKEN HILL CONSOLIDATED LIMITED, BROKEN HILL, NEW SOUTH WALES 1 o S.A. Booth1 and I.D. Blucher^ ^The Zinc Corporation, Limited, Broken Hill ^Bougainville Copper Limited, PNG Portable computers, through increased memory capacity and reduced physical dimensions, have advanced to the point where it is feasible to consider them as useful field tools for geologists. One application where significant benefit may be achieved relates to the recording of core logging data. A major exploration drilling programme coupled with an increased diamond drilling effort within The Zinc Corporation, Limited (ZC) and New Broken Hill Consolidated Limited (NBHC) mines has seen diamond drilling metreage increase from 20500 metres in 1980 to a planned 68000 metres in 1984. The evaluation of a personal portable computer to aid core logging was clearly warranted. ZC/NBHC selected an NEC-8201A portable computer to conduct the evaluation. Peripherals constituted an NEC pinwriter PI printer, a tape data recorder and an expansion RAM cartridge. For rationality and simplicity a similar computing philosophy was adopted to that employed on the technical mainframe computer (a Perkin Elmer 32/20). The main aspects are user friendly, simplicity, robust and of a forgiving nature. In addition, the system had to cater for the varied requirements of mine development, exploration and percussion drilling. The actual design for a computer based core logging system was implicit in the diamond drill recording sheet previously in use for the hand recording of information. The rules and relationships governing the type of information to be recorded, what constitutes valid data and the sequence in which this information is to be recorded are well established and at a stable stage of evolution. With the method of data collection clearly established and well tested, the role of the portable computer is reduced to simply emulating the manual method. One minor drawback of a physically small portable computer is the relatively limited data storage capacity of these devices. In the application developed at ZC/NBHC this has limited the type of data processing carried out by the portable computer to editing and the production of an A4 size proof ledger. The proof ledger is used to check for syntax and numeric errors and for initial plotting of results. After errors are corrected, the completed diamond drill hole is transferred to the tape data recorder.

Complete text processing, expansion of abbreviations and mnemonics into English and the merging of assay results with the appropriate sample interval is left to the Perkin Elmer 32/20 mainframe computer where full use can be made of superior data storage and manipulation capabilities. The final drill hole ledger is produced via a Wang wide carriage printer. The logging procedure is regarded as commencing with data recording and finishing with the production of a typed ledger, complete with assay information recorded. Preliminary estimates indicate a potential time saving of approximately 50% may be achieved. The most significant benefits are associated with data recording and the downstream areas of typing, editing and additional data input (assay information). As users become more familiar with the system the speed of data recording should be further enhanced. Other advantages of the computer aided core logging are as follows: Standardisation of logging format; provision of traps for spurious data.

Disadvantages of the system installed at ZC/NBHC include: Relatively limited data storage capacity of portable computers; file handling with BASIC is at times awkward; the LCD screen is adversely affected by direct sunlight; and "off the shelf" portable computers are not environmentally sealed, i.e., care must be exercised to ensure that it is not exposed to adverse conditions of heat, humidity and dust. To date, the NEC has been used without any protection and has shown that provided a reasonable amount of care is exercised, no problems have arisen. The project has proved a successful exercise in utilising the current direction in computing hardware for a specific task quite remote from manufacturer's expectations.

STRUCTURAL ELEMENTS AND PETROLEUM POTENTIAL OF THE PAPUAN BASIN, PAPUA NEW GUINEA E.A. Bowen Robertson Research (Australia) Pty. Limited, Sydney Papua New Guinea has, during the last 65 million years, been situated within a micro-plate complex at the leading edge of the lithospheric Indo-Australian Plate, Prior to the initiation of this regime of eastnortheasterly convergence, the region was probably situated on a passive continental margin and subjected to extensional stress. Currently the boundary between the Pacific and Indo-Australian Plates passes north of western Papua New Guinea and bifurcates eastwards to enclose the South Bismarck and Solomon Sea Plates. Most, if not all, of Papua New Guinea south of the Lagaip Fault Zone and southwest of the Papuan Peninsula is underlain by Palaeozoic continental crust. The Papuan Basin is a stratotectonic unit which represents part of an extensive post-Palaeozoic depositional province. Sedimentation ranged from supralittoral to abyssal. Within the Basin four tectogenic units are recognised on the basis of present day morphology. These are the : Kubor Anticline, Fly Platform, Aure Tectonic Belt, and Papuan Fold Belt. 72

The Kubor Anticline is a basement arch situated near the northeastern margin of the Papuan Basin. Permian granite is exposed in the core of the Anticline. It is possibly a detached fragment of continental crust. Except for a marine transgression in the Late Triassic, it appears to have been a basement high and to have influenced sedimentation in the surrounding areas since the end of the Palaeozoic. The Kubor Anticline has no petroleum potential. The Fly Platform consists of Palaeozoic, or earlier, block faulted crystalline basement, overlain by 0-3 kms of essentially flat-lying Mesozoic clastics, Tertiary limestone and Plio-Pleistocene sediments and volcanics. It is bordered on the north by the Papuan Fold Belt and, in the east, by the Aure Tectonic Belt. During the breakup of the Australian continental margin and formation of the Coral Sea in the Late Cretaceous and Paleocene, thermal bulging resulted in both erosion of previously deposited Jurassic and Cretaceous formations, and restricted sedimentation in the Paleocene. Block faulting of the basement was common on an orthogonal set of faults trending northeast-southwest and northwest-southeast. Some of these faults continued to grow during the Tertiary under a regime of predominantly compressive and shear stress following the separation of Australia from Antartica in Eocene times. Consequently, many of the faults now exhibit a complex history of normal, reverse and transcurrent motion. Gas/condensate accumulations have been demonstrated in reefal buildups at Pasca and Uramu, and shows are recorded elsewhere. A wide variety of traps are indicated ranging from basement high onlaps, pinchouts, drape and compaction features, through normal and wrench fault associated structures, to reef, algal bank, carbonate platform and detrital wedge plays. Potential reservoir rocks exist in Mesozoic clastics and Tertiary limestones. The (Jurassic) Maril Shale has source potential throughout its extent and is mature. Lateral and vertical seals need to be demonstrated but can be provided by intraformational mudstones and structure. The Aure Tectonic Belt is a 150 x 400 km belt of folded and thrust faulted sediments overlying a deep basement depression. It adjoins the Collision Zone between the continental and oceanic plates to the north and east. In the west, the boundary with the Fly Platform is defined by the Aure and Bevan Fault zones, while the southern continuation can be traced into the Gulf of Papua from seismic and aeromagnetic evidence. The formation of the Aure Tectonic Zone was initiated in Eocene times with the obduction of part of the Solomon Sea Plate along the Owen Stanley Fault Zone to form the Papuan Ultramafic Belt. Continued westerly translation led to the accretion and subsequent folding, thrusting and metamorphism of Mesozoic and Tertiary shelf and bathyal sediments beneath the Papuan Ultramafic Belt. Progressive downwarping of the basement to depths of 10 - 12 kms ahead of the deformation front continued to accommodate relatively open water sedimentation until the Early Pliocene, by which time the approach of the proto-Papuan Peninsula restricted the zone of sedimentation to approximately its present configuration. Considerable, though undemonstrated, petroleum potential possibly exists in the Eocene and Mesozoic marine sections. The top of the Eocene may be picked on good quality seismic records to the west of the Aure Tectonic Belt. Although seismic picks are not certain within the Aure Tectonic Belt the Eocene appears to thicken eastwards. Post Eocene sediments appear to be thrust into high relief anticlines well within drilling range (less than 3000 m). Good reservoir rocks are found in parts of the Early-Late Miocene Aure beds. The unit is however, poorly understood because of the complex structure.

The source of any hydrocarbon accumulations within both the Eocene and Miocene sections would most probably be from the Mesozoic. The seal for any reservoir should be provided by intraformational mudstones. In addition, a regional blanket seal is provided by the argillaceous Orubadi beds* The Papuan Fold Belt is a region of sub-parallel folds and thrust faults, 100 km wide, immediately north of the Fly Platform and south of the Lagaip Fault Zone. The Fold Belt developed during the Late Miocene and Pliocene as a result of the collision of the Indo-Australian and South Bismarck Sea Plates. This caused southwesterly directed translation of Mesozoic and Tertiary sediments originally deposited at, or near, the northern margin of the Australian continental crust. Magnetic and gravity data suggest that basement beneath the Papuan Fold Belt has been downwarped to depths of at least 10 kms. Hydrocarbon accumulations can be expected in Mio-Pliocene thrust faulted anticlines. Reservoir rocks are Jurassic and Cretaceous sandstones (e.g. Toro sandstone) sourced from Maril shale by vertical and lateral migration. Seals are provided by fault planes, interbedded Jurassic mudstones and the thick, extensive (Cretaceous) Ieru Formation. Recent drilling success at Juha is reported to be in this situation. Fractured tertiary carbonate plays also exist and have recorded hydrocarbons from at least three wells towards the southeastern end of the Fold Belt. Shows have also been reported from Plio-Pleistocene clastics. Acknowledgements. This paper results from a study of the petroleum potential of the Papuan Basin #commissioned by the Papua New Guinea Government. I wish to acknowledge the contribution of other Robertson Research staff, Flower Doery Buchan geophysicists, personnel of the PNG Geological Survey, the Australian BMR and Worldwide Exploration Consultants. The paper is published by permission of the Chief Government Geologist of Papua New Guinea.

A PRELIMINARY INVESTIGATION OF THE GRAVITY ANOMALIES IN THE GUNNEDAH-TAMWORTH AREA A.M. Bramall

I.R. Qureshi

School of Applied Geology, University of New South Wales, Sydney The Gunnedah Basin (part of the Sydney-Bowen Basin) and the adjoining Tamworth Synclinorial Zone (Scheibner, 1974) are the two major tectonic units in the area of study (Fig. 1). To the west the Permo-Triassic rocks of the basin are overlain unconformably by the Cretaceous and Jurassic rocks of the Great Artesian Basin. To the east, they are thrust over by the folded Carboniferous and Devonian rocks of the Tamworth Synclinorium against the Hunter-Mooki Thrust System. The synclinorium is separated from the Woolomin-Texas Block by another major thrust system, the Peel Fault; the block is an anticlinorium and composed of deformed Palaeozoic rocks which are extensively intruded by orogenic granites. Large bodies of mafic and ultramafic rocks are emplaced along the Peel Fault. The western boundary of the New England Fold Belt is distinctly marked on the gravity map of Australia by three parallel anomalies (Fig. 1): (1) the Namoi Gravity High that lies over the Tamworth Synclinorium; (2) the Gwydir Gravity Low that runs along the Hunter-Mooki Thrust System and (3) the Meandarra Gravity Ridge that lies over the Gunnedah Basin. These anomalies can be traced for over 500 km from the Liverpool Range in the south to Meandarra in Queensland. Their continued presence in the ground where the synclinorium and its bounding faults are buried under the Mesozoic deposits, shows their inherent connection with these structures. To the east of these anomalies there is a region of broad gravity lov/s over the Woolomin-Texas Block. 74

The present study relies upon the B.M.R. gravity data. Density for Bouguer reduction has been changed from 2.2 to 2.67 tonne m~3 and an isostatic correction based upon a two dimensional Airy-type model has been applied. Both these corrections are substantial but as they are opposite in sign, they partly cancel each other out. The resulting anomalies along profile AB are shown in Fig. 2. A small regional gradient may persist within the corrected values. The Namoi Gravity High has steep gradients on both its flanks, indicating that the high is of shallow origin and that the rocks of the synclinorium must be denser than the surrounding rocks. This inference is valid for the western side where Permo-Triassic rocks of lower density lie against the Hunter Thrust. But on the eastern side, a lower density for the Woolomin-Texas Block does not seem likely. A better explanation lies in the lower-density granites intruding the higher-density rocks of the Woolomin-Texas Block. This explanation finds support in the fact that the gradient-zone forming the eastern flank of the high follows the Peel Fault in the south where granites are in its proximity (e.g., Fig. 2) but in the north it is located 10 to 20 km to the east of the fault. The Meandarra Gravity Ridge is considered by Qureshi (1984) to extend into the western part of the Sydney Basin. Along an east-west profile, he isolated an anomaly of mgal amplitude and interpreted its sources as a mafic body of 12 km thickness underlying the basin. The amplitude of the anomaly along Profile AB is 27 mgal. The local source of this anomaly may lie in the Werrie Basalt which has a maximum thickness of 1500 m in the Werrie Basin (Branagan, 1969); if present at Gunnedah, this can produce less than a half of the required anomaly. Greater contribution may come from an older mafic body underlying the Permian rocks as is inferred in the Sydney Basin. Although preliminary modelling of the anomalies is being conducted, a reliable quantitative interpretation must await more detailed field work and collection of density information. References Branagan, D.F., 1969, Geol. Soc. Aust., J.,16, 444-455. Qureshi, I.R., 1984, Aust. J. Earth Sc.,31, (in press). Scheibner, E., 1974, Explanatory notes on the Tectonic Map of New South Wales, Geol. Surv. of N.S.W., Sydney (283 p h Fig. 1. (right) Three parallel gravity anomalies and geology based upon 1:2.5 million Geological flap of Australia. The Lachlan Fold Belt rocks outcrop in the south-eastern corner of the area. The Oxley Basin is a part of the Great Artesian Ba^in which occupies most of the western region. AB gives the position of a gravity profile shown in Fig. 2 . Fig. 2 . (below) Gravity anomalies along Profile AB and a schematic geological section. The scale on the right applies only to the ground height.

A.R.C. SELWYN PIONEER OF THE AUSTRALIAN GEOLOGICAL

PROFESSION

D.F. Branagan Dept. Geology & Geophysics, University of Sydney

Alfred Selwyn in his seventeen years in Victoria (1852-69) laid the foundations for the geological profession as we know it today in Australia.

Selwyn's seven years (1845-52) in the Geological Survey of Great Britain, in particular his association with Andrew Ramsay and J.B. Jukes mapping the rocks of Wales, prepared him extremely well for his work in Victoria, because he came well-versed in the physical characteristics of regionally metamorphosed lower Palaeozoic rocks, was familiar with coal measures, and had gained an insight into aspects of glaciated landscapes. Furthermore Selwyn was imbued with the British Survey's attention to detail in its mapping, and appreciated its tried methods of field mapping and presentation of geological data in maps and cross-sections. He was also aware of many of the practical applications of geology. Selwyn's achievements in Victoria were considerable. He began mapping the state in the way he had worked in Wales. However he and his assistants were forced to carry out much of their own topographical surveying before they could make satisfactory geological maps and this slowed the progress of the survey. Nevertheless about 60 quarter sheets (each 9 miles (14.5 kms) x 6 miles (9.5 kms)) were issued and brought considerable distinction to the Survey.

In addition Selwyn was responsible for the publication of several geological maps of the whole state and for summary statements of the geology of the colony. He made important discoveries - the first graptolites, evidence of glaciation, and the character of metamorphism among them. Selwyn also made several important short surveys in Tasmania and South Australia for the governments of those Colonies. From 1856 the Victorian Survey grew rapidly and Selwyn had the task of choosing and training potential geologists. The names of R. Daintree, C.D. Aplin, C.S. Wilkinson, H.Y.L. Brown, G. Urich, R. Etheridge, R.A.F. Murray indicate how well Selwyn both chose and trained. This corps of young men spread Selwyn's ideas and methods through many of the Surveys in Australia. Selwyn's survey was disbanded in 1869, partly through the machinations of Robert Brough Smyth, Secretary for Mines, but Selwyn had also gained some enemies amongst the politicians and entrepreneurs by his stand against questionable mining proposals, as the State's revenue from gold mining continued to decline. Cessation of the Victorian Survey coincided with the offer to become Director of the Geological Survey of Canada following the retirement of Sir William Logan. Selwyn took over in Canada just as the Dominion extended its territory to the Pacific Ocean, presenting a vast region almost entirely unmapped topographically and geologically. During his early years in Canada Selwyn once again got back into field work, covering long distances in his explorations of the Dominion. Selwyn in Canada showed the same skill in choosing and training suitable staff among them being G.M. Dawson, J.B. Tyrrell, A.P. Low, A.F. Barlow and F.D. Adams. As in Victoria Selwyn became increasingly involved in administrative affairs, particularly after the Geological Survey and Museum moved from Montreal to Ottawa in 1881. As in Victoria too Selwyn had his enemies in Canada and for much the same reasons. Initially he had not get on well with the brilliant but erratic Sterry Hunt but later Robert Bell, a member of the Survey, and passed over for the Directorship, was largely responsible for a Parliamentary committee investigation (1884) into the affairs of the Survey, but which clearly exonerated Selwyn. In his early fieldwork days Selwyn had a very cheerful disposition but in later years he seems to have become rather more taciturn in his official dealings. It may be that he was able to separate his professional activities, where he was a hard task master, from his social life, as many attest to his affability away from the office. Selwyn had a fine command of written English and was often criticized by his staff for delaying and rewriting their rather turgid reports before publication. His insistence on absolute honesty in relation to mining potential and the need for a fundamental basis of stratigraphic mapping caused him many battles in his work but time has vindicated his approach to the solution of many geological problems.

Apart from his maps and official reports in Britain, Australia and Canada Selwyn did not publish a great deal. An interesting controversy between the Canadian Survey and U.S. geologists over aspects of the Precambrian in North America is preserved, largely in official correspondence, and deserves publication as it shows Selwyn at his professional best - accurate, precise, clearly attacking the problem under contention, and upholding the integrity of the work of his Survey. Selwyn is now being recognized for the quality of the work which he maintained for the fifty years of his professional life. He is commemorated by numerous landmarks in Australia and Canada. It is appropriate that the Victorian Division of the Geological Society of Australia should now be paying tribute to his memory. While there were other important pioneers in Australian geology Selwyn's arrival marked the beginning of a professionalism which was passed down through a network of colleagues and which still continues today.

DR. ODERNHEIMER'S MAP D.F. Branagan Department of Geology & Geophysics, University of Sydney, Sydney Early in 1854, after a brief visit to the Bathurst-Sofala goldfield Dr. Frederic Odernheimer and his assistant Ernst Herborn arrived at the Peel River to undertake a geological survey of the area held by the Peel River Land and Mineral Company, a subsidiary of the Australian Agricultural Company. Odernheimer?s three reports on the mineral prospects of the area, some 330 km^ are dated 6 March, 5th August, 8 September 1854, and were published in the company's annual reports. In his first report Odernheimer mentions that 'geological maps shall be laid down, to record, in the most conspicuous manner, the results of the researches'. There is no further reference to such maps in the reports, which are concerned mainly with the character of the gold and other minerals and prospecting methods being used. However in letters to Philip Gidley King and P.E. Strzelecki Odernheimer expands on the geology of the area, and during 1855 when he had moved to Port Stephens and Newcastle, he continued work on his map of the Peel River. In January 1856 he wrote to Strzelecki in London explaining his method of mapping and presenting the data, a copy having already been sent to London. Two copies of the map were made. Only one copy, now in Canberra (Archive of Business and Labour, A.N.U.), has been located so far. Unfortunately it is damaged so that the legend is incomplete. Odernheimer intended to write a geological report and supply sections with the map. These have not yet been located. The map in two sheets (each 1.5 x 1.5 m) is a superb example of cartography, topographic and geological mapping of the period. A photographic copy (about half scale) is here publicly presented for the first time since the map was completed in 1855. The generous co-operation of the staff of the Archives of Business and Labour, A.N.U. in the study and copying of the map and access to other relevant archival material is gratefully acknowledged.

S T . PETERS

QUARRY

A MAN-MADE

ENVIRONMENT

D.F. Branagan, A.R. Norman and K.L. Williams Department of Geology and Geophysics, University of Sydney, Sydney In 1983 the last operating brick-shale quarry in the inner Sydney area ceased operations. The Sydney City Council is preparing plans to use the quarry for waste disposal, commencing in 1986. There is an opportunity to incorporate some of the geological features of the quarry in the final landscaping of the area and discussions have taken place on these matters. The abandoned quarry shows a variety of weathering and erosion processes in operation, as well as stratigraphic, palaeontological and structural features of both Triassic and Quaternary successions. In addition the development of a large man-made slump has been studied over the past five years. The quarry offers an excellent opportunity to study the processes of mass-wasting.

S E I S M I C S T R A T I G R A P H Y , BASIN S T R U C T U R E AND E V O L U T I O N OF A P A S S I V E C O N T I N E N T A L M A R G I N - O T W A Y BASIN S O U T H E A S T A U S T R A L I A J . C . Branson and D . A . Falvey B u r e a u of Mineral R e s o u r c e s , Geology & Geophysics In 1 9 8 2 , BMR recorded two long traverses across the continental slope and five traverses across the shelf (900 km t o t a l ) in the eastern Otway B a s i n . N e w p r o c e s s i n g parameters were applied to Shell Petrel 1970 scientific survey data in the same region and produced a significant improvement in the d a t a . These data tie with more closely spaced BMR traverses in the Bass and Gippsland Basins where our recent analysis provided a n e w structural interpretation of extensional m e c h a n i s m s . This w o r k is described in a companion paper (Etheridge, Branson and S t u a r t - S m i t h , this conference C 3 ) . Survey parameters were designed for areas with rugged water bottom and these results contain fault patterns related to deep structures not previously i d e n t i f i e d . The Early C r e t a c e o u s graben structures seen in the Bass and Gippsland Basins are poorly recorded in seismic data from the Otway Basin although a similar 0 2 0 ° to 0 3 0 ° trend of the major normal faults in the basement and their orthogonal w r e n c h faults are present on the s h e l f . The Early Cretaceous sediment is recorded in seismic data in faulted tilt blocks out to the limit of continental c r u s t . This early sequence occurs as faulted domino-style tiltblocks and shows a progressive oceanwards increase in extension from 20 to 3 0 % up to a m a x i m u m of 8 3 % . Early Cretaceous sediments are c o n s i d e r e d present near the o c e a n - c o n t i n e n t boundary in highly tilted and faulted blocks with poor seismic expression and lie below a thick Late C r e t a c e o u s sediment cover c o n t a i n i n g v o i c a n i c s .

On the continental shelf wrench movements at the end of the Late Cretaceous caused deep narrow troughs which were filled by fluvial sediments and contain occassional marine ingressions. At the same time the Late Cretaceous built out from the northeast in a series of offlapping sequences into a broader depression which fits the classic rift fill stage of continental margin development. At the present day ocean-continent boundary the lowermost part of the Late Cretaceous thickens due to volcanic activity. An elongate area covering at least 10 000 sq km contains prograded sedimentary fill and overlies the eastern part of the Late Cretaceous volcanics. Boeuf and Doust (1975) originally described these prograded sequences as Tertiary but we prefer to assign most of the sediment to latest Late Cretaceous and Paleocene which is more in agreement with Denham and Brown (1976). The Late Cretaceous sequences are domed and faulted by large zones of wrench movement close to the present day continental shelf edge and the upper sequences are eroded, presumably due to wavebase erosion. The main sequence overlying these Late Cretaceous faulted sediments are the Tertiary sedimentary drapes which built out from the continent from the Eocene. Only small areas of Eocene are preserved over the wrench zones, for example near Prawn-1 exploration well, however the general unconformity surface is overlain by Oligocene. A depth converted display of BMR seismic data covering a 220 km traverse across the continental slope recorded a deep seismic reflection event at 11.5 km near the present day shelf break. A similar event reappears mid-slope with a seaward dip and at the ocean-continent boundary this event appears to split into two and both events have landward dips of about 35°. These reflection events are interpreted as the decollement surfaces for the domino-style faulted tilt blocks on which the Early Cretaceous sediment slid oceanwards. This data supports a crustal thinning by extension model as a first phase in margin development . Synthetic data derived from the depth section across the Otway Basin margin can be used to provide a number of subsidence curves at points across this continental margin. These curves can be used to determine the various mechanical and thermal effects which comprise the complex history of the eastern Otway Basin. References Boeuf, M.G. & Doust, H., 1975, APEA J. 15(1), 33-43. Denham, J.I. & Brown, B.R., 1976, APEA J. 16(1), 91-98

GEMMOLOGICAL ATTRIBUTES OF THE COMMON ROCK FORMING MINERALS Rod Brightman Canberra College of TAFE, Canberra Due to the nature of their work, mineralogists and geologists frequently encounter mineral and rock specimens which are of no immediate commercial interest to them, and which are put aside as being of curiosity value only. Many of these could have some gemmological significance, and this paper is intended as an introduction to a range of gem materials available that are probably more familiar to mineralogists and geologists as the common rock forming minerals.

Gemstones are those minerals and other materials used by men and women for personal adornment. Generally speaking, a gemstone should possess the properties of 'beauty1, 'rarity1 and 'durability1. However, there are some materials which lack one or more of these and are still highly regarded as gemstones. In addition, for a mineral specimen to be regarded as having gem potential, it should either be relatively free from cracks and inclusions, or contain enough inclusions of the correct type to allow specific optical phenomena such as chatoyancy, asterism or schiller to be observed. The specimens should also be of a size and shape suitable for fashioning into a faceted, cabochon or carved gemstone. The following rock forming minerals or mineral groups are frequently encountered as gem materials by gemmologists. A selection of these will be discussed under the headings of colours, varieties, special phenomena, mineralogical associations and geological and geographical occurrences: actinolite andalusite apatite axinite beryl cordierite (iolite) corundum diopside epidote feldspar fluorite garnet jadeite kyanite nephrite olivine (peridot)

petalite prehnite quartz rho do ch ro s i t e rhodonite rutile scapolite sodalite sphene spinel spodumene topaz tourmaline vesuvianite (idocrase) zircon zoisite

HYDROGEOLOGY OF THE LATROBE VALLEY RELATED TO GROUNDWATER EXTRACTION AT MORWELL OPEN CUT, VICTORIA John Brumley State Electricity Commission of Victoria The regional hydrogeology of the Latrobe Valley Depression is documented by Brumley and Reid (1982). The Depression is known to contain up to at least 770 m of Tertiary continental Latrobe Valley Group strata, which include numerous confined sand and gravel aquifers. The aquifers can be grouped into a lower Traralgon Formation Aquifer System and an upper Morwell Formation Aquifer System. Coal winning at Morwell Open Cut requires reduction of the artesian pressures in the aquifers beneath the coal seams to prevent heaving of the open cut floor and to aid batter stability. Control of surface water, and drainage of unconfined groundwater from coal joints, also helps to maintain the batters in a stable condition.

Currently, an average of about 900 1/sec is extracted from the confined aquifers beneath Morwell Open Cut. This represents almost 2 tonnes of water for each.tonne of coal extracted, and is a significant cost penalty against coal extraction. To minimise this cost, centres of pumping are kept as close as practicable to the deepest parts of the cut. Pressure levels are monitored continuously in "key" observation bores and the pumping rates adjusted to meet predetermined target pressure levels in the aquifers. The artesian water is good quality and is pumped to Hazelwood cooling pond for power station use and fire service spraying. The history of artesian groundwater extraction at Morwell Open Cut is fully documented. The potentiometric levels have been lowered by approximately 135 m at the open cut. Regionally, the potentiometric decline extends along the main syncline of the Latrobe Valley Depression for about 35 km in the Traralgon Formation Aquifer System and for about 10 km in the Morwell Formation Aquifer System. The regional potentials are monitored regularly by a comprehensive network of water level observation bores. The decline in aquifer pressures has resulted in regional subsidence ranging from about 2 m at Morwell Open Cut to 100 mm some 20 km to the east. Detailed monitoring of the subsidence has been carried out since 1958. The principle of effective stress is used to demonstrate the changes in vertical pressure distribution that cause consolidation of the sedimentary sequence as the potentiometric pressure in the aquifers is reduced. The total volume of artesian groundwater extracted from Morwell Open Cut is about 450 x 106 m 3 . Approximately 50% is derived from aquifer recharge and 50% from aquitard and aquifer yield. Geological studies of aquifer recharge are carried out to understand the significance of recharge to the overall water balance in the Latrobe Valley groundwater system. Aquitard yield is estimated from subsidence studies which demonstrate a sustained, 1:3 relationship between the volume of subsidence and the volume of artesian groundwater extracted from Morwell Open Cut (Brumley et al, 1981 and Evans, 1983). Aquifer yield is estimated from the potentiometric monitoring program and the hydraulic properties of the aquifers. The hydrogeological data obtained from the investigations and monitoring programs at Morwell Open Cut, and throughout the Latrobe Valley Depression, have been collated and evaluated to form a hydrogeological model. This model is used as the basis for mathematical model studies concerned with groundwater aspects of open cut development and resource management. References Brumley, J.C., Barton, C.M., Holdgate, G.R., and Reid, M.A., 1981, Joint SECV/DMEV Report. Brumley, J.C., and Reid, M.A., 1982, Aust. Coal Geol. 4, pt 2.

MUSWELLBROOK VOLCANIC CENTRE - A SOURCE FOR THE CARBONIFEROUS IGNIMBRITES IN THE UPPER HUNTER VALLEY Malcolm D. Buck School of Applied Geology, University of New South Wales,Kensington Since the 1970fs crystal lineations in ignimbrites have been used to ascertain their direction of flow so as to determine the area of their source. An adaptation of the methods used in these studies has been applied to some of the larger Carboniferous ignimbrites in the Upper Hunter Valley west of Scone and Muswellbrook.

A binocular microscope was modified to enable the microscopic examination of the fabric in large slabs of ignimbrite. Together with a stage that could move in two directions and rotate, and an ocular of the scope that contained a 0 - 180° gradual, it was relatively quick to examine an area of 240 sq cm and measure the line of the elongate crystals in that area. The previous studies of crystal lineations in ignimbrites have been done using thin sections of ignimbrites, which meant that only a small number of crystals would be measured from a very small area in the normally porphyritic rocks and that crystals of 2:1 length to breadth dimensions were considered in the analyses. The larger area of the slab used in this study allowed a greater number of crystals to be viewed and only those crystals of greater elongation (>3:1) were measured. The ignimbrites in the Upper Hunter Valley are interbedded in a thick sequence of terrestrial fluviatile sediments, together making up the Native Dog Member of the Issismurra Formation. Two ignimbrites in the member are much more widespread than a number of smaller units that are present, the Curra Keith Ignimbrite at the base of the member, and the Oakfields Ignimbrite near the top. Crystal lineation vector means determined from 34 samples of the Curra Keith Ignimbrite, which had an average of 84 sq cm examined and 88 crystals counted, indicate its source probably lies in an area about 2km northwest of Muswellbrook. While 27 samples of the Oakfields Ignimbrite, which had an average area of 92 sq cm examined and 92 crystals counted, gave lineation vector means that suggest its source lies in an area about 10km south-southwest of Muswellbrook. Some of the other smaller ignimbrites within the Native Dog Member also show vector means that suggest they originated from either of these two centres. Furthermore, the determination of flow asimuths from flow direction indicators in these ignimbrites also helped establish their source as being southwest of their outcrop. The area containing these volcanic sources is named the Muswellbrook Volcanic Centre. The data obtained from the ignimbrites in the Upper Hunter Valley are statistically strong since only one data set was not significant at the 90$ confidence level, with the Curra Keith Ignimbrite samples data having an average vector magnitude of 45.3$ and an average Tukey chi square value of 35.19, and the Oakfields Ignimbrite having the respective values of 47.8J and 42.06. These compare favourably with the statistics for the Railroad Canyon and Apache Spring Ignimbrites in the Mogollon Volcanic Province, New Mexico which respectively have average vector magnitudes of 23% and 24$ and Tukey chi square values of 17.91 and 21.16. It is unfortunate that the postulated source area for the ignimbrites lie on the western side of the Hunter Valley Fault Zone, beneath the thick Permian c o a l b e a r i n g sequences. However, perhaps the existence of a positive gravity anomaly, with residual intensities up to 20 mgals, southwest of Muswellbrook and directly over the postulated source areas, suggests that they exist at depth and that they overlie a mafic-enriched intrusion that is a residue of the erupted volcanics.

FLUID INCLUSION DECREPITATION AS A GOLD EXPLORATION IN THE PINE CREEK AREA, N.T.

TECHNIOUE

K.Burlinson Burlinson Geochemical Services Pty. Ltd., Darwin The decrepitation technique is a rapid means of measuring abundances, temperatures and, to some extent, the fluid compositions of fluid inclusions in both transparent and opaque minerals. It is also frequently possible to use samples in which the fluid inclusions are too small for the normal microthermometric techniques. A microprocessor controlled instrument is used to heat samples to as high as 800°C while monitoring the decrepitation activity. The results are plotted as a histogram of decrepitation counts versus temperature, using 10°C temperature intervals. The Enterprise gold mine at Pine Creek comprises a number of overlapping quartz vein systems hosted by Burrell Creek Formation sediments. For this study, 19 quartz samples from the mine and environs, including some from each stage of veining, were collected. The results suggest that there are 4 major vein types and within 3 of these, additional small variations due to gradational changes in the temperatures and fluid compositions can be discerned. The pre-folding quartz veins are readily distinguishable both in hand specimen, where they are folded, and in the decrepigrams, which are bimodal with only very low decrepitation activity (typically a maximum of 100 counts per 10°C interval). Three additional groupings of quartz are apparent from the decrepigrams although it is not yet clear exactly how they relate to the geologically defined quartz stages. The second and third decrepitation groups also have bimodal decrepigrams, but these are markedly more active than the pre-folding veins and typically show a maximum of 1000 to 2000 counts per 10°C interval. The group 2 samples have a decrepitation peak which begins at 370°C whereas the group 3 samples have an equivalent peak at a markedly lower temperature (320°C). In both groups some samples show unusually broad peaks which are tentatively interpreted as being due to boiling of the fluids. The final group of samples have trimodal decrepigrams with a low temperature peak in the vicinity of 200°C, due to the presence of CO2 rich fluid inclusions. The gold mineralisation occurs in veins belonging to both groups 2 and 4, although not all occurrences of these vein types are mineralised. The decrepigrams provide a means of discriminating between the potentially mineralised quartz veins and the less prospective veins. In association with the above sampling at the Enterprise mine, 28 additional samples were collected from the Pine Creek area. 19 of these were from the Spring Hill and Yam Creek gold workings, the Jimmy's Knob tin workings and the Flora Belle lead workings, all of which are quartz vein systems with associated faulting. The remaining 9 samples were from various unworked, barren quartz veins in the area. Of these 28 samples only 7 had low temperature peaks due to CO2 rich fluids, the remainder lacking any evidence of C02. All of the samples from tne Spring Hill workings showed intense low temperature peaks on the decrepigrams while the sample from the Yam Creek workings and two of the Jimmy's Knob samples have distinct but less intense low temperature peaks. Hence 6 of these C02 containing samples are closely associated with known gold or tin mineralisation. The seventh sample had an intense low temperature peak and is from an unworked vein close to some present day alluvial workings. The prominent C02 peak in this sample, together with its location, indicates that this supposedly barren vein might be prospective for gold mineralisation.

Thin sections were prepared of nine samples and examined on a cool stage microscope at about 5°C for evidence of CO2 rich fluids. Four of these samples had given decrepigrams with a distinct low temperature peak, while the remaining 5 lacked a low temperature peak in their decrepigrams. CO2 rich inclusions were observed in all of the samples which had a low temperature decrepigram peak and were absent from all of the other samples. In addition, the intensity of the low temperature decrepitation peak was seen to be related to the volume of the liquid CO2 phase at the temperature of observation. Much (but not all) of the gold mineralisation in the Pine Creek area is associated with CO2 rich fluids and the decrepitation method provides a reliable, quick and economical method of recognizing quartz veins formed from these favourable fluids. Consequently the decrepitation method is a useful tool in the regional evaluation of the gold mineralisation potential of this area. Orientation surveys in other goldfields may show the same approach to be applicable.

PETROLEUM AND MINERAL RESOURCES OF THE SOUTHWEST PACIFIC R.V. Burne Bureau of Mineral Resources, Canberra. The investigation of the offshore mineral resources of the southwest Pacific is at a reconnaissance stage. Hydrocarbon potential is limited by the relatively small area of shallow shelf seas in the region. Prospects are restricted to sedimentary basins that have developed during the evolution of island arcs with many of the more promising areas lying in water too deep for development by existing technology. Placer Deposits including chromite, ilmenite, and gold deposits are locally present around some older arc islands. Research is currently attempting to locate centres of back-arc spreading that may be areas of metalliferous mud and hydrothermal sulphide enrichment. Surface Phosphate Deposits of oceanic islands have been thoroughly explored and exploited, and attention is now being given to locating atoll deposits buried beneath present-day lagoonal sediments. The Phosphorite potential of the zones of upwelling adjacent to atolls is believed to be low. Gypsum deposits have been discovered in an enclosed ephemeral lagoon on Howland Island. CobaltRich Ferromanganese Crusts have formed on the flanks of some atolls and sea-mounts at depths between 2600 and 1000m in latitudes north of 15°S. They are thought to form in a depth zone which corresponds to oxygen minimum in the water column. Manganese Nodules are found in areas of low sedimentation rates at or below the depth of the CCD. Economic grades of over 1.18% Cu+Ni are restricted to areas underlying zones of elevated surface biological productivity, particularly the zones of upwelling associated with the equatorial current system. Precious Coral, Black Coral, Pearl and Trochus Shells are locally important resources. Demands for Sand and Gravel for the construction industry have created problems of beach erosion for many island nations, and emphasis is being placed on locating alternative resources particularly offshore.

LAKE ELIZA, SOOTH AUSTRALIA, AND LAKE TEN66AN0, ISLAND: TWO POSSIBLE ENVIRONMENTS OF OIL-SHALE

RENNELL GENESIS

R.V. Bur tie Baas Becking Laboratory, Canberra Shallow hypersaline lakes, such as Lake Eliza, and deep brackish-water lakes, such as Lake Tenggano contain environments of potential oil-shale deposition. Lake Eliza is a halite-depositing lake with a biota of nonmarine lineage. Organic-rich laminated, fine-grained carbonates accumulate in areas of cyanobacterial mat colonisation along the seasonally inundated western margin of the Lake which is sheltered from the prevailing winds. Despite seasonal sub-aerial exposure, the impermeable nature of the sediments and the high salinity of the interstitial waters allow preservation of the organic material which remains following burial beneath the zone of active bacterial sulphate reduction in the upper layers. The deposits of Lake Eliza show similarities with facies described from the oil-shale bearing Wilkins Peak Member of the Green River Formation. Lake Tenggano is a large brackish-water lake with a biota of marine lineage that occupies the area of the former lagoon on the uplifted atoll of Rennell Island, one of the Solomon Islands. Water depths exceed 30m in places and the lake is floored by the thick organic gel partly of cyanobacterial origin. The anoxic bottom waters of the lake favour the preservation of this organic material which forms a deposit analogous to the major oil shales of the Green River Formation.

STROMATOLITE REEFS AND CYANOBACTERIAL MATS OF HAMELIN POOL, W•A• : SIGNIFICANCE FOR PROTEROZOIC AND YOUNGER PETROLEUM PLAYS R.V. Burne and M.R. Walter Baas Becking Laboratory, Canberra Columnar stromatolites, which lithify as they accrete, form erosionresistant structures in the shallow sub-tidal environments of Hamelin Pool. They are internally laminated and contain fenestrae, consequently, they are very porous (e.g. 35%) and permeable (e.g. 4.4 Darcy). No significant amounts of organic carbon have so far been detected preserved within the lithified material of the stromatolites. Despite permanent submergence some of the stromatolite fenestrae are filled with gases presumably of microbial origin. This may serve to preserve the porosity through early diagenesis. In places individual stromatolites have coalesced to form botryoidal masses up to 2m high which may extend for hundreds of metres to form Stromatolite Reefs. Cyanobacterial mats colonise virtually the entire inter-tidal zone at Hamelin Pool where they contribute to the deposition of a well-laminated intimate association of prostrate algal filaments and fine grained detrital carbonate. This association displays significant horizontal permeability but vertical permeability may be very low. Some organic material is degraded by bacterial sulphate-reduction immediately below the surface. At greater depths, where this process ceases, organic carbon may be preserved providing that the sediment is maintained in an anaerobic state.

Elsewhere, where interstitial waters are stagnant, total organic carbon values of up to 6% by weight have been found in sediments associated with cyanobacterial mats, but at Hamelin Pool some of the organic matter of the mats is rapidly oxidised by circulating aeorbic groundwaters of marine or non-marine origin. Holocene regression of Hamelin Pool has stranded former sub-tidal stromatolites in the intertidal zone where they are engulfed by intertidal deposits including those of cyanobacterial mat environments. This regressive association might eventually be capped by evaporites as a result of either continued regression or of subsequent transgression: continued regression would enable the lateral migration of the evaporite-bearing facies of the supratidal zone over the top of the inter-tidal deposits: subsequent transgression might be followed by desiccation of the basin and formation of a basin-fill evaporite deposit as has occurred at nearby Lake MacLeod. Either scenario would produce a facies association of a potential source rock (cyanobacterial mat deposits) juxtaposed to a reservoir lithology (stromatolite reefs) and overlain by a cap-rock (evaporites) that could result in the formation of an economic hydrocarbon accumulation. Similar associations should have developed extensively and recurrently throughout geological time, particularly during the Proterozoic and Early Palaeozoic.

USE OF HELIUM FOR HYDROGEOCHEMICAL

EXPLORATION FOR URANIUM

C.R.M. Butt and M.J. Gole CSIRO Division of Mineralogy, Perth Helium is generated during the radioactive decay of uranium and thorium which may occur in mineral deposits or be dispersed in basement or country rocks. The attractiveness of helium as a pathfinder gas lies partly in the fact that it is highly diffusive, stable and inert so that it may form a detectable dispersion halo around deposits that are deeply buried or which occur in relatively impervious host rocks. Analysis by mass spectrometry of helium in groundwater is relatively straightforward and routine analysis is capable of an accuracy of ±0.002 ppm He. Analytical error is insignificant compared to sampling errors. Equilibration of helium between groundwater and the atmosphere is rapid and careful sample collection is required to minimise degassing. A pump-sampler has been developed to allow rapid collection of standing water in drill holes and wells with a minimum of mixing with the atmosphere. Groundwater in equilibrium with the atmosphere contains 0.04 ppm He. In groundwaters containing anomalous helium concentrations the helium concentration usually increases with depth due to equilibration with the atmosphere. This degassing profile is generally steepest in the top 5-20m of the groundwater and may extend to several tens of metres or deeper.

The helium contents of groundwater in contact with mineralization at several uranium deposits are as follows; Manyingee, 0.5-3.8 ppm; Bennett Well; 10-30 ppm; Honeymoon, 22-44 ppm; Koongarra, 0.3-11.5 ppm; Yeelirrie, 0-0.13 ppm. At Manyingee the influx of 'fresh' groundwater may have diluted the helium contents from originally much higher levels. Much of the Yeelirrie mineralization is above the water-table and host rocks are very porous so that the helium enrichment is negligible. These groundwater helium concentrations are similar to those reported from uranium deposits in the United States and Canada. However, helium concentrations equivalent to and far higher than these values, occur in groundwaters that are not associated with uranium deposits. For example, in the Yilgarn Block, Western Australia, helium concentrations of up to 117 ppm have been encountered in relatively shallow groundwaters. Elsewhere, in relatively deep groundwaters (>300m) concentrations greater than 1000 ppm He occur. These high concentrations are due to accumulation, in long-lived groundwaters, of helium generated from uranium and thorium occurring at essentially normal crustal abundances. The helium may migrate along intergranular cracks, joints and faults to enrich the sampled waters. In arid terrains, where groundwaters generally have long residence times, and particularly where granitoid basement is exposed or not too deeply buried, the interpretation of groundwater helium data is likely to be problematic. Generally there will be insufficient information to enable anomalous helium concentrations to be attributed either to the presence of a uranium deposit or to slow accumulation from relatively insignificant sources. Where groundwaters are active, however, helium may have some potential as a pathfinder. At Koongarra, where groundwaters are annually recharged, anomalous helium concentrations appear to be closely related to the mineralization. A helium anomaly, supported by a high radon flux, 1km northeast of the deposit in an area of no known mineralization, appears to be a promising target. However, even where groundwaters are active, the possibility exists that anomalous helium may be due to concentration in and leakage up fractures and not be related to significant uranium mineralization.

THE STRATIGRAPHY AND AGE OF THE SILCRETE FLORAS, STUART CREEK, SOUTH AUSTRALIA R.A. Callen Department of Mines and Energy, South Australia Two superposed sandstone-siItstone sequences exist at Stuart Creek, west of the Willouran Ranges in South Australia, each associated with a characteristic silicified horizon. The lower part of the lower sequence contains excellent examples of the "silcrete floras" and Eucalypt-like capsules. Similar floras also with similar capsules exist in a similar sequence at Poole Creek near Lake Eyre. These sediments can be related to the Eyre Formation of Eocene-Paleocene age; based on regional lithostratigraphic correlation, relationships to the Mesozoic units and to the Miocene Etadunna Formation, and a detailed programme of levelling and surveying. The correlation is consistent with palynological data from the Lake Eyre bores, and suggests an early Tertiary age.

SILICIFIED CONCENTRIC RIDGES OF STUART CREEK, SOUTH AUSTRALIA R.A. Callen Department of Mines £ Energy, South Australia A remarkable series of concentric linear silicified sandstone ridges exists over an area of many hundreds of square kilometres to the west of the Willouran Ranges and as far south as Andamooka in South Australia. Silicification takes the form of "ant nest" silcretes developed on a coarsening upwards sequence of probable fluvio-lacustrine origin. These sediments overly early Tertiary deposits, and regional lithological correlation suggests they are probably older than the Miocene Etadunna Formation. However, widespread silcrete duricrusts in the region are younger than the Etadunna Formation, and similar ridges have been found near the Clayton River near Lake Eyre, developed on the Etadunna Formation. Silica cement is distributed in a manner consistent with a pedogenic origin. "Nodularity" and intensity of silica content vary according to relationships with the concentric linear mounds. The former increases and the latter decreases rapidly, at the margins of the mounds, suggesting topographic groundwater control. The softer, less silicified mounds are eroded to produce a classic reversed topography - the ridges. The mounds themselves are consistent with origin as beach deposits of a large lake, and are too coarse to be aeolian features. Topographic patterns similar to those produced by these mounds have been found east of Lake Eyre and east of Lake Frome in South Australia and in the Paris Basin of France.

BONINITE - THOLEIITE VOLCANISM IN THE SOUTHWEST PACIFIC W.E. Cameron, D.A. Walker, D.P. Windrim Department of Geology, Australian National University, Canberra Boninites are unusual intermediate (53-64% SiC^) volcanic rocks with the order of crystallisation of minerals: chromite olivine low-Ca pyroxene * augite plagioclase. Petrographically, they are very distinctive and chemically unique also. MgO is high and CaO, Al2°3 anc* TiC^ low compared with the most similar rock type, orogenic andesite. Their origin is generally considered to be subduction-related but is not known in detail. In the southwest Pacific area, boninites are found together with tholeiitic basalts and minor tholeiitic andesites and dacites. Three associations are described: the Dabi Volcanics (59±1 Ma) from the Cape Vogel Peninsula, Papua New Guinea, and Triassic and Paleocene or Eocene sequences from New Caledonia. The boninites are geochemically diverse. Tertiary New Caledonian examples have the highest SiO? (59-63% on an anhydrous basis), Zr (60-90 ppm) and high La /Yb ( ^ 3 with La N ^15) whereas the Mesozoic group has the lowest SiC^ ( 52-55%) , < 15 ppm Zr and La /Yb ratios of 0.5 to 1 with Cape Vogel boninites are intermediate chemically. The tholeiitic rocks from the three suites have been metasomatically altered to varying degrees but in general have Si02 contents ranging from 48-64%, Zr from 30-60 ppm for the PNG rocks and > 60 ppm for New Caledonian examples and flat or slightly light-REE depleted patterns with La ^ 5 (PNG) or 10-15 (New Caledonia). 143 144 Initial Nd/ Nd ratios are broadly similar for boninites and tholeiites from PNG (£ MH = +4 to +7) but differ for the Mesozoic New Caledonian rocks +2 and +8 to +9 respectively) and Tertiary New Caledonian rocks (£XTJ= +7 to +9 and +2 to +5 respectively) . Nd

Trace element and Nd isotopic data appear to support an island-arc setting for the tholeiitic rocks and, by implication, for the boninites, although the latter have not yet been found in contemporary arc terrains. The occurrence of dacitic rocks argues against a back-arc basin origin. A possible explanation for boninite-tholeiite associations would involve their formation within very small ocean basins created above subduction zones when there is a sudden and drastic change in direction of motion of the subducting plate. Such basins would be relatively easily obducted, consistent with the observation that such sequences are spatially related to ophiolites. MULTIPLE LEAD SOURCES IN THE STRATIFORM LADY LORETTA

ZN-PB-AG

DEPOSIT, NORTHWEST QUEENSLAND G.R. Carr and B.L. Gulson CSIRO Division of Mineralogy, North Ryde Lady Loretta is a stratiform Zn-Pb-Ag deposit of Carpentarian age, situated in northwest Queensland. It is similar in age, tectonic setting and style of mineralization to the HYC and Mount Isa deposits. The ores occur in a single lens which is tightly folded into a basinal structure known as the Small Syncline. Whereas the basal 10m of the lens is very hi^h grade mineralizat ion, in the upper sections base metal sulphides are diluted by layers of pyritic argillite and other fine grained sediments. Proven reserves are 8 690 000 tonnes at 18.1% Zn, 6.7% Pb and 1lOg/tonne Ag with a cut oft grade of 15% combined Pb and Zn. 90

The ores consist of layers and laminae with variable proportions of sphalerite, galena, pyrite, barite, siderite and quartz with trace chalcopyrite, pyrrhotite, tetrahedrite and muscovite. In the basal high grade zone layering is cryptic and disrupted into boudinage-style structures. However, higher in the sequence layering occurs down to a very fine scale and is defined by distinctive mineralogies and textures. Two common layer or laminae types occur: i) those consisting of very-fine grained pyrite (2-lOym) in a matrix of similarly fine-grained sphalerite and/or galena (Type A layers), and ii) those containing relatively coarser grained sphalerite and/or galena (50 to 200 pm) with subordinate coarser grained pyrite and fine grained pyrite (Type B layers). Initial studies of lead in galena from hand specimen sized drill core samples through the ore indicated that considerable isotopic variation occurs, with an apparent increase in radiogeneity from the footwall to the hanging wall. In follow up work, fine scale sampling of individual layers and laminae was carried out using a diamond tipped dental drill. This technique allowed sampling of laminae down to 1mm in width. The results presented in Figure 1 show that in each hand specimen sized drill core sample, galena in Type A laminae is isotopically relatively homogeneous and generally significantly more radiogenic than galena from Type B interlaminae which are generally heterogeneous. The apparent trend through the sequence which was observed in the initial results was probably the result of a sampling bias towards Type B layers in the high grade lower part of the sequence and Type A layers in the lower grade rocks towards the hanging wall. Such variation has not been observed in the HYC, Mount Isa-Hilton deposits and sedimentary exhalative deposits in other parts of the world (Table 1). However, to our knowledge no similar fine scale studies have been carried out in these deposits. The results indicate the existence of two major mineralizing solutions during the formation of the Lady Loretta ores.

Table 1.

Lead isotopic composition of ores from_stratiform deposits in the Carpentarian of northern Australia ( (x ± 2a)

Deposit

208 pb/ 206 pb

207 pb/ 206 pb

206 pb/ 204 pb

Lady Loretta HYC Mount Isa Hilton Dugald River

2.2099*.0050 2.2185*.0012 2.2224*.0013 2.2220*.0009 2.2273*.0015

.9517*.0028 .9571*.0002 .9586*.0005 .9587*.0005 .9608*.0004

16.257*.071 16.149*.009 16.112*.013 16.120*.013 16.055*.004

240n

24CH

250-

250

<B *C (BOO X X

250

0 XX

X *

O X* X

Figure 1.

270

7951 ' !953 ' .955 207Pb/206Pb

x0 0 x x ooo< 0 xx x o

260-

260'

260-

270-

»0X

270

'2.208'2.21 2.212*2.214 2.216 208Pb/206Pb

0 00 a

«oo x

16.22 16.26 16.3 206Pb/204Pb

Variation in lead isotopic ratios through the Lady Loretta ore lens (o = Type A layers; x = Type B layers)

SOME ASPECTS OF EUSTASY IN THE MURRAY BASIN Alan N. Carter University of New South Wales, Kensington In the western part of the Murray Basin, the Neogene transgression led to the deposition of the Murray Group limestones of late Oligocene-Miocene age. The late Miocene transgression caused truncation of this sequence in the west and at the time of low-stand of sea level, phosphatic nodules were formed in at least part of the central area of the Basin. The Pliocene transgression led to the deposition of the Bookpurnong Formation with abundant marine faunas, but a minimum of truly oceanic influence as evidenced by the extremely low pelagic/benthic ratio in foraminifera. At the top of the Bookpurnong Formation as defined, the onset of arenaceous deposition begins, accompanied by a rapid diminution in numbers of species and individuals of the marine fauna. The arenaceous rock unit is the Loxton Sand. An hitherto undescribed section at Packard Bend. Loxton, shows clearly the relationship of these two formations, particularly the continuation of a depleted "Bookpurnong fauna" into a distinctly limited basal part of the Loxton Sand, but not throughout the Loxton Sand as a whole. The main part of the Loxton Sand lacks marine fossils and the apparent confusion about identification of subsurfce sand formations may be due to a false expectation of marine fossils throughout the Loxton Sand. The early Pliocene was a time of rising sea level and the Bookpurnong Fm. is the expression of initial marine deposition in the transgressive phase. The rising base level of erosion enabled 25 m. of Loxton Sand to accumulate, despite the change to non-marine facies.

The mouth of the ancestral Murray River had hitherto been far to the east, but during the subsequent late Pliocene fall in sea level, it migrated westwards and ultimately cut at least one channel in the Loxton Sand. A still later rise in sea level led to the deposition of the marine Norwest Bend Formation in the western and south-western part of this channel and the true Parilla Sand in this channel further east. Near Loxton, the Loxton and Parilla Sands can be readily separated empirically by grain size and an unconformable relationship between the two can be seen at at least one locality. Careful recognition and separation of Loxton and Parilla Sands in bores must be made before the Pliocene-Pleistocene history of the Murray Basin will be understood.

SUBMARINE FANS, CHANNELS AND LEVEES, BOUNTY SOUTHWEST PACIFIC BASIN

TROUGH,

R.M. Carter1 and L. Carter2

1 James Cook University, Townsville N.Z. Oceanographic Institute, Wellington

The Bounty Trough is a 450 km wide, 1000 km long and up to 4 km deep submarine depression located east of South Island (New Zealand). The trough is bounded to the north by the Chatham Rise, to the south by the Campbell Plateau, and abuts the South Island continental shelf to the west. A Neogene fan system has prograded into the head of the trough, supplied with sediment from the rising southern Alps along the Alpine Fault plate boundary. Several distributary fan-channels coalesce at about longitude 174 E to form the remarkably linear, eastward running main Bounty Channel. The Bounty Channel is located towards the southern, steeper wall of the Bounty Trough, and falls from depths of c.1500 m at the head of the trough to more than 5000 m where it passes eastwards onto the southwest Pacific abyssal plain. The channel is up to 500 m deep and 1-2 km wide, and consistently possesses a higher, leveed north bank. Slopes up to 7m/km characterise the upper parts of the channel, decreasing to c. 0.3m/km on the abyssal plain. A well-studied Cretaceous-Cainozoic sedimentary sequence occurs below the eastern South Island shelf, and on the Campbell and Chatham Rises. This sequence contains abundant evidence for earlier canyon-fan-channel systems feeding into the Bounty Trough, starting in the Oligocene. The Oligocene-Recent evolution of the Bounty Trough and Channel has been controlled by regional tectonic events, especially on the nearby plate boundary, and by eustatic sea-level fluctuations.

HYDROGEOLOGIC

INVESTIGATIONS OF FAILURES AT HAZARDOUS WASTE DISPOSAL

SITES

Keros Cartwright Illinois State Geological Survey, Champaign, Illinois, USA The hazardous waste disposal site at Wilsonville, Illinois was ordered exhumed after a lengthy court battle. Exhumation was begun in September, 1983, and is expected to take four to five years. The site operated as a hazardous waste landfill from 1976 to 1981 and twenty six trenches were filled with barrels and other waste packages of liquid and solid hazardous waste. 93

For this paper, site failure is defined as the case when contamination migrated significantly faster than indicated in the site and not related to health risk posed by the site. The original site characterization report predicted that waste would migrate at velocities less than 0.02 feet per year. However, organic contaminants from the trenches have migrated as far as fifty feet from the trenches in a three year period. Detailed geologic study of the site indicates that two zones of higher permeability exist that were not described in the initial site report. In addition, there have been some geochemical interactions between the leachates and the clay-rich soils at the site. While geochemical and other factors probably contributed to the unexpected migration rates at the site, the failure to properly describe the geology of the site appears to be a major problem. This conclusion is supported by studies of other sites in Illinois which have failed to be as predicted.

ISOTOPIC STUDIES OF SOUTH-EAST AUSTRALIAN COj-RICH DISCHARGES : DEEP SOURCES AND SHALLOW SOURCES A.R. Chivas1, I. Barnes2, J. Lupton3, and K. Collerson1* Research School of Earth Sciences, The Australian National Univ., Canberra 2 U.S. Geological Survey, Menlo Park, CA, USA 3 University of California, Santa Barbara, CA, USA ^Present address: University of Regina, Saskatchewan, Canada A C02-rich discharge is defined as that of a gas containing more than 90% of CO2 by volume or as a water containing more than 1000 ppm dissolved HC03~ and with a pH less than 8.3 (Barnes et_ al, 1978). Outside the Great Artesian Basin, such springs are found in southern Queensland, New South Wales, Victoria and Tasmania. The principal districts at Daylesford, Victoria and Helidon, near Toowoomba form the basis of the mineral-water industry. There is a well at Caroline near Mt Gambier that produces liquid CO2; purportedly the only one of its kind. Waters from the mineral springs are cold (12°C to 22°C) and slightly acid (pH = 5.95 to 6.6). The oxygen (S180 = -6 to - 7 % o S M 0 W > and hydrogen (SD = -35 to ) isotope compositions of these waters are similar to non-carbonated groundwaters within each region. Their 6 18 0/6D relation approximates that of the meteoric-water line of Craig (1961); 6D = 86 18 0 + 10. The strontium isotope signature of mineral waters from each district is specific and indicates scavenging of Sr from host sediments. 87 Sr/ 86 Sr = 0.715 to 0.718 for central Victoria; 0.711 for Rock Flat, near Cooma, N.S.W.; and 0.707 for Helidon. There is little scope for the young basaltic rocks at Daylesford, which have 87 Sr/ 86 Sr of 0.704 to provide a significant source of Sr. Gas chromatographic analyses indicate that CO2 is the major gaseous phase, typically >70% by volume. Nitrogen, methane, oxygen, argon and helium are generally minor phases except in the Helidon district where methane is commonly more abundant than carbon dioxide.

In all areas, the S 1 3 C of travertine is in isotopic equilibrium with the presently emitted gaseous CO2. 6 1 3 C for the latter at Daylesford is in the range -6.0 to which is typical of the value for deep-seated carbon from carbonatites, most diamonds and volcanic gases. At Helidon, 6 1 3 C for C02 is -9.0% o and 6 1 3 C of CH** is -60 to - 6 7 % 0 . These highly negative values for methane typify methane produced by biogenic decay of vegetation in swamps. CH** indicate temperatures of equilibration of 60° to 85°C. The source of CHi+ and CO2 is likely to be from organic matter within Jurassic sandstones of the Marburg Formation. 3 He/i+He analyses of gases from Daylesford indicate R/R^ ratios, corrected for the atmospheric He/Ne component, vary between 1.2 and 3.1. Some samples have high [(He/Ne) ]/[(He/Ne) . ] and the presence of a component of mantle helium is in§icated. Forarock Flat [( He/^He) ]/ [ (3He/**He) . ] = 1.3 but [(He/Ne) ]/[ (He/Ne) . ] = 3 to 4. In t§ii case, the presence of mantle helium is less certain. However, the liquid CO2 at Caroline contains an unmistakable 3He component; R/Ra = 3.0 and [(He/Ne) ]/ A gaS [(He/Ne) . ] of >1060. air

References Barnes, I., Irwin, W.P., & White, D.E., 1978, U.S. Geol. Survey, WaterResources Investigation 78-39, 12pp. Craig, H., 1961, Science 133, 1702-1703.

Mg AND 1 8 0 CONTENTS OF NON-MARINE OSTRACODS AS A COMBINED PALAEOTHERMOMETER AND PALAEOSALINOMETER A.R. Chivas1, P. De Deckker2 and J.M.G. Shelley1 Research School of Earth Sciences, and 2Research School of Pacific Studies, The Australian National University, Canberra Ostracods are microcrustaceans with calcitic carapaces (valves) that grow by moulting and regeneration of sequentially larger valves up to nine times before reaching maturity. The Mg content of these valves is speciesdependent and is a function of their growth stage and the temperature, salinity, Mg content and Mg/Ca ratio of their host water. Newly formed, partly calcified valves of the non-marine planktic ostracod Mytilocypris hertricae have high Mg contents (100,000 ppm Mg in CaC03 at individual shell weights of 2 yg) . This relative Mg content decreases as calcification proceeds, until shell weights exceed 120 yg, whereupon the Mg content is constant and useful as an indicator of the ostracod1s environment.

Fig. 1. Plot of atomic Mg/Ca ratio In the calcltlc portion of Mytilccyprio temperature of growth.

henricae valves as a function of

Fig. 2. Graph of atomic Mg/Ca ratio In the calcltlc portion of ostracod valves as a function of Mg content of their host waters. The arrows show the changing composition offif.praenuncia from the pond near Skipton (KP-20A, B, and C). M. henriczc from KP-IA, which lie outside the general trend, derive from a lake with an extremely high Mg/Ca ratio (305).

Mg/Ca ratios in individual ostracod valves from several species of the genera Mytilocypvis and Australooypris from culture experiments and a series of Australian lakes indicate that the valve's Mg content increases as a function of increasing temperature (Fig. 1) and salinity (Fig. 2). Within the range 11°C to 25°C and for water compositions of 24 to 2325 ppm M g , the Mg/Ca ratio in these ostracods' fully calcified valves increases by 0.0015 (or 370 ppm Mg in CaCOa) per 1°C and per 125 ppm Mg in solution. For most mainland Australian lakes, a change in water composition of 125 ppm Mg corresponds to a change of 3 . 5 % 0 in salinity. At a constant Mg content, the Mg/Ca ratio of the water may vary markedly within the range of common lacustrine values without significantly affecting Mg uptake in the ostracod valves. These results can be used to provide palaeosalinities and/or palaeotemperatures for ostracods recovered from continental sequences. For Mg partitioning, an increase in temperature and salinity produce increased Mg content in ostracods, whereas for 1 8 0 fractionation in biogenic calcite an increase in temperature produces a decrease in S 1 8 0 of the ostracod and an increase in salinity leads to an increase in 6 1 8 0 of the ostracod. Thus a combination of <S 18 0 and Mg measurements on non-marine ostracods provides an unique resolution of palaeotemperature and palaeosalinity variations (Fig. 3).

temperature increase Mg

6*®o

temperature unchanged 8 Mg 611 0

>[ 1

temperature decrease

salinity increase base 1 Mg

I 6,80

Nl g

6 ">0

6m®0

salinity unchanged

< i ; Mg salinity decrease

Kjig

6,e0

Fi(7. 3. Combined variations of Mg and 6 1 8 0 in ostracod carapaces in response to increasing, unchanged, and decreasing water temperature and salinity. Each curve represents the trend that night be produced from continuous sampling of ostracods from a stratigrapnic sequence such as that recovered in drill core. In this generalized example, the single and synchronous perturbation in temperature and/or salinity is followed by a return to initial conditions, stashed lines indicate those cases where salinity and temperature changes produce compositional shifts in opposite directions and where the resultant trend depends upon the magnitude of these changes.

6 JO

GROWTH RATES OF STROMATOLITES FROM SHARK BAY DEDUCED BY C-14 AND Po-210 DATING A.R. Chivas1, T. Torgersen1 and H. Polach2 1 Research School of Earth Sciences, and 2Research School of Pacific Studies, The Australian National University, Canberra

A series of 55 radiocarbon dates on sediments and stromatolites from Shark Bay define the period during which stromatolites were growing. Dissolved bicarbonate in Shark Bay has an apparent age of 350±120 years, which is used to indicate the present environmental effect. This value has been subtracted from the ages reported here. Modern loose sediment which is bound by the algae to form stromatolites has an apparent age of 300 years. Modern sub-tidal stromatolites build on solid substrates in an otherwise loose sandy bottom sediment. The substrates are either hardgrounds with an age of approximately 700 years or fragments of older lithified sediments with minimum ages of 12,500 to 15,000 years. The earliest stromatolites which are now dead and stranded in terraces some 30 cm above present high-tide, grew and emerged during the interval 1200 to 1000 years ago. Serial sampling along the growth axes of three modern stromatolites indicates non-linear C-14 trends owing to incorporation of older carbon from shell grit and younger carbon from cements that infill fenestrae. However it is clear that these stromatolites reached their present heights of 250 to 350 mm in 500 to 600 years. These represent net growth rates of 0.4 to 0.7 mm/year, and are markedly (up to a factor of 1500) slower than those rates estimated by laminae-counting of some Precambrian stromatolites. Po-210 measurements along the growth axis of a single stromatolite indicate activities of 0.3-0.1 DPM.g""1 with a general decrease from the surface down through the stromatolite. Ra-226 analyses indicate that the Po-210 is in equilibrium with the Ra-226. The decrease in activity of Po-210 (as a measure of Ra-226) with increasing age therefore suggests that excess Ra-226 which was incorporated during growth is decaying with a halflife of 1622 years. The stromatolite growth rate based on the decay of excess Ra-226 is then 0.13±0.06 mm/yr. If the decay sequence Ra-226 to Rn-222 to Pb-210 to Po-210 is not a closed system in the stromatolite (i.e. Rn-222 loss is possible) , then the above accumulation rate represents a minimum. 97

THE AUSTRALIAN SAPPHIRE INDUSTRY - "SELLING WHEAT AND NOT KNOWING THE PRICE OF FLOUR" Terry Coldham Sapphex Pty. Ltd., Sydney In many areas along the eastern side of the Australian continent sapphire has been found in Recent alluvial deposits associated with drainage systems in areas of Tertiary basalts. There are two areas of important commercial production, one in central Queensland to the west of Emerald and one in Northern N.S.W. centering around Inverell and Glen Innes. The main product is of blue sapphire. Good yellows and greens are also found, which however mostly represent less than 5% of the value of total production. Mining is carried out by excavation by backhoe or bulldozer. The gravels are passed through a trommel and the sapphires concentrated by pulsators. Sorting of the concentrate is mainly done by hand. Depending on the individual miner, various quality and size groups are graded out. There are no quality standards and sales of mine run parcels are made to visiting buyers from Thailand. In Thailand, the material is split into smaller parcels and sold to local lapidary workshops for processing. The first part of the process is heat treatment. The greater proportion of Australian blue sapphire contains very fine exsolved rutile crystals that cause an untreated cut stone to have a dull, sometimes silky appearance. Methods of treatment vary slightly depending on the original colour and source of the stone, but in each case the sapphire is heated to a point where the exsolved rutile goes back into solid solution and is trapped thereby rapid cooling (geologically speaking). It is this process that allows Australian stone to be commercial, and for a long time it was the Australian miners1 lack of knowledge of this process that allowed the Thais to gain a monopoly on the purchase of Australian sapphire rough. The Australian miners were, and still are, to some extent, like a farmer selling wheat and not knowing the price of flour. After heat treatment the stone is cut and polished on basic but quite effective equipment and the finished stone is sold to visiting overseas buyers. Unfortunately, in the case of better quality goods, the stones are sold as production from Thailand itself, Cambodia or even Sri Lanka. Because of the buying monopoly of Australian rough sapphire the industry is indirectly controlled from Thailand. Recently this, combined with increasing mining costs, paucity of easily recoverable rough, and increased overseas production has caused a marked drop in production, especially on the Queensland fields where the overall quality of production is not as good. Despite this, as Australians gain more knowledge of processing and marketing and learning to control production the future for the industry still looks reasonable especially on the NSW fields. INCLUSIONS IN AUSTRALIAN SAPPHIRES T. Coldham1, B.J. Franklin2 and A.D. Giles2 1 9 Sapphex Pty Ltd., Sydney ^New South Wales Institute of Technology, Sydney The inclusions found in corundum are many and varied. In fact, no other gemstone species has such an abundance of both solid and liquid types. Sapphires,in particular, contain a large variety of syngenetic inclusions representing material which was enveloped by the the alumina host during crystallisation and growth. 98

Many sapphires of igneous origin undergo some solid state readjustments during cooling. This appears to increase the tendency of the mineral to form stress fractures which are "healed" by secondary (epigenetic) solids and liquids in a variety of ways. Indus ions in Thai, Kashmir and Sri Lankan sapphires have been fairly well documented by Gubelin (1979), although even this author gives only generalised observations and detailed studies of individual locations are not mentioned. Except in the broadest sense, detailed information on the types of inclusions in Australian sapphires does not exist. At best, statements such as " - fingerprints and irregular feathers, zircons with stress haloes, colour banding and fine silk characterise Australian sapphires - - - " (G.A.A. Lecture Notes, 1981) can be found. Most widely used texts in gemmology such as Anderson (1980) make no mention at all of inclusions in Australian stones. Knowledge of diagnostic inclusions which might characterise a particular Australian sapphire-bearing province is totally lacking. While some excellent work has been done on individual stones, to the authors1 knowledge, no systematic study of Australian sapphire inclusions has ever been undertaken. In the presentation of this poster paper the authors will outline the preliminary results of what is hoped to be a comprehensive investigation of sapphires from all of the major sapphire-producing provinces in Eastern Australia. Results include detailed photomicrographic studies and petrographic and microprobe identification of a small number of the most widespread and characteristic types of inclusions found in sapphires from several localities. In the light of the recent discoveries of sapphires in pyroclastic diatremes in the Inverall area of N.S.W. and the formulation of a new concept for the origin of sapphires, pointing to a possible genetic connection between sapphires and diamonds in that area (Lishmund & Oakes, 1984), the study of syngenetic inclusions takes on a new and increased significance as an indicator of conditions of origin of the mineral species. References. Anderson, B., 1980, Gem Testing,9th edition, Butterworths, 434pp. Gemmological Association of Australia, 1981, Unpublished lecturenotes. Gubelin, E., 1979, The Internal World of Gemstones, ABC Edition Zurich,234pp. Lishmund S.R. & Oakes, G.M., 1984, Geol. Surv. Quart. Note 53.

THE FORMATION OF TALC FROM MICA EFFECTED BY THE BREAKDOWN OF PYRRHOTITE W.F. Cole and C.J. Lancucki CSIRO Division of Building Research, Melbourne At Renison Bell, Tasmania, the mine waste from the treatment of the tincontaining metamorphosed sediment contains appreciable amounts of pyrrhotite which readily breaks down in stockpile. The unaltered mine waste is composed of mica, chlorite, quartz, dolomite and pyrrhotite. After alteration the pyrrhotite is lost, mica and chlorite are reduced in amount and goethite, gypsum and talc appear. The talc is probably formed at the expense of the mica. The chemical (or mineralogical) changes in the stockpile have been duplicated in the laboratory by subjecting fresh mine waste to a weekly cycle of wetting and then drying at 50°C for several months, after which time a white layer of talc and gypsum coated the rock particles. The mechanism of the alteration is discussed. Comment is made on the suitability of the mine waste as an aggregate for use in concrete.

MODERN DELTA PROCESSES AND MODELS J. M. Coleman Coastal Studies Inst., Louisiana State Univ., Baton Rouge, La., U.S.A. Deltaic deposits are found where a river debouches into a receiving basin; modern-day deltas exist in a large variety of settings and display a wide range of variations. Some deltas exist along coasts that experience negligible tides and minimal wave energy, whereas others are formed in the presence of high tides and intensive wave energy. These variations in modern deltas are a function of interacting dynamic environmental processes such as wave energy, tidal range, coastal currents, climate, sediment yield, and basin tectonics. Systematic studies of 55 world deltas, comparing approximately 400 process and form parameters, have identified the major processes that control the patterns of deltaic facies, and have permitted description of several delta models. The following deltas will be used to illustrate the variable delta facies: 1.

Mississippi Delta (USA)

Basin setting—low wave energy, low tidal range, large fine-grained suspended sediment load, rapidly subsiding basin, and temperate climate. The vertical sequence is a coarsening-upward unit in which the major reservoir sands include the delta front, distributary mouth bar, bay fill, and distributary channel fill. 2.

Klang Delta (Malaysia)

Basin setting—low wave energy, high tidal range, strong littoral currents, narrow graben basin, and tropical climate. The major reservoir sands include tidally reworked marine linear sand shoals and sand-filled distributary channels. The remainder of the deltaic facies includes tidal plain sediments capped by a thick blanket of saline and freshwater peats. 3.

Ord Delta (Australia)

Basin setting—low wave energy, extreme tidal range, low littoral currents, restricted estuarine receiving basin, and arid climate. 100

The major sand bodies consist of linear tidal shoals within the channel and estuary and migratory tidal channel belts. Supratidal and evaporite sequences make up the remainder of the section. The linear tidal shoals are well sorted and contain a significant volume of sand. The supratidal deposits contain abundant algal remains and could serve as source rocks. 4.

Burdekin Delta (Australia)

Basin setting—intermediate wave energy, high tidal range, coarsegrained sediment load, stable receiving basin, and arid climate. The vertical sequence is similar to that of the Ord Delta, but the higher wave energy results in formation of sandy tidal flats and strikeoriented beach-dune sequences. These two sequences form distinctive depositional fac les that are mineralogically and sedimentologically different from the fluvially dominated channel and tidally reworked sand bodies. 5.

Sao Francisco Delta (Brazil)

Basin setting—high persistent wave energy, intermediate tidal range, low littoral currents, steep offshore slope, fine-grained sediment load, and dry tropical climate. The high persistent wave energy results in cleaning and sorting of the riverine sediments and formation of laterally persistent nearshore and deltaic plain blanket sands. Transgressive dune deposits cap the delta facies. 6.

Senegal Delta (Africa)

Basin setting—extreme wave energy, intermediate tidal range, strong alongshore littoral currents, steep offshore slope, and dry tropical climate. As a result of the persistent wave energy and the strong littoral currents, the entire delta plain progrades as a series of beach-barrier dune complexes, which form major sand bodies that are predominantly strike oriented. Channel-fill deposits form between the sand bodies and consist of poorly sorted sandy muds. Major processes and environments of deposition will be illustrated for each delta type and a summary facies model will be presented.

THE FORMATION OF THE ABERFOYLE AND LUTWYCHE VEINS P.L.F. Collins1, M.A. Etheridge2, S. Halley3, K.J. Hellsten4, N.C. Higgins2, M. Solomon2 and V.J. Wall5 1 o Geological Survey of Tasmania, Hobart Bureau of Mineral Resources, Canberra 3 Dept. of Geology, Australian National University, Canberra ^Shell Minerals Exploration Pty. Ltd., Melbourne 5Dept. of Earth Sciences, Monash University, Melbourne The veins are hosted by interbedded mudstone and quartzwacke. They vary in strike, are up to 1.5 m thick, dip at 45-50 and occupy tensile fractures. Below the main vein system at Aberfoyle is a steep-sided cupola of albitized and greisenized aplite that is cut by minor veins and capped by quartz. The veins are of milky quartz with mainly wolframite, cassiterite, sphalerite, chalcopyrite, pyrite, pyrrhotite, muscovite, topaz, fluorite and carbonates. Horses of country rock testify to repeated vein opening, and faulting is both pre- and post-vein formation.

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Fluid inclusions in quartz are of five types: (A) 3-phase with ^ 2 ( l ) * C 0 Q , v and an aqueous solution of about 3.5 equivalent w t . % NaCl; (B; 2-phase with C0?( v and a q . solution; (C) 2-phase with a q . solution and vapour; (D) multiphase with a q . solution, vapour and daughter salts; (E) vapour with a q . s o l u t i o n . Where types A and B c o e x i s t , T h (270-360°C) and compositional data (mole % C 0 ? ) define CO -H O-NaCl s o l v i i . Pressures estimated from experimental data are between 200 and 500 ± 100 b a r s . Types D and E also coexist locally and represent the components of a C O ^ p o o r , two-phase H 2 0 - N a C l Q system; they are late and formed at high temperature (T = 304 to 489 C ) . ~. 18 6 S values of sulphides range from -3.3 to +1.3 permil and 6 0 values of quartz from +13.94 to +14.90 p e r m i l . Calculated fluid compositions indicate mainly magmatic solutions throughout the vein h i s t o r y . The suggested history of vein formation is as follows: the top of a granite pluton lay several kilometres below the surface. It was a highly fractionated biotite granite, partly crystalline, nearly saturated in w a t e r , and having a viscosity of about 10 -10 p o i s e s . At water saturation, fluid pressure within the chamber rose until it exceeded (a^+T) in the wall rocks and led to tensile fracture. Due to expansion of the magma chamber resulting from aqueous fluid exsolution, the stress field in the immediate wall rocks had approximately tangential to the pluton surface, and a ^ minimum above the p l u t o n . The steep to moderate W dip of the vein systems therefore resulted from the E dip of the top surface of the p l u t o n . The veins were localized at irregularities in the pluton upper s u r f a c e , above which was lower than elsewhere. The cupola below the Aberfoyle system provided such an irregularity, although it may have been localized itself by a step (down to E ) in the pluton surface suggested by reflection seismic data (unpubl. r e p t . , Aberfoyle L t d ) . Initiation of the tensile hydraulic fractures focussed fluid flow through the c u p o l a , giving rise to substantial subsolidus a l t e r a t i o n . The fluids entered the fracture system at 300 to 500 C and at approximately lithostatic pressure. The homogeneity, continuity and tabular geometry of the veins suggests that the fractures grew relatively r a p i d l y . This required a high rate of fluid supply so as to maintain P^ = O ^ + T at the fracture t i p . Mineral precipitation took place on the fracture walls as a result of cooling of the fluid, reaction with the wall r o c k , and pressure oscillation in the fluid. The Aberfoyle veins steepen and thin towards the present surface; the steepening occurring as the fractures passed beyond the region where the pluton influenced the orientation of the principal stress trajectories. H o w e v e r , the fractures probably extended towards the fossil surface until they entered the hydrostatic regime. The resulting drop in pressure throughout the v e i n , presumably to 200 to 500 b a r s , would have caused collapse of the fracture, dramatic precipitation of quartz and sealing of the vein system. A fluid at 500 C saturated in silica would lose two thirds of its silica content if the pressure changed from 1.0 to 0.5 k b a r s . A new cycle of fracturing and vein growth resulted from further exsolution of fluid from the cooling m a g m a , fracturing taking place mostly within and along the walls of earlier v e i n s . The cycle of fracture initiation and collapse was repeated several times, until the rate (and v o l u m e ) of exsolution from the magma dropped below that necessary to achieve hydraulic fracture.

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METALLOGENY AND TECTONIC DEVELOPMENT OF THE TASMAN FOLD BELT SYSTEM IN TASMANIA P.L.F. Collins and E. Williams Geological Survey, Department of Mines, Hobart The pre-Carboniferous geology and mineral resources of western Tasmania differ considerably from that of north-eastern Tasmania, east of the Tamar River. In western Tasmania, rocks of ?Eocambrian to Early Devonian age occur in zones between and within Precambrian regions. The largest Precambrian region (Tyennan region), underlying much of southern and central Tasmania, consists of sedimentary rocks metamorphosed during the Precambrian Frenchman Orogeny whereas the extensive Rocky Cape region which underlies north-west Tasmania consists of comparatively unmetamorphosed sedimentary sequences that were extensively folded in the younger Precambrian Penguin Orogeny. Within the Rocky Cape region is a NNE trending belt of metamorphic rocks (Arthur Lineament) which have been derived from the surrounding rocks. This belt contains apparently stratiform lenses of massive magnetite-pyrite ore associated with a mafic volcanic sequence at Savage River, which represents a Precambrian metallogenic epoch in Tasmania. The main ?Eocambrian-Cambrian trough in western Tasmania developed by extension of the Precambrian crust along a northerly trending boundary between the Tyennan and Rocky Cape Geanticlines. Early trough deposition of 1000 m of shallow marine sediments was followed by 2500 m of deep marine mudstone/turbidite sequences that were accompanied by outpourings of basaltic lava. During a later compressional phase, dismembered ultramafic and mafic igneous complexes were thrust into sediments of the trough and locally eroded. These mafic/ultramafic complexes have yielded alluvial osmiridium and locally contain nickel sulphides and chromite. The early Cambrian sequence is succeeded at an erosional boundary by a structurally conformable, 3000 m thick Middle-Late Cambrian fossiliferous turbidite sequence. This structural conformity continues through overlying OrdovicianEarly Devonian terrestrial and shallow marine stable shelf sediments (3000-4000 m thick). A considerable pile of acid-intermediate volcanic material, in which subvolcanic granite was emplaced, accumulated to the east of the Middle-Late Cambrian sediments, along the western and northern margins of the Tyennan Geanticline. A central belt of mainly lavas hosts several stratiform, volcanogenic massive sulphide deposits that dominate the Cambrian metallogenic epoch and include the massive Cu-Pb-Zn-Au-Ag deposits at Rosebery, Hercules, Que River and Hellyer, in the north of the central belt and the massive and disseminated copper ore bodies at Mt Lyell in the south. Movements along Cambrian faults near and parallel to the Tyennan Geanticline caused local unconformities above which occur un-mineralised late Middle-early Late Cambrian volcaniclastic sequences that pass conformably upward into the Ordovician-Early Devonian shelf deposits. Sedimentation in western Tasmania was interrupted by mid-Devonian deformation which extensively deformed the rocks by flattened parallel folds. The Precambrian regions behaved as relatively competent blocks during the Devonian deformation, which is expressed by two main phases of folding. In the earlier phase, folds developed in zones of closure between converging blocks, and the competent behaviour of the Tyennan Block largely

103

determined the fold patterns of northerly trend at its western margin, and of easterly trend to the north. The pre-dominantly later folds are of a gene.ral north-westerly trend, which resulted from movement from the northeast. In north-eastern Tasmania, east of the Tamar River, deep marine quartzwacke turbidite sequences were deposited during the Ordovician to Early Devonian. There is no transition between these sediments and the shallow marine shelf deposits of similar age in western Tasmania. Folding of the eastern Tasmania sedimentary beds is of similar age and northwesterly trend as those affecting pre-Middle Devonian rocks immediately west of the Tamar Tertiary trough, but result from tectonic transportation of an opposite direction. Substantial granitoid masses were emplaced at relatively shallow depths within the folded rocks throughout Tasmania from about 375 to 335 my. The granites and associated Sn-W and Ag-Pb-Zn mineralisation constitute a late Devonian metallogenic epoch. The dominantly S type granitoids in western Tasmania are slightly younger than the extensive S and I type granitoids in north-eastern Tasmania, and have different styles of associated Sn-W mineralisation. Scheelite-bearing skarns (e.g. King Island, Kara) and stanniferous skarn/replacement deposits (e.g. Renison, Cleveland, Mt Bischoff, St Dizier) are dominant in the carbonate-bearing sequences in western Tasmania, whereas cassiterite-wolframite greisen and vein deposits (e.g. Anchor, Storeys Creek, Aberfoyle) in or near apophyses of alkaline granite are dominant in north-eastern. Tasmania. Argentiferous Pb-Zn sulphide veins occur in zones peripheral to several Sn-W deposits (e.g. Zeehan, Moina, Scamander), and auriferous veins and shear zones occur throughout the State (e.g. Beaconsfield, Mathinna). The abrupt change in geology and metallogeny between western and northeastern Tasmania indicates that the Tamar Valley is the site of a major NNW trending fracture along which lateral movements brought the contrasting regions into juxtaposition. Finally, Tasmania became part of a craton, and erosion of the preCarboniferous rocks preceded deposition of Late Carboniferous and younger beds, which are flat-lying and have undergone epeirogenic deformation only. Coal and oil-shale occur within Permo-Triassic sediments and gold is associated with Cretaceous syenite south of Hobart.

Rb - Sr ISOTOPIC STUDIES OF THE MOUNT EDGAR BATHOLITH W.J. Collins1 and C.M. Gray2 1

CRA Exploration Pty. Limited, Western Australia La Trobe University, Victoria

The Mount Edgar Bathololith in the Archaean Pilbara Block is a granitegneiss terrain where granitic plutons have intruded a gneiss complex and a surrounding "greenstone" succession. Rb - Sr isotopic analysis confirms field, petrographic and geochemical studies indicating that granite plutons can be grouped as suites. These suites have statistically distinguishable total rock ages and initial 87sr/86sr ratios (IR), ranging from 3220 m.y. to 3110 m.y. and from 0.70(39 to 0.7038 respectively. The span in initial ratios indicates that the lower crust had evolved sufficiently to form distinctive source rocks prior to the generation of these suits at approximately 3200 m.y.

104

Regional samples from the central part of the gneiss complex produce a precisely defined age of 3230 ± 40 m.y. and I R OF 0.7010 ± 3. Detailed outcrop scale sampling of least modified (para)gneisses, at two localities spaced 20m apart, give two isochrons of differing age. At locality A the gneisses scatter about an ill-defined isochron with a 3060 ± 360 m.y. age (model 2), whereas samples at locality B form a perfect fit line indicating an age of 3790 ± 50 m.y., but a submeteoritic I R of 0.6985 ± 4. This "pseudochron" can only be a mixing line between an older gneiss component and younger (3230 m.y.) granitic magma. A minimum age of 3650 m.y. is constrained for the older gneiss component. An isotopic equilibration process involving mixing is proposed for the gneiss complex, using these three isochrons and field observations. At 3230 m.y., intrusion of Sr—rich granitic magma (orthogneiss) into an older (>3600 m.y.) felsic paragneiss terrain caused Sr-diffusion without physical interaction of rock types, where orthogneiss was minimal (Locality B). Where orthogneiss was more abundant (Locality A), isotopic equilibration was more efficient, but original gneissic bands were not disaggregated. Within the central gneiss complex, extensive granite magmatism, high-grade metamorphism and migmatisation resulted in disruption and partial assimilation of the banded parangeisses with orthogneiss. In this area, mixing was complete and achieved essentially by magmatic processes, to produce a regional perfect-fit isochron. The relic paragneiss age in excess of 3600 m.y. indicates that felsic rocks existed before the "greenstone" succession in the east Pilbara and implies that they formed basement to this succession. Therefore, isotopic mixing could explain the apparent "younger" ages of some Archaean gneiss terrains relative to adjacent, less deformed and less metamorphosed "greenstone" belts.

GEOCHEMICAL VARIATION OF GRANITE SUITES WITHIN AN ARCHAEAN BATHOLITH W.J. Collins 1 and A.J.R. White 2 ^CRA Exploration Pty. Ltd., Kununurra, Western Australia 2 L a Trobe University, Bundoora, Victoria The Mount Edgar Batholith in the Archaean Pilbara Block is composite, consisting of a complex gneiss terrain and seven major granitic suites, each of which consists of numerous plutons. Each suite has distinctive field, petrographic and geochemical characteristics. The oldest suite (Boodallana Suite) is characterised by dark grey tonalites containing abundant amphibolite inclusions and biotite schlieren, limited geochemical dispersion (64-707® Si02), and considerable geochemical scatter. The large Munganbrina Suite contains abundant pinkish-grey granites and most elements show distinctive curved trends on Harker diagrams. Excellent linear geochemical trends characterise the Yandicoogina Suite, which contains abundant conspicuous hornblendes. Linear variation trends also characterise the Warrulinya Suite, which is coarser grained than the other suites. All these suites are variably deformed, unlike the Chimingadgi and Coppin Gap Suites which are post-tectonic. Both these suites exhibit sublinear trends and are distinguished from each other by subtle differences in elemental abundances. The Moolyella Suite is also post-tectonic and has very distinctive geochemistry. However, its variation is extremely limited and is not discussed further.

105

Differences in chemical variation within these suites results from various differentiation processes occurring within different granitic magmas. Curved chemical trends of the Munganbrina Suite result from extreme crystal fractionation (Rayleigh-type) and can be modelled successfully using major elements. The Chimingadgi Suite rocks are also considered to have crystallised from a melt. However, sublinear chemical trends indicate that crystal fractionation was not extreme, and is considered to have occurred by crystal-melt unmixing. This process can also be modelled, and it applies equally well for the Coppin Gap Suite. Excellent linear geochemical trends in the Warrulinya Suite suggest a mixing model involving two homogenous end-members. The presence of numerous ragged mafic mineral clots suggests that the mafic end-member was either restite or basalt. However, the possibility of magma mixing involving basalt is ruled out by K2O and Rb trends which do not extend beyond 55% Si(>2 on Harker diagrams. Thus, chemical variation is considered to have been achieved by restite separation from a felsic melt. Similar arguments can be used to explain geochemical variation by restite unmixing in the Yandicoogina Suite. Although the Boodallana and Yandicoogina Suites are similar both petrographically and geochemically, there is much greater geochemical scatter in the Boodallana. This scatter is attributed to the presence of abundant schlieren throughout the suite. The type of differentiation process appears to be controlled by melt composition, which in turn affects the physical characteristics of the magma. Relatively felsic melts.form at low temperatures and are generally viscous, with differentiation usually proceeding by restite separation. More mafic magmas form at higher temperatures and are much less viscous allowing melt separation at the source region and facilitating crystal fractionation during emplacement in the upper crust.

AAPAMIRE (STRING-BOG) ORIGIN FOR STONE-ROLL SWARMS AND ASSOCIATED 'FLUVIO-DELTAIC f COALS IN THE LATE PERMIAN ILLAWARRA COAL MEASURES OF THE SOUTHERN SYDNEY BASIN: CLIMATIC, GEOMORPHIC, AND TECTONIC IMPLICATIONS

P.J. Conaghan Macquarie University, North Ryde, N.S.W. Introduction. Stone-rolls are elongate, subparallel ridges that occur on the floor of coal seams, often reaching to within a few centimetres of the seam roof, and separated by wider areas of thicker coal called 'swallows . In Australia they are known only from the latest Jurassic/Early Cretaceous Strzelecki Group of Victoria (Wonthaggi Coalfield) and the Late Permian Illawarra Coal Measures of the southern Sydney Basin, where their unanticipated prevalence as swarms has had disastrous consequences for some collieries. A literature survey suggests that stone-rolls are polygenetic in origin. Some northern hemisphere examples are probably of structural/tectonic origin, (e.g., Moore 1913), as seems likely too for the Wonthaggi examples. However the origin of the Sydney Basin stone-rolls has remained enigmatic, the various "controversial hypotheses . . . ranging in their outlook from purely 'sedimentary to purely 'tectonic with various gradations in between" (Diessel & Moelle 1967). The coal seams known to be affected by stone-rolls in the Southern Coalfield are those most intensively mined: the Bulli (most affected) and the Wongawilli (?less affected), but rolls or similar structures occur in other seams including the Woonoona (Harper 1915) and the Tongarra (Conaghan unpubl. data). All published descriptions and documentation relate to the rolls in the floor of the Bulli Coal (Harper 1915; Woolnough 1910, 1933; Diessel & Moelle 1967, 1970). 1

106

Nature of the rolls. In plan, the stone-rolls of the Southern Coalfield consist of subparallel ridges of structurally disturbed, expanded (by as much as 47%) floor rock (generally shale) and associated concentrations of siderite which Diessel and Moelle (1970) have demonstrated are concentrated in the upper levels of the roll as cm/dcmthick lenses of 'clay-ironstone1 and as interstitial cement in sandstone. Prevalence of crush-planes, slickensides, and brightly polished floor rock "show evidence of powerful compression in the roll" (Woolnough 1910). In plan-view, individual stone-rolls are variously straight, broadly arcuate, or bow-shaped (i.e., thickened arcuate middle segment with straight attenuated extremities). Sporadic bifurcations involve shorter f tie-rollsf which interconnect adjacent major rolls at oblique angles and in both directions with respect to the latter. Roll dimensions vary considerably : maximum relief ca 3m, maximum width ca 25m, and maximum observed length >600m. The geographic extent of the rolls appears to relate to major structural boundaries (demonstrably growth-faults; cf. Bunny 1972; Wilson 1975) defined on the north by the NW-trending Coledale Fault (Wilson 1975); on the south somewhere within the NWtrending zone defined by the Alpine Monocline and Macquarie and Wongawilli Faults; and on the west by the N-S-trending Nepean/Bargo Fault system. The Bulli roll-swarm parallels these and other NW-trending faults and folds within this area, and arcuate segments of individual rolls are uniformly convex towards the SW (cf. Diessel and Moelle 1970, fig.3). In contrast, the Wongawilli and Tongarra rolls trend NE-SW and their arcuate rolls are uniformly convex towards the SE (latter aspect speculative for the Tongarra because of limited data). In terms of N-S variation in character of the coals, the centre of best economic development of both the Bulli and Wongawilli Coals lies within this area, the Bulli in particular deteriorating abruptly in quality beyond these structural boundaries (Wilson 1975; Shibaoka and Bennett 1975). String-bog model. The meaning of the stone-rolls and overlying coals, not to mention numerous other stratigraphic and sedimentological characteristics and relationships of the enclosing sedimentary succession (Sydney Subgroup and basal-most Narrabeen Group), become abundantly clear if the morphology and areal pattern of the roll and swallow complexes are compared with the morphology and cryogenic dynamics of modern aapamires or string-bogs. These are patterned peatlands characterized by long ridges of peat and vegetation ('hummocks1 or 'strings') and intervening depressions ('Harks') that commonly contain vegetated ponds characterized by minero/rheotrophic, hydrophytic plants. The topographic relief and lateral dimensions of the strings and flarks in large modern aapamires is fully commensurate with that of the rolls and swallows in the Southern Coalfield: relief 2-3m; string width few m to few 10s m, length 100s to 1000s m; flark width 10s to 100s m. Moreover, aapamires characteristically inhabit gently sloping ground ( ^ 2 ° ) , with the string/flark pattern invariably arranged transverse to the gradient and the strings commonly convex downslope (Washburn 1979). Where established on steeper gradients the crosssectional shape of the complex has the aspect of a staircase. Additionally, sporadic bifurcations obliquely interconnect adjacent major strings in both directions relative to the orientation of the latter, identical to the bifurcating tie-rolls of the coal measures (e.g. see Moore and Bellamy 1974, fig.2.13; Washburn 1979, fig.5.45). Modern aapamires are commonly regarded as characteristic of the subarctic taiga where they are most commonly developed in the zone of discontinuous permafrost but known to range well into the zone of continuous permafrost (Washburn 1979). Nonalpine examples do occur beyond the present southern limits of the discontinuous permafrost zone but are interpreted as relict, formerly cryogenic forms associated with areas of thawing permafrost (Washburn 1979). The mechanism(s) that initiates the string pattern is poorly understood (reviews by Washburn 1979, and Moore 1982). However, once initiated within this climatic regime the pattern is intensified and perpetuated by the development of permafrost preferentially in the strings, involving the development of both ground-frost throughout all levels of the string peat and deep into the mineral soil as well as interspersed lenses of segregated ice up to 40cm thick. This leads to differential frost-heave between the strings and flarks with vaulting of the string surface above the water table and its progressive colonisation by more xerophytic, ombrotrophic plants (Washburn 1979; Zoltai and Tarnocai 1975). These cryogenic phenomena fully account for the stratigraphically expanded internal structure of the Southern Coalfield stone-rolls, the siderite simply occupying the interstitial pore space and cavities formerly occupied by the ice upon climatic amelioration. 107

Implications. Aapamires are sensitive indicators of subpolar climate (at low altitudes) and shallowly inclined terrain; moreover, the orientation of the string/flark complex and the polarity of the arcuate patterns in the complex are exquisite indices of the fall line. They thus have profound implications for climatic and tectonic/geomorphic reconstructions for the Sydney Basin in the Late Permian. Few data exist regarding the development of stone-rolls in the basal part of the Sydney Subgroup (Woonoona and Tongarra Coals), but on available evidence their presence there would seem to be weak. However, their presence intensifies progressively upsequence in the Wongawilli Coal and culminates in the spectacular roll-swarms of the Bulli Coal. This upsequence record of recurrent and progressively enhanced aapamire development with time has two major implications. Firstly, it reflects a pattern of long-term cyclicity of intervals of severe cold characterized by the development of discontinuous permafrost and almost exclusively phytotropic sedimentation (probably affecting the Basin at large), and intervening milder periods characterized by a trickle of clastic alluviation at the very southern distal edge of the Newcastle Piedmont (cf. McDonnell and Conaghan 1984). Secondly, the presence of aapamire development here, restricted to structural blocks bounded by growth-faults (cf. Bunny 1972; Wilson 1975), shows that the ground here was regionally broken and gently tilted towards the south in the area between the Coledale Fault and the structure now expressed at the surface by the Alpine Monocline. To the north and south of these structures the ground was evidently flatter, accounting for the abrupt facies changes and economic deterioration of the Wongawilli and especially the Bulli Coal across these boundaries. Further, facies evidence from the roof rocks of the Bulli Coal (cf. Diessel et al. 1967) suggests that the major drop in relief across this area during, and immediately following, Bulli Coal time, took place within the 30km wide zone between the Coledale Fault and the lineament now expressed at the surface by the Kemira Anticline. Assuming even tiny slopes for such terrain a substantial topographic relief is implied (e.g., 0.1°=51m; 0.2°=105m; or for steeper slopes: 0.5°=261m; 1.0°=525m). And independent evidence from the floor of the Bulli Coal confirms this because throughout this area "the trend is for increase in size and intensity [of stone-rolls] towards the north until terminating abruptly and inexplicably [!] at the Coledale Fault. In the areas of greatest intensity, the crests of some stone rolls reach the roof of the seamM (Wilson 1975). Because the lateral spacing of the aapamire strings must necessarily become smaller with increasing gradient, the "increase in size and intensity towards the north" of the rolls immediately south of the Coledale Fault indicates that the topographic gradient was progressively steepening northwards to that point. Moreover, the enhanced relief of individual rolls in this area is also readily explained because in modern aapamires the relative depth of ground-frost penetration (and presumably also the intensity of development of segregated ice) correlates inversely, first with snow-thickness, and secondly with air-temperature (Eurola 1975; Moore and Bellamy 1974). Because of their topographically more exposed aspect, insulating snow-cover is minimal over the aapamire hummocks relative to that in the flark depressions. This allows deeper penetration of the ground-frost in the hummocks relative to the flarks as well as its more permanent grip there because of the thermal insulating effect of the betterdrained but more slowly accumulating hummock peat during the summer. With the magnetic pole located to the SW within about 15® of latitude at this time (Embleton 1984; i.e., Sydney Basin less than ca 2000km from the geographic pole), the crest and upper slopes of this SW-facing 'Bulli physiographic ramp' would have been a place of especially wind-swept and bitterly cold, frontal aspect, with consequent minimal snow-cover on the aapamire hummocks, maximum penetration of permafrost and cryogenic expansion of the hummock substructure, and therefore especially enhanced vaulting of their upper surfaces. Some measure of the likely minimal rigour of this climatic regime can be gleaned from the limiting meteorological conditions that approximately define the southern edge of the present subarctic zone of discontinuous permafrost, bearing in mind though (cf. Washburn 1979), that much of this zone is possibly in disequilibrium with the present climate; namely: air temperature remains below 0 C for more than 200 days of the year, and winter precipitation (NovemberApril) is less than 300 mm (Moore and Bellamy 1974).

108

Finally, the orientation of this grossly southward-facing palaeoslope changed from a SE-facing to a SW-facing incline between Wongawilli and Bulli Coal times, as demonstrated by the conspicuous change in trend of their stone-rolls and clockwise rotation of the polarity of their arcuate segments, a palaeoslope reorientation confirmed independently by palaeocurrent directions in the clastic roof-sediments of these coals (cf. Diessel et al. 1967; Bowman 1974; McDonnell 1983). Such reorientation presumably relates mainly to tectonic rather than to sedimentaryaccretionary phenomena, and presumably stems from differential rotational movement between adjacent fault blocks. The genetic cause of the growth-faulting is debatable, but it is perhaps not without significance that the area affected here lies structurally above the upper half of the major sub-Permian basement ramp that separates the stable, thinly buried shelf area to the south from the deep central part of the Basin to the north.

References Bowman, H.N., 1974, Geology of the Wollongong, Kiama, and Robertson 1:50,000 sheets. Dept. Mines, Geol. Surv. N.S.W. Bunny, M . R . , Dept. Mines, Bull. Geol. Surv. N.S.W., No. 22 Diessel, C.F.K., Driver, R.C., <Sc Moelle, K . H . R . , 1967, Proc. Aust. Inst. Min. Met., 227, 19-37. Diessel, C.F.K., <$c Moelle, K . H . R . , 1967, Second Newcastle Symposium on Advances in the Study of the Sydney Basin, 18-19. Diessel, C.F.K., <Jc Moelle, K . H . R . , 1970, Compte Rendu 6e Congres Intern. Strat. Geol. Carbonif., Sheffield 1967, n^ 619-630. Embleton, B.J.J., 1984, Continental palaeomagnetism, Ch.II.2(a), in Veevers, J.J., (ed.), Phanerozoic Earth History of Australia, Oxford, O . U . P . (in press). Eurola, S., 1975, Annales Botanici Fennici, 12, 1-16. Harper, L.F., 1915, Dept. Mines, Mem. Geol. Surv. N.S.W., Geology, No. 7. McDonnell, K.L., 1983, Ph.D. thesis (unpub.), Macquarie Univ., Sydney. McDonnell, K.L., & Conaghan, P.J., 1984, Late Permian to Middle Triassic alluvial depositional environments of the Sydney Basin: coastal transect. 7th A . G . C . , Sydney, Geol. Soc. Aust., Abstracts No. 12. Moore, E.S. 1913, Coal Age, 3, 566-567. Moore, P.D., 1982, Nature, 300, 110. Moore, P.D., & Bellamy, D.J., 1974, Peatlands, Elek Science, London. Shibaoka, M., & Bennett, A.J.R., 1975, J. Geol. Soc. Aust., 22, 327-343. Washburn, A.L., 1979, Geocryology, Edward Arnold, London7(2nd ed.). Wilson, R . G . , 1975, Aust. Inst. Min. Met., Monograph No. 6, 206-218. Woolnough, W . G . , 1910, J. Proc. R. Soc. N.S.W., 44, 334-340. Woolnough, W . G . , 1933, Bull. Amer. Soc. Petrol. Geol., 17, 1098-1106. Zoltai, S.C., & Tarnocai, C., 1975, Can. J. Earth Sci., 12, 28-43.

DEPTH OF THE CURIE POINT BENEATH AUSTRALIA D. Conley Bureau of Mineral Resources, Canberra The depth of the 560°C isotherm (representing the Curie point) has been determined from data obtained in heatflow and gradient data bases (Cull & Conley, 1983). The gradient data base is subject to various types of systematic error, but there are sufficient data points to be able to recognise systematic trends. A simplified crustal model of a sedimentary basin of variable thickness overlying a crystalline basement was utilised in extrapolating surface temperatures to depths. The sedimentary basin was assumed to have uniform thermal conductivity and uniform heat generation from the decay of radioactive elements. 109

The thermal conductivity of the crystall ine basement was assumed to decrease with depth according to the relation •7 A

= a+bT

where X is the thermal conductivity, T, temperature and a and b are constants. This relation holds until the temperature exceeds 400°C when heat transfer by radiation may occur. For temperatures in excess of 400°C, a constant value for the thermal conductivity was assumed. Heat production throughout the basement was assumed to decrease exponentially with depth (Lachenbruch, 1970) to satisfy the linear heat flow/heat production relations observed in Australia by Sass and Lachenbruch (1979). Two distinct provinces were recognised, the Western Australian Shield (WAS) province (west of Long.126°) and the Central Australian Shield (CAS), province. It was assumed that the Eastern Australian Province has a similar heat production-depth relation as has the CAS province. The depth of the 560°C isotherm so determined ranges from a low of approximately 20km beneath the Great Artesian Basin to a high of approximately 55km below the Western Australian Shield. However the M0H0 has been described as a magnetic mineralogy discontinuity (Wasilewski et al., 1979), in which case the Curie depth in the WAS province will be mostly controlled by petrological conditions at or near the M0H0. In eastern Australia the position of the Curie point is determined by the local geothermal gradients and may bear little relation to mineralogy. The correlation between the Curie depth and the 3rd order magnetic map of Australia (Wellman et al., in preparation) is poor. This could be caused by lateral heterogeneity of crustal magnetic properties, in which case the estimated Curie depths will seVve as an important constraint to future crustal models. The temperature at a depth of 40km (representing the M0H0) across Australia has also been determined. At no point does the estimated temperature exceed that of the Basalt Dry Solidus. Beneath eastern Australia, though, the granodiorite saturated solidus is passed so some partial melting may occur in the lower crust. The above temperature estimates would therefore represent a lower limit. Temperature estimates from xenolith data (Wass and Griffin, in press) are higher than those predicted using the assumption of heating by radioactive decay. This implies the possibility of enhancement of the heatflow from non-radioactive sources and a correspondingly shallower Curie depth. References Cull, J.P. & Conley, D., 1983, BMR Journal of Australian Geology and Geophysics, 7, 11-21. Lachenbruch, A.H., 1970, Journal of geophysical Research, 75, 32913300. Sass, J.H. & Lachenbruch, A.H., 1979, Ln : M.W. McElhinny (editor), The Earth - Its origin, structure and Evolution, Academic Press. Wasilewski, P.J., Thomas, H.H., and Mayhew, M.A., 1979, Geophysical Research Letters, 6, 541-544.

110

THE

GEOLOGY

A N D M I N E R A L I Z I N G E N V I R O N M E N T OF THE K I M B E R L Y MAAR COMPLEX, FORSAYTH, QUEENSLAND

SUE

i o1 K . Brent Cookr arid John E . Nethery" *AOG Minerals Limited, Cairns A O G Minerals Limited, Sydney

The Kimberly Sue Maar Complex is located 60 km south of Forsayth, and 400 km south-west of Cairns,in North Queensland. Calc-alkaline,terrestrial,volcanism, and intrusive activity, developed in response to Permo-Carboniferous, post-orogenic, extensional tectonics, which activated north, north-east and south-east trending regional fractures. Locally, magma doming and an incipient cauldron subsidence, 20 km in diameter, of probable Lower Permian age, is indicated by; 1.

local curving of the 100 km long Delaney Fault into a tight arcuate fracture,

intersection of north-east and south-east fractures with the Delaney Fault, to form a radial doming fracture pattern.

development of a polygonal dyke set indicating incipient ring collapse fractures.

extrusive rhyolite domes and intrusive rhyolitic to andesitic plugs.

the 80 km2 Agate Creek Volcanic rift.

the Kimberly Sue Maar Complex and

the coincidence of a Bouguer gravity low of a similar size and amplitude to those associated with other cauldron subsidences in the area.

The Kimberly Sue Maar Complex is a north-east trending elongate structure, 7 km by 1.5 km, and comprises a series of broadly circular, overlapping individual maars. The north-eastern end of the structure, occupying an area of 2 km^, was upthrown relative to the rest of the maar, and consequently represents a deeper level within the maar system. This zone is known as the Bald Mountain Breccia Complex and contains three separate intrusive centres, entitled sub-complexes. Outside the maar rim, to the east of the breccia complex, is a small rhyolite dome occupying an area of 0.5 km^, and comprising both intrusive and extrusive units. Four stages of development of the maar complex are apparent : 1.

Doming and contemporaneous collapse of the metamorphics occurred both locally, and regionally in association with rise of a large pluton.

Maar style volcanism and continuing subsidence followed. Extrusive activity, at the Bald Mountain Breccia Complex during this stage, supplied some material to the maar fill.

Widely scattered intrusion and minor extrusion of viscous flow-banded, aphanitic to quartz porphyritic rhyolite followed the major volcanic stage.

Porphyritic quartz-feldspar-biotite rhyolite dykes, related to large scale incipient cauldron subsidence represent the final event.

ill

The maar fill material is a variable mixture of volcanics and Robertson River metamorphics. Injection and ejection of brecciated igneous and metamorphic rock stoped from deep within the diatreme produced rapid variations between bedded and chaotic maar fill. A continuing cycle of injection, ejection, and subsidence, characteristic of diatreme activity, and ejection of tephra beyond the crater rim resulted in a net maar subsidence. Three intrusive phases were recognized in the breccia complex. Initially, relatively passive intrusion produced an essentially homogeneous unbrecciated quartz-feldspar porphyritic rhyolite. Subsequent intrusions became more gas and liquid charged, possibly due to an increase in ground water penetration due to gas brecciation in the overlying diatreme. Repeated gas brecciation of overlying metamorphics and implosion brecciation of rhyolites occurred as the intrusions stoped upwards. These intrusive breccia plugs commonly contain metamorphic clasts. A coarser grained porphyritic rhyodacite to equigranular microadamel1ite was the last intrusive phase. At the Bald Mountain Complex pervasive sericitic and lesser siliceous, kaolinitic, adularia, and chloritic alteration occurs. Concentrations of disseminated pyrite averaging nearly 5%, with minor associated lead, zinc and copper mineralization, occur over most of the Complex. Gold, though scarce, occurs in narrow high-grade veins and disseminated in zones distal to hydrothermal centres. Visible alluvial gold can be panned from most creeks draining the Complex. These features place the Bald Mountain Breccia Complex deep within the epithermal model. West of the Pig Hole Creek fault recognition of mud pots, surface slump features, hydrothermal and explosion breccias implies a near surface setting for hydrothermal activity in the eastern Kimberly Sue Maar Complex. Advanced argil lie and carbonate alteration of the maar fill material, combined with the high Hg, Sb and As values and low Pb, Zn, Cu values, further indicates dominantly steam produced low pH alteration in the upper levels of an epithermal system. Anomalous Au values resulted from sampling of -180 micrometre stream material, while pan concentrate samples generally produced poor results. These characteristics place the maar complex near the top of the epithermal model. Exploration of this prospect is at an early stage, and this presentation represents only an interpretation derived from surface geological mapping, geochemical testing and geophysical surveys.

AUSTRALIAN

GEOLOGY:

SOME L E S S O N S

FROM

HISTORY

B.J. Cooper S.A. Department of Mines and Energy, Eastwood, S . A . Why should geologists have some appreciation of their professional history? The guestion is significant because in the economically orientated qeoscience professions, it is very easy to dismiss historical investigations as being too academic or havina no practical value. Of course, history plays an essential role in almost every geological investigation. The mere existence of a bibliography at the end of a research paper indicates that it is necessary to consider other geologists and the historical development of their ideas. In the geosciences, this historical dependence is probably greater than in other sciences oiven the discipline's reliance on classic sections, stratotypes, standards and type specimens. 112

History is also an important pre-occupation within any lonastandinn well-defined aroup of people and geoloaists are no exception. Considering the enormous post-war expansion of the geological profession in Australia, it is only natural that there is a mounting desire to maintain traditions that have been established, and to unearth those unknown historical treasures that bring greater professional Dride. There is also a normal feeling within all of us simply to set the record right. A final reason to study the history of geology is to promote community appreciation of the science and its contribution to the national heritage. There are many significant observations that could be made about the progress of Australian geology. It is valuable to try and identify these and learn from them. Four observations will be discussed here. Australian Geology has always been influenced by overseas standards and ideas. This importation, of course, has been extremely beneficial although there is a need to discern basic principles amongst these ideas and to be alert to the possibility that such importations may hinder interpretation. As a consequence of overseas influence, there is also a danger that we will not appreciate the unique features of Australian geology and of the cumulative experience of Australian-trained and Australian-based earth scientists. Since the beginnings of Australian geology, there has been an accelerating rate of specialisation within the discipline. It is coupled with the increasing numbers of aeologists, the explosion of information and developing international geological liaison. As a consequence, there is a greater need now than in the past for qeoloqists with versatility, with the capacity to obtain an overview of their subject and with the ability to work together with fellow professionals. Community appreciation of the earth sciences to a basic level must also be maintained if the profession and indeed the Australian community itself is to prosper. The exploration and development of mineral resources has lonq been a factor influencing the development of Australian geoloay. This is not a recent phenomenom but can be discerned from the South Australian Copper boom of the 1840 f s and from the Gold Rushes during the latter half of the nineteenth century. All geologists need to be sensitive that community interest in resource development is important for the continued well being of the science. Finally the role of the individual geologist is basic. Many are fundamental information gatherers, some are individual thinkers while a few have great visions of the future. If we are to continue our pursuit of geological knowledge then we must learn to tolerate, listen to and encourage them all.

SOUTH AUSTRALIAN

GEOLOGY

1940-1970:

A PRELIMINARY

REVIEW

B.J. Cooper S.A. Department of Mines and Energy, Eastwood, S . A . From both the professional and scientific perspectives, South Australian geology underwent a dramatic transformation in the 30 year period ending in 1970. A comparable, but not identical chanqe can be recognised elsewhere in Australia.

113

In the late nineteen thirties, there were probably no more than six professional geologists residing in South Australia, including two at the S . A , Department of Mines and two at the University of Adelaide. Camels were still being used as an important means of transport. A few technoloqical innovations had become available (including geophysical exploration and aerial photography) however these were at an experimental stage and not widely applied. The The Second World War w a s the major catalyst for change. introduction and ready acceptance of new technologies became easier than before. Government had to respond to war-time conditions urgently and opportunities in numerous fields including geology became available. The war-time period in South Australia and immediately after was notable for the activity and qrowth of the Geological Survey within the Department of Mines. Initial expansion resulted from the war-time need to rapidly develop the Leigh Creek coalfield. From a geoloqical staff of two in 1 9 4 0 , the Survey numbered 27 geologists a decade later and continued to expand. The Survey was the first to initiate systematic regional mapping in Australia after the war and also guickly estabished a Geophysics section. The initial establishment of what has become the Australian Mineral Development Laboratories (AMDEL) w a s also formed within the Department of Mines in 1 9 4 9 . The foundation of SANTOS in 1954 in the wake of the Rough Range oil discovery signalled the beginning of major private enterprise investigations of South Australian geology. With a local base and supported by the geological expertise of the Adelaide-based consulting company, Geosurveys, SANTOS initiated an exploration programme, which ultimately achieved success in the Cooper Basin in 1963. The University of Adelaide also expanded its staff and research during the nineteen fifties. A separate Department of Economic Geology was established in 1949 and over the ensuing decade, geological staff on campus more than doubled to reach t e n . Concluding with the 1 Nickel B o o m 1 , the nineteen sixties were years of expansion in Government, University and private enterprise. International commercial interests became manifest after the Delhi Taylor Oil Corporation acquired interest in Cooper Basin oil exploration in 1 9 5 9 . Metals exploration started a new phase with a Lease at Wallaroo/Moonta by Western Mining Corporation from 1960-1971. There were eight Special Mineral Leases This subsequently increased to 42 in 1966 and in South Australia in 1962. 159 in 1970.

SOUTH AUSTRALIAN GEOLOGY:

THE EARLY YEARS

1836-60

D.W. Corbett Centre for Environmental Studies, The University of Adelaide The early geological investigators in South Australia were a diverse and interesting group of men who reflected the varied traditions that made the formative years of the science a time of flux and controversy. The writings of Sturt, B u r r , Finniss and Menae contain elements of the Catastrophist, Plutonist, Uniformitarian and Neptunist schools of thought and something of Nature Philosophy.

114

As European traditions were imported and the principles of stratiqraphic geology were applied in Australia as elsewhere around the world at a time when the science was barely established, such diversity is to be expected. The development of later nineteenth century geology and its emergence as a global science owed much to the influence of Lyell, but egually as much to the pioneer workers in countries far away from the intellectual roots of their discipline and of whom those in South Australia provide an illuminating example. They were explorers, surveyors and interested residents of the colony, including two governors. In the days before formal trainino in aeology was available they reveal, without exception, a knowledge and appreciation of geoloaical matters that is guite remarkable. While the search for and discovery of minerals followed from the enthusiastic prognostications of Menge, the stimulation of the early finds led to preliminary attempts to delineate the stratigraphy and structure of the local ranges. Although the copper discoveries were to set the infant colony on its economic feet, the hope of coal and (after 1852) the lure of gold were among the pre-occupations which exercised the minds of such men as Babbage, Fortnum and Bruhn. Yet in the absence of any systematic approach to mineral exploration or geological investigation (the Geoloqical Survey was not established until 1882) the early mineral discoveries were not repeated. After Babbaae's failure to find gold on his 1856 expedition through the northern ranges, the government acquired the temporary services of A.R.C. Selwyn, Government Geologist in Victoria. In a rapid reconnaissance of the South Australian highland chain he was unable to locate gold or other economic minerals but his visit brouqht to the colony for the first time a professional geologist whose investigations and discoveries were to add much f valuable knowledge of South Australian qeoloqy at the end of the colony s first quarter century.

QUARRY PLANNING IN THE BRINGELLY SHALE, SYDNEY Robert W . Corkery R.W. Corkery & Co. Pty Limited, Sydney This paper examines the advantages and procedures for quarry planning in quarries extracting Bringelly Shale in Sydney's western suburbs. A range of approaches to quality control is also discussed. The Bringelly Shale This shale is a complex formation comprising (in decreasing abundance) claystone and siltstone, laminite, sandstone, coal and highly carbonaceous claystone and tuff (Herbert, 1979). The formation is generally less than 110 m thick, however, its maximum recorded thickness is 257 m in the Razorback Range. Over 80 per cent of Sydney's bricks are manufactured from material extracted from the Bringelly Shale. The variation in iron content (principally siderite) enables a wide range of fired colours to be produced from cream > buff + apricot red dark red. Deposits of cream to buff firing clay/shale are considerably more scarce than the abundant deposits of apricot to dark red firing material. Quarry Planning Advantages: There are numerous advantages in planning quarries within the Bringelly Shale, these include:

115

1. problems of local variability within each rock unit are known prior to extraction. Hence, the method of extraction chosen will ensure the correct quality is obtained; 2. the distribution of large nodular siderite and sandstone lenses can be established; 3. transport routes into and out of the quarry can be established; 4. drainage sumps can be positioned correctly; 5. the relative proportions of each material sought can be extracted and costly stockpiling can be avoided; 6. cost savings!! Procedures: The procedures for planning quarries in the Bringelly Shale adopt relatively standard geological principles. The premise for planning a quarry used in this paper is that: (a) a deposit has been defined through preliminary drilling to prove the existence and quality of the deposit, or (b) a fixed area eg. adjacent to a brick manufacturing plant or a waste disposal depot has been chosen for extraction. The following planning.

procedures

have

been

proven

very

useful

quarry

1. Establish good survey control and base plans. 2. Preliminary diamond core drilling on a wide spacing (a suggested spacing is 100 m). 3. Longitudinally split dore and fire one half in a brick kiln. Retain one half for records or prepare composite from one quarter and retain one quarter for records. 4. Geologically describe core and relate fired colour. 5. Establish whether any additional close space drilling is necessary (40 to 50 m spacing may be appropriate). 6. Prepare structure contours, isopachs and appropriate cross-sections. Note: All information prepared should be in a form for the equipment operators to understand. Quality Control Once a quarry is planned and extraction is commenced, it is imperative that the plan is closely monitored, that is, the required quality of the raw material is achieved and maintained. The need for quality control varies according to the level of variability within a quarry. Virtually all quarries in the Bringelly Shale require regular quality control checks. Quarry planning will provide the following information which will need to be regularly checked during a quality control programme. 1. The boundaries of each unit. Note: It is often impossible to visually detect such a boundary. 2. Any unwanted material eg. red firing shale or massive siderite within a unit of cream firing shale. The essential requirements for quality control are that it is quick and accurate. It needs to be done whilst equipment is operating in the quarry. Two suggested methods of quality control are: 1. Spot Sampling: Samples of shale may be obtained from the floor of the quarry and/or to a depth of 1 m by selected ripping across the floor of the quarry. Samples collected can be fired and the results known either overnight or within 6 hours.

116

2. Auger Drilling: Auger drilling at spacings of 25 to 40 m is a very accurate means of keeping a check on extraction. A permanent grid system is recommended. It is desirable that samples be taken every 0.5 m and that the total depth at each time not exceed 4 m. Depth control diminishes below this level. Briquettes of the augered shale are fired and information used to control the shale quality. An accurate record of depths is essential. Reference Herbert, C. 1979,

Geological Survey of NSW Bulletin 25.

A PROPOSED CLASSIFICATION OF ORE TYPES (FACIES) FOR THE RUNDLE OILSHALE DEPOSIT Lee Coshell University of New South Wales, Sydney A scheme of ore type classes for the Rundle Oilshale deposit is proposed in the accompanying table; eight major ore types (facies) are identified. Each ore type class is defined by geological features recognisable in the field and carries with it an implied visual estimation of oil yield. These ore type classes are further split into sub ore types mainly on structural and detailed sedimentological criteria. The concept of analysing Rundle deposit geology by ore types was initially suggested to aid the engineering assessment of the Rundle Project (Coshell, 1983). This hypothesis stated: (a) (b) (c)

(d) (e)

Samples of the same ore type from the same seam, or different seams, should not exhibit significant differences. Samples of different ore types within a seam, or within different seams, might display significant differences. The observed differences in retort and other variables between seam composites might be due to the relative percentage of each ore type comprising the seam composite. The percentage of each ore type in any seam composite will vary dependent upon the stratigraphic location of that composite sample. Distribution of ore types within the deposit is a function of the depositional environment.

Detailed examination of drill core and preliminary process response results have subsequently supported this hypothesis. The deposit comprises a cyclic succession of ore types with remarkable correlatability. Moreover, ore/waste boundaries coincide with cyclic boundaries, enabling ore and waste units to be mapped and carried through the deposit.

117

GEOLOGICAL CHARACTERISTICS OF ORE TYPES IN THE RUNDLE DEPOSIT MAJOR LITHOLOGY ORE TYPE & FACIES & GRADE LAMINATED I, V OILSHALE 120

MODERATELY IX,IV LAMINATED OILSHALE 70-120

SLIGHTLY XI LAMINATED TO MASSIVE 70 OILSHALE

BRECCIATED II OILSHALE 90

CLAYEY OILSHALE

VI 50-90

CLAYSTONE III 50

GEOLOGICAL CRITERIA FOR RECOGNITION

FACIES

SUB ORE TYPE

171 OILSHALE: Dark yellowish brown to brown, generally LAMINATED calcareous, slightly carbonaceous, laminated. Can be hard and weakly fissle where dolomitic. Slicken___ 1.2 sided surfaces generally occur where mottled and DEFECTED non calcareous. Ostracodes where calcareous, rare LAMINATED turtle, crocodile and fish remains. . OILSHALE: Greyish yellow brown to brownish grey, MODERATELY 2.1 variably calcareous, moderately carbonaceous, LAMINATED syneresis cracks, moderately laminated. Slickensided surfaces generally occur where mottled and DEFECTED non calcareous. Fills an intermediate position LAMINATED 2.2 between types 1 and 3. Ostracodes where calcareous, rare turtle, crocodile and fish remains. 3.1 POORLY OILSHALE: Olive grey to brownish grey, generally LAMINATED poorly calcareous, moderately carbonaceous, TO MASSIVE mottled, slightly laminated to massive and often showing well developed slickensided surfaces. DEF. POORLY 3 .2 Syneresis cracks are a feature. Rare turtle, LAMINATED TO crocodile and fish remains, ostracodes where MASSIVE calcareous. OILSHALE: Dark yellowish brown to olive brown, BEDDED V. 4.1 generally calcareous, rarely carbonaceous, mottled, FINE/COARSE rare discrete claystone, fragmented ostracode and BEDDED COARSE/ 4 .2 gastropod remains. Textures range from very fine V. COARSE to coarse breccia, often strongly layered. Occasional bioturbation features, minor turtle, crocodile and fish remains. BRECCIATED 4.3 OILSHALE: Olive brown to olive grey, generally VARIABLY 5.1 calcareous, rarely carbonaceous, dark green grey LAMINATED TO ostracodite, mottled, discrete claystone, MASSIVE fragmented ostracode and gastropod remains. Shows BEDDED BREC- 5.2 characteristics of both cilshale and claystone with CIATED textures ranging from laminated to brecciated. Bioturbation features and minor turtle, crocodile BRECCIATED 5.3 and fish remains. CLAYSTONE: Dark yellowish green to olive grey, VAR. LAMINATED 6.1 generally calcareous, rarely carbonaceous, dark TO MASSIVE green grey ostracodite, mottled, fragmented ostra- BEDDED 6.2 code and gastropod remains. Often shows soil like BRECCIATED textures with remobilised carbonates, relict breccia BRECCIATED 6.3 textures with clayey oilshale clasts, bioturbation BRECCIATED TO 6.4

LIGNITE: Very dark grey to black, shaley and LIGNITE 7.1 predominantly non calcareous. Laminated to LIGNITE & V. 7.2 brecciated with discrete oilshale clasts. CARBON. 0/S DOLOMITE VII DOLOMITE: Brownish grey to grey, variably CRYPTO8.1 calcareous, hard, cryptocrystalline, impure, CRYSTALLINE 50 dolomite to ankerite. Irregular disseminations and hard tabular concentrations, often shows a breccia texture and other relict features. BRECCIATED 8.2 Note: numerals indicate the now redundant ore type classification used during field work. LIGNITE

VIII 120

References Coshell, L . , 1983,

118

P r o c . First A u s t . Workshop on Oil Shale, p . 2 5 .

GEOCHEMISTRY OF CAMBRIAN VOLCANICS IN SOME DISPERSED FRAGMENTS OF EAST G O N D W A N A L A N D FOLDBELTS Anthony J. Crawford Geology Dept., Univ. of Tasmania, Hobart The Late Precambrian and Palaeozoic foldbelts which formed along the eastern margin of Gondwanaland were disrupted and dispersed during postUpper Palaeozoic fragmentation of this supercontinent. Fragments presently outcrop in Victoria and Tasmania, in the South Island of New Zealand, and in northern Victoria Land in the Transantarctic Mountains. As part of a wider project on the tectonic evolution of the east Gondwanaland Palaeozoic foldbelts, we are studying the petrology and geochemistry of Cambrian volcanics which invariably occur at or near the base of the foldbelt sequences. I present here a review of available data. Antarctica. The Bowers Supergroup, which ocupies a 350km long, narrow trough which strikes across northern Victoria Land, includes volcanics of the Glasgow formation near its base. These lavas vary from basalts through to rhyolites, but basalts and andesites predominate and have low-grade burial metamorphic mineral assemblages. Relict primary phases include cinopyroxene and Cr-rich chromites (Cr/Cr+Al=0.70-0.80). Compositions of basaltic and andesitic lavas from the central and northern parts of the trough (Weaver et al., 1984; this study) have affinities with depleted island arc tholeiites. Lavas from the southern end of the Bowers Trough in the same formation are less depleted in Ti, Zr and LILE and are intruded by sills of titanaugite-bearing transitional to mildy alkaline basalt. The poorly-known Husky conglomerate, which overlies high-grade metamorphics of the Wilson Group immediately west of the Bowers Trough, contains cobbles of siliceous high-Mg lavas with affinities to boninites (Weaver et al., 1984). New Zealand. In the NW Nelson province of the South Island, CambroOrdovician rocks have been divided into three belts separated by major N-S striking thrusts. The Central Belt contains at its base the Haupiri Group, four formations of which contain igneous rocks. The lowermost unit, the Balloon Formation, includes coarse basal conglomerates of Lower to Middle Cambrian age which contain cobbles of calc-alkaline andesite and basalt. The overlying Devils River Volcanics contains 500-2000m of calc-alkaline andesites and basalts and less abundant more evolved lavas. These are intruded by thin sills of titanaugite-bearing slightly alkaline basalts and dolerites. The fault-bounded Cobb Igneous complex was emplaced into the Haupiri Group during early Upper Cambrian. It is a stratiform ultramaficmafic layered intrusion at least 2500m thick consisting of lower cumulate lherzolite, harzburgite and dunite followed by layered orthopyroxenites and websterites, and an upper zone of gabbro/dolerite. Chromites in all lithologies are Cr-rich (Cr/Cr+Al >0.7 and <0.84); this, and the abundance of orthopyroxene rule out an ophiolite (i.e. typical ocean crust/upper mantle) origin. The Cobb Igneous Complex is interpreted as a stratiform body which accumulated below, and is comagmatic with, the Devils River Volcanics. High in the Haupiri Group, the late Middle to early Upper Cambrian Lockett Conglomerate contains abundant metavolcanic clasts, three of which were analyzed and found to be primitive high-Mg, low-Ti andesites (Crawford and Grindley, in prep.). Thin flows and sills of basalt in the overlying Anatoki Formation are compositionally identical to the more basic Devils River volcanics lithologies, and indicate that island arc magmatism continued well into the Upper Cambrian.

119

Victoria: The Stavely Greenstone Belt in western Victoria consists of two parallel sub-belts. The western sub-belt is composed of calc-alkaline orogenic andesites with chemical characteristics suggesting they were erupted through thinned continental crust at an active continental margin. The eastern sub-belt contains a >lkm thick pile of comagmatic lowTi, high-Mg andesites; in modern settings, such lavas are known only from intra-oceanic arcs and imply eruption through very thin crust. A major, NW-striking crustal discontinuity, defined by the eastern margin of the post-orogenic Grampians basin, is postulated to separate these two subbelts. The Heathcote and Mount Wellington Greenstone Belts in central and eastern Victoria respectively, show very similar stratigraphic and petrological/geochemical sequences. Low-Ti lavas, including true boninites and high-Mg andesites, underlie thick piles of evolved tholeiitic basalts which have affinities with fractionated back-arc basin tholeiites. At Licola and Jamieson in the Mt. Wellington Greenstone Belt, fault-bounded blocks of calc-alkaline to high-K orogenic andesites occur, but their relationships with the boninites and tholeiites remain unknown. Tasmania: We have only recently commenced a synthesis of geochemical data for the extensive Cambrian volcanics in Tasmania, and further field mapping and analytical studies are underway. However, we note the presence of at least four magmatic series. Late Precambrian flows interbedded with Rocky Cape Group sediments are transitional to slightly alkaline basalts possibly associated with Cooee Dolerite magmatism. Low-Ti magmatism is represented in the Dundas and Adamsfield Troughs by lavas including boninites, and layered, opx-rich ultramafic bodies. Evolved tholeiitic basalts compositionally very similar to the Victorian Cambrian tholeiites occur in a number of troughs. The Mt. Read Volcanics are thought to represent volcanism in a rift through Tyennan (Precambrian) continental crust at an active continental margin. Any attempt to reconstruct the dispersed fragments of the Lower Palaeozoic foldbelt(s) which bordered the eastern margin of Gondwanaland must incorporate constraints from basement (Cambrian) volcanics. It is evident that a complex, West Pacific-style scenario must be invoked, involving construction and foundering of arcs on both thinned continental crust and ocean crust, opening and closing of backarc basins, important transcurrent faulting and possibly attempted subduction of continental crust. Reference Weaver, S.D., Bradshaw, J.D. and Laird, M.G., 1984, Earth Planet. Sci. Lett., 68, 128-140.

BRITTLE DEFORMATION ASSOCIATED WITH JOINTS AND IRONSTONE VEINS IN TRIASSIC SANDSTONES, SYDNEY BASIN J.W. Creasey CSIRO Division of Mineral Physics, North Ryde The Triassic Narrabeen Group outcrops extensively along the western margin of the Blue Mountains Plateau, Sydney Basin. Thick lithic sandstones within the group are well jointed with a regionally developed NNW and subordinate ENE trending joint sets, and locally developed WNW and NNE trending sets. Structurally the western margin of the basin is cut by N-S to NNE trending lineaments that parallel and in some cases coincide with basement discontinuities (Shepherd et al., 1981a).

Ironstone veins have formed within dilated NNW trending joints locally on the plateau, and elsewhere joint margins have been recemented with goethite, forming vertical, resistant ridges in the sandstone. The ironstone margi ns of NNW and WNW trending joints and veins contain a 'fracture foliation* consisting of closely spaced, discontinuous fractures. Brecciation of veins and adjacent margins occurs between the endpoints of closely spaced, offset veins, especially in areas where the veining and fracture foliation are best developed. The closely spaced fracturing is not present adjacent to zones of brecciation or in other thin irregular ironstone layers throughout the sandstone. Thin sections of joint and vein margins show that the fractures are extensional and that fracturing, dilation and infilling are repetitive. Such a process has been related to brittle deformation associated with the initial development of low grade shear zones in sandstone (Knipe and White, 1979), and is similar to fracturing of sandstones in uniaxial compression tests (Dunn et al., 1973). The deformation associated with these ironstones conforms to the sequence of post-extensional compression that has been identified previously in the Permian coal measures in the Western Coalfield (Shepherd et al., 1981b). In this case, initial easterly extension caused dilation of the NNW trending joints within which ironstone veins formed. Subsequently, the vertical, planar ironstone veins and joints were highly stressed during northwesterly directed compression. Extension fracturing occurred within the planar margins of veins, while secondary fracturing and brecciation occurred in the vicinity of vein endpoints, where stress magnitudes were greater. Both the described ironstone deformation and the lineament pattern of the Sydney Basin can be related to a regional sinistral shear couple that was probably active during the Upper Cretaceous (Jones and Veevers, 1983; Mauger et al., 1984). References Dunn, D.E., LaFountain, L.J., & Jackson, R.E., 1973, J. Geophys. Res., _78_(14), 2403-2417. Knipe, R.J., & White, S.H., 1979, J. Struct. Geol., H I ) , 53-66. Jones, J.G., & Veevers, J.J., 1983, J. Geol. Soc. Aust., 30^, 305-322. Mauger, A.J., Creasey, J.W., & Huntington, J.F., 1984, Abstract Series No. 11, Geol. Soc. Aust., 28-31. Shepherd, J., Huntington, J.F., & Creasey, J.W., 1981a, Trans. Inst. Min. Metall., Sect. B, 90_, B1-B14. Shepherd, J., Creasey, J.W., & Huntington, J.F., 1981b, Proc. Australas. Inst. Min. Metall., No. 279, 19-32.

TORRINGTON TOPAZ - ITS INDUSTRIAL

POTENTIAL

M. Creech Pacific Copper Limited, Sydney Pacific Copper's Torrington Project area located 30 km northeast of Emmaville NSW, includes substantial reserves of topaz occuring within a quartz rich rock known as silexite. This rock also contains significant tungsten and bismuth mineralisation (see main abstract for further geological notes).

121

Torrington topaz is not a traded industrial commodity however current research by Pacific Copper Limited has shown this mineral offers excellent prospects for the production of high quality refractory materials and fluorine fluxes. Research is currently being conducted through the Industrial Research and Development Incentives Grant Scheme. Topaz calcines to the high temperature mineral mullite at temperatures of 1250 to 1400°C and liberates fluorine rich gases which can be converted into commercial fluxing compounds. The synthetic mullite produced from topaz compares favourably with specifications quoted by present world-wide distributors: App A1203

Fe203

CaO+MgO

K20+Na20

Porosity

App SG

Refractoriness

Example of traded specifications for synthetic mullite

min 70.0%

max 0.6%

max 0.4%

max 5%

min 2.70

Mullite from topaz

71.2%

0.11%

0.05%

SK38 rain

0.05%

2.81

SK38 - 39

As far as fluorine compounds are concerned the raw material topaz contains only 0.7 to 0.5% total impurities including 0.025% phosphorous. The major advantages of using topaz as a raw material for the production of synthetic mullite include the lower cost of the raw material and the lower power costs for topaz conversion in Australia. Research is continuing fluorine recovery using a companies.

into the process of topaz conversion and combination of research organisations and

TORRINGTON TOPAZ AND SILEXITE GEOLOGY 1 o o M.Creech-1-, S, Sangameshwar^ and B. Marshall Pacific Copper Limited and

NSW Institute of Technology, Sydney

Pacific Copper's Torrington Project area, located 30 km northeast of Emmaville NSW, includes large resources of topaz occurring within a quartzrich rock known as silexite. This rock also contains significant tungsten and bismuth mineralisation. Silexite intrudes, and is proximal to, a sedimentary roof pendant of Permian age outcropping within the Mole Granite. Topaz is not a traded industrial commodity at present, however, current research by Pacific Copper Limited has shown that it can yield high quality refractory material and fluorine products. Calcination at temperatures of 1250 to 1400°C converts topaz to mullite and liberates fluorine rich gases which can be converted into commercial compounds. Encouraged by these results, Pacific Copper Limited has been successful in applying for a Project Grant under the Industrial Research and Development Grant Scheme. Pacific Copper Ltd has also been involved in the evaluation of the background tungsten values within silexite to provide a series of low grade, high tonnage open cuts. This evaluation has shown that the silexite geology is complex and that the tungsten grade varies considerably. Silexite is essentially a quartz-rich rock containing more than 5% topaz, ± mica, wolframite, native bismuth, bismuthinite and fluorite.

122

It occurs as subvertical dykes within granite and as irregular bodies both within and adjacent to the pendant. Silexite is commonly associated with microgranite or aplite intrusions and pegmatitic veining. It can be compared to a classical greisen rock mineralogically, however, many field relationships display intrusive characteristics which are inconsistent with a simple metasomatic origin. Silexite is divisible into two types based on textural and field relationships. They are a coarse, metasomatic silexite with an inhomogeneous, inequigranular texture, which is interpreted as a greisenized granite, and an intrusive silexite with a saccharoidal texture. The intrusive silexite is believed to be derived from partial melting of the earlier formed metasomatic silexite. Evidence for the metasomatic origin of silexite includes the appearance in both outcrop and microscopic scale of relict granite textures and also the occurence of rocks which fall between granite and silexite mineralogically and chemically. However, characteristics such as sharp contacts between granite and silexite structures and the brecciation of metasediment within silexite indicates remobilisation. Fluid inclusion work by Eadington and Nashar (1978) and phase studies of the system 1 'Granite - t^O-HF by Glyuk and Anifiligov (1973) indicate temperatures of 600 - 650° for silexite formation. This is consistent with partial melting of metasomatic silexite to yield intrusive silexite. Tungsten mineralisation is believed to be independent of silexite intrusion, occurring in discrete quartz-rich pegmatitic veining. Disseminated wolframite in intrusive silexite represents chemically remobilised tungsten. Larger irregular wolframite fragments are portions of pegmatitic veining that have been mechanically (physically) entrained in the partial melt. Miarolitic cavities also contain large tungsten crystals. Thus wolframite mineralisation and silexite formation are temporally related. Based on field relationships between silexite, microgranite, pegmatitic mineralisation and metasomatism, the following overlapping sequence of events can be recognised:1. Granite emplacement, cooling and formation of a carapace. 2. Alteration of outer granite carapace and formation of greisen and metasomatic silexite (greater than 5% topaz). 3. Tungsten mineralisation associated with alteration fluids introduced as veining. 4. Continuing alteration of the granite with development of alkali-rich fluids causes partial melting of silexite and dissolution of tungsten. 5. Intrusion of microgranites and fracturing of metasediment. 6. Intrusion into metasediment of partial melt together with mechanically and chemically remobilised tungsten. 7. Further pegmatitic veining within fractured silexite and metasediment. The identification of intrusive and metasomatic silexite at Torrington has significant implications for tungsten mineralisation. Intrusive silexite includes mechanically and chemically remobilised tungsten with the latter process imparting a more consistent background grade. Metasomatic silexite includes only the pegmatitic style of mineralisation and background grades are significantly lower. Topaz mineralisation within metasomatic silexite is far more erratic and generally poorer than grades within intrusive silexite.

References Eadington and Nashar, 1978, Contrib. Mineral. Petrol., 67 433-438. Glyuk and Anfiligov, 1973, Geochemistry International Vol 10 pp 321-325.

123

APPROACHES

TO CODES

FOR THE C A L C U L A T I O N RESOURCES

COAL

Anton Crouch1 and Owen Shiels 2 1 2

Consulting geologist, Sydney Joint Coal Board, Sydney

The fifth edition of a code for calculating and reporting coal resources and reserves has recently been ratified in NSW. The work on the preparation of the new edition was begun with the aim of producing a code that would be both broad enough in its statement of principles to cover the full range of areas that might be assessed (poorly explored sedimentary basins to individual mining blocks in an operating mine) and sufficiently rigorous in its definitions to require the reporting of any calculation to be accompanied by statements of confidence limits and all economically relevant coal parameters. It was found that such an approach produced a document of considerable length and complexity and, quite late in the day, it was decided to change the approach and concentrate on the more general concepts of resources and reserves and the setting of minimum guidelines. An axiom of the first approach was the restriction of the term "resource" to a known coal deposit in a specified area, the use of which is deemed possible at the time the assessment is being made. This restricted definition of "resource11 is in strong contrast to the general use of the term which almost always includes such sub-categories as "undiscovered" and "subeconomic". Using "resource" as a universal set, other categories such as reserves can be shown on a Venn diagram and it is a simple process to graphically illustrate the relationships of the categories to the level of detail of "measured reserve". Essential characteristics of this method are that the individual categories are not additive and that categories can be created for which no generally accepted names presently exist. A further characteristic, which attracted substantial comment, is a blurring of the traditional differences between "resources" and "reserves" and a tendency to define categories on the basis of a statistical assessment of confidence. The first approach also resulted in thle preparation of a "derivation of categories of resources diagram" which, beginning with "resource", showed the paths that could be followed to produce a saleable product from an operating mine. The flow diagram attempted to identify separately those junctions at which decisions could be made on the basis of adequacy of data or the availability of the coal for use. The second approach, which led to the production of the new edition of the code, concentrated on defining the difference between "resources" and "reserves" and setting minimum guidlines for the categorisation of resources. The principal difference between the present code and the previous (1980) one is the clear distinction between "resource" as a set of categories for in-place coal and "reserve" as a sub-set of "resource" for use in cases of planned mining. Other noteworthy aspects of the new code are a definition of "point of observation" which allows the use of data obtained from down-hole gepphysical logging and the retention of an "assumed" category of resources. Reference van Rensburg, W . C . J . , 1980, Classification of coal resources and reserves. Univ. of Texas at Austin, Mineral Resources Circular no. 65

124

MAGNKTOTELLURIC SOUNDINGS AND ANISOTROPY IN PROFILES OF THE LITHOSPHERE

ELECTRICAL

J.P. Cull Bureau of Mineral Resources, Canberra Electrical methods are frequently used to provide constraints for seismic and geochemical models of the deep lithosphere. DC soundings and magnetometer arrays can be used for similar purposes but the magnetotelluric technique appears to be more versatile at mantle depths. The resistivity data obtained are complementary to any rheological data obtained by seismic methods and significant boundaries may be revealed by either. However resistivity must be considered as a bulk response and fine detail is often obscured. Consequently individual layers of low resistivity are yet to be confirmed. In many respects the problem is analogous to the detection of a low velocity layer using seismic data. Zones of anomalous resistivity can be included in models which satisfy the observations but inversion statistics demonstrate the futility of imposing fine structure. The solution remains sensitive to the configuration adopted in the starting model. In particular gradual changes in resistivity are difficult to detect at all and discrete layers must be specified in terms of the resistivity/thickness product. Interpretations are normally based on starting models which include a layer of low resistivity at the base of the mantle. In many cases this layer is included in the expectation that semi conductor mechanisms become more efficient at high temperatures. This assumption can be challenged on geochemical grounds if silicate minerals are considered to be progressively depleted at the base of the crust. Layers of low resistivity are often included at shallower depths to accommodate the primary features of the apparent resistivity curve. However anisotropy is often detected in orthogonal components at the Earth's surface. Apparent resistivities obtained over sedimentary basins should be approximated by ID models but remote contacts can cause anisotropy. Estimates of resistivity obtained near Broken Hill are highly sensitive to orientation as a result of the Precambrian contact. Apart from structural contacts at the sounding site, anisotropy can be caused by highly foliated basements and further complications result from current channelling. Compensation is required for each perturbation before apparent resistivities can be asssigned at greater depths. An extensive literature search indicates that alternative solutions can be proposed for almost all models incorporating low resistivity layers at mantle depths.

125

VOLCANIC STRATIGRAPHY AND PALAEOGEOGRAPHT OF THE EDEN - COMERONG - YALWAL RIFT ZONE Kelsie Dadd School of Earth Sciences, Macquarie University The Middle to Late Devonian Comerong Volcanics form the central part of the Eden-Comerong-Yalwal "rift zone" (Mcllveen, 1975). The volcanic complex consists of a bimodal volcanic suite with intercalated lacustrine and fluvial sedimentary rocks and associated granitoids. The complex occupies two thin belts on the eastern and western limbs of the Budawang Synclinorium in the Lachlan Fold Belt, southeastern New South Wales. The internal stratigraphy of the volcanic complex varies both laterally and vertically and cannot be readily correlated across the synclinorium-. In the area of detailed study (Fig. 1) the complex has a maximum thickness of 1200 m and 750 m on the western and eastern limbs respectively. Basalt types in the study area include both quartz normative tholeiites and transitional basalts that plot in the alkali field or near the tholeiite/alkali boundary on many basalt discrimination diagrams. Their normative composition suggests they are olivine normative tholeiites. The quartz normative tholeiites have higher total Fe, Ti, V, Rb, Th, Y and Zr, and lower Al, Mg, Ni and Cr than the transitional basalts. Quartz normative tholeiites are.fine-grained, are porphyritic with a flow-aligned groundmass and are sparsely amygdaloidal. The transitional basalts are coarse-grained, generally non-porphyritic and are more commonly amygdaloidal. On the eastern limb of the synclinorium there are two main rhyolite units consisting predominantly of rhyolite lavas with minor lenticle and airfall tuffs. Quartz normative tholeiite with interbedded lacustrine sedimentary rocks separates the two units. The overlying rhyolite unit, which is up to 350 m thick, is the uppermost unit of the volcanic complex in the south. In the north, transitional basalt overlies the rhyolite and forms the top of the volcanic sequence. Conglomerates of the Merrimbula Group conformably overlie the volcanic complex on this limb. On the western limb the basal facies are, from south to north; rhyolite lavas, rhyolite lavas and ignimbrites, and fluvial sedimentary rocks. The facies are separated by northwest-southeast trending faults which may have a syndepositional component. Basalt dominates the rest of the sequence with only minor interbedded sedimentary rocks. Quartz normative tholeiite at the base of the sequence, crops out to the north of a major fault which may have formed a topographic barrier during deposition. The overlying transitional basalt which is up to 1 km thick, interfingers with red siltstone of the Merrimbula Group at the top of the section. The volcano-tectonic setting in which the Comerong Volcanics were deposited may have been a fault bounded rift zone, suggested by the tectonic setting of similar suites of rocks, for example, the Taupo Volcanic Zone in New Zealand and the Rio Grande Rift in the western U.S.A. However, these rift zones contain a more continuous bcsalt to rhyolite spectrum of volcanic rocks in contrast to the Comerong Volcanics within the study area in which there are no rocks of intermediate composition. All these rift zones however, have large rhyolitic centres and basaltic sheets. There are no clearly defined "rift-bounding" faults to the Eden-Comerong-Yalwal rift zone, but these may have been separated from the complex during deformation.

126

The presence of a poorly sorted epiclastic breccia composed of Ordovician metasedimentary clasts is consistent with syndepositional basement uplift and faulting. Abrupt facies changes and elongate units of lacustrine sedimentary rocks in the study area, were probably controlled by faults. The preserved section of the complex is significantly smaller in extent than comparable modern rift zones, however much of the complex may have been lost through erosion or be concealed by the Sydney Basin cover. References Mcllveen, G.R.,

1975, Rec. Geol. Surv. N.S.W., 16, 245-77.

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Figure 1. Location diagram for the area of detailed study and selected stratigraphic columns for the Comerong Volcanics.

127

GKOCHEMICAL PROFILE OF THE TOOLEBUC FORMATION AT JULIA 1

L.S. Dale , J.J. Fardy , J.H. Patterson 1

and A.R. Ramsden

CREEK

CSIRO Division of Energy Chemistry, Lucas Heights 2 CSIRO Division of Mineralogy, North Ryde

The Toolebuc Formation containing Cretaceous oil shales extends over much of the Eromanga Basin in northwestern Queensland and is a potentially important source of oil shale. At Julia Creek a large area of the Formation containing low-grade oil shale is accessible to mining. At the request of CSIRO a continuous stratigraphic drill core was provided for detailed examination of the lithology and geochemistry of the Formation. This was accomplished by carrying out whole rock major element analysis and trace element analysis using a variety of analytical techniques including neutron activation analysis and spark source mass spectrometry. Data for up to 75 elements in 0.5 metre segments of the drill core were obtained. This enabled elemental associations to be detemined using concentration-depth profiles and cluster analysis based on element correlations. X-ray diffraction studies were also used to identify the mineral phases present and scanning electron microprobe analysis was used to identify trace minerals and the mineralogical residence of selected trace elements of possible economic significance of environmental impact. The results augment an earlier petrographic examination of the Toolebuc Formation at Julia Creek carried out by Ramsden. The elemental abundance data shows that*above the underlying Ranmoor mudstone there is a transition zone into the oil shale environment. The top of the oil shale unit is marked by a distinct bed of fish debris and above this the upper part of the Toolebuc Formation comprises coquinite with minor interbedded oil shale overlain by the Allaru mudstone. The oil shale unit contains significant concentrations of vanadium, molybdenum, arsenic, selenium, thallium, antimony, uranium, cadmium, bromine, zinc, copper and nickel. Those elements exhibiting an organic association include vanadium, molybdenum, nickel and sulphur. Other elements are associated with various minerals including calcite, pyrite, chalcopyrite, sphalerite and mica-type clays. The Toolebuc Formation was deposited under marine conditions and the relatively high concentrations of some trace elements such as vanadium, molybdenum, arsenic, selenium and zinc arise from their biological association with marine algae. It will be shown that rare earth element distributions also reflect this marine origin. Reference Ramsden, A.R., 1983, J. Geol. Soc. Aust., 30, 17-23.

INSTRUMENTS IN GEMMOLOGY P.J. Darragh CSIRO Division of Mineralogy, Perth As the science of mineralogy developed during the 19th Century, jewellers, (the first gemmologists), began to realise that all yellow stones were not topaz. With their knowledge of mineralogy, a hand lens and considerable experience they were able to identify all the then known gem materials.

128

After the beginning of the 20th Century another problem emerged. In addition to identification of the mineral species, gemmologists had to determine whether a gem was natural or synthetic. To aid solution of these The hand held direct problems, instruments were developed or modif ied. reading spectroscope, the refTactometer, based on measurement of critical angle, and the dark field stereo microscope are significant examples. The use of these instruments has enabled the gemmologist to answer these questions with a very high degree of certainty. Recent developments in the electronic and laser industries have resulted in better methods of synthesing naturally occurring gems, and the production of a range of new materials not known from natural sources. These developments have necessitated the application of new instruments such as the thermal probe. Unless manufacturers are willing to build some identifying feature into these synthetics, gemmology will become increasingly difficult, as the manufacturing techniques improve. It may become necessary for the better equipped gem testing laboratories to have access to technology such as EMP, SEM, ESR, XRD, etc. The application of some of these more sophisticated instruments will be outlined.

THE GEOLOGY AND GEOCHEMISTRY OF AN EMERALD DEPOSIT AT WARDA WARRA NEAR YALGOO WESTERN AUSTRALIA P.J. Darragh and R.E.T. Hill CSIRO Division of Mineralogy, Perth The Warda Warra emerald deposit is one of several deposits in Western Australia characterized by a spatial association of granitic pegmatite and ultramafic rocks. This association is common to a world-wide class of beryl deposits significant in terms of the commercial production of beryl and emerald. At Warda Warra, a zone of deeply weathered phlogopite schist contains discontinuous stringers or veins of white quartz. Green sodic and chromiferous beryl occurs as small prismatic crystals within the fringe zones of the quartz veins and within the schist close to the quartz surface. Many of the beryls in the quartz have been replaced by triclinic potassium feldspar and clay minerals. The beryls are believed to have crystallised within the phlogopite schist, as a consequence of reactions between alkaline potassium-rich beryllium bearing hydrothermal fluids and ultramafic rock. Replacement of this beryl by feldspar and minor smectite clay occurred after the crystals were encompassed by pegmatitic quartz. This concomitant re-solution of beryl and precipitation of potash feldspar and montmorillonite was accomplished by reaction between beryl and new fluid undepleted in potassium and undersaturated in beryllium. Evidence exists to identify the dissolved beryllium species as an alkali-carbonate complex. Weathering has resulted in the formation of kaolinite from beryl, potash feldspar and montmorillonite.

129

EARLY MIOCENE OIL SHALES OF THE SDTTOR FORMATION, MT. COOLON DISTRICT, EASTERN CENTRAL QUEENSLAND P.B. d'Auvergne International Mining Corporation N.L., Sydney The Tertiary Suttor Formation outcrops extensively but irregularly throughout eastern Central Queensland. Oil shale horizons have been discovered within the Suttor Formation but are not known to outcrop. International Mining Corporation has been examining distribution of these oil shale horizons since 1980 and has delineated two significant accumulations in the vicinity of the Mt. Coolon township approximately 250 kilometres west of Mackay. The larger occurrence, known as the Bungobine Deposit, covers an area of approximately 30 square kilometres. The smaller Yacamunda Deposit covers several square kilometres and lies approximately 15 kilometres south of the Bungobine Deposit. The oil shales form part of a cyclic sequence in an Early Miocene lacustrine system. The Formation consists of blue-grey kaolinite alternating with brown algal rich and black lignite rich oil shales. Individual oil shale horizons vary in thickness from a few centimetres to several metres with the maximum oil shale development drilled to date occurring over 25 metres true thickness. Structural modification of the basin throughout deposition has strongly influenced distribution of the oil shales and has interfered with cyclic development within the deposits. Oil content is variable, with highest yeilds being realised from the brown algal rich shales. Modified Fischer Assay yields (air dried samples) vary up to 220 litres per tonne. Insufficient assay data is available at present to enable estimation of a reliable mean yield for the deposits. N.M.R., G.C., G.C.-M.S. and elemental analysis of the produced oils show the oil is comparatively low in sulphur, particularly low in nitrogen and high in oxygen. The oil is relatively aliphatic and appears suitable for the production of kerosene and diesel fractions. In comparison with other Australian oilshales the oil yield appears high but water content is also very high and very high organic carbon concentrations have been found in the chars after retorting. Exploration and evaluat ion oi the Mt. Coolon deposits is continuing and it is reasonably expected that continuity between the Bungobine and Yacamunda deposits will be discovered.

130

STEADY AND TRANSIENT THERMAL REGIMES OF LITHOSPHERE

CONTINENTAL

Geoffrey F. Davies Research School of Earth Sciences, ANU, Canberra The thermal evolution of continental lithosphere subsequent to an orogeny depends on or is related to a number of geodynamic factors, including erosion, sedimentation and the abundance, vertical distribution and decay of heat sources within the lithosphere. In the shorter term (tens of Myr), erosion has two effects: upper crustal radioactive heat sources are removed, and heat is advected towards the erosional surface. These effects enhance the decline of surface heat flow due to conductive cooling of crust presumed to have been heated during orogeny. In the medium term (hundreds of Myr), isostatic rebound accompanying erosional unloading will prolong the erosional effects. The evolution in the longer term will depend on whether or not the thickness of the continental lithosphere is determined by chemical differences or by purely thermal processes. In either case, some subsidence and sedimentation may follow the erosional phase, due to continued cooling of the deep lithosphere. If the lithosphere thickens by continued cooling, like oceanic lithosphere, then several kilometers of sedimentation are likely. On the other hand, if the continental lithosphere is chemically distinct, with a constant thickness and its base temperature held constant by mantle convection, this sedimentation may be minor or absent. The long term evolution may also be affected by two other processes. On the one hand, the steady decline of radioactivity will tend to let the lithosphere cool and subside more. It is also possible, on the other hand, that heat sources are continuously and slowly added to the continental lithosphere from the deeper mantle, which will tend to warm and raise the lithosphere. Quantitative modelling of some of these phenomena has been completed. If the lithosphere is chemically defined with a constant thickness, then in the long term the thermal regime will approach a steady state. The steady state geotherm will depend on the lithosphere thickness and the amount and distribution of radioactive heat sources within it. Heat sources are probably concentrated in the upper crust and account for about half of the surface heat flux (Sclater et al., 1980). However, low concentrations of heat sources in the lower crust and lithospheric mantle may contribute significantly to the balance of the surface heat flux. For given lithospheric thickness and surface heat flux, a range of geotherms differing by several hundred degrees in the lower lithosphere is possible, depending on the amount of internally generated heat. With a geotherm constrained by South African kimberlite xenoliths, the internal heat production can range from zero to about 0.1 pW/m (ten times chondritic; Davies and Strebeck, 1982). Some recent petrological and geochemical arguments have been made that such additions of heat sources to the continental lithosphere may in fact have occurred. Models of the short and medium term thermal evolution show that when erosional effects are enhanced and prolonged by regional isostatic rebound, significant effects on the surface heat flux can persist for over 100 Myr. For example, in a simple model it is assumed that erosion rate is proportional to elevation, which results in an erosional time constant of 25 Myr in the absence of rebound. With rebound, the time constant and the thickness of crust removed are both increased by a factor of about six. If 30 km of crust is ultimately removed, the heat flux enhancement due to upward advection exceeds 10 mW/m^ (0.25 hfu) for over 100 Myr.

131

Recognition of erosion effects may affect interpretations of heat source distributions and alpine metamorphism. Correlations between heat flux and heat production in some provinces have been used to constrain the depth extent and total amount of upper crustal heat sources (Roy et al. , 1968; Lachenbruch, 1968). Preliminary estimates (Woodhouse and Birch, 1980) suggest that unrecognised erosional effects will cause both the depth scale and total amount of upper crustal heat sources to be underestimated. England and Richardson (1980) have discussed implications for interpretation of alpine metamorphism, although the flexural strength of the lithosphere will need to be considered at short (100 km or less) horizontal length scales (Stephenson, 1984). Regional erosion may also help to explain the apparently longer timescale of heat flux decline in continental lithosphere compared with oceanic lithosphere. There is a tendency for heat flux to decrease with tectonic age (with the notable exception of Central Australia), approaching shield levels after 0.5-1.0 Gyr, a much longer time scale than for the simple cooling of oceanic lithosphere in about 70 Myr. The prolonged enhancement of heat flux due to erosion and rebound described above goes some way to accounting for this apparent correlation. References Davies, G.F. & Strebeck, J.W., 1982, Geophys. J.R.A.S., 69, 623. England, P.C. & Richardson, S.W., 1980, Geophys. J.R.A.S., _62^, 421. Lachenbruch, A.H., 1968, J. Geophys. Res., 73, 6977. Roy, R.F., Blackwell, D.D. & Birch, F., 1968, Earth Planet. Sci. Lett., _5, 1. Sclater, J.G., Jaupart, C. & Galson, D., 1980, Rev. Geophys. Space Phys., 18, 269. Stephenson, R., 1984, Geophys. J.R.A.S., in press. Woodhouse, J.H. & Birch, F., 1980, J. Geophys. Res., 85, 2691.

WAS THE IMPERIAL GEOPHYSICAL EXPERIMENTAL SURVEY REALLY

(1928-1931)

NECESSARY?

Alan A. Day Department of Geology and Geophysics, University of Sydney Necessity, like beauty, is a perception. Like beauty it can be embellished in an attempt to achieve desired ends. This paper attempts to assess the differing degrees of necessity for an TGES as perceived by mining men, geologists and politicians. It also tries to assess the degree of need in relation to the rapidly changing scene of geophysical development; secrecy, independent publication and charlatanism in the late 1920s. The paper is not an attack on the integrity or skill of the participants in the IGES, but is rather a small attempt to commemorate them and their work.

132

GEOCHEMICAL CONSTRAINTS ON THE EVOLUTION OF MAGMAS AND MANTLE SOURCES BENEATH SOUTHEASTERN AUSTRALIA - EVIDENCE FROM VICTORIAN TERTIARY LAVA FIELDS R.A. Day Geology Department, Auckland University, Auckland

In Victoria, episodic volcanic activity of olivine melilitite to quartz tholeiite type spans 95-15 Ma in 14 discrete lava fields (provinces) 10-50 km across, and of 20-2 Ma duration. At least 6 provinces become more alkaline towards the end of their activity. On a regional scale there is no correlation of basalt type with age or geographic position. Each province represents a suite of oogenetic magmas produced by a separate melting event in the upper mantle. On the basis of high Mg - values (>68) and Ni 270-430 ppm, most lavas represent essentially unfractionated magma batches. Few have Mg-values <55. Abundant mantle xenoliths in alkaline rocks, including fractionated members, implies direct passage through the crust. Highly incompatible element ratios remain constant within each province but vary between provinces. A pyrolite mantle composition has been used as the basis of partial melting models in an extension of the approach used by Frey et al. (1978), using major elements alone to determine the degree of melting. Calculated % melting ranges from 1.8-24%. Without exception decreasing La, Nb, U and Th in unfractionated lavas corresponds to an increase in calculated % melting for each member within a suite. La/Yb variation in lavas and calculated residue mineralogy indicates that garnet ceases to be a residue phase between 10-13% melting. Melting models using REE and incompatible elements yield uniformly enriched sources for very different magma types within single provinces (e.g. Fig. 1). However there is distinct source variation between provinces, with La=15.2-5.8 CN and Yb=2.1-1.8 C N , and a similar degree of variability for other elements. Melting systematics indicate that apatite is not present in the source, and all P can be accommodated in garnet and pyroxene. Source P ranges from 0.03-0.07%. Also, Ti, Nb and Zr indicate that neither ilmenite nor zircon are present in the source. However comparison of model source K/Rb for Victorian basalts with estimates for the mantle, and measured values for mantle micas and amphiboles, indicates that phlogpite is the most important K-bearing accessory mineral. K, Rb and Cs behaviour shows that phlogopite may persist for up to 10% melting. Source phlogopite ranges from 0.6-1.7%. Sr behaviour in an olivine melilitite and nephelinite indicates ^1% ?dolomite at <2% melting in some sources. A diapiric model can be used to explain the pattern of short lived lava fields, each with a different uniformly enriched source. A simple numerical approach can be used to describe source enrichment by collection of incipient melt in a rising body of pyrolitic mantle. The extent of enrichment depends on diapir volume/surface area and distance travelled through the LVZ. Model Victorian sources indicate that addition of 2-12 times the volume of a 0.1-1% LVZ melt to a diapir head can generate the observed range of enriched source compositions from near chondritic (REE 2 - 5 ^ ) or even slightly depleted MORB-like sources, and close to primordial u - 2 times) abundances of most incompatible elements. Calculated LVZ melts have nephelinite trace element chemistry. Production of alkaline magmas from chondritic or depleted MORB-like sources is in agreement with some isotopic studies elsewhere. 133

METALLOGENY AND TECTONIC DEVELOPMENT OF THE TASMAN FOLD BELT SYSTEM IN NEW SOUTH WALES P. Degeling1, L.B. Gilligan2, E. Scheibner2 and D.W. Suppel2 ^Mineral Management and Securities Pty Ltd, Sydney Geological Survey of NSW, Department of Mineral Resources, Sydney Orogenic volcanics, intrusives, sedimentary facies, and assemblages of mineral deposits in the Tasman Fold Belt System (the Tasmanides) are interpreted as a record of processes operating during Phanerozoic time after an active plate margin developed along Eastern Gondwanaland in response to its interaction and convergence with the palaeo-Pacific oceanic plate.

134

A well developed west-Pacific type active continental plate margin existed in eastern Australia by earliest Cambrian time. Hence continental break-up and sea-floor spreading coupled with separation and dispersal of micro-continents, and possibly some plate convergence must have occurred during Precambrian time. Precambrian complexes resulting from these processes now constitute the basement of and internal massifs within the Tasmanides. The dispersed Precambrian micro-continental blocks became cores of separate tectonostratigraphic terranes. Collisional movement of these Precambr ian basement blocks (micro—continents) and changes in the style of subduction can explain episodes of orogeny, representing episodes of terrane accretion, which punctuated the tectonic development of the Tasmanides. The episodes of terrane accretion were followed by, or sometimes overlapped episodes of terrane dispersion. Episodes of terrane dispersion were an integral part of the episodic rearrangement of the active plate margin. Each such episode was characterised by the creation of extensional features (volcanic rifts, marginal, inter-arc and other types of basins) and subsequent closure and their inversion. Metallogenesis in the Tasmanides was linked to volcanism and plutonism during the various episodes of terrane accretion and dispersion. The principal igneous metallogenic associations are summarized in Figure 1 and accompanying Table 1. Table Is

List of metal associations & typical localities Mo,(Bi,W); Cu,Pb,Ag,Zn; Au - Bega Batholith

Cu - Grassmere

Cu - Wertago

Mo,Bi - ? Whipstick

Sn,W - Ardlethan-Tallebung

Au - Eden-Yalwal

Sn - ? Ardlethan

Mo,Cu,W,(Sn); Pb,Ag - Bathurst Granite

Pb,Ag,Zn; Mo-W-Bi; Sn-Ta - Holbrook, Walwa

Au - Mount Dromedary

Cu,Pb,Zn»Au - Bobadah, Canbelego, Mt Hope, ? Cobar

(Au,Sn) - Tumbarumba

Cu,Mn - Woolomin Formation

Sb,Au,Ag,As; (Sn) - Rockvale-Hillgrove? Watsons Creek Cr - Great Serpentinite Belt, Gordonbrook

Cu - (?) Girilambone

Cu,Mn - Hoskins Formation, ? Jindalee Beds

Sn,W,As,Ag - Mole Granite, Tingha

(Au; W,Sn) - Young Granodiorite

Mo,W,Bi; Au,Sb,Ag,As - Attunga, Kingsgate; Tilbuster

Ag,Zn,Pb,Cu, (Au) - Halls Peak

Au,Ag - Drake

Au,Sb - Poverty Point, Solferino

Au,Pt - Temora, Fifield

Cu, Au - Porkoa, Molong Rise

Cu,Au - Goonumbla, Cargo

Cr - Coolac

W,Mo,Bi(Sn); Cu,Fe - Rye Park; Broula

Cu,Pb,Zn,(Au) - Captains Flat, Woodlawn

Sn,Mo,Sb,As - Carrai, Gundle

Mo,As,Au,Sb,Ag - Valla

135

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CONCEPTION, DEVELOPMENT AND RESULTS OF GOLD EXPLORATION IN JASPILITE AND RELATED ROCKS NEAR CLONCURRY N.W. QUEENSLAND

G.M. Derrick G.M. Derrick & Associates, Brisbane Precious metal deposits associated with the various facies of iron formation (sulphide, carbonate, oxide) are relatively abundant worldwide, especially in Archaean greenstone terrains of Canada, Brazil, India, Western Australia and Rhodesia. They are less common in mainly oxide-facies Proterozoic iron formation, but recent gold discoveries by Amoco in mid-Proterozoic ironstones near Selwyn, N.W. Queensland has stimulated exploration for this class of deposit elsewhere in the region. Stratigraphic analysis suggests that Kuridala Formation host rocks to the Stara prospect at Selwyn are a possible lateral facies equivalent to the Answer Slate, which in turn is traceable northwards into parts of the Overhang Jaspilite; the latter contains flaggy sequences of grey chert and jasper, ironstone, siltstone, limestone, magnetite and hematite-bearing BIF. Regional occurrences of gold within this unit at Top Camp and Butcher Creek, together with abundant barite, manganese and tourmaline, suggest that it may be a favourable locus for syngenetic, exhaliterelated gold, possibly of the Homestake (USA) type. An abundance of ferruginous and siliceous breccias, and extensive silicification of limestone and calcareous units invite analogies also with the Nevadan gold-bearing sequences at, for example, Carlin, Cortez and Pinson mines in the U.S.A. Based on these concepts, areas near Cloncurry of extensive cross-folding, faulting, decalcification, and silicification were selected for detailed exploration, especially in areas of relatively high heat flow near younger, high-level granite intrusions. A programme of geological mapping and rock chip geochemistry established that some ironstones are mildly anomalous (to 155 ppb), that hematite-silica breccias are only weakly anomalous in copper and gold, and that barite-bearing Fe-Si breccias locally show some Zn-As-Cu-Au enrichment to (660 ppb Au). Silica flooding of various rock types (carbonates, breccias) is a dilutant of metal values, and is ascribed to lateritic, not hydrothermal processes. Stream sediment geochemistry of the +80 mesh fraction revealed abundant gold in some areas, not found in -80 mesh samples. Source of this gold could be local copper-mineralised quartz veins which invariably contain about 1 ppm Au, or possibly fine-grained sublabile clastics which contain abundant oxidised pyrite casts. Although the original jasperoidal gold search concept has foundered, recognition of goid in the coarse fraction of stream sediments led to expansion of target areas into previously unrecognised alluvial deposits, and stratiform pyritic sediments. These, together with ferruginous siliceous breccias, remain untested below the surface weathering profile.

137

INTERPRETATION

OF RADIUM ISOTOPIC RATIOS IN GROUNDWATERS B.L. Dickson

CSIRO Division of Mineral Physics, Sydney Radium is mobile in many groundwaters and is often transported to, and accumulates around, the margins of swamps and salt lakes. Studies on the radium isotopic composition of groundwaters has led to a proposal of methods for determining the nature of the source of radium in these accumulations (Dickson et al., 1983; Giblin and Dickson, 1984). This paper describes an evaluation of the ratio of the two longest-lived radium isotopes, 2 2 6 Ra (daughter of 2 3 8 U , t ^ o = 1 6 0 0 years) and 2 2 8 R a (daughter of 2 ^ T h , ^1/2 = 5*75 years) as an indicator of the Th/U ratio of source rocks. Groundwater samples from two areas of weathered granite have been collected and analysed, and comparisons have been made with radium concentration of the granites. The two study areas are (1) near Tennant Creek, NT, which has a low rainfall and (2) near Northam, WA, in a higher rainfall zone. Groundwaters from both areas were saline, with total dissolved solids ranging from 10 to 30 g/1* Sodium chloride was the predominate dissolved salt. Granite samples from area (1) were obtained as drillchips from depths similar to those at which the water samples were collected. The granite samples averaged 25 ppm U and 60 ppm Th and had a mean Th/U activity ratio of 1.04. Groundwaters contained an average 30 pCi/l 22 ^Ra and 60 pCi/l 2 2 8 R a with a mean 2 2 6 Ra/ 2 2 8 Ra activity ratio (described henceforth as RAR) of 2.8. The Th/U activity ratio in a sample is equivalent to the activity ratio of their daughter radium isotopes ( 2 2 8 R a / 2 2 6 R a ) provided radiometric equilibirum is established in both decay series. Consequently the groundwater RAR is nearly three times greater than that of the source rocks. In area (2) samples of surface outcrops of granite, seepage and artesian waters were collected. The saline groundwaters in this area result from the clearing of land for agricultural use. The granite outcrops have around 6 ppm U and 30 ppm Th with an average Th/U activity ratio of 1.5. These samples are assumed to represent the underlying granite. The water samples contained between 30 and 300 pCi/l 2 2 6 R a and between 120 and 950 pCi/l 2 2 8 Ra. The RAR ranged from 2.4 to 8.1. As in the case of area (1), the groundwater RAR is higher than that of the presumed source rocks. The level of radium in area (2) waters is considerably greater than in the groundwaters from area (1) despite the much lower uranium and thorium concentrations in the area (2) granite. This may be due to the more rapid weathering occurring in area (2) or to the acidity of the groundwaters which ranged as low as pH 2.8 (Mann, 1984). Laboratory studies were made on crushed uraninite-allanite ore samples to determine the effect of saline solutions on the leaching rate of 22 ^Ra 228 and Ra, and to determine if the decay rate of the isotope influenced the transfer to solution. The results showed that rapid cation exchange is the dominant mechanism for transfer of radium into solution and that 22 °Ra and Ra are proportionately removed into solution from the ore, despite the two parent isotopes being in different minerals. The addition of sulphate to the leaching solution depressed equally the exchange of 2 2 6 R a 228 and Ra.

138

Laboratory studies indicate that radium in solution comes primarily from recently-contacted aquifer rocks. Further, even if a water is of considerable age, the decay of a short-lived isotope is replaced by further exchange, i.e. the activity ratio of a short and long-lived isotope remains constant with time. Rapid flow or transport of precursor isotopes causes variations from this model, but in the case of 2 2 6 R a and 22^®Ra their respective parents ( 2 3 0 T h and 2 3 2 Th), have long half-lives and are relatively immobile in most groundwaters. From this model, a static groundwater should have a RAR reflecting the Th/U ratio of aquifer rocks. The field results show groundwater RAR values are usually greater, suggesting that the aquifer pathways in the granites have higher Th/U ratios than the bulk rock. Such a situation in a granite could result from weathering. Both granites studied have been subjected to weathering which removes the more 22 soluble uranium (and its ^Ra) leaving the less soluble thorium adsorbed to weathering products. The groundwaters of both areas have high dissolved uranium, up to 16 mg/1 in area (1) (A.M. Giblin, pers. coram.) and 0.1 mg/1 in area (2). The result of such a process over a long time is the enrichment of thorium relative to uranium in weathering products such as the bauxites, which in WA can have Th/U ratios of up to 20 (B.L. Dickson, unpubl. data). The 22 ®Ra from this adsorbed thorium is ideally placed for cation exchange and the RAR of the groundwaters will consequently be higher than expected. In conclusion, groundwater RAR is an approximate indicator of the Th/U ratio of the source rocksr and unusually high or low values of RAR in a groundwater may indicate high concentrations of thorium and uranium in aquifer rocks. References Dickson, B.L., Meakins, R.L., and Bland, C.J., 1983, J. Geochem. Explor., 19, 195-205. Giblin, A.M., and Dickson, B.L., 1983, in Abstracts for Conference on Geochemical Exploration in Arid and Deeply Weathered Environments, Assoc. Explor. Geochem., Perth, WA. Mann, A.W., 1984, Econ. Geol., 79_, 38-49.

CAN THE WIDESPREAD G A M M A - R A Y ANOMALY OF THE TOOLEBUC FORMATION BE USED TO DETERMINE ITS OIL YIELD POTENTIAL? 1 o B.L. Dickson1 and A.R. Ramsden "'"CSIRO Division of Mineral Physics, North Ryde ^CSIRO Division of Mineralogy, North Ryde The Toolebuc Formation, host to a large resource of oil shale, has a prominent anomaly in wire-line gamma-ray logs. In a previous study, Ramsden et al. (1982) found that the gamma-ray anomaly is due to uranium in the shale which may be correlated with its oil yield. This investigation extends the area covered previously to determine whether the uranium content of the shale provides information both as to the stratigraphic distribution of oil shale in the area and its likely oil yield.

139

Chemical and radiometric analyses were made on core samples from 15 drill-holes intersecting the Toolebuc Formation in the Julia Creek area of the Eromanga Basin, N.W. Queensland. The drill holes were located east (5 holes), south (6 holes) and west (4 holes) of the anticlinal St. Elmo structure which trends NW-SE across the study area where the Toolebuc Formation is exposed at the surface. To the east and south of this structure, interbedding of marine oil shale and coquinite indicates that this area experienced alternating periods of reducing and oxidizing conditions. The thickest sections of oil shale in the Toolebuc Formation occur west of the St. Elmo Structure. Here the oil shale underlies the coquinite and is separated from it by a well-defined 1-cm thick condensed fish-scale bed. The oil shale is believed to have been deposited in a deep marine environment as this area subsided relatively quickly along a hinge zone represented by the St. Elmo structure. The concentrations of uranium, organic carbon and phosphorus in the samples from both sides of the structure are similar but, whereas samples from east and south show good correlations between uranium and organic carbon (Table 1), those from the west do not correlate. Samples from all areas show some correlation between U and P. The linear relationships Table Is

Correlation coefficients between uranium (U), organic carbon (C) and phosphorus (P2O5) i n shale and coquinite samples.

Area

No. of samples

East South West

85 35 62

U vs C

0.77 0.84 0.32

U vs P2O5

C vs P 2 0 5

0.47 0.67 0.51

0.09 0.44 -0.37

between organic carbon and uranium in the area of mixed coquinite-shale may be used to obtain estimates of in-situ oil yields from wire-line gamma-ray results. Examination of the laboratory gamma-ray spectrometricanalyses for K, U and Th shows that conventional total-count gamma-ray logs are adequate for this purpose and no advantage would be obtained by using down-hole gamma-ray spectrometry. Lack of correlation between uranium and organic carbon in the western area indicates that the use of gamma-ray logging for estimating the oil yield of the shale in that area is not viable. However in all areas density logging could be used to measure the organic carbon in both shale and coquinite. The different U/organic C relationships found in the area west of the St. Elmo Structure and to the east and south probably relate to differences in depositional conditions rather than to subsequent alteration processes. It is suggested that uranium is removed by organic matter from sea water and transported into the oil shale through accumulation of the biomass. The thickest oil shale sections have, on average, 14±2 wt% organic carbon and 31±10 ppm U. Around 0.5% phosphate is present in the shale but appears not to introduce U into the shale. Electron microprobe analyses indicate that later reworking can remobilize U from the decomposing organic matter into the phosphatic fish remains. In coquinite, where all the organic matter is decomposed, the only remaining U is in phosphates and anc consequently P2O5 * U are correlated. The equation U = (100-x)(0.50P - 0.18) + x(31±10)/l4±2)

140

where x is the wt % organic carbon and P is the wt % P205> accounts for 70% of the variance in the full data set. An apparent correlation between uranium and organic carbon will be obtained in samples with a uniform phosphate content, as is found in the east and south of the study area. Consequently, the gamma-ray log cannot be considered as a good indicator of oil potential of the Julia Creek shale but, combined with a density log, could be used to locate phosphate beds! References Ramsden, A.R. Dickson, B.L., & Meakins, R.L. , 1982. 29, 285-296.

J. Geol. Soc. Aust.,

THE IMPACT OF THE NATURAL ENVIRONMENT ON HUMAN HEALTH IN SRI LANKA C.B. Dissanayake Department of Geology, University of Peradeniya, Sri Lanka The vast majority of the people in Sri Lanka literally live close to the soil. Only 15-25% of the people have access to safe water and less than 10% have access to piped water. The rest of the population depends directly on the groundwater for their drinking water supplies. In most cases, particularly in villages, open dug wells are the main source of drinking water for a large number of families. This fact in itself makes one believe that the chemical composition of the groundwater must necessarily affect the general health of the community. In a long-term project being carried out by the author certain interesting correlations between the chemical compositions of groundwater and certain diseases in Sri Lanka were observed. 1.

The prevalence of heart diseases in areas containing 'soft' water and the very low incidence of heart diseases in areas of 'hard1 water. The presence of excess nitrates in drinking water supply in areas of high population density, high use of fertilizer and in general in the wet zone of Sri Lanka. The abundance of fluoride in the groundwater of areas of mineralization and in the dry zone of Sri Lanka. Fluorosis is very common in these areas and dental caries are common in the regions containing low fluoride groundwater.

Studies concerning the incidence of cancer and cardiovascular diseases in relation to geographical factors encounter serious limitations owing to the large number of factors generally involved in such studies. As in the case of similar studies in other countries, the incidenc of cardiovascular diseases in Sri Lanka in relation to water hardness rests heavily upon correlation and a distinct causal relationship cannot be established. Detailed studies of many workers researching on the geochemistry of water in relation to cardiovascular diseases have shown that even through the relation is clearly equivocal, further studies are needed.

141

An Island-wide survey of the nitrate levels in the potable waters of Sri Lanka reveal that in general, the nitrate levels in the drinking water supplies are below the danger limits specified by W.H.O. The Jaffna peninsula however, represents a very special case and this region contains the highest nitrate levels (in some instances as much as 300 mg/1) observed in Sri Lanka. The large usage of nitrogeneous fertilizers such as urea, improper siting of septic tanks, the shallow water table and the presence of highly fractured limestone as an aquifer are the chief reasons for this observed abundance. The distribution of fluoride in the groundwater of Sri Lanka is geologically controlled. The highest fluoride areas are found to coincide with a mineralised belt running across the country from north to south. The impact of the natural environment on the health of the population is very clearly illustrated in this case. References Dissanayake, C.B., 1979, The Sci. Tot. Env., L3, 47-53 Dissanayake, C.B., Senaratne, A & Weerasooriya, S.V.R. 1982, Intern, J. Env. Studies. , J_9, 195-203

THE P R O B A B L E E N V I R O N M E N T A L I M P L I C A T I O N S OF THE R I V E R T R A N S F E R IN SRI L A N K A C.B. Dissanayake

and S.N. Wickremaratne

INTER-BASIN

^"Department of Geology, University of Peradeniya, Peradeniya ^Department of Geography, University of Peradeniya, Peradeniya As in most developing countries, in post-Colonial Sri Lanka too, multipurpose river development schemes have been considered pivotal in development planning, the most recent being the Mahaweli Diversion Scheme which is one of the largest river development projects in the South Asian Region0 Sri Lanka's longest river, the 206 mile long Mahaweli, which originates in the 'wet zone* of the country, covers about 1/6 of the island's land area* The probable adverse effects of this inter^basin river transfer may be broadly categorised as : 1. Hydro-geological problems 2. Deforestation 3 0 Accelerated soil erosion 4 0 Impact on wildlife 5 e Spread of diseases 6 0 Eutrophication 7« Ecosystem imbalance The development area includes some tectonic interfaces, relative movement of which may rupture the structures as has been speculated by geologistso Also, damming, especially in the 'hill country' can promote mass movement0 Diversion of the main river having a limited discharge may deprive the downstream area of large amounts of water which can disrupt hydrological equilibrium in the lower reaches0 Although it has not been proved that deforestation reduces the amount of precipitation, deforestation leads to depletion of water resources plus destruction of floristic balance, etc0

142

Accelerated soil erosion can result in low primary productivity in these areas and also, can cause premature silting of reservoirs« Even at present, soil erosion is a problem particularly in the upper Mahaweli catchment areae Also, the impact of this river transfer on wildlife can be detrimental, since habitat destruction and alteration are inevitable, which demands sound mitigation measures0 Partially stagnant water behind impoundments is a good breeding ground for the vector Anopheles causing Malaria, a resurgence of which has been recently observed in Sri Lanka0 Increased use of fertilizers and other agrochemicals supported by year-round water (as opposed to drying out of water in the dry season) in small tanks (reservoirs) in the fdry zone1 may promote growth of water weeds such as Eichornia cressipes, leading to eutrophication. The Mahaweli Basin can be looked upon as a subtle ecosystem0 The riparian 'villu* grasslands in the backswamps of lower Mahaweli flood plain have established rice cultivation and dairy farming together with limited freshwater fishery. Under the natural conditions, annual floods replenishes nutrients in these systems, but when the frequency and magnitude of floods are reduced after the scheme is completed, the villu ecology can be affected0 The ocean fishery in the Trincomalee Harbour area, where the river empties into the sea, is dependent for its food chains on the detritus brought down by the river0 Thus, damming of the river can possibly affect fish harvest as it happened in the Nile Delta area since dams can retain most of the organic debris0

VELOCITY VARIATIONS AND ISOSTATIC COMPENSATION AUSTRALIAN REGION

IN THE

J.C. Dooley Bureau of Mineral Resources, Canberra The observation that topmost mantle velocities vary from place to place is virtually proof that isostasy cannot be complete at the base of the crust. Variations in seismic velocity may be associated with changes in temperature, composition, and/or phase of the rocks forming the mantle. Any of these are normally accompanied by changes in density, and it would be remarkable if just the right combination of properties were to produce the observed variations everywhere without any changes in density. Complete isostasy at a specified depth or rock-type boundary implies that there exists a substratum of uniform density; otherwise variations in the density of the substratum would give rise to further isostatic imbalance needing compensation at a greater depth. Thus, although the relatively small amplitude of free-air gravity anomalies shows that a large degree of isostatic compensation occurs at the base of the crust, the variations in Pn velocity imply that isostasy can be complete only at some greater depth.

143

In a previous investigation, densities of crustal layers were inferred from seismic refraction velocities in Australia and surrounding marine areas. Using the thickensses of the layers, a crustal mass was calculated at the site of each refraction survey; a correction was applied for elevation. The crustal mass was compared with the mass of a column of mantle material of a selected standard density of 3.32 t / m t h e difference was named the "crustal mass deficiency" (CMD). The range of CMD values required that there should be compensating mass variations in the upper mantle. Subcrustal densities inferred from Pn velocities did not in general give the required compensation; however intra-mantle refractors at depths of 60 to 100 km in some areas suggested density differences which could lead to compensation at a depth of about 130 km. The Yilgarn Block in Western Australia remained anomalous, with a heavy crust underlain by mantle material with a high velocity. Since the previous study, many new deep seismic projects have been carried out. The present reassessment of the CMD includes data from the Lachlan fold Belt, the Pilbara-Hamersley region, the McArthur basin, and the Central Eromanga basin; also, revised models are available for many of the areas used previously. Many of these data were used by Wellman in a recent study of the relation between altitude and isostasy; he also concluded that subcrustal density variations were needed for complete compensation. Preliminary data from a recent refraction survey (Drummond, pers. comm.) show that the Yilgarn Block is not as anomalous as was thought, but nevertheless the Yilgarn and Pilbara Blocks (both Archaean) have low CMD values, and also high Pn velocities which suggest a relatively high-density upper mantle instead of the low density needed for compensation of the heavy crust. Birch has shown that velocity-density relations may differ for rocks of different composition. The relation used here corresponds to rocks of mean atomic weight about 21.5. It is probable that the rocks under Archaean shield areas have been depleted of the iron-rich component with low melting point, leaving a refractory residue of dunite or peridotite with lower mean atomic weight; such rocks would have a lower density for a given seismic velocity. However, even allowing for this, it seems that isostatic compensation cannot be attained completely until a depth of about 150 km, implying significant strength of the rocks to this depth.

144

ANALOGUE MODELLING OF THE ELECTROMAGNETIC RESPONSE OF TASMANIA AND SOUTHERN AUSTRALIA - PRELIMINARY RESULTS H.W. Dosso1, W.D. Parkinson2, and W. Nienaber1 ^"Physics Department, University of Victoria, Victoria, B.C. Canada Geology Department, University of Tasmania, Hobart Laboratory analogue model measurements, to be used to aid in the interpretation of electromagnetic soundings in fieldwork, are carried out for a model of the region including Tasmania, Bass Strait with its highly conductive deep sedimentary basins, and the south coast of Australia. The excitation source field modelled here is that of the naturally occurring geomagnetic variations (periods of min-hrs) originating with the large scale ionospheric currents. Results for an approximately uniform horizontal source field with its electric field component in the N-S direction, E polarization, and in the E-W direction, H polarization, for traverses over the modelled region are presented. Three-dimensional plots and field contour diagrams of the model electric and magnetic field components over a large number of closely spaced traverses, show large anomalies on the east and west coasts of Tasmania, with smaller anomalies in the Bass Strait region. Results for a range of model frequencies, simluating the period range of 5 min to 2 hr, show that the sharp vertical field gradient over Tasmania at short periods is highly frequency dependent, becoming almost undetectable at periods greater than 2 hrs for E polarization, but of substantial magnitude even at 2 hrs for H polarization. At these long periods, both the analogue model and field station induction arrows, point primarily southward, designating the ocean as the major electrically conducting anomaly. At shorter periods, discrepancies between the model and field station results should be useful in mapping certain geological boundaries.

THE ORIGIN OF QUARTZO-FELDSPATHIC SEGREGATIONS IN SEMI—PELITIC HOST ROCKS, BROKEN HILL, N.S.W. J.M.T. Downes and V.J. Wall Dept. of Earth Sciences, Monash University, Clayton, Vic Quartzo-feldspathic segregations are widespread in many high grade (upper amphibolite-granulite facies) metamorphic rocks. The origin and emplacement of these bodies has long been debated with hypotheses ranging from solid state differentiation or metasomatism to in-situ partial melting and injection of of more distally derived melt. In this paper we present structural, textural, bulk rock and mineral chemistry data for segregations in psammo-pelitic litholigies exposed in the granulite facies terrain around Broken Hill, N.S.W. These data are utilised to clarify the evolution of the segregations and the implications for the metamorphic conditions and processes involved. 1. The segregations are composed of K-feldspar(Or 60-90) - quartz - minor Plagioclase(An45-55) +/- garnet - biotite - cordierite sillimanite : assemblages similar to those developed at peak grade in their psammo-pelitic hosts.

145

2. The modal character of the segregations approximate that of eutectoid compositions in the K-feldspar - quartz system at moderate water pressures. Relative to this composition, segregations are frequently enriched in K-feldspar, garnet (up to 30% volume), biotite and sillimanite which results in 6-8 wt % normative corundum appearing in bulk chemical analysis. This deviation from the expected eutectoid composition is greatest in the smaller veins, which are characterised by similar Fe/Mg ratios to its host. This suggests a degree of equilibration with its surroundings, as larger pegmatites of similar mineralogy are Fe enriched. 3. Analysis of mineral phases within the segregations exhibits the following features: K-feldspars (0r60-90) co-exist with intermediate composition plagioclase (An45-55) which indicate a wide range of temperatures, but averages at 650 + 50 C (Stormer. 1975). Both phases are chemically and optically unzoned. Garnets are weakly zoned with Mg rich rims (core Aim 82% - Pyr 13%, rims 79% Aim - 16% Pyr). Fe-Mg exchange thermometry on garnet-biotite pairs within the segregation consistently give temperatures of 650+/- 50°C (Ferry and Spear,1978), some 50-70°C lower than temperature estimates by the same thermometer in the host rocks. 4. The segregations are coarser grained (av. grain size 2-3 cm) than their gneissic hosts(0.5-1.0 cm.av. grain size), and exhibit non-granoblastic textures, are non to weakly foliated, and, other than retrograde features, lack evidence of solid state deformation. The larger segregations are texturally gradational to syn metamorphic pegmatites. 5. Both the pegmatites and segregations occupy a range of structurally controlled sites similar to those of veins in lower grade metamorphic rocks. Commonly parallel.to layering and the S^ (or composite S ^/ S 2 high grade foliations) gneissosity, the segregations are also developed in the axial surface of F^ folds, thickening in F^ fold hinges and occur axial planar to rare mesoscopic F^ folds. These geometries clearly illustrate the mobilisate character of the segregations and their developement during high grade deformation. Their emplacement in dilatant zones may be related to tensile fracture at high fluid pressure (akin to hydrofracturing at lower metamorphic grades) with a strong influence of host rock anistropy on fracture orientation. The granitoid texture of the segregations, their lack of internal solid state deformation and their compositions are consonant with their partially molten character during high grade metamorphism Small (less than 10cm width) segregations often depart from an ideal eutectic -Kfspar composition. Segregation compositions are so strongly enriched in K-fspar, garnet etc., that they could not exist as 100% melts at the temperatures envisaged. This composition anomaly is attributed to mechanical inclusion of host material during the process of melt separation (filter pressing) from its source, and also diffusive exchange of the melt with its surroundings. Recent experimental data for the melting of feldspar-quartz-H O-CO systems (Bohlen et.al., 1982,1983) combined with Burnhams (1979) models2for hydrous melt thermodynamics provide a quantitative P-T-X -a grid upon which estimates of intensive parameters in the Kfspar- Q?z system are based. Melting by Kfspar-qtz-H20 breakdown will lower water activity. At the estimated 5Kb and 750-800°C and using the calibration of this reaction by Bohlen et.al., 1983, melting effectively constrains water activities to 0.75 - 0.5 with an X (melt) of 0.75 - 0.6. This indicates melt water contents of 7.5-9.0 w€%; Melting by the vapour absent biotite breakdown reaction:

146

(1) Biotite + Sillimanite + Quartz = K-fspar + Garnet + Melt is also likely at these conditions(Clemens & Wall, 1981). At 5Kb and 750°C, biotite (Phlog.40) will break down by this reaction to produce a melt with 6 wt% water (Clemens, 1981) and buffer the water activity at 0.15-0.3. These constraints on the H20 content of the melt allow a mass balance estimate of the 'water budget1 during peak metamorphism. Hydrate breakdown provides sufficient water by dehydration melting mechanisms to create the observed volume of melt, supporting a model of an internally buffered system. The isobaric cooling path suggests crystallisation at about 680-700°C. The H^O dissolved in the melt will then be released and this influx of fluid will cause retrogression at high grade. Observed retrogressive effects are limited to some back reaction of (1), which accounts for the re-equilibration of garnet-biotite pairs within the segregation. Average Kfspar-Qtz segregations at high grade are some 1000 cm in volume. If a eutectic segregation of this size, containing 7.5 wt% water, crystallised in a homogeneous host rock containing 10 wt% garnet (Kspar in excess) with all the water released available to cause retrogression, then approximately 14 times the vol ume of the melt could be completely back reacted to biotite and sillimanite. Field evidence however, demonstrates that the segregations cause little retrogression of their host suggesting either anhydrous melts or effective water removal from the crystallistion site. Bulk rock analysis of small segregations frequently show similar Fe/Mg ratios to their host rocks, suggesting equilibration as larger pegmatitic bodies of similar composition are Fe enriched. The excess peraluminous phases in the segregation may be partly related to growth in the hydrous magma due to a diffusion gradient between the melt and its host. References Bohlen, S.R., Boettcher, A.L, & Wall, V.J., 1982. Am. Mineral., 67, 451-462. Bohlen, S.R., Boettcher, A.L, & Wall, V.J., & Clemens, J.D., 1983. Contrib. Mineral. Petrol., 83, 270-277. Burnham, C.W., 1979. In Geochemistry of Hydrothermal Ore Deposits (2nd.Ed) Ed. H.L. Barnes, John Wiley & Sons, New York, p.71-116. Clemens, J.C., & Wall, V.J., 1981. Can. Mineral., 19, p.111-131. Ferry J.M., & Spear, F.S., 1978. Contrib. Mineral. Petrol., 66, 113-117. Stormer, J.C.,Jr., 1975. Am. Mineral., 60,667-674.

A PERSPECTIVE AND HISTORIC REVIEW OF INDUSTRIAL MINERALS IN AUSTRALIA 1 9 3 A. Driessen , D. Nichol^ and R. TownerJ ^Bureau of Mineral Resources, Canberra ^ Steetley Industries Ltd, Sydney Bureau of Mineral Resources, Canberra Industrial minerals make a significant, albeit unobtrusive, contribution to the national economy and in more direct ways to our standard of living. In 1982 the value of mine production of industrial minerals was $1083 million (Table 1), representing 11% of the total value of all (including petroleum) mineral production ($9655 million) which in turn accounted for 6.5% of Gross Domestic Product.

147

Comparisons of statistical gross aggregates for the years 1960, 1970, and 1982 show that the three major mineral industry sectors, energy minerals, metals, and industrial minerals, all experienced positive rates of real growth in the period 1970-1982, but for the metals and industrial minerals sectors at a lower rate compared to the previous decade. Furthermore, for industrial minerals the rate of real growth of exports in the period 1970-1982 was zero. The industrial minerals sector as discussed in this paper covers some 50 mineral and rock commodities which have been grouped as follows: (a) Construction materials - brick clay, crushed stone, dimension stone, sand and gravel. (b) Mineral sands - ilmenite, monazite, rutile, zircon. (c) Refractories - chromite, dolomite, fire clay, kyanite, magnesite, pyrophyllite, sillimanite. (d) Minerals for the fertiliser and chemical industries - arsenic, beryllium, boron, bromine, fluorspar, lithium, phosphate rock, potash, salt, sulphur. (e) Other industrials - bulk commodites - asbestos, clays (attapulgite/fullers earth, bentonite, kaolin/ball clays, other clays), gypsum, limestone, manganese, silica, talc. (f) Other industrials - specialties - abrasives, barite, diatomite, felspar, graphite, magnetite, mica, mineral pigments, peat, perlite. (g) Gem and semi-precious stones - diamond, opal, sapphire, other. The comparative statistics of the various groupings of industrial minerals (Table 2) also show different features the most noteworthy of which are a reversal from a positive (1960-1970) to a negative (1970-1982) rate of real growth for values of production and exports of mineral sands, and a similar reversal for imports of bulk commodites. The latter trend is attributable to increased domestic (and import replacing) production of asbestos, clays, manganese and talc. On the other hand the statistics also show that imports of refractories, while on a declining trend in the period 1960-1970, were on a rising trend in the subsequent 12-year period. This may be a symptom of the problems this sector is presently experiencing. The strength of this rising import trend is also understated because the statistics do not cover fabricated products containing refractory materials, imports of which are also increasing. Notwithstanding that the statistical data has yet to catch up with diamond developments at Argyle, which will have a great impact, it would generally seem that industrial minerals are not performing as well as metals and energy minerals. While metals and energy minerals are themselves presently experiencing problems, hopefully short term, it would seem that for the industrial minerals sector to grow, as metals and energy minerals have done in previous decades, it too must follow these sector down the export road. TABLE. 1. MINERAL INDUSTRY COMPARATIVE SALIENT STATISTICS 1982 CONSTANT DOLLARS (M)

1960 ENERGY MINERALS Value of mine production (ex-mine) Average annual rate of increase Value of exports (f.o.b.) Average annual rate of increase Value of imports (f.o.b.) Average annual rate of (decrease)/increase 148

1970

1982

1441 5291 11 .4% 8 .9% 594 3296 14 .2% 15 .3% 2779 624 532

616

158

(1 .6%)

14 .8%

METALS Value of mine production (ex-mine) Average annual rate of increase Value of exports (f.o.b.) Average annual rate of increase Value of import (f.o.b.) Average annual rate of (decrease)

649

2386 3281 2.7% 13.9% 2911 4360 716 3.4% 15.1% 131 103 65 (2.4%) (3.8%)

JDUSTRIAL MINERALS Value of mine production (ex-mine) Average annual rate of increase Value of exports (f.o.b.) Average annual rate of increase Value of imports (f.o.b.) Average annual rate of increase Gross Domestic Product (1981-82 prices) Average annual rate of increase

352

860

1083 1.9% 77 324 325 15.4% 0 264 142 402 6.4% 3.6% 9.3%

60 678

100 082 5.1%

147 576 3.3%

TABLE 2. INDUSTRIAL MINERAL GROUPS - COMPARATIVE STATISTICS CURRENT $S (M) 1960 1970 1982 CONSTRUCTION MATERIALS Value of mine production exports imports MINERAL SANDS Value of mine production exports imports REFRACTORIES Value of mine production exports imports FERT/CHEM INDUSTRY MINS Value of mine production exports imports BULK COMMODITIES Value of mine poduction exports imports SPECIALTIES Value of mine production exports imports GEM/SEMI-PRECIOUS STONES Value of mine production exports imports

1982 CONSTANT $S (M) 1960 1970 1982

144

628

224

•

0.4

0.5

6.9

10.0 54.8 11.4 56.4

53.4 •

•

628

1.7

473 0.3 1.6

6.9

146 123

41.9 47.8

180 185

146 123

•

—

1.5

1.7

6.3

5.6 0.3 3.9

6.1 0.9 6.0

1.2

6.1 0.9 6.0

5.0

4.3

13.8 9.5 42.2

67.5 58.2 275

18.0 45.3 67.5 1.5 31.2 58.2 63.3 138 275

13.3 31.2 3.7 14.9 11.8 22.9

168 88.5 47.1

55.7 15.5 49.4

102 48.9 75.1

0.4 0.5 2.4

1.3 4.8 6.0 1.8 5.8 24.1

1.7 2.1 10.1

4.3 4.8 5.9 6.0 19.0 24.1

1.3 2.4 3.0

15.5 16.0 7.6

5.4 50.9 10.1 52.5 12.6 24.9

• •

•

15.1

63.1 48.1 43.5

•

168 88.5 47.1

63.1 48.1 43.5

149

SEISMIC V E L O C I T I E S AS AN INDICATOR OF TECTONIC P R O C E S S E S IN THE DEEP LITHOSPHERE UNDER A U S T R A L I A B.J. Drummond Bureau of Mineral Resources, Canberra Peridotitic xenoliths found i n alkali basalts and kimberlitic intrusions are generally considered representative of the upper mantle under continents. The structural styles of xenoliths vary, even in xenoliths which have not been recrystallised or sheared by the mechanism which emplaced them in the crust. Many show an obvious preferred crystal orientation, while others, although apparently isotropic, have a preferred orientation of the crystallographic axes, particularly in the olivine crystals. The preferred orientation of the crystals is thought to be due to shearing or stress-control led recrystallisation in the mantle (Mercier & Nicolas, 1975). If the preferred orientation of the crystals persists over several hundred kilometres in the upper mantle, it should be possible to m a p the textural anisotropy by studying the corresponding seismic anisotropy. This has been accomplished in the sub-crustal lithosphere below the Archaean Pilbara Craton in northwest Australia. The travel-times of upper mantle refracted (Pn) arrivals across the Pilbara Craton have a d e f i n i t e azimuthal dependence. A time-term analysis was performed to separate the effects of structurally induced azimuthal variations of Pn times from the effects of anisotropy. An anisotropy of 3% with a mean Pn velocity of 7.99 km/s was d e t e c t e d . The direction of maximum velocity is 30 east of north, and is at right angles to the axis of the Hamersley Basin. The direction of minimum velocity parallels the axis of the Hamersley Basin. A seismic boundary was detected in the upper mantle about 15 km below the M o h o . From numerous common-depth-point fan and on-line profiles across the Pilbara Craton, it was possible to determine qualitatively that the upper mantle below the boundary is anisotropic, with the direction of maximum velocity between north and 40° west of north. Upper mantle anisotropy is generally regarded as a young feature reflecting contemporary stresses in the deep lithosphere (eg, Fuchs, 1983), and in the cases where the directions of maximum or minimum seismic velocities parallel young tectonic features, this may be the case. However, in the Pilbara, the anisotropy is more easily correlated with the Hamersley Basin axis, and therefore with ancient tectonics. The preferred explanation of the Pn anisotropy is that it was caused by shearing or syntectonic recrystallisation in the tensional environment caused at the base of the lithosphere by flexure of the lithosphere during loading by the Hamersley Basin strata. The direction o f minimum velocity below the sub-Moho boundary loosely parallels basement features in the Bangemall Basin and is interpreted as younger than the Pn anisotropy. The implication is that the lithosphere in the region, which is currently 200 km thick (Drummond et al., 1982) was much thinner in the Archaean, and has thickened with time. The anisotropy is mapping the palaeostresses active in the lithosphere as it was progressively thickened.

150

The velocity below the Moho reaches 8.2 km/s and below the sub-Moho boundary an apparent velocity of 8.35 km/s has been observed. These velocities were adjusted to 2 ^ C and 1 GPa pressure so that comparisons could be made with velocities measured in the laboratory in rocks at high pressure. The adjusted velocities are 8.3 and 8.5 km/s, respectively. Velocities as high as these are observed routinely in dunites and peridotites (ie. rocks with a high olivine content) which exhibit at least some anisotropy (eg. Birch, 1960). Pn velocities (at 2 F C and 1 GPa) of 8.3-8.4 km/s are observed under most Australian geological provinces. Under northern Australia, the velocity reaches 8.5 km/s. Sub-Moho boundaries have been observed under southeast Australia (Finlayson & McCracken, 1981) and under the Eromanga Basin (Finlayson et al., 1984) where the adjusted velocity reaches 8.6-8.7 km/s. Such high velocities are likely indicators of rocks with a high olivine content and probable anisotropy. If this is so, future seismic experiments may be able to measure the directions of anisotropy and thereby map the directions of the palaeostresses which caused crustal tectonics. References Birch, F., 1960, J . Geophys. Res., 65, 1083-1102. Drummond, B.J., Muirhead, K.J., & Hales, A.L., 1982, Geophys J . R. astr. Soc., 70, 67-77. Finlayson, D.M., Collins, C.D.N., & Lock, J., 1984, Tectonophys., 101, 267-291. Finlayson, D.M. & McCracken, H.M., 1981, J . Geol. Soc. Aust., 28, — 177-190. Fuchs, K . , 1983, Phys. Earth Planet. Int., 31, 93-118. Mercier, J-C.C. & Nicolas, A., 1975, J . Pet., 16, 454-487.

MUNICIPAL HATER

SUPPLIES

ALONG

THE N . S . W . C O A S T ,

L.W. Drury , R.C. Harwood 2

AUSTRALIA

Coffey & Partners, Sydney Water Resources Commission, Sydney

Some 30 town and villages along the coast of N.S.W. depend entirely or partly on groundwater for their municipal water supply. In recent years there has been an increased emphasis upon utilising groundwater by water authorities and local councils as the population alone the coastal fringe of N.S.W. rapidly increases because of a better understanding of coastal hydrogeology and because of a better appreciation of the advantages offered by groundwater in preference to surface water. Groundwater is extracted for municipal purposes from three types of aquifer systems found along the N.S.W. coast:(i) (a) Fluviatile sediments upstream of the Tidal limit are generally shallow (10-15 metres) and comprise sand, gravel and clay characterised by the flanking hard rock geology. Urban water supplies from this source have been obtained at Bega, Bellingen and Bowraville, Denman, south of Eden, Kempsey, Scone and Singleton.

151

(b) Fluviatile and deltaic sediments downstream of the Tidal limit* Here the alluvial plain consists of low permeability sediments containing saline groundwater and deposited under lacustrine deltaic and estuarine conditions. Exceptions are in the Bega, Manning and Myall river valleys where marine sands and fluviatile gravels provide permeable source material. Potential urban water supplies have been obtained from fluviatile gravels beneath estuarine muds near the Myall River. (ii) Unconsolidated aeolian beach and near shore marine sands of Pleistocene to Holocene age. Along the coastal fringe of N.S.W. large volumes of low salinity groundwater have been obtained from the inner and outer barrier dune sand deposits - notable examples are at Tomago, Lennox Head, Stuarts Point, South West Rocks, Seal Rocks, Moruya and Bermagui. This sand unit generally overlies estuarine muds. Exceptions to this generalised stratigraphy occur at Moruya, Mitchells Island near Taree and in the Myall River area downstream of Buladelah. (iii Fractured Rock Aquifers. Little investigation has been carried out in fractured rock aquifers for municipal supply due to the more general availability of surface water or adequate yields from shallow fluviatile sediments or dune sand material. Pumping rates available from bores in such aquifers are usually small, but the Tertiary basalts are an exception. They are generally well fractured, and collector systems into shallow fractures have produced supplies of up to 70 litres per second. Careful management of coastal aquifer systems is required to minimise pollution effects since Water tables are close to the surface and the sediments are permeable. In the coastal sand areas low pH, excessive iron and colour and the possibility of salt water contamination induced by excessive pumping are all problems that confront water supply installations. Water level and chemical monitoring and mathematical modelling of the aquifer system are sometimes required to ensure continued availability of low salinity municipal groundwater in these areas.

References Drury, L.W.D., 1982, PhD thesis. Packham, G.H., 1969 Geology of N.S.W., Geological Soc. Aust. 1-17. Pickett, J.W.. 1983, Quarterly Notes Geological Survey N.S.W. No. 52, 815. Hartwell, J. and Viswanathan, M.N.. 1983, A.W.R.C. Groundwater & Man, Vol 2 121-131. Merrick, N.P., and Drury L.W.D., 1983 A.W.R.C. Groundwater & Man, Vol 1, 211-221. Thorn, B.G., 1965, Royal Society N.S.W. - Journals & Proceedings 98, 23-36. Viswanathan, M.N, and Evans, D.A., 1983 A.W.R.C. Groundwater & Man Vol 1, 353-363. Williamson, W.H., Symposium Water Supply Demand in Towns & Cities, Nov. 1980.

152

SCUDDLES: AN ARCHAEAN-AGED VOLCANOGENIC MASSIVE DEPOSIT, GOLDEN GROVE, WESTERN AUSTRALIA

SULPHIDE

R.J. Dudley1, P.M. Ashley2, A.W. Ryall1 and E.R. May1 1 Esso Minerals, Perth

9 ^Esso Minerals, Sydney

Scuddles is one of two potentially mineable volcanogenic massive sulphide deposits known within the Murchison Province of the Yilgarn Archaean Shield of Western Australia. The deposit was discovered in 1979 and is located about 4 kilometres north of the Gossan Hill copper-zinc deposit discovered in 1971 (Frater, 1983). The in-situ geological resource estimate for Scuddles is 21 million tonnes of 1.2% Cu, 0.6% Pb, 8.2% Zn, 67 g/t Ag and 1.0 g/t Au. The top of the orebody lies 120 metres vertically below the surface, the only surface expression being a thin unmineralised laminated cherty horizon. In long-section, two tabular stratabound lenses of massive sulphide plunge steeply north over a strike length of 900 metres, and dip 75° southwest to a drilled depth of 700 metres. There appears to have been no significant post-depositional disturbance by folding or faulting. The Scuddles deposit is along strike from Gossan Hill and within a stratigraphic unit which is directly equivalent. Lead isotopic data from the latter deposit suggest emplacement at about 2730 ± 20 Ma (Vaasjoki, 1984). An 80 metre thick mineralised horizon hosts the Scuddles deposit and is comprised of felsic to intermediate ash flow tuffs, water-lain tuffs and extensive sulphidic and siliceous exhalites. A distinctive finely laminated magnetite bearing cherty exhalite (in places manganese-bearing and traceable along strike for over 20 kilometres) overlies the massive sulphide mineralisation. Either an amygdaloidal andesitic flow or a quartz-porphyritic rhyodacitic ash flow is in sharp contact with the mineralised horizon hanging-wall. The mineralised horizon merges into rhyolitic-rhyodacitic ash flow, units of the footwall. Post-mineralisation dykes of dacitic to andesitic composition cut the entire volcanic sequence and these in turn are intruded by later dykes of tholeiitic dolerite. Mapping out of individual volcanic units and dykes has been confirmed by major and trace element geochemistry, particularly by absolute abundances and ratios of the "immobile" elements Ti, V, Zr, Y and Nb. Despite the effects of alteration-mineralisation processes and of later greenschist facies (biotite isograd) metmaorphism, primary textures are well preserved. These include examples of pyroclastic and other textures suggestive of subaqueous deposition of volcanic detritus and chemical precipitates. The massive sulphide mineralisation is dominated by pyrite and sphalerite, with lesser amounts of chalcopyrite, galena, magnetite, pyrrhotite, and trace tetrahedrite. Zoning is generally well defined downwards essentially from massive sphalerite into massive pyrite and finally into chalcopyrite with or without sphalerite. Stringer and disseminated chalcopyrite and pyrite mineralisation with subordinate pyrrhotite, magnetite and sphalerite occur beneath the massive sulphides. The basal portion of the mineralised horizon is essentially a barren pyritic tuff overlying a thin stringer sphalerite zone. Hydrothermal alteration accompanying the mineralisation is extensive, being most strongly expressed in the mineralised horizon and footwall rocks. Feldspar-destructive reactions have led to the development of chlorite, quartz, sericite, carbonates, sulphides and local talc, amphiboles and magnetite. Further mineralogical and chemical details are described by Ashley (1984).

153

The morphology and style of mineralisation is strikingly similar to many of the massive sulphide deposits of the Canadian Archaean and to some extent with younger, Phanerozoic volcanogenic deposits (e.g. Japanese Kuroko). Mineralisation is interpreted to have occurred in a fault-bounded depression with hydrothermal fluids entering through a Mg-Fe-enriched linear feeder zone. The capping of the mineralisation by a manganiferous, magnetite-bearing cherty exhalite reflects waning of the hydrothermal activity. Migration and settling of metalliferous brines have resulted in distinct lateral and vertical zonation. As a result, the Scuddles deposit shows markedly different mineralogical/chemical zoning to Gossan Hill, where predominant copper mineralisation has a pod-like distribution within lenses of massive magnetite and pyrite beneath extensive gossan outcrops (Frater, 1983). References Ashley, P.M. 1984, 7th Aust. Geol. Congr., abs. Frater, K.M. 1983, Econ. Geol., _78_> 875-919. Vaasjoki, M. 1984, 7th Aust. Geol. Congr., abs.

MICRODEFORMATION AND FLUID INCLUSIONS AND THEIR SIGNIFICANCE IN MINERALIZED BRECCIA COLUMNS IN THE ARDLETHAN TIN MINE, NSW 1 2 P.J. Eadington1- and R.G. Paterson ^CSIRO Division of Mineralogy, North Ryde ^Aberfoyle Exploration Pty Ltd, East Hawthorn The Ardlethan tin deposit contains disseminated cassiterite ores in breccia columns in adamellite in close proximity to quartz-feldspar porphyry dykes. Four mineralogical-textural styles of cassiterite-bearing ore are observed. (1) Highly comminuted breccia containing predominantly angular mineral and granite fragments of 0.1 - 5 mm diameter. (2) Mixed lithic breccias consisting of 1 to 30 cm diameter fragments of altered granite, porphyry, and metasediment in fine-grained clay-sericite-chlorite interfragmental material. (3) A breccia of angular fragments of altered granite 3-4 cm in diameter in a high proportion of interfragmental material ot quartz-tourmaline-sericite. In the upper levels this breccia is bounded by a marginal zone of large mis-oriented blocks 1-2 m diameter with little intertragmental material. (4) Pipes of massive tourmaline-arsenopyrite that crosscut the other styles of brecciation and mineralization. Cassiterite is dispersed widely in the brecciated rocks but most ore grades occur in the upper 200-300 m of the pipes in a zone of intense phyllic alteration in rocks consisting of largely of sericite-chloritetourmaline-quartz. Cassiterite typically has growth zones and often occurs in vughs indicating precipitation after brecciation. Below this zone there is potassic alteration in a large zone of biotite-topaz-bearing rocks. Cassiterite is closely associated with arsenopyrite. Some orebodies contain minor chalcopyrite that is post-cassiterite. Minor sphalerite and galena occur in late vughs and fractures. Microstructures in quartz result from incremental strain due to repeated microiracturing. This is interpreted as a dilational phase of detormation at slow strain rates occurring before failure by macroscopic tracture and brecciation.

154

Fluid inclusions in the rocks are saline and CC^-rich. Inclusions formed synchronously with the microfracturing trapped a single liquid phase. The composition X h 2 o 0.78, 0.12, X^^O.l requires a pressure ot 1000 to 1500 bars. Inclusions formed after the brecciation trapped immiscible Cl^-rich vapour and aqueous liquid at pressures of about 500 bars. The textures and fabric of breccia types (1), (2) and (3) are similar to those produced in experimental fluidized beds. Fluidization may have arisen from unmixing and expansion of a C^-rich phase producing Jtorced flow of escaping fluid. Quiescent hydrothermal fluids at high temperatures (250-400°C) continued to flow through the broken rocks after brecciation causing hydrothermal alteration and imparting to the rocks new cohesion from interlocking hydrothermal minerals. The cassiterite ores were deposited during this phase of alteration.

MECHANICAL INTERACTION AND MIXING OF MAGMAS IN A BIOMODAL PLUTON, SWIFTS CREEK AREA, VICTORIA G.W. Eberz, I.A. Nicholls and V.J. Wall Department of Earth Sciences, Monash University, Melbourne The Swifts Creek Pluton (SCKP) represents the earliest event within a chemically coherent suite of metaluminous granitoid rocks. Later intrusives comprise from N to S the Tongio Quartz Diorite, the NNW elongate Doctor's Flat Biotite Granite, the Ensay and Tambo Crossing Hornblende Granodiorites. They intruded a flysch-like sequence of upper Ordovician age along the southwestern margin of the Omeo Metamorphic Belt, eastern Victoria. The suite intruded a zone of progressive metamorphism, ranging from low grade slates in the west, to Kfspar-sillimanite assemblages in the east. The NNW trend of the intrusives indicates that their emplacement was controlled by long lived structural features such as the Ensay fault system. The SCKP has been affected by the final D2-deformational event of the Benambran orogeny [1], giving rise to an E-W foliation. The deformation is clearly syn-intrusive as associated mafic-intermediate enclaves have been stretched, exceeding a length/width ratio of 100 along a narrow E-W trending zone. As enclaves are concentrated within this zone, the granitoids resemble a gneissic texture. Locally a NW trending crenulation cleavage is developed, being parallel to a NW foliation within the Tongio Quartz Diorite , both being parallel to major faults in the area. The early Devonian, 412 ± 13 [2], Doctor's Flat Granite appears unfoliated over most of the outcrop area, again approaching a gneissic texture proximal to the Ensay fault in the south. The Ensay and Tambo Crossing hornblendegranodiorites are unfoliated, post-dating major movements along the Ensay fault system. NW trending mafic-intermediate dykes when occurring in swarms may comprise up to 5% of the area occupied by granitoid rocks. Though intruding sedimentary sequences elsewhere in central and eastern Victoria, they rarely intrude country rocks within the study area. Rhyolitic dykes associated with the suite show a more random orientation and their emplacement appears to be to a lesser extent controlled by deep-seated fractures as is the case for the mafic dykes. The SCKP covers approximately 32 km and is elongate in a WNW direction. It represents a subverticaliy zoned magma chamber, as indicated by the exposure of granitic to leuco-granitic phases at the margins of the pluton and topographic highs.

155

The microgranitoid enclaves of dioritic to tonalite composition approximate 30-35% of the total pluton. They are absent from the granitic to leuco-granitic rim and roof facies but may locally account for > 60% of the total rock at the lowest level of exposure. Host rock compositions vary accordingly to the relative abundance of the enclaves from leucogranite and granite through granodiorite to tonalite. Pig, Bi, Qtz are essential constituents of the medium-coarse, slightly pig porphyritic granitoids. Hornblende is present only in the tonalite and granodiorite, microcline becoming modelly significant in granites and leucogranites. Accessories are ap, zr, mt, ± sph. Ranging from a few cm to > 10 m in outcrop, enclaves may be pillow shaped, angular or fragmental, resembling a jigsaw puzzle texture. Contacts are usually sharp; gradational or crenulated contacts are present, but less abundant. A flow foliation defined by hornblende and plagioclase is frequently observed within the enclaves parallel to enclave/, host rock interface. Engulfment of host rock phenocryst phases is evident on thin section side. Enclaves with fine grained margins are concentrated towards the centre of the pluton (lowest level of exposure). The fine grained margins are related to rapid cooling against cooler granitoid host rock, suggesting that the enclaves are of magmatic origin. This concentration towards the centre rules out the possibility of early crystallisation against cooler wall rock. The tonalitic/granodioritic host in turn was partly liquid as it sometimes differentiated to a coarse leucocratic phase between blocks and into fractures of the enclaves. The dominant enclave type has undergone variable entrainment of distinctively stoped quartz and plagioclase megacrysts. The latter usually occur as aggregates with abundant interstitial quartz and show discontinuous oscillatory zoning, patchy zoned cores and a complex twin pattern. These features and their composition are similar to those of plagioclase grains of the host rock. It is suggested that the microgranitoid enclaves are the product of variable entrainment of quartz and plagioclase megacrysts into enclave melt and incomplete mixing between interstitial host rock and enclave melt, as indicated by hornblende- and biotite-rich domains in megacryst-rich enclaves. Surface tensional effects and viscosity contrasts rule out large scale mixing at high crustal levels. The spatial association of modified and unmodified enclaves and the presence of fractured enclaves show that the mixing event was accompanied by convective motion within the pluton. Major and trace element data indicate that the compositional variation within the host rock is related to fractional crystallisation involving pig, bi, ± mt ± sphene. Differentiation within the chamber pre-dates the mixing event, as at the stage of mixing the host rock approached properties of a crystal mush, prohibiting extensive (bi)-fractionation. Straight line variations between the most mafic enclaves and granodioritic host rock substantiate the mixing origin for the majority of enclaves. Though some mafic dykes show close chemical coherence with mafic enclaves, overall scatter of data for the dykes due to extensive alteration do not allow conclusive statements about this topic at this stage. Within a regional context it is proposed that mantle upwelling, accompanied by a tensioned rifting environment which followed the early Silurian Benambran orogeny, caused widespread partial melting in the lower crust, giving rise to bimodal igneous activity. Further isotope studies are envisaged to estimate the degree of interaction between mafic, mantle derived and crustal derived magmas. t References MacLennan, M.K., 1984. M.Sc. prelim, thesis, Monash Univ., unpublished. Richards, J.R. and Singleton, O.P., 1981. J. Geol. Soc. Aust., 28, 395-421. 156

NEW MARKETS FOR AUSTRALIAN COAL George E. Edwards Consolidation Coal of Australia, Sydney Within 10 years of colonisation coal had been discovered in Australia, mining had commenced and coal was being consumed within the colony and exported. Two hundred years later coal continues to be a relatively important domestic energy source and is the greatest source of export income from one commodity. While domestic markets have shown a steady growth over the last 200 years export markets have fluctuated, reaching a peak"around the turn of the last century and, after declining, started a major growth phase about 1960. Markets within Australia concentrated on domestic and small industrial applications initially, particularly for the coarser lump sizes and finer coal (below 20mm) was often discarded. During this century the growth in consumption has been as a power station fuel and as a source of blast furnace coke at the steelworks. Coal continues to be used in industrial boilers and some plants but this market has been eroded over the years by petroleum products and recently by natural gas. Exports began to increase dramatically during the sixties when the Japanese steel industry began to purchase coking coals from new South Wales and, during the seventies, also from Queensland. This was followed by exports to steelworks in Taiwan and South Korea. During the last decade the major export demand has been for coal as a fuel source particularly for power stations and, to a lesser extent, cement producers around the Pacific Basin. A significant export trade has also been developed in Europe, the Middle East the the Indian Sub-Continent. Char derived from brown coal briquettes are also being exported. Since 1973 Australia has exported more coal than it has consumed. Substitution for steel in manufacturing and a trend away from the traditional blast furnace route to steelmaking will result in new markets for coal. Changes in power station design will allow a broader range of coals to be burned and coal will not only be fed to power station boilers as a pulverised fuel, but also in coal/water slurries and coal/oil mixtures. Markets also will develop for coal as a smokeless fuel in a briquette/pellet form in industrial and domestic markets. The major new growth market will be to produce chemicals and, later on, provide a source of liquids and gases through conversion technologies under development and being refined. Other minor markets are also being researched for new markets for coal. Inherent in all these new markets for Australian coal is the need to know the coal products being produced and being defined through exploration in much more detail than has been necessary in the past. It is also necessary for more long range market studies to be done on potential coal requirements of those countries without adequate coal resources, particularly those countries which are geographically closer to Australia and to which Australia enjoys a lower transport cost.

157

HIGH RESOLUTION ELECTRON MICROSCOPY R.A. Eggleton Department of Geology, Australian National University, Canberra HREM is a technique which allows crystalline material to be examined at the unit cell scale. Point to point resolution may be 4-5A, and line resolution about 3A. These distances are commensurate with the unit cell dimensions of most minerals, hence the crystal lattice can be clearly resolved, and defects in the lattice become prominent. Contrast in HREM arises from electron density variation and from many experimental factors, most critically crystal orientation, lens aperture, crystal thickness, electron wavelength and focus. The technique is particularly suited to imaging detail at crystal junctions, defects, and the lattice structure of inclusions or new phases which may be too small for selected area electron diffraction. Ultra-high resolution electron microscopy (UHREM) is possible with microscopes offering 2-3A point to point resolution and under ideal conditions allows atoms to be fseenf. Achieving this resolution is even more dependent on perfect instrument and crystal alignment, and requires a crystal thickness of 100-300A. Images so formed may be easily misinterpreted, and generally require computer image matching to confirm any intuitive interpretation. Examples; Some olivine crystals contain inclusions of oxide minerals in near perfect registry with the olivine lattice. Lamellae only 1.2 nm wide and a few tens of nm long are undetectable by any other method, but their presence may displace a microprobe analysis towards an unacceptably high (Mg + Fe): Si ratio. Botryoidal goethite commonly contains a few percent of Si + P, and other elements which do not readily fit the goethite structure. TEM images show that such goethite is composed of 5.0 - 10 nm diameter needles with sufficient surface area to adsorb the observed impurities. The reaction biotite - chlorite appears in thin section to be close to a constant volume reaction. Analytical studies suggest the reaction proceeds at constant Al. UHREM shows that neither conclusion is correct. Only K, Ca and ^ 0 are mobilised in the deuteric alteration of igneous biotite. The Mg content of the biotite determines the amount of chlorite that forms; the tetrahedral AlrSi ratio is constant. Minnesotaite is a rare layer silicate thought to be the iron-analogue of talc. Crystals, however, do not exceed a few microns in diameter, and have very disordered stacking sequences. Atom resolution TEM shows a structure of linked tetrahedral strips unlike that of other layer silicates.

158

BASALT WEATHERING R.A. Eggleton

IN EASTERN 1

AUSTRALIA

and K . L . Smith 2

^Department of Geology, Australian National University, Canberra Department of Physics, N.S.W. Institute of Technology, Sydney During the early stages of basalt weathering, the coherent weathering rinds developed on core-stones show a smooth depletion in element content with increasing weathering intensity. Changes in slope of such curves accurately reflect the weathering susceptibility of the basalt minerals and allow the weathering process to be modelled. Rock density at the outermost parts of the corestone falls to about -3 of its initial value and this provides a convenient reference density to compare individual element loss. Generalizing, at density decrease, R b , C a , K , Y , La have fallen by 80-90%; C e , N a , Sr M g by 60-70%; P , S i , Mn by 40-50%; C r , Z n , C u , V by 10-25%, and F e , A l , T i , N b , Zr are immobile. Ba and Ni increase by 50% or more. These trends are dependent on individual basalt mineralogy, for example K is lost less rapidly from alkali feldspar than from glass. Olivine and glass are the first phases to show signs of weathering. The weathering products of glass are smectites and Fe-Ti oxides. Under reducing conditions, olivine may transform to bowlingite if the olivine has dislocations or other structural defects at which alteration can begin; dislocation free olivine appears less prone to alteration. Initial bowlingite is randomly oriented and low in A l . As pathways open, the bowlingite grows to form well oriented crystallites of smectite or vermiculite, depending on the particular conditions. As alteration proceeds, bowlingite continues to replace olivine until the conditions become oxidizing, whereupon the bowlingite transforms to a random aggregate of montmorillonite, saponite, and goethite, as iddingsite. Where weathering occurs in an oxidizing environment from the start, olivine transforms to oriented iddingsite, a submicroscopic intergrowth of goethite and saponite. Plagioclase weathers by dissolution at twin boundaries to form etch pits containing a spherical alumino-silicate, probably allophane. The conversion ofthis material to other clays, halloysite or smectite, is still under investigation. Some of the Monaro basalts studied show intra-flow weathering profiles, possibly the result of Tertiary weathering. The most weathered profiles have a bulk density of 1.2 and are composed of halloysite, gibbsite, goethite and hematite. Element content of these bauxitic and lateritic materials suggest that no element is immobile, and indicate the possibility of L a , C r , and Cu increase at constant rock volume.

159

SIROLOG BOREHOLE LOGGING TECHNOLOGY DEVELOPMENT AND APPLICATIONS Peter Lewis Eisler CSIRO Division of Mineral Physics, Melbourne Research at CSIRO into borehole logging techniques was initiated to develop relevant applications to the Australian minerals industry. The development of the technology derived from this research, SIROLOG, commenced only in recent years after testing in several types of ore deposits. Conceptually, the techiques were an extension of those, based on nuclear geophysics, that were developed during the previous two decades for oil-well applications, mainly in the U.S.A. and the Soviet Union. Basically, all current nuclear geophysical borehole logging methods fall into three categories. These are methods using probes equipped with sources of primary gamma rays for gamma-gamma logging, primary neutrons for either neutron-neutron or neutron-gamma logging, and no source at all in order to measure gamma-radiation emitted by naturally occuring radioisotopes. All probes are equipped with one or more radiation detectors, shielded from the direct radiation of the primary source by heavy metal spacers. The purpose of SIROLOG is to provide methods for quantitative in situ measurements of the properties of mineral ore and fossil fuel deposits. Most frequently, the properties required are ore grade, chemical concentrations of critical impurities and coal-ash content. Other required properties are density, porosity and lithology. SIROLOG makes important innovative contributions to borehole logging technology through its spectrometric radiation detection system and its consequent ability to identify and to estimate several independent probe response variables simultaneously. The response variables are chosen for their correlation with the individual characteristics of the deposit and with borehole diameter. Consequently, SIROLOG systems have potential, not only for exploration, but also for pre-mine planning and grade control. Grade control, in particular, has significant cost saving potential for scheduling mine production and transport. It can also assist in control of concentrator feed. The techniques currently used for SIROLOG have evolved through . successive stages of research and field trials for different mineralized deposits. These included nickel, mineralized beach sand and iron in the early years of the programme. Later, research was applied to copper, manganese and coal.

160

M E T A M O R P H I S M AND METASOMATISM OF THE ARCHAEAN BASEMENT - THE RELATIONSHIP BETWEEN HIGH GRADE GNEISS TERRAINS AND INTRACRATONIC MOBILE ZONES FROM ENDERBY LAND, ANTARCTICA D.J. Ellis Department of Geology, University of Tasmania, Hobart Archaean granulite terrains are often cut by long, narrow zones of lower grade, younger rocks herein termed mobile zones. In Enderby Land, Antarctica, ultrametamorphism at the base of the crust (= 3100-2500 Ma ago) was followed by cooling with little change in pressure. Such a process requires both underplating of basic magma as a heat source for the metamorphism and very stable tectonic conditions. This implies that thickened crust was essentially in isostatic equilibrium with the underlying mantle. Subsequent reactivation of the crust as evidenced by the development of considerably younger (= 1000 Ma) intracratonic mobile zones reflects tectonic instability and rapid excavation of the base of crust towards the earth's surface. Reconstruction of Gondwanaland shows that these mobile zones extended for thousands of kilometres through different continents and are of considerable importance for understanding the relation between the crust and subcrustal lithosphere with time.

GEOTHERMOMETRY AND 6E0BAR0METRY D.J. Ellis Geology Department, University of Tasmania, Hobart Many geothermometers and geobarometers are based on two types of reactions. Net transfer reactions form the basis of geobarometry and should have a small AS, AH and moderate AV of reaction. Most geothermometers are based on exchange reactions and should have a large AS, AH and small AV of reaction. Geothermometers which involve a solvus or miscibility gap may be formulated as either net transfer or exchange reactions. Although the distinction between net transfer and exchange reactions is trivial in a thermodynamic sense, it is significant when considering the mechanisms of reaction and cation diffusion in multiply metamorphosed terrains. Some exchange reactions become less sensitive with decreasing temperature whereas others become more so. In solidsolid exchange reactions the equilibrium constant becomes larger with decreasing temperature whereas in some solid-liquid exchange reactions the equilibrium constant decreases and actually becomes less than 1 with decreasing temperature. For example, in the case of garnet-liquid Fe 2+ Mg exchange the liquid is Mg-richer than coexisting garnet below 850900° whereas it shows the 'normal1 relative Fe-enrichment at T > 900°C. Four different approaches to the derivation of geothermometers and geobarometers are currently used - 1. direct derivation from thermodynamic data (e.g. Newton and Perkins, 1982; Ellis, 1980); 2. extrapolation from experimentally determined univariant reactions using activity-composition models to account for the effects of additional components (e.g. Holdaway and Lee, 1977; Thompson, 1976; Bohlen et al., 1983); 3. direct derivation from multicomponent solid solution data (in either simple systems or natural rocks) over a broad P-T range. Activity-composition relations are determined by linear regression techniques from the experimental data (e.g. Ellis and Green, 1980; Harley and Green, 1982); 4. formulations based on natural rock mineral data with the assumption that P-T conditions of formation of the mineral assemblage are independently known (e.g. Thompson, 1976). 161

In the case of (1) small errors in thermodynamic data can result in large P or T errors. In the case of (2) assumptions concerning activity-composition relations may result in inconsistencies with (3). Although for (3) data may be obtained over a broad P-T range, the complexity of many systems often renders the derived thermodynamic parameters meaningless, although the geothermometer accurately determines temperatures within the desired P,T range. In the case of (4) the assumption is that the compositions of minerals reflect the P-T conditions of formation and stability of the chosen mineral assemblage. Many of the inconsistencies in Gt-Cd-Bi geothermometry and barometry can be traced back to bias choices based on which of the above methods (and assumptions) were used (or believed). Recent experimental work on Gt-Opx, Gt-Cd barometry and thermometry, and Gt-liquid thermometry at the University of Tasmania are discussed. The high pressure stability limit of coexisting Gt-Cd-Sill-Qtz of Hensen and Green (1973) has been confirmed. The relative merits of a number of alternative two pyroxene geothermometers as well as garnet-clinopyroxene geothermometers now available are discussed. It is commonly assumed that inconsistent temperature estimates based on different geothermometers (e.g. Bohlen and Essene, 1980) for a given suite of rocks imply an error in one or more of the geothermometers. The assumptions outlined for (4) above make this a necessary conclusion in this approach. In some cases this is invalid. The question of inaccurate thermometers as opposed to staggered closure temperatures needs to be considered by petrologists. Some high grade metamorphic terrains (as inferred from mineral stabilities and some geothermometry calibrations) give consistently lower temperature estimates using Gt-Bi and Gt-Cd geothermometers. In other much lower grade terrains the same thermometers give coincident temperatures. Simple cation exchange is related to volume diffusion and is dependent upon temperature and cooling rate. The extent to which different geothermometers will yield coincident temperatures will differ for metamorphic terrains which have undergone considerably different P-Ttime paths of cooling-uplift to the surface. Examples from slowly cooled metamorphic terrains are given in which the closure temperature for cation exchange in different mineral systems is documented. Such assemblages record through zoning a segment of the P-T cooling-uplift path. Rocks initially metamorphosed at temperatures higher than a given closure temperature (Tc for a given cooling rate) for cation exchange in a particular mineral pair may retain a record of cooling to this temperature but will show no record of cooling below this closure temperature. However the same mineral system can record even lower temperature events if a discontinuous net transfer reaction in which new minerals are formed occurs at temperatures well below Tc. The newly formed mineral compositions record the temperature of this reaction. P-T estimates for xenoliths in basalts are often used to deduce geothermal gradients. It is suggested here that for some minerals the high temperatures experienced by a xenolith in a basalt magma maybe sufficient to rehomogenise minerals and destroy evidence for some low T exchange and net transfer equilibria. Accordingly these xenolith suites do not record a geothermal gradient. A method for estimating ascent rates of basalt magmas on the basis of xenolith mineralogy and diffusion rates is proposed.

162

References Boh1en, S.R. & Essene, E.J., 1980, Geol. Soc. Am. Bull., 9J_, 107-109. Bohlen, S.R., Wall, V.J. $ Boettcher, A.L., 1983, Am. Mineral., 68, 10491058. Ellis, D.J., 1980, Contrib. Mineral. Petrol., 74, 201-210. Ellis, D.J. $ Green, D.H., 1979, Contrib. Mineral. Petrol., 71, 13-22. Harley, S.L. $ Green, D.H., 1982, Nature, 3^00, 697-701. Hensen, B.J. & Green, D.H., 1973, Contrib. Mineral. Petrol., 38, 151-166. Hoidaway, M.J. $ Lee, S.L., 1977, Contrib. Mineral. Petrol., 63, 175-198. Newton, R.C. & Perkins, D., 1982, Am. Mineral., 67, 203-222. Thompson, A.B., 1976, Am. J. Sci., 276, 425-454.

STRUCTURAL INTERPRETATION OF EXTENSIONAL SEDIMENTARY BASINS AND ITS RELEVENCE TO HYDROCARBON EXPLORATION - EXAMPLES FROM THE BASS STRAIT REGION M.A. Etheridge, J.C. Branson and P.G. Stuart-Smith Bureau of Mineral Resources, Canberra Since the pioneering work of McKenzie (1978), the importance of lithospheric stretching as one of the fundamental driving forces for subsidence and sedimentary basin formation has been widely accepted. Lithospheric stretching gives rise to a range of characteristic extensional structures in the upper crust. Examination of such structures in exposed extensional terrains, and, to a more limited extent, in seismic data from sedimentary basins has provided a broad basis for their understanding. However, the detailed geometry of the major extensional structures and their relationship to the subsequent structural evolution of the basin are poorly documented. Our recent study of structures from the Bass Strait basins has identified three broad phases of structural development, which we suggest provide a framework for the interpretation of extensional basins elsewhere. 1.) The Extensional Phase - The major extensional structures consist of a set of rotational (planar or listric) normal faults, and a perpendicular set of sub-vertical transverse faults. The normal faults are characterized by straight traces, gentle to moderate (<45° common) dips, and bound substantially tilted (20° to 40° common) basement blocks and half-graben. These faults are likely to dip the same way across the whole basin but they may change dip along strike (across transverse faults), or be down-to-basin or down-to-margin. Displacements on individual faults during the extensional phase will generally be larger than in later phases, and may be very large where a few faults dominate (up to 10 km in Bass Basin). The normal faults commonly have relatively short strike extents, terminating against the steep transverse faults. The transverse faults may extend across the width of the basin, or may terminate against one of the normal faults, and are accommodation structures analogous to oceanic transform faults. Displacements across the transverse faults will vary along their length, but they will generally have a dip slip component, and be interpreted as normal faults on seismic sections. Basins may develop in oblique extension by a suitable combination of normal and transverse faults - the Bass and Gippsland Basins owe their gross architecture to oblique extension.

163

2.) The Subsidence Phase - During the subsidence phase that follows extension, faults develop to accommodate the essentially vertical displacementp involved. These displacements are small compared to those of the extensional phase. Consequently, the subsidence faults will be steep, with small (<1 km, commonly only 100-500 m) displacement. In keeping with the subsidence displacement field, they will generally be down-to-basin and irrotational. They will be more prominent in the lower part of the subsidence sequence, since subsidence is greater there, and they may have decreasing displacements up dip. The subsidence faults will be distributed throughout the basin, but may be partially controlled by reactivation of earlier extensional structures. In oblique extension basins, these faults will tend to parallel the mean basin trend, rather than the underlying extensional structures. In addition to the subsidence faults, compactional structures will develop at this stage over irregularities produced during extension. Basement tilt block edges and corners provide the main locus for such structures in the Bass Basin* 3.) Tectonic Overprint - At any stage in the basin history, a change in tectonic setting may imprint one or more sets of structures on an extensional basin. The important feature of extensional basins in this respect is that the major normal and transverse faults developed during the extensional phase provide zones of weakness through a substantial fraction of the crust. Reactivation of these zones of weakness will provide an important control on the style, orientation and location of the later structures. We will demonstrate that the late Eocene and younger hydrocarbon-bearing structures in the Gippsland Basin were controlled largely by reactivation of major extensional normal and transverse fault zones. Reference McKenzie, D., 1978, Earth. Plan. Sci. Letters, 40, 25-32.

THE GEOMETRY OF EXTENSIONAL STRUCTURES IN THE BASS BASIN M.A. Etheridge, J.C. Branson, P.G. Stuart-Smith and A.S. Scherl Bureau of Mineral Resources, Canberra In 1982, the Bureau of Mineral Resources carried out a 3200 km, high quality seismic reflection survey in Bass Strait. The survey was centred on the Bass Bas in, but was tied to the adjacent Gippsland and Otway Basins and the continental margins. The survey parameters were designed to enhance the data quality below the previously largely opaque Eocene coal measures, revealing the early basin-forming structures in a detail not previously achieved. The major deep structures revealed by the BMR seismic data are Early Cretaceous shallow to moderately dipping, rotational normal faults, with associated tilt-blocks and half-graben. These faults have displacements of up to 10 km, strike consistently 290° to 300°, and mostly dip towards the south-southwest. They are planar to the maximum depth of the seismic data (6 sees TWTT; 10-12 km), and give rise to tilts of up to 35° in the basement surface. This domino-style faulting has resulted in 60% to 80% horizontal extension ($ = 1.6 to 1.8) during the Early Cretaceous, and was followed by Late Cretaceous to Pliocene subsidence. Thermomechanical modelling of the extension and subsidence is described in a companion paper (Karner, Etheridge and Branson, this symposium), and demonstrates that the extension is likely to have involved the whole lithosphere.

164

Mapping of the major Early Cretaceous normal faults using both BMR and available company data shows that they are disrupted by steeply dipping transverse faults that trend 020° to 030°, and which extend the full width of the basin. These transverse faults developed contemporaneously with the normal faults, and are thus restricted to the Early Cretaceous and older sequences. They do not simply displace the normal faults and tilt-blocks, but accommodate variations in the positions of and displacements on the extensional structures• They are therefore analogous to oceanic transform faults, and would presumably have developed into transforms had the extension proceeded to the oceanic stage. The transform-like faults in the Bass Basin progressively displace the major normal faults in a dextral (right-lateral) sense, giving rise to the basin's overall northwesterly trend. The basin therefore developed by oblique extension, with subsequent subsidence within a trough perpendicular to the mean displacement vector. Preliminary interpretation of BMR and company seismic data from the Gippsland and Otway Basins has identified Early Cretaceous normal and transverse faults with the same west-northwest and north-northeast trends. In the Gippsland Basin, systematic sinistral (left-lateral) offsets on the transverse faults gives rise to the overall east-west trend of the basin, whereas in the Otway Basin there is no uniform sense of offset on transverse faults and the basin axis is therefore subparallel to the normal fault trend.

MINERALISING AND DIAGENETIC PROCESSES IN THE DEVONIAN LENNARD SHELF, WESTERN AUSTRALIA

REEFS,

H. Etminan1, I.B. Lambert1, I. Buchhorn^, C. Chaku^, G. Murphy^ •'•Baas Becking Laboratory, Canberra, ACT, 2Shell (Metals Division), Perth, 3 BHP, Perth Most Mississippi Valley Type (MVT) Pb-Zn deposits and some major oil fields occur in Palaeozoic carbonate reefs. Despite much research into the genesis of MVT mineralisation, particularly in North America, there is still substantial disagreement on the processes involved and how these relate to generation and migration of petroleum. The late Devonian carbonate complex of the Lennard Shelf, northern Canning Basin, constitutes one of the best exposed and most pristine ancient reef systems known. Pb-Zn mineralisation occurs in various facies of the outcropping reefs, and minor petroleum has been encountered in holes penetrating sub-surface reefs to the south. Wide-ranging research is being conducted on the reef system, with emphasis on the mineralised areas at Pillara, Wagon Pass and Narlarla, in an attempt to elucidate the mineralising and diagenetic processes. Results to date imply that the carbonate cements are largely of marine origin. Later diagenetic carbonates formed at temperatures mainly between 45 and 110°C, from fluids of widely varying salinities which are interpreted as mixtures of formation waters (basinal brines) and seawater. Minor amounts of hydrocarbons were present in some of the formation waters, particularly those which caused dolomitisation. The only evidence found for meteoric water involvement is in very late stage calcite spar.

165

The mineralisation formed after the main phases of diagenetic cementation. It varies from predominantly veins and breccia infill in unaltered limestone (Pillara), to massive and disseminated in brecciated impure dolomite (Wagon Pass, Narlarla). Available data suggest that mineralisation at both Pillara and Wagon Pass formed between ca. 70 and 1JO C from fluids with major components of saline formational waters. The 6 S ranges for galena and sphalerite are predominantly positive, imply^ig the sulfur was generated by reduction of sulfate. However, distinct 6 S ranges from each deposit indicate variable conditions of reduction and/or distinct sulfate sources. In addition, the isotopic data show that much of the iron sulfide formed separately from galena and sphalerite.

MANGANESE NODULES, COBALT-RICH CRUSTS AND HTDROTHERMAL METAL DEPOSITS IN THE SOUTHWEST PACIFIC N.F. Exon Bureau of Mineral Resources, Canberra Manganese nodules are common on the abyssal plains of the Southwest Pacific in water depths exceeding 4000m, and particularly abundant on the Pacific Plate where sedimentation rates are lower and water depths are greater. Only where they are abundant, and have exceptionally high grades of combined Ni, Cu and Co, are they of potential economic significance. The only area in the Southwest Pacific where these conditions are met is in the East Central Pacific Basin between 6°N and 5°S, where mean abundances are 8kg/m2 and mean Ni+Cu+Co grades are 1.73% (Exon. 1983). Cronan (1984) has indicated that the most prospective areas are near the Line and Phoenix Islands, in some cases within the Kiribati Exclusive Economic Zone. Recent studies by German and US Geological Survey scientists have focussed attention on the existence of cobalt-rich manganese crusts in the Mid Pacific Mountains and Line Islands. The most enriched crusts lie in water depths of 500-2000m, and average 2cm in thickness; Co percentages can approach 2%. On the basis of limited data, Halbach et al. (1982) estimated a crust coverage of 40kg/m2 on seamount slopes in the Central Pacific. This indicates that metal concentrations in the crusts could exceed the value of deepsea nodule fields in the Northeast Pacific (Cronan, 1984). Hydrothermally enriched metallic deposits are known from a number of actively-spreading marginal basins in the region and are probably present in others (Cronan, 1983). They are presently known in the Lau, North Fiji and Manus Basins, and shallow-water volcano-related deposits are known from Matupit Harbour (Rabaul) and off Epi (Vanuatu). The Tripartite II geoscience cruises will further investigate some of these deposits in 1985. References Cronan, D.S., 1983, CCOP/SOPAC Technical Bulletin 4, 55pp. Cronan, D.S., 1984, South Pacific Marine Geological Notes 3(1), 1-17. hxon, N.F., 1983, Marine Mining 4(1), 79-107. halbach, P., hanheim, F.T., and Otten, P., 1982, Erzmetall. 35(9), 447453.

166

DIRECT HYDROGEOCHEMICAL PROSPECTING FOR GOLD BY SURFACE WATERS ANALYSIS J.J. Fardy1, T.M. Florence1 and T.W. Hamilton2 ^ ^CSIRO Division of Energy Chemistry, Lucas Heights Department of Chemistry, University of Wollongong, Wollongong Introduction Direct hydrogeochemical prospecting for gold, using the gold content of water as an indicator of deposits, has been of long-standing interest to the exploration and mining industry. It is known that gold concentrations of many waters in contact with gold-bearing rocks do not exceed concentration of 15 parts per trillion (ppt; ng L" ), so the analytical technique must have a detection limit below 1 ppt. This limitation greatly hindered the development and application of this type of prospecting, but the problem has been resolved by our recent development of an analytical method based on neutron activation analysis (NAA). Instrumental NAA (INAA) can measure up to 45 elements in geological samples, yielding trace levels of many elements with a very high degree of accuracy. The significance of this technique is exemplified by its ability to determine low levels of gold in rocks and surface waters for which there are few other suitable analytical methods. Instrumental NAA has been used to improve the effectiveness of geological prospecting for gold by incorporating it into a hydrogeochemical procedure and applying the technique to the analysis of waters from gold-mining areas in Australia and from several hot springs in New Zealand. Basis of the Technique Hydrogeochemical prospecting is based on two conditions. First, groundwater must come into contact with the specific mineral deposit and then transport detectable amounts of ore to the surface where it is carried away by surface water. Second, analytical data must have the necessary sensitivity to produce a unique pattern that is indicative of the location of the precious mineral. In the case of gold, concentration gradients are produced by a decrease in aqueous concentration with distance from the source. Since water is a more homogeneous medium than rock, a single water sample is more representative of a water body than a rock sample is of its surrounding geology. A water sample may also contain elements which reflect the composition of a large volume of rock with which it has been in contact. Moreover, the gold content of emerging groundwater could indicate the location of a gold deposit that has no surface expression and hence would not be discovered by classical prospecting techniques. Analytical Technique We have developed an analytical method, based on the preconcentration of gold on charcoal and its determination by NAA, that can measure the dissolved gold concentration in water samples with a detection limit of 0.3 ppt. Particulate gold is distinguished from dissolved gold by prior filtration. Water samples are collected in pretreated (nitric acid and demineralised water wash), 1 L polyethylene containers and filtered through 1.2 vm Millipore filters to remove the suspended matter and particulate gold. This is done within 12 hours of sampling to minimise losses by surface adsorption. If immediate analysis is not possible, the filtrate is frozen and stored. The filter plus residue is dried, encapsulated in a polyethylene vial and analysed by INAA for particulate gold. Samples are irradiated for 24 hours in the X6 facility of HIFAR, a 10 MW Dido class materials research reactor at the Luc^s ^eights Research Laboratories, at a thermal flux of 5 x 10 neutrons cm"* s~ . The samples are then analysed

167

for gold via the 412 KeV peak of spectroscopy.

198

Au using high resolution gamma

The filtrate is analysed for dissolved gold by adjusting the pH of the solution to between 3 and 4 using 5 M HC1; 0.1 g of activated charcoal is added and the solution is equilibrated for 5 min. before filtering through a 1.2 Mm filter. After drying, the filter plus residue is analysed by INAA. Results and Discussion Seventy water samples from the surface waters of well-defined, gold-bearing, areas in four goldfields in New South Wales and one in Victoria, and 20 samples from various hot springs in New Zealand have been analysed for particulate and dissolved gold.. The concentrations of particulate gold were widely scattered and yielded no useful information for hydrogeochemical prospecting. However, dissolved concentration data correlated strongly with known gold deposits and demonstrated the feasibility of the technique. Our studies have indicated that gold concentrations in streams are not directly proportional to the concentration of gold in the surrounding rocks and hence cannot substantiate the economic attractiveness of the gold deposit. Further, comparison of gold concentration data from different areas is unlikely to yield useful information. However, these data are most useful for locating gold anomalies and hidden deposits, particularly when a single stream and its tributaries are sampled in a carefully chosen pattern. The use of a hydrogeochemical method based on INAA offers a new dimension to gold prospecting. It offers a significant time and cost advantage over the traditional approach of geological analysis. Given the right hydrogeologic conditions, it is an ideal preliminary surveying technique because the analysis of ten water samples from an area can give the prospector as much information on the existence and location of a gold deposit as the analysis of many times that number of geological samples at a small fraction of the cost. This technique is not limited to surface water and springs but can be used for measuring the concentrations of gold in ground and lake waters.

PROPOSAL FOR A GENERALISED FACEES MODEL FOR CLASTIC SHORELINES

D.A. Feary Department of Geology, A.N.U., Canberra The most important factors controlling facies distributions on clastic shorelines appear to be fluvial, wave, and tide processes. The overall distribution and geometry of facies on any particular shoreline is a function of the relative importance of these processes. The major facies characteristics can therefore be represented by the location of the shoreline on a triangle with fluvial, wave, and tide processes as end-points. This triangular representation has the same end-points as the deltaic process model proposed by Galloway (1975), and in fact the deltaic triangle occupies the fluvial-dominated portion of the clastic shoreline model proposed here. The waveand tide-dominated portions of the process triangle represent broadly defined barrier island/beach and estuary/tidal flat environments respectively. The process triangle can only represent the relative importance of the three major processes, and therefore cannot account for the difference between low and high energy shorelines. This variation can be depicted on a third "energy" axis, so that there is a continuous gradation from a low energy triangle at one extreme to a high energy triangle at the other (see below). 168

It may eventually be possible to construct a sufficiently large number of idealised facies sequences to represent deposition controlled by the major processes throughout the shoreline spectrum. Deviations from the idealised facies sequence would result from the action of subordinate processes.

chenier plain wave-dominated delta barrier island with washover features

WAVE'

-'river-dominated muddy delta - tide-dominated delta

"'*•• RIVER

- \ - estuary

wave-dominated delta. /•.

J.* river-dominated delta possible chenier plain "tide-dominated delta

\\ «TIDE'

low gradient ' t i d a l f , a t w i t h Poorly deve, fine-grained beach °Ped *Wal exchange ' • channels barrier island with j tidal inlets " " WAVE-

-estuary wave-dominated delta beach

\ TIDE'

tidal flat

•RIVER JV

river-dominated sand/gravel delta tide-dominated - - delta - V - estuary

A ~ ' o w energy shoreline B

"moderate energy shoreline

C " h i 9 h energy shoreline

WAVE ,

steep coarse-grained beach

6 E 0 C H E M I C A L C H A R A C T E R I S A T I O N OF S I L I C I C L A S T I C R O C K S W I T H E X A M P L E S FROM THE L O W E R P A L A E O Z O I C

i TIDE

tidaf flat with well developed tidal exchange channels

SEDIMENTARY OF V I C T O R I A

Mark W. Fenton University of Melbourne, Parkville The problem of presenting geochemical data in silciclastic sedimentary rocks is that SiC^ + AI2O3 commonly ranges from 80-90% of the rock. An inverse relationship between Si02 and AI2O3 is, therefore, always the case and since quartz dilutes the aluminous mineral phases and heavy minerals all elements increase in abundance with increasing AI2O3. This anticorrelation with quartz and correlation with AI2O3 is a direct result of constant-sum closure. This can be overcome by documenting the concentration of an element in the non-quartz fraction and observing how this quantity varies with lithology. Two main distributions are observed; (1) a Sand Enrichment Distribution where [Element]/[AI2O3] ratios in the sandier lithologies are greater than mudstones and (2) a Mud Enrichment Distribution where the ratios in mudstones are greater than the sandstones. Using the Lower Devonian Liptrap Formation of the Melbourne Trough as an example it is demonstrated that although most elements have lower absolute abundances in sandstones than mudstones, there are few elements that are enriched in mudstones when the diluting effects of quartz are taken into account. Elements that have a Mud Enrichment Distribution include K, Rb, Ga, V and Sc while those that have a Sand Enrichment Distribution include Mg, Fe, Ti, Ca, P, S, Co, Zn, Ni, Sr, Cr, Zr, Y, Ce and Nd.

169

Another way of presenting geochemical data in a "diluent-free" dimension is to obtain an actual estimate of the abundance of the mineral phases and then recalculate the trace element analysis "diluent-free". However, the fine-grained nature of the minerals in graywackes together with the fact the phyllosilicate minerals form an intimate mixture means that a sophisticated technique for mineral percentage estimation is required. This is achieved by calculating a norm using minerals observed in thin section, microprobe analyses and bulk-rock analyses. The norm presented is tailored for quartz-muscovite- chlorite-feldspar rocks and this is applicable for most sedimentary rocks in the Lachlan Fold Belt. In detail, all K2O is partitioned as muscovite followed by MgO for chlorite and Na 2 0 for albite. If after calculating albite more AI2O3 has been partitioned than is present in the rock then the initial assumption that all K is present as muscovite is incorrect and K-feldspar must be calculated. This is achieved by reacting back muscovite and liberating the necessary cations. Creating K-feldspar will again create a negative AI2O3 so that this process is iteratively repeated until a best fit is obtained. Following this calculation, excess Si02 is assumed to be quartz. Using such norm calculations for the Liptrap Formation and recalculating trace element abundances "diluent-free" produces absolute abundance plots that mimic [Element]/[AI2O3] plots. A knowledge of the abundance of the various phyllosilicates together with the bulk-rock trace element content enables the calculation (using simultaneous equations) of a trace element analysis of the individual clay phases. Using all this information it can be demonstrated for the Liptrap Formation that the spectrum of lithologies has a complicated but systematic change in the relative abundances of the various phyllosilicates which would be difficult to identify using many of the more popular plots.

EVIDENCE FOR SHALLOW WATER CONDITIONS DURING THE ORDOVICIAN AT M A L L A C O O T A , VICTORIA M.W

UPPER

Fenton and C J-L Wilson

University of Melbourne

Parkville

The Late Ordovician Mallacoota Beds are composed of turbidites, shales and radiolarian rich cherts Like all the turbidite sequences in the Lachlan Fold Belt it has been ascribed a deep water origin. In this paper the superimposition of traction structures on what is ostensibly a normal turbidite sequence is discussed and equated with storm induced water currents therefore suggesting a shallow water originSix lithofacies and their associations suggest that the Mallacoota Beds were deposited in a "fan-like" environmentHowever, the identification of structures produced by episodic reworking by water currents indicate a much shallower origin. In detail, interbedded very fine sandstones and shales that frequently contain starved ripples resemble modern day storm surge deposits. These starved ripple pavements, together with rippling at the top of turbidites (associated with a grain-size break) have total palaeocurrent directions at right angles to those observed from flutes and Bouma C-division ripples. A difference in ripple migration direction between Bouma C- division ripples (representing the direction of the flow of the turbidite at the time of deposition) and water current ripples at the top of the same bed (a later superimposed effect) provides further evidence that the reworking is unrelated to the deposition of the turbidite. Multiple ripple migration directions have been observed in some beds. Conclusive evidence for reworking of the turbidites by oscillatory wave motion comes from the presence of ripple pavements with straight crests. Calculations of possible water-depths and wave conditions that would produce such ripple pavements indicates depths between 90?-200m. 170

Intense reworking of turbidites has produced major reshaping of the u p p e r s u r f a c e s of the beds producing v a r i a b l e thicknesses , lensing and swaley b e d d i n g a s s o c i a t e d with h u m m o c k y c r o s s - s t r a t i f i c a t i o n . A n a l y s e s of m o d e r n storm dominated systems indicate that both wind s t r e s s - d r i v e n currents and o s c i l l a t o r y currents are the main water c u r r e n t s o p e r a t i v e during storm c o n d i t i o n s . T h e s e currents are interpreted to have produced u n i d i r e c t i o n a l and o s c i l l a t o r y current ripples respectively w i t h i n the M a l l a c o o t a B e d s . It is noted that m o d e r n storm dominated shelves have a p r e v a l e n c e of ripple p a v e m e n t s and this is equated with what is o b s e r v e d in the s e q u e n c e . T h e problem of the M a l l a c o o t a Beds showing both "fan-like" and "shallow-water" features must be addressed if a convincing m o d e l foi? the s e d i m e n t a t i o n of the sequence is to be m a d e . It is suggested that "fanlike" features such as channelling may have been produced by storm surge where channels form seaward of rip-channels during peak hurricane c o n d i t i o n s . In this way a turbidite sequence with all the features of a fan could be produced at depths b e t w e e n fair-weather wave base and storm- w a v e base as long as tidal influences were m i n i m a l or a b s e n t . In the light of this new information it would seem that there are other turbidite sequences w i t h i n the Lachlan Fold Belt that were d e p o s i t e d within storm-wave base. It also has implications for palaeodepth i n t e r p r e t a t i o n for all turbidite s e q u e n c e s .

UPPER M A N T L E V E L O C I T I E S FOR THE CENTRAL AND EAST A U S T R A L I A N LITHOSPHERE AND COMMENTS ON Pn ANISOTROPY

D.M.Finlayson Bureau of Mineral Resources, Geology & Geophysics, Canberra. Anisotropy is observed to be the rule rather than the exception when geological features are examined at micro, macro and mega scales. However, whether this translates into in-situ observations of anisotropy in seismic velocity is still not clear. Upper mantle velocity (Pn) anisotropy has been used as a guide to lithospheric stress therefore some appraisal of the observations in Australia is worth summarising. The main difficulties in measuring Pn anisotropy are 1) finding a suitable "test" area, 2) making detailed measurements, and 3) being able to accurately recognise the seismic phases of interest. In the tectonically simple oceanic regions Pn anisotropy of 4-8% has been measured by Raitt et al (1971). However, in the continental 1ithosphere, observations are much less conclusive, the difficulties listed above being amplified in the much older cratonic regions. Anisotropy of 7-8% has been reported from southern Germany (Bamford,1977;Fuchs,1979,1983), but in other continental areas the results are inconclusive. To date there has not been a convincing experiment with a common upper mantle depth point. This paper sets out some data from three regions of central and eastern Australia. In northern Australia, between Tennant Ck. and M t . Isa, Finlayson (1982) derived a Pn velocity of 8.16-8.20 km/s at a depth of 51-54 km along an azimuth 100 deg. E of N. The upper mantle velocity increases further to about 8.3 km/s at 61 km depth. Hales and Rynn (1978) have interpreted data between Tennant Ck. and Darwin (azimuth 340 deg. E of N) and derived a Pn velocity of 8.18 km/s at 45 km depth increasing to 8.38 km/s at 76 km.

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In southeastern Australia, under the exposed Lachlan Fold Belt, Finlayson et al (1979) interpreted a Pn velocity of 8.02-8.05 km/s at depths of 42-50 km along an azimuth of 0-50 deg. E of N. Finlayson & McCracken (1981) determined a Pn velocity of 8.03 km/s at a depth of 43 km under the Sydney Basin (azimuth 20 deg. E of N) but across the northern Fold Belt they found a Pn velocity of 7.95 km/s at 43 km (azimuth 280 deg. E of N). Along this latter azimuth they interpreted a velocity reduction at 50-64 km depth with a subsequent velocity increase to a value greater than 8.0 km/s. Across the Lachlan Fold Belt from Bass Strait to Mt. Fitton (north Flinders Ranges) Muirhead et al (1977) interpreted a Pn velocity of 7.98 km/s at 35 km depth, increasing to 8.36 km/s at 100 km depth (azimuth 320 deg. E of N). Under the central Eromanga Basin Finlayson et al (1984) recorded high quality data along east-west and north-south profiles. A Pn velocity of 8.15 km/s was determined at 36-41 km depth on the east-west profile and a value of 8.13 km/s was interpreted at 39-41km under the north-south profile. Deeper in the upper mantle under the east-west line, a velocity reduction was interpreted at 46-55km with a subsequent velocity increase to 8.35 km/s at 56 km depth. In all these three regions of Australian continental lithosphere the seismic profiles are approximately at right angles to each other. The data from these three regions indicate a Pn velocity range of 8.16-8.20 km/s under the central North Australian Craton, a range of 7.95-8.05 km/s under southeastern Australia, and a range of 8.13-8.15 km/s under the central Eromanga Basin. It is evident that Pn anisotropy, if il exists in central and eastern Australia, is of the order of 1% or less rather than the 7-8% (0.5-0.6 km/s) claimed for southern Germany. It is also evident, however, that there are upper mantle inhomogeneities seen as velocity gradients and velocity reductions in the depth range 55 to 100 km before a velocity of about 8.35 km/s is reached. Because of the paucity of data, it is premature to speculate whether such deeper velocity values change systematically with azimuth. References Bamford,D., 1977, Geophys. J. Roy. Astron. Soc., 49, 29-48. Finlayson,D.M.,Prodehl,C. & Coll ins,C.D.N., 1979, BMR J. Aust. Geol. & Geophys., 4, 243-252. Finlayson,D.M.,Collins,C.D.N. & Denham,D., 1980, Phys. Earth & Plan. Inter., 21, 321-342. Finlayson,D.M. & McCracken,H.M., 1981, J. Geol. Soc. Aust., 28, 177-190. Finlayson,D.M., 1982, J. Geophys. Res., 87, 10569-10578. Finlayson,D.M.,Col 1 ins, C.D.N. & Lock, J., 1984, Tectonophysics, 101, 267-291. Fuchs,K., 1979, Tectonophysics, 56, 1-15. Fuchs,K., 1983, Phys. Earth & Plan. Inter., 31, 93-118. Hales,A.L. & Rynn,J.M.W., 1978, Geophys. J. Roy. Astron. Soc., 55, 633-644. Muirhead,K.J.,Cleary,J.R. & Finlayson,D.M., 1977, Geophys. J. Roy. Astron. Soc., 48, 509-519. Raitt,R.W.,Shor,G.G.,Morris,G.B. & Kirk,H.K., 1971, Tectonophysics, 12, 173-186.

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S E I S M I C V E L O C I T Y S T R U C T U R E S OF THE L I T H O S P H E R E U N D E R THE S H E L V E S A N D T R O U G H S OF THE C E N T R A L E R O M A N G A B A S I N

D.M.Finlayson & C.D.N.Coll ins Bureau of Mineral Resources, Geology & Geophysics, Canberra. The velocity structure within the lithosphere underlying sedimentary basins has been used as a constraint on models for basin evolution. In particular, the velocity variations in the upper crust have been used to constrain depositional history and the velocity characteristics of the lower crust and upper mantle have been used to infer replacement of "normal" crustal material with higher velocity asthenospheric rock during episodes of crustal thinning (stretching) and "sub-crustal erosion". Lack of significant reflection horizons within the upper crustal basement on deep seismic reflection records from the central Eromanga Basin suggests that faulting within the basin is not related to listric faulting or faulting above a detatchment surface. Rather the faulting is possibly associated with zones of high-angle, deep extension related to early rifting in a back arc environment. Detailed seismic refraction profiling along traverses E-W and N-S across the central Eromanga Basin highlight some features of the velocity structure of the crust and upper mantle. A 2-4 km thick zone of high velocity gradient underlies the Devonian, Permo-Triassic and JurassicCretaceous sedimentary sequences evident from reflection profiling. This zone probably represents deformed late Precambrian to early Palaeozoic sequences (Warburton Basin?) which form a basement for the Devonian Adavale Basin. The upper crustal basement has a velocity in the range 5.5 to 6.4 km/s and includes velocity reductions above a prominent mid-crustal (21-24 km depth) velocity increase. This mid-crustal feature corresponds to the top of a zone of lower crustal reflections seen on continuous profiling records. The zone is shallower under the Cheepie Shelf, in agreement with the refraction profiling depths. Such a mid-crustal horizon is prominent under other basins of similar age such as the Mississippi Embayment and also in much younger basins (rifts) such as the Rhine Graben and the Rio Grande Rift. In the Bowen Basin of eastern Australia velocity increases determined by refraction profiling at 30-32 km depth correspond again with the upper limit of a prominent reflection zone but at a deeper level than under the central Eromanga Basin. In the lower crust a velocity gradient is required to explain reflected energy arriving after the events from the mid-crustal horizon (Pc) and before the PmP reflected phases from the crust-mantle boundary (Moho). A lower crustal velocity gradient is also required to account for phases traversing the lower crust multiply reflected at the surface. There are examples of such features from basins elsewhere. In the Eromanga Basin velocities approach 7.2-7.3 km/s at the base of the crust but there doesn't appear to be a distinct high velocity (7.3 km/s) "pillow" such as that interpreted under the Mississippi Embayment. The upper mantle velocity of 8.13-8.15 km/s is reached at 36-41 km depth below the velocity gradient zone. There are no reflections from within the upper mantle evident on deep continuous profiling records. The mid-crustal velocity increase is interpreted as a metamorphic horizon formed in response to alteration of the lower crust by multiple intrusion. Such an interpretation has also been proposed for the Mississippi Embayment . The mid-crustal magma horizons interpreted for the Rio Grande Rift may be a modern analogue.

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OIL EXPLORATION AND EXPLOITATION: NEW TRENDS AND NEW GEOLOGIC CHALLENGES William L. Fisher Bureau of Economic Geology, University of Texas, Austin, Texas Oil is a finite resource. Exploration and exploitation has been pursued extensively over the past 100 years, passing through several stages requiring progressively more sophisticated application of geology and technology. How much oil is left to be discovered is unknown, in fact, unknowable. In many areas of the world, factors more fundamental than the absolute volume of yet-to-be discovered oil are the rate at which new oil is being discovered and the role of new discovery in reserve additions relative to other components. In the more established and developed basins of the world, and especially in mature U.S.A. provinces, new field discovery has become relatively low and is declining; it has substantially given way to reserve growth—enlarged recovery from existing -fields—in overall significance to oil reserve additions. Such is a logical consequence of exploration maturity, but the trend is also augmented by higher oil prices, more sophisticated oil exploitation technology, and application of detailed geologic characterization of oil reservoirs. The future challenge is substantial. The traditional sources of reserve growth have been extension drilling, new pool discovery, and secondary recovery. These are now being enlarged significantly by new sources of reserve appreciation—infill drilling, well stimulation, enhanced or tertiary recovery, development of known but previously subeconomic resources, and lower abandonment production levels. The shift of strategy from new field discovery to reserve growth development is well underway in the mature basins. It holds substantial promise but poses major challenges in application of detailed geologic modeling in better understanding and predicting fluid behavior. Recent trends in many basins of the world define the shift. In the case of U.S.A. Lower 48 oil reserve additions over the past decade [197383), reserve growth of fields discovered prior to 1968 has amounted to 13.6 billion barrels, or 70 percent of total additions. New fields discovered since 1968, along with their own reserve growth have accounted for 5.8 billion or 30 percent of total additions. Onland reserve growth from old fields has made up 80 percent of additions; in exploratory mature basins reserve growth volume has been an order of magnitude greater than new field discovery volumes. Certain basins in the U.S.A. are notable. Known ultimate recovery of the pre-1968 fields in the Permian Basin of West Texas increased at an average annual rate of 4 percent over the past decade due to intensive extension and infill drilling and some carbon dioxide flooding. Eastern New Mexico and Utah posted an average annual growth rate of 2 percent due to both extension and infill drilling. Rapid deployment of thermal recovery in the Central Valley and San Joaquin Basin of California netted an average annual increase of 2 percent. Overall average annual rate of growth in the U.S.A. was 1.6 percent, two to three times the historical rate. The pace of reserve growth also increased substantially during the decade. Texas basins holding about 35 percent of the U.S.A. 00IP provide an example. Prior to the 1970fs, reserve growth of old fields, many di scovered before 1920, grew at an average annual rate of 0.3 percent. During most of the 1970fs reserve growth was about 0.5 percent annually. From 1979 through 1982, a period when annual oil completions more than doubled the level of the 1970's, reserve growth of all pre-1969 fields increased statewide at an average annual rate of 1.8 percent. During that period new field wildcat oil completions were less than 3 percent of total oil completions. 174

In Texas arid in the rest of the U.S.A. increase in reserve growth is moderating trends in proved reserves and production. From 1974 through 1979, Texas proved reserves of crude dropped at an alarming rate of nearly 8 percent annually; since 1979 the decline has slowed to less than 2.5 percent. Production decline which began in 1973 accelerated annually to a low of 6.0 percent in 1979; since 1979 the annual crude decline rate has been cut 3.5 percent, and further moderated to 2.7 percent in the past two years. The reserve to production ratio in Texas, which dropped to well below 8 percent in 1977 and which had been slipping at an average annual rate of 3.7 percent from 1973 through 1979, has subsequently increased at an average annual rate in Texas of 3 percent. The same kind of trends are seen nationally. Non-Alaskan domestic production was declining at an annual average rate of 4 percent during the f early and middle 1970 s. Over the past seven years, an average annual rise of 0.9 percent has been posted. Beyond the volume and rate of reserve growth there is particular significance in its compositional change. In the U.S.A. Lower 48 during the 1950fs and 1960's, new pool discovery made up about 34 percent of reserve growth. In the past decade new pool contribution to reserve growth was down to 18 percent, and in the more mature Texas basins was 10 percent. Tertiary projects were negligible in the 1950's and 1960fs, but over the past decade chiefly with increased thermal recovery constituted 6 percent of reserve growth. In Texas where carbon dioxide is much more prevalent than steam recovery, tertiary additions make up about 4 percent of reserve growth. By far the most significant component of reserve growth comes from extension and infill drilling. In onland U.S.A. during the 1950's and 1960fs, these development techniques contributed 66 percent of reserve growth; over the past decade the contribution has been 76 percent, and in the mature Texas basins, 87 percent. In the complex reservoirs of the West Texas Permian Basins, extension and infill drilling contributed 93 percent of the large reserve growth, while tertiary recovery projects have contributed 6 percent and new pool discovery only 1 percent. The volume, ratio, and composition of reserve growth witnessed in several U.S.A. basins over the past decade suggest the dimension of reserve growth potential. By far the largest reserve growth has occurred in the geologically complex reservoirs such as those of the West Texas Permian Basin, and the vast part of that growth is attributable to extension and infill drilling in geologically complex carbonate reservoirs. Recovery efficiency of reservoirs is obviously controlled by a number of variables, such as drive, porosity, permeability, water saturation, residual oil saturation, viscosity, formation volume factor, among others. Although extensive statistical treatment of these parameters relative to reservoir performance shows general correlations, much unaccounted for variability remains. Beyond drive mechanism, lithology, and fluid properties, a fourth class of variables, primarily related to macroscopic heterogeneity or well-to-well variability, has recently emerged. Although a number of factors may contribute to macroscopic heterogeneity in reservoirs, the first-order control appears to be determined by facies architecture, most of which is the result of the original mode of deposition. Even in reservoirs where diagenesis is overriding, much of the fluid behavior pattern is related to original facies framework. Exceptions seem to exist only where extensive, postdepositional structural modification occurred, such as highly fractured, very low matrix permeability formations.

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An analysis of the major oil reservoirs in Texas illustrates relation of geologic origin to oil recovery. To date in Texas some 156 billion barrels of in-place oil have been discovered.Ultimate oil recovery, based on currently deployed techniques, is estimated at about 54 billion barrels or 35 percent of in-place oil. Conventional recovery is highly variable ranging from as little as 5 percent to as much as 87 percent. Of the unrecoverable oil in Texas reservoirs, about 70 percent exists as residual oil and 30 percent exists as nonresidual but not currently recoverable. Significantly, the residency of this nonrecoverable, nonresidual oil correlates directly with facies architecture owing to original depositional environment, modified in some cases by levels of reservoir energy.

Depositional System (Genetic Origin)

Current UOR/ Total Nonresidual Oil

Strandplain—wave-dominated deltas (strong drive) 2. Barrier bars (strong drive) 3. Large-scale carbonate reefs and atolls 4. Fluvially-dominated deltas (strong drive) 5. Carbonate ramps (moderate drive) 6. Barrier bars (weak drive) 7. Highly fractured carbonate platforms (strong drive) 8. Wave-dominated deltas (weak drive) 9. Fan deltas (moderate drive) 10. Fluvial systems (strong drive) 11. Fluvially-dominated deltas (weak drive) 12. Carbonate platforms (moderate to weak drive) 13. Shelf-edge reefs and banks 14. Basin-flooring turbidites (weak drive)

91 87 85 73 69 63 63 62 58 57 57 51 46 29

The above range in reservoir performance is based on analyses of 450 of the largest Texas oil reservoirs. In all cases recovery of nonresidual oil, listed in order of decreasing efficiency, relates to facies complexity, listed in order of increasing complexity. Modification is chiefly due to drive mechanism, itself largely a function of scale of the depositional system of which the reservoir is a part. For example, reservoirs that are part of large scale barrier bar systems commonly have large associated aquifers and a strong water drive; an average of 87 percent of the nonresidual oil.* is recovered. Reservoirs that are part of small scale, more stratigraphically isolated barrier bar systems commonly have weak gas solution drives with average, nonresidual oil recovery of 63 percent. Reservoirs in highly heterogeneous, stratigraphically isolated systems like basin-flooring turbidites show average efficiency of 29 percent, and may be as low as 15 percent. Based on the Texas analysis, reservoir heterogeneity in response to genetic facies composition appears to be a controlling factor in conventional oil recovery. In turn, it defines the area of investigation most essential to additional recovery and enlarged reserve growth. Historically, field development has been based on the assumption that reservoirs and fluid behavior within them are more or less homogeneous. Where heterogeneity was obvious it has been generally assumed to be more or less uniform across a reservoir. Rarely is either assumption justified although these basic assumptions have been the basis for most historical development of reservoirs. Thus, most field development is by uniform, grid spacing—geography—rather than on geologic variation and heterogeneity.

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More stratigraphically defined exploitation, based on detailed geologic characterization of reservoirs to model and predict fluid behavior promises to be an important direction in petroleum geology, especially in exploratory mature basins. The volume of oil that is conventionally unrecoverable is large, worldwide and in most basins amounting to about two thirds of the originally discovered oil. Intensive integration of detailed geologic characterization and fluid behavior models is essential to reserve growth whether through extended conventional development or application of tertiary techniques.

ELECTRON

BEAM METHODS IN GEOSCIENCES:

TEM - THE

TECHNIQUE

J.D. Fitz Gerald Research School of Earth Sciences, Australian National University, Canberra This paper is to introduce the Transmission Electron Microscope, an instrument quite different from the better known SEM and Electron Probe. All TEM's form images along geometric lines similar to those of the familiar transmitted-light microscope, but with major (costly) differences in technology involved in the generation and focussing of the imaging radiation. Unfortunately, electron beams produced at voltages up to 200 kV in TEM will only penetrate -0.5 urn thicknesses of mineral samples. Specimen preparation is consequently a critical aspect of any TEM study; so much so that TEM of most geological materials became feasible only with the advent of the ion-beam-thinning preparation method. The principal advantage of TEM imaging, far outweighing instrumental and sample difficulties, lies in the resolution of detail:- direct magnifications of 1 million times are possible (cf. optical limit of -1 thousand times). Structure imaging at the unit cell scale (HREM) is now a routine procedure. Imaging is not, however, the -only strength of the TEM: crystalline materials will diffract electrons and analysis of diffraction in TEM can yield much of the same information from submicron particles as XRD can from bulk materials. Diffraction is also used to advantage in enhancement of contrast (i.e. information) in TEM imaging modes. The dual imaging-diffraction capability of TEM has already led directly to significant advances in mineralogy, particularly through studies of exsolution and phase transformation. One other successful application of TEM has been in the field of rock and mineral deformation. The most modern TEM instruments are being equipped with sophisticated tools to aid in studies of new aspects of submicron-scale structures. The most promising developments are in the realm of microchemical analysis. Spectroscopy, using X-ray (XEDS) or electron (EELS) signals, can now deliver information about the compositions of regions as small as 10 nm in diameter. The flow of new and valuable information about geological materials at the ultra-fine scale must be accelerated by access to this sophisticated technology; such access will doubtlessly be improved by new generation TEM's equipped with scanning-beam systems (STEM's) and multiple signal-detectors and coupled to computer control and data processing facilities.

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NEPHRITE JADE NEAR COWELL, SOUTH AUSTRALIA

D.J. Flint, E.A. Dubowski & J.G.. Olliver S.A. Department of Mines and Energy, Adelaide Near Cowell on Eyre Peninsula, South Australia, nephrite jade has formed in a complex composite gneiss terrain resulting from multiphase deformation, high-grade metamorphism and metasomatism of Early Proterozoic Hutchison Group sediments and Archean gneiss during Early to Middle Proterozoic Kimban Orogeny. Cross warping, fracturing and diffusion of silica along fractures and joints during late-stage folding has produced pods, stringers and lenses of nephrite jade by reaction of migrating silica with dolomitic marble at or near the base of Hutchison Group. The larger of the 112 known nephrite jade outcrops . . are conformable with lithological layering . are up to 65 m long and 3 m wide . grade into coarse-grained tremolite schist, talc schist and massive talc + tremolite + chlorite rock. However, highest-quality finest-grained massive dark green to black nephrite jade and rarer translucent light green jade are restricted to cross fractures up to 1 m wide parallel to the axial plane of late stage cross-warping. Most other nephrite jade, eg. British Columbia and New Zealand, have formed from serpentinised ultramafics with green varieties averaging about 0.191 chromium. Cowell nephrite jade contains negligible chromium with darkness of colour related to iron content which reaches 7.9S ^2^3 in the blackest samples. From discovery in 1966 to end of 1983 an estimated 1 028 tonnes have been mined mainly from nine outcrops comprising about 351 black and 651 mid to dark green. References Barnes, L.C., Conor, C.H.H., Crettenden, P.P., Daly, S.J., Harris, R.J., Johnson, P.D., McCallum, W.S., Nichol, D., Pitt, G.M., Scott, D.C., Wildy, R.L., and Young, D.A., 1980. Some semi precious and ornamental stones of South Australia. Geol. Surv. S. Aust., Handbook 4: 11-39. Nichol, D., 1977. Mineral Resour. Rev. S. Aust., 141: 11-26. Olliver, J.G., 1983. S. Aust. Dept. Mines and Energy report 84/11 (unpublished) Parker, S. Aust. Dept. Mines and Energy report 81/114 (unpublished).

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WATER RESOURCES M A N A G E M E N T IN MINING - EXPERIENCES THE BHP COMPANY

R.J. Frost BHP Engineering, North Sydney Mining in Australia is generally characterised by the remoteness and the aridity of the mine site. Yet despite the aridity of much of Australia it is regularly subjected to flooding of considerable severity. Adding to these problems of the mining companies is the often poor quality of the groundwater encountered in mining. The summary of all these circumstances is that water must be considered a resource which often must be as carefully husbanded as the ore resource itself. Furthermore, the proper management of water, both on the supply side and on the usage side of the water balance equation is essential. The BHP Company operates or is partner in a diverse range of mines throughout Australia including iron ore, manganese, coal and bauxite. The water management situations and problems at these mines are typical of other Australian mines in similar areas. This paper describes the varied experiences of the BHP Company in this regard.

ENERGY OPTIONS AND THE ENVIRONMENT W. S. Fyfe Department of Geology, University of Western Ontario, London, Canada The present global population (4.7 billion) is largely a result of technology and in particular our use of fossil energy. In a general way, human opportunity and wealth are related to per capita energy consumption. Given the near certainty that population will reach 10 billion early next century, and given intelligent conservation, it is clear that global energy production must at least double by early next century. If it does not, the present global inequalities will become even more intolerable and we will move more and more to C.P. Snow's "State of Siege". The task of the scientist is to assist decision makers in forming rational long term plans for future energy development. Every technological development has an impact on the environment and it is here, that the planetary (earth) scientist has his vital place in the planning. We are more aware of the surface environment and its fragility over time than any other group of scientists and technologists and must accept our responsibility. Any decision on massive, future energy development will involve consideration of economic and technical feasibility and the environmental impact. As man becomes the dominant agent changing the surface environment of our planet, and as we appreciate increasingly that all places on our planet are connected, the environmental factors may well (should?) dominate over all other considerations. At this time a number of potential energy sources appear to have the potential for doubling sustained global energy production. These include, coal, biomass and nuclear energy. On a global scale hydro-power does not have the capacity, and solar energy while having many local applications, could not meet the demands of the industrial world. This may not be true in 2100. In this lecture I wish to concentrate on coal versus nuclear energy with some comment on biomass.

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There is no doubt that global coal resources could meet energy needs for several centuries. With coal, environmental problems abound but the most, striking involve, carbon dioxide emissions, acid gas emissions, trace element emissions (As, Cd, Hg, U, etc.)* There is no doubt that the global increase in atmospheric carbon dioxide has all scientists worried. Recent ice-core, ice-age data shows that climate may be very sensitive to changes in carbon dioxide. Almost all atmosphere experts expect warming to result from the present increases. There is great need for an accelerated effort in understanding climate history. But if the world went to coal as its energy source? Despite increased technology for reducing acid emissions, the acid rain problem is accelerating globally. Forests, rivers, lakes are threatened. At the present time the only solution to reducing this effect appears reduction in fossil fuel use. Coals are notorious for collecting and fixing a wide range of trace metals during the coal-forming process. The subject has received too little attention. For a metal such as uranium, the amount dispersed at the present time is about 20,000 tons per year. Each coal is unique. If restrictions were placed on acceptable U , S, Cd, Hg, A s , etc., levels, the global coal resource might be much less impressive. There is no doubt that world uranium-thorium resources and present technology, make nuclear fission energy a potential alternative. In this technology France is leading the way with reduction in coal burning, oil burning (80% in 8 years) and increased nuclear capacity (70% by 1990). And the large breeder, Superphenix will operate in 1986. As work in Sweden and France shows reactor safety is being, and can be, improved. The problems with nuclear power (at least those we think about now!) are related to mining pollution and nuclear waste disposal. Work at this university on Ra-U-Th fixation by apatite minerals indicates that mining pollution can be dramatically reduced (effluents at or below sea water levels). A multitude of schemes for high-level waste disposal are under investigation and many appear acceptable. In this field I would commend the Swedish corrosion resistant container concept (one million years) and the concept of dispersal in crystalline, low solubility phases stressed by Ringwood in this country. But most would agree that secure long term storage is necessary to reduce the heat pulse before geologic disposal. While many systems and sites for disposal are under investigation, other potential sites require investigation, in particular in the marine environment, sea floor sediments and subduct ion zones. We are not yet at the stage of knowledge to start major disposal. Geologic knowledge on the preservation of sensitive materials for tens of millions of years in rocks must guide the final decision. In general, this aspect of waste disposal has not received the attention it deserves. At first sight, the use of biomass, via combustion, fermentation to alcohol, gasification, etc., has great appeal. It is a renewable resource and, unlike fossil forms of carbon, it does not perturb the carbon dioxide balance. But given present technology (e.g. the sugar-alcohol program of Brazil) biomass for fuel must compete with biomass for food. Given that at least 1 billion at present suffer from sever malnutrition the attractions of biomass fuel rapidly diminishes. Biomass production (except for aqua-culture) requires soil and soil is becoming one of the most valuable human resources. At present we have 0.4 acres of arable land per person, by 2020 0.2 acres. And modern intensive agriculture is energy and fertilizer hungry. And our modern fertilizers (phosphates) are highly polluting. Superphosphate commonly contains over 100 ppm uranium, 90 ppm cadmium, 10 ppm arsenic. Continuous heavy use must cause local health problems.

180

But it is soil erosion that is causing increasing alarm. The world rate of fertile soil erosion of the order of 2.4 x 1016g a-1, is similar to the rate of new crust formation at ocean ridges. It takes more than a thousand years to produce fertile soil from rock. And as every acre of possible soil becomes cultivated erosion will accelerate. Clear river waters are becoming rare, the world's rivers run brown. Further,the use of agri-byproducts such as straw for fuel, leads to further soil deterioration. At this time and for decades to come, farming for food must take priority over farming for fuel. In summary, if the world's future energy needs are met by coal, the impact on climate may be disastrous, if met by biomass, human nutritional standards may further deteriorate. The only option that is perhaps environmentally acceptable and has the capacity to meet demand, is nuclear energy. A much increased involvement is required by the geological community to make sure that the best geological waste disposal methods are developed.

C E N O Z O I C A N D R E C E N T V O L C A N I S M ON THE C A M P B E L L P L A T E A U : G E O C H E M I S T R Y OF V O L C A N I C R O C K S AND AN A S S E S S M E N T OF THE SUB-CONTINENTAL MANTLE

J.A. Gamble

and P.A. Morris

"^Department of Geology, Victoria University of Wellington ^Department of Geology and Geophysics, Sydney University The Campbell Plateau south and southeast of N e w Zealand is an extensive area of submerged continental crust. Late Cenozoic volcanism established a number of shield volcanoes on this basement. Antipodes Island, Auckland Islands a n d Campbell Island consist largely of subaerially erupted lava flows and pyroclastic rocks. A n t i p o d e s i s t h e y o u n g e s t (<1 m y , K - A r ) a n d m a n y juvenile volcanic features are preserved. Campbell (~8-6 m y , K - A r ) a n d the Auckland Islands archipelago (-15-12 m y , K-Ar) are composed mostly of subaerial l a v a f l o w s o f b a s a l t a n d h a w a i i t e which- e r u p t e d f r o m d y k e f e d f i s s u r e s y s t e m s . More evolved lavas formed domes and laterally discontinuous flows erupted from localised vents. Intense dyke swarms (Auckland Islands) and texturally heterogeneous gabbroic intrusions (Auckland a n d Campbell Islands) a r e exposed in the deeply eroded cores of the shields. C o m p o s i t i o n s range from strongly u n d e r s a t u r a t e d basanites (>10% normative nepheline) on Antipodes Island to basalts and hawaiites of a mildly alkalinetransitional tholeiite character (either <3% normative nepheline o r normative hypersthene) on Campbell and the Auckland Islands. The majority have evolved 2 + compositions with Mg/Mg+Fe < 6 0 , N i <200 p p m and Cr <200 p p m . A l l show the chemical c h a r a c t e r i s t i c s (Zr/Nb <6; Y / N b <1) of a plume or intraplate tectonic setting. Rocks from a l l the centres are more or less porphyritic and multiply saturated with olivine, clinopyroxene, plagioclase and Fe-Ti oxides. Upper mantle nodules are unknown from the Auckland Islands and Campbell Island volcanoes, b u t rare corroded cores in clinopyroxene phenocrysts and aggregates of clinopyroxene a n d olivine m a y represent disaggregated nodules. Many of the lavas from Antipodes Island contain corroded and resorbed xenocrysts of red6 % b r o w n a m p h i b o l e ( M g / M g + F e = . 7 0 , A I 2 O 3 = 1 3 % , TiC>2 = ) plus complexly zoned clinopyroxene phenocrysts with sodic salite cores which w e interpret to b e of high pressure origin.

181

Primitive compositions from the Auckland Islands and Campbell show similar abundances and ratios of incompatible elements (Zr/Nb = 3.98, 3.84; Y/Nb. = 0.59, 0.56; Zr/Y = 6.73, 6.86; K/Rb = 380,. 320; K/Ba = 300, 300; Rb/Sr = 0.038, 0.042; Ce N /Y N = 4.82; 5.45 for basalt 82264, Auckland Islands and basalt 39796, Campbell Island respectively) and 87sr/ 86 sr isotopic ratios (82264 = 0.70369; 39796 =0.70372 at 12 my) indicating broad similarity in their mantle source regions. Incoherent chemical trends in the more evolved lavas result from a combination of crystal fractionation, assimilation and/or crustal contamination processes. Elemental ratios for the more undersaturated lavas from Antipodes Island compare favourably with those of Auckland Islands and Campbell Island but the absolute abundances of the elements are enriched, presumably reflecting lower degrees of melting in the source region. The Antipodes rocks resemble the basanites and basalts of the Dunedin volcanic centre more closely than those of Auckland and Campbell Islands, which are more akin to those of Banks Peninsula.

THE STUART HIGHWAY : A CASE STUDY IN GROUNDWATER SUPPLIES IN AN ARID ENVIRONMENT N.Z. Gerges

South Australia Department of Mines and Energy, Adelaide In 1862, John McDouall Stuart led the first successfull crossing of Australia from south to north. The present Stuart Highway in South Australia covers 1075 km from Pt. Augusta to the N.T. border and most of its length still consists of an unformed but graded open surface which is rough and dusty in dry weather and frequently impassable after even moderate rainfall. In late 197*+ an alternative route was selected generally following the existing highway but 150 km shorter. Sealing of this new route is expected to be completed in 1986 at a total cost of 200 million dollars. From 1978 through to 198U the South Australia Department of Mines and Energy drilled a total of 123 wells, of which 53 wells were completed successfully. Well yields varied between 0- 5-15 L/sec with salinity ranging from 1000 to 30 000 mgL~^. The standard operation is for groundwater to be discharged into cohstructed surface storages with capacities in excess of k million litres, and then into conventional road watering vehicles as required. One constraint On well siting and completions was groundwater salinity since high salinity can cause problems with bitumen bonding on the pavement. The new highway in the south traverses the Gawler Platform where PreCambrian acid plutonic and high grade metamorphic rock are overlain by thin unconsolidated Tertiary and Mesozoic sediments. As the highway route enters the area underlain by Great Artesian Basin sediments, Mesozoic and Palaeozoic sediments thicken up to 800 metres. The northern section traverses the Musgrave block where Upper Proterozoic meta-sediments and granitoid rocks, the latter intruded by dolerite dykes^are covered by a thin veneer of Cainozoic deposits. The section of particular interest covers the 300 km from Pootnoura Creek in the south to the S.A. - N.T. border. The target aquifer for the section south of Maria was the Cretaceous Cadna-owie Formation which is overlain by a thick sequence of Cretaceous Bulldog Shale.

182

The Cadna-owie Formation which consists of sand and sandstone occurs at depths varying from 100 to 150 metres "below surface. Although it is generally overlain by a thick "confining bed" (Bulldog Shale), it is not a pressure aquifer. Downhole geophysics show it is divided into unsaturated and saturated zones. The water table is almost flat with a gentle gradient to the south. Groundwater salinities also increase southward. Production tests show that the aquifer has attained a quasi-equilibrium condition. Transmissivity ranges between 1000 m^day""^ and 2000 m ^ d a y l and long term safe yields vary between 10 Lsec"! and 15 Lsec-1 per well. Groundwater exploration north of Maria required the integrated use of surface geophysics, LANDSAT imagery, aerial photo-interpretation and scout drilling to determine prospective sites and well completion methods. The use of these techniques resulted in most wells being successful with yields of up to 10 Lsec"^- being obtained from upper Proterozoic meta-sediment aquifers. Well depths were generally 100 metres. In granitoid rocks most lineaments were dykes (dolerite and micro-gabbro) and these have proven to be non-prospective for groundwater development.

183

A twenty four hour production test was performed on each well to estimate a medium-long term yield and to assess the number of storage dams required along route.

ALICE.

SPRINGS

NORTHERN QUEENSLAND TERRITORY Kulgara

26° S

"Granite Downs Maria

* OodnadaJ-fa

Poofnoura

SOUTH l

Ck.

Coobar P<2dy

AUSTRALIA Marrcc. SO°S (LE-IGH CRttK

Tarcoola

PORT A U G U S T A

[ P O R T PIQ1E.

- 3 4 °S

SCALe ioo

l o o 200

ADELAIDE.

kilometres

STUART

184

HIGHWAY

- Uocalif-y P l a o .

SALTS AND SANDS: CRYSTALLIZATION PROCESSES IN ROCK CAPILLARIES G.S. Gibbons New South Wales Institute of Technology, Broadway Conservation work on ancient rock art and historic buildings has developed a small but wide-ranging literature with relevance to broad geological processes such as natural surface weathering, sabkha diagenesis, evaporite development, and possibly also crystallization processes at deeper-seated reaction fronts. The work has been done because a major cause of weathering of porous rock is the accumulation of salts transported by natural waters. The same processes of damage can affect also such materials as concrete, mortar, and brick. Most of the work has, therefore, concerned salt crystallization at the edges of capillary fringes, but the approaches have been varied. Crystallization from aqueous solutions in weathering rocks generally occurs by evaporation, but is not localized in a single zone of supersaturation. In the first place, an appreciable amount of solution is isolated in the narrower capillaries as the saturation front retreats, and this isolated solution in the non-saturated zone crystallizes as evaporation proceeds. As the general saturation front retreats the evaporative surface solution becomes more concentrated until one or more phases begin to crystallize. Although continuing evaporation leads to a net volume loss, the crystallization may produce spongy masses with fine capillaries. These masses can act as a wick and cause continuing movement of moisture towards the stone surface, especially where cyclic drying occurs. In this case the rock saturation front continues to retreat into the stone whereas the evaporative front may be stationary or may even migrate towards the stone surface. The common phenomenon of efflorescence is probably always associated with this process. Similar effects may apply in phase-change situations, especially where free liquid is produced as a result of temperature rise. Other aspects to be considered include ion-exchange effects and chromatographic partitioning, especially where capillary movement is a major process. References Arnold, A., 1981, Nature and Reactions of Saline Minerals in Walls: in_ R. Rossi-Manaresi (ed.) The Conservation of Stone, Centro per la Conservazione della Sculture All'Aperto, Bologna, 13-33. Arnold, M., 1978, Second Report, Salt Damp Reseach Committee, South Australian Government Printer, Adelaide, 27-65. Puhringer, J., 1983, Salzwanderung und Verwitterung durch Salze (with English summary) in_ Materials Science and Restoration, ed. F.H. Wittman, Technische Akademie Esslingen, 361-366. Stambolov, T., & van Asperen de Boer, J.R.J., 1976, The Deterioration and Conservation of Porous Building Materials in Monuments:A Review of the Literature. ICCROM, Rome (86pp.). Torraca, G., 1982, Porous Building Materials - Materials Science for Architectural Conservation (2nd Ed.) ICCROM, Rome (145pp).

185

ORGANIC-RICH CAMBRIAN CARBONATES, CAMOOWEAL AREA, GE0R6INA BASIN D.L. Gibson and C.J. Boreham Division of Continental Geology, Bureau of Mineral Resources, Canberra

The Camooweal oil shale occurrence, first reported in 1945 from a water bore 115 km northwest of Mt Isa, consists of thin beds of organicrich fine carbonates in the Middle Cambrian Currant Bush Limestone, Inca Formation, and Thorntonia Limestone, units deposited in a shallow equatorial epeiric sea. Samples for this study come from the fully-cored drillholes BMR Mt Isa 1 (located close to the original discovery) and BMR Camooweal 2, 38 km to the NNE. The Currant Bush Limestone in these holes consists mainly of 1-5 m thick repetitive depositional cycles. Tan to pink laminated fine limestone containing sparse organic lamellae, with brown silicified zones (containing abundant pyrite, and some sphalerite) and intercalated lenses of massive white to pink micritic limestone occurs at the base of each cycle. The laminated limestone becomes increasingly silty (terriginous quartz, plagioclase feldspar, and muscovite) upwards, and generally passes into greengrey calcareous siltstone with organic lamellae, which in turn passes up into a thin (generally 2-15 cm), dark organic-rich fine silty carbonate. This grades rapidly into organic-lean laminated limestone at the base of the next cycle. Towards the base of the formation, the oil shales have intercalated beds of rippled fine grainstone and massive fine limestone. The laminated limestones and siltstones contain 0.2-2.7% TOC, and the organic-rich rocks 3.4-16.6%, with maximum Fischer Assay yield of 106 1/t (dry). The organic content rises up most cycles, as does the hydrogen index (measured by Rock-Eval) of the organic matter, indicating that the depositional environment may have become less oxidising during deposition of each cycle. Flattened skeletal remains, early diagenetic nodules in the siltstones and limestones, and rare silicified zones in the organic-rich rocks with a relatively low organic content (which is far less compressed than normal), all point to major diagenetic compaction, which would involve the reduction of pore space and possible removal of carbonate. The carbonate grains themselves consist of silt sized pellets of cloudy micrite in the massive beds, ranging through vaguely pelleted micrite and microspar calcite in the laminated limestones, to microspar and silt-sized dolomite rhombs in the siltstones and organic-rich rocks. The grainstones consist of pellets, microspar calcite, dolomite rhombs, and terriginous silt. The organic-rich rocks contain occasional laminae and irregular lenses of vaguely pelleted micrite. It is likely that the oxic/anoxic interface was within the sediment at all times, but that it was close to the surface during deposition of the organic-rich rocks. There are no signs of biological reworking of the cyclic sediments; exclusion of burrowing fauna is attributed to the anoxic conditions. Silicification is attributed to mobilisation of silica from sponge spicules in the organic-rich rocks and limestones, and subsequent precipitation in zones of fluid pathways where sulphides were precipitating. It is difficult to fit a depositional model to the cycles. The silt is most probably aeolian, and the presence of a marked organic maximum

186

at the point of sudden decline in silt content could result from a rapid decrease in regional wind strength causing a drop in silt supply and cessation of wind-driven water overturn. This would limit the input of nutrients from deeper water, and cause mass death of a flourishing micro-biota. Some bedding planes of the organic-rich rocks are crowded with agnostid trilobite and inarticulate brachiopod remains, also indicating mass death. The conformably underlying Inca Formation in the BMR holes consists of dark organic carbonate mudstone containing terriginous silt, which passes laterally into carbonate nodules. Beds of rippled grainstone are intercalated, and become coarse and partly dolomitised towards the base of the unit in Mt Isa 1. Pervasive silicification has affected most of the formation, especially in Camooweal 2. TOC ranges up to 9% (Fischer Assay 59 1/t dry), and beds of organic-rich rock appear to be up to 0.5 m thick. The hydrogen index of the organic matter is high, indicating strongly reducing conditions throughout the formation. Organic-rich beds in the unconformably underlying Thorntonia Limestone are most probably stylolitic concentrations of insolubles (organic matter, glauconite, terriginous silt etc.) up to 10 cm thick, containing up to 8.3% TOC. The major component of the organic matter in the Currant Bush Limestone and Inca Formation as shown by A. Hutton (University of Wollongong, unpublished data), is non-fluorescing, lamellar, 'vitrinite like' material which may be referred to as bituminite, with some fluorescing lamellar alginite, and humic acids (identified by M. Glikson, CRES, ANU). Kerogen analyses and Rock-Eval data show that the organic matter of the oil shales is Type I or II, but that organic lean rocks have Type III. Rock-Eval and extract data show that the rocks are immature to marginally mature, so even though they may not be a good oil shale prospect, they could be an excellent petroleum source rock if buried more deeply. It is tempting to assign an algal mat origin to the organic matter, as the rocks resemble Recent smooth algal mat stromatolites (allowing for compaction of the Camooweal rocks), and the organic matter displays TEM ultra-structures reminiscent of algal filaments (M. Glikson, ANU, pers. comm.). However, uncompressed silicified zones in the Currant Bush Limestone oil shales contain small (generally less than 0.2 mm long) fragments of organic matter rather than continuous lamellae expected from algal mats, so an allochthonous origin (most probably planktonic algae) is favoured here.

THE LONDON VICTORIA GOLD PROSPECT, PARKES,

N.S.W.

John F. Gilfillan and M.R.W. Garman John F. Gilfillan & Associates Pty. Limited, Sydney The Parkes-Forbes Goldfield was discovered in 1861. Recorded production from alluvial and reef mines in the area is 25.5 tonnes at an average grade of lOg/t gold. More than half of this production was from alluvial deposits. The town of Parkes is located about 365 kilometres west of Sydney. The area is within the Forbes Anticlinorial Zone of the Lower Palaeozoic Lachlan Fold Belt.

187

Locally the rocks consist of a series of shallow to deep water marine sediments with associated andesitic to trachytic volcanics and pyroclastics. The sequence has been regionally folded into a series of meridional trending folds and is bounded on the west by the Parkes Thrust. Most of the hard rock gold mineralisation is either spatially related to the Bushmans Andesite or within the unit known as the Parkes Andesite Suite. The gold mineralisation spatially related to the Bushmans Andesite is generally of the quartz vein type which cross-cuts the bedding and regional foliation. The gold mineralisation within the Parkes Andesite Suite is generally parallel with bedding and regional foliation and is within hydrothermally altered zones which may also be shear zones. Gold deposits of this type include the London-Victoria Line of Lode. The area was selected after a review of published and unpublished geological reports on the region. Evaluation of prospects and geological targets led to intensive exploration of the London-Victoria Line of Lode over a 2km strike length. This lode zone is associated with a steeply east-dipping fault system which forms the western boundary of the Parkes Andesite Suite. The fault has been identified over 9km. Lodes occur as groups of overlapping thin lenses. Fine grained free gold is disseminated with pyrite and irregular veins and veinlets of quartz-carbonate-Kfeldspar-albite within altered sericitic andesitic tuffaceous host rocks. As a result of extensive agricultural activity and poor outcrop, exploration targets were mostly defined by soil geochemistry. Mercury and lead proved to be useful pathfinder elements for regional and detailed target generation. Subsequent evaluation of the lode has entailed detailed geological investigation and sampling by diamond core drilling and trenching. Extreme weathering near surface required core sizes up to 85mm to achieve full sample recovery. All samples have been analysed by AAS. Samples containing more than lg/t Au have been checked by fire assay. Ore reserve estimates have been calculated by classical, geostatistical and in-pit geological reserve methods. The in-pit geological reserves are confined to the three proposed open pits and include internal dilution. Considerable differences in bulk density exist between weathered and fresh rock. Quoted reserves take account of preliminary estimates of these variations. The present total of probable reserves and possible ore is 837,000 tonnes grading 3.0g/t Au using a lg/t Au cut-off or 448,500 tonnes grading 4.7g/t Au at a 2g/t Au cut-off. Initial engineering studies propose three open pits to mine the London and adjacent shoots. Metallurgical testing indicates cyanide extraction exceeding 90% of the contained gold can be expected in a treatment plant using carbon-in-pulp technology. There is also considered to be good potential for the establishment of a resource suitable for underground mining techniques. A number of other areas within the Parkes Andesite Suite have been identified as having potential for containing significant gold mineralisation. The main target of the exploration programme has been gold. However, drilling in the Victoria Mine area and, subsequently, soil geochemistry to the east and south have identified a zone of lead-zinc-silver (gold) mineralisation. This zone is approximately 1200 metres long by up to 300 metres wide and forms the eastern boundary of the gold mineralisation in the southern part of the London-Victoria Gold Prospect area. The genetic relationship between this lead-zinc-silver (gold) mineralisation and the gold mineralisation has yet to be established.

188

PRECIOUS METAL - ANTIMONY - ARSENIC METALLIZATION AND MAGMATISM IN CENTRAL NEW ENGLAND, NEW SOUTH WALES L.B. Gilliqan Geological Survey of N.S.W., Sydney Systematic collection of mineral deposit data from the central part of the New England region of New South Wales for the production of the Dorrigo-Coffs Harbour Metallogenic Map has highlighted important granitoid-mineral deposit associations that may contribute to the understanding of the relationship between both I- and Stype magmatism and metallization in the New England Fold Belt. Further, this work also may help in elucidation of the vexing question of the origin of the Hillgrove antimony-gold-tungsten mineralisation. The deposits of particular interest are the gold-silver-antimony-arsenic deposits in the Tilbuster-Puddledock area, the Uralla area and the Rockvale-Coningdale area, north, southeast and east of Armidale respectively. These deposits are considered to be magmatic hydrothermal and their origin is attributed to granitic plutonism. In the Tilbuster-Puddledock area, vein gold (+ silver) - antimony - arsenic deposits occur on the southwest and northeast margins of the Tilbuster Granodiorite. In the Uralla area similar deposits are developed peripheral to the Khatoun Tonalite and along a northeasterly trending fracture in the intruded Uralla Granodiorite. The Khatoun Tonalite is a shallowly unroofed stock affiliated with the Uralla Granodiorite. Both the Tilbuster Granodiorite and Uralla Granodiorite are members of the Late Permian Uralla Plutonic Suite (Shaw and Flood, 1981). These authors ascribed the Uralla Plutonic Suite with I-type characteristics but less so than, say, the Moonbi Plutonic Suite to the south. They considered the Uralla Plutonic Suite to have formed in a region containing a mixture of metaluminous and peraluminous source rocks (gabbro and ?sedimentary rocks). The distribution of mineralization in the Rockvale-Coningdale area and the presence of roof-pendant sediment in the Rockvale Adamellite suggest this granitoid has been shallowly unroofed. Spectacularly rich silver-arsenic deposits are developed both on the granitoid margin (Tulloch silver mine) and associated with roof-pendant sediments (Ruby silver mine). Gold-pyrite-pyrrhotite-quartz vein mineralization is well developed on the northern margin (Comet gold mine). Both north and south of the Rockvale Adamellite are antimony (+ gold ± silver) deposits which are interpreted to have formed from hydrothermal solutions derived from the cooling Rockvale Adamellite. The Rockvale Adamellite is an S-type granitoid (Shaw and Flood, 1981) of the Early Permian Hillgrove Plutonic Suite. In addition to the Rockvale Adamellite there is a marked clustering of gold and/or antimony (tungsten) deposits in and adjacent to a number of Hillgrove suite plutons; e.g. gold deposits with the Kookabookra Adamellite, antimony-gold-tungsten deposits with the Hillgrove Adamellite and gold deposits with the Enmore Adamellite. No genetic association, however, has yet been established between mineralization and associated granitoids. The similarity in metallogenesis between the Uralla Plutonic Suite and the Hillgrove Plutonic Suite (Rockvale Adamellite) may indicate that the precious metalantimony-arsenic anomalism is a function of enrichment of these elements in, perhaps common, sedimentary source rocks for the respective magmas despite the apparently considerable difference in ages of the plutonic suites. Reference Shaw, S.E. and Flood, R.H., 1981. The New England Batholith, Eastern Australia: Geochemical Variations in Time and Space - J. Geophys. Res., 86, 10530-10544 * Published with permission of the Secretary, New South Wales Department of Mineral Resources, Sydney. 189

STRUCTURAL CONTROL OF COPPER-RICH DEPOSITS AT COBAR, N.S.W. R.A. Glen Geological Survey of New South Wales, Sydney The ore deposits of the Cobar Mining Field are structurally controlled. There has been much discussion whether they represent syngenetic deposits deformed by shortening and elongation in cleavage (Gilligan & Suppel 1978) or by simple shear (Sangster 1979) , or whether they are epigenetic. The deposits of the Cobar field consist of two main mineralogical types - chalcopyrite - pyrite - gold, commonly in veins or associated with silicification, and more massive or banded sphalerite - galena - pyrrhotite - pyrite. Based on recent work and review of literature, I use a structural and lithological basis to group copper-rich deposits of the Cobar field into three types. Type 1 deposits occur in two lines on or just west of two faulted sections of the contact between the Chesney Formation and the Great Cobar Slate. The faults are steep with east-block up (and some possible left-lateral) movement and cut through considerable section. The western line includes deposits from Tharsis south to the Peak area. The eastern line includes deposits from Coronation to Queen Bee. Type 2 deposits occur in faulted anticlinal hinge zones in the Great Cobar Slate. At the Great Cobar Mine this hinge is tight and plunges both to the N and S. At the Gladstone Mine this hinge is broad and S plunging. Type 3 deposits occur in the C.S.A. Siltstone and are characterized by lenses in the C.S.A. Mine. Copper-rich deposits of Types 1-3 generally consist of steeply north-plunging ore lenses within planar zones of quartz veining or silicification. Several types of quartz veins occur on the surface around deposits of Types 1-2. They include: 1) veins in S , with fibres parallel to L^, the mineral lineation, in the enclosing rocks, 2) veins in fractures lying at low angles in both dip and strike, to S , 1 3) veins perpendicular to L^, with fibres parallel to L , 1 4) veins oblique to S^ and folded about F , and 5) veins oblique to S^ and having an irregular or stockwork appearance. These veins, especially types 1,2 and 3 above, suggest syntectonic formation during the regional Carboniferous deformation, with dilatant sites forming mainly parallel or at low angles to S , but also perpendicular and oblique to S . All these veins formed by hydraulic fracturing, raising the suggestion that deposits of types 1-3 are hydraulic fracture fill deposits. Formation as fracture-fill vein systems provides another possible mechanism for concentration of sulphides in their present location, in addition to the two mentioned earlier. The deposits all occur in areas of regional S development, and there is ample evidence for solution activity, especially removal of silica from host rocks, during deformation and metamorphism. This silica may have been transported in solution and precipitated as quartz veins described above. It is worth investigating whether such metamorphic fluids could dissolve, transport and concentrate in quartz-sulphide veins, pre-existing disseminated sulphides which occur in small concentrations in rocks of the Cobar Supergroup in the Cobar Mining Field.

190

References Gilligan, L.B. & Suppel, D.W., 1978. 32 15-22. Sangster, D.F., 1979.

Quart Notes Geol. Surv. N.S.W.,

BMR Jnl of Aust. Geol. Geophys., 4, 15-24.

TRANSMISSION ELECTRON MICROSCOPY BACKED BY C-ISOTOPE ANALYSIS - A POWERFUL TOOL IN RESOLVING THE NATURE AND SOURCE OF ORGANIC MATTER IN OIL SHALE Miryam Glikson Centre f o r Resource and Environmental

Studies, Australian

National

University

Organic matter from various o i l shales studied by t r a n s m i s s i o n e l e c t r o n microscopy (TEM) and C-isotope a n a l y s i s revealed i t s nature and often i t s o r i g i n . The b a c t e r i a l o r i g i n and the l i p i d i c nature of v i t r i n i t e - l i k e organic matter (bituminite) can be demonstrated by using metal s t a i n s . Humic acids can be recognised by observing u l t r a t h i n s e c t i o n s of organic matter. TEM observations have a l s o helped to d i s t i n g u i s h between autochthonous versus allochthonous humic a c i d s . Such i n t e r p r e t a t i o n s are supported by C-isotope compositions of the humates as compared to the rest of the organic matter. The organic matter of the Lower Cretaceous Toolebuc o i l shales i s shown to originate mainly in filamentous bacteria of probable cyanobacterial a f f i n i t y . The humic acid f r a c t i o n in these o i l shales proved to have formed mostly in s i t u and did not play an important role in trace element concentration. Rare coccoid bacteria displayed high Cu concentrations. The Camooweal oil shales of s i m i l a r depositional environment as the Toolebuc show two main organic components when observed in l i g h t microscopy: (1) A very low reflectance f i n e l y laminated organic matter (Ro = 0.06 - 0.19%) and (2) a granular component of higher reflectance (Ro = 0.2 - 0.5%) in l e n t i c u l a r form or bands. TEM s t u d i e s show c l a s s 1 to be of a filamentous nature probably representing the o r i g i n a l cyanobacterial mat and c l a s s 2 proved to be humic a c i d s . Cisotope composition of the humic f r a c t i o n points to an allochthonous o r i g i n with h i g h l y 13C-depleted carbon source. The T e r t i a r y o i l shale deposits of Rundle and Condor revealed a l i p i d i c f r a c t i o n of algal nature and a hicjh proportion of humic acids derived from an outside source. The humic f r a c t i o n in these deposits proved to be from a t e r r e s t r i a l source as indicated by C- isotope compositions. Electron dense p a r t i c l e s associated with the humic f r a c t i o n proved to be mostly composed of Ti02 w h i c h h a d i t s o r i g i n in v o l c a n i c rocks in the h i n t e r - l a n d and has been mobilized and c a r r i e d by humic acids i n t o the lake system. Torbanites studied in TEM revealed filamentous bacteria of i n f e r r e d methanogenic a f f i n i t y associated with the remains of The former are r e s p o n s i b l e for the dark nonthe alga Botryococcus. f l u o r e s c i n g areas (in UV l i g h t , blue f i l t e r ) in these r o c k s , comprising the low reflectance ' v i t r i n i t e - l i k e ' organic matter. The Botryococcus remains in these o i l shales d i s p l a y u l t r a s t r u c t u r e s i d e n t i c a l to those seen in recently deposited rubbery botryococcal accumulations ('coorongi t e 1 ) . TEM observations of organic matter concentrate from the Green River o i l shale has revealed the predominant component to be of l i p i d i c - a l g a l nature, with occasional u l t r a - s t r u c t u r e reminiscent of Botryococcus t r i lamellar s h e a t h s . A humic acid f r a c t i o n f i l l i n g in spaces within the l i p i d i c matrix i s a s s o c i a t e d with h i g h l y electron dense p a r t i c l e s which

191

proved to be due to high concentrations of chromium - titanium and iron. The appearance of the Green River organic matter in TEM points to a different depositional environment and diagenetic history from any other Flow-lines within the predominant lipidic matrix may known oil shale. indicate mineral matter carried through a semi-liquid phase. The Early Miocene Mt Coolon oil shale shows a variability in its organic components and extensive biodegradation. Stages in the formation of humic acids are visible in TEM studies as well as filamentious bacteria, possibly sulphate - reducers. Bacterial degradation is supported by exceptionally high oxygen content as well as isotopically very light organic matter. Botryococcus lipid bodies identified only in TEM point to this alga as an important contributor to this oil shale. In summary, TEM observations of ultra thin sections coupled with Cisotope compositions have revealed the nature and origin of amorphous The predominent vitrinite-1ike organic organic matter in oil shales: matter in marine oil shales is shown to represent bacterial remains and their metabolites and humic acids. The source of some trace elements present in high concentrations in particular oil shales has been established by TEM/microprobe examination and C-isotope analysis. The unusual nature of the Green River oil shale has been confirmed by TEM observations, v^iich suggest that this organic matter is the result of chemical alteration of algal contributors rather than a biodegradation product.

N E A R - S U R F A C E GAS G E O C H E M I S T R Y O V E R THE G I N G I N B O O T I N E GAS F I E L D S , W E S T E R N A U S T R A L I A

AND

M.J. Gole, M.K.W. Hart and C.R.M. Butt CSIRO, Division of Mineralogy, Floreat Park, W . A . Near-surface gas samples from over the Gingin and Bootine gas fields have been analysed by mass spectrometry for helium, neon and hydrogen, by gas chromatography for Cj-C^ hydrocarbons and by emanometry for radon. One hundred and eighty semi-permanent sampling sites have been established on a 200m x 1km grid over the gas fields. Samples are collected from a depth of 6m, through 3mm ID vinyl tubes, emplaced in backfilled drill holes. This depth was chosen to ensure minimal mixing between the overburden gas and the atmosphere and to keep drilling costs down to a reasonable level. Six metres is below the depth at which barometric pumping is likely to occur. Sample gases are collected by syringe and injected into evacuated metal cylinders, sealed with a septum and a lead washer. The Gingin gas field, although large, only provided limited gas production, from low porosity sands of the Cockle Shell Gully Formation at a depth of about 4km. Seismic data shows that the field is bounded to the west by an easterly dipping fault which subcrops about 1km west of the Gingin No. 1 well.

192

Overburden gas helium concentrations range from 5-24 (atmosphere) to 6.1 ppm v/v, methane from 0.2 to 1235 ppm (atmosphere 1.2-1.4 ppm), ZC2-C4 alkanes from >0.01 to 15-8 ppm and ethylene from 0.01 to 23.0 ppm. Anomalous samples were analysed for neon and hydrogen which range, respectively, from 19*29 to 20.84 ppm (atmosphere l8.l8 ppm) and from = 1 ppm to 5%• There is, generally, a strong positive correlation between methane, alkanes, ethylene and, to a lesser extent, hydrogen. Anomalous helium (>5-40 ppm) with hydrocarbon (methane, >3.0 ppm; alkanes, >0.2 ppm) concentrations in overburden gas are only found on one traverse extending for approximately 600m in the area of the subcrop of the gas field boundary fault. Repeated sampling over several years has shown that the helium and hydrocarbon anomalies are long-lived features. The highest helium concentration of 6.1 ppm is a very significant anomaly in terms of normal overburden gas concentrations. A persistent helium anomaly (5«50-5-80 ppm), with no associated hydrocarbon anomaly, is present 1km west from the Bootine No. 1 well. Elsewhere in the survey area, however, few other sites show consistently elevated concentrations of helium or hydrocarbons, although a few are intermittently anomalous. Samples collected at depths shallower than 6m show a marked decrease in helium and methane concentrations relative to the 6m sample. At one anomalous site the 6m sample contains 5-57 ppm helium and 4.32 ppm methane whereas at 1.75m depth the concentrations are 5-33 ppm and I.84 ppm respectively. Neon is an atmospheric component assumed to be absent, as in Dongara natural gas, from Gingin gas. Normalising the anomalous helium data with neon reduces the helium concentrations to near atmospheric values and thus eliminates the anomaly. Ethylene and hydrogen are essentially absent from the Gingin gas and both are readily produced by near-surface biogenic processes. Thus the positive correlation between these gases and methane and C2-C4 alkanes imply that these latter gases are also of biogenic origin. The helium anomaly thus may be produced as an artifact of biologically produced changes in the major component compositions of the overburden gas. If, say, all the oxygen (*20% v/v) in the overburden gas is consumed and not replaced by some other component, the helium, neon and other remaining gases will increase by ^20% (i.e. for helium, from 5-24 to 6.3 ppm). To maintain an elevated concentration of highly diffusive helium, the process must be relatively active. It is not known why the overburden gas anomaly is located in a relatively restricted area over the subcrop of a fault. Apparently similar environments occur elsewhere along the fault and in other parts of the surveyed area but have no associated overburden gas anomaly. At Gingin, radon, advocated by some as a potential pathfinder for hydrocarbon deposits, reflects the distribution of lateritic ironstone which contains uranium-bearing heavy minerals. The results of this survey show that analysing soil/overburden gas for helium only is an inappropriate exploration technique. Similarly analysing only for C1-C4 alkanes is also inappropriate. Methane can be generated by biological activity and it appears that C2-C4 alkanes, at least at the low, but nevertheless anomalous, concentrations encountered in this study, can also be of biogenic origin.

193

SUPPORT OF GEOLOGICAL DEFECTS IN TUNNELS IN THE SYDNEY AREA N.M. Gray Engineering Geological Consultant, Sydney. Conventional tunnelling in the Sydney area often necessitates that support be given to the roof and the shoulders particularly and, to a lesser extent, the walls. Conditions encountered of both rock type and structure are variable, there being many differences even in tunnels of apparently similar rocks only a short distance apart. The necessity for support is viewed on a long term basis for those tunnels which are, by design, not lined or only partly lined. Tunnels which are fully lined are not being considered. Neither are T.B.M. type tunnels as the drilling of these avoids shattering of the rock and loosening of the joints which precludes much of the support normally necessary in conventional tunnels. Of the support needed, much depends on the degree of security required. It is believed that partial blockages of sewer tunnels is a more serious matter than in those for water supply. Further, the cost of maintenance must be considered and how long it would take to effect repairs. It is realised that the method of least maintenance is for the tunnel to be fully lined, though usually this is not economic, but there must be an arbitrary limit on the remedial work before commissioning that can be carried out. The bases of this discussion are what would be required in tunnel support in relation to potential instability caused by geological defects and the assessment, which must be made in each case, of the effect rock falls would have on the project and the maintenance cost involved. Each case must be examined on its merits. What will be proposed is, therefore, not a direction of how any particular defect must be treated. No matter what treatment is carried out, apart from full lining, there will always be some breakdown of the rock; the geological assessment is to limit the falls to this breakdown and to prevent major falls. Many methods of treatment are available to the engineer, and the method used at any particular location will depend on judgement of the circumstances evident at the time. Assessment of the geological conditions can indicate that treatment is required, and geological judgement is necessary to decide whether a particular treatment would be sufficient for the particular geological circumstances. Seven "treatment11 categories are suggested as follows Category 0 1 2 3 4 5 6

Treatment No treatment Sealing as by shotcrete or by gunite Structural support as well as sealing Structural support as sets Rock bolting with or without mesh Full support by concrete lining Groundwater conditions, drainage. Ac knowledgemen t s

The permission of the Metropolitan Water Sewerage and Drainage Board to present this data is gratefully acknowledged. The opinions expressed are those of the author and not necessarily those of the Board. Reference Gray, N.M., 1972, Unpubl. Rep. M.S.W. & D.B. 194

INTEGRATED ANALYSIS OF IMAGE DATA FOR MINERAL

EXPLORATION

A.A. Green, M.D. Craig and J.F. Huntington CSIRO Division of Mineral Physics, North Ryde The recent, rapid development of image processing systems has provided new opportunities for the flexible display of many different, twodimensional data sets used in mineral exploration. It is now quite possible to create "images" of geological maps, magnetic intensity, radiometric-count values, geochemistry, topographic and gravity data in addition to normal remote sensing data. All these data types can be stored in an image data—base on the same grid, and displayed using powerful image-processing techniques. Immediate benefits can be obtained from these new display-techniques. The geologist or geophysicist can make a rapid comparison between various data sets and (to a limited extent) can look at them together using combined displayprocedures such as colour-composites or pseudo-stereo images. However, the potential benefits of such an integrated data-base are much greater. The next step must be the introduction of geological and geophysical models which can relate the observed data-sets to the geological map of the area of interest. This is not a trivial problem and involves establishing a connection between observed variables at the surface (geology, geophysics, geochemistry, etc.) and geology (particularly mineralization) at depth. We can subdivide the available data types into two major groups, as follows. Potential-Field Variables

Surface-composition related variables

Gravity Magnetics

Radiometrics Geochemistry Remote sensing Surface geological mapping Topography

From a theoretical point of view, both data groups are complex functions of the same, three-dimensional rock-type distribution but, at the moment, there is no way to produce a unified model which will allow integrated interpretation of the two data groups. However, the general form of the analysis procedure required is essentially similar for both groups. Three types of information are needed: Observed data (e.g., magnetic intensity, geochemistry, etc.) A Physical Model A Geological Map In general, the observed data sets represent the various types of information that would be collected in a regional exploration-program. The physical model provides the connection between one data-type, and physical or chemical rock properties. The geological map provides the essential spatial information for the procedure. In principle, if the required rock properties were known for each rock type, one could use the geological map and the model to predict the spatial pattern of any given data type. A comparison of this predicted pattern with what is observed will almost certainly expose discrepancies which, if the model and the rock properties are correct, will highlight anomalous areas which should be investigated in more detail.

195

As we can now incorporate both the exploration data and geological maps into image data bases it remains to develop good physical models which can relate the two. In the case of potential field data these geophysical models already exist and their implementation is a matter of software development. The surface composition related variables can be treated with statistical regression procedures which estimate parameters of simplified models predicting element or mineral distribution as a function of rock type. In this paper we present four case studies which illustrate the evolution of the above concepts. The first study involves comparison of Landsat and airphoto data with mapped geology near the Teutonic Bore deposit in Western Australia. The second involves the integration of Landsat and geochemical data over the Weipa bauxite deposit in Queensland. The third involves the integration of Landsat and aeromagnetic data for nine 1:250,000 map sheets in northern New South Wales. The last case study involves the integration and modeling of geology, geochemical, topographic and Landsat data for the Forsayth 1:100,000 map sheet in NE Queensland.

THE EARTH'S LITHOSPHERE AND LOW VELOCITY

ZONE

D.H. Green Department of Geology, University of Tasmania The petrological approach to the study of the Earth's lithosphere and low velocity zone has three main strands (a) the collection of mineralogical, petrological and chemical information on the natural samples, including both crystalline rocks and magmas, derived from these regions, (b) the experimental study of actual or model mantle materials under controlled laboratory conditions simulating these present in the earth, (c) the chronological dimension of lithosphere/low velocity zone studies introduced through the study of radiogenic isotopes. The first two themes are interwoven and are the subject of this presentation. In general terms peridotite with olivine "F090, orthopyroxene, clinopyroxene and minor aluminous phases including (under appropriate physical conditions) plagioclase, spinel, garnet and amphibole is the major rock type of the lithosphere and low velocity zone. This conclusion rests on geophysical evidence, including seismic anisotropy, petrology and geological argument.

196

The experimental study of model peridotitic mantle compositions under controlled pressure/temperature conditions has established stability fields for plagioclase, spinel, garnet and amphibole peridotite. More recently experimental studies of mineral equilibria, particularly those defining aluminium partitioning between garnet and orthopyroxene, solid solution limits between co-existing pyroxenes and iron/magnesium partitioning between garnet and pyroxene, have established methods of geothermometry and geobarometry which can be applied to deduce conditions of crystallization of natural peridotite xenoliths. Applications of these studies to suites of garnet peridotite xenoliths from different localities establish geothermal gradients of contrasting type, for example, beneath Eastern Australia and Southern Africa. The South African diamondiferous kimberlite xenoliths define a distinctive MgeothermM in which a population of xenoliths defines an isobaric temperature discontinuity at 48-51kb, 1100°C-1400°C. The origin of this discontinuity is speculative but it must have been a transient feature and it is suggested that it marks the initiation of movement of the African plate, which at that time had a lithosphere of 150-170km thickness overlying a poorly developed low velocity zone. In contrast the East Australia 'Tertiary1 geotherm gives a P,T curve which intersects the peridotite solidus at 85-95km yielding a lithosphere of 85-95km thickness overlying a well-developed low velocity zone. The presence of partial melting in the upper mantle is inferred to be the cause of the low velocity zone and experiments show that melting is sensitively dependent on the nature of the volatiles (principally in the system C-H-0 or C-H-O-S) present in the mantle. Experimental studies and observations support the view that fluid phases present below the low velocity zone may be dominated by methane, that water and reduced carbon are dissolved in a melt phase within the low velocity zone and that above the low velocity zone fluids range from l^O-CHi* to H 2 0-C0 2 dominated representing a change in oxidation state both with depth and in a more local and areal manner. A principal new concept is the suggestion of a major change in mantle evolution as a 'redox front' moves into the mantle through geological time. In particular the initiation of subduction and its present role is as important in creating a mechanism for deep penetration of high fo2 materials into the mantle as it is for recycling water and possibly oxidized carbon (carbonate) and sulphur into deep mantle regions.

STABILITY OF REE-ACCEPTOR MINERALS AT HIGH AND

PRESSURES

TEMPERATURES

T.H. Green and N.J. Pearson School of Earth Sciences, Macquarie University The rare earth elements (REE) have taken an important place in evaluating geochemical models of lower crustal and upper mantle melting and crystal fractionation processes. To enable this evaluation to be carried out rigorously, it is necessary to establish (1) the potential repositories of these elements in the source regions and the stability of such REE-bearing phases in subsequent magma fractionation (2) the role of compositional and physical parameters in modifying the partitioning of REE between melt and residual crystals. Important potential hosts for the REE include the accessory minerals apatite, sphene, monazite, zircon, allanite, chevkinite-perrierite, davidite, and toernebohmite and cerite group minerals.

197

Data on the high-pressure, high-temperature stability of apatite, sphene, allanite, chevkinite-perrierite and davidite in host magma compositions ranging from basalt to rhyolite allow delineation of the potential roles of these phases. Each of these phases has a wide P,T stability in rocks of appropriate composition, where P-saturation (apatite), Ti-saturation (sphene, chevkinite, davidite) and REE saturation (allanite, chevkinite, davidite) become critical in controlling the likely appearance of the accessory phase. Compositions ranging from basalt to rhyolite have been doped with 4 to 6 REE (to levels of ^0.5% of each REE oxide) and the partitioning relationships documented. Apatite and sphene both show a markedly convex upward REE partitioning pattern, favouring the middle REE (see figs 1 and 2). Detailed data for sphene point to considerable effects of P, T, f(0o) and X(composition) on the partition coefficients (D's) and these effects appear to apply generally to the REE in silicate melts, even where the REE are essential structural constituents in the mineral phase under consideration (eg allanite, chevkinite). Thus D values increase with increasing P, decreasing T, increasing f(O^) and increasing SiCL. Sphenes crystallizing from the rhyodacite composition accommodate from 15 to 20 wt% REE and fall below a line depicting a generalized coupled substitution of £ REE + A1 + Fe t £ Ca + Ti (see fig. 3). These sphenes from the rhyodacite show increasing REE content with increasing pressure, while sphenes with ^ 17% f r o m basaltic andesite and andesite show decreasing REE content with increasing pressure. Both allanite and chevkinite have D patterns showing strong enrichment in the light REE with allanite exhibiting the greater enrichment (see figs. 4,5). In these phases, where the REE are essential structural constituents, the REE content exerts a greater control on the D values than P.T or X. Thus D values increase significantly as the REE content decreases and this points to much higherD values (but still with the same overall pattern) in natural systems* Davidite, toernebohmite(?) and cerite(?) show complex D patterns, with the davidite and toernebohmite patterns confirming 2 sites for the substitution of the REE in these phases, (fig.6). Allanite, chevkinite and sphene are recorded as important accessory phases in granitic or rhyolitic magmas, and this study clearly shows the major effect they will have in controlling the REE content of evolved granitic magmas, since they are the main REE acceptor minerals in these rocks. The wide potential P,T stability range for these 2 phases, and for davidite, indicates that they may also be important repositories for the REE in the upper mantle, and in a disequilibrium melting model (for trace elements) may strongly influence the REE patterns for magmas produced from an inhomogeneous (in the REE at least) source region. REE patterns for tholeiitic basalts from Norfolk Island may reflect this. Davidite-related minerals are recorded from kimberlites, while toernebohmite and cerite are best known from late-stage pegmatites.

198

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REE

THE D I S C O V E R Y OF THE K A M B A L D A N I C K E L D E P O S I T S - R E A L I S A T I O N OF A P R O S P E C T O R ' S A N D A G E O L O G I S T ' S D R E A M J.J. Gresham, G.D. L o f t u s - H i l l s Western Mining Corporation, Kambalda, W.A. Western Mining Corporation, Preston, V i c t o r i a Kambalda was established by gold miners early in 1897 as a small and flourishing township and in December of that year the town was o f f i c i a l l y gazetted. Major gold production ceased in 1907 but the area remained the focus of many prospectors 1 a t t e n t i o n . One such prospector was a f a r m e r , George C o w c i l l , who i n t e r m i t t e n t l y prospected the area w i t h l i m i t e d success between 1931 and 1948.

199

I n 1954, s p u r r e d on by t h e f i r s t u r a n i u m e x p l o r a t i o n b o o m , C o w c i l l a g a i n l e f t his f a r m and, r e c a l l i n g t h e o c c u r r e n c e o f blue and g r e e n m i n e r a l s in t h e r o c k s at K a m b a l d a , c o l l e c t e d m o r e samples and t o o k t h e m t o t h e K a l g o o r l i e School o f M i n e s t o be t e s t e d f o r r a d i o a c t i v i t y . T h e r e w e r e no r a d i o a c t i v e m i n e r a l s in t h e samples but B i l l C l e v e r l y , a senior l e c t u r e r in geology a t t h e School, assayed t h e s a m p l e s f o r c o p p e r and n i c k e l and r e p o r t e d t h e s i g n i f i c a n t f a c t t h a t these samples did c o n t a i n t r a c e s o f n i c k e l . The f a c t t h a t C l e v e r l y c o m m e n t e d on t h e presence o f n i c k e l in t h e s a m p l e s was e x t r e m e l y i m p o r t a n t as C o w c i l l w o u l d have p r o b a b l y d i s c a r d e d and f o r g o t t e n t h e samples if t h i s i n f o r m a t i o n had n o t been p r o v i d e d . In t h e l a t e 1950 ! s W e s t e r n M i n i n g C o r p o r a t i o n , w h i c h had g o l d m i n i n g i n t e r e s t s in K a l g o o r l i e and N o r s e m a n , m a d e a c o r p o r a t e d e c i s i o n t o d i v e r s i f y i t s e x p l o r a t i o n e f f o r t s i n t o t h e search f o r base m e t a l deposits t h r o u g h o u t A u s t r a l i a . A w a r e o f t h i s b r o a d e n i n g of i n t e r e s t , C o w c i l l m e n t i o n e d t o his l o n g - t i m e a s s o c i a t e , John M o r g a n , t h a t he had c o l l e c t e d samples f r o m K a m b a l d a many y e a r s ago w h i c h c o n t a i n e d nickel. M o r g a n and C o w c i l l r e t u r n e d t o K a m b a l d a , c o l l e c t e d m o r e samples and a c t i n g on C o w c i l l ' s b e h a l f , M o r g a n t o o k t h e samples t o Roy W o o d a l l , t h e n W M C ' s A s s i s t a n t C h i e f G e o l o g i s t based in K a l g o o r l i e . W o o d a l l had one s a m p l e sent t o a l a b o r a t o r y f o r c o m p l e t e s p e c t r o g r a p h i c analysis and t h i s showed t h e s a m p l e t o c o n t a i n about 0.5% C u as w e l l as n i c k e l , a n o m a l o u s m o l y b d e n u m and t e l l u r i u m and a f e w p e n n y w e i g h t s of s i l v e r . W o o d a l l r e c o g n i s e d t h e s i g n i f i c a n c e of these assays, and t h a t t h e samples r e p r e s e n t e d a l e a c h e d b a s e - m e t a l s u l f i d e gossan, t h e high t e l l u r i u m c o n t e n t being t y p i c a l of m a g m a t i c n i c k e l - c o p p e r s u l f i d e s . W o o d a l l v i s i t e d t h e area w i t h M o r g a n in S e p t e m b e r 1964. The e x t e n s i v e d i s t r i b u t i on of t h e gossans i n d i c a t e d t h e p o s s i b i l i t y of s i g n i f i c a n t zones o f m i n e r a l i s a t i o n , and t h e o c c u r r e n c e of t h e gossans at t h e c o n t a c t b e t w e e n u l t r a m a f i c and m a f i c r o c k s , c o m b i n e d w i t h t h e d i s t i n c t i v e g e o c h e m i s t r y o f t h e gossan samples, suggested t h a t t h e y r e p r e s e n t e d w e a t h e r e d m a g m a t i c n i c k e l - b e a r i n g s u l f i d e s , possibly of s i g n i f i c a n t dimensions. W o o d a l l i m m e d i a t e l y c o n v e y e d t h i s p o s s i b i l i t y t o t h e G e n e r a l S u p e r i n t e n d e n t o f W M C , L . C . B r o d i e - H a l l . B r o d i e - H a l l was i n s t r u m e n t a l in a c t i v e l y s u p p o r t i n g , t h r o u g h his i n v o l v e m e n t at W M C B o a r d M e e t i n g s , t h e c o n t i n u i n g e x p l o r a t i o n p r o g r a m in t h e K a m b a l d a area and his e n t h u s i a s m played a m a j o r r o l e in t h e p r o j e c t ' s success. G e o l o g i c a l m a p p i n g of t h e K a m b a l d a a r e a was c a r r i e d out by t w o u n i v e r s i t y s t u d e n t s d u r i n g t h e 1964/65 s u m m e r v a c a t i o n , under t h e s u p e r v i s i o n o f W M C g e o l o g i s t , Guy T r a v i s . This r e v e a l e d a sequence of u l t r a m a f i c r o c k s o v e r l y i n g a p i l l o w e d m e t a b a s a l t t h a t f o r m e d a d o m a l s t r u c t u r e p l u n g i n g t o t h e n o r t h and south. N u m e r o u s o t h e r gossan o c c u r r e n c e s w e r e l o c a t e d a t t h e base of t h e u l t r a m a f i c r o c k s and t h e e x t e n s i v e n a t u r e o f t h e m i n e r a l i s a t i o n was c l e a r l y i n d i c a t e d . M a g n e t i c arid i n d u c e d p o l a r i z a t i o n g e o p h y s i c a l surveys w e r e r e c o m m e n d e d p r i o r t o d i a m o n d drilling. D u r i n g t h i s mapping program,, W M C a c q u i r e d e x t e n s i v e p r o s p e c t i n g r i g h t s o v e r t h e p r o s p e c t i v e n i c k e l - b e a r i n g c o u n t r y based on s i m p l e c r i t e r i a such as s t r i k e e x t e n s i o n s t o k n o w n u l t r a m a f i c b e l t s and zones of m a g n e t i c i n t e n s i t y as d e f i n e d in r e g i o n a l a i r b o r n e m a g n e t i c surveys. This e a r l y a c q u i s i t i o n o f l a r g e areas o f p r o s p e c t i v e c o u n t r y d u r i n g a p e r i o d of l i m i t e d e x p l o r a t i o n a c t i v i t y by o t h e r c o m p a n i e s p r o v e d most a d v a n t a g e o u s t o W M C d u r i n g t h e g r o u n d pegging h y s t e r i a that followed the Kambalda discovery. F o l l o w i n g t h e c o m p l e t i o n of t h e g e o l o g i c a l m a p p i n g and r e p o r t i n g , i n d u c e d p o l a r i z a t i o n surveys w e r e c a r r i e d out in A u g u s t - S e p t e m b e r 1965 o v e r 13.7 k i l o m e t r e s o f m e t a b a s a l t - u l t r a m a f i c c o n t a c t a r o u n d t h e dome. The surveys l o c a t e d six a n o m a l o u s zones i n c l u d i n g a s t r o n g a n o m a l y in t h e a r e a o f t h e o r i g i n a l gossan. M a n y of t h e o t h e r a n o m a l i e s w e r e l a t e r f o u n d to be a s s o c i a t e d w i t h n o n - n i c k e l i f e r o u s , sulfidic metasediments. G e o c h e m i c a l soil s a m p l i n g along t h e e s t a b l i s h e d I P g e o p h y s i c a l l i n e s also d e l i n e a t e d a n u m b e r o f c o p p e r and n i c k e l a n o m a l i e s . G e o c h e m i c a l and m a g n e t i c surveys p l a y e d a s i g n i f i c a n t r o l e in subsequent e x p l o r a t i o n w o r k e s p e c i a l l y in t h e l a r g e areas s o u t h o f K a m b a l d a .

200

C o m b i n i n g the results of the geological mapping and the induced polarization survey, a diamond drill hole, K D 1 , was planned and drilling c o m m e n c e d at the end of 1965. The hole initially drilled through a barren ultramafic-metabasalt contact at 130m but on the 28th January 1966 intersected massive sulfides that assayed 8 . 3 % Ni between 145.7 and 148.4m. The K a m b a l d a nickel deposits had been discovered and the ensuing years saw a boom in exploration activity throughout Western Australia.

PROTEROZOIC SOURCE FOR GRANITES AND VOLCANICS AND SOURCE OF Ag-Au MINERALIZATION FROM THE DRAKE AREA, NEW ENGLAND Brian L. Gulson1 and Lindsay R. Bottomed ^CSIRO Division of Mineralogy, North Ryde Aberfoyle Exploration Pty Ltd, Hawthorn Permian volcanics and granites host significant Ag-Au mineralization in the Drake area of the northern New England Fold Belt (Bottomer et al., 1984). As part of a detailed Pb isotopic investigation aimed at characterizing the various mineral occurrences and establishing the source of mineralization, whole rock samples of granites and volcanics were analysed for Pb isotopic composition and U and Pb concentrations. The isotopic ratios for six samples of the Drake Volcanics define a good linear array on the 207 Pb/ 206 Pb- 2Qi+ Pb/ 206 Pb plot with an apparent "age" of 1500 Ma (MSWD 1.7). On the same plot, the granite data for five samples also fit fairly well to a line which has a different slope and thus a different apparent "age" from the volcanics of 800 Ma (MSWD 3.6). These apparent "ages" cannot represent the time of crystallization which is Late Permian and are suggested to reflect the average (mixed) age for the source material for the rocks. Precambrian source "ages" are common in Tertiary Volcanics and granites in the western U.S. (e.g. Doe et al., 1979). On both the uranogenic ( 207 Pb/ 206 Pb-2QIfPb/ ZUb Pb) and thorogenic ( 208 Pb/ 206Pb-20I*Pb/ 206 Pb) plots, the line for the volcanics passes through the average isotopic value for galenas from the major occurrence of Ag-Au mineralization, the Lady Hampden deposit. This may be interpreted as demonstrating that the Drake Volcanics are the source of the Lady Hampden style mineralization and is consistent with geological evidence. Interpretation of the granite data is less clear. The scatter of results on the 208 Pb/ 206 Pb- 2Q,4Pb/206 Pb plot was unexpected as most of the samples are from the one complex and the data would normally lie on a single line reflecting a uniform Th/U ratio for the source rocks. The scatter either reflects post-crystallization movement of Th and U, that the samples are not from the same source or Pb contamination from country rocks during emplacement, for example. Some of the granite samples lie on linear trends which do not pass through the ore value and thus preclude them from being the source of mineralization. Follow-up work, to better define the granite arrays in particular, will include K-feldspar analyses. Similar investigations are underway on granites from the Hillgrove-Armidale area. If similar old "ages" are found in the Hillgrove area, this demonstrates the sensitivity of the Pb method for petrogenetic studies as no older "ages" were detected using the Nd and Sr methods (Hensel, personal comm., 1984). The Proterozoic "ages" for the Drake granites and volcanics are not an isolated occurrence, as we have measured similar source "ages" for volcanics hosting the Benambra base metal sulfide deposits in N.E. Victoria.

201

References Bottomer, L.R., Simmons, R.J., and Joyce, R.M., 1984. Geol. Soc. Aust. Qld Div. 1984 Field Conference, Stanthorpe-Emmavilie-Drake region, p . 7990. Doe, B.R., Steven, T.A., Delevaux, M.H., Stacey, J.S., Lipman, P . W . , and Fisher, F.S., 1979. Econ. Geol. 74, 1 - 2 6 .

SAMPLING

AND LABORATORY

R. Guyot

TESTING

, H . Read

COAL

1. Manager-Coal Laboratory Sydney, SGS Australia Pty Ltd, Sydney 2. Manager-Exploration Services, SGS Australia Pty Ltd, Sydney Introduction. This paper discusses the geological aspects of coal and their influence on coal sampling, analyses and commercial utilisation. These geological aspects include rank, coal type, elemental composition and geographical/geological location. Most of these aspects were either influenced or determined by the environment of coal deposition (climate, plant type) and subsequent tectonic events (subsidence, uplift, eustatic sea levels, folding, faulting and igneous intrusions). Paleoclimate and the geological era would influence the type of vegetation from which the coal was formed, which in turn would influence the coal type. Tectonic events would influence both the coal rank (brown, subbituminous, bituminous, semi-anthracite, anthracite), and the amount of mineral matter. Both the geological setting and the physical/chemical characteristics of the coal will dictate the sampling and analytical procedures to be adopted. Some analyses, such as proximate analysis and CSN are carried out routinely on all types of coals. They are cheap and simple to perform and allow a basic characterisation of the coal. Other analyses,such as Hardgrove grindability and Gieseler plastometer are designed to test specific types of coals. Fuel coals (those intended for power stations, cement kilns, etc.) will be tested to evaluate their heating value and other properties that will affect the plant operation, such as mill performance (grindability) ash characteristics (foulding, corrosion, abrasion) and pollution (precipitation of fly ash). Metallurgical coal will be tested to determine their suitability, either alone or in blends, for coking or briquetting etc. plus identification of elements like phosphorus, which will affect subsequent coke use. Sampling. Coal sampling is required for exploration, mine planning and development; beneficiation studies; routine quality control for production, treatment and handling. While non representative samples are sometimes obtained for specific purposes, all samples which are intended to provide quantitative results must be taken according to accepted standards. Exploration and mine planning data are provided by outcrop samples, chips from non-cored holes and small diameter cores. Larger samples from large diameter borecores, shafts and trial pits are needed for proper washability studies. Routine quality control requires regular face (strip) samples; run of mine (stopped belt or mechanically sampled); washery feed, product and reject sampling; train/truck/ship loading and discharging and sampling.

202

Laboratory analyses. Laboratory analyses can be broadly c l a s s i f i e d into two categories - ' P h y s i c a l 1 and 'Chemical', although with modern instrumentation techniques there may be considerable overlap between the two. Physical testing. The physical properties of coal normally determined include relative density, Hardgrove Grindability Index, g r a i n - s i z e , Yancey Geer and Price abrasion index, caking/coking values (crucible swelling number, Gieseler plastometer, Audibert-Arnu dilatometer Roga Index) and petrography (maceral/microlithotype, v i t r i n i t e reflectance). Chemical testing. These analyses usually include total moisture, proximate (inherent moisture, ash, v o l a t i l e matter, fixed carbon) ultimate (carbon, hydrogen, nitrogen, sulphur, oxygen, carbon dioxide), specific energy (gross), forms of sulphur (organic, p y r i t i c , sulphate) and elements in coal (including trace elements). Summary. Because of c o a l ' s depositional and post-depositional history, i t s physical and chemical characteristic vary widely, necessitating careful planning of both sampling and testing programmes. Testing programmes incorporating correct sampling, sample preparation and analytical procedures are essential i f reliable information i s to be obtained, and at the same time avoid costs resulting from incorrect or unnecessary work. A summary of current Australian Standards for the sampling, sample preparation and testing of coal i s as follows:A. Sampling. Australian Standard 2646 - 1984, parts 1,2,4,6 and 8 - 'Sampling of s o l i d mineral f u e l s ' . B. Sample preparation. Australian Standard 1661- 1979 - 'Method for float and sink testing of hard coal and presentation of r e s u l t s ' . Australian Standard 2579, part 1 (1983)'Hard coal/froth flotation procedures'. C. Testing. Australian Standard 1038, parts 1-20 - 'Methods for the analysis and testing of coal and coke'. Australian Standard 2486 (1981) - 'Methods for microscopical determination of the reflectance of coal macerals'. Australian Standard 2515 (1981) - 'Determination of the maceral group, composition of bituminous coal and anthracite'.

203

HYDROCHEMISTRY

OF THE GREAT ARTESIAN

BASIN

M.A. Habermehl Division of Continental Geology, Bureau of Mineral Resources, Canberra Groundwater in the confined aquifers in the Lower Cretaceous and Jurassic sedimentary sequence of the Great Artesian Basin is generally of good quality, and contains about 500 to 1500 mg/L total dissolved solids. The water in the eastern and central parts of the Basin is chemically of the Na-HCO^-Cl type, and these ions contribute more than 90 percent of the total ionic strength of solutes in the main Basin area. Near the recharge areas Ca, Mg and SO. concentrations are proportionately higher, but these decrease basinwards. Concentrations and ratios of the major ions Na, HC0-, Cl and SO. vary along the flowlines in the Basin and are thought to reflect climatic variations in the i^ch^ge areas. The different recharge areas are characterised by different C/ C ratios, and these ratios increase downgradient from the recharge areas. In the southwestern part of the Basin groundwater is characterised by Na-Cl-SO^ type chemistry. Hydrochemical differences in the Basin relate to the sources and directions of groundwater flow patterns. Regional groundwater movement has been interpreted from hydrogeological data and the results of a computer based simulation of the Basin's hydrodynamics, and shows good agreement with the changes to the hydrochemistry. In the southwestern part of the Basin two regional groundwater flow directions, with the westward flowing water being of the Na-HCO^-Cl type, and eastwards flowing water of the Na-Cl-SO^ type, meet and mix, and are directed towards the main natural discharge area near the Basin margin. The combined groundwater flow is distinguished by Na-Cl-HCO^ and Na-Cl-HCO^-SO^ type water; salinity values increase towards the discharge area. Aquifers in the upper part of the Cretaceous sequence in the Basin contain groundwater of high salinity which is chemically of the Na-Cl-HCO^ type. Groundwater flow from the Lower Cretaceous-Jurassic aquifers to the Cretaceous aquifers across the Canaway Fault in the central part of the Basin, have been traced by use of hydrochemical differences. References Habermehl, M.A., 1980, BMR J. Aust. Geol. & Geoph., 5^, 9-38. Habermehl, M.A., 1983, Aust. Water Resour. Council Conf. Ser., 8/3), 83-98.

HYDROGEOLOGY AND DEVELOPMENT OF GROUNDWATER OF THE GREAT ARTESIAN BASIN

RESOURCES

M.A. Habermehl Division of Continental Geology, Bureau of Mineral Resources, Canberra The Great Artesian Basin is a large, multi-layered confined groundwater basin, comprising aquifers in continental quartzose sandstones and confining beds of partly marine mudstones and siltstones of Triassic, Jurassic and Cretaceous age. The Basin is up to 3000 m thick, and forms a large synclinal structure, uplifted and exposed along its eastern margins and tilted southwest.

204

Regional groundwater movement in the Lower Cretaceous and Jurassic aquifers has been interpreted from potentiometric surface and hydrogeological data and the results of a computer based simulation of the Basin's hydrodynamics. Recharge occurs mainly in the eastern marginal zone, with minor recharge in the western margin- Large-scale groundwater movement is towards the southern, southwestern and western margins. Natural discharge occurs from many^springs in these areas. Very long residence times, of more than 1 x 10 years have been determined for the Basin's groundwater with environmental isotopes, including C and CI. Isochrons derived from hydrodynamic data and from isotope results are in good agreement. The groundwater in the Lower Cretaceous-Jurassic confined aquifers in the eastern and central parts of the Basin is dominated by Na-HCCL-Cl type chemistry. In the southwestern part of the Basin the groundwater is characterised by Na-Cl-SO^ type chemistry. Hydrochemical differences relate to the sources and directions of groundwater flow patterns. Exploration and development of groundwater resources in the Great Artesian Basin dates back to around 1880. Activities in the Basin were the focus of attention throughout the first half of this century, as rapid changes occurred in discharges and pressures of flowing artesian waterwells. Development during the last 30 years has been guided by increased and improved hydrogeological knowledge and understanding of the Basin. Hydraulic conditions in the Basin stabilised during the latter period, and though development caused considerable drawdowns of water levels (more than 100 m in some areas), the potentiometric surfaces of most aquifers are still above groundlevel in most parts of the Basin. Flowing and pumped artesian waterwells are abundant, and free flows exceeding 100 L/s have been recorded. Groundwater quality is good with about 500 to 1500 mg/L total dissolved solids, and makes it suitable for pastoral, domestic and town water supplies, which are the main users. Future groundwater abstraction in the Basin will produce only minor changes according to model predictions. Much larger development is possible, though this will affect the potentiometric surface and free flows. More efficient use should be made of the Basin's groundwater by upgrading the wellheads and the distribution systems. References Habermehl, M.A., 1980, BMR J. Aust. Geol. & Geoph., .5, 9-38 Habermehl, M.A., 1983, Aust. Water Resour. Council Conf. Ser., 8(3), 83-98. PRELIMINARY STABLE ISOTOPE STUDIES OF THE HEEMSKIRK GRANITE AND ITS MINERAL DEPOSITS J. Hajitaheri

and M. Solomon

"^Dept. of Geology, University of Tasmania, Hobart ^Bureau of Mineral Resources, Canberra The Heemskirk Granite is a meta-to per-aluminous Devonian granite within Precambrian and Cambrian sediments in western Tasmania (Brooks, 1966; Klominsky, 1972). It consists of gently dipping sheets of which the major are the Red and the White Granites. The Red Granite, about 300 m thick, overlies and is intruded by the White Granite, which is over 0.5 km thick. The Red has pink feldspar and a much lower tourmaline content than the White, and the White shows local evidence of fluid saturation in the form of quartz and tourmaline vughs. The Red has lower initial Sr-isotope ratios than the White (0.7197 compared to 0.7408 ± 0.003) but similar 6 1 8 0 values (+9.8 to +10.9 permil). These results do not completely satisfy genetic models involving either assimilation of country rock (0.781 and about +15.0 permil) or independent sources for the melts. 205

Three stages of pervasive subsolidus albite growth have been found in both granites and quartz-feldspar oxygen-isotope fractionation (about 1.5 permil) indicates high "magmatic" temperatures during feldspar growth. Quartzbiotite fractionation gives similar results and 6D values for biotite (-127 to -151 permil) indicate magmatic water. Cassiterite - bearing mineralization occurs in greisens that are located on fracture zones in the Red Granite just above the Red-White contact. Quartz in greisens (quartz 4- muscovite ± topaz ± tourmaline, eg. the Federation Mine) have elevated S 1 8 0 values, probably related to lower formation temperatures (^550 C, fluid inclusion data) in the presence of magmatic water. Later quartz ± sericite ± and kaolinite assemblages within the greisens have 6 ^ 0 values from +3.7 to +7.7 permil and 6D values between -115 and -128 permil. At the temperatures of 400 to 450°C indicated by fluid inclusion measurements in quartz, a fluid with a meteoric component is indicated. 5 3 4 S values for pyrite in the greisens zones varies from +3.7 to 12.8 permil with the highest values in sericitized and kaolinized rocks and in late veinlets. It is suspected that the lower values are derived from magmatic sulphur while the higher are from groundwater sulphur; disseminated pyrite in fresh granite gave +1.8 permil. Cassiterite also occurs in polymetallic sulphide assemblages in the Red Granite near the Granite margin (eg. Sweeneys and Globe mines). The sulphides have 63l+S values from +9.7 to +15 permil, indicating little or no input of n^gmatic sulphur. Disseminated pyrite in the Precambrian country rocks yielded 6 S values of about +19 permil,and may have contributed to the polymetallic. sulphur. In summary, the mineralization of the Heemskirk Granite appears to have formed partly during magmatic-hydrothermal activity accompanying intrusion of the White Granite and partly from later groundwater that has probably circulated through both granite and country rock. Brooks, C.C., 1966, Geochemistry and the Genesis of the Heemskirk Granite, West Tasmania. Geochim. Cosmochim. Acta, 30, 633-643 Klominsky, J., 1972, The Heemskirk Granite Massif, Western Tasmania, Ph.D. Thesis, University of Tasmania.

Unpub.

A SOIL-SAMPLING ORIENTATION SURVEY TO DETERMINE THE VALUE OF GOLD, SILVER, AND BASE METALS IN DELINEATING BEDROCK GOLD MINERALIZATION D. Hall1, D. O'Neill2, P.Dl Klipfel2, G.L. Duncan2, P.M. Vanderspuy2 ^University of New South Wales, Sydney, N.S.W. Canyon Resources Pty Limited, Sydney, N.S.W. The target area at Majors Creek, N.S.W., consists of structurally controlled auriferous aplitic and greisenous dykes within the Braidwood Granite. An orientation soil sampling survey was undertaken to determine the value of low-order gold values (<100 ppb) in delineating the soil-covered auriferous dykes. In addition, the role of Ag, Cu, Pb, Zn, As, Fe and Mn as pathfinder elements was evaluated. Orientation samples were collected at 5 metre intervals on an 80-metre line normal to the assumed trend of the mineralization. +32# (500/im ), -32#+80# (—500f/m +180/um ), and -80# (-180/im ) fractions were taken from the A and the B horizons (i.e. 6 samples per site). Analysis was by AAS after aqua regia (c.HCl + c.HNO^) digestion.

206

The orientation samples exhibit good correlation between Au, Cu, Zn and Mn in the -32#+80# fraction of the A horizon. The -80# fraction in both the A and B horizons exhibits an irregular 40 metre-wide anomalous pattern for Au, Cu and Mn. Pb anomalies are subdued and Ag and As values are not anomalous. Both Zn and Cu appear to be useful pathfinders for gold in the -32#+80# A horizon material. The correlation between the various elements in the -32#+80# A horizon material is much more sharply defined than the correlation in the -80# of the A horizon or the -80# and the -32#+80# fraction of the B horizon samples which exhibit a broader but more erratic anomalous distribution. Further A horizon samples from the entire grid area are being analysed for Au, Cu, Pb, Zn and Mn and the results of the survey will be presented.

DELTAIC DEPOSITIONAL SYSTEMS, COAL DISTRIBUTION AND QUALITY, AND PETROLEUM POTENTIAL OF THE LOWER BLACK JACK FORMATION, GUNNEDAH BASIN, NEW SOUTH WALES D.S. Hamilton Department of Mineral Resources, Sydney Upper Permian sediments of the lower Black Jack Formation were deposited as a major delta system in the Gunnedah Basin, a foredeep of the rising New England Fold Belt. Two principal depositional units are recognised in the lower Black Jack Formation: the lower delta-plain facies and the shallow-marine facies (Beckett et al, 1983). A third but minor depositional unit, the western bed-load fluvial facies, is correlative with the upper part of the shallow-marine facies. Geometry of the framework sandstones indicate that the lower delta-plain facies was deposited in a combination of fluvial-dominated and wave-modified delta systems and that the shallow-marine facies was deposited in a tide-dominated system. Sediment source was predominantly from the northeast except for the western bed-load fluvial facies which was derived from the Lachlan Fold Belt region to the west. The lower delta-plain facies was deposited during a major episode of delta construction. Principal components recognised in drillcore are distributary channel, crevasse splay and splay subdelta, interdistributary bay, lagoon and marsh deposits. Trangression of the delta by a major (?) eustatic sea level rise led to deposition of the shallow-marine facies. This facies consists chiefly of beach, barrier beach, tidal sand ridge, and tidal channel-fill deposits. Subsequent lowering of sea level was accompanied by deposition of the western bedload fluvial facies. This facies consists predominantly of upwardfining fluvial channels which display considerable marine reworking toward the basin centre. A vast coalswamp established rapidly after the marine conditions regressed and is represented by the Hoskissons Coal Member.

207

Coals of commercial interest are developed within the lower deltaplain facies and above the shallow-marine fades. The lobate geometry of the coal deposits in the lower delta-plain facies mirrors the geometry of the framework sandstones and indicates a deltaic origin for coal formation. Two mechanisms for coal formation are recognised in the lower delta-plain facies. Thick, laterally extensive coals, such as the Melvilles Coal Member, are thought to have originated as blanket peats following delta abandonment. Thin, discontinuous coals formed in interdistributary depressions during active deltaic progradation. Coal above the shallow-marine facies is contained in one major seam, the Hoskissons Coal Member. Based on the associated underlying clastic facies this seam probably formed mostly as a back barrier-lagoonal peat. However on the western margin of the basin the seam overlies and interfingers with fluvial sandstone, and in the southeast it overlies deltaic facies. Depositional setting strongly influenced coal quality. Isoash trends for the Melvilles Coal Member suggest a marginal marine influence during peat accumulation. Ash content of the Hoskissons Coal Member has a similar distribution to the percentage of sandstone in the underlying shallow-marine facies. Potential exists for petroleum accumulation in the lower Black Jack Formation. Vitrinite reflectance data (Russell and Middleton, 1981) indicate that sediment below the base of the Black Jack Formation is within the conventionally accepted zone of early oil generation. Suitable reservoir rocks are present in the lower delta-plain and shallow-marine facies, and underlying prodelta facies are potential source rocks (Etheridge, 1983). References Beckett, J., Hamilton, D.S., & Weber, C.R., 1983. Geological Survey of New South Wales - Quarterly Notes 51, 1-16. Etheridge, L., 1983. Geological Survey of New South Wales - Quarterly Notes 53, 5-22. Russell, T.G., & Middleton, M.F., 1981. Geological Survey of New South Wales - Quarterly Notes 45, 1-11. Published with the permission of the Under Secretary, New South Wales Department of Mineral Resources.

208

SULPHUR SATURATION, SECOND-STAGE MELTS AND THE ORIGIN OF M A G M A T I C PGE

DEPOSITS

Paul R. Hamlyn and Reid R. Keays Department of Geology, University of Melbourne, Melbourne A model is presented for the formation of platinum group element (PGE) ores by precipitation from sulphur-deficient, PGE-rich, second-stage magmas. Numerous investigations indicate that basaltic magmas originating from undepleted or mildly-depleted source regions are S-saturated at the time of eruption (McGoldrick et al., 1979; and references therein). The Pd abundances of residual mantle-derived peridotites (Mitchell and Keays, 1981; Hamlyn and Keays, unpub. data) are too high to have originated solely from silicate melt retained in the source region at the time of segregation and imply the presence of an accessory immiscible sulphide melt to host the PGE. The very high sulphide melt/silicate melt partition coefficients of PGE would result in strong fractionation of these metals into the accessory sulphide component during the melting event. The extreme PGE enrichment of this accessory sulphide component is evidenced by the discovery of platinoid minerals in mantle nodules containing Pd (and Pt) abundances at the low ppb level (Keays et al., 1981). Magmas generated by low to moderate degrees of partial melting of undepleted mantle are therefore sulphur saturated at the time of segregation. These (first-stage) magmas become impoverished in PGE during the early stages of fractional crystallisation because of coprecipitation of an immiscible sulphide phase (e.g. MORB glasses average 0.9 ppb Pd). Subsequent (second-stage) melts derived from this source dissolve the PGErich sulphide component and hence are enriched in PGE themselves but poor in sulphur. Boninitic magmas, generally regarded as second-stage melts generated from strongly depleted mantle sources, have enhanced PGE abundances (mean Pd = 15 ppb) in agreement with the above model. During fractionation of these S-deficient magmas the concentration of PGE will build up until the onset of S-saturation and segregation of sulphides. These sulphides will have a high PGE tenor compared to those generated by first-stage melts. A marked similarity in the composition of boninitic magmas and early parental magmas proposed for the Bushveld Complex (Davies et al., 1981), and possibly other intrusions hosting PGE ores, suggests that their source regions may have evolved in a similar manner. This would explain both the timing of deposition of the Merensky cyclic unit at the top of the Critical Zone and the unusual PGE-rich nature of the Merensky Reef ores. If our model is relevant to the Bushveld PGE mineralisation then it provides a means of assessing the potential of other stratiform intrusions to host economic PGE deposits. References Davies, G., Cawthorn, R.G., Barton, jTm. Jr., & Morton, M., 1980, Nature, 287 33-35. Keays, R!R., Sewell, D.K., & Mitchell, R.H., 1981, Nature, 294, 646-648. McGoldrick, P.J., Keays, R.R., & Scott, R.B., 1979, Geochim. Cosmochim. Acta, 43, 1303-1311. Mitchell, R.H., & Keays, R.R., 1981, Geochim. Cosmochim. Acta, 45, 24252442.

209

THE PADDIN6T0N D E P O S I T , WESTERN A U S T R A L I A THE REDISCOVERY OF AN OLD GOLD MINE

*M.C. Hancock,

Q.G. Amos

Pancontinental Mining Limited, Sydney Pancontinental Mining Limited, Kalgoorlie 1

Paddington is one of a 'new generation of gold mines in Western Australia, based on the low-grade, bulk tonnage, open-pit potential of a deposit formerly mined underground for its narrow high-grade lodes. In this sense Paddington was really discovered 90 years ago when the mine was originally worked in the first gold-rush in the Kalgoorlie region in the 1890s and early 1900s. It was one of the major producers of the Broad Arrow Goldfield at that time with a 700 foot shaft and extensive underground workings. Over 60,000 ozs of gold were produced before the mine was forced to close in 1901, due to the financial collapse of the parent company. Little further activity is recorded in the Paddington area until 1934 when a company called Lochinvar Gold Mines acquired the property and commenced sinking a new shaft and dewatering the old workings. Substantial development work was undertaken but it appears that little or no production took place. However of major significance was the surface and underground drilling carried out by Lochinvar, for it was the assays and logs of these holes which 50 years later persuaded Pancontinental of the potential of the prospect. In 1974 United Goldfields Corporation acquired the five gold mining leases which covered the Paddington shafts and other lesser shafts to the south. After trenching and percussion drilling, an area to the south of Paddington was identified as having some potential and a small open pit was developed. With custom milling the project was unsatisfactory and United Goldfields began to look for joint venture partners to more fully investigate the property. Pancontinental Mining, so long frustrated in its attempt to develop its Jabiluka orebody, had at this time (1980) taken a decision to expand its exploration activities into other base and precious metals. At this opportune time a chance meeting in Newman brought together a Pancon geologist, Pancon's Land Manager and a United Goldfields director who in the course of conversation, described to them United's Paddington property - the significant widths of low grade mineralisation, the stratigraphy which appeared comparable to the Kalgoorlie Golden Mile, and the quartz-dolerite 'lode' with its apparent similarities to the Golden Mile Dolerite at Mount Charlotte. The information was passed on to the Exploration Manager in Sydney who followed it up with a site visit. He was impressed with the potential of the prospect and the good tenement position and within a few weeks an option agreement between Pancontinental and United Goldfields over the five gold mining leases had been signed. The preliminary geological assessment of the area indicated significant potential for strike extensions of the mineralisation, and also repetition in adjacent stratigraphic units. Thus it was decided to extend and consolidate the Company's property position, a programme which by March 1982 had successfully resulted in the negotiation of various mineral claims and mining lease titles over a potentially mineralised strike length of 12 kilometres.

210

Systematic mapping, trenching and sampling revealed an intrusive quartz-dolerite unit, sheared and altered and cut by a stockwork of quartz veins. Gold values in the trenches were erratic and rarely exceeded 1 gm/t, due - it was later shown - to major surface depletion. Arsenic, and to a lesser degree tungsten, however, showed significant anomalies coinciding with the zones of maximum alteration in the dolerite. Seven exploratory holes were drilled, one of which intersected a major ore zone; the others gave lesser and somewhat conflicting results. A systematic 40 x 40m grid drilling programme commenced in 1982, centred on the best intersections and investigating principally the shallow open pittable material. The surface depletion effect was confirmed, but underlying this was a zone of significant supergene enrichment with primary mineralisation below. Good continuity was established from hole to hole and section to section in a near vertical ore zone attaining a maximum thickness of 40 metres. Reserves of 5.6 million tonnes averaging 3.3 gm/t were outlined. Follow-up drilling in-filled the detail to a level adequate for initial feasibility studies and also identified an extension of the deposit along strike to the south comprising an additional 2.5 million tonnes of in-situ reserves. Feasibility studies indicate that a viable project can be realised, mining 875,000 tonnes of ore per annum from 2 open pits over a 7 year mine life. A decision has been made to proceed on this basis and Pancon anticipates bringing the Paddington mine into production by mid1985. On-site construction has already started. A timely decision, a chance meeting, the recognition of a geological model, an expansive tenement policy and good, systematic exploration and evaluation practice have effectively combined so that Paddington is set to become, once again, one of Australia's major gold producers. References Boyd, A.M. Unpublished report on work by Lochinvar Gold Mines in the 1930s., February 1982. Faul, A. W.A. Mining and Commercial Review, June 1937. Hancock, M.C. & Amos, Q.G. Unpublished Pancontinental report on activities leading to and including Paddington Ore Reserve estimations, July 1982. McCormick, C. Unpublished Pancontinental report on 1981 field activities at Paddington, May 1982, Rust, T. Unpublished Pancontinental report on Paddington property status, June 1982. THE PADDINGTON GOLD PROJECT EVALUATION AND ORE RESERVE ESTIMATION

DRILLING

^ . C . Hancock, 2 Q.G. Amos ?

"^Pancontinental Mining Limited, Sydney Pancontinental Mining Limited, Kalgoorlie

Paddington is one of a 'new generation1 of gold mines in Western Australia, based on the low-grade, bulk tonnage, open-pit potential of a deposit formerly mined underground for its narrow high-grade lodes. Paddington lies within the Broad Arrow Goldfield, 35 kilometres north of Kalgoorlie, and adjacent to the main Kalgoorlie-Leonora road and railway. The mine was first operated in 1896 and produced over 60,000 ounces of gold before closing in 1901 due to the financial problems of the parent company. There has been no significant production from the area since 1901 although the mine was reopened briefly in the 1930's, a new shaft sunk and some underground development carried out.

211

Pancontinental Mining first took an interest in the area in 1980, attracted by the significant widths of low-grade mineralisation indicated by the old records and by the quartz dolerite host rock reminiscent of the Golden Mile Dolerite at Mount Charlotte. Following reconnaissance mapping, trenching and exploration drilling in 1981, a grid drilling programme was commenced centred on the most promising initial intersections. By mid1982 a reserve of 5.6 million tonnes averaging 3.3 g/t had been outlined (Paddington I). Follow-up drilling in-filled the detail to a level adequate for initial feasibility studies and also identified an extension of the deposit along strike to the south comprising an additional 2.5 million tonnes of in-situ reserves (Paddington II). Procedures adopted for drilling, sampling and assaying were chosen so as to reduce to a minimum uncertainties with respect to ore distribution and grades. Drilling was carried out on a 40 x 40m grid to provide a regular and systematic sampling of the orebody. This spacing was later reduced by infill drilling to provide the necessary detail for mine planning. A combination of reverse circulation percussion and diamond drilling was used. All drilling in highly weathered material was carried out by reverse ciculation; diamond drilling was used to extend the RC drilling in order to sample the mineralised horizon below the water table. RC drilling was preferred near surface as core recovery was poor in the oxidised zone due to contrasting friability between the abundant quartz veins and the highly oxidised matrix. Also the larger sample readily obtainable by RC methods at reasonable cost provided a statistically more representative sample. Below the water table concern regards loss and contamination due to smearing of wet sample in the drill pipes led to the procedure of reverting to diamond drilling below this depth. Samples were collected for assay on a metre by metre basis for both RC sludges and core. Strict sample preparation procedures were specified to minimise sampling errors. All samples of potential economic interest were analysed by fire assay and a duplicate sample was prepared and check assayed for all samples assaying more than 1 gm/t. The average of the two determinations was used in ore reserve calculations. Mineralised intervals were calculated using a 1 gm/t cut off and a 40 gm/t cutting procedure. Ore reserves were initially calculated on a sectional basis and were updated and refined with additional in-fill drilling. Data was transferred to plan for open pit mining studies. A geostatistical block model has been created to assist with detailed mine planning. Feasibility studies indicate that a viable project can be realised, mining 875,000 tonnes of ore per annum from 2 open pits over a 7 year mine life. A decision has been made to proceed on this basis and Pancon anticipates bringing the Paddington mine into production by mid-1985. On-site construction has already commenced. Today, Paddington is set to become, once again, one of Australia's major gold producers. References Boyd, A.M. Unpublished report on work by Lochinvar Gold Mines in the 1930s., February 1982. David, M. & Dagbert, M. Unpublished consultants report on Paddington geostatistics, June 1984. Faul, A. W.A. Mining and Commercial Review, June 1937. Hancock, M.C. & Amos, Q.G. Unpublished Pancontinental report on activities leading to and including Paddington Ore Reserve estimations, July 1982. Hancock, M.C., Amos, Q.G. & Taylor, L.J. Unpublished Pancontinental report on Pad I and II Ore Reserve Estimates, February 1984. McCormick, C. Unpublished Pancontinental report on 1981 field activities at Paddington, May 1982. 212

THE COURSE OF HYDROLOGY ASSESSMENTS FOR MINING ENVIRONMENTAL IMPACT STUDIES S. Hancock1, C.F. Forbes2 and R.E. Black3 ^Australian Groundwater Consultants Pty Ltd, Melbourne ^Consultant to Australian Groundwater Consultants Pty Ltd, Adelaide Kinhill Stearns Engineers, Adelaide Introduction The development of a sense of responsibility for the environment in the community, coupled with the legislation requiring public and government review and approval of environmental impact assessments before major projects may proceed, requires detailed study on all aspects of the environment. This is especially true of mining projects, despite the fact that other activities, such as wholesale land clearance for agriculture, often have greater environmental impacts, yet require no formal environmental approval. Hydrological aspects from the need to provide water for mining plant and towns, the need for dewatering or depressurization, river diversions and water quality are undertaken in the public arena operating on an object of public value but one which is frequently misunderstood. The public have little concept of the investigational lead time or the expenditure involved in making a project committment. They are inclined to become concerned at the lack of clear indications from proponents in the course of what they see as expenditures of such magnitude as to be certain indication of a committment. This concern affects the course of hydrological assessments, the lives of the public and in extreme cases, the acceptance of valuable public projects. Course of Hydrological Assessments Hydrological assessments, especially where groundwaters are involved, include a full range of geological surveys as well as census and sampling of existing wells, pumping tests over areas which extend well beyond the mineral exploration area and not infrequently a level of public education about the water resources. The investigations and evaluations are necessarily staged to run parallel with mineral and project economic and engineering evaluation stages. They must serve these evaluations as well as gather data from eventual environmental impact assessment when the nature of project is fully defined. By their very nature they arouse public interest and speculation which grows with the duration of the programme. Public Communication Objectives and Results Environmental legislation plus the desire to foster good public relations makes it beholdant on project proponents to communicate with the public to keep them informed, however it is not until the Draft Environmental Impact Statement that all aspects of the project are finalized and put before the public. Prior to that date, with the best will, the proponents are seldom able to be definitive and this is not uncommonly misunderstood and misrepresented. proponents have a responsibility to keep the public informed since the project may well affect the lives and investment decisions of both individuals and the community as a whole. At present however the channels for advising the public are not defined, which leads to pressures from multiple sources not all of whom are entirely altruistic in their desire to simply seek information on behalf of the public.

213

Public meeting reports by the press and by special interest groups tends to be selective. This generates public concern and further calls for meetings at which "concerned groups" are also invited to express their views. Disclaimers by the proponents go unheard, variations in results from previous meetings reported are depicted either as minimizing the magnitude of the problems or as trends towards increasing impacts. Positions and attitudes become entrenched and special interest groups are brought in as "Experts". Draft Environmental Impact Statements The DEIS is the first authoritative public document on the project in all its aspects. Regrettably it is seldom considered objectively by the p u b l i c , because of the entrenched positions already established. "Experts" are employed to support the entrenched positions. This is done by criticisms of DEIS statements taken out of context and not infrequently by deliberate misrepresentation. The intention of the DEIS to provoke informed public comment on the project with feed back to government is thus subverted. It becomes more frequently a basis for political pressure or "status quo" maintenance. There is also a widespread misconception that approval of the final EIS constitutes approval of the project itself. The extent to which public concern is a real problem to proponents depends upon the nature of the project, the nature of the environment and the present uses and population density. In Australia uranium projects will always create a great deal of "noise" (Sir Phillip Baxter), but the same applies to gold m i n e s , coal mines and quarries where they occur in closely settled areas. The fact is that water supply d a m s , sewage disposal schemes, irrigation and agricultural land clearance may cause far greater environmental effects than relatively confined mining projects. Extreme elements of the environmental lobby do not recognize that all human activity has some environmental impact. It is always difficult to identify any one cause which specifically results in project implementation delays, major modification or abandonment, but it can be fairly said that, excluding political policy delays of nine projects for which environmental impact statements have been submitted in the past eight y e a r s , six have been or may yet be delayed because of entrenched public opposition which commenced in advance of release of the environmental impact statement. This includes a gold project in V i c t o r i a , one coal and two uranium projects in South Australia, and two other uranium projects in the Northern Territory. Conclusions The complexities of modern project assessment and definition are such that premature release of information to the public is at least unproductive and more likely to be counter productive if we try to take laymen up the hydrogeological learning curve with u s . A t the same time, the local community has a right to be informed factually of the project status so that they can reasonably take decisions on their future. The resolution of this dilemma is urgent and seems to call for the establishment of defined channels of communication, defined topics for reporting and defined reporting periods in the same manner as applies with government mining lease and environmental licence requirements or the Stock Exchange. The public may then receive this data from the designated source and assess it rationally in its own interest. The fundamental weakness with the present system (as it applies in most democratic countries) is that the proponent is required to proceed through a series of very expensive and time consuming activities, with no guarantee that the problem will end with official environmental approval. This does not seem to benefit either the community or the p r o p o n e n t .

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THE COMMERCIAL POTENTIAL OF MARINE

SANDS

J.M. Hann Geological Survey of New South Wales Department of Mineral Resources, Sydney Estuarine and inner shelf marine sand deposits are potentially immense sources of valuable mineral commodities, in particular construction and industrial sands and heavy mineral sands. Current mining of these minerals in New South Wales (value of production for 1982-83 $66 million) is restricted mainly to onshore river, dune, and beach deposits, with production concentrated in the coastal zone within and around population centres. In recent years, reserves of construction and industrial sands and heavy mineral sands available for mining in the coastal zone have been reduced to critically low levels as a result of intense competition for land use and associated environmental pressures. Fine to medium-grained construction sands are now in short supply in the Sydney region with no viable long-term alternative sources immediately available. Supplies of colourless glassmaking sands for the Sydney market are now transported some 220 km to Sydney at great cost, whilst adequate medium to long-term sources of coloured glassmaking sands for the Sydney region have not been secured. Heavy mineral sand commodities have undergone an 82% decline in production over the past 12 years due largely to widespread sterilization of reserves. Any search for alternative sources must be aimed at identifying those deposits with the greatest potential for long-term security of supply, notwithstanding environmental considerations. Clearly, widespread exploitation of onshore deposits in the future will exacerbate the current pattern of land use conflict. However, marine sand resources could provide for long-term security of supply largely unfettered by land use pressures. Apart from environmental considerations, successful large scale exploitation of marine sand deposits will depend upon identification of suitable deposits, market acceptance of the products, and economic viability. Investigations in the Sydney region by the Geological Survey of New South Wales of estuarine and innershelf depositional environments have drawn attention to a number of deposits with commercial potential for construction and industrial sand applications. Other deposits of possible commercial significance adjacent to New South Wales coastal centres are known to occur in the Coffs Harbour, Newcastle-Gosford, and Shoalhaven areas. Pilot off-shore exploration for heavy mineral sands carried out by a number of companies between 1966-1972 has identified some 2 million tonnes of inferred resources of rutile and zircon located in the nearshore zone between Sydney and Tweed Heads. A subsurface investigation of very large sediment lobes located in 25-80 metres of water between Port Jackson and Marley using vibrocoring techniques, has indicated the presence of extensive quartzose sandy deposits with considerable commercial potential. Preliminary results show that the quartz sediments comprising the two major near surface units are fine to coarse grained with a shell content ranging from 5 to 30 per cent. Large areas of the sediment lobes are located adjacent to rocky rather than sandy shorelines, greatly reducing the potential for community fears of dredging-induced coastal erosion.

215

A recent detailed programme of sediment sampling in Botany Bay using reverse circulation and vibrocoring techniques has identified significant quantities of high-quality silica sand suitable for concrete and industrial applications. A generalized stratigraphy of one area investigated shows a thin (3 m) Holocene transgressive unit comprising fine to medium-grained quartzose shelly and ironstained sands overlying a Pleistocene dune unit. The Pleistocene dune unit (10 m thick) comprises clean, fine to mediumgrained high-purity silica sands. Preliminary test results for the Pleistocene dune unit suggest that these sands would be suitable for use in concrete, as a source of silica in coloured and possibly colourless glass manufacture (Fe203 0.035 - 0.065%), and possibly for foundry applications. Inferred resources of this unit for the small area tested are in the order of 1-2 million tonnes with a strong possibility of much greater quantities being present in adjacent areas. In view of the strategic location of this deposit with respect to the Sydney market, the high quality of the sand present, and the scope for joint extraction/port development, this deposit must be recognised as a major potential source for Sydney's construction and industrial sand markets. The commercial potential of the Holocene shelly sand unit is uncertain and will depend on tested performance and market acceptance. Marine sands have remained largely untested as commercial products in Australia, in contrast to countries such as Great Britain, where since 1968 marine aggregate has accounted for more than 10 per cent of that country's aggregate production. There exists a market resistance to marine sands in Australia, particularly with respect to the presence of shell and chlorides. A research programme aimed at evaluating the commercial performance of marine sands in concrete is currently being considered by the Department of Mineral Resources. The high cost of large-scale marine sand exploitation has to date been instrumental in the general lack of commercial interest in these deposits. However, with increasing difficulties and costs associated with the development of alternative deposits onshore, the economic exploitation of marine sands will become more attractive. Conceivably, large-scale exploitation of marine sand resources in the Sydney region could become an economically viable and acceptable alternative to massive onshore sand extraction within ten years.

THALANGA

EXPLORATION

HISTORY

J.S. Hartley Penarroya Australia Pty. Ltd., Charters Towers Location. The Thalanga volcanogenic massive sulphide (Zn, Cu, Pb, Ag) deposit is situated 65 kilometres south west of Charters Towers, north Queensland. Geology. The mineralization is present as a near vertical dipping stratiform body of massive sulphides. This occurs near the top of a sequence of altered meta-rhyolitic pyroclastics, which are overlain by a relatively unaltered sequence of dacitic pyroclastics with some dominant vitric units. These volcanics form part of the Mount Windsor Volcanics near their upper contact with the conformable Cape River Beds of Ordovician age. Alteration of the underlying volcanics results in dominant sericitization, pyritization and patchy silicification.

216

The surface expression is a low profile banded to massive limonitegoethite gossan which outcrops sporadically. The ore zone averages approximately six metres thick and contains 50?o - 9Q?o sulphides with Zn + Cu •+• Pb being approximately 15?o. Depth of oxidation is approximately 30 metres with the base of supergene enrichment at approximately 50 metres. Beyond the extent of gossan outcrops, the mineralization is covered both east and west by a variable thickness (up to 70 metres) of Campaspe Beds, a series of terrestrial clayey sandstones and grits of Tertiary age. Whilst in general these are poor aquifers, the water contained often exceeds sea-water salinity. A partially eroded laterite profile exists over much of the area. Discovery. In early July 1975 after many years of unsuccessful exploration in the Lachlan Geosyncline, Le Nickel Exploration Pty Ltd - as Penarroya was then called - decided to look further afield for volcanogenic massive sulphide. R.E. Cotton, with assistance from C. Douglas-Brown, reviewed both his memory and the 1:250,000 geological maps, and recommended three areas of acid volcanics over which authorities to prospect were applied for. One of these was the western outcrops of Mount Windsor Volcanics where the map showed separate occurrences of barite and zinc in a little explored area. Whilst awaiting granting of the title C. Douglas-Brown set out later in July 1975 to conduct a brief reconnaissance. On the first day he worked his way across country from the main outcrops of volcanics to the south of Charters Towers towards the western outcrops, looking for smaller unmapped outcrops. At approximately 1 km from the marked barite occurrence (his next objective) he noted float of very sericitised limonitic (after pyrite) acid volcanics. He then traversed to the south looking for the stratigraphic top of these altered rocks and within 50 metres noted a discontinuous line of barely outcropping gossan which was chip sampled. As the authority to prospect was not yet granted, an application for a mining lease was made the next day, 24th of July 1975. Since the assay results confirmed the importance of the gossan (average 7400 ppm Pb, 361 ppm Zn, 2285 ppm Cu, 7.6 ppm Ag) additional staff were employed and detailed mapping and costeaning were initiated, followed by a five hole diamond drill programme which was completed in 1975. During this first drilling stage, The Electrolytic Zinc Company of Australasia Pty Ltd, by invitation encouraged by the then Australian Government, became equal joint venture partners. In later years, they have farmed out much of their equity to the Broken Hill Proprietary Company Ltd. Exploration Techniques. As one would expect almost all applicable techniques available have been used to some extent and, if not in a tactical sense, at least experimentally. Table 1 summarises the results of diamond drilling targets indicated by various techniques. This excludes holes drilled as infill holes for ore reserve definition and such-like. It should also be pointed out that 7 of the holes (5 Significant, 2 Nil) categorised as geological would also have been drilled on geophysical and geochemical evidence if it had been available at the time.

217

Table 1 Diamond Drilling Statistics at Thalanga

Mineralization Targets

No. of Holes Nil

Minor

Significant

Geological

Geophysical

Geological - Geophysical

Geological - Geochemical

Geophysical - Geochemical

As usual there is no technique which can be said to be the answer. The apparent high rating of geology is enhanced because many of the holes are too deep, or they have been drilled at targets which were so obvious that no corroboration was necessary. Geochemistry-Geology also looks good but this is because the depth and conductivity of Campaspe Beds make electrical geophysics unworkable. Gravity does not show up well with relatively narrow vertical bodies at often 60 metres deep or more. Magnetics is not directly useful as little of the ore zone has any significant susceptibility. Geochemistry is certainly very usefull for searching under the Campaspe Beds but because of the high cost of rotary drilling much geological direction is necessary. Conclusions. Clearly the discovery of Thalanga is due to a well directed conceptual approach refined by records search and followed by experienced and - more importantly - discerning observation of geological evidence. References Gregory, P.W., & Hartley, J.S., 1982, Geol. Soc. Aust., Field Conference Notes (Withnall, I.W. Ed).

THE DISCOVERY OF THE BALCOOMA MASSIVE SULPHIDE

DEPOSIT

K.J. Harvey Carpentaria Exploration Company Pty Ltd,

Brisbane

Balcooma is a lower Palaeozoic volcanogenic massive sulphide deposit located 240 km north-west of Townsville in north Queensland. Reserves are 3.5 x 10 6 t of 3% Cu. The deposit was discovered late in 1978 with the first drill hole intersection in April 1979. The sequence of significant events leading to the discovery was : 1. An exploration base was established in Charters Towers in January 1977 to explore the area for gold deposits and base metal deposits with significant precious metals contents. 2. Volcanogenic massive sulphide deposits were recognized as fulfilling this criteria. Potential for these deposits in the area was good and the major part of the exploration effort was therefore directed toward the discovery of these deposits.

218

3. Early in 1978 a concept oriented review of the exploration potential of north east Queensland was commenced. This highlighted the potential of the Balcooma area for volcanogenic massive sulphide deposits on the basis of C.E.C.'s understanding of the geology of the area from work in the area during the early 1970's. 4. Reconnaissance geological mapping in the area showed that the area contained a metamorphosed marine volcano-sedimentary sequence with areas of silicification, sericitisation and pyritisation and that lenses of stratiform barytes existed. These features confirmed the potential for volcanogenic massive sulphide deposits and an Authority to Prospect was applied for in August 1978. 5. During airphoto interpretation prior to carrying out geological mapping and detailed stream sediment sampling of the area, the ferruginous areas at Balcooma were noted and marked for field checking. 6. Geological mapping of these ferruginous areas led to the discovery of the Balcooma gossans in November 1978. 7. A five hole drilling programme was commenced in April 1979. DDH 1 made two intersections of massive sulphides including 7 m of 2.8% Cu and 26 m of 2.3% Cu. Techniques having a significant impact on the discovery included conceptual analysis, geological mapping, and airphoto interpretation. Although a number of techniques were employed, the discovery was essentially a geological one. The Balcooma discovery emphasises elements which are important to many successful exploration programmes including : ( i) programme; ( ii) (iii) ( iv) ( v) ( vi) (vii)

clear well defined objectives for the exploration informed conceptual approach; techniques applicable to the deposit type and area; management support; persistence of effort; highly motivated effort; a field based approach.

THE GREENBUSHES TIN-TANTALUM - LITHIUM

DEPOSIT

M . Hatcher Greenbushes Tin Ltd., Perth The Greenbushes Pegmatite is the source of cassiterite, tantalite, spodumene and kaolin production from Greenbushes Tin Ltd's mining operations in the south-west of Western Australia (70 km south of Bunbury). The main pegmatite is approximately 3.3 km long, from 50 to 230 m wide and strikes in a NNW direction dipping from 20° to 80° W . Along the strike both north and south of the main body are swarms of pegmatite veins varying from 3 to 40 m w i d e . The Greenbushes pegmatite group has intruded the amphibolites, metasedimentary schists and felsic gneisses of the Balingup Metamorphic Belt over a strikelength of 7 k m . A 1 to 5 m thick Cainozoic laterite cap is underlain by extensively weathered bedrock to depths of 20 to 50 m . Within the pegmatites feldspar and spodumene have been kaolinized. Cassiterite was discovered at Greenbushes in 1888 but it was ninety years before the extent of tin-tantalum and spodumene mineralization was realised. The following were factors affecting recent discoveries.

219

1) Widely held mining titles, State Forest Reserves and freehold farming land made land acquisition at Greenbushes difficult. The major hurdle was the Southwest Highway which ran the entire strikelength of the main pegmatite. In 1975 after ten years of negotiation including relocating the Southwest Highway, Greenbushes Tin Ltd. achieved control of the Mineral Field. 2) New markets for tantalum resulted in the emphasis of mining operations in weathered pegmatite and alluvial deposits at Greenbushes changing from cassiterite to tantalite production. In addition to rising prices, strong long-term growth in. consumption and the lack of large worldwide resources were reported by market investigators for tantalum. This and the limited weathered pegmatite and alluvial reserves was the incentive to explore the pegmatite at a depth below the weathered zone. 3) The Greenbushes pegmatite had been considered simple and homogeneous due to the lack of variation in weathered pegmatite mineralogy. Cassiterite and tantalite grades were enriched on amphibolite contacts and these were the targets of initial drilling. Ultimately, diamond drilling showed the pegmatite to be a complex zoned rare element pegmatite. Approximately 25% of the main pegmatite body has been drilled and the interpretation of the distribution of the pegmatite zone is not complete. The table below shows the main features of the zones below 250 m from the surface. Each of these broad zones varies from 100 to 150 m wide, and can be further subdivided on the basis of accessory mineral variation. Within 200 to 300 m of the surface the spodumene zone or its weathered equivalent is the only zone present. This explained the misleading homogeneous nature of the surface expression of the pegmatite. At depth a caesium and rubidium rich K feldspar zone forms a hood on the hanging wall of the pegmatite, the centre of the body is albitic with relatively strong Sn-Ta mineralization and the spodumene zone persists on the footwall.

MAJOR MINERALS

ACCESSORY MINERALS

GEOCHEMICAL CHARACTERISTICS

K Feldspar Zone

K Feldspar Quartz

Tourmaline Muscovite

K , Rb, Cs

Albite Zone

Albite Quartz Tourmaline

Muscovite Apatite Beryl K Feldspar Spodumene Tantalite Cassiterite

N a , Sn, Ta, N b , Be, B , P

Spodumene Zone

Spodumene Quartz

K Feldspar Albite Tourmaline Apatite

UNIT

220

The "lucky break" or "divine intervention" for the Greenbushes Project came when drilling for relatively small tonnage contact Sn-Ta mineralization resulted in the discovery of mineral assemblages which showed the pegmatite was a highly differentiated rare element pegmatite. This change in geological concept was fundamental to subsequent tantalum and lithium discoveries. As a result of the success of recent exploration, reserves exist to expand and continue production for decades.

IN-SEAM SEISMIC SURVEYS IN THE HUNTER VALLEY P.J. Hatherly and G.E. Holt Australian Coal Industry Research Laboratories Ltd., North Ryde The in-seam seismic method determines the location of geological anomalies such as faults and dykes within coal seams. It can be used in both mine planning and exploration. Australian Coal Industry Research Laboratories (ACIRL), with financial assistance from the Australian Coal Association, is investigating the inseam seismic method. Trial surveys are being conducted in NSW and Queensland to gain experience and test the method. In the Hunter Valley, three surveys have been conducted. Two of the surveys were made underground in the West Wallsend No.2 and Liddell Collieries (both operated by Coal and Allied Pty. Ltd.). These surveys were designed to locate dykes, old workings and to test a proposed longwall area. The third survey was made between exploration boreholes at Glennies Creek (Consolidation Coal). This survey was designed to test seam continuity between the boreholes. All surveys produced good results. The underground surveys have positively identified geological anomalies while the borehole survey indicated uniform seam conditions. This paper presents the results of these surveys and discusses the implications of this work to other multi-seam environments.

THE MARRANGAROO CONGLOMERATE - ITS DISTRIBUTION AND ORIGIN IN THE SYDNEY BASIN P. Havord1, C. Herbert1, P.J. Conaghan2, J.W. Hunt2 and K. Royce2 ^Methane Drainage Pty. Limited, Sydney 2 Macquarie University, Sydney Introduction The Marrangaroo Conglomerate was one of the earliest named stratigraphic units in the Western Coalfield of the Sydney Basin (1883). This pebbly sandstone to cobble conglomerate is unusual in the Upper Permian coal measures as it has been derived from the Lachlan Fold Belt to the southwest rather than the New England Fold Belt to the northeast. It is therefore a more quartzose formation than the rest of the quartz-poor volcanolithic coal measures. It is now recognised that the Marrangaroo Conglomerate is more widely developed across the southern and western Sydney Basin than previously thought and that correlative rocks also extend from the northern Sydney Basin to the Gunnedah Basin.

221

Depositional Environments. The Marrangaroo Conglomerate is a fluvial pebbly sandstone to cobble conglomerate which extends from the western margin to the basin centre where associated barrier-bar facies are found. Marine conglomerate and clay-pellet lateral facies equivalents are present in the top of the underlying Kulnura Marine Tongue in the basin centre. Several environmentally distinctive conglomeratic facies are recognised in the Marrangaroo Conglomerate and the Kulnura Marine Tongue. They are: Fl. An alluvial facies, which comprises up to 16m of pebbly sandstone to cobble conglomerate, fining upwards to inter-bedded fine sandstone and siltstone, usually capped by the Lithgow/Woonona Coal. This facies erosively overlies a nearshore facies described below (F3) which grades into the Kulnura Marine Tongue. F2. A beach-bar facies, which comprises granule to pebble conglomerate only a few metres thick. It has an erosive base into the Kulnura Marine Tongue and a sharp top overlain by marine siltstones of the Wilton Formation. The Woonona Coal is absent over the top of this facies. F3. A nearshore marine facies, which comprises a coarsening upwards sequence of bioturbated pebbly sandstone to pebble conglomerate interbedded with black sandy siltstone up to 11.5m thick. This sequence grades conformably down into the silt stones of the Kulnura Marine Tongue. It is either overlain directly by the Woonona Coal or erosively by the alluvial facies, which is overlain in turn by the coal. F4. A shoreline clay-pellet facies, which comprises a few metres of sandstone to granule conglomerate composed of rounded claystone fragments with variable amounts of quartz. It grades down into the Kulnura Marine Tongue and is overlain by the Woonona Coal. Provenance. Pebble- and point-count data show that the predominant epiclastic ingredients of the Marrangaroo/Blackmans Flat Conglomerate are: quartzose rock fragments (ca 70%: largely quartzite/metaquartzite, plutonic/metaplutonic, and vein quartz); other (mainly siliceous) rock fragments (ca 27%: comprising mainly porphyry volcanics (11%) fine-grained quartzose sandstone and siltstone (11%), and black chert/argillite (3%)). Feldspar (ca 1%) and dickite-pseudomorphed feldspar (ca 3%) occur as sandgrade material. Palaeoflow, reconstructed on the basis of crossbedding, ranges clockwise from northwest to southeast and on average is centripetal (northeastward) with respect to the basin margin. These data are consistent with derivation from the belt of siliceous volcanics and quartzose sediments/metasediments and granites/metagranites, that occupy the immediately adjacent Lachlan Fold Belt. The alluvial facies extends eastwards from the Palaeogeography. western margin of the Sydney Basin as a broad presumably originally braided alluvial sheet. Just east of a meridional "hingeline" near the centre of the basin the Marrangaroo Conglomerate changes character and is represented by the nearshore facies which occurs as a north-south linear body of sediment. At the southern limit of the occurrence a beach-bar facies can be recognised. These sediments grade laterally into the shoreline claypellet facies which may represent an area starved of extraclastic sediment. The distinctive dull Lithgow/Lidsdale/Woonona Coal formed on the alluvial platform over virtually the entire western and southern Sydney Basin. The beach-bar facies, not apparently covered by the coal, may have sourced thin coarse and pebbly sandstone layers in the basal transgressive marine siltstone of the overlying Wilton Formation.

222

Tectonics* The Marrangaroo/Blackmans Flat Conglomerate was evidently deposited in response to a basin wide tectonic event that depressed the lower Tomago Coal Measures by about 200m in the central part of the basin and resulted in the accumulation there of the Kulnura Marine Tongue. In contrast that part of the basin west of the hingeline approximately coincident with the Lapstone Monocline/Nepean Fault System remained static, but with progressive uplift likely westwards and beyond the basin margin. This led to erosional truncation of progressively older basin-fill units towards the west (Fig. 1). Erosive stripping of the basin margin and adjacent craton sourced the rapid influx of alluvial conglomerate and pebbly sandstone across the western shelf domain to the basin centre. Here conglomeratic sediments were also deposited into the retreating finer-grained marine sediments of the Kulnura Marine Tongue.

Figure 1.

Schematic east-west cross-section of the western half of the Sydney Basin showing suggested stratigraphic relationships (variable scale). F1, F2 and-F3 as in text.

STRATIFORM COPPER DEPOSITS HOSTED BY LOW ENERGY SEDIMENTS NATURE OF METAL TRANSPORTING WATER AND CONTROLS ON METAL RATIOS D . W . Haynes 1 , M.S. B l o o m 2 •'•Western Mining Corporation, P.O. Box 157, Preston, of Earth Sciences, Monash University, C l a y t o n , Victoria

2Dept.

S t r a t i f o r m copper deposits hosted by low energy sediments are an important copper resource. Examples are occurrences in Shaba Province, Republic of Zaire, in the Z a m b i a n C o p p e r b e l t , and in the Lubin area, Poland. These deposits are chracterised by relatively high copper contents, and by variable contents of cobalt, lead, zinc and silver, and by low ironand nickel contents. C h a r a c t e r i s t i c s of associated alluvial fan sediments, associated authigenic minerals, and stratigraphic relations between the alluvial fan sediments and the ore host rocks shows that metal transporting waters involved in formation of the s t r a t i f o r m copper deposits were closed-basin 3 molal N a C l waters saturated w i t h anhydrite, carbonate and hematite. Temperatures of the waters were less than 50°C, and pH values were likely to have ranged between 7.3 and 7.7. 223

M o d e l l i n g of C u , A g , F e , M n , N i , C o , Pb and Z n solubilities in comparable waters produced by computer simulated evaporation of closed-basin inflow waters derived f r o m felsic volcanic or granite and mafic volcanic provenances respectively was performed using oxygen fugacities ranging from that below the pyrite-hematite join up to that on the M r ^ O j - M r ^ join. C h o i c e of the provenances of the inflow waters was determined by compositon of provenances of the alluvial fan sediments associated with the stratif rom copper occurrences. Solubilities displayed a marked dependence on o x y g e n fugacity variation in the hematite stability field and were similar f o r both waters. C o p p e r showed a distinct narrow peak of solubility of 2000 parts per minion (p.p.m.) between the cupritea t a c a m i t e and native-copper-chalcocite joins (10"^ to 10 bars); silver displayed a maximum solubility of 200 p.p.m. above the cuprite atacamite join; lead and zinc displayed m a x i m a of 30 and 60 p.p.m. respectively above the galena-pyromorphite join (10~ 6 t * Cobalt displayed similar solubility behaviour to copper, reaching a m a x i m u m of 150 p.p.m.. M a n g a n e s e solubilities reached 200 p.p.m. between 10 bar and 1 0 " ' ° bar. Iron and nickel concentrations were very low at all o x y g e n fugacities. M e t a l abundance within the sediments sourcing metal transporting waters exerted greatest control on metal concentrations in the waters. C o n c e n t r a t i o n s of copper, cobalt and silver were constrained below saturation concentrations in the windows of maximum solubility for both waters and were highest in closed-basin waters derived from mafic volcanic provenances. Lead, zinc and nickel contents of such waters were low relative to copper contents. C l o s e d basin waters derived from granite or felsic volcanic provenances contained lower concentrations of copper and zinc, and minor concentrations of cobalt. L e a d contents of both waters are similar. A computer simulated titration of the waters with reduced sulphur, to approximate reduced sulphur addition as a result of bacterial sulphate reduction, resulted in an order of appearance of sulphides similar to observed spatial relations between sulphides. Modelling showed that amounts of directly precipitated pyrite and copper-iron sulphides are very small, and that a m o u n t s of cobalt, lead and zinc sulphides precipitated are determined by availability of reduced sulphur in the metal precipitating environment. Modelling shows that metal ratios in s t r a t i f o r m copper deposits hosted by low energy sediments are thus determined by source sediment composition, and hence, metal transporting water composition, and by availability of reduced sulphur in the sulphide-precipitating environment.

H Y D R O G E O L O G I C A L D O M A I N S B E H I N D T H E E A S T W A L L OF T H E W O O D L A W N OPEN CUT AND IMPLICATIONS FOR SLOPE STABILITY R.K. Hazeldene and W.J. McKay Woodlawn Mines, Tarago, N.S.W. The Woodlawn Zn-Pb-Cu open cut mine, situated in southeast New South Wales, commenced production in 1978. As the mine has developed ground water problems have become significant. The major problems created are (i) instability of final high walls; (ii) flooding of drop cut developments; (iii) wet blast-holes necessitating use of expensive slurry explosives and reducing the reliability of grade control sampling; (iv) corrosion of pipe and pumping equipment due to low pH; and (v) wet ore promoting oxidation and blockages in ore bins.

224

The east wall of the pit is a footwall slope that incorporates two passes of the ore/waste haulage road. Disruption or loss of this access would have severe economic consequences for the mine. Engineering geology and hydrogeological studies of interim walls showed that large scale plane and wedge failures were possible in initial designs of final high wall profiles. Calculations also showed that ground water pressure would induce failure if not relieved and on the lowest benches could induce slope heaving despite conservative slope angles. An extensive network of piezometers installed early in the mine life indicated that (i) the water table was close to surface; (ii) the pit bottom was developing up to 50m below the induced cone of depression, and (iii) the footwall sequence had low transmissivity. The massive sulphide orebody is contained within a sequence of late Silurian volcanics, fine grained sediments, chert and black shales. The footwall sequence is predominantly sediments with a zone of hydrothermal alteration in the southeast associated with stockwork copper mineralization. Regional deformation has produced a strong foliation (schistosity and slaty cleavage)that is generally parallel with bedding in the east wall. Most lithologies are confined aquifers with poor intergranular porosity. Ground water flow is primarily confined to fractures and along the foliation. Faulting and associated fracturing in the northeast wall define a different hydrogeological domain from the rest of the wall, hereafter referred to as the central and southern domains. Investigations by ground water consultants concluded that horizontal drains would be the most cost effective method for dewatering the upper levels in all domains. Lengths and spacings of drains were determined from hydraulic heads in the piezometers and observations of natural drainage from the walls. Drains in the central and southern domains of the wall were spaced at 10m intervals and drilled up to 100m into the slope. Hole spacing was increased to 20m coming round into the northeast domain. A specialised drill similar to the Aardvark design was used to drill holes 110cm in diameter. Holes were inclined upward at 3-6° and cased with slotted PVC pipe. A drilling and casing rate of 1-2 holes per day was achieved. Despite low flow rates from the south and central domains (ave. 0.5 £/min.) the rate of water table draw down was rapid (Fig. 1A). Initial flow rates of up to 26.0£/min with an average of 16.3£/min in the northeast domain resulted in very rapid draw down*(Fig. IB). Draw down influences between adjacent piezometers in this more permeable zone indicated that 20m spacing between holes was close to optimum.

225

Fig.1A

Fig.1B

East Wall (central domain)

Northeast domain

WT. prior to drainagt ift. following drainage

P45

Mine Level

—W.T. prior to drainage •W.T. following

^drainage

Mine Level

P21 Water Level

P 29 Water Level

27«0T

2780 +

2760"•

2770 -•

2740-•

2760-

£ c

i 2720

May 'june 'july ' Aug '$«pt.' Oct.' Nov.' Doc.

2750 May 'jurw'july 'Aug'sept.' Oct.'Nov.' Dec.'

1963

The success of horizontal drains in the east wall of the Woodlawn pit has nullified the threat of high wall instability posed by initial unrelieved ground water pressure. Outflows from drains and water levels in associated piezometers are being monitored to further define the distribution of wall structure permeability. This information continues to refine the design and layout of drains and represents a valuable data base for planning and construction of possible underground openings.

HYDROTHKRMAL TRANSPORT AND D E P O S I T I O N OF MODELLING AND I M P L I C A T I O N S 1

M.M. Hedges , V.J. Wall

and M.S. Bloom

URANIUM: 2

^Australian National University, Geology Department, Canberra Monash University Department of Earth Sciences, Clayton, Vic The pioneering work of Hostetler and Garrells (1962) provided significant insight into the transport and deposition of uranium in nearsurface environments. However there is little information applicable to processes under the higher temperature conditions attending the formation of most large uranium deposits (eg unconformity-related types) and encountered in high-level nuclear waste disposal sites. In this paper we present the results of our modelling of the aqueous geochemistry of uranium (to 200°C) and discuss the implications thereof for ore genesis.

226

The prime source of thermochemical data for aqueous uranium species was the compilation of Lemire and Tremaine (1980), supplemented, where necessary, by critically assessed and extrapolated data for other crystalline and aqueous species. Aqueous speciation and uraninite solubilities were computed for a broad range of redox conditions, pH and solution compositions. For geological applications, ligand concentrations, f 0 2 and pH were constrained by gangue mineral assemblages and/or fluid inclusion data for uranium deposits. Redox constraints involved U 0 2 - U4O9 and phase relations in the system Fe-O-S whereas equilibria among combinations of muscovite, kaolinite, albite, chlorite and carbonates define pH ranges. Fluoride ion activities were limited by fluorite/fluorapatite and sulphate ion activities by anhydrite saturation. f C 0 2 was varied from 0-1000 bars. (i) Hexavalent and pentavalent species account for most uranium transport under most of the range of geologically common conditions. U species are only potentially important at very low f 0 2 and low pH or at higher temperatures (T > 400°C). 2+ (ii) U 0 2 and U 0 2 phosphate, chloride, fluoride, carbonate and sulphate complexes can each or in combination be responsible for potentially ore forming (ppm-ppb) concentrations of aqueous uranium. Pentavalent uranium is important at intermediate oxygen fugacities and pH's whereas hexavalent uranium species are significant under more oxidising conditions. Of the U (VI) complexes, chloride, fluoride and sulphate species are important at acidic to neutral pH values, phosphate species predominate under near-neutral conditions whereas hydroxyl and carbonate species are significant at neutral to alkaline pH values. Uranyl chloride, fluoride and carbonate complexes become less stable with increasing temperature, however phosphate and sulphate species show increased stability. (iii) For the pH range of fluids inferred from ore deposits, transport of uranium at ppm.- ppb. levels requires extremely oxidised fluids ( f 0 2 » hematite-magnetite) or extreme/unusual ligand concentrations. Such fluids are uncommon in regional metamorphic settings and would mostly involve near surface conditions or evaporite dissolution in their path history. Ideal uranium source rocks should have, low redox capacity (eg granitoids) to allow fluids to remain oxidised enough to transport uranium out of them. (iv) Reduction of uranyl-bearing fluids is the most effective mechanism for uraninite deposition in the pH range inferred for many deposits formed at elevated temperatures. This reduction may result from + interraction with graphite or Fe^ -bearing wall rocks or by mixing of the oxidised transporting fluids with more reduced (e.g. CH 4 bearing) fluids. Such processes appear to contribute to the localisation of mineralisation in Australian and Canadian unconformity-related deposits. pH changes and other mechanisms of uranyl complex destabilsation may also contribute to ore formation, but are probably of lesser importance. (v) The low solubilities of uraninite over a broad range of conditions indicate that very high fluid to rock ratios ( 1 0 3 ~ 4 ) are needed to form large, high grade uranium deposits. Such estimates however, are consistant with the mass transfer required to effect the intense, associated alteration. The vast quantities of fluids involved are indicative of effective fluid focussing mechanisms and also very large, unusually long lived hydrothermal systems which require specialised tectonic settings (eg. Johnston and Wall; Koul et. al; this volume).

227

GEOMORPHOLOGY, SEISMOLOGY AND MINERAL TARGETS - AN EXPLORATION APPROACH THROUGH TECTONIC STUDIES? E.J. Heidecker and J.M.W. Rynn Department of Geology & Mineralogy, University of Queensland, Brisbane The northeastern Queensland region provides scope for integration of structural geomorphology, seismology, tectonics and mineral exploration. These aspects of the earth sciences have yielded data suggestive of many correlations. T o r instance: (i)

The region's morphology (defined by river courses, escarpments and topographic surfaces) is widely influenced by linear, block and domal structures in response to substantial neotectonism and recent volcanicity;

(ii)

There is an emerging spatial pattern to the seismicity in northeastern Queensland in which the known epicentral distribution appears confirmed by structural boundaries, and thus defines particular seismic domains;

(iii)

Northeastern Queensland is of tectonic interest as it is the site of transverse structures which interrupt the meridional trends of the Tasman Zone. Two competing hypotheses prevail: either the Tasman Orogen is interrupted and rotated by transverse structures, or secondly, that such transverse structures have developed upon structures of the (meridional) Tasman Zone;

(iv)

The delineation of lineaments has been widely studied. These features are now accepted and have been used by the mineral exploration industry.

Coincident morphostructural features and earthquake distributions have provided the basis for recognising meridional Tasman trends at depth. This favours the second hypothesis (above) in that the transverse structural zone has developed upon a framework of Tasman structures. Similar data sets for other regions, such as in southeastern Queensland and northeastern New South Wales (New England Fold Belt), are also indicative of correlations between geomorphology and seismology. This, again, will be an important aid in studies of the tectonics and possible mineral targets in these areas. Such observations are thus essential in providing models to determine the depth of orogens in the Tasman Zone and in decisions to select and use lineaments as guides to resources exploration.

228

H Y D R O T H E R M A L GEOCHEMISTRY OF ARSENIC IN RELATION TO CASSITERITE - ARSENOPYRITE - BASE METAL SULFIDE MINERALIZATION IN NEW ENGLAND Christoph A. Heinrich and Peter J. Eadington CSIRO Division of Mineralogy, North Ryde Thermodynamic calculations based on low-temperature data for the system As-S-O-H and corresponding-state correlations were combined to estimate the stability of aqueous As-species and the solubility of Fe-Sarsenides at high temperature. They indicate that H3As03 is likely to be an important As-transporting species in sulfur-bearing neutral to acid solutions. The stability of thioarsenite complexes such as H 2 As 2 S4 may be underestimated by the calculations because of the less reliable entropy correlations for such complexes. Predicted stability relations with H3As03 as the main aqueous As-species compare well with natural occurrences of hydrothermal As-minerals. Deposition of lollingite (FeAs2), with or without pyrrhotite, from sulfide solutions is restricted to high temperatures and low oxygen fugacities, in agreement with its natural occurrence as an early phase in high-T deposits. Arsenopyrite is likely to be precipitated in the 400°-300° range in systems saturated with pyrrhotite while together with pyrite, arsenopyrite deposition can extend below 200°C. Oxygen fugacities are generally below Ni/NiO so that H 2 S is the dominant S-species in neutral to acid arsenopyrite-depositing solutions. Solubility equilibria likely to be important are pH-independent and involve only neutral species. The small temperature dependence of the heat capacity of non-ionic species is probably one reason why the relatively crude calculations are successful in explaining natural arsenide associations. Textures and fluid inclusions in the Sundown (S. Qld) sheeted vein deposit indicate two main stages of mineralization of veins transecting pelitic hornfels and underlying biotite granite. In a first stage, a phengitic muscovite selvage was overgrown by large euhedral crystals of cassiterite, fluorite, topaz, arsenopyrite and quartz, which crystallized between 400 and 340° from a solution with a salinity equivalent to lm NaCl. Any remaining vein space was filled in a second stage at 320-290°C with pyrrhotite, chalcopyrite, sphalerite and minor arsenopyrite. Pyrite locally replaces pyrrhotite. Mostly during the first stage, host rocks containing feldspars, biotite and chlorite reacted to zoned alteration haloes rich in phengitic muscovite and quartz, suggesting that the early arsenopyrite may have formed at the expense of ferrous sheet silicates. To describe and test this observation, a model reaction K F e 3 A l S i 3 O 1 0 ( O H ) 2 + F e 5 A l 2 S i 3 O 1 0 ( O H ) g + 8H 3 AsC> 3 + 8H 2 S = 8FeAsS + K A l 3 S i 3 0 1 Q ( O H ) 2 + 2 4 H 2 0 + 3Si0 2 + 6C>2 ( a ) (in biotite)

(in chlorite)

(asp)

(in phengite)

has been balanced for the reduction of aqueous As(IlI) to As(-I) in arsenopyrite. Calculated contours for this equilibrium at different concentrations of H3ASO3 and H 2 S are shown in Fig. 1 together with calculated and experimental solubilities for cassiterite, pyrrhotite and chalcopyrite in 1 m chloride solutions. A cooling path A-F shows a possible chemical evolution of an Sn, As, S, Fe^ Cu (Zn) rich fluid which is originally buffered by granitic Fe^+ bearing minerals near the Ni/NiO - buffer (line A-B), until it reaches cassiterite saturation at B. Unless in continuing contact with unaltered granite (path B-Cf), f(0 2 ) may drop until at C reduction of aqueous As(III) to arsenopyrite provides 0 2 for cassiterite co-precipitation (C-D; corresponding to first stage at Sundown). At D the solution has precipitated all its Sn and most of its As, but can still contain >lm Fe and 10~^m Cu. Pyrrhotite and chalcopyrite solubility drops drastically

229

log fCCb) - T - diagram (scaled to 1/T) showing contours at different activities (log a indicated by the figures) of H3ASO3 (As), SnCl2 (Sn) and H2S (S) etc. according to the equilibria given below.

log f(02) -25 (bars)

(Fe)tot

-3

(S)

-3

-30

-35

buffered by + K-feldspar + muscovite + (K+) = 0.1m + (Cl-)= 1.0m

(S) (As) - 2 '

-2

-3"

-4 T 200 " 3

( °C )

400

300

2 SnCl2 + O2 + 2 H2O 2 H3ASO3 + 2 FeS CuCl + H2S + 0.25 O2 + FeS

= 2 Sn02 + 4 Cl~ + 4 H+ = 2 FeAsS + 3 H 2 0 + 1,5 0 2 = CuFeS2 + 0.5 H 2 0 + H+ + Cl~

FeCl-2+n +

u S

FeS

500

+ 2 H+ + n Cl"

between D and E to form second stage base metal mineralization at Sundown. At E the fluid is so depleted in sulfide that only traces of late pyrite are formed (E-F). Conclusions* Although order-of-magnitude estimates, the thermodynamic calculations explain the fluid inclusion data, alteration, and paragenetic sequence at Sundown, which are similar to other deposits (e.g. Cornwall; Ardlethan; Mt Pleasant, Canada). Even if the model is only qualitatively correct it exemplifies the importance of redox reactions on economic cassiterite mineralization. Under such reducing conditions as prevail in ilmenite series granitoids or reduced metasediments, hydrothermal fluids do not contain any free oxygen. Since tin deposition most likely involves oxidation of Sn(II) aqueous complexes to Sn(IV)02 (e.g. (b)), continuing cassiterite accumulation requires reduction reactions to proceed simultaneously in the rock-fluid system. The availability of reducable species in the cooling system will determine how efficiently tin is extracted from the solution over a given temperature gradient. Hence reducing agents will influence cassiterite bulk ore grades so economically critical in greisen and sheeted vein deposits. The calculations indicate that reduction of aqueous As(III) complexes to arsenopyrite (involving ferrous silicates, or 2+ also Fe carried in solution) could couple with oxidation of Sn(II) complexes to cassiterite in tin deposits in which the two minerals precipitate together.

230

CHEMICAL DIFFERENCES BETWEEN MINERALS FROM MINERALIZING AND BARREN INTRUSIONS FROM SOME NORTH AMERICAN PORPHYRY COPPER DEPOSITS 1

D . A . F . H e n d r y , A . R . Chivas , J.V.P. L o n g

and S.J.B. R e e d

"'"Department of Geology and Geophysics, University of Sydney, Sydney Research School of Earth Sciences, Canberra Department of Earth Sciences, Cambridge, U . K . Major-element analyses (by electron microprobe analysis) and copper contents (by ion-probe) are reported from primary biotite, amphibole, magnetite, pyroxene, ilmenite, sphene and secondary biotite from intrusive rock types from mineralizing and barren stocks. Those districts studied include Christmas, Globe-Miami, Sierrita and Tombstone, all in Arizona; Bingham and A l t a , Utah; Ely, Nevada; and Brenda, British Columbia. Amphiboles from barren rock types are relatively iron-rich and display only minor compositional variation. In contrast, amphiboles from mineralizing rocks cover the field from magnesio-hornblende to actinolite, commonly, even within one grain. Trends in biotites are n o t so well defined, b u t biotites in mineralizing intrusions are also commonly more Mg-rich than those in barren rock types. From temporal and field relations alone, we distinguish two categories of barren intrusions, which for simplicity, we refer to as types A and B . Type A barren intrusions are deep-level temporal equivalents of Cu-bearing porphyritic rocks. These barren intrusions are commonly described as larger equigranular stocks and may have gradational contacts with productive porphyries. Examples from this study are the main phase of the Schultze Granite from the Globe-Miami district, Weary Flat quartz monzonite from Ely and the Last Chance stock at Bingham. Type B barren intrusions occur outside known mining districts or are significantly older or younger than productive intrusions in areas of known mineralization. Examples include the Schieffelin granodiorite a t Tombstone, which is remote from known copper mineralization. In the Christmas area, the hornblende andesite porphyry dykes are 9 to 14 Ma older than the mineralizing event. Similarly, the Granite Basin pluton, McDonald stock and other dykes of hornblende rhyodacite porphyry are 7 Ma older than the Christmas intrusive complex. A t Ely, the Lane Valley sill is post mineralization. Using this subdivision of intrusions that are either mineralizing, barren type A or barren type B , barren type B (isolated or temporally unrelated intrusions) have minerals with higher copper contents than those For example, the Cu contents of intrusions from the other categories. biotites (av. 23 ppm) and magnetites (97 ppm) from barren type B intrusions contrast with those from mineralizing intrusions, with biotites containing 7 p p m C u and magnetites 3 p p m C u . Primary amphiboles from all intrusive rock types have low copper contents, typically 2 to 5 p p m . The low copper content of mafic minerals from mineralizing and barren type A intrusions reinforces a suspected genetic link that various workers suggested based on field relations. It also supports the loss, or nonincorporation, of copper from silicate phases during magmatic fluid exsolution. W e can now propose that copper is abstracted or partitioned from not only the narrow cylindrical productive porphyries themselves b u t also from parts of the deeper level coarse-grained progenitors.

231

In an earlier study on Koloula deposit in Guadalcanal (Hendry et al., 1981), we demonstrated the copper-content deficit in biotites of mineralizing vs barren intrusions is sufficient to account for the observed copper mineralization. This is not the case for the continental deposits investigated herein where the Cu contents of biotites (av. 23 ppm) and magnetites (97 ppm) from barren type B intrusions contrast with those from mineralizing intrusions with biotites containing 7 ppm Cu and magnetites 3 ppm Cu. A simple calculation indicates that if a mineralizing quartz monzonite composed of 6 weight percent biotite and 1 weight percent magnetite were able to extract 20 ppm Cu from that biotite and 100 ppm Cu from the magnetite a total of only 2 ppm Cu would be liberated from the whole rock. If such a process were to operate in an igneous body with a volume of 100 km3 (equivalent to a cube with a side of 4.65 km) sufficient copper could be released to form an orebody of 100 million tonnes of 0.5% Cu ore. Even so, the amount of copper liberated seems unrealistically low. The possibility remains that mineralizing intrusions were initially richer in copper, prior to the exsolution of magmatic fluids, than barren type B stocks which we have taken, by inference, as a measure of the initial composition of all stocks of a given region, despite differences in age and geological setting. An alternative source of copper is provided by country rocks through which meteoric water circulates in response to heating by igneous intrusions. Reference Hendry, D.A.F., Chivas, A.R., Reed, S.J.B. & Long, J.V.P., 1981, Contrib. Mineral., 78, 404-412.

STRUCTURE OF ACTIVE 6E0THERMAL SYSTEMS AND IMPLICATIONS FOR THE ORIGINS OF SOME HYDROTHERMAL GOLD AND BASE METAL ORE DEPOSITS R.W. Henley Chemistry Division, DSIR, Taupo Geothermal systems are extraordinarily abundant in the tectonically active zones of the earth's crust and may be broadly classified according to their plate tectonic setting and principal source of heat (Table 1). Chemical differences arise from the sources of recharge water and contribution of gases from magmatic or metamorphic sources. Table 1. Crustal host

Oceanic

Continental

232

Magmatic

Ridge hotspot, back-arc basin Magmatic Arc Crustal extension (Hot spot, Rift)

Amagmatic

Plate Collision Plate Interior Basins

Each of these classes appears to have some analogue preserved in the geologic past and most commonly recognized as one or other of the various families of hydrothermal ore deposit. For magmatic systems, these range from ophiolite hosted massive sulfides through the polymetallic massive sulfides of island arcs to the porphyry copper and epithermal deposits of terrestrial continental terranes, while for amagmatic systems these range from the Mississippi Valley and related base metal deposits of sedimentary basins to post-metamorphic vein deposits associated with orogeny. The first part of this paper describes the chemical structure and hydrology of terrestrial magmatic and collision-related systems and is based on the results of recent geothermal investigations. The second part of the paper focusses on application of these data to the modelling of the environments of deposition of epithermal precious metal deposits. Coll ision-related amagmatic hydrothermal systems Only recently have data become available from geothermal investigations in mountain belts. In the Southern Alps of New Zealand, for example, hot springs occur in the central, relatively aseismic region of highest uplift rate (rLO - 20 mm/year) where the combination of uplift and erosion "exposes" a thermal anticline with near surface gradients up to 150°C/km. A similar environment is proposed for hot springs in other collision-related mountain belts. Recent drilling at Yangbajing (Tibet) and in the Parbati Valley (N. India), for example, has located hot waters up to 170°C which are dominantly meteoric in origin but contain low He to He ratios typical of helium of deep crustal origin. The uplift setting of these hydrothermal systems is perhaps analogous to that of late Mesozoic post-metamorphic gold and scheelite veins in the South Island (New Zealand) and, by inference, similar deposits in much older (Archaean) terrane. Examples are the gold veins of the Valdez group (S. Alaska), Mother Lode (California) and at Yellowknife (N.W.T.) and Kalgoorlie (W. Australia). In each of these, in contrast to the epithermal precious metal deposits discussed below, vein quartz is enriched 1

in 0 relative to host rocks. This feature has led many workers to suggest a metamorphic origin for the hydrothermal fluid. It is possible however to generate these same isotope characteristics by interaction of meteoric water and rocks at low water to rock ratio. This may occur in any uplift terrane within which a thermal * anticline is developed, so that the tectonic setting may not be purely analogous to that in the present day Southern Alps or Himalaya. Where deuterium data are available for the more recent deposits (e.g. the Alaskan deposits) there is an apparent similarity to present day meteoric waters. An advantage of considering a relatively shallow origin for these vein deposits is that chemical modelling may be applied under the constraint of hydrostatic: rather than lithostatic pressure and allows (in the system ^ 0 CO2-X) that phase separation and associated pH/redox changes may be responsible for ore deposition.

233

Terrestrial magmatic hydrothermal systems By contrast, systems in volcanic terrane have high ^He to ^He ratios characteristic of helium of direct or indirect mantle origin. Temperatures encountered during drilling range up to 380°C and waters are dominantly meteoric in origin. Although some highly saline fluids are evolved in rift zones such as the Imperial Valley (California), salinities are typically low clustering around 10,000 mg/kg CI (1.6 wt% NaCl equivalent) in andesitic terrane, 1000 mg/kg in rhyolite terrane and much lower in basaltic terrane. Dissolved gas, always dominated by CO2, effects a major contrast between systems ranging from very low (0.01 wt % CO2) at Wairakei (New Zealand) and Ahuachapan (El Salvador) to several wt % at Broadlands and Ngawha (New Zealand). Other dissolved components are controlled by mineral-fluid and gas-gas reactions. Alteration assemblages correspond closely to those encountered in epithermal and porphyry style deposits. The deep hydrologic structure of the terrestrial systems is controlled by the convective upflow of chloride waters but above depths of around 1 km surface topography plays a major role in the dispersion of the chloride water by introducing a lateral flow component toward topographic lows. Boiling occurs as chloride water rises through the system, the resultant steam migrating to the surface independently where near surface condensation and oxidation of co-transported H2S produces sulfatedominated steam-heated waters. The relatively high relief of andesite terrane results in lateral flows of hot chloride water for up to 20 km while the occurrence of near surface magmas exsolving gases (HC1, SO2, etc) often produces high temperature fumaroles and/or acid sulfate-chloride crater lakes. These latter features, with their associated intense advanced argillic alteration, probably represent the upper portions of the type of hydrothermal systems responsible for gold (enargite) sulfide deposits such as Goldfield (Nevada), Summitville (Colorado), Bor (Yugoslavia) and elsewhere. Active gold, silver and base-metal sulfide deposition occurs in a number of active geothermal systems. At Waiotapu (New Zealand) ore-grade gold, with antimony, arsenic, silver and thallium is deposited as an amorphous precipitate on the rim of a hot spring as a result of mixing of relatively oxidized surface waters with upflowing chloride waters. By contrast, base metal sulfides appear to be deposited in response to boiling with gas loss and concomitant pH increase. These two processes, in conjunction with selective bisulfide and chloride complexing of metals, are responsible for the metal zoning commonly observed in present-day systems and analogous epithermal deposits. Many of the hot-springs hosting metalliferous precipitates are associated with hydrothermal eruption vents. Similar vents and vent breccias occur in "hot springs" type gold deposits such as Round Mountain (Nevada) and McClaughlin (California). Many of the environmental indicators observed in epithermal ore deposits may be applied to the interpretation of the polymetallic Kuroko and Archaean massive sulfide environments. Many of these contain evidence of explosive brecciation at the sea-floor and some inclusion data allow that boiling may have occured below the discharge vent that focussed ore deposition. These deposits may be considered as telescoped equivalents of the depth-zoned epithermal deposits of the terrestrial hydrothermal systems.

234

Implications Recognition of the correlation between water-type and alteration style, together with the recognition of vent breccias, allows the partial reconstruction of the near-surface hydrology of many epithermal precious metal deposits and this in turn may be a valuable guide for mineral exploration. An apparent disconcerting dissimilarity between the salinities of active systems and of inclusion fluids from epithermal deposits arises in part from the effect of dissolved CO2 masquerading as a salt in inclusion fluids and in part from an inappropriate comparison from different sample populations. A sample bias is introduced by the energy focus of geothermal exploration while the salinity range highlighted by fluid inclusion studies represents only those few fossil hydrothermal systems which generated ore sensu stricto. Remaining chemical differences reflect important distinctions between the crustal environment of most active geothermal systems and those hosting ore deposits. Base metal sulfide deposits require rather higher salinity for significant metal transport than the mean of the active system fluids while gold transport is favoured by fluids relatively enriched in dissolved gas (H2S, Cf^-**)* The evolution of the hydrothermal fluid is therefore as, if not more, important than the evolution of host or so-called 'source1 rocks. Ore formation therefore results from the time sequence of favorable tectonic and geochemical events in a segment of the crust. Gold - telluride ore formation at Thames (New Zealand), for example, may have resulted from a rhyolite heated hydrothermal system superimposed upon an earlier, but unroofed, weakly mineralized andesite hosted system. As shown by the studies, reviewed here and the analogous studies of the sulfide deposition in active spreading centres, such as in the east Pacific at 21°N, quantitative observations of geochemical processes in a wide range of present day environments provide a powerful tool for both the interpretation of ore forming environments and for the guidance of mineral exploration.

FLUID EVOLUTION IN GRANULITES FROM THE ARUNTA BLOCK, CENTRAL AUSTRALIA B.J. Hensen

and R.G. Warren

•'"School of Applied Geology, University of New South Wales, Kensington Bureau of Mineral Resources, Canberra An explanation of the evolution of the fluid phase during granulite facies metamorphism and subsequent cooling needs to account for the following observations: 1 )

Anhydrous, pyroxene-bearing mineral assemblages that indicate low water activity during the peak of metamorphism,

Pervasive, but incomplete, hydration during cooling (the biotite stage of Warren, 1983) producing an essentially random fabric without evidence for deformation.

Localised complete hydration, restricted to shear-zones and fractures, never penetrating by more than a few metres into surrounding granulites. The localised nature of the hydration is taken as evidence for low permeability of the granulites during cooling.

235

The occurrence of the assemblage meionite-calcite-wollastonitegarnet in calcsilicates. This assemblage is stable only at high temperature (>750°C) and high water activity, but occurs in lenses in granulites (cf. Valley et al.f 1983).

No fluid inclusion data are available for the Arunta rocks. The widely reported occurrence of high CO2 inclusions in granulite minerals suggests that a CO2 -rich fluid attends granulite facies metamorphism.

Minor partial melting of essentially dewatered upper amphibolite rock, containing hydrous phases, durifig granulite facies metamorphism, with no or limited liquid segregation or escape, and subsequent in situ crystallization on cooling, can explain the above observations. This model accounts for the widespread, but limited, availability of water for partial hydration, which cannot otherwise be explained without assuming high permeability for which there is negative evidence (point 3 above). Partial melting has previously been invoked as a mechanism to explain the anhydrous nature of granulite facies assemblages (Fyfe et al., 1978, Wall et al., 1983, Barnicoat, 1984) but it has generally been assumed that the absence of migmatitic textures indicates that either no melting has taken place or that the melt fraction has been removed from the rock. However, recent studies on migmatites (Johannes & Gupta, 1982, McLellan, 1983) and experimental work on partial melting (van der Molen & Patterson, 1979) indicate that at low levels (<30 percent) of melting, melt segregation does not necessarily take place. We contend that most or all of the melt fraction may be contained by the rock and, on cooling, react with the anhydrous solids to form hydrated phases. As might be expected textural evidence for this process is ambiguous, but spectacular pegmatite like patches of indigo blue sapphirine euhedra enclosed in white orthoclase and similar sapphirine and kornerupine euhedra surrounded by albite are suggestive of formation in a crystal-liquid environment. The hydration reactions suggested by Warren (1983b) to explain the retrograde reaction textures can be modified by assuming liquid instead of K-feldspar + H 2 0 as one of the reactants; e.g., sapphirine+orthopyroxene+liquid+cordierite+biotite rather than sapphir ine + or thopyroxene + orthoclase + H2O -•cord ierite+biotite, to explain cordierite rims on euhedral sapphirine crystals surrounded by perthitic Kfeldspar and biotite. The widespread occurrence of quartzo-feldspathic migmatites within the granulite terrain (Warren, 1983a) indicates that felsic rocks underwent extensive partial melting at the time of formation of mafic and silica undersaturated granulites. The calc silicate rocks must have been invaded by hydrous fluid, presumably during amphibolite metamorphism, during a period of devolatilisation enhanced permeability (Rumble et al., 1983) with subsequent internal buffering of the fluid at high water activity by the mineral assemblage. Fluid exchange with the surrounding rocks during granulite metamorphism can only have been minimal (cf. Valley et al., 1983). The rocks contain evidence of reintroduction of water during cooling,, where they adjoin shear zones. As partial melting can also account for the generation of a C02~rich fluid in equilibrium with solids and water undersaturated liquid (Valley et al., 1983, Wall et al., 1983) we see no need to invoke a flushing event with externally derived CO2 to explain the observed mineral assemblages or the fluid inclusion evidence reported from elsewhere. We concur with Barnicoat, 1983, Wall et al., 1983 and Valley et al., 1983, that partial melting is a viable dehydration mechanism for granulite facies metamorphism. Partiial or complete melt retention may be responsible for the widely described minor hydration of granulites by a melt-residuum reaction during isobaric cooling.

236

References Barnicoat, A.C.,1983, J. Metamorphic Geol. 163-182. Fyfe, W.S.f Price, N.J., & Thompson, A.B., 1978. Fluids in the Earth's Crust, Elsevier. Johannes, W., & Gupta, L.N., 1982, Contrib. Mineral. Petrol., 79^ 114-123. McLellan, E.L., 1983, J. Metamorphic Geol., 1^2*41-262. Rumble, D., Ferry, J.M., Hoering, T.C., & Boucot, A.J., 1982, Am. J. Sci., 282, 836-919. Valley, J.W., McLelland, J., Essene, E.J., & Lamb, W., 1983, Nature, 301, 226-228. van der Molen, I. & Paterson, M.S.,1979, Contrib. Mineral. Petrol., 70, 299-318. Warren, R.G., 1983a, Nature 305, 300-303. Warren, R.G., 1983b, BMR J. Aust. Geol. Geophys., 8^ 139-145. Wall, V.J., Clemens, J.D. & Bohlen, S.R., 19083, Geol. Soc. Australia. Abst. Ser. 9, 60-61.

THE GEOLOGY OF THE NAGOORIN OIL SHALE DEPOSIT D.A. Henstridge1, J.F. Ivanac2, A.W. Lindner3 and T.R. O'Dea4 ^"Central Pacific Minerals N.L., Sydney ^Consulting Geologist, Cairns Consulting Petroleum Geologist, Sydney ^Southern Pacific Petroleum N.L., Sydney The Nagoorin Oil Shale Deposit lies in the Nagoorin Graben located about 70 kilometres south of the port of Gladstone, central Queensland. Two Authorities to Prospect 2442M and 2268M cover the deposit. The former is a joint venture between Southern Pacific Petroleum N.L. (SPP) Central Pacific Minerals N.L. (CPM), Esperance Minerals N.L. and Greenvale Mining N.L. and the latter between SPP and CPM and Eastern Resources of Australia Limited. Tertiary sediments were recorded in 1885 by Rands who reported carbonaceous shale, shale and sandstone. Later investigators identified oil shale and lignitic coal. Dear et al (1971) outlined the surface extent of the Tertiary sequence which was named the Nagoorin Beds. Exploration by SPP and CPM commenced in 1980 and by 1983 SPP and CPM geoscientists had mapped the surface extent of the basin, completed gravity, ground magnetic and Sirotem surveys and drilled 73 core holes aggregating 14,420 metres. Four thousand samples were assayed by modified Fischer method. Surface mapping and drilling showed that the prospective oil shale beds lay within a Tertiary basin, drilled over a strike length of 16 kilometres and width of 2\ kilometres. A Tertiary basalt vent as well as dykes and sills were mapped - 69 metres was intersected in one drill hole with a carbonised zone extending 28 metres above the hanging wall and less than one metre into the footwall. The gravity survey suggested that depth to basement in the larger of the two gravity minima outlined was about 1,400 metres. Drilling has confirmed a minimum thickness of 870 metres. Outcrops of Tertiary sediments are sporadic because of a thick cover, up to 21 metres, of Quaternary alluvium, sands and gravels.

237

The Tertiary beds consist of a conformable sequence of carbonaceous oil shale (coaly in part), brown oil shale, green claystone and siltstone, sandstone, conglomerate and minor limestone. Ostracods and gastropods have been recorded. Careful geological logging of drill core and systematic compilation of the results of modified Fischer assay histograms has enabled the sediments to be subdivided into 9 units, 5 containing oil shale and including an undifferentiated sandstone unit. The sequence contains two main oil shale types (i) a distinctive black carbonaceous oil shale (the highest yielding unit is Cc) ranging from 32 to 71 metres thick and assaying 176 litres per tonne at zero moisture with average organic carbon content of 49%; and (ii) brown oil shale similar to Rundle type, laminated in part and of dense texture. The mineralogy consists dominantly of quartz, opaline silica, montmorillonite and interstratified illite and kaolinite with siderite (5 to 20% of mineral matter), minor feldspar, calcite, gypsum, halite and pyrite framboids. The organic matter in the carbonaceous oil shale is dominated by vitrinite with lesser exinite whereas within the oil shale the organic matter is dominated by alginite. The beds generally strike NNW and dip 15° W. They have been disturbed by strike and cross faults. Regionally the graben is localised at the intersection of two major structural trends, the NW trending Boyne Valley Rift and a NE lineament or structural corridor. The oil shale deposit is tabular and contains in situ resource in excess of 3 billion barrels of shale oil in oil shale averaging 89 litres per tonne zero water as determined by modified Fischer assay. A nominal cut-off grade of 50 litres per tonne zero water over a minimum mining interval of 4 metres have been used to calculate the in situ or geological resources. Waste to ore ratio is 0.7:1 overall and ranges 0.6 to 1 in the northern part to 1.57 to 1 in the southern part. Of particular interest was diamond drill hole No.l (NDD1) which was drilled to 687.25 metres and bottomed in oil shale. This hole intersected 528 metres (line-of-hole) oil shale assaying 87 LTOW or 0.55 barrels per tonne shale oil. The Nagoorin Beds, using palynological evidence, are mid to late Eocene and were deposited in a freshwater intermontane lake. Fluvio-deltaic, swamp, lacustrine and shallow lacustrine/deltaic environments can be interpreted from lithology and sedimentary structures. An important national resource has been outlined which is equivalent to more than ten years requirement of liquid hydrocarbons for Australian industry. Reference Dear, J.F., McKellar, R.G. and Tucker, R.M., 1971, Geology of the Monto 1:250,000 Sheet Area. Geol. Surv. of Qld., Rpt. No.46.

238

REHABILITATION

STONYFELL

SOUTH

QUARRY

NEAR

ADELAIDE

AUSTRALIA

M . N . Hiern Department of Mines and Energy, Adelaide Rehabilitation of mineral workings is the key to future access to land to supply the continuing demand of our mineral dependent society. Much is now being done to reduce the impacts of the production phase of mining by designing operations in advance and ensuring that incompatible land uses are not established in the vicinity of undeveloped resources. However public acceptance of mining will not be complete while degraded land remains after operations have finished and the site is abandoned. Mineral extraction is but a temporary use of land and every mine site has the potential to be developed for further use which either adds value to the land or provides a community need. Thus rehabilitation is both essential and logical. One of the aids to rehabilitation in the South Australian Mining Act is the Extractive Areas Rehabilitation Fund. The Act defines the commonly used construction materials as "extractive minerals" and provides for the royalty on these to be paid into the Fund and used for: a)

The rehabilitation of any land disturbed by mining operations for the recovery of extractive minerals.

The implementation of measures designed to prevent, or limit, damage to, or impairment of, any aspect of the environment by mining operations for the recovery of extractive minerals, and

The promotion of research into methods of mining engineering and practice by which environmental damage or impairment resulting from mining operations for the recovery of extractive minerals may be reduced.

Grants may be made from the Fund by the Minister for rehabilitation projects at both abandoned sites and operating quarries, regardless of whether or not the owner has paid into the Fund. There is no requirement for a contributor to receive back as much as he has paid i n . Rehabilitation of Stonyfell Quarry is a recent major project sponsored by the Fund. Located in the natural bushland of the western face of the Mr Lofty Range overlooking the city of Adelaide, the quarry had grown by 1955 to a stark white face over 100 m high. New safety regulations limiting the height of working faces to 20 metres resulted in a sudden and dramatic expansion of the visual scar as the quarry expanded horizontally and vertically to maintain its production rate of over X million tonnes per year. By the mid 1960*5 Stonyfell had become the epitomy of all of the adverse impacts of mining in daily view to 3/4 of the population of the State and the many visitors to Adelaide.

239

Geological mapping in 1976 established that the Stonyfell workings could be extended southwards into the adjacent Greenhill Quarry by cutting a slot behind a remnant naturally vegetated hill on the face of the range. During 1980, over 400,000 c. metres of overburden from the slot development were placed on the now redundant eastern benches of Stonyfell which had hitherto created the greatest visual impact from the city and surburbs. This was graded into a landform similar to the adjacent undisturbed hill slopes and planted with seeds and seedlings of indigenous vegetation collected from the property. Planning regulations prevent the site from being used for anything other than open space. Although the overall cost of $1.3 million for the project exceeds the value of the land for this purpose, rehabilitation of such a prominent and controversial site has contributed significantly to public acceptance of mining as an unwanted but nevertheless essential land use.

SOME ASPECTS OF THE METAMORPHIC AND MAGMATIC HISTORY OF THE SIX NILE WELL NICKEL DEPOSIT, W.A. R.E.T. Hill CSIRO Division of Mineralogy, Perth The Six Mile Well nickel prospect is a low grade disseminated iron-nickel sulfide deposit hosted by a layered semiconcordant lens-shaped ultramafic complex (900m x 400m) located 45km north of the Agnew nickel deposit within the Agnew-Wiluna greenstone belt, Western Australia. The deposit is one of the dunite-associated group and has been the subject of studies by Naldrett et al., (1977) and Hill (1982, 1983). Within the present limits of diamond drilling, the ultramafic complex can be conveniently subdivided into four major units at its southern end, each with characteristic igneous textures, bulk chemical compositions and contained olivines. Textural and chemical data indicate a magmatic origin for the sulfides and an evolution of the complex by the fractionation of komatiitic liquids. Dominant igneous textures range from evolved olivine orthocumulate, characteristic of the upper and western portion of the complex, to olivine mesocumulates and adcumulates in the three lower units. Some disseminated sulfide is present in all of the units but significant sulfide as a cumulus phase is present in only two of these which exhibit contrasting sulfide assemblages. Pyrrhotite, pentlandite and minor chalcopyrite constitute the sulfide mineralogy of the upper of the two zones, an olivine mesocumulate (unit 2). Pentlandite with only traces of chalcopyrite exists in the lowermost zone intersected by diamond drilling, an olivine adcumulate (unit 4). The magmatic properties of the deposit are determinable factors despite a history of intense static metamorphic alteration. Apart from a central core of largely unaltered olivine adcumulate the rocks have been extensively altered to a variety of phases dominated by serpentine, brucite, magnetite, ferroan-magnesite and pyroaurite-iowaite. A petrographic and mineralogical study has indicated that despite chemical and modal modification of the sulfides during metamorphism the distribution of contrasting sulfide mineral assemblages in the complex was present prior to the alteration.

240

There is no evidence to suggest that the pyrrhotite in the upper sulfide-bearing zone was formed solely as an alteration product of pentlandite and magnetite during extensive serpentinization and prograde carbonate alteration as proposed by other workers for similar nickel deposits in Western Australia. Olivine pseudomorphs composed of irregular mesh-textured a-lizardite variably replaced by prograde y-antigorite forms the predominant texture of the altered rocks. The lizardite forms an intimate mixture with fine dusty magnetite and submicroscopic brucite. Prograde recrystallization to antigorite has produced both non-pseudomorphic random interpenetrating lath textures and mesh or hour-glass textures. In the upper more evolved rocks near the margin of the complex the latter textures predominate and the antigorite is accompanied by significant carbonate. In the mineralized zones recrystallization to crossfibre antigorite has been to a large extent accompanied by brucite formation. Textural evidence exists to show that some pre-lizardite ferroan-magnesite replacement of intergranular sulfides has occurred. This carbonate forms irregular recrystallised intergrowths with sulfide pseudomorphing original intergranular lobate shapes. This carbonate is accompanied in some instances by early coarse interlocking antigorite blades after intercumulus silicate phases. Pyrrhotite-pentlandite assemblages and pentlandite where it is present alone, are veined and replaced by magnetite formed during subsequent lizardite replacement of olivine. The associated earlier carbonate and antigorite have remained unaffected although blades of the latter have been broken and disrupted. Variable replacement of the early carbonate by brucite has accompanied prograde recrystallization of lizardite to antigorite. Small, rounded sulfide grains composed of pyrrhotite and pentlandite, included within the cores of magmatic chromite lend corroborative evidence to the presence of primary pyrrhotite-pentlandite assemblages in the upper of the two sulfide zones. References Naldrett, A.J. & Turner, A.R., 1977, Precambrian Res., 5, 43-103. Hill, R.E.T., 1982, West. Austral. Geol. Dept. Ext. Serv. Publ. 7, ClOl-109. Hill, R.E.T., 1983, CSIRO, Div. of Min. Res. Review, Ed. W.E. Ewers, 45-47.

241

WOOLTANA METABASALT: LATE PROTEROZOIC CONTINENTAL THOLEIITIC RIFT SEQUENCE, ADELAIDE 6E0SYNCLINE, SOUTH AUSTRALIA David Hilyard School of Applied Geology, S.A. Institute of Technology, Adelaide. The Wooltana Metabasalt consists of variably metamorphosed continental tholeiitic basalt of Early Adelaidean age in the northeastern part of the Adelaide Geosyncline. It is part of a widespread metabasic suite near the base of the Adelaidean sequence, which here lies unconformably above Lower-Middle Proterozoic crystalline basement of the Mount Painter Complex. It is the uppermost formation of the Callanna Group in that area, overlain unconformably by Burra Group fluviatile sandstone. Metabasalt is the predominant lithology in the less metamorphosed eastern exposures with subordinate tuff, dolerite-gabbro, fluviatile quartz sandstone, calcsilicate metasediment, and breccia. Basalts are massive coherent flows l-20m thick with amygdaloidal oxidized tops. The flows are lens-shaped with a lateral extent of up to 1 km. There is no evidence of submarine eruption. Laterally equivalent, more highly metamorphosed sequences west of the Mount Painter Complex contain abundant calcsilicate metasediment and represent a facies deposited further from the eruptive centre. The structural setting, thickness and facies changes, and sedimentary facies of the enclosing rocks indicate a continental rift setting for the early part of the Adelaide Geosyncline. The Wooltana Metabasalt has a tholeiitic composition. Despite the clearly continental setting, Ti-Zr-Y ratios plot in both the ocean floor basalt and within plate basalt fields.

242

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NATURE OF ARCHAEAN GOLD-BEARING ORE FLUIDS: A FLUID INCLUSION STUDY OF HYDROTHERMAL GOLD DEPOSITS, WESTERN AUSTRALIA Susan E. Ho Geology Department, University of Western Australia, Nedlands Fluid inclusions from Archaean hydrothermal gold deposits provide information on the composition, temperature and pressure of the ore-forming fluid. Studies of vein quartz from a variety of geographic and lithologic settings indicate similar ore-fluids and depositional conditions for a range of host-rock compositions. Emphasis has been placed on the small Red Hill gold deposit at Kanowna, Western Australia, because it contains large and well-preserved primary fluid inclusions that are similar in all respects to inclusions from more major gold deposits. Primary fluid inclusions in quartz occur as isolated three-dimensional groups, planar groups parallel to crystal faces, or as isolated inclusions, and range in diameter from 10 to lOOym, usually 20ym. At room temperature, they are either two- or three-phase and consist of H 2 0-liquid (10-70 OU is vol.%), CO 2 -liquid (0-90 vol.%) and C0 2 -vapour (0-20 vol.%). detected in fluid inclusions representing ore fluids which have interacted with carbonaceous metasediments. The only daughter minerals observed (halite, dawsonite) are in inclusions which have leaked. Phase separation of H 2 0-rich and C0 2 -rich fluids occurred late in many deposits and intermittently during deposition in a few. Heating-freezing data indicate that the ore fluid was low salinity (<2 wt% NaCl equiv. in the H 2 0-liquid phase). Homogenization temperatures range from 250-325°C for the Kanowna Main Reef, to 295-360°C for Mt Charlotte, Kalgoorlie. Although the C0 2 -H 2 0-NaCl system is not well-documented for fluids of the above salinity, calculations to determine the range of depositional conditions suggest fluid temoeratures of 280 to 400°C + 30°C and fluid pressures of ca 1-2 kbar. It has been suggested that the ore fluids were metamorphogenic and the chemistry of the fluids is a potential test for this model. Crushing-leaching experiments indicate an average Na/K atomic ratio of 10. This is of considerable interest as it is distinct from values for magmatic fluids (£a 1) and seawater (present-day ca 47). Using phase diagrams appropriate for the observed alteration assemblage, the calculated depositional (P,T) conditions and the measured Na/K atomic ratio, a near-neutral pH is suggested for fluid/wallrock equilibrium at 350°C for the Red Hill deposit. Preliminary Raman-spectroscopic analyses of the vapour phase in primary fluid inclusions in Red Hill samples detected C0 2 , H 2 S and N 2 , in order of decreasing abundance; CH^ and CO were not detected. It is thought that gold was carried in the ore fluid as a thio-complex. The nature of the sulphur species in solution thus has important implications for transport mechanisms.

244

PRELIMINARY

USE OF T H E R M O L U M I N E S C E N C E

IN GOLD

EXPLORATION

9 o M.B.M. Hochman- -, D.W. Russell"1 and J. Van Moort •*"Dept. Economic Geology, University of Adelaide, Adelaide Tasmanian College of Advanced Education, Launceston ^Geology Dept. University of Tasmania, Hobart In his book on the geochemistry of gold, Boyle (1979, p.169-182) mentions that until the present time, no geochemical technique has been able to differentiate between what may be barren and what may be auriferous quartzes. The major cause of this failure is the presence of fine-grained solid inclusions or contaminating minerals such as sulphides, sericite etc. within the quartz. Such contaminating minerals may mask any geochemical difference between barren and auriferous quartzes during bulk analysis. Thermoluminescence (TL) is a measure of defects in a crystal lattice such as impurity ions, atomic vacancies etc. Many of the contaminating minerals that confuse bulk analyses of quartz are only weakly or nonthermoluminescent and secondly, are solid inclusions rather than structural impurities, so should not have as marked an effect on resultant TL glow curves as structural impurities alone. Any difference in the quartz lattice between barren and auriferous quartz should therefore be detectable by TL. The impurities causing such a difference may either be gold itself in the quartz lattice (Townsend and Kelly, 1973) or may be other structural impurities or vacancies. The only previous major work utilizing TL to distinguish between quartzes associated with gold deposits was by Anufriyev et al. (1973), who used a number of specialized geochemical techniques to distinguish between pre-ore, ore-bearing and post-ore quartzes associated with the Kochkar gold deposits in the Urals. Their results indicated: (1) a higher overall concentration of defects in the ore-bearing quartz; (2) some of these impurities were structural defects rather than entirely solid inclusions and (3) that there was a difference in TL glow curve intensity between the ore-bearing quartz and other quartzes associated with the deposit. Preliminary results on a number of quartzes from Tasmanian gold deposits indicate a more marked difference in TL glow curve between goldbearing and barren quartzes than that noted by Anufriyev et al. (op. cit). Gold-bearing quartzes from the Royal Tasmania Mine, Gladstone; reef quartz from Lefroy; clear quartz from Moina and New River Mine, all have a most prominent glow peak in the 170°C-230°C temperature range, whereas the only barren quartz sample measured (from the Ophir Mine) did not exhibit this glow peak. The latter three auriferous quartzes also have minor glow peaks at* 150°C and 270°C which indicates a further similarity in quartz type. Two samples of barren quartz from the Sandy King Mine, Kalgoorlie, and the Central Norseman Mine, exhibit small glow peaks at 170°C and 260°C, whereas a gold-bearing quartz from Central Norseman exhibited no TL. This diminution of TL has also been noted within the ore zones of certain carbonate hosted base metal deposits and may be attributed to concentrations of lattice defects beyond a threshold level. These preliminary results indicate: (1) that although it may not be possible to find a general TL glow curve indicative of gold-bearing quartz (given that other factors relating to provenance will also affect the TL glow curve), that (2) within given areas where all other factors affecting the TL of quartz will be equal, it may be possible to differentiate between auriferous and ucirren quartzes due to the additional lattice defects present in the former.

245

References Anufriyev, Yu,N., Stupakov, G.P., and Moskalyuk, A.A., 1973, Int. Geol. Rev. L6, 4, p.405-416. Boyle, R.W., 1979, Geol. Surv. Canada Bull. 280. Townsend, P.O. and Kelly, J.C., 1973, Colour Centres and Imperfections in Insulators and Semi conductors. Sussex Univ. Press, London.

LANDSLIDE RISK ASSESSMENT FOR LOCAL AUTHORITIES IN QUEENSLAND Gerhard W. Hofmann Geological Survey of Queensland, Brisbane Landslides have long been a consequence of intensive rural land development in some districts of southeast and coastal Queensland, but did not attract the attention of planning authorities prior to the ruralresidential subdivision boom of the early 1970s. Similarly, residential development on steep slopes previously avoided became necessary or attractive in a number of expanding urban areas. The Geological Survey of Queensland became involved first in inspections of damage caused by landslides and later to advise Local Authorities on proposed subdivisions in landslide-prone terrain. Regional risk assessment studies of potential slope failure were carried out for two areas at the western outskirts of Brisbane in the late 1970s to assist the Brisbane City Council in the preparation of development control plans (O'Flynn, 1978; Trezise, 1980). Subsequent studies in various districts of southeast Queensland, where Local Authorities sought guidance on planning constraints to residential development resulting from landslide hazards, continued the geological (as opposed to engineering) approach to landslide risk assessment. Such an approach has been applied in various parts of Australia to cover large areas for which only limited data on material properties were available. In essence, it relates existing landslides to topographic position, slope angle, lithology, and groundwater conditions (where known). Zones of different risk perception, based on combinations of these parameters, were then delineated. The selection and number of zones may vary according to the geological setting, but usually four to five zones, sometimes with further subzones, are employed. Studies of this type have been completed for the eastern slopes of Toowoomba (Holmes, 1981), for Tamborine Mountain (Willmott, 1981) and the Darlington-Beechmont Ranges (Willmott, 1983a) in the Gold Coast hinterland, for the Mapleton-Maleny Plateau (Willmott, 1983b) in the Sunshine Coast hinterland, and for the Brisbane metropolitan area (Hofma nn & Willmott, 1984). They provide advice in the early stages of Local Authority planning by showing the distribution of relative stability in a district and discussing suitabilities for subdivision and building. Several Local Authorities have incorporated the recommendations in strategic plans and development control plans. References Hofmann, G.W., & Willmott, W.F., 1984, Geol. Surv. Qld Rec. 1984/10. Holmes, K.H., 1981, Geol. Surv. Qld Rec. 1981/2. 01Flynn, M.L., 1978, Geol. Surv. Qld Rec. 1978/47. Trezise, D.L., 1980, Geol. Surv. Qld Rec. 1980/31. Willmott, W.F., 1981, Geol. Surv. Qld Rec. 1981/14. Willmott, W.F., 1983a, Geol. Surv. Qld Rec. 1983/64. Willmott, W.F., 1983b, Geol. Surv. Qld Rec. 1983/9.

246

GEOLOGICAL

INVESTIGATION OF CONSTRUCTION MATERIAL FOR PLANNING PURPOSES

RESOURCES

Gerhard W. Hofmann Geological Survey of Queensland, Brisbane The first investigation by the Geological Survey of Queensland of construction materials for integrated planning purposes was carried out from 1959 to 1965, following a request from the Brisbane City Council (Houston, 1967). Unfortunately, the information was largely ignored in the subsequent town plan. In the early 1970*s, concern over rapid alienation of resources led to industry pressure on the State Government and an examination of the dispersed administration of extractive operations. The Geological Survey carried out an assessment of the future availability of construction materials in Brisbane and environs as part of that examination. Although administrative changes were not introduced, the establishment of a new section in the Geological Survey at the end of 1974 provided a unit for systematic investigations of the construction material resources of Queensland. The knowledge of the State's resources up to that date is summarised in volume 4 of the Economic Geology of Australia and Papua New Guinea (Knight, 1976). Initially, the growth areas around Brisbane and along the Gold Coast and Sunshine Coast were surveyed at reconnaissance scale for operating and disused quarries and pits, their output and reserves, and materials produced. Potential deposits within reasonable distance from markets were inspected and occasionally drilled to determine overburden and material quality. Such potential deposits were separated into (1) significant sources and (2) possible or minor sources depending on quality, likely resources and level of information. The information was reported on a Local Authority basis, in unpublished GSQ Records accompanied by maps at 1:100 000, in order to provide planning recommendations quickly to the Local Authorities concerned. Publication of this information in a rock and mineral resources series on standard 1:100 000 sheets commenced in 1978. This program was summarised by Willmott (1979). Apart from the surveys of Local Authority areas, more detailed investigations of key sand and gravel deposits in the Coomera valley, the Pine Rivers alluvium, the Brisbane River, and Oxley Creek (all in the eastern Moreton Region) were carried out at the request of Local and State government bodies. Following the completion of resource surveys in the populous eastern Moreton Region in 1978, the Geological Survey extended its inventories to other parts of the State. These describe workings and materials, comment on problems of supply, and establish priorities for follow-up investigations. They are published in the Queensland Government Mining Journal. These inventories cover now almost all of the eastern seaboard from the New South Wales border to Mossman, and extend inland to include the Darling Downs, Burnett district, central Queensland coalfields, and Atherton Tableland. A new program of 1:100 000 geological mapping of provincial cities and their environs involves the revision of some of this regional information on industrial rocks and minerals; this is released as unpublished GSQ Records.

247

The acceptance of recommendations for resource protection, made in the various reports to local planning authorities, has on the whole been negative. This is perhaps a result of the limitation of planning legislation in Queensland to town planning schemes, which do not readily lend themselves to resource planning. Local Authorities tend to view quarrying as a noxious industry, which hinders the attraction of a residential rate base; a view reinforced by experiences with environmentally insensitive and careless operators. The rationale behind the Geological Survey's work was to have resources identified in town plans and thus prevent their alientation or the premature closure of a quarry by encroaching subdivision. However, apart from investigated key deposits, the potential resources identified during the reconnaissance surveys lacked sufficient definition to be ranked in order of importance and to be delineated by real property boundaries, so that definite planning options could be determined. Fear of compensation for denied development is also strong. An improvement of the planning situation has occurred with the introduction of strategic plans, which some farsighted Local Authorities use to show identified resources. In the main, approvals for new quarries are difficult to obtain, particularly when objecting residents use the judicial review system provided for in the Local Government Act. The information collected by the Geological Survey has been sought eagerly by the extractive industry, which accepts the reconnaissance nature of the work and uses it as a guide for more detailed exploration. The number of workings inspected has reached six hundred, and a computer file of quarries and pits is currently being established. The data present the first integrated information system on Queensland's extractive industry and form a sound basis for future work. A detraction is the lack of collection of meaningful and comprehensive production figures by the State government, which makes local resource planning impossible. References Houston, B.R., 1967,

Geol. Survey Qld Publ., 325.

Knight, C.L. (ed.), 1976, Economic Geology of Australia and Papua New Guinea. Industrial Minerals and Rocks. Aust. Inst. Min. Metall., Melbourne. Willmott, W.F., 1979,

Qld Govt Mining J., 80(934), 393-418.

HYDROCARBON POTENTIAL OF THE PORTLAND TROUGH AREA G.R. Holdgate1, G. Mackay1 and G.C. Smith2 ^State Electricity Commission of Victoria, Melbourne ^Present Address: ARCO Australia Ltd, Brisbane Approximately 90% of Australia's oil production and 50% of her gas production comes from thick Tertiary and Upper Cretaceous aged sediments in the offshore Gippsland Basin of Victoria. Thick Tertiary-Upper Cretaceous sequences of similar generative potential are comparatively rare in most other Australian basins with the main exceptions being the Bass Basin and Otway Basin.

248

The Portland Trough in the central Otway Basin contains an unusually thick (>2.0 km) sequence of Tertiary sediment (2/3rds Wangerrip, 1/3 Heytesbury/Nirranda Groups). Beneath the Tertiary is an unconformity below which a similarly thick but largely undrilled Upper Cretaceous sedimentary sequence occurs (the Sherbrook Group). Lower Cretaceous Otway Group forms effective tight basement. Most of the trough occurs onshore in the central area of the Otway Basin, and has an axis trending west north-west from Portland, ending near the state border. Low angular unconformities package the Late Cretaceous-Early Tertiary into two major deltaic sequences. The lower sequence consists of thick prodelta shales (Belfast Mudstone) which thicken southwards into the Portland Trough and offshore, overlain by interbedded sand shale sequences (Curdies-Paaratte Formations) which represent delta slope and platform and predominate to the north of the Trough. This sequence is truncated by a Cretaceous-Tertiary angular unconformity with erosion of the section in the northern areas. Overlying is a second major deltaic sequence comprising a prodelta shale (Pember Mudstone), exceeding 0.5 km thickness within the Trough, grading up through regionally correlative delta slope and platform cycles (Dilwyn Formation) into Middle Eocene marine shales (Burrungule Member). Late Eocene to Middle Miocene marine carbonates (Heytesbury-Nirranda Groups) unconformably overlie and truncate Wangerrip Group beds again with some loss of section particularly to the north and south of the Trough. The deltaic shales demonstrate largely euxinic features (pyrite, disseminated carbonaceous matter, restricted marine foraminifera). They form widespread stratigraphic marker horizons and represent potential source rock and seal for hydrocarbons. Vitrinite reflectance measurements were performed on the dispersed organic matter in core material from 17 bores within and around the Trough. The following results were obtained: 1. Vitrinite reflectance increased^ with depth down hole at a gradient varying between 0.08 and 0.25% RQmax per km with the higher gradients generally occurring in bore locations outside the Portland Trough. 2. A step-like reflection jump occurs across the Tertiary-Upper Cretaceous boundary confirming the existence of an unconformity at this boundary, and indicating some coalification had proceeded prior to Tertiary deposition.

249

3 . Vitrinite iso-reflectance lines through the Trough indicate Lower Tertiary and Upper Cretaceous sediments exceed 0.5% R max and are mature enough for hydrocarbon generation (Smith & Coofc, 1984). North and south (offshore) of the Portland Trough vitrinite reflectance over 0.5% is only reached in essentially tight Cretaceous sediments thereby reducing the prospects of these areas. Structural-stratigraphic unconformity traps probably exist at the main unconformity boundaries. Some of the potential traps are similar to those in the offshore Gippsland Basin. Oil generation is occurring within the Trough area as shown by the Lindon No 1 well on the northern margin where 8.0 m of oil saturated sandstones (908.5 - 916.5 m) were recovered from the Pebble Point Formation immediately above the Tertiary-Upper Cretaceous unconformity. Wells north of the Trough show this level to have low reflectance, hence, the oil has probably been derived by northward updip migration from the deeper parts of the Portland Trough. Further exploration in this Portland Trough area appears justified by the foregoing results.

Reference Smith, G. C. and Cook, A. C., 1984, APEA _12, 196-216.

CHARACTERISING ZIRCON-CORUNDUM ASSEMBLAGES IN EASTERN AUSTRALIA Julian D. Hollis University of Melbourne, Melbourne A zircon-corundum-spinel-ilmenite ('zircospilic') association is widespread in alluvials generated from the erosion of alkali volcanics, erupted through granitic areas of Eastern Australia. Although basalts and trachytes have been proven as their hosts, the origins of large (2mm) zircons and corundums remain enigmatic. Both cognate and accidental types may occur and their recognition is a major target for present research. Zircospilic minerals are frequently euhedral but show rounded, fused and corroded surfaces that suggest disequilibrium with their host magmas. Abrasion features are readily distinguishable and lack the fine textures of corrosion surfaces. In the sapphire fields of central Queensland and northern New South Wales, blue-grey corundums and red zircons exceed 5cm. These crystals are unlikely to have formed in an alkali basaltic magma, especially in hosts that ascended rapidly from the mantle. Cognate zircons are suspected from certain trachytes, notably those in the. Macedon area, Victoria. These show sharp, uncorroded crystals and are not associated with corundum, spinel or ilmenite. Basalt zircons are larger and occur with other zircospilics as probable xenocrysts. Source rocks for these could include alkali granitoids such as nepheline syenites and related gneisses. Such rocks from the Kola, Norway and Canada contain large crystals that are identical to those found in Eastern Australia. Here, no such rocks have been found, being probably concealed in the root areas of granitic plutons.

250

Fission-track dating of zircons yields host volcanic ages. U-Pb results have been conflicting, with some ages close to fission track and one much in excess. Variable resetting is suspected. Pink Cr-corundums from the Barrington Tops and Walcha areas, New South Wales, could be derived from mantle eclogite sources as some are found with diamonds. This paper outlines zircospilic associations from north-central Victoria, New England, New South Wales and the Anakie-Rubyvale area, Queensland. A tentative zircon grouping system is based on a census of crystals.

ZIRCON GROUPS FROM ALKALINE VOLCANICS OF EASTERN AUSTRALIA GROUP NAME

USUAL CRYSTAL PRISM: INDICES & COLOURS PYRAMID

HOST ROCK AND CRYSTAL SIZES

OCCURRENCE

Newbury

101,100 Scarlet

0 - 1

Alk.ol.basalt 0.5-17mm. (8)

Widespread.1,4,5, 7,8,12,17,18,23

Lyonville

101,100,211 Orange

0.2- 2

Bio-anorthtrachyte (10) 0.2-lmm.

Restricted.7,10

Daylesford

101,100 minor 211 Mauve-orange

Alk.ol .basalt l-8mm. (9)

Restricted.9,11

Inverell

Wide range prisms dominant Sherry

0.2- 3

Alk.ol.basalt l-25mm. (5)

Widespread.1,5,12, 15,18

Nundle

101,110 to incr 211,100 Mauve-orange to brown

0.2- 1

Alkali basalt 1-12mm (2)

Widespread.2,3,5,6, 16,19,22

Boatharbour

110,101 to incr 100 Scarlet

0.2-1

Alkali basalt 0.5-20mm (14)

Restricted.14

Bullenmerri

101,minor 110 Y e 1 low-b r own

- 0.5 Basanitic tuffs 1.4-17mm (13)

Restricted.13

20,21.

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LOCALITIES 1. Ruby vale, Qld. 2. Mt. Moffat, Buckland, Qld. 3. Brigooda & Ballogie, Proston, Qld. 4. Rocky River, Uralla, N.S.W. 5. Hanging Rock, Nundle, N.S.W. 6. Horse Gully, Inverell, N.S.W. 7. Loddon River, Lyonville, Vic. 8. Newbury, nr Trentham, Vic.' 9. Leonards Hill, nr Daylesford', Vic. 10. Blue Mountain, nr Trentham, Vic. 11. Lai Lai Ck, Bullarook, Vic. 12. Blue Creek, Trentham, Vic. 13. Lake Bullenmerri, Camperdown, Vic. 14. Sisters Creek, Boatharbour, nr Wynyard, Tas. 15. Tomohawk Ck, nr Clermont, Qld. 16. Drayton Rd, Toowooiriba, Qld. 17. Oban, N.S.W. 18. Tingha, N.S.W. 19. Lava Plains, Qld. 20. Mt. Wilson & Babbingtons Hill, nr Bullarto, Vic. 21. Camels Hump & Hanging Rock, nr Woodend, Vic. 22. Tea Tree Ck, Lancefield, Vic. 23. South Bullarto, Vic.

EVALUATION OF IMAGERY FROM THE CARR BOYD MINERALS/CSIRO AIRBORNE MULTISPECTRAL SCANNER F.R. Honey1, J.L. Daniels2, and P. Wilson3 •'"Geoscan Pty Ltd, Perth, 2Carr Boyd Minerals Ltd, Perth 3 CSIR0 Division of Mineralogy, Perth Carr Boyd Minerals, in a collaborative research and development program with CSIRO has developed an extremely flexible 15 channel airborne multispectral scanner with several unique features. Detailed design and construction of the instrument was performed by Fairey Engineering Ltd in Adelaide, South Australia. Invaluable scientific and technical advice was provided by the Defence Research Centre, Salisbury S.A. The scanner is to be used in Australia and overseas for mineral and hydrocarbon exploration, geolog ic and soils mapping, and for agricultural, vegetation and environmental monitoring. The partially completed scanner was tested near Perth, in the Eastern goldfield, and near Adelaide January - February 1984. Although the eight spectral channels used during these flights were conservatively chosen, and the electronic system had several earthing and noise problems which have been subsequently eliminated, the imagery acquired demonstrated the tremendous potential of the scanner as a mapping and monitoring tool. Planned refinements to the scanner will further enhance its capabilities and extend the application to bathymetric mapping and atmospheric studies. The scanner was flown in a partially completed state late January 1984 for approximately 5000 line kilometres, primarily in the Eastern Goldfields of Western Australia. The imagery acquired during these test flights has been analysed and all sources of data or image degradation identified. For the test flight s, the pitch and yaw correction hardware was not operating. Only eight channels in the visible and near infrared regions were used. The wavelength ranges of the channels tested were:

252

Channel 1 2 3 4 5 6 7 8

Bandpass (micrometres) 0.45 - 0.50 0.55 - 0.60 0.65 - 0.70 0.83 - 0.87 0.93 - 0.97 1.98 - 2.08 2.15 - 2.25 2.30 - 2.40

Examples of the Imagery acquired will be presented, and the systematic processing procedures which have been developed for this "spectral" imagery, which are particularly important for a physical interpretation of the data are described in detail. Specific examples of the capability of the scanner data to discriminate areas of differing clay and carbonate content, either from weathering or hydrothermal alteration will be presented. Results of other processing procedures, to highlight the slope between 0.4 and 0.7 micrometres due to charge transfer transitions in iron oxides, and methods for reducing the masking effect of vegetation, particularly by absorption bands in the 2-2.5 micrometre region will be discussed.

CONTRAST IN WALL-ROCK TEXTURES AND SEDIMENTARY TEXTURES OF SOME ORE DEPOSITS

HOST

Tim Hopwood Mineral Exploration Consultant, North Adelaide Many ore deposits pass outwards into barren pyritic (or anhydritic) stratigraphic units, plainly sedimentary. Nevertheless, although the host stratigraphy is often deformed (with schistose or slaty preferred orientation textures), the textures of minerals of the alteration halo surrounding the ore deposit are often decussate, randomly oriented and by implication undeformed (implying post strain recrystallisation in the area immediately surrounding the ore). This implies that the alteration halo around such ore deposits is developed post-strain, implying metasomatic wall-rock reactions have continued subsequent to deformation of the metal deposit. This implies that many potential sulphur sources for mineralisation are pre-strain and sedimentary but that metal sources (metal bearing brines) and metal deposit formation is syn-strain, with metasomatic activity and alteration continuing to post-strain stages resulting in static recrystallisation and random textures in the alteration halo. Furthermore, the effect of brine-movement during strain (both in brittle fracture and a ductile environment) is such that such brines accelerate strain rates in their flow regimes, and induce the complex structures, characteristic of many metal deposit sites. The implication of this is that the metal bearing brines in reacting with the sedimentary sulphur sources, create a structural site for the orebody which eventually forms at the sulphur-metal reaction site. This paper focuses on a fundamental and ignored problem area of ore genesis viz. the reconciliation of the metasomatic aspects (metal bearing brines?) and the sedimentary textural aspects (sulphur sources?) of many metal deposits.

253

GEOSCIENTIFIC RESEARCH AND DEVELOPMENT IN BANGLADESH Anwar Hossain Atomic Energy Research Establishment, Savar, Dhaka Bangladesh recognizes the importance of geo-scientific research for development of its natural resources and their contribution to a stable economy and a better future. The present geoscience programmes, both short and long term cover a wide range and have been placed third in national priority after population control.and agricultural improvement. Bangladesh has recently formulated a National Science Policy and created an autonomous National Council of Science and Technology (NCST) to look after the country's scientific needs. For geo-scientists there is ample opportunity to play a vital role in implementing this scientific policy. As a LDC (least developing country), Bangladesh has already made some remarkable developments in natural gas resources. It has, in general, identified the most important geological areas for the utmost development of gas. Priority sectors have been outlined for immediate geo-scientific activities and these are - natural gas and fossil fuel, mineral exploration (including nuclear raw materials), space research (use of LANDSAT imagery for geological information), hydrology, hydrogeochemistry and allied fields of study. During the last decade, the nation has gradually built up exploration techniques for gas-field discoveries. At present, of a dozen natural gas fields, more than half are in production making the country self sufficient in natural gas. Exploration is underway for other fossil fuels, and considerable progress has been made with the help of overseas assistance. Bangladesh is in great need of metals and industrial minerals. Substantial progress has been made in finding some economic minerals such as heavy minerals, coal, limestone, clay and glass sand etc. The country is at present badly in need of technical assistance for the exploitation of these mineral resources. Search for the nuclear minerals or raw materials is in progress - as Bangladesh desires to establish atomic power for scientific and technological developments. An IAEA aided project on uranium exploration is in progress and the author, being a member of the exploration team, is undergoing a six months training programme on advanced laboratory techniques for the study of uranium mineralization. Bangladesh has been actively participating in the Space Research Programme in the SE Asian region. A ground receiving station for satellites has already been set up within the AERE (Atomic Energy Research Establishment) campus of BAEC (Bangladesh Atomic Energy Commission). The use of LANDSAT imagery for the study of uplift of the coastal landmass and its reclamation provided new encouragement for geo-scientists of the nation. Hydrology and hydrogeochemistry cover a substantial field of research and development in the country. A number of present research sectors are inter-dependent to these geosciences and only insignificant progress has been made. Advanced technology and assistance are badly needed in these fields. Bangladesh invites the cooperation, ^and assistance of more developed countries in joint geo-scientific research and development and to so help the poorer nation achieve a better economic growth.

254

FINITE ELEMENT MODELS OF CONTINENTAL COLLISION - THE DISTRIBUTION OF STRAIN AND STRAIN RATE IN CENTRAL ASIA Gregory Houseman1 and Philip England2 1

Research School of Earth Sciences, Australian National Univ., Canberra department of Geological Sciences, Harvard University, Cambridge, MA

We have used the finite element method to obtain numerical solutions of the equations governing the deformation of a thin viscous sheet representing the continental lithosphere. A mesh of continuously deforming elements is used to calculate stresses and strain rates in a region (representing Central Asia) that is bordered on one side by an indenting boundary (representing India). We assume a depth averaged, strain-rate dependent, rheology for the lithosphere, as in England and McKenzie (1983), so the deformation is effectively controlled by the coolest (i.e. uppermost) part of the mantle, which deforms in a ductile manner. The strain rate field is numerically integrated forward in time to obtain the parameters of finite deformation and the distribution of crustal thickness. The latter is the main constraint on the parameters controlling the rheology; the stress-strain exponent, n, and the ratio of gravitational stresses to viscous stresses, known as the Argand number, Ar. Although the deformation at depth is assumed to be continuous, the calculated strain rate fields can be interpreted in terms of the style and magnitude of faulting in the overlying brittle upper crust. For an incompressible strain rate field imposed on the brittle crust, there will in general be two orthogonal fault systems active. The strain rate field determined from the finite element calculations can thus be used to show the distribution of different tectonic styles (fault types) and the rate of moment release of the various fault systems. The tectonic style depends strongly on the parameters which describe the viscous rheology, n and Ar, and changes with time as the indentation progresses. However, apart from a small region of crustal thinning beside the indenter, the models generally predict a combination of thrust and strike-slip faulting, with horizontal P-axes approximately radial to the indenter. The orientation of the P-axes is in good agreement with that inferred from the distribution of active faults in central Asia (Tapponnier and Molnar, 1979, Fig. 17). In the model, thrust faulting tends to dominate strike-slip faulting in most of the region at time zero (before the indenter has advanced any distance). However, as the crust is progressively thickened, gravitational forces tend to resist further thickening (for Ar > 1) and strike-slip deformation becomes more important. We calculated the average strain rate tensors for several sub-regions of the finite element domain corresponding to the regions of Central Asia considered by Molnar and Deng (1984), who calculated average strain rate tensors for the last 80 years, based on all the large earthquakes of that period. The strain rate magnitudes (i.e. second invariant of the tensor) predicted by the model are in very good agreement with those estimated by Molnar and Deng (1984), though compared with the data, the model predicts a greater proportion of thrust faulting relative to strike-slip faulting in the Mongolia-Baikal and Eastern Tibet-Gansu regions.

255

The Lagrangean (or material) reference frame used iri the finite element program facilitates the calculation of cumulative strain h i s t o r i e s , which are presented as a sequence of ellipsoids of deformation. The strain histories of particular regions m a y be quite complex because of the changing orientation and magnitude of the principle strain rate axes during deformation. We show an example from a point near the side of the indenter (corresponding to the Burma-Yunnan region) w h e r e , after 40 M a , the principle compressive strain rate axis is rotated approximately 60° relative to the material vector which was initially coincident with that axis. In c o n t r a s t , the deformation field directly in front of the indenter (corresponding to the Tibet plateau) is approximately progressive pure s h e a r , although the magnitude of the strain rates decreases continuously as the crust is thickened. The zone of maximum strain rates migrates o u t , further from the indenter, and after 40 Ma is located in the areas corresponding to the Tian Shan and Nan Shan r a n g e s , as verified by the seismic d a t a . References England, P.C. & McKenzie, D . P . , 1 9 8 3 , Geophys. J . R . astr. Soc., 73, 523-532. M o l n a r , P . & D e n g , Q . D . , 1 9 8 4 , J . Geophys. R e s . , in p r e s s . Tapponnier, P . & M o l n a r , P . , 1 9 7 9 , J . Geophys. R e s . , 8 4 , 3425-3459.

(a) Initial (t=0) and (b) final (t=40Ma) finite element mesh configurations for n=10 and A r = 3 . Only the right half of the symmetric problem is shown. The fixed sides of the box are 5000km long and the circular segment corresponds to the indenting arc of the H i m a l a y a s , (c) principle deviatoric stresses and (d) contours (5km interval) of crustal thickness at t=40Ma. The initial crustal thickness is 3 5 k m .

256

DYNAMICAL MODELS OF LITHOSPHERE EXTENSION AND SEDIMENTARY BASIN FORMATION Gregory Houseman 1 and Philip England 2 "^Research School of Earth Sciences, Australian National University, Canberra Department of Geological Sciences, Harvard University, Cambridge, MA In recent years lithosphere extension models such as the one proposed by McKenzie (1978) have been used increasingly to explain the tectonic subsidence, thinned crust and high heat flow found on Atlantic type continental margins and in many sedimentary basins. In its simplest form the extension model calls for uniform horizontal extension by a multiplicative factor 3, accompanied by lithospheric thinning, in a time which is brief compared to the thermal time constant of the lithosphere. More recent versions of the model have included variation of £ with depth and/or with location across the basin, separate phases of extension, lithosphere flexure, and the nature of the two-dimensional deformation field during the extension. However all of these models are incomplete to the extent that they are kinematic models; either the velocity or the strain rate distribution is imposed, without reference to the origin or magnitude of the forces driving the extension. In. the dynamical model proposed here we suggest that the extensional stress field may in some cases be caused by convection in the underlying upper mantle, which subjects the base of the lithosphere to spatially varying vertical normal stresses. We assume that in the absence of convective flow the depth of isostatic compensation would be at the base of the lithosphere of thickness, L. In addition, it follows from the basic stress equations that the horizontal normal stress integrated over the thickness of the lithosphere, So dz, is the same for any column of lithosphere, provided there are no significant shear stresses acting on the base of the lithosphere. It follows that the depth-averaged horizontal deviatoric stress in any given column of lithosphere is (for a two-dimensional extension field): vxx = TyT 2L (fo* zz dz - Sozz dz) where O z z is the vertical stress in the given column and a*z is the vertical stress in a reference column which is known to be lithostatic. The range of integration is again the thickness, L, of the lithosphere. Faute de mieux we take the column beneath the mid-ocean ridge as a reference column, because its elevated temperature and hence low strength render it incapable of supporting any significant deviatoric stresses. Note that the two depthintegrals in the above equation are equal to minus the gravitational potential energies of the respective columns (relative to the base level of isostatic compensation). We assume that the column of continental lithosphere is (in the absence of sub-lithospheric convection) in mechanical equilibrium with the mid-ocean ridge column, by which assumption we imply isostatic equilibrium, and in addition, equality of gravitational potential energy (implying there is neither extensional nor compressional horizontal deviatoric stress on the continental column). The latter condition is often ignored, though Le Pichon (1983) attributed extension in the Aegean Sea to the difference in gravitational potential energy between the Aegean Sea and the neighbouring Hellenic trench.

257

However, when we consider that the lithosphere overlies a convecting mantle it is apparent that perturbations to the vertical stress on the base of the lithosphere will not only disturb the isostatic balance, but will also perturb the relative gravitational potential energy balance and hence introduce horizontal deviatoric stresses. Above a hot rising thermal sheet or plume the lithosphere is elevated (McKenzie, 1977) so its potential energy is increased, and the lithospheric column will be subject to horizontal extension. Under the assumption that the extension is two-dimensional and independent of depth in the lithosphere, we derive an equation relating the rate of extension to the magnitude of the stress perturbation and the temperature dependent strength of the lithosphere. The latter factor is generally unknown, and may vary by orders of magnitude due to differences in composition, Moho depth and geothermal gradient. Thus in some cases there may be no significant compression or extension in spite of a relatively large deviatoric stress. Where the elevated lithosphere is sufficiently weak, it will tend to spread horizontally under its own weight until cooling of the upper mantle causes a large increase in the strength of the lithosphere (England, 1983). If extension is to occur on a timescale of 10 to 50 Ma in response to an initial uplift of 1 k m , then the depth-averaged 21 effective viscosity of 1the lithosphere would be between 3 x 1 0 (3 x 10 23 2lt poise) and 10 kgnf^s"" (10 poise). Numerical solutions of the coupled dynamic and thermal equations, using both linear and non-linear rheologies, show that for typical mantle parameters, an initial dynamic uplift of 1 km could well result in an extension factor of about 2.5 and accompanying sediment laden subsidence of about 4 km. We emphasize that extension commences immediately in response to the dynamic forces; we have not as yet included the thermal effects of the convection plume. Because of the initial uplift, predicted depths below sea-level are initially less than those predicted for McKenzie's (1978) simple stretching model, although the eventual removal of the thermal plume would result in the same total subsidence. References England, P.C., 1983, Geophys. Res., 88, 1145-1152. Le Pichon, X . , 1983, in Mountain

building

processes

(ed. K.J. Hsu),

Academic Press, 201-211. McKenzie, D.P., 1977, Geophys. J . R . astr. Soc., 48, 211-238. McKenzie, D.P., 1978, Earth planet. Sci. Lett., 40, 25-32.

258

THE UNESCO-IUGS PHOSPHORITE PROGRAM - A MODEL OF SUCCESSFUL SCIENTIFIC COOPERATION Peter F. Howard School of Earth Sciences, Macquarie University, North Ryde Since the International Geological Correlation Program Project 156: Phosphorites was established in early 1977, it has grown into an active group of 250 geoscientists from 36 countries assisted financially, logistically or organisationally by some 75 bodies including 17 mining or exploration companies. UNESCO and the International Union of Geological Sciences which jointly fund the project with basic seed money see it as the most successful international program to have developed under its auspices. It is here proposed that it is a model of successful scientific cooperation which should be used for other commodities by neighbouring countries in Asia and the Southwest Pacific, using local expertise to initiate and develop programs of scientific and practical exploration value. Project 156 was first mooted in 1975 but it was not until 1976 during the 25th International Geologic Congress, held in Sydney that international opinion was canvassed. As a result of the overwhelmingly favourable response to it, a proposal was submitted to the IGCP Board late in 1976 and official acceptance followed in early 1977. The initial idea was that such a project stood the greatest chance of scientific success if it focused on a specific question rather than considering phosphate deposits in general. It was decided that this focus should be the Proterozoic and Cambrian phosphorites, a decision in part determined by the fact that Australian geologists, both explorationists and researchers, had gained international recognition resulting from the discovery of large reserves in the Cambrian sediments of the Georgina Basin. It was hypothesized that this Australian province may be a portion of a much larger Australian-Asian phosphogenic province which, if shown to exist, would be of direct application to the search for new deposits in Southeast Asia and Asia in general. Having determined that both scientific and economic interests were best served by focussing on sediments of Proterozoic and Cambrian age, Project 156 developed as a forum for bringing together the phosphate researchers of the world. As a consequence, the original intention to limit the stratigraphic scope of the Project has evolved into a rallying point of scientists interested in deposits of all ages and not only in Asia but also in Africa, Europe and South America. Thus, the Project has changed from a study of the older sediments of the Asian region to one with a world-wide view. The mechanism for attaining this objective was to program a series of annual field workshops and seminars at key points where phosphate deposits existed, and where interested geoscientists were working. For some it was necessary to receive financial assistance from Project funds, or, more importantly, to receive financial support from their national organisations whether governmental, institutional or company. In real terms funding from IGCP and IUGS has not exceeded A$10,000 per annum and support from companies an additional few thousand dollars per annum. It is clear that such meagre funds could only provide seed money to assist individual scientists as a supplement to funds from other sources. The hidden costs of government and institutional support in most countries is inestimatable. The international workshops became the means of collaboration, the attainment of a better understanding of the phosphogenic systems studied and their interrelationships, assistance in exploration and help in the definition of topics for cooperative research.

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Since 1978, Project 156 has organised international field workshops and associated seminars in which geoscientists have focused their expertise on a particular annual theme. The Project commenced with an examination of the Middle Cambrian deposits in Australia (1978), followed by an examination of the Late Cambrian potentially-phosphatic sediments in the Great Basin in western USA (1979), the phosphorites believed to be close to the CambrianOrdovocian Boundary in the central Himalaya (1981), Proterozoic or Early Cambrian deposits in the Mongolian People's Republic (1980), Early Cambrian deposits in China (1982) and Kazakhstan (1984), Proterozoic Phosphorites in India (1981) and China (1982). In addition, members of the Project have had the opportunity to compare Late Proterozoic and Cambrian phosphorites with younger phosphorite deposits in the Permian Phosphoria Formation of western USA (1979), the Late Cretaceous and Early Eocene deposits of Morocco and Senegal (1983), and the Oligocene deposits of Baja California, Mexico (1980). During this period it was recognised that various working groups would be necessary to address the wide range of topics including the most important phosphogenic episodes. The initial Working Group, 1, studied the ProterozoicCambrian system, Working Group 3 the Miocene-Recent, Working Group 4 the Cretaceous-Eocene while Working Group 2 concerned itself with establishing a data base for world phosphate resources of all types and ages - information of great socio-economic importance. In addition other groups evolved such as the Committee on Rock Phosphate Standards (CORPS), and National Working Groups which made contact with the Project Leaders through National Representatives. Central as a link to all these groups has been the Project Newsletter which appears quarterly and contains abstracts of current publications relevant to the project, letters and commentaries to the Editor, personal addresses and regular news of the activities of the participating membership, all of which have made the Newsletter a forum for advancement of ideas by correspondence between and also during the workshops. The Project has been outward-looking by holding joint meetings with organisations such as the Resource Systems Institute of the East—West—Centre, Honolulu and the Geological Society of London. It has also held training courses on phosphate geology for geologists from developing countries in Sydney, Bangkok, Daka, and Greenville, N.C. The scientific aims of all participants have been to develop a better understanding of the distribution, nature and origin of phosphate deposits, together with the practical aim, by definition of these features, of the formulation of successful exploration programs especially in developing countries. The findings of the seven-year-old program are incorporated in a four part series of multi-authored volumes entitled "Phosphate deposits of the World", the first two of which, "Proterozoic and Cambrian Phosphorites", and "World Phosphate Rock Resources" are now with the publisher, Cambridge University Press. The success of IGCP Project 156 has applicability to other commodities including coal and tin, which are the topics of papers immediately following this address. It is proposed that the essential ingredients for success are to use the knowledge and expertise of Australia, ASEAN, Southwest Pacific and Asian countries to focus on an initially narrow but attainable objective which will result in scientific and practical cooperation rather than contractual aid programs having confined terms of reference and, in many cases, the sole use of consultant organisations.

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D I S T R I B U T I O N OF GROUP MINERALS

SPERRYLITE, SDDBURYITE IN THE K A M B A L D A N I C K E L AUSTRALIA

AND OTHER DEPOSITS,

PLATINUM WESTERN

D.R. Hudson CSIRO Division of Mineralogy, Perth The Kambalda nickel sulphide ores have been mined since March, 1967 and the presence of minor platinum group elements (PGE) in the ores was recognized early in the development of the deposits. Western Mining Corporation L t d . (WMC), who mine the deposits, are credited for a percentage of the PGE that are largely concentrated in high-grade nickel matte produced from sulphide concentrates at WMC's Kalgoorlie nickel smelter. Further PGE are recovered in some refinery products at WMC's Kwinana nickel refinery, near Perth, but substantial improvements in overall recovery of PGE could still be made. Estimates of average concentration levels of PGE, gold and silver in Kambalda ores can be derived from monthly composite samples of carted ores from individual production centres (Ross and Keays, 1979), from bulk ore samples (Keays & Davison, 1976) and from estimated levels in nickel matte, assuming 100% recovery. The following bulk composition of Kambalda nickel ore was published by Hudson and Donaldson (1984): Ni 2.96%, Cu 0.22%, Co 0.07%, S 8.09%, Pt 326ppb, Pd 425ppb, 0s H O p p b , Ir 60ppb, Ru 220ppb, Au 339ppb, Ag 1170ppb. Although the concentration of PGE in Kambalda nickel ores has been systematically studied by sampling bulk ores, mill feeds, drill core and mine samples, no similar investigation has been undertaken on the mineralogy of PGE. Descriptions of discrete PGE phases, which are believed to occur at low concentration levels and to be very irregularly distributed within the ore environment, are restricted to a few in-situ occurrences that have been observed during routine documentation of mine development. Michenerite, PdBiTe, and testibiopalladite, PdSbTe, have been described from a telluride-rich quartz-carbonate vein that intersects massive sulphide ore in Lunnon Shoot (Hudson et al., 1978). Moncheite has been observed in chalcopyrite-rich stringers, and sudburyite occurs as inclusions in nickeline in a quartz-carbonate veinlet (Hudson and Donaldson, 1984)Few discrete PGE minerals have been found within the massive and matrix ore zones in the Kambalda ore-shoots, and the geochemical distribution of PGE suggests that the formation of some discrete PGE phases may be related to post-magmatic processes - in particular, metamorphic segregation of sulphides, and the interaction of the ore sulphides, containing PGE in solid solution, with younger hydrothermal fluids. This has resulted in local redistribution of the PGE, with concentration in footwall stringers and veins, and in reaction zones. Study of gravity concentrates from the gold-recovery circuit of the Kambalda nickel mill has enabled an assessment to be made of the nature, relative abundance and compositional variability of PGE minerals and other associated heavy minerals that are present in the nickel deposits (Hudson & Donaldson, 1984). The major platinum minerals are sperrylite, PtAs2, and moncheite, (Pt,Pd,Ni)(Te,Bi)2, and the major palladium minerals are sudburyite, (Pd,Pt,Ni)(Sb,Te,Bi), stibiopalladinite, Pd^Sb^, and palladoarsenide, Pd2(As,Sb), together with a palladium antimonicfe and a palladium arsenide that have not been fully characterized. Palladian melonites, which contain up to 10 wt % Pd, and palladian nickeline are also important PGE hosts. Sperrylite and sudburyite are by far the most abundant discrete minerals in the gravity concentrates. Sperrylite, in

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particular, is a mineral that can be separated from sulphide ores by gravity concentration. However, the only previous report of in-situ sperrylite from Kambalda was made by Roberts (1969), who described a grain from supergene massive sulphide ore at Fisher Shoot. Bulk samples (20-100kg) of ore from a variety of geological environments at Kambalda were collected to assess both the distribution and size range of sperrylite and sudburyite. Samples included massive ores, matrix ores, disseminated ores, stringer zones, gold-bearing quartz-carbonate veins, and younger intrusive porphyries. Sperrylite and other heavy minerals were recovered in gravity concentrates prepared by crushing the samples and separating the heavy fraction on a small Wilfley Table. Sperrylite was identified in heavy concentrates from massive sulphide ores from stopes in Juan Shoot and Ken Shoot, and from chalcopyrite-rich massive sulphide ores from ore stockpiles at Ken Shoot and the Kambalda nickel mill. Subsequent SEM and optical microscope study of polished samples of these ores confirmed the presence of discrete sperrylite grains up to lOOym in diameter. The ratio of PGE contained in discrete PGE minerals to the total PGE in bulk ore has not been established, but it is clear that some scope exists for gravity concentration of PGE minerals from Kambalda sulphide ores. References Hudson, D.R. & Donaldson, M.J., 1984, Transactions Inst. Min. Metall. (in press). Hudson, D.R., et al., 1978, Can. Mineralogist, 16, 121-126. Keays, R.R. & Davison, R.M., 1976, Econ. Geol., 71, 1214-1228. Roberts, D.E., 1969, Unpublished WMC Exploration Division Report K69/8. Ross, J.R. & Keays, R.R., 1979, Can. Mineralogist, 17, 417-435-

DULL COAL SEAMS - THEIR DISTRIBUTION AND ORIGIN IN THE PERMIAN BASINS J.W. Hunt CSIRO Division of Fossil Fuels, now at Macquarie University, Sydney Introduction. Gondwanan coals exhibit a marked provinciality when compared with coals of other ages, and are probably best known because of the common presence of "dull" (vitrinite poor) coal seams. Hunt (1984) has characterised the Permian coals in terms of their vitrinite contents, and in particular the medium and low vitrinite (<60%) categories are addressed in this paper. The coals may be further be classified by the type and proportion of inertinite they contain using the "semifusinite ratio" - the ratio of structured (semifusinite and fusinite) to other inertinite (mainly inertodetrinite). This ratio varies markedly between coals from different types of basins. Distribution. Inertinite content and composition of the Permian coals can be related to the general tectonic setting of the Permian basins. The basins are classified as marginal - the Sydney, Gunnedah and Bowen, or cratonic - the Cooper and Galilee and Oaklands, depending on their relationship the the Permian craton. The smaller Blair Athoi and Wolfang Basins adjacent to the Bowen, probably developed on basement faults and are called fault-angle basins.

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Marginal Basins, The Sydney and Bowen Basins contain mainly low and medium vitrinite coals with medium semifusinite ratios in the regressive top of the Upper Permian coal measures. These coals consist of alternations in the decimetre range of vitrinite rich and vitrinite poor plies both with medium semifusinite ratios. An unusual low vitrinite interval with a low semifusinite ratio - the Bayswater seam interval, in the base if the Upper Permian sequence from the Sydney and Gunnedah Basins is discussed in detail by Hunt et al., (1984). 2* Cratonic Basins. The large cratonic Cooper Basin contain mainly low to medium vitrinite coals with low semifusinite ratios at the composite level. However subsection data for the Cooper Basin show that the coal consists of alternations of low vitrinite plies with low semifusinite ratios and high vitrinite plies with variable semifusinite ratios. In the Galilee Basin low vitrinite seams with low semifusinite ratios are present in proximal alluvial facies in the northeast. In the southeast medium to high vitrinite coals with medium semifusinite ratios are found in more distal facies. The smaller cratonic Oaklands Basin contains a single thick seam which is low in vitrinite with low semifusinite ratio, at both the composite and subsection level. 3_. Fault-Angle Basins. Thick seams in the Blair At hoi and Wolfang Basins are low in vitrinite with low semifusinite ratios at the composite level. At the subsection level the semifusinite ratio increases up the seam in the Wolfang Basin. Discussion. Many researchers have attempted to explain the origin of inertinite rich coals of different ages, resulting in a multitude of sometimes contradictory theories, ranging from subaerial to subaqueous oxidation (wet and dry durites). Smith (1962), on the basis of a petrological and palynological study of Carboniferous coals formed under sub-tropical conditions, postulated a transition from vitrinite rich, woody associations, through herbaceous associations, to vitrinite poor, inertodetrinite rich coals of indeterminate affinity, by a lowering of the water table (upwards drying cycle). Flooding however produced a vitrinite poor lithology with semifusinite dominant. This sequence was not (as Smith observed) borne out in Snyman's (1961) petrological and palynological study of South African Gondwanan coals. Hacquebard and Donaldson (1969), largely following the work of Teichmuller (1.962) on Tertiary brown coals (also formed in sub-tropical conditions), proposed a scheme in which most inertinite rich coals were formed in submergent facies. Marginal Bas ins. When considering the semifusinite-rich lithologies in the top of the Upper Permian coal measures from the southern Sydney Basin, Shibaoka and Smyth (1975) proposed an upward drying cycle to account for the upward increase in inertinite (with semifusinite dominant). Coals of similiar composition but with even higher semifusinite ratios in the northern Sydney Basin were formed on braided alluvial piedmonts probably in positions of positive relief. An oxidative subaerial origin is also invoked to account for the origin of these coals. 2. Cratonic Basins. Coals formed in the cratonic basins show evidence of widely fluctuating water table levels. Up to 10% band macrinite can be present in Cooper Basin coals and this is interpreted as evidence of the lowering of the water tables with oxidation of the vitrinite precursors (Diessel, 1982). Snyman (1961) postulated that seasonal drying followed by flooding led to the hypautochthonous formation of inertodetrinite rich coals under similiar conditions in the South African basins. Low mineral matter contents in the Cooper Basin coals might however suggest that redeposition was minimal, and intense sub-aerial oxidation following complete withdrawl of the water table in the slowly subsiding setting may also account for the highly oxidised lithologies.

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3. Fault-Angle BasIns . Seams in the fault-angle basins are remarkable because of their thickness, high inertodetrinite contents and the small amount of mineral matter present. Smyth (1980) proposed that the above seams formed as "raised bogs", analogous to modern concentric domed mires, implying subaerial oxidation. Some sections of the Big seam in the Wolfang Basin show a macroscopically brighter base, which may be evidence for the initial formation of a primary mire in a topographic basin. Whether the inertinite rich coals represent significant changes in trophic conditions and the peat forming flora has yet to be tested by palynological studies. References Diessel, C.F.K., 1982. Aust. Coal Geol., _4(2), 474-483. Hacquebard , P.A. and Donaldson, J.R., 1969. Geol. Soc. Am., Spec. Pap., 114, 143-191. Hunt, J.W., 1982. Aust. Coal Geol.,4_(2), 484-502. Hunt, J.W., 1984. Proc. 18th Symp. on Advances in the Study of the Sydney Basin, Newcastle University, 31-34. Hunt, J.W., Anderson, A., Brakel, A.T., McMinn, A. and Smyth, M., 1984. Abstracts of the 7th AGC, Macquarie University Shibaoka, M. and Smyth, M., 1975. Econ. Geol. _7£, 1463-1473. Smyth, M., 1980. Aust. Coal Geol., 2(2), 53-76. Smith, A.H.V., 1962. Proc. Yorkshire Geol. Soc., Ji3(4), 423-474. Snyman, C.P., 1961. A comparison between the petrography of South African and some other Palaeozoic coals. Publn of the University of Pretoria. Teichmuller, M., 1962. C.R., 4e Congr. Strat. Geol. Carbonif., Heerleen 1958, 3, 699-722. THE BAYSWATER SEAM AND ITS EQUIVALENTS - ORIGIN, DISTRIBUTION AND UTILISATION IN THE SYDNEY AND GUNNEDAH BASINS J.W. Hunt1, A. Anderson2, A.T. Brakel3, A. McMinn^ and M. Smyth5 ^CSIRO Division of Fossil Fuels, now at Macquarie University 2 CSIR0 Division of Fossil Fuels, now at ACIRL, Sydney 3 BMR Division of Continental Geology, Canberra ^NSW Department of Mineral Resources, Sydney 5 CSIR0 Division of Fossil Fuels, Sydney Introduction. The Bayswater seam and equivalents comprise a petrographically unique coal towards the base of the Upper Permian in the Gunnedah, Gloucester and Sydney Basins. The Bayswater seam can be correlated petrographically with the Woonona, Lithgow, Lidsdale and Ulan seams in the Sydney Basin, the Bowens Road seam in the Gloucester Basin and the Hoskissons seam in the Gunnedah Basin (Hunt, 1984a; Hunt et al., 1983). However the Ulan seam is a little younger than the others on the basis of its palynology (McMinn, 1984)• Distribution and Depositional Associaton. The Bayswater seam and equivalents were formed following transression throughout the Sydney, Gunnedah and Gloucester Basins which produced a widespread, shallow marine marker horizon. The interval is underlain by barrier facies over most of its range. However, in the Sydney Basin, the Lithgow and Lidsdale seams in the west, and the Woonona seam in the south overlie and interfinger with quartzose, presumably braided alluvial deposits derived beyond the western margin in the Lachlan Fold Belt. The Hoskissons seam on the western margin of the Gunnedah Basin overlies quartzose alluvial sediments derived from a western cratonic source (Hamilton, 1984), and the Bowens Road seam in the Gloucester Basin is also intercalated with coarse, probably alluvial sediments (Hunt et al., 1983). 264

Petrography and Utilization. Seams in the interval are recognised as thick, dull coals with variable mineral matter contents. The seams are unusual in the base of the Upper Permian sequences because of their overall low vitrinite content. This has led to their almost exclusive use as a thermal coal. However, the seams are petrographically unique in the marginal basins, because of predominance of inertodetrinite in the inertinite, which accounts for their low semifusinite ratios (ratio of semifusinite + fusinite. to other inertinite - Hunt, 1984b) compared with other seams. However subsection data for the Hoskissons, Bowens Road, Bayswater and Woonona seams show a high-vitrinite basal ply (Britten and Smyth, 1973; CS1R0, 1977; Hunt et al., 1983; Hunt, 1984a) which approaches a '•normal-* petrographic composition (high vitrinite and medium semifusinite ratio). This ply may be selectively mined to produce a soft coking coal. The Bayswater seam in Liddell Shaft DDHS1 also contains an upper section with a "normal" composition, where it is separated by a 3m parting from the overlying Ravensworth seam. Origin. Britten and Smyth (1973) proposed that the unique composition of the Bayswater seam was related to deposition in a lacustrine or lagoonal setting, inferred from the depositional environment of the substrate. The low semifusinite ratio was interpreted as evidence of an herbaceous flora (compared with the usual woody vegetation), implying more oligotrophic conditions for the development of the main part of the seam. The coal type, however, does not have a unique deposit ional association and was formed in palaeotopographically low (barrier-lagoonal) and high (alluvial fan) settings. Furthermore a genetically comparable shallow marine interval higher in the sequence, which also culminates in a widespread barrier sand (Waratah Sandstone), is overlain by a petrographically "normal" seam (Borehole seam). Data recently available for the Woonona seam, which overlies the Marrangaroo Conglomerate for large distances into the Sydney Basin (Havord et al., 1984), shows that it always has a "normal" petrographic composition in the base. In the top, however, there is a trend from low vitrinite with a low semifusinite ratio on the basin margin, to low vitrinite with a medium semifusinite ratio in the basin centre (Hunt, 1984a). This pattern could be interpreted in several ways. If the seam was formed due to an "instantaneous" climatic and floral change then dull coal facies would be expected in the centre of the basin (Hunt et al., 1984). However the petrographic facies in the basin centre is "normal". Furthermore, palynological examination of the Ulan seam (McMinn, 1984) reveals that its microflora is similar to that of other seams in the sequences, implying that there was no major change in the palaeoflora. If, however, the Bayswater coal facies is the result of intense subaerial oxidation due to a lowering of the water table, this lowering could have resulted either from tectonism or from a global drop in sea level, and could be expected to be more intense towards the basin margins. Brakel (1984) argues for a tectonic cause for the Kulnura marine incursion, citing the development of the braided alluvial facies of the Marrangaroo Conglomerate along the western basin margin contemporaneously with the Kulnura Marine Tongue, and the over-riding of the Kulnura by the Marrangaroo in the AOG Kirkham 1 well. The presence of "normal" coal in the base of the Bayswater seam and equivalents, with the inertinite rich upper ply more degraded towards the basin margin, suggests that following initial development within the water table, water table levels in the marginal regions were lowered relative to the centre of the basin. The peat, however, continued to accumulate although it was degraded due to subaerial oxidation, the intensity increasing towards the more elevated margins.

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References Brakel, A.T., 1984. Ch. 3. Permian Coals of Eastern Australia. Report on NERDDC Project 78/2617• Britten, R.A. and Smyth, M., 1973. Proc. Australas. Inst Min. Metall., 248, 37-47. CSIRO, 1977. Fuel Geoscience Unit, Location Report 392 (unpub.). Hamilton, D., 1984. Abstracts of the 7th AGC, Macquarie University. Havord, P., Herbert, C., Conaghan, P.J. Hunt, J.W. and Royce, K., 1984. Abstracts of the 7th AGC, Macquarie University. Hunt, J.W., 1982. Aust.Coal Geol., 4(2), 484-502. Hunt, J.W., 1984a. CSIRO Div. Fossil Fuels Restr. Invest. Report 1413R, (unpub). Hunt, J.W., 1984b. Abs. of the 18th Symp. on Advances in the Study of the Sydney Basin, Newcastle University, 31-34. Hunt, J.W., Philp P.R. and Telfer. A., 1983. CSIRO Div. Fossil Fuels Restr. Invest. Report 1413 R, (unpub). Hunt, J.W., Brakel, A.T., Bennett, A.J.R., Ledsam, J. and Smyth, M., 1984. CSIRO Div. Fossil Fuels Restr. Invest. Report 1429R, (unpub). McMinn, A., 1984. GSNSW Paly. Rept. 1984/3 (unpub.).

SULFUR IN COAL - IMPLICATIONS FOR BASIN ANALYSIS IN COAL BEARING SEQUENCES J.W. Hunt1 and A.T. Brakel2 CSIRO Divis ion of Fossil Fuels, now at Macquarie University, Sydney BMR Division of Continental Geology, Canberra Introduction. A recent study of sulfur in coals from the eastern Australian Permian basins (Hunt and Brakel, 1984) showed that certain levels of sulfur can be related to the depositional environments of the enclosing clastics. Sulfur in the Permian coals is mainly organically bound, and is assumed to be derived from the originally organically bound plant sulfur. High pyrite contents are usually related to the incorporation of marine sulfate into peat. Although there is a small change in sulfur content with petrographic composition (Hunt, 1984), the variation does not significantly affect the use of sulfur as an indicator of palaeoenvironment. Thus sulfur in the Permian coals can be used to discriminate between proximal and distal facies within coal bearing sequences as well as identifying areas of marine influence. Sulfur and Environment. Sulfur contents of the Permian coals have been classified as: high, >1%; medium, 0.55 to 1.0% and low, <0.55% (on a dry ash free basis - daf). The data have been reduced to a dry ash free basis to account for the diluting effect of variable amounts of detrital mineral matter. The limiting values are based on a correlation between seam sulfur and depositional environment in the Illawarra Coal Measures from the southern Sydney Basin. The limits apply to clean coal (excluding discrete mineral matter bands) or 1.60 relative density float fraction samples. Total sulfur content of the raw coal is marginally higher. High sulfur content in the Permian coals is commonly indicative of increased sulfate levels associated with marine transgressions. Coals found in lower delta plain facies have medium to high sulfur contents. Upper delta plain and fluvial facies contain mainly low sulfur coals. The pattern of increasing sulfur content in the more distal facies probably reflects down slope ponding and concentration of terrestrial sulfate. There may also be a contribution of marine sulfate in the lower delta plain facies. Proximal fluvial facies contain only low sulfur seams probably reflecting access to only terrestrial sulfate. 266

Sulfur and Basin Analysis* In the following section lateral variation in sulfur content is discussed in relationship to depositional environment and palaeogeography for three intervals in the marginal Permian basins (Sydney, Gunnedah and B o w e n ) . Sulfur content has been averaged over all seams at each control p o i n t . The categories of h i g h , medium and low sulfur content are u s e d , but where values alternate between the medium and low categories, a fourth "alternating" category has been employed. Middle Coal Measures (Greta Coal Measures and equivalents). In the Bowen Basin r e g i o n , low sulphur coals formed under fluvial conditions in upland basins (Blair Athol and Wolfang B a s i n s ) , whereas medium and high sulfur coals formed in paralic environments (Aldebaran Sandstone and Collinsville Coal M e a s u r e s ) . High sulfur coals in the southern Sydney Basin (Clyde Coal Measures) are juxtaposed with marine strata, having been formed in marginal marine environments. In the northern Sydney Basin high sulfur coals of the Greta Coal Measures were deposited in paralic conditions adjacent to the present Hunter T h r u s t . The Gunnedah Basin was completely cut off from the sea in the east and only low sulfur coals are found in the proximal sediments of the Maules Creek Formation. Medium to high sulfur seams are present west of the Boggabri Ridge in the Leard Formation. Lower Part of Upper Coal Measures (Tomago Coal Measures and equivalents). The coals of this age in the Bowen Basin (German Creek Formation and Moranbah Coal Measures) have predominantly medium sulfur contents, but grade to high sulfur coals in a southeasterly direction. This reflects a change down the palaeoslope from upper delta dominance to lower delta and other paralic regimes. Most of the Sydney and Gunnedah Basins contain medium sulfur coal deposited in lower delta plain facies in this interval (Tomago and Wittingham Coal Measures and lower Illawarra and Newcastle Coal Measures and Black Jack Formation). In the northeast medium and low sulfur seams are intercalated probably reflecting the alternation of deltaic and fluvial regimes because of proximity to the bordering highlands. _3. Upper Part of Upper Coal Measures (upper Newcastle Coal Measures and equivalents). The exposed part of the Bowen Basin saw a persistence of the southeasterly palaeoslope during deposition of the Rangal Coal Measures and Bandanna Formation. Low sulfur coals deposited in fluvial conditions in the northern and western parts of the basin give way to the east and southeast to medium sulfur coals formed in a lower delta plain setting. In the southeast the Baralaba Coal Measures include fluvial facies in the south and deltaic facies in the n o r t h . Sulfur in the coal shows a clear increasing northerly trend. The overall distribution is consistent with a pattern of centripetal drainage and a residual central ponded facies, based on palaeocurrent mapping by Jensen (1975). In the Sydney and Gunnedah Basins this interval comprises the upper few seams of the Newcastle and Illawarra Coal Measures and the Black Jack Formation. The northeastern half of this region was dominated by proximal alluvial fans which are associated with low sulfur coals. In the southern part of the Sydney Basin a more distil fluvio-deltaic regime e x i s t e d . L o w sulfur coals are also present on the southern margin of the Sydney Basin although medium sulfur coals are sporadically present in the basin centre and western m a r g i n . The distribution is consistent w i t h an overall northeast to southwest drainage pattern (Herbert, 1980; Conaghan et a l . , 1982) w i t h some ponding in the basin centre, possibly due to a stepping of the basin topography (Conaghan, pers. c o m m . , 1982, Jones et a l . , in press). Interpretation of the high sulfur coals in the the top of the Gunnedah Basin sequence is problematic.

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References Conaghan, P.J., Jones, J.G., McDonnell, K.L. and Royce, K., 1982. J. Geol. Soc. Aust.,_2i> 55-70. Hunt, J.W., 1984. Abs of the 18th Symposium on Advances in the Study of the Sydney Basin, Newcastle University, 31-34. Hunt, J.W. and Brakel, A.T., 1984. Ch. 24. In Permian Coals of Eastern Australia. Report on NERDDC Project 78/2617. Herbert, C., 1980. Geol. Surv., NSW Bull. 10-52. Jensen, A.R., 1975. Aust. Bur. Miner. Res. Bull. 154. c Jones, J.G., Conaghan, P.J., M Donnell, K.L., Flood, R.H. and Shaw, S.E., in press. Ch. 5(ii). In Veevers, J.J., (Ed.), Phanerozoic Earth History of Australia, Oxford Univ. Press.

IRON MOBILITY AND THE GEOCHEMISTRY OF GROUNDWATERS IN THE HAWKESBURY SANDSTONE OF THE SYDNEY BASIN P.A. Hunt1 and A.M. Giblin2 2

^Macquarie University, North Ryde CSIR0 Division of Mineralogy, North Ryde

Introduction. It is implicit in the concept of lateritisation that an episode of "intense" or "tropical" weathering occurring in a landscape of low relief will result in the seasonal remobilisation and concentration of iron in the near surface zone. In Australia, it is widely accepted that such special weathering conditions have occurred periodically throughout the Tertiary and can account for the ferruginsation of bedrock, sediments and soil materials that would otherwise be deficient in iron. In the Sydney Basin of eastern Australia the formation of abundant hematite cements and occasional laterite profiles in the Hawkesbury Sandstone has been linked to a period of "intense" chemical weathering (Faniran, 1971). This period of lateritisation was supposedly terminated towards the end of the Miocene after a marked climatic change and uplift of the peneplain surface. An underlying assumption of this model of laterite formation is that the extent of iron mobility in the present humid, temperate weathering regime of the Sydney region is insufficient to generate the abundant iron cements observed in the Hawkesbury Sandstone. In this study, a detailed examination of the geochemistry of a range of groundwaters from the unit has been carried out in an attempt to assess the extent of contemporary iron mobility in the region and the geochemical factors that may affect this. The Hawkesbury Sandstone Groundwaters. In previous studies (e.g., Fitzpatrick, 1967) two hydrologically distinctive regions have been identified. Throughout most of the Basin the sandstones are regarded as poor aquifers, characterized by low flow rates (< 1.0 1/s). However, in the central region of the Basin where the Hawkesbury Sandstone is overlain by a thin capping of Wianamatta Shale, much higher flow rates and chemically distinctive waters have been reported.

268

In this study a total of twenty bores were sampled; nine from an area of typical sandstone groundwaters on the northern Hornsby Plateau (Area 1) and eleven from the hydrologically different area of the Basin, in the vicinity of The Oaks and Thirlmere (Area 2 ) . Groundwaters from both regions were typically low in dissolved solids with ionic strengths varying between 0.0007M and 0 . 0 3 4 M . In contrast to previous reports of higher salinities in Area 2, the ionic strength of groundwaters from Area 1 was generally slightly higher (mean I=0.010M) than those sampled from The OaksThirlmere area (mean I=0.009M). The major aquifer and chemical characteristics of the waters from each region are summarized in Table 1. A significant feature of these analyses is the generally low pH of the groundwaters, especially from Area 1 . Small amounts of iron were found in almost all these samples but it was present in particularly high concentrations in most of the waters from Area 2 . A correlation matrix was generated from the full set of chemical and physical data which demonstrates a significant correlation (at the 99% confidence level) between total Fe and flow rate (r=.63), pH (r=.60) and Eh (r=-.70).

Table 1 .

Area 1 Area 2 (Hornsby Plateau) (The Oaks-Thirlmere) Mean Range Mean

Flow Rates (1/s) PH eH (mV) Total F e . (mg/1)

0.51 4.2 +570 2.2

0.13 - 0.91 3.7 - 5.1 +433 - +637 0.1 - 10

5.8 5.5 +327 41.2

Range

0.75 - 11.3 3.7 - 6.4' +132 - +572 < 0.1 - 152

It is generally argued that the amounts of iron actually dissolved in natural waters are limited by the solubility of the ferric oxyhydroxides, either carried in suspension in groundwaters or precipitated in aquifer zones. For each sample, an overall activity product of hydrous oxides containing ferric iron (pQ) has been calculated (using E h , pH, total Fe and + F e ^ ) and compared to the theoretical values determined for ferric oxyhydroxides of varying crystallinity. The values calculated ranged from pQ=25.9 to 3 6 . 1 . These are generally significantly lower than the minimum predicted value (pQ=37.1 - Whittemore and Langmuir 1975) thus confirming that in these waters Total Fe contains significant amounts of F e ^ + and also suggesting that strict, theoretical solubility equilibria may not a p p l y . Siderite, is a widespread primary iron mineral in the Hawkesbury Sandstone and is the most likely source of the iron in these groundwaters. Its average concentration has been estimated at 4.3% and even in the relatively small aquifer zones of Area 1 (< 10 V ) such a disseminated source could maintain the iron concentrations observed in this study for periods of 10^ to 10" y e a r s . In the Wianamatta shales siderite and pyrite are often abundant and both may be contributing to the much higher iron mobility in Area 2 . Approximate rates of contemporary iron mobility have been estimated for the groundwaters in each region. Assuming the complete and continuous deposition of iron from the individual aquifers sampled in this s t u d y , m e a n maximum rates of iron deposition have been calculated for an average aquifer at 0.2 K g / y r . (Area 1) and 27 K g / y r . (Area 2 ) .

269

Conclusions. The extent of contemporary iron mobility observed in this study suggests that an "intense" or "tropical" weathering regime is not necessary for the mobilization of significant amounts of iron in groundwaters. Indeed, the maximum theoretical rates of mobility today are sufficient to account for the formation of most of the supposedly "lateritic" iron observed in individual outcrops of Hawkesbury Sandstone, in periods of 1 to 1,000 years. This conclusion is reinforced by recent palaeomagnetic evidence (Bishop et al. , 1982) suggesting that iron deposition has been a continuous process in the region for some 15 million years, and that the formation of hematite within a single bed of sandstone may take place over a period of 10 to 10 years. References Bishop, P., Hunt, P. and Schmidt, P.W., 1982, J. Geol. Soc. Aust. , 29^, 319326. Faniran, A., 1971, J. Geol. Soc. Aust.,_18, 159-164. Fitzpatrick, K.R., 1967, N.S.W. Geol. Surv. Rpt., (Unpub.), No. 3, p.20. Whittemore, D.0. and Langmuir, D., 1975, Groundwater, 13(4), 360-365.

IMPLICATIONS OF VISIBLE, NEAR AND SHORTWAVELENGTH INFRARED AND MID INFRARED REMOTE SENSING FOR EXPLORATION IN AUSTRALIA J.F. Huntington, A.A. Green, A.R. Gabell, C. Horsfall and S. Fraser CSIRO Division of Mineral Physics, North Ryde, NSW In the past ten years the development of remote sensing has been considerable. It has been stimulated to a large extent by the huge success of the Landsat Multispectral Scanner system (MSS). The MSS was, in a sense, a first generation remote sensing system. For, although it was designed to be primarily an agricultural satellite, it is able to provide valuable new information in many other disciplines, including geology. It was also the catalyst which taught us about the immense value of image processing and display of many exploration data sets. We should not, however, think that merely because it is available, it is the most appropriate tool for geological purposes, indeed it is not. The second generation of sensors, which are now becoming available, have been designed for much more specific applications. In particular, it is clear that it is possible to design systems which will be sensitive to certain types of mineralogy. These are both line-trace, profiling systems, imaging systems and field instruments. The range of minerals which can be sensed is limited to those which have diagnostic optical properties in the atmospheric windows. Information is available in three wavelength regions; viz: Region Visible - near infrared (VNIR) (0.4 - 1.0 ym) Short wavelength infrared (SWIR) (1.0 - 2.5 ym) Thermal or emitted infrared (TIR) (8 - 14 ym)

Minerals Detected

Iron Oxides Phyllosilicates and Carbonates Quartz content and Carbonates

Although the number of minerals which can be detected is limited, it has been demonstrated in Australia that some very subtle discriminations can be made within each group.

270

The interesting thing about these three regions is that the phenomena detectable, the iron oxides, phyllosilicates and silicification, are significant targets in exploration as well as being an inherent part of the weathering process. The MSS's four spectral bands are merely broad, average samples of an otherwise continuous spectral response curve. At various specific wave lengths on this curve different minerals give rise to definitive absorption features. The need in remote sensing in the 80's is to be able to sense this entire curve or place scanner spectral bands at positions that coincide with these absorption features. Australian experience as to how to do this is now well advanced. The applications of these new systems cover three topics of interest: alteration mineralogy, weathering and mapping. Economically the most important of these, the spectral recognition of the mineralogical products of alteration, is possible at the outcrop and with airborne sensors, where the primary mineralogy is still intact. Sericite, smectite, alunite, pyrophyllite, kaolinite, epidote, talc all have diagnostic SWIR absorption characteristics and can be mapped in Australia with correctly designed sensors. Examples also exist that show that various substituting elements into mineral lattices give rise to unusual but detectable, spectral features. Spectral recognition of alteration products that are generally not produced by weathering is particularly critical in Australia. Under chemical weathering conditions there is a general convergence of mineralogy resulting in the development of iron oxides and kaolinite, sometimes independent of parental rock type. Therefore remote determination of clays alone is not enough. Aircraft and satellite thematic mapper data are making an important general contribution to clay determination but are not precise enough to allow the species mapping we believe is necessary in this country. The major value of remote sensing in geology is the uniformity and objectivity of its coverage. Evidence exists that shows that in some areas optimum, multi-channel remote sensing systems have a very considerable mapping capability; a capability to replace some meaningless formation names on maps with mineralogical characteristics. Finally the greatest challenge to remote sensing in much of eastern Australia (and it may be impossible) is to seek very subtle spectral characteristics in the vegetative cover that may relate to the subsurface chemical environment. Evidence is presented that shows it is at least worth looking for such features.

PETROGRAPHY OF OIL SHALES AND GEOCHEMISTRY OF SHALE OIL, DUARINGA A.C. Hutton, J. Korth, J. Ellis, P. Crisp University of Wollongong, Wollongong The Duaringa oil shale deposit is part of the Tertiary sequence of the Duaringa Basin, an elongate north-northwest trending basin centred 110 km west of Rockhampton, Queensland. Kirkegaard et al., (1970) described the Duaringa Basin as an elongated trough located between a folded zone to the west and the Connors Arch and Gogango Overfolded Zone to the east. Mapping and drilling has indicated a normal fault along the western margin of the basin and seismic studies, together with structure contours constructed from drilling data have delineated three sub-basins which correspond to topographic highs (Green et al., 1979). 271

An extensive drilling programme by Southern Pacific Petroleum NL and Central Pacific Minerals N L , in 1978-79, delineated oil shale seams in the upper half of the sequence. A subsequent stratigraphic h o l e , drilled by the Geological Survey of Queensland, intersected a number of oil shale seams in the lower half of the sequence. The two oil shale-bearing units are hereafter termed the upper and lower units. The two units are separated by a thick claystone unit. The upper unit contains two laterally extensive oil shale seams. The lower seam is 10 to 15 m thick with shale oil yields of 63 to 92 L T O M . 20 to 25 m of mudstone separates the lower oil shale seam from the upper seam which' averages 8 m in thickness. Grades for the younger seam range from 46 to 66 L T O M . Combined in-ground resources of 9 both seams (based on 40 LTOM cutoff) is estimated at 4.88 x 10 barrels of shale o i l . Intensive weathering to a depth of up to 60 m has removed much of the organic matter in the upper seam, especially near the edges of uplifted areas. The seam as a consequence, is poorly defined in m a n y areas. Samples from the upper unit have been dated at Early Miocene to Late Oligocene (Hekel, 1972) and Middle to Late Eocene (McMinn, 1980). Foster (cited in Green et al., 1979) assigned an age of Early Miocene to Late Oligocene for the interval 725.09 to 729.03 m in the stratigraphic h o l e . The lower unit has several thin oil shale carbonaceous oil shale, brown coal and claystone.

seams

interbedded

with

The oil shales, termed lamosites as defined by Hut ton et a l . (1980), from the two units have markedly different hand-specimen and petrographic properties. Lamosite from the upper unit is typically olive to olive-grey and contains abundant green to greenish-yellow fluorescing lamalginite, much of which is derived from the algae Pediastrum and the dinoflagellate Septodinium, and telalginite derived from Botryococcus. Samples contain up to 35% lamalginite and up to 25% telalginite (although mostly less than 5%). In many hand-specimen samples Botryococcus occurs as w h i t e , ovoid spots up to 1 mm diameter. An above-average abundance of Botryococcus accounts for the high shale oil yields obtained from stratigraphically equivalent intervals in several drill holes. Lamosite from the lower unit is typically brown to dark greyish-brown and contains orange to yellowish-orange fluorescing lamalginite, part of which is derived from Pediastrum, and telalginite derived from Botryococcus. Samples contain up to 45% lamalginite but less than 2% telalginite. Carbonaceous oil shale, termed carbonaceous lamosite, also occurs and is of two forms. The first comprises interlaminated (generally microlaminated) coal and lamosite whereas the second form is dominantly a lamosite with greater than 5%, ubiquitous vitrodetrinite. Both forms are dark greyish-brown to black. Brown coal contains vitrinite (composed of ulminite (R 0 max of 0.4%), corpohuminite and minor resinite) and clarite (comprising ulminite, corpohuminite, attrinite, resinite, sporinite and cutinite). Thus the lamosite, carbonaceous lamosite and brown coal of the lower unit contain macerals with the same optical properties as corresponding macerals in lamosite from the Rundle-Stuart deposit. Differences between the properties of macerals in the lamosites from the upper and lower units suggest that the environments of deposition in which the two were formed were not the same. Furthermore the shale oils derived from the two lamosites are unlikely to have identical chemical compositions. Oils from different shales, such as those from the upper and lower units of the Duaringa deposit can be compared on the basis of their pyrolysis-GC profiles with characterisation of each shale oil obtained from a retort purged with nitrogen sweep g a s . Additional information may be gained using gas chromatography-mass spectrometry using a modified version of the open-column chromatography procedure of Regtop et al (1982).

272

Analysis of shale oil from the upper unit is near completion and a comparative study of the shale oil from the lower unit is being undertaken. Results to date indicate that the oil obtained from shale taken from the upper unit is highly aliphatic (H/C = 1.7) and its chemical composition corresponds closely to that of shale oil derived from both Condor and Rundle oil shales. Dominant constituent groups are alkanes, alkenes, nitriles and alkanones. This study shows that at least two types of oil shales may be found in a given Tertiary sequence. Furthermore the two oil shale-bearing units may be separated by a thick sequence of claystone. Oil shale occurrences of the above types may be overlooked during exploration unless the sequence is drilled to pre-Tertiary basement. Acknowledgements Samples for the study were provided by Southern Pacific Petroleum NL (SPP), Central Pacific Minerals NL (CPM) and the Geological Survey of Oueensland. SPP/CPM supplied Fischer assay data and resource estimates. References GREEN, P.W., DIXON, D.A., and POPE, G.J. , 1979. Report, Q66, (Unpub.). HEKEL, H., 1972.

Southern Pacific Petroleum

Geol. Surv. Qld. Pub., 355, Palaeontological Paper, 30.

HUTTON, A.C., 1982. Organic Petrology University of Wollongong).

of Oil

Shales.

(PhD

Thesis,

HUTTON, A.C., COOK, A.C., KANTSLER, A.J. and MCKIRDY, D.M., 1980, APEA J., 20, 44. KIRKEGAARD, A.G., SHAW, R.D., and MURRAY, C.J., 1970. Report, 38. McMINN, A., 1980. REGTOP,

R.A.,

Geol. Surv. Old.

NSW Geol. Surv. Report, GS1980/4 (Unpub.).

CRISP,

P.T.

and

ELLIS,

F U N D A M E N T A L S OF THE ION

J.,

1982,

Fuel,

61,

185.

MICROPROBE

T.R. Ireland Research School of Earth Sciences, Australian National University, Canberra Applications utilising the unique capabilities of the ion microprobe have become more common in recent years, and will continue to grow, with the increasing availability of commercial machines. The ion microprobe has long promised to be a major breakthrough in the microanalysis of geological specimens but progress has been somewhat arduous owing to the complex nature of the physical processes involved. In contrast to the electron microprobe which excites X-rays in a target by electron bombardment, the ion microprobe physically erodes, or 'sputters1, ions from the target surface using a focused beam of primary ions. The electron microprobe sensitivity is limited by background radiation, and restrictions in the detection of long wavelength X-rays generally prevent quantitative analysis of elements lighter than sodium. As the ion microprobe detects discrete charged particles, it is capable of sensitivity orders of magnitude greater than the electron microprobe and can also analyse all elements from hydrogen to uranium, as well as molecular species. 273

The layout of an ion microprobe is exemplified by the sensitive high resolution ion microprobe (SHRIMP) constructed at the A.N.U., Canberra [l]. Primary ions are generated in the primary column with lens systems to accelerate and focus the beam to a spot (20-30 ijm) on the sample. On SHRIMP the ion source is a duoplasmatron in which the source gas (O2 or Ar) is ionised under an electric discharge and contained magnetically as a plasma bubble. The ion beam is extracted through a 150 or 300 ym aperture and accelerated to energies of 10-15 keV. Divergence limiting apertures and three einzel lens systems demagnify the beam to its final size. The sputtered secondary ions are extracted electrostatically and then focused by the beam matching system to ensure maximum transmission. The mass analyser system consists of a cylindrical electrostatic analyser to produce an energy focus, a quadrupole lens to reduce aberrations, and a magnet to produce mass separation. The major feature of SHRIMP is its size (magnet turning radius 1m) which enables operation with physically wide slits for high sensitivity while maintaining high mass resolution. SHRIMP routinely operates at mass resolution 7500R (1% peak overlap) and is capable of distinguishing molecules that differ in mass by less than 1 part in 25,000. The magnet is computer controlled to facilitate peak switching in data collection. The detection system can operate with an ion counter for low intensity beams, or a faraday cup may be inserted before the ion counter when the ion flux is sufficiently large. The prime capabilities of the ion microprobe hinge on its ability to directly analyse a sputtered volume of the sample. In the sputtering process, primary ions impinge on the surface and have sufficient energy to penetrate several atomic layers. The imparted kinetic energy is transferred back towards the surface and if a surface atom acquires sufficient kinetic energy, it may be ejected from the surface. The ejected atom thus acquires its energy from other surface atoms rather than directly from the primary ion. The back transfer of energy is rather inefficient and so ejected atoms have relatively low energies of the order of lOOeV. The time and place of ionisation and the number of secondary ions produced per primary ion are still matters of conjecture and no generally accepted model exists. Secondary ion emission is known to vary with atomic species, matrix composition, sampling conditions and instrumental factors as well as concentration [ 2 ] . The sputtered material consists predominantly of neutral atoms and molecules but a small fraction are ejected as ions. The ion yield increases over orders of magnitude when a reactive species such as oxygen or cesium is introduced into the sputtering environment. In geological specimens the resulting mass spectra are extremely complex owing to the presence of molecular species and result in interferences at the same nominal atomic weight (isobaric interferences). Although atomic isobaric interferences are common, the problem is largely overcome by monitoring another isotope of the interfering element and subtracting the calculated contribution at the desired mass. The existence of molecules in the secondary ion spectrum creates difficulties as the intensity of the molecular species cannot be easily obtained due to the large number of possible isobars contributing to both the desired mass as well as neighbouring peaks. Molecular interferences may be dealt with by operating under conditions of sufficiently high mass resolution, or by a method of energy filtering. The regular variation in mass deficiency of the elements with increasing atomic weight results in mass differences between atomic and molecular isobars which may be resolved with sufficient mass resolution. For example, all significant interferences are resolved in U-Pb dating of zircons at 6500R. However, in rare earth element spectra mass resolutions of the order of 25,000R are required. Energy filtering relies on the molecular ions being emitted from the sample surface with lower kinetic energy so they may be eliminated by a suitable bandpass [3]. These methods involve a tradeoff between reduced interferences at the expense of beam transmission. 274

Metson and others [4] have recently described the specimen isolation technique for the suppression of molecular ions in rare earth element spectra by allowing the sample to become electrically charged under the primary beam. This creates an extreme potential gradient between the sample surface and the secondary accelerating field allowing the lower energy molecular species to be discriminated against. During the sputtering/ionisation process, the isotopes of an element are fractionated. The effects can be quite large, for example, titanium is fractionated in SHRIMP by -2% per amu. The magnitude is dependent upon the matrix but always follows a Rayleigh fractionation trend allowing normalisation of observed abundance ratios. The present major geological applications of the ion microprobe utilise its ability to obtain highly sensitive isotopic analyses with high spatial resolution. The ion microprobe is also used in a depth profiling mode where the secondary ion intensity of a species is monitored as the primary beam continuously erodes the surface. This capability is applied in diffusion studies where the gradients produced are in the order of a few microns. References [1] Clement, S., Compston, W., & Newstead, G., 1977, Proc. Int. SIMS Conf., Muenster (ed. Benninghoven, A.), (Springer, Berlin, 1977). [2] Wittmaack, K., 1980, NUcl. Inst. Methods, 168, 343-356. [3] Steele, I.M., Hutcheon, I.D., Solberg, T.N., Smith, J.V., & Clayton, R.N., 1977, Int. J. Mass. Spec. Ion Phys., 23, 293-305. [4] Metson, J.B., Bancroft, G.M., Nesbitt, H.W., & Jonasson, R.G., 1984, Nature, 307, 347-349.

THE USE OF PETROPHYSICAL DATA IN THE INTERPRETATION OF SEISMOLOGICAL MODELS OF THE CONTINENTAL LITHOSPHERE I. Jackson, M.S. Paterson, S.L. Webb and H. Niesler Research School of Earth Sciences, Australian National University Seismological studies of the variation of wave velocities and attenuation within the lithosphere provide some of the most direct information concerning its deep structure. The interpretation of such seismological models in terms of chemical composition, mineralogy, fabric and temperature requires laboratory data for well-characterized rocks and minerals under controlled conditions of pressure and temperature. Elastic wave velocities are most easily measured in the laboratory by ultrasonic techniques. Procedures developed by Birch (1960) have subsequently been widely applied to the measurement of the travel time of elastic waves of MHz frequencies through jacketed rock samples under conditions of high confining pressure. It has been demonstrated that pressures of a few 100 MPa (a few kilobars) are sufficient to close most of the relatively high aspect ratio voids in igneous and metamorphic rocks. Under these conditions measured velocities are determined by the chemical composition and mineralogy of the rock and not by its porosity. More precise techniques of ultrasonic interferometry are used in the characterization of single crystals.

275

Published elasticity data for mafic and ultramafic rocks, which allow interpretation of seismological models of the lithosphere, will be critically reviewed. Of these rock types, dunites F09Q) and orthopyroxenites Eng5) have been particularly thoroughly studied (Babu^ka, 1972; Christensen 1971, 1974). Compressional wave velocities at 1000 MPa (10 kbar) are respectively 8.4 and 7.9 km/s in agreement with aggregate elastic properties calculated from single-crystal data. Clinopyroxenites, websterites and harzburgites are characterised by intermediate velocities typically 8.1-8.3 km/s (Kroenke et al., 1976). Data for 'fertile 1 peridotites are lacking but calculations by Jordan (1979) based on elasticity data for the constituent minerals indicate that the compressional wave velocity is insensitive to the degree of depletion in low melting point components. New ultrasonic data for spinel lherzolite will be presented. The densities and elastic wave velocities for mafic rocks such as gabbros, granulites and eclogites vary widely with chemical composition and mineralogy. Under these circumstances, laboratory wave velocity measurements are useful only in conjunction with detailed chemical information including the pressure and temperature of equilibration. A study of this kind was recently conducted by Jackson and Arculus (1984) on the mafic granulite and eclogite xenoliths from the Calcutteroo (S. Aust.) kimberlite pipe. Most of these xenoliths have densities between 3.2 and 3.4 Mg m~3 and compressional wave velocities (at 400 MPa) of 7.2-8.0 km/s. Correction of these elastic wave velocities to the inferred pressures (800-1200 MPa) and temperatures (800-900°C) of equilibration requires knowledge of both the pressure and temperature derivatives of wave velocity. The latter, in particular, are poorly known although ultrasonic measurements by Fielitz (1971) under conditions of simultaneous high pressure (410 MPa) and high temperature (to 750°C) indicate that 3Vp/3T is about -5x10"1* km s~ 1 for both peridotite and eclogite. Such corrections applied to -the measured velocities for the Calcutteroo granulites and eclogites result in rather high values of lower crustal velocities of 6.9-7.7 km/s which compare well with the recent seismological model of Finlayson et al. (1979) for the Lachlan Fold Belt. It is therefore concluded that mafic granulites and eclogites may constitute a significant proportion of the S.E. Australian lower crust. All of this analysis is based upon the assumption that ultrasonic measurements of elastic wave velocities are directly applicable at seismic frequencies. However, at the relatively high subsolidus temperatures of the upper mantle and lower crust it is possible, even probable, that there will be significant dispersion (frequency dependence) of wave velocities between ultrasonic and seismic frequencies. Accordingly a new apparatus has been built to facilitate the measurement of shear wave velocities at seismic frequencies under conditions of simultaneous high pressure and temperature. The operation of this new apparatus will be described and some preliminary seismic frequency data will be presented. References Babuska, V., 1972, J. geophys. Res. 77, 6955-6965. Birch, F., 1960, J. geophys. Res. 65, 1083-1102. Christensen, N.I., 1971, Geol. Soc. Amer. Bull. 82, 1681-1694. Christensen, N.I., 1974, J. geophys. Res. 79, 407-412. Fielitz, K., 1971, Z. Geophys. 37, 943. Finlayson, D.M., Prodehl, C., Collins, C.D.N., 1979, BMR J. Aust. Geol. Geophys. 4, 243-252. Jackson, I., Arculus, R.J., 1984, Tectonophys. |_01_, 185-197. Jordan, T.H., 1979 in The Mantle Sample: Inclusions in kimberlites and other volcanics (eds. Boyd, F.R. and Meyer, H.O.A.) AGU, Washington. Kroenke, L.W., Manghnani, M.H., Rai, C.S., Fryer, P. and Ramananantoanaro, R., 1976, in The geophysics of the Pacific Ocean basin and its margins (eds. Sutton, G.H. et al.) AGU, Washington. 276

HYDROCARBON

G E N E R A T I O N IN THE A M A D E U S BASIN, AUSTRALIA i

K.S. Jackson , D.M. McKirdy'1 and J.A. Deckelman

CENTRAL 3

^"Shell Development (Australia) Pty Ltd., Perth 2 AMDEL, Adelaide ^Magellan Petroleum Australia Limited, Brisbane The Proterozoic to Devonian Amadeus Basin of Central Australia contains two hydrocarbon fields - oil and gas at Mereenie, and gas at Palm Valley, both within Ordovician sandstone reservoirs. Significant gas and oil shows also have been recorded from Cambrian sandstones and carbonates in the eastern part of the basin. The hydrocarbon generation histories for documented source rocks, determined by Lopatin modelling, largely explain the distribution of the hydrocarbons. The best oil and gas source rocks occur in the Ordovician Horn Valley Siltstone. Source potential is also developed within the Late Proterozoic sequence, particularly the Gillen Member of the Bitter Springs Formation, and the Cambrian. Consideration of organic maturity, relative timing of hydrocarbon generation and trap formation, and oil/source typing leads to the conclusion that the Horn Valley Siltstone charged the Mereenie structure with gas and oil. At Palm Valley, only gas and minor condensate occur because the trap was formed too late to receive an oil charge. Differences in organic facies may also, in part, account for the dry gas and lack of substantial liquid hydrocarbons at Palm Valley. In the eastern Amadeus Basin, the Ordovician is largely absent but Proterozoic sources are well placed to provide the gas discovered by Ooraminna-1 and Dingo-1, where any oil charge would have pre-dated trap timing.

THE EVOLUTION OF THE CLEVELAND G R E I S E N - V E I N - S K A R N A GEOLOGICAL, FLUID INCLUSION AND T H E R M O D Y N A M I C

SYSTEM, STUDY

P.G. Jackson and T.A.P. Kwak Department of Geology, La Trobe University, Bundoora, Vic. The Cleveland (Tas.) Sn-Cu(-W) deposit, comprises three styles of mineralization: (1) Greisenized skarn. (2) Greisenized quartz porphyry dyke. (3) Vein halo around the dyke. A now greisenized k-f eldspar-quartz porphyry dyke has intruded a sequence of sub-greywackes, cherts, argillites, calc-arenites and minor limestone. The highly fractured dyke, which does not reach the surface, has served as a conduit for fluids which have produced much of the mineralization. A number of mutual stages are recognised in the genesis of the deposit. These stages can be spatially and temporally inter-correlated to the mineralization in each of the ore styles of the system as follows:

277

Stage

Dyke

Serlcltlzatlon of feldspars, silicification.

Formation of amphibole, chlorite skarn.

Quartz dominant veins, largely barren.

Formation of muscovitequartz grelsen.

Annite-fluorite alteration of primary skarn.

Mica, k-feldspar, quartz, wolframite, molybdenite vein filling.

III

Formation of topaz-quartz grelsen.

Fluorite-tourmaline alteration of Stages I and II, casslterlte stage.

Topaz-fluorite dominant veins, cassiterite stage.

Sulphide alteration.

Sulphide alteration of Stages I,II and III.

Topaz, fluorite, sulphide, tourmaline, siderite and casslterlte veins.

Carbonate alteration.

Carbonate alteration of earlier formed minerals.

Carbonate-fluorite veins.

Replacement bodies

Veins

The early ore solutions (Stages I and II)+were largely buffered by the muscovite-quartz-k-feldspar buffer, consuming H and increasing pH, After the reaction of all the k-feldspar, unbuffered, low pH solutions produced Stage III and IV mineralization. Stage V mineralization is related to meteoric water mixing. Homogenization temperatures from fluid inclusions in minerals associated with the major Sn-transporting stages (Stages III and IV) fall within a narrow temperature range (425-455 C). Freezing data indicate that low - moderately saline fluids (8-]4 wt. % NaCl equivalent) are involved in the mineralization. No chlorides have been identified, although first melting (eutectic) temperatures range from -28 to -35 C. Thermodynamic calculations show that during Stages III and IV, log f /f n values are higher than -4*5.

ENGINEERING GEOLOGY AND HYDROGEOLOGY AS FACTORS IN DEVELOPMENT G. Jacobson Bureau of Mineral Resources, Geology & Geophysics, Canberra Engineering geology and hydrogeology have a vital role in both rural and urban development. In the context of development aid programmes these applications of geoscience are a direct and worthwhile contribution to the alleviation of poverty and disease, the provision of basic human needs and the promotion of economic growth. Rural development is of growing importance in the national strategies of most developing countries. The bulk of the population is still rural, and their quality of life can be greatly improved by safe water supplies and sanitation, efficient transportation systems and other facilities. In rural areas, the provision of safe water supplies is of particular importance; mortality rates caused by impure water are still high in much of the world. Hydrogeological surveys of village water supplies can have a dramatic effect, especially if followed up by appropriate implementation of improvement. For instance, in Papua New Guinea a representative selection of about 1000 villages were surveyed over a period of several years, and water supplies improved to a safe level. Groundwater drawn from dug wells and bores was particularly useful as it is generally safe bacteriologically, and requires little or no treatment in the humid tropics. Country towns also can develop effective safe water supplies using groundwater; an example is the provincial centre of Kota Bumi in Indonesia, where a population of 50 000 can be served by four bores in an alluvial aquifer.

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Engineering geology can contribute to the design and construction of rural roads by locating sources of construction materials and by geotechnical studies of unstable terrain. Some examples of regional scale engineering-geological problems include the complete lack of adequate construction materials in many parts of Borneo, which are underlain by soft Tertiary rocks; the slope instability of particular formations and terrain such as the Chim Shale in the New Guinea highlands; and soil problems affecting road construction, such as the volcanic ash soils with deleterious geotechnical properties which are common in parts of New Guinea. Geological maps form the basis for development planning, including the identification of natural resources, geological hazards and other development constraints. However conventional stratigraphic maps are not always suitable for development planning and there is a need for regional-scale thematic maps showing engineering-geological and hydrogeological parameters. Urban populations are expanding rapidly. The phenomenon of urban drift is well known and in most countries defies attempts at control. The growing urban and urban fringe populations require safe water supplies and sanitation, transportation systems, buildings and other engineering structures, and refuse disposal systems. Engineering geology is an important factor in the provision of these facilities. Special geological problems of the urban environment include foundation problems associated with particular tropical soils and with deep weathering; water supply, with groundwater commonly an important and underutilised resource; construction materials, especially where deep weathering makes hard rocks scarce; landslides, common in hilly terrain because of the wet climate and thick superficial deposits; and in some cases volcanic and seismic hazards. As well as problem-orientated investigations, the provision of urban geological maps for development planning is an important part of the geologist's role. Examples of the profound importance of geological factors in urban growth and development are given in Table 1 which relates to two developing cities in Papua New Guinea and two in East Malaysia. These four cities have populations of about 100 000 and their urban geological constraints represent a microcosm of the more severe and complex problems affecting larger cities. Growing concern about the environment in industrialised countries is likely to be matched in developing countries as living standards improve. Specific environmental-geological concerns such as erosion, desertification, and water pollution, are already apparent. The present situation with regard to engineering geological and hydrogeological services is far from satisfactory in most developing countries. There is a lack of specialists, and many large cities and important regions have no geological service, or geotechnical maps or data bases. Many geologists who have been trained in the academic tradition, are not orientated towards practical problems. There is commonly a lack of appreciation on the part of planners about the importance of geological factors (not only developing countries have this problem!). There are few papers in the geotechnical literature on the problems of developing countries and poor budgets restrict field work and technical conferences. Engineering geology and hydrogeology are directly applicable to improving the living conditions of large numbers of people, and are therefore a most relevant component of development aid programmes.

279

Table

PORT MORESBY

LAE

GEOLOGY

CONSTRUCTION MATERIALS

I. Urban geology constraints of four cities

SANDAKAN

Tert iary sedimentary Quaternary al luvium

KOTA KINABALU

Tertiary sedimentary rocks Quaternary alluvium

Quaternary al luvium

Tert iary sedimentary

Alluvial gravel plentiful but high grade aggregate has quality problems

Problem - limited supplies of hard rock virtually depleted; long haulages for h igh grade aggregate.

Problem - only soft rocks available; Cement stabilisation used for roads.

Problem - sandstone hauled considerable distances; large amounts of fill required for coastal reclamat ion.

rocks

rocks;

SLOPE

STABILITY

Minor problem wet climate but limited hillslupe deve 1 opine n t

Dry cliinate and limited hillslope deve lopnien t

Problem undercut bedding planes in shale/ sandstone sequence combined with wet climate and hilly terrain

Some landslides and embankment failures; wet climate and hilly terrain

WATER

SUPPLY

Groundwater in alluvial aquifers; need to avoid pollut ion

River offtake for city supply. Limited groundwater usage

Groundwater in sandstone aquifers for city supply

River offtake for city supply; groundwater not used.

Piled foundations general

Piling in coastal and valley a 1 luv ium

Piling in alluvium and coastal reclamation areas

Piling for larger buildings in alluvium

High seismic risk; river and coastal erosion

Swelling clays; road pavement 1ai lures due to moisture changes

BUILDING FOUNDATIONS

OTHER GE0TECHN1CAL PROBLEMS

MAIN

DEVELOPMENTS

Land

ownership

Water supply 1 iniitat ions

Consolidations of peaty soil ir. swampy alluvial areas

Mountainous h inter land

POLLUTION OF SHALLOW AQUIFERS BY URBAN DEVELOPMENT CASE STUDIES FROM CANBERRA

G, Jacobson Bureau of Mineral Resources, Geology & Geophysics, Canberra Canberra has grown from a population of about 100 in 1913 to a population of 250 000 in 1984, spread over an urban area of 200 km « In this area, groundwater occurs in shallow alluvial and colluvial aquifers and in fractured-rock aquifers. The unpolluted groundwater is generally of potable quality, with total dissolved solids in the range 200-1000 mg/1. Shallow groundwater aquifers are susceptible to pollution by various contaminants. In Canberra point-source pollution of shallow aquifers has been discovered in six localities (Table 1). This includes three cases of groundwater pollution by hydrocarbons which have spilled or leaked from tanks. One of these cases - the Canberra city case - involved a fatal accident when petrol entered the basement of a building. The source of the petrol was probably leaking underground

280

installations at a nearby service station. Remedial action has been undertaken for several years by pumping from a deep bore to depress the water table over the affected area, and removing the petrol that collects in the cone of depression. About 40 percent of the original spill has been removed, but the rate of recovery has dropped. In the Braddon case, petrol has also entered the basement of a building on several occasions as a result of a rising water-table after heavy rain, and can also be traced to spillage from an underground tank. In the Mitchell case, pollution of groundwater by oil can be related to a spillage from an above-ground storage tank which was washed into stormwater drains. Groundwater in discontinuous sand aquifers at the Hume industrial estate has been polluted by kraft effluent and the pollution extends for about one kilometre downstream from a timber mill. Recent monitoring of dissolved organic carbon in the groundwater system indicated that the pollution plume is still spreading. At a disused landfill site at Pialligo, leachate has spread into adjacent groundwater and is still being generated nearly 10 years after the final filling of the site. Presently operating landfill sites in Canberra are better designed and have groundwater monitoring systems. At Duntroon an investigation to determine the feasibility of re-using treated sewage effluent for irrigation of parkland, ran into difficulties when it was discovered that the groundwater system was already polluted by leakage from septic tanks. The area has since been sewered! The total area of Canberra known to be affected by groundwater pollution is about 135 ha, a small area but significant considering the time scale of groundwater pollution, the difficulty of rehabilitating an aquifer, and the possibility of undiscovered cases and of future incidents. The Canberra city water supply is at present mainly derived from surface water sources and groundwater is but lightly used to supplement it. Neverthless the future groundwater resource potential is considerable. Shallow aquifers are highly vulnerable to pollution from urban development, and legislative controls are needed to safeguard these future water resources. Prevention is better than cure!

Table 1.

Groundwater pollution cases, Australian Capital Territory.

Location

Area Aquifer affected type (ha)

Canberra city Braddon Mitchell industrial estate Hume industrial estate Pialligo

0.5 0.03 15 50 40

Duntroon

Fractured mudstone Limestone Fractured mudstone Alluvium Aeolian sand on mudstone Colluvium

Pollutant

Petrol Petrol Oil Kraft effluent Leachate Sewage

281

METHODS FOR ESTIMATING FUTURE DISCOVERY AND SUPPLY OF HYDROCARBONS F.S. Jeffries Esso Australia Ltd,

Sydney

Both government and industry need to answer four questions when analysing the merits of hydrocarbon exploration. 1.

How many and what kind of hydrocarbon pools remain to be discovered?

In what order will these pools be found?

In what time framework will these discoveries occur?

What will it cost to make these discoveries and will the rewards be worth the effort?

The first question covers three problems. What was the original population of hydrocarbon pools, what has been discovered and what remains? If we accept that explorers have a bias towards finding larger pools early in an exploration cycle and that populations of discovered pool sizes tend to fit log normal populations, then the original population is likely to to have a pool size population with a smaller mean but larger standard deviation than the population of discovered pool sizes. por undiscovered pools both the mean and standard deviation of pool sizes should be smaller than the parameters of the discovered pool sizes. Trial and error estimates based on the mean and standard deviation of discovered pool sizes can be coupled with geological data to simulate models of the original pool size distribution and used to give a relative picture of all three populations. Recent literature has proposed that the probability of discovery of any pool is proportional to the size of that pool compared to the sum of sizes of all undiscovered pools. While this may be a reasonable assumption for a single hydrocarbon play, such estimates appear to be very optimistic when industry is exploring many plays. Less biased probability density functions can be derived to approximate the discovery sequences which have been recorded in historic exploration programs. Historic pool discovery rates can be used as a guide to the annual rate of pool discoveries to convert a pool discovery sequence to a volume versus time plot of hydrocarbon available for exploitation, ^rom this discovery timing it is possible to add estimates of development lag times and production rates to estimate production profiles. When suitable estimates of drilling and development costs are added in addition to estimates of product prices and government taxes the entire exploration and development sequence can be converted to a cash flow profile for standard economic analysis.

282

Since there are very many stages of estimation in this process and there is often extreme uncertainty about the various parameters, the system is best analysed using monte-carlo techniques. Also, since there is no need for a single answer the results can be readily mapped as an array of outcomes. Consequently only a few hundred monte carlo trials are needed to outline the more likely outcomes. A system of this kind clearly illustrates that the initial assumption about the parameters of the undiscovered pool size distribution causes variations in financial outcomes of about five times the variation caused by other assumptions such as drilling rates, price changes or taxes.

TERRIGENOUS SEDIMENTATION ALONG THE EASTERN AUSTRALIAN SLOPE AND ABYSSAL PLAIN - A STARVED CONTINENTAL MARGIN C.J. Jenkins Ocean Sciences Institute, Sydney University, Sydney Seismic stratigraphy, direct sediment sampling, detailed bathymetry and bottom photography outline the major elements in terrigenous Cenozoic deposition east of Australia. The Neogene and Palaeogene upper slope sediment wedges result from shelf-edge biological accumulation, transport by the East Australian Current and nearer shore processes at low sea-level stands. Turbidite fans at the base of the slope are small and local structures, clearly divisible into upper, middle and lower (i.e. abyssal plain) reaches. Seismic sections show several major episodes of fan progradation off the N.S.W. north coast. Where fans are not developed (i.e. 50% of the margin) flat or inwards-sloping abyssal plain abuts directly against exposed Palaeozoic/Mesozoic basement. In these areas moating is sometimes seen (<12% of the margin), which is due to sediment winnowing where the Western Boundary Undercurrent is intensified. A very significant sediment drift 610 km long, 30 km wide and up to 300 m high has been built along the eastern boundary of that current north of 33°S. Terrigenous silts/clays accumulate along the drift in a Stillwater zone between the WBUC and opposed currents to the east.

HEAVY METAL DISTRIBUTION AND BEHAVIOUR IN THE M0L0NGL0 RIVER SYSTEM DOWNSTREAM FROM CAPTAIN'S FLAT, NEW SOUTH WALES I.F. Johnson and K.G. McQueen Geology, Canberra CAE, Belconnen, A.C.T. Since the Captain's Flat lead-zinc-copper mine was closed in 1962 there has been concern about metal pollution in the Molonglo River downstream from the mine site. Extensive rehabilitation of the site was carried out in 1975-76 in an attempt to reduce this hazard and since then monitoring of stream water, sediment analysis and studies of biological samples (e.g. Brooks, 1981; Norris, 1983) have indicated some reduction of metal levels in the water, but little change in pH or metal concentration in the total system.

283

A detailed geochemical study of stream sediments collected from 15 sites along 34 km of the river, from Captain's Flat to the Molonglo Gorge, was undertaken to determine the concentration, distribution, transport mechanisms and water-sediment transfer behaviour of Zn, Pb, Cu and Cd. A range of materials including fine mud, silt-sand and organic rich sediment was collected at each site. It was found that all metals show their highest concentrations in the finer fraction sediments (muds) and organic rich samples (up to 4000 ppm Zn, 2600 ppm Pb, 360 ppm Cu and 8 ppm Cd) . Sands and coarser fraction sediments, sampled for possible clastic metal carriers, have lower concentrations (up to 3000 ppm Zn, 1500 ppm Pb and 270 ppm Cu). Each metal shows a particular distribution pattern along the river related to its mobility under the varying conditions of pH, Eh and sediment cation exchange capacity. Water pH varies from 3.5 at the mine site to between 5.5 and 6 at Carwoola Flat (12 km downstream), to 7.2 near Molonglo Gorge. Measured cation exchange capacity increases in the finer sediments and with increasing organic content. Copper and Pb levels are highest in sediments closer to the mine site (within 3 km), with Pb showing an affinity for inorganic colloids and Cu a preference for organic colloids. The behaviour of Pb is also strongly influenced by high sulphate concentrations and sharply increased pH immediately downstream of the mine. Zinc is much more mobile and the highest Zn levels occur in sediments along the marshy Carwoola flood plain. Adsorption of Zn into sediments appears to be partly pH dependant but is also strongly controlled by the higher cation exchange capacity of the fine, organic rich sediments in this part of the river system. Much of the Zn is loosely bound in these sediments and approximately 25% of the total nitric-perchloric acid soluble Zn can be extracted by short term leaching with neutral pH buffered, distilled water. Since mine rehabilitation, water conductivities close to the mine have increased four fold (Dept. Housing and Construction, written comm.), possibly indicating a higher dissolved ion content relative to sorbing sediment load. These values decrease by half after the water has passed through the Carwoola flood plain. Significant precipitation of gypsum is occurring in the flood plain sediments suggesting high sulphate levels in the water upstream. Removal of this sulphate and Ca to form gypsum may also be affecting the behaviour of Zn in the sediments. This study indicates that there are still high concentrations of heavy metals in the Molonglo River system, particularly in the finer and organic rich sediments. Remobilisation of these largely adsorbed metals, especially Zn, by water leaching as a result of flood flushing or changes in pH has potential for causing metal pollution further downstream. References Brooks, D.A., 1980, N.S.W. Dept. Mines Record 1980/424. Norris, R.H., 1983, Report to N.C.D.C. Brief No. E/162/81.

284

GEOLOGICAL EMERGENCY

H A Z A R D S : A S S E S S M E N T , M I T I G A T I O N , AND D I S A S T E R / R E S P O N S E S IN THE S O U T H W E S T - P A C I F I C / S O U T H E A S T ASIA REGION R.W. Johnson

and R . J . Blong

^Bureau of M i n e r a l R e s o u r c e s , C a n b e r r a ^ M a c q u a r i e U n i v e r s i t y , Sydney A P a n e l D i s c u s s i o n a n d W o r k i n g G r o u p during the 7th A u s t r a l i a n Geological C o n v e n t i o n w i l l review p a s t , and explore f u t u r e , c o - o p e r a t i v e , g e o s c i e n t i f i c w o r k in the field of g e o l o g i c a l h a z a r d s b e t w e e n A u s t r a l i a and other countries in the S o u t h w e s t - P a c i f i c / S o u t h e a s t - A s i a region.* Hazards of particular concern to m a n y countries in the region are e a r t h q u a k e s , v o l c a n i c e r u p t i o n s , l a n d s l i d e s , and t s u n a m i s , b e c a u s e of their sudden impact and p o t e n t i a l l y d i s a s t r o u s consequences to l i f e , p r o p e r t y , and land usage. Other g e o l o g i c a l h a z a r d s include c o a s t a l erosion and d e p o s i t i o n , soil erosion and s e d i m e n t a t i o n , e x p a n s i v e s o i l s , and ground s u b s i d e n c e . The relative importance of a l l these h a z a r d s is different from one country to the next and from one part of a country to a n o t h e r : coastal erosion and tsunamis are of concern to atoll c o m m u n i t i e s , landslides to settlem e n t s in e a r t h q u a k e - p r o n e areas of high r e l i e f , soil erosion to agriculturalists in d r o u g h t - s t r i k e n r e g i o n s , e x p l o s i v e v o l c a n i c eruptions to those living in island-arc a r e a s , and so o n . The G o v e r n m e n t of A u s t r a l i a is one of several in the Pacific area capable of responding to requirements during g e o l o g i c a l emergencies and following g e o l o g i c a l l y - c a u s e d d i s a s t e r s , b y means of an infrastructure i n v o l v i n g , p a r t i c u l a r l y , the D e p a r t m e n t of D e f e n c e ' s N a t u r a l D i s a s t e r s O r g a n i s a t i o n and the D e p a r t m e n t of F o r e i g n A f f a i r s 1 A u s t r a l i a n D e v e l o p m e n t A s s i s t a n c e B u r e a u . It h a s a s s i s t e d , for e x a m p l e , m o s t recently w i t h the current R a b a u l V o l c a n o A l e r t . F u r t h e r , there are several i n t e r n a t i o n a l , m a i n l y UN organisations that h a v e rapid-response capabilities for assistance during emergencies and following disasters - for e x a m p l e , after the 1976 earthquakes in Irian J a y a , a n d during the M o u n t Galunggung lahar emergency in 1982. In c o n t r a s t , there are relatively few co-ordinating regional programs devised for the i d e n t i f i c a t i o n , a s s e s s m e n t , and m i t i g a t i o n of g e o l o g i c a l h a z a r d s . These m a t t e r s w i l l b e discussed b y the G e o l o g i c a l H a z a r d s w o r k i n g group w h i c h h o p e s to identify the most pressing needs in this area of r e g i o n a l g e o s c i e n t i f i c d e v e l o p m e n t , and to m a k e recommendations for future c o l l a b o r a t i v e w o r k . *This P a n e l D i s c u s s i o n a n d W o r k i n g Group is o n e of four comprising the A G I D - I L P W o r k s h o p 'Geosciences for D e v e l o p m e n t : D e v e l o p i n g Countries N e e d s and the A u s t r a l i a n R o l e in A s i a a n d t h e P a c i f i c '

WHY UNCONFORMITY-RELATED

U DEPOSITS

ARE U N C O N F O R M I T Y

J.D. Johnston and V.J. Wall D e p a r t m e n t of E a r t h S c i e n c e s , M o n a s h U n i v e r s i t y , M e l b o u r n e A l t h o u g h such d e p o s i t s c o n s t i t u t e a s i g n i f i c a n t p o r t i o n of t h e w o r l d ' s e c o n o m i c u r a n i u m m i n e r a l i s a t i o n , t h e role of the u n c o n f o r m i t y in their e v o l u t i o n h a s , u n t i l n o w , b e e n little u n d e r s t o o d . In this p a p e r w e examine the g e o m e t r y and d e v e l o p m e n t of b r i t t l e - d u c t i l e s t r u c t u r e s w h i c h control m i n e r a l i s a t i o n and associated a l t e r a t i o n in t h e East A l l i g a t o r R i v e r u r a n i u m field ( E A R U F ) . This leads to a g e n e r a l s t r u c t u r a l m o d e l for u n c o n f o r m i t y - r e l a t e d d e p o s i t s and also h a s i m p l i c a t i o n s for local and r e g i o n a l scale fluid m i g r a t i o n in l o w g r a d e r e g i o n a l m e t a b m o r p h i c s e t t i n g s .

285

High grade uranium mineralisation in the EARUF is localized in reverse fault zones and associated kinked, chevron folded and brecciated regions in a strongly foliated basement which is overlain unconformably by a gently dipping cover of massive quartz sandstones. The reverse faults have nonplanar surfaces controlled by the mechanical anisotropy of the basement schists and their contrast with the overlying sandstone : the faults preferentially occur within schistose basement units, transform along the unconformity to form flats and ramp steeply through the massive quartz sandstone forming narrow zones within it. Breccia zones and mineralisation are best developed where faults are sub-parallel to the basement foliation and the breccias were initiated by hydraulic fracture, commonly in kink hinges. The breccias evolved by intensive dissolution into stylobreccias. Chloritic and other styles of magnesian alteration are most strongly developed in the brittle-ductile deformation zones related to the faults. The vast mass-transfer required to effect the alteration provides evidence that large volumes of fluid have been focussed through these zones and emphasises the role of structurally enhanced permeability in their development. Autoradiographic, optical and scanning electron microscopic studies indicate that pitchblende can form crustiform linings in breccia pores, replacements and fracturefills. There is a continuum of morphological styles from disseminated to vein mineralisation. We conclude that the essential role of the unconformity is a consequence of the contrasting permeability and rheology of the cover and basement rocks. (a) The reverse fault zones, although the product of regional compression, had their trajectories and extent strongly influenced by the mechanically anisotropic schistose basement, the overlying strong, massive sandstone and the weak cohesion along the unconformity surface between them. These factors controlled the distribution of dilational regions which provided enhanced permeability and the space for deposition of ore and gangue minerals. (b) Pervasive, transient dilatant hydrofracturing of the schistose basement in the vicinity of the fault zones greatly increased the permeability of the basement in contrast to the sandstone cap, the permeability of which had been reduced by diagenetic processes. This had the effect of focussing fluid flow through the broad zones in the rocks beneath the unconformity and to narrow fracture zones above it. Fluid inclusion- and stable isotope- and fission-track (Koul, Wall and Johnston, this volume) based thermal history data are compatible with the operation of a regional hydrothermal system attending the burial of the cover rock sequence. Oxidised fluids derived from or above the cover rock sequence are essential to transport the uranium, but traversed the basement from which at least part of the uranium was derived. Local reduction of the oxidised fluids largely resulting from mixing of C-O-H fluids containing methane sourced in nearby graphitic schists was the prime cause of uranium deposition. (Hedges, Wall & Bloom, this volume). Fluid migration the very low grade metamorphic systems operating during Middle Proterozoic time in the EARUF (and also in the Athabasca region, Saskatchewan) was controlled by fracture permeability constrained to approximately semi-infinite, two dimensional (fault) regions. Episodic regeneration of fluid circulation by further faulting could account for the spread of ages of mineralisation and alteration over several hundred m y . The long term burial in a stable intracratonic environment that characterises the EARUF (Koul et. al., 1984) and other Proterozoic terrains may be an important factor in the evolution of large unconformity-related deposits therein.

286

References Hedges, M., Wall, V.J. and Bloom, M.S., Hydrothermal transport and deposition of uranium : Modelling and Implications. This volume. Koul, S., Wall, V.J. and Johnston, J.D. Fission-track studies of the East Alligator Rivers uranium field (N.T., Australia) and their implications. This volume.

GEOLOGICAL DISPOSAL OF NUCLEAR FUEL WASTES: ENGINEERED BARRIERS IN THE CANADIAN PROGRAM Robyn Johnston University of New England, Armidale The Canadian Nuclear Fuel Waste Management Program is responsible for demonstrating the suitability of a concept for the permanent disposal of nuclear fuel wastes from Canada's nuclear electricity generating stations, which produce about 12% of Canada's electricity. Research in support of the program is being carried out by the Atomic Energy of Canada, Ltd at Whiteshell Nuclear Research Establishment in Manitoba. Decay to levels of radioactivity comparable to those of the unprocessed uranium ores requires in excess of a million years, so isolation of the wastes from the biosphere must be assured for very long periods of time. The current concept is that of geological disposal, in mined repositories at 500 to 1000 metres depth in stable granitic or gabbroic plutons in the Canadian Precambrian Shield. Circulating groundwaters represent the only pathway by which radionuclides can return to the biosphere. The four barriers used to prevent radionuclide solution and transport are insoluble wasteforms, sealed containers, engineered barriers (buffer, backfill, grouts and seals) and the geosphere (1) # Nuclear fuel wastes from CANDU reactors are in the form of fuel elements consisting of U0 2 ceramic pellets, housed in zircalloy sheathing. After irradiation the fuel elements contain a wide variety of radioactive fission products and transuranic elements in addition to U. It is possible that in the future used fuel may be reprocessed to recover fissile U and Pu. The resulting liquid wastes would be immobilized by incorporation into a solid wasteform such as borosilicate or aluminosilicate glass, or sphene-glass ceramic. The wasteform (fuel rods or reprocessing wastes) will be placed in sealed containers, probably titanium. This waste package will be emplaced in the repository either in rooms or boreholes, and surrounded by clay-based buffer material. The remainder of the repository will be backfilled, and the access shaft and major fracture zones sealed and grouted. Reflooding of the vault by groundwaters is expected to occur within 5 to 50 years of closure. The major function of the buffer and backfill is to retard access of groundwater to, and radionuclide migration from, the waste container by preventing flow and imposing diffusion control on mass transport. Comparative studies of bentonite and illite clays show that both have suitably low hydraulic conductivities for use as buffer/ backfill materials. Bentonites have higher cation exchange and sorptive capacities, and swelling properties which enhance self-sealing and effectively retard water movement by expanding to fill available cracks and fractures (2). Studies of sand/clay mixtures indicate that addition of up to 50% filler sand (quartz or crushed rock) to the clay improves mechanical strength without decreasing hydraulic conductivity or swelling capacity (at low to medium compacted densities) (3).

287

Heat produced by radioactive decay will raise the temperature of the disposal vault but maximum temperatures will be kept below 100° to 150°C by appropriate spacing of waste containers. Temperature transients are of the order of 105 years for used fuel, 10 3 years for reprocessing wastes. Groundwaters at depth in the Canadian Shield have been found to be highly saline Na-Ca-Cl brines, with low K contents (4). Buffer/backfill materials must display long term stability under these hydrothermal conditions. Illites are geologically stable up to 200-250°C. Bentonitic clays (smectites) are known to convert to illite in diagenetic systems in the temperature range 50 to 150°C. ' However the reaction requires more than 106 years under conditions expected in a disposal vault (5). Buffer additives may be used to condition the chemical environment in the disposal vault. For example, ferrous compounds may be added to consume available oxygen and provide reducing conditions, under which many radionuclides are highly insoluble. Adsorption of radionuclides onto clay minerals in the buffer is an important mechanism in retarding radionuclide migration in the near field, and diffusion coefficients for radionuclides in clays are very low. Research is being carried out into the effects of microbial mediation of radionuclide transport (6). An Underground Research Laboratory (URL) is being constructed at a depth of 300 metres in the Lac du Bonnet Batholith in Manitoba to test the concepts involved in geological disposal of nuclear fuel wastes. The URL provides a unique opportunity to monitor the effects of excavation and heating on groundwater flow patterns and rock mechanical properties. No radioactive wastes will be used in the URL, but it will contain full scale vaults to test backfilling, sealing and grouting techniques. References (1)

Boulton, J., & Gibson, A.R., 1979, 1st Ann. Rep. Canadian Nuclear Fuel Waste Management Program, Atomic Energy Canada Ltd Report AECL-6443.

(2)

Oscarson, D.W., & Cheung, S.C.H., 1983, AECL Report AECL-7812.

(3)

Dixon, D., Gray, M.N., & Thomas, A.W., 1984, Proc. Imp. Symp. on Clay Barriers for Isolation of Toxic Chemical Wastes, May 28-30, Stockholm.

(4)

Fritz, P., & Frape, S.K., 1982, Chem. Geol., 36, 179.

(5)

Johnston, R.M., & Miller, H.G., 1984, AECL Report (in prep.).

(6)

Champ, D.R., Merritt, W.F., & Young, J.L., 1982, in Lutze, W. (ed), Sci. Basis Rad. Waste Man. Vol. 5, p. 745, Elsevier.

OIL SHALE : GEORGINA BASIN, N.W. QUEENSLAND C.J. Jones BHP Minerals Limited, Brisbane Middle Cambrian age marine sequences of kerogenous, finely laminated limestone/shale occur within the Georgina Basin which is situated in north-west Queensland and the Northern Territory. This material is similar in some respects to the kerogenous laminated marls which constitute the Green River oil shales of the western U.S^A.

288

In October 1981, BHP investigated the Georgina Basin laminites in A. to P. 2109M which was situated at "Yelvertof t" on the eastern margin of the basin some 100km west of Mt. Isa. A four-hole diamond drilling programme was carried out to investigate the extent and oil yield potential of the kerogenous sequence. The most kerogenous zones occur within the lower portion of the Currant Bush Limestone and the Beetle Creek Formation, but only low-yielding material was intersected by the drilling. The best average yield was of 26 litres/tonne over 28 metres, with a peak yield of 38 1/t (using a cut-off of 16 1/t), which was obtained from YL1 between 52 and 80 metres depth. Beneficiation tests were behaviour of the kerogenites.

carried

out

investigate

the upgrading

Analysis of down-hole lithologies in the "Yelvertoft" area indicate that the Inca Formation is a laterally disposed post-depositional weathering artifact of the Currant Bush Limestone rather than a depositional-environmentally controlled facies change from limestone to siltstoneshale. In this area, the Inca Formation forms a residual silty weathering mantle over Currant Bush Limestone and is void of kerogenous material.

DEVELOPMENT OF GEOLOGICAL CONCEPTS IN THE YOUNG VOLCANIC PROVINCE OF VICTORIA, AUSTRALIA E.B. Joyce Department of Geology, University of Melbourne, Parkville The extensive young volcanoes and basaltic lava flows of central and western Victoria were first recognised by Major Mitchell during his expedition in 1836, although aborigines must have lived through periods of active volcanism in the region for many thousands of years before. Earlier explorers had seen but failed to recognise the volcanic features of Victoria, and the reasons for this have been discussed elsewhere (Joyce 1976). After this rather late start, the development of understanding of the volcanic features of the region promptly followed geological advances being made overseas and later was to provide several examples of aspects of volcanism of international significance. In the period from first settlement in the 1830's to the gold-rush of the 1850' s little further was published although the diaries and letters of the early settlers record their interest and understanding - as Mitchell had said in 1838 "every settler is under the necessity of becoming a geologist". During this period the surveyor Tyers (1840) recorded volcanic featurs in his report on western Victoria, and Westgarth (1848) described the volcanic plains, extinct volcanoes and stoney rises in his book on Australia Felix.

The appointment of Selwyn as Government Geologist in 1852 led to the mapping of the first Quarter Sheets which recorded in detail the volcanic features of the area between Melbourne and the goldfields of the highlands. Also at this time scientific articles by Wathen (1953), Brough-Smyth (1858) and Selwyn (1859) appeared in overseas journals, and books by Bonwick in 1858 and Tenison Wood in 1862 informed local readers, A notable summary by Selwyn and Ulrich in 1866 distinguished craters such as Tower Hill from the other volcanoes, tabulated the known volcanoes and gave a distribution map, provided analyses of basalts, and gave the earliest detailed description of a lava cave. They thus introduced four of the aspects - morphology, cataloguing, petrology and speleology - which were to be recurrent themes to the present day. In the intervening 100 years to the 1960's, when modern studies can be considered to have begun, several major periods of activity can be distinguished. Late 19th and early 20th century studies by Dennant, Hart, Hall, Gregory and Hunter concluded with the publication in 1910 of a major study of the central part of the Western District Volcanic Plain by Grayson and Mahony, in which the authors made the erroneous claim, to be repeated by many later writers, that "it is the third largest plain of its kind in the world11. Grayson and Mahony subdivided the basalts into "earlier" and "later" groups, a practice still followed today, and described in detail scoria cones, maar craters and associated tuffs, and made comparisons with volcanoes of other countries. The next major studies were those of the late 1930's. Skeats and James in 1937 described the young stony rises and lava caves of the Porndon area, making comparisons with Hawaii which Skeats had visited in 1934. As Skeats and James noted, this was the first scientific account to be published of these remarkably youthful and well-preserved volcanic features. They also described the lava caves at Byaduk in far western Victoria, and developed a theory of lava cave origin. Edwards in 1938 provided a petrological study which was to be the major reference for more than thirty years, and Hills in 1934, 1938 and 1940 summarised the physiography and probable ages of the volcanics with arguments which were to largely stand the test of radiometric dating in the 1960's. From 1940 to 1963 regional studies predominated and nine areas within the volcanic province were studied and mapped in detail. Thus by the 1960's a good background was available for the studies which now attempted to understand the province as a whole. These studies have included the four aspects already mentioned - morphology, cataloguing, petrology and speleology - and also radiometric dating, tectonic setting of the province, and detailed geochemistry and geophys ics. They coincided with the increased world-wide interest in volcanism which has been inspired by advances in space exploration. References Brough-Smyth, R., 1858, Q. Jl. geol. Soc. Lond., 14^, 227-235. Joyce, E.B., 1976, Abstracts, 25th International Geological Congress, Volume 3, 924. Selwyn, A.R.C., 1859, Q. Jl. geol. Soc. Lond., JU6, 145-150. Tyers, C.J., 1840, Report of an expedition to ascertain the boundary .... between New South Wales & South Australia. Wathen, G.H., 1853, Q. Jl. geol. Soc. Lond., 9_, 74-79. Westgarth, W., 1848, Australia Felix or a historical and descriptive account of the settlement of Port Phillip. 290

THE MID-CENOZOIC EXTENT, CONTINUITY AND GEOTECTONIC DEVELOPMENT OF A CONTINENTAL RIFT SYSTEM THROUGH WESTERN NEW ZEALAND: IMPLICATIONS FOR THE AGE OF ALPINE FAULT INCEPTION Peter J. J. Kamp University of Waikato, Hamilton A comprehensive analysis of the structure and sedimentary geology of onshore and offshore western New Zealand has identified the middle Eocene to early Miocene occurrence, and development, of a 1200 km long and 100-200 km wide continental rift system. Four phases of rift development occurred: (1) infra-rift subsidence, (2) active axial trough subsidence, (3) expanded rift subsidence involving collapse of the rift shoulders, and (4) incipient seafloor spreading. The spatial and temporal distribution of these phases identify a northern rift segment and a southern rift segment, and also that rifting propogated from both the north and the south. A new synthesis of the seafloor spreading history of the Southwest Pacific shows that the northern rift segment linked with a seafloor spreading centre in the Norfolk Basin, and the southern segment linked with the Southeast Indian Ridge. This is corroborated by the good correlation between the ages of seafloor magnetic anomaly lineations colinear with the rift and the biostratigraphic ages of rifting. The age and continuity of the rift system preclude any pre-Miocene transcurrent displacement on the Alpine Fault; a 23 My B.P. early Miocene age of inception is indicated by the age and pattern of rift disruption attributed to compression originating at the Australia-Pacific plate boundary.

SEDIMENTARY BASIN MODELLING: 1

CONSTRAINTS FROM THE BASS BASIN 2

G.D. Karner , M. Etheridge , J. Branson2 and A.S. Scherl2 ^Department of Geological Sciences, University of Durham, Durham 2 Bureau of Mineral Resources, Canberra Stretching of the lithosphere by brittle and ductile failure of the crust and mantle respectively results in competing isostatic effects of crustal subsidence and sub-lithospheric uplift. This results in a sedimentary basin characterised by two fundamental phases of subsidence; an initially rapid isostatic subsidence which forms the rift valley, followed by a slower decaying thermal subsidence which results in the thermal or flexural basin. Further, the relationship between the rift and flexural basins is controlled by the degree of depth-dependent stretching in which the crust and mantle are extended by different amounts. As this type of stretching is characteristic of a number of sedimentary basins (for example, the Vienna and Pannonian Basins and the Californian Miocene Basins), it must be considered in basin development. The form of subsidence within both the rift and flexural basins and the regional crustal structure are strongly modified by the thermo-mechanical properties of the lithosphere which become reset during basin initiation.

291

We have modelled the behaviour of the lithosphere following depthdependent stretching by assuming that its post-stretch response to surface and sub-lithospheric loads approximates that of an elastic plate overlying a weak fluid. The temporal and spatial variations of plate rigidity relate to the re-equilibration of the plate's temperature structure by vertical and lateral heat flow following rifting. With this model, it is possible to investigate the tectono-stratigraphic development of the resulting sedimentary basin, its evolving crustal structure and in particular, its free-air gravity effect. Since the stretching history of a basin is intimately linked wi£h the thermal structure and hence rigidity of the lithosphere, the observed gravity anomaly of a sedimentary basin can feasibly be used to infer the thermal and stretching history of the basin. The gravity anomaly of a sedimentary basin is the result of a complex interaction between the mechanical properties of the lithosphere, the sediment loading history within the basin, and the thermal age of the basin. The magnitude of the anomaly is a direct indication of the basement rigidity at the time of maximum sediment loading, whereas the anomaly shape is primarily related to the width of the rift basin. Large positive anomalies are characteristic of basins with relatively rigid basements while large negative anomalies occur over basins with relatively weak basements. The total sediment thickness has only a minor effect on the anomaly amplitude or shape which can be readily appreciated by comparing the anomalies of the Bass Basin 15 mgals, 6-9 km), Gippsland Basin 40 mgals, 6-10 km), and Torquay Basin 40 mgals, 3-4 km). Modelled gravity anomalies are generally small (± 10 mgals), consistent with observations from many sedimentary basins. For old sedimentary basins (> 100 m.y.), the gravity anomaly is dominated by the effects of rift and flexural basins. However, for younger basins, the thermal anomaly within the sub-lithosphere contributes a competing gravity effect related to the degree of lithospheric stretching. We have applied this modelling philosophy to the Bass Basin using reflection seismic and gravity data from the 1982 BMR Bass Basin survey. The observed distribution of gravity anomalies within the Bass Basin suggests that the basin centre is characterised by maximum crustal (brittle) stretching of 6 v 1.45 and mantle (ductile) stretching of S v 1.4. These stretching values imply maximum thicknesses of ^ 3 . 2 km and ^ 5.0 km for the flexural and rift basins respectively. However, stretching on the periphery of the Bass Basin proper is more consistent with essentially only crustal stretching (max. 5 ^ 1.25), developing flexural and rift basins of ^1.3 km and ^ 4 . 1 km maximum depth respectively. As the distribution of ductile and brittle stretching must be balanced over the extended area, the local imbalance of 6 and $ suggests that ductile stretching must be regionally developed over the Bass Basin and adjacent areas while brittle stretching tends to be localised, thereby producing numerous crustal rifts (or rift basins) and related depocentres overlain by poorly developed flexural basins.

292

THERMALLY INDUCED UPLIFT AND LITHOSPHERIC FLEXURAL READJUSTMENT OF THE EASTERN AUSTRALIAN HIGHLANDS 1

Garry D. Karner^ and Jeffrey K. Weissel

^"Department of Geological Sciences, University of Durham, Durham Lamont-Doherty Geological Observatory, Palisades, New York Australia can be subdivided into three fundamental regions that differ in topographic wavelength, basement flexural rigidity and crustal heatflow: (1) Western and central Australian topography is characterised by 8001600 km wavelengths, regional isostatic compensation (or its equivalent parameterisation, Te, the effective elastic thickness of the lithosphere, 80<Te<100km) and relatively low heatflow. (2) Northeastern Australia, in contrast, is characterised by intermediate wavelengths of 400-800km and basement strength (10<Te<20km). (3) The southeastern highlands, however, are anomalous; they are characterised by essentially local compensation (Te ~ 0), small wavelengths (200-400 km) and elevated crustal temperatures. Also, MAGSAT data, which is considered to reflect the temperature structure of the crust, shows a close association with the observed wavelength distribution of Australian topography. It appears, therefore, that the thermal and flexural properties of the southeastern Australian lithosphere have been significantly reset relative to northeastern, central and western topography. We suggest that this resetting process and subsequent thermal re-equilibration of the lithosphere helps to explain many geophysical and geomorphological features of southeast Australia. We accept that the southeastern highlands represent remnant mountains of the Palaeozoic Lachlan fold belt and that the abundant evidence for river rejuvenation reflects both regional isostatic rebound of the highlands due to erosional unloading and tectonically induced variations in stream base level. We believe that the highlands, rather than being tectonically quiescent since their formation, have been thermally overprinted by a major event in the upper Cretaceous - Lower Tertiary. Such a thermal event results in a rapid, initial isostatic uplift of any pre-existing topography due to thermal expansion of the lithosphere. Our preferred source for this event relates to the thermal anomaly associated with rifting of the Australian continent which produced the Tasman Sea. Lateral heatflow from the developing rift progressively reduces the flexural rigidity of adjacent lithosphere while rapidly diminishing with time and distance from the rift. Its initial amplitude is highly dependent on the lithospheric stretching history. The close association of margin width with topographic wavelength along the east coast attests to the relationship between stretching history, topographic asymmetry, and lithospheric rigidity. The failure of other Australian (passive) margins to develop rift induced topography relates to the time interval over which the rift develops and the nature of the transition between stretched and unstretched lithosphere. Evidence for a short-term, high intensity thermal event is suggested by elevated palaeo-temperatures as determined by vitrinite reflectance and secondary thermally-induced rock magnetisation components within the Sydney Basin. Low palaeo-temperatures, however, exist along the southern margin as determined by fission track data. Uplift is simply demonstrated by the subsurface elevation of marine sediments from the Sydney, Gippsland and Otway Basins. Widespread Tertiary lava fields and hotspot/hotline related volcanic centres throughout the eastern highlands are considered to play only a secondary role in modifying the thermal structure of the crust. In particular, volcanic activity is capable of generating uplifts of 50-100m. This observed uplift has resulted in stranded dune systems in the Mt. Gambier region of South Australia and probably controls the drainage divide of the entire highlands. 293

Associated with the lateral propagation of heat is an isostatic adjustment of the surface and hence a change in stream-erosion baselevel. Flexural rebound of the topography due to renewed higher erosion and denudation rates amplifies the thermal uplift, thereby of the southeastern producing the characteristically asymmetric form highlands. After the initial thermal uplift and during the renewed erosion of the topography, the flexural rigidity of the lithosphere is reset at a rate determined by the thermal diffusivity of the lithosphere. The short phase of rigidity resetting reactivates loads, such as surface topography, and results in a short wavelength subsidence which competes with the longer wavelength thermal uplift. Load reactivation also results in an increased crustal thickness relative to the pre-thermal event thickness. However, the excessive crustal thicknesses of the southeast highlands (45-53km) suggest the existence of loads in addition to the surface topography. Similar loads are required to explain the observed crustal thicknesses and foreland basin development within the Alps, Appalachians, Apennines and Carpathians. As the lithosphere thermally re-equilibrates, the increasing flexural rigidity with time results in the subsidence of adjacent areas. Cenozoic deposition within the Murray Basin and submergence of the southeast coast (resulting in drowned river valleys) reflects this peripheral mountain-related subsidence.Erosion continues to modify the readjusting highland topography.

PETROLEUM

POTENTIAL

IN THE

SW-PACIFIC

ISLAND

ARCS

H.R.Katz Pacific Geo Consultants, Lower Hutt, New Zealand From the Manus-New Ireland basin in the northwest to Tonga in the southeast, 5 major regions are discussed which exhibit a potential for petroleum. In these island arcs - located along the Indo-Pacific plate boundary - , basins have formed up to many hundred kilometres long that are filled with 3-5 km thick sediments of Tertiary age. The oldest sediments in the various basins are late Eocene in Tonga and Fiji, Oligocene in New Ireland, and early Miocene (perhaps including late Oligocene) in the Solomons and New Hebrides; in Tonga, an early Tertiary sequence nearly 1 km thick was drilled into. Because of the open-marine, volcanic archipelago setting of the basins, sediments are restricted to indigenous, mixed volcanic and organic components. The latter are related to reef and reef-associated environments, forming fringing and pinnacle reefs or reef-derived breccias and calcarenites. Organic limestones developed as carbonate platform deposits exist particularly in the northwest (New Ireland and partly Solomons), but also in Tonga. Volcaniclastics which make up the bulk of sediments range from rudites to greywacke silt-sandstones and shales, and are of depositional environments that range from near-shore to bathyal; slump deposits and turbidite sequences are widely present. Pelagic shales and marls occur locally.

294

F i g . l - Hydrocarbon-prospective sedimentary basins (hachured) in the SW-Pacific island arcs. Bathymetric contour is 2000 m.

295

Little is known about the potential of hydrocarbon generation in these sediments. No possible source rock formations have been identified, but environments of restricted circulation with possibly euxinic conditions may have developed in stagnant backreef and lagoonal areas;* the mainly algal derivation of most limestones may have enhanced the source quality of deposits. Rapidly buried forereef slopes and the formation of silled basins in deeper water, between rising volcanic edifices, may have provided additional environments with a potential for source rocks. Volcanic activity may have favourably contributed to the generation and maturation of hydrocarbons by providing for both a high heat source and the conditions for anoxic environments. Where sufficient organic matter was included in the sediments, these could thus .become mature source rocks. The presence of mature hydrocarbons, both oil and gas, has indeed been confirmed in Tonga and Fiji. Potential reservoirs are mainly seen in reefal limestones. These are widespread and locally attain great thickness. Sandstones are mostly impure, quartz-deficient and tight. Locally, however, volcaniclastic, turbiditic sandstone and calcarenite, particularly when fractured, may provide suitable reservoirs. Traps are of both stratigraphic (bioherms, unconformities) and structural type, the latter in fault blocks and anticlines chiefly along basin margins. The total prospective area amounts to 200-220,000 km2. Most of this lies offshore in water depths of a few hundred to 2-3,000 m. A total of 13 wells has been drilled of which 4 were on offshore locations; 4 wells were abandoned before reaching their target. Total depth drilled is 23,961 m; the deepest wells are in Fiji (Great Sea Reef no.l, 2839 m) and Tonga (Kumimonu no. 3, 2636 m). Thus exploration in these island arcs is at a very early stage. The potential for hydrocarbons is there, however, and there is every reason to intensify active search for these resources.

296

THE TRAINING OF BAREFOOT VILLAGE PROSPECTORS FOR RESOURCE EXPLORATION IN THE DEVELOPING COUNTRIES OF ASIA AND THE PACIFIC

M.B. Katz School of Applied Geology, University of N.S.W., Kensington The 1970 UN report on mineral resource development with particular reference to developing countries stressed the role that villagers, farmers, herdsmen and nomadic tribes can play as potential prospectors. As the most important resources of developing countries are the human resources, the contribution of these individuals to natural resource development can be important if these people are trained or exposed to the fundamentals of geosciences. Strategies for geoscience education in developing countries place the most emphasis on tertiary level institutional building and on strengthening both the graduate and post graduate sectors. The role of geoscience education at the secondary and even primary levels is now also receiving some attention. However a practical, direct and grass roots approach to this problem of geoscience education would be to establish training courses in prospecting in the ruralvillage areas. These prospecting training schemes can be made to be an important and vital complementary activity to the more formal training of geoscientists at the universities. The villager-herdsmen have an intimate, instinctive knowledge of their environment and they are aware of the topography, water holes, rock types and consciously, or otherwise, monitor for volcanic activity, landslides, earthquakes, floods and other natural hazards. These rural people often set up cottage industries in quarrying, ornamental and gem stones, rock crafts and building stones, and they are keenly aware of rocks of unusual colour, lustre, density, and breakage and shaping properties. Thus they can, with little training, be converted into barefoot prospectors trained in prospecting for economic minerals, energy and water resources. In certain situations they also can be trained to take routine measurements on, and possibly maintain, various geological, geophysical and geochemical equipment including monitoring devices for flood control, volcanoes, earthquakes and landslides. These rural barefoot geoscientists in the developing countries could be as important to natural resource development as the legendary prospectors of Canada, U.S.A., Australia, Finland and elsewhere. Large numbers of barefoot prospectors could be trained at little expense if an overall plan is developed by the geoscientific institutes of these countries. The role of these geoscientific education institutes would be to set up training courses for village prospectors and to plan and co-ordinate all field training activities. The syllabus and detailed curriculum would be formulated with the aid of the planning authorities with special educational needs designed for the speedy training of semiliterate - illiterate rural folk. Audio visual methods would be most important and special sets of economic minerals, rocks, charts, maps and other geoscientific educational material would be collected and assembled into portable kits. These kits would be distributed to the geological surveys, university field research teams and state and multinational corporations. Other potential instructors in larger rural towns could be local headmasters and science teachers.

297

One of the leading agencies for these training programs would be the geological survey. During survey activities in various parts of the country the local villagers, herdsmen and even tribesmen would be encouraged to participate in survey activities and at the same time be trained in elementary prospecting techniques. Ideally when the survey completes its work it should leave behind trained cadres of prospectors that could continue their prospecting with promises of substantial rewards if they find anything. The geological survey could accommodate this program without any particular increase in general cost or time, and although the program would be scattered and sporadic it would be concentrated in resource potential areas. Gaps in this program could be filled by University field research groups where staff and students investigations in remote areas would also have a compulsory element of training local prospectors. The geological societies could also play an important role here by publicizing these programs of training and educating the rural populations to be aware of the mineral, water and energy resource potential of their areas, as well as the problems related to local natural hazards. Obviously state mining corporations and even the multinational companies should be encouraged to support these training programs. These prospector training schemes can be made to be an important and vital complementary activity to the more sophisticated and modern techniques of resource exploration. In some countries regional centres of prospecting training or local schools of mines could be established to formalize the training on a more technical level and these schools could be located in well known mineral centres. These geoscientific cadres would be a great and important source of general geological information. Remote and unknown outcrops would be identified and access routes established and this would assist regional mapping and inventory surveys. Sites of instability, unusual phenomena, anomalous water levels and other harbingers of possible natural disasters could be identified by these cadres and brought to the attention of the authorities. The geoscientific education of the rural folk would not only be of great potential importance in locating mineral, water and energy resources, but would also contribute to the mitigation of natural geological hazards. This program would be an important contribution to self reliance and to the social and economic development of the country.

298

CONTROLS OF GOLD MINERALIZATION IN THE WOODS DYKE SWARM, VICTORIA

POINT

Reid R. Keays 1 and Terry H. Donnelly2 -^Department of Geology, University of Melbourne 2 Baas Becking Laboratory, Canberra The Woods Point dyke swarm is comprised of hundreds of narrow subparallel igneous dykes and dozens of pipe-shaped "dyke bulges11 within strongly deformed early Palaeozoic turbidites of the Melbourne Trough. The bulk of the total gold produced (98,000 kg) has come from three regional curvilinear lineaments the most important of which, the Ross Creek Structure, coincides with the axial trace of the Walhalla synclinorium and stretches for 120 km. These lineaments represent tensional breaks along which the dyke swarm was introduced prior to major Upper Devonian silicic volcanic activity. They also acted as channelways for the later introduction of gold-bearing solutions from deeper in the dyke swarm system. The dykes range in composition from hornblende peridotite and hornblendite through gabbro porphyries and basalts, lamprophyres, and diorite porphyries to quartz-feldspar porphyries and aplite (junner 1920; Green 1974); the parental composition of the dyke swarm magma was probably basaltic andesite. Individual dykes are zoned laterally with mafic margins to more leucocratic interiors; the swarm as a whole also appears to be zoned vertically, from ultramafic at depth to dioritic at higher levels. Although gold mineralization can be developed in any of the rock types, the most important host is dioritic. The ultramafic members of the dyke swarm contain appreciable quantities of Pt-Pd-Au bearing Cu-sulphides; one of these (the Thomson River Copper Mine) has been mined for these metals. In general, the dykes conform to the dip and strike of the sedimentary host rocks. They are narrow, averaging about 2m in width (Junner, 1920) but locally can broaden into pipelike bulges up to 600 m x 100 m in plan. The dyke bulges are, in general, the main repositories of gold mineralization. However the single richest "line of reef11 in the entire state, Cohen's Reef at Walhalla, is associated with a severely altered dyke that averages a metre in width but pinches and swells and has been strongly deformed subsequent to its emplacement. Mineralization is associated with a variety of quartz veins. The classic ladder veins of the Al and Morning Star Mines occur in reverse faults that offset the dykes. Mineralization also occurs in reefs along the walls of the dykes, in stockworks and gash reefs within the dykes, and in quartz stockworks within the adjacent sediments. Vein margins to the quartz veins have been hydrothermally altered forming wall rock alteration zones from 10 cm to 3 m wide. The hydrothermally altered rock in a number of dykes averages 0.7 gm/tonne gold. In some cases, much of the dyke rock is altered and weakly mineralized; taken together with the mineralized quartz reefs (which averaged close to 30 grams/tonne in most of the dyke swarms) the extensively altered dykes constitute potential for bulk tonnage mining. A good example of such a dyke is the Loch Fyne Mine which may have potential reserves of 6,000,000 tonnes averaging 3.6 grams/tonne above the 5 level.

299

Isotope studies of sulphides, carbonates and quartz from mineralized veins in the A1 mine suggest that the vein constituents were derived from three different sources (Green et al., 1982). The carbon and oxygen isotopic composition of the carbonates suggest a magmatic origin for the C02 while the oxygen isotope composition of the quartz suggests a metamorphic origin for the silica. Sulphur isotopic determinations indicate the vein sulphur could not have been derived from adjacent sedimentary rocks, nor exclusively from the dykes; metamorphic waters of marine origin are the preferred source for sulphur. It is suggested that a genetic link exists between gold mineralization and the magmatism that produced the dyke swarm. The .mineralizing process was initiated when tensional rifting permitted the introduction of sulphurundersaturated, gold and platinoid-enriched magmas of either deep crustal or upper mantle origin into high crustal levels. The magma became sulphursaturated when emplaced within the wet geosynclinal sediments. As a result, gold-and platinoid-enriched immiscible sulphide droplets settled out of the magma together with early formed olivine, pyroxene and hornblende which lagged behind the magma to produce hornblende peridotites and hornblendites containing weak to strongly disseminated Au-Pt-Pd copper sulphide mineralization. The Au-Pt-Pd-depleted magma continued to move upwards to generate dioritic and other rock types. Hence, at the end of the magmatic stage the dykes were zoned from ultramafic at depth to dioritic at shallower levels. As the dykes cooled to less than 350°C, ascending solutions containing CO2 of magmatic origin leached gold from the immiscible magmatic sulphides in the ultramafics and transported it upwards to deposit it in structures created within the overlying more competent (and brittle) dioritic rocks. According to this model, mineralization should be developed anywhere the deep seated lineaments intersected favourable structural sites (e.g. ladder veins in diorites), lithologies (e.g. black, graphitic slates as in Cohen's Reef) or where the solutions may have ponded at the tops of dykes (e.g. Loch Fyne Mine, Al Gold Mine). References Junner, N.R., 1920, Proc. Aust. Inst. Min. Metall. 39 — 127-258. Green, A.H. 1974, Unpubl. M.Sc. Thesis, Uni.Melbourne Green, A.H., Donnelly, T.H., Jahnke, F.M., & Keays, R.R,., 19S2, Mineral Deposita, 17, 175-192.

SULPHIDE IMMISCIBILITY AND THE GENESIS OF HYDROTHERMAL ORE DEPOSITS: THE UPPER MANTLE CONNECTION Reid R. Keays and Paul R. Hamlyn Department of Geology, University of Melbourne, Melbourne A model is developed which accounts for the genesis of hydrothermal Au and volcanogenic Cu-Zn-Au deposits. This model requires the emplacement of specialized, high magnesium magmas of upper mantle origin into rifted oceanic or continental crust. A feature of these magmas is that they become S- saturated at a late stage and that when solidified the ore metals are hosted by reactive immiscible magmatic sulphides. Second stage melts such as boninites may be especially important as these are enriched in the oreforming metals. The recognition of these specialized magma types and their tectonic settings can be used to design exploration programmes. 300

It will be shown that sulphide immiscibility of mafic silicate melts plays a major role in the formation of not only "magmatic" sulphide deposits but also of many hydrothermal ore deposits. Most silicate melts are S-saturated when emplaced into the upper crust and as a result are significantly depleted in many of the ore-forming chalcophile and siderophile metals such as Ni, Cu, Pt, Pd and Au. These metals have high partition coefficients in favour of sulphide melts and as a result of early S-saturation of silicate melts are scavenged by immiscible droplets which remain either in the source regions of the magmas or in high level magma chambers. Evidence for widespread S-saturation of basic silicate melts is provided by FeO and S relationships in MORB glasses as well as the platinoid metal contents of upper mantle spinel lherzolites, both in continental and oceanic regions. Indirect evidence that sulphur saturation of partial melts must be a widespread phenomenon is provided by considerations of core- mantle equilibria. If the Fe-Ni core of the earth contains FeS, as moment of inertia considerations and analogies with iron meteorites demand, then this must have segregated from a mantle in which the silicate melt fraction was S-saturated. Hence, the partially solidified upper mantle consisted of silicate crystals sitting in a sulphide-saturated silicate melt. During magma genesis all of this former "interstitial" melt is consumed and hence produces partial melts which are generally S-saturated. The enhanced precious metal contents of high temperature magmas such as komatiites and picrites indicate that these magmas did not become Ssaturated until they were emplaced into the upper crust or that fractional crystallisation has been minimal. The reason for this is that the S capacity of silicate melts increases dramatically with increasing temperature, each 100°C increase in temperature producing a 5-7 fold increase in the S capacity of the magma (Haughton et al., 1974). The elevated precious metal contents of boninites (unpublished data, Keays & Hamlyn) are believed to result from the fact that the parental magmas to these lavas were second stage melts which inherited sulphides left behind by S-saturated first stage melts. Previous work (Keays and Scott, 1976) has demonstrated that the mineralogical siting of Au in rocks determines in large part the suitability of the rock as a source for Au. Only Au associated with sulphides is available for the ore- forming process; that which is locked up in oxide and silicate phases is generally inaccessible. The same principal applies to other elements such as Cu and Zn. There are several reasons why the mineralogical siting of ore-forming metals in sulphide droplets is important. The concentrations of metals in the sulphide are up to 1000 times greater than they are in the rock as a whole. The sulphides sit in highly accessible sites along grain boundaries. They react very rapidly with pore fluids compared to the sluggish reactions of silicates. In the case of Au, reaction of the sulphides with aqueous fluids produces HS which forms the highly stable Au(HS) complex. In contrast, reactions between pore fluids and silicates are not only sluggish but will buffer the composition of the fluids and may therefore prohibit metal transport. For example, active serpentinization of ultramafic rocks produces conditions that are so reducing that sulphides in the rocks are often reduced to native Fe, Ni, Cu and platinoids. The reducing conditions are generated by the oxidation of ferrous iron in the ferromagnesian minerals to form ferric iron in magnetite and other oxides. Metal transport will generally be inhibited until reactions between pore fluids and the ferromagnesium minerals in mafic and ultramafic rocks have gone to completion.

301

In summary it is suggested that high level convecting hydrothermal systems will only generate major hydrothermal Au and volcanogenic base metal mineralization if they interact with precious metal-enriched sulphides in igneous rocks generated from high Mg magmas. Convecting systems that do not tap such favourable source rocks will fail to generate significant mineralization.

References

Haughton, D.R., Roeder, P.L. & Skinner, B.J., 1974, Econ. Geol. 69, 451-467. Keays, R.R. & Scott, R.B. 1976, Econ. Geol. 71, 705-720.

BORECORE TESTING FOR ASSESSING KEY ASPECTS OF COAL UTILISATION Norbert V.P. Kelvin and John Baker ACIRL, North Ryde Examination and analysis of borecore samples of coal provide good indications of the preparation behaviour of the coal and the ability of the coal represented by the sample to be used economically for: - combustion - coke production - conversion to gas and liquid fuels and pure carbons The mass of borecore sample determines the extent of testing and analysis that can be carried out. The greater the mass of sample available, the more extensive the testing that can be carried out and consequently, the better the prediction of behaviour in commercial operations. 1 • Coal preparation characteristics. As more Australian coals require to be prepared before use, the most important study on any new sample is that of assessing its preparation characteristics. ACIRL has developed a borecore pretreatment procedure to ensure that subsequent laboratory float-sink data can predict with greater certainty the coal's preparation characteristics in commercial washery. Sample pretreatment and washability studies require four main steps: (a)

controlled breaking of the borecore to conform to expected washery feed size distribution

(b)

wet tumbling to simulate physical degradation of coal matter and effect of water on the coal's mineral matter

(c)

float-sink testing and analysis of each wet-tumbled size fraction

(d)

examination of the very fine coal to identify suitable treatment methods

This data is then combined and fed into a computer prediction model of behaviour in a commercial washery. However, pilot plant trials on larger samples (10 - 100 tonnes) are still required to give a more satisfactory prediction of preparation behaviour.

302

2. Combustion characteristics. Tests are available which are suitable for predicting the behaviour of coal for most aspects of its combustion in conventional fired installations when a borecore size sample of the coal is available. ' Of particular interest at the present time to both coal marketers and users is pulverised coal combustion in both electric power stations and the cement industry. ACIRL is developing a complete coal technology package to provide a service in this area. Part of that package allows borecore size samples of coal to be tested to predict its large scale handling and combustion behaviour: (a) spontaneous combustion that can be expected while storing the coal, (b) handling problems that can be expected in bins and transfer points, (c) milling behaviour in pulverising the coal, (d) combustion behaviour in the boiler or kiln, (e) slagging and fouling that can be expected in the boiler, (f) requirements for the control of solids emission from the boiler stack. Techniques are already available to cover these aspects and developments continue. Of particular interest for Australian coal marketers and users are the areas of coal milling and the control of airborne solids emissions. Milling. Standard tests such as the Hardgrove Grindability Index and Abrasion Index are available but have been found to be less than completely satisfactory. For this reason improved tests already exist and continue to be developed. Solids emissions. An extensive service has been developed to enable electrostatic precipitation requirements to be predicted from borecore size samples of coal. This service has been used by the majority of Australian electricity generating authorities and many overseas power station consultants. With the growing popularity of fabric collectors a parallel service is developing which ultimately will be able to be used when large borecore size samples are available. 3. Conversion characteristics. Chemical and petrographic tests can indicate potential suitability for either liquefaction or gasification. Liquefaction. ACIRL has developed a semi-continuous 4-L autoclave procedure for determining oil yields on samples in the range 0.5-10 kg. This test generally gives a good prediction of oil yields likely to be obtained in bench-scale continuous reactor studies. ACIRL's continuous reactor requires a minimum sample of 250 kg for a single continuous run and preferably 500-1000 kg to enable duplicate continuous runs. Moreover, sufficient oil samples are generated in continuous runs for further upgrading and refining studies by petroleum laboratories. The heavy deashed liquefaction products can be carbonised to produce samples of electrode carbons for preliminary evaluation in, say, aluminium smelting. Gasification. Borecore samples can be tested to give an indication of gasification behaviour in either slagging (e.g. Krupp-Koppers) or fixed bed (e.g. Lurgi) gasifiers. Properties such as swelling and caking propensity and ash/slag viscosity-temperature characteristics can be determined on borecore samples. 4. Carbonisation. The best predictor of commercial carbonisation behaviour is the 280-kg coke oven which would require several large diameter cores to be composited. Smaller samples can be carbonised in a 7 kg oven which does not predict coke strength quite as well as the 280 kg test. ACIRLfs 280 kg capacity oven can also be used for testing coking potential of small borecore samples. This involves testing of individual coals and blends in specially prepared coke oven charge segments.

303

METALLOGENY AND TECTONIC DEVELOPMENT OF SOUTHEASTERN AUSTRALIA Kazys J. Kemezys Consultant, Canberra Relatively recent drilling in the Gulf of California has suggested that in an environment of high sedimentation above a zone of accretion, mantle material does not flow out to the surface as submarine basalts to form ridges and rises, but is dispersed throughout the sedimentary sequence in the form of dolerite sills and dykes. To quote from the Deep §ea Drilling Project Scientific Staff, 1979: "We envisage a model of crustal formation and sea-floor spreading in the Guaymas Basin involving intrusion of basaltic magma into soft, wet, young sediments as sills, dikes, and other intrusions. Therefore, oceanic layers 1 and 2 become completely intercalated with a gradational contact." Lonsdale and Lawver (1980) add that: "Similarly, at the head of the gulf basaltic rocks are found only as intrusions in the thick alluvial fill of the Salton Trough (...), although lighter fractionated magmas have risen to form rhyolite domes ..." The common occurence of dolerite sills and dykes in the Siluro-Devonian rocks of the Newell Basin part of the Lachlan Fold Belt (Kemezys, 1978) may indicate that the Newell Basin was at that time an accretion zone similar to that of the Gulf of California. The dolerite intrustions occur mainly as sills within the Wellington - Cooma facies, as plugs within the Louth Mitta Mitta facies, and as dykes towards the Omeo Land area (Kemezys, 1978, fig. 2). Granitic intrusion in the Newell Basin - Omeo Land area commenced at about 440 my and was continuous until about 360 my. Considering sedimentation and intrusion together it is possible to envisage the following situation: Some time in the Silurian (440 my granites) the Newell Basin becomes an extension or spreading zone in a marine environment. Thinning of the crust results in increased heat flow which melts part of the Ordovician and older sedimentary pile producing in places stratiform granite melts, in places granite intrusion and volcanism, and in many places large and small hydrothermal systems. The crust breaks apart and faults tap mantle material which is intruded into wet sediments as dolerite sills and plugs. Hydrothermal systems initiated by sharp heat gradients produce a variety of metal deposits - massive sulphides, porphyry copper, lode tin, gold, etc. - whose specific characteristics are directly related to the variety of geological environments within the Newell Basin. A separate episode of continuous granitic intrusion took place in the Melbourne Basin (Kemezys, 1978, fig. 2) in the period 380-320 my. This episode adds weight to the identification of the Melbourne Basin as a separate entity in southeast Australian geology. The granites have in places associated volcanic rocks. Metallogenically, these granites are tin and/or tungsten bearing both in Victoria (Beechworth) and Tasmania (Aberfoyle) and have produced some very big mines where they have intruded late Proterozoic reactive carbonates in western Tasmania and King Island.

304

Whereas the Newell Basin hydrothermal metallogenic systems operated in a marine environment, the Melbourne Basin systems operated in a subaerial environment. The western Tasmanian Cambrian tectonic and metallogenic province is probably geologically similar to that of the Newell Basin Siluro-Devonian, but it is likely that the exposed part represents only a small portion of a much more extensive system now concealed under younger rocks. The tintungsten deposits on the one hand and the massive sulphide deposits on the other hand are fortuitously closely associated in space, but are totally separate metallogenic systems. References Deep Sea Drilling Project Scientific Staff, 1979, Geotimes, 24, 6, 18-20. Kemezys, K.J., 1978, J. Geol. Soc..Aust., 25, 2, 97-107. Lonsdale, P. & Lawver, L.A., 1980, Bull. Geol. Soc. Am., I, 91, 555-569.

COAL,THE CHALLENGE OF THE FUTURE FOR INDONESIA Roeslan Kendarsi Directorate of Coal, Bandung The development of coal in Indonesia is not caused by the economic law of demand and supply. It is based on the government policy to diversify the energy. In order to continue the National long term development program, oil must be the main export commodity. Consequently, coal will substitute for oil for domestic supply. The coal will be utilised for powerplant and industries such as cement manufacturers. In the long run, coal will also be utilised for other purposes. Coal production is projected to increase from 700,000 M Ton/year in 1984 to 14,400,000 M Ton/Year in 1990. The development of coal however, involves a coal - chain process, that is the development of mining, transportation and consumers. Moreover, the geographical location of coal deposits in terms of its consumers, in infrastructure facilities, the reserves and quality are some of the constraints being faced. The development will also meet a considerable challenge in the field of technological know how, the environmental aspects, the progress of peat, nuclear and geothermal energy sources. In the long run however, coal will only be a substitute for oil. It cannot replace the role of oil as the main source of government revenue. Together with the development of other sources of energy,it will form the economic energy of Indonesia. Energy conservation is the best answer to safeguard and maintain oil as the main source of government income.

305

THE SEARCH FOR TIN DEPOSITS IN PENINSULAR MALAYSIA T.T. Khoo Department of Geology, University of Malaya, Kuala Lumpur The search for new tin deposits in Peninsular Malaysia in hardrocks and unconsolidated sediments has been continuously active since the discovery of tin in the peninsula. With the development of the tin mining industry it was eventually recognized that the peninsula can be divided into longitudinal western and eastern tin belts separated by a central gold belt. Tin deposits were recognized to be spatially and genetically related to the granitoids of the western and eastern belts. These two observations became major considerations for future research and exploration for tin in Peninsular Malaysia. With the depletion of alluvial tin deposits which have yielded most of the country's tin production, exploration for tin deposits in hardrocks has been encouraged for the past 25 years. Studies have been made to test the applicability of geochemical exploration methods for the location of tin deposits. General applicability of the methods such as residual soils analysis has been shown. Further studies are being actively pursued by SEATRAD Centre, Ipoh. Large scale regional geochemical exploration programme to search for hardrock tin, however, has yet to be done. Instead, the importance of diversification, has prompted the implementation of regional geochemical and geophysical exploration programmes for base metals and other minerals in the central belt by the Geological Survey of Malaysia. Studies into distinguishing tin-bearing from tin-barren granitoids have been made since the 1960fs. Trace element contents of granitoids associated and not associated with tin mineralization have been investigated and elements such as tungsten appear to be good indicators. But to date a wider study has not been made to ascertain the validity. A K-Ar and Rb-Sr age dating programme showed that tin-bearing and tin-barren granitoids cannot be distinguished by age except for the few bodies of Cretaceous granitoids in the central belt which are not tin-bearing. Tin mineralization is associated with both Upper Palaeozoic and Triassic granitoids which make up the bulk of the granitoids in the peninsula. The Cretaceous granitoids are found to belong to the magnetite-series granites which are not associated with tin mineralization. But the granitoids of the western and eastern belts associated with tin mineralization belong to the ilmenite-series. However, within the ilmenite-series granitic terrains, tin deposits do not occur everywhere. All these studies are hampered by poor knowledge of the granitoids which have hardly been mapped. Therefore, field mapping, search for characteristic wallrock alterations, heavy minerals provenance studies, etc. are still invaluable for exploration of hardrock tin deposits in the peninsula. Recent interesting speculations on the tectonic settings of economic deposits are evidently of little use for the exploration of tin deposits in the peninsula as what is really required are ways to locate more deposits within the already known tin belts. The search for tin deposits in alluvial and marine unconsolidated sediments has been extensively carried out by governmental bodies and private concerns. With the technical co-operation of various bodies the Geological Survey of Malaysia has carried out exploration for tin deposits in the Straits of Malacca and the South China Sea. Nearshore areas adjacent to onshore tin fields have also been investigated. No large tin deposits have been found in the offshore areas to date. However, the investigations have not been very detailed. Interesting results

306

have however been obtained from onshore exploration. In some places, tin deposits have been found in deep unconsolidated sediments. The geology of the bedrock and the unconsolidated sediment cover of the onshore and nearshore coastal areas of the peninsula is hardly known and the tin potential of these areas has not been thoroughly investigated. There are indications that the provenance of the deeper tin deposits may have no relation to outcropping or presently known source rock terrains. For the exploration and evaluation of the tin potential of these areas, it is essential to have a better understanding of the bedrock geology under the relatively thick core of unconsolidated alluvial and marine sediments, the Quaternary (and possibly Pliocene) geology, processes and events, the history of uplift and denudation of the Upper Palaeozoic and Triassic granitoid ranges and their cover, etc.

HYDROGEOLOGICAL PROBLEMS OF MINING UNDER WETLANDS, WAITAKO COALFIELD, NEW ZEALAND C.H. Kidd Groundwater Consultants (N.Z.) Ltd, Auckland Much of the coal reserves of the Waikato Coalfield in the north island of New Zealand underlies wetlands. The expansion of surface and underground mines must therefore include provision to control the flow of both surface and underground water into the mines. However dewatering of the unconsolidated sediments under the wetlands causes compaction of the peats and silts leading to settlements of the land surface which is unacceptable because of the environmentally sensitive nature of the area. This paper outlines some of the problems encountered and the approach taken to solve them.

PALAEOCURRENTS AND PROVENANCE OF CONGLOMERATES IN THE LAMBIE AND CATOMBAL GROUPS, CENTRAL WESTERN NEW SOUTH WALES Colin L.A. Killick Macquarie University, North Ryde Significant input of oligomictic conglomerate follows a major Frasnian/Famennian marine transgression in many locations in the Lambie and Catombal Groups. In the Mt. Horrible Syncline a prominent band of oligomictic conglomerate up to 120 m thick overlies marine sediments. In a few locations this is preceded by several metres of cross-bedded coarse sandstones and pebbly sandstones. Palaeocurrent measurements from the cross-beds show sediment transportation was from the southwest. Thickness isopachs and clast-size measurements in the conglomerate band indicate a western provenance. Deposition is considered to have occurred in an alluvial fan environment. A thin band of conglomerate above marine sediments in the Rydal Syncline, southeast of Mt. Horrible, may be distal deposits of the same alluvial fan system. Palaeocurrent measurements from the Curra Creek Conglomerate and underlying fluvial Kurrool Formation in the Mt. Arthur Syncline show sediment transport was towards the west. No conglomerate is found in outcrops west of Molong, possibly because of insufficient exposure. However, in the southern Catombal Group oligomictic conglomerate is again encountered above marine sediments. Measurement of palaeocurrent indicators in the conglomerate and in the predominantly silty, fluvial unit above indicate transport was towards the northwest. 307

B .Section measured along unnamed creek west jjj.^

GR 8 0 0 0 955^ •

Creek

Thickness In "metres

U00

.Section measured along Hiddle Arm

V/e I l i n g t o n .

Red and grey siltstone with beds of ollgom i c t i c c l a s t s u p p o r - Palococurrtnls. All locotions ted c o n g l o m e r a t e . mminfd. N« nf ~ III! iij n» 119 Oligomictic conglo-

P r e d o m i n a n t l y red s 111 s t o n e . Some fine, grained lltharenlte u n i t s u p to 2 m t h i c k w i t h troughs a n d paraJ* lei l a m i n a t i o n s . Son*, pebbly sandstone beds.

Palococurrtnls H I Arthur M

Sync I in*

V e r y f i n e to f i n e grained welI - Indurated quartzarenltes. Averaqe bed thickness 25 cm. Common parallel laminations, some cross-beds. Many shelly fossil horizons.

.Section measured along unnamed creek ENE of GR 5198 8229 Mudgee

K00

merate. Clasts predominantly rounded f i n e - g r a i n e d q u a r t z - Mt Horrible arenl te. l«r rib! Synclinf iidine M e a n o f 10 l a r g e s t I* axes " 3' c m .

1200

p m g o m i c 1 1 c , clastsupported conglomerate. Rounded, very fine-grained quartzarenlte clasts. Mean l e n g t h o f 10 l a r g e s t apparent axes • 19.3 c m .

Thickness in metres

V e r y f i n e to f i n e grained welI-Indurated quartzarenlte. Thin shelly fossil horizons throughout. Commonly thickly bedd e d (I m e t r e p l u s )

n*45

All locations examined Predominantly stones .

red

slit-

Predominantly dark grey si I t s t o n e w i th t h i n beds of r i p p l e d and bioturbated quartz* arenlte

Jligomictic, clastIsupported conglomerate. I R o u n d e d , very flne' grained quartzarenite c l a s t s . M e a n l e n g t h o f Ifj l a r g e s t a p p a r e n t long axes • 22.2 c m .

i 0

V e r y fine to finegrained quartzarenlte and sublItharenite. Some shelly fossil horizons. Beds usually <23 c m t h i c k , sometimes u p to I m .

° P r e d o m i n a n t l y red siltstone. S o m e finegrained litharenites and pebbly sandstones.

to c o a r s e - g r a i n e d q u a r t z a r e n l t e s a n d litharenites. Proportion of r e d si 1 1 s t o n e b e d s Increases upsequence. Some shelly fossils.

Polymictlc conglomerate. Average clast size 2 c m . Clasts of vein quartz, chert, f.g. q u a r t z I t e , silicic voles.

U Wellington

.Section measured along Canangle

Ck.

Mudgee,

Thickness In

4t. Arthur Syncline P r e d o m i n a n t l y red s 1 1 1 — s t o n e . Common beds of carbonate-cemented cong l o m e r a t e u p to I m thick.

0i i g o m i c t Ic c lastsupported conglomerate Clasts mainly very fine-grained quartza r e n l t e . M e a n o f 10 POlaeocurrents largest long axes • oil locations 22 c m . examined. Soul hern Colombo! Group

F i n e to v e r y f i n e grained quartza r e n l tes a n d s u b l I t h areni tes. Red s111stone increasing upsequence.

Mt. Frome Syncline

SILUR0-DEV0NIAN HILL END TROUGH Sofa Mt. Dulabree Syncline Mt Horrible Syncline

Orange

Bathurst 10 klm.

308

Rydal* Syncline

In some locations basal conglomerates occur below sediments of the marine transgression. In the Mt. Frome Syncline a polymictic basal conglomerate reaches thicknesses of as much as 120 nw This conglomerate is not considered to be related to the widespread oligomictic conglomerates on stratigr'aphic grounds. The age of the sediments in the Lambie and Catombal Groups is generally only very poorly constrained, not allowing precise correlation between synclines. However, the marine transgression does provide a useful, albeit diachronous, marker horizon. The occurrence of conglomerates in both the Lambie and Catombal Groups soon after retreat of the sea from those areas may indicate that they are at least roughly correlative and related to the same event, possibly an uplift in the area of the Siluro-Devonian Hill End Trough.

GEOLOGY OF PALEOZOIC AND MESOZOIC COALFIELDS IN SOUTHERN KOREA Bong Kyun Kim Seoul National University, Seoul, Korea The Korean Peninsula consists largely of Precambrian metamorphic rocks which are intruded by the Jurassic and Cretaceous granites. The Paleozoic and Mesozoic coalfields in South Korea are mostly confined to a NNE-SSW trending belt of the Ogcheon Zone. The northeastern part of the zone consists of non-metamorphosed sediments, while the middle and south-western parts consists of metamorphosed sediments, resulting in the change of coal beds into anthracite or graphite. Low-grade anthracite coal beds are found in the continental Cretaceous sequence, the so-called Gyeongsang Group, distributed in the southeastern part of Korea. Lignite beds of subordinate quality are found in the Neogene formations, scattered along the east coast of Korean Peninsula. However, the Cretaceous and Neogene coal beds are poor in quality and quantity, and not minable economically. Paleozoic coals, especially in the middle and southwestern parts of the Ogcheon Zone, are metamorphosed and pulverized to form graphitic coals in most areas. About 40% of the total reserves of Paleozoic and Jurassic anthracite is of low quality, having calorific values of 3,500 to 4,500 Kcal/Kg. Estimated total reserves in South Korea are 1.45 billion MT, of which about 90% is contained in the Permian Jangseong Formation and the rest in the Jurassic strata. Annual coal production has been increased from 13 million tons in 1971 to over 20 million tons in 1983.

THE HIMALAYAN ARC:

CONTINENTAL ANALOG OF OCEANIC

SDBDUCTION

Chris T. Klootwijk Bureau of Mineral Resources, Geology & Geophysics, Canberra Comparison of palaeomagnetic results from the Himalayan Arc and southern Tibet with simulated apparent polar wander paths (APWP's) for the Indian plate shows a pattern of rotations relative to the Indian shield, gradually varying from 45 degrees clockwise in the northwestern Himalaya to slightly counterclockwise in the Lhasa region. This pattern implies oroclinal bending in post-Early Miocene times and continental underthrusting of Greater India beneath the Tibetan Plateau over at least 650 km at the longitude of Western Nepal.

309

Available palaeomagnetic observations support Powell and Conaghan's (1) and Seeber et al's (2) steady state model for formation of the Himalayan Arc with refinements as follows: 1) Collision between Greater India's straight northern boundary (1,3) and southern Asia occurred at equatorial latitudes, with progressive suturing from about the Cretaceous-Tertiary time boundary in the Northwestern Himalaya till about 55 Myr in the Eastern Himalaya. 2) Continuing convergence and indentation of Greater India into southern Asia over about 2000 km up to the Early Miocene resulted in southeastwards extrusion of Indochina. 3) Plane indentation became then of limited importance, and convergence was taken up mainly by counterclockwise rotational underthrusting of Greater India along the Main Central Thrust (MCT) beneath the Higher Himalaya and the Tibetan Plateau up to the Kun Lun region, i.e. over a distance of up to about a 100 km. 4) At a late stage in this underthrusting process when the Narbada-Son lineament and the Aravalli tectonic trend on the Indian shield had advanced in proximity to the MCT, a conical downwarp developed in the underthrusting Indian lithosphere. Its shape predetermined by these tectonic trends, this downwarp facilitated oroclinal bending of the Tethyan Himalaya and adjacent southern Tibet through a more extensive southward overthrust of the central Himalayan region relative to the extremities of the arc, consequently creating an east-west extensional regime in southern Tibet and the Tethyan Himalaya. The telescoped schuppenzone of the underthrusted Lesser Himalaya followed the bending of the Arc. The underthrusting model is proposed as a continental analog of largescale oceanic subduction beneath island arcs, where a conical downbuckle in the underthrusting oceanic lithosphere induces bending of the arc and backarc spreading. A firm date on the timing of oroclinal bending in relation to initiation of the Plio-Pleistocene extensional regime in southern Tibet, development of the Ganges Basin and a downwarp of the Great Vindhyan Basin in northern India is essential to test the validity of the model. This can be achieved through palaeomagnetic studies of rotation patterns in Murree-Siwalik profiles along the Lesser Himalayan Belt and in the Tethyan sequence of the Higher Himalaya.

References

1. C. McA. Powell, & P.J. Conaghan, 1973, Earth Planet. Sci. Lett., 20, 1-12.

L. Seeber, J.G. Armbruster, & R.C. Quittmeyer, 1981, in: ZagrosHindu Kush-Himalaya Geodynamic Evolution, H.K. Gupta and F.M. Delaney (eds.), Geodynamic Series 3, 215-191. 3. J.J. Veevers, C. McA. Powell, & and B.D. Johnson, 1975, Sci. Lett., 27, 383-387. THE NATURE OF THE LOWER CRUST AND UPPER MANTLE BENEATH EASTERN AUSTRALIA AS INFERRED FROM XENOLITH STUDIES J. Knutson 1 , Suzanne Y. O'Reilly 2 , M.B. Duggan 1 , A.L. Jaques 1 ^Bureau of Mineral Resources, Canberra Macquarie University, North Ryde

Basaltic provinces (dominantly Cainozoic) parallel the eastern continental margin of Australia. Xenoliths derived from high pressure zones are distributed in basaltic hosts throughout the entire province and in some localities are very abundant. The xenoliths sample upper mantle and lower crustal rock types otherwise inaccessible at the surface of the Paleozoic eastern Australian fold belt.

310

Cr-diopside type lherzolites (Type I xenoliths) are the dominant xenolith type (greater than 95%). Garnet lherzolites have been identified at only three localities: Mt.Shadwell, Victoria; Jugiong, N.S.W.; and Bow Hills, Tasmania. Other xenolith rock types include mafic granulites, Ti-Al augite series xenoliths (Type II xenoliths), mafic and ultramafic rocks metamorphosed to granulite and eclogite facies,and amphibole-dominant rock types. Some mafic plagioclase-bearing granulites appear to be representative of the lower crust. They have a wide geographical distribution from Tasmania to north Queensland. Type II xenoliths are generally interpreted as high pressure frozen basaltic liquids and cumulates.The reequilibrated mafic and ultramafic rocks include both spinel and garnetbearing pyroxenites exhibiting a wide range of microstructures produced by exsolution and recrystallisation. They may represent original basaltic crystallization products readjusted to ambient P/T conditions. Some amphibole-dominant rock types may record metasomatic events within the mantle. Cr-diopside lherzolites are interpreted to be mantle wall rocks. Xenoliths with contact relationships show that both unmodified and recrystallised basaltic cumulate xenolith types occur as veins and lenses within the upper mantle Cr-diopside lherzolite zone. Geothermobarometry calculations (mostly using garnet websterite assemblages) indicate that these rock types were derived from depths ranging from 35-55km. at temperatures ranging from 900 to 1100 degrees C in some regions (eg western Victoria). A combination of the contact relationships and P/T information, along with available geophysical data such as seismic refraction profiles, allow the construction of deep stratigraphic columns for some regions. The major conclusions are that: 1.

The lower crust beneath the eastern Australian fold belt is dominantly mafic.

The uppermost mantle consists of a complex rock mix with regions of basaltic and basaltic cumulate compositions within Cr-diopside lherzolite wall rock.

Microstructure (eg strong preferred orientation) can be important in affecting seismic velocities and in identifying regions of tectonic flow.

These provide important constraints for interpreting both the nature and geophysical parameters of the crust/mantle boundary. The inferred rock type mix and the range of microstructures of basaltic-derived rock types (cumulate to recrystallised) in the upper mantle also suggest that underplating has been an episodic and significant process throughout the evolution of the Paleozoic crust of eastern Australia.

FISSION-TRACK STUDIES OF THE EAST ALLIGATOR RIVER URANIUM FIELD (NORTHERN TERRITORY, AUSTRALIA) AND THEIR IMPLICATIONS S. Koul1, V.J. Wall2 and J.D. Johnston2 2

^CSIRO Division of Chemical Physics, Clayton, Vic Dept. of Earth Sciences, Monash University, Clayton, Vic

Fission track investigations on suites of minerals can provide accurate data on the temperature-time relations of their host rocks and also of uranium distribution on the grain scale. To date, such methods have rarely been applied to the evaluation of the thermal history of ore forming systems, nor has their potential for clarifying the distribution of uranium been fully 311

realized. In this paper we present the results of fission track studies on zircon, garnet, muscovite, chlorite and apatite from the East Alligator River Uranium Field (EARUF). We discuss their implications for the thermal and tectonic history of the Field, the hydrothermal systems involved in uranium mineralisation and geochemical aspects of uranium distribution. The EARUF represents one of the world's major uranium provinces. Archean granitoids (> 2450 ma; all radiometric ages are from Page et al. (1980) unless otherwise stated) are the oldest exposed rocks in the region and form basement to a Lower Proterozoic metasedimentary sequence, regionally metamorphosed and intruded by syntectonic granitoids around 1850 ma. Following some uplift and erosion this metamorphic belt was intruded by (y 1760 ma) post-orogenic granitoids and locally covered by associated volcanics. The U-deposits occur in Lower Proterozoic rocks at or near a major unconformity with the shallow dipping, Middle Proterozoic Kombolgie Sandstone 1650 ma). U/Pb ages on uraninite from the deposits are scattered between 900-1400 ma (Hills and Richards, 1976; Gulson and Mizon, 1980) whereas Rb/Sr ages on associated sericite-chlorite alteration range between 1300 and 1550 ma : Mineralisation and alteration are evidently diachronous and polyphase but are related to reverse faulting of the basement-cover sequence (Johnston and Wall, this volume). Other geological events include phonolite dyke emplacement (y 1300 ma) and possibly erosion/deposition in the Cambrian and Cretaceous. Mineral suites for fission track studies were collected from the Proterozoic rocks (mainly from below the major unconformity, but some samples from the Kombolgie Sandstone) both within the deposits and distant from them. Zircon, garnet and apatite separates were all dated by EDM (external detector In the latter spontaneous method) as well as the population method (PM) . tracks in zircon, garnet and apatite were respectively annealed at 700°C, 625°C, 400°C for two hours to remove natural tracks and then irradiated with thermal neutrons. Samples analysed by EDM were sandwiched between muscovite detectors for the registration and counting of induced tracks. The EDM samples (including muscovite, biotite and chlorite) were etched under similar conditions to those of the population method; whereas treatment with 48% HF for 50 minutes was used to reveal induced tracks in muscovite detectors. The integrated thermal neutron dose to which the samples were exposed was determined by counting tracks in a muscovite detector irradiated in contact with NBS glasses SRM962 and SRM963. Independent measurements on Au and Cu foil were in good agreement with these values. For EDM dates a geometric factor of 0.5 was used, assuming the etching rate and counting efficiency for external detectors to be the same for each sample. Table 1 summarises the fission trace data (after annealing corrections) together with estimates of geologically effective track retention temperatures from the literature and our work, as well as the uranium content of the minerals. Although the fission trace dates are among the oldest yet recorded, the ages for the minerals are substantially younger than their age of formation. This indicates that the fission trace dates result from thermal resetting of the fission track clocks. The precision of the data is excellent and is consistent with a similar thermal history over the extent of the EARUF sampled. The EARUF sequences remained buried for over 1000 my with temperatures declining over this period and last exceeding 90-100°C around 450-500 ma. This suggests a very slow average uplift/erosion rate. Thus the EAR region represents an exceedingly stable intracratonic environment through one third of Earth's history. Regional temperatures of around 260°C were achieved before 1450 ma, postdating peneplanation and the deposition of the Kombolgie sandstone (1650 ma). As geothermal gradients of 40-50°CC/km would be maximal in any sedimentary basin, such temperatures would imply minimum burial of 4-5 km. This may be ascribed to the deposition of this thickness

312

of overlying McArthur Basin sediments (or equivalents) - an evaporitic sequence occurring to the east of the EARUF but evidently erosionally stripped from the latter. The timing of 200°C regional temperatures inferred overlaps with the 1300-1550 ma ages of alteration associated with uranium mineralisation. Fluid inclusion (Ypma and Fuzikawa, 1980) and stable isotope data (Sun and Binns, 1983) indicate temperatures around 200°C for mineralisation/alteration - similar to the regional temperatures operative at this time. The range of U/Pb dates on uraninite also broadly coincide with the time during which the EARUF was at T > 150°C. Our fission track data thus support the contention (Johnston and Wall, this volume) that hydrothermal fluids responsible for mineralisation were part of large-scale and long-lived circulation systems following burial of the EARUF by Mid-Proterozoic sediments. Such circulation systems could involve the large volumes of fluid required to satisfy the fluid/ rock ratios inferred by Hedges, Wall and Bloom (this volume) for ore deposits in the EARUF without specialised heat sources.

Mineral

Number of Samples

Average Age (m.y.)

Precision

U-cont. (ppm)

Geological Track Retention Temperature 106 yr 108 yr (°C)

Zircon

1415

±88

55--110

< 253

< 179

Garnet

1346

±76

45-- 83

< 205

< 159

Muscovite

1064

±59

5-- 13

< 185

< 150

Biotite

932

±49

~ 8

< 170

< 140

Chlorite

713

±44

3--

< 160

< 130

Apatite

463

±36

9-- 17

< 110

< 86

The brines responsible for alteration and mineralisation could have been derived by solution of evaporites in the Mid-Proterozoic sequence inferred to have been overlying_the EARUF between 1000-1500 ma. Such fluids would also have high S0I*~/H 2 S ratios i.e., be highly oxidised and capable of mobilising and transporting uranium (Hedges, Wall and Bloom, this volume).

THE GEOLOGICAL DISTRIBUTION, MINING AND UTILISATION OF INDUSTRIAL GRADE MAGNETITE IN EASTERN AUSTRALIA E. Kreutzer1 and D. Nichol2 ^Steetley Industries Limited, Newcastle Steetley Industries Limited, Sydney Industrial grade magnetite ( F e ^ ) has a high specific gravity (5) and special magnetic properties and is particularly suitable as a dense medium in coal-washing, the process which removes shale and other rock fragments from the coal. The dense medium consists of a slurry of finely ground magnetite particles artificially suspended in water and is normally required to have a specific gravity between 1.3 and 1.9, that is, intermediate between the coal and the waste materials. Consumption of industrial grade magnetite for coal processing currently exceeds 80,000 tonnes yearly.

313

Geologically, magnetite bearing rocks are associated with layered basic igneous intrusions, banded iron formations, chromite-serpentinite bodies and some base metal sulphide deposits and porphyry copper deposits as well as sedimentary placers and heavy mineral beach sands. However most industrial grade magnetite is associated with skarn type deposits. In skarns, the magnetite bodies are typically lensoid or discontinuous in form and usually lie at or near the contact between granitic intrusions and carbonate country rocks and particularly within volcanoclastic units. In Tasmania, the Savage River Magnetite Deposit lies within a Precambrian sequence of volcanic extrusives and carbonate rocks and in Victoria, the Nowa Nowa Magnetite Deposits formed within the Snowy River Volcanics of Devonian age. The skarn type magnetite bearing zones in New South Wales are geologically distributed principally within two belts of acid volcanic rocks of Silurian age and in the Angullong Tuff, a sequence of andesite volcanic rocks of Ordovician age. Most skarn type magnetite deposits in southern and central Queensland are associated with acid igneous rocks of Permian and Carboniferous age and are predominantly confined to the Great Dividing Range. To the north, the Coen, Yambo and Georgetown Inliers contain magnetite bearing skarns within volcanoclastic units associated with acid igneous complexes of Devonian and Precambrian age. Important industrial grade magnetite deposits also occur within the Precambrian Mount Isa Inlier in far western Queensland. Here, both magnetite bearing skarns and replacement magnetite orebodies are represented. At Mount Biggenden Magnetite Mine in the Maryborough district of Queensland, lenses of magnetite ore occupy the steep contact zone between the Early Permian Biggenden Beds, a sequence of limestones, andesitic volcanics, conglomerates sandstones and claystones and the Degilbo Granodiorite, a high-level post-orogenic intrusion of Lower Triassic age. The magnetite ore consists mainly of fine to medium grained aggregates of euhedral and subhedral magnetite grains in varying proportions, other constituents such as garnet, calcite, hornblende and chlorite as well as hematite, bismuthinite and chalcopyrite are present as impurities. The main magnetite orebody measures approximately 150 metres long by up to 30 metres wide and at least 120 metres deep. In 1976 the Mount Biggenden Magnetite Mine was converted to an underground operation. The ore is extracted from working levels which are spaced at vertical intervals of sixteen metres and connected by spiral declines. Each working level is advanced along the full length of the orebody and the decline is cut in the footwall to the next level. The magnetite ore is hauled to the processing plant at the surface and crushed, cobbed, wet-milled and beneficiated to comply with the particular requirements of each coal-washing plant. The Broula Magnetite Deposit at Cowra in central New South Wales is scheduled to commence production in 1985-86 not only to augment production from Mount Biggenden Magnetite Mine but also to introduce a new range of grades for specialist applications. MAFIC DIKES FROM THE VESTFOLD HILLS»

ANTARCTICA

S.M. Kuehner and D.H. Green Geology Department, University of Tasmania, Hobart The Vestfold Hills block of the East Antarctic Shield is a high grade metamorphic complex crossed by hundreds of mafic dikes. Previous studies have shown that the last granulite facies event to effect the whole of the Vestfold Hills ended about 2400 m.y. Intrusion of mafic dikes followed at ca. 2350 m.y., 1850 m.y. and 1300 m.y. Evidence of a younger granulite facies metamorphic event (-1100 m.y.) is observed mainly in the southwest portion of the Vestfolds. The mafic dikes represent batches of

314

liquid periodically removed from the subcontinental mantle over a time period equivalent to nearly \ of the Earth's history. They thus record events in the chemical evolution of the Proterozoic mantle beneath the Vestfold Hills. Based on chemical and petrographic evidence, 12 distinct groups of dikes can be recognised (Fig. 1). The largest group (A) is a chemically heterogeneous group broadly referred to as lamprophyres. These rocks are typically olivine and clinopyroxene phyric, some also have phlogopite phenocrysts. The olivines are serpentinized but often have relict, unaltered cores. Clinopyroxene is colorless but usually has dark brown rims. Nearly all samples contain carbonate ocelli. A number of the lamprophyres have the chemical features thought to represent unmodified f primary liquids, i.e. Mg values in the mid 70 s, high Cr and Ni contents (both over 900 ppm). Group B is a suite of orthopyroxene (Mg85) phyric, high Mg tholeiites. These rocks have Mg values ranging from 58-73, Cr contents reach 1500 ppm and Ni 400 ppm. Olivine phenocrysts (Mg80-85) also occur in the more mafic samples and are invariably rimmed by pigeonite (Cal2, Mg74). Chromites [Cr(Cr+Al) = 70-80] are rare, and usually enclosed by olivine. Group C is predominantly composed of orthopyroxene (Ca5, Mg75), clinopyroxene (Ca34, Mg74), plagioclase (An80) phyric rocks, although the more magnesian samples lack orthopyroxene. Chromium (95-170 ppm), Ni (75-92 ppm) and Mg values (<50) all suggest fractionated liquids. Trend D is divided into separate groups mainly on the basis of chemistry. All the groups have clinopyroxene + plagioclase ± olivine phenocrysts, though one group (E) is orthopyroxene + clinopyroxene + plagioclase phyric. Phenocryst compositions from 3 of the groups plotting along trend D show little chemical variation: olivine (Mg62-65), clinopyroxene (Ca28-31, Mg55-52), plagioclase (An80-62) .

6 Ti02 3

0 FIG. 1.

FE0/MG0 FeO/MgO vs. Ti0 2 plot illustrating some of the geochemical characteristics of Vestfold Hills mafic dikes.

315

Although the dikes can be divided into separate groups based on major element chemistry and petrography, the field evidence and minor element abundances require further subdivisions. The oldest dikes are olivine + orthopyroxene phyric group B rocks. Prior to the intrusion of the more evolved olivine free variety of group B, a suite of group C dikes were emplaced. Other group C dikes post-date all group B rocks. Trace element patterns of the 2 group B suites are distinctive, whereas group C dikes have progressively enriched, parallel patterns. The relative chronology of trend D groups is not yet complete, but it is clear the observed chemical pattern (Fig. 1) is not simply due to crystal fractionation. Also, the 1amprophyres pre-date 3 of the trend D groups.

A MODEL RELATING SULPHIDE CASSITERITE TO Sn-W MAGNETITE SKARN REPLACEMENT DEPOSITS T.A.P. Kwak La Trobe University, Bundoora, Victoria Proximal Sn-W skarns close to igneous pluton contacts (<200 meters) constitute the main economic source of W but not Sn although proximal Sn-W skarns are common. Conversely Sn-sulphide deposits, which constitute one of the main sources of economic Sn, occur in distal replacement skarn usually greater than 300 meters from igneous contacts* In W-skarns, early primary garnet + pyroxene ± magnetite skarns are usually leached of high Mo-scheelite which is transported and precipitated in areas of secondary, retrograde (i) amphibole-epidote (ii) biotitechlorite or, in rare cases (iii) muscovite chlorite assemblages as low Mo scheelite ± M0S2 or even wolframite ± M0S2. W increases from 0.2-0.4 wt in primary skarn up to 2.0 wt % in later skarn types. In Sn-skarns, proximal calcic primary Sn(-W) magnetite or garnet skarns have low Sn(<l wt %lin economically unrecoverable form. Leaching of Sn from such skarn by solutions which precipitate retrograde assemblages similar to those in W-skarns usually produce Sn-bearing silicates, or Sn is largely lost to solution, even if the retrograde skarn is largely sulphide (pyrrhotite ± pyrite). Economic Sn - sulphide skarns occur in high level environments with little or no magnetite or Ca - Mg silicates except talc or chlorite. Thus Sn is more soluble in retrograde skarn solutions and because Sn has only limited solubility in retrograde skarn minerals, it is generally lost to other ore style environments (veins?). Sn precipitation as cassiterite is generally independent of sulphide or magnetite stability. In many proximal Sn magnesian skarns Sn-bearing borates such as hulsite and vonsenite-ludwigite form which retrograde to cassiterite, schoenfleisite or wickmanite. Such environments are equally uneconomic.

HIGH IRON SOLUBILITIES IN NATURAL HYDROTHERMAL SYSTEMS: ITS RELATION TO ZONING IN SOME ORE DEPOSITS T.A.P. Kwak1, W.M. Brown2, P.B. Abeysinghe1, and Tan Teong Hing3 ^-Department of Geology, La Trobe University, Bundoora ^Western Mining Corporation, Kambalda Jabatan Geologi, Universiti Kebangsaan Malaysia, Kuala Lumpur In many hydrothermal deposits including porphyry, skarn and many veinstyles there is a distinct zonation of Fe and related ore minerals. In fact Fe is usually the major introduced element precipitated in nearly all hydrothermal systems which probably infers it is a major anion if not the major anion in hydrothermal solutions, particularly orthomagmatic ones. 316

The Fe solubilities of fluids present in very saline fluid inclusions have been determined using the phase volume method. Fe daughter minerals include magnetite, pyrite, amarantite and FeCl-2 hydrate (FeCl-2 .2^0?). The fluid inclusion liquid compositions are inferred from a combined analysis of first melting temperatures ( = eutectic temperatures of the salt system), solid mineral identification by S.E.M. and optical means, and relevant published experimental salt solubilities. Maximum Fe solubilities show a near-exponential increase to at least 9 weight percent Fe with increasing total anion content of the fluid, especially in the 20 to 30 weight percent interval. Temperature, f Q and fg appear to have minor influence on the total Fe solubilities. ^ 2 Some of the samples contain solid crystals which coexisted with the fluid inclusions and probably buffered Fe at the appropriate a^ e (and Femolar) values during genesis, but most fluids were apparently Feundersaturated at the temperature of formation. Apparent maximum Fe solubilities of fluids tended to decrease in the following order when the following Fe-bearing daughter crystals are present, magnetite > pyrite > FeCl2*2H20 » amarantite although reversals to this trend occur. The Fe solubility data is used to explain some Fe mineral overprints (stage II, III) of skarns, magnetite-Fe-chlorite-cassiterite veins in tin granites and the zonal pattern in porphyry copper systems. The Fe data suggests that the highly saline Fe-bearing solutions present in the cores of porphyry systems and other near-contact deposits are not a result of increased salinity of hydrothermal fluids due to boiling of meteoric derived solutions but are inherent from an orthomagmatic source as are probably the ore metals (e.g. Cu, Au).

CHEMICAL AND PHYSICAL VARIATION OF VEIN IN SOME PLUTONIC ENVIRONMENTS

SYSTEMS

T.A.P. Kwak and G.J. Plummer La Trobe University, Bundoora, Victoria Economic metallic quartz vein systems spacially associated with igneous plutons are different from quartz vein systems developed in regional metamorphic terrains. The former are zoned spatially relative to the pluton/metasediment contact. Vein morphology, mineralogy, metal content and formation (paleo) temperatures are found to vary away from the contact. Both endo- and exo-contact types occur, all of which form at low to moderate temperatures (180-450°C), at low pressure (300-1000 Bars), and from a hydrothermal solution which generally exhibits continuous or intermitent boiling. Fracture propogation is by hydrofracturing in response to fluid overpressure. As little as one hundred bars fluid overpressure, over lithologic pressure is needed to cause fracture propagation in granite while as little as one third over the load pressure will maintain open spaces at high crustal levels. The veins can not vent or vein genesis will stop. The progression of veins in Sn-W systems is generally in the order ofssilicate/oxide stage ** fluoride/sulphide stage-^carbonate stage and metal progression is:Mo + W; W + Mo; Sn + W; Sn + Cu; Pb + Zn + Ag ± Cu temporally and spacially. Some notable exceptions to this occur (eg. Sungei Lembing - Malaysia). Mo, W and Sn mineralization occurs in the silicate/oxide stage and Cu, Pb, Zn, Ag mineralization occurs is the fluoride/sulphide stage. The temporal variation of Low F veins to high F veins with time may reflect the solubility of Cl<H20<F in granitic melts.

317

Fluid inclusion studies indicate that silicate/oxide stages vein formation occurs in the presence of fluids of low to moderate salinity (5-20 wt 7o NaCl equivalant) and moderate temperatures (250 - 450°C). Later fluoride/sulphide stage vein fill precipitates in the presence of fluids with low salinity (5 15 wt 7o NaCl equivalent) and lower temperature (180 - 300°C). Last formed carbonate vein fill precipitates from fluids of very low salinity (0-10 wt % NaCl equivalent) and low temperature (70 - 200°C). Generally these vein systems are associated with greisen type post magmatic alteration of the pluton. Greizen formation has been shown to occur in the presence of high salinity (>40 wt % NaCl equivalent) and high temperature (400 - 500°C) post magmatic fluids. C,0 and S isotopic data indicate that the early silicate/oxide and fluoride/sulphide stages form in the presence of derived fluids. The later formed carbonate stage is found to be associated with the influx of meteoric water into the convecting system. Most exocontact vein systems morphologically zone outwards following the five story model suggested by Chinese workers as follows 1 - pinch out zone in or nearest the pluton., 2 - thick veins., 3 - thin veins., 4 - veinlet and 5 - stringer zones. Commercial or near commercial W and/or Sn can occur in all zones except 1 which in Australia includes thick veins., (Mt. Carbine, Qfld., Oakleigh Creek, Tasmania)., thick veins to thin veins (Aberfoyle, Tas., Folleys zone, Cleveland., Tasmania., Shepherd and Murphy Mine, Tasmania) and veinlet to stringer zone (Great Pyramid, Tasmania., Bischoff North, Tasmania., Sundown, N.S.W.) Endo-contact zone models consist of 1:- pinch out zone., 2:- thick vein zone and 3:- stringer zone (often in overlying metasedimentary cover). There are few examples of this known in Australia.

ACID VOLCANIC PRECURSOR TO POTOSI GNEISS AT BROKEN HILL AND ITS IMPLICATIONS FOR ORE GENESIS

W.P. Laingl, S.S. Sun2 and R.W. Nesbitt3 1 James Cook University of North Queensland, Townsville 2 Bureau of Mineral Resources, Canberra 3 The University, Southampton The garnetiferous quartzofeldspathic gneisses familiarly known to many as Potosi gneiss, have long been recognised as one of the important lithological units within the granulite facies metamorphosed sequence vhich hosts the Broken Hill FbfZn+Ag orebodies. The complete re-texturing of Potosi gneiss has prompted speculation on a variety of precursor rocktypes. The origin of Potosi gneiss which flanks the Broken Hill orebodies in a lateral, and possibly also in a vertical sense, is crucial to our understanding of ore genesis (eg. Mackenzie, 1968? Laing, 1977, 1980). Recent convergence of ideas toward an acid volcanic precursor have been based on a recognition that the Broken Hill orebodies have a number of characteristics found in known volcanogenic deposits, including a Potosi gneiss composition consistent with an acid volcanic precursor (Johnson and Klingner, 1975). Recent regional mapping has shown that Potosi gneiss lithologies are widespread in two horizons within the Broken Hill Group, the Hores Gheiss and the Parnell Formation (Willis et al., 1983). The search has however been impeded by a lack of confirmatory textural and field evidence, although Brown et al. (1983) described features which they speculated might be of depositional and tuffaceous origin.

318

Textural, field and chemical evidence from the Hores Gneiss at Yanco Glen, 50 km north of Broken Hill/ unequivocally demonstrates its origin as a porphyritic rhyodacite of probable ash flow emplacement. The Hores Gheiss is stratigraphically equivalent to the Potosi gneiss at Broken Hill but is o£ lower, amphibolite facies grade and is distinctly finer-grained and relatively unstrained. It thus provides a "window" into "primary" Potosi gneiss. The textural transition into coarse granoblastic, non-porphyr it ic Potosi gneiss, achieved by metamorphic coarsening of the groundmass, is readily observed southward frcm Yanco Glen. At Yanco Glen the unit is 7km in strike with a thickness varying frcm 40m (in the N) to 200m (in the S). It comprises a uniformly textured "massive" facies with a very minor lenticular "bedded" facies in the middle and the upper portions. The massive facies has 0.5-4 irm phenocrysts (2-10%) within a fine groundmass (0.05-0.2rtm) of predominantly quartz+biotite+ Kfeldspar+ plagioclase (An25-40). The quartz-dominated phenocrysts are euhedral to subhedral and cxmmonly have bipyramidal shapes indicating inversion frcm high-temperature beta-quartz. Feldspar phenocrysts are sericitised and commonly indistinct. The polygonal granoblastic groundmass represents the recrystallisation of a finely crystalline or glassy matrix. Biotite (2-10%) occurs in characteristic flattened lenticles of fine aggregate up to 15rrm in diameter, similar to a eutaxitic texture, and possibly represents deuteric chloritic alteration of fianme. The bedded facies is fine-grained and feldspathic, in contrast to the mature, suggesting a non-feldspathic metasediments enclosing the Hores Gneiss, tuffaceous origin oogenetic with the massive facies. Isolated small clasts of fine metasediment within the massive facies may represent reworked bedded facies. The field relations are consistent with emplacement of the Hores Gneiss as several massive, ash flew crystal tuffs, separated by deposition of minor laminated ashfall or subaqueous reworked tuffs. The base of the Hores Gneiss is sharp and planar, but the top is irregularly tourmal inised and/or brecciated, suggesting hydrothermal activity coeval with the acid volcanism. Barnes (1983) documents stratiform tungsten within Hores Gneiss at Yanco Glen. Massive Hores Gneiss has a subalkaline rhyodacitic composition similar to Potosi gneiss but with significantly lower Mn and K and higher Na (Table 1). The composition of Potosi gneiss is thus inferred to be the result of hydrothermal alteration of precursor rhyodacite with the pristine composition of Hores Gneiss. Figs. 1 and 2 illustrate the reasonably orthodox chemical behaviour of Hores Gneiss in the critical areas of K/Na and Fe/Mg. REE patterns in Potosi gneiss show strong fractionation, indicating a crustal source (LREE=150—250x chondrite, HREE=30x chondrite). The Parnell Formation at Yanco Glen, 200m stratigraphically below the Hores Gheiss, comprises an amphibolite intercalated with a fine-grained quartzofeldspathic lithology similar to Hores Gneiss, but vhose chemistry consistently shows lower Fe, K and higher Mg, Na (Table 1). These features indicate a similar acid volcanic, or high-level intrusive origin for the quartzofeldspathic phase of the Parnell Formation. The disparate values of the chemical indices Fe/Mg and K/Na, between the I&rnell Formation and Hores Gneiss (Figs. 1 and 2) are all the more striking in view of the similarity between the remaining major elements. Their trends on the AFM plot follow a normal pattern of calc-alkaline fractionation, as do major element variation diagrams (including Ti vs P and (Fe/Fe+Mg) vs Si) . The stark difference between the K/Na value of each unit can be explained by fractionation or by post-anplacement alteration. Relations in the Mine area can now be explained in terms of two phases of magmatic activity, whose pristine characteristics can now be urmasked.

319

The 100m thick massive facies of HDres Gneiss , the "Yanco Glen facies" gives way to a dual facies in other parts of the region, the "Maybell facies" which consists of a massive facies at top and bottcm separated by a bedded facies (Fig. 3). This dual "Maybell" facies occurs in the southern extensions of ZC/NBHC. The orebodies are laterally flanked by the dual facies, but do not cane into contact with Fotosi gneiss, either laterally or underneath; they are 'contained in an envelope of metasediments vhich tend to be quartz- and garnet-rich. In the northern leases of ISbrth Mine and at RDckwell-Little Broken Hill, another facies of the HDres Gneiss contains only 5-10%, lenticular Itotosi gneiss, with the remainder of this "North Mine facies" being siliceous/ garnetiferous metasediments containing sporadic base metal mineralisation and "lodey" indicator minerals. . These three facies types of HDres Gneiss define a regional trend frcm north to south (Fig. 3). The unit has dimensions of the order of 100m x 1000km2 = 100km3, comparable to large single eruptions in other acid volcanic terrains. The wide dispersal of the bedded facies indicates that ashfall deposits were plinian or phreatoplinian, vhile the massive ashflow deposits were more restricted and possibly ignimbrites. This model is consistent with the interlayered nature of the twD facies types (Vfelker, 1973). Both styles may have been submarine in part. The associated volcanic activity may have been at one or a number of vents, and was undoubtedly spectacular. The Parnell fbrmation in the Mine area is similar lithologically and chemically to its Yanco Glen counterpart. In a confirmation of both the stratigraphic correlation between the two areas and of the igneous nature of the HDres Gneiss and the Parnell Fbrmation, the twD units in the Mine area can be distinguished by their respective K/Na ratios just as at Yanco Glen (Table 1). It is clear that the Broken Hill orebodies were relatively distal frcm volcanic activity. This contrasts with the obvious proximal nature of the orebodies with respect to hydrothermal activity. What then is the role of Fotosi/HDres Qieiss in ore genesis? It appears that volcanism was not a primary factor in locating the ores. Hovever the ore-flanking disposition of Potosi/HDres Gneiss and its demonstrable chemical vector toward ore (Main et al., 1983), suggest a genetic role based on permeability and/or ccmposition and/or (seafloor?) topography. In a wider context the massive hydrothermal activity vhich produced the orebodies was undoubtedly genetically linked with the regional cessation of volcanic activity vhich followad the largescale eruption of the HDres Gneiss. Exploration models should incorporate the following: (a) relative absence of massive facies, (b) high K/Na, (c) low K+Na and/or (d) strongly variable K+lSk. (2) (i) (3)

FLg.l. PEA Plot. Fig.2 K/tfe. pdot with other Australian Prcterozoic acid VDloanirsfcrcaipariscn.

320

TABLE 1 .

MINE AREA

Si0o A1 2 FeOip MgO CaO N a 20

%T i>0 2

mS5 FeOip/FeOrp+MgO K 20/Na20

YANCO GLEN

Parnell

Hores (Potosi)

Parnell

Hores

68.63 13.51 8.91 1.04 2.94

66.91 15.10 7.54 0.92 2.93

69.79 14.56 4.92 1.11 2.09

67.93 13.81 7.39 0.83 1.83

1.82 1.57 0.71 0.111 0.414 0.90

0.80 3.62 0.81 0.174 0.444 0.89

3.61 2.14 0.57 0.147 0.143 0.82

2.60 3.58 0.67 0.176 0.128 0.90

,1.09 (n=21)

,4.42v (n=168)

,0.5? (n=8)

,1.38 x (n=37)

References Barnes, R.G., 1983, Geol. Soc. Aust. J., 30(2), 225-39. Brown, R.E., Stevens, B.P.J., Willis, I.L., Stroud, W.J., Bradley, G.M., & Barnes, R.G., 1983, Geol. Surv. N.S.W. Rec. 21 (1), 127-226. Johnson, I.R., & Klingner, G.D., 1975, A.I.M.M. Monograph 5 , 476-91. Laing, W.P., 1977, CRAE Report N o . 9119, 23pp. (unpubl.). Laing, W.P., 1980, Geol. Surv. N.S.W. Rec. 20 (1), 71-85. Mackenzie, D.H., 1968, A.I.M.M. Monograph 3, 161-69. Main, J.V., Mason, D.O., & TUckwell, K.D., 1983, A.I.M.M. Conf. Ser., Broken Hill Conf., 115-31. Walker, G.P.L., 1973, Geol. Rundsch., 62, 431-46. Willis, I.L., Brovn, R.E., Stroud, W.J., & Stevens, B.P.J., 1983, Geol. Soc. Aust. J., 30 (2), 195-224.

OLYMPIC

D A M , SOUTH AUSTRALIA

- THE D I S C O V E R T

HISTORY

J.H. Lalor Western Mining Corporation, Preston, Victoria The Olympic Dam deposit was discovered in July 1975 with the intersection of 38 m of 1.05% copper in diamond drill hole RD 1. A further eight holes were drilled with only marginal encouragement. In November 1976 RD 10 cored 170 m @ 2.12% copper and 0.58 kg/tonne U3O8, and an economic discovery was confirmed. Western Mining Corporation then announced "It is clear that a very large body of copper mineralisation has been discovered but a great deal more drilling will be necessary to establish the grade of the occurrence.". After an extensive programme of further drill testing the Company announced on the 12th October, 1982 "The estimated amount of mineralisation so far drilled on a 200 metre grid is about 2,000 million tonnes at an average grade of 1.6% copper, 0.6 kg/tonne U3O8 and 0.6 grams/tonne gold commencing approximately 350 metres below surface". The project commenced in 1972 with the application of conceptual models which led to the selection of areas of interest. Target definition for strati graphic drilling on the Stuart Shelf was based on interpretation of the available geophysical data combined with a tectonic evaluation of the area. Siting of the stratigraphic diamond drill hole was determined by data from reconnaissance ground magnetic traverses. 321

The discovery is an excellent example of co-operation between exploration management and exploration scientists. It illustrates the importance of the need to support new ideas, particularly where these result in area selection in untested ground, and the importance of persistence in mineral exploration.

DEEP CRUSTAL STRUCTURE BELOW CENTRAL AUSTRALIAN

BASINS

Kurt Lambeck and Craig Penney Research School of Earth Sciences, Australian National U n i v G , Canberra The basin evolution model proposed by Lambeck for the Amadeus, Officer and Ngalia basins predicts a significant undulation of the m o h o G This aspect of the model has been tested by an analysis of teleseismic travel time anomalies across the structure. Late arrivals occur at sites located within the basins and early arrivals occur at sites on the exposed and eroded basement. The late arrivals correspond to the gravity lows and the early arrivals to the gravity highs. The travel time anomalies show considerable azimuthal variation. Their inversion yields both the depth of the moho and the dip of this surface below each of 25 stations. Moho undulations of ±10 km are deduced with the moho being deepest near the margins of the basins, and shallow beneath the Musgrave and Southern Arunta Blocko References Lambeck, K . , 1983, Geophys.J., 74, 843-886. Lambeck, K . & Penney, C . , 1984, Phys.Earth Planet.Int., J34, 46-56.

COPPER METALLOGENY OF THE ADELAIDE GEOSYNCLINE STUART SHELF REGION

Ian B . Lambert, J . Knutson, T . H . Donnelly and H . Etminan Baas Becking Laboratory, Canberra, ACT In the Adelaide Geosyncline-Stuart Shelf region of South Australia, late Proterozoic (Adelaidean) to Cambrian strata accumulated largely in shallow water to emergent environments on middle Proterozoic and older basement. Copper (uranium, gold) mineralisation is associated with hydrothermal alteration and brecciation in crystalline basement rocks and pre-Adelaidean sedimentary-volcanic sequences. In contrast, disseminated to bedded copper (lead, zinc) deposits, with variable proportions of veinlet sulfides, occur in unaltered Adelaidean strata. The copper minerals partly rim and replace biogenic pyrite. The sulfur isotope compositions of the copper sulfides and pyrite are similar and the mean 6 S values increase progressively with decreasing age of the Adelaidean units. This isotopic trend is most readily interpreted in terms of deposition in intracratonic basins with restricted or no access to ocean water. Alternatively, there may have been major g^gbal tectonic processes which resulted in very major progressive S enrichment of ocean water during the late Proterozoic.

322

The main deposits in Adelaidean and older rocks of the Stuart Shelf, and the main deposits in Adelaidean and Cambrian strata of the Adelaide Geosyncline, are situated along lineaments parallel to the Torrens Hinge Zone. These lineaments are probably reflecting the influence or major basement structures on the Adelaidean sequence. It is likely that the metals in the Adelaidean deposits were leached from metal-enriched basement rocks, from basement-derived clastics, and/or from basic igneous rocks. The metalliferous brines ascended via permeable strata and structures to deposit their metals at moderately low temperatures in anoxic sedimentary environments. Copper introduction or remobilization continued after early diagenesis in most cases, and there are some examples of totally epigenetic deposits. Sulfide-carbonate veinlets are particularly common in the copper deposits of the Geosyncline and these formed from their host strata during sediment dewatering and subsequent low-grade metamorphic processes.

SULFUR ISOTOPE COMPOSITIONS OF ARCHAEAN GOLD DEPOSITS: THEIR SIGNIFICANCE FOR GENESIS, EXPLORATION AND GEOBIOCHEMICAL EVOLUTION MODELS 1 2 I.B. Lambert , G.N. Phillips , T.H. Donnelly

1 3 3 , D.I. Groves , F. Neall .

^Baas Becking Laboratory, Canberra ^University of Witwatersrand, Johannesburg, South Africa University of Western Australia, Perth. Diverse styles of sulfide mineralisation and disseminated sulfides in Archaean greenstone sequences are characterised by 6 S values of 0 ± 4 ° / o o ) regardless of metamorphic grade. This marked concentration of sulfur isotope compositions around the mantle value indicates that remobilisation of sulfur in the Archaean crust by metamorphic, hydrothermal and sedimentary processes occurred generally in systems with little or no oxidised sulfur species. Many epigenetic gold deposits in Archaean sequences are considered to have formed at 350-450°C from ascending metamorphic fluids in which gold was present mainly as reduced sulfur complexes, the sulfur having been released during breakdown of pyrite and/or leached from rocks traversed by the flij^ds. Iron sulfides from most of the Archaean gold deposits studied have 6 S values close to 0 ° / o consistent with the importance of reduced sulfur species in the transport and precipitation of the gold. In contrast, the only giant deposit within the Archaean greenstone b e l t ^ o f Australia, Kalgoorlie Golden Mile, is distinguished by pyrite with 6 S values in the range -10 to - 4 ° / o o and by sporadic development of anhydrite and b a r i ^ , which indicate partial oxidation of the auriferous fluids. The lowest 6 S values are in the most magnetite-rich units of the fractionated Golden Mile Dolerite, implying that magnetite in the host rocks played a key role in this oxidation and resultant gold precipitation. It follows that the Kalgoorlie mineralising fluids had a relatively high degree of interaction with the host rocks (that is, water to rock ratios were low). Another corollary of significance in exploration is that Archaean gold deposits in magnetite-rich mafic rocks or BIF a^g likely to be very large if they contain abundant pyrite with negative 6 S values. It should be emphasised that large Archaean deposits in host rocks with a paucit^of minerals capable of oxidising the mineralising fluids should have 6 S values closer to 0°/ O O ) and that sulfur isotope compositions cannot be interpreted in the same manner for deposits formed after sulfate became abundant throughout the hydrosphere. It is noteworthy that the giant Archaean Hemlo gold deposit of Canada is associated with abundant barite and minor anhydrite. O

323

Other Archaean gold deposits in which unusual sulfur isotope compositions have been documented are in mafic-ultramafic volcanic sequences at Hunt Mine, Kambalda, and Dicken^gn Mine, Canada. Both contain iron sulfides with relatively h^gh 6 S values, up to 8°/ 00 . These can be explained by reduction of S-enriched sulfate in fluids with very low reduced sulfur contents; the sulfate could have formed as a re^lt of wallrock reactions lower in the systems, and been redded by Fe minerals in the host rocks. Had the fluids been reducing, such S-enriched sulfide minerals could only have formed under very high pH conditions; further work is needed to elucidate whether highly alkaline conditions can be generated by interactions with ultramafic rocks. There are several examples of barite in Archaean sequences, testifying to the presence of sulfate in local environments. The global increase in sulfate in the hydrosphere should be represented the geological record by the earliest widespread appearance of marked 6 S variations from 0± 4°/ 00 amongst sedimentary and exhalative sulfides. This event is likely to have paralleled the build up of a significant oxygen level in the atmosphere, and to have been accompanied by proliferation of sulfate reducing bacteria. Current estimates place it between 2.7 and 2.0Ga; more sulfur isotope studies of accurately dated sequences from around the world should narrow down this range. It is important to exclude from such considerations any systems in which major sulfur isotope fractionations can be ascribed to wallrock reactions in metamorphic-hydrothermal systems, like those discussed above.

THE DEVELOPMENT OF DEEP SEA MINING IN THE

INTERNATIONAL

AREAS OF THE OCEANS E.J. Langevad United Nations, Law of the Sea, New York The exploitation of offshore mineral resources has, until the last 50 years, been confined mainly to those resources which could be worked from a land base or between the high and low water of tidal areas and those which could be recovered from fairly close offshore. From historical times, nations have treated these close offshore areas as part of the national domain and questions concerning the right to exploit and ownership have been settled within the national legal system. The area over which this control extended was formalised in the 18th century at a width of 3 nautical miles from the low water mark of the adjacent coast. In the 1940s, deep water drilling beyond the accepted limits of the territorial sea became a practical proposition and the ownership of the resources so explored, mainly hydrocarbons at that time, became a legal problem. This led to a number of countries, including Australia (September 1953), to unilaterally proclaim their exclusive right to exploit the resources of the continental shelf adjacent to their coasts. This was an attractive concept for many countries and an international convention came into force in 1964 which established the right of the coastal states to exploit the resources of the continental shelf to a depth of 200 metres or where the depth admits of exploitation. In the late 1960s, the exploitation of the deep ocean mineral resources beyond the continental shelf seemed to be feasible. The minerals which raised the interest were the manganese nodules covering many areas of the ocean floors and which contained economic quantities of nickel, copper, cobalt and manganese and some 50 other trace elements. Their existence had been known for a long time but the advances in technology and concerns about the depletion of landbased mineral resources lead to active research 324

projects being set u p . T h i s , in turn, focussed attention on two significant deficiencies in the existing law of the sea; the very loose and unsatisfactory definition of the limit of the continental shelf and the fact that there was no international understanding covering the rights to exploit and the ownership of the mineral and non-renewable resources in the international zone beyond the continental s h e l f . As a result, a convention was set up and a new and comprehensive law of the sea was adopted in 1982 and now awaits ratification by 60 states to come into force. The new law of the sea, amongst the many other matters with which it dealt, introduced a completely new concept of an exclusive economic zone for a distance of 200 nautical miles from the coast and in which the coastal state has the exclusive right to exploit the natural r e s o u r c e s . T h i s , however, does not subsume the existing rights over the continental shelf but does impose certain conditions on the exploitation. It also establishes a regime for the exploitation of the mineral resources of the international zones of the oceans and an operative mechanism which is intended to take account of the interests of the internatonal community as a whole. The convention has been signed by more than 130 countries but nevertheless has not gained universal acceptance and is opposed by several of the major industrialised countries including the U . S . A . The m a i n objection is that the convention is considered to be too restrictive of the rights to exploit the mineral resources in the international zone. As an alternative, it is proposed by some of these countries to carry out the exploitation of these resources by means of a series of bilateral t r e a t i e s . During the 1970s, several consortia of international industrial and mining groups carried out a considerable amount of research into developing the deepsea mining technology. The main problems which have to be overcome are the fact that the dredging of the nodules will take place at depths of between 3 to 5,000 metres and the fact that the nodules are very porous with a high moisture content. However, these consortia claim to have devised several dredging and processing procedures, at least up to laboratory and field test stages and possibly up to pilot p l a n t . Despite this progress, work is now reported to be practically at standstill, mainly because of the long delays in reaching international agreement on the terms for exploitation and the continuing recession in the mineral industry. How far the technology has actually now been developed is not made public but it is probable that a further prototype plant stage w i l l be necessary before the commerical production can commence. This itself w i l l require a heavy financial commitment and is unlikely to eventuate until agreements have been reached which satisfy not only the political concerns but also those of the financial sector w h i c h , in the end, have to finance these projects. The main targets for deepsea mining are nickel, copper, cobalt and manganese and this industry w i l l be closely linked with the economics of these landbased sectors of the mineral industry. This has lead to considerable involvement by these landbased producers in devising and drafting the production policy embodied in the treaty. The costs of production of these metals from the seabed were in the early d a y s , expected to be considerably lower than those of the landbased production. This raised concern amongst the landbased producers w h o pressed for a policy of control of production from the seabed for a period of 20 years to avoid disruption of the economy of the industry as a whole. Current estimates however suggest that seabed mining costs may be as high or higher than landbased production.

325

The exploitation of the mineral resources of the deep ocean beds now seems to be a practical possibility but under the present economic conditions, the arguments for their urgent development to supplement dwindling landbased resources put forward in the 1970s, no longer seem validHowever, there is no doubt that, at the appropriate time, seabed mining will become an important sector of the world wide mineral industry. The United Nations Convention on the Law of the Sea (Montego Bay convention) has presented, in principle, solutions ~to the legal problems attending their exploitation and has proposed a mechanism by which the exploitation can reflect an effective international participation.

DEVELOPING GENETIC MODELS FOR VOLCANOGENIC MASSIVE SULPHIDE ORES - DO THEY CONTRIBUTE TO EXPLORATION SUCCESS? Ross R. Large University of Tasmania, Hobart Palaeozoic massive sulphide deposits in Eastern Australia vary in size from less than 100,000 tonnes up to 100 million tonnes, with a median of just over 2 million tonnes. Although the volcanogenic class has a lower median tonnage than the sediment-hosted class, they commonly have a higher precious metal content (2-4 g/t Au and 100-200 g/t Ag) and therefore represent an attractive exploration target even in the present depressed exploration scene. Since the 1950fs there have been major advances in our understanding of volcanogenic ore-formation. Pioneering work by Stanton (1955, 1960), Gilmore (1965), Sangster (1972) and Sato (1974) has contributed significantly by stimulating research and leading to major revisions of the previous scientific dogmas. Geological features such as exhalites, volcanic breccias, lava domes and stringer zones, plus geochemical features such as chloritesericite alteration, sodium depletion and metal zonation are now accepted by explorationists as important parameters of the model. Although geophysics still remains a prime tool for target definition, use of the geological model has important implications in the area selection and ore body definition phases. References Gilmore, P., 1965, Geol. Assoc. Canada Proc., v.16, 63-81. Sangster, D.F., 1972, Canada Geol. Survey Paper, 72-22, 44p. Sato, T., 1972, Japan Geol. Survey Bull., v.23, 457-466. Stanton, R.L., 1955, Econ. Geol., v.50, 681-714. Stanton, R.L,, 1960, Trans. Can. Inst. Mining Met., 53, 22-36.

326

WAVE AND RIVER-DOMINATED DELTA SYSTEMS OF THE EARLY PERMIAN WOORAMEL GROUP, CARNARVON BASIN I.H. Layering Petroleum Branch, Bureau of Mineral Resources, Canberra Two different types of delta system are recognised in the Early Permian (Artinskian) Wooramel Group of the Carnarvon Basin, Western Australia. A sand-prone wavedominated delta is recognised in the lower part of the group; the Cordalia and Moogooloo Sandstones. A shale-prone river-dominated delta system is recognised in the overlying Billidee Formation. Both delta systems were fed by a southeasterly extending drainage network which covered the granitic and metasedimentary terrain of the Precambrian. Eustatic lowering of sea level was associated with the development of the arcuate, sand-rich, wave-dominated delta system. This prograded northwestwards onto a marine shelf depositing pro-delta sand, silt and clay (Cordalia Sandstone), and nearshore silt and sand, deltaic sand and a braided-stream sequence (Moogooloo Sandstone), and covered an area 1.2 x 10^ km^. The seaward margin of the sandprone delta consisted of broad shoals of silty sand which passed into feldspathic sands at the mouth of the active delta. Channel-fill sand bars formed upstream of this as planar cross-stratified and rippled units. A non-marine braided-stream system supplied all detritus for the sandy delta and in turn received run-off and detritus from the easterly source area. A low tidal range in nearshore areas of the delta resulted in a dominantly northwestward palaeocurrent regime. Wave energy was dominant in the delta, choking the distributaries with sand. The delta was oriented at high angles to the shoreline trend, allowing fine clastics to pass in suspension onto the shelf and reworked sand to be distributed to shorelines adjacent to the active delta. A subsequent eustatic rise in sea level inundated the Cordalia-Moogooloo delta system, reducing wave energy, shifting the shoreline landwards, raising the watertable in the non-marine area and deposited a fine-grained marine shelf sequence on top of the sandy delta. Renewed clastic influx from the established drainage system produced prograding lobes in the form of a river-dominated delta. Switching of this delta system, to follow the maximum depositional gradient, and gradual compaction produced vertically-stacked delta lobes with low sand/shale ratios. Tidal range was low during the development of the delta system, so little or no sand-grade material was transported alongshore from the delta lobes. Each lobe consists of a gradually coarsening-upwards sequence with silt, clay and finely laminated silty sand, at the base. This is overlain by coarser, wave and ripple-laminated sand, in the form of a delta-front sheet, and an upper layer of distributary channel deposits. Crevassesplay units are evident in inter-lobe areas and comprise cycles of fine to coarse to fine sediment deposited by breaching of channel levees and infilling of bay areas between major distributaries. Outcrop ridges of the Wooramel Group around the margin of the basin illustrate the lateral relationships between genetic units within the two types of delta. The vertical succession within each delta system is evident from the wireline-log characteristics in two petroleum exploration wells, Quail No. 1 and Kennedy Range No. 1. In these wells the wave-dominated delta consists of a massive Tblocky! sand pile (50 m thick) and the river-dominated delta is expressed as either a series of coarsening-upwards, vertically-stacked deltaic lobes, up to 15 m thick, or a deltaplain sequence of thin sand, shale, silt and thin poor-quality coal seams.

327

ORE IMMOBILIZATION AT BROKEN HILL L.J.Lawrence Consulting Geologist, Sydney Remobilization of.base metal ore occurred at two different stages in the protracted evolution of the Broken Hill orebody. The first remobilization was essentially physical and the second distinctly chemical (Lawrence, 1973). Throughout the orebody •there is abundant evidence of an early annealing recrystallization of both ore and gangue at granulite grade. This annealing would be ift response to stress set up during one or more of the earlier prograde events and would require a confining pressure i.e. a physically closed system. The ensuing folding of the axial plane schistosity initiated several high grade epi-metamorphic processes as follows: a. b. c.

e. f.

extensive brecciation of the more brittle minerals throughout much of the orebody, development of ore-gangue boudinage, formation of various ore-bearing parapegmatites often discordantly intrusive into pre-existing ore — all components being derived from within the orebody, injection of mobilized silica plus lead and zinc into the orebody, from which they were derived, to form large metamorphogenic ore-bearing quartz reefs, formation of innumerable smaller quartz veins carrying various sulphides including much chalcopyrite, possibly even localized flux-aided melting (Lawrence, 1967; Plimer, 1984).

Each of these involve remobilization but the first (a) initiated large scale movement of a physical nature. The ore breccia formed a "mush" of already annealed sphalerite and gangue fragments held in a matrix of progressively deforming galena. As the compression increased the folds were pierced with the ore "mush" invading the country rock transgressively over distances of 100m or more. These downward projecting masses are known as "droppers"; similar but smaller upward projecting spurs are not uncommon (Maiden, 1976). Some 1200 m.y. later during the retrograde epoch further folding faulting and shearing resulted in a chemically and tectonically open system. Chemical fractionation occurred under a shearing stress with the more mobile accessory minerals of the main orebody passing locally into solution and being filter-pressed through the less soluble galena and sphalerite and out into discordant shear fractures. These would correspond with Schniederhohn's "secondary hydrothermal" fluids. These fluids, rich in silica and carbonate, travelled at least 300m away from the main lode horizon and precipated silver, antimony, cobalt and nickel minerals with accessory lead and zinc in a quartz, calcite, siderite lode - the A.B.H. Console Lode (Markham and Lawrence,1962). Similar silver-rich veins were encountered cutting through the orebody in the South Mine area (Lawrence, 1968). Ihe Thackeringa quartz-siderite lodes may also be "secondary hydrothermal".

328

References Lawrence, L.J., 1967., Mineral. Deposita, 2j 5-10. Lawrence,L.J. , 1968., Proc. Australas. Inst. Min. and Metall. , No. 226 Pt.ls 47-57. Lawrence, L.J., 1973., Mineral. Deposita, 8: 211-236. Maiden, K.J., 1976., Proc. Australas. Inst. Min. and Metall.,No. 257: 1-8. Markham, N.L. & Lawrence, L.J., 1962., Proc. Australas. Inst. Min. and Metall., No. 201: 43-80. Plimer, I.R., 1984., Mineral. Deposita, _19, Is 19-25.

PROCESSES RESPONSIBLE FOR THE DEVELOPMENT OF INDUSTRIAL RESOURCES IN COASTAL SANDS, EASTERN AUSTRALIA

SILICA

Brian G. Lees GEO-EXEN, Sutherland, N.S.W. The general specifications for industrial silica sands fall into two main groups. The first group, often colloquially termed 'glass sand', is characterised by low values of iron, aluminium, chromium, titanium, cobalt, calcium and magnesium. The second, used mostly as foundry sand, is low in calcium with the values of other elements rather less critical. Along the east coast of Australia the character of industrial silica sand deposits depends, to a large extent, upon the processes which transported them and formed the present deposit and the length of time the deposit has been exposed to sub-aerial weathering. There is not a confusion of ages in the coastal deposits of eastern and northern Australia, rather there is a degree of synchroneity of formation probably related to climatic variations. The stratigraphies of dune complexes along the east coast of Queensland record an episodic history of aeolian sedimentation. Most dunefields consist of dunes from a number of episodes of formation. At Cooloola, some 175 km north of Brisbane, eight distinct phases of dune building have been recognised of which three formed within the last 10,000 years. -The older systems extend back to at least the last interglacial which ended about 140,000 years B.P. (Thompson, 1981). A phase of dune building prior to about 7,500 years B.P. can be identified along much of the east coast as can phases about 3,500 years B.P., 2,000 years B.P. and at the present time. Dates vary around these figures but there are sufficient examples ranging from the south coast of N.S.W. to Cape York to indicate that this was the result of a widespread change in conditions (Thorn et al., 1978). These variations in the form of coastal progradation are also found across northern Australia (Lees, 1984). Weathering of many of the mid-Holocene dune sands has removed sufficient shell carbonate from the upper parts of the weathering profile to permit use of sand from these more recent deposits in foundries, but has not removed sufficient iron and aluminium to permit use as 'glass sand*. The early Holocene dune sands have developed weathering profiles with white 'A1 horizons up to 6 metres deep forming attractive sources of glass sand. Very little of these early Holocene dune deposits survive in the southern part of N.S.W. It appears that much of the deposits have been eroded away and only traces, in the form of cliff-top dunes, remain. Remnants can be found in the Royal National Park, at Wamberal, at Dudley near Newcastle and on Broughton Island off Port Stephens. The accessible deposits have almost all been extracted. Further north into Queensland and up to north Queensland the surviving areas of this early Holocene dune deposit become more extensive. This is the deposit presently being worked by Cape Flattery Silica Mines in Cape York.

329

In New South Wales this has been offset by the ready availability of Pleistocene inner-barrier sands at Tanilba but equivalent deposits in central and north Queensland tend to be covered with rainforest making their development difficult. References Lees, B.G., 1984. Ph.D. thesis, University of Sydney, pp. 367. Pye, K. , 1983a, Zeitschrift fur Geomorphologie, 45, 175-204. Pye, K. , 1983b, Proceedings of the Royal Society of Queensland, 94, 33-39. Pye, K. & Switsur, V.R., 1981, Search, 12^, 225-226. Thorn, B.G., 1978, In: Landform Evolution in Australia, A.N.U. Press Canberra, pp. 197-214. ' Thompson, C.H., 1981, Nature, 291, 59-61.

RECENT DELTAIC SEDIMENTATION IN THE SOUTHERN BONAPARTE GULF, NORTHERN AUSTRALIA

JOSEPH

Brian G. Lees Box 309, Sutherland, N.S.W. The sediment distribution of Joseph Bonaparte Gulf indicates that, whilst the major diffusive processes within the Gulf are tidal currents, the dominant advective processes are wind and wave driven currents associated with the seasonally persistent south-east trade winds. Transgression across the shelf of the inner shelf zone of deep erosion during the most recent rise of sea level has destroyed the primary characteristics of previous shorelines developed on the shelf during interstadial high sea levels. Sediments eroded from these deposits have been distributed across the shelf by a combination of tidal and wind driven currents. Overlying this autochthonous pattern of shelf sedimentation is a lobe of recent sediments indicating a change from an autochthonous regime of shelf sedimentation to an allochthonous regime of shelf sedimentation. Recent terrigenous sediments have originated from the rivers of the southeastern part of Joseph Bonaparte Gulf. These rivers include the Victoria, Keep, Fitzmaurice and, until the late Holocene, the Ord. The largest of these is the Victoria River. The modern Victoria Delta is markedly asymmetric due to the effects of the dominant advective process, wind driven currents associated with the south-east trade winds. The greater extent of the sub-aerial delta is composed of bare mud flats, which cover some 1,320 sq km. Heavily vegetated fresh water swamps, areas of modern stromatolite growth, cheniers and beach ridge plains are minor features of the delta. The wide expanse of bare mud flat between the pre-recent surface which forms the inner limit to the delta and the chenier complex which formed about 2,350 years B.P. is uninterrupted by older chenier ridges. Throughout northern Australia periods of chenier building have been identified which may indicate variations in fluvial input to the coast (Rhodes, 1980). Periods of chenier building took place in northern Australia between 4,500 and 2,900 years B.P., between 2,350 and 1,700 years B.P. and between 1,300 years B.P. and the present (Lees, 1984). These have been identified at Shoal Bay (Hickey, 1981), at Point Stewart (Clark et al., 1979) at various locations in the Gulf of Carpentaria (Rhodes, 1980) and on the east coast of Cape York (Smart, 1976). Evidence from Dortch (1972, 1977) indicating varying fluvial input to the Miriwun rock shelter deposit in the Ord valley shows that this effect extended to the

330

catchments of the Ord and the Victoria. The lack of cheniers on the Victoria Delta dating within the 4,500 to 2,900 years B.P. period suggests that the change from an autochthonous regime of shelf sedimentation to an allochthonous regime took place between about 2,900 years B.P. and 2,3 50 years B.P. Prior to this the Victoria River and its early Holocene tributaries, the Ord and Keep Rivers, appear to have been infilling an extensive, structurally controlled estuary. The rapid progradation of the sub-aerial delta reflects the size and character of the drainage basin. The Victoria River and its now diverted tributaries, the Keep and the Ord, had a combined drainage basin of 155,730 sq km, an average annual discharge rate of about 386.9 cu m/sec and an estimated maximum discharge rate of 19,000 cu m/sec. As 85% of the precipitation falls within four months and the rivers effectively cease to flow for half the year the average annual discharge rate is the less meaningful of the two flow rates. Assuming conditions similar to the present, and using crude measures of sediment yield derived from the Ord Dam Project, it is estimated that more than 100,400,000 tonnes of material were delivered to the delta each year. Following diversion of tributaries to routes with a gradient advantage this input has reduced to some 64,800,000 tonnes per year. The distribution of sediments in the Joseph Bonaparte Gulf reflects the local hydraulic environment. On the high energy inner shelf the erosion and dispersal downstream of material gives a seawards fining pattern. Much of the terrigenous material on the floor of the Gulf is palimpsest, reworked from older deposits and transported under present conditions. A distinct lobe of recent sand sized material has prograded onto the shelf from the shallow, south-eastern part of the Gulf. The terrigenous sand sized component is characterised by the presence of a significant proportion of feldspar. The sand sized fraction of this lobe is dominated by calcarenite, probably from the destruction of young shell material and echinoids on the high energy inner shelf. This lobe of recent terrigenous calcarenite prograding onto the shelf from the Victoria Delta represents the onset of allochthonous sedimentation in the southern Joseph Bonaparte Gulf. This study formed part of a Ph.D. supervised'initially by L.D. Wright and, following his departure overseas, by A.D. Short. It was partly funded via a Commonwealth Research Scholarship and University of Sydney Research Grants. References Clark, M.F., Wasson, R.J. & Williams, M.A.J., 1979., Search, 10(3): 90-92. Dortch, C.E., 1972., Australian Institute of Aboriginal Studies Newsletter, 3j 13-18. Dortch C.E., 1977., J.Roy .Soc.W.A., _60^: 23-30. Hickey, S.H., 1981., N.T. Geol.Svy., Tech. rep. GS81/1. Lees, B.G., 1984., Ph.D. thesis, University of Sydney, pp. 367. Rhodes, E.G., 1980., Ph.D. thesis, Australian National University, Canberra. Australia, pp. 357. Smart, J., 1976., J. Aust. Geol. Geophys., Is 211-218.

331

SEISMICITY OF IRIAN JAYA 1900-1980 Horst Letz Department of Minerals & Energy, Port Moresby

The investigation of seismicity in Irian Jaya is based on data published by international and national seismological organisations, covering the period 1900-1980. At least 1818 earthquakes of given location and origin time have been connpiled and evaluated. Data of large Irian Jaya earthquakes which have occurred during the last century have been extracted frcm literature. The seismicity of Irian Jaya is alinost (90%) shallow (h < 70 km). It extends along the north coast, around Genderawasih Bay and widely through Irian Jaya. The strain release per square degree (1° x 1°) for the period 1900-1980 shews sharply defined zones of high strain release (9010l° erg0*5) in the eastern Central Mountain range and along the northern coast in the Biak-Japen area (70-1010 erg0-5). The total strain release is 1.05-1013 erg0-5. Dividing Irian Jaya into 12 seismic zones, strain release and magnitude frequency distribution for every single zone has been canputed. The western part of Kepala Burung (132°E) and the Irian Jaya border region (141°E), because of their extreme low seismicity have been recognized as "seismic gaps" and thus potentially dangerous. The pattern of seismicity leads to the concept of two plate fragments; the continental Kepala Burung fragment and the oceanic Cenderawasih fragment. While in eastern Irian Jaya thrust faulting is associated with subduction, the movenent of the Cenderawasih fragment has been interpretated as left lateral strike slip with thrust faulting also occurring in the southeast. The Kepala Burung fragment shows left lateral strike slip. The slip-rates decrease frcm east (5.9 om/yr) to west (1.9 cm/yr).

SHEAR ZONE AND LINEAMENT CONTROL OF MINERALIZATION, BROKEN HILL, NEW SOUTH WALES W.R. Leyh North Broken Hill Limited, Broken Hill Geological studies of shear zones within the Early Proterozoic Willyama Supergroup (Stevens et. al.) indicate that such zones are extremely complex in origin; this complexity is evident at all scales. The shears are defined by zones of ductile retrograde schist deformation intersecting regionally metamorphosed gneisses of the amphibolite-granulite facies transition and contain mineral assemblages indicative of the lower amphibolite facies (Vernon and Ransom, 1971). The shears occur as complex cross-cutting, bifurcating and anastomosing fault structures whose principal strikes are generally NE, NW and EW with several subordinate sets. Detailed studies of the ENE trending Globe Vauxhall lineament and its extensions NE of Broken Hill suggest a complex, variable and probably rotational movement picture (Offler, 1973; Laing, 1977). Highly variable stratigraphic displacements are probably a result of plunge variation and oblique transection of folds across the shears (Hopwood, 1976) and synchronous staggered block movement related to splayed shear systems (Leyh, 1980).

332

In the Globe Vauxhall - Western Shear system the interpretation of preserved internal structures and deformational features is complicated by the presence of dislocated folds of variable plunge. Multiple deformation zones of prominent dislocation separating areas of major discordance in two generations of retrograde folds (Hopwood, 1975) are present together with later cross shears and late stage fault breccia zones. There is a variability in lineations defined by elongated relict high grade garnet, retrograde crenulations and multiple deformed quartz vein pods. Displacement estimates from retrograde stretch lineations of a variable nature are only partially successful. Such lineations can only be assumed to indicate the principal elongation direction of the shear strain ellipsoid; earlier lineations may be obliterated near the centre of the shears where schistosity is sub-parallel to the zone boundaries and shear strain -> 00. Shear zones are intimately related to the principal regional fold structures as demonstrated by distinct changes in prograde structural regimes across the zones and by microfabric studies of regional and shear retrograde schistosities (Laing, op. cit.). In the North Mine area (Hopwood, op. cit.) interprets the principal concordant shears as being initiated by extensive disruption of limb zones of variably plunging prograde folds. Studies of the Springs Shear Zone, a complex splayed zone which represents a northerly extension of the Globe Vauxhall lineament indicate related areas of rapid plunge reversal in prograde fold structures. These occur particularly in zones bordering the main shear and correlation of fold axes across this shear is not possible (Leyh, 1980). An extended history of movement of the lineament in the Springs area is indicated by several factors:- (1) control on dolerite dyke emplacement (2) lineament control of serpentinite plugs (3) variation in petrology, composition and origin of amphibolites across the main shear (4) distribution of regional retrogression and migmatization of metasediments (5) a change in fold styles across the main shear and (6) control of amphibolites (gabbroic dyke intrusion) with splay shear development axial plane to fold structures. Shear zone control of amphibolite intrusion is recognised at Broken Hill by Hopwood (1976). The Broken Hill massive Pb-Ag-Zn sulphide ore bearing fold structures are intimately associated with and partly controlled by shearing in a structure called the Main Shear and occur within a belt of attenuation (Gustafson et. al., 1950). As indicated by Laing (1977), the configuration of the ore lenses appears to be controlled for much of their length both by shearing and tight attenuated folding within a highly disrupted antifomal structure. The on-going process of shear control of mineralization is further illustrated by a variety of late stage vein mineralization associated with sheared areas and retrograde schist zones in the Broken Hill Block. This mineralization is interpreted to have formed via retrograde hydrothermal recycling of metals originally deposited in pre-metamorphic sedimentary/ volcanic rock sequences of the Willyama Supergroup (Barnes, 1983). Lineament studies on a megatectonic scale have effectively linked the retrograde schist zones with the occurrence of regional trends in mineralization, fold structures and intrusive activity (O'Driscoll, 1968, 1983; Katz, 1976). Considering the complexity of the shear zones and their probable influence upon numerous geological parameters over an extended period it is difficult to consider these zones and related controlling lineaments simply as late stage retrograde metamorphic fault zone structures. The possibility of deposition of mixed chemical/sedimentary/volcanic rock sequences in premetamorphic penecontemporaneous fault controlled troughs should be considered more widely. The base of the Sundown Group (Suite 5) in the North Mine area is marked by the transition from fine grained garnet bearing psammitic and psammopelitic gneisses hosting the ore within the

333

Broken Hill Group (Suite 4) to a more monotonous sequence of coarse grained garnet bearing essentially pelitic gneisses of Suite 5 (Leyh and Larsen, 1983). In addition, a zone of fine grained almandine garnets occurs in Suite 4 around the ore lenses in the area between the underlying amphibolite unit and the base of Suite 5. This sharply defined transition in the mines area from Suite 4 to Suite 5 suggests a rapid deepening in the basin of deposition, and a change in chemical sedimentation, together with cessation of distal acid-intermediate volcanism as represented by quartzofeldspathic gneisses and also a cessation of basic intrusion/extrusion as represented by amphibolites. The interpretation of integral lineament control- of structure, igneous activity, sedimentation and mineralization at Broken Hill may not be in conflict with existing data; it is a concept which, following further more detailed study of shear zones and related lineaments within the Willyama Block, could be applicable to practical exploration for metal deposits in the area. References Barnes, R.G., 1983, Broken Hill Conference, 1983, Centenary Volume, Aus. I.M.M., 71-79. Gustafson, J.K., Burrell, H.C. and Garretty, M.D., 1950, Bull. Geol. Soc. Amer., (61, 1369-1437. Hopwood, T.P., 1975, Consultant's Report to North Broken Hill Ltd, 138 p, (unpub.). Hopwood, T.P., 1976, Consultant's Report to North Broken Hill Ltd, 177 p, (unpub.). Katz, M.B., 1976, J. Geol. Soc. Aust., _23, 275-285. Laing, W.P., 1977, Structural and Metamorphic Geology of a Critical Area Adjacent to the Broken Hill Orebody, Willyama Complex, Australia. Ph.D. Thesis, Adelaide University. Leyh, W.R., 1980, The Structural and Metamorphic Geology of the Springs Area, Broken Hill, N.S.W.- Ph.D. Thesis, University of N.S.W. Leyh, W.R. and Larsen, D.F., 1983, Broken Hill Conference, 1983, Centenary Volume, Aus. I.M.M., 133-156. O'Driscoll, E.S.T., 1968, Broken Hill Mines 1968, Monograph Series 3, Aus. I.M.M., 87-102. O'Driscoll, E.S.T., 1983, Broken Hill Conference, 1983, Centenary Volume, Aus. I.M.M., 29-48. Offler, R., 1973, Consultants' Report to the Broken Hill Mine Managers' Association, (unpub.). Stevens, B.P.J., Willis, I.L., Brown, R.E. and Stroud, W.J., 1983, N.S.W. Geol. Surv. Rec., 21 (2) 407-422. Vernon, R.H. and Ransom, D.M., 1971, J. Geol. Soc. Aust., 18 (3), 267-277.

SAPPHIRES AND DIAMONDS IN NSW - ARE TERTIARY DIATREMES AND RELATED PYROCLASTICS THE ANSWER? S.R. Lishmund and G.M. Oakes Geological Survey of New South Wales, Sydney Sapphires have recently been discovered near Inverell in Tertiary ? pyroclastics and rocks which have an evident relationship to ?pyroclastics. Field observations throughout NSW provide clear support for the hypothesis that such rocks may have hosted much of the sapphire/ and perhaps the diamond/ occurring in this State.

334

Until recently, it has been commonly held that Tertiary basalts were the most likely source of sapphire in New South Wales (MacNevin 1972). Proponents of this view relied principally on the distribution of sapphire in recent sediments (always in drainage patterns radiating from Tertiary basalts) and the apparently ubiquitous presence of pleonaste in the heavy fraction of sediments containing sapphire - coupled with the fact that pleonaste was commonly observed as megacrysts in the basalts. However, sapphire was only rarely seen in basalt, and has never been found in situ in basalt. Fragments of basalt have been occasionally found with embedded sapphire megacrysts. Observations by the authors, and others, of rocks present either immediately beneath or within the Tertiary basalt pile in a number of areas in NSW indicate that clay-rich sediments of probable pyroclastic origin may have hosted sapphire (and other minerals) prior to weathering of these rocks and incorporation of these minerals in the heavy fraction of derived fluvial sediments. These pyroclastics and breccias appear to occur in close proximity to eruptive centres. It is suggested that the eruptive centres correspond to deep-seated intrusions, some of which have kimberlitic affinity. The comparative abundance of sapphire and diamond in Recent and Tertiary sediments suggests that rocks containing diamond have been isolated from weathering and erosion since some time in the Tertiary, while sapphirebearing rocks have become more exposed to such phenomena since that time. It is arguable that both minerals could have been carried to the surface in dissimilar magmas ascending the same conduits at different times. Wyllie, 1980, suggested a kimberlite generating mechanism that involved a series of intrusions along the same conduit. Application of such a concept to the observed situation in NSW would see a first intrusion (or series of intrusions) emplacing diamondiferous material, while a later 'phase 1 of intrusive activity may have yielded the sapphires, and a subsequent phase may have produced barren, pleonaste-bearing, alkali basalts; While the evidence for such a sequence of events occurring statewide is still fragmentary, it includes the following: Inverell-Glen Innes a) sapphires recovered from ? pyroclastic rocks near the base of Tertiary basalt pile at Elsmore, accompanied by euhedral zircons and rare pleonaste. b) sapphires recovered from conglomerates containing fragments of ? pyroclastics, and from pyroclastics in a sequence of sediments of probable Tertiary age (beneath basalts) at Kings Plain. Pleonaste is much more abundant here than at Elsmore. Ebor: (?) pyroclastics and breccias underlying Tertiary basalts and overlying granite. Deep-seated inclusions and spinels observed in these rocks. Thumbprint aeromagnetic anomaly associated with this occurrence. Capertee area: multiple diatremes some with abundant deep-seated inclusions, diamonds and subeconomic sapphires in Tertiary sediments. Tumbarumba: fine-grained ? pyroclastics observed near base of basalt pile in close proximity to recent stream sediments containing euhedral zircons, and pleonaste and sapphire. The diatreme and pyroclastic activity has been assigned an Early Tertiary or Late Cretaceous age on the basis of circumstantial evidence acquired from a number of localities. Such an age broadly corresponds with the postulated breakup of Gondwanaland - thereby placing the activity at a time of major tensional stress such as that described by Wyllie (1980) as a precursor to the generation of kimberlites.

335

Possible Implications for Exploration Anyone seeking to apply this proposed model to exploration for sapphire and/or diamonds in NSW should consider the following points in framing exploration parameters. 1 Magnetic -expressions of diatremes need not be large to represent possible economic targets as mineralized effusive material need not have a pronounced magnetic signature. 2 Commercial concentrations of sapphire with zircon in pyroclastic material may only occur close to vents. 3 Second-phase pyroclastics may incorporate diamond-bearing material or diamonds liberated during weathering of ? kimberlite material prior to the second-phase volcanism. 4 The pyroclastics are very prone to weathering once exposed and therefore may not be readily recognized without careful examination. 5 Classical stream sediment indicator search in NSW may only be useful where the diatremes and associated pyroclastics are exposed or were exposed in the recent past. The presence of well-crystallized zircons in stream sediment samples may indicate the presence of mineralized volcaniclastics. 6 Where extensive basalts presently mask possible conduits/diatremes and associated vents then sub-basaltic pyroclastics should be sought. 7 Areas where tensional forces were concentrated at or about Late Cretaceous to Early Tertiary times may be foci for the deposition of sapphire and/or diamond bearing material - particularly where other phenomena (like extensive basaltic volcanism) may have preserved pyroclastics and diamtremes. References MacNevin, A.A., 1 9-35. Wyllie, P.J.,

1972 , NSW New South Wales Geological Survey - Records 14(1),

1980, journal of Geophysical Research, 85(B12), 6902-6910.

SOLOMON SEA STRUCTURE FROM SEISMIC REFLECTION

DATA

Jo Lock Bureau of Mineral Resources, Canberra The Solomon Sea Basin is bounded in the north by the New Britain Trench and in the south by the Trobriand Trough (Fig. 1) and Woodlark Rise. The New Britain Trench is active, with a well-defined Benioff Zone and active volcanic arc. Seismic reflection data show that the Trobriand Trough, also, is an active or recently active trench (Fig. 2), and the Trobriand Basin possibly a fore-arc basin. Lamington and Victory volcanoes on the Papuan mainland probably are related to this trench, but lack of seismicity indicates that the subduction system currently is inactive, or subducting only slowly (Davies, Symonds & Ripper, 1984, BMR Journal of Australian Geology & Geophysics, 9 (1)) Because the lithosphere of the Solomon Sea Basin has been subducted both to north and south it is arched about an east-west axis, and has ruptured to form a series of west-northwest-trending horsts and grabens (Figs 1,2). The horsts form basement ridges in the eastern and central part of the basin, but are buried beneath sediment in the west. Finsch Deep (Fig. 1) is a silled basin which is structurally linked with the New Britain Trench. Markham Canyon (Fig. 1) also is structurally controlled. Seismic reflection data were collected in December 1983-January 1984 by Japanese, Australian, Papua New Guinean and U.N. scientists aboard Japanese research vessel Natsushima. 336

S12 Jo Lock Figure 1

NEW

BRITAIN

Finsch Deep PtMBSvi*

lyuuuu i

Solomon

Sea/Basin

Trend of the Markham / Submarine V^- Canyon Trpbriand

TROBRIAND

PLATFORM Trobriand Islands 80 km

New Britain

—A—

Trobriand Trough sediment raised by normal faulting or thrusting

Trench

Sediment in New Britain Trobriand Trough

I : j Undeformed sediment in the I: I • I • 1111 Trobriand Trough [:;V/.:.•.'.'•;•'] Raised Trobriand Trough

Figure 1:

Solomon Sea Basin with 300m of pelagic sedimentary cover

Trench

n o

(JJ ( j sediment

Slumped

Direction of transport of —|—

sediment

Ridge Slope

Slumping Sediment in perched

sediment

basins

Normal

-L-

Reverse fault

fault

Main structural elements of Solomon Sea

337

S12 Jo Lock . . . Figure 2

17h30m

18h 0 0 m

18h 3 0 m

19h00m

19h 3 0 m

20h00m

20 h 30m

21 h 00m

21 h 30m

PDR Dapth 5 3 2 f l m (uncorractad) 5 3 Z 8 m

22h00m

5198m

4591m

5187m

5083 m

5133m

5124m

5112m

4458m

3404m

Time

Figure 2: Single-channel seismic r e f l e c t i o n p r o f i l e , part o f Line 60 f shows normal f a u l t i n g on outer (northern) margin o f Trobriand Trough. 30-minute time i n t e r c e p t s are 7 km a c r o s s . 338

SEDIMENTARY CONTROLS ON THE HYDROTHERMAL SYSTEM THAT FORMED THE H.Y.C. DEPOSIT AT McARTHUR RIVER, NORTHERN TERRITORY

Ross G. Logan and Neil Williams Carpentaria Exploration Company Pty. Ltd., Brisbane, Queensland Stratiform Pb-Zn mineralization at McArthur River is hosted by the Carpentarian (M.680 m.y. old) H.Y.C. Pyritic Shale Member of the Barney Creek Formation. Mineralization is widespread in the Member, but only reaches significant grades and dimensions in the H.Y.C. deposit. Two main sedimentary facies are recognised in the Member, a shallow-water and a deeper-water one. The indicators of the shallow-water facies are dessication structures and cyclic units of carbonate nodules set in a matrix of distorted siltstone. The facies has been compared with nodular carbonate-bearing sediments that form today in emergent sabkha and salinelacustrine environments (Williams and Logan, 1981). The deeper-water facies contains abundant graded turbidites and laminated siltstones that are indicative of submergent conditions. The contrasting facies indicate that sedimentary conditions varied widely during deposition of the Member. It is envisaged that the depositional environment was either a salinelacustrine or nearshore-lagoonal complex that developed on the eastern edge of the Batten Trough, during a period of instability along the bounding Emu Fault Zone. This interpretation contrasts markedly with earlier ideas of a deep submarine depositional environment (Brown et al., 1978; Lambert, 1976). Detailed sedimentological studies, utilising isopach and isolith maps, have delineated subtle but significant paleogeographic changes in the H.Y.C. area during deposition of the H.Y.C. Pyritic Shale Member. While the sediments above and below the H.Y.C. deposit were forming, the area lay on the eastern margin of a large lake or lagoon that extended well to the west of the present western edge of the H.Y.C. deposit. The depositional environment was therefore a relatively open one in which a shallow to emergent zone adjacent to the Cooley Dolomite gave way westwards to deeper water conditions. By contrast, while the host sediments to the H.Y.C. deposit were forming, the area was occupied by a much smaller lake or lagoon that was comparable in size to the area of the H.Y.C. mineralization. The lake or lagoon was deepest immediately adjacent to the Cooley Dolomite, and it was bounded by frequently emergent areas where sabkha facies sediments were formed. From these findings it is concluded that the paleogeography of the H.Y.C. area played a critical role in the formation of the H.Y.C. deposit, with the relatively restricted lake or lagoon being the main factor controlling the location of the deposit. It is postulated that the lake or lagoon acted as a hydrologic trap for the hydrothermal solutions that mineralized the H.Y.C. Pyritic Shale Member and that this trapping led to the high concentrations of galena and sphalerite in the deposit. By contrast, during the deposition of the sediments above and below the deposit the hydrothermal solutions were dispersed in the more open environments and were only able to form minor concentrations of galena and sphalerite. References Brown, M.C., Claxton, C.W., &. Plumb, K.A., 1978, The Proterozoic Barney Creek Formation and some associated units of the McArthur Group, Northern Territory : Australia Bur. Mineral Resources Rec. 1969/145 (unpub.), 59p. Lambert, I.B., 1976, The McArthur Zn-Pb-Ag deposit : features, metallogenesis and comparisons with some other stratiform ores, iji Wolf, K.H., ed., Handbook of stratabound and stratiform ore deposits, v.6 : Amsterdam, Elsevier, p.535-585.

339

Williams, N., and Logan, R.G., 1981, Depositional environments of the sediments hosting the McArthur River stratiform Pb-Zn deposits (Abs) : Geol. Soc. Australia, Fifth Australian Geo!. Convention, Perth 1981, Programmes and Abstracts, p.8.

THE DISCOVERY

OF T H E

FRIEDA RIVER PORPHYRY PAPUA NEW GUINEA

COPPER

DEPOSIT,

J.R. Lord Carpentaria Exploration Company Pty. Ltd.f

Brisbane

A decision to explore for porphyry copper and gold deposits in the Western Highlands and West Sepik Districts of Papua New Guinea was made by C.E.C.'s Manager, Mr. E.M. Bennett, and District Geologist, John Hartley, in Papua New Guinea in 1967. Hartley had been working all that year at Porgera and was well aware that the mountains to the west were prospective 2 and unexplored. Accordingly, a Prospecting Authority (of 7800 k m ) was applied for on August 10, 1967, subsequently approved as P.A.58 on January 3, 1968, and granted on March 20, 1968. During the latter part of 1967 the B.M.R. was reconnaissance sampling the May River and Ambunti 1:250 000 Sheets but at the time C.E.C. applied for the Prospecting Authority no knowledge of what the B.M.R. might have found was available. In October 1967 Hartley spoke to Duncan Dow of the B.M.R. after he returned from the Sepik. Dow advised that he had seen an area he called the Knob which contained minor intrusions of porphyry with gossan and other indications of mineralization, and that the area would be a good one 1 for prospecting. The 'Knob Dow referred to occurred on P.A.58 towards its western end. This advance knowledge of potential mineralization preceded C.E.C.'s planned stream sediment reconnaissance which started in February 1968. That reconnaissance subsequently covered all of P.A.58 and very clearly outlined the Frieda River Prospect and other prospects in Upper 0k Binai (Pb,Zn,As), Lower 0k Binai (Cu), Nena River (Cu) and Gufug Creek (Cu). The stream sediment reconnaissance around Frieda showed a very strong anomaly for copper with local creeks carrying >1000 ppm Cu (1-3 km 2 catchments) and the main 0k Uwaii and Kokomo Creeks carrying 320 and 750 ppm respectively. These creeks both empty into the Nena River which below both their junctions carries 80 ppm in a catchment of about 250 k m 2 . In Upper 0k Binai a local creek contained 600 ppm Cu, in Lower 0k Binai another contained 235 ppm Cu and north of the Nena River a small creek contained 380 ppm. Upper 0k Binai also gave a lead-zinc-arsenic anomaly (indicating a potential gold target). All of these stream sediment anomalies were known by mid-1969, and the next major thrust was to soil sample them as a prelude to outlining drilling targets. Most of the effort was centred on the Frieda Complex anomalies. This outlined the following targets at the >1000 ppm Cu level :

340

Location

Area (km 2 )

Pish-Bully Koki-Ekwai Horse Lower 0k Binai

0.28 0.60 0.20 0.33

The Nena anomaly was visited, shown to contain malachite float on resampling but not further investigated till the middle seventies. Pish-Bully, Koki and Horse became the drill targets of 1969 and they showed reserves as follows. : Koki 262 x 106 t x 0.41% Cu & 0.23 q/t Au Horse 105 x 106 t x 0.54% Cu & 0.42 g/t Au Pish-Bully Nil The drilling had found a large body of mineralization but no high grade core - as CRAE had found at Panguna - that might pay for the capitalisation of a major operation. By 1972/73 a decision was made to farm out the area and spread the risk of any subsequent development. At the same time the author became aware of work by Learned and Boissen in a similar environment in Puerto Rico. They identified two porphyry copper anomalies at Piedra Hueca and Cala Abajo, one of them having a median concentration of 2300 ppm Cu (P.H.) and therefore quite comparable to the drilled targets at Frieda, and the other with 300 ppm Cu (C.A.) and similar to undrilled areas at Frieda. These authors however found when the same anomalies were tested for gold that the median concentrations were 0.19 ppm Au (P.H.) and 0.15 ppm Au (C.A.). Drilling showed that together these two deposits contained 100 x 10 6 t x 0.8% Cu, but one is simply a hypogene deposit while the other is intensely leached. The leaching had removed the copper but not the gold. The application of this principle to Frieda seemed obvious, and a new major soil sampling programme was commenced in 1973 with the express purpose of outlining new drilling targets defined by the gold distribution. One target to emerge from this investigation subsequently became known as Ivaal. Concurrently, the farm-out arrangements were proceeding and the farmee (a consortium of Japanese companies) arrived to take over the exploration. Subsequent detailed geological work led to the discovery of chalcocite mineralized outcrops in the Ivaal area. The next few years saw the drilling out of the target to establish today's reserve in an assumed open pit for the combined Horse-Ivaal area of 592 x 106 tonnes x 0.54% Cu and 0.34 g/t Au. Early in their tenure the Japanese consortium investigated the Lower 0k Binai anomaly but drilling did not add to reserves. They also turned their attention to the known but otherwise uninvestigated anomaly north of the Nena River, where they were successful in locating mineralized outcrops. Limited drilling here outlined a highly complex mineralogical suite of copper, arsenic, gold and silver minerals. The mineralization had a discontinuous length of some 1500 m, but due to intermixed supergene and primary mineralization the resource in uneconomic. Exploration since that time has seen further drill holes in the known anomalies and more intensive mapping and sampling of the area. The picture to emerge from the mapping shows a vertical section of the Frieda Complex from the top (around Nena) where enargite/gold/mercury mineralization is known, to the deeper porphyry copper zone about 3 km to the SE where the copper/gold assemblage with some molybdenum is predominant. Much of the porphyry copper complex is covered by a pyritic pyroclastic unit which when probed beneath is bound to indicate much more widespread mineralization. References Dow, D.B. et al., Bull. Bur. Miner. Resour. Geol. Geophys. Aust. No. 133, 1972, 88p. Learned, R.E. and Boissen, R., In Geochemical Exploration 1972, Jones, M. J., ed. (London: IMM, 1973), p. 93-103. Lord, J.R., Eleventh Commonwealth Mining and Metallurgical Congress Proc., Vol. 11, 1978, p. 463-474. Hirata, Y., Personal communication. Sweet, L.M., Internal C.E.C. Correspondence, October 1967. Wall, L.N. and Henry, D.D., MMIJ/Aust. IMM Joint Symposium 1983, Sendai, p. 47-63. 341

THE NATURE AND ORIGIN OF KAOLINITE

CLAYROCKS

F. C. Loughnan University of New South Wales, Sydney Kaolinite clayrocks (Loughnan, 1978) are massive, indurated and unusually dense sedimentary rocks composed essentially of kaolinite with or without minor amounts of boehmite, diaspore, siderite, hematite, quartz, illite, anatase and members of the aluminophosphate gorceixite-goyazite group. The kaolinite is generally well-ordered although the disordered form of the mineral is frequently present additionally and in places may predominate. Many of these clayrocks are very fine grained and break with a conchoidal fracture and as such bear a superficial resemblance to chert or flint. The majority however, are arenaceous or rudaceous comprising oolites, pisolites, pellets or clasts of kaolinite set in a matrix of similar composition. The clasts may be angular or wellrounded with some containing residual volcanic textures in which the felspars and groundmass of the original lava are completely replaced by kaolinite and less frequently boehmite, while others have aggregate birefringence and undoubtedly are of intraclastic origin. Nevertheless, vermicular crystals of kaolinite are commonly present and every gradation into rocks containing a preponderance of these is apparent. All textural types may occur in a single hand specimen or even a thin section. The colour of these clayrocks varies according to the content of organic matter with greys predominating, but some are white and all tend to yield lighter shades on calcination. Kaolinite clayrocks have most of the characteristic features of flint clays (Keller, 1968) as well as of kaolinite tonsteins (Burger et al., 1962) and at least some bauxitic clays (Wilson, 1922). In the Sydney Basin and adjoining areas kaolinite clayrocks are widely distributed and attain extraordinary thicknesses. In the Early Permian (Artinskian), Late Permian (Tatarian) and Early Jurassic (Toarcian) they form part of coal measure sequences but in the Early Triassic (Scythian) they are associated with redbeds and other organic deficient continental strata.For the most part they represent a basin-margin facies but nevertheless, are remarkably persistent particularly over the shallower parts of the basin, and are used as marker beds for stratigraphic correlation. Currently, deposits of Early Permian and Early Jurassic age are being worked for production of refractory bricks. Generally they are used in the uncalcined state but at one locality near Wingen natural chamotte (calcined kaolinite clayrock) resulting from combustion of coal seams, is being quarried. The specifications for refractory grade material are a low iron content (preferably 0.5%), a calcined density exceeding 2.50 gem"-5 and a minimum pyrometric cone equivalent of 33 (Orton). The origin of kaolinite clayrocks has long been a controversial issue with dissension centred on whether they are primarily autochthonous or allochthonous. Nevertheless, there appears general agreement that they are the product of a humid and warm to hot climate; a conclusion that is however, at variance with the commonly held concept that cold to glacial conditions prevailed in the Sydney Basin throughout the Permian. References Burger, K., Eckhardt, F. 3. and Stadler, G., 1962, Fortschr. Geol. Rheinld, Westf. 3. 525-540. Keller, W. D., 1968, Clays and Clay Minerals, 12, 129-151. Loughnan, F. C., 1978, Clay Minerals, 13, 387-400. Wilson, G. V., 1922, Memoirs. Geol. Surv. U.K., 1-28.

342

CROCKERS WELL AND ASSOCIATED MINERALIZATION: U, TH, PB GEOCHRONOLOGY OF ORE AND HOSTS 1 o K.R. Ludwig1 and J.A. Cooper^* ^The University of Adelaide, Adelaide (on leave, U.S. Geological Survey, Denver, Colorado) 2The University of Adelaide, Adelaide Sub ore-grade amounts of U-Th-Ti and U-Fe-Ti-Th minerals are found in certain Proterozoic granitoids of the Olary sub-domain of the Willyama Block of South Australia. A few early isotopic measurements on ore minerals and more recent regional Rb/Sr studies have left the timing of metamorphism, intrusion and mineralization of this region undefined. U-Th-Pb isotopic analyses on zircons from all granitoids associated with the Crockers Well brannerite deposit indicate that they were intruded within a short time span which is close to the 1579+1.5 Ma age of the brannerite host rock. The zircon isotopic systems are unaffected by the early Palaeozoic Delamarian Orogeny although it is quite intense in this region. However the best defined zircon chords show a well defined lower intercept of 43.5+6.5 Ma, which can only be associated with early Tertiary block faulting, uplift and cover removal. Pb-U-Th isotopic analyses on ore minerals was less rewarding. Brannerite from the Crockers Well deposit, and davidite from the Mt. Victoria deposit and the classic Radium Hill deposit, yield badly scattered and discordant apparent ages which suggest a primary age at least as old as the Crocker Well granitoids, followed by a severe disturbance in the early Palaeozoic. This scattering helps explain the confusion arising from the few old measurements.

A GEOLOGICAL PERSPECTIVE ON ANALYTICAL ELECTRON MICROSCOPY Ian D. R. Mackinnon Microbeam Inc., Mail Code SN4, NASA Johnson Space Center, Houston TX. The analytical electron microscope (AEM) offers a wide variety of techniques for the sub-micrometer characterisation of materials. Measurement of all signals produced from interaction of the electron beam with a sample allows many operating modes to be employed (e.g. SEM, TEM, STEM). Currently available commercial AEMfs provide these capabilities without significant loss of resolution for individual operating modes. A combination of energy dispersive spectrosopy (EDS) and electron energy loss spectrosopy (EELS) using the AEM can provide qualitative analyses from areas <20nm in size for all elements with Z > 5. Only important aspects of secondary X-ray analysis using EDS are discussed below. However, the combination of structural and chemical data from sub-micron sized samples provides a very powerful tool for the geologist. In an electron microprobe, the spatial resolution for chemical data is limited by the X-ray excitation volume in a thick flat polished sample [1]. Thus, for most purposes the minimum size for analysis is usually -3 \xm [1]. Positioning of the probe may also be restricted by the light optics of the system. In recent microprobes, the introduction of a secondary electron detector has improved sample targeting. Nevertheless, reliable analyses of individual grains (<1 \xm) in fine-grained samples (eg. soils, shales, coals, clays) is difficult using the electron microprobe. In the AEM, the X-ray excitation volume is considerably reduced due to the use of thin specimens (as foils, sections or crushed grains). Thus, spatial resolution for data collection is limited primarily by the size of the electron probe. Many commonly available AEM1s provide focussed probes <2.5nm at the specimen [2], 343

though instrument and specimen limitations [3] increase the practical analytical resolution to ~10.0nm. Thus, spatial resolution for chemical analysis is approximately two orders of magnitude less than an optimized microprobe. Furthermore, objects of interest can be precisely targeted using the AEMs1 superior electron imaging capabilities. Instrument parameters and operating conditions will influence the quality and nature of EDS analyses in an AEM. Accelerating voltage, while critical to imaging resolution in the analytical mode, also affects X-ray intensities, electron beam spreading, signal-to-noise ratio, degree of penetration and electron-induced radiation damage. All of these factors are important in the analysis of geological materials. For example, the rate of beam induced radiation damage for illite is reduced by about a factor of two for imaging at 100kV versus 200kV operating voltages, while relative X-ray intensities from the same thin foil are also improved. However, the production of spurious X-rays from the microscope column and specimen chamber is severely increased. These spurious X-rays can be identified [4] and, in most cases, eliminated by choice of specimen substrates and holders, additional microscope modifications [5] or judicious purchase of a commercial AEM. Specimen damage under focussed beam conditions (eg. imaging, "spot" analysis or convergent beam diffraction) is a vexing problem with geological samples and is receiving increased attention [6]. In general, an increase in voltage is advantageous for analyses of rock-forming silicates. Recent trends are towards dedicated AEM's with operating voltages in the range 100kV to 400kV [ 7 ] . Increased flexibility in the choice of instrument parameters is possible with the use of microprocessor controlled optics and operating modes. The thin-film criterion provides a basis for quantitative analysis of multi-element phases [8]. In a homogeneous specimen containing elements A and B, the intensity ratio of the two characteristic X-ray lines is directly proportional to the corresponding ratio of weight percent compositions Of the elements [8]. Thus, Cb/ca r Kba(Ib/Ia)> where C and I are concentrations and intensities of the appropriate elements, and Kfca = kaea/kbeb* The parameters k and e, are functions of X-ray generation in the sample and the relative detector efficiency, respectively. Thus, calibration curves for Kba factors may be developed to determine the composition of an unknown specimen . Si is a convenient reference element for most geological analyses [9]> while Fe may be used for non-silicates [10]. The technique is not without pitfalls in data acquisition and recognition of instrumental artifacts [4]; variations in detector efficiencies ensure that accurate analyses are machine dependant [10]. Absorption of X-rays is a function of sample mass absorption coefficient and thickness. A commonly used limit for the neglect of absorption corrections is for all values 0.9 < Kba < 1.10. This thin-film criterion breaks down at a thickness of~170nm for Si02 at 100kV [11]. Improved instrumentation suggests that K b a criteria may be reduced to <5% and accordingly, specimen thicknesses for which absorption corrections apply are reduced (eg.-15nm for Si02) [11]. Thin edges (<15nm) in most crystalline silicates can be readily produced during specimen preparation by cleavage or ion-milling. In general,thin edges are more difficult to prepare for metals, alloys and materials of high symmetry. AEM allows explicit identification of minor minerals in fine-grained rocks. For example, pore-filling clays in reservoir sandstones may be 1:1, 2:1 or mixed-layer clays of variable composition [12]. High resolution TEM combined with EDS analyses provides data on the structure type as well as the sub-group (eg. kaolinite vs illite; kaolinite vs serpentine). Similar analyses of bituminous coals show that sub-micrometer calcite, kaolinite, pyrite and quartz are common in vitrinites [13]. Other applications of AEM include quantitative site occupancy determination of selected silicate minerals (eg. Fe and trace elements in olivine [14]), the characterisation of lamellar intergrowths in micas [15] and micro-chemical variations in glass phases induced by shock processes [16].

344

References: 1: Heinrich, K. Electron Beam X-ray Microanalysis, Van Nostrand Reinhold Co. New York, 1981 2: Thompson, M.N. Electron Optics Reporter 30 1-23 1983 3: Goldstein, J.I. in Introduction to Analytical Electron Microscopy (eds. J.J. Hren et al.) Plenum Press New York, 83-120 1979 4: Zaluzec, N.J. 121168 op. cit. 5: Allard, L.F. and Blake, D.F. Microbeam Analysis 1Q82 8-20 San Francisco Press CA, 1982 6: Veblen, D.R. and Buseck, P.R. Proc. Elect. Micros. Soc. Amer. 41st Meet, 350-353 1983; McElfresh, D.K. and Howitt, D.G. 380-381 op. cit. 7: Hagemann, P.N. Electron Optics Reporter 30 31-49 1983 8: Cliff, G. and Lorimer, G.W. J. Microscopy 103 203-207 1975 9: Nord Jr., G.L. Ultramicroscopv 8 109-120 1982 10: Zaluzec, N.J. Proc. Workshop on Analytical Electron Microscopy, (ed. R.H. Geiss) 47-53 San Francisco Press CA, 1981 11: Williams, D.B. and Goldstein, J.I. 39-46 op. cit. 12: Almon, W.R. and Davies, D.K. Clays and the Resource Geologist (ed. F.J. Longstaffe) 81-103 MAC Short Course, Co-op Press Edmonton, 1981 13: Minkin, J.A. et al., Microbeam Analysis 1Q8^ 27-30 San Francisco Press CA, 1983 14: Tafto, J. and Spence, J.C. Science 218 49-51 1982; Self, P.G. and Buseck, P.R. Proc. Elect. Micros. Soc. Amer. 41st Meet. 178-181 1983 15: Veblen, D.R. Am. Mineral. 68 554-565 1983 16: Lambert, P. and Mackinnon, I.D.R. i . Geophvs. Res. 89 B685-B699 1984.

GEOLOGIC, PARAGENETIC AND FLUID INCLUSION STUDIES OF GOLDSULPHIDE- SULPHOS ALT VEINS, CASSILIS, VICTORIA M. MacLennan and M.S. Bloom Department of Earth Sciences, Monash University, Clayton Documentation of the Cassilis and Ceresa Mines in the Cassilis gold field, Victoria has concentrated on production and locations of mine workings relative to the reef systems. Few specimens of the gold-sulphidesulphosalt mineralisation have been preserved, and detailed investigations of the auriferous veins are unknown. We here describe the mineralogy, paragenesis, fluid inclusion geochemistry, and possible causes of mineralisation as shown by or inferred from intersections of mineralised reefs in drill core below the developed mine levels, and by detailed mapping of surface and accessible underground exposures. Mineralisation is hosted by a sequence of polydeformed pelitic schists, phyllites and psammites of probable Upper Ordovician age. An early regional deformation (D^) has first folded a marine turbidite succession into isoclinal recumbent folds. Solid-phase inclusion trails of biotite and quartz contained within prograde cordierite (db andulusite), and aligned at high angles to subsequent cleavage development, define S 1# The sequence has been refolded about dominantly east-west trending, upright axial surfaces. The open and shallowly plunging second generation (F2) folds have wavelengths of approximately 2 km. Anastomosing foliation of sillimanite and K feldspar about cordierite + biotite defines second generation (S2) schistosity. Development of a crenulation cleavage (S3) has been associated with a third regional deformation (D3) and with retrograde muscovite growth. Folds are cut by abundant fault-related fracture systems which are steeply to moderately west-dipping and strike approximately parallel to D^ fold axial traces. The fractures formed late during the regional folding history in a high fluid pressure regime. Mineralised structures are discordant with both S2 and S3 cleavage, indicating ingress of ore-forming fluids late relative to fold growth and cleavage development.

345

Several paragenetic stages have been recognised in crustiform textures from dilatant fractures. The generalised sequence of ore deposition observed is 1) pyrite-arsenopyrite ± gold; 2) pyrrhotite-sphalerite-galena; and 3) chalcopyrite-pyrite. An horizon of quartz, locally with terminations directed • into larger dilatent structures, delineates the boundary between gold-arsenopyrite and base-metal sulphide mineralisation. Minor muscovite and (ankeritic?) carbonate are also associated with this and later stages of gangue deposition. Replacement textures are exhibited by sphalerite, galena and chalcopyrite (replacing pyrite), sphalerite (replacing arsenopyrite) and carbonate (replacing quartz). A late generation of barren quartz cross-cuts mineralised structures at high oblique angles. This sulphide/gangue paragenesis is consistent throughout the Cassilis, Ceresa and other relatively minor (Snake, Blacksmiths, Cripps) vein systems and suggests variation of ore fluids in time, but not necessarily in space. There is as yet no evidence for precipitation of silver and silver-lead sulphosalt minerals as observed on the Sunnyside goldfield (Birch, 1981), 50 km to the north and hosted by similar highgrade metamorphics. Most veins exhibit features indicative of growth during an extended history of repeated increments of cracking by hydraulic fracture and sealing by deposition of quartz and other phases (Cox and Etheridge, 1983). Syn-mineralisation and post-mineralisation deformation are inferred from cataclastic textures in pyrite and arsenopyrite, plastic deformation in late-stage galena and sphalerite, and fine, subparallel trails of fluid and mineral inclusions along incompletely healed crack-seal growth sites in quartz. As a result, it is difficult to distinguish primary from secondary fluid inclusion populations. Undifferentiated populations include both aqueous and CC^-rich inclusions. Salinities of the inclusion fluids are low (3-6 equivalent weight percent NaCl), and their homogenisation temperatures uncorrected for pressure range from 180° to 260°C. Considering the pressure fluctuations inferred by the crack-seal mechanism (Pf < aj), application of a constant pressure correction is unwarranted; nevertheless, mineralisation temperatures in the region from 280° to 320°C are indicated. Preliminary measurements of sulphur isotope fractionation between galena and sphalerite also suggest temperatures near 300°C. Aqueous inclusions contain rare anisotropic (muscovite?) and opaque (hematite?) plates; CC^-rich fluids occur predominantly in early stages of quartz deposition, and indications of boiling are not evident. Gold-sulphide-sulphosalt precipitation in the vicinity of pyritic/carbonaceous units by mixing of locally-derived, reducing fluids, with more oxidised solutions traversing structural pathways of fluid migration (Wall and Ceplecha, 1976; Cox et al., 1983) may not be a feasible mechanism of ore deposition here, and alternate processes must be considered. Mesoscopic alteration envelopes adjacent to mineralised structures attest to disequilibrium between the wall rock and ore-forming fluid, and the alteration assemblage (muscovite-quartz) requires acid solution compositions. We propose that isothermal water/rock interaction of the metamorphic mineral assemblages with reduced solutions enriched in gold, arsenic and base metals would produce the observed paragenesis as reaction progressed toward overall equilibrium. A regional metamorphic derivation for the gold-bearing solutions is consistent with our observations and those of Green et al. (1982) and Cox (1984) for goldsulphide (± sulphosalt) mineralisation in syntectonic slate-belt deposits. We cannot discount the possibility of non-metamorphic or modified metamorphic ore-forming fluids, directed by the continued opening of fractures and derived from granitoid intrusions exposed immediately to the south of the Cassilis goldfield (Eberz et al. , 1984), to account for the base-metal mineralisation later in the paragenesis.

346

References Birch, W.D., 1981. Mineral. Magazine, 44, 77-78. Cox, S.F., 1984. Geol. Soc. Australia Abst., 11, 23-26. Cox, S.F. and Etheridge, M.A., 1983. Tectonophysics, 92, 147-170. Cox, S.F., Wall, V.J., Etheridge, M.A., Sun, S.S., and Potter, T.F., 1983. Geol. Soc. Aust. Abstr., 9, 260-261. Eberz, G. , Nicholls, I.A., and Wall, V.J., 1984. Geol. Soc. Aust. Abst., 12. Green, A.H., Donnelly, T.H., Jahnke, F.M., and Keays, R.R., 1982. Mineral. Deposita, 17, 175-192. Wall, V.J. and Ceplecha, J.P., 1976. XXI st. Int. Geol. Congr., 1, 142143.

THE ALPHA OIL SHALE DEPOSIT - THE RESOURCE AND ITS POTENTIAL D.A. Madre Alpha Resources Limited, Sydney The Alpha Oil Shale deposit is located approximately 500 km west of Rockhampton and around 60 km south of the township of Alpha in Central Queensland. Geologically it is located on the eastern flank of the Galilee Basin. Impressions of Glossopteris and Gangamopteris and seedlike structures occur within the Alpha sequence indicating Permian age. Woolley (1941) placed these beds in the Colinlea Formation. A drilling programme of twelve holes and three shafts, totalling 465m, was carried out by the Queensland Mines Department during World War II. The results were later reported by Connah of the Geological Survey of Queensland, who concluded that the deposit consists of an ovate lens of torbanite enclosed by a pod of canneloid coal. A minimum resource of around five million barrels of oil, from the torbanite alone, was calculated over an area of approximately 2.5 sq.km.

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More recently work on the reflectance properties and maceral composition of samples from Alpha indicate that the enveloping material is not cannel coal but a low grade carbonaceous torbanite. It was probably formed in a marginal lucastrine environment where the imput of higher plant debris was a factor during deposition. The low grade carbonaceous torbanite represents a significant part of the deposit's oil resource. Since 1978, Alpha Resources Limited has conducted exploration in which the total section of oil bearing material is considered as the resource under study. This is referred to as the Alpha seam. Eighteen further holes, totalling 647m, have been drilled. Drilling has shown that the deposit has an area of approximately 9.5 sq.km. with a thickness of around 2.5m in the east, where the seam consists of high grade torbanite enclosed by low grade carbonaceous torbanite, and lm to 1.5m in the west, where the seam consists of only low grade carbonaceous torbanite. A total resource of around 18.6 to 19.3 million barrels of oil has been calculated. Within the Alpha seam the torbanite, along with its associated carbonaceous sequences, appears conformable with the surrounding strata. It is likely that the limiting factors to the size of the ore body are the dimensions of the environmental conditions that existed at the time of deposition. The deposit appears restricted to the north and south by non deposition, and to the east by outcrop and truncation. Westward, the torbanite appears to thin by facies change into low grade carbonaceous torbanite. Around 60% of the oil is concentrated in the east of the deposit within the lens of torbanite material. An outline of an area with potential for open cut mining has been defined in this portion of the resource. This 3 area contains 47,170,000m of overburden, 5,327,000m3 of shale, 10,843,000 barrels of oil. The overburden to shale ratio calculated on a volume to volume basis is 8.86 to 1 with an average shale grade of 240 1/tonne calculated by modified Fischer assay.

Potential development possibilities are: 1. A surface retort combined with a hydrotreating and hydrocraking process plant to produce around 3,500 B.P.D. of diesel fuel. Such a plant would produce around 1,155,000 bbls of oil per year for marketing in the local area. Possible recoverable reserves estimated at around 16 million barrels would give the project a life span of about fifteen years.

348

2. A novel direct chemical additive use in the extraction of nickel from laterite nickel ore has been isolated for Alpha oil shale. The application is made possible by the rich oil content and the low sulphur content of Alpha torbanites. Laboratory tests carried out by Queensland Nickel at the Yabaloo nickel refinery indicate that the approach has great potential. The next development step in the commercialisation of the process involves a full scale plant trial to confirm the laboratory results. If successful, the development could be immediate and would be the first such direct use application of oil shale in the world. References Connah, T.H. 1964 Geological Survey Queensland Report No. 3. Exon, N.F. 1970 Tambo Qld. Geological Series - Explanatory Notes. Hutton, A.C., Kantsler, A.J., Cook, A.C., McKirdy, 1980 APEA J. Vol. 20. Hutton, A.C. 1981 ANZAAS Congress. Brisbane. Swarbrick, C.F.J. 1974 Oil Shale Resources of Queensland. G.S.Q. Woolley, J.B. 1941 Shell Queensland Development Pty. Ltd. G.S.Q. Lib.

DELTAIC DEPOSITIONAL E N V I R O N M E N T S IN THE RANGAL COAL M E A S U R E S , CURRAGH MINE, CENTRAL BOWEN BASIN, QUEENSLAND C.W. Mallett1, L. Grimstone2, J. Gorman^ and J. Woods3 ^"CSIRO Division of Geomechanics, Mt Waverley ^L. Grimstone & Associates, Eight Mile Plains Curragh Queensland Mining, Blackwater Depositional models have been developed for the coal and terrigenous sediment systems extending from the Orion to Aries Seam between Blackwater and the Mackenzie River. They represent a complex of channels and splays within a fully freshwater terrestrial section of the palaeodelta. Distinct distributaries have been identified and their distribution mapped for the major sedimentary wedges within the mining lease. The analysis is based on approximately 1500 boreholes with an average spacing of 70m, and detailed mapping of successive highwall exposures in the mine. Coal plies and partings have been identified throughout the area. These have been correlated to the depositional events in the overlying interseam, allowing interpretation of the dynamic interaction of the mobile sedimentary systems with the extensive and long-ranging peat swamps. The Orion - Pollux interseam thins west to east from 16 to 4 metres. Zones of thickened isopachs approximately 500m wide are oriented very roughly east-west, and correspond to sand concentrations.These sandy zones are the high energy cores of splay wedges derived from major distributaries not found in the study area. In the northern portion of Curragh Mine, the sandy zones are arranged in a birdsfoot radiating pattern. Sediment sources for this interseam interval was from the northwest. Initial deposition over the Orion Seam appears to have been almost synchronous over the area of study, and interseam sediments dip only gently onto coal.

349

The Pollux - Castor interseam resembles that of the underlying interseam in the southern half of the mine. In the northern part of the mine major sandstone feeder distributaries are encountered. These trend to the southeast and southwest, with a source to the north or northwest of the mine. Distributaries show lateral migration into the peat swamps with high angles of dip with respect to the enclosing coal seams. Although the percentage of sand is higher in these channels, individual sandstone bed thickness is generally less than 1 metre, and laterally grade into siltstone in highwall sections. Successive cuts show that the sandstone bodies continue as linear strips in the direction of channel flow. In the southern half of the mine, the splay wedges encroach from both the east and the west. The Aries and Castor Seams are separated by a sandy channel which has a maximum thickness just to the east and south of the proposed mine development. Over most of the area to be extracted, the Aries-Castor will be mined as a single seam, although the individual characteristics of the two seams are maintained. Intrasea.m splits thicken to the north, south and east of the mine development. The position of rapid thickening of split sediment from 0 to 1 metre thickness shifts successively to the southeast in younger seams.

THE IDENTIFICATION OF FAULT ZONES IN COAL MEASURES, BLACRWATER DISTRICT, CENTRAL QUEENSLAND 1

C.W. Mallett , L. Grimstone , J. Gorman

and J. Woods

^CSIRO Division of Geomechanics, Mt Waverley ^L. Grimstone & Associates, Eight Mile Plains ^Curragh Queensland Mining, Blackwater Low angle and bedding plane thrusts are difficult to recognise in borehole exploration programs, and are frequently overlooked in coal measures. A technique for identifing thrust zones from closely spaced borehole data has been developed for the Curragh Mine Area. The analysis is based on the ability to recognise effects of thrusting, such as thickened or thinned seam and interseam sections, or where sections are disrupted by secondary faults splitting off the major thrust planes. The Blackwater area is traversed by a number of linear features which show up as lineaments on photographs and satellite imagery. Some of these lineaments cross the strike line of the coal measures, displacing the seams, and causing the strike of the open pits to swing. Where the lineaments cut an open pit the nature of the structure can be determined, and one example exposed in Curragh Mine has been mapped as a thrust. Surface mines throughout the Blackwater Area consistently show strong compressional faulting, with low and high angle thrusts, and mapping in the early pits at Curragh confirmed their presence there also. Tectonic movements have taken place on bedding plane shears in or close to coal, and on low to high angle reverse faults cutting the interseam sediments. The resultant of these movements is low angle thrusts with an average dip of 5-15°. Large bodies of sediment remain undisturbed, but are bounded by thin bedding plane shears top and bottom, and near vertical thrust zones, which may be restricted to one interseam section.

350

The effects which can be detected to allow mapping of the structural dislocations are: 1. Zones of tectonically thickened interseam sediments where adjustment to shortening of the section is accommodated. A prerequisite for this is an accurate sedimentological model of the area which gives the predeformation thickness isopachs. 2. Zones of thickened or thinned coal, inconsistent with the regional ply and split patterns. The density of borehole data has allowed these zones to be mapped, and a structural model for the area to be constructed. The major element is a regional lineament striking 140o, shown to be an overthrust from the northeast. The central zone of this thrust is approximately 1km wide, where movement has been concentrated on the Pollux Seam. This is bounded on each side by zones of low angle thrusts, which zigzag through the section with bedding plane and steep reverse fault steps. Displacement on the central thrust zone has been approximately 0.5km. The thrust system has been cut by northeast - southwest strike slip faults with about the same ammount of displacement. These techniques have provided a reliable method to predict areas of structural disturbance within a thrust faulted section, for use as a predictive tool in mine planning. Regionally the study has shown the northwestsoutheast lineaments in the Blackwater Areas to be thrusts, and the northeastsouthwest .set to be strike slip faults.

UNESCO'S P R O G R A M M E IN EARTH

SCIENCE

S.T. Mailing UNESCO, Djakarta The aims of Unesco in the field of Earth Science can be summarized as follows: -

to promote research and international co-operation; to promote exchange of information: to assist in the training of Earth Scientists at the post-graduate level

to assist in the assessment, prediction and mitigation of natural hazard of geological/geophysical origin.

The Earth Science Division (SC/GEO) of the Science Sector is primarily responsible for the realization of the above aims with involvement from Marine Science Division (SC/OCE), Environmental Science Division (SC/ECO) and the International Commission (IOC). In all its programmes in Earth Science Unesco depends heavily on the co-operation from the International Scientific Community. Research in Earth Science is mainly promoted through the International Geological Co-operation Programme (IGCP) in collaboration with the International Union of Geological Scientists (IUGS). Currently, about 50 IGCP projects are carried out, most are international but a few are regional, there are 3 in the region of Southeast Asia. A major regional project "Geology for Development" is presently undertaken in sub-Saharan Africa on the Precambrian with the view to improve knowledge of the structure, stratigraphy and economic potential. Similar major projects will be developed in other regions. 351

Preparation and publication of thematic maps of research findings in the various branches of Earth Science is done in collaboration with competent governmental and non-governmental organizations. Post-graduate training in various topics of Earth Sciences is carried out in collaboration with Universities and other institutions for higher education. Currently, some 20 training courses are undertaken on a recurrent basis intended for post-graduates from developing countries. The duration of the courses is from 6 weeks to 2 years and approximately 15 participants are admitted to each. Ad hoc training courses of short duration, 1-3 weeks, in selected topics are carried out on a regional basis in collaboration with regional networks for Geoscience and appropriate institutions., governmental and nongovernmental organizations such as the Association of Geoscientists for International Development in the region of Southeast Asia. Other regional activities such as workshops, seminars, meetings etc. , are also carried out on an ad hoc basis to enable geoscientists to exchange views on particular topics and to formulate strategies for future development in Earth Science. With regard to natural hazards, such as volcanic eruptions and earthquakes, a particular concern to Southeast Asia Unesco in collaboration with appropriate organizations is endeavouring to assist in risk assessment by collection and interpretation of pertinent data with a view to improving the understanding of natural phenomena and their mechanisms. Further multi-disciplinary studies to develop natural hazard warning systems are promoted.

JULIA CREEK SHALE OIL: TECHNICAL AND ECONOMIC ADVANCES J. Mandelson Larbert Pty Ltd (for CSR Limited), Sydney CSR completed a pre-feasibility study of the Julia Creek shale oil project in 1979-80 which was updated in 1982. The first study concentrated on geology as much as process technology. After the first study, work has been solely concerned with technology, such as retorting, in-situ retorting, oil hydrotreating, power generation and environmental studies. The cost of the studies and the technical work which followed from them was in excess of $3 million. CSR's oil shale deposits at Julia Creek lie on the Euroka Arch, alongside the Townsville-Mount Isa railway: they represent only a small part of the vast Toolebuc Formation. Total oil resources in the title areas are about 20 billion barrels, approximately half being in shale suitable for open-cut mining. With more than 1,000 holes drilled in the region, the geology is well understood. Below the 15-18m zone of oxidation, the oil shale is about 7m thick and contains about 18-20 weight per cent of the oil bearing component, "kerogen". The open-cut deposits are almost horizontal and would be mined in a simple back-fill operation. The shale is mainly calcite and quartz, but pyrite, clay and gypsum are also present. Technical studies have been mostly concerned with oil extraction (retorting) and hydrotreating (refining). In-situ retorting is a long term possibility.

352

The retorting work commenced with an engineering appraisal of the Tosco II process for the first feasibility study. Following that, collaborative research between CSR and CSIRO had two significant results; first, it established the technical possibility of using "spent" (retorted) shale as a fuel for retorting and providing the project with its electricity; then, it opened a new pathway for retorting, which is now patented. The new CSIRO/CSR retorting process is particularly exciting. It has a number of advantage s, the main one being its apparent cheapness of construction stemming from its simplicity. Other advantages include generating retort heat from the reaction of free lime with sulphur, CO2, silica and water vapour, and eliminating H2S from retort gas and doubling its hydrogen content. The oil would be refined with hydrogen, which would be a by-product of retorting. CSR has a pilot hydrotreater which it uses to establish the technology. Diesel fuel and kerosene have been made to major specifications and heavy residue has been hydrocracked into lighter fuels, such as diesel. Volumetric yields are typically more than 100 per cent. The naphtha (gasoline) is more difficult to refine, because the objective is to remove nitrogen from the naphtha without destroying the aromatics in it. However, naphtha, with as little as 3 ppm of nitrogen, has already been made. The economic outcome of these technical achievements has been to reduce the gap between the required price of refined shale from Julia Creek and its actual equivalent market price. Much work remains to be done, of course, but preliminary assessments of the financial benefits of the new technology indicate that the overall project cost could be reduced by about 12 per cent below the estimate in the first pre-feasibility study or, say, between $700 million and $800 million. With that economic incentive in mind, CSR?s objective is now to have all of the major technical problems solved in time for the next significant oil price increase.

MINERALOGY AND PALEOENVIRONMENT OF QUATERNARY SEDIMENTS CORED IN THE RASHIMA SEA OFF THE EAST COAST OF CENTRAL HONSHU, JAPAN S. Manickam1*2 and H. Okada1 ^•Laboratory of Marine Geology and Sedimentology, Institute of Geosciences, Shizuoka University, Shizuoka, Japan Now at Centre for Water Resources, Anna University, Madras, India

To reconstruct the paleoenvironment of the Quaternary System in the Pacific-Kashima Sea off the east coast of central Honshu, Japan, bore-hole sediment samples up to a depth of 500m were analysed. Sedimentological and mineralogical studies show that there are anomalies in the sedimentological record at 240m, 270m, 300m, 350-370m, and 450m i.e., in the Pleistocene Series (Fig. 1). A sudden apearance of more carbonates and disappearance of clay minerals between 360m and 440m is observed which might be due to pronounced biologic activity and to the low rate of (terrestrial) sedimentation as a result of sea level rise during the Early Pleistocene for which a warm climate was proposed.

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3 HX n> a 0 Kn>) h 3 H(D M PJ H KJ >0 M O M Hrt (D

IO t n ° well depth O o o O o O o o O. O (m) 1.1.1,1. 1 i 1 . 1 If 1|1 i1 I( 1 i 1 i 11 i1 11 ii 11 i 1 1 1.i(ill I I 1 I 1 1 HOLO A G E PLIoJ P L E I S T 0 C E N E environment INNER NERI TIC U P P E R B A T H Y A L OUTER NERITIC

it N K il

M •• lUil

i S

M It i

ocr cr|

O f

0s K

. - A /

£V \l \

/a /Q

_ -

\J \l

we11 crystallised well <jryst< Crystallised \ Poorly Crystallised Cr;

smectite crystallinity : ] (Biscaye,1965)

illite crystallinity (Chamley,1980)

^ 3:^oM 3* S 2R 3 ^ 3 (A fl> 3 (A

0) (A O rt 0 H - hh rt

fl> v£J

>I0D n h v o 0 3P RP1>oH o ^ rt ( CD b illite/ smectite ratio

Kaolinite- the most unstable mineral among the clays - is not observed in this bore-hole. Chlorite, the larger grain size clay mineral, is found in abundance whereas smectite (montmorillonite), which is finer grained and lighter, is present in very small concentrations. This is due to their differential settling, indicating that this area was always under water. Pyrophyllite(?) a hydrothermal metamorphic mineral, is observed at three levels, and is derived from terrigenous sediments.

354

The main source area of Kashima SK-1 sediment could be the adjoining land mass which was constantly subjected to tectonic movements, volcanic activity, occasional global climatic and sea level changes. The Kuroshio current did not play a role in mineralogical changes, but the differential settling phenomenon of clay minerals proved significant. These sediments were transported mainly during the Early Pleistocene by wind and glacier and during the Late Pleistocene and Holocene by water and wind.

LATERITIC WEATHERING AND ITS IMPLICATIONS FOR GEOCHEMICAL EXPLORATION OF NEAR-SURFACE GOLD DEPOSITS A.W. Mann CSIRO Division of Mineralogy, Perth Mineralogical observations and geochemical interpretation of weathering events in the near-surface zone of some Western Australian gold deposits suggest extensive remobilization of many elements, including silver and gold. Ferrolysis, or hydrolysis and oxidation of iron is believed to be a fundamental factor in the production of acid during the laterite-forming process. Combined with the high chloride content of saturated laterite profiles, this acid is sufficiently strong to cause dissolution of gold/silver alloys and the mobilization of gold and silver under oxygenated conditions as chloride complexes. Subsequently, gold of high purity is reprecipitated by chemical reduction as small very pure crystals, or as thin films and in wire form, on or near iron-oxide. The near-surface zone of many lateritized deposits frequently contains a broadzone of lower-grade "secondary" gold, overlying the vein or lode-system. Other associated elements, including silver, are more mobile under the extreme weathering conditions believed to have been present during lateritization, and are often extensively leached.from supergene/oxidized zones. One exception, which does not have a strong chloride complex and which is strongly adsorbed to iron-oxide in acid solution is arsenic; this element has been extensively used on the Yilgarn Block as a pathfinder for gold. The consequences of the geochemical processes occurring during lateritization are manifest in the exploration, analytical, mining and metallurgical phases of development.

A SUITE OF TESCHENITIC INTRUSIONS FROM THE COALFIELDS OF NEW SOUTH WALES D.J. Martin School of Earth Sciences, Macquarie University, North Ryde Work is in progress on a suite of nepheline-normative teschenitic intrusions from the Southern coalfield, the Hunter Valley and the Gunnedah Basin. Prospect Intrusion is included for comparison. A study of drilllogs of 100 evenly-spaced drillholes from the Gunnedah Basin showed that

355

39% of holes have one or more igneous intersections, whose size-frequency distribution is strongly skewed towards thicknesses of less than 5 m; most are less than 1.5 m, though 6% are thicker than 50 m. Those intruded on coal show a similar size distribution. However, when grouped into series (each assumed to be one intrusion) with less than 5 m of sediment between igneous units, the modal thickness of intrusions on coal is larger than the mode in sedimentary sequences. Some stratigraphic control is evident, e.g. in the area east of Rylstone, intrusions are confined to the Long Swamp, Glen Davis and Farmers Creek formations. Petrology and mineralogy are very uniform. Titansalite, calcic plagioclase (commonly labradorite-bytownite), titanomagnetite and rare to common titanian biotite compose the teschenite. Increasing amounts of olivine occur in olivine teschenite and picrite. . In layered sequences, bands of residual syenite occur, in which the pyroxenes are first Feenriched at constant Ca, and become more acmitic in the late stages. Biotite or kaersutite may also be present in syenite. Intrusions examined in detail all exhibit varying degrees of late-stage Fe and Na enrichment. Four styles of differentiation are found, absence of a picrite and/or a pegmatite unit. with chilled marginal MgO content.

based on the presence or Some correlation is found

Type 1 contains picrite but not pegmatite, and is commonly on cindered coal. Detailed study of a primitive intrusion of this type, containing spinel lherzolite microxenoliths, suggests that the adjacent coal seam (probably fluidised by the high temperature of intrusion) acted as a heat sink, absorbing superheated steam from the intrusion in the endothermic reactions occurring during cindering. Where an equal thickness of coal occurs on each side of the intrusion, the picritic unit develops centrally, but it is displaced away from a single or a thicker coal band, or from a near-surface, rapidly cooling sedimentary contact. No correlation with MgO content can be seen. Type 2 has one or several pegmatite units but no picrite. Pegmatite formation, with a higher content (or greater retention) of volatiles, and less intense effect on adjacent coal, could imply a lower temperature on emplacement. Those examined have a chilled margin MgO content of less than 7 wt.%. Type 3 intrusions (including Prospect) are more than 60 m thick, and so cooled more slowly. Both basal picrite and stratigraphically higher pegmatite units occur. Chilled margin content of MgO is more than 8 wt.%. Those examined so far are not intruded on coal. Type 4 is characterised by complex grain-size and compositional layering with ocelli of hydrated silicates common in the chilled margins. Intermediate MgO values are usual, though some overlap with other groups occurs. This type is common in the Gunnedah Basin. Liquid immiscibility has been considered as a differentiation mechanism but was rejected on microstructural and geochemical grounds in favour of fractional crystalisation. It is tentatively suggested that the various differentiation styles may be due to intracrustal fractionation of olivine, and to'varying degrees of volatile retention during solidification. The latter may be linked with temperature of emplacement and reaction with coal. I am grateful to the N.S.W. Department of Mineral Resources for the use of drill-logs and core, and to personel of the Coal Geology Division for their generous assistance.

356

THE USE OF QUANTITATIVE RELATIONSHIPS IN TERTIARY STRATIGRAPHIC PALTNOLOGT IN THE MURRAY BASIN, NEW SOUTH WALES Helene A. Martin School of Botany, University of New South Wales Near the eastern edge of the Murray Basin, thick sections of Oligocene-Early Miocene sediments cannot be sub-divided using conventional palynological zonation yet some stratigraphic control within these sections is necessary. The possibility of using the exceptional abundance of certain taxa, i.e. quantitative relationships, for stratigraphy was investigated. The quantitative methods devised (see Martin, in press a) have provided some of the required stratigraphic control in the Murrumbidgee area (Martin, in press b) but they are less successful in the Lachlan area (Martin, in press c). The reasons for the difference between the two areas are palaeoecological. The ecological tolerances of the selected taxa form a series, with Phyllocladidites mawsonii in wettest, swampy habitat, Nbthofagidites flemingii intermediate, requiring a wet climate but a reasonably well drained habitat and Myrtaceae in the driest habitat. Thus P. mawsonii becomes abundant at times when swampy habitats are widespread, N• flemingii at times of increased drainage and Myrtaceae when the climate becomes drier. In the Murrumbidgee area, where the basement is deeper and the sediments better preserved: (1) P. mawsonii abundant in latest Eoceneearliest Oligocene; (2) N. flemingii is abundant at two levels in the Early and Late Oligocene, respectively and (3) Myrtaceae becomes abundant in latest Oligocene-earliest Miocene time. There is a reasonable correspondence with changes in sea level: (1) high sea levels produced the swampy habitat suitable for P. mawsonii; (2) lowered sea levels induced better drainage required by N. flemingii and (3) a time of high sea level and swampy habitat but a drier climate, unsuitable for a return of P. mawsonii but suitable for Myrtaceae. In the Lachlan area, abundant N. flemingii is found throughout the Oligocene. Here the basement is higher and more irregular, factors which would improve drainage, irrespective of changes in sea level. Thus quantitative relationships may be useful stratigraphically but they cannot be extrapolated to other areas without due consideration of the controlling palaeoecological factors. References Martin, H.A. (in press a). The use of quantitative relationships and palaeoecology in stratigraphic palynology of the Murray Basin in NSW. Alcheringa. Martin, H.A. (in press b). The stratigraphic palynology of the Murray Basin in N.S.W. II. The Murrumbidgee Area. J. and Proc. Roy. Soc. NSW. Martin, H.A. (in press c). The stratigraphic palynology of the Murray Basin in NSW.III. The Lachlan Area. J. and Proc. Roy. Soc. NSW.

357

DIAGENESIS OF THE ALDEBARAN SANDSTONE IN THE YELLOWBANK AND SPRINGYALE GAS FIELDS, DENISON TROUGH, QUEENSLAND K. R. Martin Consultant, Brisbane, Qld. The main hydrocarbon reservoir of the Yellowbank and Springvale Gas Fields in the Denison Trough, Queensland, is the early Permian Aldebaran Sandstone. Reservoir intervals consist of mostly nearshore marine, medium grained, moderately sorted sandstones which have a framework of quartz together with smaller amounts of rock fragments and feldspar. Recalculation of the rock composition to QFR components indicates -that the sandstones are sublitharenites. Diagenetic changes during burial exert a major influence on porosity and permeability although a relationship between textural characteristics, particularly grain size, and porosity and permeability is still evident. Most diagenetic processes have acted to reduce porosity. Cementation by quartz overgrowths and carbonates, including dawsonite, ankerite and siderite, plays a significant role in porosity reduction. The formation of authigenic kaolinite and illite-smectite clays also causes porosity reduction as well as increasing the microporosity component of total porosity. A small amount of grain margin dissolution to form sutured grains and microstvlolites further reduces porosity in some places. The combined effect of these processes is severe reduction, and in some cases, an almost total loss of primary porosity. The reduction in primary porosity is partly offset by the formation of secondary porosity which is due to dissolution of some feldspars, rock fragments and carbonate cements. As a result of the diagenetic influence, the pore system in the Aldebaran reservoir sandstones is highly variable with respect to pore size, shape and distribution. However, the most permeable sandstones tend to be those in which primary porosity is still obvious. The reservoir rocks in Yellowbank 2, 3 and Springvale 1 which are gas filled, and also the water-bearing interval in Yellowbank 4 are generally similar in character and all contain abundant dawsonite. The occurrence of this mineral is probably related to the bicarbonate-rich character of the typical Aldebaran waters in the Denison Trough. In Springvale 2 where the reservoir interval is water-bearing, porosity and permeability are higher than in the other three wells, dawsonite is absent and authigenic kaolinite is the only clay present in abundance. These differences suggest that the pore Waters in Springvale 2 are fresher and have, probably been more actively flowing late in the burial history than is the case at Yellowbank.

358

HYDROLOGY OF A REFORESTATION EXPERIMENT ON A SALINE AGRICULTURAL CATCHMENT M . W . Martin 1.

and R . A . Stokes

Geological Survey of Western Australia, Perth 2 . Public Works Department, Perth

The Wellington Reservoir, located near the western edge of t h e Archaean Yilgarn B l o c k , is one of the largest surface water storages in south western A u s t r a l i a . Clearing of eucalypt forest on the 2830 k m ^ drainage basin for agriculture has altered the water balance by reducing transpiration and increasing streamflow and recharge. The increased recharge h a s resulted in rising groundwater levels, remobilisation of soil salts and development of saline seepages in the lower landscapes. Consequently, stream and reservoir salinities have increased significantly (Loh and Stokes 1980). In the eastern area of the b a s i n , where there is lower rainfall and higher salt storage, a programme to rehabilitate salinised areas w a s commenced in 1980. 2

A 12.8 km sub-catchment of which 53.4% is cleared was selected for reforestation trials. In an attempt to modify the hydrology 2 and rehabilitate the catchment, 1.82 k m (26% of the cleared area) along the low^r slopes above the severely salt-affected valley were planted with during the 1981 and 1982 eucalypts (E. nudiss E. wandoo, E. oamaldulensis) winters. In 1982, the catchment w a s instrumented for measurement of rainfall, streamflow and stream-water quality. Four seismic traverses were run over an aggregate distance of 4400 m . A total of eighty nine piezometers were installed at eighteen sites along the seismic lines, and at four other sites, to monitor groundwater quality and hydraulic head distribution. Core samples from each site were geologically logged and analysed for salt storage. The climate is mediterranean with h o t dry summers, and, about 80% of the 650 m m average annual rainfall is received during the mild winter period from M a y to October. Rainfall exceeds p a n evaporation for only about four months of the y e a r . The area is underlain by granite rocks and minor mafic dykes. These have been weathered and lateritised to a thick (20-30 m ) saprolite. Laterite occurs on the divides, and thin colluvium, on the hillslopes, interfingers with alluvium in the valleys. The alluvium is generally 2-4 m thick. Groundwater occurs in the saprolite and in the overlying alluvium in the valley; hydraulic connection exists between b o t h . Flow within the saprolite is from the valley flanks to the stream, and hydraulic gradients range from 0.01 t o 0.03. Where the saturated thickness decreases, t h e gradient increases, which suggests a uniform regional hydraulic conductivity and flow distribution. Groundwater isopotentials beneath t h e valley flanks are vertical b u t within 100 - 150 m of the stream they indicate an upward component of flow. Beneath the stream, t h e isopotentials are horizontal with upward flow into the alluvium from gradients of 0.02 - 0 . 0 6 . Groundwater in the alluvium extends about 200-300 m from the stream. The piezometric surface is continuous over the contact between the alluvium and saprolite. Around the margins of the saturated alluvium there is downward leakage to the saprolite. In the central part of the alluvium towards the stream, there is an upward component of flow which discharges as seepages.

359

Groundwater salinity (total soluble salts) in the saprolite ranges from 10,000 mg to 20,000 mg and increases in the direction of flow. Leakage at the margins of the alluvium tends to locally reduce groundwater salinities in the saprolite* Further up the valley, the relict soil salt distribution is preserved below the piezometric surface with little modification by the present flow system. This upstream transition is consistent with remobilisation of soil salt by a rising water table indicating a headward progression of the equilibrium front together with the migration of salinised areas. Near the margins of the alluvium, groundwater salinities are less than 1,000 mg IT 1 , but discharge of saline water from the-saprolite together with evaporation increases the salinity in the alluvium towards the stream. 5 3 — 1 —1 Approximately 1.2 x 10 m yr of groundwater, with 15,000 mg L average salinity, flows from the saprolite to the discharge area. This represents an average input of 1.8 x 10^ tonnes of salt to the discharge area per year. The convergence of the groundwater flow lines in the discharge area indicates that the major output of salt from the catchment is in streamflow. Stream discharge has been recorded for 1982 and 198o, and in those years, salt output was 1,660 tonnes and 3,200 tonnes respectively. In comparison, salt input to the whole catchment, calculated using average regional inputs of rainfall and salt dryfall (Hingston and Gailitis, 1976), is 38.2 T Thus salt output from the catchment is fifty to sixty times the input. Although a short period of record is available, the data indicates that most of the salt discharged from the catchment is from groundwater in the saprolite. The success of the reforestation trial in reducing saline seepages and decreasing the salinity of stream water will depend on the ability of the vegetation to utilise the groundwater discharge and lower the water level. It is estimated that the time lag between reforestation and salinity improvement will be ten years or more (Sadler and Williams, 1980). By quantifying the components of the hydrological cycle together with the salt balance on a small scale reforestation catchment, optimum techniques can be designed for rehabilitation of the whole drainage basin. References Hingston, F.J., and Gailaitis, V., 1976, Aust. J. Soil Res., 14: 319-335. Loh, I.C., and Stokes, R.A., 1981, Agric. Water Manage., 4, 227-254. Sadler, B.S., and Williams, P.J., 1981, Agric. Water Manage, 4, 353-381

AN OIL SHALE BOREHOLE CORE DENSITY ANALYSER P.J. Mathew, T.B. Fogg and J.G. Miles CSIRO Division of Mineral Physics, Port Melbourne Density of subsurface formations is an important geophysical parameter in prospecting and deposit evaluation. Accurate measurement of the density of formations is needed for ore reserve calculations, in porosity determination and in predicting fragment size distribution in blasting practice. Crushability of rocks, similarly, requires a knowledge of parameters such as bulk density and porosity. Density is also important in the estimation of formation strength.

360

No satisfactory instrumental techniques have been available in the past for the production logging of drill cores in the field. The CSIRO Division of Mineral Physics has developed a transportable device for this purpose. The instrument, known as CORAN*, has been designed to meet the needs of logging oil shale drill cores. CORAN is based on gamma-ray attenuation, a brief description of which has been reported earlier [1]. In the narrow-beam geometry, the attenuation suffered by a high-energy gamma-ray beam (>300 keV) is related to the density of the drill core section by the equation p =

a d

b In I —

,, x c

(1)

where p and d are the density and diameter respectively of the drill core section, and I is the intensity of the transmitted gamma-ray beam, a, b and c are constants to be determined experimentally. The basic analyser consists of a gamma-ray source ( 6 0 Co or 137 Cs) and a Nal(Tl) gamma-ray detector and counting system. The gamma-ray source is collimated to provide a parallel beam of gamma rays. The borehole core section is placed on a core rack located between the source and the detector. A microcomputer reads the output of the gamma—ray counter and calculates the density of the drill core section using a calibration equation. The diameter of the drill core is measured with a Vernier caliper. In the more advanced version, the microcomputer is used to automate the analyser. Two mini-conveyor belts, situated on either side of the source-detector assembly, driven by a stepper motor controlled by the computer, support the core rack and form the basis of the core-feeding device. The diameter of the borehole core is measured with a gauge consisting of a wheel attachment to a linear variable differential transformer (LVDT) through a lever. The core rack, capable of accepting 1 m drill core sections, is provided with movable marker strips. The marker strips, when passing a sensor, generate a signal to control the logging sequence. The marker strips assist in logging regions of interest of the drill core and in avoiding badly damaged sections. The computer reads the output of the gamma-ray counter and the diameter gauge, and calculates the mean density after scanning a given section of the drill core defined by marker strips. The computer can also log drill cores in point-to-point mode. In this mode, the analyser determines the density of a 5 mm section, then the core is advanced by a predetermined distance for the next measurement. This mode is suitable for high-resolution logging of drill cores. The computer stores all pertinent data (hole number, dates of drilling and logging, depth information of the borehole core section and its mean density) on diskettes. From the basic theory of gamma-ray scattering [2], Eq. (1) can be used to predict accurately the density of a geologic material only if the Z/A ratio (i.e., atomic number/atomic weight) of the constituent elements remains constant. For most low-Z elements (Z <50) which form the earth's crust, this ratio is very nearly 0.5. The Z/A ratio for hydrogen is 1. Because oil shale drill cores contain 2-4% hydrogen by weight, significant errors can occur if the results are not corrected for hydrogen contents of drill cores. Such errors due to composition of drill cores are overcome in the present work by using calibration standards made up of representative samples from the exploration area. The analyser has been subjected to extensive field trials, which have shown that it can be used for the routine logging of drill cores with an accuracy (1 a) of 0.015 g cm"3 for the measurement of a single 10 cm drill core section at a logging speed of 1 m/min. The instrument is simple in design and easy to use in the field environment. A semi-skilled operator can be trained in a few hours to use the instrument.

361

The authors wish to thank Southern Pacific Petroleum NL, Esso Australia Ltd, and National Energy Research Development and Demonstration Council for the support given to the development and field trial of the borehole core analyser.

References 1. McCracken, K.G. and Mathew, P.J., 1982, Austr. Coal Geology, 3, 31-36. 2. Mathew, P.J., 1976, in Geophysical Techniques in Borehole Applications, Australian Mineral Foundation Incorporated, Adelaide, 70-98. *An acronym for CORe ANalyser. CORAN is manufactured under licence to CSIRO by MCI Pty Ltd~Adelaide.

PYROLYSIS STUDIES OF SOME QUEENSLAND SHALES R.T. Mathews and S.J. Ham University of Melbourne, Melbourne Kerogen was isolated from a Triassic shale associated with coal (Ipswich field), and from eight samples of "oil-shale11, six being quartzclay-carbonate rocks of Tertiary age (The Narrows, Casuarina and Hillsborough Basins), while two were more richly calcareous sediments of Cretaceous age (Toolebuc Formation, Eromanga Basin). Whole rock (carbonatefree except in the case of the Cretaceous samples); isolated kerogens; and one kerogen of lowest ash content (1.1%) mixed with montmorillonite, were subjected to pyrolysis-gas chromatography, heating being for 20 seconds at 700°C. The resulting "pyrograms11 all showed very similar hydrocarbon distributions, except in the case of the kerogen-montmorillonite mixture, where the differences were not very great. Thus the results do not support the possibility of mineral catalysis of the degradation of organic matter in rocks during formation of hydrocarbons. Inferences respecting the origin of the kerogens can be drawn from the pyrograms, and these in general support the geological evidence. In the non-marine samples (Tertiary and Triassic), while the pyrolysis products show strong maxima below C^Q, as expected if aquatic plants were the main source of the organic matter, compounds up to around C^Q are also well represented, testifying to contributions from land-plant material transported into the fresh-water basins. There is (albeit slight) odd-overeven predominance in the long-chain n-alkanes, again an inheritance from land-plants. The marine Toolebuc Formation samples show much less in the way of long-chain compounds, with no odd-over-even predominance. Evidently land-plant contributions were not great while these calcareous sediments were being deposited. The pyrogram of the Ipswich shale kerogen shows very little material above C2o> doubtless as a result of strong diagenesis (vitrinite reflectivity above 0.8), causing breakdown of higher molecularweight material. Thanks are due to B. Schumann, A. Chaffee and P. Nichols, formerly of the Department of Organic Chemistry, University of Melbourne, for assistance with the pyrolyses and interpretation of the pyrograms.

362

THE MUNGANA RED DOME DEPOSIT W.E. Matthews and P.D. Timms Amoco Minerals Australia Company, North Sydney Mungana is located 15 kilometres west of Chillagoe and 160 kilometers west of Cairns in north east Queensland. The Mungana ore bodies are comprised of the Lady Jane and Girofla silver-lead deposits, and the more recently discovered Red Dome gold deposit* Silver-lead ore was discovered on Chillagoe Station in 1887. Mining was commenced in 1897 by the Chillagoe Company, but production was restricted by the extreme haulage costs. Representation was made to the Queensland State Government to extend the Mareeba railway to Chillagoe and this was completed in 1900. Subsequently in 1901 the Chillagoe Smelters were opened. Production continued intermittently until 1914, when the smelters were closed due to the inadequate supply of ore. In an attempt to establish a State owned mining and smelting enterprise, the Queensland Labour Government purchased the smelters in 1919. Inadequate ore supplies severely hampered the economic operation of the smelters and further mine acquisitions were advocated by Ted Theodore, the Deputy Premier. The Lady Jane and Girofla mines were purchased from Mungana Mines Limited for cash and royalties. Despite this vertical integr ation of the sources of supply, the smelters continued to run at a loss until they were finally closed in 1925, due mainly to low metal prices, high interest rates and the high cost of developing the mines at Mungana. The Auditor-General's report of 1926 indicated that the purchase and royalty payments to Mungana Mines Limited were largely responsible for the vast financial losses. The subsequent disclosure of the Premier's and Deputy Premier's shareholdings in Mungana Mines contributed to the 1929 defeat of the State Labour Government and the resignation of Ted Theodore, then Treasurer and deputy leader of the Federal Labour Party. The Mungana area lay dormant until the late 1960's and Amoco began exploration there in 1976. Exploration to date has included: landsat imagery studies; stream sediment, rockchip and soil sampling; surveys; detailed geologic mapping; airborne magnetic and radiometric surveys, detailed ground magnetics, induced polarization, electromagnetic and gravity surveys. The gold-copper-zinc-silver mineralisation at Red Dome occurs within calc-silicate skarn, breccia, quartz veins, stockworked rhyolite porphyry and sandstone. The mineralisation appears to be spatially and temporally related to Carboniferous aged quartz-feldspar porphyry dykes ^nd stocks intruding a sequence of Siluro-Devonian limestones, sandstone, chert and andesite. The Red Dome deposit lies within a north-west trending metallogenic belt, thought to represent a Siluro-Devonian Island Arc System. Initially acid-intermediate volcanism occurred in association with the deposition of reef limestones. With ongoing subduction, fracturing occurred on a general east-west orientation, with subsequent emplacement of dykes, breccias and quartz stockworking along these lines of weakness. Gold and base metal mineralisation has accompanied this intrusive phase.

363

The gold ore zone is approximately 400 metres long by 100 metres wide and has a vertical pipe-like shape which has only been drilled to a depth of 300 metres. Drilling to date has outlined a resource of 17.5 million tonnes grading 2 g/t gold, 0.46% copper, 1.8% zinc and 4.6 g/t silver. Weathering has produced an oxide zone which extends to approximately 150 metres. The primary zone contains a four percent total sulphide system, composed mainly of chalcocite, chalcopyrite and bornite. The gold occurs for the most part as free gold with a subordinate amount contained within the crystal lattice of the sulphides.

LAND USE ASSESSMENT FOR DEVELOPMENT: SCIENTISTS

THE ROLE OF EARTH

J.R. McAlpine and D.N. Body CSIRO Division of Water and Land Resources, Canberra The CSIRO Division of Water and Land Resources began life as a Division in CSIRO with the title Land Research and Regional Survey. It has been responsible for the development of the methodology of integrated surveys and their application over much of the least developed parts of Australia, see Christian and Stewart (1968). Integrated survey methods are based on the f land system1 method of landscape classification and seek to integrate geology, geomorphology, soils and vegetation information so as to arrive at an assessment of land use capability. Similar and related survey methods have been developed and applied by a number of development agencies and consultants, e.g. U.K. Directorate of Overseas Survey, and Hunting Technical Services, see Stewart (1968). The technique has been applied by CSIRO to the greater part of Papua New Guinea and used by Australian consultants in a number of developing countries, Thailand, Philippines and Indonesia, in some cases using CSIRO scientists as consultants. The present paper will outline and reference the applications in Papua New Guinea and tropical Australia and discuss the problems and usefulness of the method. More recent developments in incorporating computer based methods and digitized remote sensing techniques such as airborne and satellite scanners in visible, infared and radar wavelengths will be alluded to and a progress report given on the major current project of the Division of Water and Land Resources involving the development of a computer based land use planning data base for the Government of Papua New Guinea. References Christian, C.S. and Stewart, G.A. 1968 - Methodology of integrated surveys. In Aerial Surveys and Integrated Studies. Proc. Toulouse Conf. 1964, (UNESCO, Paris) : 233-280. Stewart, G.A. editor, 1968. Melb. -392pp.

364

Land Evaluation

pub. Macmillan of Australia,

UN'S ROLE IN THE DEVELOPMENT OF THE GEOSCIENCES IN SOUTHEAST ASIA AND THE PACIFIC James F . ESCAP R e g i o n a l M i n e r a l

McDivitt.

Resources D e v e l o p m e n t C e n t r e ,

Bandung,

Indonesia

The U n i t e d N a t i o n and i t s various branches and s p e c i a l i z e d agencies have played a s i g n i f i c a n t role in the d e v e l o p m e n t of geosciences in A s i a and the P a c i f i c d u r i n g t h e last 30 years. I n i t i a l l y t h i s involved assistance and advice on the e s t a b l i s h m e n t and s t r e n g t h e n i n g of n a t i o n a l services d e a l i n g w i t h geology and m i n e r a l resources and s u p p o r t f o r new t r a i n i n g p r o g r a m m e s in the u n i v e r s i t i e s , but as the s i t u a t i o n in the region has i m p r o v e d m o r e emphasis is being given t o research p r o g r a m m e s and f a c i l i t i e s , advanced t r a i n i n g in specialized f i e l d s and assistance in d e v e l o p i n g and m a i n t a i n i n g regional linkages designed t o p r o m o t e geosciences and m i n e r a l d e v e l o p m e n t . The m a i n U N i n s t i t u t i o n s involved in t h i s are the U n i t e d N a t i o n i t s e l f , i t s regional b r a n c h , the E c o n o m i c and Social C o m m i s s i o n f o r A s i a and the P a c i f i c (ESCAP) and Unesco ( t h e U n i t e d N a t i o n s E d u c a t i o n a l , S c i e n t i f i c and C u l t u r a l Organization) all of w h i c h depend to some e x t e n t on the United Nations D e v e l o p m e n t P r o g r a m m e f o r f u n d i n g , along w i t h the f i n a n c i n g a f f i l i a t e s of the U . N . system such as the W o r l d Bank and the A s i a n D e v e l o p m e n t B a n k . W i t h i n t h e U N S e c r e t a r i a t , n a t i o n a l p r o j e c t s are c a r r i e d o u t by t h e D e p a r t m e n t of T e c h n i c a l C o o p e r a t i o n f o r D e v e l o p m e n t , w h i c h i m p l e m e n t s a n u m b e r of p r o j e c t s in t h e region i n c l u d i n g m i n e r a l d e v e l o p m e n t in India and s t r e n g t h e n i n g the g e o l o g i c a l survey in the Philippines. D T C D also organizes some training a c t i v i t i e s in the r e g i o n , such as the s e m i n a r on gold e x p l o r a t i o n t o be held in India in e a r l y 1985. R e g i o n a l p r o j e c t s are handled by ESCAP and at present include t h r e e large UNDP p r o j e c t s , CCOP, CCOP/SOPAC and R M R D C as w e l l as some activities handled by t h e ESCAP S e c r e t a r i a t itself. The C o o r d i n a t i n g C o m m i t t e e for O f f s h o r e P r o s p e c t i n g in East Asian W a t e r has developed an a c t i v e p r o g r a m m e of research, t r a i n i n g and advisory services, and has played an i m p o r t a n t r o l e in assisting t h e c o u n t r i e s of the region in the i d e n t i f i c a t i o n , d e v e l o p m e n t and m a n a g e m e n t of t h e i r o f f s h o r e m i n e r a l resources; p a r t i c u l a r l y oil and gas. CCOP has evolved i n t o a very a c t i v e o r g a n i z a t i o n with a staff of well qualified s p e c i a l i s t s , and access to a wide range of f a c i l i t i e s and i n f o r m a t i o n r e l a t e d t o geosciencies in the region. The C o o r d i n a t i n g C o m m i t t e e f o r O f f s h o r e Prospecting in the South P a c i f i c plays s o m e w h a t b r o a d e r role since the resource s t r u c t u r e of its region is d i f f e r e n t . It is a m a j o r f a c t o r in assisting and advising the governments of the island c o u n t r i e s of the South P a c i f i c on d e v e l o p m e n t of t h e i r m i n e r a l resources, b o t h onshore and o f f s h o r e , and in d e a l i n g w i t h various aspects of t h e i r m a r i n e m i n e r a l resources. CCOP/SOPAC serves as visible evidence of the a p p l i c a t i o n of science and is one of the m a i n -bodies p r o m o t i n g the a p p l i c a t i o n of science and t e c h n o l o g y t o the d e v e l o p m e n t of the region. The R e g i o n a l M i n e r a l Resources D e v e l o p m e n t C e n t r e c a r r i e s o u t a s i m i l a r range of a c t i v i t i e s designed to p r o m o t e onshore m i n e r a l d e v e l o p m e n t in a l l of the ESCAP r e g i o n . A group of high level s p e c i a l i s t s , seconded by t h e i r g o v e r n m e n t s f o r periods of up t o t h r e e years, provides advisory services, f r e e and on request, t o g o v e r n m e n t s in the region. C u r r e n t l y the seven s p e c i a l i s t s ( i d e a l l y this w i l l build up t o 1 2 - 1 5 ) u n d e r t a k e advisory missions of 10 days to t w o m o n t h s t o assist c o u n t r i e s in f i e l d s i n c l u d i n g m i n e r a l e x p l o r a t i o n , e c o n o m i c g e o l o g y , g e o physics, g e o c h e m i s t r y , h y d r o g e o l o g y , s m a l l - s c a l e m i n i n g , m i n e m a n a g e m e n t and analytical chemistry.

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The Centre also organizes t r a i n i n g courses, workshops and regional research programmes, where possible in cooperation w i t h , and w i t h support f r o m other organizations, assists countries in assessing and preparing inventories of t h e i r mineral resources, and is p r o m o t i n g plans to upgrade mineral i n f o r m a t i o n f a c i l i t i e s through development of a regional i n f o r m a t i o n system for Asia. R M R D C serves as a focus for coordination of regional activities related to mineral development and collects and disseminates i n f o r m a t i o n on all related a c t i v i t i e s . The t w o CCOP's are semi-autonomous w i t h their own governing bodies but are administered by ESCAP w i t h UNDP support. RMRDC comes d i r e c t l y under ESCAP. A l l three of these regional bodies rely to an increasing extent on support f r o m non UN sources, for the most part b i l a t e r a l , and A u s t r a l i a which is a part of the region which they serve, is looked upon as one of the main sources. A t the same t i m e the CCOP's and RMRDC have the c a p a c i t y t o i d e n t i f y , implement and f o l l o w - u p on useful and relevant projects in the region, and so are an e f f e c t i v e mechanism for channelling such b i l a t e r a l assistance into the development system. The ESCAP Secretariat monitors these programmes and also carries out a number of projects i t s e l f , including publication of regional resource maps and organizing a series of meetings, workshops and conferences related to various aspects of the geosciences. The main specialized agency of the UN system concerned w i t h geosciences is Unesco, although others including UNIDO and FAO have related a c t i v i t i e s . Unesco's main geoscience activities in the region come under the International Geological Correlation Programme, which is carried out j o i n t l y w i t h IUGS. A number of IGCP projects are based in Asia, and Asian scientists p a r t i c i p a t e in many others. Unesco also supports a number of a c t i v i t i e s in the region through its Regioanl Offices for Science and Technology in Jakarta and New Delhi, including support for the Southeast Asian Geoscience N e t w o r k , and a series of training courses and workshops some of which jare carried out in cooperation w i t h AGID. The World Bank and the Asian Development Bank have loan programs in the region to assist in the development of mineral deposits, mainly f o r coal and cement, and ADB has projects for mineral exploration (a major geophysical survey in Thailand) and for strengthening of geological surveys (Indonesia and under consideration in the Philippines). These projects provide t r a i n i n g and equipment as well as advisory services. Beyond this, the various c o m m i t t e e s and subsidiary groups of the UN system provide a f o r u m in which representatives f r o m the region can meet w i t h one another and w i t h their counterparts f r o m other countries to discuss m a t t e r s of mutual interest. A u s t r a l i a , which is an active member of the U n i t e d Nations, c o n t r i b u t e s to all of these activities, and in many cases supplements them through giving support to activities w i t h i n the Asia/Pacific region, where it has special i n t e r e s t and a high level of competence in technical fields such as the geosciences.

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L A T E P E R M I A N TO M I D D L E T R I A S S I C A L L U V I A L D E P O S I T I O N A L E N V I R O N M E N T S OF THE S Y D N E Y B A S I N : C O A S T A L T R A N S E C T K . L . McDonnell and P.J. Conaghan Macquarie University, North Ryde, N . S . W . In the Sydney Basin, the Late Permian through Middle Triassic succession, exposed in cliffs of the north coast, south coast and Blue Mountains, includes sandstones in which quartz content increases up-sequence and palaeocurrents swing from southwesterly through southeasterly to northeasterly. These basinwide phenomena are interpreted to have resulted from the northeasterly migration of a fluvial drainage net, in which northeasterly-flowing tributaries bearing quartz sand from the craton met southwesterly-flowing tributaries bearing labile sediment from the arcuate rim-orogen, and blended in southeasterly-flowing trunk streams down the axis of the foredeep. Migration of the drainage net accompanied the retreat of the arc-derived clastic wedge in the latter part of a megacycle which extends from the top of the mid-Permian Nowra Sandstone to the top of the mid-Triassic Hawkesbury Sandstone. Composite vertical profiles for the exposed coastal transect are divided into four macrofacies on the basis of whole-rock percentage quartz content of sandstones and vector mean crossbed dip azimuth (i.e. Lsw, Lse, Sse, Qne; cf. Conaghan et aL, 1982). Within each macrofacies, lithofacies at meso- and microlevels are recognized on the basis of gross geometry, lithology and bedding features. Each of these is believed to represent a particular process or depositional environment. Transition matrix analysis of the composite vertical profiles enables the construction of model lithofacies profiles; these show in condensed form the essential characteristics of each macrofacies in terms of relative frequencies of occurrence and mean thicknesses of constituent meso/microfacies, their preferred ordering and the character of the transitions between them. Transition matrix analysis also enables the construction of histograms illustrating the up-sequence trends in relative proportions of lithofacies transition-frequencies attributed to various depositional processes. These histograms are the bases of palaeogeographic maps depicting a succession of alluvial environments consistent with the dynamic drainage net model described above. In the Late Permian, expansion of the Newcastle piedmont (Lsw) involved the following succession of alluvial environments. Extensive lakes and swamps, in which vegetation flourished and peat accumulated rapidly, acted as a sediment trap for epi- and pyroclastic detritus from the orogen; in the region of the north coast (NC), gravelly and sandy fan-deltas built into the lakes (Fig. 1A); then, as the piedmont expanded, alluvial fans and gravelly/sandy braidplains spread to the west and south, colonised at times by blanket mires (Fig. IB); eventually the lakes disappeared and a dominantly fluvial regime was established across the Basin; at N C , sand and mud from the now deeply dissected mountain terrain to the northeast accumulated on the floodplains of southwesterly-flowing streams of moderate sinuosity (Fig. 1C). The drainage net then migrated northeast in response to declining activity in the orogen, and the piedmont was overrun by the channel/floodplain environments of the trunk stream system (megafacies QSLse; Fig. 1D,E). These were followed in turn by the channel-dominated, low-sinuosity stream environments of the northeasterly-flowing tributaries (Qne; Fig. IF). Reference Conaghan, P.J., Jones, J.G., McDonnell, K . L . , and Royce, K . , 1982, J. Geol. Soc. Aust., 29, 55-70.

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N d - S r I S O T O P I C C O M P O S I T I O N S OF B A S A L T S F R O M S O U T H E A S T E R N AUSTRALIA: IMPLICATIONS FOR MANTLE ISOTOPIC VARIATION

W.F. McDonough and M.T. McCulloch Res. School of Earth Sci., Aust. Nat. Univ., Canberra Sr and Nd isotope compositions for Tertiary-Recent basalts from the Newer Volcanic Province, Victoria and the Tasmanian Volcanic Province 87 86 display a large, coherent variation in e N and Sr/ Sr. This data generally plots to the left of the "oceanic mantle array" (Fig. 1). The geochemistry of some of the Victorian and Tasmanian basalts studied here are reported in Frey et al (1978). Samples of primary magmas identified by Frey et al, plus additional samples interpreted as primary magmas based on 1 Frey et a l s criteria, define this broad range in Sr-Nd isotope composition. Significant major and trace element and isotopic differences exists between the Tertiary basalts of Tasmania and the Tertiary-Recent basalts of Victoria. The Tasmanian basalts vary from olivine nephelinites to olivine tholeiites and show distinctly lower 8 7 S r / 8 6 S r (.7026 to .7033) and higher t 0 e than the olivine analcimitic to quartz tholeiitic Newer Nd basalts of Victoria (Fig. 1). No correlation is found between major element and isotopic composition in either province; the range in 87 S r / 8 6 S r for olivine nephelinites/olivine melilite (.7026 to .7033) encompasses the total observed 8 7 S r / 8 6 S r variation for non-crustally contaminated Tasmanian basalts. The Newer basalts are enriched in 87 S r / 8 6 S r (.7038 to .70^9) and depeleted in e (+3 to -3) compared with the Tasmanian basalts. The anomalously Y and REE enriched basalts reported in Frey et al (2177, 2152, 69-1026) have lower e N d and higher 8 7 S r / 8 6 S r compositions compared with the other Newer basalts. This variation is considered a mantle signature and not the result of crustal contamination. Spinel lherzolites from M t . Leura, Victoria show a large variation in 87 S r / 8 6 S r (.7035 to .7076) and e (+7.5 to -7.5) (Burwell, 1978; Chen and Frey, 1981). The range in Nd-Sr isotopic compositions for both basalts and spinel lherzolites from southeastern Australia is oomparable to that observed for the oceanic mantle(Fig. 1). Since many of these basalts have been identified as primary mantle melt compositions and the Nd-Sr isotopic compositional range for spinel lherzolites found in these basalts is as large as that found in the oceanic basalts, we conclude that crustal contamination has not contributed to the observed Nd-Sr isotopic variation. The range in e and 8 7 S r / 8 6 S r in these basalts results from the tapping of a chemically ana isotopically heterogeneous mantle. The Nd-Sr isotope array for these basalts falls to the left of the "oceanic mantle array", and overlaps with Nd-Sr isotopic data from other continental environments (i.e., Kiama/So. Highlands, Menzies and Wass, 1983; Basin and Range, Menzies et al, 1983; Kenya, Norry et al, 1980; West Antartica, Futa and Le Masurier, 1983) indicating that this may be a distinctive feature of the subcontinental mantle. We suggest that the mixing of more than 2 components within the mantle has produced the observed isotopic variations in the southeastern Australian basalts. Some of these components may be common to the subcontinental and suboceanic mantles. The trace element and isotopic difference between the Tasmanian and Victorian basalts indicates that their respective mantles have undergone separate histories.

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Time a

Time 'd /e '

Piedmont gravelly ffgyj braidplain Piedmont sandy braidplain

Riverine sandy floodplain

Riverine s a n d y / s i l t y VO^V^I floodplain

Mire and lake • ' A ' ^ I I I Mountain arc with MW ^ active volcano

Fig. 1. Palaeogeographic reconstructions of Sydney Basin, Late Permian and Triassic. Points NC and SC are designated locations of composite stratigraphic profiles. Solid arrows indicate mean crossbed dip azimuth. Time planes a to e ^respectively figures B to F) are defined in Conaghan et al. (1982). Time a lies within the Adamstown Subgroup (NC) and within (and towards the top of) the lower half of the Sydney Subgroup (SC).

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.702

.704

87Sr/86Sr

.706

Figure 1: e ^ - 8 7 S r / 8 6 S r isotopic data for Tertiary-Recent Tasmanian and Victorian basalts, (this study), MORB, ocean island basalts, (White and Hofmann, 1982), and Kiama/So. Highlands basalts (Menzies and Wass, 1983).

References Burwell, A.D.M., 1975, Earth Planet. Sci. Lett. 28:69-78. Chen, C.Y. and Frey, F.A., 1981, EOS 62:415. Frey, F.A., Green, D.H. and Roy, S.D., 1978, J. Pet. 19:463-513. Futa, K . and Le Masurier, W.E., 1983, Contrib. Mineral. Pet., 83:38-44. Menzies, M.A. and Wass, S.Y., 1983, Earth Planet. Sci. Lett. 65:287-302. Menzies, M.A., Leeman, W.P. and Hawkesworth, C.J., 1983, Nature 303:205-209. Norry, M.J., et al, 1980, Phil. Trans. R.Soc. 297:259-271. White, W.M. and Hofmann, A.W., 1982, Nature 296:821-825.

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ISOTOPIC AGES, MAGNETOSTRATIGRAPHY AND BIOSTRATIGRAPHY FROM THE EARLY PLIOCENE SUVA MARL, FIJI Ian McDougall1, P. Rodda2, R.A. Cassie3, D.A. Falvey1*, R. Todd5 and J.A. Wilcoxon6 Australian National University, Canberra ^Mineral Resources Department, Suva 3 E S S O Australia Limited, Sydney 4 Bureau of Mineral Resources, Canberra 5 Formerly U.S. Geological Survey, Washington, D.C. 6 Wil coxon Group/Paleontologic International, Singapore The Suva Marl, Fiji, is Early Pliocene in age from biostratigraphic data, lying almost wholly within planktonic foraminiferal zone N19. Within the nearly flatlying 180-m sequence occur a number of tuffaceous beds, from some of which biotite has been separated and used for K-Ar dating. The measured isotopic ages plotted against stratigraphic position within the Suva Marl yield a good straight line relation (Figure 1), from which it is inferred that deposition occurred at the rate of 83 ± 5 m/Ma, and that the formation was deposited between about 5.2 and 3.2 Ma ago. Palaeomagnetic measurements on samples from the Suva Marl indicate that it is mainly of reverse polarity but that three normal polarity zones are found within the sequence (Figure 1). Direct comparison with the geomagnetic polarity time scale shows that AGE (Ma) the Suva Marl was deposited wholly within the Gilbert reverse chron. The three normal M K GAUSS NORMAL CHRON polarity zones in the Suva Marl 534 can be dated by using the regression, and are found to match the older three subchrons of the Gilbert chron remarkably well. On this basis the Cochiti normal polarity subchron should be recorded in sediments at about the level of the Purple Marker in the Suva Marl, and its apparent absence is difficult to explain. These data provide physical age and magnetostratigraphic control for the Suva Marl, and enable numerical ages to be assigned to certain biostratigraphic zone boundaries. Calcareous nannoplankton within the Suva Marl allow identification of several zonal boundaries with the following estimated ages, rounded off to 0.05 Ma: NN12/NN13 = 4.8 Ma, K-ARAGE NN14/NN15 = 3.85 Ma, NN15/NN16 = 3.5 Ma, generally a little Figure 1 older than earlier estimates. Planktonic foraminiferal datum planes have proved difficult to locate precisely within the Suva Marl. However, the first coiling direction change of Pulleniatina took place in the interval 4.1 to 3.9 Ma ago, and the base of zone N21 is dated at 3.24 Ma or slightly younger.

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THE GOLD MINE AT KULUMADAU, PAPUA NEW GUINEA, A CAUTIONARY TALE W.A. McGee Nord Resources (Pacific) Pty Ltd, Sydney In contrast to the success stories usual in documented mining histories, this paper presents the study of an unsuccessful, but persistent, operation. The mine is at Kulumadau on Woodlark Island, in Papua New Guinea and was active in the period between 1899 and 1918. Woodlark is a remote, waterlogged, unhealthy and generally unpromising coral island that has nevertheless yielded some 5 tonnes of gold. About half of this was obtained from the Kulumadau mine. Gold at Kulumadau came to the attention of the Australian public in July 1899 when a promoter, one Alex Johnson, arrived in Sydney from Woodlark. He brought a parcel of 17 hundredweight of material which on smelting yielded gold at the rate of 22 ounces per ton (660 grams/tonne). Bouyed by the engendered excitement, the Woodlark Island Proprietary Company was floated and immediately became a high flyer on the market. The shares moved rapidly from 3 shillings to 35 shillings with the publication of results of further small parcels. The first substantial shipment, 80 tonnes was milled in March 1900 but disappointingly, yielded only 1 ounce per ton, an unprofitable figure. Despite this two companies were floated in June 1900, one in Adelaide, the "Ivanhoe Company", and one in Charters Towers, the "Kulumadau Company". The marvellous grades of the early shipments were never seen again and none of the ventures were profitable. The Ivanhoe Company spent freely on equipment but as it had no ore, retired from the field in 1902. The Proprietary Company managed a solitary dividend of 3d per share in 1904 and eventually sold its assets to the Kulumadau Company in 1907. The Kulumadau Company sustained operations till 1918 occasionally paying small dividends but never managed to repay capital. After the failure of this company the mine was abandoned. A partial explanation of the course of events is provided by the geology of the deposit as we now know it. Woodlark Island is an elevated reef-lagoon complex on a volcanic basement. The Kulumadau area, now a prominent hill, represents an old island of volcanics within the lagoon and had fringing gravel beach, mud banks and coral reefs, now conglomerates, mudstone and limestones. The surface of the volcanics is deeply weathered and displays incipient laterltisation. The gold mineralisation is epithermal and within a zone of development of clay, quartz, carbonates and sulphides. As the mineralisation predates the sedimentary rocks, alluvial gold is widely distributed at the unconformity between the sediments and the volcanics. The earliest workings were by alluvial methods and were extremely rewarding. These exploited both recent alluvials and basal conglomerates in the immediate vicinity of the lode outcrop and the oxidised clays of the lode itself. The alluvial miners rejected masses of limonite and silica, being the gossanous remnants of quartz-sulphide bunches contained in the hypogene zone of the lode. As the gold occurs preferentially with the sulphides, these lumps would have been very enriched. The promoters1 early parcels were of this selected material. When the companies commenced mining, the oxidised material had largely been removed and the stockpile of rejected stone was exhausted, so the spectacular grades could not be maintained.

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The lode in the hypogene zone averaged about 15 dwt/ton (22 grams/ tonne), but as the gold was very fine and associated with considerable clay, losses were high. Other factors also contributed to the troubles. The leases were unfavourably positioned so as to split the lode between the Proprietary and Kulumadau companies, forcing the use of awkward mining methods. Productivity was low due to high sickness rates and poorly skilled staff. Ground water flows into the mine were heavy but mill water was scarce and much crushing time was lost. Transport costs were always high and these were exacerbated by the First World War. The mine was always short of capital for development. Half the money initially raised had been paid to the lease vendors and after the disappointment of the early days and the continuing poor returns, investors were reluctant to venture further mcmey. Had the promise of the original parcels been fulfilled none of these problems would have arisen. The final closure seems to have been forced by the greatly increased costs of transportation and labour due to the War and by increasingly high water flows encountered as the mine deepened. Despite the persistence of the mining operation for almost twenty years, the only apparent beneficiaries were the vendors of the original claims. References McGee, W.A., 1978, Geological Survey P.N.G., Rep. 78/17. Trail, D.S., 1967, Bur. Miner. Resources Aust., Rep 115.

STONE RESOURCES FOR THE MELBOURNE METROPOLITAN AREA I.W. McHaffie Minerals and Energy Department, Melbourne An estimate of total hard rock reserves in current Extractive Industry Licence areas in the Greater Melbourne Area (about 620 million tonnes (Mt)) compares favourably with a forecast of requirements to the year 2010 (330 Mt). In spite of this, companies are continuing to seek approval for new resource areas in strategic locations around the outer metropolitan area in order to satisfy their own particular goals. Basalts which now provide abojut 67% of Melbourne's total needs of about 9.5 Mt per annum, have traditionally been obtained from deep quarries situated in valley flows, close to the city. Extensions to quarrying of such deposits is now severely restricted by urban development and companies have been forced to look towards the thinner sheet flows north and west of Melbourne where high grade rock occurs in relatively shallow ridge deposits, beneath which the rock is commonly weathered and of poor grade. Similarly, planning constraints have practically halted any new quarry developments in acid volcanic, hornfels and granite areas to the east and south east, and within about 50 km of the city, and some companies are seeking to establish quarries further afield but with rail access.

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A major problem is developing with respect to supply of concrete sands to Melbourne, The Heatherton-Dingley area, situated about 25 km southeast of the city currently supplies about 2.5 Mt per annum or about 65% of total requirements and has reserves of about 20 Mt. how~ ever most of the reserves under licence are held by two companies. In 1978 the D.M.E. investigated a possible replacement source of concrete sand at Lang Lang, situated about 80 km south east of Melbourne, where a resource of about 60 Mt was outlined. Formulation of an extraction policy for this area has been frustrated by several factors including the difficulty in preparing an acceptable plan for large scale extraction of sand from below water table. A consequence of the delay in making the Lang Lang sand resources available for extraction is that some sand producers are obtaining supplies from small, scattered deposits in areas where planning constraints are perhaps less stringent.

ADVANCES

IN A U S T R A L I A N

OSTRACODE

STUDIES

K.G. McKenzie Riverina College of Advanced Education, Wagga Wagga, N.S.W. In recent years a variety of techniques for utilising the well known sensitivity of Ostracoda to environmental factors have become established and/or refined. They are now being applied in Australian Tertiary and Quaternary sequences. The variation in size of the vestibules of Krithe and Parakrithe, two deepwater genera, is linked to blood concentration and hence to CO2 content of the ambient ocean/sea zones in which these animals live - thus enabling more precise understanding of the likely palaeohydrology in Cainozoic sediments which carry these genera. An example is given from the Miocene of Victoria. The same site provides an example of the use of ornamented Ostracoda to pinpoint variations in the rhopic factor (Ca/Mg concentration); and of the association of blindness with deepwater versus sightedness (possession of an eye tubercle) in shallower water (<800m). A refinement of coarse fraction analysis as applied to Ostracoda consists of counting the percentages of valves/carapaces, fragments/entire individuals, juveniles/adults, and pyritised/non pyritised specimens. The results allow interpretations of the palaeoenergy, of the rate of sedimentation, and of the bottom conditions (oxygenated vs anoxic). They are also used to separate allochthonous and autochthonous elements in the assemblages. An example is given from the Tertiary of South Australia. Greater knowledge of the distribution of modern Ostracoda around the Australian coastline leads to more confident interpretations of the marginal palaeoenvironments represented by fossil assemblages. An example is given from the Quarternary of New South Wales. All these techniques find application in the perennial search to establish greater reserves of energy resources, particularly petroleum.

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OPTICAL AND PYROLYTIC CHARACTERISATION OF PRE-DEVONIAN OIL-PRONE KEROGENS D.M. McKirdy1, B.L. Watson1 & B.A. Mooney2 Australian Mineral Development Laboratories, Adelaide 2 Ampol Research Laboratory, Brisbane Current petroleum exploration activity in several Australian intracratonic sedimentary basins, notably the Amadeus, Canning, Officer and McArthur, is predicated (wholly or in part) on the existence of source beds and contiguous reservoir rocks of Middle Proterozoic to Early Palaeozoic age. However, source rock studies of these basins are hampered by a dearth of published information on the organic petrology of pre-Devonian sediments; and by the lack of a standard method for determination of thermal maturity that is generally applicable to rocks which antedate the appearance in the geological record of abundant vascular plant remains• The present study is based on a suite of organic-rich (TOC = 0.4-14%), fine-grained clastic and carbonate rocks from the McMinn Formation (Proterozoic, McArthur Basin), Observatory Hill Beds (Cambrian, Officer Basin), Tempe Formation (Cambrian, Amadeus Basin), Inca Formation (Cambrian, Georgina Basin), Horn Valley Siltstone (Ordovician, Amadeus Basin) and Guttenberg Formation (Ordovician, Wisconsin, USA). Optical microscopy (reflected light and fluorescence mode), Rock-Eval pyrolysis (whole-rock) and pyrolysis-gas chromatography (kerogen) were used to characterise their oil-prone organic matter at maturation levels ranging from immature to overmature for hydrocarbon generation. Low rank, oil-prone, pre-Devonian kerogens may be classified Type I (atomic H/C = 1.2-1.4) or Type II (atomic H/C = 0.9-1.2) according to their elemental composition and Rock-Eval hydrogen index values (HI = 250-750). They comprise lamalginite, bituminite and discrete phytoplankton in association with lesser amounts of vitrinite-like and inertinite-like organic matter. In mature and overmature source rocks lamalginite and bituminite are pseudomorphed by micrinite, and the residual kerogen assumes a secondary Type III composition. Poorer quality Type II-III kerogen (oil and gas-prone) is present in parts of the Horn Valley Siltstone (Gorter, 1984; Jackson et al.3 1984). Pyrolysis-GC analysis readily discriminates oil-prone kerogen (Types I & II) from primary gas-prone kerogen (Type III) in pre-Devonian rocks, even at maturation levels approaching the oil deadline. Vitrinite-like material (VLM) occurs as angular phytoclasts (isolated or concentrated in laminae), and as stringers subparallel to bedding. Its reflectance (R0 = 0.4-1.3%) displays a positive correlation with Rock-Eval Tmax (427-460°C) over an extended maturation range which encompasses the oil-generation window. Intrusion of the 1450 Ma old McMinn Formation by a 50 metre thick dolerite sill at the site of the Sherwin Creek iron deposits, Northern Territory (Peat et al.3 1978), provides an ideal field situation in which to study the coalification of Proterozoic VLM at still higher ranks (up to R 0 ^2.7%). References Gorter, J.D., 1984, APEA J., 24(1), 66-90. Jackson, K.S., McKirdy, D.M., & Deckelman, J.A., 1984, APEA J., 24(1), 42-65. Peat, C.J., Muir, M.D., Plumb, K.A., McKirdy, D.M. & Norvick, M.S., 1978, BMR J. Aust. Geol. & Geophys., 3, 1-17.

375

PENECONTEMPORANEOUS FAULTING AND VOLCANOGENIC MASSIVE SULPHIDE DEPOSITS R.L. McLeod1 and A. Taube2 1

D.D.I.A.E., o * Toowoomba Consultant Geologist, Rockhampton The Mount Warner Volcanics, considered to be equivalent to the Mine Corridor Volcanics which host the Mount Morgan copper-gold deposit in central Queensland, comprise a Middle Devonian acid volcanic pile of crystal and crystal-lithic tuffs, agglomerates, chemical sediments, ash-flow tuffs, and intrusive porphyries. Minor outcropping base-metal sulphide mineralisation and significant stream-sediment geochemical anomalies in the Upper Nine Mile Creek area to the south-east of Mount Morgan led to a program of detailed mapping, geochemistry, geophysics, and drilling. The drilling revealed a zone of massive lead-zinc mineralisation stratigraphically underlain by disseminated and veinlet chalcopyrite. The style of sulphide mineralisation and the nature of the host rocks are characteristic of volcanogenic massive sulphide deposits worldwide. Within the Upper Nine Mile Creek prospect area, the stratigraphically lowest rock in the sequence, informally called the Footwall Tuff, are light grey-green chloritic fragmentals which commonly display a distinct alignment of chloritic fiamme representing original pumice fragments. This eutaxitic foliation is restricted to the footwall in this area, and these rocks are considered to be subaerial ash-flow tuffs. Overlying the Footwall Tuff is an interbedded sequence of siliceous and chloritic crystal and crystal-lithic tuffs. Cherty interbeds are characteristic of this unit, and these generally display evidence of soft sediment deformation. Thin limestone beds are also common, and a single thick limestone (50m) occurs on the downthrown side of a major fault. This unit acts as host to most of the massive base-metal mineralisation in this deposit. Quartz-feldspar crystal lithic tuffs and siliceous ash tuffs overlie the host unit. Thin jasper beds occur within the ash tuffs, and minor mineralisation may be present at the contact of these lithologies. The stratigraphic top of the prospective sequence is indicated by the occurrence of a conspicuous manganiferous and hematitic siltstone which, in places, reaches 10m in thickness. Hanging-wall rocks in this area are dacitic to andesitic lithic lapilli tuffs and lavas. Mineralisation is of two distinct styles. Well-bedded lenses of massive sulphide carrying predominantly pyrite, sphalerite, and galena, with significant silver and minor gold, are underlain by stringer-style veinlets of chalcopyrite. The mineralisation appears to be genetically related to a footwall penecontemporaneous fault. Copper and zinc grades in the footwall increase markedly towards the fault, and alteration, as reflected by the amount of chlorite and phengitic muscovite in the rocks, is more pronounced around this structure. These phyllosilicates display consistent compositional trends suggesting the fault to have been the solution conduit. The Upper Nine Mile Creek deposit can be set, in a regional framework, on one edge of a central graben within a caldera structure.

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I G N I M B R I T E AND A S H - F A L L TDFF F R O M A L A R G E M A G N I T U D E R H Y O L I T I C HYDROVOLCANIC ERUPTION: LATE CARBONIFEROUS CANA CREEK T U F F , NORTHEASTERN N.S.W. J . McPhie U n i v e r s i t y of N e w E n g l a n d , A r m i d a l e The Cana Creek Tuff is the o l d e s t of four silicic i g n i m b r i t e m e m b e r s of a L a t e C a r b o n i f e r o u s v o l c a n o g e n i c c o n g l o m e r a t i c b r a i d p l a i n s e q u e n c e (Currabubula F o r m a t i o n ) 1 . 5 to 2.5 k m t h i c k , exposed along the w e s t e r n m a r g i n of the T a m w o r t h B e l t in n o r t h e a s t e r n N . S . W . A l t h o u g h on a v e r a g e only 70 m t h i c k , the Cana C r e e k Tuff is w i d e s p r e a d , e x t e n d i n g for 55 k m n o r t h to south along strike and spanning 20 k m east to w e s t . T h e existing e x p o s u r e s p r e s e r v e only the m e d i a l to d i s t a l p o r t i o n s of the original layer a n d a r e p r o b a b l y some tens of k i l o m e t r e s from s o u r c e . The Cana C r e e k Tuff c o m p r i s e s a d i s t i n c t i v e c o m b i n a t i o n of primary p y r o c l a s t i c facies (ignimbrite a n d a s h - f a l l tuff) a n d redeposited v o l c a n i clastic facies ( s a n d s t o n e , p a r a c o n g l o m e r a t e ) , a l l of w h i c h a r e composed of c r y s t a l fragments (quartz, K - f e l d s p a r , p l a g i o c l a s e ) , relic v i t r i c l a s t s (pumice, s h a r d s , fine a s h ) a n d a c c i d e n t a l dense l i t h i c s . Five detailed sections through the Cana C r e e k Tuff display a similar internal a r r a n g e m e n t : v o l c a n i c l a s t i c facies occur a b o v e and b e l o w the p y r o c l a s t i c f a c i e s . T h e latter typically consists of a s h - f a l l tuff b e t w e e n two intervals of ignimbrite. E r u p t i o n c h a r a c t e r . T h e m a g n i t u d e of an e r u p t i o n is assessed in terms of the D e n s e R o c k E q u i v a l e n t (DRE) v o l u m e of the ejecta compared i+ 3 12 3 (Newhall and S e l f , 1 9 8 2 ) . w i t h a scale ranging from < 1 0 m to > 1 0 m The D R E v o l u m e of the Cana C r e e k Tuff is 1 0 1 1 m 3 (114 k m 3 ) for the inferred 2 o r i g i n a l e x t e n t (2500 k m ) , and it is clearly the p r o d u c t of a v e r y large m a g n i t u d e e r u p t i o n . T h e ignimbrites a r e a l l c a l c - a l k a l i n e rhyolites using the c h e m i c a l c l a s s i f i c a t i o n of P e c c e r i l l o a n d Taylor (1976). H y d r o v o l c a n i s m refers to v o l c a n i c p h e n o m e n a p r o d u c e d b y the interaction of m a g m a o r m a g m a t i c h e a t w i t h a n e x t e r n a l source of w a t e r (Sheridan and W o h l e t z , 1 9 8 1 ) . T h a t the e r u p t i o n r e s p o n s i b l e for the Cana C r e e k Tuff w a s h y d r o v o l c a n i c h a s b e e n concluded from the following c h a r a c t e r i s t i c s of its m e d i a l to d i s t a l d e p o s i t s . (i) A c c r e t i o n a r y l a p i l l i a r e w i d e s p r e a d a n d n o t confined to the a s h fall tuff; b o t h i g n i m b r i t e and v o l c a n i c l a s t i c rocks also contain accretionary l a p i l l i in a v a r i e t y of c o n t e x t s . F o r m a t i o n of accretionary l a p i l l i requires suspended fine a s h a n d steam or w a t e r in a s u b a e r i a l s e t t i n g . They a r e a common p r o d u c t of h y d r o v o l c a n i s m (Sheridan and W o h l e t z , 1 9 8 1 ) . (ii) Ignimbrite remained n o n - w e l d e d after e m p l a c e m e n t , even though locally thicker than 50 m . Shards and n o r m a l p u m i c e v e s i c l e s a r e u n d e f o r m e d , w h i l e tube p u m i c e h a s random o r i e n t a t i o n . Such low-grade ignimbrite may b e the result of w a t e r - c o o l i n g in a s t e a m - r i c h eruption column (Self, 1983). (iii) R e l i c v i t r i c l a s t s in the primary p y r o c l a s t i c facies h a v e p a r t i c u l a r l y fine grain s i z e . P u m i c e is typically less than 3 cm in ignimbrite a n d less than 0 . 5 c m in a s h - f a l l t u f f , and b o t h rocktypes contain s u b s t a n t i a l p r o p o r t i o n s of s u b - m i l l i m e t r e p y r o c l a s t s . H y d r o v o l c a n i c e r u p t i o n s a r e thought to involve two stages of m a g m a f r a g m e n t a t i o n , p r o d u c i n g p y r o c l a s t s of fine grain size in a b u n d a n c e (Self a n d S p a r k s , 1 9 7 8 ) . (iv) P r i m a r y p y r o c l a s t i c facies a r e a c c o m p a n i e d b y c o m p o s i t i o n a l l y e q u i v a l e n t v o l c a n i c l a s t i c f a c i e s , interpreted to b e d e p o s i t s of sheetflooding initiated a s a b y - p r o d u c t of the e r u p t i o n . Such a n association is d i a g n o s t i c of large m a g n i t u d e h y d r o v o l c a n i s m w h i c h g e n e r a t e s v o l u m i n o u s , w a t e r - s a t u r a t e d granular sediment r a p i d l y . A l s o , if steam entrapped in p r i m a r y p y r o c l a s t i c flows c o n d e n s e s w i t h d i s t a n c e from s o u r c e , there is a l a t e r a l transition to p u m i c e o u s d e b r i s flows a n d u l t i m a t e l y to sheetw a s h floods (Sheridan and W o h l e t z , 1 9 8 1 ) .

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Large magnitude hydrovolcanism requires a substantial water supply at the site of eruption. The hydrovolcanic eruption of the Cana Creek Tuff may have involved meltwater from glacier ice or snow, as the Late Carboniferous sedimentary facies of the region reflect a provenance affected by alpine glaclation (e.g. Whetten, 1965). In addition the existence of calderas in the source area of the Currabubula Formation has been inferred from consideration of the ignimbrite sheets it contains (McPhie, 1983). A caldera depression, probably already containing a lake, is thus a plausible reservoir for meltwater. Eruption sequence. The course of the Cana Creek Tuff hydroeruption began with high water:magma mass ratios, recorded by volcaniclastic sheetwash flood sandstones and paraconglomerates which interrupt the ambient alluvial plain gravel sedimentation of medial to distal settings. At peak magma discharge water-cooled pyroclastic flows escaped to distal localities. Steam-rich fine ash clouds, accompanying the eruption at vent and elutriated from the moving pyroclastic flows, provided the necessary components to generate rains of accretionary lapilli. A pause in the discharge, possibly due to vent blockage and source area subsidence, allowed permanent deposition of fine grained ash and accretionary lapilli from the steam- and ash-laden atmosphere. Resumption of the eruption, perhaps in response to recovery in the magmatic volatile content, produced a final pulse of pyroclastic flows. In distal areas, volcaniclastic sedimentation at the close of the eruption registers a high water:magma ratio which may have been due to waning magma supply. The eruption duration was probably measurable in days or weeks. Facies scheme. The Cana Creek Tuff is similar in volume, composition, facies and internal stratigraphy to the 20,000 year old Wairakei Formation, generated by a phreatomagmatic eruption from the Taupo Volcanic Centre, North Island, New Zealand (Self and Sparks, 1978; Self, 1983). Together these two units are the basis of a facies scheme for the proximal to remote deposits from a large magnitude explosive hydrovolcanic eruption. Close to source, the deposits are predominantly primary pyroclastic in character but the stratigraphy is incomplete due to erosion attendant on the eruption. Redeposited volcaniclastic facies are more conspicuous in medial to distal regions, with the remote record being widespread but thin and fine airfall ash. References McPhie, J., 1983, Geol. Mag., 120, 487-503. Newhall, C.G., & Self, S., 1982, J. Geophys. Res., _87, 1231-1238. Peccerillo, A., & Taylor, S.R., 1976, Contrib. Mineral. Petrol., 58, 63-81. Self, S., 1983, J. Vole. Geotherm. Res., 17, 433-469. Self, S., & Sparks, R.S.J., 1978, Bull. Vole., 41, 196-212. Sheridan, M.F., & Wohletz, K.H., 1981, Science, 212, 1387-1389. Whetten, J.T., 1965, Geol. Soc. Amer. Bull., 76, 43-56.

POST—OROGENIC BASIN EVOLUTION MODELS H.W.S. McQueen & K. Lambeck Research School of Earth Sciences, A.N.U., Canberra Vertical movements of the crust in coastal areas are a significant factor in controlling the long term patterns of sediment deposition in shallow marine environments along with sealevel changes and variations in sediment supply. These vertical movements have a short term component associated with the exchange of mass between the oceans and ice caps and a longer term component associated with orogenic processes or with the more passive readjustment of the crust to erosion and sedimentation. We are concerned here with this last component. As elevated areas erode, a 378

regional rebound occurs in response to the removal of mass; as the eroded sediments are deposited"on the flanks of the mountains, the crust there is depressed. We examine here the two coupled processes through a model of a shallow marine basin on continental crust lying adjacent to a highland region. The model approximates the early period of the Gippsland Basin and the Victorian Highlands. The model is constructed around a two dimensional mesh of quadratic finite elements which deforms viscoelastically in response to loading. The topography is assumed to be initially in isostatic equilibrium and at each time step erosion proportional to the height of topography removes a layer from the highlands and deposits some or all of it in the basin. The crust then responds viscoelastically to the load redistribution for the duration of the time step before further erosion occurs. The crust is assumed to have horizontally uniform Theological properties under the basin and highlands. Basin development continues as long as there are adjacent highlands to provide a sediment supply. The evolution of the edge of the margin is a result of three factors, the erosion driven regional rebound, the sediment loading of the basin, and the relaxation of the stresses created, by the other two processes. The combined effect is that the line of zero elevation moves in time. Sealevel fluctuations have not been considered at this stage. Stresses can be computed through time and a concentration of deviatoric stress is found at the edge of the basins. These stress differences can amount to several hundred MPa and failure may occur on faults parallel to the basin margin. The basin will be downthrown but the nature of faulting is dependent on the regional stress field.

SULPHIDIC SEDIMENTS AND BASE METAL SULPHIDE MINERALISATION IN THE QUIDONG BASIN, SOUTHEASTERN NEW SOUTH WALES K.G. McQueen Geology, Canberra CAE, Belconnen The Quidong basin in southeastern N.S.W. contains a Late Silurian sequence of shallow marine limestones, shales, siltstones and sandstones unconformabiy overlying Early Silurian flysch rocks. At the base of this sequence there is a sulphidic facies containing chloritic, pyrite-rich siltstones and shales with minor interbedded fine grained tuffs and some thin cherty exhalite layers. These sulphidic sediments are enriched in MgO (up to 19%), total Fe (up to 25%), S (up to 29%) and Mn (up to 3200 ppm) and also show variable but anomalous base metal contents with total Cu, Pb and Zn ranging from backgrbund values of 70-1000 ppm up to 3% in sulphide-rich samples. The sediments are low in CaO (generally less than 1%) and have very low K2O and Na2 0 contents. These compositions reflect derivation of the sediments from: (a) feldspar and mica depleted detritus reworked from underlying quartz-rich flysch; (b) magnesium-rich clay or chlorite precipitated from hydrothermal exhalations into the basin at the time of deposition; and (c) sedimentary pyrite formed by reaction of iron in clays or oxides with reduced sulphur provided by bacterial sea-water sulphate reduction and exhalative activity. Three different but related styles of base metal sulphide mineralisation occur within the basin including: (a) weak syngenetic concentrations of base metals in the sulphidic sediments; (b) stratabound and fault controlled bodies of massive and semi-massive sulphides containing higher grade Pb, Zn and Cu concentrations; and (c) small vein and cavity fillings of galena and barite in limestones. 379

Syngenetic mineralisation consists of minor to trace chalcopyrite, sphalerite and galena associated with framboidal, bedded and recrystallised pyrite. Chalcopyrite also occurs in larger disseminated blebs (up to 5 mm in diameter), replacing carbonate in fossil fragments. The stratabound and fault controlled sulphide bodies are up to 9 m thick and generally occur within the sulphidic facies. They are highly pyritic with typical epigenetic textures and appear to have formed by remobilisation of metals and sulphur from the syngenetic mineralisation during deformation and dewatering. Sulphide remobilisation was at low temperature (<200°C) and accompanied by considerable solution activity in the enclosing rocks. Textural observations reveal a complex history of sulphide development involving deposition of massive pyrite, brecciation and infilling with sphalerite, galena and lesser chalcopyrite, localised replacement of pyrite by pyrrhotite and later oxidation of pyrrhotite to fine grained pyrite and magnetite. The small galena-barite veins have also been deposited from low temperature solutions moving out along faults and other permeable structures in the overlying limestones. This mineralisation is typically vughy with crustiform textures, and is accompanied by dolomitisation of the enclosing limestone. The presence of geochemically anomalous sulphidic sediments above the Mid Silurian, Quidongan unconformity shows that hydrothermal and exhalative processes operated in this shallow marine environment, concomitant with regional uplift and thermal activity. In areas to the north, major felsic volcanism was initiated at this time and resulted in the development of thick sequences of subaerial volcanics in volcanic arch settings and the deposition of submarine volcanics and sediments in narrow rift grabens. Each of these settings has a characteristic style of associated mineralisation. The sulphidic sediments and related sulphide bodies at Quidong represent a third, distal style of sediment hosted stratabound mineralisation developed in shallow marine basins peripheral to the major volcanic centers.

EPIGENETIC GOLD MINERALISATION AT COWARRA, SOUTHEASTERN NEW SOUTH WALES K.G. McQueen 1 , I.F. Gordon 1 and T. Potter 2 1 Geology, Canberra C A E , Belconnen, A.C.T. o '"Swan Resources Limited, Chewton, Victoria

The Cowra Creek goldfield northeast of Cooma, contains a number of pyritic, epigenetic gold deposits localised along cleavage parallel fracture zones in Ordovician flysch rocks. This belt of mineralisation is up to 1.5 km wide and lodes are developed sporadically over a length of 15 km. At least five subparallel lines of lode occur in the main part of the field. A t Cowarra, the largest known deposit, mineralisation is developed over a strike length of 450 m in one major and several minor lodes. The main lode varies from 0.6 to 4.5 m wide with gold grades up to 90 g/t in primary ore (13 g/t is considered representative of average ore, Canavan, 1965j N.S.W. Dept. Min. Res., 1984). The ore consists of massive and irregular sulphide veins, stringers of sulphide in gangue and banded sulphide-calcite material. The sulphides are dominantly pyrite with minor arsenopyrite and pyrrhotite and trace chalcopyrite, sphalerite, galena and gold. A number of texturally distinct sulphide types can be recognised including: (a)

380

Coarse (0.1-3 mm) subhedral to euhedral pyrite, generally with numerous inclusions of pyrrhotite, arsenopyrite and chalcopyrite.

(b)

Coarse (0.1-1.5 mm) subhedral arsenopyrite with rare sulphide inclusions, associated with subhedral pyrite.

(c)

Large irregular replacing pyrite.

(d)

Fine grained, irregular pyrite, commonly with intergrown magnetite, which encloses and rims earlier subhedral pyrite and partially replaces pyrrhotite.

(e)

Fine grained arsenopyrite, generally developed in late stage veins which cut the other sulphides.

aggregates

pyrrhotite

containing

arsenopyrite

and

Gold generally occurs as tiny (0.002-0.25 mm) bleby inclusions in subhedral pyrite, as irregular grains and threads in fractured pyrite and in some cases in the enclosing gangue. It has also been observed as inclusions in pyrrhotite and chalcopyrite, but does not appear to occur in arsenopyritel Gangue minerals include quartz, chlorite, calcite, epidote and albite and there is limited wall rock alteration (mainly chloritisation) associated with the mineralisation. Individual lodes in the area show a clear structural control related to shearing and development of dilational fractures, particularly between contrasting lithologies. This shearing post dates major folding and cleavage development in the Ordovician host rocks, although there is some suggestion that the lodes are elongated parallel to fold plunge directions. Fluid inclusion data, arsenopyrite compositions and mineral assemblages at Cowarra indicate sulphide-gold deposition at temperatures of 300° to 400°C from neutral to weakly alkaline, low salinity fluids. Fluids became more oxidising with time and there appears to have been an increase in A s activity towards the closing stages of deposition. The origin of these fluids is still uncertain. Aeromagnetic data suggest the presence of magnetic, I-type granites at shallow depth beneath the mineralised area and these may have provided hydrothermal fluids (a number of gold deposits in southeastern N.S.W. are associated with magnetic I-type granites, e.g. in the Braidwood-Araluen area). Mineralising fluids may also have been derived, at least in part, by metamorphic dewatering of the Ordovician sedimentary pile. High grade metamorphic rocks occur less than 2 km east of Cowarra and there appears to have been a steep geothermal gradient during metamorphism, so that fluids could have been driven out to lower grade areas from these and underlying high grade rocks. References Canavan, F., 1965, Aust. Inst. Mining and Metallurgy, 216, 13-16. N.S.W. Dept. Min. Res., 1984, Minfo, 3, 1-3.

THE BANDA SEA EARTHQUAKE OF 24 NOVEMBER 1983: EVIDENCE FOR INTERMEDIATE DEPTH THRUST FAULTING IN THE BENIOFF ZONE Marion 0. Michael-Lebia Bureau of Mineral Resources, Canberra On 24 November 1983, a major earthquake occurred at 180 km depth beneath the Banda Sea. In the focal mechanism solution the pressure axis o o is almost horizontal ( azimuth 191 9 plunge 02 ) and the tension axis nearly vertical (plunge 88 ). A comparison with the foreshock-aftershock pattern suggests that shear failure took place within the north northwesterly dipping Benioff zone by thrust faulting along a southerly dipping plane. The focal mechanism solution does not conform to the usual pattern of the tension or compression axis being roughly parallel to the dip of the Benioff zone. Consequently the faulting could not have been caused by down-dip tension or compression within a sinking slab. 381

HYDROCARBON MATURITY OF THE SOUTHERN CONTINENTAL MARGIN OF WESTERN AUSTRALIA M.F. Middleton Geological Survey of Western Australia, Perth Analysis of the structural style of offshore sedimentary basins on the 'southern margin1 of Western Australia suggests a left lateral transcurrent movement of some 250 to 300 km between Australia and Antarctica starting in the Late Jurassic. The transcurrent movement caused the formation of two depocentres with Jurassic and Early Cretaceous sediment fill off the Western Australian 'southern margin'. The eastern depocentre is the Eyre Sub-basin of the Eucla Basin. The name "Albany Sub^basin" is proposed for the western depocentre, which is in the Bremer Basin. The map (below) shows Early Cretaceous tectonic elements of the western 'southern margin1. Seismic studies have shown the structural features of the Albany Sub-basin to be similar to those of the relatively better known Eyre Sub-basin. Seismic stratigraphic units can be dated on the basis of structural correlation between the two sub-basins.

A sequence of seismic geohistory reconstructions in both sub-basins shows hydrocarbon generation to have been highly probable, and entrapment possible in stratigraphic traps on tilted basement blocks. However, in realistic terms, the hydrocarbon potential is low due to large water depths, remoteness of locality and the poor track record of the Otway and other western 'southern margin' sedimentary basins.

LITHOSPHERIC PROCESSES INVOLVED IN THE FORMATION OF THE CANNING BASIN, WESTERN AUSTRALIA M. F. Middleton Geological Survey of Western Australia, Perth Intracratonic sedimentary basins can form in response to processes at newly forming plate boundaries, to processes at existing intracontinental plate boundaries or to anomalous stresses within cratonic blocks. The Canning Basin depositional history appears to be strongly influenced by the first of these processes. For this study, the depositional histories of a number of the subbasins in the Canning Basin were examined. The-sub basins studied were: the Lennard Shelf, the Fitzroy Trough, the Broome Platform and the Kidson Sub-basin. Subsidence versus age for all these tectonic sub-units shows an approximate (age)^ proportionality to subsidence for Late Devonian to Middle Carboniferous sedimentation. This behaviour is characteristic of a thermal cooling lithosphere.

382

Maps from Smith, Hurley and Briden (1981) are shown below with Silurian and Devonian plate tectonic interpretations. The maps are based on palaeomagnetic data, and are consistent with similar maps published elsewhere in the literature.

SILURIAN

DEVONIAN

The tectonic history of the Canning Basin based on the plate tectonic regime depicted above is: (i)

DOMING PRIOR TO RIFTING, 440 Ma. Folding of Ordovician sediments in the north of the basin (Lennard Shelf). (ii) RIFTING AND SEAFLOOR SPREADING, 400 Ma. Deposition of the Carribuddy Formation (evaporites) in the central and southern Canning Basin. (iii) THERMAL SUBSIDENCE, 360 Ma. Rapid subsidence in the Fitzroy Trough and Kidson Sub-basin during Late Devonian and Early Carboniferous. Thermal model calculations indicate a significant thermal anomaly to have devaloped in the lithosphere under the Fitzroy Trough during the rifting episode. It is possible that hot asthenospheric material spread eastward under the axis of the Fitzroy Trough during the formation of the major east-west transform fault, off-shore from the Canning Basin (see above figures). The calculations show that the upper mantle and deep crustal temperatures were increased beneath the Fitzroy Trough by between 500 and 700 degrees Centigrade during the Silurian rifting episode. Reference Smith, A.G., Hurley,A.M., & Briden, J.C., 1981, Phanerozoic continental World Maps, Cambridge University Press, 102p.

Paleo-

THE MT. MACEDON DACITE: ORIGIN AND EVOLUTION OF A WEAKLY PERALUMINOUS MAGMA OF INTERMEDIATE COMPOSITION E.J. Mikucki and V.J. Wall Department of Earth Sciences, Monash University, Clayton Although earlier studies emphasized the strongly peraluminous and quartz-rich nature of S-type igneous rocks (e.g. Chappell and White, 1974), weakly peraluminous, more silica-poor varieties have also been recognized (Arth and Hanson, 1975; Bini, 1982). In this paper we examine the geochemical and petrological evidence pertaining to the origin of the Mt. Macedon Dacite of central Victoria: a weakly peraluminous (A/CNK ~ 1.06), crystal-rich ignimbrite of intermediate composition 63wt% Si02>.

383

The Mt. Macedon Dacite is mineralogically and chemically homogeneous and represents the erosional remnant of a large volume (>100 km) subsidence-fill ash flow unit of Upper Devonian age. Bulk rock chemical analyses have been recalculated to account for crystal-ash fractionation during eruption of the dacite. The calculated original magma compositions average - 66wt% Si02 and show moderate to low A/CNK 1.04), K 2 0/ Na20 (~1.09) and MgO/MgO + FeO (0.27). Textural evidence indicates <1% restite component within the dacite. For example, the predominance of oscillatory zoning in plagioclase and the common occurrence of primary silicate melt inclusions within euhedral opx crystals clearly support a magmatic origin for the dacitefs major phenocryst phases. Inclusion and crystal-melt reaction relationships indicate early crystallisation of plag (An 64 ) + opx (En 44 ) + garnet (Alm76Py22)Later stages of crystallisation were characterised by reaction between early-formed garnet and melt and by the crystallisation of quartz phenocrysts. Biotite and K-feldspar occur only in the groundmass. Rock types which could possibly represent parental magmas for the dacite are not exposed within the Mt. Macedon Igneous Complex. Therefore, the dacite may best be modelled as a lower crustal melt. Thus the observed crystallisation sequence, major and trace element geochemistry place constraints on the partial melting conditions and source rock lithology for the Mt. Macedon magma. Moderate to low Si02, A/CNK and K20/Na20 as well as the distinctly fnon-minimum melt' chemistry of the dacite are compatible with extensive partial melting of mildly peraluminous quartzofeldspathic rock types (Clemens and Wall, 1981). Derivation from an I-type, metaluminous source (Cawthorn and Brown, 1976) is not favoured due to the absence of early cpx or hornblende phenocrysts and low K/Rb ratios within the dacite. Early depletion of quartz, biotite and K-feldspar within the source region can be inferred from the observed crystallisation sequence and indicate anatectic temperatures well above those associated with biotite melting reactions (T>850°C at P = 5-10Kb) and initial melt water contents of <3.3wt%. The above observations for the Mt. Macedon Dacite lend further support for extensive crustal anatexis during a Devonian granulite facies metamorphic event within the lower crust of Victoria (Wall et al. , 1983) and have important implications as to the composition, thermal history and tectonic evolution of the lower crust in this region. References Arth, J.G. & Hanson, G.N., 1975, Geochim. Cosmochim. Acta, 39_> 325-362. Bini, A.J., 1982, Unpubl. Hons. Thesis, Monash University. Cawthorn, R.G. & Brown, P.A., 1976, Journ. Geol., 84^ 467-476. Chappell, B.W. & White, A.J.R., 1974, Pac. Geol., 173-174. Clemens, J.D. & Wall, V.J., 1981, Can. Mineral.,^, 111-131. Wall, V.J. et al., 1983, Geol. Soc. Aust. Abstr. Ser. 9, 160.

FOUNDATION DAMAGE IN WATER-AFFECTED PERMIAN ROCKS NEWCASTLE, N.S.W. 1 2 Konrad H.R. Moelle^ and David F. Branagan ^"Department of Geology, University of Newcastle ^Department of Geology & Geophysics, University of Sydney Newcastle, N.S.W., a large industrial city (poulation approximately 350,000) which is spread over an area of nearly 500 square kilometres, has very complex foundation conditions compared with most Australian cities. The complexity stems from the highly variable stratigraphy of the Permian Newcastle Coal Measures. 384

T h e presence of relatively thick, laterally extensive, expansive clay rocks is of major significance. The claystone layers occur in association with relatively impermeable coal seams, conglomerates and a variety of lutites. Arenites vary in composition and consequently also in p e r m e a b i l i t y . Whereas the sedimentary succession has not been affected by major tectonic deformation events, it is gently folded, moderately faulted and has several well-developed joint systems. Numerous basaltic dykes have intruded this sequence. This Permian succession is overlain in places by alluvial and aeolian deposits of Quaternary age with varying thicknesses. Within the alluvial deposits expanding clays occasionally occur. Erosion has produced a varied topography and has exposed the expansible clay rocks in numerous o u t c r o p s . C o a l mining since 1800, and a wide variety of developments (roads, tunnels, b r i d g e s , major buildings, harbour w o r k s ) have brought about an interaction between engineering and geology to a considerable d e g r e e . While there are many examples of slumping and slope failure which have been documented, two cases in the Tickhole Tunnel area are of particular interest because engineering structures have been affected during m o v e m e n t s and the record of deformation in each case can be used to reconstruct the modes of failure. There have been periods of rapid m o v e m e n t , notably in 1968 and 1974, in addition to periodic movements at other times. Creep probably also contributes to slope m o v e m e n t s . While photographic methods and road distortion can show much of the deformation which is occurring, the deflections of a post and metal rail fence can be measured to demonstrate the movement picture and the variation in strain which have occurred at one s i d e . Adjacent to the Tickhole Tunnel itself a water-pipe resting on a series of independent footings may be used to measure the movement of the underlying foundation r o c k s . This movement is caused mainly by creep, although there have been occasional rapid m o v e m e n t s . This area is the site of a new railway tunnel and a modified m a i n road. It w i l l be interesting to see whether modifications to the landscape and the drainage will alleviate the problems outlined a b o v e , most of which can be attributed to the presence of water-sensitive clay rocks. In addition to problems experienced by major engineering w o r k s , private dwellings have occasionally had their foundations damaged when founded in expansive claystone layers. The need for adequate drainage systems is often not recognised, and unsuitable foundations are sometimes constructed in expanding clay that is exposed during construction and subsequently wetted and dried periodically. Erosional patterns are significantly influenced by occurrence of claystone bands and layers in numerous outcrops. Progressive differential erosion of several road cuts can be clearly attributed to the preferential failure of expanding clay h o r i z o n s . Examples can be found in several suburbs of Newcastle, particularly in the lower and middle portions of the Newcastle Coal M e a s u r e s . The clay layers occur chiefly in the immediate roof- and floor- strata of the major coal seams. Delineation of the zones characterised by clay occurrences in the Newcastle City and Lake Macquarie Shire areas reveals that a significant proportion of the total area available for building and construction could be subject to failure or other forms of instability.

385

THE NATDRE OF THE ORE FLUIDS AT THE SANGDONG SCHEELITE DEPOSIT, KOREA 1 2 K.J. Moon1- and M. Solomon ^Korea Institute of Energy and Resources, Seoul 2Bureau of Mineral Resources, Canberra The Sangdong deposit is one of the world's largest tungsten producers and in addition yields molybdenum, bismuth and gold. Scheelite occurs in quartz veins and in stratabound skarns that replace gently dipping Cambrian limestones; the skarns are of Cretaceous age. Skarns occur in limestones of several stratigraphic horizons but most production has come from the Main orebody, the central parts of which grade 6% W03. The Main orebody shows zonal distribution of the major skarn minerals from metre to centimetre scale: a central quartz-mica zone is surrounded by an amphibole-rich zone which is enveloped by a pyroxene-garnet zone having abrupt outer contacts with unaltered Cambrian limestone. 6 1 8 0 values in skarn quartz (+ 10.8 permil), 6 3 4 S in skarn sulphide (+ 3.9 to + 6.1 permil) and 6 1 3 C and 6 1 8 0 in skarn carbonate ( - 8 . 1 and +11.8 permil respectively) indicate derivation from magmatic fluids, and the high temperatures indicated by the mineralogy and fluid inclusions (up to 600°C) suggest a magmatic heat source. Recent drilling has intersected altered granite within Precambrian rocks over 500 in below the skarns, and has also revealed additional reserves of molybdenite-quartz veins. Upward fluid movement appears to have been focussed by NE fractures, resulting in elongate skarn zones. The skarn assemblages appear to have formed under equilibrium conditions by lateral fluid movement outward from the central mica-rich zone. The mineralogical zones grew outward, widening with time, leaving relics of earlier assemblages throughout the deposit. During skarn growth the fluid temperature declined from nearly 600°C to about 250°C, and from a two phase to a single phase condition. It is assumed that the characteristics of the central zone may be used to indicate the nature of the magmatic fluid during the later stages of fluid evolution. Some parameters have been estimated as follows: Fluid system: T°C:

H 2 0 + NaCl + CaCl2 ± MgCl2 ± C02, single phase

^350°C

P atm:

^800 bars (from sphalerite composition)

pH:

^4.0 (inferred from mineralogy and solubility of tungsten in equilibrium with scheelite)

ES:

^2.5 x 10~3 m

log fo2:

-30 to -32 atm

log fs2:

-9 to -11 atm

%2S:

5l8

°H 2 0:

613C

EC:

+ 4.5 to + 5.3 permil + 6.6 to + 8.5 permil -

-5 permil

Quartz-wolframite and quartz-molybdenite veins formed in and around the skarns throughout skarn growth, but later quartz-sulphide veins cut the skarns. It is tentatively suggested that the magmatic fluid circulated within a cylindrical column above the granite source. Steep temperature and compositional gradients were maintained at the skarn limits by double diffusive mechanisms between magmatic fluids and heated groundwater.

386

EPMA ANALYSIS OF ULTRAMAFIC NODULES FROM OBERON, NSW: MINERAL CHEMISTRY AND THERMOBAROMETRY Paul A. Morris Department of Geology & Geophysics, University of Sydney, NSW Ultramafic nodules in Tertiary alkali basalts from Oberon, NSW comprise spinel lherzolite and rare websterite, harzburgite, and spinel dunite. In terms of modal mineralogy, these nodules strongly resemble Group I (i.e. Crdiopside type) inclusions discussed by Frey and Prinz (1978). A cumulate origin for the Oberon nodules Is indicated by the (albeit rare) occurrence of exsolution in pyroxene, and poikilitic enclosure (e.g. olivine enclosing clinopyroxene; olivine enclosing spinel). Most igneous features have been obliterated by a metamorphic overprint, indicated by curved grain boundaries, kink-banding of olivine primocrysts, and lack of mineral zoning. The resultant texture is similar to protogranular I of Mercier and Nicolas (1975). Representative nodules have been analysed using the electron microprobe. Olivine, pyroxenes and spinel compositions grade between Group I and Group II (i.e. Al-augite type) inclusions. These mineral data have been used to estimate equilibration temperatures using three mineral thermometers (Wells, 1977; Wood and Banno, 1973; Sachtleben and Sech, 1982). Temperatures range from 840-1160°C, although for any one method, the range is only in the vicinity of 120°C. Temperature and pressure estimates were also made using the single-pyroxene method of Mercier (1980), although these values were rejected as they involved values in the garnet lherzolite field, and occasionally produced negative pressure estimates. Using the mineral thermometry values in conjunction with the proposed NSW geotherm (Ferguson et al., 1977), equilibration occurred at depths of 40-50km (i.e. 13-15kb). Decreasing equilibration temperatures are accompanied by increasing Ti and decreasing Cr in clinopyroxene; this, combined with textural evidence for a cumulative origin, indicates that nodules crystallised from a chemically evolving melt with decreasing temperature (i.e. fractional crystallisation). As there is no consistent change in modal mineral proportions with decreasing temperature, it is at present unclear whether all nodules examined are genetically related by this process, or whether they crystallised separately from liquids of variable composition prior to entrainment. References Ferguson, J., Ellis, D. J., & England, R. N., 1977, Geology _5, 278-280. Frey, F.A., & Prinz, M., 1978, Earth & Planetary Sci. Letters, 38, 129-176. Mercier, J-C. C., 1980, Tectonophysics, 70, 1-37. Mercier, J-C. C., & Nicholas, A., 1975, J. Petrology, 16, 454-487. Sachtleben, T., & Sech, H.A., 1982, Contr. Miner. Petrol., 78, 157-165. Wells, P.R.A., 1977, Contr. Miner. Petrol.,.62, 129-139. Wood, B.J., & Banno, , 1973, Contr. Miner. Petrol., 42, 109-121,

387

THE RENISON MINE SEQUENCE AND ITS RELATIONSHIP TO TIN MINERALIZATION

Gregg W. Morrison James Cook University, Townsville The Renison mine sequence, which hosts the Renison tin deposit extends for 20km, is approximately 250m thick and consists of a lower unit (Success Creek Group) of quartz sandstone and siltstone with black shale and dolomite and an upper unit (Red Rock) of red sandstone, siltstone and conglomerate with dolcmite and chert. Recently discovered in situ stromatolites and microfossils are considered comparable to those of Middle to Late Proterozoic age in the Adelaidean of South Australia (Morrison & Preiss, in prep.)* A gross correlation of major units is possible throughout the strike length of the sequence, but three major facies variants can be defined. In the northwest there is massive oolitic and enterolithic dolcmite comparable to the Smithton Dolomite underlain by non-carbonaceous siltstone and sandstone; in the central area strcmatolitic and oolitic dolcmite is underlain by sandstone-siltstoneshale cycles? and in the southeast, or mine area, there are three discrete laminated pelletal dolomites that are part of sandstone- siltstone-shale-dolcmite cycles. The overall facies progression represents a change in depositional environment from continental platform sabkha to tidal flat fringe and tidal flat proper. The Red Rock which partly erodes and partly inter fingers with the dolcmite consists of fluvial channel-full conglcmerate-grit-sandstone-siltstone sequences and cherty and dolcmitic siltstone that formed in ponds and marshes adjacent to the channel levees. Individual cycles with the Renison mine sequence near the mine consist of massive sandstone with pebble beds? graded and flaser bedded sandstone and siltstone? flaser to tidal bedded siltstone and black shale? nodular dolcmite and tidal bedded dolcmitic siltstone ? and laminated pelletal dolcmite. This sequence corresponds to the sandflat, mixed flat, mud flat, salt marsh and algal flat environments in modern carbonate-clastic tidal flats. The textural similarities of cycle subunits, complex block faulting, structural thinning of units and the presence of local mini-cycles make correlation in the mine area difficult. The carbonate units in the mine area are pelletal and laminated and exhibit early diagenetic recrystallisation, late diagenetic cavity fill and silicification and weak contact metamorphic recrystallisation with formation of talc and tremolite. All these features are obliterated by the hydrothermal mineralisation and do not affect its distribution. Contour plans of the carbonate units suggest that away from the faults vhich were conduits for the hydrothermal fluid, the margins of the mineralised zone are approximately parallel to specific thickness contours. Impure bands vfoich locally characterise the upper and lower stratigraphic contacts of the host dolomites can be traced through the outer margins of the mineralisation and into the orebodies proper. The ore is lower grade in such margins as if it had been diluted by impurities in the host and grainsize decreases with increasing impurity content for all hydrothermal mineralisation. This leads to total exclusion of mineralisation at high impurity levels. Considering the Proterozoic age of the sedimentary units, the fluvial origin of iron formation and red clastic rocks and the close association of mineralisation with supratidal dolomites it seems unlikely that the Renison

388

mine sequence is time equivalent or genetically related to the Mount Read Vblcanics of the Duhdas Trough. The cross-cutting relationship of mineralisation to dolcmite lamination and to contact metamorphic products and the correlation between ore grade and impurities in the host rock suggest the ore is an epigenetic replacement of dolcmite.

THE BASE OF THE LITHOSPHERE UNDER AUSTRALIA K.J. Muirhead Australian National University The base of the lithosphere is interpreted as the depth to the top of the low velocity zone (LVZ) in the upper mantle. This follows from the common assumption that at some depth the local thermal gradient intersects the mantle solidus and this results in a small degree of partial melt with a consequent reduction in shear strength and an increase in anelasticity (lower Q). Using this interpretation, the depth to the base of the lithosphere under the Palaeozoic region of eastern Australia is significantly less than under the shield region of central and northern Australia. In southeastern Australia, the amount of seismic data which can place constraints on the lithospheric thickness is not great and is somewhat conflicting. From surface wave analyses, the depth to the LVZ is interpreted to be between 80 and 120 km and this contrasts with a depth of around 160 km which has been derived from seismic refraction studies. In central and northern Australia, a LVZ is not required to satisfy the surface wave data at the longest measured periods and refraction studies indicate that the first resolvable LVZ starts at a depth near 230 km.

THE ROLE OF GEOLOGICAL FAULTING IN SOUTH-EAST AUSTRALIA, AND ITS BEARING ON THE SEISMICITY OF THE REGION Ivan A. Mumme CSIRO, Division of Mineral Physics, Lucas Heights, Sydney The purpose of this paper is to interpret the historic intraplate seismicity of S.E. Australia, a region of quite high heat flow, in terms of available geological and geophysical information. The reason for carrying out this investigation is because to date no specific correlations have been made between earthquake epi-centres and the many known specific tectonic features such as exposed fault and lineaments that occur within this study area. The current seismic activity has been found to be centred well below these exposed structural features at an average depth around 9 km, and therefore inaccessible to direct study by surface geological methods. Resolving this problem as well as the nature of the present geodynamic processes which give rise to this activity are important in evaluating earthquake hazards at sites of projected structures in the general region whose integrity is essential to the health and safety of the populations surrounding them. The fundamental feature of the geological structure of this broad region is that it is composed of five physio-graphic provinces namely the Lachlan fold belt which forms a central inner core and portions of the Sydney, Murray and Otway basins and the Gippsland basin, largely formed

389

since Permian times as depressions on it flanks- Both the regional seismic and gravity work show a rapid thinning of the crust from beneath the exposed Lachlan fold belt to the east. This is indicative of a thinning of the crust in this area by a stretching mechanism at the time the Sydney Basin was formed on Lachlan fold belt basement rocks, and its connection with intensive volcanic activity during early stages of sedimentation in the Sydney Basin. Basaltic volcanism has also been a feature of the eastern Australian margin over the last 80-85 m year. This volcanism accompanied epeirogenic uplifts and extensions of this continental margin as seafloor spreading opened the Tasman sea and southern ocean. One of the most important sources of information for helping us to understand the processes giving rise to seismic activity in this general region is the epicentral m a p . The most obvious feature of this map is that the earthquake activity appears to be distributed fairly uniformly throughout this intraplate environment except in a few areas where clusterings of earthquakes occur. Thus apart from several areas where somewhat higher than background seismic activity occurs (eg. Robertson Bowral, Picton, Blanket Flat, Yass - Bowning, Snowy Mountains region, and Foster - Yarram areas) the seismicity pattern suggests that the whole region behaves as one seismotectonic province in which small to moderate earthquakes have so far been recorded. Although the historic earthquake record is short for S.E. Australia, there seems to be a greater likelihood of larger earthquakes occurring in the short term in the areas of enhanced seismic activity mentioned above than in the remainder of the study area. In N.S.W. these areas of clusterings appear to be tectonically reworked areas which have been affected by deep seated magmatic and metamorphic processes. The great majority of in-situ stress measurements conducted to date in Australia including those in this study area (except close to the east coast) show surprising uniformity - with the average direction of the largest-horizontal principal stress being approximately E J W . Also the directions of the pressure axes obtained from earthquake focal mechanisms analysed in S.E. Australia largely confirm a compressive stress region. As a result, some details of the rock failure mechanisms and slip mechanics occurring with earthquakes in this region are now understood. (D. Denhara et al., 1979) Useful information about the strength of the rocks can also be derived by considering the following arguments. Firstly the seismic moment MQ of ^n earthquake is approximated by the equation : MQ = MA u = (16/7) Ao.r , where M is the rock shear modulus, A is the fault area, u is the average fault displacement, Aa is the stress drop, and r is the radius of a circular fault of area A . If we relate the earthquake magnitude M ^ to the seismic moment Ho by the empirical equation : ^

- (log M q - 16)/1.5

and apply known information from various recorded earthquakes in S.E. Australia we obtain Ao less than 10 b a r s . As it is generally found that measured stress drops for earthquakes range from about 1 bar to 100 bars, a moderate value being 30 bars, it would seem that rocks fail at depths in S.E. Australia at low stress drops and are weak. This is in agreement with studies of the isostatic behaviour of crustal blocks in this intraplate region.

390

In conclusion, an analysis of the seismic activity characteristics in S.E. Australia suggest that it results from the release of compressive and residual stresses present in the crustal rocks. Because of the probable existence of many fault planes and weak rock layers present at depth in this region as a result of stresses caused by igneous intrusions and orogenic cycles, it is believed that this stress is relieved before excessive strain energy accummulates* Thus away from the areas of localized patterns of higher seismic activity, the general region can be considered to possess uniform seismicity and the seismic hazard assessment can be based on the uniform seismicity approach developed by Cornell. In the proximity of such seismic sources of enhanced earthquake activity, however, the variable seismicity approach to evaluate seismic risk should be adopted. Reference Denham D. f Alexander L.G, and Uorotnicki G., 1979, Stresses in the Australian crust : evidence from earthquakes and in-situ stress measurements. B.M.R. Journal of Australian Geology and Geophysics 4, 289-295.

METALLOGENY AND TECTONIC DEVELOPMENT OF THE TASMAN FOLD BELT SYSTEM IN QUEENSLAND C.G. Murray Geological Survey of Queensland, Brisbane The Tasman Fold Belt System in Queensland consists of three main segments, the Thomson, Hodgkinson-Broken River, and Yarrol Fold Belts. The Thomson Fold Belt (Murray & Kirkegaard, 1978) is largely concealed by younger sediments. Its western margin is faulted against the Precambrian Mount Isa Inlier along the Diamantina River lineament. The earliest deposits (orogenic or pre-cratonic stage) are regarded as Cambrian and Ordovician in age, and are exposed in the Anakie Inlier and LolworthRavenswood Block. The tectonic setting of the low grade metamorphics of the Anakie Inlier is unknown, but these rocks were certainly marine. They are host to gold of possible volcanic-exhalative and metamorphic vein origin which has sourced Early Permian glacial placers at Clermont, and to one significant copper deposit (Peak Downs). Calc-alkaline volcanics and volcaniclastic sediments of the Mount Windsor Volcanic Arc in the south of the Lolworth-Ravenswood Block contain volcanogenic massive sulphides (Thalanga, Liontown) and gold (Highway). The most extensive unit in the Lolworth-Ravenswood Block is the Ordovician to Devonian Ravenswood Granodiorite which was the source of major vein-type gold deposits at Charters Towers and Ravenswood, and minor copper and molybdenum mineralisation. Unconformably overlying the early sequences of the Thomson Fold Belt are Devonian to Early Carboniferous sediments and volcanics (transitional stage) of the Adavale (concealed), Drummond and Burdekin Basins. Widespread, dominantly silicic volcanics occur at the base of the Adavale Basin (possibly in part a volcanic rift or rifts) and the Drummond Basin (possibly a foreland basin west of the Connors-Auburn Volcanic Arc of the Yarrol Fold Belt). Virtually no mineralisation is known from these transitional tectonic units apart from minor gold. The Hodgkinson-Broken River Fold Belt (Arnold & Fawckner, 1980) is faulted against Precambrian rocks of the Georgetown and Yambo Inliers to the west. The bounding Palmerville and Burdekin River Faults were previously considered to be relatively simple structures reactivated several times, but recent work has recognised major mylonite zones and suggests a more complex history. The oldest rocks are restricted to the Broken River Province, and comprise quartzose flysch of possible Ordovician age and a relatively small area of Late Ordovician limestone and volcanics which has been compared to island arc assemblages. 391

The bulk of the fold belt consists of very extensive flysch sequences with limestone-rich shelf deposits along the western margin. Deposition was older in the Broken River Province (Early Silurian-Middle Devonian) than in the Hodgkinson Province (Late Silurian-Late Devonian). The SilurianDevonian tectonic setting is a matter of dispute. Some authors (Cooper et al., 1975; Arnold, in Arnold & Fawckner, 1980) suggested a forearc setting, with a major provenance from an Andean-type volcanic chain, now represented only by linear batholiths of possible Devonian age, along the eastern edge of the Precambrian craton. However, as clearly pointed out by White (1965) and de Keyser & Lucas (1968), volcanic detritus is rare in the flysch of the Hodgkinson-Broken River Fold Belt, and the major source of sediment was the Precambrian craton itself. The data appear to rule out the possibility of an arc-related setting, even some-type of back-arc basin, and are more consistent with interpretation as a rifted continental margin (Fawckner, 1981). Mineralisation is widespread in the Late Silurian-Devonian rocks of the Hodgkinson Province, including volcanogenic massive sulphide deposits (Dianne, OK and Mount Molloy) and metamorphic gold-stibnite quartz veins. In addition, the ultimate source of base metals in many skarn and fissure zone deposits along the western margin of the province may also have been volcanic. In contrast, the Ordovician to Middle Devonian rocks of the Broken River Province, and the overlying Late Devonian-Early Carboniferous sediments of the transitional Bundock and Clarke River Basins, are almost devoid of mineralisation. The Greenvale nickel orebody is concentrated in the lateritic weathering profile developed on ultramafics of Proterozoic or Early Palaeozoic age. Deformation in the Early Carboniferous marked the end of the orogenic or pre-cratonic stage of the Hodgkinson-Broken River Fold Belt. From midCarboniferous to Early Permian time, the entire fold belt, and adjacent areas of the Georgetown and Yambo Inliers and the Thomson Fold Belt, were the site of intrusion of granitic batholiths and eruption of extensive comagmatic silicic volcanics. The volcanism has been compared with that in the present day Andes and attributed to a westward dipping subduction zone by Bailey et al. (1982). Numerous relatively small, rich ore deposits of widely varied type are associated with the plutonic and volcanic activity, including Sn, W, Mo and Bi in granites and contact rocks (Vulcan, Herberton, Annan River, Kangaroo Hills, Wolfram Camp, Mount Carbine, Bamford Hill etc.), gold in breccia pipes (Kidston, Mount Leyshon, Mount Wright) and skarns (Red Dome near Mungana), disseminated porphyry-type copper (Ruddygore), uranium in volcanics (Maureen, Ben Lomond), and base metals in skarns and fissures (Mount Garnet, Shannon-Zillmanton etc.). In recent years, alluvial cassiterite has accounted for most of the tin production. The Yarrol Fold Belt (Day et al., 1978) was characterised by the repeated development of west-dipping subduction zones in late Palaeozoic time, accompanied by granite emplacement, calc-alkaline volcanism, deposition of thick volcaniclastic sediments in forearc settings, and a variety of mineralisation styles. The oldest rocks were deposited in the Late SilurianMiddle Devonian Calliope Island Arc, which extended from Warwick to Broad Sound and was separated from the Australian continent to the west (Anakie Inlier) by a marginal sea. The major gold-copper orebody at Mount Morgan, currently interpreted as a pipe-like volcanogenic massive sulphide deposit, is hosted by submarine silicic pyroclastics of the Calliope Island Arc. Following a late Middle Devonian orogeny and intrusion of granodiorite plutons, the marginal sea was partly cratonised or closed and uplifted, and an Andean-type continental margin developed in Late Devonian-Early Carboniferous time. From west to east, deposition occurred in the continental ConnorsAuburn Volcanic Arc, the shallow marine, volcanic-rich Yarrol Shelf, and on the continental slope (Wandilla Slope and Basin) where volcanics were much less abundant. Andesitic volcanics of both the volcanic arc and the marine shelf locally contain disseminated copper mineralisation, and may have been 392

a source for epigenetic skarn and fissure zone deposits of the Yarrol Shelf. In c o n t r a s t , the deep water flysch-type sediments of the Wandilla Slope and B a s i n , w h i c h are separated from the Yarrol Shelf by a major serpentinite b e l t , are generally lacking in base metals but do contain some gold deposits in metamorphic quartz veins and stockworks. Volcanism ceased or greatly declined in the Connors-Auburn Arc in the Late C a r b o n i f e r o u s , and granitic batholiths were e m p l a c e d . Only very minor mineralisation is associated with these granitoids, possibly because of deep erosion l e v e l s . Marine sedimentation was greatly restricted on the Yarrol Shelf, with a much reduced volcanic component, and may have continued to the east in the Wandilla Slope and Basin. Renewed volcanism in the Early Permian saw the development of the calcalkaline Camboon Volcanic Arc along the site of the former Connors-Auburn A r c . The Early Permian arc w a s short lived but of major proportions. Volcanism w a s also widespread at this time over the Yarrol Shelf and uplifted Wandilla Slope and B a s i n , and marked the beginning of deposition in the Gympie Province to the e a s t . Volcanics and associated sediments were both subaerial and submarine. Mineralisation in these rocks ranges from obviously volcanogenic (Mount Chalmers gold-copper, Mount Mosquito gold) to volcanichosted but possibly epithermal (Cracow g o l d ) , to sediment-hosted (Gympie gold). In the Gympie Province, marine sedimentation persisted into Early Triassic time, but the remainder of the Yarrol Fold Belt was uplifted in the Late Permian when emplacement of Permo-Triassic granites commenced. The granitoids are restricted to the area south of Broad Sound, vary in size from small stocks up to large batholiths, and range in age from Late Permian to Late Triassic. Distinct belts of low grade disseminated porphyry copper and molybdenum deposits have been recognised in these granitoids (Horton, 1978), gold, base metals and bismuth occur in fissure veins and replacement deposits near intrusive contacts, and molybdenum occurs locally in quartz p i p e s . Two continental volcanic rifts, the Esk and Abercorn Troughs, were sites of rapid and thick deposition in Middle Triassic t i m e . The volcanics were dominantly andesitic to basaltic rather than a more typical bimodal suite. The Esk Trough contains mercury and gold mineralisation near Kilkivan. Relatively thin Late Triassic continental volcanics, mainly of andesitic to rhyolitic composition, are widespread in southeast Queensland, and locally overlie the Esk Trough deposits unconformably. The low grade disseminated gold occurrence at Mount Rawdon is associated with these volcanics. The Jurassic-Early Cretaceous Maryborough Basin, east of the Gympie Province, received continental and marine sediments and andesitic v o l c a n i c s , but appears to lack significant mineralisation. Several Early Cretaceous granitoids, ranging in size up to batholithic dimensions, were emplaced in the northern part of the former Connors-Auburn and Camboon Volcanic A r c s . Some of the granitoids carry disseminated porphyry copper-type mineralisation (Horton, 1978), and gold occurs in quartz veins at intrusive contacts. Mid-Cretaceous volcanics in the Proserpine area consist dominantly of silicic to intermediate pyroclastics and rhyolite flows, erupted suberially. The N e w England Fold Belt is represented in Queensland only by the Silverwood and Texas Blocks south of W a r w i c k . Early to Middle Devonian sediments and volcanics of the Silverwood Block are believed to be part of the Calliope Island A r c . These rocks are in fault contact with ?Late Devonian-Carboniferous flysch-type sediments of the Texas Block containing limestone lenses and blocks which are at least in part allochthonous. Both these sequences are overlain unconformably by marine Permian sediments and rhyolitic v o l c a n i c s , and all units are intruded by Triassic granitoids

393

forming the northern extremity of the New England batholith. The most important types of mineralisation are gold in metamorphic veins in Late Devonian-Carboniferous sediments, base metal sulphides in Early Permian sediments, and tin in Triassic granitoids. Tertiary deep weathering events were responsible for the formation of some orebodies in the Tasman Fold Belt System in Queensland, including lateritic nickel deposits on ultramafics at Greenvale and Rockhampton, and surficial manganese concentrations from disseminated mineralisation in deep water cherts and jaspers, notably in the Wandilla Slope and Basin sequence. References Arnold, G.O., & Fawckner, J.F., 1980, in Henderson, R.A., & Stephenson, P.J. (eds) The geology and geophysics of northeastern Australia, Geol. Soc. Aust., Qd Div., Brisbane, 175-189. Bailey, J.C., Morgan, W.R., & Black, L.P., 1982, J . Geol. Soc. Aust., 29, 375-393. Cooper, J.A., Webb, A.W., & Whitaker, W.G., 1975, J . Geol. Soc. Aust., 22, 285-310. Day, R.W., Murray, C.G., & Whitaker, W.G., 1978, Tectonophysics, 48, 327-364. de Keyser, F., & Lucas, K.G., 1968, Bur. Miner. Resour. Aust. Bull., 84. Fawckner, J.F., 1981, Ph.D. thesis, James Cook Uni., Townsville. Horton, D.J., 1978: Econ. Geol., 73, 904-921. Murray, C.G., & Kirkegaard, A.G., 1978, Tectonophysics, 48, 299-325. White, D.A., 1965, Bur. Miner. Resour. Aust. Bull., 71. THE LOGICAL DEVELOPMENT OF DEEPLY WEATHERED

PROFILES

Burton Murrell CRA Exploration P t y . Ltd., Canberra Deeply weathered profiles are widespread throughout the world and are of particular importance in Australia as the nutrient-poor parent materials of extensive soils and because they add to the difficulties of exploration for ore deposits. Empirical observations of constant associations in these profiles has led to their description as entities resulting from a single poorly understood process. Application of simple bulk chemistry, basic groundwater hydrology and well known weathering processes allows these profiles to b e understood in terms of a simple repeatable sequence of development which requires neither special pleading nor drastic climatic variation.

BRECCIATION AND MINERALISATION AT THE RIDSTON GOLD NORTH

DEPOSIT,

QUEENSLAND

Harry Mustard Placer Pacific Pty Limited, Townsville Kidston is a large (1300 m x 920 m) gold bearing breccia pipe, hosted in Proterozoic granodiorite and metamorphic rocks associated with Middle Carboniferous rhyolitic intrusions. The breccia pipe is ovoid in plan, funnel shaped in cross section and is surrounded by a 10 to 20 metre zone of crackle breccia. Sets of parallel, "sheeted" quartz veins, overlap the margin of the breccia pipe. A suite of rhyolite dykes have intruded into the breccia pipe, some of which are restricted to it. 394

Fragments of granodiorite, metamorphics and rhyolite are present in the pipe and mix in various proportions to form gradational lithological domains. The breccias in the pipe can be divided into three main zones, a thin outer zone of monomictic breccia that reflects the lithology of the adjacent country rock, an inner zone of bimictic breccia where rhyolite fragments are mixed with the monomictic breccia, and a core of polymictic breccia where mixing is the greatest and rhyolite, granodiorite and metamorphic fragments are present. All fragments are randomly orientated and increase in size when approaching the margin. Rhyolite fragments are typically angular in contrast to granodiorite and metamorphic fragments that tend to be rounded and are thought to be the source of rock flour in the matrix. Breccia which contains a high proportion of rhyolite fragments possess much more open space than breccia composed of granodiorite and metamorphic fragments. Four main stages in the genesis of the brecia pipe are recognised: 1.

Pre-breccia events, which include formation of stockwork quartz veins, breccias cemented by quartz and tourmaline, and the development of crenulate bands of quartz crystals interlayered with microgranite known as brain rock, all of which occur as fragments in the breccia pipe.

Formation of the breccia pipe by the explosive release of volatiles from a magma.

Post-breccia events that involved the filling of cavities in the breccias with quartz, carbonate, sulphides and gold.

Development of sheeted veins, which are sets of parallel inward dipping fractures that cut the breccias and cavity infill and have been filled with quartz, carbonate, sulphides and gold.

Fluids which formed the stockwork quartz veins and tourmaline breccias possessed temperatures averaging 420°C and up to 550°C and salinities up to 53% NaCl equivalent. A major change in the nature of the fluids in the hydrothermal system occurred after formation of the breccia pipe, when solutions with temperatures between 250°C and 400°C and salinities less than 10% NaCl equivalent deposited minerals in vughs and sheeted veins. Events of stage one were initiated when magmatic fluids released from a hydrous, silica rich magma shattered an overlying cupola of the intrusion forming the stockwork quartz veins. A second release of fluids from the magma caused localised brecciation, cemented by quartz and tourmaline, which partly overlapped the stockwork quartz veins. The release of fluids caused undercooling of the melt and contributed to the formation of the brain rock. The breccia pipe was formed by the explosive release of volatiles from the same magma overprinting all events of stage one. Rhyolite dykes that had intruded the site of the breccia pipe prior to its formation were brecciated. Following brecciation gold bearing solutions with a significant groundwater component passed through the breccias localised by permeable rhyolite breccia, and mobilised by resurgence of the magma and dykes which cut the breccia pipe. The rising magma superimposed sets of conical fractures on the breccia pipe that were filled with hydrothermal minerals, including gold.

395

SOME ASPECTS

OF G E O L O G Y F O R P R E - P R O D U C T I O N OF T H E H I L T O N M I N E MT I S A

MINING

B.K. Mutton Mount Isa Mines Limited, Mount Isa The role of geology, its significance and importance in the preproduction (feasibility) phase of mine project development cannot be understated. The geological information must be complete and thorough so that design concepts may be developed and planning decisions made. Significant geological work has been undertaken at the Hilton Mine, particularly in the two areas of:A.

ore distribution and definition through the use of geostatistics, and

groundwater studies.

Ore distribution and definition has, since confirmatory drilling from underground sites,shown a degree of poor continuity and complexity. Observed grade variations and ore outlines between nearby holes were tested by sample reduction and analytical variance by the use of geostatistics. The geostatistical work called for a large amount of close spaced sampling to determine the variability of the mineralisation at the scale of selectivity for proposed mining methods. The resulting work provided optimal drill spacings for stope design, grade-tonnage curves with sufficient accuracy to select or maintain head grades within specified levels and ore reserves estimates to enable detailed mineral inventory calculations, for short to medium term planning. Significant groundwater studies have also been undertaken of a major aquifer which overlies the orebodies. A comprehensive program of acquifer delineation from drilling data and geophysical surveys has enabled definition of the acquifer zone. Monitoring and analysis of a base network, drawdown tests and initial mine dewatering has enabled aquifer parameters to be established. The resulting work is facilitating choice of the optimum dewatering system and design of a component pumping system to meet the determined dewatering rate which will ensure safe and efficient production mining. In summary, both the areas of investigation discussed above have made a significant contribution, which impacts greatly and has a fundamental influence on the planning and design process.

THE P R I M A R Y

HALO

ROSEBERY

W . Naschwitz and J.C. van Moort Geology Department, University of Tasmania, Hobart The Rosebery deposit is located at the west coast of Tasmania within the Mt Read Volcanic Belt. It is a typical Zn-Pb-Cu-bearing exhalative massive sulphide deposit which was generated in a pile of acid pyroclastics during a period of reduced volcanic activity. The two tabular orebodies (N-orebody and S-orebody) forming the deposit are hosted in a 45° E-dipping shale horizon. They are separated by a barren gap and show the general vertical zonation of a Cu-rich bottom sequence and an increased content of Zn in the upper part. 396

The footwall, and to a minor degree the hangingwall, have been subjected to hydrothermal alteration. In the field the alteration is marked by quartz-sericite schists which extend for about 2 km in N-S direction and have a maximal E-W width of roughly 1 km. The schists occasionally contain moderately to completely altered feldspars. Geochemically the alteration is expressed by a clear pattern of enrichment for Si02, K 2 0, S and Mo and depletion for A1 2 0 3 , Ti02, Ca, Nb, Y, Sr and Zr. Other elements are less conclusive. Apart from the pervasive alteration in the field there is evidence for two separate hydrothermal vents based on underground geology and geochemistry. Below the N-orebody a central area of approximately 200 m in diameter is totally devoid of feldspars. This aureole of intense alteration is largely composed of siliceous augen-schists with an increased amount of disseminated ore which is also reflected in the distribution pattern of the ore 'forming metals including sulphur. Its position roughly coincides with the location of the maximum metal content in the overlying orebody. This area is surrounded by schists containing moderately to completely altered feldspar. These less affected rocks extend into the barren gap. The location of the maximum metal content of the larger S-orebody is also in fair agreement with the underlying feeder channel (Green et al., 1981). It is possible to combine surface alteration with underground alteration to a three-dimensional picture. Reference Green, G.R., Solomon, M., § Walshe, J.L., 1981, Econ. Geol., 76(2), 304338.

TECTONIC EVOLUTION AND METALLOGENESIS, ROCKHAMPTON—MARYBOROUGH AREA, QUEENSLAND C. R. Nash Hunting Geology and Geophysics (Australia) Pty. Limited, Canberra A detailed photogeological investigation over the RockhamptonMaryborough area in southeastern Queensland has provided a structural overview of this sector of the New England Orogen (Nash, 1984). Prominent WNW, NNW and NE structural trends are clearly visible from statistical analysis of lineament data. These structures appear to have been generated during the final phases of Palaeozoic accretionary tectonics in the region and to have provided the regional fabric exploited during Mesozoic-Cainozoic extensional tectonics associated with opening of the Tasjnan Sea. Intermittent reactivation of major NNW- and WNW-trending structures may be invoked to explain the observed trends of rift basins containing Triassic volcano-sedimentary piles and subsequent Mesozoic and Cainozoic continental and marginal-marine sedimentary sequences. Prominent 'dog leg1 deflections of major basins coincide with intersecting basement structural corridors, a characteristic of grabens noted elsewhere (lilies, 1981; Harding, 1984). Spatial analysis of lineament data also suggests the presence of discrete zones of NE-oriented structures in the Rockhampton-Maryborough area. These appear to be significant in the emplacement of Cretaceous volcanic complexes.

397

The observed structural features provide a more comprehensive framework than previously available in which to examine the spatial distribution of mineral deposits in the region. The NNW-trending alignment of Permo-Triassic hydrothermal mineralisation (Horton, 1982) and NW-trending 'gold belts1 (Lacy, 1980) are considered within this context. Prominent circular features visible on Landsat imagery, which may represent the eroded remnants of Mesozoic calderas (Baker and Nash, 1984), provide a further possible local control of mineralisation. References Baker, M.C., & Nash, C.R., 1984, Proc. 3rd Australas. Remote Sensing Conf., Gold Coast, 350-354. Harding, T.P., 19_84, Am. Assoc. Petr. Geol. Bull., 68, 333-362. Horton, D.J., 1982, Qld. Dept. Mines, Publ. 378, 59p. lilies, J.H., 1981, Tectonophysics, 73.* 249-266. Lacy, W.C., 1980, in: The Geology and Geophysics of Northeastern Australia, 269-277. Nash, C.R., 1984, Proc. 3rd Australas. Remote Sensing Conf., Gold Coast, 433-441.

SYSTEMATIC LANDSAT INTERPRETATION, DATA INTEGRATION AND TECTONIC

SYNTHESIS

C. R. Nash, A. C. Theron, M. M. Coupard & B. R. Minty Hunting Geology and Geophysics (Australia) Pty. Limited, Canberra Considerable emphasis in contemporary literature is placed upon the spectral properties of remotely sensed data, often to the detriment of the significant amounts of spatial information contained in these data. Systematic interpretation of Landsat imagery yields structural and geomorphic information which may be integrated with regional geophysics and available geological data, providing an effective technique for regional tectonic synthesis and selection of areas for detailed exploration. A recommended methodology, derived from extensive Landsat studies in Africa, Australasia and North America, is illustrated in Figure 1. Systematic structural interpretation of Landsat imagery should include not only 'traditional' lineament patterns, but also bedding and foliation trends, interpreted fold structures and geological boundaries. The importance of complete structural annotation is illustrated by an example from the Wawa sub-province of the Archean Superior Province, Canada, in which post-tectonic plutons are recognisable by virtue of displaced foliation trends. A further example of the value of Landsat structural data from the Canadian Shield concerns the numerous Upper Proterozoic carbonatite complexes known in the area (Currie, 1976). Integration of Landsat, aeromagnetic and mapped lineaments reveals the presence of a prominent N-S trending structural corridor along which a majority of known carbonatites occur; a situation possibly analogous to the linear controls of the Pilanesberg alkaline province in South Africa suggested by Ferguson (1973).

398

1)1:250,000

scale

LANDSAT IMAGERY

REGIONAL GEOPHYSICAL DATA

PUBLISHED GEOLOGICAL DATA

STRUCTURAL

GEOPHYSICAL

GEOLOGICAL

INTERPRETATION

SYNTHESIS

GEOMORPHIC

TECTONIC

INTERPRETATION

SYNTHESIS

METALLOGENIC TARGET MAP

METALLOGENIC DATA AND MODELS

2)1:1,000,000

scale

REDUCTION

TO OVERVIEW

THEMATIC

Figure 1.

MAPS

Schematic flowchart for compilation and integration of Landsat data in regional studies.

Systematic geomorphic interpretation of Landsat imagery provides a method of locating buried structure in regions of deep weathering and Cainozoic cover, particularly in sedimentary basins (Theron et al., 1984). Recognisable morphotectonic features indicative of reactivated deep structure include disposition of palaeodrainage systems, tilting of residual profiles, linear erosional escarpments and topographic highs. Examples of these features, and their correlation with basement structure interpreted from geophysical data, are provided from a regional Landsat study of the Gawler Block, South Australia, (Hunting Geology and Geophysics, 1984).

References Currie, K.L., 1976, Geol. Surv. Can., Bull., 239. Ferguson, J., 1973, Trans. Geol. Soc. S.Afr.,

241-270.

Hunting Geology and Geophysics (Aust.) Pty. Ltd., 1984. (unpubl.). Theron, A.C., Nash, C.R., Lockett, N.H., and Baker, M.C., 1984, Proc. Canning Basin Symp., Perth, June 1984. (in press).

399

FLUID-WALLROCK INTERACTION AROUND ARCHAEAN HYDROTHERMAL GOLD DEPOSITS: A THERMODYNAMIC MODEL

Fiona B. Neall 1 and G. Neil Phillips 2 department of Geology, University of Western Australia, Nedlands 2 Department of Geology, University of Witwatersrand, Johannesburg. Many large Archaean gold deposits comprise epigenetic veins and associated alteration haloes in mafic rocks, but there is great diversity in the nature of veining and the types of wallrock alteration assemblages developed. Most deposits in Western Australia can be explained by a simplified model of channelways providing fluid access and allowing interaction with favourable host rocks. This resulted in important changes to the fluid, including gold solubility, and synchronous alteration of the wallrocks. The original composition of the wallrocks is critical to the type of interaction that occurs and, in particular, Fe-rich host rocks are favourable for development of large gold deposits. Gold mineralisation at the well-documented Hunt mine, Kambalda, (Phillips & Groves, 1984) is situated in a major, steeply-dipping schist zone within a thick sequence of metabasalts. Zonal alteration of the schist occurred around fractures which acted as conduits during alteration. Limited major element mobility ensured assemblages of 6-8 phases over most of the alteration zone, providing suitable conditions for the use of thermodynamics in conjunction with detailed petrographic, geochemical (electron microprobe analysis of mineral compositions) and fluid inclusion studies (microthermometry). Equilibrium equations involving fluid components and alteration minerals are used to determine conditions during the alteration event and, in particular, activity gradients of components across the schist zone. Pairs of equations, involving chl - mt - po - py - qtz - fluid, to determine a(02), and a(H2S), do not give the same values. Profiles show increasing H 2 S around auriferous veins (log a(H 2 S) = -1.9 to >-1.7) but constant 0 2 (log a(0 2 ) = -30.6). These results bracket the mt-po-py triple point at 350°C and explain the pyrite (adjacent to the vein) - pyrrhotite magnetite zonation sequence in the alteration. The profile of potassium activity, calculated from bi-chl-fluid equilibrium, shows increases around + veins. The a(Na ) profile, from chl-ab-fluid equilibrium, shows increases around only veins with high gold values (>3ppm) in the alteration. In both cases pH is assumed constant at 5-5.5. The a(C0 2 ) profile, from chl-ank-cc-fluid equilibria, is flat and this is used to suggest that the profile for a(H 2 0), the other major fluid component, is also flat. These profiles are interpreted as the result of infiltration of an H 2 0 - C 0 2 - H 2 S fluid along channelways, now represented by quartz and carbonate veins, and subsequent diffusion of fluid components, C 0 2 , H2S(+AU) and K, into the wallrock. The distances moved by most components, except C 0 2 , away from individual veins, are small enough (<10m) to suggest that intergranular diffusion could have been the most important transporting mechanism between major fluid conduits, on a timescale of 6 around 10 years. Infiltration at intergranular level, for a similar period, would have obliterated the observed activity gradients. Reference Phillips, G.N., & Groves, D.I., 1984, Geol. Soc. Zimbabwe, Spec. Publ., 1 , 689-712.

400

Nd-Sr

ISOTOPE RATIOS IN D L T R A P O T A S S I C ROCKS FROM A U S T R A L I A AND THEIR IMPLICATIONS FROM THE S U B C O N T I N E N T A L LITHOSPHERE

D. R. Nelson

M.T. McCulloch

and A. L. Jaques

S.E.

hies. School of Earth Sci., Aust. Nat. Univ., Canberra ^Bureau of Mineral Resources, Canberra Popular models of mantle structure assume that while the differentiation of the continental crust has resulted in an upper mantle depleted in LIL- and LRE- elements, the lower mantle has remained largely undifferentiated, with primitive Sm/Nd, Rb/Sr andU/Pb(?). However, a number of recent studies of rock types believed to be derived from deep (i.e., >100 km) subcontinental sources, such as kimberlites and related 1983; Collerson and ultrapotassic rocks (e.g., Vollmer and Norry, McCulloch, 1983; McCulloch et al, 1983) indicate long histories of LIL- and LRE- enrichment. In an attempt to assess the isotopic character of the deep subcontinental mantle beneath eastern Australia, we have analysed Cainozoic olivine leucitites from central New South Wales for Nd and Sr isotopic compositions. The lavas are characterized by high Ti, K , P, Cr, Ni and Mg/(Mg + Fe) (Cundari, 1973) and have steep LREE-enriched REE patterns (Nd - 200x chondrites). Although the possibility of contamination by crustal rocks prior to or during emplacement must be considered, the high contents of REE and Sr make the Nd and Sr isotopic character relatively insensitive to crustal contamination. Sr and Nd isotopic compositions are quite uniform, ranging from 0.7050 to 0.7055 and e N d -1.2 to -2.5 respectively, and plot within the mantle array slightly below Bulk Earth on the e^d versus eg r diagram. S r U R and NdcnuR model ages are <200 Ma, while using depleted mantle parameters gives model ages of -700 M a . Several interpretations of our results are possible, the simplest being that the New South Wales olivine leucitites were derived from primitive undifferentiated mantle and were generated shortly (i.e., <200 Ma) before their emplacement. However, the bulk chemistry of the most primitive leucitites (Mg/(Mg + Fe) ^70, Ni >400 ppm) shows significant 1 enrichment in 'incompatible elements (K, Rb, Sr, Ba, Ti, Zr) except for Na suggesting derivation from a non-chondritic source. Alternatively, the agreement between Nd and Sr depleted mantle model ages may be indicative of their derivation from depleted mantle, requiring the enrichment event to have occurred up to 700 Ma prior to emplacement. A third alternative is that the Nd and Sr isotopic compositions result from the mixing of depleted and enriched mantle components as has been suggested for the lamproitic rocks from the Fitzroy area, Western Australia (McCulloch et al, 1983). However, the uniformity of the isotopic characteristics does not appear to favour this hypothesis. We are presently analysing representatives of the suite for Pb isotopic composition in an attempt to distinguish between these alternatives. Our results contrast with those obtained for the Cainozoic alkali basalts of southeastern Australia (McDonough and McCulloch, this meeting) which appear to be derived from shallower, more depleted (less radiogenic Sr for equivalent e ^ ) mantle sources. The overlap of the isotopic compositions of the New South Wales leucitites with ocean islands data suggests that the deep (>100 km) subcontinental and oceanic lithospheres may have had similar histories.

401

Sr/ 86 Sr(I)

Figure 1s e^d - 87 Sr/ 86 Sr of the NSW leucitites (•), compared with those of ocean islands, MORB, Gaussberg, ( • ) diopsides from kimberlite nodules, (<*>) South African kimberlites and ( • ) West Kimberley lamproites (Data sources as in McCulloch et al, 1983).

References Collerson, K.D. and McCulloch, M.T., 1983, Proc. 4th Symp. Antarctic Earth Sci. Cundari, A., 1973, J. Geol. Soc. Aust. 20(4):465-492. McCulloch, M.T., Jaques, A.L., Nelson, D.R. and Lewis, J.D., 1983, Nature 302:400-403. Vollmer, R. and Norry, M.J., 1983, Earth Planet. Sci. Lett. 64:374-386.

ARE THE MOUNT ISA LEAD-ZINC ORES REALLY

STNGENETIC?

Martin Neudert SEDCON, Brisbane The stratiform Mount Isa Lead-Zinc ores have long been known as prime examples of ancient synsedimentary deposits of metal sulphides. However a recent sedimentological study of the ore bearing sequence has provided new evidence which challenges the established syngenetic, exhalative ore formation models. Based on facies analysis and sedimentary petrology of sulphide-rich as well as barren sediments it can be shown that these models (i) do not fit the observed facies affiliation of the metal sulphides and (ii) are inconsistent with the interpreted mode of deposition of the sulphide-rich sediments. These syngenetic models, therefore, are inappropriate for describing the mineralizing process (or processes) which formed this famous orebody. 402

The banded Mount Isa Lead-Zinc ores occur laterally adjacent to major stratabound Copper orebodies (Mathias and Clark, 1975) in the pyritic Urquhart Shale of the Middle Proterozoic Mount Isa Group. This mainly fine-clastic (coarse to fine siltstones) sedimentary sequence accumulated in a fault-bounded basin on top of a thick sequence of continental flood basalts and associated shallow water sediments (Plumb et al., 1980). The sediments formed in Terrigenous Sandflat, Carbonate Floodplain, Playa, and Perennial, Saline Lake Subenvironments (Neudert, 1981; 1983; Neudert and Russell, 1981). Sulphide ores (fine grained pyrite, sphalerite, galena, pyrrhotite) occur both in the playa and in the slope to basin facies of an ancient saline lake. Distinct sulphide-rich sedimentary layers which alternate with layers of more or less sulphide-free sedimentary rock constitute the ores. The thickness of layers is generally of the order of centimetres to tens of centimetres. Most of the sulphiderich layers exhibit thin lamination (tens to hundreds of microns) of a kind that is also found in seme sulphide-free layers, yet conmonly the sulphide-free interlayers are not laminated. Barren Urquhart Shale laterally adjacent to the orebody similarly shows a pattern of laminated layers alternating with non-laminated ones. The obvious difference from the mineralized part of the sequence is the lack of sulphides in the laminites. Until now these laminated layers have been regarded as !,pelagic,! deposits that accummulated slowly in a considerably deep basin. Sulphiderich laminites were thought to have formed when exhaled ore fluids entered the water column causing sulphide particles to settle together with fine pelagic sediment. This model is challenged by the sedimentological constraints of (i) water depth and (ii) mode of deposition of the sulphide-rich layers. Constraints by Water Depth. Most laminated sulphide ores are hosted by slope to basin facies sediments which formed in an ancient saline lake. Its facies context (Neudert and Russell, 1981) indicates that the maximum water depth was of the order of tens of metres rather than hundreds to thousands of metres as was postulated previously from the style of mineralization of the Mount Isa Copper-Lead-Zinc deposit (Finlow-Bates and Large, 1978; Plimer and Finlow-Bates 1978). It follows that high-temperature (250°C - 300°C, Finlow-Bates and Stumpfl, 1979) exhaled ore fluids would have boiled prior to entering the basin floor and thereby lost their ore constituents in the vent below. Such hot exhaled solutions, therefore, cannot have formed the layered Lead-Zinc ores of this facies. However these depth constraints alone do not rule out the possibility of syngenetic sulphide deposition from low-temperature (less than 100° C) exhalations. On the other hand in the sulphide-bearing playa facies evidence of frequent subaerial exposure of the host sediments provides severe depth constraints eliminating any syngenetic ore formation model for a significant proportion of the Urquhart Shale sequence. Constraints by Mode of Deposition of Sulphide-Rich Layers. Contrary to previous opinion the finely laminated sediments are not pelagic deposits. Instead sedimentary petrology shows that the laminites of both the playa and the slope to basin facies originally were deposited from turbulent suspension currents. Only the interbedded and generally sulphide-free non-laminated sediments are consistent with deposition via settling from the water column. They may either represent the fine tail of the currents that formed the laminites or may be regarded as hemipelagic deposits.

403

The current deposits underwent diagenetic modification which brought about the fine, carbonaceous lamination or enhanced an originally present but coarser current lamination. These modified current deposits contain the bulk of the sulphide mineralization in either facies of the Urquhart Shale. It follows that deposition of the Mount Isa Lead-Zinc ores cannot have been a simple pelagic settling of sulphides as is required by the syngenetic volcanogenic (or other) exhalation models. Indeed if such exhalations had occurred at all in the Urquhart Lake then the bulk of the sulphides would have been deposited together with its hemipelagic sediments. Due to their comparatively low sedimentation rate they would have had ample opportunity to collect significant amount of; exhaled sulphides. They did not. Indeed the most basinal facies of the Urquhart Shale which contains the highest ratio of hemipelagic over current deposits is usually completely barren of sulphides. These sedimentological lines of evidence demand a departure from synsedimentary exhalative ore-formation models for the Mount Isa LeadZinc ores. An alternative model in which the sulphides form as postsedimentary products will be discussed. References Finlow-Bates, T., and Large, D.E., (1978) Geologisches Jahrbuch, D.30:27-39. Finlow-Bates, T., and Stumpfl, E.F., (1979) Annales de la Societe Geologique de Belgique, T.102:497-517. Mathias, B.V. and Clark, G.J. (1975) In C.L. Knight (Ed.) Economic Geology of Australia and Papua New Guinea. Vol 1; Metals (p. 351-372) Aust. Inst. Min. Met. Neudert, M . K C , (1981) Abst. No. 3, Sediments through the ages. 5th Aust. Geol. Conv., Perth 1981, p.7. Neudert, M.K., (1983) Thesis, RSES, ANU, Canberra, ACT. Neudert, M.K. and Russell, R.E., (1981) Nature, 293: 284-286. Plimer, I.R. and Finlow-Bates, T., (1978) Mineralium Deposita, 13: 339 - 410.

DISCOVERY HISTORY OF RENISON BELL TIN DEPOSITS L.A. Newnham Gold Fields Exploration Pty. Limited, Burnie. The Renison Bell district is estimated to host approximately 40 million tonnes of 1% tin mineralisation in commercially available ore zones within a region measuring 2 kilometres by 1 kilometre aerially and 1 kilometre deep. These tin deposits, which are Australia's largest, form an important component of the globally significant Western Tasmanian tin province. Initial discovery of tin at Renison Bell in early 1890 was made during a period of intensive base and precious metal ground prospecting in Western Tasmania, and followed close on the heels of the discoveries of the Mt. Lyell copper-gold and the Zeehan silver-lead.deposits. The initial discovery of tin has been credited to Ringrose Nicholson who panned tin in the Ring River immediately east of the main ore deposits, and then pegged his first claim in June 1890.

404

George Renison Bell who was prospecting the region for gossans similar to those recently discovered at Zeehan actually located the large gossans over the Renison deposits in May 1890 and pegged four leases over them for s i l v e r , lead and zinc. I t i s believed that he d i d n ' t recognise their t i n potential until several months l a t e r . The a l l u v i a l deposits never amounted to much, and i t was the pursuit of the gossans that was grandly rewarded. The almost simultaneous discovery of a l l u v i a l tin and large stanniferous gossans by these early prospectors was followed up by extensive exploration by way of trenching, tunnelling, and core d r i l l i n g . In 1898, George Renison Bell wrote: 11

.... gossan i s the principal outcrop and i t was this that led to the acquisition of your property and the subsequent exploration work being done." He further observed: 11 in many places huge gossanous iron formations protrude above the surface, indicating mineral deposits below. This i s particularly the case on your Leases, the s o l i d gossan in places covering many acres of ground, and standing in masses 15 feet above the surface."

At that same time he had a clear understanding of the basic geology: 11 the source of t i n i s the pyrites lode completely disintegrated by the action of the weather, and the t i n liberated in i t s present state."

During the f i r s t twenty years of mining, exploration and subsequent ore discovery was achieved by trenching and tunnelling. These were very effective techniques in an area of steep topography and shallow oxidation. For the f i r s t forty years up until the 1930's, the vigor of exploration and the rate of ore discovery were governed not by prospecti v i t y but p r i n c i p a l l y by t r e a t a b i l i t y in combination with poor markets and property fragmentation. In the past t h i r t y years, the continuing process of ore discovery has largely been the result of a recognition of the geological factors controlling ore deposition combined with a commitment to substantial core d r i l l i n g programs and the inspired v i s i o n s and confidence of several people. Whilst core d r i l l i n g , which commenced in 1912, has always played a prominent role in ore discovery at Renison, geophysics and geochemistry have not. Geophysical surveys commenced at Renison in 1929 and the plethora of surveys completed since then have succeeded in confirming the responsive nature of the mineralisation but have not to date played any role in ore discovery other than providing a "comfort factor" to guiding already conceived d r i l l patterns. Geochemistry has to date not played any role in ore discovery at Renison.

405

DETERMINATION OF RARE-EARTH ELEMENT PARTITION COEFFICIENTS FOR EXPERIMENTAL CALCIC CLINOPYROXENE-BASALTIC LIQUID PAIRS: INTERPRETATION AND MICROPROBE ANALYSIS OF ASSEMBLAGES I.A. Nicholls Department of Earth Sciences, Monash University, Melbourne Application of trace element abundance data for igneous rocks in magma genesis models requires information about the dependence of crystal-liquid partition coefficients upon physical variables and phase compositions• For rare-earth elements, partition coefficients for olivine, pyroxenes, amphiboles and garnets in mafic-intermediate systems .increase with increasing acidity of liquids and decreasing temperature (e.g. Irving, 1978; Harrison and Wood, 1980; Nicholls and Harris, 1980). There is recent evidence that partition coefficients also increase with increasing pressure (Green and Pearson, 1984). The dependence of crystal-liquid partition coefficients for trace elements upon trace element concentrations in crystals has been intensively studied, with emphasis on determining concentration ranges for Henry's Law dilute solution behaviour. The dependence of partition coefficients upon the major element compositions of crystals has received relatively little attention. However, Nicholls and Harris (1980) and Stosch (1982) have noted that partition coefficients for light REE should correlate with the Ca content of clinopyroxenes, since (REE)3 ions enter 8-coordinated sites normally occupied by Ca. Substitution of A1 for Si may influence the size and symmetry of both 8- and 6- coordinated sites, and hence also influence the entry of (REE)3+. The main aims of this study are to: 1) Experimentally determine partition coefficients for representative light and heavy (REE)3+ ions (Sm, Yb) in equilibria between a range of calcic to sub-calcic pyroxenes with varying A1 contents, and Fe-free basaltic liquids at mantle conditions (20 Kb, 1300°-1400°C, X ^ S = 2wt.%). H2U 2) Examine relationships between Henry's Law limits and major element parameters for experimental clinopyroxenes. This requires assessment of their point defect chemistry (Morlotti and Ottonello, 1982). Since P, T and X ^ S effect the structures of silicate liquids, and 2 hence trace element partitioning behaviour (Mysen, et al., 1982), variation in Ca/Mg and Al/Si ratios of near-liquidus clinopyroxenes for basaltic compositions must be produced mainly by varying liquid compositions systematically to keep parameters such as liquid Si/0 ratio nearly constant. Three "end-member" compositions, related by mole-for-mole replacements between CaO, MgO and AI2O3, have been chosen to satisfy this criterion (Table 1). At temperatures around 1400°C, the liquidus clinopyroxene compositions closely reflect these bulk compositions. In charges run under conditions very close to the liquidus, primary crystals (clinopyroxene, orthopyroxene, garnet) accumulate at the bottom of capsules, leaving a large volume of liquid above. Back-scattered electron imaging has shown that, on cooling, quench outgrowth of primary clinopyroxenes is ubiquitous, and that garnet and orthopyroxene are fringed by quench clinopyroxene. Energy-dispersive microprobe analysis shows that glass interstitial to primary crystals is strongly depleted in Ca and Mg relative to large areas of glass above these.

406

Table 1 : Starting glass compositions (molecular percent)

Si0 2 Ti02 A1203 MgO CaO Na20 k2o

I (Base)

II (High-Ca)

III (High-Al)

46.3 1.3 16.6 20.0 9.7 5.6 0.5

46.3 1.3 16.6 15.4 14.3 5.6 0.5

46.3 1.3 21.2 15.4 9.7 5.6 0.5

Charges have been doped with 1000 ppm of Sm and Y b , and primary crystals and glass remote from"crystals analysed by wavelength-dispersive microprobe analysis at 30 k V , 100 n A . Routine detection limits of around 50 ppm have been achieved. Using synthetic glass standards, precisions of determinations on apparently unzoned crystals are around ± 10%, while those on glasses are better than ± 5%. Early results (Table 2) suggest that for 500-800 ppm REE in calcic clinopyroxenes, values of D ^ for compositions I (base) and II (highCa) are indistinguishable, while that a for high-Al composition III is significantly higher. Values of Dy^*""^*! ^ e indistinguishable for compositions I and III, slightly lower for II. Table 2 : Partition coefficients, D

bm IL, id

1<*)

III

0.45 (0.07)

0.46 (0.09)

0.66 (0.05)

0.69 (0.09)

0.57 (0.09)

0.63 (0.12)

Further work on compositions intermediate to I - III is required to distinguish trends in D values as a function of clinopyroxene Ca/Mg and Al/Si ratios. Improved precision of REE determinations on crystalline phases must also be achieved. fl

Experiments with the autoradiographic ( |3-track mapping") technique of 151 partition coefficient determination of Mysen and Seitz (1975), using Sm 11 as radioisotope, have indicated that "maps do not indicate the complexities of assemblages due to quench crystallization, even when primary crystals and areas of glass are large. Detailed microprobe analysis appears a superior technique for trace element levels > 100 ppm. Proton or ion microprobe analysis are preferred for lower levels. References Green, T.H. and Pearson, N.J., 1984. Abst., International Workshop High-P, High-T Geochem., Monash Univ. Harrison, W.J. and Wood, B.J., 1980. Contr. Mineral. Petrol. 72, 145-155. Irving, A.J., 1978. Geochim. Cosmochim. Acta 42^, 743-770. Morlotti, R . and Ottonello, G . , 1982. Phys. Chem. Minerals 8^, 87-97. Mysen, B.O. and Seitz., M.G., 1975. J . Geophys. Res. 80, 2626-2635. Mysen, B.O., Virgo, D . and Seifert, F.A, 1982. Rev. Geophys. Space Phys. 20, 353-385. Nicholls, I.A. and Harris, K.L., 1980. Geochim. Cosmochim. Acta 4-4, 287308. Stosch, H.-G., 1982. Geochim. Cosmochim. Acta 46^, 793-811.

407

E P I T H E R M A L PRECIOUS METAL DEPOSITS IN V O L C A N I C ROCKS OF THE WESTERN USA - GEOLOGICAL SETTING A N D E X P L O R A T I O N M O D E L S Richard L . Nielsen Nielsen Geoconsultants, Inc., Evergreen, Colorado, U.S.A. Epilhermal precious metal deposits in volcanic settings generally are located near calderas, caldrons and eruptive centers. Banded, vuggy, c r u s t i f o r m veins, stockworks and breccias are emplaced along low angle detachment or thrust faults and along high angle tensional dip slip or compressional strike slip faults. Stratigraphic features in the volcanic pile control geometry and f o r m of the deposits. Veins tend to form in well indurated welded t u f f s and flows; disseminated deposits in lake beds, sediments, agglomerates and t u f f s . Precious metal values generally are restricted to a vertical interval of up to 1000 meters, commonly 350 meters w i t h a district-wide constant elevation at its base. Magma-series chemistry of associated igneous rocks seems to correlate w i t h deposit characteristics. Metaluminous calc-alkalic series yield disseminated and vein gold deposits, alkalic-calcic series host the large silver deposits, alkalic series are associated with high-grade gold veins. Epithermal deposits form at low to moderate temperatures in a near surface environment. Silica, kaolinite, alunite, native sulfur, barite, f l u o r i t e , pyrite, sulfosalts, As, Sb, T 1 and Hg tend to be concentrated in the upper part of the system. Vuggy quartz, adularia, hydromica, pyrite, gold, silver, tellurides, selenides are concentrated in the intermediate productive part. Propylitic alteration, base metal sulfides, pyrite and adularia are found in the lower parts. A c t u a l zoning patterns depend on geometry of the plumbing, composition of host rock and chemistry of the hydrothermal solutions. Stable isotope data suggest that the hydrothermal fluids are predominantly of meteoric origin. Fluid inclusion studies suggest the deposits f o r m at 150° to 300°C f r o m diluted alkali chloride solutions, but unequivocal evidence of boiling is rare. Three generalized models are being used in exploration: A hot springs model in which precious metals are deposited in the near surface part of a geothermal system in hot springs, fumaroles and geysers, w i t h the mineralization occurring beneath the vents as breccias and stockworks, presumably as a result of explosive release of pressure. A stacked hydrothermal cell model in which precious metals are deposited along the interface of cooler near surface circulating waters and a deeper hot hydrothermal cell, resulting in compressed v e r t i c a l and attenuated lateral mineral zoning. A single cell hydrothermal model in which precious metals are deposited along an open channel way with patterns attenuated in a v e r t i c a l direction. Tendency for major precious metal deposits to lie along regional magnetic highs suggests mineralized systems developed where primary or p r i m i t i v e mafic magmas welled up and plated beneath a thinned crust and came in contact w i t h deep circulating meteoric hydrothermal waters. Ore metals were leached f r o m mafic rocks and deposited near the surface. Areas of eastern Australia permissive for epithermal precious metal mineralization include Drake Volcanics of Permian age in northeast New South Wales and areas of upper Paleozoic subaerial volcanic rocks in the Ravenswood block and Drummond and Gympie Basins.

408

AN E X P L O R A T I O N M O D E L FOR T A N T A L U M PEGMATITES WITH AN EXAMPLE FROM THE P I L G A N G O O R A A R E A , P I L B A R A , WESTERN A U S T R A L I A

B.W. Nisbet Geoscience Field Surveys Pty. Ltd., Perth Pegmatites account for a large proportion of u/orld Ta reserves, important deposits being Tanco in Manitoba and Greenbushes in Western Australia. A survey of Ta pegmatites indicates that the most economically significant bodies have a number of common characteristics which may be incorporated into an exploration model. Features of this model are; 1. The most prospective host rocks are Archean greenstone sequences, in particular mafic to ultramafic rocks vi/ithin them. When the host is granitic or composed dominantly of metasediments, pegmatites tend to occur in sheeted svi/arms or stockworks instead of large, discrete bodies. 2. Preferred age of the pegmatite and associated granitoid is Archean, often around 2.6 billion years. Younger pegmatites tend to be smaller vi/ith lou/er Ta contents. 3. Classic bodies exhibit pronounced Li, C s , Rb (Be,B) enrichment, vi/ith high TasNb ratios; the so-called Rare-Metal Pegmatites. 4 . Ta Pegmatites are strongly zoned (e.g. Tanco) vi/ith quartz cores, Li-Cs rich centres, and Ta concentrated in various parts of the body. Crystallisation is generally not simple, and later phases often replace earlier phases. 5. A dispersion halo of Li, Rb, Cs and B is found in host rocks for hundreds of metres from the pegmatite in some cases, and this may be used to infer the depth to a 'blind1 deposit or the dip of the body. 6 . Ta Pegmatites usually have no strong geophysical response, though the Tanco body has an associated Bouguer gravity anomaly. Radiometrics may be useful in some cases. 7 . Regional zoning in pegmatite composition from bodies in or close to the granitic source to those intruding the country rocks reflects progressive differentiation of the pegmatite fluid u/ith time. This feature may be useful in predicting the presence of non-outcropping bodies. In the Pilgangoora area of Western Australia, pegmatites intrude Archean greenstones of the Warrau/cona Group and appear to be related to 2.6 billion year old granitic rocks of the Carlindie Batholith. Mapping has defined a regional zoning from simple quartz-microcline-muscovite pegmatites vi/ith lou/ Ta, Rb, Cs and Li levels and low Ta:Nb ratios occurring close to the granitoid-greenstone contact to spodumene-quartz-albite pegmatites in a zone tvi/o kilometres from the contact. The zone is tvi/o by eight kilometres in size, and parallels the granitoid-greenstone contact. Host rocks in the zone are mafic to ultramafic in composition. Spodumenerich pegmatites are quite large, u/ith strike-lengths of hundreds of metres and thicknesses of tens of metres not uncommon. Pegmatites in thfe zone show pronounced Ta, Rb, Cs and Li enrichment and high Ta:Nb ratios. They exhibit moderately to poorly developed internal zoning, from quartz cores to spodumene-rich centres to microcline-rich margins. Anomalous Rb, Cs and Li has been identified in the host rocks for up to eighty metres from the pegmatite. There is excellent potential for locating an economic Ta reserve at Pilgangoora and \i/ork is continuing in evaluating the area.

409

T A S M A N I A N COALS - P R O D U C T S OF T H E I R

ENVIRONMENTS

Ray Nolan Nolan & Associates Pty Ltd, Bowral, NSW Known coal deposits in Tasmania are the Early Permian, Late Permian and Late Triassic deposits in the Permo-Triassic Tasmania Basin plus Early Tertiary deposits formed in Tertiary graben structures. The petrography of the coal deposits is not well known and many seam descriptions and analyses were made more than 50 years ago. However, it is possible to relate the lateral and vertical distribution of the coal seams and their thickness, type and rank to the structural and sedimentary environments of deposition and to the time of, and climate during, their formation. The Early Permian Mersey Coal Measures and their stratigraphic equivalents were deposited in generally stable areas. Slow, steady subsidence and little sediment transport produced coal measures rarely exceeding 30 metres thickness and containing only a few seams, usually less than one metre thick. (Hills et. al. 1922) The seams generally have relatively low ash contents; those deposited on the even more stable western basin margin contain cannel coal with very low ( 5%) ash content. The climate, probably cold to cool, restricted types of plant material mainly to the smaller varieties, resulting in small phyteral size, (Cook, 1981) higher exinite contents and high-hydrogen coals. Lack of subsequent burial resulted in rank being generally lower than high-volatile bituminous except where igneous intrusions locally have increased coal rank up to sub-anthracite. More marine conditions resulted in high sulphur contents for the pyrite-rich uppermost seams in the north-western deposits. The Late Permian Cygnet Coal Measures and their equivalents also were deposited in relatively stable environments. However, thickness variation up to about 100 metres indicates relative subsidence with a depocentre along the western basin margin (Spry and Banks, 1962). The few seams formed generally are less than one metre thick and have coal rank relatively low for their age. The warmer climate, although probably still cool - temperate, allowed larger trees to grow, producing larger phyteral size and more vitrinite-rich, less exinite-dominant coals. The Late Permian coal seams tend to have higher ash but lower sulphur and hydrogen contents than the Early Permian seams. The Late Triassic coal measures are associated with the uppermost, lithic sequence of the Upper Parmeneer Super-Group. The environment in the Tasmania Basin, during deposition of the mixed fine to coarse grained coal-bearing sequence, appears to have been more geosynclinal. Sedimentation commenced near the western basin margin, where it was continuous from the Permian, and migrated eastward, where it is disconformable. Subsidence was more rapid during the Early Triassic in the western part of the basin. Although conditions generally were more stable during the Late Triassic, relative subsidence may have continued because brighter (more vitrinite-rich) coals are indicated by descriptions of some seams in the more western deposits. Elsewhere, relatively dry coal-forming environments and slow subsidence produced seams with generally high ash contents, rich in inertinite and with low but variable vitrinite contents. (Smyth, 1980; Bacon 1983) Overall subsidence was sufficient to produce, in some areas, at least eight coal seams (some up to three metres thick) in a sequence up to 400 metres thick. Rank variations mainly relate to the effect of later igneous intrusions.

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There appears to have been little structural change during Permian and Triassic deposition in the Tasmania Basin. The present faulted nature of the Permian and Triassic coal deposits resulted mainly from Late Triassic/Early Jurassic north north-westward trending tensional faulting, the associated large-scale intrusion of dolerite sheets and the major horst/graben structures which developed during the Tertiary. The Early Tertiary sediments were deposited within the north-westward trending graben structures which had developed during the separation of Tasmania and the mainland. Those structures continued to develop during Tertiary deposition and accumulated at least 300 metres of sediments but the coal seams, formed early in the period, generally filled pre-Tertiary "basement" lows. Consequently, the seams are restricted in area and, because relative subsidence was minor, thick seams were not developed; individual seams usually are thinner than one metre and groups of seams comprising deposits rarely exceed • 10 metres thickness. The relatively stable environment, the young age and the shallow depth of burial resulted in high moisture, low rank, medium to high ash coal seams. References Bacon, C.A., 1983, Geol. Surv., Tasm. Unpubl. Rept. 1983/33. Cook, A.C., 1981, Bull. Centres Rech. Explor. - Prod. Elf-Aquitaine, 5, 2, 443-459. Hills, L., Reid, A.M., Nye, P.B., Keid, H.G.W. & Reid, W.D., 1922, The Coal Resources of Tasmania, Miner. Resour. Geol. Surv. Tasm. 1. Smyth, M., 1980, J. Coal. Geol. Group Geol. Soc. Aust. 2, 4, 161-178. Spry, A., Banks, M.R., 1962, Geology of Tasmania, J. Geol. Soc. Aust., 9, 2. DEPARTMENTAL STRATIGRAPHIC DRILLING IN QUEENSLAND TERTIARY BASINS T.A. Noon G e o l o g i c a l S u r v e y of Q u e e n s l a n d , B r i s b a n e T h e Q u e e n s l a n d D e p a r t m e n t of Mines has c a r r i e d o u t d r i l l i n g and r e l a t e d i n v e s t i g a t i o n s in T e r t i a r y b a s i n s s i n c e 1 9 1 3 . E a r l y d r i l l i n g p r o g r a m s in the L o w m e a d Basin (Ball, 1 9 1 6 ) , D u a r i n g a Basin ( S w a r b r i c k , 1974) and t h e N a r r o w s G r a b e n ( B a l l , 1946) w e r e i n i t i a t e d in r e s p o n s e to the s h o r t f a l l in f u e l s u p p l i e s d u r i n g the First and S e c o n d W o r l d W a r s , and w e r e a i m e d at e s t a b l i s h i n g an i n d i g e n o u s s o u r c e of f u e l . T h e D e p a r t m e n t d r i l l e d two b o r e s in the H i l l s b o r o u g h B a s i n , GSQ P r o s e r p i n e 1 - 2 R A and 3 , in 1 9 7 1 . O i l s h a l e w a s e n c o u n t e r e d in GSQ P r o s e r p i n e 1 - 2 R A b e t w e e n 160 m and 336 m , but w a s n o t a n a l y s e d ( G r a y , 1 9 7 5 ) . D e p a r t m e n t a l A r e a 7 5 D , l o c a t e d s o u t h e a s t of R o c k h a m p t o n , is r e s e r v e d for the p u r p o s e of e x p l o r a t i o n for salt o n l y . * During 1978 s e v e r a l e x p l o r a t i o n c o m p a n i e s s o u g h t a p p r o v a l to e x p l o r e for T e r t i a r y o i l s h a l e in this a r e a . T h e s e r e q u e s t s w e r e d e n i e d , and the D e p a r t m e n t i n i t i a t e d the d r i l l i n g of G S Q R o c k h a m p t o n 1 to test for T e r t i a r y s e d i m e n t s , i n c l u d i n g o i l s h a l e . T h e b o r e i n t e r s e c t e d 565 m of T e r t i a r y s e d i m e n t a r y r o c k s w h i c h h a v e b e e n a s s i g n e d to t h e C a s u a r i n a b e d s (Noon, 1 9 8 0 ) . S e l e c t e d s a m p l e s of o i l s h a l e w e r e analysed? some yielded more than 200 L / t . A c o n c u r r e n t g r a v i t y s u r v e y o v e r the C a s u a r i n a Basin d e m o n s t r a t e d t h a t t h e r e w o u l d b e in e x c e s s of 1100 m of Q u a t e r n a r y and T e r t i a r y s e d i m e n t s in t h e d e e p e s t p a r t of t h e b a s i n ( H u b e r , 1 9 8 1 ) .

411

To increase the knowledge of Tertiary basins, the Department extended the drilling program to other basins in central Queensland. As part of this program drilling took place in 1979 and 1980 in the Duaringa Basin (Noon, 1982a). GSQ Duaringa 1-2R and 3-5RD were drilled in the southern and northern parts of the basin respectively. GSQ Duaringa 1-2R intersected more than 1215 m of Tertiary rocks with oil shale present between 70 m and 120 m, and with scattered oil shale beds between 700 m and 1200 m. GSQ Duaringa 3-5RD intersected 1180 m of Tertiary sedimentary rocks, with oil shale present between 85 m and 120 m, 570 m and 630 m, 740 m and 820 m, and 980 m and 1025 m. Concurrent with the drilling in the Duaringa Basin two bores were drilled in the southern part of the Narrows Graben, within the Stuart Oil Shale Deposit. GSQ Rockhampton 2 was designed to provide a fully cored reference section and to assess the economic potential of the strata which underlie land allocated for an industrial estate. GSQ Rockhampton 3 was drilled to provide information on the nature of the structures controlling the shape of the southern part of the Narrows Graben. The two bores proved a thickness of more than 800 m of Tertiary sedimentary rocks including oil shale (Noon, 1981). GSQ Rockhampton 2 has been used to establish the formal stratigraphic subdivision in the Narrows Graben (Henstridge & Missen, 1982). The final bore in the program, GSQ Monto 5 was drilled in the northern part of the Biloela Basin. In excess of 340 m of Tertiary rocks, including oil shale, were encountered in the bore (Noon, 1982b). An attempt was made to wireline log all bores, however poor downhole conditions limited open hole wireline logging, and precluded the use of density logging tools. The wireline logs obtained, mainly gamma ray, are of little use for correlation or for oil shale assessment. All the basins studied are grabens or half-grabens which formed in response to epeirogenic uplift during the Late Cretaceous to Eocene (Day & others, 1983). Attempts to date the rocks accurately have been unsuccessful. Palynological studies have been hampered by poor preservation of species but suggest an age of mid to late Eocene (Foster, 1980). Volcanics which overlie and underlie the Duaringa Formation, and underlie and intrude the Biloela Formation are pervasively altered and unsuitable for isotopic dating. A broad correlation can be made between the sequences encountered during the drilling. Following activation of the boundary faults, deposition of conglomerates and sandstone suggest high energy environment of deposition. Eventually, deposition appears to have kept pace with the rate of subsidence, resulting in a shallow lacustrine environment of deposition over a long period of time. During this time the oil shale and related coal and lignite sequences were deposited. The Duaringa Formation contains two separate zones of oil shale; the lower occurs at depths greater than 600 m and the upper is present between the surface and 130 m. The upper part of the Duaringa Formation may represent a sequence of rocks the equivalent of which was not deposited in, or has been eroded from, basins closer to the coast. The fully cored reference sections provided by the drilling are stored permanently at the Department of Mines Core Library, Brisbane, and are.available for examination and sampling for detailed investigations.

412

References Ball, L.C., 1916: Qld Govt Min. J., 17, 13-16. Ball, L.C., 1916: Qld Govt Min. J., 47, 176-179. Day, R.W., & others, 1983:- Geol Surv. of Qld, Pub. 383. Foster, C.B., 1980: Geol Surv. of Qld, Pub. 381. Gray, A.R.G., 1975: Qld Govt Min. J., 76, 272-276. Henstridge, D.A., & Missen, D., 1982: Bull. AAPG, 66, 719-731. Huber, R.D., 1981: Geol Surv. of Qld, Rec. 1981/39 (unpub.). Noon, T.A., 1980: Qld Govt Min. J., 81, 261-266. Noon, T.A., 1981: Qld Govt Min. J., 82, 310-316. Noon, T.A., 1982a: Geol Surv. of Qld, Rec. 1982/40 (unpub.). Noon, T.A., 1982b: Qld Govt Min. J., 83, 450-456. Swarbrick, C.F., 1974: Geol Surv. of Qld, Rep. 83. 1

T.A. Noon publishes with the permission of the Chief Government Geologist, Department of Mines, Queensland.

AGID'S PROGRAMS IN SOUTHEAST

ASIA

P. Nutalaya Asian Institute of Technology, Bangkok Since the founding of the Association of Geoscientists for International Development (AGID) in St. Johns, Newfoundland, Canada in 1974, AGID has been involved in many successful geoscientific development activities in Southeast Asia. At the 1st AGID General Assembly and Symposia at the 1976 IGC, Sydney, several aspects of development aid in Southeast Asia were discussed. In 1978, with the Geological Societies of Malaysia and Thailand, a tin training course was held in Kuala Lumpur and Phuket, which served as a model for follow-up AGID activities in Bolivia and Brazil. The first AGID Training Program for Geologists in Development (TPGD) in Engineering Geology was successfully held at the Asian Institute of Technology (AIT), Bangkok in 1979 with the support of the Australian Government (ADAB) and with the assistance of Australian instructors. At this time AGID,together with UNESCO, contributed to the development of the Asian Geoscience Network, which publishes a newsletter among other activities. When AGID HQ was transferred to AIT, Bangkok from the Venezuelan Ministry of Mines, Caracas, in 1981, AGID activities in Southeast Asia received new impetus. At the Geology of the Southeast Asia (GEOSEA) Meeting in the Philippines in 1981, AGID organized a Geoscience Education Workshop and a Geothermal Geology training course. In response to the growing problems of land use especially in developing countries, AGID organized the multidisciplinary 1st LANDPLAN Meeting in Bangkok in 1982. A meeting on Rocks as Construction Material- ROCKON 1 was held the same year in Kuala Lumpur. ADAB provided support for the principal Australian instructor and travels of 4 southeast Asian participants. In its expanding role in co-operation with UN agencies, AGID contributed to the UNESCO Regional Training Course on Phosphate held in Sydney in 1982, which was attended by Southeast Asian participants. In 1983 workshops and seminars on regional geological development were held at the UN, Bangkok, in cooperation with CCOP, UN-ESCAP, UNESCO, IUGS and IGCP. Arising from these meetings, 2 IGCP Projects for Southeast Asia on Quaternary Processes and Events and Tin-Tungsten Granites were recently accepted and launched. At the same time, a Phosphate seminar was organized with the USGS at AIT and an AGID Workshop on the Methods of Teaching Earth Sciences in Asian High Schools was held at Chiang Mai, Thailand. AGID also had input in the Indonesian Mining Association 1983 Workshop on Mineral Development in Southeast Asia. Mention should also be made of the AGID Sponsored 1983 1st 413

Symposium of the Geology of Sri Lanka which led to the founding of the 1st Geological Society of Sri Lanka. AGID has also supported the Workshop on Stratigraphic Correlation of Thailand and Malaysia organized by the Geological Societies of Thailand and Malaysia in September, 1983. The 1984 AGID program in Southeast Asia continues to develop with the LANDPLAN II Meeting which was recently held in Kuala Lumpur and the 2nd TPGD on the Geology of Quaternary Sediments which will be held at AIT with the assistance of the Government of the Netherlands.

PERMIAN GLACIOLACUSTRINK

DELTAS IN CENTRAL VICTORIA

P.E. O'Brien Division of Continental Geology, B.M.R., Canberra Three small bodies of deltaic sediments deposited in Permian glacial lakes in the Bacchus Marsh district of central Victoria display a range of sedimentary structures and textures unlike typical Gilbert deltas commonly found in lacustrine settings, yet they may still be understood in terms of the variations in processes known to operate in lacustrine deltas. Delta 1 rests on prodelta pebbly mudstones and consists of bottomsets of mudstones and fine sandstone beds displaying climbing ripple crosslaminations. These are overlain by 40m of parallel laminated and massive medium to fine sandstone beds, mostly 10 to 15cm thick but reaching maximum thicknesses of 3m, graded fine sandstone beds 1 to 2cm thick and mudstone beds up to 30cm thick. The lower 3m of this sandstone sequence has slumped with the underlying mudstones, producing a sandy diamictite bed 3m thick. This delta was probably deposited in a shallow lake with a sloping bottom so that underflows reached supercritical flow conditions on the foreset resulting in the dominance of massive and parallel laminated sandstone in the deposit and a low depositonal dip on the foreset beds. Delta 2 consists of two pods of trough cross-laminated medium sandstone up to 9m thick which pass down current into beds and lenses of massive and parallel laminated fine and medium sandstone up to lm thick which are separated by mudstone beds a few centimetres thick. Some of the massive sandstone beds contain distinct blocks of similar medium sandstone floating in them. These deposits rest on sandy diamictite containing abundant thin, folded sandstone laminae and are overlain by 30cm of mudstone followed by a thick tillite. The pods of sandstone were deposited where two small streams entered a lake just above the level of the lake bottom. The beds and lenses of sandstone downstream and around the edges of the pods are probably the deposits of underflows and grainflows generated by slumping of the sands after deposition at the stream mouths. Delta 3 is a complex pile of poorly sorted conglomerate, coarse sandstone and diamictite beds and lenses. The conglomerates and sandstones are typically massive or parallel laminated and the diamictites are either massive with thin folded sandstone laminae and deformed sandstone bodies or thinly bedded with clusters of dropstones. The sediments are folded into broad synclines and attenuated anticlines with amplitudes of about 10m. This complex deposit is the result of rapid dumping of sediment at a lake edge. The massive diamictites are mudflow sediments, the laminated diamictites are ice-rafted sediments and the sandstone and conglomerate facies are the deposits of high energy underflows and possibly subaerial streams which dumped their loads on encountering still water. Violent dewatering of the sediment pile formed the large folds.

414

PROCESSES ON A JURASSIC FLOODPLAIN, THE MARBURG FORMATION IN SOUTHEAST QUEENSLAND P.E. O'Brien and A.T. Wells Division of Continental Geology, Bureau of Mineral Resources, Canberra The Marburg Formation of the Clarence-Moreton Basin was deposited by fluvial systems flowing towards the north-west and the north across southeast Queensland. In the Laidley Sub basin, the formation consists of variable proportions of two major facies groups. Channel belt sandstones and conglomerates constitute most of the Marburg Formation but this paper is concerned with the second facies group which comprises mudstone and thin sandstone bodies deposited in overbank environments. Four types of sandstone bodies are interbedded with the mudstones: 1. Sheets of fine to medium sandstone up to 30cm thick and laterally continuous for 100m or more which may be massive, parallel laminated or ripple cross-laminated. 2. Compound sheets up to 2m thick consisting of several coarse to fine sandstone beds which may be parallel laminated, ripple cross-laminated, large-scale planar cross-laminated or massive. Bedding within many of these compound sheet sandstones is gently inclined relative to the base of the sheets. Some compound sheets rest on scour surfaces. 3. Lenses of medium to fine sandstone up to 2m thick and up to about 10m across which are grouped together into larger lenses several tens of metres across, several metres thick and elongate parallel to the direction of palaeocurrent indicators in the lenses. Individual sandstone lenses rest on erosion surfaces, and are large-scale planar cross-bedded or parallel laminated at the base passing up into parallel laminated or ripple crosslaminated sandstone at the top. 4. Beds of fine, parallel laminated and ripple cross-laminated sandstone and siltstone in epsilon cross sets up to 2m thick. In the best exposed example, the succesive epsilon cross beds become finer laterally until the cross sets are mudstone beds up to lm thick separated by fine sandstone beds about 10cm thick. The sheet sandstone bodies (Types 1 and 2) are interpreted as crevasse splays. Their internal grain size variations and sedimentary structures are controlled by the hydrology of individual crevassing events and the sediment supplied from the rivers from which they emanate. The inclined bedding within some compound sheets reflects the depositional dips of overlapping splay surfaces. The groups of overlapping sandstone lenses (Type 3 sandstone bodies) are the deposits of ephemeral flood channels which were active as distributaries carrying water away from major channels to be lost in the floodplain, or as return flow channels bringing water back to main channels from the flood plain. Sand was deposited in them mainly by vertical accretion late in the flood cycle. Type 4 sandstone bodies are the deposits of small meandering streams migrating across the floodplain. Sandstone-mudstone couplets on the epsilon cross sets represent deposition during single floods. The small amount of sandstone in these units suggests that these streams did not receive water and sediment directly from the main streams but drained channel water which had stood on the floodplain or drained rain water which fell directly onto the floodplain.

415

METAMORPHIC PRESSURES AND TEMPERATURES EVIDENCED BY AMPHIBOLITES OF THE IRINDINNA SUPRACRUSTALS, HARTS RANGE R.L. Oliver1 and D.G. Boyer2 ^The University of Adelaide, Adelaide ^Santos, Adelaide An area in the Harts Range, 200 km northeast of Alice Springs, consists of a sequence of intercalated amphibolites and subsidiary pelitic metasediments. The sequence is part of the Harts Range Metaigneous Complex of the Irindinna Supracrustals, as defined by Ding, et al. (1983). The amphibolite, of theoleiitic composition, consists predominantly of calcic amphibole (edenite) and plagioclase (labradorite) in approximately equal proportions. Other mineral phases present include clinopyroxene (06%), garnet (0-10%), sphene and ilmenite (0.5-3%). This mineralogy is compatible with an upper amphibolite facies crystallisation evironment, as is that of the associated meta-pelites (viz. quartz-plagioclase-biotite-garnet-sillimanite). In the amphibolites the common occurrence of sphene rimming (and presumably replacing) ilmenite is indicative of pressure-temperature conditions and temperature-log f02 conditions pertaining to this transition. The intersection of Spear1s (1981) curves for this transition with the amphibole-clinopyroxene curve is at 7-800°C and 6.5 kb. Based also on Spear1s (1981) experimental work the titanium content of the amphibolitic hornblendes indicates a temperature of 650-780°C and similarly the sodium content suggest 680-780°C. These two elements in the hornblendes suggest also a log f02 range from -12 to -17. Applying this to the sphene-ilmenite transition curve on the temperature-log f02 diagram (Spear 1981), a temperature of 670°C is denoted. Si, Al total and Al° in hornblendes record a P f (at 700°C) of 5-9 kb. Graphic comparison by Binns (1969) of hornblende Ti content and metamorphic facies supports amphibolite facies crystallisation for the amphibolites of the Harts Range Metaigneous Complex. f\

Plots also of Al v A1H by Zakrutkin (1968) also suggest amphibolite facies crystallisation for these hornblendes. The above temperatures and pressures tend to be further supported by the application of geothermometers and geobarometers as indicated in Tables 1 and 2 below.

Table 1.

Garnet-Clinopyroxene Geothermometer (Temperatures in °C)

Ga--cpx pair Raheim & Green (1974) Ellis & Green (1979) Ganguly (1979)

416

1 2 3

6 Kb

8Kb

6 Kb

8 Kb

6Kb

8Kb

578 557 582

591 569 594

718 673 684

723 678 690

779 750 764

783 755 769

Table 2 . GarnetHBiotite Geothermometer (Temperatures in °C) Ga-biot pair

Goldman & Albee (1977) 5th Rank 2 Params

Ferry & Spear (1978) 8 Kb 6 Kb

Saxena (1969)

Thomson (1976)

723

670

884

717

713

733

695

920

738

763

772

723

670

873

715

708

717

722

713

660

854

709

694

702

720

695

889

735

758

767

730

705

899

741

772

782

723

695

684

734

754

764

730

705

890

738

763

772

730

695

883

733

752

761

References Binns, R.A., 1969, Spec. Publ. Geol. Soc. Aust. 2, 323-332. Ding, P., James, P.R. & Lawrence, R.W., 1984, (Submitted to Tectophysics). Ellis, D.J. & Green, D.H., 1979, Contrib. Mineral. Petrol. 71, 13-22. Ferry, J.M. & Spear, F.S., 1978, Contrib. Mineral. Petrol. 66, 113-117. Ganguly, J., 1979, Geochim. Cosmochim. Acta 43, 1021-1029. Goldman, D.S. & Albee, A.L., 1977, Amer. Jour. Sci. 277, 750-767. Saxena, S.K., 1969, Contrib. Mineral. Petrol. 22, 259-267. Spear, F.S., 1981, Amer. Jour. Sci. 281, 697-734. Thomson, A.B., 1976, Amer. Jour. Sci. 276, 425-454. Zakrutkin, V.V., 1968, Zap. Uses. Mineral. Obsch. 96, 13-23.

GOVERNMENT

SUBSIDISED EXPLORATION

FOR OPAL AT

ANDAMOORA

AND COOBER PEDY

J.G. 01liver & L.C. Barnes S.A. Department of Mines and Energy, Adelaide f South Australia produces about 75? of the world s precious opal from Coober Pedy, Mintabie and Andamooka. Recent geological investigations began at Andamooka in 1975 and culminated in subsidised exploration during May - September 1976 when 65 shafts were sunk and 399.5m of drives were developed along the opal level. Payment to participating miners totalled $6 018.30. The opal level was intersected to 54 shafts and was well developed in 39 of those shafts. Opal, mainly potch or dead matrix, was reported in 15 of the 54 shafts and the new fields of Stans Hill and Yarloo West were established. Geological investigations at Coober Pedy restarted in 1980 with a study of Fourteen Mile and Seventeen Mile fields. Preliminary mapping of the Precious Stones Field began in June 1981 followed by subsidised exploration in August-October 1981 when 221 shafts were drilled. Subsidy payment totalled $30 280.20.

417

Precious opal or potch was reported in 11 shafts and follow up work resulted in a major new field, Southern Cross, and a smaller field, 2 km east of Browns Folly. Understanding.of the relationship between opal and the weathered profile has increased and 34 shafts encountered a type of weathered profile highly prospective for opal. The limits of opal-bearing ground have been established at Andamooka and particularly favourable areas have been designated. In contrast, investigations continue at the more complex.and extensive Coober Pedy fields. Nonetheless, large areas prospective for opal and significantly, areas with low potential for opal have been located. References Barnes, L.C., & Townsend, I.J., 1982. Opal, South Australia^ Gemstone. Handbook No. 5. S. Aust. Dept. Mines and Energy. Carr, S.G., Olliver, J.G., Conor, C.H.H., & Scott, D.C., 1979. Andamooka Opal Fields. The geology of the Precious Stones Field and the results of the subsidised mining program. Rept. Invest.f geol. Surv. S. Aust., 51. Scott, fi.U, & Robertson, R.S., 1983. Coober Pedy Opal Fields - results of the subsidised exploration program, 1981 S. Aust. Dept. Mines and Energy report 83/7 (unpublished).

A X E N O L I T H - D E R I V E D G E O T H E R M FOR S O U T H E A S T E R N A N D ITS G E O P H Y S I C A L I M P L I C A T I O N S

Suzanne Y . O'Reilly

and W.L. Griffin

AUSTRALIA,

North Ryde ^School of Earth Sciences, Macquarie University, f Mineralogisk-Geologisk Museum, Sars Gate 1, Oslo, Norway Xenoliths in basaltic flows and cinder cones, sampled over a 1000-km (N-S) zone in SE Australia, are fragments of the lower crust and upper mantle. They range in age from Jurassic to Recent but are mainly Tertiary-Recent. P-T calculations for 30 garnet pyroxenites define a geotherm passing through 900°C/10 kb, 1050°C/15 Kb and 1200°C/25 Kb. Comparable T calculations for the dominant spinel lherzolite xenoliths, and contact relations in composite xenoliths, indicate that the crust-mantle boundary in this region is a 20-30 km transition zone made up of interleaved Cr-diopside lherzolites and mafic granulites, cumulates and intrusive rocks. In this depth range Vp increases from 7-0-7-6 km/sec, with a rapid increase to ^ 8.0 km/sec at 50-60 km. Calculations based on measured densities and compositions explain the Vp profiles, if the proportion of mafic rocks decreases with depth. The seismically defined "Moho" probably represents the spinel 1herzolite-garnet lherzolite trans i t ion. The xenolith geotherm is consistent with the high regional heat flow (^2 h.f.u.); this may have persisted since Jurassic time, perhaps as a series of discrete thermal events. The geotherm lies well above a steady-state one at depths <60 km, but resembles model geotherms that assume convective heat input from underplating and/or dike intrusion accompanying rifting. The high geotherm indicates a Curie-point depth of <12 km, consistent with MAGSAT data showing magnetic lows over SE Australia.

418

The opening of the Tasman Sea ^80 MA ago coincided with tectonic uplift and the onset of Tertiary vulcanism along the rifted coastline. The xenolith-derived geotherm for this region reflects the thermal effects of these events. In contrast, xenolith data from the margin of the craton to the west define P-T conditions typical of a continental steady-state geotherm. F A C I E S A S S O C I A T I O N S IN A P R O B A B L E A N C I E N T SILICIC V O L C A N I C C A L D E R A T E R R A I N , L O W E R D E V O N I A N SNOWY R I V E R V O L C A N I C S OF SOUTHEASTERN AUSTRALIA 1

K . O r t h , R.A.F. C a s , and J.V. Wright

^Geological Survey of Victoria, Melbourne ^Department of Earth Sciences, Monash University, Melbourne B.P. Petroleum Development Ltd., Cairo, A.R. Egypt The Lower Devonian Snowy River Volcanics consist of rhyolitic to basaltic volcanics and volcanigenic sediments outcropping in eastern Victoria. They were deposited under predominantly terrestrial conditions in a probable continental rift basin. The stratigraphy of an area studied near the top of the Snowy River Volcanics is marked by a complex of units with lensoidal geometries. This area can be divided into five domains displaying distinctive facies and facies associations: Domain 1 Extensive and restricted welded ignimbrites occur in this domain. Co-ignimbrite lag breccias also occur along with abundant erosional contacts and intervening lenses of fluvial sediments. Vitric and pumice rich sediments, including minor conglomerate, cross-bedded sandstones with channel-form structures and interbedded sandstones and mudstones form a large component of the stratigraphy. This overall upward fining sequence appears to represent a deepening basin and transition from a fluvial to lacustrine depositional regime. A minor unit of airfall and surge deposited ash, rich in accretionary lapilli and low angle cross-beds occur within these sediments. All these facies are cross-cut by small and large bodies of intrusive rhyolite, some hydrothermal veins and faults. Domain 2 Extensive multiple flow unit ignimbrites occur with thin intercalated co-ignimbrite airfall ashes and lesser lenses of high energy fluvial sediments. A pumice and lithic rich breccia is present at the base of one ignimbrite and may represent a pumice fall deposit. A rhyolite body is faulted against this sequence in the northern portion of the domain and a small intrusive dome is found cross-cutting the sequence further south. Domain 3 A complex of restricted laharic breccias, valley-filling ignimbrites and sedimentary units are interbedded with more extensive ignimbrites and thin .airfall ashes. The sediments include thin lenses of lacustrine turbidites, minor sedimentary breccia and an upward fining sequence of fluvial sandstones and siltstones. Contacts commonly display erosional features. Domain 4 Thick extensive ignimbrites dominate the stratigraphy, overlying lensoidal lacustrine sandstones and mudstones, small high energy fluvial sediments, eroded pumice fall and airfall ash deposits. Erosional contacts are common between all these facies. Domain 5 Lensoidal bodies of high energy fluvial deposits and basaltic lava flows represent the in-filling of valleys eroded into extensive welded ignimbrite units. A thin extensive non-welded ignimbrite is found near the top of the sequence along with more extensive basalt lava flows and the remnants of a basaltic tephra deposit.

419

Recent studies of modern silicic volcanoes and their products allow the formulation of a schematic facies model for subaerial silicic centres. In this model proximal near-vent and distal facies associations are distinguished. The proximal area is characterised by intrusive and extrusive rhyolite bodies, rapid facies variations with cross-cutting and faulted contacts. Lensoidal units of co-ignimbrite lag breccias, airfall and surge deposited ash and vitric rich lacustrine and fluvial sediments are common amongst restricted and extensive ignimbrite units. The distal areas are dominated by thick extensive ignimbrite units which are intercalated with thin airfall ash, pumice fall deposits and restricted bodies of lacustrine and fluvial sediments. Stratigraphic complications arise from the interaction of several volcanic centres. This model was applied to the facies associations recognised in the upper Snowy River Volcanics: Domain 1 conforms to the proximal region of the model and may have been deposited within a caldera. Domain 2 is also considered proximal although it displays fewer facies variations than domain 1. It may have formed within or on the flanks of a caldera centre. Domains 3, 4 and 5 all represent distal facies associations. Two silicic centres, other than the proximal region of domain 1, have influenced these areas. These centres lie to the south and east of the study area and were recognised by plotting isopleth maps of lithic clast sizes in ignimbrites. Domain 5 has also been influenced by a basaltic centre. The formulated silicic centre model combined with a facies approach to mapping ancient silicic volcanic terrains could prove useful in understanding their often complex stratigraphies. Furthermore delineation of silicic centres, utilising facies and their associations, could pinpoint areas of high potential in mineral exploration for subvolcanic stockwork deposits.

MICROBEAM METHODS IN MANGANESE OXIDE MINERALOGY J. Ostwald BHP Co. Ltd. Central Research Laboratories, Newcastle The determination of the mineralogy of the manganese oxides is traditionally considered difficult because of their fine grain size, complex mixtures and often poor crystallinity (Schouten, 1962). Recent research has shown that lack of well-defined determinative features, especially in the tetravalent manganese oxide of low temperature origin, may result from the existence of hybrid structures in these oxides. As an example, nsutite, battery active Mn02» consists of microdomains of pyrolusite structure (space group P42/mnm) in a ramsdellite (space group Pbnm) host (Giovanoli and Stahli, 1970). In the BHP Central Research Laboratories the mineralogy of a range of manganese oxide deposits, including the Groote Eylandt manganese orebody; numerous terrestrial occurrences and marine manganese deposits have been investigated, chiefly by optical and microbeam methods, together with X-ray diffraction (XRD) and more recently Fourier Transform Infrared (FTIR) techniques. Specific applications of microbeam techniques in manganese oxide research include: (1) Mineral Identification. Of the 19 higher oxides and hydrates listed by Roy (1981) 13 occur in the Groote Eylandt deposit. The identification pf pyrolusite, ramsdellite, nsutite, hollandite, cryptomelane, romanechite, todorokite, vernadite, manganite, groutite, chalcophanite, birnessite and lithiophorite was greatly assisted by electron probe microanalysis (EPMA). 420

(2) Mineral Composition. EPMA has shown that Groote Eylandt todorokite is barium-rich in contrast to many marine todorokites. Quantitative analyses of vernadite (natural delta Mn02) in the ore show it is also barium-rich, and that its structural water content is close to 25 wt%, in agreement with analyses quoted in Burns (1979), (3) Reaction phenomena. X-ray line and area scans offer evidence for the evaluation of mineral alterations and mechanisms of formation. As an example, lithiophorite is commonly observed as a reaction product of lateritic gibbsite and manganese oxides. (4) Element geochemistry. Microbeam methods may supply data on element association which are difficult to obtain by other techniques, e.g. mode of cobalt in specific manganese nodule minerals. (5) Applied research applications. The disordered mineral vernadite in the Groote Eylandt ore is highly battery-active. EPMA studies on polished specimens of Leclanche cell discharge products have shown the discharge voltage at which hetaerolite ZnMn204 develops. References Burns, R., 1979, Marine Minerals.

Min. Soc. America, 380pp.

Giovanoli, R. and Stahli, E. (1970): Roy, S., 1981, Manganese Deposits.

Chimia, 24, 49-88.

Academic Press, 458pp.

Schouten, C., 1962, Determination Tables for Ore Microscopy, 242pp.

Elsevier^

GEOLOGY, GEOCHEMISTRY AND GEOPHYSICS OF OIL SHALE IN THE TOOLEBUC FORMATION S. Ozimic* and J.D. Saxby^ * Bureau of Mineral Resources, Canberra 2 CSIRO Division of Fossil Fuels, Sydney The widespread Early Cretaceous oil-shale-bearing Toolebuc Formation in the northern Eromanga and southern Carpentaria Basins (Fig. 1) consists of various proportions of calcareous oil shale and coquinite. The Formation is sheet-like, with an average thickness of 22 metres and a maximum thickness of 35 m. To the south of a line joining Charleville and Bedourie the Formation passes laterally into time equivalent sequences lacking oil shale. These are the Wooldridge Limestone Member of the Oodnadatta Formation and the Urisino Beds, which consist of coquinite, limestone, siltstone and sandstone. The oil shale, which contains bituminite (generally dominant), lamalginite, telalginite and sporinite, appears to have resulted at least in part from the accumulation and preservation of planktonic and mat-like algae in a relatively deep (below wave base) restricted marine basin that shallowed southwards. This basin formed in the early late Albian following a major regression. The interbedded coquinites are made up of the remains of benthonic shelly scavengers whose establishment was favoured by periodic increases in oxygen levels. The conditions favouring oil shale deposition were apparently terminated after about 2 million years with a return of normal marine conditions, probably the result of an increase in saltwater inflow with rising sea level and other factors limiting productivity in the euphotic zone.

421

Where kerogenous shales (oil shales) of the Toolebuc Formation have been sampled in bore holes they are invariably associated with a marked gamma-ray anomaly. The converse is not true, since a gamma-ray anomaly occurs within the Wooldridge Limestone Member and also below the Urisino Beds. Identification of kerogenous shale from individual and/or suites of wire-line logs appears possible, but not with sufficient precision to predict oil shale grades.

Weathered 50-200m

^//y

zone

(Non-productive)

Possible open-cut mining area Productive

>200m

FIG. 1 L O C A T I O N

Possible in-situ

retorting

area

A N O R E G I O N A L S E T T I N G OF THE TOOLEBUC F O R M A T I O N A N O ITS E Q U I V A L E N T S

Organic geochemical and oil yield data for 259 Eromanga Basin core samples from 22 locations show that organic contents and oil shale grade broadly decrease towards the south. The atomic H/C ratio of Toolebuc kerogen is relatively constant (1.1 ± 0.2), indicating more than 50% aromaticity. On average, 27% of the Toolebuc organic matter is converted to oil on pyrolysis, up to 28% gas is produced and more than 45% remains as char in the spent shale. Evidently this low conversion to oil is a reflection of the high content of insoluble aromatics in the unheated 422

shale. The proportion of kerogen converted to oil rather than gas or char increases with organic carbon content. The distribution of compounds in Toolebuc shale oil is considerably different from that in other shale oils such as Rundle. Unsubstituted or methyl-substituted aromatic or heterocyclic sulphur compounds dominate in Toolebuc pyrolysis products. Rundle and similar Tertiary shales produce mainly long-chain alkanes and alkenes. Potentially productive oil shale in the Toolebuc Formation extends over an area of 0.48 x 10" km^, if the weathered zone from the surface to 50 metres, in which kerogen is absent or extensively oxidized, is excluded. Significant oil shale ranges in thickness from 6.5 to 7.5 metres, has a specific gravity of 1.9, and yields an average 37 litres of oil per tonne. The total potential shale oil source within the Toolebuc Formation is estimated to be 250 x 10^m3. Approximately 20% could possibly be produced by open-cut raining at depths between 50 and 200 metres. Below 200 metres production of oil by in-situ retorting becomes a possibility. Acknowledgement. Support for this work was provided National Energy Research Development and Demonstration administered by the Department of Resources and Energy,

under the Programme

THE GEOLOGY AND STRESS STATE OF THE MESAVERDE SECTION IN THE PICEANCE BASIN f COLORADO, AND ITS EFFECT ON HYDRAULIC FRACTURE STIMULATION I.D. Palmer Oral Roberts University, Tulsa, OK, U.S.A. The Multi-Well Experiment (MWX) is a major field test being conducted by the U.S. Department of Energy in Colorado as part of the Western Gas Sands Program. The MWX is designed to test the latest technology and determine whether recovery techniques are viable in the tight gas sand reservoirs characterizing this area . Three wells in a triangular geometry (100-200 ft apart) have been drilled to around 8,000 ft in the Mesaverde section in the Piceance Basin of northwestern Colorado. The formation contains lenticular sandstone sequences, which are the main goal of study. A wide battery of logs and core measurements have been obtained in order to derive a geological model for the lenticular sands. To further characterize the section, in situ stress measurements have been made over a height of 1300 ft in one of the wells using mini-fracs. Marked contrasts in minimum in situ stress (1300-2000 psi) have been found between one blanket.sand and adjoining shales. Even in the Paludal zone, which contains lenticular, distributary channel sandstones formed in a lower delta plain environment, surprisingly high stress contrasts of 1200 psi have been measured. These stress variations are of great importance in controlling the vertical growth of induced hydraulic fractures needed to produce gas from the tight sands. Although many such stimulations are planned for the MWX, the first one was completed in December 1983. In the Paludal zone at 7100 ft an 80 ft sand lens interval was perforated, and 30,000 gallons of gelled fluid were pumped into the formation . Measurements which include bottomhole pressure and temperature, a borehole seismic system, and a surface electric potential system, have been used to infer the shape and size of the fracture. The apparent length of the fracture (1 wing) was ^400 ft, and the total height ~150 ft . The wellbore pressure rose to ^1100 psi at the end of pumping. 423

One important aspect of this particular experiment is to test the theory of fracture prediction. The height of the fracture is strongly affected by the contrasts in minimum stress between the payzone and the bounding zones. In the first MWX stimulation, the payzone (perforated interval) was bounded by layers in which the stress was higher by 520 psi (above) and 1195 psi (below), as measured by mini-fracs. A hydraulic fracture simulator has been used to predict the shape and extent of a vertical fracture produced by a 30,000 gal stimulation . The wellbore pumping pressure is also predicted. The principal discrepancy between theory and measuremeni is wellbore pressure — theory predicts ^400 psi, measurement gives xL100 psi. Some suggestions are made to account for the discrepancy, and the implications discussed. Since ordinarily it is difficult to measure the shape and. size of a hydraulic fracture at this depth (~7000 ft), the MWX provides a good opportunity to test and improve fracture models based upon in-situ stress, fracture diagnostic, and production test data. References 1.

Northrop, D.A., Sattler, A.R., Mann, R.L., & Frohne, K.H., 1984, SPE/D0E/ GRI 12868, Proceedings Unconventional Gas Recovery Symp., Pittsburgh, Pa., USA, p. 351-358. 2. Hart, C.M., Engi, D. , Fleming, R.P., & Morris, H.E., 1984, SPE/DOE/GRI 12852, Proceedings Unconventional Gas Recovery Symp., Pittsburgh, Pa., USA, p. 221-228. 3. Palmer, I.D., & Craig, H-R., 1984, SPE/DOE/GRI 12879, Proceedings Unconventional Gas Recovery Symp., Pittsburgh, Pa., USA, p. 453-462.

METALLOGENY AND TECTONIC DEVELOPMENT OF THE TASMAN FOLD BELT IN SOUTH AUSTRALIA A.J. Parker South Australian Dept. of Mines & Energy, Eastwood, S.A. In South Australia the earliest development of the Tasman Fold Belt is considered to extend back to early Adelaidean time when alkaline volcanism and continental sedimentation developed within a rift system somewhat analogous to the East African Rift system (von der Borch, 1980) . Episodic continental sedimentation was maintained with the Adelaide Geosyncline through to ca 800 Ma when a major transition to dominantly marine relatively shallow water sedimentation occurred. This sedimentation occurred within an environment analogous to modern passive continental margins (Preiss, 1983) with episodic subsidence in fault controlled marginal basins. Alternating euxinic shales, clastic turbidites, shelf and lagoonal limestones, and tidal sandstones define regional sedimentary cyles related to local tectonic disturbances (Jenkins & Gostin, 1983). _ Throughout much of the Adelaide Geosyncline Early Cambrian sediments of the Normanville and Hawker Groups are transgressive across the Adelaidean and pre-Adelaidean rocks. On the Stuart Shelf, Yorke Peninsula and in the central Flinders Ranges these earliest Cambrian sediments are largely supratidal to shallow marine clastics and carbonates. However, to the south and east of Adelaide similar sediments are overlain by phosphatic shales likely deposited in a deeper water, basinal marine environment. Mafic volcanics at Truro north-east of Adelaide occur immediately below these shales and may represent rifting and early graben development in an extensional tectonic environment.

424

Subsequent Early Cambrian sedimentation, the Kanmantoo Group, reflects rejuvenated tectonic activity (Kangarooian Movements) and a sudden influx of poorly sorted sands and silts into a rapidly subsiding basin (Daily & Milnes, 1971) or marginal shelf. These flyschoid sediments contain local turbidites most likely of proximal origin but no evidence of mafic volcanism or volcanic detritus. While it is possible that the Kanmantoo Group was deposited on an abyssal plain on oceanic crust in the outer Fleurieu Arc south of Kangaroo Island and east of Kanmantoo (von der Borch, 1980) this cannot be substantiated. It is clear however that the Kanmantoo Group was deposited in an extensional tectonic regime. During the Mid to Late Cambrian the Cambrian ocean closed or retreated easterly due to major orogenic activity and compressional tectonics (the Delamerian Orogeny). Mancktelow (1979) concluded that the "macroscopic structure of the southern Adelaide Fold Belt is largely a result of the first deformation" which occurred just prior to emplacement of the Encounter Bay Granites (ca 515 - 506 Ma, Milnes et al., 1977). The present shape of the Adelaide Fold Belt developed largely during this deformation due to compression around the margins of the older Precambrian cratonic nucleus. Copper and to a lesser extent gold, was locally remobilized during the Delamerian Orogeny. The Kanmantoo Copper Deposit consists of a series of flattened podiform lenses elongated to the north-east within the axial planar schistosity of macroscopic south plunging folds. The mineralization occurs Within an andalusite + garnet + pyrite + pyrrhotite + magnetite + chlorite mica schist which appears to be structurally thickened by folding. Most mineralization within the Kanmantoo Group appears to be related to this and other pyrite/pyrrhotite sulphide rich horizons. One of the more significant sulphide rich horizons in the Kanmantoo—Nairne region is the Nairne Pyrite Member which is correlated with the Talisker Calc-silicate of southern Fleurieu Peninsula. The Talisker Calc-silicate hosts minor arsenopyrite mineralization in an area of possible syn-sedimentary faulting. Therefore, while in a regional context all sulphide horizons appear to be essentially stratiform albeit modified during deformation, there may be underlying structural controls of local importance. References Daily, B. & Milnes, A.R., 1971. R. Soc. S. Aust., Trans., 95, 199-214. Jenkins, R.J.F. & Gostin, V.A., 1983. Geol. Soc. Aust., Abstr. 1<0, 39-44. Mancktelow, N.S., 1979. Unpubl. Ph.D. thesis, Univ. Adelaide. Milnes, A.R., Compston, W. & Daily, B., 1977. Geol. Soc. Aust., J., 24, 87-106 Preiss, W.V., 1983. Geol. Soc. Aust., Abstr., 10,13 - U . von der Borch, C.C., 1980. Tectonphysics, 70^, 115-134. WHICH WAY DID THE FLUIDS FLOW THROUGH THE FORTESCUE METABASALTS? T.C. Parks CSIR0 Division of Mineralogy, Perth It is proposed that pore fluids were selectively permeable to electrons during sub-greenschist facies metamorphism of basalts. Consequently, physically remote minerals were able to react together to buffer oxidation potential, while gradients in other chemical potentials were developed. The evidence is as follows: 1. Linear trends in Al:Mg:Fe ratios of pumpellyite appear to represent constant values of Fe^+/Fe^ and x in the formula (Parks, 1983); Ca 4 [(Fe 2+ ,M8) 2 _ x (Al,Fe 3+ ) x ] (Al,Fe3+)4

Si.O^OH)^ 425

This is supported by average Fe^+/Fe* ratios published for each of two pumpellyite metadomains, which contribute to a linear trend for metabasalts of the Western Australian Fortescue group (Smith et al, 1982). Published FeO/MgO ratios for chlorites coexisting with pumpellyites in the Abitibi belt of Canada are further support (Jolly, 1980). 2. During the growth of nearly monomineralic domains of epidote, iron was immobile, but was entirely oxidized within the domain and extensively reduced outside it (Jolly, 1980). Electrons may be readily transported by exchange between altervalent species in a fluid. The implication is that the pore fluid was rich in iron in ferric as well as ferrous forms. However, since iron itself was immobile, it was probably complexed and/or polymerized. This would also permit high concentrations while the activities of the formal ferric or ferrous ions were low. The flow of electrons must be balanced by a flow of counter ions, involving the species which were most numerous and mobile, locally, e.g. H + , OH" or the alkalies. This could explain the segregation of monomineralic domains around nuclei of epidote or pumpellyite, the albitization and enhanced destruction of nearby basalt minerals, and the tendency of fractures to bound such domains. References Parks, T.C., 1983, CSIRO Min. Res. Labs. Div. Mineralogy Rept. FP27 Smith, R.E.S., Perdrix, J.L. and Parks, T.C., 1982, J. Petrology, 23, 75102. Jolly, W., 1980, J. Petrology, 21, 323-363.

AN ELECTRON-PERMEABLE PORE FLUID DURING BURIAL METAMORPHISM: EVIDENCE AND IMPLICATIONS T.C. Parks CSIRO Division of Mineralogy, Perth Pumpellyite, an important indicator mineral in metamorphism of mafic rocks, has the idealized formula: Ca4[(Fe2+,Mg)2_x(Al,Fe3+)x] (Al,Fe3+)4

the

low-grade

S i ^ ^ O H ) ^

Analyses from a given locality often follow a linear trend of Al:Mg:Fe substitution on a triangular plot. Such a linear trend would arise if two conditions are met simultaneously in the pumpellyite formula: (i) (ii)

The "H2O deficiency", x, in constant. The ratio Fe3+/Fe* (Fe* = total Fe) is constant.

The ratio, Fe^+/Fe*, is related to the inclination of the trend but is independent of its location on the triangular plot. The value of x is related to the trend's intercept on the Al-Mg side of the triangle, regardless of the inclination of the trend (Parks, 1983). In the Fortescue metabasalts north of the "Paraburdoo Hinge Zone" (Horwitz, 1982) in Western Australia, most of the pumpellyite analyses (Smith et al., 19821 fall on the intersection of two linear trends, one with x « 1.33 and Fe3+/Fe* > 0.80, the other with Fe3+/Fe* < 0.47 and x - 1 (Parks, 1983). At the lowest metamorphic grades, a third trend has Fe#+/Fe* • 0.86 and x = 1. These two rational values of x suggest a crystallographic control such as different schemes of ordered hydrogenbonding, but they probably also distinguish geological extremes in the 426

fugacity of l^O. Trends with the higher value of x are attributed to lithostatic values of fluid pressure, because aqueous fluids are less ideal and dissolve more CO2 and solid components, as pressure is increased. Besides simply diluting the H 2 0, C0 2 would increase the acidity of the fluid and induce pumpellyite to release MgO and FeO in exchange for the sesquioxides. Conversely, trends with x = 1 indicate hydrostatic values of fluid pressure. The two trends with high Fe3+/Fe* are believed to relate to pumpellyite which was segregated into domains within a basalt undergoing burial metamorphi sm. The most prevalent composition is of pumpellyite formed at the front of an expanding domain, where all phases were in contact and Gibb's Phase Rule allowed no variation in composition. Behind the front, late-formed pumpellyite was free to vary its Fe* content. However, Fe /Fe* remained constant due to widespread equilibration of oxidation potential through an • electron-permeable pore fluid (Parks, 1983; Parks, this conference). The segregation occurred when fluids were sealed in at lithostatic pressure, except at the shallowest depths of burial. Subsequently, fractures were opened and the fluid pressure fell to hydrostatic values. Consequently, the existing, segregated pumpellyite became more hydrated, and the iron in it may have been reduced, correspondingly, in a metastable redox reaction. Also, water was then able to circulate in an artesian system. The linear trend with Fe /Fe* less than 0.5, cent red on the most prevalent AlrMgsFe* proportions, is attributed to downward flow of Fe-rich solutions, north of the Paraburdoo Hinge zone. Thus the trend is towards Fe* enrichment at the higher metamorphic grades, and towards lower Fe* at the lower grades. Upwelling of the fluids would have occurred south of the hinge zone, which was topographically lower during most of the geologic past (Horwitz, 1982). Horwitz' reconstructions (1982) are useful in estimating the times and locations for fluids to have reached the surface through previous exposures of the Fortescue group. References Parks, T.C., 1983, CSIRO Min. Res. Labs. Div. Mineralogy Rept. FP27. Smith, R.E.S., Perdrix, J.L. and Parks, T.C., 1982, J. Petrology, 23, 75102. Horwitz, R.C., 1982, Precambrian Research, 19, 191-200.

EXTRAPOLATION OF LABORATORY RHEOLOGICAL BEHAVIOUR IN TECTONOPHTSICS M.S. Paterson Research School of Earth Sciences, Australian National University At relatively low temperatures and pressures rocks fail under nonhydrostatic stress by brittle fracture. However, they tend to become ductile as temperature and pressure are raised, although the presence of high pore fluid pressures can greatly extend the brittle field. At lower crustal and upper mantle conditions, ductile behaviour is usually assumed, except where the occurrence of earthquakes points to brittle failure. In this talk I shall deal only with creep of rocks in the ductile field. Such creep is invoked in considering large scale tectonic processes in the lower crust and upper mantle and therefore the predictions of creep behaviour under natural conditions from laboratory observations would be very useful in constraining tectonophysical models. It will be argued, however, that at present this prediction is hampered by many uncertainties and lack of knowledge, even concerning what are the potentially important variables, so that current extrapolations of laboratory flow laws are of very questionable value. 427

In relating laboratory observations to tectonophysical processes, three types of consideration enter: (a) The form of the flow criterion for general stress states (b) The environmental and internal variables that need be considered (c) The circumstance that different mechanisms may dominate behaviour under different conditions, giving rise to a variety of flow laws for a given rock, I shall discuss these in turn. Almost all laboratory rheological measurements have been made in axial compression under superposed confining pressure, that is, with a-| > 02 = 03 where a-|, a2* 03 are the principal stresses (compression positive). The quantity 0 = 0 1 - 0 3 is reported as the "flow stress", determined as a function of the axial strain rate e<\ = e (shortening positive) at a given temperature T and confining pressure 02 - 03. Not much attention has been given to the analysis of transient creep. The test results are usually fitted to a steady state "flow law" of the form e = Aa

exp | ^

(1)

where A, n and Q are empirical parameters, R is the gas constant and T the absolute temperature. In tectonophysics other types of stress states are involved and so a generalization of this flow law is needed. In engineering creep calculations for general stress states it is often assumed, following Odqvist, that the flow law can be expressed in terms of an "effective stress" a* and an "effective strain rate" e*, in the form (neglecting elastic strains): 2 2 2 a* = (1//2){(o1 - a 2 ) + (o 2 - o 3 ) + (o 3 - a,) }*'*

.* .* .* 2 .* .* 2 .* + a2 + (e3 e = U2/3){(e1 - e2 ~ V ~

. * 2 1/2 } 1

In this case it is seen that 0 - o<\ " 0 3 and e = e-| in the experiments can be viewed as effective stress and effective strain rate and that it is appropriate to extend (1) to general stress states in terms of a* and e*, remembering, however, that the form (1) is essentially empirical at this point and that other forms might have been used. Even accepting (1) as the basic form of flow law, f(e*>a*,T) = 0, with primary variables e , a and T, the flow behaviour in practice can be influenced by the following additional variables: (a) Pressure or mean stress. The influence of pressure is relatively small in the laboratory range and no precise measurements are available. However, it is thought to be significant in extrapolating to upper mantle conditons, when it can be allowed for by increasing the value of Q. (b) Grain size. Under some conditions the creep rate can be strongly dependent on grain size. In this case the pre-exponential factor in (1) is rewritten as A/dP where d is the grain sze and p is another empirical constant, usually in the range 0 to 3. (c) Water activity. Intragranular hydrolytic weakening is an effect of major importance, well known in quartz and olivine and probably occurring in other silicates, although the exact manner in which the dependence on water activity should be incorporated in the flow law has yet to be established. Other thermodynamic variables such as oxygen activity may also prove to be important in particular cases. (d) Presence of fluid phases. The pore pressure effects that are well known in the brittle field are probably unimportant in the ductile field. However, the presence of fluids in the grain boundary regions can have important rheological effects if conditons are such that diffusive transfer of material through the fluid phase contributes significantly to the strain or if it assists intergranular accommodation. These effects can be expected to introduce some grain size dependence in A and possibly affect the other parameters too. 428

(e)' Preferred crystallographic orientation. This would tend to introduce anisotropy of flow stress, requiring different choice of parameters for different orientations. Little is known about flow laws for anisotropic rock. The third aspect of flow behaviour to be considered is the variety of deformation mechanisms or rheological regimes. Many mechanisms are known or are conceivable, by means of which rock can flow. The flow law can therefore be expected to vary, in values of parameters and in the variables that need to be incorporated, according to the mechanisms predominating. These mechanisms may include dislocation movement controlled by a variety of factors, displacement of material by diffusion via various paths, and cataclastic processes involving microcracking and granular flow. Correspondingly, laboratory measurements have established different rheological regimes within which different values of the parameters are found when flow law (1) is fitted- and different dependences on variables such as grain size appear. Before making any justifiable extrapolation of a laboratory-determined flow law, valid for certain ranges of strain rate, stress, temperature and other variables, to tectonophysical conditions in the Earth it must be established that the same flow mechanism or rheological regime is involved. Microstructural evidence on flow mechanism in laboratory and field is therefore of primary importance in guiding the application of laboratory findings in geology. In the absence of this evidence, prediction by extrapolation must be seen as speculative unless the general form of the. rheological behaviour within the Earth can be independently established. When the latter is possible, comparison with experiment may permit conclusions about conditions within the Earth, such as temperature and other thermodynamic variables. Otherwise, on present knowledge, only very broad limits can be placed on the rheology of the lower crust and upper mantle by extrapolation from experiments.

GEOTECHNICAL ASPECTS OF STOPE DESIGN AT THE ELURA MINE, C0BAR 9

NSW

J.M. Pearson Electrolytic Zinc Company of Australasia Limited, Cobar The Elura orebody is a massive sulphide silver, lead and zinc deposit hosted by monotonous lower Devonian distal turbidites of the Cobar Trough. It has a vertical pipe shape, approximately 100 x 200 metres in plan and over 500 metres deep. There are three main structural domains; the orebody, the country rock remote from the orebody and the country rock adjacent to the orebody. A detailed study of the structures in the deposit and the adjacent country rock have influenced a revision in the stope design. Within the orebody sub-horizontal joints are the major type of discontinuity. These have a mean dip orientation of 10° towards 010°, and an average trace length of 5 metres but may be up to 40 metres long. Joint surfaces tend to be rough and undulating and major joints may be wet, vughy and clay filled. By lowering a camera on a trolley in two 70 metre vertical raises and photographing every metre it was estimated that overall 95% of the spacings between major sub-horizontal joints were less than 6 metres. Sub-vertical jointing is less significant and has a scattered distribution generally occurring closer to the boundaries of the orebody. A third set of intermediate joints have been observed with dips between 30°60° usually towards the north-east, and smooth planar surfaces with trace lengths greater than 10 metres. Discontinuities in the country dominated by partings along bedding jointing are also prevalent.

rock remote from the orebody are and cleavage. Minor shearing and 429

The country rock adjacent to the orebody is characterised by the same bedding and cleavage partings which are generally steep, and dip away from the orebody. The intensity of fracturing in these contact zones is variable. Frequently concentrations of sub-horizontal quartz/clay veins cause areas of very weak ground. Stress measurements were carried out in both ore and country rock using the CSIRO Hollow Inversion Stress Cell. The results showed that the major horizontal principal stress is east-west, the intermediate principal stress is north-south, and the vertical stress is approximately equal to overburden. The rock properties measured indicate that the orebody is a strong, brittle, competent rock, and the surrounding siltstone is markedly less strong. A conventional longhole open stoping layout was considered. This comprised vertical-sided open stopes which were 18 metres wide (northsouth), a variable east-west length of up to 110 metres, and 70 metres high. Groups of 3 or 4 stopes were separated by a 10 metre wide rib pillar and an 8 metre crown pillar. The long axes of the stopes were aligned parallel with the major principal stress to increase the confinement on the east-west walls. As the adjacent stopes were mined the north-south backspan would have increased to 54 metres. This would have resulted in the crown stability deteriorating progressively as the stope span increased. Sub-horizontal jointing would cause extensive slab failure which cable bolting or backfill would have been unlikely to control except in the initial 18 metre wide stope. Numerical modelling suggested that the crown pillar would have to be 20-25 metres thick to be stable under these conditions. The intensity of the sub-horizontal jointing would have influenced the stability of the rib pillar. Under vertical loads, open or clay filled joints would collapse and reduce its inherent strength. A new stoping design was developed known as "Sloped Wall Blasthole Stoping" and the mining sequence was revised so that ore extaction started at lower levels and progressed upwards. This obviated the need for thick crown pillars and eliminated load bearing rib pillars. Numerical modelling suggested that tensional stresses would still develop within the crown pillars and lead to slab failure without some additional support. Consequently buttress pillars were introduced on the east and west sides of the orebody to reduce crown pillar spans. The new stope layout still has problems associated with geology, the most important being the contact zones and the distribution of joints in ore. At the contacts severe siltstone dilution may occur unless reinforced, or an ore membrane is left. All diamond drill core and development in ore are logged for discontinuities, and ore contacts mapped on a 1:100 scale to gain further knowledge of these areas.

FRIABLE SANDSTONES OF THE SYDNEY BASIN-A MAJOR SOURCE OF INDUSTRIAL AND CONSTRUCTION SAND FOR THE SYDNEY MARKET S.R. Pecover Geological Survey of New South Wales, Sydney Extensive deposits of deeply weathered friable sandstone have been identified at various localities in the Sydney Basin. These include the Newnes Plateau, the Somersby Plateau, and at Darkes Forest west of Wollongong. Deeply weathered friable conglomerates belonging to the Munmorah Conglomerate have also been identified north of Wyong. These deposits constitute a potentially immense source of industrial and construction sand for the Sydney market. 430

The deepest and most areally extensive deposits of friable sandstone yet discovered are on the Newnes Plateau (located approximately 110 km west of Sydney), extending south to Blackheath and Medlow Bath. These deposits are developed in Narrabeen Group sediments belonging mainly to the Banks Wall Sandstone of the upper Grose Sub-Group. Surface mapping and reconnaissance drilling by the Department of Mineral Resources have identified a number of areas containing resources of approximately half a billion tonnes of readily extractable sand suitable for processing into a wide range of industrial and construction sand products (Pecover, in prep). Friable sandstone contains higher void volumes and exhibits a correspondingly higher porosity than equivalent (in terms of grain size and sorting characteristics) harder sandstone. The content of siliceous cement and the degree of secondary intergrowth between adjacent quartz grains is much less in friable sandstone than in harder sandstone. Furthermore, the intergrowth between interstitial kaolin minerals is less, with authigenic kaolinite and dickite commonly occurring as delicate free-growing rosette and roulex crystal clusters lining the sides of pore cavities. Such observations suggest several episodes of dissolution and subsequent regrowth of quartz and kaolin minerals, thereby weakening the overall fabric of the rock. The distribution of friable sandstones, particularly on the Newnes Plateau and adjacent high areas, can be correlated with the regional fracture pattern developed along the western margin of the Sydney Basin. The drainage pattern is strongly modified by this regional fracture pattern with many streams following NNW joints, and some very long streams following meridional NNE-SSW lineaments (Shepherd et al. 1981). Two exceptionally long lineaments, the Deans Creek Lineament and the Happy Valley Lineament, dominate the hydrology in the central part of the Newnes Plateau; their position being characterised by narrow, long, shallow heath swamp valleys. These valleys contrast markedly in orientation with the deeply incised easterly drainage pattern developed throughout much of the Blue Mountains and Wollemi national parks. This suggests a palaeo-drainage pattern on the Newnes Plateau that is considerably older than drainage regimes that have formed many of the deeply incised valleys throughout the Western Blue Mountains. Drilling and field investigations in the vicinity of the Deans Creek Lineament and the Happy Valley Lineament has revealed that the friable sandstone is in places over 100 m deep. Friable sandstone in the vicinity of major fracture zones is characterized by extensive ferricrete bands composed of goethite and hematite. The distribution of these bands is random, bedding and joint-controlled, with the most noticable feature being their position relative to porosity changes within the sandstone. The mineralogical composition and petrographic nature of the friable sandstones suggests a prolonged high degree of solution transfer of silica, alumina, and iron which appears to have been aided by structurally induced pathways through the body of the rock. The existence of numerous perched water tables associated with discontinuous claystone beds within the Banks Wall sandstone on the Newnes Plateau appear to have increased localized wetting of the sandstone. However, the great extent of friable sandstone suggests some degree of past climatic influence. Palynological evidence for eastern Australia suggests that at various times climatic conditions during the Oligocene-Miocene were characterised by very high rainfall. Furthermore, the existence of small isolated remnants of Tertiary basalt near the northeastern edge of the Newnes Plateau suggests that the present surface may be at or near the position of a palaeo-land surface of Tertiary age or older (S. Lishmund pers. comm. 1983). Thus over a long period of geologic time (perhaps stretching back to the end of the Triassic) a combination of extensive

431

fracturing together with numerous perched water tables appears to have aided large volumes of downward percolating waters to leach out cementing material thereby reducing haird rock to soft and friable sandstone. This process is likely to have been accelerated during periods of extremely wet climatic conditions such as thos6 that occurred during the Tertiary. Evidence from field observations indicates that deep weathering is still going on today in the vicinity of fracture zones, aquifer zones, and perched water tables. Because of the high variability of grainsize within the Banks Wall Sandstone, the friable sandstone deposits on the Newnes Plateau have the potential to produce a wide range of construction sand and special industrial sand types for use in a variety of applications including concrete manufacture, glassmaking, and foundry use. In addition, the high-crystallinity kaolinitic clay fraction shows considerable potential for use in a number of industrial applications including refractories, whiteware ceramics, and paper coating. The Department's recent investigation of the friable sandstone resources of the Newnes Plateau demonstrates the enormous potential that this type of deposit has for supplying large quantities of construction and industrial sand products to the Sydney market. Moreover, these and other similar deposits may provide greater insight into the geological and geomorphic history of the Sydney Basin.

References Pecover, SR., in prep. New South Wales Geological Survey - Report GS1984/098 (unpubl). Shepherd, J. , Huntington, J.F., & Creasey, J.W., 19.81. Trans. Instn. Min. Metall. (Sect. B: Applied earth sci.), 90, B1-B14.

GEOLOGY OF GREEN RIVER FORMATION AND OIL-SHALE GENESIS IN UINTA BASIN, NORTHEAST UTAH, U.S.A. M. Dane Picard University of Utah, Salt Lake City, Utah, U.S.A. Geologists have studied oil shale of the Paleocene-Eocene Green River Formation in northeast Utah, northwest Colorado, and southwest Wyoming for more than 60 years. In that time, because of the great geologic interest in the oil shale, solid hydrocarbons, tar sandstone, oil and gas fields and saline minerals, the Green River Formation has become the most intensively studied sedimentary sequence in the world (Picard and High, 1981). Examples of colossal resources in the Uinta Basin of Utah are: the Red Wash field with an estimated ultimate recovery of 130 million barrels of oil (Ritzma, 1972); various tar sandstone deposits with 11 BBO in place (Demaison, 1977); and oil shale resources in the eastern Uinta Basin of 154 billion barrels (Trudell and others, 1982). If deposits that range down to 15 gallons oil per ton are included, oil shale resources in the Piceance Creek Basin of northwest Colorado reach 1,200 billion barrels or more. The Uinta Basin is an intracratonic sedimentary basin within the northern Colorado Plateau. The geographic basin is bounded on the south by the Book Cliffs, on the west by the southern and central Wasatch Mountains, on the north by the Uinta Mountains, and on the east by the Douglas Creek arch. The area of the Uinta Basin underlain by the Green River Formation is roughly elliptical - - about 120 mi (193 knO long, eastrwest, and 90 mi (145 km) wide, north-south. It covers about 6500 mi (16800 km ).

432

During latest Cretaceous through Eocene time, 16400 ft (5000 m) of beds were deposited in central and northeast Utah. In the Late Cretaceous, sediment derived from the Sevier-Laramide fold-and-thrust belt was transported to the east and southeast. Extensive coalescing alluvial fans prograded eastward from the active orogenic belt. Paleocurrent measurements in the Currant Creek Formation (Maestrichtian to late Paleocene?), which unconformably overlies the Upper Cretaceous Mesaverde Formation, give a dominant southerly transport direction and a minor component to the east (Isby and Picard, 1984). Coarse-grained material was probably derived mainly from the northwest, fine-grained material dominantly from the north. Uplift of the Uinta Mountains had not begun by early Maestrichtian time. During the early Paleocene the thrust belt continued as a major highland. Major uplift of the Uinta Mountains occurred. The Currant Creek lobe graded southward and eastward into alluvial plain and paludal-lacustrine facies of the North Horn Formation. By the middle Paleocene there was an extensive lake that regressed during the late Paleocene uplift of the Uinta Mountains. Lacustrine facies are termed Flagstaff Formation. Alluvial fan and alluvial plain facies are termed Colton Formation. Alluvial deposition extended well into the basin during the late Paleocene. Lake Uinta reached its maximum size during the middle Eocene. Beginning in the early Eocene, it transgressed to its maximum extent in northeast Utah and over the Douglas Creek arch into the Piceance Creek Basin. The expansion led to great organic productivity and formation of the Mahogany zone and other rich oil-shale deposits in the Parachute Creek and underlying Garden Gulch members of the Green River Formation. The areal extent of open (oil shale) and marginal lacustrine deposition - - oolitic, algal and ostracodal carbonate settings - - was the most extensive. Alluvial deposition occurred in a thin band on the north and in a wide band on the south and west. During the late Eocene, Lake Uinta regressed. Near the end of the epoch the lake expired. Two Uinta Formation facies - - saline and the sandstone and limestone - record the regression and the last several million years of lacustrine deposition in this long-lived (13 my) lake. Lower (early Duchesnean) and upper (late Duchesnean) conglomeratic intervals of the Duchesne River Formation record major episodes of uplift in the Uintas during latest Eocene. Deposition was in relatively small, rapidly aggrading, southward-flowing, braided streams. The Wasatch Mountains are part of a marginal foreland fold-and-thrust belt. In the northern Wasatch Mountains, pre-Late Cretaceous thrust-fault plates were folded as part of a large ramp-anticline cored by allochthonous crystalline basement. Foreland thrust-belt structures formed in the central Wasatch Mountains. Eastward movement on the Hogsback thrust was transferred in the Paleocene onto the adjacent Uinta axis and Uinta Mountains structure, causing about 12.5 mi (20 km) of sinistralslip in the western Uintas. Deformation in the Uinta Mountains continued following cessation of movement on the Hogsback thrust system. A south-dipping fault-ramp was located beneath the Uintas, extending to depths of 9-12.5 mi (15-20 km). Obliqueslip on this ramp probably resulted in about 20 km of crustal shortening perpendicular to the trend of the mountains (Bruhn, Picard, and Beck, 1983). Although several interpretations of the Early Tertiary alluvial and deltaic rocks have arisen, debate on genesis of these beds has been mild. In contrast is the spirited controversy on oil shale genesis. Two archetypes dominate: (1) a stratified lake (Bradley, 1929, 1931) in which anaerobic conditions in the hypolimnion led to preservation of organic material and fine laminae in the oil shale; (2) a playa lake where oil shale formed in a shallow, non-stratified lake fringed by broad mud flats or playas. The stratified-lake archetype best explains the physical and chemical characteristics of oil shale such as the hydrogenated nature of the kerogen, the vertical uniformity in mineralogy, the delicate laminations and their lateral persistence, and the distribution of sulfur isotopes in sulfide minerals (Desborough and Pitman, 1974; Cole and Picard, 1975, 1978). The minerals in the offshore organicallyrich rock are attributed mostly to authigenic and diagenetic formation. Advocates of the playa-lake archetype (Eugster and Surdam, 1973; Lundell and Surdam, 1975) believe it accounts for shallow-water sedimentary structures and a low topographic gradient.

433

Several basins with different sedimentary patterns existed. During the maximum transgression, the Uinta Basin was the deepest, then the Piceance Creek Basin, followed by the Green River Basin of southwest Wyoming. Lacustrine deposition lasted longest in the Uinta Basin and shortest in the Green River Basin. The lack of good modern analogues restricts interpretation of oil shale settings. The applicable modern processes, particularly dolomite formation, are poorly understood. Still, the stratified-lake archetype explains the major features of the oil shale. In Wyoming where the playa-lake interpretation was largely developed, few true oil-shale beds occur. Organic content is low. There are lithified, blue-green algal, mat-like deposits that resemble oil shale. Dyni and Hawkins (1981) suggested that lacustrine turbidity currents produced streaked-and-blebby oil shale in the low.er Parachute Creek Member in the Piceance Creek Basin. Turbulent suspension and traction transport carried large volumes of mineral and organic matter into the open-lacustrine environment (Cole, 1984). Such processes occur in modern large lakes, particularly relatively deep ones. Oversteepening and slumping of sediment, seismic events, major storms and lake overturns probably triggered the turbidity currents. Detailed studies indicate laminated oil shale originated during meromictic phases of Lake Uinta in the Piceance Creek Basin (Cole, 1984). Deposition was regular. The laminated shale contains large amounts of nahcolite, dawsonite, quartz, K-feldspar and calcite, but less dolomite/ankerite and albite than streaked-and-blebby oil shale. Compositions of Ca-Mg-Fe carbonate minerals in laminated oil shale show greater variability than those in streaked-and-blebby oil shale. Episodic, non-channelized turbidity currents deposited the streaked-and-blebby oil shale. This oil shale contains more kerogen and a greater diversity of kerogen particles than laminated shale (Cole, 1984). When each shale type is retorted, these variations may yield different pyrolysis reactions. The "surplus" of oil in the United States is largely an artificial one related to conservation measures and foreign imports. Energy problems have not been solved. At best producers have gained a few months. In the long run the United States and most other countries are close to an energy crisis. Oil imports largely come from unstable or potentially unstable regions of the world. With present technology, synthetic fuels are uneconomic in the United States, even if production commenced tomorrow. Industry has not gained the necessary engineering experience. For at least four decades the estimated cost per barrel of producing shale oil has kept a steady 25 percent or so above that of crude oil. That gap is larger now with estimates from work in the Piceance Creek Basin of $44 per barrel. Shale oil coproduced with other minerals from the saline zone oil-shale deposits of northwest Colorado could be an exception. Studies of oil shale and tar sandstone should proceed vigorously. Unfortunately, interest in the United States is lower than it has been in severed decades. At the recent meeting of the American Associaton of Petroleum Geologists in San Antonio fewer than a hundred people sometimes attended the session on oil shale and tar sandstone.

References Bradley, W. H., 1929, U. S. Geol. Survey Prof. Paper 158, 87-110. Bradley, W. H., 1931, U. S. Geol. Survey Prof. Paper 168, 58 p. Bruhn, R. L., Picard, M. D., & Beck, S. L., 1983, Utah Geol. & Min. Survey Studies, 59. 63-88. Cole, R. D., 1984, in 17th Oil Shale Symp. Proc., Colo. Sch. Mines, Golden, in press. Cole, R. D., <5c Picard, M. D., 1975, Utah Geology, 2, 49-67. Cole, R. D., & Picard, M. D., 1978, Geol. Soc. A m . Bull., 89, 1441-1454. Demaison, G . J., 1977, A m . Assoc. Petroleum Geologists Bull., 61, 1950-1961. Desborough, G. A., and Pitman, J. K., 1974, Rocky Mtn. Assoc. Geol. Guidebook, 8189.

434

Dyni, J. R., & Hawkins, J. E., 1981, Geology, 9, 235-238. Eugster, H. P., & Surdam, R. C., 1973, Geol. Soc. Am. Bull., 84, 1115-1120. Isby, J. S., & Picard, M. D., 1983, Contributions to Geology, 22, 91-108. Lundell, L. L., & Surdam, R. C., 1975, Geology, 3, 493-497. Picard, M. D., & High, L. R., Jr., 1981, SEPM Special Publication 31, 233-259. Ritzma, H. R., 1972, in Geologic Atlas Rocky Mtn. Region, RMAG, 276-278. Trudell, L. G., Mason, G. M., Smith, J. W., & Beard, T. N., 1982, 15th Oil Shale Symp. Proc., 38-49.

EVALUATION OF THE POTENTIAL FOR ENHANCED OIL

RECOVERY

IN AUSTRALIA W.V. Pinczewski School of ChemicalofEngineering & Industrial Chemistry, University New South Wales, Kensington Australia is facing an increasing shortfall between production and consumption of hydrocarbon liquids. At present Australia produces some 65% of its hydrocarbon liquid needs and on the basis of industry forecasts this level of self sufficiency will decline steadily over the next two decades to a figure well below 50%. Clearly, there is a pressing need to increase the level of crude oil recoverable reserves. This may be achieved by increasing exploration activity and/or improving recovery efficiency from existing fields. The former option is well understood both by government and industry, however, despite relatively high levels of exploration expenditure, domestic crude oil reserves continue to decline. The latter option is not so well understood and at this time plays no role in enhancing the national oil resource. Conventional methods of oil recovery, primary production and secondary waterflooding, may be very inefficient and leave some 25 to 75% of the original oil-in-place trapped as residual oil in the reservoir. This residual oil represents a massive national resource which has the potential of contributing significantly to Australia1s future crude oil reserves. Enhanced oil recovery techniques (EOR) are a series of technologically sophisticated oil extraction processes which can recover some of this residual oil resource. In this paper I briefly review the major EOR technologies which may be applicable for Australian conditions and describe recent work which is being carried out in Australia to facilitate the future implementation of these technologies in the field. The work is funded by the Australian government and is part of a combined research program involving a number of Australia's leading tertiary institutions and co-ordinated by the Bureau of Mineral Resources. % It is concluded that EOR technologies will play a significant role in adding to Australia's future crude oil reserves. The research facilities and local expertise now being established will play major roles in the timely introduction of these technologies.

435

TWO FUNDAMENTAL TYPES OF SEDIMENT-HOSTED EXHALATIVE

Pb-Zn

DEPOSITS I.R. Plimer University of New England, Armidale Broken Hill- and Mt Isa-type deposits are regarded as two contrasting fundamental types of Proterozoic submarine exhalative Pb-Zn deposits. Examples of the former are Broken Hill and Pegmont, Australia and the latter are Mt Isa, Lady Loretta, Dugald River, McArthur River, Australia. A number of deposits are regarded as intermediate between the two end members, examples being Gamsberg and Aggeneys, South Africa, Franklin and Sterling, U.S.A., and deposits of the Bergslagen area, Sweden. The former characteristically occur in high metamorphic grade EarlyMiddle Proterozoic deep water distal turbidite-metavolcanic sequences whereas the latter occur in Middle Proterozoic low metamorphic grade shallow water hypersaline emergent shale-carbonate sequences and Palaeozoic low metamorphic grade shallow to deep water shale-carbonate sequences. Both deposit types form immediately after sudden deepening of an ensialic rift. The most common associated igneous rocks are tholeiitic to subalkaline basalts and, with Broken Hill-type deposits, silicic volcanism is not uncommon. A great diversity of unusual rock types with no obvious sedimentary or igneous precursor which derive from water-rock interaction or competing chemical-clastic sedimentation are associated with Broken Hill-type deposits. Exhalite facies for both types are zoned from proximal siliceous and manganiferous facies to distal calcareous and boron-rich facies with no regular distribution for ferruginous, zincian and barian facies. Exhalative Cu-Zn, W and Sn deposits are associated with Broken Hill-type deposits whereas Mississippi Valley Pb-Zn and brecciated sediment Cu deposits are associated with Mt Isa-type deposits. Zonation from Cu-*Zn+Pb-*Mn for Broken Hill-type deposits is in contrast to Mn-*Pb-Zn+ Cu-*Pb-Zn->Mn zonation for Mt Isa-types. The non sulphide fraction of the FeS2-(FeS)-ZnS-PbS Mt Isa ores is identical to the enclosing sediments whereas the non sulphide fraction of Broken Hill-type deposits is enriched in Mn, Ca, P, Fe, F and C0 2 - Primordial S, Sr and Pb isotopic compositions, S-poor phases and base metal-bearing non-sulphides from Broken Hilltype deposits contrast with crustal/biogenic isotopic compositions and S-rich phases for Mt Isa-type deposits. It is suggested that Mt Isa-type deposits form as a result of aborted rifting of thick piles of sediments where convective seawater geothermal systems are established or hypersaline formation waters are exhaled whereas Broken Hill-type deposits form as a result of successful rifting of thin crust, intrusion/extrusion of mafic volcanics, consequent elevation of geothermal gradient and ascent of C029 F, P-rich mantle fluids which induce sediment melting and silicic volcanism, and exhalation of these mantle fluids which mix with seawater at or near the seafloor.

436

THE MURCHISON G O R G E , TASMANIA - A POSSIBLE CROSS SECTION THROUGH A MASSIVE SULPHIDE CIRCULATION SYSTEM 1

D.A. Polya , M . Solomon , C.J. Eastoe 1

and J . L . W a l s h e

9 University of Manchester, U . K . ^Bureau of Mineral Resources, Canberra University of Arizona, Tucson, U.S.A. Australian National University, Canberra

Our current understanding of the geology of the M t Read volcanic belt suggests that most of the numerous massive sulphide deposits between Mt Farrell and M t Darwin are of similar a g e . Near M t Farrell a siltstone dominated unit about 700 m thick (the Farrell Slates) contains several sulphide bodies including the North Mt Farrell galena-sphalerite-pyrite deposits. The Farrell Slates overlie about 3 km thickness of rhyolitic and dacitic volcanics (the Murchison Volcanics) that are exposed, steeply dipping, in the Murchison G o r g e . The base is intruded b y a sill-like granitoid (the Murchison Granite) that extends along strike for about 9 km and is about 1.5 k m thick. Volcanics and sediments beneath the sill are exposed further up the Murchison Gorge. The Slates, Volcanics and Granite may represent the ore horizon, permeable m e d i u m , and heater (respectively) of the classical convection model for the genesis of massive sulphide o r e deposits. The Murchison Volcanics and the Murchison Granite appear to b e comagmatic and coeval, and like calc-alkaline volcanics of orogenic continental margins. The Granite varies from monzonite to quartz monzonite. Both Volcanics and Granite are altered, alteration varying from the Granite to the Farrell Slates as follows (Sericite Zone at top): Sericite Zone Sericite + quartz Sericite + quartz + calcite + K-feldspar + chlorite + hematite Sericite + quartz + chlorite + calcite + hematite ± K-feldspar ± albite Chlorite Zone Chlorite + sericite + albite ± hematite ± magnetite Epidote Zone Epidote + chlorite + calcite + magnetite ± biotite ± allanite Biotite Zone Chlorite + epidote + calcite 4- K-feldspar + biotite The increasing predominance of hematite over magnetite towards the top of the section coincides with a decline in vanadium content and is consistent with an increase in fo2 with distance from the Granite. Neglecting crossfibre, metamorphic-vein chlorites, chlorites from the four zones define fairly clear fields on a M g O v FeO p l o t . Decreasing M g O and increasing FeO coincides with increasing distance from the Granite, trends consistent with decreasing temperature. Pyrite and chalcopyrite occur in the section and display increasing 3t+ 34 6 S values upwards. There is a continuum between 6 S values of sulphides in the Granite (+ 10 permil) and those in the North M t Farrell ores (+ 15 permil). The values are too high to b e solely of magmatic origin, whether from the Granite or the Volcanics, and a major contribution from Cambrian seawater sulfate is indicated. 437

Though not proven, it seems likely that the alteration and 63l+S values are consistent with the type of deep hydrothermal circulation thought to be responsible for massive sulfide formation, and the fluid appears to be largely of seawater origin.

TECTONOSTRATIGRAPHY OF THE DEVONIAN-?CARBONIFEROUS

LAMBIAN

FORELAND BASIN C . M c A . Powell, P.J. Conaghan <5c E.I. Prendergast School of Earth Sciences, Macquarie University, North Ryde, N . S . W . The Lambian Foreland Basin is a NNW-trending Late Devonian to possibly Early Carboniferous basin in eastern N.S.W. between a continental magmatic arc on the east and the Australian craton on the west (Fig. 1). The basement to the basin is the uplifted and deformed Lachlan Fold Belt (LFB), and sedimentation was terminated by the mid-Carboniferous Kanimblan folding. A n incomplete 4.7 km section from one of the structural remnants of the basin near Taralga (Fig. 2) records the interplay of volcanolithic sediment derived from the arc to the northeast and quartzose sediment from the L F B and Australian craton to the west, and, together with palaeocurrent measurements from other structural remnants of the basin, has been used to reconstruct the tectonostratigraphy. A late Frasnian/Famennian transgression (Fig. la) at the base of the section extended as far west as Parkes, and was followed by coarse oligomictic conglomerates and debris-flow pebbly mudstones derived from intra-basinal uplifts. In the Taralga region, these conglomerates have been shed eastward into a N-draining trunk fluvial system. This lower 1 km of the succession is of highly quartzose provenance, and constitutes the widely recognised "Lambie facies11.

The overlying recessive units consist of mudstone, siltstone and volcanolithic sandstone derived mainly from a northeasterly source (Figs, lb and 2). Devitrified microlitic and feldsparphyric volcanic rock fragments and discrete phenoclastic grains of euhedral B-quartz and plagioclase reflect derivation from a dacitic, or possibly andesitic source. Sporadically through the section, and more especially

438

towards the top, are pulses of SW-derived quartzose sediment reflecting the cratonic or LFB source. Regional palaeodrainage in the upper 3.7 km of the section was related to a SE-flowing trunk stream. sand m

L l S i f _

Lithic ^ arenite

sample loc.

l 1

Quartz arenite

O QUARTZOSE SEDIMENT FROM SOUTH

• (2)

•

8*2)

LITHIC

SEDIMENT FROM

<A = 9)

NORTH <n»13)

•(2)

-40

PERCENTAGE

QUARTZ v s

120

VECTOR M E A N

CURRENT

160 CDA

DIRECTION

200

240

280

(OEGREES)

Fig. 2. (A) Measured stratigraphic section with palaeocurrents. Solid black denotes recessive strata. (B) QFR diagram for sandstones from Taralga section. (C) plot of % quartz versus palaeoflow direction, with plus and minus one standard deviation. 439

DEPOSITIONAL AND SOURCE CONTROLS ON THE COMPOSITION CRUDE OILS

T.G Powell Bureau of Mineral Resources, Geology and Geophysics, Canberra The composition of crude oils is the product of the interaction of a number of geological processes, but depositional and source controls are the main arbiters of crude oil composition particularly during the early stages of maturation. The generation of crude oil from terrestrial organic matter is explicable in terms of the mixture of hydrogen-rich and hydrogen-poor components in the source. Hydrogen-rich components include cuticle, spores, suberin, and resin and are capable of generating oil on maturation wheras the structural parts of plants (wood etc) are hydrogen-poor components and generate only gas on maturation. With the exception of resin, the hydrogen-rich components are largely aliphatic and produce paraffinic oils which are depleted in aromatics, oxygen, nitrogen and sulphur bearing compounds and asphaltene. Wax contents are variable. High wax oils are favoured where fungal and bacterial attack on the cellulose and lignin components of terrestrial organic matter concentrates the cuticular components in the source. This occurs during flooding of a peat swamp or in a lacustrine setting. Resinite-rich terrestrial organic matter gives rise to oils enriched in cyclic and aromatic components, but depleted in ONS and asphaltene components. These oils tend to form at an earlier stage of maturation because of the thermal lability of resinite. The composition of marine oils is dependent on the nature of the source environment. Oils derived from source rocks formed in clastic environments are paraffinic-naphthenic to intermediate in composition and have low sulphur contents. Oils from source rocks formed in restricted environments (meso-saline or hypesaline conditions) are aromatic to asphaltic in composition and have high sulphur contents. These differences reflect variations in the depositional and early diagenetic conditions in the source. In clastic environments detrital iron oxides react with hydrogen sulphide produced by sulphate-reducing bacteria to form iron sulphides. In carbonate source rocks significant concentrations of iron oxides are absent and the hydrogen sulphide reacts with organic matter, to give sulphur-rich kerogens which appear to be more thermally labile than their clastic counterparts.

THE ROLE OF PETROLEUM GEOCHEMICAL RESOURCE EVALUATION

STUDIES IN

T.G. Powell Bureau of Mineral Resources, Geology and Geophysics, Canberra Geochemical considerations of the processes of petroleum generation and entrapment are important components of the resource evaluation process particularly in frontier regions. Geochemistry attempts to answer the following questions: 1. Does the section have the potential to source hydrocarbons? 2. What is the nature of the hydrocarbon product? 3. Has migration occurred? 4. What is the relationship between the reservoired hydrocarbon to the sequence in which it is reservoired? Namely is the source local or distant a) from a maturation standpoint and b) from a source facies standpoint? 440

5. 6. 7.

What is the timing of hydrocarbon generation to trap formation? What are the amounts of hydrocarbons that might have migrated? What are the effects, if any, of alteration on the reservoired hydrocarbon?

In new exploration regions, there is a high degree of uncertainty concerning the answers to these questions and in play evaluation specific answers and risks must be assigned. Further, a general application of oil and gas generation model can be extremely misleading. As data becomes available it is necessary to develop and apply the specific variant of the oil and gas generation model appropriate to the region concerned if meaningful use of geochemistry in resource evaluation is to be achieved.

GEOCHEMISTRY

OF LOWER PALEOZOIC OILS AND ROCKS, ONTARIO, CANADA

SOURCE

T.G. Powell Bureau of Mineral Resources, Geology and Geophysics, Canberra Oils from southwestern Ontario can be divided into three genetic families which are broadly related to the stratigraphic level of their reservoirs: Cambro-Ordovician, Silurian and Devonian. The families have been defined on the basis of gross composition, n-alkane distributions, pristane to phytane ratios, carbon isotope distributions in the saturate and aromatic fractions, distributions of twenty-five gasoline range hydrocarbons and ring distributions in the aromatic fractions. The specific family compositions permit recognition of two instances in which there has been migration from Ordovician source beds into Silurian reservoirs. Analysis of rock samples has led to the identification of petroleum source rocks in Ordovician and Silurian strata and an immature potential source in Devonian strata. Crude oil source correlations are based on characteristics of saturate and aromatic fractions and carbon isotope distributions. The composition of Cambro-Ordovician and Devonian oils is fairly typical of oils derived from marine organic matter, but the composition of the Silurian oils reflects the restricted nature of the source environment which is transitional between the open marine conditions of the underlying carbonate platform and the restricted environment of the overlying evaporites. The aromatic fractions of the Silurian oils contain large concentrations of aryl isoprenoids ranging from CJJ to £>22* ^^ely precursors are aromatic carotenoids which are found in some photosynthetic bacteria. The concentrations of these compounds can be attributed to depositional conditions in which the species diversity is restricted because of high salinity, but the productivity is high because of the availability of nutrients.

ROLE OF ORGANIC MATTER IN PRECIPITATION OF LEAD-ZINC SULPHIDES AT PINE POINT,CANADA T.G. Powell1 and R.W. Macqueen2 1

Bureau of Mineral Resources, Geology and Geophysics, Canberra ^University of Waterloo, Ontario, Canada

Bitumen is a common associate of carbonate-hosted lead-zinc deposits. The Pine Point lead-zinc field, NWT Canada is typical in this regard. It is located in a Middle Devonian carbonate barrier complex and is thought to have originated by normal sedimentary and diagenetic processes. Organic geochemical studies indicate that the host rocks occur 441

at the threshold of petroleum generation (ca 60°C) and that the heavy oilbitumen has originated, more or less in situ, from the relatively immature organic-rich rocks in the barrier complex. Fluid inclusion data indicate that the dolomitised and mineralised zones represent thermal anomalies (up to 100°,C) with respect to the host rocks. Within these zones, heavy oils and bitumens, have been altered by heat and reaction with sulphur to form an insoluble pyrobitumen. Unaltered bitumens have atomic H/C ratios of ab^jit 1.4, sulphur contents of about 7.8% and sulphur isotope ratios (6 S) of about +4.6 per mil. Altered bitumens have atomic H/C ratios of about 1.02, the sulphur contents average 22% and the 6 S values are about 12.4 per mil. Samples with the lowest atomic H/C rat^s have the highest atomic S/C ratios. There is also an increase in 6 S valire with increasing sulphur content and the most altered bitumens have the most positive 6 S values. Isotopically heavy sulfur was added during the alteration process. The transformation of an unaltered bitumen to an altered bitumen by reaction with sulfur must have the form: (1)

10C30H45SC)+98S(C30H30S4)1003+7H20+68H2S

Hydrogen sulphide is a major product of this reaction and could be the means of precipitating the metals at Pine Point. 34 . • The increase in 6 S values of bitumen with thermal alteration is similar to that observed for sulphur in oils and gases in some petroleum basins which is thought to occur by the following processes. (2) SO,2" + 3H0S — » 4S° + 2Ho0 + 20H~ 4 z I (3) 4S° + 1.33 (CH2) + 2.66 H 2 0

4H 2 S + 1.33 C0 2

Equation 3 represents complete oxidation of organic matter whereas at Pine Point (Eq 1) oxidation of bitumen was incomplete and was accompanied by extensive sulphurisation. Hydrogen sulphide is both a reactant and a product and is required to initiate the reaction. 2Sulphur ^sotopic data from the various sulphur species at Pine Point (SO^ , S , S , and Organic-S) are consistent with a mechanism for sulphide generation based on equations (2) and (1). Mass balance considerations also show that the amount and degree of alteration is more than adequate to account for the reduced sulphur species (lead, zinc and iron sulphides) deposited at Pine Point. This mechanism may have provided an important means of generating the large volumes of sulphide necessary to precipitate sulphide ore bodies in sedimentary carbonate rocks.

THE GEOCHEMISTRY OF PHONOLITES AND TRACHYTES FROM THE SUMMIT REGION OF MT. KENYA R.C. Price1, R.W. Johnson2, C.M. Gray1, and F.A. Frey3. 1 La Trobe University, Bundoora Bureau of Mineral Resources, Canberra 3 M.I.T., Boston, Massachusetts

The summit region of the Pliocene-Pleistocene volcano of Mt. Kenya is dominated by phonolitic extrusives and intrusives. The main eruptive phase phonolites and syenites have 8 7 Sr/ 8 6 Sr initial ratios in the range 0.70359-0.70365, although two of the oldest samples studied have higher initial ratios (0.70373-0.70380). The central main phase activity was post-dated by flank eruptions of trachyte, phonolite and basalt. The later felsic eruptives are less undersaturated than the main phase volcanics and intrusives and have lower initial 87 Sr/ 86 Sr ratios. 442

All the samples examined in this study appear to have similar mantle sources and the suite is characterised by constant Zr/Nb ratios and Zr/Th ratios; a feature of individual volcanoes associated with the East African Rift system. The suite of analysed samples represents a variety of processes operating at different levels within the crust and possibly the upper mantle and although individual groupings appear to be related by a specific crystal fractionation controlled process combination of all the data leads to apparent trends on variation diagrams which are unusual. For example, within the main eruptive phase MgO and Zr are positively correlated. The Mt. Kenya suite reflects the variety of processes which can lead to phonolitic residual melts within individual alkalic provinces.

GEOCHEMICAL AFFINITY OF VOLCANIC ROCKS FROM THE NORTHERN MELANESIAN BORDERLAND R.C. Price 1 , K.T.M. Johnson 2 , and J.M. Sinton 2

Trobe University, Bundoora Hawaii Institute of Geophysics, Honolulu

During the first leg of the tripartite funded cruise of the R/V Kana Keoki in 1982, igneous rock samples were dredged from 11 sites along the general line Samoa to the Vitiaz Trench, enabling definition of petrographic provinces which have some bearing on the tectonic interpretation of the region. The Samoan alkalic magmatic province extends westward with increasing age to Combe Bank. Some of these lavas are ultra-alkalic and are probably similar to the post-erosional lavas of Samoa. Tholeiitic lavas of two types were recovered. The basalts of the North Fiji and Lau Basins are typical of spreading centre lavas from elsewhere. In contrast tholeiites dredged from the flanks of the H o m e Islands are strongly depleted in large ion lithopile elements and may represent primitive arc volcanism associated with subduction along the LauVitiaz system. Quaternary alkalic volcanism is widespread throughout the region, e.g. Wallis, Rotuma and Taveuni and relates to plate reorganisation in the region.

GEOCHEMISTRY OF BASALTS FROM THE WEST INDIAN OCEAN TRIPLE JUNCTION: EVIDENCE FOR PRIMARY MAGMAS AND MAGMA MIXING AT AN ACTIVE RIDGE SYSTEM R.C. Price 1 , M.R. Sneeringer 2 and F.A. Frey 2 ^La Trobe University, Bundoora M.I.T., Boston, Massachusetts

Fresh basalts from the West Indian Ocean triple junction have major and trace element contents similar to MORBs from other active ridges. K (762-925 ppm), Rb (1.07-1.30 ppm), Cs (0.015-0.22 ppm), and Ba (13-15 ppm) are all low in abundance and the chondrite normalised rare earth element patterns show a depletion in light relative to heavy rare earth elements. The West Indian Ocean triple junction basalts are enriched in radiogenic strontium relative to basalts from other active ridges, suggesting that depletion of the mantle in large ion lithophile elements occurred later in the southern Indian Ocean Basin than in mantle underlying the other ridge systems. 443

P l a g i o c l a s e p h e n o c r y s t s i n b a s a l t s from t h e W e s t Indian O c e a n t r i p l e junction show reverse zoning i n m a n y c a s e s . G l a s s i n c l u s i o n s w i t h i n reverse-zoned p l a g i o c l a s e p h e n o c r y s t s v a r y s y s t e m a t i c a l l y i n c o m p o s i t i o n from t h e core to t h e r i m o f t h e h o s t a n d this v a r i a t i o n is correlated w i t h compositional v a r i a t i o n in t h e h o s t . T h e reverse zoning a n d g l a s s inclusion compositional v a r i a t i o n m a y indicate that m a g m a m i x i n g w a s a n important p r o c e s s in t h e g e n e r a t i o n o f t h e h o s t b a s a l t s . T h e effects o f disequilibrium crystallisation o n p l a g i o c l a s e growth is n o t clearly understood and could b e important i n t h e d e v e l o p m e n t o f reverse z o n i n g . R a r e , h i g h l y - c a l c i c , p l a g i o c l a s e m e g a c r y s t s contain glass inclusions which are strongly depleted in T i 0 2 a n d K 2 0 a n d h i g h l y e n r i c h e d in M g O , relative to F e O , and i n C a O . These inclusions appear to r e p r e s e n t a near p r i m a r y m e l t which originated at r e l a t i v e l y h i g h p r e s s u r e . A l l other glasses h a v e compositions suggestive o f low p r e s s u r e e q u i l i b r a t i o n a n d crystal f r a c t i o n a t i o n .

GEOPHYSICAL

E V I D E N C E FOR THE R I F T I N G OF THE U N D E R L Y I N G THE SYDNEY BASIN

BASEMENT

I.R. Qureshi University of N e w South W a l e s , Sydney

The Sydney Basin contains mainly sedimentary rocks belonging to the Permian and Triassic periods, whilst the Lachlan Fold Belt has moderately folded rocks of the Lower Palaeozoic era. The average density of the Sydney Basin rocks is considered to be 2.45 tonne m"3 and that of the Lachlan Fold Belt rocks 2.7 tonne nf3. The general configuration of the basin is known from deep wells and a seismic reflection survey (Mayne et al. f 1974). The maximum thickness of the sediments exceeds 3 km. An earlier gravity survey conducted by the Bureau of Mineral Resources indicates an eastward increase in gravity, culminating in a gravity high across the western flank of the basin (op.% cit.). A fresh survey was undertaken to further delineate and investigate the nature of this high (Qureshi, 1984). Measurements were made at a spacing of 2 to 3 km along selected traverses and terrain corrections were applied. The accuracy of reduced Bouguer anomalies is estimated to be 1 mgal. Quantitative interpretation of the anomalies is carried out along a representative east-west profile between Bathurst and Sydney. An Airy-type isostatic model is used to compute the gravity effect arising from the Blue Mountains and the continental margin on the assumption of a thickness of 33 km for the continental crust and a density contrast of 0.35 tonne m~3 at the crust-mantle boundary. The effect of the Sydney Basin sediments is computed up to the ground surface. These two effects are subtracted from the Bouguer anomalies. A small regional gradient of 0.14 mgal/km persists in the corrected anomaly profile implying perhaps a greater crustal thining than the one assumed in the isostatic model. The dominant feature of the corrected profile is, however, a slightly asymmetric gravity high of some 44 mgal magnitude with its apex about 10 km east of the Lapstone Monocline (Fig. 1). The 'half-width' of the anomaly being 35 km, sources with realistic density contrasts are likely to lie within the upper crust and probably just below the basin sediments i.e., the base of the Early Permian Rutherford Formation. An aeromagnetic anomaly has contours of similar shape and coincides with the gravity high and this is indicative of the mafic nature of the source. Although Early Permian Dalwood Group and its equivalents have significant mafic componets and deep wells have intersected up to 1 km of the Group (without bottoming), they extend over the whole width of the basin and have a southern boundary whereas the gravity high 444

extends beyond this boundary and occupies only the western part of the basin. This suggests that the major source of the anomaly my be an older igneous complex probably of Carboniferous age. The gravity high is modelled on the assumption that its source lies beneath the Rutherford Formation. Models with density contrasts ranging from 0.15 to 0.25 tonne m"3 are considered acceptable and the one with the median value is shown in Fig. 1. The western flank of the source has easterly dips ranging from H0° to 70° with an average value of 53° (in contrast to an average dip of 11° at the base of the Rutherford Formation). These steep dips indicate the presence of a major basement fault beneath the Lapstone Monocline-Kurrajong Fault System. The westerly dips on the eastern flank range from 21° to 33° and this flank may be formed by a series of step faults. Although these inferred faults did not propagate upwards into the Permo-Triassic strata, the western fault seems to have controlled sedimentation (Harrington & Brakel, 1981) and is expressed as a warp. There is evidence for small scale movement and deformation along the LapstoneKurrajong Fault System since the Permian and the recent earthquake activity may be ascribed to small adjustments that may be taking place along the basement fault. Both the shape and the size of the source are indicative of the rifitng of the basement underlying the basin. The inferred steep and inward dipping faults are similar to the boundary faults of a typical rift structure and the large size of the source gives a measure of the considerable crustal extension that preceded the development of the Sydney Basin. Scheibner (1973) postulated the existence of such a rift in Proto Sydeny Basin during the Late Carboniferous-Early Permian times. Fig. 1

The gravity high and its interpreted source on natural scale. Dots represent the calculated effect of the source underlying the Sydney Basin (shown by full thick lines). The broken line with a dip of 53° is the best straight line that fits the eight depth points on the steep portion and marks a major basement fault inferred to underlie the Lapstone Monocline. Broken lines to the east show that this side may well be formed by a series of step faults. The horizontal scale follows the map grid of Figure 1.

mga!

445

References HARRINGTON, H.J. & BRAKEL, A.T., 1981, Western Coalfield Symp., Abstr. N.S.W. Inst. Technol. MAYNE, S.J., NICHOLAS, E., BIGG-WITHER, A.L., RASIDI, J.S. RAINE, M.J. 197^, Geology of the Sydney Basin - a review. Aust. Bur. Miner. Resour.,Geol. Geophys., Bull., 1^9. Qureshi I.R., 1934. Geol. Soc. Aust. J. (in press). SCHEIBNER, E., 1973, Geol. Soc. Aust., J., 20, 405-26.

C O A L SEAM G E O M E T R Y AS A P R E D I C T I V E TOOL TO I N T E R P R E T D E P O S I T I O N A L E N V I R O N M E N T S A N D P A L E O G E O G R A P H Y OF ASSOCIATED CLASTIC ROCKS R.A. Rahmani Canadian Hunter Exploration, Calgary, Alberta During the past 20 years coal sedimentologists have extensively utilized the facies models approach of clastic rocks to interpret depositional environments of their enclosed coal deposits. Concurrently, workers on modern peats related various chemical and physical parameters of peat to surrounding sediments, therefore supplying invaluable data to help sharpen predictive models of coal depositional environments. Commercial coal deposits were found associated with alluvial fan, fluvial, deltaic and backbarrier environments. Deltaic sequences appear to contain the most prolific coal deposits. Although coal facies models are now undergoing and will still see considerable modifications and refinements, we now seem to be reaching a stage whereby we can utilize the existing array of coal facies models to extract a set of diagnostic coal geometries which in turn can be used to interpret the depositional environments of their host clastic rocks. Exploration geologists of the petroleum industry, for some time now, have been using the distribution, geometry and seaward termination of coal seams to infer various aspects of the paleogeography of the areas they are exploring, such as positions of shorelines. In areas where samples and cores are sparse, where sandstones are diagenetically highly altered, or where gamma logs are in short supply, coal distribution maps made from available geophysical logs can be quite helpful in shedding some light on the interpretation of associated clastic rocks. Furthermore, coal is much easier to characterize than sandstone in digitized logs, making it a simpler lithology to computer-map from digitized logs. Such computer-generated maps can be generated at the earliest stages of exploration to help in the early recognition of thick reservoir buildups, based on the premise that thickest sandstone occurs in areas of very thin or no coal. It should be pointed out, however, that for this approach to be sound and effective, the coal and associated clastic rocks should be genetically related. The following examples, as well as others, will be used to illustrate this potentially useful predictive tool. Fluvial and upper delta plain coals from Upper Cretaceous of Alberta and Eocene of Texas occur as basinward, dip-elongated belts forming between bifurcated networks of similarly trending sandstone belts. The potential reservoir-type fluvial sands can be prospected for in between areas of thick coal. In the lower delta plain of river-dominated Upper Cretaceous Ferron Sandstone delta in Utah, coals occur as narrow linear belts parallel to shoreline, some predictable distance landward from the shore - parallel delta-front sandstone. In this example reservoir-type sandstones of the delta-front are predictable some distance seaward of the shoreline-parallel coal. This and similar examples from the Upper Cretaceous Blackhawk Formation of the Wasatch Plateau in Utah and from the Lower Cretaceous 446

Falher Member of northwestern Alberta show a complicating effect that contemporaneous distributary channels exert on this simple model. The channels will break up the simple coal linear belts into stringbean-shaped pods of thick coal, with the thins being underlain by a potentially reservoir quality channel sandstone. In the Blackhawk Formation example, the coals associated with the upper reaches of the distributary channels, — updip from shoreli ne parallel coals, are pendicular to shoreline.

RECOGNITION OF MINERALIZING PLDTONS IN GRANITOID TERRAINS: A CASE HISTORY IN THE ARABIAN SHIELD Colin R. Ramsay Directorate General of Mineral.Resources, Jeddah, Saudi Arabia Calc-alkaline granitoid rocks in 80 or more plutons of late Proterozoic age underlie about 60 percent cf the mountainous Midyan region, east of the Gulf of Aqabah and the northern Red Sea. Following the discovery (by radiometric methods) of a large radioactive granite, the Saudi Arabian Directorate General of Mineral Resources has conducted an integrated regional assessment of about 20,000 sq. kms of this terrain, using Landsat interpretation, mapping, radiometric surveys, drainage sediment geochemistry, and petrological studies. The plutonic rocks have been grouped into five lithostratigraphic suites on the basis of their field, petrographic, and chemical features (Ramsay and others, in press a). Two of these suites are "mineralizing" in the sense that they were parental to mineral occurrences of some economic interest; the others appear to have no mineral potential. The barren suites include most of the plutonic rocks. The oldest is the Muwaylih suite, consisting of trondhjemite, tonalite, quartz diorite, diorite and gabbro, emplaced in an oceanic island arc environment about 725 Ma ago. The most voluminous is the Ifal suite, an assemblage of biotite-hornblende monzogranite, granodiorite and quartz monzodiorite, emplaced about 625 Ma ago in large oval to irregularly shaped plutons with numerous intra-plutonic dykes. The Atiyah monzogranite unit consists of massive biotite monzogranite to syenogranite, formed about 599 Ma ago, probably by fusion of igneous lower crustal material. These three suites are of I-type, with unexceptional trace element compositions. The mineralizing suites consist mainly of alkali-feldspar granite varieties : (1) The Midyan suite consists of coarse grained, equigranular, arfvedsonite-perthite alkali granite and hornblende-perthite alkali-feldspar granite. These rocks are peralkaline to metaluminous, with distinctively low contents of CaO, MgO and Sr, and a characteristic agpaitic trace element signature with high Be, Ce, La, Nb, Nd, Y, Zn and Zr. Minor specialized phases are more strongly enriched in these trace elements. (2) The Haql suite consists mainly of coarse grained, equigranular perthite leucogranite with traces of biotite. These rocks are metaluminous and highly siliceous (72-78 percent Si02). Contents of Ti02, A1 2 0 g , total Fe, MgO, CaO and P 0 are low, and the trace element signature is 4tlso distinctive, with low ba, Li and Sr, but high Rb. Specialized varieties have enhanced contents of Be, F, Li, Nb, Rb and Y, very low Ba and Sr, and sporadically high values of Sn, Ta, and W. Mineralization of two types is known : (1) Nb, Zr, rare earth elements, and other rare metals are disseminated in veins, pegmatites and mineralized alkali granites spatially and genetically related to the Midyan suite (Drysdall and others, in press); and (2) Sn, in some cases with W, Ta, and/or Nb, is concentrated in small metalliferous pegmatites and quartz veins associated with specialized varieties of the Haql suite. 447

Recognition of the mineralizing suites. Roof zones, cupolas, daughter stocks, and contact zones of Midyan and Haql suite plutons, and comparable rocks elsewhere in the Arabian Shield, are favourable exploration target areas. These mineralizing suites can be recognized by a number of qualitative and univariate quantitative parameters, but the most efficient technique is the computerized application of multivariate classification functions which have been derived using stepwise discriminant analysis (Ramsay and others, in press a,b). Classification functions based on major oxide analyses give a high rate of classification success; functions based on more readily available (even semi-quantitative) trace-element analyses can also be successfully applied. Plotting two canonical variables, as in the figure, provides a graphical means of classifying samples, but is not as successful as using the classification functions. C7> O O m CN

*t b* ^ o O 0)

CANONICAL VARIABLES FOR RECOGNIZING MINERALIZING GRANITES IN THE MIDYAN REGION T

1 Fields of mineralizing suites are shaded.

S CN +

c O 5 CD in m r» o

Xci o CN id 2

5 o+

Midyan suite QiSSoiv\

Ifal suite

N. \

ywuwaylih suite

•

in CO

Haql suite

Atiyah suite

<fq £ ? gj. o

I -5.0

0.0

i 5.0

•

10.0

-0.500(SiO 2 )+0.540(MgO)-0.313(Na 2 O)-2.828(K 2 O)-0.711(FeO t )+50.139

The mineralizing suites of the Midyan region (and the multivariate classification functions which identify them) may well be different from those of other regions, but the techniques outlined above may well be useful elsewhere. They can be used for preliminary, automated screening of pre-existing analytical data-bases in prospective areas, or for more refined classification and assessment in better studied regions.

References Drysdall, A.R., Jackson, N.J,, Ramsay, C.R,, Douch, C.J,, & Hackett, D., in press, Economic Geology. Ramsay, C.R., Drysdall, A.R., Clark, M.D., & Odell, J., in press a, Saudi Arabian Deputy Ministry for Mineral Resources Bulletin. Ramsay, C.R., Rowaihy, M.N., & Odell, J., in press b, King Abdulaziz Univ. (Jeddah) Fac. Earth Sci. Bull.

448

METALLOGKNY AND TECTONIC DEVELOPMENT OF THE TASMAN FOLD BELT SYSTEM IN VICTORIA W.R.H. Ramsay and A.H.M. VandenBerg Geological Survey, Department of Minerals and Energy, Melbourne Current evidence suggests that most of Victoria is underlain by a relatively thick (20km + ) basement of sialic composition of assumed Proterozoic age. This basement is nowhere exposed and its structural relationship with exposed Palaeozoic rocks is conjectural. This uncertainty has resulted in both ensimatic and ensialic tectonic settings being proposed for Victoria during the Cambrian. Mineralization associated with Cambrian igneous activity shows a variety of styles from minor orthomagmatic chromite deposits, through Au and Cu deposits of syngenetic or epigenetic origin, to Fe-Mn, Ba occurrences of exhalative volcanogenic affiliation. Cambrian volcanism and associated sedimentation was followed by the deposition of dominantly quartz-rich turbidites with interbedded shale and siliceous units. Associated black shales may be phosphatic, but economic concentrations are scarce. Subsequent to the Benambran Orogeny, late Silurian crustal extension caused several rifts to open along roughly orthogonal NW-SE aligned fractures, representing the first phase of the Buchan Rift. Within the fault-bounded depressions, thick acid volcanic sequences (Thorkidaan Volcanics, Mitta Mitta Volcanics) were deposited in close association with shallow marine sediments (Enano Group, Wombat Creek Group: mudstone, limestone, and quartz-rich sediment). Mineralization in these Upper Silurian rocks comprises polymetallic base-metal sulphide lenses and minor disseminations. At least in some instances (Currawong and Wilga prospects) these sulphide concentrations appear to be of exhalative volcanogenic type and are time-equivalents of the Captains Flat and Woodlawn deposits of NSW. The Silurian rifts were obliterated and their rocks strongly deformed during the Bindian (Bowning) deformation at about the Silurian - Devonian boundary. This in turn was followed by another episode of crustal extension and rifting, during which the formation of a broad meridional trough marks the second phase of the Buchan Rift. A very thick sequence of largely subaerial acid volcanics (Snowy River Volcanics) is overlain by shelf limestone and mudstone (Buchan Group). A variety of base metal, barite, manganese, iron mineralization is hosted by the Snowy River Volcanics and subsequent shelf sediments and active company exploration is continuing in these areas. The Tabberabberan Orogeny was followed in the Late Devonian by acid volcanism and granite intrusion, and "redbed" type non-marine sedimentation . In Central Victoria, thick acid volcanics were erupted into a series of cauldron subsidences and intruded by comagmatic granites. Acid volcanism also occurred in the Howitt Province further east, but was followed by deposition of extensive fluviatile and lacustrine sediments (mainly mudstone and sandstone, minor conglomerate). In the Mansfield Basin, these contain minor sedimentary copper occurrences. There are four distinct episodes of granite emplacement in Victoria namely Late Cambrian - Early Ordovician (Delamerian) in the Glenelg Zone; Early Silurian (Benambran) in the Highlands Zone; Early Devonian (Bindian) in the Grampians, Ararat - Bendigo, Highlands, and Mallacoota Zones; and the Middle Devonian - Carboniferous (post Tabberabberan) in the Ararat Bendigo, Melbourne, Howqua, and Highlands Zones. In and immediately adjacent to the Melbourne Zone several intrusions are closely associated (comagmatic) with thick sequences of extremely rapidly extruded acid cauldron

449

volcanics. Data for the Delamerian granitoids are sketchy, but in the remaining groups S-type granitoids predominate with the exception of eastern Victoria, east of the Yalmy Fault (S-I line), where I - and A type granitoids only occur. A variety of Sn, Mo, W deposits and prospects are associated with .the Benambran and younger intrusive phases. Economically the single most important mineral in the history of Victoria has been gold. Total recorded production to the end of 1981 is 2 449 388 kg of which some 40% came from reef workings. Primary gold occurs in a number of geological settings including veins and disseminations spatially associated with mafic Cambrian volcanism previously discussed, as vein deposits in turbiditic sequences of central and eastern Victoria, as veins within mafic intrusives of Mid to Late Devonian age, and as trace amounts associated with a variety of mineralizing styles and associations - such as the Ararat copper body which contains 0.6 g/t Au.

A REINTERPRETATION OF THE BALLARAT EAST GOLDFIELD D.M. Ransom1 and F.L. Hunt2 1Consultant, Adelaide, 2Consultant, Melbourne The Ballarat East Goldfield produced 32,469 kg of gold from 3,738,886 tonnes quartz mined in the period 1861 to 1917, Mining commenced in 1858 and production peaked about 1905. During the period 1887-1918, nine significant mines operated on the field, which became geographically defined as a narrow corridor about 400 metres in width and 6 kilometres in length extending south from the centre of the present City of Ballarat, Of these mines seven operated without a significant break during this time, together producing about 98,000 tonnes of quartz yielding about 1,050 kg gold per year. Non-geological factors constrained the operating companies largely to along strike and vertical development. Hence outside the corridor defined by the known mineralization, gold potential is undefined. Despite the economic significance of the Ballarat East Goldfield, the geological interpretation has remained unchanged since the publication of Baragwanath (1923). The present interpretation has been compiled from available published and unpublished mining and geological data dating from the commencement of mining in Ballarat. These include the factual material used in Baragwanath (1923). The Ballarat region is underlain by Lower Ordovician sandstones and shales and by Tertiary to Pleistocene lake deposits, alluvials, and basalt flows. The Ordovician sequence contains certain thin (<0.05m) marker horizons of moderate continuity, mainly carbonaceous shales, some of which are associated with the gold-quartz lodes and known as "Indicators". The Ordovician rocks are folded about approximately meridional mainly shallow south plunging axes, and intruded by acid and basic dykes. On a regional scale, axial surfaces of folds are usually subvertical but within the Ballarat East mineralized corridor they are westerly dipping at about 70 degrees. Three types of quartz lode are associated with these easterly tilted folds, namely "leather jacket" reefs, "breached fold axis" reefs, and "spurs". The first two are closely associated with the eastern limbs of the tilted anticlines. Leather jacket quartz lodes are 45 degree west dipping bodies associated with pug-filled faults which are optimally developed between the axial planes of an anticline to the west and a syncline to the east. Leather jacket reefs occasionally form vertical arrays, with individuals separated by about 50 metres. The breached fold axis reefs are steep west dipping stockwork-like zones which lie along the axial surfaces of the folds, preferentially at the terminations of the leather jacket reefs. They may be a form of saddle reef. Spurs, which are narrow east dipping fissures, occur throughout the corridor and on the margins of the other quartz bodies, occasionally defining them.

450

They are noted for their nuggets where they intersect the Indicators. A single anticline (the First Chance Anticline)/syncline pair, about 100 metres in width and 6 kilometres in length, contains most of the worked quartz orebodies of Ballarat East. A further series of significant quartz lodes occurs in the Sulieman Pasha Line 150 metres to the west, which defines the western boundary of the mineralized corridor. The leather jacket reefs are mineralized shear fractures of apparent reverse fault geometry empirically associated with the eastward tilted folds. Cause and effect are difficult to distinguish but the writer favours the view that the tilting is a manifestation of regional kinking which post-dates the regional folding, and that the quartz reefs and their associated structures are the product of related brittle-ductile failure. The leather jacket faults associated with the mineralization are coeval with quartz deposition and certain dyke intrusions. They fade out in the western limb of the First Chance Anticline and do not appear to be through-going structures. The leather jacket reefs and the spurs are symmetrically related. The spurs are geometrically and morphologically identifiable as tension gashes and are normal to the principal strain axis as interpreted from the geometry of the leather jacket reefs. The leather jacket reefs and spurs bear an asymmetrical relationship to the fold axes. A model of roughly coeval deformation, metamorphism and gold introduction is proposed. Gold was presumably introduced from depth at the time of late deformation and the quartz probably derived from local metamorphic fluids. The carbon content of the Indicators is no doubt a significant factor in nugget formation. The leather jacket reefs at Ballarat East are analogous to the Wattle Gully Reef at Chewton, the main difference being their repetitive nature. Two Indicator beds are recognized in the present interpretation, as opposed to the one interpreted by Baragwanath (1923). The northern, or lowermost stratigraphically is "The Indicator" which is folded out of the anticline/syncline zone in the Normanby North Mine in the south and near the Queen Shaft of the Victoria United Mine in the north. To the south of the Normanby North Mine, the "Eastern Indicator" is the main Indicator bed. The enveloping surface of the folds at Ballarat East is interpreted as dipping 25 to 30 degrees to the south-east. Gold localization is almost entirely dependent on structure, unrelated to stratigraphy except in the broad sense of being located in rocks of somewhat more shaly character, hence possibly more amenable to brittle-ductile failure. Recognition of two Indicator beds implies these sediments are not unique within the stratigraphy but are important only in localization of the coarser nuggets. The critical structural feature of the environment of Ballarat East is the tilting or overturning to the east of fold axial planes, which sets the Ballarat East Goldfield apart from its surroundings. Further tilted folds occur to the east of the main anticline/syncline zone but probably not to the west of the Sulieman Pasha Line. The auriferous corridor terminates at Black Hill in the north where the leather jacket reefs lose their continuity and become zones of spurs, and on a major cross-fault in the south, past which quartz reef structures of the Ballarat East-type are only weakly developed. Potential for further gold orebodies at Ballarat East is seen primarily in a repetition of the main ore-bearing structure to the east of the main productive zone and also in unexplored extensions of quartz bodies mined previously. A parallel tilted fold structure, the Eastern Anticline, is known to contain gold-quartz reefs which were incompletely developed prior to the flooding of the lower levels of the mines in 1916. An exploration programme to drill this structure in late 1984 is planned.

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Eastern Copper Mines N.L. and Kinglake Mining N«L« are acknowledged permission to publish this paper.

for

Reference Baragwanath, W., 1923, Geol. Surv. Vict., Memoir 14.

AUSTRALIAN ROLE IN GEOSCIENCE EDUCATION - AID IN MODERN 6E0SCIENCE CURRICULUM DEVELOPMENT IN SOME ASIAN TERTIARY INSTITUTIONS - A CASE STUDY Anwarul Qadeer Rathur Western Australian Institute of Technology, Bentley

As one of the aims of this workshop is to identify the geoscientific needs of the developing countries in Asia and how Australia can best aid to fulfil some of these needs, this paper presents a brief background to the development of geoscience education in Pakistan with Punjab University, Lahore, as the example. Australia has played an important role in the development of geology at Punjab University since it started in 1953 under the auspice of UNESCO. It provided teaching staff through UN agency and also later trained Pakistani staff to take over the role of geoscience education in Pakistan. Lately Australia has been participating in cooperative efforts of a different type. In 1972, under the International Commission on Geodynamics, the Geological Survey of Pakistan initiated a project on "Geodynamics of Pakistan11 in which there were active participation and contributions from Macquarie University and Australian National University. Even Farah and DeJong (1979) has acknowledged this cooperation in the following manner, 11 Several Pakistani earth scientists received advanced training. Some went abroad (USA and Australia) to participate in the study of rock samples from Pakistan in specialised laboratories, others presented the results of their research at conferences and 11 seminars . The author has been involved in geoscience curriculum development at Punjab University recently and feels that Australia can help by providing assistance in this direction in two ways. Firstly to develop geoscience curriculum in order to improve geoscience education in Pakistan. The second purpose of geoscience curriculum development is to make geoscience education more relevant to needs of local industry and government. All this is aimed to lay a strong foundation for natural resources development in Pakistan. This can be achieved both at personal and institutional level with different governmental agencies acting as coordinator. Reference Farah, A., & DeJong, K.A. 1979, Geodynamics of Pakistan: An Introduction in Geodynamics of Pakistan (Abul Farah & Kees A. DeJong, editors): Geological Survey of Pakistan, Quetta, 1-4.

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GEOLOGY

OF RUBY HILL A N D O T H E R B R E C C I A - F I L L BINGARA, N.S.W.

DIATREMES

L.R.Raynor Department of Geology and Geophysics, University of Sydney, Sydney At least four breccia-fill diatremes occur in the Bingara area. All are close to major fault systems,the Ruby Hill and Miowera diatremes just west of the Peel Fault system,and two unnamed diatemes near the HunterMooki Thrust 50km to the west. Ruby Hill exposes two episodes of breccia fill and two of basalt intrusion; the basalt occurs as rounded blocks in the breccia and as radial dykes intruding it. The Miowera diatreme, which consists of at least two (and possibly four) separate, closely spaced diatremes contains two episodes of breccia fill, but no basalt. The two unnamed diatremes near the Hunter-Mooki Thrust are virtually unexposed, but also appear to contain no basalt. Two main inclusion types are found at Ruby Hill in both the basalt and the breccia, although those from the latter are highly altered. These are: (a)

Upper crustal inclusions (mainly clastic sediments, with rare metabasalt blocks), sometimes in blocks up to one metre across. These inclusions are common in the breccia but rare in the basalt.

(b)

Smaller lower crustal to upper mantle types, mainly of garnet pyroxenites and garnet granulites, with some spinel lherzolites.

Study of garnet chemistry has shown distinctions between garnet from pyroxenites and granulites. Similar grouping of garnet analyses from heavy mineral concentrates prepared from the Miowera breccia suggests that this diatreme contains a suite of inclusions similar to that of Ruby Hill; however no high pressure inclusions are recognisable at Miowera due to extensive alteration of the breccia. The Ruby Hill and Miowera diatremes are suggested to relate to the same intrusive event.

THE S T A T U S

OF THE C O N D O R OIL SHALE

PROJECT

P. J. Redann Southern Pacific Petroleum N.L., Sydney The Condor Oil Shale deposit is the largest Tertiary oil shale deposit in Australia and is located south-east of the North Queensland town of Proserpine. The deposit has a total insitu oil resource in excess of 9 billion barrels, at a cut-off grade of 50 litres per tonne. The shale subcrops in an area running roughly north-west, south-east for a distance of about 18 kilometres, and the subcrop is about 1.5 kilometres wide. From the subcrop the shale deposit dips at about 14 to the north-east. The Authority to Prospect the deposit is held by Southern Pacific Petroleum NL and Central Pacific Minerals NL (SPP/CPM). In December, 1981, an agreement was signed between SPP/CPM and the Japan Australia Oil Shale Corporation to jointly investigate the technical and economic feasibility of developing the Condor deposit. The total budget for this investigation was US$24 million, funded entirely by the Japanese party.

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In return for the funding, SPP/CPM's main obligations to the Japanese party are exclusive rights to negotiate on future developments for a period of one year following the conclusion of the feasibility study, and payback of 50% of the study costs when a successful development is built. The short study period dictated that little developmental work could be undertaken, so the main work thrust was to take existing, developed oil shale and other relevant conventional, commercial technologies and adapt them to the Condor material. The Condor Oil Shale Feasibility Study was completed on 30th June, 1984 on schedule and within budget. STUDY APPROACH The project team, which comprised equal numbers of SPP/CPM and Japanese personnel, conducted in-house studies and managed about 320 contracts in the following areas: Resource, Mining and Materials Handling Retorting and Upgrading Processes Infrastructure and Environment Common Facilities, Production and Marketing and Design and Construction Administration TECHNICAL AND ECONOMIC FEASIBILITY The study results support a conclusion that the development of the Condor oil shale deposit would be feasible provided all study assumptions are fulfilled. All technologies involved, except retorting, are already in conventional commercial operation in other industries. Retorting is not yet in operation at the scales envisaged. Smaller scales of similar plants successfully process other materials. Pilot plant testing of Condor and other oil shales support a viewpoint that ultimately large scale production will become a reality. Production and marketing studies have determined that the product oil, which is low in nitrogen and sulphur and of better quality than Arabian Light Crude, would be acceptable to Australian and Japanese refineries. Project economics, which were developed largely from estimates, were subjected to close scrutiny and analysis. supportive of development.

detailed consultant The results are

THE FUTURE A negotiation period of one year, until July 1985, will allow the Partners time to judge whether a development of the deposit is beneficial. If a decision is reached to proceed, a programme of further investigations will be initiated to build on the existing information base with the objective of ultimately establishing a commercial operation.

454

EARLY HISTORY OF OIL EXPLORATION IN AUSTRALIA R.E. Relph Consultant Geologist, Sydney As no true oil seepages had been found in Australia the early oil explorers concentrated on areas that had shown signs of hydrocarbon when drilling for water, or in the case of Salt creek in South Australia on the wrong premise. Their activities, with a few exceptions, could until 1917 be best described as like "flies around a honey pot". It was in 1917 when the Vacuum Oil Company carried out a reconnaissance geological survey of the main access routes of all of the Australian States that the first serious overall view of the Australian geology with respect to possible oil accumulation was undertaken. This company carried out several geological surveys until 1930 when its activities were concentrated in New Zealand. Companies such as Vacuum, Freney-Kimberley Oil Search and Australian Roma Oil Company contributed much to the exploration for oil in Australia but the major incentives came from the Commonwealth Government. In 1926 it showed its concern when it passed the Petroleum Prospecting Act and employed a geological advisor. Again, sums were appropriated in 1936 to investigate the petroleum industry and to subsidise drilling operations, geological surveys etc., but the main impetus in exploration was generated by the passing of the Petroleum Search Subsidy Act in 1957, after the finding of oil in Rough Ranger No. 1 by Wapet in 1953. Individuals also contributed greatly to the search, both in a geological sense and in the corporate sphere. People like H.G. Raggatt, E.A. Rudd, R.C. Sprigg, A. Wade, W.G. Walkley and T.W.H. Dee, to name but a few, felt sure that Australia had the potential to produce economic quantities of oil and gas and it was their vision and persistence that stands to their credit. All that was needed were concentrated geological exploration, suitable exploration techniques and sufficient capital to fully investigate Australia's potential and these were not to be found until the early 1950fs. References Clapp, F.G., 1926, The Oil Problem in Western Australia. Econ. Geol. 19(2) 157-168. Condit, D. Dale., 1935, Oil Possibilities in Northwest District Western Australia. Econ. Geol. 30(8) 860-878. Conybeare, C.E.B., 1980, Oil Search in Australia. A.N.U. Press Canberra. Raggatt, H.G., 1964, Progress in the Search for Petroleum. A.O.G. Journ. 11(2). Raggatt, G.H., 1968, Mountains of Ore. Landsdowne Press Melbourne. Rudd, E.A. and Sprigg, R.C., 1966, History of Oil Search in Australia and Papua New Guinea. Proc. 8th Com. Min & Met. Cong. Vol. 5, 4-11. Tissot, B.P. and Welte, D.H., 1978, Petroleum Formation and Occurrence. Springer-Verlag New York. Vacuum Oil Company Pty. Ltd., 1939, The Search of Oil. G.W. Green & Sons Pty. Ltd., Melbourne. Wilkinson, R., 1983, A Thirst for Burning. David Ell Press Sydney.

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MICROWAVE REMOTE SENSING - UNIVERSITY OF NEW SOUTH WALES PARTICIPATION IN THE SIR-B EXPERIMENT J.A. Richards School of Electrical Engineering and Computer Science, and Centre for Remote Sensing, The University of New South Wales, Kensington Microwave remote sensing of the earth's resources using airborne or spaceborne imaging radars offers a number of advantages over the use of image data gathered in the visible and infrared wavelength regimes. Since it is an active system (ie, it carries its own source of illumination) radar imaging is independent of season and time-of-day. Also, owing to the long wavelengths used, effective imaging can be carried out through clouds and mist, both of which are significant barriers to acquiring visible and infrared images of the earth. Microwave imaging from aircraft has been available for some time. This involves the use of side looking radars that acquire data normal to an aircraft flight line by differential time delay measurement, as in conventional air traffic control radars, and data parallel to the flight path by using the aircraft movement for along track scanning. By altering aircraft bearing, structural features of interest can be illuminated and imaged from different directions. When a side looking radar is translated to satellite altitudes to enable a synoptic view of a large region to be gained, high spatial resolution cannot be maintained; to do so would require an impracticably large antenna to be carried on the spacecraft. High resolution can be obtained from space however if the motion of the space vehicle is used to synthesise an effectively long antenna. Typically, travel over 2km or so in orbit is required to produce a ground resolution of 25m. Microwave remote sensing systems that utilize this concept are referred to as synthetic aperture radars (SAR). There have been two successful spaceborne remote sensing SAR missions to date. In 1978 a synthetic aperture radar was carried on the Seasat satellite for the purpose of providing all weather imaging of the earth's oceans and land masses. The mission was cut short by a failure of a power supply on the satellite. The second was known as SIR-A (Shuttle Imaging Radar - A). This was carried on the second flight of Space Shuttle in November 1981, and returned some quite remarkable images of many parts of the world. Perhaps some of the most striking SIR-A data collected is that of the Sudan in which significant penetration of the radar energy into the extremely dry Sahara desert revealed ancient bedrock structures and watercourses several metres below the sand. A third spaceborne SAR mission was flown as part of the recent Spacelab pallet on Shuttle. This was the West German MRSE (Microwave Remote Sensing Experiment); however for reasons as yet unknown this failed to operate. The next mission, to be known as SIR-B, will be carried on the 17th Shuttle flight, currently scheduled for October this year. The instrument will be identical in many respects to that on Seasat and SIR-A (operating with a wavelength of 23.5cm); however whereas the angle of incidence was fixed with the previous missions (20° for Seasat and 47° for SIR-A) the angle of incidence for SIR-B will be variable between 15° and 60°. This is an important consideration for mapping structural detail. The SIR-B experiment is to be administered for NASA by the Jet Propulsion Laboratory in Pasadena California; in addition, NASA has chosen a number of research teams around the world to carry out specific aspects of the experiment. Fourteen of these are outside the United States, including 3 in Australia. The Australian teams come from the Defence Research Centre in Salisbury, South Australia, the CSIRO/BMR acting as a consortium, and the University of New South Wales. 456

The objectives of the SIR-B experiment are: (i)

To conduct innovative geo-scientific studies using spaceborne radar imagery and to determine the value of using microwave data in conjunction with visible and infrared remote sensing imagery. (ii) To understand the manner in which microwave radiation interrogates the properties of vegetation-covered and sand-covered surfaces, (iii) To investigate the effects of surface characteristics on radar return as a function of illumination geometry and thus to determine optimum geometries for surface observation, (iv) To conduct research in radar remote sensing techniques development. After providing an overview of spaceborne SAR and an outline of the SIR-B project the paper will describe in some detail the nature of the SIR—B experiments to be carried out by the University of New South Wales, coordinated by its Centre for Remote Sensing. Five major research programs will be summarised: The first is designed to assess the value of SIR-B data for geological and geomorphological mapping and will be carried out at Fowler's Gap, (110km north of Broken Hill, at which the University has an arid zone research station) and in the Amadeus Basin. The second program is directed towards modelling the nature of the radar response expected from heterogeneous media such as soil/sand/gravel and bedrock combinations. The remaining programs are addressed to cartographic, urban and agricultural uses of SIR-B data. The paper will conclude with a look at the follow-on NASA shuttlebased synthetic aperture radar programs, and the free flying radar missions planned by other countries (including Canada, the European Space Agency and Japan) and will outline arrangements being made at the University of New South Wales for establishing a SAR image processing facility.

SOUTH PACIFIC MINERAL POTENTIAL, GOVERNMENT POLICIES, AND MISPLACED ADVICE R.N. Richmond Australian Petroleum Exploration Association Limited, Sydney Gold in Papua New Guinea, Fiji and the Solomon Islands, copper in Papua New Guinea and Fiji, manganese in Fiji, Vanuatu, and Papua New Guinea - these are some of the minerals that are being mined or were mined in the South Pacific since the turn of the century, and that are responsible for the continuing interest in the area. Over the past decade additional exploration has proven deposits of gas and condensate in Papua New Guinea, copper and gold in Papua New Guinea, Fiji and the Solomons, bauxite in the Solomons and Fiji and manganese nodules in the offshore areas of the Cook Islands. Exploration is continuing for these same minerals in many parts of the South Pacific. Petroleum exploration is also being pursued in Tonga, Fiji and Papua New Guinea with some companies also looking at the petroleum potential of the Solomon Islands and Vanuatu. Government policies in the South Pacific have largely been those of encouraging exploration and granting licences in the classical concession system. Mining and petroleum laws, where they exist, have usually been inherited through their colonial heritage. Where newer legislation has recently been enacted they have tended to follow those of our more developed close neighbours like Australia. Taxation has usually been according to the existing taxation laws of the country unless special taxation agreements were negotiated with the mining companies. Only Papua New Guinea has enacted specific mineral taxation legislation to deal specifically with this situation. 457

The only new mineral project going ahead today in the whole South Pacific is the OK Tedi project in Papua New Guinea - after a delay of many years, and only because of the richness of its gold and copper orebody. Copper and bauxite in Fiji and the Solomon Islands are far from the development stage because of the economic downturn, the surplus of metal supplies, and the lower quality and size of the orebodies. It appears unlikely that these projects will become economically viable in the near future unless there is a substantial economic recovery in the world. During this period of economic slowdown and reduced exploration activity it is relevant to look at Government policies and the role played by advisory organizations in their formulation. One of the advantages in being an underdeveloped country much behind in mineral development is that these countries should hope to benefit from hindsight experience of other developing countries. In this respect the backlash against multinational corporations over the past decade has had far reaching influences on the backward South Pacific nations in their dealings with these corporations. When countries reach the stage of preparing to enact new laws, negotiate taxation agreements, or determine new government policies, they find that help is available from a number of international organizations. These include such organizations as the United Nations Center for Transnational Corporations and the Commonwealth Fund for Technical Co-operation. Concerning new mining and petroleum legislation, advice from these organizations, particularly the CFTC, can be most useful and practical. However, where advice on government policies and negotiations with mining companies are concerned it is my experience that realistic advice is not always given. Too much of the experience of these international organizations comes from Africa, South East Asia and South America with little relevance to the real needs of the South Pacific. The other nations referred to 'all have proven mineral and petroleum resources and all have some history of alleged past exploitation by multinational companies. That advisory organizations should seek to right the wrongs that may have occurred elsewhere and to try to ensure that similar mistakes are not made in the South Pacific are certainly worthy and laudable causes. However, in advising these smaller countries to flex their sovereign powers, to ensure that they gfet the maximum possible returns from any mining enterprise, and to totally distrust any multinational companies, is I believe putting the cart before the horse. Only Papua New Guinea among the South Pacific Islands can be considered to have sufficient mineral and petroleum potential to have firmer guidelines for exploration. Other South Pacific island countries are not so lucky. They certainly have mineral and petroleum potential, but without any large scale operating mines with significant impact on their economy, they should concentrate more on providing the necessary policies and infrastructure to attract companies to explore in their countries. These countries are not in a position to demand 60 to 70 per cent of the slice of the cake from the very beginning: they need to find and prove the resource first. The priority for South Pacific island countries should be first, to ensure that they have a good, workable, up-to-date mining and petroleum legislation, second, that they have good geological survey backup, third, that their policies attract exploration companies with a minimal amount of bureaucratic paperwork and fourthly, that they have a reasonable income tax act which can be applied to mining projects, with special agreements to be negotiated if necessary.

458

MINING INDUCED FRACTURES IN COAL L.K. Rixon and J. Shepherd Australian Coal Industry Research Laboratories Ltd, North Ryde Mining induced fractures (MIF) form around underground mine openings in response to stresses induced during the mining process, principally by a reduction in confining pressure close to the mine walls (ribs). In contrast the geological fractures are present throughout the strata before mining. MIF can be distinguished from geological fractures on the basis of surface texture, mineral fillings and orientation with respect to the direction of mine drivage. MIF surfaces typically have a rough appearance with little gouge and no mineral fillings. Typical MIF that develop close to an advancing face appear sub-vertically in the ribsides and form an acute angle of about 20° to the drivage direction. MIF that develop later in response to roof convergence may form parallel to the ribs. MIF commonly exploit or interact with pre-existing geological fracture systems such that rib stability is adversely affected, particularly at pillar corners. The intensity ,of MIF development (spacing of fractures) is also an important indication of pillar loads and coal strength. An understanding of MIF development and its relationships to pre-existing fractures can be used to help improve rib and roof stability, thereby reducing support costs and lost time through injury to the workforce.

THE QUALITY ASPECTS OF COAL UTILISED IN THE CEMENT INDUSTRY Malcolm J. Robinson Blue Circle Southern Cement Limited, Sydney Cement manufacture involves the calcination of a pulverised raw material blend consisting predominantly of limestone (80%) with a 20% or so addition of silica, alumina and iron oxide usually in the form of readily available materials such as sand, shale, clay and iron ore. Until the introduct ion of the rotary kiln some 90 years ago calcination was a batch process carried out in shaft kilns or beehive ovens in which the raw material was layered with the coal or wood fuel and baked for a period of several days. The resulting clinker was ground with a small percentage of gypsum to produce cement. The advent of the rotary kiln permitted continuous process operation and the trend through most of the 20th century was to progressively larger kilns, some exceeding 200 m in length. Most kilns constructed prior to 1970 adopted the wet process of clinker manufacture, mainly because this facilitated grinding, homogenisation and materials handling. Improvements in technology, specifically the advent of the more fuel efficient suspension preheater process led to increasing preference for dry process plants during the 1960fs and this was further accelerated by the energy crisis of the 1970fs. The process involves preheating of the raw feed in a series of cyclone heat exchangers using hot gases from the kiln. Because the feed enters the kiln at a temperature of about 800°C, only a relatively short kiln, typically about 75 metres in length, is required to raise it to the necessary 1500°C or so to complete the calcination process. A variant of the preheater system which has a separate combustion chamber (precalciner) ahead of the kiln has become increasingly common in the last 10 years, especially in Japan. Up to 60% of the total fuel used is consumed in the precalciner and over 90% of the calcination takes place before the material enters the kiln. Although any improvement in fuel efficiency is only nominal there are a number of 459

other advantages of the precalciner system, most importantly an increase in the throughput capacity of a given kiln by a factor or two or more. The largest PC kilns now have capacities up to 10000 tonnes per day. Cement kilns can be fired by oil, gas or coal, including brown coal and lignite, or a mixture of more than one of these. Before the energy f crisis of the 1970 s oil or gas tended to be the preferred fuel except in plants close to coal deposits. A high proportion of cement plants throughout the world have been converted to coal firing in recent years and any new plants are likely to be so fuelled except in local areas where oil or gas may be cost competitive. With the possible exception of high sulphur oil, neither oil nor gas contribute to the cement raw material; in the case of coal however the ash is absorbed, more or less totally into the cement clinker. As such it becomes part of the cement raw material and must be allowed for by adjustment of the raw feed chemistry. It has long been known that minor constituents in cement raw materials such as M g O , Na and K can detrimentally affect product quality; with the introduction of the more chemically sensitive preheater kilns it became apparent that minor constituents such as SO3, N a , K and CI could additionally cause severe process problems. As coal ash constitutes a raw material the levels of these constituents is important and may be critical. No coal specification for the cement industry as a whole can be given. It is the total material input to the kiln which is important and a coal specification cannot be defined without a knowledge of the raw material composition, kiln type, cement type and so on. Most coals are however suitable provided that the cement raw materials are high grade and do not contain near critical levels of certain minor components. Some comment is appropriate in relation to particular coal properties: 1. Moisture - apart from its obvious effect on specific energy moisture is rarely high enough to be of concern in black coal. It is however very high in brown coals, which are usually dried to a maximum of about 15% moisture. 2. Specific energy - a coal of lower specific energy will require increased coal grinding and handling facilities. 3. Volatiles - although high volatile coals are easier to ignite low volatile coal can achieve the same ignition characteristics by finer grinding. 4 . Hardgrove and abrasion indices - have an obvious effect on grinding costs. Certain coals with high levels of free silica or similar material cannot be handled by certain types of coal mill. 5. Ash percentage. Consistency of ash level is often more important than the absolute level. Although coal containing up to 35% ash is used in the cement industry in N.S.W. this is only possible because there is access to high grade limestone as the primary raw material component. The cement industry in Victoria, South Australia and Western Australia for example is largely dependent on marginal grade limestone, and the addition of non-carbonate material from a coal containing only 5-10% ash would necessitate the use of a higher grade limestone which may not be available or which would cause rapid depletion of limestone resources. Export specifications may often require ash levels lower than 15%, but this may be more a function of transport economics than a statement of the maximum acceptable at the particular plant. 6. Ash Analysis. Most ash analyses are similar to the argillaceous component of the raw m i x . If they differ significantly for instance by containing high silica or high alumina levels it may not be possible to make the necessary correction, and there could be consequential effects on the process and cement quality. The volatile constituents of the ash namely alkalis, chlorides and sulphur are those most likely to create process difficulties. Chloride is volatilised in the burning zone and returns to the back end of the kiln or preheater where it condenses forming alkali chlorides; these return to the kiln with the raw m i x , revolatilise and continue to circulate. This causes the build up of an alkali chloride coating which ultimately requires shut-down of the kiln. The phenomenon 460

can be prevented by bleeding off a percentage (10-25%) of the kiln gases at the back end, a procedure usually adopted if the chloride content of the mix (including coal ash) exceeds 0.015% CI. An alkali bypass such as this has implications for capital cost and thermal efficiency. In a wet process kiln chloride is lost from the system and is not a problem. The sulphur and alkali constituents in the fuel also volatilise and will condense to form compounds based on alkali carbonates and alkali or calcium sulphates. For the most part these enter the clinker which may therefore have high sulphate levels. The maximum SO3 allowable in clinker is usually about 17o to allow for the necessary addition of gypsum without exceeding the 3.1% maximum acceptable in cement. In general terms the affects of the minor constituents are insignificant where ash levels are less than 5%, and can usually be handled where ash levels are between 5 and 15%; some coals may be unacceptable with above 15%.ash. There are of course exceptions,for example certain Victorian brown coals which, although containing less than 5% ash are unacceptable because of high sulphur levels. BACKSCATTERKD ELECTRON IMAGING AS AN AID TO GEOLOGICAL AND MINERALOGICAL STUDIES V.N.E. Robinson The University of New South Wales, Kensington Many different techniques are available to assist geologists and mineralogists in the study of the composition of the Earth's crust. In many studies, it was desirable to know the size of individual mineral particles and with what they were associated, as well as the particular minerals present and the elements contained within them. Optical microscopy has been used extensively in studies of the size, association and distribution of minerals. In recent years, the techniques available for characterizing materials in a scanning electron microscope (SEM) have resulted in the SEM being used increasingly in geological/mineralogical studies. Of the many SEM techniques available to the geologist, two of the most widely used analytical techniques are energy dispersive x-ray spectrometry (EDS) and backscattered electron (BE) imaging. By identifying the heavy elements, EDS has enabled the positive identification of many minerals in simple or well known situations. Although EDS is much more positive and rapid than other SEM techniques, used by itself it is still too slow for a large number of applications. Backscattered electron imaging, used in conjunction with a SEM and EDS provides a very useful technique for geological studies. There are two major reasons for this. Firstly, the BE signal is heavily dependent upon atomic number (Z). Secondly, BE detectors are available which have a high bandwidth (>5MHz), allowing rapid or real time viewing of samples. These features of the BE image have a number of advantages. include: -

These

(i) Images of fracture surfaces display variations in the composition of the surface, as well as the shape of the surface. This enables users to visualise and rapidly identify simple known situations, for example, galena and quartz in sphalerite. Each phase visually detected can be examined by EDS for the major heavy elements (>1% concentration, Z>10). Often this is sufficient for positive mineral identification. But more importantly, EDS analysis after BE imaging enables positive detection, discrimination and possibly identification of the major phase difference components. As a brief guide, it is possible, when these features are combined with a charge neutralization system to examine the surface of a rock sample, typical dimensions 3 cm to 5 cm, with a high phase detection probability, in a short time period, typically 2 to 10 minutes, after it is first brought into laboratory (Robinson and Robinson, 1978, Robinson and Nickel, 1979). 461

(ii) When polished sections are examined, the BE image can display much smaller differences in composition. The advantages described for rough surfaces extend to much smaller differences in atomic number for polished sections. Differences lower than 0.005Z have been detected. (iii) A technique has been developed which quantifies the BE signal into the atomic number factor (ANF) of the material being studied (Robinson et al, 1984). This ANF is a functionally calculable combination of all of the elements present in the material, including the light elements, Z<10, indetectable in normal EDS. When combined with EDS, this technique enables element and compound information over the whole range of the periodic table, from Z=1 to Z=92, to be studied. It provides another technique for identifying minerals, this time using their chemical formula. From the chemical formula of most of the common minerals, a table of the ANF and heavy elements, Z>10, has been.compiled. Minerals can be identified from the heavy elements detected by EDS and the ANF detected by this quantification of the BE signal. Using this technique, many minerals having the same heavy elements, and differing only in light elements, can be easily and rapidly distinguished, e.g. FeO, Fe 2 03> FeC03. Also, many minerals differing only in the ratio of heavy elements can be positively discriminated from a knowledge of the heavy elements, plus the ANF, without having to know the heavy element ratios. Where positive identification is possible, it is much faster than other, more traditional methods. Backscattered electron imaging greatly increases the rate of geological analyses can be obtained. References f

Robinson, V.N.E., and Robinson, B.W., 1978, SEM/1978, SEM Inc., AMF O Hare, II., Vol. 1, 595-602. Robinson, V.N.E., Cutmore, N.G., and Burdon, R.G., 1984, SEM/1984, SEM Inc., AMF O'Hare, II., In press. Robinson, B.W., and Nickel, E.H., 1979, Amer. Min., 64, 1322-1328.

MUSCOVITE

6E0THERM0METRY

J.M. Rodgers

and J.L. Walshe

1 9 Esso, Sydney, - Australian National University, Canberra Muscovite is a non stoichiometric mineral which occurs in a wide range of geological environments. Ideal muscovite, K A l 2 S i 3 A 1 0 1 0 ( 0 H ) 2 , may undergo a number of compositional substitutions as functions of T , P and fluid conditions. One important exchange is 4+

(interlayer vacancy) + ( S i )

= (A1 )

+ (interlayer K )

which gives the illite solid solution series. Temperature and compositional constraints on muscovites from the Salton Sea geothermal system (McDowell and Elders, 1980) has allowed calibration of the exchange reaction K A l 2 S i 3 A 1 0 1 0 ( 0 H ) 2 + 4Si0 2 = A l 2 S i 4 O 1 0 ( O H ) 2 + KAlSi 3 0 8 11

for which log K = log a® - log a™". & py • mu The activity of muscovite has been calculated assuming random mixing and equal interactions of atoms on energetically equivalent sites. The activity of the pyrhophyllite component in muscovite as assumed equal to its mole fraction. 462

For a quartz muscovite assemblage this geothermometer gives a minimum temperature estimate whilst the equivalent exchange reaction on the kaolinite buffer, as given below, will give a maximum temperature estimate. A l 2 S i 4 O 1 0 ( O H ) 2 + H 2 0 = A l 2 S i 2 0 5 ( O H ) 4 k a o l + 2Si0 2 Studies of muscovites in quartz muscovite assemblages in several hydrothermal systems have given values compatible with fluid inclusion filling temperatures assuming K-feldspar equilibrium. This indicates that the aK /aH + is close to the K-feldspar - muscovite buffer. Reference McDowell, 310.

S.D.,

& Elders,

W.A.,

1980,

Contrib. Mineral. Petrol. 74,

293-

GEOCHEMISTRY AND SEISMIC VELOCITIES OF THE LOWER CRUST IN NORTHEAST QUEENSLAND: EVIDENCE FROM GRANULITE FACIES NODULES IN RECENT BASALTS R.L. Rudnick, S.R. Taylor and I. Jackson Res. School of Earth Sci., Australian National University, Canberra

Granulite facies xenoliths erupted in Recent basalts from the Chudleigh, McBride, and Atherton volcanic provinces (Stephenson and Griffith, 1976), north Queensland provide direct information on the composition of the lower continental crust. Lower crustal nodules were collected from 6 vents: Batchelor's Crater, Airstrip Crater, and Sapphire Hill in the Chudleigh province; Hill 32 in the McBride province; and Lake Eacham, and Mount Quincan in the Atherton province. Chudleigh Province These granulite nodules are invariably mafic and form two groups based on texture, mineralogy, and chemistry. The first' type is the most abundant lithology collected and consists of plagioclase (pc) with varying proportions of clinopyroxene (cpx), orthopyroxene (opx), spinel, garnet, and olivine. These minerals are often in complex coronal arrangements (see Kay and Kay, 1983) and exhibit varying degrees of compositional zonation. Electron probe analyses of adjacent mineral rims for opx-cpx, garnet-cpx and garnet-opx pairs can be used to obtain temperature (Lindsley 1983; Wells, 1978; and Ellis and Green, 1979) and pressure (Harley and Green, 1982) estimates of last equilibration. These P-T estimates fall into two regions depending on which thermometer is used: 690 to 800°C, 5.5-9.5 kbars, using the Lindsley opx thermometer and the Harley-Green barometer, or 850 to 960°C, 10 to 14 kbars, using the Wells or Ellis-Green thermometer and Harley-Green barometer. Irrespective of which P-T estimation is more accurate, these xenoliths clearly equilibrated in the lower half of the continental crust. There is limited variation in major element chemistry of these xenoliths, despite large variations in modal mineralogy, with -50% Si02, 20% A1 2 0 3 , 9-11? CaO, and Mg/(Mg + Fe) from 41 to 76. ' They have low concentrations of REE (La = 4-12 times chondrite); typically with LREE > HREE, and strong positive Eu anomalies. The large ion lithophile elements (LILE) are in very low concentrations except Ba, which is enriched in these xenoliths (15 to 180 times chondrite). This Ba enrichment has been noted in other mafic lower crustal xenoliths from southeastern Australia (Arculus et al. 1984) and is present in other mafic lower crustal xenoliths from Algeria (Leyreloup et al., 1982) and South Africa (Rogers, 1977).

463

The second type of lower crustal xenolith in the Chudleigh province is also mafic, but is composed primarily of opx and cpx with lesser amounts of pc (<205&) and rutile (<5%). These pyroxene-rich xenoliths are coarse-grained, and compositionally banded without coronal textures. Minerals .are in chemical equilibrium (shown by a lack of compositional zoning); coexisting pyroxenes yield equilibration temperatures of 710°C (Lindsley opx temperature) or 900°C (Wells temperature). Pressure estimates are not directly available for these xenoliths, however, if it is assumed they lie along the same geotherm defined by the first group, their pressure of equilibration would range from 6.5 to 13 kbars. These xenoliths possess -50% Si0 2 , 9-10% A 1 2 0 3 , < 0.1* K 2 0 , and 14-16% MgO, with Mg/(Mg + Fe) > 73. Chondrite normalized REE patterns are flat with a LREE depletion ( L a V Y b N = .5 to .7), and have no Eu anomaly. Concentration of the middle REE and HREE in this group are slightly higher than that of the pc-rich xenoliths. LILE,' including Ba, are depleted. McBride Province Lower crustal xenoliths from Hill 32 exhibit a wide range of compositions: high-grade, banded, garnet-opx bearing metasediments; intermediate, calc-alkaline meta-igneous rocks; and mafic granulites. The metasedimentary and intermediate calc-alkaline xenoliths yield temperatures and pressures of equilibration of 800 to 960°C, 8-9 kbar (Newton and Perkins, 1982). Their major and trace element chemistries are similar to unmetamorphosed equivalents except for depletions in U, Th, K, and Rb, as is sometimes observed in other granulite facies rocks. The mafic xenoliths are similar to the pc-rich xenoliths from the Chudleigh province in major and trace element chemistry; they have REE concentrations up to 20 times chondrite with large positive Eu anomalies (O'Brien, 1983). Atherton Province Crustal xenoliths from Lake Eacham and Mt. Quincan in the Atherton province are sparse and generally highly altered. A mica schist xenolith from Lake Eacham is believed to be upper to mid-crustal;' quartz-plagioclase-garnet xenoliths from Mt. Quincan are clearly metamorphic, but their pressure of equilibration is not determinable. These xenoliths are often severely melted and invaded by the host basalt, consequently, their chemistry has not been determined. Inferred Origin The predominance of mafic xenoliths which have equilibrated at lower crustal conditions suggests that these mafic rocks make up a significant portion of the northeast Queensland lower crust. The depleted chemistry and positive Eu anomalies of the pc-rich xenoliths suggest these rocks are either restites remaining after partial melting of a mafic parent or cumulates from a mafic magma. Their mafic mineralogy, high Mg numbers, and coronal relationships, coupled with trace element variations suggest that the cumulate origin is the most reasonable model for these rocks. The pyroxene-rich mafic xenoliths found in the Chudleigh province are believed to be pyroxene cumulates from a mafic magma; the modal pc must have formed as a subsolidus phase. None of the mafic xenoliths is believed to represent liquid compositions; both types of mafic xenoliths may represent different portions of a layered mafic intrusion near the base of the crust. Metasedimentary and intermediate meta-igneous granulites from Hill 32 possess features in common with other high grade supracrustal gneisses. These xenoliths may be from a buried extension of the Precambrian gneisses of the Georgetown Inlier which crops out -60 km to the west. If this is the case, they probably are not fragments of the present lower crust; the mafic xenoliths may better represent the present lower crust. Laboratory measurements of the densities and elastic wave velocities of these xenoliths will be compared with seismological veloctiy-depth models in order to provide an additional constraint on the average composition and mineralogy of the lower crust.

464

References Arculus, R.J., et al.f 1984, Proc. Eclogite Symposium, (in press). Ellis, D.J., and Green, D.H., 1979, Contrib. Min. Petrol. 71: 13-22. Harley, S.L., and Green, D.H., 1982, Nature 300: 697-701. Kay, S.M., and Kay, R.W., 1983, Am. Jour. Sci. 283A Leyreloup, A., et al., 1982, Contrib. Mineral. Petrol. 79: 68-75. Lindsley, D.H., 1983, Am. Min. 68: 477-493. Newton, R.C., and Perkins, D., 1982, Am. Mineral. 67: 203-222. O'Brien, T., 1983, PhD thesis, Cornell Univ., 205 pp. Rogers, N.W., 1977, Nature 270: 681-684. Stephenson, P.J., and Griffith, T.J., .1976, Excurs. Guide 7A, Int. Geol. Conf., 39 pp. Wells, P.R.A., 1977, Contrib. Mineral. Petrol. 62: 129-139.

25th

AN INTEGRATED GEOLOGICAL AND SOIL GEOCHEMICAL EXPLORATION PROGRAMME FOR GOLD AT MT. McDONALD, N.S.W. Craig S. Rugless Consultant, Sydney The Mt. McDonald and Milburn Creek areas, 25 km east-southeast of Cowra and 2 km west of Wyangala Dam, have a long history of mining. Copper was discovered at Milburn Creek in 1871 and was soon followed by the discovery of gold at Mt. McDonald to the south in 1880. Total field production has been 1.89 tonnes gold and 500 tonnes copper. Gold and copper deposits exhibit a common lithological association with calc-silicate metasedimentary units of the Ordovician Abercrombie Beds, and a spatial relationship with northeastsouthwest, north-south and to a lesser extent northwest-southeast structures apparent as photo-linears. The host metasedimentary Abercrombie Beds have been regionally metamorphosed to greenschist facies and occur as a roof pendant surrounded to the east and southwest by elements of the early Silurian (Stevens, 1975) Wyangala Batholith which is regarded as syntectonic in part (Hobbs 1965). Mineralization occurs both as high grade structurally controlled quartz lodes and as lower tenor, fracture-filled veinlets and sulphide (pyrrhotite + pyrite + arsenopyrite + chalcopyrite) disseminations. A grid controlled soil geochemical sampling programme was thought to provide the best method of identifying either structurally and/or lithologically controlled extensions to mineralization in the area. Approximately 1300 B-horizon soil samples were collected by hand auger at 20m interval stations along traverses (400m to 1100m length) turned off at 100m intervals along the 4.5 km baseline. The baseline follows a north-south ridge which dominates the undulating topography of the area. Elevations vary from 500m to 731m at the highest point at Dunleary Trig. Residual soil development is variable with relatively thin cover ( 10-15 cm) on hilltops and stronger development (>50 cm) on hillsides and upper creek valleys. Both -40 + 80# and -80# soil fractions from an orientation soil sampling survey line across abandoned gold shafts near Dunleary Trig were analysed for Cu, Pb, Zn, Fe, Mn, As, Hg* Cppb levels), Ag and Au (ppb levels) by AAS, AAS hydride generation and AAS carbon furnace methods by S.G.S. Laboratories, Sydney. Base metal and gold anomalies over the main mineralized zones were apparent in both fractions although the finer fraction effectively outlined additional Au anomalies not apparent in the coarser fraction. Arsenic proved an effective pathfinder for Au in both soil fractions while Hg failed to outline gold mineralization as definitive anomalies. On this basis the finer soil fraction was employed for the soil sampling programme, and analysed for Cu, Pb, Zn, Co, As and Au.

465

The soil geochemical survey can be interpreted in terms of the geology in the area. High background Au values (2>15 ppb) coincide with calc-silicate and argillaceous metasedimentary units interpreted to occur within the core of a tight, north-south elongated, keel-shaped synclinorium defined by a distinctive phyllitic unit in the centre of the roof pendant. The reappearance of the same calc-silicate unit along the refolded south-eastern limb of the syncline coincides with high background Au values associated with gold mineralization. North-south and northeast-southwest trending faults/fractures provide an additional control on the Au geochemistry and appear to define corridors enclosing locally increased values within the favourable calc-silicate and argillaceous hosts. High background As values (^15 ppm) broadly follow the gold geochemistry. Generally higher Cu soil values in the northern part of the area are consistent with the south to north metal zoning trend of increasing Cu (Ag) relative to Au (As) values in rock chip samples. Argillic alteration at Milburn Creek is associated with high background to anomalous Cu and Co values surrounded by locally enhanced Zn and Pb values. Application of Spearman's Correlation method to the soil geochemical data set indicates strong Co-Cu correlation (0.7) and Pb-Zn correlation (.0.62)y moderate Au-As correlation (0.53) and poor Cu-Au correlation (0.3). The localization of the major mineralized lodes within favourable lithological/structural sites and the Au to Cu metal zoning apparent at Mt. McDonald and Milburn Creek are suggestive of a magmatic-hydrothermal origin for the mineralization. The demonstrable association of faults/fractures with granite intrusion supports a granite source for these hydrothermal fluids. A comparison may be drawn with mineralization at Battle Mountain, Nevada, where gold associated with pyrite, pyrrhotite, arsenopyrite and chalcopyrite has been deposited in chlorite-clay altered calc-hornfels adjacent to an intrusive stock (Boyle, 1979). References Boyle, R.W., 1979.

Geol. Survey, Canada, Bull. 280, 584 pp.

Hobbs, B.E., 1965. J. Geological Society Australia 12, ppl - 24. Stevens, B.P.J., 1975. New South Wales Geol. Survey.

GELIFICATION OF VICTORIAN SOFT BROWN COAL WOOD N.J. Russell CSIR0 Division of Fossil Fuels, North Ryde Introduction. Extensive studies by coal scientists in Germany of the relationship between the petrography of soft brown coal and its utilization have resulted in the selective mining of individual lithotypes for specific processes. Although, for a variety of reasons, the brown coal deposits in the Latrobe Valley, Gippsland Basin, Victoria do not lend themselves to selective mining, similar studies have also been carried out by the State Electricity Commission of Victoria (George, 1982). The degree of gelification of soft brown coals influences their technological behaviour during processing, e.g. briquette strength (Jacob, 1968). The degree of gelification of huminite, the vitrinite precursor, is established during the peat and soft brown coal stages of coalification in response to factors such as Eh and pH (Teichmuller and Teichmuller, 1968). It can influence huminite and vitrinite responses to organic solvent treatment (Shibaoka et al., 1979), including solvent treatment under conditions employed in coal conversion processes (Shibaoka, 1981, 1982).

466

This paper reviews the results of combined microscopic and chemical studies of the gelification of Victorian soft brown coal woods (xylites) collected from the Yallourn and Morwell opencut mines (Philp et al., 1982; Russell, 1984; Russell and Barron, 1984). These studies were undertaken in collaboration with Dr. Peter Barron (solid state NMR analyses) and Dr. Paul Philp and M r . Trevor Gilbert (pyrolysis - gas chromatography - mass spectrometry analyses). Petrology. Discrete woody material (xylite), often associated with bodies of yellow resinite derived by polymerization of bled resin, occurs in Miocene soft brown coal lithotypes in the Latrobe valley coal deposits. In hand specimen the xylites range from fibrous, reddish brown ungelified material that is flexible when wet, to dark brown to black, brittle, doppleritic (gelified) xylite. The latter exhibits a vitreous, conchoidal fracture akin to that of bituminous coal vitrain. The atomic H/C ratio is a reliable guide to the degree of gelification, decreasing from ~ 1.3 for ungelified xylite to ~ 0.8 for doppleritic xylite. Microscopic and chemical changes associated with gelification* The microscopic appearance and gross chemical structure of the Victorian xylites were compared with those of Pinus radiata and Eucalyptus regnans woods, and their lignin and holocellulose fractions. Our studies indicated a strong affinity between the Victorian xylites and the modern gymnosperm (conifer) lignin, consistent with the generally accepted coniferous origin for discrete soft soft brown coal wood fragments (e.g. Nobes, 1922; Patton, 1958). The following changes were observed in the Victorian xylites with increase in the degree of gelification. (1) Increase in the total huminite reflectance due to a combination of increase in the reflectance of the individual huminite submacerals and an increase in the proportion of the higher reflectance huminite submacerals. (2) Loss of humotelinite autof luorescence that can be correlated with the elimination of dark textinite A , the principal cellulose-bearing humirite submaceral. (3) Progressive loss of cellulose and methoxyl groups as observed in the NMR and infrared spectra. (Cellulose is absent from doppleritic xylite.) As cellulose is eliminated from the cell walls, swelling of cell walls and compression of open cell lumens occur, with concomitant modification of the xylite lignin structure, including further loss of methoxyl groups and minor oxidation. These changes in gross chemical structure are reflected by an increase in the carbon aromaticity. Gelification and geological conditions. The full range of xylite gelification, from high-cellulose xylite to doppleritic xylite, occur in a single opencut mine, which suggests that this gelification is not time dependent. The Yallourn and Morwell seams occur under a thin overburden and consequently they are unlikely to have been subjected to pressures and temperatures that are much above ambient values. A separate study of resinite associated with Yallourn seam xylite has shown that diagenetic conditions were very mild, since exocyclic olefinic groups in the resinite have not undergone sterically favourable cyclization; polymerization of bled resin to form resinite is thought to be a photochemical process (Wilson et al., 1984). Reference to the literature suggests that there is an overall increase in soft brown coal gelification with increase in the age of the deposit. Presumably this is because biochemical gelification, which occurs under extremely mild diagenetic conditions in response to pH and Eh conditions, grades into geochemical gelification, which results from in increasing depth of burial and dewatering of the soft brown coal to form lignite.

467

References George, A.M., 1982, Aust. Coal Geol., _4, 111-130. Jacob, H., 1968, Proc. Australas. Inst. Min. Metall., 277, 27-37. Nobes, E.D., 1922, Trans. R. Soc. S. Aust., 46, 528-536. Patton, R.T., 1958, Proc. R. Soc. Vic.,_7£> 129-143. Philp, R.P., Russell, N.J., Gilbert, T.D., & Friedrich, J.M., 1982, J. Anal. Appl. Pyrol., 143-161. Russell, N.J., 1984, Int. J. Coal Geol., 4^ (in press). Russell, N.J., & Barron, P.F., 1984, Int. J. Coal Geol., (in press). Shibaoka, M., 1981, Fuel, 60, 240-246, 945-950. Shibaoka, M., 1982, Fuel, 6^, 265-270. Shibaoka, M., Stephens, J.F., & Russell, N.J., 1979, Fuel, 5^, 515-522. Teichmuller, M., & Teichmuller, R. 1968, In: Coal and Coal Bearing Strata (Eds. D.G. Murchison and T.S. Westoll), Oliver and Boyd, Edinburgh, pp. 233-267, 347-379. Wilson, M.A., Collin, P.J., Vassallo, A.M., & Russell, N.J., 1984, Org. Geochem. (in press).

SEALION:

A PERMIAN GAS PLAY IN THE OFFSHORE SYDNEY BASIN T. G.Russell Sydney Oil Company Limited, Sydney

Petroleum exploration drilling undertaken in the onshore Sydney Basin since 1910 has resulted in a number of non-commercial gas discoveries in Permian and Triassic sandstone reservoirs. To date, no exploration drilling has been carried out in the offshore portion of the basin. Seismic exploration commenced in the offshore Sydney Basin in 1964, with the acquisition of a 1,496 km marine seismic survey for Shell Development (Australia) Pty. Limited. To date, six marine seismic surveys comprising 5,056 km of multi-fold seismic data have been acquired in the Offshore Sydney Basin. The most recent of these surveys was the 1981 Offshore Sydney Basin Marine Seismic Survey, comprising 1,742 km of 48-fold data acquired by Western Geophysical Company of America for ESP Exploration Pty. Limited, Operator for the consortium holding the current offshore exploration permit PEP 9. Despite severe data quality problems interpretation of this seismic data has enabled the mapping of several prominent structural closures in the offshore Sydney Basin. The Sealion structure was first recognised from seismic data acquired by United Geophysical Company for Longreach Oil Limited in 1969. Subsequent surveys for Longreach and later for Endeavour Oil Company N.L. confirmed structural closure on the Sealion prospect. The Sealion structure is a large, north-south trending anticline bounded to the east by a down-to-the-west normal fault. The apex of the structure, located during the 1981 seismic survey, occurs in 41 m water depth, 7 km offshore. As mapped from the 1981 seismic data, the Sealion prospect has an independent four-way dip closure covering 59 km 2 with 140 m vertical closure, and a fault dependent areal closure of 130 km 2 with 250 m of vertical closure. The compilation of regional 'maturation and palaeo-heatflow data for the onshore Sydney Basin has indicated that the Permo-Triassic sequence has attained the highest maturation levels in the vicinity of Sydney. Extrapolation of maturation data from adjacent onshore wells to the Sealion region would suggest that the base of the oil window is as shallow 468

as 500 to 800 m subsea, becoming shallower towards the south. Permian reservoir objectives in the Sealion structure are confidently assumed to lie largely within the gas-condensate window. The Sealion structure is therefore considered to be primarily a Permian gas play. Exploration in the onshore portion of the basin together with detailed reservoir studies have suggested that the failure to establish commercial hydrocarbon production from the Permo-Triassic sequence of the Sydney Basin is largely a function of reservoir quality. This is attributed in part to the low initial porosity of many of the sands together with diagenetic processes which have tended to adversely affect reservoir quality. A number of palaeogeographic scenarios can be created for the offshore Sydney Basin which allow for the development of potentially clean reservoir sands within the Permian sequence in the area of, for example, the Sealion structure. However, until such time as the sequence is drilled, reservoir quality in the offshore part of the basin must remain conjectural. The Sealion prospect undoubtedly has the potential to host significant gas reserves in Permian reservoirs. Its location in shallow water immediately offshore from ' the major population and industrial concentration in Australia of the Wollongong-Sydney-Newcastle region provides a strong incentive for the testing of the structure with an exploration well.

DEVELOPMENT AND MANAGEMENT OF 6E0THERMAL WATER RESOURCES FOR SPAS AND DOMESTIC HEATING IN NEW ZEALAND W.J. Russell and S. Nichol Groundwater Consultants (N.Z.) Ltd., Auckland The Auckland and Bay of Plenty regions of New Zealand have scattered areas where hot water at relatively shallow depth can be tapped for spas, hot pools and domestic heating. The most famous of these areas is the Rotorua Geyserland area. Exploitation of these hot waters has seriously depleted the resources at several resorts and investigations to develop management policies have been carried out. This paper outlines some of the problems, investigations and the resulting management policies.

ALLUVIAL SEDIMENTARY MODELS Brian R. Rust Department of Geology, University of Ottawa, Ottawa, Canada Most modern alluvial systems can be classified into one of three types on the basis of channel pattern. Braided systems have multiple, low-sinuosity channels; meandering systems have single, high-sinuosity channels and anastomosing systems have multiple channels with varied, but generally high sinuosity. These systems can be characterised broadly by their channel processes and the nature and disposition of their overbank deposits. The high lateral mobility of braided channels gives rise to sheet sands or gravels, with poor differentiation between channel and overbank deposits. This differentiation is well marked in meandering and anastomosing systems, which differ in that meandering channels migrate laterally, thereby generating sheet sands. Anastomosing channels undergo little lateral migration, but relocate laterally by avulsion, a process that gives rise to shoestring channel sands. 469

Braided alluvium varies from gravelly proximal to sandy distal systems, with a rare silt-dominated distal type. Proximal braided gravels accumulate on alluvial fans and proximal braidplains or braided rivers. Fans form adjacent to high bedrock relief, which normally has either tectonic or paraglacial origin. Fans are characterised by radially symmetric morphology, and their deposits by radial transport, rapid (within kilometres) downslope facies change (chiefly fining from gravel to sand facies) and, commonly, the presence of debris flow deposits. Flood sedimentation or switching of depositional sites gives rise to repetitive upward fining or coarsening-then-fining on a scale of a few metres. Episodic tectonism produces coarsening-up or coarseningthen-fining sequences on scales of about 10-100 m. Proximal braidplain and braided river gravels are dominated by horizontal stratification. Unlike fan deposits, downstream fining is gradual (over tens of kilometres), debris flow deposits are rare, and repetitive vertical sequences are lacking. Like the gravels, proximal sands contain abundant horizontal strata, but trough cross-stratification is also common. Distal braided gravels are characterised by upward-fining sequences from trough cross-bedded gravel, through sand to mud facies. The gravels accumulate in the lowest, most active tract of the system, the sand in tracts activated during moderate flood, and the mud in high-flood areas, which are vegetated in late Palaeozoic and younger deposits. Migration of these tracts gives rise to the repetitive fining sequence. Distal braided sands also form repetitive fining sequences with abundant trough cross-stratification if the river tract is deep and terraced, but planar cross-strata are dominant on broad, shallow, distal braidplains. Meandering fluvial systems commonly form fining-upward channel sequences, with upward decrease in the scale of sedimentary structures. These sequences result from lateral migration of point bars, and are best developed in the downstream segment of the point bar. The channel deposits are mainly sand-dominated, commonly with basal gravel lags, but some comprise subequally interstratified sand and silt. They accumulate by lateral accretion on point bar surfaces, with palaeocurrents parallel to point-bar strike. Such deposits are characteristic of meandering-fluvial deposits, but their recognition requires good exposure. Absence of lateral-accretion (epsilon) cross-strata may be due to lack of variation in the fluvial load, lack of stage fluctuation, or interference by smaller bedforms. Overbank sandstones deposited on levees and crevasse-splays are thinner and finer than channel sandstones. They commonly support vegetation and pass laterally into floodplain muds. If floodplain subsidence keeps pace with plant growth and clastic sediment is excluded, extensive economic coal seams may form between major channels. More rapid subsidence gives rise to lacustrine deposition, whereas emergence may produce soil horizons. Anastomosing fluvial systems have sand-dominated channels, which show only a moderate tendency to migrate laterally. Instead, they accrete in a predominantly vertical manner, and relocate laterally by avulsion. On a large scale this gives rise to shoestring channel sands isolated within overbank deposits. Internal erosion surfaces are common in the channel sands, but upward fining and an organised arrangement of sedimentary structure are not characteristic features. The overbank deposits are similar to those of meandering systems, but floodplain deposits, including coals, have less lateral extent, because the channels are more closely spaced. External controls on the development of alluvial systems are complex, and include relief (tectonically induced), climate, source lithology and vegetation (evolution- and environment-controlled). Temporal changes in one or more of these controls ultimately lead to changes in alluvial style. Sedimentary facies modelling should aim to identify not only the style of ancient deposition, but also how changes in style reflect changes in external controls. Important economic benefits can result. For example, a 1.5 km fining-upward Pennsylvanian succession in the Sydney Basin of Nova Scotia reflects environmental change from proximal through distal braidplain to a meandering system. The nature of preserved coals changes correspondingly from transported mats to sub-economic seams to basin-wide economic seams. Other economic deposits influenced by aspects of alluvial sedimentation include placer gold and uranium, hydrocarbons and sediment-hosted base metal deposits. 470

SOME AUSTRALIAN EXPERIENCE IN GEOSCIENTIFIC COOPERATION DEVELOPING COUNTRIES

WITH

R.W.R.Rutland Bureau of Mineral Resources, Geology and Geophysics, Canberra Because of its size and range of geological environments and its particular morphotectonic history, the Australian continent offers a variety of geological and geophysical models that differ significantly from those that can be derived from other continents.. As a consequence Australia has developed a range of expertise in this resource-related sector, and it provides opportunities for the growing number of developing country geoscientists who are taking part in fieldwork in Australia for exDerience and training. The modern tectonic settings to the north and east of Australia, in southeast Asia and the Southwest Pacific, in turn provide Australian geoscientists with a broader framework for the interpretation of Australian geological history and with analogies that can be applied to the older folded terrains. BMR's involvement with the developing countries of the region include a number of facets. These include: geological and geophysical mapping, and training, in Kalimantan in the Indonesia Australia Geological Mapping Project; the production of international maps (CGMW, ESCAP, Circum-Pacific Map Project); involvement in international programs, eg IGCP 32 Correlation of sedimentary basins in the ESCAP region, and 156 Phosphorites; participation in the Tripartite (USA-New Zealand-Australia) marine research cruises in the Southwest Pacific; the provision of technical advice - to CCOP, CCOP/SOPAC, ESCAP Committee on Natural Resources; broad-ranging activities under international agreements, such as the MOU with the Chinese Ministry of Geology and Mineral Resources signed in 1983; activities in specific fields, such as engineering geology, groundwater and geological hazards; participation in missions, such as the June 1984 mineral development mission to Burma. Wherever practicable BMR seeks to coordinate available Australian geoscientific expertise. Much of Australia's geoscience activities in the south/southeast Asia-Southwest Pacific region have been carried out with aid funds. The Committee to Review the Australian Aid Program (the Jackson Committee) has recently reported to the Government. The Government has yet to react, but the Report itself does provide an insight into Australian attitudes. Of importance in it is the need for a more strategic approach to individual developing countries, and a better definition of types of aid in relation to geographic sectors. The Report also advocates that Australian aid should exploit its relative sectoral strengths: our aid is presently concentrated in agriculture, but the report recognises a number of other fields where Australian expertise is available - among them 'mineral exploitation1. The further development of geoscience activities in the region, within the broader spectrum of.scientific cooperation, depends in some measure on the development of communications so that proposed projects can be carefully evaluated, their merits assessed, and priorities determined.

471

THE INITIATION OF DEBRIS FLOWS ON STEEP MOUNTAIN SLOPES IN HONG KONG Bryan P. Ruxton Canberra College of Advanced Education, Canberra Hong Kong is a series of islands and part of the mainland of China made up dominantly of mountains rising up to 900 metres above sea level. It has a seasonal climate in the humid tropics and periods of intense rainfall often causing widespread landslides. The threshold of intense rain necessary to cause numerous landslides is believed to be over 70 mm/hour (Brand et al. 1984). Seismic activity is rare and weak. The greatest mass movement has been on semi-continuous scarps developed where intrusive granite cupolas have domed up the acid volcanic rocks and incision and erosion has caused a basin form. Hong Kong harbour is the best example. Scarp profiles have upper rocky slopes at 50° to 90° above debris slopes often at 38° and these lead down to concave lower slopes from 25° gradually decreasing to 10° or less. The rocks are deeply weathered with abundant corestones, some of large size (10 metre long diameter), set in a residual clayey silt (volcanic) or clayey sand (granite). The dominant clay mineral is halloysite and there is no montmorillonite. Clay seams are rare. Boulder colluvium drapes the hillslopes below scarps (Berry and Ruxton, 1960); a few metres thick on the debris slopes and up to 30 metres thick on some lower slopes. In places it extends down onto the flats, but much of it is believed to have been eroded off during high sea level periods (Public Works Department, Hong Kong 1982). The colluvium ranges from coarse breccias to abundant boulders floating in an unsorted matrix of gravel, sand, silt and clay. Typically, all size grades are represented. Detailed studies on the flanks of Victoria Peak, Hong Kong Island, included many pits and boreholes and the installation of tensiometer networks. Tensiometer results revealed water ponding up at several levels at each site. Size distribution analysis on the fraction less than 6 mm diameter revealed a uniformity of size distribution between these levels suggesting a layering of the colluvium with layers 2-4 metres thick. Microscopic examination of the fine sand fraction demonstrated that several minerals, sphene, allanite, monazite, topaz, epidote, fluorite and garnet, were diagnostic of certain layers. In places, sedimentary structures include laminar-texture, eddies and swirls suggesting movement of masses by debris flow. In one locality (University Drive, Hong Kong Island) the colluvial layer displayed a wholly laminar structure with randomly arranged boulders which are enclosed in a sheath of matrix. This gives the impression of laminar flow with rotating boulders, which has recently been witnessed (Wasson, 1978). A recent slide (Po Shan Road, 1972) had the characteristics of a debris flow. Samples of the colluvium matrix were examined under the microscope and showed a complete lack of directional structures. Rock fragments often have a clay rim and there is a small percentage of voids, probably entrapped air. The breaking pattern of the samples was completely irregular. In general around Hong Kong Harbour, the boulder colluvium occurs in composite lobes with a less weathered, coarser colluvial assemblage resting on a more weathered lower finer colluvial assemblage. In the lower layers all the boulders are rotten, but in the upper layers some fresh boulders have a thin weathered rim 10 mm thick. This suggests an Upper Pleistocene age for the upper layers. Carbon does occur but not in sufficient quantities for dating purposes.

472

Individual debris flow units have not been fully mapped out, but the largest units would be up to 10 metres thick, 100 metres wide and two kilometres long. In places, they would interfinger with fan, alluvial and marine deposits. Present reslipping of the colluvium may be due largely to human factors. For the most part the colluvium is armouring many slopes and slope ridges, and is therefore a fossil deposit formed in wetter or more seismically active periods than the present. Slope retreat appears to be episodic; the formation of thick colluvium mantles is followed by a long period of weathering and reslipping before further slope retreat takes place. Retreat of the rock cliffs by 50 to 200 metres would account for all the colluvium produced. References Berry, L., & Ruxton, B.P., 1960, Z. Geomorph., 4 , 97-115. Brand, E.W., Premchitt, J . , & Phillipson, H.B., 1984. Proc. 4th Int. Symp. Landslides, Toronto, in press. Public Works Department, Hong Kong Government, 1982. Mid-levels Study. Goetechnical Control Office, 264 p . Wasson, R.J., 1978, Geogr. Annlr., 60A, 151-159.

THE AUSTRALIAN ROLE IN 6E0SCIENCE EDUCATION AND

TRAINING

K.K. Sappal Western Australian Institute of Technology, Bentley, W.A. The Australian continent is richly endowed with mineral and energy resources and because of its enormous mineral wealth Australia is in the unique position of being a wealthy country surrounded by less developed countries of the Asian and Pacific region. In an interdependent world community, it is obviously in Australia's interest to co-operate with other countries of the region in tackling the serious economic and social problems. One way to tackle these problems is the development and enhancement of education and training in geosciences for less developed countries, which will assist in the development of mineral and energy resources. The term Geoscience in this paper refers to specialities of geology e.g. geophysics, geochemistry palaeontology, stratigrpahy, petrology etc. The 1983-84 Australian Overseas Development Assistance Program is of the order of $836.6 million according to the Budget Paper No. 9 circulated by the Minister for Foreign Affairs. The program represents 0.48 percent of GNP in comparison to 0.47 percent for the previous year. The international target for development, assistance is 0.7 percent of GNP and thus the Australian program is below the target. The education and training component of the program is $31.9 million for 1983-84 and only a minor fraction of this may be spent on geoscience education and training. This paper briefly summarises the existing overseas education and training in which the geoscience component is not separately identified. The paper identifies the importance of the mineral and mining sectors for less developed countries in the region and justifies the enhancement of geoscience education and training. A case for the establishment of the Australian International Geoscience Centre (AIGC) is proposed in the paper, and the centre when established would be responsible in the following areas:-

473

Identification of geoscientific needs of less developed countries in South-east Asia and South-west Pacific region.

Preparation of long term proposals in consultation with experts from less developed countries for government funded programs in the region.

Commissioning approved programs of research and training by Australian Institutions funded by private and public sectors.

Liaison with international organisations for multilateral aid programs in areas of mineral and energy resources development.

Establishment of bilateral contacts and exchange of geological specimens and publications between academic institutions of recipient and host countries.

Establishment of a Development Assistance register consisting of details and qualifications of geoscientists who may be able to contribute in a collaborative or consultative way to programs in less developed countries.

COMPOSITIONALLY ZONED PLUTONS BY DOUBLE-DIFFUSIVE SIDEWALL FRACTIONATION PROCESSES: EVIDENCE FROM THE PALISADE CREST SUITE 9 CENTRAL SIERRA NEVADA, CALIFORNIA Wayne N. Sawka and Bruce W. Chappell Geology Dept.

Australian National University, Canberra

Two nested and compositionally zoned plutons were examined to determine the mechanism by which crystals are separated from a magma. The Tinemaha pluton has a continuous compositional variation (58%-67% SiC^) and surrounds the McMurry Meadows pluton which is bi-modal with an outer margin of mafic granodiorite (59%-60% SiC^) and an inner core of granite (66%-69% SiC^). Extreme differentiates also occur within the suite as small isolated masses and may contain up to 76% SiC^* Both plutons are isotopically homogeneous with initial 87/86 Sr of 0 70719 and 0 70651 respectively. The Tinemaha pluton is both horizontally and vertically (^1000m) zoned. Vertical trends in relative mineral percentages do not support crystal settling. The vertical and horizontal whole rock variations in chemistry (50 elements , mineralogy and accessory mineral LREE zoning are directly relatable to side-wall crystallization and accumulation which produced a less dense melt fractionate that buoyantly moved toward the magma chamber top. A portion of the side-wall "feeder zone" has apparently been solidified there, before completing the buoyant rise upward. This feeder zone is gradational within the pluton and exhibits chemical features found only in the the top of the pluton some 900 metres higher. The compositional gap in the McMurry Meadows pluton results from a similar though more efficient, side-wall fractionation process, related to a relatively higher proportion of melt to crystals in the initial magma and slower side-wall solidification due to the enclosing Tinemaha pluton creating a thermal blanket. If such a crystal fractionation process occurs in volcanic magma chambers it implies that: (1) erupted phenocryst assemblages are not necessarily representative of the fractionating phases (2) compositional gradients in crystal poor ash flows may be due to crystal fractionation rather than liquid state diffusion, and, (3) some rhyolite plus zoned intermediate volcanics with large compositional gaps may be differentiates of a single magma. 474

THE BEHAVIOUR OF CLAY RICH ROCKS DURING MINING R.W. Seedsman CSIRO Division of Geomechanics, Mt. Waverley The surface mining of black coal and oil shale involves the handling of large amounts of clay rich rocks. In underground coal mining, both the roofs and floors are typically of clay-rich rocks. Many geotechnical problems, for example highwall and spoil-pile failures in surface mines and floor heave and roof falls in underground mines are directly related to the presence of clay rich rocks. The strength of clay rocks and their loss of strength during mining is controlled by a wide range of factors including depositional environment, diagenesis, tectonic activity, weathering, and changes brought about by the mining procedures. This paper will discuss the factors controlling the intact strength of clay rocks, the mechanisms by which clay rocks can lose strength on exposure to water, and the complicating effect of mining activity. Factors that will be discussed include the role of organic matter and carbonate, the influence of clay mineralogy, and the crystalline and osmotic swelling of clay minerals. Examples of how knowledge of.the structure and behaviour of clay rocks has been applied to problems of mine design and the study of mine instability will be presented.

THE MESOZOIC SEQUENCE OF THE NORTH EASTERN CARPENTARIA BASIN - A SERIES OF MARINE TRANSGRESSIONS N. Senapati and D.J. Bourke Comalco Aluminium Ltd, Brisbane The Carpentaria Basin is an intracratonic downwarp filled with Mesozoic sediments. The basin overlies crystalline and sedimentary rocks that range in age from Proterozoic to Lower Permian. Superimposed on the basin is the dominantly Cainozoic Kurumba Basin. The stratigraphy and structure of the north eastern Carpentaria Basin was established on the basis of reconnaissance mapping and sparse shallow stratigraphic drilling done by the BMR in the early 1970fs in order to compile the 1:250,000 geological maps covering the area. In the late 1970fs and early 1980?s the north eastern Carpentaria Basin was explored for coal by Utah Development Co. and Comalco Aluminium Ltd. Data from these exploration programmes is mainly in the form of chip and core samples, downhole geophysical logs and measured sections of outcrop. Using this data it has been possible to refine the stratigraphy and postulate on the palaeoenvironments of deposition. The eastern margin of the basin is defined by the Coen Inlier, which has rocks similar to those of the basement. The basement deepens to the west, however there is some relief on the basement surface that is characterised by a series of NNW-SSE trending ridges and troughs. This relief is probably a result of faulting within the basement, forming a series of half grabens. Basement relief has had a strong influence on the sedimentation. Gentle dips in the Mesozoic sediments in proximity to major lineaments, as seen on landsat images, may represent drapes or flextures over pre-existing basement structures. 475

At the onset of Mesozoic sedimentation, each trough had similar but independent fluvial systems depositing mainly conglomeratic quartz sandstones. In some of the basal erosional surfaces, fine grained sediments and coal were deposited. The sedimentary features consist predominantly of cro&s-beds, horizontal bedding and numerous scours. The cross-beds indicate a unimodal transport direction to the west. This unit may be equated to the Garraway Beds. Following the initial period of fluvial sedimentation a small marine transgression deposited oolitic, chamositic sandstones which covered most of the area, onlapping and covering the emergent ridges. The unit is very distinctive and has a very characteristic geophysical signature. A regression followed, re-establishing a fluvial system which deposited more quartz sandstones, with tabular cross-beds indicating a westerly transport direction. The fluvial system matured to a lower delta plain environment where medium to coarse grained sandstones were deposited interbedded with siltstones and mudstones. Sedimentary features consist of rare burrows, woody impressions and tabular and trough cross-beds indicating a weak easterly transport direction. These features suggest that the unit was possibly deposited in an environment that fluctuated from a deltaic to moderate wave energy shallow marine environment. The marine transgression continued and units which can be equated to the Gilbert River Formation were deposited. Siltstones interbedded with massive, subhorizontally bedded, glauconitic sandstones were deposited.

Depth

Hole

35104 m

STRATIGRAPHY (After Smart, et.al. 1980)

cu 3 0 u u 1 X) 3 w n

100

>i . c s tp r-» is

AGE

Late Albian

Rolling uuwua Group Albany

Aptian to Early Albian

Pass Beds

Gilbert 200

Neocomian

River Formation Helby Beds

Late Jurassic

300 Garraway Beds basement

Middle? to Late Jurassic

1400

Figure 1 Reference Smart, J., Grimes, K.G., Doutch, H.F. & Pinchin, J., 1980, Bur. Miner, Resour. Aust. Bull. 202.

476

Bioturbation in these units is common and includes various types of burrows. Other sedimentary features observed are ripple bedding, possible hummocky cross-stratification, low amplitude scours, and rare large scale cross-beds. The units indicate they were deposited in a shallow marine environment. Marine conditions continued in the NE of the basin withr the deposition of monotonous glauconitic mudstones which are bioturbated throughout. This mudstone unit can be equated to the basal mudstones of the Rolling Downs Group. The three layer stratigraphy (Figure 1) of the north eastern Carpentaria Basin with the Garraway Beds overlain by the Gilbert River Formation and then the Rolling Downs Group is somewhat simplistic. At least six units within the Mesozoic sequence are recognizable as shown in the example of hole 35104 (Figure 1). The units are correlatable over a wide area. The sequence has thtee fluvial events and three marine transgressive events. The change from a dominantly fluvial environment to a dominantly marine environment took place as a series of small marine transgressions, increasing in size and ultimately covering the basin with a wide shallow sea. The recognition of the various depositional environments has enabled the establishment of a meaningful stratigraphy.

DISPLACED CRETACEOUS NANNOFOSSILS AND MIDDLE EOCENE MARINE SEDIMENTATION ALONG THE AUSTRALIAN WESTERN AND SOUTHERN MARGIN Samir Shafik Bureau of Mineral Resources, Canberra Displaced Upper Cretaceous calcareous nannofossils link broadly coeval middle Eocene assemblages in four basins along the Australian western and southern margins. These assemblages were deposited at about the same time as a major change in the spreading rate south of Australia, which coincided with global plate reorganisations. In the Carnarvon and Perth Basins (western margin) the assemblages represent pronounced changes in depositional environment. In the Carnarvon Basin they occur within a nannofossil-rich sequence and are associated with a regional break. In the Perth Basin they are separated from both older and younger Tertiary assemblages by barren intervals, indicating a short-lived transgression. In the Eucla and Otway Basins the assemblages represent different stages in the development of open-marine conditions on the southern margin. In the Eucla Basin they occur at the base of the marine section, and probably represent the advent of the transgression. In the Otway Basin they occur in horizons separated from each other and from the marine section above by barren intervals, and thus represent ingressions preceding the (essentially late Eocene) transgression. In situ Upper Cretaceous nannofossils are abundant in sediments widely distributed along the western margin of Australia and in the Indian Ocean, but are not known from the southern margin nor in the Southern Ocean. Source areas for the displaced Cretaceous nannofossils associated with the southern Australian middle Eocene horizon are therefore difficult to locate. The Naturaliste Plateau, off southwestern Australia, is thought to be a possible candidate. Upper cretaceous sediments on the plateau contain abundant nannofossils and there is some good evidence to suggest that these sediments were exposed to submarine erosion during the middle Eocene.

477

AID PROGRAM EXPERIENCE WITH ENGINEERING GEOLOGY FOR MAJOR CONSTRUCTION WORKS K.R. Sharp Snowy Mountains Engineering Corporation, Cooma The Snowy Mountains Authority and the Snowy Mountains Engineering Corporation have been involved with Australian Aid Projects in the field of hydro-electric and irrigation engineering since 1960. This paper deals only with those Australian aid projects which have had a geotechnical component, and these mainly consist of Feasibility Studies or Design and preparation of Contract Documents for large dams, power stations and associated works. Such aid projects in the AsianPacific area have been undertaken in the Solomon islands, Papua New Guinea, Indonesia, Malaysia, Thailand, Cambodia (now Kampuchea), Lao and China, but similar non-aid, or non Australian aid work has been carried out in other Asian countries including Nepal, Burma and Sri Lanka. The project team varies from job to job, depending on the technical requirements of the particular project and the availability and qualifications of counterpart staff. Typically for a large project, an engineering geologist, a geotechnical engineer, a soils technician and a diamond drilling supervisor would be full time team members, with a senior engineering geologist and geotechnical engineer as visiting specialists. Counterpart training is an important facet of aid programs, but in some cases effectiveness needs to be critically examined. Diamond drills and drilling equipment have been provided to several countries under aid, and drilling supervisors have been responsible for training drillers. Drilling supervisors have continued to train drillers on some of the more recent projects, but the use of experienced contract drillers is becoming more common. Specialised geotechnical equipment may at times be loaned, or supplied, as part of the aid program. Examples of loans included seismic refraction%equipment and down hole pressure meters. Examples of equipment supplied are soils laboratory apparatus and earthquake recording equipment.

S-TYPE GRANITOIDS IN THE PENINSULAR RANGES BATHOLITH, SOUTHERN CALIFORNIA S.E. Shaw1, V.R. Todd2, J. Cooper3 and J.R. O'Neil2 ^•Macquarie University, North Ryde U.S. Geological Survey, Menlo Park University of Adelaide, Adelaide 2 Over 300 km of S-type granitoids occur in the central and eastern parts of the Peninsular Ranges batholith, southern California. They are present as highly deformed plutons and anatectic migmatites within metapelitic wallrocks that have been metamorphosed to upper amphibolite facies. From field evidence, the granitoids overlap in age with and have undergone a similar structural history to the 120-105 Ma I-type granitoids that occur mainly to the west. Initial 87 Sr/ 86 Sr ratios (0.7079-0.7154) and 6 0 values (11.8-19.8) 'indicate a significant metasedimentary component in the granitoid source rocks.

478

The distribution of I- and S-type granitoids in the Peninsular Ranges batholith is similar to those of the Lachlan Fold Belt in eastern Australia, with the westernmost development of S-type granitoids defining an I-S line that parallels the continental margin. This I-S line lies close to the metamorphic, gravity, age, isotopic and prebatholithic lithology contrasts within the batholith, and together these features are considered to mark a fundamental change of the underlying crust. If the western part of the batholith represents an Upper Jurassic and Lower (?)Cretaceous accreted tectonostratigraphic terrane, then the zone marked by these contrasts probably represents a terrane boundary.

RAPID DECAY OF SLATE ROOFING TILES IN SERVICE A. Shayan and C.J. Lancucki CSIRO Division of Building Research, Highett, Victoria It has been found that slate roofing tiles containing pyrite (8.3%) have undergone a rapid decay aft;er only two years of service in a suburb of Melbourne. The cause of the decay is the oxidation of pyrite and the production of highly hydrated iron sulfates. As well, Fe-rich chlorite contained in the slate is attacked by the very acidic environment resulting from the oxidat ion of the pyrite, and produces additional highly hydrated sulfates of iron and aluminium. The minerals identified by X-ray diffraction in the decayed tiles, in addition to the original quartz, muscovite mica and iron-rich chlorite, are hydronium jarosite Fe3(S04)(OH)5.2H20, melanterite FeS0^.7H20, and halotrichite FeAl2(SO^)^.22H2O. Scanning electron microscopy and energy dispersive Xray analysis were used to confirm the presence of hydronium jarosite rather than potassium jarosite, through the lack of K in the reaction product. This indicated that the muscovite was probably unattacked by the pyrite oxidation. A milder decay in another slate tile is thought to have been due to the oxidation of small amounts of pyrrhotite, leading to blistering and fretting of the slate. Formation of elemental sulfur, goethite, gypsum and hydronium jarosite were associated with this form of decay. Great increases in the molar volume of the reaction products relative to that of the original components are responsible for the disintegration of the slate. The work shows that slate intended for use in buildings must be free of pyrite.

ELECTRICAL RESISTIVITY INVESTIGATION OF THE SCHOFIELD HIGH-LEVEL WATER BODY, OAHU, HAWAII K.V.Shettigar Dept. of Geology and Geophysics, Univ. of Hawaii, Honolulu Nineteen deep Schlumberger soundings (AB/2 2000 to 3000 m) and three gradient profiles (AB around 4000 m) were conducted over the Schofield high-level water body to accurately locate and study the nature of its boundaries.

479

The high-level water body (HWB) is so called because of the anomalously high hydraulic heads within it. The HWB is bound by the dike systems of the volcanic mountain ranges - Waianae and Koolau on the west and the east respectively (Fig.l). The nature and the locations of the boundaries on the north and south are not well known. The figure shows the boundary locations suggested by the earlier workers. Regarding the nature of the boundaries the models considered are 1. Waianae ridges buried under the younger Koolau flows, and 2. dike intrusives. Principle behind the survey; The HWB is surrounded by basal water bodies which obey the Ghyben-Herzberg relationship. Swartz (1940) has shown that the depths to the saltwater within the HWB is much higher than those in the basal waters. Considering the contact between the saltwater and freshwater as a marker horizon, it is believed that the boundaries of the HWB may be located by mapping it. The resistivity soundings are used to map the marker horizon (MH) and the gradient profiles to locate the boundaries between the soundings and to determine their nature. Haleiwa

158*15'

T OAHU

- 21*30'

21*15*

i — I High level water b o d y - D a l e A T a k a t a k i (1976) Creat of Waianae range Koolau range

L i i J

GEND • sounding location . 3 la gradient profile with number _ boundary delineated by 8 w a r t z ( i g 4 0 ) Broadbent ( 1 9 8 0 ) ~ limits of high-ievel water - f r o m 1 - D sounding Interpretation resistivity high structures ABCD - f r o m 2 - D num. modeling

®14

well location with hydraulic head In ft. highway

Town

Interpretation: Initially the soundings are interpreted using a 1-D inversion program. Considering the depths to the MH and the well data,the limits for the boundaries of the HWB are drawn (see figure). Starting with the 1-D model obtained from the sounding(s) on each profile, the gradient profiles are interpreted using 2-D numerical modeling. From the 2-D models back computation is done to obtain the sounding curves on the profiles. The process is repeated till a 2—D model satisfies both the sounding curve and profile. Numerical modeling: The finite difference program of Dey and Morrison (1979) is used for 2-D modelling. The program solves the potential field in a transformed space. The transformed potential Vf (Fourier cosine transform of potential V in real space) is solved as a function of a preassigned set of wave numbers. At each grid point the function Vf is approximated to an exponential or a linear function between adjacent wave numbers in order to inverse-transform Vf by integration. It is apparent that the accuracy of V is dependent on the distribution of the wave numbers and the type of interpolation used.

480

A new approximation: In the present study a combination of exponential integrals and Incomplete Gamma functions is used to integrate the Vf function and it is found to yield more consistent results for moderately varying geoelectric models and wave numbers. This approximation reduces considerably the need to calibrate and assign a new set of wave numbers between repeated runs of the models with minor modifications. Results: From the limits of boundaries drawn in Fig.l it is seen that the southern boundary closely follows the previously known locations. On the north there is considerable deviation except for the boundary drawn by Dale and Takasaki (1976). Regarding the nature of the boundaries, the 2-D models of the gradient profiles in conjunction with the sounding data reveal the following: A total of 4 resistivity-high structures (resistivity around 300 ohm m) are discernible. In the north the resistivity-high D is due to swarms of shallow (less than 10 m) resistive rocks. The numerical model for the location shows the absence (or great depth) of the MH to the east of D. This suggests that the resistive rocks are impermeable which probably means that the northern boundary of the HWB is due to dikes. In the south, the resistivity-highs A and B appear to be situated on the southern boundary. The 2-D models show a disruption of the MH to the north of these locations. The resistive body is around 100 m. below A and less than 30 m below B. The location A is 45 m above B, which means the resistive body at A is. at a deeper level than that at B. A buried ridge cannot explain this phenomenon satisfactorily. These observations tend to support the view that the southern boundary is also dike related. However, the study at this stage is inconclusive. The resistivity-high C is vaguely discernible on profile 2. Its estimated depth is 15 m. Interestingly, the MH continues under this structure and progressively gets deeper. This structure is probably a buried ridge of the Waianae range. Acknowledgement The author thanks the U.S .Geological Survey and the Water Resource-s Research Center,Univ. of Hawaii, for supporting this investigation References Dale, R.H., & Takasaki, K.J., 1976, U.S.G.S. Water resources investigations 76-47 - Report. Dey, A., & Morrison,H.F., 1979, Geophysical Prospecting, 27, 106-136 Swartz, J.H., 1940, Trans. A.G.U., 20. 292-298 Broadbent, E.W., 1980, Report, Amfac Inc., Honolulu

GROUNDWATER POLLUTION BY DAIRY FACTORY EFFLUENT AT ALLANSFORD, VICTORIA A. Shugg Department of Minerals & Energy, Melbourne At Allansford on the coastal plain near Warrnambool in Western Victoria a large dairy factory complex has for the past 20 years been using underground waste disposal techniques to dispose of its effluent. The effluent is a mixture of cheese whey, butter whey and washing water. A 40m deep injection bore is used to dispose of the waste into the Miocene limestone aquifer. Groundwater in the limestone aquifer is of good quality and has been used for farm and irrigation supply. The factory complex disposes of up to 1M1 of waste per day. More than 8 000 000 tonnes of dairy effluent has been injected into the aquifer. 481

The cheese and butter whey waste stream has been injected into the aquifer at a temperature of around 38°C, it has an initial pH of between 3 and 4. The waste is mainly composed of soluble organic material which ferment and become anaerobic and odorous. The pollution effects of these wastes usually relate to oxygen demand after the formation of heavy black sludge with a strong butyric-acid odour. Whey has a soluble solids content of about 5%, a BOD (5 day) of 20 000 - 30 000 and an inorganic dissolved load of around 3000 mg/1. The anaerobic digestion of the whey has produced large quantities of methane and carbon dioxide in the aquifer. Flows of these gases have been encountered in bore holes. The waste disposal activities occur in the upper 40m of the Miocene limestone aquifer. This section consists of a fine grained porous and friable calcarenite. It has a residual primary porosity of between 0.2 and 0.3. In addition solution enlarged conjugate joint sets have been developed by .the karst processes which have been active in the aquifer. The aquifer is unconfined and has a hydraulic conductivity of between 1 and 5 m/d. A hydraulic gradient of 0.01 is usual and groundwater flow is towards the south west. Karst topography of low relief has been developed on the limestone. A plume of contaminated water has been traced from the disposal operations. The plume may be differentiated chemically and thermally from the ambient groundwater conditions. The thermal axis of the plume indicates that the waste floats on the cooler groundwater body. The plume has a temperature range of between 20°C to 30°C and extends a distance of more than 1000m from the injection site, probably not equibilibrating with ambient groundwater temperature of 16°C until it is 2000m from the injection point. The waste plume has very high concentrations of various nitrogenous species. Ammoniacal nitrogen exceeds 300 mg/1 and remains as high as 150 mg/1 in an observation bore 700m from the disposal. The nitrate levels in the plume do not descend below the W.H.O. D.W.S. until the plume is 2000m from the disposal site. Other inorganic constituents of the water may be used to trace the plume in particular HC03> K and Total Dissolved Solids (inorganic). Arsenic concentrations in the plume have been recorded between 0.15 and 0.37 mg/1, which exceeds the ambient range of 0.005 to 0.01 mg/1. The presence of arsenic is attributed to the reagents used in the process washing cycle. Potassium is a useful parameter for mapping the extent of the contamination plume. The potassium concentrations in whey may be as high as 1000 mg/1, the levels in the aquifer are around 1 mg/1. The underground disposal of dairy factory wastes at Allansford has led to the formation of a lobate plume of contaminated groundwater. The plume can be identified on a chemical and thermal basis. It occupies the top 20 to 30m of the aquifer, attains a width of around 700m and extends more than 2500m from the disposal point. It has led to the abandonment or deepening of farm bores and egress of pungent smelling gas has resulted in several complaints.

References Barnett, S.R., Armstrong, D.W. and Emmett, W., 1977, Dept. Mines S.A. Rept. Bk. No. 77/21. Drew, W.M. and Martin, W.R.B., 1975, J. Aust. Water and Wastewater Ass. 2, No. 1 9-14. Smith, P.C. and Schrale, G., 1982, J. Aust. Water and Wastewater Ass. J9, No. 1 21-25. Nemerow, 1971, Liquid Waste of Industry Theory, Practices and Treatment. Addison Wesley 5264. 482

AN ACCELERATOR LABORATORY FOR THE EARTH SCIENCES S.H. Sie CSIRO Division of Mineral Physics, North Ryde Energetic ion beams from particle accelerators with energies in the MeV regime have proven to be versatile analytical tools for a considerable range of applications. Interaction of these particles with matter gives rise to Rutherford backscattering spectrometry (RBS), Particle induced Xray emission (PIXE) and nuclear reaction analysis (NRA) techniques. A more recent addition to these is the accelerator mass spectrometry (AMS), permitting isotopic ratio measurements in the 1:1012 range or better. The newly commissioned (October 1983) Heavy Ion Analytical Facility (HIAF) Laboratory of the CSIRO Division of Mineral Physics at North Ryde was conceived in recognition of the demonstrated and potential importance of the application of these techniques in the geosciences, to complement and extend established methods. The laboratory is based on a 3 MV Tandetron, a tandem electrostatic accelerator. It is capable of producing up to 6 MeV proton beams, 9 MeV alpha particles, and heavy ion beams of virtually any element in the periodic table with energies up to 18 MeV. The first stage operational at commissioning provides for RBS, NRA and macroscopic PIXE analysis. For mineralogical applications, a microprobe lens for shaping the beam down to the micron dimension has been constructed and is currently undergoing test. The AMS system is planned to be operational towards mid 1985. The RBS method is particularly useful for stoichiometric and structural studies of thin films and crystalline structures. It is a powerful method for determining the location of impurity atoms in a lattice; its application in mineralogy can be viewed as an extension of the XRD (X-ray diffraction) technique. PIXE extends the conventional electron microprobe technique to detection of trace elements in the ppm range, by virtue of the much higher yield of characteristic X-ray production and lower continuum background radiation. In the NRA technique, an assortment of specific nuclear reactions, mainly resonant reactions is exploited to yield depth distribution information of specific elements. Most reactions are induced by protons or alpha particles, but using ^ F or ^ N beam, hydrogen can be detected with a few ppm sensitivity and nanometers depth resolution. This can be used for example to detect water or OH occuring in small quantities (<0.2%) in samples, such as quartz. The advent of ion-microprobe spectrometry, which combines high sensitivity probing with isotopic detection capability, created considerable excitement amongst the geoscientists. However, application of this technique has been beset by molecular and isobaric interference problems, requiring very high mass resolution (>7000) usually at the expense of detection efficiency, often leading to unfeasible measurements. The AMS technique alleviates this problem by accelerating the secondary ions, i.e. those sputtered off the sample, to MeV energies, destroying most molecular ions in the process. The resultant atomic ions could then be resolved with moderate resolution and high efficiency. Isobaric interferences are resolved by means of particle identification techniques available only at MeV energies. These cosmogenic

advantages lead to the feasibility of exploiting several radioisotope as tracers for a number of geological problems.

483

has Be (T^/2 = 1*5 been used for instance to show that volcanic rocks from island arcs originate from subducted ocean floor. Other important applications include possibilities of dating petroleum and determining 36 t = exposure age of rocks. Cl ( i/2 300,000Y) can be used to trace groundwater movement. Applications of AMS in detection of ultratraces (ppb range) has been shown to be feasible. Considerable development is still needed before AMS can be applied routinely.

In summary, the HIAF laboratory is designed to facilitate the development and applications of ion-beam analysis techniques to the geosciences in general, for the ultimate introduction to the minerals industry, particularly the exploration sector.

THE HIAF PARTICLE MICROPROBE FACILITY S.H. Sie*, C.G. Ryan* and D.R. Cousens^ 1

CSIRO Division of Mineral Physics, North Ryde 2 CSIRO Division of Mineralogy, North Ryde

A heavy ion microprobe is being developed by the CSIRO Division of Mineral Physics, in collaboration with the Division of Mineralogy. This heavy ion analytical facility (HIAF) is to combine the analytical techiques of Particle-Induced X-ray Emission (PIXE) , Rutherford Backscattering (RBS) , and Nuclear Reaction Analysis (NRA) for determining the major and trace element composition of a sample (Sie, 1984). The heavy ion microprobe will also be capable of providing the spatial distribution of the component species within the sample.

CHANNEL-NUMBER

Figure 1 484

Comparison of PIXE and electron microprobe spectra of a biological sample (Cahill et al., 1980)

A 3.0 MV Tandetron accelerator is used to produce a probe beam with energies of up to 6 MeV for protons, 9 MeV for alpha particles and around 15 MeV for heavy ions . For spot analysis and element mapping the beam will be focussed in1 an all-electrostatic, quadrupole lens, configured as a 'Russian Quadruplet , to produce a beam-spot anticipated to be less than 10 microns in diameter. Electrostatic deflection will then be employed to scan the beam over an area of approximately 100 x 100 microns. An energy dispersive Si-Li detector will be used to detect particle induced x-rays and both x-ray energy and spatial information will be stored on-line using a high speed CAMAC system being developed for the HIAF laboratory. With this system x-ray images for all elements will be collected concurrently providing a single-pass, multi-element x-ray imaging. Examination of the distribution and calculation of the composition of any point can then be performed on the computer off-line without any further beam time. The trace element capabilities of the PIXE technique with elemental sensitivities of the order of 1 ppm or less will be of particular interest. The inherently low production of continuum Bremmstrahlung radiation and the large characteristic x-ray production cross-sections of proton and heavy ion beams result in clean spectra with high peak to background ratios and greatly increased sensitivity 'over electron microprobe techiques. The inherent sensitivity of PIXE analysis can be seen in comparisons between proton-microprobe and electron microprobe data from identical samples (Figure 1). The major advantage of the PIXE trace element analysis compared to conventional trace element techniques (e.g. XRF, ICP, AAS, etc.) will be the ability to analyse at ppm sensitivities individual mineral grains of micron size and to determine the spatial distribution of such elements in a mineral assemblage. Further examples of PIXE and electron microprobe spectra from samples of two glass trace element reference standards, each with 16 trace elements at concentrations of ^ 5 ppm and ~ 50 ppm respectively (Myers et al., 1976), and samples of ilmenite and spinel will be presented. The element intensities will be converted to compositions by the application of corrections for the reduction of the observed intensities by ion scattering, x-ray absorption and secondary x-ray fluorescence. These differ, primarily in the spatial distribution of the characteristic x-ray production, from the ZAF correction procedures for the electron microprobe and will have to be developed to allow quantification of the analyses. A major potential application of this technique will be in the study of trace element distributions in the geochemical haloes surrounding ore bodies. The multi-element detection at ppm levels together with the spatial selectivity will provide data unobtainable with currently used techniques. References Sie, S.H., 1984, this conference. Cahill, T.A., 1980, Ann. Rev. Nucl. Part. Sci., 30, 211. Myers, A.T., Havens, R.G., Connor. J.J., Conklin, N.M., Rose, Jr., H.J., 1976, USGS Prof,. Paper 1013.

485

EXPLORATION TECHNIQUES USED IN THE EVALUATION OF TWO LIMESTONE DEPOSITS IN CENTRAL QUEENSLAND J.E. Siemon and M.S. Biggs CSR Limited Coal Division, Brisbane

Two potential cement and/or chemical grade limestone deposits in structurally complex settings in Central Queensland (Figure l), have "been investigated by a combination of several exploration techniques to provide sufficient reliable data to enable reserve calculations to proceed.

The first is located 10km east of Monto where unaltered carbonate sediments of the Early Carboniferous Caswell Creek Group (Yarrol Shelf) crop out on the western limb of the Tellebang Anticline. The largest limestone deposit, the Cannindah limestone, constitutes a number of lenses of oolitic, reefal and detrital limestone, interbedded with mudstone, siltstone, fossiliferous feldspatho-lithic sandstone and calcareous pebble conglomerate. The second is situated 60km south-west of Gladstone where lenses of indurated fossiliferous limestone and marble are interbedded with a suite of calc-alkaline volcanic flows, tuffs and volcaniclastic sediments. This sequence crops out on both flanks of a steeply folded anticline and belongs to the Early - Middle Devonian Calliope Beds (Calliope Block). Initial investigations involved collation and interpretation of regional remote sensing and geophysical data in both areas to provide a broad outline of the regional structure. Comparison of overlays of lineaments, physiography and spectral colour from enhanced Landsat MSS subscenes and photogeological coverage were combined with qualitative interpretations from available aeromagnetics and gravity. This work was supported by reconnaissance mapping and rock chip sampling. Within this broad structural framework, correlation of limestone lenses was attempted using information from ground geophysical surveys (magnetics at Boyne; electromagnetic profiling at Cannindah) and detailed tape and compass grid mapping. Areas prospective for high grade (50-55$ CaO; 2-12% Si02) limestone were then targeted for percussion chip and diamond core drilling, which provided samples for oxide and trace element analyses and physical property testing.

486

Sufficient reliable geological, geophysical and analytical data was collected from both deposits to establish a computerised database for topography and limestone thickness at a specified datum, for individual lenses. These allowed accurate, computer-based reserve calculations to be carried out.

MULTIBEAM STUDY OF THE FLORES AND WETAR BACRARC EASTERN INDONESIA

THRUSTS,

Eli A. Silver Earth Sciences, University of California, Santa Cruz, CA Multibeam (using SeaMARC 2) and seismic reflection studies of the Wetar and Flores backarc thrusts in eastern Indonesia document the growth patterns of normally and obliquely convergent submarine thrust belts. NE and NW trending faults cut the Flores arc and the lower plate strata north of the Flores thrust. Superimposed on these structures are the trench turbidites and accreted thrust packets, composed mainly of deformed trench turbidites. The frontal thrust of the accretionary wedge is scalloped, and a new thrust front is beginning to form where the Flores turbidite basin is widest. The deformation front, in general, lies north of the frontal thrust, as shown by the presence of small folds which do not cut through to the surface. Abnormally high fluid pressures are probably present in the wedge and at the deformation front, as seen by the presence of mud volcanoes and diapirs. Several lines of mud volcanoes trend N10E, parallel to the direction of maximum horizontal stress inferred for the forearc region, based there on orientations of conjugate fractures (Breen et al., in prep.). The depth of the deformation front is 1 km + 200m. This thickness of overburden may be required to develop sufficiently high overpressures to allow the propagation of the basal decollement. Because turbidite basins grow episodically, the basal decollement may have propagated episodically as well. The Wetar thrust shows much more pronounced scalloping of the thrust front. Overlapping thrusts are documented here, and the order is for western thrusts to overlap their eastern neighbors. Mud volcanoes are common here as well. Several narrow NE-trending faults can be mapped along the shelf region adjacent to NW Wetar, and these features may indicate a local direction of cross-arc transport. A large gap seems to occur between the thrust front off NW Wetar and its extension west to northern Alor. In the northern region, the thrust narrows significantly and small seamounts are entering the thrust. These seamounts are calc-alkaline (D. Schwartz, J. Gill, and others, in prep.) and have just been dated at 400,000 years (R. Duncan, written commun.). Thus it appears as if arc volcanism here now occurs just north of the arc and the youngest volcanoes are in thrust contact with the older part of the arc.

487

MODERN TECTONICS OF THE WESTERN INDO-PACIFIC REGION AS A MODEL FOR THE MESOZOIC NORTH AMERICAN CORDILLERA Eli A. Silver Earth Sciences, University of California, Santa Cruz, CA The Western North American Cordillera flanks the craton and is composed of a fold and thrust belt and an outer, complex region of 'suspect terranes' on its western margin. The terranes are composed largely of fragments of island arcs and disrupted terranes (ancient accretionary wedges), with lesser proportions of oceanic plateau and continental crustal fragments. Seamounts and small pelagic fragments are scattered throughout the mountain belt. In the extreme eastern part in the U. S. segment but not the Canadian, the craton has been faulted by deep rooted thrusts making up the Laramide province. Two modern settings have been proposed as an analog to this complex mountain system. One is the Andean belt (Jordan et al., 1983) and the other is the western Indo-Pacific (Silver and Smith, 1983). The Andes have a nicely developed foreland thrust belt and locally regions of rooted 'Laramide type' uplifts east of the thrust belt. The proposed driving mechanism is low angle subduction. No documented terrane accretion is occurring along the Andean mountain system south of Ecuador, making this an acceptable model for the fold and thrust belt and for the Laramide belt, but not for the suspect terranes. In contrast, the Indo-Pacific region is composed of numerous island arcs, backarc basins, accretionary wedges, colliding oceanic plateaus, and non-terminal collision events, all occurring off the northern margin of Australia. The Ontong-Java plateau collision appears in many ways analogous with the Wrangellian dispersed terrane. Collision of this plateau with the Solomon arc may result in backarc basin collapse to produce a suite of ophiolites much like those of the Sierran foothills (Saleeby, 1983). Ophiolite emplacement by collision is documented in Sulawesi (Silver et al., 1983), and blueschist emplacement by the same process is highly suggestive. The accretionary process has resulted in the development of a foreland fold and thrust belt in northern Papua New Guinea and Irian Jaya, and the collision between the Australian continental margin and the eastern Sunda arc show s the initial stages of foreland thrust belt development. Rooted folds m the foreland of Irian Jaya (Wing and Mueller, 1975) may represent the early stages of Laramide style uplifts. From these observations I suggest that the North American Cordillera was initiated and shaped to a major degree by processes of terrane accretion closely analogous to those occurring in the equatorial IndoPacific, including the development of the Rocky Mountain fold and thrust belt and the initiation of the Laramide uplifts. Evidence of rapid subduction of relatively young oceanic lithosphere in the Paleocene to middle Eocene of the eastern Pacific (Jurdy, 1984; Engebret son, 1982), and paucity of major terrane accretion in the Cordillera after the Mesozoic (Monger et al., 1982), indicates that low angle subduction continued to drive the mountain building processes during the early Cenozoic.

488

References Engebretsen, D.C., 1982, Thesis, Stanford Univ., 211 pp. Jordan, T.E., Isacks, B.L., Allmendinger, R.W., Brewer, J.A., Ramos, V.A., and Ando, C.J., 1983, Geol. Soc. Am. Bull., 94, 341-361. Jurdy, D.M., 1984, Tectonics, 2, 107-113. Monger, J.W.H., Price, R.A., and Tempelman-Kluit. D.J.f 1982, Geology, 10, 70-75. Saleeby, J.B., 1983, Ann. Rev., 15., 45-73. Silver, E.A., McCaffrey, R., Joyodiwiryo, Y., and Stevens, S., 1983, J. Geophys. Res., 88, 9419-9435. Silver, E.A., and Smith, R.B., 1983, Geology, 11 f 198-202. Wing, R.S., and Mueller, J.C., NASA TMX - 58168, 1-B, 599-604.

DUALISM IN THE DISCOVERY OF THE QUE RIVER AND HELLYER POLYMETALLIC SULPHIDE DEPOSITS IN WESTERN TASMANIA E.H. Skey Aberfoyle Ltd, Melbourne The history of these discoveries, of approximately 10 million tonnes of potentially ore grade polymetallic sulphides extends from 1970 to the present. The earliest exploration steps comprised straightforward regional geological mapping and stream sediment surveys of essentially unexplored Cambrian Mt. Read Volcanics. These volcanics contained substantial orebodies at Mt. Lyell and Rosebery. This coverage was proving effective at finding stream sediment lead anomalies. The decision to import and apply the H400 airborne EM system was taken in the context of a sense of urgency. A 300 metre line spacing was chosen. Combined with diligent literature search these steps lead to target selection in a multidisciplined, yet simple, approach. The eighth rated, oneline airborne EM anomaly was ranked first when combined with geochemistry and old prospect data. The first ground follow-up line of EM in January 1973 providentially detected the southern limit of the target. Further HLEM and VLEM surveys recognised a 250 metre long conductor which was tested by DDH QR1, intersecting 11.4 m at 2.0% Cu, 5.1% Pb, 7.3% Zn and 105 g/t Ag. Mapping revealed disseminated sulphides and intensely sericitised volcaniclastics, whilst progressively closer spaced soil sampling showed two strong anamalous trends. The eastern one, semi-coincident with the conductor represented S lens, a relatively copper rich deposit; the western target was shown to be a pyrite-sphalerite-galena lens of 5 million tonnes at 0.3% Cu, 5.9% Pb, 10.2% Zn, 104 g/t Ag, 2.3 g/t Au. The failure of state-of-the-art (1973) ground EM to identify the western (P/Q) lens made us think it was non-conductive. IP was used extensively and identified! a belt of pyritic volcanics bounded by resistive andesites, with strong frequency effect anomalies being prime drill targets. We applied this ore finding recipe tof stream geochemistry, soil geochemistry, IP and diamond drilling for several years. We probably underdrilled in many areas, but aside from extensions of the Que River orebody and the Mt. Charter barite occurence, all we found was andesite with occasional pyritisation and trace of lead and zinc sulphides. Meanwhile drilling and underground exploration was showing the mineable ores were too limited to justify a dedicated mill. Only after delivery of ore parcels to EZ (Rosebery) did the establishment of a mine, selling ore direct to Rosebery, become a real opportunity. Mining of the western (P/Q) lens commenced in 1979 at 200,000 tpa. S lens is untouched.

489

By 1980 we concluded that no substantial massive sulphides existed less than 50 metres from surface within our ground and that IP was not capable of seeing below 75m with sufficient precision for drilling control. Mine mapping identified barite as an ore affiliate, and showed chrome mica arid chlorite-carbonate alteration to be key visible alteration types. Collaborative studies with CSIRO proved valuable and are continuing. Continued geophysical orientation surveys developed the belief that P/Q lens was fairly conductive, but too deep for 1973 systems. New time domain units, particularly those capable of measuring early time channels, (<lms) provided encouragement to persist in the field. Simultaneously the Hydro-Electric Commission, preparing for a new power transmission line, created outcrop which we mapped with beneficial results. Comparison of the Que River environment with deposits of this kind elsewhere in the world suggested potential for several discrete ore lenses in our district. We decided to survey with a new EM technique. The possibility that a previously drilled IP anomaly with coincident lead soil anomaly, might not have been fully explored by one hole, caused field staff to extend the EM survey and to extend it again when a 100m deep conductor was observed. Barite and chrome mica alteration gave us the encouragement to drill and HL 3 intersected 24.4m at 0.3% Cu, 4.4% P b , 12.6% Zn, 157 g/t Ag and 1.9 g/t Au in the Hellyer prospect 125 metres below surface. Intepretation of early Hellyer drilling data enabled recognition of near horizontal volcanic stratigraphy, contrasting with the vertical deposition of rocks at Que River 3 km to the south. The EM data revealed only one edge of the lens and the lead soil anomaly is a hanging wall phenomenon 100-150m above ore. Planned components of our exploration included: selection of prospective rocks based on regional geology and a general knowledge of massive volcanogenic sulphides, utilising the latest technology, especially electrical geophysics, as part of a multidisciplinary program, allowing competent field staff to excercise initiative in extending surveys maintaining research at the mine and applying the results in exploration, committing money and people to persistent ground follow-up in hostile # terrain. Divine components are: the position of the initial airborne EM traverse lines, which could have straddled S lens at Que River, the occurence of a shallow conductive lens next to the P/Q lens ore body, the inadequacy of resources for a dedicated mill, discovery of the Hellyer EM conductor one line north of the northernmost line of the survey as planned in the office, timing of HEC Power line preparation creating outcrop and better access at Hellyer, location of the Hellyer deposit under the new power line. We look forward to more discoveries from this dualism. The author acknowledges the permission of the joint venturers, Aberfoyle Ltd and Paringa Mining and Exploration Co. PLC. to publish this information and recognises the contribution from a large number of company staff over 14 years.

490

ENVIRONMENTS AND PROCESS OF ORE DEPOSITION OF THE SEAFLOOR Brian J. Skinner Department of Geology and Geophysics, Yale University, New Haven, USA Investigation of centers of hydrothermal mineralization at several sites along the east Pacific rise reveal a consistency in the chemistry of deposit ion between sites, but an apparent relationship between style of mineralization and the spreading rate* Massive sulphide deposits are associated with shallow magma chambers and fast spreading rates; stock-work deposits with deeper magma chambers and slow spreading rates. The tectonic setting of modern sites of massive sulphide deposition does not correspond closely with inferred tectonic settings of deposits in the geological record; it is likely that many modern deposits remain to be discovered in still unlisted tectonic settings. The geological record suggests that the largest and most diverse massive sulphide deposits are associated with compressive edges of plates and form during periods of plate uncoupling. One of the most intriguing questions that remains to be answered is the apparent time control on massive sulphide deposits. They seem to have started forming about 2.7 B.Y. ago and to have continued forming to the present day. The reason, I suggest, is that the chemistry of the ocean was not suitable for the depositing process to proceed at an earlier time even though submarine volcanism was a dominant terrestrial process during the Archean.

PROCESSES IN SILICIC MAGMA CHAMBERS - EVIDENCE FROM RHYOLITE ERDPTIVES IN THE TAUPO VOLCANIC ZONE, NEW ZEALAND Ian E.M. Smith and Colin J.N. Wilson Department of Geology, University of Auckland, Auckland Volcanic activity in the central North Island of New Zealand during the past 2Ma has been dominated by the eruption of rhyolite magma represented by complex overlapping air fall ash and ash flow deposits together with a minor proportion of rhyolite lava. The rhyolitic volcanism is concentrated within a 125 X 60 km area forming the central Taupo Volcanic Zone and is expressed largely as six major caldera volcanoes each showing activity spans of 150 to 600 Ka and erupted volumes of at least 300 to 1000 km^ of magma. In terms of longevity and average magma eruption rate the central Taupo Volcanic Zone is comparable to major rhyolitic volcanic provinces elsewhere (e.g. Yellowstone, U.S.A.) but individual eruptions have much shorter intervals of recurrence and smaller volumes. Geochemical studies of tephra sequences show that multiple eruptive events can be grouped to' define large ^10^ km3 batches of rhyolite magma which have erupted in volumes of the order of 10 - 10 km3 at intervals of 1-5 Ky. As an example the Taupo 186AD eruption is represented by five major tephra units totalling about 40 km3 and is the latest in a series of eruptive events from the volcano in the past 10 Ky. Geochemical analyses of a large number of samples from the 186 AD eruption sequence show no significant compositional variation. Reconnaissance geochemical studies of several other eruption sequences from a number of the central Taupo Volcanic Zone volcanoes indicate that compositional homogeneity is typical within tephra sequences representing large volumes of magma. We conclude that batches of magma with volumes of 10^ - 103 km have existed beneath the central North Island for periods of at least 10 years without undergoing significant chemical fractionation. This result is suprising in view of recent North American work which suggests that magma batches >1 km in 491

volume are invariably zoned. Since the existence of large static bodies of magma appears intuitively unlikely we suggest that strong active convection is the predominant process in these magma chambers; this is compatible with the observed high heat flow and eruption rate. A second process, evidenced by the presence of mixed and hybrid pumices in some tephra units, is the interaction of basaltic mantle-derived magma with the lower levels of rhyolite magma chambers. Basaltic magma appears to act both as a thermal trigger to major rhyolite eruptions and as one end member in a process of magma mixing which produces intermediate compositions.

AQUIFER CONTAMINATION WITH CHEESE FACTORY WASTE P.C. Smith1 and G. Schrale2 As.A. Department of Mines and Energy, Adelaide 2 S.A. Department of Agriculture, Adelaide In the Lower South East of South Australia the karstic Gambier Limestone unconfined aquifer has been the recipient of a variety of agricultural and industrial wastes. One such site is a cheese factory located about 7 km north of Mount Gambier, a city of 20 000 people, which is solely dependent upon groundwater for its reticulated supply. For many years wastes from the cheese factory located upgradient of Mount Gambier were discharged into a nearby disposal well. In compliance with the Water Resources Act, 1976, waste water from the cheese factory is now sprayed onto agricultural land. The extent of aquifer contamination at the cheese factory was investigated by using surface resistivity surveys and groundwater monitoring. Resistivity results showed the presence of an ovoid plume of polluted water extending in the direction of groundwater flow for about 1 700 m, with a width of 750 m. The thickness of the plume was interpreted to be 10 m near the disposal well and gradually tapers off in the groundwater flow direction. The plume contains about 380 ML of contaminated groundwater. The dissolved salt load of the plume is 450 tonnes of which 300 tonnes were introduced by wastewater disposal. The N and K loads are about 14 tonnes each and the P load is insignificant. To verify these estimates of introduced contaminants investigations wells were drilled along the major axis of the plume. The holes were cored and bailed as the drilling progressed. and core analyses indicated the following. 1* 2.

three

The water

The bulk of the phosphate introduced into the aquifer is fixed onto the formation with only dissolved in the groundwater. The major proportions of nitrogen and potassium are bound to the formation; less than 10% and 5% respectively is in the groundwater as a soluble form. High ammonium levels were found where the C/N ratio was < 10, which indicate active transformation of the organic nitrogen. Organic carbon in the core is about 100 times greater than the fraction in the groundwater.

The core analyses indicate that the nutrients of the waste are deposited and/or bound to the formation and can be remobilised by reversing cation exchange and biological transformation. Thus the nutrient release would continue for a considerable time after the existing soluble slug has been replaced. It is proposed that the contaminated aquifer be rehabilitated using insitu digestion of organic nitrogen by injection of carbohydrate.

492

DIFFICULTIES IN ESTABLISHING QUARRYING OPERATIONS UNDER THE NEW SOUTH WALES PLANNING LEGISLATION Val Smith Resource Planning, Newcastle

The New South Wales Planning and Assessment Act and Regulations were introduced in 1979-80. Under this Act, new quarry proposals are deemed 'designated development' and applications for consent to establish a quarry must be accompanied by an environmental impact statement. The Act is specific with regard to procedures for Development Applications which must be followed by the quarrying company in preparing the documentation and lodging the application and by the consent authority in processing the application. The consent authority is usually the local Council, although where the proposal is considered of "regional significance" the Minister of Planning and Environment may determine the application. Whether the quarrying company prepares the application and environmental impact statement itself or' engages consultants, the procedures are the same. The Director of the Department of Environment and Planning is required to be consulted as to the required "form and content" of the environmental impact statement and in addition, specific topics listed in the Regulations must be addressed. The environmental impact statement is exhibited for 28 days and public submissions are made to the local Council during the exhibition period. Submissions received by the local Council are forwarded to the Department of Environment and Planning for comment and following raceipt of the Department's views, the local Council usually determines the application. Provision is again made for the Department of Environment and Planning to intervene upon receipt of the submissions if considered appropriate. This paper addresses the problems that can be experienced by the quarrying company in following these procedures; problems which may stem from the original advice from the Department of Environment and Planning on the "form and content" of the environmental impact statement. This advice is normally given site unseen and in more recent times has a standard format often containing requirements which are irrelevant to the proposal and which would have been clearly recognised if a site inspection had been carried out. The Act includes no provisions for the applicant to make comments on submissions received after the exhibition of the environmental impact statement, even though it can generally be clearly demonstrated that many submissions are based on misconceptions and misunderstandings about the proposal and are matters that can be frequently cleared up by discussion and negotiation prior to determination. While the quarrying company has made public its proposals it appears there are no reciprocating rights on the submissions made by the public during the exhibition period. How does the local authority decide on what is fact or fiction in view of the fact that the Department of Environment and Planning rarely intervenes? While a few proposals have been deemed of 'regional significance' and a public inquiry has been held where the significance of the proposal has been demonstrated, the determination of regional significance appears to be arbitrary and essentially politically founded. Potential exists for proposals which are of regional significance with regard to the supply of construction materials to be refused with detrimental consequences for the region. Who decides what projects are of regional significance and how is it decided? 493

These are some of the problems associated with establishing quarrying operations in New South Wales and it is suggested that many of these may be overcome by modification of the New South Wales Environmental Planning and Assessment A c t 1979 to enable the quarrying company to make a greater input into the decision-making process after submission of its development application, as is currently given to the general public under existing provisions.

ON-LINE BULK ANALYSIS OF RUNDLE OIL

SHALE

B.D. Sowerby and K.E. Davies CSIRO Division of Mineral Physics, Lucas Heights On-line bulk analysis of oil shale on conveyor belts could lead to significant savings in the mining and processing of oil shale deposits. On-line analysis of oil yield could be used to either reject low grade material before retorting or to control blending. An analysis accuracy of about 10% relative is probably adequate for both these applications. Nuclear techniques based on penetrating neutron and gamma radiation can be used for on-line conveyor belt analysis. The neutron inelastic scattering technique which determines the total carbon content of bulk shale samples is the most favourable technique. The correlation between carbon content and oil yield for 540 Rundle oil shale samples of average grade 72 L/t shows that oil yield can be predicted from a measurement of total carbon to within about 11 L/t. An alternative method based on the determination of hydrogen content by neutron moderation does not look as favourable, as the rms deviation between oil yield and total hydrogen content for the above 540 Rundle oil shale samples was 32 L/t. Laboratory experimental measurements on seventeen 30 kg Rundle oil shale samples showed that neutron inelastic scattering can be used to determine total carbon and oil yield to within about 0.6 to 1.0 wt%C and 8 to 10 L/t respectively. Particle size was shown to have little effect on gauge accuracy for sizes up to 100 mm. A practical gauge for application 2 l + 1 on a 23 mm thick reinforced conveyor belt could employ a 5 Curie Am-Be neutron source and a <(>150 x 100 mm NaI(T£) detector. With this gauge, the analysis time to achieve a counting statistical error of 0.8 wt%C should be about 5 minutes.

EVOLUTION OF THE MOLE GRANITE AND ITS Sn-W-Bi-Mo MINERALIZATION - NORTHERN N . S . W .

BASEMETAL

Craig L. Stegman CRA Exploration, Papua New Guinea The Mole Granite, a Late Permian polyphase leucogranite of the New England Batholith, is the source of a wide range of Sn-W-Bi-Mo-basemetal mineralization occurring within and peripheral to the granite. The bulk of the Mole mass consists of a seriate variant which grades out to a thin (100m) porphyritic carapace. These two variants are cut by dykes and irregular sheet- and boss-like masses of microgranite0 Six episodes of mineralization are associated with the southern central margin of the Mole Granite0 In order of decreasing age these are: 494

(i) sheeted vein Sn-basemetal mineralization; (ii) complex pegmatite Sn mineralization; (iii) stockwork Mo-W-Bi mineralization; (iv) white muscovite-biotite greisen W-Bi-Mo-Sn-basemetal mineralization; (v) green muscovite-chlorite greisen Sn-W-Bi-basemetal mineralization; (vi) kaolinite-basemetal vein mineralizationQ This sequence of mineralization styles reveals a succession of changes to the physical and chemical properties of the hydrothermal system associated with the Mole Granite which can be attributed to the crystallization and emplacement history of the granite. Similarly this crystallization and emplacement history is thought to have controlled the distribution of the mineralization. Burnham's (1979) general model for the emplacement of a near surface magma associated with fporphyryf style mineralization is the basis of the following model proposed for the evolution of the Mole Granite and its mineralization. During its emplacement the Mole Granite exploited structural weakness in the overlying country-rocks and, as a consequence, a series of northeasterly trending ridges formed on the roof of the granite. The early crystallization of the outer polphyritic carapace trapped metal-rich aqueous fluids within the granite and led to their concentration in the apical portions of the ridges0 Evidence for this concentration process is seen in the chemistry of the granite. Samples of the porphyritic variant and the microgranite from one of these ridges are enriched in F (modal topaz), Li, Rb/Sr, Na and A1 relative to other parts of the granite0 Subsequent periodic rupturing of the carapace at the apices in the granite roof resulted in pulses of ore-fluid emanating from these points« Consequently, each granite roof apex is associated with several episodes of mineralization. Sn and basemetals were partitioned into the early hydrous fluid phase while W, Bi and Mo were preferentially retained in the Mole Granite melt. As a result the pre-microgranite episodes of mineralization, the sheeted vein and complex pegmatite mineralization, were Sn-basemetal rich and W-BiMo-poor0 The development of complex pegmatite mineralization after the sheeted vein mineralization indicates an increase in the temperature of the hydrothermal system which is attributed to the late emplacement of the microgranite. W-Bi-Mo-rich ore-fluids separated from the microgranite magma and collected in the Sn-basemetal-rich apices as well as in apices formed during the forceful emplacement of the microgranite (hence Sn-base metal poor)0 The episodes of post-microgranite mineralization reveal a steady decrease in the temperature of the hydrothermal system. As well, the locus of mineralization retreated into the granite. Initially, Mo-Bi-W stockwork mineralization formed in the country-rock and was succeded by an episode of Sn-W-Bi-Mo-basemetal-bearing white muscovite-biotite greisens which developed at the granite contact0 At this stage circulating groundwater gained access to the granite and diluted and further reduced the temperature of the hydrothermal system. This favoured the formation of Sn-W-Bi-basemetal-bearing green muscovite chlorite greisens which occur well within, as well as outside of the graniteQ The last episode of mineralization recognised is the relatively insignificant kaolinite-basemetal vein mineralization and this mineralisation is the product of an even more dilute, lower temperature hydrothermal systemo Continuation of this trend of temperature reduction and dilution of the hydrothermal system is thought to have led to the cessation of hydrothermal activity associated with the Mole Granite. References Burnham, W.CG, 1979, In: Barnes, H.L0 (ed), Geochemistry of Hydrothermal Ore Depositso, John Wiley and Sons, New York, pp 71-136.

495

EROSION—ISOSTATIC REBOUND MODELS FOR UPLIFT: TO SOUTH-EASTERN AUSTRALIA

AN APPLICATION

Randell So Stephenson1 and Kurt Lambeck2 Geological Survey of Canada, Calgary, Alberta, Canada Research School of Earth Sciences, Australian National Univ., Canberra

Vertical movements of elevated terrain may be indicative of either active tectonism or of the passive isostatic rebound of the crust and lithosphere to the erosion of older highlands. Mountain ranges experience both processes. Uplift is first driven by tectonic mechanisms during the constructive phase. Upon termination of this process, erosional forces unload the crust and isostatic rebound occurs such that the earlier base level of the terrain is regionally uplifted. It is this latter phase that is modelled here. The model we adopt is one of a mountain range, initially in isostatic equilibrium, on a viscoelastic lithosphere. Erosion of these mountains is assumed to be proportional to their height above sealevel at any time t, with an erosional time constant T e # Other model parameters are the effective flexural ridigity D and relaxation time T v of the lithosphereo For a given present-day distribution of topography the uplift, erosion, past topography, gravity and stress state can be computed throughout time depending on the model parameters. One region where we believe this model to be appropriate is southeastern Australia. Most discussions of the uplift observed in the highlands of this region are in terms of the active tectonic phase. We argue instead that these highlands are a residue of the Palaeozoic Lachlan fold belt and that the observations of rivers cutting through Cainozoic basalts reflects the regional isostatic rebound of the crust to the erosional unloading. The comparison of the model with uplift observations suggests the following range of permissible model values: Te=150-250 Ma, DTv=(l-5)1023 Nm Ma for continental lithosphere. The time by which the erosional-rebound mechanism became the dominant landscaping process is 180-200 Ma agoQ The late Palaeozoic fold-belt topography is about 75% greater than the presentday values. Topographic depressions are predicted onshore of the present coastline, including the Gippsland basin, part of the Sydney Basin and areas to the west of the present highlands0 Within the highland area erosion generally exceeds uplift but in some areas the two are approximately equal, in keeping with some geomorphological observations. The flexural stresses associated with the erosion initially increase with time. Maximum values are predicted to occur in late Cainozoic time, with the stress state near the surface being mainly tensional.

THE PROTEROZOIC WILLYAMA SUPERGROUP, BROKEN HILL N.S.W. AND THE SEARCH FOR A TECTONIC MODEL B.P.J* Stevens Geological Survey of N.S.W., Sydney Deposition of the Willyama Supergroup was characterized by a deepening sedimentary environment, accompanied in the early and middle stages by basic and acid volcanism. Iron, copper, cobalt and minor lead-zinc-silver mineralization accompanied early tholeiitic basic volcanics, and very sodic, probably altered, acid volcanics. The Broken Hill lead-zinc-silver orebody, numerous minor Broken Hill type deposits, and a range of tungsten deposits accompanied later tholeiitic basic volcanics (some highly fractionated) and tholeiitic acid volcanics. The upper part of the sequence comprised sediments with no direct volcanic component, and is host to pegmatitic tin deposits. 496

Deposition probably occurred at about 1820 Ma and no earlier than 2200 Ma. By 1660 Ma the sequence, originally about 7-10 km thick, had been deformed by recumbent and more upright folding, and buried to depths of up to 20 km, with temperatures up to 800 C. The relatively high thermal gradient (about 40 C/km) during deformation may have continued from the time of deposition (abundant acid and basic volcanism, possibly relatively shallow tholeiitic basaltic melting, and high level fractionation of basalt). Minor granitic intrusion at 1490 Ma completed cratonization. Major uplift and erosion occurred before 1100 Ma. How do the above features fit possible tectonic models for the Proterozoic? There are no andesites, ophiolites, blueschists or melanges in the Willyama Supergroup. The depositional environment can be fitted into a plate tectonic context only by avoiding those parts of the model requiring the above rocks. The Miocene Nishikurosawa stage in Japan contains the Kuroko type Cu-Pb-Zn deposits, and- represents rifts in a developing andesitic arc. Volcanism in the rifts is predominantly bimodal acid-basic. The Silurian rocks in the Captains Flat-Goulburn Synclinorial Zone contain bimodal acid-basic volcanics and stratiform Cu-Pb-Zn deposits. They were deposited in a rift in folded flysch sediments in a back-arc area, at some distance from the frontal andesitic arc. The Willyama Supergroup cotfld fit such a situation of a volcanic rift in the back of a developing arc-trench system. However it appears that worldwide there are virtually no andesites, ophiolites, blueschists or melanges in Early-Mid ProterOzoic rocks. This casts doubt on the existence of subducting oceanic lithosphere. A suggestion that the andesites etc. were systematically eroded away following continental collisions, is difficult to accept in the light of preservation of abundant supracrustal sediments and volcanics. Glikson (1980) concluded that the abundance of intrasialic crustal environments and well developed continental crust, with little evidence for contemporaneous sima, could best be explained by a much smaller Earth diameter and a completely sialic crust. However, until the physical processes by which major Earth expansion could take place, and anomalies such as the required tremendous increase in ocean volume, are explained, alternative models are sought. Condie (1973) suggested that average thickness of continental crust since 2500 Ma has been no less than 90% of the present average. Assuming constant Earth diameter, volume considerations indicate that the surface area of sialic crust has not significantly exceeded present values since 2500 Ma. This indicates that oceanic crust has existed since 2500 Ma. During the Early to Mid Proterozoic there was well developed, stable, continental crust (Windley 1977) and oceanic crust. There was also extension, producing intracontinental and continent margin rifts (the Willyama Supergroup appears to have been deposited on a continental margin), but there is no evidence for oceanic subduction. With constant Earth diameter, extension in rifts must have been taken up as compression elsewhere, either as some "form of deformation of oceanic crust (no relics of which have been identified) or as deformation within the continents. The rifts may represent the locus of upwelling mantle plumes, with complementary crustal thickening and compression occurring above areas of downgoing mantle. Alternatively the rifts were transtension (or pull-apart) basins formed as a result of irregularities in transcurrent fault systems between major plates, and were later closed by transpression on the same fault system. The original extent of the Willyama Supergroup (more than 100 km in either direction) is too great for a transtension basin. Perhaps deposition occurred above an upwelling plume at about 1820 Ma, and by 1660 Ma that part of the crust had drifted off the plume towards an area of downwelling mantle, leading to compression and recumbent folding.

497

If mantle plumes and oceanic crust existed, one might expect mid-ocean spreading. It is unlikely that the continents were contracting in size, and there is no evidence of subduction. There is no obvious means of accommodating an expansion of the surface area of oceanic crust. Each option examined above contains major anomalies. It is apparent that one or more of the following conclusions and assumptions is incorrect: 1. There was no oceanic subduction in the Early-Mid Proterozoic. 2. Earth diameter remained constant. 3. Average thickness of continental crust since 2500 Ma has been no less than 90% of the present average. 4. The oceanic crust could not remain rigid without spreading or subduction, while continental crust underwent extension and compression. 1. above can only be incorrect if all the evidence is either eroded away or buried, or if subduction took a different form from that of the Phanero zo i c. 2.

Earth expansion could explain many observed phenomena.

3. With an average thickness of about 10-15 km the present volume of continental material could cover the entire Earth's surface. Many lines of evidence suggest that the crust was thicker, and palaeomagnetic data indicate that the sialic crust did not undergo such a fundamental re-organization between Proterozoic and Palaeozoic times. 4. There may have been no creation nor destruction of oceanic crust in the Early-Mid Proterozoic, or perhaps destruction occurred in a manner different from in the Phanerozoic. References Condie, K.C., 1973, Bull. geol. Soc. Amer., 84, 2981-2992. Glikson, A.Y., 1980, Tectonophysics, 63, 193-234. Windley, B.F., 1977, The Evolving Continents. Wiley, London.

STRATIGRAPHIC, PETROGRAPHIC AND PETROPHYSICAL FEATURES OF THE TIRRAWARRA SANDSTONE IN THE BIG LAKE FIELD B.G. Steveson1 and D.I. Gravestock2

1. AMDEL, Adelaide Department of Mines & Energy S.A., Adelaide.

The Tirrawarra Sandstone (sensu stricto) is a mineralogically mature, indistinctly horizontally bedded and occasionally cross-bedded quartz sandstone; conglomerates are uncommon, interbedded mudrocks are rare. Cores indicate multistorey sandstones deposited in low-sinuosity fluvial channels (Williams & Wild, 1984), with no downward transition into glacigene sediments of the Merrimelia Formation yet intersected in Big Lake wells. A locally thick but laterally variable (0-60 m) conglomeratic facies occurs above the Tirrawarra Sandstone, but we favour its inclusion in the Sandstone rather than in the overlying Patchawarra Formation. The conglomerate is a matrix-supported, crudely stratified fine gravel (up to 1 cm) with coarse, poorly sorted sandstone. Clay as irregular laminae and in the matrix appears to be of primary and not secondary origin. The depositional environment is problematical since little core has been recovered, but the conglomerate may have originated as gravel bars formed on humid alluvial fans (proximal and medial facies of Boothroyd & Nummedal, 1978). If so this represents an important local perturbation of an idealised model evolving through glacigene, then bedload-dominated fluvial systems of the Merrimelia Formation and Tirrawarra Sandstone (Williams & Wild, 1984) to sandstone, mudrock and coal of the fluviatile Patchawarra Formation. 498

A high gamma-ray response is associated with the conglomerate (Stanley & Halliday, 1984) but may not be restricted to this facies. The response is attributed principally to thorium on gamma-ray spectroscopic (NGS) logs and it is alluring to evoke an origin from granites exposed in the Early Permian in the Moomba area to the north. However, the complete absence of feldspar (altered or otherwise) tends to preclude such a source for the conglomerate. Sandstone is well-sorted and fine- to medium-grained. Detrital material shows a large proportion of argillaceous clasts. There is little evidence of a genuine argillaceous muddy matrix - all the clay is pseudomatrix (Dickinson, 1970) and is therefore interpreted as being derived from lithic clasts. Major diagenetic processes were: (i)

crystallisation of optically continuous quartz overgrowths (by precipitation from pore water). Quartz grains show long and concavo-convex boundaries and hence the secondary silica is thought to have been produced within the immediate local system,

(ii)

ductile deformation of soft lithic clasts between quartz grains,

(iii)

late deposition of small carbonate crystals.

The absence of authigenic clays at Big Lake is in marked contrast to the Tirrawarra Sandstone at Tirrawarra where the sandstones contain fewer lithic clasts and a significant amount of authigenic kaolinite. Conglomerate is ill-sorted and notably argillaceous. Between angular quartz and mica grains is a dense mosaic of fine-grained clay, mica and quartz which is interpreted as deformed clasts. Physically the material behaves as a clay matrix which separates the framework grains. There are small amounts of authigenic kaolinite and carbonate - particularly in stylolitic zones. The rocks have the following mean values of permeability (gas) and porosity:

Sandstone Conglomerate

Ambient Pressure

Overburden Pressure

K (yd)

• (%)

<f> <%)

Kn/Ka* %

<f>n/<f>a

5.6

2.8

4.8

12.5

1680

5.5

17.8

4.3

1.1

*Kn = permeability at nett overburden pressure (28,000 KPa). Ka = permeability at ambient pressure. <j> = porosity Permeability is very sensitive to the application of nett overburden pressure (i.e. deeper burial), more so in the case of the conglomerate which is not supported by rigid framework grains. Porosity shows a decline but this is by no means as marked as for permeability. Permeability is probably due to a very fine system of channelways within clay aggregates; under pressure these collapse, with consequent marked blocking of pore throats. More work is in hand on the Tirrawarra Sandstone both at Big Lake and elsewhere in the Cooper Basin.

499

References Boothroyd, J.C. & Nummedal, D., 1978, In Miall, A.D. (ed.) Fluvial Sedimentology. Mem. Can. Soc. Petr. Geol., 5, 641-668. Dickinson, W.R., 1970, J. Sed. Petr., 40, 695-707. Stanley, D.J. & Halliday, G., 1984, Apea J. 24(1), 180-195. Williams, B.P.J. & Wild, E.K., 1984.

Apea J. 24(1), 377-392.

ASBESTOS-BEARING ROCKS IN CONSTRUCTION OPERATIONS - POTENTIAL HAZARDS I.E. Stewart Department of Main Roads, N.S.W., Sydney

Asbestos fibre, in the form of respirable dust, is recognised as a significant health hazard, being associated with various lung diseases, including asbestosis, and a greatly increased risk of lung cancer in smokers (NH&MRC, 1982; Ross, 1981). Health authorities in Australia, as elsewhere, impose strict limits on industrial exposure to asbestos dust. These currently limit the respirable fibre content of air to between 2.0 and 0.1 fibres/ml, depending on the type of asbestos. A respirable fibre is defined as a particle of length > 5 width < 5 jam and ffaspect ratio" > 3 : 1 (NH & MRC, 1983). A road deviation currently under construction for the DMR NSW passes through rocks of the North Mooney Complex, east of Coolac. The Complex is a sequence of mainly ultramafic and mafic rocks, thought to be part of an ophiolite (Ashley et. al, 1979, 1983; Franklin, 1975). Specimens from outcrop and limited core drilling were examined in thin section to determine whether asbestos was present. Three types of asbestos occurrence have been identified. Serpentinised wehrlites contain chrysotile in cross-cutting veins and in veinlets representing initial alteration of olivine. Clinopyroxene in these rocks is variably altered to amphibole (? tremolitic) which is partly fibrous and sometimes asbestiform. Disseminated single fibres of this mineral may also be found. Elsewhere, the wehrlites contain veins and disseminated fibres of (probably) tremolite, without chrysotile or alteration of pyroxene, Gabbros contain rare veins of amphibole asbestos, but alteration of clinopyroxene and sometimes hornblende to fine-grained tremolite is common. Much of this is fibrous or asbestiform. Also believed to be present, but not outcropping, are serpentinised dunites and localised fault zones which are expected to be asbestos-bearing, strongly so in the latter case. As asbestos is relatively resistant to chemical attack, it is expected to persist in the weathering products of the rock. The presence of asbestos in the major rock types within the Complex means that a potential health hazard exists, particularly for personnel engaged in dust-producing operations such as drilling, blasting and crushing. Attempts to further assess the hazard, in terms such as the likely airborne fibre concentration and the consequent need for precautions such as respirators and dust control, raise a series of problems. Some of these have been mentioned in the literature, although not in this exact context (e.g. Zoltai, 1981).

500

The most obvious problem is limited knowledge of the effects of asbestos. Medical studies are inevitably based in the asbestos industry, and are effectively limited to only a few minerals (chrysotile, anthophyllite, grunerite and crocidolite). The effects of these substances are reasonably well understood and differ from one another, particularly in the last case. There is virtually no information on other asbestos-forming minerals, of which there are a number (Ross, 1981). In addition, current standards are based on an assumed lifetime industrial exposure, not on the relatively short periods involved in projects such as road construction. Of the two asbestos minerals known to be present in the North Mooney Complex rocks only one, chrysotile, is used in industry. Tremolite, despite being a commonly occurring type of asbestos, is not commercially exploited. Coupled with the short exposure period involved, this means that there is considerable uncertainty about the magnitude of the hazard presented by these minerals. This uncertainty is magnified by ambiguities in the definition of respirable fibre. The criteria used include not only particles which are asbestiform in the strict mineralogical sense, but also others of different growth habits such as "fibrous", "acicular" or "elongate" which are quite distinct and present a much less serious hazard. Cleavage fragments of.larger grains may'also be included. The minerals found in this study odour in a variety of habits, ranging from strictly asbestiform (as veins or single fibres), through fine-grained masses which are variously described as fibrous, fitted, matted or feathery. Individual crystals may or may not be asbestiform. In the case of tremolite, larger elongate crystals also occur. All of these are potentially capable of meeting the definition, although their effects will differ widely. There is no reliable way of estimating the proportions of each type present. Closely related to this is the question of release of the fibres into the air. The potential sources of fibre are detected petrographically, in the intact rock. Health standards are based on airborne dust. The nature of the dust formed will depend on the operation being carried out, the type of mineral and its growth habit, the texture of the rock and the degree of weathering of the rock. It would be expected that fibre would be most easily released from veins and least easily from some of the non-asbestiform growth habits, and that the greatest quantities would arise from operations such as drilling and crushing which pulverise fairly large quantities of rock. There is no obvious method of quantifying these expectations prior to the start of work. Overall, it appears that investigation of potential asbestos hazards of the type described here will be limited to simple description until the following three questions, at least, are answered: How can "asbestos fibre" be better defined? What are the health effects of the "non-commercial" varieties of asbestos? To what extent do engineering operations release fibre.into the atmosphere, and how can this be predicted? References Ashley, P.M., Brown, P.F., Franklin, B.J., Ray, A.S. & Scheibner, E., 1979, J. Geol. Soc. Aust., 2Lt 45-60. Ashley, P.M., Franklin, B.J. & Ray, A.S., 1983, Geol. Mag., 1£Q, 1-20. Franklin, B.J., 1975, Ph.D. Thesis, Univ. of N.S.W. (unpubl.). National Health & Medical Research Council, 1982. Report on the Health Hazards of Asbestos. Comm. Dept. of Health, Canberra. , 1983, Threshold Limit Values, 1983-84, Comm. Dept. of Health, Canberra. Ross, M., 1981, Rev. Min, SA, 279-319. Min. Soc. Amer. Zoltai, T., 1981, Rev. Min, M 9 237-278. Min. Soc. Amer. 501

AN EMPIRICAL APPROACH TO ASSESSING THE IN SITP STRESS FIELD AND ITS ROLE TOWARD IMPROVING COAL MINE ROOF CONDITIONS Ian J. Stone BP Coal Australia, Narellan Tahmoor Colliery mines the Bulli Coal at depths of 390m to 430m in the Southern Coalfield of N.S.W. Dominant in situ horizontal stress causes fracture and failure in the immediate shale and laminite roof strata. In a series of overcore tests, Walton (1983), reports sigma 1 ranges from 18.0 to 21.3 MPa, the ratio of the near horizontal stress components sigma 1/sigma 2 ranges from 1.23 to 1.64/1. and sigma 1/sigma 3 ranges from 1.59 to 2.09/1. By using the orientation of particular shear fractures in the coal mine roof to estimate the sigma 1 direction a good correlation was obtained with the sigma 1 azimuth at each overcore site. The measurement of these shear fractures on a mine wide basis has shown that there is a gradual swing in the azimuth of sigma 1 from NNE, in the north of the mine, to WNW in the southern end of the mine - a distance of just over 2 km. Detailed study of roof fracturing and failure in a panel driven 1.5 km into a virgin area , remote from other mine workings, indicated that the distribution of different types of roof failure are not random but are closely associated with variation in the characteristics of the in situ stress field. Both short term roof failure (low angle conjugate shearing, arching, and mining induced fracturing) and long term roof conditions (good, sag, gutter, and cantilever) are recognised in the study panel. Long and short term roof conditions were found to: (i) vary between heading and cut-through (c.t.) direction; (ii) change in headings with the order of drivage; (iii) be generally worse in c.t.'s. Two important aspects of the long term failure types were that firstly, the proportion of each type changed along the panel, and secondly, the dominant roof type in each area changed along the panel so that certain areas were characterised by a particular failure type. Significantly, the greater the amount of short term failure (a probable indicator of immediate strain release), the greater the amount of long term failure. Arch failure is a stable long term roof condition. The variation of roof conditions in Tahmoor mine can be related to two f types1 of in situ stress field; (i)

the virgin in situ stress which changes in both magnitude and orientation; and (ii) the modification of the virgin in situ stress by the mine development, which can be recognised on three scales, i.e. roadway, panel and minewide.

The changing characteristics of the virgin in situ stress field have been responsible for the distribution of various roof conditions in the study panel. The angle between the mine roadway direction and the azimuth of sigma 1 (theta) determines: (i) the type of short term failures; and (ii) the long term roof type most likely to be dominated in a roadway segment. Theta varies between 35° and 81° in the study area. In the range of theta where roof failure dominates good roof, gutter and cantilever failure occupy different ranges of theta but sag is more widespread.

502

Mining induced redistribution of stress is thought to occur in three observable modes which have consequences for roof conditions. Firstly, as concentrations of stress around corners of the rectangular mining face can be predicted from the lateral stress field. Secondly, the order of drivage of adjacent roadways can determine which subsequent roadways will receive benefit from "stress relaxation11. Thirdly, redistribution and concentration of stress around corners of large areas of mine workings. Recognition of the origin of the stress causing poor roof conditions can lead to: preferential location of the bolting pattern on a roadway scale; a suitable order of drivage on a panel scale; the pre-development of roadways out of areas of likely stress concentration as may occur around corners of an area of concentrated mine workings; a more suitable mine layout and appropriate roof support design to counter expected failure modes if there is a knowledge of the minewide, or regional, stressfield. This type of empirical approach to 'assessing roof conditions is limited to observational methods but is more adaptable on a minewide basis than the detailed and accurate instrumentation whose results are often site specific. The combination of both methods is necessary for present mining practice. Reference Walton, R.J., CSIRO Aust, Division of Applied Geomechanics, Geomechanics of Coal Mining Report No.46.

THE COMPOSITE LITHOSPHERE OF EASTERN AUSTRALIA RECORDS FROM VOLCANIC ROCKS 1

F.L. Sutherland, and 2J.D. Hollis

^"Division of Earth Sciences, The Australian Museum, Sydney ^Geology Department, University of Melbourne, Melbourne Widespread xenoliths in eastern Australian basalts record a diverse, deep lithosphere. Composites from twenty sites provide fine detail for some of the local and regional heterogeneities found in both the upper mantle and lower crust. Mantle variations include (1) spinel lherzolites, (2) spinel lherzolites and pyroxenites, (3) spinel/garnet lherzolites with spinel/ garnet pyroxenites, (4) spinel lherzolites with garnet pyroxenites and pegmatoid garnetites, (5) metasomatised and MARIDic suites, (6) disrupted, metasomatised suites, (7) diamondiferous suites. Lower crustal variations include (1) calcic mafic granulites, (2) calcic mafic/ultramafic granulites, (3) disequilibrium granulites, (4) sodic mafic/ultramafic granulites, (5) sodic/calcic granulites/garnet granulites, (6) gabbroic/cumulate suites, (7) zircon/corundum-bearing suites. Basalt geochemistry also indicates inhomogeneous source regions. Large scale inhomogeneities include LILE and probably phlogopite-enriched mantle peridotite up to 700 km across (olivine leucitite zones) and LILE and initial 8 7 Sr/ 8 6 Sr enriched mesosphere over a 1000 km across (Tasmanian tholeiites). Smaller scale heterogeneities up to 200 km across include LILE and REE enrichments/depletions tied to variable amounts of phlogopite/ amphioble/apatite in the mantle (K-rich/sodic, high/low Ti:V alkali basalt provinces). Basalt diatremes, pipes and flows associated with C02/hydrous phase inclusions and sometimes exceptional high pressure inclusions, can form clusters over 10 km across. These suggest discrete zones of volatile enriched mantle. 503

Considerable differences in magmatic introduction into the lithosphere are deduced from petrological contrasts between volcanic provinces. Five orders of magmatism over the last 200 Ma are recognized, ranging from relatively restricted undersaturated melting to widespread subcrustal tholeiitic melting. Palaeogeotherms established for the lithosphere from xenolithic suites indicate high geotherms over most of the eastern Australian basalt belt in the last 200 Ma. Lower heat flows may occur in underplated regions or away from strong melting. The most depleted mantle, found in the Younger basalts of Victoria, also shows considerable MARIDic metasomatism. The extent of bulk mantle depletion, crustal underplating, hot palaeogeotherms and young 'patent1 metasomatism may be linked to proposed Mesozoic and Cainozoic 'hot spot' trails.

r30

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Tasmanian PT Plots

N. Nebo, M.McBride

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-16

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PT fields from xenolith suites from a range of localities and ages, E, Australia. Fields l.argely based on the Ellis and Green 1979 geothermometer (T°C, Fe2+=FeT) and Wood 1974 geobarometer (PKb) and the Herzberg 1978 geothermometer/barometer which can give broadly similar results (Griffin, et al., 1984), K (Permian), C (Jurassic), D & J (Mesozoic?), P & Tasmanian plots (early/late Tertiary), N, A & B (late Tertiary/Recent).

504

THE McARTHUR BASIN - A MIDDLE PROTEROZOIC PROVINCE?

HYDROCARBON

I.P. Sweet and K.A. Plumb Division of Continental Geology, Bureau of Mineral Resources, Canberra Proterozoic basins are widely considered to be too old, too metamorphosed, and too deficient in organic matter to generate hydrocarbons. This is not so! Many ancient basins are only mildly deformed and virtually unmetamorphosed. Algal material, as evidenced from widespread stromatolites, was abundant. Black shales contain ample organic carbon and kerogen. Economic reserves of hydrocarbons are already known from late Proterozoic rocks in Siberia and Oman. The McArthur Basin of northern Australia demonstrates a potential extending back to at least 1400-1700 Ma. The McArthur Basin has long been known to contain a thick unmetamorphosed sequence, rich in algal matter and carbonaceous shales; indeed, kerogen from near the top of the Roper Group was shown to be actual ly immature with respect to oil generation (Peat et al., 1 978). BMR found oily and solid pyrobitumen material in vughs within silicified carbonates of the McArthur Group (Muir et al., 1 980), at about the same time that Kennecott Exploration Co. encountered a gas blowout in a mineral exploration hole. The basin is only mildly to moderately deformed, appropriate for the development of suitable structural traps. The result is that Amoco International and Kennecott jointly commenced a comprehensive exploration program for hydrocarbons in the McArthur Basin in 1 981, culminating with the spudding in of their Broadmere No. 1 well in May, 1984. At the same time BMR is carrying out independent stratigraphic, sedimentological and organic petrological and geochemical assessments of the hydrocarbon potential of the McArthur and Roper Groups. The Batten Subgroup, at the top of the McArthur Group, is a regressive hypersaline evaporative complex more than 1000 m thick. This complex grades from a euxinic sublittoral black shale sequence of either marine or lacustrine origin at the base, through intertidal and sabkha facies, to ephemeral lakes at the top; the whole sequence was deposited in a fault-controlled half graben, with broad structural similarities to the Persian Gulf. The basal black shale averages about 100 m thick over some 3500km? with most TOC values 0.5% or greater. Indeed, one locally thickened section averages 0.6% over 400 m,with intervals up to 3.44%. Kerogen from these thicker sections are now overmature, but thinner sections nearer the basin margins are marginally immature to mature. These overmature rocks must have originally contained much higher TOC contents. Similar results can be expected from other units lower in the sequence, but have not been measured (by BMR) yet. The Roper Group comprises a series of alternating shale, siltstone and sandstone units totalling between a few hundred metres thick in the east to over 5000 m in the southwest. The thickest section, from geophysics, lies beneath thin Phanerozoic cover in the southwest near

505

Daly Waters (Cull, 1982; Collins, 1 983). The basin developed through several cycles of marine transgression and regression, probably from the west or southwest, across a gentle regional downwarp; non-marine (fluvial) environments appear to be represented only in the Limmen Sandstone, at.the base of the Group. Shales of the thick open-shelf Mainoru and Corcoran Formations have not indicated good source-rock potential yet, but the Velkerri Formation contains, at least locally, TOC values averaging 4.8% and up to 6.0% over an 80 m interval. Rock-Eval analysis shows that the organic matter is oil-prone and falls within the "oil window". The Abner and Bessie Creek Sandstones are particularly widespread marine-shelf quartz-sand sheets with reservoir potential. Both are known to be excellent aquifers, at least locally. At depth they show widespread silica cementation but, from the sparse data so far available, porosities up to 14% and permeabilities up to 30 millidarcies are indicated from the Bessie Creek Sandstone. Many studies remain to be done to fully evaluate the prospectivity of this particular basin: regional /variations in source-rock maturity, reservoir characteristics, diagenesis, hydrocarbon migration, and so on. However, in the more general sense, the data already available unequivocally demonstrates that basins of this type and age can indeed generate hydrocarbons. Economic accumulations may result if there are appropriate structural traps, appropriate timing of hydrocarbon migration, and most particularly, adequate seals for the very long times required. But are these not the classical requirements for any basin of any age? References Collins, C.D.N., 1983, BMR J. Aust. Geol. Geophys., 8, 19-34. Cull, J.P., 1982, BMR J. Aust. Geol. Geophys., 7, 275-286. Muir, M.D., Armstrong, K.J., & Jackson, M.J., 1980, BMR J. Aust. Geol. Geophys., 5, 301 -304. Peat, C.J., Muir, M.D., Plumb, K.A., McKirdy, D.M., & Norvick, M.S., 1978, BMR J. Aust. Geol. Geophys., 3;, 1-17.

GEOLOGY AND HYDROCARBON POTENTIAL OF AUSTRALIA'S LEGAL CONTINENTAL SHELF BEYOND THE EXCLUSIVE ECONOMIC ZONE P.A. Symonds Bureau of Mineral Resources, Canberra, A.C.T. The Convention of the Law of the Sea was adopted at the Eleventh Session of the Third United Nat ions Conference on the Law of the Sea, and was signed by Australia in late 1982,but has not yet been ratified by government- Key elements of the Convention are that coastal States have sovereign rights over living and non-living resources in a 200 nautical mile Exclusive Economic Zone (EEZ); and they have sovereign rights with respect to sedentary species and non-living resources of the sea-bed and subsoil over a legal continental shelf, which is basically the continental margin, subject to certain limits.

506

The Convention gives Australia control of any petroleum resources in an enormous offshore area. The area of the EEZ alone around Australia and its territories is about 8.4 million km 2 , and the total area of its legal continental shelf is about 10.8 million km2,- approximately 407o bigger than the area of the Australian landmass, and one of the largest legal continental shelves on Earth. Eight zones of the legal continental shelf lie beyond the EEZ - Lord Howe Rise/Norfolk Ridge (A), Macquarie Ridge (B), South Tasman Rise (C) Great Australian Bight (D), Naturaliste Plateau (E), Exmouth/Wallaby Plateaus (E), Argo Abyssal Plain (G) and the Kerguelen Plateau (H) (Figure). Within six of these zones (A, C, D, E, F and H) there are at least some areas of relatively thick sediment (greater than about 2000m thick) which may be prospective for hydrocarbons. The western and eastern Lord Howe Rise and the southern Kerguelen Plateau stand out as having the greatest potential for future discovery and production of hydrocarbons. Water depths in these areas typically exceed 1000m, but are generally less than in the other areas. They are considered to be continental in origin, to have a structure and stratigraphy related to passive continental margin development, and to contain potential petroleum plays of a kind that have been tested elsewhere in Australia and worldwide. The western Lord Howe Rise is* underlain by a 200 km wide zone of basins mainly grabens and half grabens - which probably formed during the rift phase preceding the opening of the Tasman Basin. The eastern flank of the Lord Howe Rise has the form of a classic pull-apart margin, and may have formed an ancient seaboard of the Australian-Antarctic supercontinent. Prospective sediment beneath the western and eastern Lord Howe Rise is estimated to cover an area of about 80 000 km2 and have a volume of 200 000 km 3 . The Kerguelen Plateau has been regarded as an uplifted piece of a Mesozoic ocean basin by some, but the sparse data over the feature lends at least as much support to a continental origin. Seismic profiles show that in places over 3000m of sediment may be present and in some areas the structural style is similar to that of rifted continental margins. Prospective sediment is estimated to cover an area of about 66 000 km 2 and have a volume of 165 000 km 3 . Two other areas beyond the EEZ stand out as having clear hydrocarbon potential based on the amount of prospective sediment present - the New Caledonian Basin (43 000km^ or 129 000 km 3 ), and the lower slope and basin floor province of the Great Australian Bight (20 000 km 2 or 130 000 km 3 ). These are very deep water areas (greater than 3000m deep), where theoretical source, reservoir and seal configurations can be envisaged which could provide favourable conditions for the occurrence of hydrocarbons. The remote locations, deep water, and often difficult to extreme operating conditions mean that all of the prospective areas of Australia's legal continental shelf beyond the EEZ can only be considered as long-term prospects for hydrocarbon exploration and exploitation. For any of these areas to be economically viable 'giant1 fields (greater tahn 500 million barrels of recoverable oil) would need to be found, unless there is a dramatic change in the economics of exploration and exploitation.

507

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200 nautical mile Exclusive Economic Zone (EEZ) and the legal continental shelf around Australia and its territories. Continental shelf zones beyond the EEZ are labelled A, B, C, etc.

FLUV10—DELTAIC DEPOSITIONAL SYSTEMS AND SHELF DEVELOPMENT IN THE CENTRAL GREAT BARRIER REEF REGION P.A. Symonds and P.J. Davies Bureau of Mineral Resources, Canberra, A.C.T. The development of the continental shelf in the central Great Barrier Reef province has been deduced from shallow, intermediate and deep focus seismic reflection profiling in conjunction with modern process studies. Throughout much of its history the province was dominated by terrigenous 508

sedimentation, principally controlled by the relative height of sea level. During periods of low sea level, alluvial processes affected the shelf, while fluvial and wave-dominated deltaic progradation into deep water occurred at the shelf edge. During periods of high sea level sedimentation was generally restricted to coastal deltaic progradation into the shallow water of the inner shelf and onlap of the continental slope by submarine fans concomitant with extensive upper-slope erosion. Boomer profiles and vibrocores indicate that sediments related to the Holocene transgression are thin and patchy. Sedimentation related to the present stabilised high sea level is limited to the inner shelf, where muds and muddy sands are being deposited as prodeltaic sediments of the Burdekin and Herbert Rivers. Modern coastal progradation rates for large tracts of the north Queensland coast are l-l.5km.10~ 3 yrs resulting from an estimated total annual sediment input of 28 million tonnes from all north Queensland rivers (Belperio, 1983). The Burdekin River, which is the largest single contributor, has an annual pointsource fluviatile input oi about 3.5 million tonnes of sediment resulting in progradation rates locally as high as 4km.10" 3 yrs (Belperio, 1983). Throughout much of the inter-reef area boomer profiles show sequences containing extensive and repeated channelling, multi-generation infill, levee-bank deposits, and complex progradational channel fill, all features characteristic of fluvial systems. Thus it appears that the shelf is underlain by late Pleistocene terrigenous facies related to fluvial and deltaic low sea-level depositional systems. The modes of deposition of the late Quaternary units are analogues for seismic facies units recognisable on the intermediate and deep focus seismic sections. The oldest sedimentary sequences beneath the shelf occur eastwards of a major fault zone lying beneath the middle shelf, and forming the western boundary of the Queensland Trough rift basin. The basal ?Late Cretaceous rift-fill sequence containing volcanics is overlain by Paleocene to late Eocene marine onlap facies, which are in turn overlain by oblique, complex sigmoid-oblique and sigmoid low sea-level progradational facies of probable late Oligocene (PI), late Miocene (P2) and PIio-Pleistocene (P3 + P4) ages (Symonds & others, 1983). These latter facies produced significant continental shelf construction (Fig. 1). The seismic reflection patterns of the prograding units are characteristic of fluvial and wave-dominated deltas, which formed at the shelf edge during low sea-level periods. The progradational units have produced about 10km of shelf outbuilding off Cairns, and about 50km off Townsville.

Coastal wave-dominated

Fig. 1 Schematic profile indicating the types of depositional systems involved in the development of the continental shelf in the central Great Barrier Reef province.

509

In the central Great Barrier Reef the reef facies was established during the Pleistocene. The reefs, which appear to be only 150-250m thick, grew on siliciclastic fluviatile and deltaic sediments during short periods of high sea level, and were subaerially eroded during the intervening and longer periods of low sea level. A submerged shelf-edge barrier reef system occurs along much of the central region, and has served to restrict and modify upper slope deposition during periods of low sea level. References Belperio, A.P., 1983, Proceedings of the Great Barrier Reef Conference, Townsville, 29 August - 2 September 1983, 71-76. Symonds, P.A., Davies, P.J., & Parisi, A., 1983, BMR J. Aust. Geol. & Geophys., 8, 277-291.

THE MOUNT MORGAN GOLD-COPPER MINE AND ENVIRONMENT, QUEENSLAND: A VOLCANOGENIC MASSIVE SULPHIDE DEPOSIT ASSOCIATED WITH A POSSIBLE VOLCANIC CAULDRON STRUCTURE A. Taube Consultant Geologist, Rockhampton, Qld The Mount Morgan Mine was closed in July 1981, having yielded 237,896 kg of gold (7,648,533 oz.) and 360,616 tonnes of copper from 50 million tonnes of ore, an average grade of 4.75 g/t Au and 0.72% Cu. It has been Australia's largest single gold orebody and fourth largest gold-producing area after the Kalgoorlie Golden Mile and the Bendigo and Ballarat areas (Woodall, 1979). The orebody is hosted by acid volcanic rocks of Middle Middle Devonian (Eifelian) age, older than the Late Middle Devonian (Givetian) age previous ly attributed to the rocks. The deposit occurs in the core of a complex regional anticline in the Calliope Block, a belt of middle Palaeozoic volcanic rocks within the Tasman Orogenic Zone. The mine comprised the "Main Pipe" orebody of pyritic massive sulphide and the adjacent "Sugarloaf" orebody of siliceous stringer mineralization. When the host stratigraphy is re-oriented with respect to regional dip and local faulting, the two orebodies are shown to form a pipe-like "volcanogen ic massive sulphide" configuration nearly perpendicular to the stratigraphy Minor stratiform pyritic beds in the host rocks adjacent to the stratigraph ic top of the orebody grade down dip away from the orebody to a sequence of jasperoidal beds in the same stratigraphy. The host stratigraphy shows gross thickening and change of character on either side of the orebody, suggesting that the orebody formed along a penecontemporaneous fault. The fault appears to be part of a large, poorly preserved volcanic cauldron subsidence structure, in which the regional anticline represents a resurgent dome and the Mount Morgan Tonalite the central pluton. Reference Woodall,.R., 1979.

510

Pubis. Geol. Dep. & Extension Service, Univ. West, Aust

THE TIN RESOURCES OF SOUTHEAST ASIA D. Taylor CRA Exploration Pty. Ltd., Canberra The tin mining industry of S.E. Asia has supplied more than 60% of the western world's tin since the middle of the 19th century. This tin has come overwhelmingly from soft-rock deposits in the Thai-Malay peninsula and the islands of Bangka and Billiton: hard rock underground mining has yielded barely 2% of the recorded production. The introduction of western technology and capital between 1910 and 1930 greatly increased productive capacity and by 1960 the large-scale mining method, dredging, and the western mining corporations which used it had dominated the tin mining industry for 40 years. From 1960 to 1981 the industry changed back to a dependence on small scale, short term production methods and the western corporations largely withdrew from active participation. The long-term decline in the use of tin in tinplate and the certainty of further large stockpile releases means that in real-terms tin prices will fall from their 1980 .peak and remain at lower levels for the foreseeable future. The small-scale, high unit cost industry which has grown up over the past 25 years will be unable to continue in its present form because 130 years of production has essentially removed the high-grade shallow deposits which alone could allow it to produce economically. For substantial production to be maintained the very large deep alluvial deposits, both on and offshore, will have to be developed at a scale sufficient to allow major economies of scale to be obtained. In addition any large high-grade primary deposits, comparable in grade and tonnages to Renison though not necessarily of the same geological type, must be found and developed. Large technical problems exist in the way of such developments. Two particular areas of applied geology are highly relevant to the development of the deep onshore alluvials. 1.

The engineering geology of very large soft sediment openpits, in particular slope stability factors, is poorly known but economically vital. Ore reserve delineation particularly grade estimation and control will need to be much improved to permit forward mine planning and selective ore extraction to be optimized.

Skills in these areas are lacking in Southeast Asia at present and will need to be developed, drawing on expertise from both mining and civil engineering operations, and integrated with the existing techniques of large scale dredging to develop a new alluvial mining technology adapted to the local conditions. The varied tinfields of the region have clearly different styles of mineralization and major differences in the relationships of the cassiterite (and other metals) to the ubiquitous, but poorly understood, bodies of granite. The very minor role of hajrd-rock mining for tin in the past means that the primary deposits are poorly known and concepts of ore genesis and the development of models of ore occurrence have not been developed to the useful stage of providing guidance to exploration in southeast Asia. The form and style of the primary mineralization also controls the potential for generating placers of varying kinds, including large concealed deposits offshore and in coastal plain situations. This is an area of geological endeavour which should be persued at a co-operative international level between the countries of southeast Asia and their tinproducing neighbours, Australia, China and Japan, where the exploration for and mining of primary concentrations is better understood. 511

UPLIFT AND THE SOUTHEASTERN HIGHLANDS OF NEW SOUTH HALES A REVIEW or

Do Highland Rivers know where the Coast is? Graham Taylor Geology, Canberra C A E , Bruce, A C T

A resurgence of interest in the evolution of the Eastern Highlands of Australia has been shown by various authors over the last few years. Instead of the earlier cyclical model for landscape evolution in response to cyclical uplift which held currency until recently (e.g. Browne, 1969; King, 1959) and is still supported by some (Jones & Veevers, 1982), there are now two continuous uplift models (Wellman, 1979; Stephenson & Lambeck, 1984). A number of recent detailed studies of pre-basaltic terrains in the Southeastern Highlands of N.S.W. (Bishop & Y o u n g , 1980; Ruxton & Taylor, 1982; Taylor et al. in press; Young, 1977 & 1981) have come to similar conclusions. These are, that the major drainage systems of the Lachlan/ Wollondilly, Shoalhaven and Murrumbidgee/Snowy Rivers have been established in essentially their present form since the earliest Cainozoic or earlier. The question which arises from these studies i s , do the findings have implications for the tectonic history of the Southeastern Highlands? Wellman (1979) argued that the rivers within the Highlands responded rapidly to external base-level changes by eroding their beds at a rate of about 0.01 mm/year. Evidence from detailed studies in the Lachlan and Monaro show that post-basaltic erosion rates are about 0.004 mm/year in the Lachlan and between 0.005 and 0 mm/year in the Murrumbidgee. If these rivers are eroding at these rates in response to external base-level f changes, then they are doing so much more slowly than W e l l m a n s (1979) uplift model suggests and are more in keeping with the much earlier 1 commencement and longer time scale of uplift of Stephenson & L a m b e c k s passive isostatic uplift model. These arguments aside, the question of whether the Highland rivers are responding to Cainozoic base-level changes is not answered by the Highland landscape studies. Perhaps erosion in these areas is merely a response to the filling of the river channels by basalt following an essentially pre-basaltic uplift. If the streams have not responded to Cainozoic base-level changes, then studies of landscape history within the Highlands will reveal little about possible uplift. If they h a v e , then it is clear that at least in the Lachlan, Shoalhaven and Monaro regions, Wellman's (1979) model of 1 continuous uplift, and the Jones & Veevers (1982) model of cyclical uplift are both inapplicable. Further, Ollier's (1982) suggestion that uplift is post-basaltic would appear to be invalid. A solution to these apparently conflicting hypotheses may lie in detailed studies of landscape history in regions flanking the Highlands. Young & McDougall (1982) argue that the coastal lowlands on the south coast of N.S.W. are at least pre-Oligocene and that there has been no significant relative uplift of the Highlands since then. However, their arguments have been challenged (Brown, 1983); and further work in the area would seem to be warranted. The implications of terrestrial volcanics near sea level associated with Cretaceous intrusions of M t Dromedary further to the south need to be further investigated. There would also appear to b e scope for more detailed studies on the western flanks of the Highlands.

512

References Bishop, P. & Young, R.W., 1980, J. geol. Soc. Aust., 29, 117-9. Brown, M.C., 1983, J. geol. Soc. Aust., 30, 247-8. Browne, W.R., 1969, J. geol. Soc. Aust., 1J3, 559-69. Jones, J.G. & Veevers, J.J., 1982, J. geol. Soc. Aust., 29, 1-12. King, L.C., 1959, T. Proc. geol. Soc. S. Af., 62, 113-38. Oilier, C.D., 1982, J. geol. Soc. Aust., _29, 13-23. Ruxton, B.P. & Taylor, G . , 1982, J. geol. Sqc. Aust., _29, 239-46. Stephenson, R.S. & Lambeck, K., 1984, J. Geophys., in press. Taylor, G. et al., 1984, Aust. J. Earth Sci., in press. Wellman, P., 1979, J. geol. Soc. Aust., 24, 1-9. Young, R.W., 1977, Z. Geomorph., 21_, 262-83. Young, R.W., 1981, Aust. Geogr., L5, 77-88. Young, R.W. & McDougall, I., 1982, J. geol. Soc. Aust., 2^9, 425-30.

HYDROTHERMAL FLUIDS FROM THE HILLGROVE DEPOSITS G.R.

TUNGSTEN-GOLD-ANTIMONY

Taylor and 2E.C. Comsti

^ University of New South Wales, Sydney Philippine Bureau of Mines and Geosciences, Manilla Fluid inclusions within quartz and scheelite accompanying several stages of mineralization at Hillgrove are described. Earliest formed scheelite from the deepest levels contains numerous very small inclusions (less than 5 mm) of both a two-phase vapour-dominated type and a twophase liquid-dominated type. These indicate that scheelite deposition occurred during boiling of the ascending fluids. Two-phase, liquid dominated inclusions within pyrite-arsenopyrite-gold mineralization have uncorrected filling temperatures of between 195°C and 250°C and within stibnite-antimonide-siderite and stibnite-calcite mineralization have fill?ing temperatures between 100°C and 195°C and a bimodal distribution of temperatures peaking at 175°C and 145°C. These peaks possibly correlate with the two latest stages of mineral deposition (Comsti and Taylor, 1984). Secondary included fluids within an earlier generation of deformed barren quartz veins are derived from hydrothermal fluids contemporary with the main-stage mineralizing fluids described above. Primary inclusions within barren late-stage, cross-cutting quartz-chlorite-calcite veins show these veins to be unrelated to the mineralization. No daughter crystals were observed in any of these inclusions. Although, because of their very small size, no homogenization or salinity data are available for the scheelite fluid inclusions, it is unlikely that they are comprised of fluids significantly more saline than the 5% equivalent salinity determined for the later-stage fluids. The observed restriction of scheelite to the deeper part of the vein system coincidently with inclusions suggestive of boiling, would be compatible with a deposition mechanism in which#the boiling or unmixing of a C02-H20 fluid at depth causes tungsten-bearing carbonate/bicarbonate complexes to become unstable. Higgins, 1980 suggests that tungsten in deposits of both granite and metamorphic association is transported as carbonate and bicarbonate complexes at temperatures in excess of 300°C in C02-rich fluids under high pressure. Although the parameters for such a fluid at Hillgrove have not yet been precisely substantiated its existence is in accordance with the observed deposition of scheelite at depth, the later deposition of carbonates and the intense brecciation of veins due to C02-driven hydraulic fracturing.

513

A correlation between filling temperatures and salinities of inclusions within quartz accompanying later stibnite mineralization indicates that this mineralization occurred during the mixing of a hot, partly saline, fluid (at 5% equivalent NaCl) with cooler, less-saline meteoric or connate water. Over a vertical distance of 200m, equivalent mineral assemblages were deposited over the same temperature ranges. Studies on single crystals suggest rapid deposition with fluid temperature dropping 45°C during their growth. It is concluded that mineral parageneses and fluid inclusion data suggest that the metals were transported by sulphur-poor, moderate temperature, low-salinity solutions, possibly as carbonate/bicarbonate complexes. A vertical zonation of the W-Sb-Au mineralization is compatible with the boiling of this hydrothermal fluid and then subsequent mixing with cooler groundwater. Regional metallogenic and geological considerations suggest that ore metals are derived from the remobilization of deep-seated stratabound deposits (Plimer, 1982) or from metamorphic fluids expelled from deep-seated volcanoclastic sediments. References Comsti, E.C. & Taylor, G.R. 1984. In press. Higgins, N.C., 1980. Can. J. Earth Sci. 17, 823-830. Plimer, I.R., 1982 in New England Geology. Eds. Flood & Ruggegar. Univ. of New England. 277-284.

THE MOBILISATION OF TIN FROM GRANITOID MAGMAS J.R. Taylor, V.J. Wall and M.S. Bloom Department of Earth Sciences, Monash University, Clayton Understanding the evolution of magmatically derived tin deposits requires quantitative evaluation of the physiochemical constraints on the extraction of tin from granitoid magmas and its subsequent hydrothermal transport. We report our experimental investigations on melt-aqueous phase tin partitioning and the solubility of cassiterite in high temperature hydrothermal solutions. Such data enables modelling of the magmatichydrothermal transition in the development of tin mineralisation. Partitioning experiments (700-800°C, 1-3 kb), examined the distribution of tin between haplogranite melts and an aqueous phase (0-8 molal (Na + K)C1) over a range of oxygen fugacities (FQM - 1 ^J^uW^^-f 0 Hm/Mt - 1 log unit), utilizing a double Au capsule method. Kg^ increased strongly with increasing chloride molality and also with The solubility of Sn02 in NaCl/KCl decreasing f02 in the higher range. bearing fluids coexisting with albite/kfspar-sillimanite-quartz also increases markedly with chloride molality, with an f02 and pH dependence + which suggests the predominance of Sn^ hydroxy-chloro complexes. These results attest to the efficacy of tin mobilisation and transport by acid, chloride-bearing fluids under high temperature, relatively reducing conditions. Using models based on natural systems, such fluids, generated by resurgent boiling, can account for economic tin enrichment. Adequate concentrations and quantities of tin may be extracted from comparatively common granitic compositions or more effectively from geochemically fractionated variants. Sn02 deposition from the magmatic aqueous phase is favoured by decreasing temperature, decreasing acidity or increasing f02.

514

APPLICATION

OF FTIR SPECTROSCOPY TO STUDIES OF VOLATILE SOLUBILITY MECHANISMS

MAGMATIC

W.R. Taylor and S.F. Foley Geology Department, University of Ta smania, Hobart Recent experimental studies have established the important role played by volatile components in magma genesis and evolution. The major effort in this area has been placed on determining either relative shifts in liquidus mineral phase boundaries or measurement of bulk physical and thermodynamic quantities. The latter studies have led to development of empirical models for volatile-silicate melt interactions. Such models may not bear any resemblance to the actual processes occurring on an atomic or ionic scale, and as a consequence can be extrapolated only with difficulty into complex natural systems. Technological advances in the field of vibrational spectroscopy now make possible a better understanding of volatile-melt interactions at the level of interacting species that should eventually lead to models of wider applicability. High resolution Fourier Transform Infrared 1 spectroscopy over the range.4000-80 cm"" allows access to regions of both internal anionic unit and metal-anion vibrations for all geologically important elements. We have applied FTIR spectroscopy in determining the detailed mechanism of C 0 2 , CHi* and fluoride solubility in simple-system silicate melts. (1) Dissolution mechanism of oxidised carbon: Mid and Far I.R. spectra of nepheline and soda-melilite glasses containing dissolved C0 2 reveal large splittings of the V3 carbonate mode (Fig. 1) and a strong bonding interaction between large metal cations and carbonate. In 0 nepheline glass we identify the complexes [NaC0 3 ]~, [Na 2 C0 3 ] and [Na 3 C0 3 ] and find no evidence for molecular C 0 2 . Difference spectra reveal C0 2 dissolution is accompanied by changes in Al-coordination, for a soda-melilite unit; IV + VI 0 NaCa[Al Si 2 0 7 ] + C0 2 + [NaCaC0 3 ] + [A1 0 2 ]~ + [Si^t*] (2) Dissolution mechanism of reduced carbon: Methane, likely to be a major volatile constituent of the Earth's mantle, has previously been regarded as an essentially inert volatile component. However, FTIR studies reveal that CHi+ is readily soluble in jadeite and soda-melilite 1 melts producing 0-H bonds (-3580 cm"" ), reduced bonds between Si and C 1 VI (-800 cm" ) and changes in A1 coordination (Al^Oi* • A 1 0 6 ) . The identification of dissolved reduced carbon has important implications for the origin of diamond and control of magmatic f02. (3) The dissolution mechanism of fluoride is being studied in the system kalsilite-forsterite-silica, to which fluorine is added by direct substitution (F 2 0_ 1 )• Glasses of composition Ks^itFo39QtZi7, which is close to the piercing point (Fo+En+PHL-L) and thus a basic rock analogue, were made with 0%, 4% and 10% F 2 0.!. At low fluoride contents the FTIR 1 spectra show absorbance bands in the region 450-150 cm" corresponding to vibrations of F coordinated with all network modifying cations K, Mg and A1. These are accentuated at higher fluoride contents where the silica network undergoes substantial polymerisation indicated by shifting of Si-0 absorbance bands to higher wavenumbers. Preference of F for network-modifying cations results in immiscibility at 10% F 2 0 _ 1 giving liquids enriched in aluminosilicate or M g F 2 . Operation of a similar polymerising dissolution mechanism at high pressure is confirmed by experiments at 28 kb in which the phase volume of enstatite relative to forsterite is expanded compared to the volatile-free system.

515

988 A

A. NEPHELINE GLASS C30 KBARD C02 SATURATED

445

1609 1

C02

VAPOUR — —

1398 1

/ /

I 1

702

1278

^ "T

2500

2000

1500

570

1000

S00

WAVENUMBER/CM-l FIG. 1.

FTIR spectrum of C02 saturated nepheline glass showing multiple V3 bands (1609, 1398, 1278 cm"1) associated with dissolved sodium-carbonate complexes. Bands at 702 and 570 cm"1 are due largely to vibrations of AlOi, and A106 polyhedra respectively.

DISTRIBUTION AND POSSIBLE ORIGIN OF DIAMONDS IN EASTERN AUSTRALIA P.A. Teiriby1 , F.L. Sutherland2, J.D. Hollis3 1

CRA Exploration Pty. Ltd., Tasmania Australian Museum, Sydney University of Melbourne, Melbourne Diamonds are known from numerous localities down the eastern margin of Australia, principally in the highland areas. Regional differences in physical characteristics such as colour and morphology are evident. Alluvial deposits of past or present commercial interest occur at Copeton, Bingara, Wellington and Capertee. The distribution of diamonds is broadly coincident with the distribution of basaltic volcanic provinces, many of which have associated breccia pipes. High pressure xenoliths of upper mantle origin may be present in both the basalts and the breccia pipes, which range from Permian to Recent in age. Diamonds have been recorded from a dolerite dyke at Copeton; the presence of granitic minerals in the dolerite suggesting possible accidental contamination by diamondiferous sediment. 3

516

Indicator minerals typifying South African kiiriberlites are very rare although broadly similar minerals occur in many of the xenoliths and are found in some basalts and breccia pipes. The xenoliths give experimental P.T. data indicative of high geothermal gradients and pressure less than 24 kilobars, suggesting that the environments sampled are well outside the area of diamond stability. Inclusions in diamonds from N.S.W. include coesite, omphacite - coesite, garnet - coesite and rare highly magnesian olivine and clinopyroxene. A dominantly eclogitic but also peridotitic source region is suggested by the inclusion data. The inclusion suite differs from other regions in the presence of grossular garnet and much more abundant coesite forming a new 'grospyte1 assemblage. Hollis et al (1983) suggest a sudden outgassing model for some alkali volcanic diatremes which may initially produce deep origin (diamond facies) material prior to alkali basaltic volc'anism. Early eruptive material in such diatremes may be rapidly eroded leaving variably preserved diatremes filled principally with later eruptive material. These pipes would then be associated with diamondiferous alluvial deposits. Localities where barren pipes occur close to diamondiferous alluvial deposits include Capertee, N.S.W.? Proston, Qld.; Walcha, N.S.W.; and Bingaraf N.S.W. Rare earth concentrations that might support the outgassing model for basalt diatremes is found in a garnet lherzolite-bearing basalt at Bow Hill, Tasmania. Structural controls on the regional distribution of some breccia pipes were proposed by Stracke et al (1977). The spatial association between diamonds, alkali basaltic rocks and the Great Divide is noteworthy and may reflect regional structures adjacent to the margin of Eastern Australia. 'Kimberlitic1 metasomatism is recorded in the mantle at this margin, but true kimberlites are not yet identified amongst the breccia pipes. A considerable amount of exploration for diamonds has been carried out in Eastern Australia, principally concentrating on areas known to produce diamonds. The diamonds from Copeton are characterized by exceptional hardness and unusually heavy isotopic composition in carbon. These characteristics could reflect conditions of formation. Significant regional variations in upper mantle lherzolite bulk chemistry are present in Eastern Australia which suggest the 'indicator mineral1 characteristics need evaluation on a relatively local scale. Application of southern African indicator characteristics has not located significantly diamondiferous breccia pipes in Eastern Australia. Reliable indicators elsewhere, such as G10 garnets, are unlikely as they are not found as inclusions in the diamonds. Grossular garnet may prove to be important in this respect.

DIFFUSION OF Zn AND Fe IN SPHALERITE A.J.B. Thompson1 and S.D. Scott 2 ^B.P. Minerals Australia, Brisbane ^University of Toronto, Canada The iron content of sphalerite is often used as an indicator of the conditions of sulphide deposition or peak metamorphism. Calculations of geobarometry and fs2 from the composition of sphalerites, however, assume constant iron content from equilibration. More accurate application of sphalerite composition requires determination of the Zn and Fe diffusion rates.

517

Conventional radiotracer diffusion experiments were carried out at the University of Toronto to determine Zn self-diffusion rates over the temperature range of 500-800°C. Two methods of analysis were used on the diffusion couple; 1) bulk analysis of each cube, and 2) sectioning of the receptor cube. Neither method of analysis produced reliable diffusion coefficients, due to grain boundary diffusion and vapour transfer. True values of D are estimated to be lower than the rates produced from sectioning, i.e. *3.8xlCr 1 3 cm 2 /s at 700°C. An alternative method was employed using microprobe scans to measure inter-diffusion rates of (Zn-Fe) in (Zn,Fe)S. The resultant equation for D reads; D

(4.76xlO- 7 )exp(-31kcal/RT)

(cm2/ s )

for sphalerite near the pyrite plus pyrrhotite buffer. Thermodynamic calculations suggest the inter-diffusion rate is very close in value to the volume self-diffusion rate. Sphalerite is confirmed as a refractory mineral, with true volume diffusion rates lower than previously described. The rate determined in this study and that of Mizuta (1978) may be applied with caution to natural assemblages. Grain size, fractures, fs2 and thermal history must all be considered. Applications include the determination of blocking temperatures (Dodson, 1973) and their relation tp geobarometer (Scott, 1975) and cosmobarometer (Schwarz et al, 1975) calculations. The failure of most attempts to use the geobarometer on the ores at Ducktown, Tennessee is explained. In addition, the length of time needed for observed iron zoning patterns to form in metamorphosed or primary sphalerites may be approximated. These calculations of profiles support the use of Kuroko sphalerites to indicate f$2 conditions. More experimental work is needed to refine the results from this study. In particular, experiments need to be devised which can measure rates in the lower temperature range of interest, 300-600°C. References Schwarz, H.P., Scott, S.D., & Kissin, S.A., 1975, Geochim. Cosmochim. Acta, 39, 1457-1466, Scott, S.D., 1973, Econ. Geol., 68, 466-474. Dodson, M.H., 1973, Contr. Mineral, and Petrol., 40, 259-274. Mizuta, T.,.1978, Program Joint Meet. Soc. Mining Geol. Japan, Mineral. Soc. Japan, and Japan Assoc. Mineral. Petrol. Econ. Geol., Abstr. B-34.

T H E A P P L I C A T I O N OF S O L I D S T A T E 2 9 S I A N D 1 3 C N U C L E A R M A G N E T I C R E S O N A N C E ( N M R ) S P E C T R O S C O P Y TO T H E S T U D Y OF C L A Y MINERAL-ORGANIC INTERCALATES AND THEIR NATURALLY OCCURRING ANALOGUES John G. Thompson James Cook University, Townsville, Qld Solid state NMR techniques have only recently been applied to naturally occurring systems in earth science. Solid state ^^C has been used to examine the nature of the organic component of petroleum source rocks, coal and oil shale. ^ S i n^R. has been able to determine the short range ordering and distribution of silicon and aluminium in minerals, including clay minerals. This paper describes the application of both techniques to the study of inorganic-organic interactions in clay mineralorganic intercalates and to preliminary investigations involving oil shale.

518

In kaolinite intercalates, decreasing levels of hydrogen bonding interaction between the silicate layer of the clay m^eral and the intercalate is reflected in increased shielding of the Si resonance. The " c resonances of intercalating organics were shifted downfield (up to 3ppm) in response to increased hydrogen bonding after intercalation. 9 The Si resonance of expandable 2:1 clay minerals was shielded approximately lppm when the hydrated cation was exchanged with alkylammonium cations, again indicating a weakening of hydrogen bond interaction from 0—H..0 to N—H..0. Clay minerals are presumed to play an important catalytic role in fossil fuel formation. The observation of illites containing ammonia, associated with super-mature sediments, and the results of laboratory experiments suggest that clay mineral-organic interactions are significant in fossil fuel formation. Such interactions can only be observed "in situ". The ability of solid state NMR to observe short range bonding effects non-destructively makes it ideally suited to such investigations. The main difficulty in observing the above phenomena in naturally occurring systems via solid state NMR is the broadening effect of both scalar nuclear-electron spin-spin coupling and local modulation of the applied magnetic field due to the presence of unpaired efectrons in the form of paramagnetic centres * (Fe^+, Mn^+) and free radicals (abundant in immature organic matter). Until such interference can be overcome solid state NMR will be restricted to the study of a small range of relatively ideal sediments. Investigations are currently in progress towards this goal. References Thompson, J.G., 1984, Clays Clay Miner, (in press). Thompson, J.G., 1984, Clay Minerals (in press).

THE ROLE OF LINEAMENTS IN THE YILGARN BLOCK S.A. Tomich Consultant, Perth Regional linear features are not uncommon in the Archaean Yilgarn Block. Though imperfectly exposed and not fully understood, many seem to be surface expressions of earth sutures probably active at various times from the Archaean, up to the present. Some lineaments are considered to be controls of volcanism and/or associated mineral deposits; others control regional uplift or sedimentation and have some influence on zones of metamorphism. Based on their individual characteristics the lineaments fall into two natural types: 1) those within large granitoid areas, particularly the South Western Division., and 2) lineaments associated with greenstone belts. In a few places the two overlap. Those in the granite country have appreciable linear physiographic expression, in some instances indicative of geologically recent movement. The greenstone lineaments, though devoid of topographic expression as a rule, are impressive fault zones of considerable magnitude, but the field evidence permits no correlation of displaced strata other than to give an impression of semiregional facies changes, tectonically enhanced. The location of some primary gold and nickel sulphide districts, or groups of deposits, appears to have been influenced by completely unmineralised lineaments or regional faults, either singly or in combinations of intersecting sets, in the greenstone areas. Lineaments in granitic terrain seem to have influenced the disposition of deposits of bauxite (in elevated ground) and coal, etc. (in depressed areas). 519

Unlike the situation in greenstone belts, actual outcrops of lineament structures in granitic areas can seldom, if ever, be pinpointed, except at linear granite margins. This is probably due to the nature of the lineaments themselves - those in granite terrain may be broad zones consisting of spaced fractures as distinct from the concentrated intensely schisted zones typical of greenstone lineaments or regional faults that indicate strike-slip or reverse movements. The frequent alignment of greenstone strata almost parallel to regional faults suggests elongation along the structures and possible relocation of contained metalliferous ores resulting in dispersal with successive grade depletions in much-fractured zones, as at Kalgoorlie. Scarps apparently signifying largely dip-slip displacement are confined to granitic areas or their margins, and the recognition of both smoothed and relatively unsmoothed scarps indicates continuing isostatic movements up to geologically recent, and even modern times. Regional linear contrasts in topographic relief might be tied-in with the development or intrusion of granites, e.g. lighter homogeneous, discordant granite may still be rising isostatically whilst heavier, concordant, foliated granites and gneisses are not doing so, or have risen at a lesser rate. On this basis, large greenstone belts would be generally relatively depressed. Where separate lineament -and associated greenstone - trends are superimposed, one on the other, the dominant set is on a NNW strike, apparently older than a NW set. A significant lineament (regional fault) on NNW strike, marking economically important facies changes, passes through the west side of Kalgoorlie. Another set of lineament and greenstone trends, less conspicuous, is on NE strike, and is also truncated by the NNW set, but the time-relationship between the NE and NW sets is uncertain. Most of the major granite lineaments of the SW are capable of some form of verification on regional aeromagnetic and gravity maps, suggesting that they represent deep-seated sutures. But there are also lineaments that can be drawn on the maps that cannot be, or have not been,verified in the field, or appear to be meaningless. With greenstone lineaments regional geophysical confirmation is more subtle, or disjointed, even though the structures are certainly real enough, juding by their field exposures. One lineament, the Merredin Lineament on NNW strike, appears to embody faulting features of both granite and greenstone types along different parts of the same line with possible different movement at various times. Significantly perhaps, in the northern stretches of this lineament, large, layered ultramafic - mafic (Archaean or Proterozoic?) complexes occur exclusively on the side that is persistently elevated and characterized by numerous physiographically prominent "Granite Rocks11 in clusters. This is the opposite side from the high-grade metamorphic terrain of the batholithlike region of the SW, in which the emphasis is on differentiating degrees of metamorphism across lineaments, implying differential vertical movements. The question is whether displacement actually varies contemporaneously from dip-slip in granite to strike-slip in greenstones along the same structural line?

OIL SHALE

THE QUIET REVOLUTION

John S. Turner Southern Pacific Petroleum N.L., Sydney Largely unheralded, the proponents of a modern Australian oil shale industry have been quietly working towards commercial development. So intense have been their activities over the past five years that today, the prospects for commencement have never been more real. At least $80 million has been expended in various feasibility studies currently undergoing evaluation. 520

In other parts of the world too, the exploitation of oil shale is beginning to emerge from the shadows which briefly fell across its development path. In USA, for example, the first commercial-scale project is in commissioning, while in Brazil an existing commercial plant is being supplemented by another with four times the present output. The Japanese are examining oil shale technology newly acquired from their recent wide-ranging studies,with a view to diversifying Japan's liquid fuel sources. It is cautiously forecast that first development of Queensland oil shales could begin within the next five years, and even without another world oil crisis, commercial production of oil from shale could be achieved in the early 1990 f s. The technical and economic conditions supporting this forecast are outlined together with the geological structures on which such developments are likely to be based. At the heart of oil shale conversion is the retort, the process machinery which heats the rock and converts kerogen to useful liquids and gases. Enhanced confidence in retorting has resulted from recent engineering studies and testwork. These latest results, together with detailed project evaluations, indicate that Australian shale oil could be produced and sold at prices comparable with natural crude oil. Subject to conditions imposed by 1 Government, and to investors assessment of risk, such projects can now demonstrate satisfactory returns on investment.

THE

TELFER GOLD

DEPOSIT, WESTERN

AUSTRALIA

David S. Tyrwhitt Newmont Holdings Pty. Ltd.,

Melbourne, Victoria

Sporadic and rubbly outcrops of auriferous gossan remained until the early 1970's unrecognized and unsampled in a series of low sandstone ridges near the Paterson Ranges, over 100 kilometres into the Great Sandy Desert. The first geological map of this area was prepared by the Bureau of Mineral Resources (Wells, 1959) and concentrated largely on the younger sedimentary cover rocks of Mesozoic age, since this formed part of a regional survey oriented more towards oil exploration. Much earlier than this, in 1896, Hubert Trotman had explored the area lying south and east of Telfer and camped for several days at Christmas Pool, one of the rare seasonal rock pools known to the aboriginal people in the desert, a mere 20 kilometres from the present mine site. It was not, however, until August 1971, that two geologists, Ronald Thomson, assisted by Philippe Koen, working for a small West Australian exploration company, discovered and sampled the Telfer gossans and obtained highly anomalous gold assays. The'then low price of gold and very remote location of the prospect ruled against development. Not only did this company not stake any mineral claims but, along with so many of the recently formed exploration groups, they moved away from the mineral industry in the general slow down of exploration effort in 1971-72. Early in 1972, Mr. Thomson joined Newmont on a contract and drew our attention to the prospect he had worked on about a year previously. Our early assessment of the meagre surface indications of the auriferous reefs confirmed and extended the anomalous gold zones located by Thomson.

521

It also clearly demonstrated the stratabound nature of the gold horizons, providing some optimism regarding their lateral continuity. The mineral claims we staked were the first recorded mining titles in this entire district, which once again underscores the formidable barrier that the Great Sandy Desert had proved throughout the gold rush years of 1886, through until the Great Depression. We have no doubt that had the quartz and limonite reefs, with occasional small nuggets of visible gold, been within a day's walk or ride of the Pilbara gold field to the west, prospectors would long since have located and mined out the deposit. Reference Wells, A.T., 1959, Paterson Range 4-Mile Geological Series. Notes Bur. Miner. Resour. Geol. Geophys. Aust.

Explan.

GEOCHRONOLOGICAL AND GENETIC IMPLICATIONS OF LEAD ISOTOPIC DATA FROM THE ARCHAEAN MASSIVE SULFIDE DEPOSITS AT GOLDEN GROVE, TEUTONIC BORE AND SALT CREEK, WESTERN AUSTRALIA Matti Vaasjoki CSIRO Division of Mineralogy, North Ryde Lead isotopic analysis of 185 samples from three massive sulfide deposits in the Archaean Yilgarn and Pilbara Blocks have been carried out. Two of the deposits investigated, Golden Grove and Teutonic Bore occur in the greenstone belts of the Murchison and Eastern Goldfields provinces of the Yilgarn Block, while Salt Creek occurs within the Whim Creek Group of the Pilbara Block. At Golden Grove, the Pb isotopic data suggest that the mineralization and its wall rocks were emplaced 2730±20 Ma ago, but that the sulfide mineralization lost its U during an event of unkown nature in Middle Proterozoic times, which results in an apparent age of sulfide separates of about 3400 Ma. The least radiogenic lead from the deposit, derived from galenas of the minor Zn-Pb mineralization, plots within experimental error on average lead evolution curves. At Teutonic Bore, the dispersion of the lead isotopic compositions is too small to allow any isochron calculations. However, the bulk of the orebody material is isotopically homogeneous and plots below average global lead evolution curves, which is suggestive of a significant mantle component within the ore. The lead model "age" is consistent with other dating results from the Eastern Goldfields Province. RAB-hole and sulfide samples from Salt Creek form a well-defined linear trend which yields an age estimate 2940±20 Ma and is consistent with data from the overlying basalts. The lead isotopic data for the high-Pb samples plot within experimental error on the average lead evolution curves, indicating a very short crustal residential time for the lead. The model "age" of the galenas is the same as derived for the isochron. At this stage it seems that: (i) the emplacement of significant base metal mineralization into the Archaean greenstone belts in Western Australia occurred during a relatively short span of time, probably about 2700-3000 Ma ago; (ii) within the Yilgarn Block, it may be that greenstone belts in the Eastern Goldfields province contain a larger mantle-derived component than those from the Murchison Province.

522

INVOLVEMENT OF SUBCONTINENTAL MANTLE IN ARC EVIDENCE AND

PETROGENESIS:

IMPLICATIONS

R. Varne Geology Department, University of Tasmania, Hobart Eastern Sunda arc volcanics become richer in potassium towards the collision zone between northwest Australia and the arc. Isotopic and geochemical evidence shows that potassium-rich material from subcontinental mantle is appearing in the arc volcanoes, apparently becoming available after the continent-arc collision began. The distinctive geochemistry of arc volcanics could be mainly due to efficient extraction and mixing of small mantle melt fractions, in convergent tectonic settings.

GEOLOGY, TECTONIC EVOLUTION AND PETROLEUM POTENTIAL OF THE CENTRAL SOLOMONS BASIN:- RESULTS OF RECENT TRIPARTITE CRUISES J.G. Vedder2, D.L. Tiffin3, J.B. Colwell1 and others2 ^Bureau of Mineral Resources, Canberra United States Geological Survey, Menlo Park, California ^CCOP/SOPAC, Suva The Central Solomons Basin (Central Solomons Trough or The Slot) occurs in an intra-arc position, between the twin chains of the Solomon Islands. It has been intensively studied during two Australian-New Zealand-United States research cruises by the ship R/V S.P. Lee, These cruises, which took place in 1982 and 1984, involved the collection of over 2000 n. miles of multichannel seismic data, 40 sonobuoy refraction lines, high-resolution reflection profiles, gravity and magnetic data, and geological (core and dredge) samples. Initial results of this work indicate that: 1. The basin can be broadly subdivided into four segments (the Shortland, Russell, Iron Bottom and Indispensible sub-basins) each of which contains 1-5 km of sedimentary fill. 2. Seismic refraction arrivals provide maximum layer depth estimates of 10-12 km beneath the island arc and adjacent ocean basins. Velocities of crustal rocks beneath the sedimentary section range from 4.8-7.5 km/sec. The acoustic basement, in part metamorphosed, has velocities of 4.8-5.8 km/ sec; a deeper layer, which has a velocity of 6.4-7.5 km/sec, lies 3-4 km below acoustic basement. These higher velocity rocks may include deeper crustal igneous rocks similar to those exposed on some of the islands. 3. Several sedimentary sequences separated by unconformities can be recognised in each of the sub-basins. The unconformities can generally be related to major tectonic events in the region. 4. Structural deformation in the basin includes faults and low-amplitude folds and is confined largely to the basin margins and to the eastern Russell and Iron Bottom sub-basins. 5. The petroleum potential of the region depends largely upon the existence of suitable carbonate-reef reservoirs and suitable source rocks. The existence of thick sequences of Volcaniclastics, the water depth and the shortage of structures over much of the area, tend to downgrade its petroleum potential.

523

REVIEW OF THE GEOLOGY AND HYDROCARBON P O T E N T I A L OF G I D G E A L P A G R O U P IN T H E N O R T H E R N C O O P E R B A S I N

THE

P.W. Vincent Vamgas Ltd., Melbourne The Permo - Triassic Cooper Basin is a large intracratonic basin straddling the Queensland and South Australian border. It is separated into a northern and southern area by a major east - southeasterly trending ridge extending from the Arrabury hinge line through Wackett to the Jackson Trend (Battersby 1976). Deposition in the southern Cooper Basin was dominated by deep rapidly subsiding troughs separated by prominent anticlinal trends. The hydrocarbon prospectivity of Permian sediments in the southern part of the basin has been long recognised (Brooks 1971). Due to a less favourable structural history and thinner Permian section the northern Cooper Basin has been considered less attractive for hydrocarbon exploration (Zwigulis 1983). However, the recent discovery of several Permian gas fields and oil in Pepita No. 1 has enhanced the potential of this area. The anticlinal trend separating the northern and southern Cooper Basin was active during deposition of the Cooper Basin sequence and Permian sediments thin abruptly onto this high. North of this trend, major anticlines generally have a northerly and northwesterly trend. Permian thinning is observed over some of these structures but deposition generally occurred in a more stable tectonic setting. Many features have surface expression and were formed, or at least rejuvenated, during the Tertiary.

524

The Gidgealpa Group has a maximum d r i l l e d thickness of 1020' in the southern part of the northern Cooper Basin and the section thins regionally towards the Canaway Ridge to the northeast. An Early Permian and a Late Permian sequence are recognised. Over much of the northern Cooper Basin the upper part of the Early Permian sequence i s absent and the Late Permian Toolachee Formation disconformably or in some cases unconformably o v e r l i e s the Patchawarra Formation. The E a r l y Permian section is most complete in the s o u t h e a s t e r n part of the basin around Jackson. L a c u s t r i n e and marginal l a c u s t r i n e sediments of the Murteree Shale and Epsilon Formation are not interpreted in t h i s area due to l a t e r a l f a c i e s changes towards the basin margin. Upper Stage 4 i s represented by f l u v i a l and floodplain sediments of the Patchawarra Formation which i s conformably o v e r l a i n by Roseneath S h a l e . The T i r r a w a r r a Sandstone has not yet been recognised in exploration wells to the north of the Wackett Trend. The lower, sandy unit of the Patchawarra Formation ranges in age from Stage 3b to Upper Stage 4a. Permian r e s e r v e s in the northern Cooper Basin are currently about 250 BCF s a l e s gas, 30 x 106 bbls gas liquids and 1 x 106 bbls of recoverable oil. Source rocks in the Toolachee Formation and Patchawarra Formation p l o t as type I I I and type 11 /111 mix with low H/C r a t i o s in relation to 0/C r a t i o s . Total organic parbon contents are h i g h , g e n e r a l ly > 5.0% but the organic matter i s comprised dominantly of v i t r i n i t e and i n e r t i n i t e with lesser amounts of exinite. Hydrocarbon y i e l d s increase through the o i l window but are g e n e r a l l y low, < 10 mg/g. The Toolachee Formation i s marginally mature to mature along the Jackson and Wackett Trends but elsewhere Permian sediments exceed v i t r i n i t e reflectance levels of 0.7% Permian source rocks are mature for oil in the southern and eastern p a r t s of the northern Cooper Basin but become overmature in the Windorah Trough area to the northwest. Maturation modelling indicates that in the southern part of the b l o c k , generation from Permian source rocks commenced during or a f t e r a period of r a p i d subsidence in the E a r l y to Late Cretaceous. Permian sediments are capable of and have generated large volumes of gas and lesser amounts of liquid hydrocarbons. Gases r e s e r v o i r e d in the Toolachee and Patchawarra Formations have wet gas i n d i c i e s ranging from 4- 30 and CO2 contents varying from 3.5% to 18%. Gas compositions show a general trend towards decreasing wetness and increasing CO2 content with increasing thermal maturity of the sourcing sediments. Anomalously low wet gas indicies (< 10 percent) for accumulation adjacent the Nappamerri Trough and Windorah Trough probably indicate migration from more thermally mature areas. Permian sourced o i l s are p a r a f f i n i c with a high p r i s t a n e to phytane ratio (> 3.4). The n-alkane distribution and low odd-even predominance indicates thermally mature o i l s . D i a g e n e s i s has caused a reduction of primary p o r o s i t y and much of the porosity i s secondary, resulting from dissolution. Secondary p o r o s i t y development i s e r r a t i c but a general trend towards decreasing reservoir quality with increasing thermal maturity of the sediments i s apparent. R e s e r v o i r q u a l i t y of Permian sandstones decreases towards the north with increasing depth of burial. The southern part of the northern Cooper Basin has been identified as a wet gas province. In more thermally mature areas towards the north, gases tend to become drier and reservoir quality is poorer.

525

References Battersby, D.G., 1976; In: Leslie R.B., Evans H.J.,and Knight C.L. (eds). Economic Geology of Australia and Papua New Guinea - 3. Petroleum. Australas. Inst. Min. Metal 1., Melbourne, 321 - 368. Brooks, J.D., Hesp, W.R. and Rigby, D . , 1971. 11 (1) : 121 - 125.

Aust. Pet. Explor. Assoc.J.,

Z w i g u l i s , M . , 1 9 8 3 . In: Permian Geology of Queensland, Geological Society of Australia, Queensland Division, Brisbane, 43 - 49.

G E O L O G I S T S F R O M 1930 - 1 9 8 0 , S O M E PERSONALITIES AND THEIR CONTRIBUTIONS A . H . Voisey Sedimentary Holdings Ltd., Sydney Much has been written on Australia's pioneer geologists of the pref David era. They were small in numbers and even in the late 1 9 3 0 s I believe that I knew more than half of those who were active personally. Since then numbers have increased to the stage when they are now somewhere in the vicinity of 6,000. My coverage, therefore, has to be in the nature of a Gallup pole related more to those with whom I have been in contact rather than those whose contributions have been most important. It is easier to evaluate the work of David who compiled a Geological Map of the Commonwealth in 1932, than that of those who contributed to Osborne's vision of a Tectonic Map and the extensive larger scale coverage of Australia by members of the State Geological Surveys and the Bureau of Mineral Resources. The study of mineral deposits and the search for hydrocarbons once the responsibility of government surveys moved to mining and oil companies in the "thirties" and since then most achievers are lost in organizational anonymity appearing only as some do in the presentation of papers to scientific society meetings with company permission. My first impressions of Geologists were obtained . from those on university staffs and members of surveys, many of whom were met through attendance of the Royal Society meetings in Sydney, and of Section C (Geology) of A.N.Z.A.A.S. at various capitals over the years. Names I must mention (initials omitted to save space) were senior members of university staffs:- Sydney - Cotton, Browne, Waterhouse, Osborne; Melbourne - Skeats, Summers, Singleton, Sherbon Hills; Queensland - Richards, Bryan, Whitehouse; Adelaide - Mawson, Madigan, Alderman; Western Australia - de Courcy Clarke; Tasmania - Arndel L e w i s . Details of the subsequent appointments to university staffs are given by Summers (1948), and to Sydney University by Branagan (1973). The role of the geological surveys and names of the members is treated very fully by Johns (1976). I knew Andrews, Kenny, Booker, Raggatt, D u n , Mulholland and Rayner of the N.S.W Survey very well and Baragwanath, Thomas (Victoria); Ball, Reid, Denmead, (Queensland); W a r d , Jack, Dickinson and Segnit (South Australia); Ellis (Western Australia); and Henderson and Blake (Tasmania). Others who later joined the Aerial Geological and Geophysical Survey of Northern Australia were N y e , Finnucane, Hossfeld, Honman, Broadhurst and Jenson. Other prominent personages were Woolnough, Chapman, (Commonwealth Government); Anderson, Hodge-Smith (Australian Museum); Walkom (Linnean Society); Sussmilch (Sydney Technical College and Author of "Geology of New South Wales"). Stillwell (C.S.I.R.0.) and Stanley (Oil Search Limited).

526

There was little communication between universities and survey geologists except through A N.Z.A.A.S but attendance was severely limited by finances, transport and leave conditions; there were no plane services, and few of those mentioned above owned cars. Neither Browne nor Waterhouse for instance ever learned to drive and the same was often said by those who accompanied Whitehouse's expeditions throughout Queensland. Geological work in Australia before the second world war differed little from the expeditions of the early explorers. Madigan, for example, went through my Arltunga camp (A.N.Z.A.A.S. in 1355) riding a camel. 1933, and 1934, were important, innovative years in exploration Campbell was probably the first geologist to be fully employed by a mining company - Western Mining Corporation. Carey went to Papua New Guinea and Rudd for Oil Search Limited to the Carnarvon Basin. Fisher was appointed Government Geologist of New Guinea and I joined Loftus Hills in the search for gold in Central Victoria. The Aerial Geological and Geophysical Survey of Northern Australia started in 1935, and by 1946, had become the Burfeau of Mineral Resources, Geology and Geophysics. The Central Geological Survey at Broken Hill by Gustafson, Burrell and Garretty had carried out detailed mapping. Haddon King and other oompany geologists were among new appointments. Over this period and subsequently women made major contributions to teaohing and research for example, Ida Browne, Heather Drummond, Dorothy Carroll, Kathleen Sherrard* Dorothy Hill, Florrie Cuodling, Germaine Joplin, Betty Robbins, Joyce Brister, Joan Moy, Beryl Nashar, Joan Beattie, Helen Thorburn, Irene Crespin, Joyce Gilbert Tomlinson. Among Sydney graduates over the pre-war period later to become well known were Game, Hanlon, Harrison, Mosher, Noakes, 0. Rayner, Whiting, Lloyd, Dulhunty, Moye, Adamson, Rickwood, Banks, Stevens, Webb and Conlon. Those from other universities included Prider, Wilson, Sullivan, Singleton, Edwards, Gradwell, Mathews, Gaskin, Baker and Sprigg. In the immediate post-war period there oame a number of geologists from overseas - Tiechert, Glaessner, Opik, Marshall, Routledge, Wiltshire, den Tex, Campana and many others. The universities greatly expanded their numbers with returned servicemen producing for instance - Foskett, Glasson, Joklik, Walpole, McGarry, Vallance, Branagan, Loughnan, Lovering and Phipps, starting a great influx of geoscientists making further treatment here only possible by showing slides of those whom I happened to catch with my camera. References Branagan D.F., 1973, Rocks - Fossils - Profs. Science Press Sydney. Johns R.K., 1976, Government Geological Surveys in Australia Government Printer S.A. Rayner J.M., 1972, Rec. Aus. Acad. Sci. _2 iii. Summers H.S., 1948, J. Roy. Soc. N.S.W. 81, ii, 123-146. Sussmilch C.A., 1914, The Geology of New South Wales. Angus and Robertson. Vallance T.G., 1978 Rec. Aus. Acad. Sci. i.

527

EVOLVING MINERAL EXPLORATION TECHNIQUES AND AVAILABLE FACILITIES OVER FIFTY YEARS - 1934 TO 1984 Alan H. Voisey Sedimentary Holdings Ltd., Sydney History generally is expressed as a synthesis of records and observed facts which may be fossils, artifacts, articles, buildings, inscriptions, documents diagrams books or verbal accounts. Case histories of mineral discovery have relied on mining records, maps, plans, photographs and scientific observations and measurements. In all cases the human mind is exercised in developing ideas and concepts. This contribution is concerned not with the discovery of ore bodies themselves but the means available to those who search for them and particularly those which evolved over the last fifty years. Basic geology must be recorded on maps and plans and at least during the last decade their availability has been taken for granted by many without realising the blisters, sweat and swearing that went into their preparation. I did all ray early geological mapping before and even after 1934 on parish or county land maps. Very few Military Maps (1 inch to 1 mile) were available. The only way to get the geological data was to walk and mark off boundaries by pace and compass traverse or more accurately by the use of a theodolite and staff or chain. To get to starting points the pioneers depended on animal transport - Clarke by horseback, Andrews by horse and sulky. I used a bicycle and on one occasion traded sermons with a cleric in return for transport around Drake in a T model Ford in 1934. Automobiles were very scarce and air services non-existant until the "forties". There was often active departmental discouragement of basic geological mapping by state surveys - geologists being directed to work in known mining fields or places of some political interest. David's 1932 map of the Commonwealth was financed by a special grant. Most of the detailed maps outside mining areas were prepared by university staff and students mainly as requirements for higher degrees. Drafting materials were restricted and to get copies one used tracing linen and printed by putting a frame into the sun. Variations in scale were a constant irritation. Enlarging and reducing were achieved by means of a pantograph or with squared paper. Progress in these fields has advanced until now there is a great flexibility in map making, duplication and reproduction. The setting up of the Aerial, Geological and Geophysical Survey of Northern Australia based on the recommendations of Sir Herbert Gepp brought in the new techniques in 1935, and establishment of the Bureau of Mineral Resources in 1946 led to competition with the mines departments of other states and big increases in financial support. The National Mapping Council was established in 1945, but until 1969 topographic maps were produced on the Australian National Grid in yards. In the early stages of the Northern Australia Survey the geological and geophysical operations were started in different localities but experi ence led to the recognition of the need for selection of the appropriate method required to supplement the known geological setting. Geochemical work aided by the development of new instruments and rapid analysis of stream sediments as well as bore cores became another valuable exploration tool. The quantity and quality of data available or attainable today have to be appraised and selected according to the concepts held and the finance available. Computing too is adding a new dimension to the exploration field. These developments are, of course, in line with the changes in society and technical advances in other areas.

528

It is not surprising perhaps that I personally lay great emphasis on the geological approach and regard the other geosciences as ancillary but most important tools to be used when the occasion demands. Above all much depends on the quality of maps and the details they portray. Without the contributions of the governmental surveys many of the more spectacular discoveries would probably not have been made. Even with the coverage now available I believe that there is much more to be done on larger and larger scales. I urge most strongly the continuation of this work. It has obviously been impossible for me to detail the facilities to which I have referred above - they are well known to most of you but I have tried to emphasise how difficult the work was without them. Nevertheless the study of rocks in the field - best done on foot - is still useful and there is a need for strong boots and some more old-fashioned prospecting. Without much information outside that derived from areas prospected and mined during the latter part of the nineteenth century there was little for the company geologists of the "thirties" and "forties" to work on and while finances remained low concepts could not be tried out by drilling. Field geologists assessed the value of drag-folds, graded bedding and other sedimentary features in working out structures and seeking new ore bodies by analogy with those whose positions were known. The ore-bed concept integrated into the study of 'environments gave impetus to the development of new ideas leading to comparisons between the mineral deposits of McArthur River, Mount Isa and Broken Hill. Isotope studies, improvements in instrumentation and in particular the electron probe opened up new fields. Other papers presented to this meeting will illustrate the variety of modern experimental approaches and examples of their contributions to the search for ore.

THE ROLE OF FLUID - ROCK INTERACTION IN SANDSTONE

DIAGENESIS

V.J. Wall and J.M. Bodard Department of Earth Sciences, Monash University, Clayton Diagenetic progress has traditionally been regarded as deleterious to the porosity of sandstones. However, in recent years it has become increasingly apparent that porosity reduction with depth is not monotonic, primarily as a result of secondary porosity evolution (Schmidt & McDonald, 1979). Many major hydrocarbon reservoirs (in the Gippsland Basin, for example: Bodard, Wall & Cas, 1984; Bodard & Wall, 1984) largely owe their characteristics to such diagenetic processes. These may in turn have been influenced by earlier diagenetic processes - cementation, mineral authigenesis, compaction et cetera, and do not simply reflect sandstone mineralogy or depositional environment. Factors such as pore fluid composition, fluid flux, geothermal gradients and organic maturation, and their changes with time may significantly affect the course of sandstone diagenesis. Better predictive models that include these variables will, when coupled with structural, stratigraphic and hydrocarbon generation models, permit the relative timing of porosity evolution, reservoir development, and hydrocarbon migration and entrapment to be more ably resolved. Such models will become increasingly important as the search for hydrocarbons turns towards more subtle and deeper traps.

529

To illustrate some of the problems involved and approaches to understanding porosity evolution in sedimentary basins we utilise examples from the Latrobe Group of the offshore Gippsland Basin. At a relatively early diagenetic stage sandstones, over a large portion of the basin, were extensively cemented by dolomite, occluding pre-existing porosity (Bodard, Wall & Cas, op. cit.). The dolomite was precipitated from externally derived fluids, that is the Ca, Mg, and C required was not indigenous to the sandstones. Stable isotope data indicate that carbon species in the dolomite was of organic derivation, and futhermore, 180 enrichment probably reflects a non-marine fluid provenance as well as isotopic exchange with the rocks through which they passed. Chemical modelling of dolomite - fluid equilibrium suggests that C02 addition at near neutral pH was a major contributor to dolomite precipitation, and that very large quantities of fluid were involved. We may thus infer that these fluids were derived primarily from mudrock compaction, their C02 contents resulting from the decarboxylation that characterises the lower temperature range of organic maturation. This may further imply that fluid movement was essentially stratafugic during dolomite cementation, the fluids focussing through sandstone aquifers. Fluid migration patterns, of this nature, among other constraints, provide an explanation for the regional distribution of dolomite cements.

More advanced diagenesis involved the extensive dissolution of dolomite to produce secondary pores, the chief form of porosity in several of the major hydrocarbon reservoirs. Some kaolinite precipitated at this stage, in close temporal association with hydrocarbon emplacement. To effect dolomite dissolution large quantities of more acid (and probably C02-poor) fluids were required. The sources, migration paths and chemical evolution of these fluids is less clear, but basin hydrology may have differed significantly from the earlier stratafugic phase. Relationships to present-day basin hydrology are also uncertain.

Diagenetic patterns similar to those in the Gippsland Basin have developed in other hydrocarbon-prone sedimentary basins, suggesting to us that there are intrinsic and fundamentally similar controls on the post-depositional evolution of these basins. However, better documentation of the time, temperature, and chemical environment attending diagenetic processes is necessary, requiring integrated petrological, electron and ion microprobe, stable isotope, thermal and burial history studies. To develop more predictive porosity models we must wed investigations of (i) the volumes of diagenetic fluids, their migration paths and how these change as a basin evolves, (ii) the geochemistry of these fluids - especially pH controls and their relationship to organic diagenesis, (iii) fluid - rock interaction models and the mass transfer involved, (iv) the relationships between depositional and tectonic environments, and diagenetic adjustments. Such an approach has the potential to yield valuable insights into hydrocarbon migration and entrapment.

References Bodard, J.M., Wall, V.J., and Cas, R.A., 1984, A.P.E.A* Jour,, v. 24, part 1, p. 314-335. Bodard, J.M., Wall, V.J., 1984, Clay matrix diagenesis and the evolution of Gippsland Basin oil reservoirs. This volume. Schmidt, V., and McDonald, D.A., 1979, p. 175-207 in: P.A. Scholle and P.R. Schluger, eds., Aspects of diagenesis: Soc. Econ. Paleontol. Miner. Spec Publ. No. 26, 443 p. 530

HOW CAN G O V E R N M E N T

BODIES

SET ASIDE EXTRACTIVE

FOR FUTURE

RESOURCES

DEVELOPMENT?

I. Wallace BMI Limited, Sydney When our early settlers and our first geologists examined the available natural construction materials such as building stone and brickmaking clays, they generally found them in abundance. They declared the reserves to be "inexhaustible". They did not reckon on later urban development which would sterlize most of those resources close to the development. For decades, geologists in State geological surveys in Australia have been advising planning authorities to set aside and secure sufficient extractive resources, close to major cities and growth centres, for future development. During that time, numerous important resources have continued to be sterilized due to urban encroachment and ill-informed planning. In most cases, the same advice still needs to be given and, more importantly, heeded by planning authorities. Most planning bodies agree that communities need sufficient extractive resources set aside for future u-se. This is to ensure optimum quality resources are available for building and construction purposes at a minimal price. Further, they generally agree that it is the responsibility of government planning bodies to provide for the future need. The extractive industry, also, has a responsibility to look after its own future requirements, but exactly how it does this in a planning context is unclear. There are many instances where companies have tried to secure their future requirements by purchasing land containing potential quarry resources but ha ve had their initiative frustrated by conflicting land use demands. Clearly, initiatives by the industry to secure future extractive resources need to be taken in close co-operation with government planning authorities. The industry, on its own, cannot take the necessary planning initiatives to protect resources from conflicting land use pressures, nor can it co-ordinate the future intentions of companies with other regional development. The following questions need to be considered by planning bodies, and by the extractive industry, in their joint endeavours to set aside and secure extractive resources for future development. How much resource is required? What is the best estimate of the future market? For what period do we attempt to plan - 20 years, 40 years, or longer? Where, ideally, should the resources be located? These are questions that have taxed the minds of regional planners for some time. It is difficult to predict future requirements but the best estimate seems to be gained by extrapolating from previous consumption data over, say, the last 15-20 years. This avoids relying unduly on short term growth spurts. Planners are generally reluctant to plan for periods greater than 20 years. Clearly, however, planning for future extractive industry must recognize a much longer term requirement, possibly more than 40 years. The location of extractive resources is fixed; they cannot be moved to another, more suitable, location. This is sometimes difficult for planners to appreciate. Regionally important resources should be defined by industry in conjunction with government bodies such as State geological surveys. Sufficient geological investigation should be undertaken to assure planners that "reserves" are proven or, at least, indicated. An assessment of quality, uniformity, and suitability of the resource for future market requirements should also be made. However, who does this work and who pays? Is it the role of government or of industry to define and prove resources for the

531

future? If a company pays for the work, what assurance can be given that the resource will ultimately be available for that company to extract? Without some assurance, companies will be reluctant to commit funds for detailed investigation. The concept of a "consent in principle" for a quarry development, well in advance of its need for commencement, should be considered. An effective method needs to be devised to determine precisely which resources will be set aside for future use. This may be particularly difficult if the resources are privately owned and the owners do not want extractive industry in the future. Who decides? Preferably, government and industry, in close liaison, should devise a strategy for future orderly development of extractive resources. The strategy should be publicised and made known to all relevant government departments and councils. The strategy should be implemented through regional environmental plans. Such planning should not be left in the hands of local councils. Planning for resources of regional significance should be undertaken by planners at State level with appropriate technical input from the extractive industry. Planners must plan for the future by taking positive initiatives. They must not merely react to crises. The regional plans should contain specific land zoning for future resources and buffer zones. This zoning must prevent conflicting development. All possible planning action must be taken to prevent sterilization of resources before development pressures commence. How much land should be set aside? How much buffer zone should be included around the proposed quarry? The size of the buffer should be sufficient to minimise the impact of quarries on neighbouring activities and vice versa. The proposed future use of land surrounding the quarry must therefore be considered. Having prepared and implemented a regional plan, authorities must then resist the urge to change the plan in the future to accommodate competing land use pressures. Unless it can be demonstrated clearly that a resource is no longer required, it should continue to be protected by appropriate land zoning.

PROGRESS IN THE DEVELOPMENT OF THE SIX COMPONENT CHLORITE SOLID SOLUTION MODEL AND THE SEARCH FOR UNIQUENESS IN CHEMICAL MODELS OF HTDROTHERMAL ORE DEPOSIT FORMATION J.L. Walshe Australian National University, Canberra A unique definition of the physico-chemical conditions of formation of hydrothermal ore deposits is commonly difficult to achieve and the chlorite solid solution model is being developed to assist in this task. The non-stoichiometry of the chlorite in the 6 component system Si02~ c a n conveniently represented by the thermodynamic components given below. Of these 6 components only clinochlore (C2) is well characterized. CI and C5 are hypothetical endmembers equivalent to the compositions of the 7A structures chrysotile and kaolinite respectively. Data on chlorites from the Salton Sea and New Zealand geothermal systems, the OH vein system, Creede, Colorado, and the Quaama Granite, NSW, are being used together with standard techniques for estimating heat capacities, third law entropies and free energies to develop the solid solution model.

532

Activity/composition relations for CI, C2 and C3 are best modelled assuming random mixing on energetically equivalent sites. For C4, C5 and C6 these appear to be best modelled assuming a^ = Xi where the activity coefficients (Y^) approaches unity as the mole fraction (X.^) approaches unity. C4 and C5 mixing is apparently close to ideal. C6 mixing is apparently nonideal. Generally there appears to be a difference in mixing behaviours between the structural components, CI, C2 and C3 and the minor components C4, C5 and C6, which mix as integral species within a chlorite 'solution'. Thermodynamic Data at 298.15° and 1 bar bxl0 +3

cxlO -5

126 .03

186 .36

27.32

-51.45

-2 ,116 ,964

111 .20

166 .50

42.10

-37.47

No.

AH°

Mg 6 Si 4 O 10 (OH) 8

-2 ,074 ',767

Mg 5 Al 2 Si 3 0 10 (0H) 8

5 Al 2 Si 3 O 1 0 (OH) 8

Component

-1 ,692 ,360

142 .50

176 .21

43.76

-33.82

Fe 2 + 5 Fe 3 + 2 Si 3 0 1 0 (0H)g

-1 ,491 ,220

151 .26

172 .21

59.54

-28.99

Al 4 Si 4 0 10 (0H) 8

Al 2 S130!10Hy

-1 ,690 ,243

A H° cal/mole;

S° cal/mole/°K

4 Fe

Units:

135 .65

172 .28

46.87

-34.85

Sources: C2. Data for clinochlore. Helgeson et al. 1978. C3, C4, C6. AH° this study. S° and heat capacity coefficients estimated. Helgeson et al. 1978, CI. AH°, S° and heat capacity coefficients this study. Thermodynamic data for CI have been derived from the reaction C2 + KAlSi 3 0 8 + 1/3 H 2 0 ( 1 ) + 1/3 Si02 - KAl3Si3010(OH)2 + 5/6C1 for which the equilibrium constant has been determined utilizing composition/temperature constraints on chlorites from the Salton Sea geothermal system (McDowell and Elders, 1980). The enthalpies of formation of the iron end-members have been established by obtaining a best value for chamosite (C3) from which the enthalpies of formation of C4 and C6 may be estimated. The Quaama and Creede chlorites have been used to constrain both the activity/composition relations for C4 and C6 and the best value for the enthalpy of formation of chamosite. Thermodynamic data on C5 may be obtained from the reaction 2C2 + 14/3 Si02 + 8/3

= C5 +

which may also be calibrated by utilizing composition/temperature constraints on the Salton Sea chlorites. -However this requires prior knowledge of the Fe and H2O contents of the chlorites. Attempts are currently being made to utilize the constraint imposed by the Gibbs-Duhem equation on the H2O and Fe^ + content of chlorites, together with the reaction, C2 + 5/7 C4 + 3/7 C3 + 25/21 Si02 - 10/7 C6 + 5/6 CI + 5/21 H 2 0 ( 1 ) 3+ to calculate the H 2 0 and FeJ contents of chlorites in a 6 component, 3 phase system assuming that the pressure and the Si, Al, Mg and Fe T contents of the chlorite are known. 533

Such a procedure depends in a large part on the quality of the thermodynamic model outlined above. If successful it will permit unique determinations to be made of the physico-chemical conditions of chlorite formation in 4 phase systems e.g. quartz-chlorite-magnetite-water using microprobe analyses. References Helgeson, H.C., Delany, J.M., Nesbitt, H.W., & Bird, D.K. , 1978, Am. J. Sc., 278-A. McDowell, S.D., & Elders, W.A., 1980, Contrib. Mineral. Petrol., 78, 293310.

PROTEROZOIC

AND P A L A E O Z O I C

STROMATOLITIC

AND R E S E R V O I R S

FOR

CARBONATES

SOURCES

PETROLEUM

M.R. Walter Baas Becking Laboratory, Canberra Carbonate reefs are prime exploration targets for petroleum because some are highly permeable and porous, and because frequently they are contiguous with source rocks. It is commonly stated in the literature that reef development began in the Cambrian with the advent of calcareous skeletons in metazoans. However, reefs have a much longer history; huge, lithified wave resistant structures were also built by cyanobacteria, the history of which extends back at least to the late Archaean. There are many examples of Proterozoic and Palaeozoic stromatolite reefs, on a scale as large as any metazoan reefs. Well described examples occur in the Early Proterozoic Athapuscow Aulacogen in Canada and Transvaal Basin in South Africa, the Late Proterozoic of the Canadian Cordillera, the Amadeus Basin and the Devonian of the Canning Basin. Somewhat smaller Holocene examples are found in Shark Bay in Western Australia. The organic matter of stromatolite-building microbial mats has a significant chance of being preserved to form an organic-rich sediment because it forms at the sediment-water interface, unlike detrital organic matter most of which oxidises as it falls through the water column. In addition, in Proterozoic times, the absence or at least inefficiency of bioturbating metazoans would have resulted in less oxidation of buried organic matter. Both Holocene and ancient stromatolite environments contain organic-rich lithofacies, particularly in the form of stratiform stromatolites. Thus the stromatolite flmega-facies,f may contain the two main components of oil generation and accumulation systems - source and reservoir rocks. That this is indeed so is demonstrated by the occurrence of producing petroleum fields in several sequences of this type.

EFFECT OF DYKES ON COAL STRUCTURE AND QUALITY P.R. Warbrooke BHP Geology Department, Newcastle Igneous dykes are particularly common in the Newcastle Coalfield and may be a considerable problem to modern mechanised mining. Also the thermally metamorphosed coal (TMC) associated with dykes may affect the coal quality of products produced from the coal.

534

Dykes in the Newcastle Coal Measures are composed of dolerite (teschenite) and range in thickness upto 3 m in "the clastic strata but due to bulging, may reach 6m thick in coal seams. They are typically surrounded by a zone of thermally metamorphosed coal (TMC). The width of this altered coal is usually similar to the thickness of the dyke and can be divided into four visually distinctive units (Table 1). Samples were collected from these zones adjacent several dykes and subject to petrographic, chemical and spectroscopic analyses. Under the microscope samples from the unaffected zone appeared to be typical for the seam being examined while samples from the heat affected zone were similar although the rank had increased slightly. Material from the cinder zones had a compact coke structure with small pores and walls exhibiting typical coke mozaic texture. The mean maximum vitrinite reflectance decreases away from the dyke, returning to normal in coal immediately adjacent the heat affected coal zone. Volatile matter (dmmf) decreases towards the dyke and indicates that the cindered material is only a semi-coke. Figure 1 shows the trends of the major coal elements using volatile matter as the measure of coal carbonization. These results are similar to those obtained in the formation of artificial semi-coke, suggesting a similar process. Fourier Transform Infrared spectroscopy shows a decrease in the aliphatic C-H stretching bands and a slight increase in the aromation C-H stretching bands as the dyke is approached. Carbon-13 Nuclear Magnetic Resonance spectroscopy indicates an increase in the aromaticity towards the dyke. Molten magma invading the coal measure strata heats the coal but because of the coals low thermal conductivity, the zone heated sufficiently to affect the coal is fairly narrow. Devolatization of the coal adjacent the dyke leads to the formation of semi-coke with the bulk of the volatile matter escaping into the magma. Although the chemistry of natural coke formation appears to be similar to artificial coke formation the physical characteristics are different. The natural coke is very dense and compact with little pore space, probably the result of being formed under the high pressures brought on by devolitization. Semi-coke formation stops with falling temperature however sufficient heat remains to affect the adjacent coal allowing it to become plastic and increase its rank (by processes similar to those of normal coalification). Washability tests show that 55% of the TMC will float at a density of 1.60, hence small proportions (usually < 5%) may find its way into washery products. Tests show that laboratory carbonization properties deteriorate with small additions however coke oven tests indicate only slight deterioration in coke properties with addition of 5% - 10% TMC. Chemical properties show only small changes with the introduction of 5% TMC and there is no change in the HGI. Ash fusion temperatures of the TMC are lower than for the unaffected coal. The results indicate that routine samples can be taken close to dykes without being affected by the dyke, Also some TMC may end up in the washery product but if the quantity is small and well blended, it will only have a minor effect in the coking and energy properties of the coal.

TABLE 1 ZONE

DESCRIPTION

MASSIVE > CINDER

Coked material, dull, massive

BANDED CINDER

Coked material, vague bedding, overall dull

HEAT AFFECTED COAL

Not coked but rank increased, folded, friable

UNAFFECTED No apparent heat J25 COAL affect H O

§ 21

Volatile

Matter

(dmmf)

Figure I.

CLASSIFICATION AND SYSTEMATIC DESCRIPTION OF COAL-BEARING ROCKS IN DRILL CORES Colin R. Ward1 , Jon Comino2 and Andrew Waltho2 University of N.S.W., Kensington N.S.W. Institute of Technology, Broadway

Supported by a grant under the National Energy Research, Development and Demonstration Program, a study has been made of the lithology, texture, composition and other features of the non-coal rocks in the Permian and Triassic strata of the Western Coalfield, New South Wales. The objects of this study were to derive a simple, yet consistent and reproducible method for describing these strata in drill cores, and to prepare a photographically illustrated catalogue of the rock types and sedimentary features in the sequence to assist in using this method for drill core logging in coal exploration and mine geology. 536

A total of over 2000 samples of non-coal materials has been taken, representing each change in lithology over the cored intervals of 13 strategically located boreholes in the area between Dunedoo and M t . Victoria. These samples have been sorted into groups on the basis of their lithologic properties, with further investigation of selected specimens by thin section petrology, x-ray diffraction and geomechanical tests. Photographs have been taken, under studio conditions, of over 100 specimens to illustrate the various features present. A l l b u t a small proportion of the rocks in the sample suite can be grouped into four fundamental categories, namely rudites (conglomerates), arenites (sandstones), laminites (interstratified sandstones and shales) and lutites (shales and mudstones). Further classification and detailed description of individual specimens is then based on the actual combination of features present, selecting from lists giving a limited number of terms under each of the following headings:Texture: A more precise indication of particle size and, in many cases, grain fabric o r packing arrangements, than is given by the rock type name alone. Particle size is the main factor considered for arenites and rudites, b u t the fabric of the sediment (i.e. any lamination o r fissility) is more significant in lutite descriptions. For interstratified arenites and lutites, textural description is based on the relative proportions of the two components and the thickness of the layers in which they occur. Gross Composition: A general indication of the type of material from which the rock is composed. For the rudites and arenites it is based on the mineralogy of the framework particles and the strength of the binding material, while for finer grained and interstratified rocks it reflects the overall colour of the sediment. Minor Constituents: Any components in the rock that are not fundamental to its classification, but are significant in characterizing the material more precisely. These include minor bands o r phases of different particle size, inclusions of coaly material or intraformational fragments and any veins, nodules o r distinctive cementing materials. Structure: A brief description of the shape o r form of any stratification, and of other significant features such as the type of fracture developed. A concise, systematic description of a particular rock or interval of strata can be made up by listing one, or in some cases two, features from each group. Further comments, where necessary, can be added in prose form. Simple abbreviations have been established to enable the descriptions to be readily input, if required, to computer processing systems, and a BASIC program has been developed to allow direct encoding, entry, verification and storage of data in the field using portable computer equipment. References Mallett, C.W. and W a r d , C . R # / 1982, Standardization of geological data in coal measures; Australian C o a l Geology, 4(2), 400-412. Ward, C.R., 1983, Standardization of bore core descriptions for use in coal mine geology; Unpublished end of grant report, National Energy Research, Development and Demonstration Council, Canberra, Project N o . 81/1148, 76pp.

537

OIL SHALE OCCURRENCES IN SOUTHWESTERN

AUSTRALIA

Hector J . Ward Openpit Mining & Exploration P t y . Ltd., Perth Oil shale has been found in Tertiary sediments beneath a Quaternary cover of sandy loams, clays and silts in basins within the Yilgarn Block of Western Australia. Deposition of marine and terrestrial sediments up to 115 metres thick on the irregular Archaean surface of the Block was probably initiated by epeirogenic downwarping. The known occurrences of oil shale, bituminous muds and lignites are within the terrestrial succession. The basinal sediments have been correlated palynologically with sediments and lignites of the Werillup Formation of the Eocene PIantagenet Group in the Albany-Denmark and Esperance Regions and the Eundynie Group of the Norseman district. The oil shale found at Coolgardie in 1899 yielded 13^ litres per tonne of crude oil when retorted in 1904. Analysis of eight samples on average reported 21.94% moisture, 26.13% volatile hydrocarbons, 10% fixed carbons and 4.93% ash. However, the deposit being of small extent is not commercially viable. No further oil shale exploration work was done but drilling for base metals and water in the 1970 1 s showed that Tertiary carbonaceous and bituminous clays were in areas hidden by Quaternary cover in the extremely wide palaeodrainage channels of the region. In 1979 at the instigation of the writer the Western Australia Mines Department threw open the Eastern Goldfields region for oil shale exploration and development which had then become attractive due to the then increasing price of oil. Magnum Minerals Pty. Ltd. and Openpit Mining S Exploration Pty. Ltd. carried out a limited exploration drilling on two permits granted them before the economics of oil recovery from oil shale caused cessation of work. The drilling done did reveal, however, that further occurrences of Tertiary oil shales in the palaeodrainage channels. Samples from two drill holes near the junction of Lake Lefroy and Lake Cowan gave an analyses of 53 litres per tonne over 4 metres and 68 litres per tonne over 19 metres. Thus further exploration could discover oil shale deposits when additional petroleum is required from such sources.

IDENTIFICATION OF GENETICALLY BASED SEDIMENTARY FACIES IN PERMIAN DRILLCORE IN THE SYDNEY - GUNNEDAH BASIN C . R . Weber, J . Beckett, D . S . Hamilton, M . B . L . Hill, I . McDonald, R . S . Moffitt, and V . Z . Tadros Northern Coalfields Section, Coal Geology Branch N.S.W. Department of Mineral Resources, Sydney During the last two years, detailed studies were undertaken on drillcore from coal exploration programmes in the Gunnedah region and the Upper Hunter to determine the origin of the rock sequences intersected. As a result of this work it is now possible to identify a substantial number of genetically based sedimentary facies in drillcore from Permian sequences within the Sydney - Gunnedah Basin. All sedimentary facies identified can be found in modern day alluvial, deltaic, or marine systems.

538

The "poster paper" is in fact an exhibition of drillcores from a number of coal exploration boreholes in the Upper Hunter and Gunnedah regions. The cores show the major diagnostic features used to interpret their origin. Examples of the following deposits are on display: prodelta and distal delta front, proximal delta front, including distributary mouth bar, barrier beach and beach, crevasse splay and interdistributary bay, meandering and non-meandering distributary channel, floodplain, braided river, alluvial fan, colluvial and alluvial, fan delta. These genetically based sedimentary facies can be used to determine environments of deposition and, ultimately, to generate a basin model. The cores are arranged in sequence from marine to terrestrial, as if they had been deposited by the progradation of a delta.

GOLD AND SILVER IMMOBILIZATION DURING THE OXIDATION OF SULPHIDE-BEARING CARBONATE ORE J.G. Webster University of Western Australia, Perth Of the sulphur oxyanions produced during sulphide oxidation, metastable thiosulphate (S 2 03 2 ~) is the most stable under the alkaline condit— ions created by simultaneous carbonate dissolution. Other sulphur-bearing anions occurring in weathering fluids include tetrathionate (S^Og2"") and sulphate (SO4 ), produced by acidic oxidation of sulphide, bisulphide (HS~), introduced to the oxidizing system by reduced groundwaters or hydrothermal fluids, and minor sulphite (SO^2""). Only thiosulphate and bisulphide, however, are known to be capable of dissolving gold. Total gold and silver activity in the S-H2O-O2 system may be calculated from equilibrium stability and solubility constants for variable pH, f02 and total dissolved sulphur activity, at 25°C. Gold is soluble at neutral to alkaline pH as AuS~* in reducing, and Au(S203)2 in moderately oxidizing solutions. Silver is soluble under moderately oxidizing conditions as AgS203~~ at neutral, and A g f ^ O j ^ at neutral to alkaline pH. At elevated f02 the activity of Ag is high at low pH. Although silver forms a number of insoluble sulphur-bearing compounds, including argentite Ag2S) and silver sulphate, gold solubility is limited only by native gold metal. Silver - solubility is, however, greater than that of gold in non-reducing solutions, offset by the relatively high activity of monovalent silver ion. Experimentally determined solubility of gold-silver alloys of 20-40 at% and >90 at% Ag, and natural electrum, in thiosulphate is greater than that of other alloys, colloids or pure crystalline gold. The ratio of gold to silver dissolved from natural electrum, and in the precipitate formed by destabilization of the thiosulphate complex, remains constant. The practical implications for a natural thiosulphate-bearing weathering system include; a) that primary electrum of fineness 700-900 and native silver are most susceptible to corrosion, and b) that there is unlikely to be any fineness increase in secondary relative to primary electrum. If remobilized as a thiosulphate complex, gold and silver will also

539

demonstrate a distinctive pattern of near-surface redistribution, related to zones of major Eh (or fOo) or pH change in the weathering profile. An example of thiosulphate-induced precious metal secondary mobilization exists in the active weathering profile of a manganese carbonate lode system at the Upper Ridges mine, in Papua New Guinea.

GEOPHYSICS OF SOME GRANITOID RELATED MINERAL DEPOSITS S.S. Webster N.S.W. Department of Mineral Resources, Sydney The proportion of non-outcropping mineral discoveries is progressively increasing and exploration is tending to be based on conceptual models and the use of remote sensing techniques to locate tenure areas for detailed prospecting. To these aims the physical parameters and geological setting of some granitoid related mineral types have been classified to permit geophysical techniques to be optimally applied. The relationship between particular granitoids and some mineral assemblages has been noted by many authors, however, just as important are the broadscale geological and structural environments of the mineral domains. Regional geophysics can be utilised to extrapolate relevant geology in areas of poor outcrop, such as the Lachlan Fold Belt. The central NSW tin Belt is characterised by non-magnetic S-type granitoids within a prominent linear gravity low, which can be traced for 450 kms. Structural offsets in this trend, reflected in regional gravity and magnetic data, provide control on granite emplacement and locii for mineralised late-phase solutions. Radiometric techniques can also be used to delineate outcropping S- and A- type granitoids which are relatively enriched in radioactive minerals. The individual tin deposits are spatially related to local magnetic anomalies. Examples are given to illustrate the signature of the Ardlethan and Kikoira-Gibsonvale deposits within the regional environment. Porphyry/hydrothermal gold and/or copper deposits have been related to I-type granitoids, which are often magnetic. In the eastern Lachlan Fold Belt such deposits are related to island arc environments with andesitic volcanics. These environments, eg. Molong High and Parkes Terrace, are indicated by prominent gravity highs with strong magnetic anomalies delineating the extent of andesitic units. In such environments, however, the mineralised I-type intrusives are indicated by gravity and magnetic lows. The lower density of the intrusion explains the gravity features, however, the magnetic lows may be caused by either; (i)

magnetite depletion due to magma intrusion and/or alteration associated with mineralisation.

(ii)

oxygen fugacity/temperature conditions resulting in ilmenite or hematite being the primary iron oxide.

(iii) reversed polarity of the remanent magnetic vector. Examples are given to illustrate the geophyscial signatures of the Parkes Goonumbla porphyry system and possible granitoid related hydro-thermal gold deposits in the Molong area.

540

AUSTRALIAN LONG-WAVELENGTH MAGNETIC ANOMALIES Peter Wellman and A.S. Murray Bureau of Mineral Resources, Canberra Comparison of magnetic anomaly maos derived from 2° gridded nearsurface observations and derived from 2 gridded 300 km altitude satellite observations confirms the reality of the anomlies measured by satellite. Upward continuation of the near-surface anomalies suggests that the MAGSAT map of Langel et al (1982) is smoothed, possibly by uncorrected variation in satellite altitude. ' The long-wavelength magnetic anomaly lows are only slightly negative, and have only low-amplitude medium-wavelength anomalies. Long-wavelength highs have a higher amplitude, and they are associated with high-amplitude medium-wavelength anomalies. The long-wavelength highs correlate with positive free air anomalies. In the eastern half of Australia they overly wide and approximately symmetrical basement uplifts, and in the western half of Australia they overly asymmetrical obduction structures at block boundaries. The long-wavelength magnetic anomalies are thought to be caused by rocks of high magnetization in the upper or lower crust. These conclusions suggest that the long-wavelength anomalies over Australia will not be useful in determining the thickness of the crust or the depth to Curie Point. Reference Langel R.A., Phillips, J.D., & Horner, R.J., 1982, Geophy. Res. Letters, 9, 269-272.

STYLES OF CHANNEL SEDIMENTATION IN THE MARBURG FORMATION, NORTHERN CLARENCE-MORETON BASIN, SOUTHEAST QUEENSLAND A.T. Wells and P.E. O'Brien Bureau of Mineral Resources, Canberra The Marburg Formation in the Laidley Sub-basin of the Clarence-Moreton Basin consists of labile sandstones and shales deposited by streams generally flowing to the north. Basement terrains to the south of the Laidley Sub-basin supplied most of the sediment. In the Laidley Sub-basin, the stratigraphy of the Marburg Formation indicates the three major phases of deposition of the Formation. The Gatton Sandstone Member and the overlying Winwill Conglomerate Member are the earliest phase of sedimentation. They are mostly coarse to medium sandstone with some very coarse sandstone and conglomerate in multistorey sediment bodies, and minor amounts of mudstone. A typical sandstone body consists of 2 to 4m of massive, pebbly coarse sandstone overlain by up to 10m of large-scale planar cross-bedded medium to coarse sandstone beds overlain by shallow, low angle trough cross sets of medium to fine sandstone at the top. Such sequences are commonly incomplete with many erosion surfaces, and preferential preservation of the massive sandstone facies. These members were deposited by bedload streams in mobile channel belts. The second phase of deposition is represented by the Ma Ma Creek Sandstone Member. It is composed mostly of mudstones with comparatively thin sandstone bodies. It also contains some thin coals and thin chamositic oolite beds. Sandstone beds in this member are typically 5m of trough cross-bedded medium sandstone overlain by parallel laminated siltstone. In

541

places, tabular bodies consisting of one or two tabular cross-sets of fine sandstone are interbedded in the mudstones. Sandstone bodies in the Ma Ma Creek Sandstone Member were deposited by mixed load and suspended load channels moving across a plain which featured swamps and a large lake at one stage. The number and thickness of sandstone bodies increases from the Ma Ma Creek Sandstone Member up into the Heifer Creek Sandstone Member. Sandstone units in the Heifer Creek Sandstone Member are, in the central part of the Laidley Sub-basin, multistorey sheets up to 100m thick. These sheets are made up of interfingering lenses of parallel laminated, planar and trough cross-bedded and massive coarse to medium sandstone with pebble bands and mudstone drapes. Erosion surfaces are common. This part of the Heifer Creek Sandstone Member represents a return to deposition by bedload streams which displayed a high degree of channel switching and reworking of their channel belts. On the eastern side of the Laidley Sub-basin, the Heifer Creek Sandstone Member contains less sandstone than in the sub-basin centre, and includes a greater variety of sandstone bodies. As well as the sheet sandstones typical of the central part of the sub-basin, there are sandstone bodies composed of trough cross-bedded coarse and medium sandstone 10m thick overlain by ripple cross-laminated, fine sandstone beds and medium sandstone bodies 5m thick displaying epsilon cross-bedding. This variation in sandstone body type across the Laidley Sub-basin suggests that the thick sequence of sheet sandstone in the sub-basin centre was deposited in a major fluvial axis following the sub-basin axis. The vertical changes in fluvial style reflected by the sandstone bodies of the Marburg Formation in this part of the Clarence-Moreton Basin were probably caused by a single rise in relative base level. The change from the Winwill Conglomerate Member to the Ma Ma Creek Sandstone Member represents the initial backwater effect of the base level rise and the coarsening-up sequence from the Ma Ma Creek Sandstone Member through the Heifer Creek Sandstone Member represents the gradual re-establishment of a near-grade bedload stream system.

CAMBRIAN PALAEOENVIRONMENTS AND SOURCE ROCKS OF THE EASTERN OFFICER BASIN G. Westel, R.E. Summons2 D.M. McKirdy^, p.N. Southgate2, R.L. Henryl & A.M. Brewer*. 1. Comalco Aluminium Limited, Adelaide. 2. Baas Becking Geobiological Laboratory, Canberra. 3. Australian Mineral Development Laboratories, Adelaide. Early Cambrian marine transgression established an epeiric sea over the Officer Basin. Initial transgression deposited thick sandstones (Murnaroo Sandstone and Clutterbuck Beds). An arid environment increased the sea's salinity causing deposition of a thick evaporitive carbonate sequence intersected in SADME Wilkinson-1. This sequence has been considered part of the Observatory Hill Beds (Pitt et al., 1980), but is older and depositionally unrelated. It is here referred to as the 'Wintinna Formation1. The epeiric sea regressed and extensive sabkhas developed in the eastern Officer Basin depositing red bed siltstones over the 'Wintinna Formation' carbonates. An alkali playa lake sequence then developed in restricted areas on the red beds depositing the carbonates and calcareous siltstones of the Observatory Hill Beds intersected by SADME Byilkaoora-1. The climate became less arid and the fluvial to marine Trainor Hill and Lennis Sandstones were deposited across the Officer Basin. Both the 'Wintinna Formation' and the Observatory Hill Beds contain organic-rich sediments.

542

A marine depositional environment for the 'Wintinna Formation 1 is d e m o n s t r a t e d by the presence of t r i l o b i t e s and by a carbonate 87Sr/86Sr value of 0.7090 + 0.0006 w h i c h f i t s previously d e t e r m i n e d data f o r C a m b r i a n marine carbonates (Veizer & Compston, 1976; Burke e t al., 1982). The environment was arid, subequatorial and highly evaporative resulting in the p r e c i p i t a t i o n of h a l i t e as interbeds w i t h i n the basal p o r t i o n of the 'Wintinna Formation 1 . Gypsum and anhydrite w e r e p r e c i p i t a t e d as blebs and nodules, l a t e r being p a r t i a l l y mobilised into veins. The most c o m m o n rock t y p e is l i m e mudstone. D o l o m i t e is generally a minor secondary constituent. A l g a l boundstones, i n t r a c l a s t wackestones, oolites and frequent dessication f e a t u r e s indicate a shallow subtidal t o i n t e r t i d a l environment. Organic m a t t e r occurs in f l a t a l g a l - l a m i n a t e d l i m e mudstones which show only very minor disruption, i n d i c a t i n g a subtidal e n v i r o n m e n t . Organic m a t t e r was not preserved in the i n t e r t i d a l carbonates. A non-marine depositional environment is demonstrated f o r the Observatory H i l l Beds by the high 8 7 S r / 8 6 s r (0.7222 + 0.0007) of t h e i r carbonate f r a c t i o n w h i c h corresponds to source w a t e r s derived f r o m t e r r e s t i a l l y exposed old sialic rocks (Burke et al., 1982). Any marine component would have resulted in a s i g n i f i c a n t l y l o w e r value. A playa lake environment is demonstrated by the anomalous alkaline c h e m i s t r y (pH 9) of the pseudomorphed evaporites in Byilkaoora-1, possible only in non-marine ground waters derived f r o m non-marine rocks; and by sedimentological comparison w i t h the Green R i v e r F o r m a t i o n (White & Youngs, 1980). In B y i l k a o o r a - 1 organic m a t t e r occurs in the main semi-permanent lake development phase, (Member 3), i n c y c l i c , t h i n l y bedded, black, calcareous and d o l o m i t i c mudstone containing abundant a l k a l i evaporite pseudomorphs. The organic m a t t e r accumulated during lake highstands. A t y p i c a l cycle commenced w i t h an influx of water into the lake, o f t e n r e w o r k i n g clasts f r o m a preceding cycle crust. As the lake became established cyanobacteria bloomed in the alkaline environment. A f t e r some years the lake evaporated to dryness and a chert crust p r e c i p i t a t e d as the f i n a l evaporative stage of the c y c l e . L i m i t e d subaerial exposure resulted in minor erosion of the c h e r t c r u s t . The organic m a t t e r was preserved f r o m oxidation by the sealing nature of this crust and by the anoxic nature of the contained brines. Both the Observatory H i l l Beds playa lake and 'Wintinna Formation 1 marine carbonates are lean to moderately r i c h in organic m a t t e r (TOC = 0.2-1.3%). The w o r l d wide average f o r carbonates t h a t are proven oil-source rocks is TOC = 0.67% (Palacas, 1983). There is a d i r e c t relationship between organic richness and source quality. R o c k - E v a l hydrogen index values of 300-600 mg hydrocarbons/g T O C characterise oil-prone source beds which c o n t a i n Type I and I I kerogen ( a t o m i c H / C = 0.95-1.35). In organically leaner carbonates, low hydrogen index values (50-150 mg hydrocarbons/g TOC) signify the presence of gas-prone Type III kerogen. M a t u r a t i o n levels deduced f r o m l i p t i n i t e fluorescence colour and i n t e n s i t y , kerogen H / C and O / C a t o m i c r a t i o s , and sterane molecular parameters are appropriate f o r o i l generation (equivalent v i t r i n i t e r e f l e c t a n c e approximately 0.8%) ( M c K i r d y et al., 1983). R o c k - E v a l Tmax values (410-440°C) are anomalously low due to the asphaltic nature of the e x t r a c t a b l e organic m a t t e r associated w i t h the kerogen. The main organic geochemical d i f f e r e n c e s between the non-marine and marine oil-prone carbonates sampled are as f o l l o w s : Observatory H i l l Beds Byilkaoora Kerogen Pristane/Phytane Steranes

Type I & II 0.9-1.3 c 28>c29»c27

.'Wintinna Formation 1 Wilkinson Type I I only 0.4-0.9 c 28>c27>c29

543

In both cases, lamalginite is the principal component of the dispersed organic matter; and acyclic isoprenoid alkanes (C43-C26 regular; C3Q-C4Q irregular, including squalane) are present in high concentrations. These isoprenoids are derived largely from the lipids of methanogenic and/or halophilic archaebacteria (Holzer et al., 1979; Chappe et al., 1982). The unusual sterane distributions of the Byilkaoora rock extracts and oil shows (McKirdy and Kantsler, 1980; McKirdy et al., 1983) are remarkably similar to those of Devonian lacustrine sediments from Caithness, Scotland (Hall and Douglas, 1983). References Burke, W.H., Denison, R.E., Hetherington, R.B., Koepnick, H.F., & Nelson, J.B., 1982, Geology, 10, 516-519. Chappe, B., Albrecht, P., & Michaelis, W., 1982, Science, 217, 65-66. Hall, P.B., & Douglas, A.G., 1983, In Advances in Organic Geochemistry 1981 (eds. Bjoroy, M. et al.), Wiley, Chichester, 576-587. Holzer, G., Oro. J., & Tornabene, T.G., 1979, J. Chromatogr., 186, 795-809. McKirdy, D.M., & Kantsler, A.J., 1980, APEA J., 20(1), 68-86. McKirdy, D.M., Aldridge, A.K., & Ypma, P.J.M., 1983, In Advances in Organic Geochemistry 1981 (eds. Bjoroy, M. et al.), Wiley, Chichester, 99-107. McKirdy, D.M., Kantsler, A.J., Emmett, J.K., & Aldridge, A.K., 1983, In Petroleum Geochemistry and Source Rock Potential of Carbonate Rocks (ed. Palacas, J.G.), A A P G Mem., in press. Palacas, J.G., 1983, Proc. 11th World Petroleum Congr., London, Wiley, Chichester, Panel Discussion 1, Paper 3, in press. Pitt, G.M., Benbow, M.C., & Youngs, B.C., 1980, APEA J., 20(1), 200-220. Veizer, J., & Compston, W., 1976, Geochim. Cosmochim. Acta, 40, 905-914. White, A.H., & Youngs, B.C., 1980, J. Sed. Pet. 50, 1279-1286.

EVOLUTION AND PETR06ENESIS OF THE BATUR VOLCANO, BALI G.E. Wheller and R. Varne Geology Department, University of Tasmania, Hobart The evolution of the active Batur volcano in northern Bali involved 3 major stages: (1) precaldera stage: construction of the volcano to about 2000 m height by basaltic and andesitic lavas and pyroclastics; (2) caldera stage: generation and explosive eruption of siliceous magmas leading to caldera formation; (3) postcaldera stage: construction of the present volcano within the caldera by renewed basaltic volcanism. Lavas of the precaldera stage have medium-K calcalkaline chemistry and contain olivine, clinopyroxene, plagioclase and magnetite as phenocrysts. They are overlain by the siliceous deposits of the caldera stage which now form the 300-700 m high walls of the present caldera except at one locality where a basal sequence of basaltic flows is present. The outer rim of the caldera is elliptical in shape, 13 km by 9 km, and there is an inner, circular zone of collapse 7 km in diameter. The caldera stage rocks are almost entirely pyroclastics, although siliceous lava flows occur at one place in the caldera walls and outcrops of epiclastic deposits are widely scattered outside the caldera. The Bali ignimbrite is volumetrically dominant and covers all of the southern 2 plain of Bali (about 200 km ). It is mostly an homogeneous, incipientlywelded, grey ash in which large (up to 10-15 cm), sometimes rounded, black pumice clasts become more abundant upwards. The western, southern and eastern margins of the ignimbrite are thick pumice breccias. Other deposits include a welded air-fall tuff and overlying non-welded pumice flow sequence of about 60-70 m total thickness, thin (<1 m) pumice flows and surges, bedded air-fall pumice deposits and at least 6 welded and non-welded pyroclastic breccia flows 3-4 m thick. 544

The caldera morphology suggests formation by some kind of doublecollapse mechanism, although not necessarily involving multiple ignimbrite-forming eruptions. The large volume and uppermost stratigraphic position of the Bali ignimbrite suggests that it is associated with the formation of at least the inner collapse zone. After caldera formation a series of air-fall pumice deposits was produced, probably from a vent at the edge of the inner collapse zone. These deposits are up to 1.3 m thick at the caldera edge and drape erosional gullies inside the caldera. Black, porphyritic, glassy dacitic material is a ubiquitous component of the volcaniclastic deposits. It occurs as small, angular, lithic clasts, as larger bombs and as highly vesiculated pumice. Many of these rocks are prominently banded. Plagioclase, olivine, clinopyroxene and magnetite form phenocrysts and plagioclase-phyric microxenoliths are abundant in some rocks. The postcaldera lavas contain the same phenocryst assemblage as the precaldera lavas and are chemically similar. They were erupted from the active stratovolcano within the inner collapse zone and emplaced across the caldera floor as relatively small volume, vesicular flows. Eight lava flows were produced between 1849 and 1974 and there are many older flows. In detail, 3 groups are present, based on subtle variations in K-group element contents. Rocks from each group occur among the historical lavas, suggesting the concurrent availability of 3 largely independent magma compositions. Concentrations of FeOt, MgO, CaO, Sc, V, Ni and Cr in the pre- and postcaldera lavas decrease smoothly with increasing Si0 2 , whereas increases occur in Na 2 0, K 2 0, P 2 0 5 , Ba, Rb, Zr, Nb, La, Ce, Nd and Y contents. Ti02 levels remain approximately constant and A1 2 0 3 and Sr concentrations reach a maximum at 54-55 wt.% Si02. The dacites lie generally on extrapolations of these trends to higher Si02 but are separated from the mafic lavas by a 6 wt.% Si02 gap. In contrast to the mafic lavas the dacites show decreasing concentrations of P 2 0 5 and Ti02 with increasing Si02. On molecular ratio diagrams the dacites lie on different trends to the mafic lavas, suggesting control of compositional variation by a different phenocryst assemblage. The Batur volcano is particularly significant petrologically because it features (1) the generation of siliceous magmas after a long period of mafic magmatism, possibly by fusion of young, volcanic crust and involving mixing with basaltic liquids., culminating in caldera formation, and (2) the apparent resurgence of mafic magmatism after the caldera was formed - did this magmatism ever stop or even slow down?

PROPOSED CHEMICAL TRAP FOR GOLD

PRECIPITATION

A.J.R. White 1 , J.R. Holloway2, and T.A.P. Kwak1

^Department of Geology, La Trobe University, Bundoora, Vic, Department of Earth Sciences, Arizona St^ate University, U.S.A.

Major primary gold deposits have many common features. When considered in conjunction with solubilities of gold in chloride and bisulphide complexes (Seward, 1979) and with phase eqilibria in the carbon - oxygen-hydrogen system (Holloway, 1982) these features provide information on the physical and chemical conditions of gold precipitation. We are not here concerned with the source of the gold nor with the origin of auriferous hydrothermal solutions but with the depositional environment.

545

Veins consisting dominantly of quartz with variable amounts and types of sulphides, normally pyrite, mainly occur within phyllites, feldspathic greywackes or greenschists near or within graphitic rocks. Metamorphic grade is normally lower greenschist facies. Examples with these characteristics are Ballarat-Bendigo, Kalgoorlie, Mother Lode of California, Otago, New Zealand (e.g. Cox et al, 1983: Woodall, 1979). Wall rock alteration includes production of carbonates and lesser sericitization. Fluid inclusions have virtually no daughter crystals, limited freezing temperature data indicate first melting temperatures near - 62°C, which corresponds to the eutectic in the CHi+-H20 system, and filling temperatures are within the range 250°C ± 50° s the common occurrence of both gas-dominant and liquid-dominant inclusions is indicative of phase separation ("boiling") during genesis. The common occurrence of sericite and occasional presence of feldspar probably buffers the pH of the hydrothermal solutions at values near 5. Under these conditions gold is soluble at relatively high oxygen fugacities and insoluble at lower values. We examine this phenomenon at 300°C and 1 Kbar. Carbonate precipitation reactions depend on the dominant species in the fluid. If CO2 is present reaction is of the form:CO2 (fluid)

MCO3 carbonate (e.g. ankerite)

MO * metal oxide in silicate or oxide (e.g. MgO/FeO in chlorite)

[1]

If there is insufficient CO2 or CHi+ then reaction is of the form:C graphite

MCO3

[2]

oxygen in fluid

Further reaction of the form:2C

-I- 2H2O

CHt4

[3]

results in significant units of methane in the fluid. Precipitation of carbonate by these reactions results in a progressive decrease in fQ (Fig.l). Since methane and water are only miscible above about 300°C (a? virtually any pressure) production of methane by reaction (3) causes a phase separation of methane-rich fluid from the aqueous hydrothermal solution. The production of another phase means that a degree of freedom is lost and the fp 2 for the system CH^ - H2O - C becomes fixed for a given pressure and temperature. At 1 Kbar and 300°C the resultant phase assemblage (graphite + aqueous liquid + methane-rich fluid) buffers f Q 2 at X0~35'8 corresponding to the minimum solubility of gold in either chloride or bisulphide complexes. We propose that gold is precipitated when an aqueous hydrothermal solution initially at relatively high f()2» reacts with graphite in country rocks. This reaction results in the formation of carbonate in the wall rocks, lowers the fo 2 of the solution and produces a separate methane-rich fluid. During carbonatization, fQ 2 decreases gradually at first and then falls rapidly just before the point of methane production (Fig. 1). Gold precipitation occurs at this discontinuous change in fo2* ^he phase separation of methane and water is a type of boiling: it explains the presence of two types of fluid inclusions and the resultant volume change is a possible cause of the local brecciation seen in many gold deposits. We suggest that precipitation of gold is thus preceeded and accompanied by solution of graphite and precipitation of carbonate, and coincides with evolution of methane. Methane is not the cause of gold precipitation rather it is a by-product of the carbonatization process (c.f. Cox et al., 1983). In our model, graphite of the host rock is partly consumed in the carbonatization reactions. However, in some deposits graphite may also be precipitated if methane reacts with oxidized groundwater.

546

-33.

3 00 C -34.0-

One

F i g . 1 . V a r i a t i o n o f f^ 2 w i t h c o m p o s i t i o n in the s y s t e m C 0 2 - H 2 0 C H ^ at 300°C and 1 K b . A l l f l u i d s a r e in equilibrium with graphite. F i g u r e s a l o n g the c u r v e are s o l u b i l i t i e s of A U ( H S > 2 from Seward ( 1 9 7 9 ) .

1Kb

fluid

-34.5-

-35.5-

aqueous +

liquid

methane

fluid

-36.0-

C02

H2O

•8

\ 2

rc w h

References C o x , S . F . W a l l , V . J . , Etheridge, M . A . , Sun, S-S., & Potter, T.F., 1983, G e o l . Soc. A u s t . A b s . 9^, 260-261. Holloway, J . R . , 1982, G e o l . Soc. A m . A b s . Prog. 14, 5 1 9 . Seward, T.M ., In: G l o v e r , J.E., & G r o v e s , D . I . , (eds.) 'told Mineralization", G e o l . D e p t . & Extension Service, Ihiv. W e s t . Aust., 45-55. Woodall, R . , 1979, In: G l o v e r , J.E., & Groves, D . I . , (eds.) "Gold Mineralization", G e o l . D e p . & Extension Service, Ihiv. W e s t . A u s t . , 3 , 1 - 1 7 .

THE MT READ VOLCANICS AT QUE RIVER: PRIMARY GEOCHEMICAL AFFINITIES AND REE GEOCHEMISTRY D.J. Whitford 1 , D.B. Wallace 2 ^CS£R0 Division of Mineralogy, North Ryde Que River Mining Pty. Ltd., Burnie The Que River volcanogenic base and precious metal ore deposit is located in the Cambrian Mt Read Volcanics of western Tasmania. Massive Zn-Pb-Cu-Ag-Au mineralization occurs as several conformable lenses in a sequence of steeply dipping, predominantly volcaniclastic rocks. The sequence has undergone regional prehnite-pumpellyite facies metamorphism at ca. 400ma. The metamorphic grade and the degree of metamorphic recrystallization are somewhat lower than those observed further south at Rosebery and Mt Lyell. The host rocks can be divided into four petrographic groups: andesites, dacites, polymictic volcaniclastic rocks and hydrothermally altered rocks. The hydrothermally altered rocks include silicified, chloritic and phengitic varieties whose primary volcanic textures have been largely if not completely obliterated, presumably during alteration related to mineralization. Except for some of the dacites, almost all the host rocks are fragmental; rounding of some fragments together with some grading suggests epiclastic deposition for many of the rocks. The polymictic rocks are characterized by the presence of abundant pumice together with more massive, typically porphyritic lithic fragments.

547

The geochemistry of the host rocks at Que River is complex and not readily amenable to quantitative evaluation, particularly at the scale of an individual sample. The primary geochemistry of the rocks may have been modified by several processes, including submarine eruption and/or deposition, mineralization, and regional metamorphism. Nevertheless knowledge of the primary geochemical affinities of the host rocks is essential in understanding both the tectonic significance of the Mt Read Uolcanics, and alteration related to mineralization (primary dispersion halo). Variation patterns among the so-called immobile elements (Ti, Zr, Nb, Y and HREE) are relatively simple. When plotted against each other, linear trends that characteristically project towards the origin are well developed. In plots involving TiO^, two trends can be discerned, corresponding to andesitic and dacitic compositions respectively. The linear trends that project to the origin imply that ratios between the immobile elements have remained essentially constant, absolute abundances having been modified by addition or subtraction of mobile components. When plotted on a diagram of Zr/TiO^ vs Nb/Y (Winchester and Floyd, 1978), the host rocks from Que River plot in a tight group in the subalkaline fields defined by andesite and rhyodacite-dacite (cf. Finlow-Bates and Stumpfl, 1981). There is no evidence for either basalts or rhyolites. The sub-alkaline character of the rocks, the low absolute abundances of TiO^ and particularly Nb, the preponderance of intermediate compositions, the primary porphyritic textures and the LREE-enriched chondrite-normalized patterns suggest intermediate- to high-K calc-alkaline primary geochemical affinities. By analogy with Recent calc-alkaline lavas, the Mt Read Volcanics at Que River appear to be related in some way to subduction perhaps along a continental margin (cf. Corbett,1981). Except for Eu, the REE have apparently remained immobile in all but the intensely altered hydrothermally altered rocks. The andesites have typical chondrite-normalized calc-alkaline patterns ((Ce/Yb) N ~ 8 ) , whereas the dacites are characteristically more fractionated (uJe/Yb)^ ~ 1 2 ) . The polymitic rocks, where primary geochemical affinities cannot be readily discerned petrographically, show typically andesitic REE patterns, consistent with the other immobile elements. Negative Eu anomalies are similar in both the andesites and dacites (Eu/Eu*~ 0.7) but somewhat larger in the pumice-bearing rocks. By analogy with Recent calc-alkaline rocks, and from the occurrence of larger Eu anomalies in pumice-bearing rocks that were presumably more porous and permeable during mineralization, it appears that Eu has been mobilized during alteration. The hydrothermally altered rocks are characterized by a variety of REE patterns, ranging from those similar to the andesites and dacites, to relatively unfractionated patterns with large negative Eu anomalies (cf. Campbell et al., 1982). The correlation between the relative depletion in the light REE and the Eu anomaly suggests that these patterns are not primary, rather they are the result of hydrothermal alteration. Although Eu is relatively enriched in parts of the ore and in some minerals such as barite, the fate of most of the leached Eu remains unclear. References Campbell, I.H., Coad, P., Franklin, J.M., Gorton, M.P., Scott, S.D., Sowa, J. and Thurston, P.C., 1982, Can. J. Earth. Sci. \9_, 611-623 Corbett, K.D., 1981, Econ. Geol. 76, 209-230 Finlow-Bates, T. and Stumpfl, E.F., 1981, Mineral. Dep. 16, 319-328 Winchester, J.A. and Floyd, P.A., 1977, Chem. Geol. 20, 325-344.

548

THE RAMAN MICROPROBE - A UNIQUE TOOL OF INCLUSION

RESEARCH

Ronald W.T. Wilkins CSIRO Division of Mineralogy, North Ryde When a material is irradiated with monochromatic radiation, part of the radiation is scattered in all directions of space. A small part of this radiation is scattered with frequencies less than the exciting radiation. This is the Raman effect. The frequency differences are related to the vibrational frequencies ot the molecules in the material. There is therefore a close relation between the interpretation of Raman and intra-red spectra. Although the Raman effect has been known since 1928 only recently have advances in optical instrumentation and laser technology made it possible to construct a Raman microprobe. A particular advantage of being able to use radiation in the visible region (usually green argon laser radiation X = 514.5 nm) is that a conventional petrological microscope can be employed. The instrument is operated by focusing the laser radiation through the microscope objective lens into a one micron diameter spot on the inclusion to be analysed. The scattered radiation is collected through the same lens and analyzed by an optical filter system. Although the inclusion may be at the surface, the special feature of the instrument is that the inclusion may be at any depth in a transparent mineral host. In an alternative mode ot operation, the instrument functions as a Raman microscope using a special objective with annular optics. Mineralogical applications using two early versions of the Raman microprobe are given in Rosaco et al. (1975) and Dhamelincourt (1979). Raman spectra may be excited from solids, liquids and gases. In applications ot the Raman microprobe it is necessary to bear in mind that the instrument is a molecular analyser. It is capable of determining all diatomic and polyatomic gases, but it does not register the presence of monatomic species because these have no molecular vibrations. Although it is not easily possible to determine quantitatively the amount of a particular gaseous species in an inclusion, the molecular proportions in a N mixture ot the common gases such as CC>2> 2> ^H^, and higher hydrocarbons are readily determined with the aid of their known scattering cross sections. Satisfactory spectra can be excited from gaseous inclusions with pressures down to one atmosphere. Similar remarks apply to liquids in inclusions. Liquid water has low Kaman activity in contrast to high infra-red activity, and this is of particular importance in the study of polytomic anions and metal ion complexes in aqueous solution. The Raman microprobe has been particularly useful in the determination of the concentration of sulphate ion in aqueous inclusions, using the relative intensities of bands associated with the symmetric stretching mode of the sulphate ion, and the bending mode of water molecules. At present the limit of detection of sulphate ion in aqueous solution is about 200 ppm. The sharp line spectra resulting from Raman scattering contrast with the broad bands of infra-red spectra, and even mineral polymorphs are usually readily distinguishable. Individual daughter crystals in a fluid inclusion, especially carbonates and sulphates, may be identified by tocusing the beam onto them in turn. However a number of common daughter crystals such as the alkali halides do not give useful Raman scattering. In addition, some coloured crystals absorb the exciting radiation strongly and decomposition of these crystals is possible. This is a particular problem with solid or liquid organic matter. One solution to the problem posed by alicali halides either as crystals or in solution, is to freeze out their hydrates which have quite distinctive spectra. 549

The particular advantage ot the Raman microprobe approach to inclusion studies is that it is possible to obtain a large amount of information on individual inclusions, without the modifications and contaminations which inevitably follow their opening for other methods of analysis. With rapid advances in instrumentation now in progress, including specialization into monochannel and multichannel types, sensitivity for many species will be greatly increased, analyses will become more rapid, and applications such as some isotopic analyses will become a reality. References Dhamelincourt, P., Beny, J-M., Dubessy, J. and Poty, B., 1979, Bulletin de Mineralogie 102, 600-610. Rosaco, G.J., Roedder, E. and Simmons, J.H., 1975, Science 190, 557-560.

THE INFERENCE OF BOILING OR MIXING OF FLUIDS FROM FLUID INCLUSION

DATA

R.W.T. Wilkins and A.H. Ewald CSIRO Division of Mineralogy, North Ryde There are problems in the interpretation of fluid inclusion data for the identification of environments in which boiling or mixing of fluids may have contributed to the localization of ore. It is also important that boiling be recognized because the pressure regime during the formation of a deposit can be readily determined if boiling can be demonstrated to have occurred. Theoretical criteria of boiling (Pichevant et al., 1982; Ramboz et al., 1982), which include the co-existence of liquid and gaseous phases having compositions and densities determined by temperature, pressure and phase relations of the fluid system, put severe constraints on the interpretation of fluid inclusion data in these terms, but are difficult to apply in practice. Some reasons for this are as follows. 1. Liquid and vapour phases seem sometimes to be homogeneously and sometimes to be heterogeneously trapped in growing crystals. 2. Even inclusions which formed by the trapping of a single fluid phase may be subsequently modified by necking-down in a way that produces an assemblage of inclusions which superficially resembles those resulting from boiling. 3. It is only rarely that the co-existence in time of liquid and gaseous inclusions can be convincingly demonstrated. The inclusions in any sample represent the time-integrated history of fluids passing through the rock so that in general unless the relative chronological sequence of the incluions can be determined, criteria of boiling cannot be confidently applied. 4. An environment in which the fluids have intermittently boiled is probably one in which condensation and mixing of fluids has also occurred. 5. Ductile deformation of rocks containing fluid inclusions may also lead to liquid-rich and vapour-rich inclusions which have a superficial resemblance to a boiling assemblage. The problems posed by these complexities require that sufficient fluid inclusion data is obtained that an appreciation of the evolution of the hydrothermal system both in time and space is obtained. In addition it is important to note that the processes of boiling (with homogeneous trapping), boiling (with heterogeneous trapping), and necking-down result

550

in different possible ranges of bulk fluid density (Ahmad and Rose, 1980; Darimont and Coipel, 1982). A careful consideration of the volumes and compositions of the liquid and gaseous phases in the inclusions can therefore be useful in discriminating between these possibilities. References Ahmad, S.N., & Rose, A.W., 1980, Econ. Geol., J75_, 229-250. Darimont, A., & Coipel, J., 1982, Chem. Geol., 37_y 151-163. Pichevant, M., Ramboz, C., & Weisbrod, A., 1982, Chem. Geol., 37_y 1-27. Ramboz, C., Pichevant, M., & Weisbrod, A., 1982, Chem. Geol. , 37, 28-47.

'DEEPWATER 1

GIPPSLAND BASIN

J . B. Wi.ll cox Bureau of Mineral Resources, Canberra, A.C.T. The Gippsland Basin is the easternmost of a series of extensional features (including the Bremer, Eyre. Great Australian Bight. Duntroon, Otway, and Bass basins) which developed in Late Jurassic and Early Creataceous time, as a precursor to the formation of the southern margin of the Australian continent. Only the Gippsland and neighbouring Bass basins remained largely intact following continental breakup. The eastward extent of the syn-rift and infra-rift stages of the Gippsland Basin (sometimes referred to as the Strzelecki Basin) has been conjectural. There appear to be four possibilities: (i) the rift basin once extended onto what is now the Lord Howe Rise, in the region due east of Sydney, (ii) it terminated near the present continental margin at a strikeslip fault which was later (Late Cretaceous) to form the northern arm of a triple junction in the Tasman Sea, (iii) the rift bifurcated with widely divergent arms stretching along the coastal regions of Tasmania and New South Wales, (iv) two almost perpendicular rift systems, both existing in the Early Cretaceous, were overprinted in the region east of the Gippsland Basin. Modern multichannel seismic sections indicate that the Gippsland Basin is downflexed eastward, beneath the continental slope, and that a deepwater part of the basin extends at least as far as a broad ridge which strikes meridionally at 149-150°E. This ridge is composed of both sedimentary and volcanic rocks, and bears marked similarity to the Dampier Ridge. Furthermore, both ridges appear to terminate abruptly at the opposite ends of a major transform fault, indicating that the Dampier Ridge is probably a pre-breakup feature which was split laterally during spreading in the central Tasman Sea. If the ridges were formed in response to tensional shear, it seems unlikely that the Gippsland basin extends seaward of the present continental margin (i.e. possibility (ii), above). East-southeasterly striking extensional faults, offset by north-northeasterly strike-slip faults, give rise to an en echelon configuration for the Gippsland Basin margins (Etheridge et al., 'this Volume). These characteristic marginal faults are not obvious in the deepwater downflexed, part of the basin. This is probably due to a change in extensional regime across a major north-northeasterly striking fault which in many places underlies the upper continental slope. Seismic stratigraphy shows that the prospective Late Cretaceous-Eocene Latrobe Group passes from its well-known fluvial-lacustrine facies into shore-face facies below the outer continental shelf. Marine onlap within the upper Latrobe occurs in the deepwater part of the basin, and indeed shallow marine Latrobe Group has been dredged from its outcrop on the continental slope (Packham, pers. comm.). 551

The prospectivity of the deepwater part of the basin is restricted by the considerable water depth (1000+ metres) and availability of drillable structures. Hydrocarbons generated in the Latrobe section may have migrated updip into traps roughly below the present shelf-break; the more obvious of these traps have, however, already been tested.

RESERVOIR GEOMETRY AND ALLUVIAL ARCHITECTURE OF THE TOOLACHEE FORMATION, MOOMBA FIELD 9 SOUTH COOPER BASIN B.P.J. Williams South Australian Oil & Gas Corporation Pty. Ltd., Adelaide and Department of Geology, University of Bristol, England The Late Permian Toolachee Formation of the South Cooper Basin comprises a maximum 152m thickness of alluvial and lacustrine clastic sediments. Detailed core facies analysis has resulted in the refinement and modification of the original wireline-log subdivisions of the formation, and has provided much additional information on the reservoir geometry, depositional architecture and potential hydrocarbon traps in the formation within the Cooper Basin. Three major facies associations are identified within the formation and their salient characteristics are best displayed in the 292m of core analysed from 5 wells in the Moomba Field. Association 1 is the lowest division and comprises sandstonedominated, thick (up to 6m), upward-fining facies transitions, thinner and rarer upward-coarsening sequences and thin, mainly autochthonous coals. The association appears to be the product of a mixed-load alluvial channel system of moderate to high sinuosity, the channels possessing a moderate width/depth ratio and high relief on their basal scoured surfaces. Simple and punctuated lateral bar forms, chute and ephemeral floodbasin lake deposits are all recognised within Association 1. Multistorey sandstone channel fills preserve both bed and bank accretion features and the channel 4 geometry would appeal as a sinuous, complex, beaded-belt on a sandstone isolith map. These sands are the major hydrocarbon reservoirs of the Moomba Field. Association 2 is extremely well defined in the Moomba Field where it mainly consists of a mudrock and coal-dominant sediment assemblage arranged in multiple, thin, upward-coarsening sequences. Such fine-grained sequences are commonly the product of overbank flooding and result in levee progradation. Other upward-coarsening facies transitions are very distinctive in that they demonstrate perennial, floodbasin-lake infills, with rhythmites grading up into wind-wave affected sediments and finally into unidirectional crevasse sand inputs. It appears that this latter style of sedimentation took place more or less synchronously in an extensive lake system that covered the Moomba area in late Permian times. These lacustrine sediments provide an extremely important datum for reconstructing the alluvial architecture of the hydrocarbon-rich sandstones of Association 1. Association 3 is best displayed in the Gidgealpa Field and is only locally developed in the Moomba area. At Moomba Association 3 exhibits a reversion to coarse-grained, upward-fineing sediments indicating reestablishment of high sinuosity alluvial channels which contrast with the low sinuosity, bedload-dominant channel sediments that are found in the Gidgealpa Field.

552

Whereas mainly autocyclic mechanisms of sedimentation can be invoked for the reservoir geometries and alluvial-lacustrine to account architecture of Association 1 and 2, allocyclic mechanisms (renewed tectonism and/or base level lowering) are suggested as the control on the architecture of the final phase of Toolachee Formation deposition as exhibited by Association 3.

LATK C A R B O N I F E R O U S - E A R L Y PERMIAN SANDSTONE RESERVOIR A N A L Y S I S IN HYDROCARBON EXPLORATION OF THE 6IDGEALPA SOUTHERN COOPER BASIN 9 SOUTH A U S T R A L I A

FACIES GROUP,

B.P.J. Williams and E.K. Wild South Australian Oil & Gas Corporation Pty. Ltd., Adelaide, and Department of Geology, University of Bristol, England The sedimentology of the Permian Gidgealpa Group of the Southern Cooper Basin is currently being evaluated to ascertain the tectonosedimentologic evolution of the basin and to determine the architecture of the clastic suite in order to generate exploration plays. The study has produced a new understanding of the relationship between the hydrocarbon-rich Tirrawarra Sandstone, of dominantly fluvial origin, and the, as yet little explored, glacigenic Merrimelia Formation. The facies states and transitions of both formations interdigitate and typical porous 'Tirrawarra-type' fluvial facies are clearly evident within glaciolacustine 'Merrimelia-type' sediments. The Merrimelia Formation was examined regionally in 29 cored wells. The formation attains a maximum thickness of +300m and representative facies include glaciofluvial outwash, terrestrial and subaqueous diamictites and glaciolacustrine, wave-affected and ripple-laminated sandstones, with thick, monotonous mudrock sequences containing claydominant rhythmite horizons. The Tirrawarra Sandstone, analysed in 32 cored wells, comprises four major facies associations throughout its maximum 75m thickness. These associations indicate a temporal and spatial evolution of a fluvioglacial to predominantly fluvial system. Initial deposition on low slope, outwash fans, where braided processes operated is indicated. This sedimentation style evolved into a low sinousity, bedload-dominant, sandy braided system, with high width/depth ratio channels. Allocyclic control mechanisms are invoked for 'late Tirrawarra' sedimentation as the facies reveal proximaldistal patterns and the fluvial style changes to a mixed-load channel system. The interfacing and evolutionary pattern of the deposystem indicates that additional reserves potential exists for reservoirs developed locally within the Merfimelia Formation. GEOCHEMISTRY

BY ION

MICROPROBE

I.S. Williams Research School of Earth Sciences, ANU, Canberra The ion microprobe mass analyser has been described as perhaps the ultimate weapon of the geochemist, and understandably so. An ion microprobe makes spot analyses of the surface of solid samples with a spatial resolution better than 20 ym. It is sensitive to all elements independent of mass, with detection limits commonly less3 than a few parts per million. It analyses a surface layer about 5 x 10 ym thick, but can also determine concentration profiles to depths of several micrometres. It is capable of ion imaging and spot isotopic analysis. 553

Ion microprobes are widely used in electronic engineering and materials science, but much less so in geochemistry. The principal reason is that, with the instruments presently available, the analysis of geological materials is often very difficult. The difficulty arises from the chemical complexity of most geological samples. They produce complex spectra of many different atoms and molecules, making it a major task to separate and identify, let alone quantify, the species present. Even then, there is as yet no direct method of calculating the target chemical composition. A number of laboratories have nevertheless made substantial progress in applying ion microprobes to geochemical problems. The following examples illustrate that progress and also the future potential of the instrument. Trace elements in silicates. Despite the lack of a generally accepted theory that quantitatively describes secondary ion emission, moderately accurate (10%) determinations of elemental concentrations can be made using standards and a working curve approach. Using synthetic glass standards with compositions in the diopside-albite-anorthite system doped with trace elements such as Rb, Sr, Ba, Ti, Cr, Ni, REE, Hf, Zr and U, Ray and Hart (1982) have shown that calibration curves can be constructed in which the ratio of trace element ions to ions of silicon is a linear function of the trace elements' concentration. Detection limits for all elements were better than 3 ppm. Importantly, the calibration curves for the glasses were not the same as those for natural clinopyroxene, showing that glass standards cannot necessarily be used to calibrate ion microprobe analyses of crystals. Water in silicates. Using glasses of natural basalt and obsidian and synthetic albite, Delaney and Karsten (1981) produced calibration curves showing a different linear relationship between (corrected for total oxygen) and water content for each matrix. They used these curves to study the diffusion of water in rhyolite. Cylinders of rhyolite that had been held at 850°C, 700 bars water pressure for different times were sectioned and H 2 0 concentrations measured at intervals of 20 to 200 ym from the edge. The H2O diffusion coefficient was shown to increase exponentially with water concentration over the range 0.2 to 3.7 wt% water, implying that water affects the structure of rhyolite. It also was concluded that fluid inclusions in minerals are probably water-rich relative to a coexisting melt. Re-Os dating. The Re-Os decay scheme has great potential for dating some rocks that cannot be dated directly by other methods, for example sulphide ores and iron meteorites. However, even the most favourable minerals rarely have Re concentrations greater than a few tens of ppm. As Re and Os also ionize poorly, Re-Os analysis by conventional solid source mass spectrometry is very difficult. Luck and others (1980) overcame this difficulty by mounting the Re and Os extracted from their' samples on pure aluminium discs and using their ion microprobe as a sputter source mass spectrometer. Their analyses of six meteorites showed that the iron meteorites and ordinary chondrites probably formed within a short time with the same Os isotopic composition. Assuming the meteorites1 age from Rb-Sr and U-Pb, they also calculated the x°7Re decay constant and a limiting age for the Galaxy of 13,300 - 22,400 Ma. Pb isotopes in galena. Bulk analyses of galenas from the Buick mine, Missouri, show large variations in Pb isotopic composition (Sverjensky et al., 1979). Ion microprobe analyses by Hart and others (1981) of a single, early-formed, octahedral galena crystal showed concentric zoning of the Pb isotopic composition on a millimetre scale over a range greater than previously reported for the whole mine. The Pb in a single late-formed cubic galena was more radiogenic than any in the octahedral crystal, and did not plot on the same compositional trend. The authors concluded that the early galena was deposited throughout the mine at about the same time from the same hydrothermal solutions, but that the late galena came from a new batch of solution from a source of different Th/U.

554

U-Pb dating of zircon in thin section. When sample is scarce or knowing the petrographic association of a particular zircon crystal is critical to interpreting its age, it is an advantage to be able to date zircon in thin section. Thin sections of a granite clast in lunar breccia 73217 contain four zircons, one of which can be related petrographically to the clast assemblage. Compston and others (1984) determined the U-Pb ages of those zircons directly by measuring their Pb isotopic compositions and Pb/U by ion microprobe. Pb/U was calculated using a calibration curve const£ucted+for a known Sri Lankan zircon which related the ion beam ratio 206pb /238u t o t h e t£ue+target ratio 206pb/23.8u v i a t h e simultaneous^ measured parameter UO /U . The four zircons gave the same age, 4356_^ Ma, and all were within 10% of concordance. This was interpreted as the age of the igneous rock from which the clast mineral assemblage was derived. References Compston, W., Williams, I.S. & Meyer,.C., 1984, J. Geophys. Res., 89, Suppl., B525-B534. Delaney, J.R. & Karsten, J.L., 1981, Earth Planet. Sci. Lett., 52.* 191-202. Hart, S.R., Shimizu, N. & Sverjensky, D.A., 1981, Economic Geol., 76, 1873-1878. Luck, J.M., Birck, J.L. & Allegre, C.J., 1980, Nature, 283, 256-259. Ray, G. & Hart, S.R., 1981, Int. J. Mass Spectrom. Ion Physics, 44, 231-255. Sverjensky, D.A., Rye, D.M. & Doe, B.R., 1979, Economic Geol., Ik^ 149-153.

RESEARCH IN OVERCOMING THE PROBLEM OF INSTANTANEOUS OUTBURSTS OF COAL AND GAS AT COLLINSVILLE R.J. Williams1, F. Hungerford1, B.B. Beamish1, B. McKavanagh2 1

Collinsville Coal Company, Collinsville, ^Geophysical Consulting, Flaggy Rock

High gas and outbursting condtions have been intermittently experienced at Collinsville since the first occurrence of an outburst in 1954. In that incident, 500 tonnes of coal were ejected and 14 000 nr of carbon dioxide released, resulting in seven fatalities. Since then, a further twenty-one outbursts have been recorded in different areas of the field. All outbursts have been confined to the Bowen seam. It dips to the south at an average of 8°, and has been mined from outcrop to a maximum depth of 290 m. Generally, high-gas, outbursting conditions have been encountered at depths in excess of 220 m. This has resulted in mining being confined to the shallow, low-gas reserves which are rapidly being depleted. The medium to long-term future of underground exploitation of the Bowen seam depends upon the development of safe, economical methods of mining these high-gas, outburst-prone reserves. An intensive research program was initiated in 1979. It addresses the problems to both planning and operations and consists of the following projects. a) b) c)

The assessment of regional outburst proneness. The assessment of outburst proneness at an active working face. Alleviation of the problem through gas drainage.

Over 200 gas content and composition determinations have been carried out to define the degree of gasiness of the various seams in the Collinsville Coal Measures. Empirical data from the Bowen seam show that outbursting conditions are produced when certain types and magnitudes of

555

faulting occur in combination with desorbable gas contents of greater than 5nr/t of carbon dioxide. The seam gas generally consists of greater than 95% carbon dioxide. Isotopic studies show that this gas has most likely originated from associated igneous intrusions (Gould, Hart and Smith 1983). Desorbable gas contents of up to 25 nr/t have been measured. The investigations relating to the assessment of outburst proneness at the working face aim at providing a more reliable proneness index. Two techniques are being studied involving on-line monitoring to a surfacelocated computer. These are continuous gas monitoring and rock noise monitoring. The quantity of gas evolved during mining is related to the gasiness of the seam. Research to date has shown that a gas-make of greater than 3nr/t per "mining episode" can promote outbursting conditions. Rock noise monitoring trials are as yet, inconclusive. The most effort has been directed toward alleviation of the problem by gas drainage. Initial studies by ACIRL (Gray and Truong, 1983) provided basic design parameters. Consideration of this and mining requirements showed that a viable solution lay in long-hole drilling and gas drainage where entire mining blocks are gas drained to provide uninterrupted mining. One panel has been gas drained using a Diamec 251 rig drilling inseam boreholes to 300 m depth. A total of 6900 m has been drilled. Results of drainage monitoring show that the gas has been drained to non-outbursting levels over most of the panel. Mining of this panel is about to commence. The effectiveness of drainage will be assessed from gas and rock noise monitoring and the rate of coal production. The research program has succeeded in defining a potentially viable and safe method of mining high-gas coal. The definition of gas contents for all seams has, in conjunction with gas drainage data, allowed mine planning to proceed on the basis of acceptable rates of production. The long-hole drilling technique provides the most cost-effective method of drainage from both the drilling and drainage view point. References Gould, K.W., Hart, G. , and Smith, J.W., 1983, Final Report NERDDC Project No. 79/9106. Gray, I. and Truong, D., 1983, ACIRL PR83-2.

HYDR06E0L06Y AND HYDROCHEMISTRY OF GROUNDWATER ASSOCIATED WITH THE YODNG GRANODIORITE NEAR YOUNG, N.S.W. R.M. Williams Water Resources Commission, North Sydney. The groundwater associated with the weathered fractured and jointed zones of the Young granodiorite flows both to north and south, sympathetic to the topography, from the major drainage divide between the Lachlan and Murrumbidgee Rivers south of the Young township. Bores tapping the granodiorite aquifers yield between 0.2 and 8 L/s. Those with a yield in excess of 2 L/s are generally used for irrigation purposes whilst lower yielding bores are used for stock and/or domestic purposes. After initial charging of groundwater with CO2 gas as it passes through the soil zone, the groundwater chemistry changes along the flow lines due to a series of processes including minor ion exchange, kaolinisation of feldspars, alteration of ferromagnesian minerals to aluminosilicates, change of kaolinite to Na-montmorillonite and cation ion exchange of Ca for Na. The groundwater also undergoes simple concentration

556

along the flow lines. The chemical changes along the flow lines caused by these reactions and increase in ion concentrations limit the groundwater usefulness for certain purposes due to increased electrical conductivity, hardness and sodium hazard to irrigated soils. Local point sources of potential groundwater pollution are identified although not quantified. The area of groundwater suitable for irrigation usage is confined in the general area between Wombat and Maimuru. While the extraction and development rate of groundwater has increased rapidly in the last 5 years the study shows that both present and projected rates of extraction are less than the groundwater recharge rate. The table below indicates the change in the volume of groundwater used and the area irrigated for the 1977-1982 period. Annual volume of groundwater irrigation usage for period 1977-1982. For bores tapping the Young Granodiorite in the study Area.

Year

Bores

Volume Used (ML)

77/78 78/79 79/80 80/81 81/82

14 15 19 24 29

8.4 9.6 54.6 135.9 150.6

Area Irrigated ha Used Authorised 23 23.5 38.4 40.8 32.4

149.8 151.3 160.5 218.8 279

The study recommends the area be monitored on a 3 yearly basis to determine any changes in groundwater usage and that it can be adequately managed within the existing bore licensing system. References Fitzpatrick, K.R., 1979, Mine Data Sheets to accompany metallogenic map Cootamundra 1:250 000. Dept. Min. Res. and Development. Freeze, R.A. and Cherry, J.A., 1979, Groundwater. Prentice-Hall, Inc. N.J. Garrels, R.M., and Christ, C.L.1 1965, Solutions, Minerals and Equilibria. Harper and Row, N.Y.

KARPINKA LAKE, SASKATCHEWAN, CANADA: A RARE EXAMPLE OF A PROTEROZOIC ROLL-TYPE URANIUM DEPOSIT

"'Anthony E. Williams-Jones and ^lyron J. Sawiuk bept. of Geological Sciences, McGill University, Montreal Anaconda Canada Exploration, Ltd., Vancouver Karpinka Lake is a non-economic, stratabound uranium deposit hosted by Aphebian meta-sediments, which is located immediately to the south of the important unconformity-type uranium deposit at Key-lake, The uranium occurs as finely disseminated uraninite and subordinate brannerite in sillimanite gneisses which are interpreted to represent metamorphosed arkoses. The mineralized gneisses are acconpanied by up to 10% sulphides (mainly pyrrhotite) and are flanked by sulphide-poor gneisses which are rich in titanomagnetite. The uraninite is commonly in contact with sillimanite and the brannerite is invariably rimmed by sulphide. Both minerals have similar U/Th ratios (35:1). Bulk-chemical analyses suggest that the host rocks were leached of sodium prior to metamorphism. The mineralised rocks show anomalously high concentrations of Copper, molybdenum, and vanadium. 557

U-Pb isotopic analyses of the uraniferous phases indicate that the deposit is at least 1800 Ma in age. This is the same as the age of the Hudsonian orogeny and is interpreted to reflect metamorphic resetting of the isotopic clock. The deposit is unquestionably older than the nearby unconformity-type deposits which have been dated at approximately 1100 Ma. It is proposed that Karpinka lake is a metamorphosed roll-type deposit. A model is presented which involves sulphidation of Fe-Ti oxide rich arkoses and subsequent oxidative alteration of these rocks by uraniferous solutions. The uranium mineralization is interpreted to have concentrated as a result of the reduction of the altering solution by sulphide minerals. The uranium minerals are, however, not considered to have precipitated from solution directly. Instead, it is suggested that uranium was adsorbed onto kaolinite produced by the alteration of tuffaceous fragments and onto titania sponges formed by sulphidation of the Fe-Ti oxides; subsequent metamorphism is considered to have transformed these uraniferous phases into uraninite and brannerite respectively, and the kaolinite into sillimanite. The existence of Aphebian stratabound uranium mineralization and the observation that the Saskatchewan unconformity-type deposits are controlled by faults parallel to the Aphebian gneissosity gives credibility to suggestions that the basement supplied the uranium for the younger unconformity-type deposits.

SOIL GEOCHEMICAL RESPONSE IN THE DRAKE FIELD, N.S.W. 1 9 J.R. Wilmshurst1 and L.R. Bottomer* ^"CSIRO Division of Mineralogy, North Ryde ^Aberfoyle Exploration Pty Ltd, Armidale Precious and base metal mineralisation occurs in the Drake Field within a volcanic sequence of Permian age, as described especially by Offenburg and Cochrane (1975) and Bottomer, Simmons and Joyce (1984). Mineralisation is of three types, fissure lode, stockwork and disseminated. Of these, stockwork (White Rock) and disseminated (Lady Hampden) are the most significant. The mineralisation of these two deposits shows distinct differences in composition, the nature of the host rocks and the topographic setting. Hence geochemical soil surveys were made across each to provide both absolute and relative data on the geochemical response which could be expected under exploration conditions. The Lady Hampden mineralisation occurs within a subhorizontal volcaniclastic member. Surface relief is generally low, with clay-rich The ore elemental soils well developed and . ranging to 2-3 m in depth. association consists of Ag, Au, Cu, Pb, Zn, As and Hg. The sampling traverses crossed mineralization at depths of from near-surface to rather more than 100 m. The behaviour of the ore element association within the soil profile is complex with individual element maxima within the soil horizons frequently displaced laterally. The data indicate a preferred use in exploration of deeper, or "C" horizon soil sampling. Both As and Hg show significant anomalies over buried mineralisation, most likely related to the observed sub-vertical faulting. The geochemical response is in fact dominated by the high levels of Cu, Pb, As and Hg which occur over a NNE trending fault. This anomaly also is best defined in the deeper sampling.

558

Ill contrast, the Whits Rock deposit is in an area of higher relief, with the mineralisation occurring as a quartz vein stock-work within an intrusive rhyolite breccia. Along the sampling traverses, the soils are poorly developed or skeletal. Mineralisation occurs at depths of 60 to more than 100 m where crossed by the traverses. A similar geochemical association to that at Lady Hampden is observed but with a lower Au and higher base metal content. The presence of mineralisation is indicated by anomalies of high contrast but only in As and Hg. These correspond with the projection-to-surface of defined sulfide mineralisation. Here also the use of "C" horizon soil sampling is indicated. In soil samples from White Rock the ratio Hg/As is greater with increased distance from the mineralisation, in both C soil horizon and rock chip samples. This reflects a primary geochemical zonation, and reveals that Hg was relatively more mobile than As during mineralisation. References Bottomer, L.R., Simmons, R.J. and Joyce, R.M., 1984, in Herbert and Rynn (Eds), GSA 1984 Field Conference, 79-90. Offenburg, A.C., and Cochrane, G.W., 1975, in Knight (ed), Economic Geology of Australia and New Guinea, Aus.I.M.M. Monograph 5, 721-774.

THE APPLICATION OF STABLE ISOTOPES TO THE GENESIS OF GOLD DEPOSITS IN EASTERN AUSTRALIA Allan F. Wilson and Suzanne D. Golding Department of Geology & Mineralogy, University of Queensland, St Lucia The Charters Towers fissure veins were formed during hydrothermal activity associated with Lower Devonian Ravenswood 18 Granodiorite Complex. The systematic change of 6 0 from 12.2 to 15.7 per mil in a group of related quartzes is apparently depth-dependant, with the highest value coming from the Brilliant Deep (820m). The calculated ore fluids have typical magmatic 6 1 8 0 values of about 8 per mi 1. Mt. Morgan displays S 1 8 0 values for lode quartzes, cherts, limestones and altered acid volcanics of less than 10 per mil. The calculated ore fluids fall in the range -3.0 to +3 per mil, which indicate a major component of sea water. Auriferous vein quartzes hosted by the Proterozoic Forsayth Batholith of N. Queensland . have a mean 6 1 8 0 of 15.0 ± 0.7 per mil. Although current isotope data are not clearly definitive, they are compatible with a magmatic derivation. The Ukalunda Field (Carboniferous -mineralization), SW of Bowen, has auriferous and Au-Bi fissure veins, and silver mineralization. Reconnaisance oxygen isotope studies reveal that meteoric waters have been involved in convective hydrothermal cells associated with some acid volcanic plugs and granitoids. 6 1 8 0 values of the hydrothermally altered rocks and ore quartzes range from -0.4 to 8.3 per mil.

559

Cracow, in central Queensland, displays argillic alteration about quartz fissures and breccia zones in the Permian Camboon Andesite. 18 The strongly 0-depleted quartzes (about -2.7 per mil) and host volcanic rocks (-4.6 to +4.7 per mil), together with the fluid inclusion and mineral equilibrium temperature of 250 ± 50 C indicate an ore fluid with 6 * 8 0 -12 ± 3 per mil. This is interpreted as involving cold meteoric waters when Cracow was in high latitudes during the late Palaeozoic. The Kilkivan region of S. Queensland has auriferous fissure veins in serpentinite/greenstone at the old Rise and Shine Mine where quartz 6 1 8 0 is about 15.2 per mil, and calcite 6 1 8 0 is about 10.0 per mil with S ^ C is about -2.5 per mil PDB. These data imply a calculated composition for the fluid in equilibrium with the quartz of about 6 per mil at 250 C. The carbonate minerals deposited in the late phases of mineralization are not in isotopic equilibrium with the quartz but suggest an increasing component of meteoric water in the ore fluid. Mineral and isotopic data from hydrothermal fissure nrineralization associated with the Black Snake Diorite Porphyry indicate a temperature of about280°C, and an 1 8 0-depleted fluid composition close to 4.5 ± 0.2 per mil. Gympie mineralization comprises pyrite-rich quartz veins, commonly enriched in gold near, carbonaceous layers in the Permian sediments. Quartz has S*80 of about 15.5 per mil but in the absence of 18 D/H data, the quartz 0 data are compatible either with fluids sweated from the sediments or from well buffered granitic fluids. Oxygen isotope data for quartz from auriferous veins hosted by Carboniferous greywackes and slates in the Talgai Goldfield, Warwick District, S.E. Queensland range from 19.4 to 20.8 per mil. Based on 350 C, the ore fluid was metamorphic, with 6* 8 0 about 15 per mil. However, at Mt. Gammie there is also evidence of high level igneous activity. At Expedition in the Drummond Range, about 19 km W. of Clermont, several distinctive types of quartz veins cut the pelitic rocks of the Anakie Metamorphics. Quartzes from a widespread group of more or less pyrite-bearing K-feldspar quartz veins (not known to be auriferous) have 6 1 8 0 from 14.7 to 15.3 per mil, and are presumed to be derived from a hidden granitic body. Other quartz veins and boulders of rusty more or less gos^anous quartz from the gold-bearing alluvials have 6 0 values from 14.9 to 15.9 per mil. This group is also not known to be auriferous. However, all known gold-bearing veins (sulphide-bearing) and quartz-bearing gold nuggets have 6 1 8 0 values higher than 16 per mil (range 16.5 to 20.2 per mil). These oxygen isotope data are consistent with a metamorphic fluid. However, as the host phyllite 6 1 8 0 values range from 12.1 to 14.0 per mil and <5 values for quartzofeldspathic hosts range from 15.9 to 16.3 per mil, the source of the presumed auriferous metamorphic fluids are not local, nor locally buffered. A similar range of oxygen isotope values for quartz pertains to the Clermont district itself. Many quartz oxygen isotope values from Victorian gold-bearing veins appear to fall into several geographic zones: 1 2 3

4 5 560

Bendigo - Maryborough - Fryerstown - Chewton, 17.4 per mil; Ballarat - Smythesdale - Pigoreet, 17.6 per mil; Beaufort - Dayesford, 19.1 per mil; (this zone geographically separates 1 and 2, and may represent a cooler E-W ridge of metamorphic ore fluids). Stawell - St. Arnaud - Donnelly, 15.8 per mil; Walhalla - Gaffneys - Marysville, 20.2 per mil.

We suggest that the data for zones 1, 2 and 3 imply the dominance of metamorphic fluids, whereas zone 4 is dominated by igneous fluids. Zone 5 implies a non-igneous ore fluid for the quartz, notwithstanding the deep-seated origin of the CO 2 associated with the Woods Point Dyke Swarm. Smaller bodies of oxygen isotope data are assembled from Nanima and Dalton in N.S.W., and reconnaisance data from about 20 other localities in eastern Australia. Further detailed studies using fluid inclusions, sulphur i s o t o p e s a n d fineness of gold studies are planned.

D/H

and

EXAMPLES OF THE USE OF NEUTRON ACTIVATION ANALYSIS OF GOLD IN WATERS TO IDENTIFY GOLD PROSPECTS 1 1 2 Allan F. Wilson , M.J. Thomas* and J. Fardy* ^"Department of Geology & Mineralogy, University of Queensland, St Lucia 2 CSIR0 Division of Energy Chemistry, Lucas Heights A method of analysing water samples for gold at levels of parts per trillion (ppt), using activated charcoal extraction followed by Neutron Activation Analysis, was tested. Samples from Gold Creek near Brisbane, and several streams and hot springs in Northland, New Zealand have been analysed. In New Zealand basic volcanic flows and tuffs, representing highly altered fossil hydrothermal systems, are iron-rich clays which yield gold values of 20000 - 50000 ppt, with some reaching the ppm range. Streams eroding these rocks contain about 50 ppt Au in solution and particulate gold of about 10 ppt. The carbon of a fossil tree fern washed by these streams reported over 7000 ppt Au. Some mercury-bearing hydrothermal springs amounts of gold in solution and as particulates.

at Ngawha

carry

similar

The insights into gold transport mechanisms are of importance to geologists. Studies of the amount of gold in the sub-1.2 micron ("dissolved") and over-1.2 micron ("particulate") fractions revealed that in the areas tested more gold is carried in the smaller size range. Despite this, a significant portion of the gold is carried as particulates. The particulate fraction probably consists of clay particles aggregates, spores, pollens and bacteria. It represents an intermediate step between the transport and deposition of the gold. Equilibration between particulate and dissolved gold species with changes in stream chemistry appears to be slow. No correlation between pH and gold concentration was found, although a bimodal distribution of pH was observed in the New Zealand samples, with centres at 3.6 and 6.4, where the lower pH is caused by sulphide oxidation. Advantages and limitations of the techniques as an exploration are discussed.

tool

561

THE RIDSTON

GOLD M I N E ,

QUEENSLAND

G.I. Wilson, R.W. Lewis, J . Gallo Placer Exploration Limited,

Sydney

The Kidston Gold Mine is an example of a deposit discovered by traditional prospecting which is now being developed as the result of modern exploration practice, innovative mining and an adequate metal price. Prospecting began in the 1880's but the field became public knowledge in 1907. Small scale underground and open cut mining proceeded to 1924, then in a desultory fashion to 1942. Recorded production was 200,900 tonnes of 6 g/t Au. The open cut potential was recognised early in the mining history by Government geologists but no attempt at major development was made, probably due to isolation and inadequate gold price. In the period 1966-77 Anaconda Australia Inc. explored the deposit, recognising the breccia pipe and drilled 14 holes which partially outlined the main gold deposit at Wises Hill and identified one other area of significant mineralisation. Placer Exploration Ltd. optioned the property in March 1978 after recognising the bulk mining potential of the deposit. An aggressive exploration programme was instigated, in which core drilling totalling 20,500 metres, engineering studies and a feasibility study were completed by late 1980. Further evaluation recognised the opportunity for an enhanced production rate in the early years of mining due to the metallurgical characteristics of the deeply oxidised upper portion of the Wises Hill ore body. This improved the economics of the project and resulted in the recent decision to proceed with the project. The current construction phase of mine development commenced in early 1984 and mining is scheduled to begin in April 1985.

THE G O L D E N H A N D P R I N T : A S T R U C T U R A L I N T E R P R E T A T I O N OF THE EASTERN GOLDFIELDS, WESTERN A U S T R A L I A , FROM NOAA-AVHRR IMAGERY

P. Wilson 1 , I.J. Tapley 2 and F.R. Honey 2 1

CSIRO, Division of Mineralogy, Floreat Park, W.A. CSIR0, Division of Groundwater Research, Floreat Park, W.A.

There have been very few applications of small scale continental coverage satellite imagery for mapping structural and geomorphologic features. Lathram (1972) mapped several extensive lineaments in Alaska using imagery from NIMBUS III and IV. The initial investigations into the application of NOAA-AVHRR data for structural and lithologic mapping are described by Honey (1982), and more detailed studies have been presented by Honey et al. (1984a, 1984b), and Wilson et al. (1984). The NOAA satellite series has been described in detail by Hussey (1979) and Schwalb (1979)* The satellites in the series are near polar orbiting spacecraft, orbiting at an altitude between 870 and 930 km, with an orbital period of 102 minutes, resulting in slightly more than 14 orbits per day. Generally two satellites are operational at any time, approximately ninety degrees out of phase. The Advanced Very High Resolution Radiometer (AVHRR) on these satellites is a five (NOAA-7) or four (NOAA-8) channel multispectral scanner with an instantaneous field of

562

view of 1.3 milliradians, resulting in a ground resolution at nadir of 1.1 km. The AVHRR have either four (NOAA-8) or five (NOAA-7) spectral channels ranging from the visible to the thermal infrared. The bandpasses of these channels are: Channel 1 2 3 4 5

visible visible reflected IR day reflected IR/ night thermal IR thermal IR thermal IR thermal IR

Bandpass 0.58 0.55 0.725 3-55 10.3 10.5 11.5

0.68 0.68

1.10

NOAA-7 NOAA-8

3.93

- 11.3 - 11.5 - 12.5

NOAA-7 NOAA-8 NOAA-7 only

Digital enhancement of day-time reflected and night-time thermal imagery from the NOAA-AVHRR satellite series has highlighted the presence of abundant macroscopic geological structures traversing the major geologic units of the Eastern Goldfields region of Western Australia. The 1 km spatial resolution of the NOAA-AVHRR images highlights lineaments which extend for more than11 200 km in a N-NE and E-W direction. The extent of these "linear zones suggests they are the result of deep-seated tectonic activity which has produced a change in mineralogy and subsequent increase in soil moisture and change in vegetation type and density. The combined alteration of mineralogy and vegetation types renders the lineaments visible on both day and night imagery as distinct tonal and/or spectral differences. Enhancement of the thermal infra-red bands of the NOAA-AVHRR 11 highlights a "hand-print of sharp and precise linear zones in the central region of the goldfields. More than 50 percent of observed linear features have a N to NE trend which has been offset by major E-W linear zones. These northerly linear features represent the oldest linear trends throughout the Yilgarn goldfields and many represent Archaean granite/greenstone boundaries which can now be interpreted beyond any known geological information. Although many of the linear zones observed do represent lithological boundaries there are centres of structural complexity which appear to be deep-seated as implicated by magnetic data. The prominent E-W linear zones correspond in most cases to Proterozoic dykes which are now known to display either a magnetic or non-magnetic response. A comparison of NOAA-AVHRR data with geological information has revealed that all known major faults lie along these linear zones and the major gold producing areas of the region lie directly along and at the complex intersections of these linears. Many historic gold mining areas coincide with the complex intersection zones of the linears and many new areas of interest have been delineated by the intermediate resolution of the NOAA-AVHRR data. References Honey, F.R., 1982, Proc. International Symposium on Remote Sensing of Environment, Second Thematic Conference: "Remote Sensing for Exploration Geology", II, 519-525, 6-10 December 1982. Honey, F.R., Tapley, I.J., & Wilson, P., 1984a, Proc. International Symposium on Remote Sensing of Environment, Third Thematic Conference, Remote Sensing for Exploration Geology, Colorado Springs, Colorado, April 1984. Honey, F.R., & Tapley, I.J., 1984b, Proc. of Third Australasian Remote Sensing Conference, Queensland, May 1984.

563

Hussey, W.J., 1979, The TIROS-N/NOAA Operational Satellite System: Washington D.C., National Oceanic and Atmospheric Administration, National Environment Satellite Service. Lathram, Ernest H., 1972, Science, 175, 1423-1427. Schwalb, A., 1979, NOAA Technical Memorandum NESS 95, United States Dept. of Commerce NOAA/NESS, Washington D.C. Wilson, P., Tapley, I.J., & Honey, F.R., 1984, Proc. of the Canning Basin Symposium, Perth, W.A., June 1984-

NATURE OF FLUIDS AND SOME CONTROLS ON FLUID EVOLUTION ASSOCIATED WITH ALKALI METASOMATISM AND GREISENIZATION OF A TIN-MINERALIZED GRANITE W.K. Witt James Cook University, Townsville Go-Sam Granite, a medium grained, equigranular granite in the Irvinebank area of the Herberton-Mt. Garnet tinfields, N.E. Queensland displays evidence of widespread subsolidus mineralogical and textural modification (background alteration). The same granite hosts more localized, selvage-style, fracture-controlled alteration. Both types of alteration consist of successive stages of metasomatic activity which occurred in the following sequence: 1. 2. 3. 4.

early K-felspathization albitization greisenization late K-felspathization

Late K-felspathization has been definitely identified only as selvagestyle alteration. Fracture-controlled alteration overprints background alteration. Petrographic evidence indicates that fracture-controlled felspathic metasomatic rocks consist of a framework of altered granite and interstitial vughs filled with quartz, fluorite, mica and cassiterite. Textural and mineralogical evidence suggests that the vugh-filling events in early K-felspar rocks and albitites are temporally equivalent with spatially associated greisenization and occurred shortly after felspathic alteration. Quartz and fluorite in vughs of the felspathic rocks and spatially associated greisens contain similar populations of fluid inclusions. These occur singly, in clusters (primary?) and in swarms of subparallel and intersecting trails (pseudosecondary and secondary?). Inclusions in each rock type display the same wide range of homogenization temperatures and salinities indicating a history of repeated fracturing in the presence of a cooling fluid of evolving composition. SEM-microprobe analyses of daughter minerals, and heating and freezing data indicate some compositional similarities amongst the fluids responsible for the four stages of alteration. All are dominantly Na-K-CaFe chloride solutions of high salinity (up to ~ 60 wt% NaCl equiv.). Some relatively minor variations in composition are indicated and other subtle variations in fluid composition may not be recognizable by the techniques used. Homogenization temperature data are complex, and will sustain at least two interpretations. Maximum temperatures are similar (500-600°C) in all rock types investigated. Saline inlcusions homogenize by daughter crystal dissolution. Plots of these temperatures versus temperature of vapor bubble disappearance produce linear trends parallel to the homogenization 564

temperature axis. Plots for different alteration assemblages produce varying degrees of spread towards higher vapour disappearance temperatures. The data may be interpreted as indicating: 1) 2)

a saturated fluid (or fluids) of evolving composition without significant decrease in temperature. a cooling saturated fluid of evolving composition.

It is concluded that the same fluids were responsible for the four stages of alteration investigated. High homogenization temperatures and high salinities suggest fluids of magmatic origin. Different alteration assemblages result from relatively subtle changes in solution chemistry (mainly K/Na and K+Na/H ratios), and possibly decreasing temperature. Changes in pressure may also have been important. Thermodynamic considerations indicate that decreasing temperature may have opposed some of the implied mineral/fluid reactions during early stages of alteration. Similar fluid inclusion populations with similar homogenization temperatures, compositions and salinities in Go-Sam Granite away from prominent fractures suggest that the same fluids were responsible for the widespread background alteration in that rock. Fluid evolution under conditions of more or less constant temperature is in marked contrast to the'fluid evolution models for comparable rocks proposed by Russian authors (Beus & Zalashkova, 1962, Scherba, 1968). Fluid inclusion data is capable of an interpretation consistent with Soviet theories of fluid evolution controlled by decreasing temperatures. References Beus, A.A. & Zalashkova, N.Ye., 1962., Int.Geol.Review, 6(4) p. 668-681. Scherba, G.N., 1968., Int. Geol. Review 12 p. 114-150, p. 239-255.

USE OF COAL WASHERY WASTE AS A CONSTRUCTION

MATERIAL

G.W. Won1 and R. Hodgins2 1 2 Department of Main Roads, Sydney, Department of Main Roads, Wollongong Coal washery waste (or coal wash) has been used in recent years as pavement subbase material, both without and with additions of lime9 up to 5% by mass. This material is abundant within a 200 km radius of Sydney whicti has adjacent coalfields to the north, west and south. In the southern area alone, coal wash production totals 4 million tonnes per year and is increasing. Disposal of this material is a problem, and thus the coal wash is available free of charge at washing plants. Only the coarse washery reject material is suitable for roadworks; the particle size ranging from 2 to 60 mm. This coal wash is variable in composition, consisting mainly of carbonaceous shale and mudstone with some sandstone and coal (Foreman, 1981). The loss on ignition ranges from 25 to 40$, and spontaneous combustion can occur in loose material. However, it is not likely to occur if the material is well compacted (Lundie, 1980). The suitability of a number of coal wash materials for use as subbase has been assessed by grading requirements and the Texas Triaxial test. For subbase, a maximum allowable Texas Classification Number of 4.0 is required. Typical values are given in Table 1 together with compressive modulus values, for materials from two collieries.

565

TABLE 1 TEXAS TRIAXIAL TEST RESULTS FOR UNSTABILISED AND LIME TREATED COAL WASH

Source

Lime Content

Moisture Content

(%)

Texas Classi fication Number

Compressive Modulus (MPa)

Lithgow Valley Colliery

3.7

3.3

Lithgow Valley Colliery

6.7

3.9

Coalcliff Colliery

(Wollongong)

9.4

3.0

Coalcliff Colliery

(Wollongong)

8.4

3.2

TABLE 2 TEST RESULTS FOR COALWASH FROM COALCLIFF COLLIERY

Reinforced Earth Specification

Test

(WOLLONGONG)

Test Results

Grading 75 urn Sieve

< 15%

Resistivity

> 5000 ohm cm

666 3 ohm cm

5 < pH < 10

9.4

pH Sulphate

< 0.10*

0.07%

Sulphide

< 0.03%

Nil

The material has been used successfully as both fill and subbase for various Main Roads in the Wollongong area, N.S.W. Possible problems in using coal wash may relate to the presence of soluble sulphates or the pH level of the material, coupled with adverse permeability or resistivity levels. These properties can be determined readily, if warranted by the proposed conditions of use. The coal washery waste in the Wollongong area also complies with minimum requirements for reinforced earth select backfill material as shown in Table 2 and compares favourably in cost with other backfill materials.

References Foreman, I.K., 1981, M.E. Thesis, Univ. of Wollongong (unpubl.) entitled "Suitability of coarse coal washery refuse for the various stages of pavement construction". Lundie, R.C., 1980, B.E. Thesis, Univ. of Wollongong (unpubl.) entitled "Use of oolliery shale as a road construction material".

THE HYDROGEOLOGICAL FRAMEWORK OF THE NEW SOUTH WALES SECTION OF THE MURRAY BASIN D.R. Woolley and R.M. Williams Water Resources Commission of N.S.W., Sydney The Murray Basin has an area of 300 000 km2 of which 135 000 km2 is in south-western New South Wales. It contains a sequence of Tertiary and Quaternary deposits with a maximum known thickness of about 600 metres, which are mostly of marine origin. Framework tectonics provide the primary control on the development of the Basin although within this context sediment accumulation appears to have been sensitive to secondary eustatic, palaeoclimatic influences and to consequent fluctuations in the erosive and depositional potential of the fluviatile systems that drain the Basin and its catchment areas. 566

There has been an Increasing interest in the groundwater associated with the deposits within the Basin in recent years due to its potential as a usable resource, its interrelationship with surface water and the implications of shallow saline water. As development of the high yielding aquifers in the eastern areas has continued it has become apparent that groundwater extraction will equal and pass natural recharge. A licensing policy is being developed to provide control over the effects of groundwater withdrawal on long term decline of water levels and on ancillary effects related to surface water conditions and salinisation. Most groundwater recharge occurs near the Basin margin where the rivers whose headwaters are in the eastern highlands cross the highland front. The potentiometric surface of aquifers within the basin show to varying degrees that groundwater flow is generally towards the centre and away from the recharge areas. There are artesian flows from bores tapping the deeper zones immediately east of Balranald and north of Mildura, which are near the centre of the basin, where the potentiometric surface is above ground level. The implications for land use within the Basin are that water lost from irrigation areas in the east by infiltration into the groundwater system will cause a long term rise in the potentiometric surface across the Basin. This could lead to an increase in saline groundwater inflows to the Murray. River downstream of the Murrumbidgee River confluence and to the need for additional drainage and disposal works such as those already in operation at Buronga. Some presently inactive playas and springs may also be reactivated. Further study is needed to enable estimates of the likely magnitude and time scale of these effects. References Williams R.M., 1983, International Conference on Groundwater and Man, Sydney. Woolley, D.R. and Williams, R.M., 1978, _In Storrier, R.R. and Kelley, I.D., (Editors) - Symposium on the hydrogeology of the Riverine Plain of southeastern Australia. Australian Society of Soil Science pp. 4565.

A PRELIMINARY EVALUATION OF QUARRY BENCH BLASTING DESIGNS IN SINGAPORE FOR FLYROCR CONDITIONS Lee Kim Woon Public Works Department, Republic of Singapore In Singapore, flyrocks from bench blasting pose a high risk to life and property in view of the proximity of all its sixteen quarries to fairly densely populated settlements. Accordingly, the Sand and Granite Licensing Unit of the Public Works Department of Singapore decided - as a first step in studying ways for minimising flyrocks - to make an evaluation of production blast designs of its twelve quarries. A comparative evaluation of the designs with the 'standard blasting* ratios of Ash (1963) and the National Association of Australian State Road Authorities suggest that almost all our quarries have burdens and/or stemming depths which may be considered inadequate for the control of flyrocks. The burdens are generally less than I/4 of the bench heights and blasthole lengths, and hence appear to be too small in relation to their bench heights and blasthole lengths, and stemming depths are about, as often as not, less than the burdens.

567

An independent check using the Crater Method of Blast Design confirms our comparative evaluation. In doing so, it has also enabled the Unit to classify the quarries in 5 'safety1 classes in a relative manner. In addition, the Unit has - with the Method - suggested relatively safer blast design parameters on burden, stemming depths, and powder columns for individual quarries for trial blasting, Flyrocks can also be caused by any of these factors such as excessive charges, inappropriate delay patterns, unfavourable joint orientation,zones of different hardness in the rock mass, presence of erratic boulders, etc. It obviously follows that these factors must also be assessed by the Quarry Unit in its determined attempt to minimise the occurrence of flyrocks in the quarries. In this respect, additional work and assistance are required in (a) evaluating its suggested blast design parameters for safer blasting (b) recommending other loading methods, hole lay-outs,and delay patterns that can help to control flyrocks and (c) training its staff in recognising unfavourable geological conditions that promote flyrock conditions, and ultimately formulating guidelines to quarry operators for safer blasting. References Ash, R.L., The mechanics of rock breakage, Pit Quarry 50, pp 98-118 (1963). Havers, J.A. & Stubbs, F.W., Handbook of Heavy Construction, Section 19, pp 26-32 (1971) National Association of Australian State Road Authorities., Explosives in Roadworks-User?s Guide, pp 95-109 (1982).

THE SIGNIFICANCE OF TOURMALINE BRECCIAS AT MT BISCHOFF, TASMANIA J.H. Wright Geology Department, La Trobe University, Melbourne At the Mt Bischoff tin deposit in western Tasmania a series of breccia occurrences has close spatial and temporal relationship to tin mineralized greisenized rhyolite porphyry dykes and tin mineralized exogreisens. The breccias are found adjacent to greisenized dykes, within the dyke conduit and as thin, irregular, tabular bodies cutting altered dykes and their sedimentary hosts. Breccia found close to dykes has a high proportion of dark, fine grained, matrix schorl in which are supported angular to rounded clasts'of host sediments and greisenized porphyry. Shale and silty clasts are generally replaced by tourmaline whereas porphyry clasts show pre-brecciation topaz and mica greisen assemblages with occasional quartz or quartz-tourmaline vein swarms. Breccias found at a greater distance from porphyry dykes are clast supported with a dusty,tourmaline free, matrix. Clast fracturing, presumably due to post brecciation collapse and consolidation, is seen in the latter breccia types. Cassiterite is occasionally seen within the tourmalinized breccia matrix, the greisenized porphyry clasts and in sericite alteration shells around some sediment clasts. However, the more usual mode of cassiterite occurrence is as a component of a later siliceous interclast replacement and void fill.

568

Tourmaline rich breccias in dyke conduits are commonly intruded by wisps and small apophyses of dyke material. Selvedges of tourmalinized breccia and trails of breccia clasts can also be found along dyke edges. Dyke greisenization dates from the period of intrusion or soon thereafter and the effects are seen to be controlled by migration of hydrothermal fluids within the body of the dykes. Fluorine and boron rich exogreisen replacement bodies occur where greisenizing fluids, at temperatures of 350 to 400 degrees centigrade, are released from the confines of the dyke conduit and interact with a sedimentary dolomite horizon adjacent to the dyke. These exogreisens have provided the majority of the high grade tin ore mined at Mt Bischoff to date. The closeness.of the association of breccia and altered porphyry dykes and the mutually interpenetrant relation between breccia and dyke indicates that dyke intrusion, brecciation, alteration and mineralization were phased but geologically coeval events within a zone of multiple dyke development during a major phase of granitoid intrusion in Devonian-Carboniferous times. The breccias at Mt Bischoff are similar in origin to intrusive type breccias described by Grant et al(1980), Sillitoe et al(1975),Halls et al(1978),Sotnikov et al(1971) and various authors on porphyry copper deposits. They indicate the explosive venting of flash-heated groundwater &/or gas/vapour phase separation from crystallizing rhyolite por.phyry intrusives. Hydrothermal events follow the initial explosive brecciation to produce tin mineralization and alteration patterns of a porphyry tin style system. References

Grant, J.N., Halls, C., Sheppard, M.F., & Avila, W., 1980, Mining Geology Special Issue, No.8, 151-173. Halls, C., Rankin, A., Ferriday, I., Blain, C., Bristow, C., & Gronow, C, 1978, Journ. Geol. Soc. Lon., Vol 135, p256. Sillitoe, R.H., Halls, C., & Grant, J.N., 1975, Econ. Geol., Vol. 70, 913-927. Sotnikov, V.I., Nikitina, Ye.I., Lavrentyev, Yu.G.,& Semenov, V.I.', 1971, Geochem. Int., Vol.8, 97-106.

569

ORIGIN OF ZIRCONS AND SAPPHIRES IN STANNIFEROUS DEEPLEADS OF NORTHEAST TASMANIA W.S. Yim1, A.J.W. Gleadow2, J.C. van Moort3 ^University of Hong Kong, Hong Kong 2University of Melbourne, Melbourne ^University of Tasmania, Hobart Two types of zircons with different appearances are found associated with sapphires in the stanniferous deepleads of northeast Tasmania. The first type is euhedral and up to about 2 mm in length, while the second type is anhedral, usually over 2 mm in length and may exceed 1 cm occasionally. A heavy mineral provenance study using sediment samples collected from exposures in alluvial and eluvial mine workings, present day river banks and beds has indicated that the anhedral zircons and the sapphires could be traced to the same basaltic source rocks on the Blue Tier. This is confirmed by the fission track dating on the two types of zircons separated from the panned concentrates in two selected samples. The euhedral zircons in one sample gave a combined age of 367 Ma thus verifying their derivation from Late Devonian, granites. On the other hand, the anhedral zircons in two samples gave combined ages of 46.3 Ma and 47.1 Ma respectively. These Early Eocene dates concurred with the potassium-argon radiometric dates obtained for the Blue Tier basalts (Sutherland and Wellman, personal communication). Both the anhedral zircons and the sapphires may have originated from megacrysts and xenocrysts (Sutherland and Hollis, 1982). Reference Sutherland, F.L. and Hollis, J., 1982.

J.Volcan.Geotherm.Res. 14, 1-29.

CAINOZOIC 6E0M0RPH0L06ICAL EVOLUTION AND GENESIS OF STANNIFEROUS PLACERS IN NORTHEAST TASMANIA W.W.-S. Yim University of Hong Kong, Hong Kong A heavy mineral provenance study based on sediment samples collected from alluvial and eluvial mine workings, present day river banks and beds in northeast Tasmania has provided clues on geomorphological evolution and the genesis of stanniferous placers. Potassium-argon radiometric dating of basalts, fission track dating of alluvial zircons and palynological evidence have revealed that the Pioneer deeplead was formed during the Early Eocene to Late Oligocene. Before the emplacement of the Ringarooma-Winnaleah basalts in the Middle Miocene, the northwest flowing streams on the Blue Tier were connected to a protoBoobyalla River system. These basalts caused drainage diversion forming the present Ringarooma River system. Both the silcretes and laterites occurring in the Mount Cameron Basin postdated these basalts and are postMiddle Miocene in age. The average rate of sedimentation of the deeplead at Briseis Mine is estimated to be about 0.3 mm per hundred year. This slow rate of sedimentation supports that considerable reworking by winnowing is required in the formation of stanniferous placer deposits. Furthermore, the immobility of cassiterite is indicated by the existence of cassiterite composite grains and nuggets which are found close to the mineralized source rocks.

570

INDEX Abeysinghe, P.B. 11, 12, 14, 29, 30, 316 Adam, J.D. 11, 31 Ahmad, R. 14, 32 Alexander, R. 6, 32 Ambler, E.P. 2, 33 Amos, Q.G. 14, 17, 210, 211 Anderson, A. 7, 264 Andrew, A.S. 11, 34, 36 Archibald, D.A.C. 10, 38 Ashley, P.M. 13, 39, 153 Atkinson, W.J. 17, 40 Aubrey, M.C. 9, 41 Baczynski, N.R.P. 14, 22, 42 Baillie, P. 22, 43 Bain, J.H.C. 18, 44 Bajwah, Z.U. 11, 13, 44, 45 Baker, C.K. 19, 46 Baker, E.M. 18, 48 Baker, J. 7, 302 Baker, W.E. 10, 49 Balce, G.R. 28, 50 Banfield, J.F. 15, 20, 51, 53 Barnes, I. 3, 94 Barnes, L.C. 1, 2, 54, 55, 417 Baxter, J.L. 14, 56 Beamish, B.B. 7, 555 Beckett, J. 6, 538 Bell, D.H. 22, 57 Bhatia, M.R. 4, 58 Biggs, M.S. 2, 486 Bilgrami, S.A. 28, 59 Binns, R.A. 11, 14, 34, 59 Birch, W.D. 19, 61 Black, L.P. 18, 44 Black, R.E. 4, 213 Blong, R.J. 28, 285 Bloom, M.S. 11, 12, 14, 62, 64, 223, 226, 345, 514 Blucher, I.D. 14, 71 Bodard, J.M. 5, 66, 529 Body, D.N. 28, 364 Bone, Y. 20, 67 Booth, S.A. 10, 14, 69, 71 Boreham, C.J. 8, 186 Bottomer, L.R. 9, 11, 201, 558 Bourke, D.J. 23, 475 Bowen, E.A. 26, 72 Boyer, D.G. 15, 416 Brakel, A.T. 5, 7, 264, 266 Bramall, A.M. 22, 74 Branagan, D.F. 15, 21, 23, 76, 78, 79, 384 Branch, C.D. 27 Branson, J.C. 5, 24, 79, 163, 164, 291

Brewer, A.M. 6, 542 Brightman, R. 1, 80 Brown, W.M. 12, 316 Brumley, J. 22, 81 Buchhorn, I. 13, 165 Buck, M.D. 15, 82 Burlinson, K. 10, 84 Burne, R.V. 6, 8, 27, 85, 86 Butt, C.R.M. 2, 5, 87, 192 Callen, R.A. 15, 16, 89 Cameron, W.E. 15, 90 Carr, G.R. 13, 90 Carter, A.N. 16, 92 Carter, L. 24, 93 Carter, R.M. 24, 93 Cartwright, K. 4, 93 Cas, R.A.F. 4, 15 Cassie, R.A. 16, 371 Chaku, C. 13, 165 Chappell, B.W. 19, 474 Chivas, A.R. 3, 12, 16, 94, 95, 231 Coisy, P.H. 4, 58 Coldham, T. 1, 98 Cole, W.F. 22, 100 Coleman, J.M. 23, 100 Collerson, K. 2, 94 Collins, C.D.N. 24, 173 Collins, P.L.F. 11, 21, 101, 103 Collins, W.J. 15, 104, 105 Colwell, J.B. 26, 523 Comino, J. 7, 536 Comsti, E.C. 10, 513 Conaghan, P.J. 23, 24, 106, 221, 367, 438 Conley, D. 25, 109 Cook, K.B. 18, 111 Coope, B.M. 2 Cooper, B.J. 21, 112, 113 Cooper, J.A. 19, 343, 478 Corbett, D.W. 21, 114 Corkery, R.W. 2, 115 Coshell, L. 8, 117 Coupard, M.M. 9, 398 Cousens, D.R. 20, 484 Craig, M.D. 9, 195 Crawford, A.J. 21, 119 Creasey, J.W. 22, 120 Creech, M. 1, 11, 121, 122 Crisp, P. 9, 271 Crouch, A. 6, 124 Cull, J.P. 25, 125 Dadd, K. 22, 126 Dale, L.S. 9, 128 Daniels, J.L. 9, 252

Darragh, P.J. 1, 128, 129 d'Auvergne, P.B. 8, 130 Davies, G.F. 25, 131 Davies, K.E. 9, 494 Davies, P.J. 24, 508 Day, A.A. 21, 132 Day, R.A. 18, 133 De Deckker, P. 16, 95 Deckelman, J.A. 6, 277 Degeling, P. 21, 134 Derrick, G.M. 18, 137 Dickson, B.L. 3, 9, 138, 139 Diessel, C.F.K. 19, 46 Dissanayake, C.B. 3, 141, 142 Dooley, J.C. 25, 143 Donnelly, T.H. 10, 12, 18, 229, 322, 323 Dosso, H.W. 24, 145 Doutch, H.F. 28 Downes, J.M.T. 19, 145 Driessen, A. 2, 147 Drummond, B.J. 25, 150 Drury, L.W. 3, 151 Dubowski, E.A. 1, 178 Dudley, R.J. 13, 153 Duggan, M.B. 25, 310 Duncan, G.L. 9, 206 Eadington, P.J. 11, 154, 229 Eastoe, C.J. 14, 437 Eberz, G.W. 19, 155 Edwards, G.E. 7, 157 Eggleton, R.A. 15, 20, 51, 53, 158, 159 Eisler, P.L. 6, 160 Ellis, D.J. 18, 25, 161 Ellis, J. 9 Elliston, J.S. 27 England, P. 24, 26, 255, 257 Etheridge, M.A. 5, 11, 24, 101, 163, 164, 291 Etminan, H. 10, 13, 165, 322 Ewald, A.H. 12, 550 Exon, N.F. 27, 166 Falvey, D.A. 16, 24, 79, 371 Fardy, J.J. 3, 9, 10, 128, 167, 561 Feary, D.A. 23, 168 Fenton, M.W. 15, 169, 170 Finlayson, D.M. 24, 25, 171, 173 Fisher, W.L. 5, 27, 174 Fitz Gerald, J.D. 20, 177 Fletcher, I.R. 14, 56 Flint, D.J. 1, 178 Florence, T.M. 3, 167 Fogg, T.B. 9, 360 Foley, S.F. 19, 515 Forbes, C.F. 4, 213 Franklin, B.J. 1 572

Fraser, S. 9, 270 Frey, F.A. 19, 442, 443 Frost, R.J. 22, 179 Fyfe, W.S. 1, 27, 179 Gabell, A.R. 9, 270 Gallo, J. 17, 562 Gamble, J.A. 19, 181 Garman, M.R.W. 18, 187 Gerges, N.Z. 1, 182 Gibbons, G.S. 15, 185 Giblin, A.M. 3, 268 Gibson, D.L. 8, 186 Giles, A.D. 1 Gilfillan, J.F. 18, 187 Gilligan, L.B. 18, 21, 134, 189 Glasson, K.R. 27 Gleadow, A.J.W. 1, 570 Glen, R.A. 10, 190 Glickson, M. 8, 191 Golding, S.D. 18, 559 Gole, M.J. 3, 5, 87, 192 Gordon, I.F. 18, 380 Gorman, J. 6, 7, 349, 350 Gravestock, D.I. 5, 498 Gray, C.M. 15, 19, 104, 442 Gray, N.M. 23, 194 Green, A.A. 9, 195, 270 Green, D.H. 19, 24, 196, 314 Green, T.H. 18, 197 Gresham, J.J. 17, 199 Griffin, B.J. 20, 67 Griffin, W.L. 26, 418 Grimstone, L. 6, 7, 349, 350 Groves, D.I. 12, 323 Gulson, B.L. 11, 13, 90, 201 Guyot, R. 7, 202 Habermehl, M.A. 3, 204 Hajitaheri, J. 11, 205 Hall, D. 9, 206 Halley, S. 11, 101 Ham, S.J. 8, 362 Hamilton, D.S. 6, 7, 207, 538 Hamilton, T.W. 3, 167 Hamlyn, P.R. 13, 209, 300 Hancock, M.C. 14, 17, 210, 211 Hancock, S.J. 4, 28, 213 Hann, J.M. 2, 215 Hart, M.K.W. 5, 192 Hartley, J.S. 17, 216 Harvey, K.J. 17, 218 Harwood, R.C. 3, 151 Hatcher, M. 17, 219 Hatherly, P.J. 7, 221 Havord, P. 23, 221 Haynes, D.W. 12, 223 Hazeldene, R.K. 4, 224 Hedges, M.M. 14, 226

Heidecker, E.J. 22, 228 Heinrich, C.A. 11, 36, 229 Hellsten, K.J. 11, 101 Hendry, D.A.F. 12, 231 Henley, R.W. 12, 232 Henry, R.L. 6, 542 Hensen, B.J. 19, 235 Henstridge, D.A. 8, 237 Herbert, C. 23, 221 Hiern, M.N. 2, 239 Hill, M.B.L. 6, 538 Hill, R.E.T. 1, 13, 129, 240 Higgins, N.C. 11, 101 Hilyard, D. 15, 242 Hing, T.T. 12, 316 Ho, S.E. 12, 244 Hochman, M.B.M. 10, 245 Hocking, B. 28 Hodgins, R. 22, 565 Hofmann, G.W. 2, 23, 246, 247' Holdgat'e, G.R. 5, 248 Holland, H.D. 3 Hollis, J.D. 1, 19, 250, 503, 516 Holloway, J.R. 12, 545 Holt, G.E. 7, 221 Honey, F.R. 9, 252, 562 Hopwood, T. 10, 27, 253 Horsfall, C. 9, 270 Hossain, A. 28, 254 Houseman, G. 24, 26, 255, 257 Howard, P.F. 28, 259 Hudson, D.R. 13, 261 Hughes, F.E. 17, 40 Hungerford, F. 7, 555 Hunt, F.L. 10, 450 Hunt, J.W. 5, 7, 23, 221, 262, 264, 266 Hunt, P.A. 3, 268 Huntington, J.F. 9, 195, 270 Hutton, A.C. 9, 271 Ireland, T.R. 20, 273 Ivanac, J.F. 8, 237 Jackson, I. 25, 275, 463 Jackson, K.S. 6, 277 Jackson, P.G. 11, 277 Jacobson, G. 4, 28, 278, 280 Jaques, A.L. 25, 26, 310, 401 Jeffries, F.S. 5, 282 Jenkins, C.J. 16, 283 Johnson, I.F. 4, 283 Johnson, K.T.M. 26, 443 Johnson, R.W. 19, 28, 285, 442 Johnston, J.D. 10, 14, 285, 311 Johnston, R. 23, 287 Jones, C.J. 8, 288 Joyce, E.B. 21, 289 Kamp, P.J.J. 24, 291

Karner, G.D. 24, 25, 291, 293 Katz, H.R. 5, 294 Katz, M.B. 27, 297 Keays, R.R. 13, 18, 209, 299, 300 Kelvin, N.V.P. 7, 302 Kemezys, K.J. 22, 304 Kendarsi, Roeslan 28, 305 Khoo, T.T. 28, 306 Kidd, C.H. 4, 307 Killick, C.L.A. 23, 307 Kim, B.K. 28, 309 Klipfel, P.D. 9, 206 Klootwijk, C.T. 26, 309 Knutson, J. 10, 25, 310, 322 Korth, J. 9, 271 Koul, S. 14, 311 Kreutzer, E. 2, 313 Kuehner, S.M. 19, 314 Kwak, T.A.P. 11, 12, 14, 29, 30 277, 316, 317, 545 Laing, W.P. 13, 318 Lalor, J.H. 17, 321 Lambeck, K. 22, 24, 322, 378, 496 Lambert, I.B. 10, 12, 13, 165, 322, 323 Lancucki, C.J. 22, 100, 479 Langevad, E.J. 27, 324 Large, R.R. 17, 326 Layering, I.H. 23, 327 Lawrence, L.J. 13, 328 Lee Kim Woon, see Woon Lees, B.G. 2, 23, 329, 330 Letz, H. 26, 332 Lewis, R.W. 17, 562 Leyh, W.R. 10, 332 Lindner, A.W. 8, 237 Lishmund S.R. 1, 334 Lock, J. 26, 336 Loftus-Hills, G.D. 17, 199 Logan, R.G. 13, 339 Long, J.V.P. 12, 231 Lord, J.R. 17, 340 Loughnan, F.C. 2, 342 Lovering, J.F. 27 Ludwig, K.R. 19, 343 Lupton, J. 3, 94 MacQueen, R.W. 13 MacKay, G. 5, 248 MacKinnon, I.D.R. 20, 343 MacLennan, M. 11, 345 Madre, D.A. 8, 347 Mallett, C.W. 6, 7, 349, 350 Mailing, S.T. 28, 351 Mandelson, J. 8, 352 Manickam, S. 16, 353 Mann, A.W. 10, 355 Marshall, B. 11, 122 573

Martin, D.J. 15, 355 Martin, H.A. 16, 357 Martin, K.R. 5, 358 Martin, M.W. 4, 359 Mathew, P.J. 9, 360 Mathews, R.T. 8, 362 Matthews, W.E. 17, 363 May, E.R. 13, 153 McAlpine, J.R. 28, 364 McCulloch, M.T. 26, 368, 401 McDivitt, J.F. 27, 365 McDonald, I. 6 , 538 McDonnell, K.L. 23, 367 McDonough, W.F. 26, 368 McDougall, I. 16, 371 McGee, W.A. 21, 372 McHaffie, I.W. 2 , 373 McKavanagh, B . 7 , 555 McKay, W.J. 4 , 224 McKenzie, K.G. 16, 374 McKirdy, D.M. 6, 277, 375, 542 McLeod, R.L. 10, 376 McMinn, A . 7, 264 McPhie, J . 15, 377 McQueen, H.W.S. 24, 378 McQueen, K.G. 4, 13, 18, 283, 379, 380, 441 Michael-Leiba, M.O. 26, 381 Middleton, M.F. 5, 24, 382 Mikucki, E.J. 19, 383 Miles, J.G. 9, 360 Minty, B.R. 9, 398 Moelle, K.H.R. 23, 384 Moffitt, R.S. 6 , 538 Moon, K.J. 12, 386 Mooney, B.A. 6, 375 Morris, P.A. 19, 20, 181, 387 Morrison, G.W. 11, 388 Morton, W.H. 28 Muirhead, K.J. 25, 389 Mumme, I.A. 24, 389 Murphy, G. 13, 165 Murray, A.S. 25, 541 Murray, C.G. 21, 391 Murrell, B . 15, 394 Mustard, H . 18, 394 Mutton, B.K. 14, 396 Naschwitz, W . 14, 396 Nash, C.R. 9 , 21, 397, 398 Neall, F.B. 12, 323, 400 Nelson, D.R. 26, 401 Nesbitt, R.W. 13, 318 Nethery, J.E. 18, 111 Neudert, M . 13, 402 Newnham, L.A. 17, 404 Nichol, D . 2, 147, 313 Nichol, S . 4 , 469 Nicholls, I.A. 19, 20, 155 574

Nielsen, R.L. 18, 408 Nienaber, W . 24, 145 Niesler, H . 25, 275 Nisbet, B.W. 12, 409 Nolan, R . 6 , 410 Norman, A.R. 15, 79 Noon, T.A. 8, 411 Nutalaya, P . 28, 413 Oakes, G.M. 1, 334 O'Brien, P.E. 23, 24, 414, 415, 541 0'Dea, T.R. 8 , 237 Offler, R . 11, 13, 44, 45 Okada, H . 16, 353 Oliver, R.L. 15, 416 Olliver, J.G. 1, 2, 55, 178, 417 0'Neil, J.R. 19, 478 O'Neill, D . 9 , 206 O'Reilly, S.Y. 25, 26, 310, 418 Orth, K. 15, 419 Ostwald, J . 20, 420 Ozimic, S . 8 , 421 Palmer, I.D. 6 , 423 Palmieri, V . 16 Parker, A.J. 21, 424 Parkinson, W.D. 24, 145 Parks, T.C. 16, 425, 426 Paterson, M.S. 25, 275, 427 Paterson, R.G. 11, 154 Patterson, J.H. 9 , 128 Pearson, J.M. 14 Pearson, N.J. 18, 197, 429 Pecover, S.R. 2, 430 Penney, C . 24, 322 Phillips, G.N. 12, 323, 400 Picard, M.D. 8 , 432 Pidgeon, R.T. 14, 56 Pinczewski, W.V. 5, 435 Plimer, I.R. 13, 436 Plumb, K.A. 6 , 505 Plummer, G.J. 11, 317 Polach, H . 16, 97 Polya, D.A. 14, 437 Potter, T . 18, 380 Powell, C . McA. 23, 438 Powell, T . G . 5, 6 , 13, 440, 441 Prendergast, E.I. 23, 438 Price, R.C. 11, 19, 26, 30, 442, 443 Qureshi, I.R. 22, 24, 74, 444 Rahmani, R.A. 6 , 446 Ramsay, C.R. 12, 447 Ramsay, W.R.H. 21, 449 Ramsden, A.R. 9 , 128, 139 Ransom, D.M. 10, 450 Rathur, A.W. 28, 452

Raynor, L.R. 15, 453 Read, H. 7, 202 Redann, P.J. 8, 453 Reed, S.J.B. 12, 231 Relph, R.E. 21, 455 Richards, J.A. 9, 456 Richmond, R.N. 28, 457 Rixon, L.K. 7, 459 Robinson, M.J. 7, 459 Robinson, V.N.E. 20, 461 Rodda, P. 16, 371 Rodgers, J.M. 12, 462 Royce, K. 23, 221 Rudnick, R.L. 25, 463 Rugless, C.S. 10, 465 Russell, D.W. 10, 245 Russell, N.J. 7, 466 Russell, T.G. 4, 468 Russell, W.J. 4, 469 Rust, B.R. 23, 469 Rutland, R.W.R. 27, 471 Ruxton, B.P. 15, 472 Ryall, A.W. 13 Ryan, C.G. 20, 484 Rynn, J.M.W. 22, 228 Sangameshwar, S. 11, 122 Sant, M. 27 Sappal, K.K. 28, 473 Sawiuk, M.J. 14, 557 Sawka, W.N. 19, 474 Saxby, J.D. 8, 421 Scheibner, E. 21, 134 Scherl, A.S. 24, 164, 291 Schrale, G. 4, 492 Scott, S.D. 12, 517 Seccombe, P.K. 11, 13, 44, 45 Seedsman, R.W. 7, 475 Senapati, N. 23, 475 Shafik, S. 16, 477 Sharp, K.R. 28 Shaw, S.E. 19, 478 Shayan, A. 22, 479 Shelly, J.M.G. 16, 95 Shepherd, J. 7, 459 Shettigar, K.V. 3, 479 Shiels, 0. 6, 124 Shugg, A. 4, 481 Sie, S.H. 20, 483, 484 Siemon, J.E. 2, 486 Silver, E.A. 26, 487, 488 Sinton, J.M. 26, 443 Skey, E.H. 17, 489 Skinner, B.J. 13, 27, 491 Smith, C.B. 17, 40 Smith, G.C. 5, 248 Smith, I.E.M. 19, 491 Smith, K.L. 15, 159 Smith, P.C. 4, 492

Smith, V. 2, 493 Smyth, M. 7, 264 Sneeringer, M.R. 19, 443 Solomon, M. 11, 12, 14, 101, 205, 386, 437 Southgate, P.N. 6, 542 Sowerby, B.D. 9, 494 Stanton, R.L. 20 Stegman, C.L. 11, 494 Stephenson, R.S. 22, 496 Stevens, B.P.J. 22, 496 Steveson, B.G. 5, 498 Stewart, I.E. 2, 500 Stokes, R.A. 4, 359 Stone, I.J. 7, 502 Stuart-Smith, P.G. 5, 24, 163, 164 Summons, R.E. 6, 542 Sun, S.S. 13, 318 Suppel, D.W. 21, 134 Sutherland, F.L. 1, 19, 503, 516 Sweet, I.P. 6, 505 Symonds, P.A. 5, 24, 506, 508 Tadros, V.Z. 6, 538 Tapley, I.J. 9, 562 Tassell, G.W. 9, 41 Taube, A. 10, 376, 510 Taylor, D. 28, 511 Taylor, G. 16, 512 Taylor, G.H. 27 Taylor, G.R. 10, 513 Taylor, J.R. 12, 514 Taylor, S.R. 25, 463 Taylor, W.R. 19, 515 Temby, P.A. 1, 516 Theron, A.C. 9, 398 Thomas, M.J. 10, 561 Thompson, A.B.J. 12, 517 Thompson, J.G. 8, 518 Tiffin, D.L. 26, 523 Timms, P.D. 17, 363 Todd, R. 16, 371 Todd, V.R. 19, 478 Tomich, S.A. 10, 519 Torgersen, T. 16, 97 Towner, R. 2, 147 Turner, J.S. 8, 520 Tyrwhitt, D.S. 17, 521 Vaasjoki, M. 13, 522 VandenBerg, A.H.M. 21, 449 Vanderspuy, P.M. 9, 206 van Moort, J.C. 1, 10, 14, 245, 396, 570 Varne, R. 19, 523, 544 Vedder, J.G. 26, 523 Vincent, P.W. 4, 524 Voisey, A.H. 17, 21, 526, 528

575

Walker, D.A. 15, 90 Wall, V.J. 5, 10, 11, 12, 14, 19, 64, 66, 101, 145, 155, 226, 285, 311, 383, 514, 529 Wallace, D.B. 14, 547 Wallace, I. 2, 531 Walshe, J.L. 12, 14, 437, 462, 532 Walter, M.R. 6, 86, 534 Waltho, A. 7, 536 Warbrooke, P.R. 7, 534 Ward, C.R. 7, 536 Ward, H.J. 8, 538 Warren, R.6. 19, 235 Watson, B.L. 6, 375 Webb, S.L. 25, 275 Weber, C.R. 6, 538 Webster, J.G. 9, 539 Webster, S.S. 22, 540 Weissel, J.K. 25, 293 Wellman, P. 25, 541 Wells, A.T. 23, 415, 541 Weste, G. 6, 542 Wheller, G.E. 19, 544 White, A.J.R. 11, 12, 14, 15, 20, 30, 105, 545 Whitford, D.J. 14, 59, 547 Wlckremaratne, S.N. 28, 142 Wilcoxon, J.A. 16, 371 Wild, E.K. 4, 553

576

Wilde, S.A. 14, 56 Wilkins, R.W.T. 12, 20, 549, 550 Willcox, J.B. 5, 551 Williams, B.P.J. 4, 552, 553 Williams, E. 21, 103 Williams, I.S. 20, 553 Williams, K.L. 15, 79 Williams, N. 13, 339 Williams, R.J. 7, 555 Williams, R.M. 3, 556, 566 Williams-Jones, A.E. 14, 557 Wilmshurst, J.R. 9, 558 Wilson, A.F. 10, 18, 559, 561 Wilson, C.J.L. 16, 170 Wilson, C.J.N. 19, 491 Wilson, G.I. 17, 562 Wilson, P. 9, 252, 562 Windrim, D.P. 15, 90 Withnall, I.W. 18, 44 Witt, W.K. 11, 564 Won, G.W. 22, 565 Woods, J. 6, 7, 349, 350 Wooley, D.R. 3, 566 Woon, Lee Kim, 28, 567 Wright, J.H. 11 Wright, J.V. 15, 419, 568 Yim, W.W.S.

1, 16, 570