Abstract 32 - 11th AGC Earth Sciences Computers & the Environment Ballarat Uni Jan 1992

Geological Society of Australia

ABSTRACTS Number 32 ELEVENTH

AUSTRALIAN

GEOLOGICAL

EARTH SCIENCES COMPUTERS AND T

_

T H E ENVIRONMENT

BALLARAT UNIVERSITY COLLEGE JANUARY 18-251992

"The committee would like to acknowledge the generosity of APPM, who donated the paper for this volume."

Geological Society of Australia

ABSTRACTS Number 32

EARTH SCIENCES, COMPUTERS AND THE ENVIRONMENT

ELEVENTH AUSTRALIAN GEOLOGICAL CONVENTION JANUARY 18-25, 1992 BALLARAT UNIVERSITY COLLEGE

Example citation for paper in this volume: Carey, S.W. 1992. Pangaea, the Pacific, and Cosmology. Geol. Soc. Aust. Abstracts v32, pi6-20.

Published by the Geological Society of Australia Challis House, 10 Martin Place, Sydney 1992

ISSN 0729-01IX

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Eleventh Australian Geological Convention Ballarat 1992 Organising Committee Dr W.R.H. Ramsay Bloomsbury Convention Services

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Geological Society of Australia ABSTRACTS Number 32

Table of Contents page iii

Session Summary Keynote Papers

Sir Douglas Mawson Lecture Science in Search of Earth's Secrets - Dynamic evolution of the Great Barrier Reef- ODP and Beyond Peter J. Davies International Geological Correlation Program Lecture Mafic Dyke Swarms as a Guide to precambrian Tectonics A.J. Parker

S.W. Carey Symposium

5

Scientific Papers (in program order, followed by posters) A1 A2 A3 A4 A5 A6 A7 A8 A9 A10 All A12 A13 A14 A15 A16 A17 A18

Regional Geology (Lachlan Fold Belt): Tasman Fold Belt-Tectonics, Structural Evolution and Palaeogeography Minerals Exploration and Metallogenesis: Tectonics and Metallogeny: Future Directions for Exploration Economic Geology: Conceptual Thinking in Ore Discovery Geology of Energy Resources: Sequence Stratigraphy, Petroleum and Coal Sedimentology and Volcanology: Surface Processes, Environments and Models- Physical Sedimentology and Physical Volcanology Paleontology: Paleontology: Computers and Other Advances Petrology: Igneous Pterogenesis in the SW Pacific and Eastern Australia Structural Geology: Shear Zones, Sutures and Fold Belts Engineering Geology Hydrogeology Environmental Geology Geophysics: Imaging the Earth and its Resources Remote Sensing Computers in Geology: Geological Databases: Geological Database Management for Sustainable Development History of Geological Sciences: Old Mines, Old Data, Old Ideas: What Future? Geological Education: Earth Sciences, the Community and the Environment Economic Geology-Corporate

21 39 49 103 133 171 185 223 249 255 271 283 303 313 325 333 339 357

Author Index

359

Subject Index

365

ii

iii

| SIR DOUGLAS MAWSON LECTURE

T

SCIENCE IN SEARCH OF EARTH'S SECRETS - DYNAMIC EVOLUTION OF THE GREAT BARRIER REEF- ODP AND BEYOND Peter J. Davies

INTERNATIONAL GEOLOGICAL CORRELATION PROGRAM LECTURE

3

MAFIC DYKE SWARMS AS A GUIDE TO PRECAMBRIAN TECTONICS A.J. Parker

S.W. CAREY SYMPOSIUM

5

CONVENOR: GORDON LISTER C 1 C2 C3 C4 C5 C6 C7 C8 C9

GLOBAL VISION: S.W. CAREY AND THEORIES OF THE EARTH H.E. Le Grand MOUNTAIN BUILDING Peter Molnar EXTENSION CONTEMPORANEOUS WITH SHORTENING WITHIN MOUNTAIN BELTS B. C. Burchfiel THE BENDING OF OROGENIC BELTS Ian W. D. Dalziel THE ORIGIN AND EVOLUTION OF MOUNTAIN BELTS J.F. Dewey THE ORIGIN AND EVOLUTION OF-SEDIMENTARY BASINS A. R. Green, S. R. May T. S. Loutit SEISMOGENIC CRUST R.H. Sibson THE ROLE OF STRUCTURAL GEOLOGY IN THE ANALYSIS OF TECTONIC PROCESSES John G. Ramsay PANGAEA, THE PACIFIC, AND COSMOLOGY S. Warren Carey

A 1: REGIONAL GEOLOGY (LACHLAN FOLD BELT)

21

CONVENOR: A.H.M VANDENBERG A 1.1

A 1.2 A 1.3 A 1.4

KEYNOTE: ACCRETION OF AUTOCHTHONOUS TERRANES :THE KEY TO THE TECTONIC DEVELOPMENT OF THE LACHLAN OROGEN AND TO ITS MAJOR GOLD DEPOSITS R.A.Glen, E.Scheibner and A.H.M Vandenberg GEOLOGY OF THE REEDY CREEK AREA, NORTHEASTERN VICTORIA. J. W. Bradley and L. H. Thorne GEOLOGY OF THE BEAUFORT REGION, WESTERN VICTORIA ASPECTS OF THE DEPOSITIONAL AND STRUCTURAL STYLE OF THE EASTERN STAWELL ZONE. Ross A. Cayley THE LACHLAN FOLD BELT OF SOUTHEASTERN AUSTRALIA: INTRAPLATE DEFORMATION IN A CONVERGENT OROGENIC SYSTEM Peter J. Coney and Christopher L. Fergusson

iv

A 1.5 A 1.6 A 1.7 A 1.8 A 1.9 A1.10

A 1.11 A 1.12 A 1.13 A 1.14 A 1.15 A 1.16 A 1.17

EARLY TO MIDDLE CAMBRIAN GEOCHEMISTRY AND TECTONICS OF NORTHWESTERN N.S.W. B.PJ. Stevens and AJ. Crawford HUNTER-BOWEN OROGENY: LATE PERMIAN-TRIASSIC DEFORMATION OF THE LATE PALAEOZOIC ACCRETIONARY PLATE MARGIN OF EASTERN GONDWANA R.A. Henderson, C.L. Fergusson and E Leitch PRELIMINARY GEOLOGICAL RESULTS FROM DEEP SEISMIC REFLECTION PROFILING IN THE GUNNEDAH BASIN AND NEW ENGLAND OROGEN R J . Korsch, K.D. Wake-Dyster and D.W. Johnstone ANOMALOUS NORTHEAST-TRENDING FOLD-THRUST BELT IN THE NORTHERN NEW ENGLAND OROGEN E.C. Leiteh, C.L. Fergusson, R.A. Henderson- and V.J. Morand THE TASMANIAN PRECAMBRIAN AND BASEMENT INVOLVED THRUSTING D.E. Leaman TECTONIC AND THERMAL HISTORIES OF THE BALLARAT AND STAWELL ZONES CENTRAL W VIC: RESULTS OF ILLITE CRYSTALLINITY AND BO PARAMETER STUDIES. S.W. McKnight and R. Offler MELBOURNE TROUGH PALAEOCURRENTS AND TECTONIC IMPLICATIONS C. McA. Powell, P.W. Baillie and A.H.M. VandenBerg THE RIFT IN NORTHERN KENYA -VOLCANO-TECTONIC INTERPRETATION B.D.Hackman, T.J.Charsley, R.M.Key and A.F.Wilkinson THE SERPENTINITE BELTS OF SOUTHERN NEW SOUTH WALES - SLICES OF PALAEOZOIC UPPER MANTLE? Brenda J. Franklin, Ian T. Graham and Brian Marshall THE EXTENT AND SIGNIFICANCE OF THE EARLY CAMBRIAN TRURO VOLCANICS C G Gatehouse, J B Jago, L R Rankin, B J Clough, D I Gravestock and A J McCulloch CAMBRIAN GREENSTONES ON PHILLIP ISLAND VICTORIA D. A. Henry and W. D. Birch DEVELOPMENT OF THE LOWER DEVONIAN BUCHAN RIFT K. Orth and A.H.M. VandenBerg POLYMICTIC CONGLOMERATES OF THE FRAMPTON VOLCANICS: PRE-BENAMBRAN VOLCANIC ARC DERIVATIVES OR THE PRODUCTS OF POST-BENAMBRAN UPLIFT? C.G.Skilbeck, E.Frankel, K.Dadd, and E.CLeitch

POSTERS A 1.18 A 1.19

THE 1991 BMR DEEP SEISMIC REFLECTION PROFILE IN NORTHERN NEW SOUTH WALES K.D. Wake-Dyster, D.W. Johnstone and R.J. Korsch THE STRUCTURAL DEFORMATION OF PALAEOZOIC ROCKS IN THE WESTERN STAWELL ZONE VICTORIA. Julia Caluzzi

A2: MINERALS EXPLORATION AND METALLOGENESIS

39

CONVENORS: CEC MURRAY AND ERWIN SCHEIBNER A 2.1

A 2.2

ACTIVE BASE METAL SULPHIDE DEPOSITION IN THE MANUS BACK-ARC BASIN BISMARCK SEA, PAPUA NEW GUINEA. F. Vanderhor, K.A.W. Crook, A.P. Lisitsyn , L.P. Zonenshain, Yu.A. Bogdanov, K. Muravev, and M.E., Fellows KEYNOTE: GOLD MINERALIZATION IN SEAFLOOR BACK-ARC SPREADING CENTRES OF THE WESTERN PACIFIC Peter M. Herzig and Mark D. Hannington

V

A 2.3

A 2.4 A 2.5

A 2.6

A 2.7 A 2.8 A 2.9

A 2.10

DISCOVERY OF ACTIVE HYDROTHERMAL SULFIDE DEPOSITION ASSOCIATED WITH SUBMARINE FELSIC VOLCANISM, PUAL RIDGE, EASTERN MANUS BASIN, PAPUA NEW GUINEA R.A. Binns S.D. Scott and PACMANUS Participants LINKING TECTONICS METALLOGENESIS AND MINERAL EXPLORATION Michael Solomon DEEP SEISMIC OF THE COBAR BASIN-I: STRUCTURE AND IMPLICATIONS FOR MINERAL PROSPECTIVITY R.A. Glen, B J . Drummond, B.R. Goleby, D. Palmer and K.D. Wake-Dyster DEEP SEISMIC OF THE COBAR BASIN-II: A RAMP BASIN CONTROLLED BY A MID CRUSTAL DETACHMENT. B J . Drummond, R.A. Glen, B.R. Goleby, K.D. Wake-Dyster and D. Palmer GOLD METALLOGENY FOR THE LATE PALEOZOIC OF NORTH QUEENSLAND Gregg W. Morrison, Nicholas M. Tate and Heather J. Johns METALLOGENESIS RELATED TO LONG TERM TRENDS IN GLOBAL TECTONICS M.E. Barley and D Groves SEAFLOOR ACOUSTIC FACDES CONTEXT OF THE EASTERN MANUS BASIN HYDROTHERMAL SYSTEMS Melissa E. Fellows and Keith A. W. Crook A POSSIBLE CONNECTION BETWEEN MANTLE PLUMES AND METALLOGENY Ian H. Campbell and Robert I. Hill

A3: ECONOMIC GEOLOGY

49

CONVENOR: PHILLIP SECCOMBE A 3.1 A 3.2

A 3.3

A 3.4 A 3.5 A 3.6 A 3.7

A38

A 3.9

A 3.10

A 3.11 A 3.12 A 3 13

KEYNOTE: EMPIRICISM AND CONCEPT IN SUCCESSFUL MINERAL EXPLORATION Roy Woodall THE EVOLUTION OF A NEW CONCEPT IN AN OLD AREA THE KANOWNA BELLE CASE HISTORY Kim Stanton-Cook THE WHITE DEVIL GOLD DEPOSIT TENNANT CREEK : RECOGNISE THE CLUES IN YOUR OWN BACKYARD! Paul Hunter and Bruce D. Kay GEOLOGY OF THE PLUTONIC GOLD DEPOSIT WESTERN AUSTRALIA M Rowley THE CENTURY ZINC DEPOSIT, NORTH WEST QUEENSLAND John Main MINERALOGY OF THE CENTURY DEPOSIT, NORTH QUEENSLAND S. W. McKnight THE OSBORNE DEPOSIT: A DISCOVERY WHERE "ORE MODEL" DOGMA AND PERSISTENCE PAID OFF Tim Jauristo ORE GENESIS AND EXPLORATION MODELS FOR PLATINUM-GROUP ELEMENT MINERALIZATION IN LAYERED MAFIC/ULTRAMAFIC INTRUSIONS Reid R. Keays- Paul R. Hamlyn and Shane J. Reeves USE OF CONCEPTUAL MODELS FOR GOLD EXPLORATION IN NORTH QUEENSLAND - A DECADE OF RECOGNITION AND DISCOVERY Gregg W. Morrison THE GEOLOGICAL SETTING OF THE GOLDEN PLATEAU MINE CRACOW CENTRAL QUEENSLAND, AUSTRALIA Miles R. Worsley , Subhash Jaireth Gregg Morrison THE GOONUMBLA PORPHYRY CU/AU DEPOSIT, NSW Paul Heithersay, G.J.GEOLOGY Jones and J.C. DISCOVERY AND OF Walshe THE LAKE COWAL NSW GOLD DEPOSIT MLove SYNCHRONOUS DEFORMATION, ALTERATION AND AU-MINERALISATION IN THE TEMORA SHEAR ZONE HOSTED ADVANCED ARGILLIC SYSTEM A.H. Allibone

A 3.14 A 3.15 A 3.16 A 3.17 A 3.18 A 3.19 A 3.20 A 3.21 A 3.22

A 3.23 A 3.24

A 3.25 A 3.26 A 3.27 A 3.28 A 3.29

A 3.30 A 3.31 A 3.32 A 3.33

EVAPORITES AND BROKEN HILL -NEW CONCEPTS IN AN OLD AREA Ian R. Plimer SODIUM BICARBONATE-RICH BRINES DENISON TROUGH: POTENTIAL ORE FLUIDS? Hugh K. Herbert and H. Roy Krouse MOBILIZATION OF THE PLATINUM GROUP ELEMENTS BY LOW TEMPERATURE FLUIDS: IMPLICATIONS FOR MINERALIZATION IN RED BED ENVIRONMENTS Reid R. Keays, Malcolm W. Wallace and Victor A. Gostin STRESS MAPPING - THE CALCULATION OF STRESS FIELDS DURING DEFORMATION AND THE PREDICTION OF SITES OF HYDROTHERMAL FLUID FLOW. John Ridley AN INVESTIGATION OF MINOR SULPHIDE OCCURRENCES IN THE LOWER DEVONIAN BUCHAN CAVES LIMESTONE VICTORIA D. C. Arne, P. Cromie, J. A. Webb and J. R. Richards THE WOODCUTTERS PB-ZN OREBODIES: DEFORMED EPIGENETIC MINERALIZATION, N.T. AUSTRALIA Serge Smolonogov and Brian Marshall EXHALITES ASSOCIATED WITH BROKEN HILLTYPE MINERALISATION: GENETIC IMPLICATIONS AND EXPLORATION POTENTIAL. J.M. Parr THE STRUCTURAL CONTROLS ON MINERALISATION AT RENISON TIN MINE WESTERN TASMANIA. Paul A. Kitto and Ron F. Berry THE ORIGIN OF BRECCIA-HOSTED URANIUM DEPOSITS IN CARBONACEOUS METASEDIMENTS OF THE IBERIAN PENINSULA: STABLE ISOTOPE STUDIES OF THE FE DEPOSIT, SALAMANCA PROVINCE, SPAIN R. A. Both and A. Arribas A FLUID INCLUSION STUDY OF MINERALIZATION AT CORONATION HILL NORTHERN TERRITORY, AUSTRALIA. T.P. Mernagh, J.F. Leckie, D.P. Carville, R.K. Valenta, and L.A Wyborn HYDROTHERMAL DEPOSITS OF FRANKLIN SEAMOUNT, WESTERN WOODLARK BASIN, PAPUA NEW GUINEA R.A. Binns, G.E. Wheller, S.D. Scott, Yu.A. Bogdanov, A.P. Lisitsin and SUPACLARK Participants CONDITIONS OF GOLD MINERALIZATION IN LAU BASIN BACK-ARC SULFIDES P.M. Herzig, M.D. Hannington, Y. Fouquet, U. von Stackelberg and S. Petersen THE RELATIONSHIP BETWEEN STRUCTURE, FLUID FLOW PATTERNS AND ORE SHOOTS IN A MESOTHERMAL SHEAR ZONE HOSTED GOLD DEPOSIT J.M.A. Hronsky and J.R. Ridley HYDROTHERMAL ALTERATION AND GEOCHEMISTRY AT THE WAIHIEPITHERMAL AU-AG DEPOSIT, NEW ZEALAND. Keenan Jennings HOST ROCK GEOCHEMISTRY AND ALTERATION IN THE PALAEOZOIC MOUNT AUBREY EPITHERMAL GOLD DEPOSIT, NSW S. Hopf STABLE ISOTOPE EVIDENCE FOR MULTIPLE SOURCES OF COMPONENTS IN LODEGOLD DEPOSITS OF THE EASTERN GOLDFIELDS PROVINCE, WESTERN AUSTRALIA N. J. McNaughton, M. Gebre-Mariam, S. D. Golding, David I. Groves S.G. Hagemann and J.M.A. Hronsky A FLUID INCLUSION STUDY OF AURIFEROUS QUARTZ VEINS- HILL END GOLDFIELD, NSW, AUSTRALIA Jianchun Lu and Philip K. Seccombe ISOTOPE STUDIES FROM THE MILPARINKA-TIBOOBURRA DISTRICT, NW-NEW SOUTH WALES: AGE RELATIONSHIPS AND INDICATIONS FOR THE SOURCE OF GOLD O. A. R. Thalhammer A REGIONAL STUDY OF LATE STAGE GOLD BEARING FLUIDS IN SHEAR ZONES FROM THE BENDIGO FIDDLER'S CREEK AND STAWELL GOLDFIELDS, VICTORIA, AUSTRALIA N. Green, A. Changkakoti and T.A.P. Kwak THE ARCHAEAN LODE-GOLD DEPOSITS AT WILUNA WESTERN AUSTRALIA: EXAMPLES OF FLUID MIXING AT SHALLOW CRUSTAL LEVELS. S.G. Hagemann J.R. Ridley D Groves and N.J. McNaughton

vii

A 3.34

INITIAL LEAD ISOTOPE COMPOSITIONS OF ARCHAEAN LODE GOLD DEPOSITS: A RECORD OF ARCHAEAN CRUSTAL-SCALE HYDROTHERMAL SYSTEMS AND CRATONSCALE SOURCE HETEROGENEITIES Neal J. McNaughton, David I. Groves and Walter K. Witt POSTERS A 3.35 STRUCTURAL CONTROLS, ALTERATION HISTORY AND GENESIS OF ARCHAEAN GOLD DEPOSITS AT CORINTHIA-HOPES HILL NEAR SOUTHERN CROSS, WESTERN AUSTRALIA Erik J.M. Bioem, J.R. Ridley- D Groves, TJ. Jackson and N.M. Edwards A 3.36 GEOCHEMISTRY OF BLACK SLATES AND ITS RELATIONSHIP WITH GOLD MINERALIZATION IN CHEWTON VICTORIA, AUSTRALIA Z. Gao and T.A.P. Kwak A 3.37 EXPLORATION FOR SAPPHIRE IN THE GLEN INNES / INVERELL AREA. P G L Harlow A 3.38 BALLARAT WEST AREA F L Hunt A 3.39 ON THE SEDIMENTATION-REWORKING GENESIS OF SOME STRATIFORM COPPER DEPOSITS Renmin Hua A 3.40 IRON FORMATIONS CHEMICAL SEDIMENTS AND BASE METAL MINERALISATION AT BROKEN HILL NEW SOUTH WALES W.R. Leyh D.F. Larsen and I.D. Oppy A 3.41 THE CHARACTERISTICS OF THE FLUID INCLUSION IN MINEROGENETIC QUARTZFOR SOME TYPES OF GOLD DEPOSITS IN CHINA Li Li, Zheng Chao Yu Zhikai and Mao Dongqing A 3.42 NUGGET FACTOR-GREEN FACTOR IN PLACER GOLD EVALUATION: THE AMERICAS' PERSPECTIVE ON COARSE GOLD TAILS AND FINE GOLD TAILINGS AND AUSTRALIA'S TALES OF GROWTH AND MOBILITY. Michael W.Milner A 3.43 GOLD MINERALISATION IN THE STAWELL ZONE WESTERN VICTORIA: IMPLICATIONS FOR EXPLORATION P.J. O'Shea AND K. Inan A 3.44 REGIONAL GEOPHYSICS OF THE MATHINNA - ALBERTON GOLDFIELD NORTHEAST TASMANIA MJ.Roach A 3.45 PLATINUM-GROUP ELEMENTS IN THE GREAT SERPENTINE BELT OF NEW SOUTH WALES: A PRELIMINARY STUDY K. Yang and P.K. Seccombe

A4: GEOLOGY OF ENERGY RESOURCES CONVENOR: GREG SMITH A 4.1 A 4.2 A 4.3 A44 A 4.5

103~~

KEYNOTE: SEDIMENT SUPPLY, TECTONISM AND SILICICLASTIC DEPOSITIONAL SYSTEMS AND SEQUENCES William E. Galloway LARGE-SCALE SEDIMENT ARRANGEMENTS IN ALLUVIAL BASINS AND SEQUENCE STRATIGRAPHY P.E. O'Brien and A.T. Wells HOW WELL DO THE SEA-LEVEL CURVES COMPARE WITH THE CLIMATE RECORD L. A. Frakes and A. A. Krassay THE APPLICATION OF CARBONATE SEQUENCE STRATIGRAPHY IN A THRUSTFAULTED TERRAIN: STRETCHING THE LIMITS? Thomas Bernecker and John A. Webb SEISMIC IMAGING OF PLEISTOCENE DEEP-SEA CYCLOTHEMS:IMPLICATIONS FOR SEQUENCE STRATIGRAPHY R.M. Carter and L. Carter

viii A 4.6 A 4.7 A 4.8 A 4.9

A 4.10 A 4.11 A 4.12 A 4.13 A 4.14

A 4.15 A 4.16 A 4.17 A 4.18 A 4.19 A 4.20 A 4.21 A 4.22 A 4.23 A 4.24 A 4.25 A 4.26

DEPOSITIONAL SYSTEMS OF TROUGH-FILL, SEAWARD OF THE GREAT BARRIER REEF D. Johnson SEQUENCE STRATIGRAPHY OF THE TERTIARY SUCCESSION IN THE PORT CAMPBELL EMBAYMENT OF THE OTWAY BASIN VICTORIA. P.A. Arditto LITHO-STRATIGRAPHY AND SEQUENCE STRATIGRAPHY OF A MID-CRETACEOUS SHELF ENVIRONMENT IN THE GULF OF CARPENTARIA A.A. Krassay and L.A. Frakes SEQUENCE STRATIGRAPHIC ANALYSIS OF THE PERMIAN SUCCESSION IN THE WESTERN BOWEN BASIN QUEENSLAND IMPLICATIONS FOR HYDROCARBON EXPLORATION V. Ziolkowski, C.R. Fielding' M. Wilkinson and J.J. Draper SEQUENCE STRATIGRAPHY OF PERMIAN SILICICLASTICS IN THE FITZROY TROUGH CANNING BASIN WESTERN AUSTRALIA P.E. O'Brien J.F. Lindsay MJ. Jackson J.M. Kennard P.N. Southgate and MJ. Sexton A NEW STRATIGRAPHY FOR THE ILLAWARRA COAL MEASURES, SOUTHERN SYDNEY BASIN A C Hutton, W J Bamberry and B G Jones EARLY DEVONIAN SEQUENCE STRATIGRAPHY FROM BUCHAN AND BINDI EASTERN VICTORIA John A. Webb LATE DEVONIAN REEFS OF THE CANNING BASIN: A SUBSURFACE SEQUENCE STRATIGRAPHIC PERSPECTIVE P.N. Southgate , J.M. Kennard M.J. Jackson P.E. O'Brien J.F. Lindsay and MJ. Sexton. FACIES ANALYSIS OF PERMIAN MARINE SHELF DELTAIC AND COASTAL PLAIN DEPOSITS IN THE WESTERN BOWEN BASIN QUEENSLAND IMPLICATIONS FOR RESERVOIR DESCRIPTION Christopher R. Fielding BROWN COALS AND RESERVOIR SANDS: RESPONSES TO RELATIVE SEA LEVEL CHANGES AND TERTIARY COASTAL ONLAP, GIPPSLAND BASIN. G.R. Holdgate RELATIONSHIP OF COAL FACIES WITH SEA LEVEL IN THE BASS BASIN Peter Baillie CORRELATION OF THE ILLAWARRA COAL MEASURES, SOUTHERN AND WESTERN COALFIELDS, SYDNEY BASIN A C Hutton COAL COMPOSITION AND SEQUENCE STRATIGRAPHY Claus F. K. Diessel TECTONICS AND SEDIMENTATION IN THE MAE MOH COAL BASIN, NORTHERN THAILAND Colin R. Ward and P.R. Evans THE SEQUENCE ASSOCIATED WITH THE ALBIAN MAXIMUM FLOODING SURFACE IN AUSTRALIA, OR THE GREAT ANTEDILUVIAL FLOOD G.C. Smith, B.E. Messent and R.A. Henderson PRECISE RESERVOIR GEOMETRY MODELLING K R Johnson SEDIMENTOLOGICAL ANALYSIS CAN EXPLAIN THE EVAPORITE/HYDROCARBON ASSOCIATION John K Warren STOCHASTIC MODELLING OF SEDIMENTATION SYSTEMS: SOME IMPLICATIONS FOR SUBSURFACE GEOLOGY John C. Tipper BASIN ANALYSIS: A HIDDEN DILEMMA Mike F. Middleton THERMAL MATURATION MODELLING: A SCIENCE, AN ART OR A CRAFT? N. J. Russell PARAMETERS OF TIME AND HEAT IN ORGANIC MATURATION: A CASE STUDY FROM THE BUCHAN LIMESTONE C.E. Barker, Y. Bone, and C.R Dalgarno

ix

A 4.27 A 4.28 A 4.29 A 4.30 A 4.31 A 4.32 A 4.33

RODDA BEDS EASTERN OFFICER BASIN: ANATOMY OF A LEAN NEOPROTEROZOIC PETROLEUM SOURCE ROCK David M. McKirdy, Stephen D. Pell and Michelle Smyth SEQUENCE STRATIGRAPHY OF A COAL SEAM Michelle Smyth and Michael Buckley PETROLOGY AND PALYNOLOGY OF CATTAMARRA COAL PERTH BASIN WESTERN AUSTRALIA K. K. Sappal and A. Islam PETROLOGY AND GEOCHEMISTRY OF TERTIARY COALS IN WEST ACEH BASIN SUMATRA, INDONESIA Hadiyanto, A Hutton and C J. Boreham ORGANIC PETROLOGY OF PERMIAN COAL VASSE SHELF PERTH BASIN WESTERN ASUTRALIA. B. Santoso and K.K. Sappal ORGANIC PETROLOGY OF HILL RIVER COAL PERTH BASIN WESTERN AUSTRALIA N. Suwarna and K.K. Sappal PALAEOGEOGRAPHY AND SEQUENCE STRATIGRAPHY J. Bradshaw, M.T. Bradshaw, J.E. Blevin, G.E. Wilford and R.P.Langford

A5: SEDIMENTOLOGY AND VOLCANOLOGY CONVENOR: R.A.F. CAS

A 5.1 A 5.2 A 5.3 A 5.4 A 5.5 A 5.6 A 5.7 A 5.8 A 5.9 A 5.10 A 5.11

13 3

VOLCANICLASTIC MEGATURBIDITES IN DEEP MARINE BASINS -THE LATERAL EQUIVALENTS OF SUB AERIAL IGNIMBRITES? EXAMPLES FROM THE PALEOZOIC OF SOUTHEASTERN AUSTRALIA. R.A.F. Cas, R.L. Allen and D. Hutton SUB-VOLCANIC FACIES ANALYSIS WITHIN AN INTRUSIVE BRECCIA AND IGNEOUS COMPLEX (HOSTING THE MT. LEYSHON GOLD MINE NE QLD.). P.J. Wormald DEPOSITIONAL CONTROLS AND CHARACTERISTICS OF SUBAQUEOUS BEDDED VOLCANICLASTICS OF THE LOWER DEVONIAN SNOWY RIVER VOLCANICS. Stuart W. Bull and R. A. F. Cas THE PASSAGE OF A SUB AERIAL PYROCLASTIC FLOW INTO WATER: A PROTEROZOIC EXAMPLE FROM THE PINE CREEK INLIER N.T. Elizabeth A. Jagodzinski and Ray A.F. Cas LATERAL VARIATIONS IN A MIDDLE SILURIAN VOLCANICLASTIC APRON: THE INIER-RELATIONSHIP OF THE GOOBARRAGANDRA VOLCANICS AND THE BLOWERING FORMATION OF SOUTHEASTERN N.S.W. K. A. Dadd KEYNOTE: FACIES ANALYSIS IN SUBMARINE VOLCANIC SEQUENCES: LESSONS BEING LEARNT IN THE MOUNT READ VOLCANICS CAMBRIAN, WESTERN TASMANIA J. McPhie INTERACTION BETWEEN VOLCANISM AND SEDIMENTATION IN THE SILURO-DEVONIAN WOLLONDILLY BASIN C. J. Simpson ERUPTIVE DRAINAGE STRUCTURES WITH IN SITU BOULDER MILLING A MODEL FOR LOCAL DERIVATION OF CERTAIN CONGLOMERATES PROVIDED BY TOOMBA FLOW QLD. E.J. Heidecker KEYNOTE: RECENT DEVELOPMENTS IN CLASTIC SEDIMENTARY FACIES ANALYSIS Christopher R. Fielding FLUVIAL ARCHITECTURE AND SEDIMENTOLOGY OF THE LATE JURASSIC-EARLY CRETACEOUS STRZELECKI AND OTWAY GROUPS. Andrew Constantine VOLCANICLASTIC LACUSTRINE FACIES OF THE LATE DEVONIAN ROCKFIELDS MEMBER BROKEN RIVER PROVINCE NORTH QUEENSLAND Simon C. Lang and Christopher R. Fielding

X

A 5.12 A 5.13 A 5.14 A 5.15 A 5.16

A 5.17 A 5.18

A 5.19 A 5.20 A 5.21 A 5.22 A 5.23 A 5.24

A 5.25

CONGLOMERATE-DOMINATED TROPICAL FAN-DELTAS (PLEISTOCENE) IN A COLLISION ZONE, THE MARKHAM VALLEY PAPUA NEW GUINEA Keyu Liu and Keith A. W. Crook THE DEPOSITIONAL ENVIRONMENT AND PROVENANCE OF THE GRAMPIANS GROUP GRAMPIAN RANGES, WESTERN VICTORIA. Merren A. Jones and Ray A.F. Cas SEDIMENTOLOGICAL RESPONSE TO FORELAND DEFORMATION: THE TRIASSIC OF THE BOWEN BASIN Jochen ICHSSSTI SEDIMENTOLOGY OF THE LATE PROTEROZOIC ACRAMAN IMPACT EJECTA HORIZON SOUTH AUSTRALIA Malcolm W. Wallace, Victor A. Gostin and Reid R. Keays SM-ND ISOTOPIC EVIDENCE FOR THE PROVENANCE OF SEDIMENTS FROM THE ADELAIDE FOLDBELT AND SOUTHEASTERN AUSTRALIA WITH IMPLICATIONS FOR CRUSTAL GROWTH MODELS S.P Turner J.D. Foden M. Sandiford and D. Bruce THE RECOGNITION AND EFFECTS OF DIAPIRIC STRUCTURES IN THE NORTH EAST AMADEUS BASIN CENTRAL AUSTRALIA. Martin Kennedy SEDIMENTOLOGY AND STRATIGRAPHY OF THE REYNELLA SILTSTONE MEMBER ELATINA FORMATION: A LATE PROTEROZOIC GLACIGENIC SEQUENCE IN THE ADELAIDE GEOSYNCLINE. I.A. Dyson SILURIAN - DEVONIAN CARBONATE RAMP DEPOSITION AT THE WESTERN MARGIN OF THE HODGKINSON BASIN NORTH QUEENSLAND Thomas Bernecker and John A. Webb SHALLOW-WATER SILURIAN LIMESTONE-CHERT ASSOCIATION WITHIN THE HODGKINSON BASIN, NORTH QUEENSLAND John A. Webb and Thomas Bernecker PERITIDAL CARBONATE CYCLES IN THE EARLY DEVONIAN LILYDALE LIMESTONE CENTRAL VICTORIA Raia Wall and John A. Webb MODERN COOL-WATER CARBONATE/SILICICLASTIC OPEN PLATFORM SEDIMENTS, LACEPEDE SHELF SOUTHERN AUSTRALIA. Yvonne Bone and Noel P. James MODERN CARBONATE MUD IN LAKE REEVE VICTORIA: SOME COMPARISONS WITH THECOORONG Richard A. Davis, Jr. DIAGENESIS OF SANDSTONES IN THE PERMIAN SEDIMENTARY SEQUENCE OF THE DENISON TROUGH BOWEN BASIN QUEENSLAND: IMPLICATIONS FOR HYDROCARBON EXPLORATION R. Ahmad, J. C. Tipper R. A. Eggleton and J. L. Walshe DETRITAL SYNSEDIMENTARY DOLOMITE WITHIN COOL-WATER CARBONATE SEDIMENTS, LACEPEDE SHELF SOUTHERN AUSTRALIA Yvonne Bone, Noel P. James and T. Kurtis Kyser

POSTERS A 5.26

A 5.27 A 5.28

RECOGNITION OF DOLOMITIC CARBONATE MICROFACIES IN THE HOLOCENE BIRD LAKE COORONG REGION, SOUTHEAST SOUTH AUSTRALIA: A STATISTICAL APPROACH R. Ahmad HOLOCENE EVAPORITE AND DOLOMITIC CARBONATE SEDIMENTATION IN HALITE LAKE, SALT CREEK AREA COORONG REGION, SOUTH AUSTRAL! R. Ahmad and P. B. Hostetler TURBIDITE FACIES AND DEPOSITIONAL ENVIRONMENTS OF THE PRECAMBRIAN LABOUCHERE FORMATION PADBURY GROUP,W. A. D.McB. Martin

A6: PALAEONTOLOGY

171

CONVENORS: NEIL ARCHBOLD AND DAVID BRIGGS A 6.1 A 6.2

A 6.3 A 6.4 A 6.5 A 6.6 A 6.7 A 6.8 A 6.9 A 6.10

A 6.11 A 6.12 A 6.13

A 6.14

A 6.15

A 6.16 A 6.17

A 6.18

MULTIVARIATE STATISTICAL METHODS IN PALAEOECOLOGY AND PALAEOBIOGEOGRAPHY Guang R. Shi LATE LOCHKOVIAN-PRAGIAN SILICIFIED FAUNAS AND CONODONT BIOSTRATIGRAPHY OF THE GARRA LIMESTONE AT WELLINGTON, NSW George A. Wilson DEVONIAN CHITINOZOAN BIOSTRATIGRAPHY OF EASTERN AUSTRALIA Theresa Winchester-See to EARLY AND MIDDLE DEVONIAN ATRYPID BRACHIOPODS FROM UKALUNDA AND THE BROKEN RIVER NORTH QUEENSLAND Glenn A. Brock LATE MIDDLE AND EARLY LATE DEVONIAN (GIVETIAN-FRASNIAN) FAUNAS FROM CHITRAL NORTH-WEST PAKISTAN Richard J. Morante SILURO-DEVONIAN CONODONT BIOSTRATIGRAPHY AND SILICIFIED SHELLY FAUNAS IN THE CUMNOCK-LARRAS LEE AREA, NSW John R. Farrell EASTERN AUSTRALIAN SILURIAN AND DEVONIAN ALGAL FLORAS John Johnstone THE DEVONIAN SUCCESSION AT RAVINE (SNOWY MOUNTAINS), NSW. Mario Biasutti MIDDLE CAMBRIAN TRILOBITES FROM ALLOCHTHONOUS BLOCKS IN THE MURRAWONG CREEK FORMATION N.S.W. Terrence R. Sloan INTERNATIONAL GEOLOGICAL CORRELATION PROGRAMME 328: PALAEOZOIC MICROVERTEBRATE BIOCHRONOLOGY AND GLOBAL MARINE/NON-MARINE CORRELATION - NEW EVIDENCE FOR CORRELATION OF PALAEOZOIC FISH BETWEEN CENTRAL AUSTRALIA AND THE CANNING AND GEORGINA BASINS Gavin C. Young and Susan Turner AUSTRALIA'S EARLIEST ORNITHIS CHIAN DINOSAURS: FOOTPRINT EVIDENCE FROM THE EARLY JURASSIC OF QUEENSLAND Tony Thulbom MIDDLE PALAEOZOIC EXTINCTION EVENTS: QUEST FOR ISOTOPIC SIGNATURES John A. Talent, Ruth Mawson, Anita S. Andrew, P. Joseph Hamilton, and David J. Whitford EARLY DEVONIAN-EARLIEST CARBONIFEROUS STRATIGRAPHY AND CONODONT BIOFACIES:BROKEN RIVER AREA, NORTH QUEENSLAND Ruth Mawson and John A. Talent CONODONT CHRONOLOGY AND PALAEOCOMMUNITY SEQUENCE IN THE TAEMAS LIMESTONE (EARLY DEVONIAN, EMSIAN), N.S.W. Catherine E. Humphrey MOLONG PLATFORM AND HILL END TROUGH (NSW) IN THE EARLY DEVONIAN: A PATTERN OF PLATFORM EXPOSURE AND RECIPROCAL CARBONATE SEDIMENTATION OFFSHORE Ruth Mawson and John A. Talent MORPHOLOGICAL PLASTICITY IN CAMBRIAN TRILOBITES Nigel C. Hughes REVISED AGES FOR EARLY CARBONIFEROUS MARINE INVERTEBRATE ZONES OF EASTERN AUSTRALIA J. Roberts, P.J. Jones and T.B.H. Jenkins LATE TERTIARY OSTRACOD BIOSTRATIGRAPHY OF THE SORRENTO GRABEN VICTORIA, AUSTRALIA. M. T. Wame

xii POSTERS A 6.19 CAMBRIAN PALAEONTOLOGY AND BIOSTRATIGRAPHY OF IHEWIRREALPA AROONA CREEK AND RAMSAY LIMESTONESOF SOUTH AUSTRALIA Glenn A. Brock and Barry J. Cooper A 6.20 MIDDLE CAMBRIAN NON-TRILOBITE SHELLY FAUNA FROM ALLOCHTHONOUS BLOCKS IN THE MURRAWONG FORMATION NSW Michael J. Engelbretsen and Glenn A. Brock

A 7: PETROLOGY

CONVENOR: RICHARD PRICE A 7.1

185

ND-ISOTOPIC EVIDENCE FOR ULTRA-DEPLETED MANTLE IN AN EARLY PROTEROZOIC BACK-ARC SETTING : IMPLICATIONS FOR MANTLE EVOLUTION W.J. Sivell and M.T. McCulloch A 7.2 TRACE ELEMENT PARTITIONING AND MANTLE METASOMATISM T.H. Green, J. Adam and S. Sie A 7.3 MANTLE TERRANES: GEOCHEMICAL, GEOPHYSICAL AND GEOCHRONOLOGICAL DISTINCTIONS Suzanne Y. O'Reilly, W.L. Griffin and Y. D. Chen A 7.4 CONTRASTING BEHAVIOUR OF SR ZR AND TI DURING MANTLE METASOMATISM: A PROTON MICROPROBE STUDY A. Greig, I.A. Nicholls and S.H. Sie A 7.5 CARBONATITE METASOMATISM: OBSERVATIONS AND IMPLICATIONS G.M. Yaxley, D.H Green and A J Crawford A 7.6 A POSSIBLE CONNECTION BETWEEN MANTLE PLUMES AND METALLOGENY Robert I. Hill and Ian H. Campbell A 7.7 COMPARATIVE GEOCHEMICAL EVOLUTION OF THE SOUTHERN AFRICAN, SIBERIAN AND AUSTRALIAN CRATONIC LITHOSPHERES W.L. Griffin, G. Ryan, J J. Gurney, and N.V. Sobolev A 7.8 SAMPLES OF A MOHO MAGMA CHAMBER FOR NEWER BASALTS, NEWLYN WESTERN VICTORIA F.L. Sutherland, J.D. Hollis, W.D. Birch and L.R. Raynor A 7.9 THE LITHOSPHERE OF EAST AND WEST ANTARCTICA FROM XENOLITHS IN BASALTS: IMPLICATIONS FOR THE PACIFIC RIM John A. Gamble, Richard J. Wysoczanski and Martin A. Menzies A 7.10 KEYNOTE: DEVELOPMENT OF ARC SYSTEMS IN THE WESTERN PACIFIC: RESULTS FROM THE 1989-'90 OCEAN DRILLING PROGRAM Richard J. Arculus A 7.11 PETROLOGY AND GEOCHEMISTRY OF BACK-ARC BASIN BASALTS FROM LAU BASIN SPREADING RIDGES AT 15, 18 AND 19°S T J. Falloon, A. Malahoff L.P. Zonenshain and Y. Bogdanov A 7.12 PETROGENESIS AND TECTONIC SIGNIFICANCE OF THE HELLYER BASALT MOUNT READ VOLCANICS W TASMANIA Anthony J. Crawford and David J. Whitford A 7.13 TRACE CU U AND AG MINERALISATION IN THE LAKE BOGA GRANITE NORTHWESTERN VICTORIA. W. D. Birch and D. A. Henry A 7.14 CHANNELLED FLUID FLOW AT STEPHEN CROSS QUARRY QUEBEC CANADA I. Cartwright, N.H.S. Oliver, and T.R. Weaver A 7.15 PETROGENESIS OF AN EVOLVING PSAMMO-PELITIC MIGMATITE: AN EXAMPLE FROM THE WONGWIBINDA METAMORPHIC COMPLEX EASTERN AUSTRALIA T.R. Farrell A 7.16 ON THE ORIGIN OF PERALKALINE GRANITES Allan J R White

xiii

A 7.17

A 7.18 A 7.19

A 7.20

A 7.21 A 7.22 A 7.23 A 7.24 A 7.25 A 7,26

GRANITOID GENESIS IN THE CHAELUNDI COMPLEX NORTHEASTERN NEW SOUTH WALES: IMPLICATIONS FOR THE PETROGENESIS OF A-TYPE GRANITES OF THE NEW ENGLAND BATHOLITH B. Landenberger and WJ. Collins DISTRIBUTION, GEOCHEMISTRY AND ORIGINS OF THE YOUNGEST LAVAS OF HEARD ISLAND SOUTHERN INDIAN OCEAN G.E. Wheller and J. Barling GEOCHEMICAL AND ISOTOPIC STUDIES OF PROTEROZOIC MAFIC DYKE SWARMS IN CENTRAL AUSTRALIA Jian-xin Zhao, Malcolm T. McCulloch, and Alfredo Camacho CHEMICAL ZONING IN SMALL VOLUME BASALTIC VOLCANOES IN THE AUCKLAND VOLCANIC FIELD NORTHERN NEW ZEALAND: EVIDENCE FOR SUB-CRUSTAL FRACTIONATION PROCESSES. Ian E.M. Smith DISTRIBUTION AND NATURE OF MESOZOIC AND EARLY-MID TERTIARY ("OLDER VOLCANICS") MAGMATIC ACTIVITY IN VICTORIA I.A. Nicholls and R.A. Day THE BROCKMAN RARE-METALS DEPOSIT HALLS CREEK MOBILE BELT, WESTERN AUSTRALIA: GEOCHEMISTRY OF THE HOST TRACHYTIC VOLCANICS. W.R. Taylor, G. Esslemont, R. Page, N.M.S. Rock and D Chalmers AMPHIBOLITE FACIES METAMORPHISM OF A COMPOSITE IGNEOUS BODY, SOUTH VICTORIA LAND, ANTARCTICA T. Aslund, C. R. Walcott and D. Craw EARLY EXTRATERRESTRIAL IMPACTS AND THE ARCHAEAN CRUSTAL RECORD A.Y. Glikson THE BROKEN HILL OXIDISED ZONE W. D. Birch and A. van der Heyden INTERACTION OF MAFIC INTRUSIVES WITH METEORIC AND METAMORPHIC FLUIDS MARY KATHLEEN QUEENSLAND N.H.S. Oliver, I. Cartwrightand T. Aslund

POSTERS A 7.27

A 7.28 A 7.29 A 7.30 A 7.31 A 7.32 A 7.33 A 7.34

A NEW PB-AS MEMBER OF THE ALUNITE-JAROSITE FAMILY FROM THE OXIDISED ZONE AT BROKEN HILL NSW. W. D. Birch CHARACTERISTICS OF THE MESOZOIC SHOSHONITE SERIES IN EASTERN CHINA Kerong Chen DATING THE CRATONIC LOWER CRUST BY SHRIMP: A U-TH-PB ISOTOPIC STUDY ON ZIRCONS FROM LOWER CRUSTAL XENOLITHS FROM KIMBERLITE PIPES Chen Y. D., O'Reilly, S. Y„ and Kinny, P. DEEP KAOLINIZATION IN MEDIUM-GRADE METAMORPHICS OF THE MOUNT LOFTY RANGES SOUTH AUSTRALIA J.L.Keeling* S.G.McClure, M.D.Raven and P.G.Self THE PETROLOGY AND GEOCHEMISTRY OF ERUPTIVE VENTS IN THE MONARO VOLCANIC PROVINCE SOUTHEASTERN N.S.W. I Roach, K.G. McQueen and M Brown SM-ND ISOTOPIC STUDY OF MANTLE-CRUST INTERACTION IN THE HARTS RANGE META-IGNEOUS COMPLEX: IMPLICATIONS FOR THE ORIGIN OF ANORTHOSITES WJ. Sivell, G.E. Mortimer and M.T. McCulloch ORIGIN OF SAPPHIRE IN EASTERN AUSTRALIAN BASALTS: INFERRED FROM INCLUSION STUDIES J.F. Guo, S.Y. O'Reilly and W.L. Griffin A STUDY ON QUANTITATIVE CRYSTAL OPTICS Zhu Zhongyi

xiv

A8: STRUCTURAL GEOLOGY CONVENOR: VINCE MORAND A 8.1 A 8.2 A 8.3 A 8.4 A 8.5 A 8.6 A 8.7 A 8.8 A 8.9 A 8.10 A 8.11 A 8.12 A 8.13 A 8.14 A 8.15 A 8.16 A 8.17

223

FRACTALS IN GEOLOGY Bruce E. Hobbs and Alison Ord STRESS AND STRAIN ASSOCIATED WITH A FAULT EMBEDDED IN A DUCTILE MEDIUM Terence D. Barr and Gregory A. Houseman EXPERIMENTAL MODELLING OF TRANSCURRENT SHEAR ZONES AROUND RIGID BODIES L. B. Harris CONTROLS ON FLUID PUMPING DURING DEFORMATION Alison Ord and Nick Oliver ANTARCTICA, TWO SUPERCONTINENTS, A HANDFUL OF OCEAN BASINS, AND A BUNCH OF TERRANES Ian W. D. Dalziel, and Eldridge M..Moores THE POSSIBLE ROLE OF FLEXURAL-SLIP FOLDING MECHANISM IN THE DEVELOPMENT OF NATURAL CHEVRON FOLDS FROM THE BENDIGO-CASTLEMAINE AREA, VICTORIA T.J. Fowler and C.N. Winsor STRAIN DISTRIBUTION AND FOLD INTERFERENCE IN OBLIQUE CONTRACTION: COBAR BASIN John V. Smith and Brian Marshall AGE RELATIONSHIPS BETWEEN GRANITE INTRUSION, METAMORPHISM,AND DEFORMATION IN THE MOUNT ISA INLIER K.A. Connors and R.W. Page GEOPHYSICAL CONSTRAINTS ON STRUCTURE AND ALTERATION IN THE SOUTH ALLIGATOR VALLEY, NT R.K. Valenta, L.A Wyborn and M. Morse KEYNOTE: FLUID FLOW RELATED TO FAULTING IN DIFFERENT TECTONIC ENVIRONMENTS R.H. Sibson FAULT AND SHEAR ZONE MINOR- AND MICRO-STRUCTURES AND FABRICS ASSOCIATED WITH LARGE SCALE THRUSTING IN THE TALISKER AREA OF THE SOUTHERN FLEURIEU PENINSULA, SOUTH AUSTRALIA T. FlOtmann, P.R. James, T. Johnson and J. Rogers YARRAMYLJUP FAULT ZONE: EASTERN BOUNDARY OF GLENELG RIVER COMPLEX AND POSSIBLE CRUSTAL SUTURE IN WESTERN VICTORIA G M Gibson THE PITFIELD-AVOCA FAULT SYSTEM: THE LOCUS OF A CRYPTIC-DISCONTINUOUS GREENSTONE BELT IN CENTRAL-WESTERN VICTORIA WRH Ramsay, JM Stanley, M Hughes, V Morand and RP Carroll STRUCTURAL, IGNEOUS AND TECTONIC IMPLICATIONS OF THE COOLAC SERPENTINITE/YOUNG GRANODIORITE BOUNDARY, SOUTHEASTERN N.S.W. Brian Marshall and Brenda J. Franklin THE NATURE OF INTRAPLATE OROGENY AS ILLUSTRATED BY THE ALICE SPRINGS OROGEN IN CENTRAL AUSTRALIA R.D. Shaw, P. Zeitler, L.P. Black, I. McDougall and P.R. Tingate THE EFFECT OF PROTEROZOIC REGIONAL EXTENSIONAL SHEAR ZONES ON THE GEOMETRY OF GRANITE-GREENSTONE BELTS OBSERVATIONS FROM THE QUADRELATERO FERRIFERO, BRAZIL Stephen Marshak- Fernando F. Alkmim, and Hanna J. Evangelista MICROSTRUCTURE OF A METAMORPHIC CORE COMPLEX:THE NORTHERN SNAKE RANGE Anja-Karina Pahl and Gordon S. Lister

XV

POSTERS A 8.18 STRUCTURAL AND METAMORPHIC ASPECTS OF A NAPPE DEFORMED BY MANTLED GNEISS DOMES, NEW HAMPSHIRE, U.S.A. Rebecca Askew A 8.19 THE ROLE OF NON-UNIFORM BEDDING-PARALLEL SLIP ON FOLD NUCLEATION AND GROWTH FROM EXPERIMENTAL MULTILAYER DEFORMATION C.N. Winsor and T.J. Fowler A 8.20 TECTONIC EVOLUTION OF THE SOUTHERN ADELAIDE FOLD BELT A STRAIN AND BALANCED-SECTION APPROACH T Flotmann and P.R James A 8.21 A REVIEW OF CRUSTAL LINEAMENTS AND RINGS IN SOUTHEASTERN AUSTRALIA R Glenie A 8.22 PROGRESSIVE DEFORMATION DURING MID-PROTEROZOIC THRUSTING IN THE EASTERN ALBANY MOBILE BELT, WESTERN AUSTRALIA L.B. Harris, M J. Pascoe and W. Witham A 8.23 THREE PHASES OF FOLDING IN AN INLIER IN THE BUSHVELD COMPLEX, SOUTH AFRICA. B. Mortimer A 8.24 THE STRUCTURAL GEOLOGY OF THE TREPHINA GORGE AREA, A BASAL PART OF THE ARTLUNGA NAPPE COMPLEX, CENTRAL AUSTRALIA: IMPLICATIONS FOR THE TECTONIC DEVELOPMENT OF THE NORTHERN MARGIN OF THE AMADEUS BASIN David Selley A 8.25 THE ROLE OF GRANITIC MAGMATISM IN THE FORMATION OF METAMORPHIC CORE COMPLEXES IN THE D'ENIRECASTEAUX ISLANDS, EASTERN PAPUA NEW GUINEA E. J. Hill, S. L. Baldwin and G. S. Lister

A9: ENGINEERING GEOLOGY CONVENOR: PETER THORNTON

A 9.1 A 9.2 A 9.3 A 9.4

KEYNOTE: ENGINEERING GEOLOGY AND ENVIRONMENTAL CONTROLIN PROJECTS ADJACENT TO THE WORLD HERITAGE AREA, TASMANIA FJ.Baynes VICTORIAN COASTAL VULNERABILITY STUDY R.W.Buckley INTRODUCING THE VOLUME "THE ENGINEERING GEOLOGY OF THE MELBOURNE REGION" j L, Neilson snd W A Peek THOMSON SADDLE DAM: GEOLOGICAL CONSIDERATIONS IN DAM STABILITY P.N. Thornton and P. Styles

A10: HYDROGEOLOGY CONVENOR: RICHARD EVANS A 10.1 A 10.2

249

255

KEYNOTE: APPLICATION OF FIELD-SCALE TRACER TESTS IN THE EVALUATION OF SOLUTE TRANSPORT BEHAVIOUR David L. Rudolph CAMPASPE VALLEY CONJUNCTIVE USE STUDY M. Dudding, F. Chiew and A.Brinkley

xvi A 10.3

OPTIMAL GROUNDWATER PRODUCTION USING GENERAL-PURPOSE OPTIMISATION SOFTWARE N.P. Merrick and R Harwood A 10.4 MINE DEWATERING OPERATIONS AT MORWELL OPEN CUT J Schaeffer, B Llewellyn, P Wood and R Friday A 10.5 HYDROGEOLOGICAL PROCESSES BENEATH THE BASALT PLAINS, S.W. VICTORIA B.S. Mann, D.A. Stanley, P.F. Bolger and J. Nolan A 10.6 CHLORINE-36 DATING OF VERY OLD GROUNDWATER IN THE GREAT ARTESIAN BASIN, AUSTRALIA M.A. Habermehl, T. Torgersen and F.M. Philips A 10.7 MIXING OF GROUNDWATER WITH ISOTOPICALLY DISTINCT SIGNATURES IN SHALLOW DEVONIAN OIL-BEARING FORMATIONS IN SOUTHWESTERN ONTARIO, CANADA. Tamie R. Weaver, Shaun K. Frape, and John A. Cherry A 10.8 MICROCOMPUTER MANAGEMENT OF GROUNDWATER RESOURCES IN THE SALINAS VALLEY, CALIFORNIA Philip Hall and MattZidar A 10.9 KEYNOTE: WHERE DO HYDROGEOLOGISTS COME FROM? A NORTH AMERICAN PERSPECTIVE ON THE EDUCATION OF GROUNDWATER SCIENTISTS AND ENGINEERS. Ronald V. Nicholson A 10.10 ASSESSING THE PERMEABILITY OF COAL BEARING STRATA IN SOUTH AFRICA C A Jermy and A Van As A 10.11 IDENTIFICATION OF NUTRIENT LEVELS IN GROUNDWATER WITHIN THE MURRAY DARLING BASIN, AUSTRALIA John Nolan and Greg Hoxley A 10.12 EARTH SCIENCE, COMPUTERS AND THE ENVIRONMENT :THE 'HYDROGEOLOGY OF THE MURRAY-DARLING BASIN PROJECTEXAMPLE R.Brodie, R.Cooper and A.Tucker A 10.13 DEVELOPMENT OF AN INTEGRATED DATA COLLECTION AND PROCESSING SYSTEM FOR GROUNDWATER MONITORING AROUND LATROBE VALLEY MINES G. Reinsch and C. Daniels A 10.14 HYDROGEOLOGICAL INVESTIGATIONS FOR DRYLAND SALINITY MANAGEMENT PLANS Susan Ryan

All: ENVIRONMENTAL GEOLOGY CONVENOR: ANTHONY LANE A 11.1 A 11.2 A 11.3 A 11.4 A 11.5 A 11.6 A 11.7 A 11.8

271

KEYNOTE: GEOLOGY- A KEY COMPONENT IN UNDERSTANDING AND MANAGING OUR ENVIRONMENT J.P. Trudinger BREACHES OF ENVIRONMENTAL LAWS AND SITE REHABILITATION: PENALTIES AND LIABILITIES R A North REHABILITATION OF A DISUSED SITE IN LEEDS, U.K. F.G. Bell and A.W. Bell ARSENIC IN THE VICTORIAN ENVIRONMENT David Welsh, Michael Jones and Geoff Clarke MT. TAYLOR KINGSTON GOLD MINE: SITE RECOVERY PROJECT R J Morphet, R G Fridayand R J Parker MODELLING OF THE SUBSURFACE ENVIRONMENT USING STRATA3" CASE STUDIES IN ENVIRONMENTAL GEOLOGY. A.S. Stenning and S.P. Bentley PROTECTING OUR INESTIMABLE EARTHLY HERITAGE E.B. Joyce and E.M. McBriar PROTECTING SIGNIFICANT GEOLOGICAL FEATURES IN VICTORIA, SOUTH AUSTRALIA AND QUEENSLAND R.L. King, E.M. McBriar and P. Harlow

xvii

POSTERS A 11.9 RECLAMATION OF COLLIERY SPOIL HEAPS AT BARNSLEY, YORKSHIRE. F.G. Bell and A.W. Bell A 11.10 REHABILITATION OF A SAND QUARRY D. Sceney and A. Wissenden

A12: GEOPHYSICS

283

CONVENOR: GREG HOUSEMAN A12.1

MAGNETIC PROPERTIES OF THE CRATONIC LOWER CRUST AND UPPER MANTLE N.J. Pearson, D.A. Clark and S.Y. O'Reilly GEOPHYSICAL CHARACTERISTICS OF THE LITHOSPHERE AND THEIR IMPLICATIONS FOR THE FORMATION MECHANISM OF THE EROMANGA BASIN IN CENTRE-EASTERN AUSTRALIA S. Zhou A12.3 KEYNOTE: GEOLOGICAL MAPPING USING AIRBORNE GEOPHYSICS - NEW FRONTIERS D F Pridmore A12.4 THE FORESHOCK SEQUENCE AT TENNANT CREEK IN 1987 Emmanuel Bouniot, Trevor Jones and Kevin M Cue A12.5 EARTHQUAKE HAZARD IN THE CANBERRA REGION Marion Michael-Leiba A12.6 SEISMIC WAVE ATTENUATION IN DUNITE AT HIGH SUB-SOLIDUSTEMPERATURES: AN EXPERIMENTAL STUDY Ian Jackson, M.S. Paterson and J.D. Fitz Gerald A 12.7 ADVANCES IN GEOPHYSICAL BORE LOGGING IN THE LATROBE VALLEY W.Wood, R.Moss, Z.Smith A 12.8 SEAFLOOR ELECTRICAL CONDUCTIVITY AND OCEAN CURRENTS F.E.M.(Ted) Lilley, Jean H. Filloux and Ian J. Ferguson POSTERS A 12.9 SURFACE FAULTING AND EARTHQUAKE RECURRENCE IN AUSTRALIA J. R. Bowman, A.J. Crone, M.N. Machette, J.R. Prescott and K. Tanaka A 12.10 UNDERPLATING OF THE SOUTHERN NEW ENGLAND OROGEN ? D. M. Finlayson and D. N. Collins A 12.11 THE THERMAL STRUCTURE OF MANTLE PLUMES Gregory A. Houseman A 12.12 COMPUTER MODELLING OF THE STRUCTURE AND TECTONIC EVOLUTION OF THE CANNING BASIN H.W.S. McQueen and J. Braun A 12.13 ATTENUATION OF STRONG EARTHQUAKE GROUND MOTION IN TASMANIA Marion Michael-Leiba A 12.14 ELASTICITY OF OLIVINE AND ITS HIGH-PRESSURE POLYMORPHS AND THE COMPOSITION OF THE TRANSITION ZONE Sally Rigden, Ian Jackson, Gabriel Gwanmesia and Robert Liebermann A 12.15 THE MAGNETIC ANOMALY MAP OF AUSTRALIA C.Tarlowski, P.Milligan and F.Simonis A 12.16 PRECAMBRIAN TIDAL RHYTHMITES AND THE EARTH'S PALAEOROTATION George Williams A 12.17 DECONVOLUTION OF VERTICAL SEISMIC (VSP) DATA Marianne Windhofer and Christopher Juhlin A 12.18 GEODYNAMIC MODELLING OF THE CAINOZOIC EPEIROGENY OF THE EAST MIDLANDS SHELF, BRITAIN. J. M. Wood and G. A. Houseman A12.2

c

xviii A 12.19 THE ENIGMATIC LATE PROTEROZOIC GLACIAL CLIMATE: THE LOW PALAEOLATITUDE OF LATE PROTEROZOIC GLACIATIONS George Williams, Phillip Schmidt and Brian Embleton

A13: REMOTE SENSING

303

CONVENOR: JOSEPH LEACH A 13.1 THE USE OF TM IMAGERY TO MAP RECHARGE AND DISCHARGE ZONES IN THE GRENVILLE AREA OF CENTRAL VICTORIA. Joseph HJ. Leach A 13.2 THE REGIONAL SETTING OF THE MURRAY TRENCH USING NOAA-AVHRR IMAGERY Patrick Hnlcwood A 13.3 THE APPLICATION OF AIRBORNE RADIOMETRIC CLASSIFICATION TECHNIQUES TO SALINITY STUDIES IN WESTERN VICTORIA. P. A. McDonald and G. R. Pettifer A 13.4 THE USE OF TM IMAGERY IN TERRAIN UNIT MAPPING OF THE BALLARAT REGION E.B. Joyce and Joseph H.J. Leach A 13.5 MAPPING MICROCRACKS AND ROCK JOINTS AUTOMATICALLYUSING DIGITAL IMAGE ANALYSIS S J D Cox, T J Green and M W Jessell . A 13.6 KEYNOTE: REMOTE SENSING: AN OPERATIONAL TOOL Taylor A 13.7 GEOLOGICAL APPLICATIONS AND LIMITATIONS OFAIRBORNE MULTI-SPECTRAL SCANNERS; THEIR AVAILABILITY, COST EFFECTIVENESS AND FUTURE R.A. Agar A 13.8 A REMOTE SENSING STUDY OF KIMBERLITE AND LAMPROITE PIPES USING GEOSCAN AIRBORNE MULTISPECTRAL SCANNER IMAGERY: EXAMPLES FROM THE KIMBERLEY, WESTERN AUSTRALIA. A. Hatch, W.R. Taylor, and R.A. Agar POSTERS A 13.9 THE APPLICATION OF LANDSAT TM DATA TO GROUNDWATER INVESTIGATIONS IN THE NEWER VOLCANICS PROVINCE OF WESTERN VICTORIA Patrick Halewood A 13.10 THE XP-1 "CURLEW" - A LOW COST SYSTEM FOR HIGH RESOLUTION, LARGE SCALE AIR PHOTOGRAPHY. Joseph HJ. Leach A13.ll GEOLOGY OF THE BALLARAT REGION: A DETAILED AIRBORNE SURVEY Robert Carroll and Joseph H.J. Leach

A14: COMPUTERS IN GEOLOGY CONVENOR: ANDREW WALTHO

313

A 14.1 COMPUTER SYSTEMS IN BROWN COAL - EXPERIENCES FROM THE LATROBE VALLEY R.Gaulton, W.Wood, G.Simpson, A. Bell A 14.2 USE OF INDICATOR KRIGING AND 3D GEOLOGICAL MODELLING FOR ORE RESOURCE ESTIMATION AT MARVEL LOCH OPEN PIT GOLD MINE, WESTERN AUSTRALIA N. Schofield and P.J. Rolley A 14.3 KEYNOTE: GEOLOGICAL CONTROL IN COMPUTER-BASED RESOURCE ESTIMATION A.A. Cram A 14.4 DIGITAL PHOTOGRAMMETRY OF FAULT SURFACES M.WJessell, P.Schwarze- SJ.D.Cox, and W.Power

xix

A 14.5 A 14.6

LIMCO - A COMPUTER BASED LITERATURE COMPILATION OF DIAMOND INDICATOR MINERALS AND A NEW APPROACH FOR ASSESSING DIAMOND PROSPECTIVITY R. R. Ramsay EDUCATING GEOLOGISTS IN THE USE OF COMPUTERS C A Jermy

POSTERS A 14.7

GEOLOGICAL AND MINE MODELLING OF THE BALLARAT GOLDFIELD John Duke A 14.8 COMPUTER APPLICATIONS IN RESOURCE MODELLING AT THE CSA MINE, COBAR, NSW M. Erickson, J. T. Carswell, N. Schofield and B. J. Larkin A 14.9 GRAPHICAL DISPLAYS IN A MULTI-DIMENSIONAL ENVIRONMENT Farrelly A 14.10 COMPUTER-AIDED RESTORATION OF DEFORMED FOSSILS: METHOD AND APPLICATION. Nigel C. Hughes and Peter A Jell A 14.11 GEOLOGICAL AND GEOPHYSICAL DATA INTEGRATION IN A GIS: STRUCTURAL APPLICATIONS FROM THE 51 MILE WELL AREA, EASTERN GOLDFIELDS, W.A. Mark S. Rattenbury and Alan J. Whitaker A 14.12 A RESOURCE MODELLING OF THE CENTURY ZINC-LEAD DEPOSIT, NORTH QUEENSLAND Andrew Waltho A 14.13 A COMPUTER SIMULATING MODEL OF CLASTIC SEDIMENTATION AT BOTH CONTINENTAL MARGIN AND INLAND BASIN SETTINGS. S. Zhou

A15: GEOLOGICAL DATABASE MANAGEMENT 325 CONVENOR: DAVID RICHARDS A 15.1 A 15.2 A 153 A 15.4 A 15.5 A 15.6 A 15.7 A 15.8

B.I.I.K. Bye RETHINKING THE DESIGN OF LARGE GEOLOGICAL MAP DATABASES Cuirie MINERALOGICAL AND GEOLOGICAL REFERENCE DATABASES IN THE MUSEUM OF VICTORIA. D. A. Henry and W. D. Birch GDB - VICTORIA'S GROUNDWATER DATABASE A.J. Brinkley and B.J. Kingsbury REGIONAL RESOURCE EVALUATION AND AREA SELECTION USING GEOGRAPHIC INFORMATION SYSTEMS M Aubrey and K.M. Chan KEYNOTE: GEOLOGICAL INFORMATION IN MINERAL EXPLORATION T M Porter THE NATIONAL EARTH SCIENCES REFERENCE DATA BASE AND ASSOCIATED INFORMATION SERVICES G R T Hudson and D A Tellis EXPLORING IN HYPERSPACE: GETTING MORE OUT OF YOU EXPLORATION DATABASE C.A. Laughton

POSTERS A 15.9

MANAGING GROUNDWATER DATA AT THE RURAL WATER COMMISSION OF VICTORIA A.J. Brinkley

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A 15.10

COMPUTERISED GEOLOGICAL FIELD DATA MANAGEMENT IN QUEENSLAND - SIX YEARS OF REGMAP I.W. Withnall, K.G. Grimes, S. Lang and M.P. Thornton

A16: HISTORY OF GEOLOGICAL SCIENCES

333

CONVENOR: DAVID BRANAGAN A 16.1

A 16.2

A 16.3

A 16.4

KEYNOTE: JAMES COOK (1777) TO CHARLES GOULD (1869) MARITIME EXPLORERS TO GEOLOGICAL SURVEYOR MAINLY IN VAN DIEMENS LAND Max Banks THE ETHERIDGE / BROWN CORRESPONDENCE : AN INSIGHT INTO SOUTH AUSTRALIAN GEOLOGY IN THE LATE NINETEENTH CENTURY Barry J. Cooper NEWCASTLE COLLIERIES - PAST PROSPERITY, PRESENT DERELICTION, FUTURE HAZARD? G.H. McNally AN UNEXPLOITED RESOURCE: GEOLOGISTS' PERSONAL ARCHIVES Margaret R Dwyer

A17: GEOLOGICAL EDUCATION

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CONVENORS: LLOYD HAMILTON AND GABOR MARKOVICS A 17.1

CURRENT ISSUES IN GEOLOGICAL EDUCATION L. H Hamilton A 17.2 ENVIRONMENTAL GEOLOGY, VALUE JUDGEMENTS AND EDUCATION Bronte Nicholls A 17.3 KEYNOTE: GEOLOGICAL EDUCATION AND THE ROLE OF THE GEOLOGICAL COMMUNITY I F Clark A 17.4 INITIATIVES IN ENVIRONMENTAL EDUCATION FOR THE GEOLOGY AND GEOLOGICAL ENGINEERING COURSES AT THE ROYAL MELBOURNE INSTITUTE OF TECHNOLOGY J Brumley A 17.5 CONTINUING EDUCATION FOR EARTH SCIENCE GRADUATES IN THE MINERALS AND PETROLEUM INDUSTRIES Geoff Hudson and David Pollard A 17.6 WHAT DO ANCIENT EUCALYPTS AND VOLCANOES HAVE TO DO WITH GEOLOGY EDUCATION? THE USE OF WILSON BOTANIC PARK, BERWICK AS A RESOURCE FOR SCIENCE TEACHING Neville Green and Robert Hill A 17.7 ROADSIDE GEOLOGY AS A RESOURCE IN PROMOTING GEOLOGY A.T. Grenfell A 17.8 EXCURSION GUIDES - A NEW APPROACH William G. Shackleton and Mary-Anne N. Binnie A 17.9 TERTIARY GEOLOGICAL EDUCATION - A COMMENT ON TWO APPROACHES TWO SYSTEMS D.A. Gust A 17.10 EARTH SCIENCE AND THE PRINTED MEDIA Dawn Hendrick A 17.11

AUSTRALIAN MINING INDUSTRY COUNCIL-SPONSORED PRACTICAL GEOSCIENCE SHORT-COURSES FOR PRIMARY AND SECONDARY TEACHERS (IN THE ACT) Phil Smart and Dianne Stuart

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A 17.12 GEOLACT: A GEOSCIENCE EDUCATION LIAISON NETWORK IN THE ACT. DJ. Perkin, K.G. McQueen, W. Mayer and T.J. Munson A 17.13 HOW TO BUILD A SECONDARY EARTH SCIENCE DEPARTMENT. Phillip G. L. Harlow A 17.14 EARTH SCIENCE IN PRIMARY SCHOOLS Wolf Mayer A 17.15 A BRIEF LOOK AT SOME GEOLOGICAL SOFTWARE FOR SCHOOLS Darold E. Klindworth A 17.16 VOCATIONAL AND TECHNICAL EDUCATION IN GEOSCIENCEWITH EMPHASIS ON GEOPHYSICAL EXPLORATION James A. Madonna A 17.17 THE PACSCHOOLINFOLINE - ELECTRONIC MAIL BULLETINBOARD SERVICES PROVIDING GEOLOGICAL EDUCATION RESOURCES M.P. Thornton POSTERS A 17.18 THE ROLE OF GEOLOGICAL EDUCATION IN CONSERVATION I. F. Clark and P. R. James A 17.19 WHEN AND WHY DO STUDENTS BECOME INTERESTED IN GEOLOGY Phillip G. L. Harlow A 17.20 COMPUTER ANIMATION AND MULTIMEDIA PRESENTATION SOFTWARE AS AN AID TO LECTURES AND WORKSHOPS IN TERTIARY AND FURTHER GEOLOGICAL EDUCATION P.R. James and I .Clarke A 17.21 EVIDENCE FOR SEA LEVEL RISE AT POINT LONSDALE 1988-1991 N.W. Schleiger A 17.22 THE E. DE C. CLARKE GEOLOGICAL MUSEUM -AN EDUCATIONAL RESOURCE FOR THE WHOLE COMMUNITY Georgina M. Rockett

A18: ECONOMIC GEOLOGY- CORPORATE CONVENOR: ROSS FARDON

A 18.1 A 18.2 A 18.3

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CORONATION HILL - CASE STUDY AND IMPLICATIONS FOR OTHER PROJECT DEVELOPMENTS C E Palethorpe, D P Carville, J F Leckie, C F Moorhead and J G Rayner THE ROLE OF GOVERNMENT GEOLOGICAL ORGANIZATIONS IN RELATION TO THE MINERAL EXPLORATION INDUSTRY J N Cramsie B.I.I.K. II Tyrwhitt

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SCIENCE IN SEARCH OF EARTH S SECRETS DYNAMIC EVOLUTION OF THE GREAT BARRIER REEF ODP AND BEYOND Peter J. Davies Bureau of Mineral Resources, Geology and Geophysics, Canberra. In September and October 1990 the passive carbonate dominated continental margin of northeast Australia was the focus of Less 133 of the Ocean Drilling Program - the world's largest and most successful international geoscience research program of the past two decades operating in the world's largest carbonate province. The Ocean Drilling Program defines ultimate test for the scientific exploration of the oceans - the Record in the Rocks. Northeast Australia represents a global laboratory par excellence for understanding slope to basin sedimentary evolution adjacent to huge rift basins. Sixteen holes were drilled along two transects (Figure 1) connecting the three major platforms of the Great Barrier Reef, the Queensland Plateau and the Marion Plateau. Drilling defined a record of Cenozoic tectonic, eustatic, palaeoclimatic and palaeooceanographic dynamism which has driven platform and basin formation: new scenarios of carbonate platform evolution have emerged along with new ideas on the biological evolution of the Great Barrier Reef and a high resolution sealevel and climatic data set essential to the understanding of global climate change and the sedimentologic response of margins to changing environment. Initiation, exposure, drowning and re-development of the platforms are related to the interaction of continuous horizontal tectonics and two phases of subsidence acting both in consort and against global sealevel variations. Thus different margins of the same basins exhibit different sedimentary responses to relative sealevel change. Platform growth directly reflects Australia's latitudinal position throughout the Tertiary. The origins of the Great Barrier Reef lie in the development of the first carbonate platform in the area on the Queensland Plateau in the earliest Eocene while northeast Australia was in Latitude 430S. This was a temperate platform composed of bryozoan/ foraminiferal grainstones. With continued seafloor spreading in the Southern Ocean and movement of Australia northwards, the temperate limestones were replaced first in the Late Oligocene by subtropical rhodolith/bryozoan/large foram boundstones and then suddenly in the Early Miocene by tropical coral rich boundstones and wackestones. The rapidity of the

Geological Society of Australia Abstracts Number 32, Ballarat 1992

change to tropical carbonates at around 17 Ma is suggestive of a critical oceanographic threshold, probably the first switch-on of the east Australian boundary current. Concomitant and continuous slow subsidence affected both the Queensland and Marion Plateaus throughout the Palaoegene. On the Queensland Plateau, the reefs grew as pinnacles on basement highs and as barrier reefs along the northern margin of the Townsville Trough Transgression of the Marion Plateau occurred in the latest Oligocene / earliest Miocene when huge middle Miocene barrier and lagoonal reef complexes expanded over an earlier subtropical platform. The initial Great Barrier Reef therefore first developed along the northern margin of the Marion Plateau, the thickness of reefs being greater than on the Queensland margin at the present time. Thereafter the history of the Queensland and Marion plateau was drastically affected by an absolute mid Miocene sealevel fall of 150m, resulting in total exposure and karstification of the platform. In the same time frame on the opposite side of the Townsville Trough, the Queensland Plateau succumbed to a massive subsidence so that reef drowning occurred at the same time as eustatic sealevel was falling. Both plateaus suffered a substantial reduction in the area of reef growth n the mid Miocene. Further subsidence in the Pliocene led to an even greater reduction in the area of reef growth on the Queensland Plateau and drowning and conversion of the Marion Plateau into a pelagic tropical platform. The development of the Great Barrier Reef along the Queensland margin, defined a resurgence in tropical platform development which occurred only in the middle to late Pleistocene Step back from the Marion Plateau to the Queensland continental margin did not accompany the Pliocene drowning. Rather, the reef growth along the margin was inhibited for some three million years. Once initiated however, the largest carbonate platform on earth spread in leass than one million years, growing only in the high sealevel periods, and surviving some twenty catastrophic sealevel oscillations. It will continue to spread southwards concomitant with Australia's drift to the north and any global warming which spreads tropical influences to the south. Substrates for reef growth are

2 currently being prepared off southern Queensland. The extreme youth of the system testifies either to an extremely rapid rate of biological evolution or a source of biological variation external to the province. From where has it come? Further, the repeated destructions indicate that the Reef, far from being a fragile ecosystem, is instead a biologically robust structure easily capable of dealing with fundamental natural

Geological Society of Australia Abstracts Number 32, Ballarat 1992

catastrophies. A relevant scientific question in such circumstances is why it has repeatedly regenerated and which conditions precipitated its repeated regrowth. The answers to such questions lie in the high resolution climatic and environmental signals encapsulated in the sediments and which are currently being decoded.

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INTERNATIONAL GEOLOGICAL CORRELATION PROGRAM LECTURE MAFIC DYKE SWARMS AS A GUIDE TO PRECAMBRIAN TECTONICS A J. Parker South Australian Department of Mines and Energy, 191 Greenhill Road, Parkside, SA 5063 Mafic dyke swarms are unique in the study of earth science: not only do they record the chemistry and composition of the Earth's interior but they are also reliable strain indicators recording tectonic processes both during and subsequent to emplacement. All major Precambrian provinces throughout the world contain mafic dyke swarms and the Australian Precambrian is no exception. Furthermore, many Precambrian dykes and dyke swarms have considerable economic significance. This paper will review Precambrian dyke swarms, emplacement mechanisms and tectonics in relation to evolution of the Australian continent and Gondwana. The paper has evolved from IGCP Project 257, "Precambrian mafic dyke swarms", which was concluded in late 1991. Mafic dyke swarms can be classified into three broad categories: radial, concentric and linear. Radial and concentric swarms are commonly associated with local heterogeneities in the Earth's crust or point sources such as volcanoes (Smith, 1987) or meteorite impact structures. They form at shallow depths, are generally of limited aerial extent, and are rare in Precambrian terrains. Linear dyke swarms on the other hand, are extremely common in the Proterozoic, are laterally extensive (often several 100 km long yet relatively narrow), and were frequently emplaced at moderate depths (ca. 10 km) within the crust. They indicate either continental-scale extension, long linear lithospheric magma sources or major crustal shear zones. The association of dykes with shear zones is a common feature of the Proterozoic (Cadman et al., 1990). Recent work has emphasized the importance of horizontal flow and propogation in mafic dykes. Sigurdsson (1987) and Lister & Kerr (1990) have shown that vertical flow is important at deeper levels of the crust (ie the feeder zones), but that as magmas reach a certain level, the 'level of neutral buoyancy', they spread rapidly and horizontally as either dykes or sills along zones of least resistance. Although mafic dykes were emplaced within all Australian Precambrian provinces during the Proterozoic, current evidence would indicate that there were specific intervals during which dyke intrusion was common. One such interval is the period 1000Geological Society of Australia Abstracts Number 32, Ballarat 1992

1200 Ma when dykes were emplaced throughout central Australia (Musgrave and Arunta Blocks), Mount Isa Block, Pine Creek Geosyncline, Gawler Craton and Yilgarn Craton (Parker et al., 1987). This was also an important period of dyke emplacement in other continents including North America (the Keweenawan and Abitibi dykes of the Canadian Shield), the Amazonian Craton of South America, Fennoscandia and southern Africa. This similarity in ages of dyke emplacement has intriguing implications with respect to emplacement mechanisms and crustal tectonics. Fahrig (1987) has suggested that the Keweenawan and Abitibi swarms of the Lake Superior region represent failed arms of a major Mesoproterozoic rift system; the Gairdner Dyke Swarm of the eastern Gawler Craton may also represent a failed Mesoproterozoic rift. Mesozoic dykes which border the Central Atlantic in eastern North America, western Africa and northeastern Brazil (Gibbs, 1987; Greenough & Hodych, 1990; Oliveira et al.,1990) formed during the early stages of continental rifting and represent a global-scale tectonic event that led to the breakup of Gondwana. Therefore, by analogy, it is possible that the Mesoproterozoic interval of global-scale dyke emplacement represents a similar tectonic event or process. Mafic dyke swarms are not only reliable indicators of extensional regimes, but they are also useful markers for correlating tectonic provinces across oceanic basins and for tracking the motions of continental plates relative to each other and the Earth's magnetic field. The key to making global comparisons is the availability of comprehensive dyke swarm maps accompanied by reliable age, geochemical, palaeomagnetic and associated data. Compilation of palaeomagnetic data, critical not only for tracking plate motions but also for quantitative analysis of aeromagnetic maps, is progressing (Byland & Pesonen, 1987; Buchan & Halls, 1990; Schmidt, 1990) but on a global basis is still in its infancy. For Australia, dyke swarm maps and associated information have been compiled in a preliminary form and included in a computerized geographic information system (GIS). This has enabled correlation of dykes and dyke swarms between different Precambrian

4 provinces. For example, Neoproterozoic dykes in the northwestern Yilgarn Craton, western Capricorn Orogen and Pilbara Craton constitute a major dyke swarm which is of relatively consistent orientation and composition despite transgressing three major crustal provinces. This confirms that those provinces have been adjacent to each other and relatively stable since the Mesoproterozoic. However, pre-Neoproterozoic dykes in the Yilgarn and Pilbara regions are quite different A similar situation applies to the relationship between the Musgrave Block and Gawler Craton; the Gairdner Dyke Swarm occurs in both domains essentially along strike from each other despite being separated by a major very deep Neoproterozoic and Palaeozoic basin (Officer Basin). This implies that the

Geological Society of Australia Abstracts Number 32, Ballarat 1992

southern Musgrave Block may be a subdomain of the Gawler Craton and that the Officer Basin is truly intracratonic. References All references cited are within the following two publications: Halls, H.C. & Fahrig, W.F. (eds), 1987. Mafic Dyke Swarms. Geological Association of Canada Special Paper 34. Parker, A.J., Rickwood, P.C. & Tucker, D.H. (eds), 1990. Mafic Dykes and Emplacement Mechanisms. A.A.Balkema, Rotterdam. 541pp.

5

S.W. CAREY SYMPOSIUM CONVENOR: GORDON LISTER

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GLOBAL VISION: S.W. CAREY AND THEORIES OF THE EARTH H.E. Le Grand University of Melbourne

My thesis is taken from a quotation from one of Professor Carey's critics and a president of the American Geophysical Union: "...Carey is an important figure in the development of thought about the evolution of the Earth. He was one of the earliest proponents of continental drift, a key figure in developing many of the ideas that went into the theory of plate tectonics, and has assembled an impressive array of arguments for the hypothesis of an expanding Earth. In addition, he is one of those rare scientists with a wealth of detail at his command and the intellect and imagination to put it to productive use" In my brief remarks I will focus upon Carey's "global C 2

vision", for it is upon his development and defence of often controversial theories of the Earth that his international reputation rests. Yet, this represents only a part of Carey's scientific work: pioneering surveys in New Guinea and Papua, consultancies to engineering projects and firms, the geology of Tasmania, contributions to seismology and other branches of geology and geophysics, and, as the charismatic Foundation Professor of Geology at the University of Tasmania, to the education of the present generation of geologists.

MOUNTAIN BUILDING Peter Molnar

Massachusetts Institute of Technology, Dept. of Earth, Atmospheric and Planetary Sciences Cambridge, MA 02139 USA This talk will focus on active mountain building where convergence of continental blocks occurs. I will quickly review the large scale Cenozoic evolution of the Himalaya and briefly contrast it with the Tien Shan, the world's most active "intracontinental" mountain range. Then I will dwell at more length on a subject where our ignorance particularly impedes our understanding of mountain building: dynamic processes occurring in the mantle beneath mountain belts. Finally, I will address an area that holds a key to understanding these dynamics, but that is currently mired in misunderstanding: paleo-altimetry of mountain belts. India collided with Eurasia some time between Late Cretaceous and Late Eocene time. The Indian subcontinent, following ocean floor subducted beneath southern Tibet, was flexed down and also was Geological Society of Australia Abstracts Number 32, Ballarat 1992

underthrust beneath southern Tibet. Slices of India's northern margin have been stacked atop one another and compromise the rock exposed in the present range. Underthrusting continues. The apparently intact Indian Shield is underthrust beneath the Lesser Himalaya on a very gentle plane dipping 3° ± 15°) at least as far as about 100 km from the southern edge of the range. The rate of underthrusting, deduced from ages of sediment deposited south of the range, is between 10 and 25 mm/a, and therefore is only 20%50% of the total rate of convergence between India and Eurasia. The abrupt wall of high mountains comprising the Greater Himalaya may be result of its overlying a steeper segment of the currently active thrust fault, so that the Greater Himalaya is ramped up onto the intact India Shield. The exceptional strength of the flexed Indian Shield surely contributes to the

6 Similarly, there seems to be an east - west gradient great height of the range. Unlike the Himalaya, the Tien Shan formed within of upper mantle structure beneath the Tien Shan. The western part is underlain by hot material and seems to one continent; the last ocean floor was subducted in Paleozoic time, and the Tien Shan was technically be in isostatic equilibrium. The eastern part departs quiet in late Mesozoic time. Presumably the thrust from such equilibrium by 100 mgals as if some faulting that has accommodated crustal shortening and process has pulled the Moho down a few kilometers crustal thickening in Neogene and Quaternary time below its equilibrium depth. We presume that occurs in response to India's collision with Eurasia convective downwelling is responsible for this. A history of surface uplift of a mountain belt or 1000-2000 km south of the Tien Shan. Fault plane solutions of earthquakes indicate dips of roughly 30° high plateau could constrain the timing of such mantle (±15°) and focal depths show such deformation occurs processes, especially if that history could be correlated well below the sedimentary cover. This deformation with other geologic processes. The subject of uplift, is analogous to that responsible for Laramide however, is muddled in part by different uses of the deformation in Colorado and Wyoming and probably word, referring to different reference frames. The word is commonly used to indicate uplift of rock toward the to that surrounding the Amadeus Basin. If crust is shortened horizontally, so ought the Earth's surface, which tells us nothing about uplift of underlying mantle lithosphere. Isostatic compensation the surface with respect to a more meaningful reference of thickened mantle lithosphere could, at least frames such as the geoid. An additional complication temporarily, maintain a thickened crust with only a seems to be that much of the evidence used to infer minor mountain range above it. Thickened mantle uplift could be the result of climate change instead of lithosphere also requires the creation of marked lateral tectonic processes. The common inference that temperature gradients that are likely to induce mountain ranges rose in Quaternary time, regardless of convective removal of such a thickened lithospheric when deformation occurred, may simply be a result of root. The replacement of a lithospheric root by hot climatically induced changes in erosion and asthenosphere should then lead to further uplift of the sedimentation. Paleobotany seems to offer the best hope for quantifying paleo-altimetry, provided that Earth's surface. Such convective processes may be underway effects of climate change on flora are properly beneath Tibet and the Tien Shan. The crustal accounted for. It appears that the processes responsible for thickness beneath Tibet varies by 15 - 25 km, whereas the overlying surface is especially flat. The thinner mountain building are quite different from those used crust (50 - 60 km) is clearly associated with a hot to describe plate tectonics and that plate tectonics has upper mantle — low seismic wave velocities, high not helped much in gaining what little understanding attenuation, and basaltic volcanism. The largest we have. Although some of the techniques that were lateral gradient in velocity and presumably also used to demonstrate plate tectonics clearly are useful in temperature, is east -west, not north - south, the study of mountain building, to understand the suggesting that the mantle dynamics does not mirror dynamics of such regions will require techniques hitherto ignored in large scale tectonics. the finite deformation observed at the surface. C 3

EXTENSION CONTEMPORANEOUS WITH SHORTENING WITHIN MOUNTAIN BELTS B. C. Burchfiel

Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Intsitute of Technology Cambridge, MA, Massachusetts, 02139, USA Contemporaneous large-scale extension and shortening during mountain building are commonly viewed as incompatable. Gravitational potential energy is stored in mountain ranges relative to adjacent areas of lower elevation, and increases as the height of the mountains increases. Simple mechanical models show that under certain conditions the high parts of a mountain range could undergo extension during continued shortening on its flanks (Molnar and LyonCaen, 1988). Examples, such as in the Andes of South America (Dalmyrac and Molnar, 1981), appear Geological Society of Australia Abstracts Number 32, Ballarat 1992

to fit such models, however the magnitude of extension in such regions is samll. More recently examples of large-scale extension contemporaneous with shortening have been described from at least three different types of tectonic settings: (1) where longitudial strike-slip faulting occurs during mountian building (eg. the European Alps), (2) where back arc extension occurs during shortening due to retrograde motion of subducting slabs (eg. the Apennines) and (3) where gravitational potential energy coupled with specific crustal conditions have caused different types

7 of large-scale extensional phenomena (eg. the Himalaya/southern Tibet). Examples from the first two types of tectonic settings have been published recently. The third tectonic setting has not been fully described in print and will be discussed in more detail. All three types of tectonic settings develop extensional structures that are similar or identical to those present in areas of regional extension. During post-collisional deformation in the Alps of western Europe continued plate convergence has resulted in development of longitudal and oblique strike-slip faults. Such a tectonic setting can cause extenison oblique or parallel to the mountain range. In Austria (Selverstone, 1988) and Switzerland (Mancktelow, 1985) extension occurs on low-angle to moderately dipping faults that juxtapose shallow level crustal rocks in their hanging walls against deeper level crustal rocks in their footwalls. Many of these faults were mapped originally as thrust faults and while they carry older allochthonous units in their hanging walls kinematic indicators and geological relations indicate they are normal faults. The faults commonly are spalys or releasing bend segments of major strike-slip faults. Fault related features include footwall mylonites with generally down-dip lineations and brittlly deformed hanging wall mylonites. Some of the faults unroof high-grade metamorphic complexes and may be responsible for the rapid exposure of middle and lower crust. Mountain ranges formed during roll back of subducting slabs are characterized by back arc extension and normal faulting that is contemporaneous with shortening and development of a thrust belt along the subduction zone (Royden and Burchfiel, 1989). Such relations were first described from oceanic regions where accretionary prisms (thrust belts) formed contemporaneously with the development of remnant arcs and marginal seas. Within the Mediterranean region similar relations exist within a intracontinental settings and lead to rapid superposition of extensional structures on slightly older shortening structures as the thrust belt and back arc extension both migrate in the direction of the foreland during slab roll back. In the Apennines active extension occurs within 50 km of the contemporaneous thrust belt and normal faults and associated sedimentary basins are superimposed on thrust faults formed only a few million years earlier. Unroofing of deeper level crustal rocks on low-angle normal faults has occurred in the region of the Aegean Sea and in northern Greece. Ancient examples have been proposed for tectonic settings of Paleozoic age in the Ouachita and Cordilleran orogens and Precambrian age in the Wopmay orogen of North America. At least two different types of extensional phenomena occur in the Himalaya/southern Tibet region that are caused by gravitational energy acting on a crust with specific specific properties. First, geological relations indicate that a crustal wedge, Geological Society of Australia Abstracts Number 32, Ballarat 1992

bounded by a south-vergent thrust fault below and north-vergent normal faults above, has been ejected southward from beneath the Himalaya and southern Tibet (Burchfiel and Royden, 1985; Burchfiel et al., in press). The contact between the Tibetan zone sedimentary rocks and the underlying Greater Himalayan crystalline zone is a gently north-dipping normal fault, the South Tibetan detachment system. Down-to-the-north movement on the detachment fault was Miocene to perhaps Pliocene in age and contemporaneous with structurally lower southvergent thrusting within the Himalaya to the south; thus, shortening and extension were contemporaneous and parallel at two different levels within the Himalayan and south Tibetan crust. Rocks in the footwall of the detachment contain garnet+sillimanite or locally garnet+kyanite mylonitic metamorphic rocks that show progressively more brittle deformation during normal faulting. They are juxtaposed against mostly unmetamorphed sedimentary rocks with conodonts that yield coloration indicies indicating temperatures no higher than 350°C. Temperature pressure relations across the detachment fault suggest that about 10 km of crust has been cut out. At least 40 km of northward displacement is demonstrable along the profile at Qomolangma (Everest). The hanging wall of the detachment system contains mostly north-dipping normal faults, many of which are thought to sole into the detachment at depth. In the western-most profile a large north-vergent synformal anticline has the geometry of a typical retrocharriage structure and the fold is interpreted to be part of a broad zone of down-to-the-north normal shear. The two eastern profiles indicate at least two periods of movement on the South Tibetan detachement system, and the eastern profile contains a north-dipping normal fault that cuts the detachment system. Mapping indicates that the South Tibetan detachment system continues for at least 700 km along strike in the High Himalaya, and regional relations suggest that the detachment system may traverse nearly the entire 2000 km length of the Himalaya. North of the South Tibetan detachment system, normal faults extend for about 100 km, normal fault bounded Neogene basins are present and at least one Miocene metamorphic core complex is recognized. Thus the High Himalaya and southermost Tibet contain late Cenozoic structures typical of areas of regional extension, although they were formrd in an area of regional shortening. These relations are interpreted to result from gravity acting on a highstanding plateau. Convergence occurred at lower crustal levels and extension at higher crustal levels as a wedge of crustal material moved relatively southward out from beneath the high topography of the the Miocene Tibetan plateau. Such a displacement would extract a thick section of rocks from the middle or lower crust. Conditions necessary to develop the large

8 scale extension in the Himalaya and southern Tibet may be associated with the widespread formation of leucogranites, conditions that need not be present in other mountain ranges. The second type of extension that occurs in the Himalaya/Tibetan region is east-west extension on north-south trending normal faults. These currently active faults were superimposed during the past few million years on the older north-south extensional structures in the High Himalaya, and they extend into large regions of Tibet (Armijo et al., 1986). Thus shallow parts of the crust, driven by gravitational potential energy, continue to extend above deeper levels of north-south crustal shortening within the Himalaya, however the direction of extension has changed about 90° from Miocene-(?) Pliocene time. Extension during mountain building often is referred to as collapse, however this term is denotes the wrong type of mechanics. In the case of the Himalaya/southern Tibet region the movement of the land surface may have increased in elevation rather than subsided. The range of extensional phenomena occuring during mountain building has not been fully explored. In the western Alps, for example, the emplacement of the Surreta nappe may suggest that crustal wedges bounded by thrust and normal faults may move at intermediate crustal levels, but not be associated with extension. New and different examples of extensional phenomena within convergent regimes will emerge from field studies, and additional tectonic settings will undoubtly be discovered.

1986, Quaternary extension in southern Tibet: Field observations and tectonic implications: Jour. Geophys. Research, v. 91, p. 13803-13872. Burchfiel, B. C., and Royden, L. H., 1985, Northsouth extension within the convergent Himalayan region: Geology, v. 13, p. 679-682. Burchfiel, B. C., Chen, Z., Hodges, K. V., Liu, Y., Royden, L. H., Deng, C., and Xu, J., in press, The southern Tibetan detachment system, Himalayan orogen: Extension contemporaneous with and parallel to shortening in a collisional mountain belt: GeoL Soc. Amer. Spec. Paper 269. Dalmyrac, B., and Molnar, P., 1981, Parallel thrust and normal faulting in Peru and constraints on the state of stress: Earth Planet. Sci. Letters, v. 55, p. 473-481. Mancktelow, N., 1985, The Simplon lone: A major displacement zone in the western Lepontine Alps: Ecolage Geol. Helv., v. 78, p. 73-96. Molnar, P., and Lyon-Caen, H., 1988, Some simple physical aspects of the support, structure, and evolution of mountain belts, in Clark, S. P., Burchfiel, B. C, and Suppe, J., eds., Processes in continental lithospheric deformation : Geol. Soc. Amer. Spec. Paper 218, p. 179-207. Royden, L. H., and Burchfiel, B. C., 1989, Are systematic variations in thrust belt style related to plate boundary processes? (The western Alps versus the Carpathians): Tectonics, v. 8, p. 5161. Selverstone, J., 1988, Evidence for east-west extension in the eastern Alps: Implications for the unroofing history of the Tauern window: Tectonics, v. 7, p.87-105.

References Armijo, R., Tapponnier, P., Mercier, J., and Han, T.,

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THE BENDING OF OROGENIC BELTS Ian W. D. Dalziel

Institute for Geophysics, University of Texas, 8701 Mopac Boulevard, Austin, TX 78759-8397 A glance at a world map reveals that mountain belts are not all rectilinear. The concept that some of those with curvilinear map patterns were originally straight, oroclinal bending, is widely associated with the name of Sam Carey. One of his type-examples was the Cape Horn orocline of southernmost South America (Carey, 1955), more commonly known today as the Patagonian orocline. For over 40° of latitude, from Lake Titicaca to the Strait of Magellan, the Andean cordillera trends just west of south. At the South America-Scotia plate boundary it swings abruptly due east along the North Scotia Ridge (Figure 1). Recently-acquired paleomagnetic data of high quality support the concept that the Andean magmatic

Geological Society of Australia Abstracts Number 32, Ballarat 1992

arc has indeed been rotated counterclockwise by 90° since the mid-Cretaceous (Figure 2). It therefore appears that Sam Carey was correct in identifying this feature of the earth's crust as an "orocline". But how and why did the bend develop, and what were the consequences beyond a change in map pattern? What general implications are to be learned about oroclinal bending from this example? The orocline is located where the Antarctic Peninsula separated from South America. It corresponds to a salient in the reconstructed Gondwana craton and the location of the Rocas Verdes marginal basin that opened along the Pacific margin during the Late Jurassic to Early Cretaceous (Figure 3).

Inversion of this basin in the mid-Cretaceous accompanied rapid opening of the South Atlantic and the initiation of left-lateral motion between South America and Antarctica (Figure 4). It is therefore likely that oroclinal bending began at that time. At present the Antarctic plate is moving at -20 mm/yr eastward relative to the South American plate, the motion being taken up along the northern and southern margins of the Scotia plate and along the Shackleton fracture zone. A small component of northeast-southwest directed compression is resulting in subduction of the South American plate beneath the Scotia plate along the northern margin of the North Scotia Ridge. Hence the Patagonian orocline is still being accentuated. I suggest that this present day transpressional regime is an analog for the closure and inversion of the Rocas Verdes basin, and hence for the formation of the Patagonian orocline, during the Cretaceous. The Andean magmatic arc appears to have been rotated counterclockwise and obducted onto the South American craton along the normal fault-bounded edge of the marginal basin (Figure 4). Finally, while transpression persists to the present day along the North Scotia Ridge, an extensional regime developed to the northwest of Cape Horn at the end of the Cretaceous. This resulted in the tectonic unroofing of the crust overthickened during inversion of the Rocas Verdes basin, and the uplift of the Cordillera Darwin core complex in the core of the orocline (Figure 5).

We have recently shot multi-channel seismic reflection profiles through the fiords that dissect the southernmost part of the Andean Cordillera in the heart of the oroclinal bend. They are still being processed at the time of preparation of this abstract, but they will be available by the time of the symposium and should shed light on the deep structure of this fascinating feature that was drawn to the attention of the earth science community by Professor Carey. References Carey, S.W., The orocline concept in geotectonics. Proc. R. Soc. Tasmania, 59, 255-288, 1955. Grunow, A.M., Kent, D.V., and I.W.D. Dalziel, New paleomagnetic data from Thurston Island: Implications for the tectonics of West Antarctica and Weddell Sea opening. J. Geophys. Res., 96, 17,935-17,954, 1991. Cunningham, W.D., Klepeis, K.A., Gose, W.A., and I.W.D. Dalziel, The Patagonian orocline: New paleomagnetic data from the Andean magmatic arc in Tierra del Fuego, Chile. J. Geophys. Res., 96, 16,061-16,067, 1991. Dalziel, I.W.D., and R.L. Brown, Tectonic denudation of the Darwin metamorphic core complex in the Andes of Tierra Del Fuego, Southernmost Chile: Implications for cordilleran orogenesis. Geology, 17, 699-703, 1989.

1. Geologic sketch map of the Patagonian orocline with South Georgia restored to its Early Cretaceous position (Cunningham etal., 1991). Geological Society of Australia Abstracts Number 32, Ballarat 1992

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2. Cretaceous paleomagnetic poles (Cunningham et al., 1991) from stable South America and the Andean magmatic arc south of the Patagonian orocline (Peninsula Hardy, see Figure 1).

3. Gondwana reconstruction for 150 Ma (Grunow et al., 1991). RVB - Rocas Verdes Basin

4. Gondwana reconstruction for 90 Ma (Grunow et al., 1991). Open teeth - upper plate during inversion of the Rocas Verdes Basin Geological Society of Australia Abstracts Number 32, Ballarat 1992

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5. The Cordillera Darwin metamorphic core complex (Dalziel and Brown 1989).

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THE ORIGIN AND EVOLUTION OF MOUNTAIN BELTS J.F. Dewey Department of Earth Sciences, University of Oxford, Parks Road, Oxford, 0X1 3PR, England.

Mountain belts, resulting from continental collision/convergence, the contractional collapse/i nversion of rifts and ultrarifts and continental margin subduction, and orogenic denudation by collapse and erosion, may be linked mainly, though not exclusively, to episodic global Wilson cycles of several hundred million years wavelength, of continental assembly (late Silurian/early Devonian, late Carboniferous/early Permian), extension and fragmentation (latest Pre-Cambrian, early Mesozoic), and dispersal (Cambro-Ordovician, early Carboniferous, Tertiary) involving both body forces and forces generated by relative plate motion and punctuated by spasmodic minor collisions of smaller continental fragments, oceanic plateaux and seamounts. This results in a broad global relationship Geological Society of Australia Abstracts Number 32, Ballarat 1992

between continental distribution, mountain building and destruction, stress, large-scale polyphase orogenic strain sequences, basin inversion, metamorphism, igneous activity/climate sea-level change, clastic sediment flux, and carbonate deposition. During the earliest stages of continental collision, convergent feathering of margins yields a direct relationship between plate slip vector and structure, commonly in the blueschist facies. Continental collisional convergence and tightening leads to enlarging zones of crustal/ lithospheric thickening in linear arcuate thrusts belts and broad plateaux, with widespread inversion of intracontinental rifts and reactivation of basement lineaments (ancestral Rockies), Orogenic plane strain bulk co-axial shortening to a crustal thickness of 70 km is buffered at about 50% by an

12 isostatically-compensated elevation of around 3 km but the non coaxial contraction of thinned continental margin crust can lead to shortening of over 80% in linear-arcuate belts. Much greater crustal thicknesses (up to at least 150 km) evidenced by coesite-bearing assemblages with concomitant greater shortening may be achieved by the eclogite transformation (west Norway) in the lower crust, even leading to regional elevations less than 3 km. This early orogenic phase of vertical plane strain is succeeded by a more or less protracted phase or horizontal plane strain dominated by strike-slip faults with pull-apart basins above granites. The final phase is body-force-generated extensional collapse following the advective removal of the orogenic boundary conduction layer root and isostatic uplift to regional elevations of 5 km, accompanied by heating, partial melting and late tectonic granites, the eclogite-amphibolite transformation, and the eduction of middle and lower high-grade crustal rocks in metamorphic core complexes and mantled gneiss domes beneath extensional detachments and juxtaposed with supracrustal rocks. Extensional collapse rather than erosion may be the principal mechanism by which mountains are denuded and returned to normal or less than normal crustal thickness; most older mountain belts are characterized by the widespread preservation of extensional sedimentary basins and pre-orogenic supracrustals, insufficient clastics in surrounding basins to account for erosional denudation, and rapid marine transgression/widespread post-orogenic unconformity, commonly showing instantaneous flooding of sub-sea level terrains. Orogenic extension is enhanced by continental breakup aided by subduction roll-back in marginal extensional arcs and C 6

is dependent also upon collapse 'escape routes . Collapse may be 'balanced' by continental separation, lateral escape wedging or by thrusting where escape is retarded (Betics). Marginal thrust systems at or below 3 km around collapsing orogens show clear bodyforce-related spreading components combined with plate slip vector partitioning components. Continental break-up along orogenic belts is commonly preceded by plume-generated hot spot basaltic outpourings that act like stamp-perforations and may have been initiated as a result of the advective removal of the orogenic boundary conduction layer. Continental separation, oceanic widening and continental dispersal leads to the eventual dominance of ridge-push forces, the development of compressive Andean orogenic arcs that collapse, with ophiolite obduction and blueschists metamorphism (early Ordovician, late Cretaceous) the earlier extensional arcs that led to continental breakup. At times of collisional continental assembly, sea-level drops leading to widespread continental aridity and a large clastic flux from the growing orogens and emerging continents (early Devonian, Permo-Triassic). At times of continental dispersal, sea level rises with the growth of carbonate platforms and global amelioration of climate and anoxic oceans (mid-Ordovician, late Cretaceous). The kinematics of relative plate and continental motion, and orogenic tectonic sequence and style leads to the conclusion that plate mosaics are driven by body forces, are uncoupled from convective ascent in plumes, drive return flow in subduction zones and are modified and influenced by small-scale convection in the upper mantle and by long wavelength thermal anomalies in the mantle. 1

THE ORIGIN AND EVOLUTION OF SEDIMENTARY BASINS A. R. Green*, S. R. May, T. S. Loutit Exxon Production Research Company

The evolution of sedimentary basins is controlled by a hierarchy of processes ranging from lithosphereasthenosphere interactions to the deposition of sediment grains. The complex interaction of these processes, through time and space, is presently manifested by about 900 unique sedimentary basins. Despite the uniqueness of each, it is possible to predict the sequence of events and hierarchy of processes that influenced any one basin. The key to developing a sound model of a basin is to understand the frequency and geographic extent of each geological process involved in the formation of that poarticular sedimentary basin. Geologic processes controlling Geological Society of Australia Abstracts Number 32, Ballarat 1992

sedimentary basins can be grouped into two major categories: those that control the shape, crustal setting and the geographic position of the container (high accommodation processes) and those that influence the supply of sediment to, and within, the container (low accommodation processes) through time. Processes related to plate motions control the dynamic location and the bulk of the accommodation available for sediment deposition during the life of a basin. Plate motions, characterized by short periods of rapid change ("events") and longer periods of stable continuous motion, and the resulting intra-plate deformation, create niches for sedimentation by three

13 primary mechanisms: by mechanically extending the lithosphere, thermal cooling of the extended lithosphere and flexural loading of the lithosphere. Geohistory analysis has been used to document the response of the lithosphere to these processes. Basins in similar tectonic settings generally exhibit similar patterns of subsidence (basin phases) reflecting the subsidence mechanism. It is possible to predict the timing and nature of first and second order sedimentary accommodation cycles (mega-sequences) from a knowledge of plate kinematics, crustal thickness, and crustal type/ fabric within tectonostratigraphic provinces. Although subsidence mechanisms associated with intracratonic basins are poorly understood, their response to plate interactions is often recognized. First and second order technically driven accommodation cycles interact with higher order eustatic and climatically driven accommodation cycles

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(within a paleogeographic framework) to control stratal geometry and depositional environments during the evolution of a sedimentary basin. Secondary forcing functions include river drainage areas, the location of river discharge points and sediment fill direction, all of which are controlled indirectly by tectonic and climatic processes. The interaction of a hierarchy of geologic processes during the Phanerozoic has produced two plate fragmentation/suturing cycles that have played a fundamental role in controlling the geographic distribution, age and type of sedimentary basins by regulating first order (and to a lesser extent second order) eustasy and second order regional subsidence/uplift patterns. These fragmentation/ suturing cycles have exerted a primary control over the natural history of the world's sedimentary basins and thus the distribution of sediment-hosted resources such as water, hydrocarbons, and ore deposits.

SEISMOGENIC CRUST R.H. Sibson*

Department of Geology, University ofOtagoP.O. Box 56, Dunedin, New Zealand

Carey's illuminating 1954 paper, "The Rheid Concept in Geotectonics", emphasized the role of time as a key factor determining the response of rock masses to deformation, contrasting seismological and geological views of Earth rheology. Modern seismological studies, combined with experimental rock deformation and the mapping of crustal scale shear zones have led to the development of rheological models for the crust which emphasize the importance of fast, intermittent deformation on short time-scales as well as the finite strains developed over long time periods. With the advent of plate tectonics has come increased awareness of the dominant role of fault discontinuities and zones of intense shearing strain in accommodating the large-scale motion of lithospheric plates and crustal blocks. In addition, much subsidiary deformation in the upper crust, including folding, is now seen as arising primarily from irregularities on major fault discontinuities. The picture that emerges from regional seismicity studies in California, Japan, and elsewhere (e.g. Hill et al.y 1990; Ito, 1990) is of a fragmented, seismogenic carapace overlying zones of localised aseismic shearing or distributed strain at depth. Intermittent earthquake rupturing is the normal mode of fault slip in the upper crust, accommodating much of the motion along plate boundaries and affecting many subsidiary processes. For a given crustal composition, temperature Geological Society of Australia Abstracts Number 32, Ballarat 1992

appears to be the primary factor controlling the depth of seismic activity (the zone of unstable frictional sliding), but strain rate and fluid access also play a role. In quartz-rich continental crust, the critical isotherm governing the lower bound of seismic activity appears to be 300-350°C, in feldspathic crust it is ~450°C, and in olivine-rich oceanic lithosphere, perhaps 600-800°C (Sibson, 1983, 1984; Chen & Molnar, 1983; Bergman & Solomon, 1988). Thus, for actively deforming continental regions with moderate to high heat flow (away from areas of active subduction where the thermal structure is grossly distorted), the seismogenic regime is largely restricted to the upper 10-15 km of the crust, but may shallow to as little as 4 km in regions of intense hydrothermal upwelling. Exposures of the mid-crust corresponding to the base of the seismogenic zone (e.g. Archean granite-greenstone terrains such as the Abitibi belt) generally reveal extensive low-strain regions laced by a mesh of high strain shear zones of mixed continuous/ discontinuous character. A range of strain-rate dependent rheological models are required to account for the different characteristics of interplate and intraplate seismicity. Within the deep- driven transcrustal fault systems defining plate boundaries, the depth of seismic activity within individual fault zones is determined by the transition to localised, fast strain rate (~10 _ 1 1 /s) aseismic

14 shearing in tabular mylonite belts. In such settings, large ruptures generally nucleate towards the bottom of the seismogenic zone defined by background activity (e.g. the 1989 M7.1 Loma Prieta earthquake in California). However, such models are probably inapplicable to areas of diffuse intraplate seismicity within cratonic crust (e.g. the eastern United States and Australia) where, despite the low heat flow and the fact that some patches of microseismicity extend to depths of 25 km or so, moderate to large ruptures nucleate at surprisingly shallow depths (5-10 km) (Fredrich et a/., 1988). A more appropriate model for intraplate activity is perhaps to view the upper levels of cratonic crust as a flawed stress guide, where timedependent failure is induced through processes such as stress corrosion or localised fluid access. Seismogenic failure can only occur when the bulk loading strain rate is faster than the potential rate of flow relaxation within the focal volume, giving rise to an important size effect. In plate interiors, the bulk strain rate affecting seismogenic depth is inversely related to the recurrence interval between successive earthquakes, and may be extremely low (<10~ /s). A range of intermediate behaviour exists between these endmember rheological models for faulting. Development of mid-crustal decoupling horizons, allowing upper crustal flaking (Oxburgh, 1972), becomes possible in quartz-rich crust with moderate or greater heat flow, and may contribute to the blurred seismic definition of plate boundaries in continental crust. New ideas are emerging on the evolution of fault zones with increasing displacement in seismogenic crust, and the manner in which this affects the style of seismic activity. Within continental transform systems, large displacement fault zones apparently grow through the amalgamation of smaller faults within strike-slip corridors, leading to progressively decreasing structural complexity with increasing displacement (Wesnousky, 1988). The size of "characteristic ruptures" along the constituent faults is controlled by the distribution of major structural irregularities (both geometrical and rheological), with only the smoother, large displacement faults capable of producing great earthquakes. Structural controls on rupturing tend to be transient and migrate within the corridors, giving rise to switchyard tectonics, with lateral movement transformed on a very localised scale into areas of rapid uplift and subsidence (Sibson, 1989). There is abundant geological evidence for the role of fluids in all aspects of the faulting process. Fluid 16

Geological Society of Australia Abstracts Number 32, Ballarat 1992

overpressures appear to be directly involved in rupture nucleation in at least some tectonic settings, giving rise to fault-valve action with postfailure flushing of overpressured fluids along rupture zones. Restoration of fluid overpressure in the nucleation site may play at least as great a role in determining recurrence as the reaccumulation of tectonic shear stress (Sibson, 1990a). Suctions induced at dilational irregularities in fluid-saturated crust form an important rupture arrest mechanism, and postseismic redistribution of fluids helps to account for the time-dependent decay of aftershock activity. The linkage of fracture permeability, fluid pressure fluctuations, and fluid flow to the seismic stress cycle appears integral to the genesis of many hydrothermal mineral deposits (Sibson, 1990b). Ubiquitous stress cycling within deforming seismogenic crust thus impacts a range of allied processes. Mountain building and fold amplification, basin subsidence, mass movement, turbidite sedimentation, and the migration of hydrothermal and hydrocarbon fluids through fracture systems in the upper crust all tend to occur episodically in increments coupled to the earthquake stress cycles of the dominant active structures within a region. Geologists accustomed to think of steady, slow-acting processes must take account of the inherently episodic character of deformation in the upper, seismogenic crust. References Bergman, E. & Solomon, S., 1988, J. Geophys. Res. 93: 9027-9057. Carey, S.W., 1954, Geol. Soc. Aust. 1: 67-117. Chen, W.P. & Molnar, P., 1983, J. Geophys. Res. 88: 4183-4214. Hill, D.P., Eaton, J.P., & Jones, L.M., 1990, U.S. Geol. Surv. Prof. Pap. 1515: 115-151. I to, K., 1990, /. Phys. Earth 38: 223-250. Fredrich, J., McCaffrey, R., & Denham, D., 1988, Geophys. J. R. Astr. Soc. 95: 1-13. Oxburgh, E.R., 1972, Nature 239: 202-204. Sibson, R.H., 1983. Geol. Soc. Lond. 140: 741767. Sibson, R.H., 1984, J. Geophys. Res. 89: 57915799. Sibson, R.H., 1989, J. Struct. Geol. 11: 1-14. Sibson, R.H., 1990a, Bull. Seism. Soc. Am. 80: 1580-1604. Sibson, R.H., 1990b, Min. Assoc. Can. Short Course Handbook Vol 18: 93-132. Wesnousky, S. 1988, Nature 335: 340-343.

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THE ROLE OF STRUCTURAL GEOLOGY IN THE ANALYSIS OF TECTONIC PROCESSES John G. Ramsay ETH Zurich, Switzerland

Over the past three decades the subject of structural geology has made many advances, particularly in establishing the significance of outcrop scale structures observed in the field and how these features may be used to understand the rheological properties of deforming rocks and larger scale tectonic features of the Earth's crust. The classic work on rock deformation by Ernst Cloos (1947) in the Appalachian mountain belt showed how strain data could greatly enhance our understanding of rock structures, and the techniques he used have been refined today into keen-edged practical working tools for field geologists. Those investigating the features of naturally deformed rocks seek finite- and incremental-strain data because this data offers the key to understanding the significance of the different types of tectonically formed planar and linear fabrics as well as to the reasons for the wide rangeing geometry of large and small scale folds and fractures observed in nature. The understanding of tectonics, both from kinematic and mechanical viewpoints, has in the past generally proceeded from exploration mapping outlining the overall geometric framework of a deformed region, to the mapping of fold and fault patterns establishing tectonic style and, perhaps as an end product of research, to calculations of the overall regional shape changes, displacements and stress fields responsible for the tectonic activity. At all stages of such a research campaign the study of the nature and orientation of outcrop scale structures has much to

Geological Society of Australia Abstracts Number 32, Ballarat 1992

offer in clarifying rock geometry and mechanical processes. The way such integration of structural observations with tectonic development can go forward will be presented using examples of work carried out by an ETH research group in the Himalayas of north east Pakistan. The use of clay analogue models to study the formation of fractures and folds developed by Hans Cloos in the 1930's proved to be a very stimulating method for realising the mechanical development of tectonic structures. Over the past 20 years analogue models have been increasingly used to help this understanding, with materials more appropriately chosen to simulate, at the model scale, the properties of rocks as we now know them from laboratory rock testing, and with more sophisticated control over strain rates, displacements and deformations in the models. Perhaps the greatest revolution in modelling technique over the past decade, and one likely to control much future work, is numerical modelling using fast digital computers. Such studies have added much to our understanding of fold development, fracture and shear zone propagation. Finite element and finite difference methods are extremely powerful tools because they allow geometric predictions to be made over a wide range of ductile and materials including those with non-linear stress-strain and stress-strain rate properties. What needs to be undertaken in the future are more precise checks between the predictions of the numerical models and the actual features of naturally deformed rocks seen in the field.

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S. Warren Carey Graduated from the University of Sydney as Bachelor or Science with First Class Honours in 1932, Master of Science in 1933 and Doctor of Science in 1938. From 1932 to 1940 he worked in New Guinea and Papua as a geologist for Oil Search Limited and the Australasian Petroleum Company, and from 1942 to 1944 he served as a paratroop commando in the Australian army. From 1944 to 1946 he was Chief Government Geologist of Tasmania, and since 1946 he has been Professor of Geology at the University of Tasmania. He is a past president of the Australian and New Zealand Association for the Advancement of Science and the Geological Society of Australia! In 1962 Professor Carey was awarded the Gondwanaland Gold Medal, and in 1972 the Clarke Medal. In 1970 the University of Papua New Guinea conferred an Honorary Doctorate of Science. He is an Honorary Life Member of the Geological Society of London and of the Royal Society of New South Wales, and is an Honorary Foreign Fellow of the Indian Academy of Science. C 9

PANGAEA, THE PACIFIC, AND COSMOLOGY S. Warren Carey University of Tasmania

Pangaea reconstructions by Wegener in 1915, Carey 1945, Dietz and Holden 1970, and more recent writers, differ only in detail. All begin by closing the Atlantic and show Pangaea occupying a hemisphere, with an enlarged Pacific Ocean filling the hidden

hemisphere. All assumed constant Earth radius, and that newly added area was balanced by subduction in the trenches. Ager, reviewing 35 years of study of Mesozoic brachiopods wrote:

It difficult to accept different explanations for the same phenomena which occurred in the various great oceans of the world. On balance, I prefer to think that all the oceans have been expanding since early Mesozoic times. If then, we begin by closing the Pacific, the reconstructed Pangaea fills a hemisphere with the expanded Atlantic occupying the hidden hemisphere (Figure 1). Closure of the Pacific solves many anomalies. A Pacific source is needed for a million cubic kilometres of Devonian micaceous sand in Bolivia, Peru, and northern Argentina. The missing continuation of the Proterozoic of North America, which is truncated by the Cordilleran, complements the missing cratons Kuroshio and Oyashio in the Pacific Ocean east of Japan, which supplied pebbles to the basal Triassic conglomerates in the Kitikamo Mountains. Likewise the Torlesse facies of New Zealand and New Caledonia require an extensive eastern source, Archaeofijia, where only deep ocean exists today. The disrupted Proterozoic, Palaeozoic, and Cretaceo-Tertiary orogenic belts are restored. The Arctic Ocean has opened 30° radially from the early Mesozoic pole while palaeomagnetic investigations have established that the Gulf of Alaska has opened some 50° about the same centre. This combination is only possible with Geological Society of Australia Abstracts Number 32, Ballarat 1992

gross expansion. Apart from Ager's concern about brachiopods, many other fossil distribution disjuncts are anomalous: the close relations of Permian corals and fusulinids across the Pacific between North America and east Asia; the occurrence of Cathaysian Cycadeoidea of apparent North American origin in Mongolia and Japan, barred from a Bering bridge by the Arctomesozoic Phoenicopsis flora; similarly the horned dinosaurs; the hungalid-calemenid trilobites in southeast Asia Australia and South America and virtually nowhere else; some 70 graptolite species, common in the Ordovician of eastern Australia and western North America, have higher similarity indices than other regional comparisons; the Pacific province of Devonian conodonts linking east Australia and western North America; tropical butterfly families with Mesozoic ancestry in New Guinea and Central America; Shields claims that Australian marsupials entered both Australia and South America via Central America before the opening of the Pacific and that comparative morphology and serology indicate

17 subsequent independent evolution. The combination of a closed Atlantic and a closed Pacific is only possible on a very much smaller early Mesozoic Earth. Great oceans date only from the Cretaceous. Symmetrical growth from spreading ridges found in the Atlantic has been falsely assumed to be general and applied to the north Pacific. Subduction is a myth and all ocean floor that ever was, still is.. A greatly reduced radius with unchanged mass would imply much greater surface gravity as recently as the Palaeozoic, which we would certainly have observed. The alternative is that mass and volume have increased pari passu. Many cosmologists have invoked spontaneous mass accretion. Jeans and McRea postulated mass creation in the cores of galaxies where mass is already most concentrated, while Stothers argued that mass is created in the depths of space where it is lacking because it is lacking. If a mass be added to the universe, potential energy is added as attraction to every other mass in the universe; this added energy is equal and opposite to the added mass; Mass and energy are like two sides of a coin—one cannot exist without the other. In the beginning, the mass-energy sum was zero. It remains zero now, and forever more. The Big-bang theory requires the whole mass-energy of the cosmos to appear spontaneously from nothing. Earth expansion implies similar expansion throughout the solar system. Rising internal temperature reduces density through both thermal expansion and mineral paramorphism, but because of feedback, convective ascent becomes increasingly localized to form surface tumours, and asymmetry of figure such as Earth's 'pear-shape'. But as departures from isostasy relax in times geolocically short, diapiric tumours, while standing higher isostatically, have greater moment of inertia, which perturbs rotation. The rotation axis creeps towards the axis of maximum moment of inertia. Earth's poles have 'wandered' throughout geological history as orogenic tumours and new oceans disturbed the inertia moment balance. Much more new ocean crust has been inserted in the southern hemisphere than the northern, and continents have generally migrated northward. Similarly the rotation axes of most planets and their satellites are oblique to the ecliptic following their expansion asymmetry. The 'back' face of Moon stands higher isostatically then the near face. The southern hemisphere of Mars stands higher than the northern hemisphere, which was periodically flooded by Oceanus Borealis, and glaciation was much more extensive in the south. All the current volcano tumours on Mars are in one hemisphere., and the great equatorial rift system is confined to one hemisphere. Mercury shows a global polygonal fracture system which cuts across the craters. Jupiter's Great Red Spot indicates that planet's asymmetry. Geological Society of Australia Abstracts Number 32, Ballarat 1992

Empirically, rate of expansion is a function of mass. Some 3,000 asteroids less than 100 km in size are irregular rocks. 30 asteroids and 11 planetary satellites between 100 and 250 km are irregularly shaped with density less than 2. Above 250 km radius and mass 1 0 kg, five asteroids and eight satellites become spherical, tend to show polygonal surface fractures, and the first signs of vulcanism and outgassing, though still on the flat part of the quasiexponential growth curve. At 1 0 " kg, which includes Moon, Mercury, and Mars and the six largest satellites (all still on the flat part of the growth curve), density exceeds 3, vulcanism becomes prominent, and there may be a tenuous atmosphere. At 10 kg, which includes Earth and Venus, now on the steepening growth curve, density exceeds 5, with extensive vulcanism, a fluid core, rapid expansion disrupting the lithosphere, and thick atmosphere. Above 10 kg, which includes Uranus, Neptune, and Saturn, a threshold of rapid expansion is passed, density drops to below 2, and rings appear. At 10 kg (Jupiter) the planet becomes a net radiator, like an embryo star. At 10 kg we enter the field of brown dwarf stars, like Van Briesbroek 8B radiating in the infrared at 2000° K. Expansion through the solar system, implies general mass creation throughout the cosmos. The great majority of stars fall on a sigmoidal curve called the Hertzsprung-Russell Main Sequence, from brown dwarf stars with mass one hundredth of the mass of Sun, through red stars half the mass of Sun, yellow stars like a-Centauri and Sun, to white stars like Sirius about twice Sun's mass, to blue-white (3Centauri nearly ten times as massive as Sun, to Sandaleuk 69° 202 in the Large Magellanic Cloud, about 18 solar masses, which exploded as a Supernova in 1989 (Figure 2). This empirical star distribution is called the Main Sequence, but it is not treated as a sequence because mass is falsely regarded as constant, and therefore each star is confined to the ordinate of the graph. On the contrary, I claim that it is a sequence and that as they grow in mass, stars progress along the sequence from Jupiter through brown dwarfs, red, yellow, white, and blue stars to final supernova explosion, to a final pulsar stage and black hole. On the way they pass through several nova episodes and pulsation variables. Some 10 years ago when Sun was half its present mass it exploded as a nova, exactly like Betelgeuse and Antares now (red giants half Sun's mass but radius but 500 times Sun's and density one thousandth of air). That was the so-called gas cloud from which the solar system evolved. Such red giants soon return to the main sequence, because they are so luminous that if they survived long there would be very many more of them now visible. When Sun's mass increaces by half, it will become a Cepheid variable, which would of course destroy any 2 0 - 2 1

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18 life on Earth. Every galaxy in the cosmos is surrounded by its Newtonian centripetal gravity tension which, in a finite cosmos, would lead to inward collapse of its bounding surface. In an infinite cosmos without any bounding surface and without any unique centre to focus collapse, universal tension prevails, and every galaxy perceives itself to be at rest while its neighbour is receding, and the next galaxy receding twice as fast, and the more distant galaxies receding at speeds increasing with their distance—hence Hubble's empirical law. Newton's Law and Hubble's law are two aspects of a single gravitational law: Newton's law of the field of a single mass, and Hubble's law for the field of all cosmic matter: Force

=

Mm G (1/d - ad H / c ) Newton Hubble 2

2

4

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(a is a pure number scaling factor) Newton's empirical law was based on Kepler's analysis of the orbit of Mars, on which scale the Hubble term is undetectable, but Hubble's empirical law was based on galactic distances, 10 times as great. The Newton term diminishes with the square of the distance while the Hubble term, vanishingly small at first, increases with the square of the distance until it cancels the Newton term at the Newton-Hubble null, beyond which the Newton's term rapidly becomes insignificant (Figure 3). The billion billion galaxies in the universe are a gaussian distribution in size, but conventional physics has no reason for this size rather than a million times larger or smaller. The precise reason now becomes clear. Within the Newton-Hubble null, matter is under gravity control of the galaxy. Beyond the Newton-Hubble null, matter moves away from the galaxy. The nearest neighbours of our galaxy are the Magellanic Clouds already a little beyond the null, hiving off from our galaxy. The great galaxy M31 in Andromeda is about twelve times that distance. Our local group of galaxies, the Milky Way galaxy, Magellanic Clouds, M31, and a dozen others budded from a single galaxy. Conventional physics begins cosmology assuming a zero stress field, but the universal cosmic tension affects matters on all scales from Planck distances of 10~ to cosmic distances of 1 0 m. For any observer, the universe is limited by the distance where matter appears to him to be receding at the velocity of light, whereas an observer there would consider himself to be at rest while the first observer appears to recede from him at the velocity of light, like the reciprocal relations of two mariners who each sees the other on his horizon. There are as many horizons as there are mariners, and there are as many universes as 11

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Geological Society of Australia Abstracts Number 32, Ballarat 1992

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there are observers to define them. In conventional theory, cosmos and universe are synonyms, but our universe is our physically knowable domain, while the cosmos is the infinite realm with an infinity of universes each defined from a point from which it is observed. The hypervolume of a universe is constant (C /H ), which has the dimensions, L , as galaxies constantly appear to reach the velocity of light, and pass beyond our physical ken. Mass of a universe is also constant as new matter is created (along with exactly equal potential energy). Thus each universe is a steady state like a sample of rain forest where old trees constantly die and new seedlings replace them, or a reach of a river where water constantly enters at the higher end and leaves at the lower. The Big Bang theory was conceived by Gamov in the thirties to explain the universal recession of galaxies just discovered by Hubble. The recession had nothing to do with an explosion, but merely to Newton's law in an infinite cosmos. When Penzias & Wilson in the sixties accidentally found a universal background radiation, it was interpreted as the last gasp of the big bang explosion and Gamov's big bang was accepted as proven. But such a universal background radiation is inevitable in any steady-state cosmos. At the limit of the best telescopes (at redshift z= 4), there are as many galaxies as there are stars in our Milky Way galaxy. But they are already so faint as to be scarcely detectable, and the angle separating galaxies averages only 4n x 1 0 " steradians, an extremely small angle. But galaxies continue on unseen beyond, until the decreasing angular separation between them reaches the Raleigh criterion of resolution limit which depends only on focal length and aperture. Beyond this distance galaxies cannot be separated by the telescopes and fuse into a continuous field of radiation (Figure 2). But at this distance, the Hubble red-shift has gone far beyond the visible spectrum into the microwave band a couple of degrees above absolute zero. Here indeed is the universal white-out predicted by Olbers, not at the blazing temperature of the Sun's surface as he expected, but at 2.7° K. Apart from the collapse of its raison d'etre, the bigbang theory is fraught with anomalies, such as the unsolved horizon, smoothness, flatness, and singularity problems. What triggered the bang, before which neither time nor space existed, nor even laws of nature? The concentration of all the mass-energy of the cosmos should have meant total gravitational collapse, not expansion. Actually the theory postulates that the beginning was pure radiation, and that matter only appeared a thousandth of a second later, at which point or soon afterward with the waning of the 'strong force', gravitational collapse should have occurred. 4

4

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19

Figure 1. Pangaea with closed Pacific, and presaent Earth radius. Mollweide projection. Coarse stipple: Tethyan orogenic belt. Medium stipple: Caledonian-Appalachian-Tasmanide orogenic belt.. Fine stipple: Cordilleran orogenic belt: B, Broken Ridge. C, Crozet. K, Kerguelen. L, Laccadive. M, Maldives. P, Pole. S, Seychelles. T 15M0

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20 UNIVERSE

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Geological Society of Australia Abstracts Number 32, Ballarat 1992

COSMOS

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21

A 1: REGIONAL GEOLOGY (LACHLAN FOLD BELT) CONVENOR: A.H.M

VANDENBERG

KEYNOTE: A 1.1 ACCRETION OF ALLOCHTHONOUS TERRANESrTHE KEY TO THE TECTONIC DEVELOPMENT OF THE LACHLAN OROGEN AND TO ITS MAJOR GOLD DEPOSITS R.A.Glen *, E.Scheibner and A.H.M Vandenberg 1

1

2

Geological Survey of New South Wales, Department of Mineral Resources, Box 536 P.O. St Leonards, NSW 2065. Geological Survey of Victoria, Department of Manufacturing and Industry Development, Box 173 P.O. East Melbourne, Vic.3002 1

2

Where is the boundary between the Lachlan Orogen and the Delamerian Orogen to the west? What does this boundary look like? Why are there S-type granites in Central Victoria, where the oldest rocks are of oceanic island arc affinity? What is the substrate to the Lachlan Orogen? Why are folds and thrusts in central Victoria almost all east verging, in contrast to the mixed vergence farther east in the orogen? What events caused the thin-skinned deformational style of the Lachlan Orogen? Why is this thin-skinned style partitioned into meridional and latitudinal+strike-slip structures? Why do the central Victorian Ordovician turbidites host phenomenally rich gold deposits? Why are Ordovician turbidites of New South Wales and east Gippsland extremely poor in gold? Are there tectonostratigraphic terranes in the Lachlan? Where was Tasmania during the Palaeozoic? How wide was the Lachlan, and was there ever a gigantic Bengal-type fan needed to deposit Ordovician turbidites? These important questions can be answered by proposing a model for the evolution of the Lachlan by major transpressional duplication of crustal flakes, that is, by the amalgamation of allochthonous tectonostratigraphic terranes into the Lachlan. The Lachlan Orogen is divided into four structural belts which themselves represent amalgamations of smaller structural zones (Fig.l). Critical to this paper are the relationships between the Southwestern Belt (incorporating the Bendigo-Ballarat and Melbourne zones and the northeastern part of Tasmania), and the Central Belt (Wagga-Omeo zone) with the Eastern and Western belts. The allochthonous nature of the Southwestern Belt is indicated by: 1) the unique presence of a Cambrian greenstone-chert association; 2) differences between its Ordovician history (especially in the east) and the Ordovician of the Howqua zone in the Western Belt Geological Society of Australia Abstracts Number 32, Ballarat 1992

across the Mount Wellington Fault Zone to the east; 3) similarities between its Ordovician to Early Devonian history and that of the Eastern Belt, and to a lesser extent that of the Mathinna beds of northeasten Tasmania. These points lead to the conclusion that: 1) the Southwestern Belt constitutes the MelbourneMathinna terrane which, from the CambrianOrdovician to the Late Silurian, lay along strike from the Eastern Belt, southeast of the mainland and separated from it by a major transfer zone. This transfer marked the changeover between thinned Precambrian continental crust to the north and Cambrian oceanic crust to the south. The transfer zone was later reactivated as a tear, shielding the terrane from mid-Palaeozoic deformation to the north. In this position, the Melbourne-Mathinna terrane was distal to the deforming Delamerian Orogen and did not experience any deformation or receive any classical molasse; and 2) the Central Belt (Wagga-Omeo terrane) was not formed in its present position but during the Ordovician lay to the north. Southward migration of the Central Belt as a crustal flake occurred in the Late Ordovician. Transpressional amalgamation with other parts of the Lachlan led to formation of latitudinal and meridional structures, including thrust sheets, and LP-HT metamorphism centred on the Wagga-Omeo zone which formed the leading edge of a multisided deforming wedge and underwent most crustal thickening. Deformation spread outward from this belt. Northward drift (escape tectonics) of the Melbourne-Mathinna terrane as a crustal flake with adhering Cambrian greenstone basement can first be detected in the Early Devonian. For the first time, there was an eastern edge to the so-called Melbourne

22 Trough, with the Walhalla Group deposited from the Benambran highlands to the east. Accretion of this terrane with the Delamerian Orogen occurred in the Early Devonian. In Tasmania, the terrane was thrust over the Australian neocraton along the Tamar fault. On the mainland, the terrane was thrust as a tectonic wedge into the Australian neocraton, with the Avoca fault being the frontal splay off a passive roof thrust. Subsequent amalgamation of the Melbourne-Mathinna terrane with other parts of the Lachlan occurred to the north, by thrusting onto the "missing" miogeocline of the Lachlan Orogen, and to the east, by thrusting onto the extended and subsided Western Belt east of the MWFZ. East vergent structures coupled with strikeslip along major faults resulted from both events. Fluid circulation generated during accretion/

amalgamation of the Melbourne-Mathinna terrane scavenged gold from the Cambrian greenstones at the base of the crustal flake (some 12-15 km thick). This gold was subsequently deposited in structural traps higher up in the Ordovician and Siluro-Devonian sequences. Recognition of strike-slip duplication in the Lachlan Orogen reduces its post-deformational width from 500-600 km down to about 350 km and obviates the need to postulate a super giant Bengal-type fan to deposit the Ordovician turbidites. Published with the permission of the DirectorGeneral, New South Wales Department of Mineral Resources, and the Director, Geological Survey of Victoria.

Figure 1. Subdivision of the Lachlan fold belt into four structural belts. A 1.2

GEOLOGY OF THE REEDY CREEK AREA, NORTHEASTERN VICTORIA. J. W. Bradley and L. H. Thorne Department of Mining, Geology and Materials, Ballarat University College, Victoria.

The Reedy Creek area is located approximately sixty kilometres north of Buchan in northeastern Victoria. Rocks found in the area belong to the Buchan Zone (Gray et. al. 1988) of the Lachlan Fold Belt. This zone was active from Ordovician to Mid Devonian times. The Ordovician rocks comprise deep marine turbiditic quartzitic sandstones and interbedded siltstones (Broadbent River Formation), thin Geological Society of Australia Abstracts Number 32, Ballarat 1992

interbedded light sandstones and dark siltstones (Sunlight Creek Formation) and black shales (Warbisco Shale). During the Silurian the depositional environment was that of a submarine fan, with sediments (Seldom Seen Conglomerate, Towanga Sandstone) being derived from uplifted Ordovician rocks and deposited in a subsiding trough. The onset of primarily rhyolitic volcanism

23 (Thorkidaan Volcanics) during mid-Silurian times suggests that rifting of the basin floor had commenced (Cowombat Rift). Grey green siltstones and minor sandstones (Cowombat Siltstone) were also deposited and are considered time equivalents of the Thorkidaan Volcanics. An angular unconformity separates the Cowombat Siltstone from the rhyodacitic/rhyolitic ignimbrites of the Snowy River Volcanics which are of Lower Devonian age. At least three stages of deformation affect the area: 1) a cleavage preserved in the porphyryblasts of Ordovician metasediments, 2) a strong east-west striking regional cleavage and, 3) a later crenulation cleavage. Regional faults differ from that of the rest of the

Lachlan Fold Belt in striking predominantly east-west rather than north-south, possibly indicating a sense of dextral shear. Gray et. al. (1988) found similar structures of Early to Mid Silurian age (Benambran Orogeny) to the east in the Tabberabbera Zone. The metamorphic grade of the area regionally is greenschist, however evidence of retrogression in porphyryblasts (cordierite to biotite) in Ordovician metasediments is present. References Gray, D., L., Allen, R., L., Etheridge, M., A. et. al. (1988): Structure and Tectonics. In (Douglas, J.G.. & Fergusson, J., A., Eds), Geology of Victoria, Vic. Div.Geol. Soc., p 5-36.

A 1.3 GEOLOGY OF THE BEAUFORT REGION, WESTERN VICTORIA; ASPECTS OF THE DEPOSITIONAL & STRUCTURAL STYLE OF THE EASTERN STAWELL ZONE. Ross A. Cay ley Geological Survey of Victoria, 115 Victoria Parade, Fitzroy, Vic.3065, Australia. The Stawell Zone of western Victoria represents the easternmost extension of the Adelaide Fold Belt into Victoria. Late Proterozoic metavolcanic rocks are overlain by unfossilliferous ?Cambrian turbidites of the St Arnaud Beds. This sequence has been subjected to two major periods of deformation, between which the Late Silurian-Early Devonian Grampians Group was deposited in an extensional basin. Di to D3 events predate the Grampians Group, and were accompanied by regional middle to upper greenschist facies metamorphism, while post-D3 structures deform them and are also superimposed regionally upon the earlier structures. (Wilson et al., in press). Early Devonian post-kinematic granites intrude the entire sequence. Due to similarities between rocks of the Glenelg and Stawell zones, the western margin of the Stawell Zone is difficult to define, perhaps lying beneath the Grampians, while the eastern margin of the Stawell zone probably coincides with the high-angle, northerly-trending Avoca Fault (Gray & Willman, 1991). The eastern Stawell Zone: Between Ararat and the Avoca Fault it has been possible to recognise a number of stratigraphic units within the St Arnaud Beds (Group). The temporal relationship between these units, and the distribution and/or presence of large scale structures is hampered by the lack of any biostratigraphic control, and poor outcrop. However, distinct packages of turbidites are recognised using sand/shale ratios, mean bed Geological Society of Australia Abstracts Number 32, Ballarat 1992

thickness, and variations in fold style. Sand-poor (phyllosilicate rich) sequences tend to be more thinly bedded, and display lower structural competence than the sand-rich sequences. Consequently, the bulk of the deformation has been accommodated in generally westdipping zones of high strain developed in the weakest (sand-poor) units adjacent to thrust faults which juxtapose sand-poor and sand-rich sequences as in the Landsborough Fault Zone. Early deformations (D1-D3) are responsible for the regional folding and accompanying thrusting in this part of the Stawell zone. The effects of this early (preLate Silurian) deformation extend eastwards to the Avoca Fault zone where they become reoriented and overprinted by crenulations associated with later juxtaposition of the Stawell and Ballarat-Bendigo zones during the Middle Devonian Tabberabberan event (Gray & Willman, 1991). Late crenulations observed adjacent to early thrust faults within the Stawell zone suggest partial reactivation. Breccias occasionally preserved adjacent to the granites possibly relate to 'roof uplift' during intrusion. Miarolitic cavities within some of these granites indicate shallow levels of emplacement, possibly facilitated by regional uplift of country rocks above the ascending plutons. Breccias developed between lifted and in situ country rocks provided a fracture zone exploited by the ascending magma. This model helps explain the abrupt granite-country rock contacts, often cutting regional bedding trends, that typify the Stawell zone.

24 Australia. Aust. J. Earth Sci., 38: 171-201. Wilson, C.J.L., Will, T.M., Cayley, R.A., & Chen, S., 1991. Geologic framework and tectonic Gray, D.R. & Willman, C.E., 1991. Deformation in evolution in Western Victoria, Australia. the Ballarat Slate belt, central Victoria and Tectonophys. in press. implications for crustal structure across SE

References

A 1.4 THE LACHLAN FOLD BELT OF SOUTHEASTERN AUSTRALIA: INTRAPLATE DEFORMATION IN A CONVERGENT OROGENIC SYSTEM Peter J. Coney and Christopher L. Fergusson * 1

2

Department of Geo sciences, University of Arizona, Tucson, Arizona 85721, USA Department of Geology, University ofWollongong, PO Box 1144, Wollongong, NSW 2500, Australia 1

2

The Lachlan belt of southeastern Australia is an atypical continental margin orogenic belt with the following distinctive characteristics: (1) a wide zone of Silurian to Carboniferous (100 Ma) deformation now up to 700 km in width characterized by isoclinal folds, thrust faults, and cleavage development representing 50-70% shortening, and some evidence for zones of strike-slip and intermittent extensional faults, all superimposed on a remarkably homogeneous exposed crust dominated by minor deep marine Cambrian greenstones, thick Ordovician greywacke, and Silurian-Devonian clastic and volcanic rocks. (2) a similar broad extent of silicic plutonic rocks showing an erratic pattern of distribution that often exhibits a close relationship to timing of deformation with plutonism concentrated in regions that have just experienced regional deformation. For example, some of the youngest deformation and plutonism is in the centre of the belt. The tectonic evolution of the Lachlan belt has been an enigma for years as the exact plate tectonic setting has been unclear. An intercontinental "Himalayan" collision setting seems unlikely since no large

Geological Society of Australia Abstracts Number 32, Ballarat 1992

continental object can be identified in past or present Pacific palaeogeography. A continental margin "Andean" subduction driven setting is more likely, but explanation of the complex deformational and magmatic patterns by "flapping" Benioff zones such as has been proposed in western North America seems, although possible, somewhat "ad hoc" and contrived. We propose instead to focus on the intraplate character of the system and suggest that the belt developed on a somewhat unusual highly attenuated (?) up to 2,000 km wide "Pan African" quasi-oceanic-continental lithosphere caught in a generally convergent setting between rigid oceanic lithosphere in the "Pacific" realm in the "east" and rigid continental lithosphere in the Gondwanaland realm to the "west". The 100 Ma deformational history was perhaps characterized by subduction of Pacific lithosphere (early New England belt?) and occasional "roll-backs" from the "east", but a significant percentage of the relative convergent motion was absorbed by intraplate failure, crustal thickening and melting, possible aborted attempts at intraplate subduction and/or delamination, oblique intraplate strike- slip shear and occasional extension which finally consolidated the Lachlan belt into cratonic Australia by mid-Carboniferous time.

25

A 1.5

EARLY TO M I D D L E CAMBRIAN GEOCHEMISTRY AND T E C T O N I C S OF N O R T H W E S T E R N N.S.W. B.P.J. Stevens 1 * and A.J. Crawford2 1 Geological Survey of New South Wales, Broken Hill NSW Department of Geology, University of Tasmania, Hobart Tas

2

Outcropping Early to Middle Cambrian rocks in northwestern NSW are largely confined to the Kanmantoo Fold Belt. West of the Koonenberry Fault they rest on and are faulted against probable Proterozoic rocks. East of the fault, no Precambrian rocks are known. Turbidites of the Teltawongee Beds (Mills, in prep.) are widespread east and west of the Koonenberry Fault, as far north as Koonenberry Mountain. They contain no volcanics, but east of the fault are intruded by quartz dolerite-diorite dykes with calc-alkaline arc affinity. The Beds were strongly folded in the late Middle Cambrian during the Delamerian Orogeny. Volcanics and shallow marine deposits of the Gnalta Group (Mt Wright Volcanics, Cymbric Vale Formation, Coonigan Formation) occupy a small area (100 sq. km) west of the Mt Wright Fault. This fault contains serpentinites with tectonic inclusions of amphibolite with marginal sea basalt chemistry resembling that of the adjacent Proterozoic Ponto Beds. The Mt Wright Volcanics exhibit calk-alkaline continental arc and transitional within-plate affinity. The calc-alkaline volcanics are predominantly andesitelatite, but include minor pantellerite-comendite. The one calc-alkaline dyke analysed is a micromonzonite. The within-plate rocks are alkaline microdolerite and trachyandesite. The Volcanics are intruded by minor very fine grained rhyolite dykes and overlain by the Cymbric Vale Formation which contains rhyolitic tuff with well-preserved shard structures. Both formations also contain shallow marine sediments, including limestone. The Gnalta Group was deformed during the Middle to Late Cambrian. At Mt Arrowsmith the Middle Cambrian Pincally Formation comprising shale, siltstone, tuffaceous sandstone and limestone, is overlain conformably by further shallow water deposits, which are unconformably overlain by Ordovician sediments. "Andesite" and acid volcanics below 3100m of Late Silurian-Devonian sediments in hole Bancannia South No. 1, in the Bancannia Trough, have been correlated with the Gnalta Group (Planet Exploration Co. Pty Ltd). Analyses of two samples of "andesite" show trachyandesite-dacite chemistry similar to some rocks in the Mt Wright Volcanics, but probably closer to that of volcanics in the Late Silurian-Early Devonian Mt Daubeny Formation. The Tibooburra-Milparinka Inliers contain highly deformed sediments, volcanics and intrusives of Geological Society of Australia Abstracts Number 32, Ballarat 1992

possible Early-Middle Cambrian age. The Tibooburra Inlier is part of the Thomson Fold Belt, separated from the other inliers by the Olepoloko Fault. The ages are poorly constrained. Deltaic metasediments of the Tibooburra Inlier predate the 410 Ma Tibooburra Granodiorite. The Warratta Inlier contains deltaic to shallow marine sediments, including minor limestone and phosphate, and trace fossils of latest Proterozoic to Early Ordovician age. A dioritic dyke from the Mt Poole Inlier gave a K-Ar date of 372±8 Ma (Webb, 1990), probably reset during deformation. The Tibooburra-Milparinka Inliers contain a range of volcanics and sills/dykes. In The Gorge Inlier there are great thicknesses of rhyolitic tuff indicative of a major pyroclastic centre, possibly with cauldron subsidence and giant ignimbritic eruptions. Thinner acid volcanic units in other inliers may be distal equivalents. The Mt Poole Inlier contains monzodolerite dykes and the Tibooburra Inlier contains alkali basalt sills or volcanics which have very similar within-plate, alkaline chemistry. The Tiboobura Inlier also contains minor shoshonite/latite with calc-alkaline affinity. The Warratta Inlier contains latite to alkali rhyolite dykes, and the Mt Poole Inlier contains dioritic dykes with transitional chemistry. The inliers are situated 140 km along strike from the Teltawongee Beds, but the rocks bear little resemblance. They are either different in age or have suffered a different tectonic history. Scheibner's (1974) tectonic model for the Early to Middle Cambrian comprised from west to east: the Proterozoic continent, the Bancannia Marginal Sea, the Mt Wright Volcanic Arc (on microcontinental basement), the Gnalta Shelf, the White Cliffs Deeper Terrace and a westward-dipping subduction zone. Current information requires some changes, but has so far not produced a unique interpretation. There is now no evidence for a Bancannia Marginal Sea; the Bancannia Trough was more likely a Late SilurianDevonian continental rift. The Mt Wright Volcanic Arc is greatly reduced in size and credibility since Edwards (1979) showed the Mt Arrowsmith volcanics to be alkaline and Mills (in prep.) assigned them to the Proterozoic Kara Beds. The "Arc" now comprises a small area of volcanics near Mt Wright and perhaps the tuffaceous Pincally Formation near Mt Arrowsmith. Similarly the Gnalta Shelf appears to be confined to isolated areas near Mt Wright, Mt

26 Arrowsmith and Comarto. These are fault-bounded slices and their relationships with the Teltawongee Beds turbidites are unknown. Scheibner's (1974) White Cliffs Deeper Terrace was confined to the area east of the Koonenberry Fault and represented by the Copper Mine Range Beds. These are now incorporated into the Teltawongee Beds which occur on both sides of the fault. The inliers between the Koonenberry and Olepoloko Faults, in the Milparinka area, lie along strike from the White Cliffs Deeper Terrace, but contain deltaic to shallow marine sediments, acid volcanics and within-plate intrusives, suggesting a more stable, continental basement. Alternative tectonic models involve either the existence of a collection of unrelated terranes (Leitch et al.,1987), or eastward dipping subduction below elements of the Thomson Fold Belt, leading to collision along the Olepoloko Fault.

A 1.6

References Leitch, E.C., Webby, B.D., Mills, K.J. and Kolbe, P., 1987. Terranes of the Wonominta Block, far western New South Wales. In: E.C. Leitch and E.Scheibner (Editors), Terrane accretion and orogenic belts, American Geophysical Union, Washington D.C., 31-37. Mills, K.J., in prep., Tectonic evolution of the Wonominta Block. Tectonophysics. Planet Exploration Co. Pty Ltd, 1968. Planet Bancannia South No.l. Geol.Surv. N.S.W. Well Completion Rept 129 (unpubl.). Scheibner, E., 1974. A plate tectonic model of the Palaeozoic tectonic history of New South Wales. J. Geol. Soc. Aust., 20, 405-426. Webb, A., 1990. K-Ar geochronology. Amdel Rept G 8852/91 (unpubl.). Published with permission of the Director, Department of Mineral Resources.

HUNTER-BOWEN OROGENY: LATE PERMIAN-TRIASSIC DEFORMATION OF THE LATE PALAEOZOIC ACCRETIONARY PLATE MARGIN OF EASTERN GONDWANA R.A. Henderson *, C.L. Fergusson and E.C. Leitch 1

1

2

3

Department of Applied Geology, University of Technology, Sydney, Broadway, NSW Department of Geology, University of Wollongong, Wollongong, NSW 3Department of Geology, James Cook University, Townsville, Queensland 2

Regional Late Permian through Triassic the rotation of steeply dipping accretionary packages deformation characterises a meridional belt up to 400 during thrust transport to the west. For the forearc, km wide along the eastern margin of Gondwana. It magmatic arc and the bulk of back-arc assemblages overprints a classic active margin tectonostratigraphic one main deformation occurred with broad, open terrane composite of Late Silurian-Permian age upright folds and the local development of steep axial containing subduction complex, forearc basin, plane cleavage, especially in the east where lower magmatic arc and back-arc extensional basin elements. stratigraphic elements may show greenschist (chlorite Ultramafic-mafic rocks and associated sedimentary and zone) metamorphism. In contrast, the eastern metasedimentary assemblages are thought to comprise perimeter of the back-arc extensional basin (Gogango a poorly constrained continental borderland composite Overfolded Zone and Folded Zone of the Bowen Basin) of pre-Late Silurian age exhumed by Hunter- Bowen experienced tight, westerly verging to upright folding, deformation from a crustal position beneath the forearc intense cleavage development, and local greenschist basin. Although accretion of dissimilar outboard (chlorite zone) metamorphism. Fold generation in terranes is recognised for the eastern part of the belt, assemblages inboard of subduction complex terranes assembly long preceded orogenesis. All of the terranes was a consequence of shortening within thrust sheets. are regarded as para-autochthonous. High values of shortening in the Gogango Overfolded Our studies in the northern part of the belt have Zone and Folded Zone of the Bowen Basin are shown that deformation was thin-skinned and attributed to compression of a crustal tract weakened heterogeneous in character. Here outboard subduction by prior extension. In the eastern part of the deformed complex assemblages show polyphase deformation and belt, emplacement of an extensive Late Permianvariable, upper greenschist (biotite zone) and Triassic plutonic suite, especially prevalent for the amphibolite facies metamorphism. The dominant forearc basinal assemblage, followed deformation. structural fabric is in general gently dipping and was Uplift in the east sponsored a foreland basinal phase of induced by shear associated with thrusting. infill for the Bowen Basin represented by deposition of Substantial tracts of overturned strata are attributed to Late Permian coal measures and the Triassic Rewan Geological Society of Australia Abstracts Number 32, Ballarat 1992

27 Group. The locus of Hunter-Bowen deformation migrated progressively to the west with time as shown by Late Triassic folding of the Bowen Basin infill and

A 1.7

its cratonic apron represented by Permo-Triassic strata of the Galilee Basin.

PRELIMINARY GEOLOGICAL RESULTS FROM DEEP SEISMIC REFLECTION PROFILING IN THE GUNNEDAH BASIN AND NEW ENGLAND OROGEN R.J. Korsch*, K.D. Wake-Dyster and D.W. Johnstone Bureau of Mineral Resources, Geology & Geophysics, GPO Box 378, Canberra, ACT 2601

In early 1991, the Bureau of Mineral Resources undertook a program to acquire deep seismic reflection data in northern New South Wales to address several geological problems related to the origin and development of the Gunnedah and Surat basins. Some of these problems are: 1. The geometry of the structural units of the Gunnedah Basin. 2. The nature of the Meandarra Gravity Ridge. 3. The geometry of the Mooki Fault. 4. Whether the Tamworth Belt is thin skinned, and overriding the Gunnedah Basin. 5. The geometry of the Peel Fault (the eastern margin of the Tamworth Belt) and its relationship to the Gunnedah Basin and Tamworth Belt. 6. The relationship between the Lachlan and New England Orogens. A single, east-west oriented, deep seismic reflection profile 253 km long was acquired at about the latitude of Boggabri, across the Gunnedah Basin and Tamworth Belt and farther east across the Peel Fault in the New England Orogen. Recording parameters were selected to acquire data to 20 s record length to enable the relationships between basin geometry and crustal structure to be examined (see Wake-Dyster & others, this volume). In the vicinity of the seismic line, the Gunnedah Basin succession is relatively thin and consists of three sub-basins separated by two ridges. The maximum thickness of sediment appears to be greater than 2 km (about 1.6 s TWT) on the western side of the West Gunnedah Sub-basin. The seismic data suggest that the two ridges are not structurally controlled, and also there is no evidence of major structures that can be interpreted as bounding faults to the three sub-basins. Within the basement below the Gunnedah Basin there is an apparent lack of dipping structures, which possibly could indicate that this part of the line was not affected by major extensional or contractional structures. The Mooki Fault is not imaged clearly but appears have a shallow dip to the east. The Tamworth Belt appears to have been thrust over the eastern margin of the Gunnedah Basin for at least 6 km. The western half of the Tamworth Belt of the New Geological Society of Australia Abstracts Number 32, Ballarat 1992

England Orogen displays a relatively simple structural geometry dominated at the surface by the Rocky Creek Syncline. There appears to be a relatively thick succession in the syncline (at least 5 km, 2 s TWT). To the east, the succession in the Klori Anticline appears to be over 4 km thick (1.6 s TWT). The succession in the Yarramanbully Anticline about 10 km west of the Peel Fault is not as thick. At two-way travel times of 1-4 s, the western half of the Tamworth Belt appears to be disrupted by faults that dip shallowly to the east, whereas in the eastern half of the belt the faults appear to dip moderately to the west. Directly beneath the surface position of the Peel Fault, at a depth of about 1 km (0.4 s TWT), there are reflections that dip moderately to the west indicating that this is the likely dip direction of the fault. Immediately east of the Peel Fault in the Tablelands Complex of the New England Orogen there are a series of reflections which also dip to the west. These possibly represent thrust faults within the accretionary wedge succession. The eastern end of the line was acquired on outcrops of the Bundarra Plutonic Suite. The pluton appears to have a shallow pancake shape with its floor at 6-9 km (2-3 s TWT). Although the pluton is predominantly non-reflective, a few internal structures dip to the west, confirming the results of the earlier test seismic survey. Deep crustal structures are relatively rare in the seismic profile, although strong reflections dip to the west in a zone from 10 km east of the Peel Fault to about 10 km west of the fault. The reflections have a depth of about 12 km (about 4 s TWT) in the east and about 21 km (about 7 s TWT) in the west. The Moho has a reasonably constant depth of 30-35 km (about 10-12 s TWT) across the entire profile. Reference Wake-Dyster, K.D., Johnstone, D.W. & Korsch, R.J., this volume - The 1991 BMR deep seismic reflection profile in northern New South Wales. Geological Society of Australia, Abstracts.

28 THE NORTHERN NEW ENGLAND OROGEN E.C. Leitch1*, C.L. Fergusson2, R.A. Henderson3' and V J . Morand 4 1 Department of Applied Geology, University of Technology, Sydney, Broadway, NSW ^Department of Geology, University ofWollongong, Wollongong, NSW 3 Department of Geology, James Cook University, Townsville, Queensland 4 Division of Engineering and Science, Ballarat University College, Ballarat, Victoria The northern New England Orogen contains a western terrane dominated by Devonian and Carboniferous volcaniclastic rocks (Yarrol terrane) outboard of which is a zone containing an ophiolitic assemblage (Marlborough terrane) and then a series of accretionary subduction complexes (Wandilla and Shoalwater terranes). These terranes are interleaved in a complex fold-thrust belt that extends over a distance of at least 125 km from Marlborough to the Percy Isles. The sense of thrusting is northwesterly and thrust sheets show progressively greater internal

A 1.9

ductile deformation and folding of thrust faults towards the southeast. The strike of the belt contrasts markedly with other thrust systems in the New England Orogen to the south and those in the Bowen Basin despite its similar Late Permian-Triassic age. Possible explanations for the anomalous strike of the belt are: (1) later bending, (2) deformation controlled by a pre-existing promontory in the Carboniferous continental margin arc, (3) a jog in a major sinistral strike-slip fault system, and (4) crustal extension in the Broad Sound region (sphenochasm).

THE TASMANIAN PRECAMBRIAN AND BASEMENT INVOLVED THRUSTING D.E. Leaman* Leaman Geophysics, GPO Box 320 D, Hobart, Tas. 7001

The Proterozoic rocks of Tasmania have long been presumed to be deformed exposures of the thin Tasmanian crust and to have controlled deposition and structuring due to crustal anchorage. This entire view may be challenged. Modern erosion levels have breached the cores of an array of Late Proterozoic and Early Palaeozoic alpine orogenic developments. Structural and geophysical analysis has revealed widespread basement involvements even though substantial occurrences of Precambrian rocks provide the appearance of true basement. A widespread cover of post Carboniferous rocks and difficulties in correlation of Late Precambrian and Cambrian units serves only to obscure and compound the problems of structural appraisal and relationships. Gravity and magnetic data (Leaman, 1986a, b), granitoid and hydro- carbon seepage distributions (Bendall et al, 1991), have established basic relationships between many Precambrian blocks and pre Devonian rocks. It is still unclear how much of this material actually represents indigenous Tasmanian crust since there is evidence for displacement in every block. All Lower Palaeozoic structural, stratigraphic and intrusive elements, including location of mineralisation, must be reconsidered in light of these conclusions. Geological Society of Australia Abstracts Number 32, Ballarat 1992

Many Precambrian blocks appear to have been displaced eastward before the Middle Cambrian and then to have been re-arranged, stacked and deformed by westward motions during the Devonian alpine deformations. Most Precambrian blocks have been intruded by Devonian granitoids and Precambrian rocks of "west" Tasmanian type extend east of the so- called Tamar Lineament into and beneath the "east" Tasmania "terrane". The Badger Head Block, on the central north coast, represents a piece of Precambrian basement moved westward from beneath the Mathinna Beds east of the Tamar River (Leaman et al, 1973). Parts of the Tyennan "nucleus" (Leaman, 1988) and the Hatfield and Dundas Blocks (Leaman, 1986a, b) and Cape Sorell (Leaman, 1987) have also been moved westward consistent with inferences by Carey & Berry (1986). Some other blocks near Cape Sorell, Zeehan, Temma, Smithton and the entire Rocky Cape Block have been moved eastward. Lower Cambrian ultramafics are involved in many thrust surfaces and provide part of the means to map them at depth. References Bendall, M.R., Volkman, J.K., Leaman, D.E., & Burrett, C.F., 1991. APEA /., 74-84. Carey, S.P., & Berry, R.F., 1986. Symposium Abstracts, Geol Soc Aus Burnie, November, p 35. Leaman, D.E., 1986a, b. Mt Read Reports, Dept,

29 Mines Tasm. Leaman, D.E., Symonds, P.A., & Shirley, J.E., Leaman, D.E., 1987. Cape Sorell. Mt Read Report. 1973. Dep. Mines Tas, Pap. 1. Dept. Mines Tasm.

A 1.10 TECTONIC AND THERMAL HISTORIES OF THE BALLARAT AND STAWELL ZONES, CENTRAL W VIC: RESULTS OF ILLITE CRYSTALLINITY AND BO PARAMETER STUDIES. S.W. McKnight * and R. Offler 1

1

2

School of Mining, Geology and Materials, Ballarat University College, Victoria. Department of Geology, University of Newcastle, New South Wales. 2

The Cambro-Ordovician Ballarat and Stawell zones are major structural units of the Lachlan Fold Belt and south-eastern Australia, juxtaposed by a poorly defined but obviously important suture known as the Avoca Fault Zone or The Wedderburn Line. The application of illite crystallinity (IC) and bo spacing parameters to study of the low metamorphic grade flyschoid quartz rich pelites typical of both slate belts has proved to be a sensitive indicator of metamorphism of rocks in which the penological evidence is cryptic. When the strong but localized influences of Devonian magmatism are excluded, illite crystallinities show a uniform lower greenschist facies metamorphism regionally across both zones, consistent with thin-skinned tectonic models proposed recently for the Ballarat Zone (Cox et al., 1991). A 1.11

A significant trend in the Palaeozoic geothermal gradient, however, is indicated by by spacing values within the Ballarat Zone, increasing easterly away from the Avoca Fault and displaying a marked increase in the vicinity of the N-S trending Muckleford Fault. The abnormally low Palaeozoic geothermal gradient implied by IC and bo parameters for a large tract of the Lancefieldian sequence of the Ballarat Zone, west of the Muckleford Fault is not indicated in the Cambrian Stawell Zone rocks, forming the hanging wall sequence of the Avoca Fault Zone. References Cox, S.F., Etheridge, M.A., Cas, R.A.F. and Cliffoid, B.A., 1991, Aust. J. Earth Sci. 38:151170.

MELBOURNE TROUGH PALAEOCURRENTS AND TECTONIC IMPLICATIONS

C. McA. Powell *, P.W. Baillie and A.H.M. VandenBerg 1

2

3

1 Geology Department, The University of Western Australia, Nedlands, W.A., 6009 Department of Resources and Energy, P.O. Box 56, Rosny Park, Tasmania 7018 3Geological Survey of Victoria, P.O. Box 173, East Melbourne, Vic. 3002. 2

Palaeocurrent and provenance measurements in marine turbidite units of the Mount Easton Province of the eastern Melbourne trough show a great range of compositions and palaeocurrent directions, but a high correlation between particular sandstone compositions and flow directions. Sole marks (flutes, grooves and scours) and cross-laminations from Bouma-C division of graded beds were used to measure palaeocurrent directions. Three patterns emerged: (1) East to northeasterly palaeocurrent directions are associated with relatively well-sorted, clean, fine-grained quartzose sandstones, commonly of distal turbidite facies. (2) West to southwesterly palaeocurrent directions are associated with fine- to coarse-grained, Geological Society of Australia Abstracts Number 32, Ballarat 1992

locally conglomeratic, lithic sandstones of proximal turbidite facies. (3) North to northwesterly palaeocurrent directions are associated with medium- to fine-grained sandstones of variable quartzose to lithic composition. Petrographic analysis shows that there is little feldspar in any of the samples, and that most of the lithic fragments were derived from a silicic volcanic source. This linked palaeocurrent and provenance pattern is interpreted as indicating an asymmetric NNW-trending basin geometry from latest Silurian to Middle Devonian, with a gently-sloping western side and a steep, technically active eastern side. The pattern of palaeocurrents and provenance is

30 The palaeogeography of these two assemblages can be interpreted in terms of an eastward-facing passive continental margin from Early Ordovician until midSilurian. By the Late Silurian uplift or emplacement of a silicic volcanic terrane to the east put the Melbourne trough in a back-arc or foreland-basin position in relation to the main locus of tectonic activity. This change in tectonic setting appears to have occurred during an interval of significant dextral translation of the eastern Lachlan Fold Belt towards the SSE along the Wellington and associated fault zones (VandenBerg & Stewart, 1992).

remarkably similar to that determined for the coeval Mathinna basin of Northeastern Tasmania (Powell et al. 1992), and suggests that the eastern Melbourne trough and the Mathinna basin are part of the same basin, or system of basins, which developed along the western edge of the Wagga-Omeo Metamorphic Belts in the latest Silurian to Middle Devonian. Northern correlatives include the Mt Hope trough (a volcanotectonic graben) and the Cobar trough (Powell & Baillie, 1992). Consideration of the entire fill of the Melbourne trough suggests there are two turbiditic tectonostratigraphic assemblages. The lower, of Early Ordovician to mid-Early Devonian age, is thicker, coarser and more proximal in facies in the west. The upper, of mid-Early Devonian to Middle Devonian age, is thicker, coarser and more proximal in facies in the east, even though there is a marked shallowing of all facies from late Early Devonian onwards. The upper turbiditic assemblage passes upwards into shallow-marine and ?terrestrial sandstones of the Cathedral Beds.

A 1.12

References Powell, C.McA. & Baillie, P.W., 1992, Tectonophysics (in press). Powell, C.McA., Baillie, P.W., Conaghan, P.J. & Turner, N.J., 1992, Aust. J. Earth Sci. (in press). VandenBerg, A.H.M. & Stewart, I.R., 1992, Tectonophysics (in press).

T H E RIFT IN N O R T H E R N KENYA 1

2

-VOLCANO-TECTONIC 3

B.D.Hackman *, TJ.Charsley , R.M.Key and A.F.Wilkinson

INTERPRETATION 4

1 "LEMIGAS", P.O. Box 1089/JKT, Cipulir - Kebayoran Lama, Jakarta 10010, Indonesia. 2 British Geological Survey, Keyworth, Nottingham NG12 5GG, U.K. 3 British Geological Survey, Murchison House, West Mains Rd., Edinburgh, EH9 3LA, U.K. 4 "Bodion", 56930, Plumeliau, Morbihan, Bretagne, France The Cenozoic rift system in northern Kenya comprises a complex pattern of grabens and multicentre volcanic shields which diversify the topography of the Kenya Dome. The most prominent negative feature is the Gregory Rift, the greater part of which is an asymmetric half-graben. The asymmetry is also manifest at the regional level when the axial graben is compared with the northern and eastern fringes of the dome. Structural weaknesses in the Proterozoic basement (Mozambique Orogenic Belt) have controlled many of the rift trends, which deviate from the northerly trend of the Gregory Rift. Thus on the eastern margin of the Kenya Dome fissures trending NE and ENE reflect parallel basement structures dated at about 500 Ma.In a transtensional stress regime secondary faults, associated with a flexure in the main rift, for example south of Lake Baringo, have given rise to "boxfaulting" and related ramp structures, also to a "shark tooth" array effect due to en echelon offsetting of the eastern side of the rift. Vulcanicity in the axial graben dates back to the Oligocene in the area east of Lake Turkana. Although the Gregory Rift has been maintained as a salient Geological Society of Australia Abstracts Number 32, Ballarat 1992

tectonic feature since the Miocene, the effects of complementary tensile stresses have shifted in time towards the east, where multicentred volcanic shields have evolved in the Plio-Pleistocene. The regional pattern is consistent with continental extension over a broad N-S zone, in which different elements of the tectonic mosaic inherited from the Precambrian basement have come into play during successive episodes in the Cenozoic. The alkaline to ultra- alkaline petrochemistry of the Cenozoic volcanics is patterned in a manner which offers a broad correlation with the asymmetry of the rift system, and with recent seismicity surveys. This interpretation is based on geological mapping on a scale of 1:250,000 of an area of about 125 000 sq km by a British Geological Survey team in cooperation with the Kenya Mines and Geological Department between 1980 and 1986, based on

31 systematic ground investigations, aerial photographs and satellite imagery. The work formed the major objective of an aid project, including helicopter

A 1.13

reconnaissance of the remote Northern Frontier Desert region, which was funded by the British Overseas Development Administration.

THE SERPENTINITE BELTS OF SOUTHERN NEW SOUTH WALES SLICES OF PALAEOZOIC UPPER MANTLE? Brenda J. Franklin*, Ian T. Graham and Brian Marshall,

Department of Applied Geology, University of Technology, Sydney, PO Box 123 Broadway, NSW, 2007. A number of alpine-type ultramafic belts crop out in the southern portion of the Bogan Gate Synclinorial Zone in the Lachlan Fold Belt of NSW. Emplaced into a variety of early and middle Palaeozoic strata, the belts (Fig.l) are exposed over a total linear distance of 230 km and range from narrow lenses a few tens of metres in length to a single massive body cropping out continuously over 56 km and with a width ranging up to 2.5 km. The ultramafic belts are dominantly composed of variably serpentinised and foliated harzburgite, dunite and lherzolite (minor), together with numerous rodingite and other similar dykes, podiform chromitites, minor platinum group element mineralisation, cupriferous pyrite deposits and talccarbonate bodies. In close spatial association with a number of the belts are cumulate wehrlite-clinopyroxenite-gabbro complexes and massive gabbro-basalt-plagiogranite associations of ocean-floor (ophiolitic) geochemical affinity. A section of the longest continually exposed ultramafic belt, the Coolac Serpentinite Belt, together with its cumulate and non-cumulate associates, has been named the Coolac ophiolite suite (Ashley et al., 1979). The ultramafic belts vary widely, both in the intensity and in the nature of their alteration, metamorphism, mineralisation and deformation. The harzburgite of the Coolac Serpentinite Belt ranges in character from an almost pristine peridotite to a completely serpentinised lizardite-chrysotile assemblage, while other belts exhibit a variety of ultramafic and mafic mineral assemblages indicative of a range of conditions extending from lower greenschist to uppermost amphibolite facies - a temperature range

Geological Society of Australia Abstracts Number 32, Ballarat 1992

of alteration and metamorphism from approximately 350°C to as much as 700°C+. Observable structures range from gross lithological and mesoscale mineral layering to fibre-vein foliations and S-C dominated shear zone fabrics (Warner et al., 1991). Controversy currently exists as to the relative and absolute age, the emplacement history and the possible consanguinity of these belts (Basden et al., 1987; Stuart-Smith, 1990). This paper presents a comparison of the overall characteristic features of all of the belts - mineralogy, geochemistry, metamorphic grade, mineralisation, and deformational history in an attempt to address the problem. The comparison reveals both significant differences and striking similarities in all of the above features and the results are evaluated with respect to the differing structural and tectonic models proposed for the region. References Ashley, P.H., Brown, P.F., Franklin, B.J., Ray, A.S. & Scheibner, E., 1979, J. Geol. Soc. Aust., 26:45-60 Basden, H., Franklin, B.J., Marshall, B. & Waltho, A.E., 1978, in Leitch, E.C. and Scheibner, E. eds., Terrane Accretion and Orogenic Belts, Amer. Geophys. Union Geodyn. Ser., 19:57-66 Stuart-Smith, P.G., 1990, Bur. Miner. Res. Aust., Record 1990/78 Warner, P.J., Marshall, B. & Franklin, B.J., 1991, Aust. J. Earth Sci., 38:(in press)

32

A 1.14 THE EXTENT AND SIGNIFICANCE OF THE EARLY CAMBRIAN TRURO VOLCANICS C G Gatehouse1*, J B Jago 2 , L R Rankin1, B J Clough1, D I Gravestock1 and A J McCulloch1 1

South Australian Department of Mines and Energy, Parkside, South Australia. 2 University of South Australia, Adelaide, South Australia.

The Truro Volcanics in its type section north of Dutton consists of steeply dipping altered vesicular and amygdaloidal andesite, trachyte and metabasalt. Volcanism is indicated by 236 m of individual flows, minor tuffs and intraformational conglomerate at the type section. Higher in the succession, and possibly in fault contact, is a 60 m thick marble correlated by Forbes et al. (1972) to the Fork Tree Limestone. A Geological Society of Australia Abstracts Number 32, Ballarat 1992

flow of porphyritic andesite occurs within a volcaniclastic sequence about 30 m above the marble.This is overlain by 10-20 m of conglomeratic sediments containing shale clasts and fragments of scoriaceous material reworked from the Truro Volcanics. This, in turn is overlain by Heatherdale Shale. One kilometre to the north Mt Rufus 1 intersected 300+ metres of volcanics near outcropping

33 pillow basalt. Other outcrops of Truro Volcanics, also in association with Heatherdale Shale, occur at Accommodation Hill, Red Creek and east of Sedan Hill. At these locations the volcanics occur as tuff bands (now chloritised), basalt flows and occasional pillows at Red Creek. One tuff bed in the Heatherdale Shale at Sellick Hill has been dated by U-Pb in zircon at 526±4 Ma (Cooper et al. in press). Several tuff bands, in drill core on Yorke Peninsula testify to widespread volcanic activity. These are overlain by archaeocyath-rich limestone of late Early Cambrian (late Botomian) age. Geochemical analyses of drillcore from Mt Rufus 1 near the type section give a range from subalkaline tholeiite through alkaline basalt to undersaturated nephelinite, consistent with within-plate' rift volcanism. The volcanic succession and geochemical composition are similar to that of the Peebinga 1 basement drillcore from near the Victoria/South Australia border. Peebinga 1, located at the northwestern extension of the magnetically determined Stavely Belt contrasts compositionally with the island-arc affinities assumed for this belt. Recent drilling of the Murray Basin basement (Rankin et al 1991a,b) indicates that a suite of deformed metadolerites with MORB affinities separates the Peebinga occurrence from the Truro Volcanics type locality. Company drilling in the Coonalpyn-Yumali district has also exposed deformed within-plate metabasic volcanics. The geochemistry of the deformed alkaline metabasic volcanics and the localised nature of the y

x

outcrops in the type area suggests they are analogous to the central volcanic complexes seen in alkaline volcanic provinces, associated with rifted continental margins. If crustal extension occurred in the formation of the Kanmantoo Trough then the volcanics in Peebinga 1 may have been closer to the present Truro Volcanics outcrops. References Cooper, J.A., Jenkins, R.J.F., Compston, W. and Williams, I.S. (in press). Ion-probe zircon dating of a mid-Early Cambrian tuff in South Australia. Geological Society. Journal. Forbes, B.G., Coats, R.P. and Daily, B, 1972. Truro Volcanics. South Australia. Geological Survey. Quarterly Geological Notes, 44:1-5. Gatehouse, C.G., Jago, J.B. and Clough, B.J., 1991. A progress report on a measured reference section at Red Creek for the Kanmantoo Group in the Karinya Syncline. South Australia. Department of Mines and Energy. Report Book, 91/27. Rankin, L.R., Clough, B.J., Farrand, M.G., Barnett, S.R., Lablack, K., Gatehouse, C.G., and Hough, L.P., 1991a. Murray Basin Basement Transect Project: 1990 well completion reports. South Australia. Department of Mines and Energy. Report Book, 91/15. Rankin, L.R., Clough, B.J. and Gatehouse, C.G., 1991b. Mafic suites in basement beneath the Murray Basin: new data for the Early Palaeozoic history of the Tasman orogenic province. South Australia. Department of Mines and Energy. Report Book, 91/44.

O

Basolt

( Peebinga I )

O

Truro

Volcanics

( Mt R u f u s 1) V

Bosolt - Andesite

•

Meiodoleritcs

( Yumali - Coonalpyn ) (MORB) ( Fields a f t e r

Geological Society of Australia Abstracts Number 32, Ballarat 1992

Peorce a n d C o n n ,

1973)

34 A 1.15

CAMBRIAN GREENSTONES ON PHILLIP ISLAND, VICTORIA D. A. Henry* and W. D. Birch Department of Mineralogy & Petrology, Museum of Victoria, Victoria.

Outcrops of altered mafic volcanic rocks (greenstones) occur near Watt Point on the south coast of Phillip Island, Victoria. They are unconformably overlain by Tertiary agglomerate and basalt belonging to the Older Volcanics. The greenstones range from metabasalts to metadolerites, with less common metacumulates. All show typical greenschist facies alteration assemblages of albite, amphibole, chlorite, albite, epidote and prehnite. The original mafic minerals have not survived alteration. Geochemical data for total Fe, Mg, Ti and trace elements Cr, Ni, Zr, Y, Sc, and V indicate that the Phillip Island greenstones belong to the low-K tholeiitic suite which dominates the Cambrian Heathcote and Mt Wellington Greenstone Belts in Victoria (Crawford, 1988). However the Phillip Island greenstones appear to represent more primitive magmas on the fractionation path for the Victorian Cambrian tholeiites. A 1.16

The occurrence lends support to a model involving detachment in a near-continuous basal layer of Cambrian metavolcanics during Middle Devonian deformation of the Lachlan Fold Belt in central Victoria (Gray and Willman, 1991). References Crawford, A. J., 1988, Cambrian. In Douglas J. G. & Ferguson, J. A. (Eds), Geology of Victoria. Victorian Division Geological Society of Australia. 37-62. Gray, D. R., & Willman, C. E., 1991, Deformation in the Ballarat Slate Belt, central Victoria, and implications for the crustal structure across southeast Australia. Australian Journal of Earth Sciences, 38, 171-201.

DEVELOPMENT OF THE LOWER DEVONIAN BUCHAN RIFT K. Orth and A. H. M. VandenBerg

Geological Survey of Victoria, P.O. BOX 173 East Melbourne 3002, Victoria. The Buchan Rift formed as an extensional feature in eastern Victoria during the Lower Devonian. Recent mapping by the Geological Survey of Victoria has subdivided these volcanics, between Buchan and Wulgulmerang, into seven major and several minor units. These reflect three main phases of rift development. Phase 1 (Fig. 1) marks the initiation of rifting and the onset of volcanism. A valley cut into basement was rapidly filled with locally derived, fluvial sedolithic conglomerate as the floor of the rift subsided in the SW. The commencement of volcanic activity here is shown by the appearance of volcanic clasts in the basal conglomerate and breccia of the Timbarra Subgroup, along with basaltic to andesitic lavas and ignimbrites. Marine turbidites in this area suggest that at times in the early part its history the southern part of the rift was marine. In the NW early rifting formed a subaerial basin which filled with the Wombargo Subgroup. Basal conglomerate is followed by ignimbrite intercalated with progressively finer-grained and more volcanic rich sediments. Pre-rifting topography was rugged and can be seen in the NE where it is preserved beneath the White Monkey Geological Society of Australia Abstracts Number 32, Ballarat 1992

Subgroup. In the centre of the rift ignimbrite eruptions of the Marroo Subgroup were the main activity with minimal reworking. Phase 1 is separated from the second phase of activity by an erosional break. Phase 2 (Fig 2) marks the widening of the rift and encompasses horst and graben formation. As a result many of the sediments and ignimbrites were ponded. The Devils Den Conglomerate was deposited from a south-flowing braided river system. The high proportion of non-volcanic clasts (60-90%) indicates major input form outside the rift, possibly from a reactivated margin, and from adjacent highs. The complex Meadow Creek Fault Zone formed a horst between this river system and the thick ponded Tulloch Ard Ignimbrite to the east. To the west the Emu Egg Fault separates the conglomerates from the similarly ponded, feldspar dominated Mount Dawson Subgroup. A spectacular megabreccia marks the reactivation of the NE rift margin and is overlain by quartz lithic ignimbrite suggesting renewed volcanism accompanied fault activity. These two form the Berrmarr Subgroup. Phase 2 was followed by a prolonged period of

35 erosion, expressed as a regional unconformity. In phase 3 (Fig 3) rifting ceased to be the factor controlling depositional processes. Volcanism became more foccussed, with the products of at least three eruptive centres recognised in the Munindal area. The Woongulmerang Caldera in the north is the only caldera so far identified, with a thick fill of pumiceous ignimbrite overlying breccia and base surge deposits. At least two other volcanic centres erupted: one south of Murrindal which produced feldspathic and vitric § 5

ignimbrites; the other further east forming red quartz rich ignimbrites. Extensive sediments overlie the major ignimbrites. These include fluvial and lacustrine deposits as well as localised base surge and airfall ash. Eruption of lavas, including extensive rhyolite and smaller valley filling andesite and basalt became more common at this time, especially in the south. In the sediments of some areas there is an increasing marine influence, heralding the formation of the entirely marine calcareous Buchan Group.

BUCHAN GROUP

FIGURE 1.

FIGURE 3. (Little River Subgroup)

Timbarra Subgroup

^ ^

Feldspathic & vitric ignimbrites

Wombargo Subgroup

Quartz ignimbrites White Monkey Subgroup Sediment Marroo Subgroup Basalt and andesite lava

FIGURE 2. Berrmarr Subgroup

Rhyolite lava

Mt Dawson Subgroup

Gelantipy Subgroup

Tulloch Ard Ignimbrite

m

Devils Den Conglomerate

••

SNOWY RIVER VOLCANICS

FIG. 1: DISTRIBUTION OF PHASE 1 UNITS. ORDIVICIAN & SILURIAN SEDIMENT, GRANITE & VOLCANICS

FIG. 2: DISTRIBUTION OF PHASE 2 UNITS.

Geological Society of Australia Abstracts Number 32, Ballarat 1992

FIG. 3: DISTRIBUTION OF PHASE 3 UNITS.

36

A 1.17 POLYMICTIC CONGLOMERATES OF THE FRAMPTON VOLCANICS: PREBENAMBRAN VOLCANIC ARC DERIVATIVES OR THE PRODUCTS OF POSTBENAMBRAN UPLIFT? C.G.Skilbeck*, EJFrankel, K.Dadd, and E.C.Leitch Department of Applied Geology, University of Technology, Sydney P.O. Box 123, Broadway NSW 2007 The Silurian Frampton Volcanics in the Gundagai region of southern NSW includes a prominent conglomeratic component as well as rhyolitic, andesitic and basaltic flows and pyroclastic deposits. The conglomerate forms sequences up to several hundred metres thick and, although many sedimentary features have been destroyed by intense deformation it shows characteristics suggestive of accumulation in a rapidly subsiding basin, close to source, and at least in part from mass-flows. Thus the conglomerates are illsorted, show a wide range in clast-to-matrix ratio, include abundant "intraformational" debris, are rarely internally stratified, and have a matrix that ranges from sandstone to siltstone. Clast diversity characterises the conglomerate. There is a wide range of volcanic rock types as well as granite, granodiorite and diorite, quartzite including garnetiferous varieties, metasandstone, slate, siltstone and limestone. Relative proportions of the different clast types range widely between outcrops.

Two contrasting interpretations of the Frampton conglomerate are assessed in the light of new sedimentological and provenance data. The suggestion that the rocks are pre-Benambran and related to the Molong Volcanic Arc implies that the magmatic chain continued activity for longer than has generally been recognised, that a wide variety of volcanic rocks were extruded late in its history by which time plutonic masses had been exposed, and that the Arc included a metasedimentary component. Alternatively a postBenambran age, which better accounts for the range of clasts, when allied with recent structural interpretations leads to a more complex deformational history for the region than has previously been recognised. The implications of the two interpretations for the history of the Gilmore Fault and the identification and inter-relationship of lithostratigraphic terranes in this part of the Lachlan Fold Belt will be discussed.

POSTER SESSION A 1.18

THE 1991 BMR DEEP SEISMIC REFLECTION PROFILE IN NORTHERN NEW SOUTH WALES K.D. Wake-Dyster*, D.W. Johnstone and R.J. Korsch

Bureau of Mineral Resources, Geology & Geophysics, GPO Box 378, Canberra, ACT 2601 A deep seismic reflection profile across the Peel single east-west traverse. Processing of the seismic and Mooki fault systems was proposed by Erwin data is in progress, with final stack data to be released Scheibner and other members of the NSW ACORP to the general public, on or before 31 December 1991. Committee, as a major priority, to test models To generate a multidisciplinary geophysical data set, proposed for the structure of the fault systems and gravity readings were made at 360 m intervals along their relationship to the Gunnedah Basin (Scheibner, the seismic line. In addition, the seismic line was 1985). flown for aeromagnetics and radiometrics at flight To test possible tectonic and structural models for heights of 500 ft and 3000 ft AGL. the Gunnedah Basin (see BMR Record 1990/93), the Prior to the recording of the deep seismic reflection BMR carried out a deep seismic reflection survey profile across the Gunnedah Basin and margins, a test across the Gunnedah Basin in the Boggabri-Manilla seismic survey was carried out in May 1989 (Korsch area during the first half of 1991. The seismic survey & others, 1990). The test seismic survey was was of eight weeks duration, with 253 km of new deep undertaken to determine optimum acquisition reflection seismic data to 20 seconds two-way travel parameters at five sites with different surface geology. time and 8 fold CMP data coverage recorded, along a Test seismic lines were 5.7 km in length (96 Geological Society of Australia Abstracts Number 32, Ballarat 1992

37 channels, 60m geophone group interval, 360m shotpoint interval). Seismic testing including charge size comparisons, charge depth comparisons, noise shoots and uphole shoots were performed at sites where additional data were required to optimise recording parameters. Seismic test sites included the following locations; 1) East of the Peer Fault over the Bundarra Plutonic Suite. 2) Tamworth Belt between the Mooki and Peel Faults. 3) Across the Mooki Fault. 4) Eastern margin of the Rocky Glen Ridge on very porous Jurassic Pilliga Sandstone, regarded by industry as a poor seismic data area. 5) Gilgandra Trough to test for Triassic-Permian sub-basins west of the Rocky Glen Ridge, as interpreted from gravity data. The seismic test site data were all of good quality which encouraged recording of the major deep seismic A 1.19

reflection line by BMR in early 1991. Highlighted in the poster display are deep seismic reflection sections from both the 1991 deep seismic reflection profile and the 1989 seismic test survey. Incorporated with the seismic sections are the gravity and aeromagnetic data recorded at the same time as the 1991 seismic survey. Prominent gravity features include large positive anomalies over the Gunnedah Basin (Meandarra Gravity Ridge) and Tamworth Belt. References Scheibner, E., 1985 - Proposal for an ACORP profile through the Gunnedah Basin and New England Fold Belt. Bureau of Mineral Resources, Australia, Record, 1985/7, 27-29. Korsch, R.J., Wake-Dyster, K.D. & Finlayson, D.M., 1990 - Land seismic data acquisition proposal: Gunnedah Basin, New South Wales. Bureau of Mineral Resources, Australia, Record, 1990/93.

THE STRUCTURAL DEFORMATION OF PALAEOZOIC ROCKS IN THE WESTERN STAWELL ZONE, VICTORIA. Julia Caluzzi Ballarat University College, Ballarat.

Situated on the western margin of the Lachlan Fold Belt, the Stawell Zone is subdivided into two terranes along the Stawell Fault,the Grampians-Stavely Terrane to the west and the St. Arnaud Terrane to the east. Economic interest has resulted in detailed study of the structural deformation at Stawell. Wilsonand Watchorn (1988) have proposed 6 episodes of deformation, D1-D6. D1-D3 represent episodes of ductile deformation, probably in the pre-Mid Silurian, whilst D4-D6 mark a period of brittle deformation, in the Early Devonian. Mt. Drummond, located 20km north-west of Stawell in the Grampians-Stavely Terrane, outcrops a sequence of highly jointed Cambro-Ordovician hornfels. Abutting against the north-west trending Jallukar Fault , the sequence shows localised smallscale thrust faults. It is shallow dipping and overturned and probably forms the lower limb of a large-scale recumbant isoclinal fold. Cambrian metavolcanics at Mt. Asler , thrust emplaced along the Jallukar Fault, may have also thrust up a Cambrian turbidite sequence at Lake Lonsdale. This sequence is steeply dipping

Geological Society of Australia Abstracts Number 32, Ballarat 1992

and displays localised mesoscopic kinking and folding. Analysis of slickensided surfaces along the northeastern margin of the Grampians, indicates normal faulting with components of oblique (sinistral) movement and upslip along the Golton Fault, disrupting the Upper Silurian-Lower Devonian Grampians Group. Correllations of this structural deformation with Wilson and Watchorn's D1-D6 are not broad. D4 large-scale thrusting and faulting is evident in the Grampians and the Mt. Drummond-Lake Lonsdale area. However, the lack of cleavage and penetrative folding at Mt. Drummond, located on theJallukar Fault, appears inconsistent with regional observations. References Wilson, C.J.L., and Watchorn, R.B., 1988. Structure of the Stawell Zone : In Douglas J.G. and Fergusson, J.A., (eds), Geology of Victoria, second edition. Geological Society of Australia, Victorian Division, Special Publication, 7-10.

38

/

Geological Society of Australia Abstracts Number 32, Ballarat 1992

39

A2: MINERALS EXPLORATION AND METALLOGENESIS CONVENORS:

A 2.1

CEC MURRAY

& ERWIN

SCHEIBNER

ACTIVE BASE METAL SULPHIDE DEPOSITION IN THE MANUS BACK-ARC BASIN, BISMARCK SEA, PAPUA NEW GUINEA. F. Vanderhor 1 *, K.A.W. Crook 1 , A.P. Lisitsyn 2 , L.P. Zonenshain 2, Yu.A. Bogdanov2, K. Muravev2, and M.E., Fellows1

1

Geology Department, Australian National University, G.P.O. Box 4, Canberra, ACT 2601, Australia. Shirsov Institute of Oceanology, USSR Academy of Sciences, 23 Krasikova Street, Moscow 117218, USSR.

The Manus Basin comprises the eastern part of the Bismarck Sea. It is a Pliocene-Recent back-arc basin to the north of the New Britain arc-trench system on the souhwestern boundary of the Pacific plate. The development of the basin is characterised by noncoaxial transtension resulting from the interaction of the obliquely moving Pacific and South Bismarck Plates. Structurally, the Manus Basin can be subdivided into two main sub-basins bordered by sinistral transform faults. The eastern Manus Basin, bordered to the southwest by the Djaul Island Transform and to the northeast by the Weitin Transform, is a pull-apart basin that is associated with the break-up of the inactive New Ireland island arc. The dominant structural feature of the Western Manus Basin, west of the Djaul Island Transform, is a 120 km long northeasterly trending active spreading ridge (Manus Spreading Centre). Total spreading rates progressively decrease from 118 mm/yr at the southwestern end of this ridge to less than 8mm/yr at its northeastern tip (Mallonee,1989). The differences in spreading rates are reflected in the morphology of the ridge with a central graben in the northeastern part of the spreading centre gradually changing into a central ridge towards the southwest. Evidence for seafloor hydrothermal activity in the form of temperature/ water column anomalies and characteristic vent fauna has been recorded at several places along the Manus Spreading Centre (Both, et al., 1986; Tufar,1990). However, active mediumtemperature venting and associated base metal

Geological Society of Australia Abstracts Number 32, Ballarat 1992

deposition has so far only been observed along the northeastern, "slow-spreading", section of the spreading centre. This hydrothermal field, known as "Wienerwald" ("Vienna Woods"), extends for about 1000m along strike and is outlined by inactive and active massive sulphide chimneys within the central graben (Tufar, 1990). Active white and grey smokers within a 300m by 100m area of the field at 3° 9.86'S, 150° 16.7812 were first reported in June 1990 during a cruise of the Russian oceanographic research vessel R/V "Akademik Mstislav Keldysh". This active hydrothermal site ("Gothic Forest") occurs at a water depth of 2500m and contains up to 14m high sulphide chimneys on a barite-rich pedestal. Representative sulphide samples collected during manned submersible dives are generally Zn-rich (wurtzite, sphalerite) with lesser amounts of Cu- and Pb-minerals (chalcopyrite, galena). The mineralogy is in good agreement with measured hydrothermal fluid temperatures of around 275°C. References Both, R., Crook, K., Taylor, B., Brogan, S., Chappell, B., Frankel, E.JLiu, L., Sinton, J., & Tiffin, D., 1986, EOS, 67: 489-490. Mallonee, R.L., 1989. Extensional responses to transtension in the Manus backarc basin. Unpublished MSc thesis University of Hawaii. Tufar, W., 1990, Mitt. Osterr. Geol. Ges., 82: 183210.

40 A 2.2 KEYNOTE:

GOLD MINERALIZATION IN SEAFLOOR BACK-ARC SPREADING CENTRES OF THE WESTERN PACIFIC Peter M. Herzig * and Mark D. Hannington 1

2

^Institute of Mineralogy andGeological EconomicSurvey Geology, Aachen Ottawa University Technology, of Canada, K1AofOE8, Canada D-5100 Aachen, Germany 2

Since 1986, a number of sulfide deposits have been located in intraoceanic and intracontinental back-arc spreading centres of the western Pacific. These include the Lau Basin, North Fiji Basin, Manus Basin, Mariana Trough, Okinawa Trough, and the Western Woodlark Basin. Polymetallic sulfides from the Valu Fa Ridge in the Lau back-arc have revealed gold contents of up to 28.7 ppm Au (about 1 oz per ton) with an average of 3.1 ppm Au. These samples are among the most gold-rich hydrothermal precipitates yet reported from the modern seafloor, and they are the first known examples of visible primary gold in polymetallic sulfides at active vents (Herzig et al., 1990, 1991). In the Okinawa Trough, gold-rich sulfide deposits with up to 14 ppm Au occur in a back-arc rift within continental crust and resemble Kuroko-type massive sulfides (Halbach et al., 1989; Urabe et al., 1990). High gold contents up to 21 ppm Au have been found in barite chimneys in the Western Woodlark Basin, where seafloor spreading propagates into continental crust off Papua New Guinea (Binns et al., 1991). Sulfides in the Mariana Trough are associated with a mature back-arc spreading centre floored by true oceanic crust and contain 0.1-1.7 ppm Au. Preliminary analyses of sulfides from other deposits in mature MORB-dominated back-arc settings such as the Manus Basin (Both et al., 1986) and the North Fiji Basin (Auzende et al., 1989) indicate average gold contents of about 1 ppm Au. Gold appears to be most abundant in sulfides associated with immature back-arc rifting in continental or island arc crust. These settings are dominated by calc-alkaline volcanics including andesites, dacites, and rhyolites (i.e., Lau Basin, Okinawa Trough, Woodlark Basin). Sulfide deposits related to mature back-arc spreading centres associated with MORB-type volcanics (e.g., North Fiji Basin, Manus Basin) have gold contents which are more similar to sulfide deposits on the mid-ocean ridges.

Geological Society of Australia Abstracts Number 32, Ballarat 1992

Preliminary data suggest that the gold contents of back-arc lavas are not significantly different from those of ordinary MORB, and therefore these rocks probably do not represent an enriched source. However, the source-rock geochemistry is an important factor in controlling the composition of the hydrothermal fluids and their ability to carry gold. Known gold-rich seafloor deposits in the western Pacific occur along the axis of a major gold belt extending from Japan through the Philippines, New Guinea, Fiji, Tonga, and New Zealand (Sillitoe, 1989). Although the porphyry-type stockworks and epithermal gold deposits in this region are associated with island arc volcanoes (as opposed to back-arc rifts), the close proximity of modern seafloor hydrothermal systems to these volcano-plutonic arcs is striking. Active seafloor hydrothermal systems may be operating on the submerged portions of some island arc volcanoes in the western Pacific, and the potential exists for the discovery of a gold-rich massive sulfide deposit with distinctive epithermal characteristics in this environment.

References Auzende, J.M., Urabe, T., Deplus, C. et al., 1989, Eos 70:1382 [abs.] Binns, R.A., Boyd, T. & Scott, S.D., 1991, GACMAC 16:A12 [abs.] Both, R.A., Crook, K., Taylor, B. et al., 1986, Eos 67:489-490 Halbach, P., Nakamura, K., Wahsner, M. et al., 1989, Nature 338:496-499 Herzig, P.M., Fouquet, Y., Hannington, M.D., & von Stackelberg, U., 1990, Eos 71:1680 [abs.] Herzig, P.M., Hannington, M.D., Fouquet, Y. et al., 1991, Econ. GeoL [subm.] Sillitoe, R.H., 1989, Econ. Geol. Mon. 6:274-291 Urabe, T., Marumo, K. & Nakamura, K., 1990, Geol. Soc. Am. 22:A9 [abs.]

41 A 2.3 DISCOVERY OF ACTIVE HYDROTHERMAL SULFIDE DEPOSITION ASSOCIATED WITH SUBMARINE FELSIC VOLCANISM, PUAL RIDGE, EASTERN MANUS BASIN, PAPUA NEW GUINEA R.A. Binns1* S.D. Scott2 and PACMANUS Participants J

CSIRO Division of Exploration Geoscience, North Ryde, NSW Department of Geology, University of Toronto, Toronto, Canada

2

In September-October 1991 the PACMANUS Cruise (Papua New Guinea - Australia - Canada Manus Basin; RV "Franklin") found what may be the closest modern analogue yet discovered for Precambrian and Phanerozoic volcanogenic massive sulfide ore deposits. After the Jade Deposit in the Okinawa Trough (Halbach et al., 1989), it is the second known occurrence of high temperature hydrothermal venting associated with truly felsic submarine lavas and pyroclastic deposits. The PACMANUS deposits overlie dacite eruptives at 1650-1680 m depth on an elevated knoll of Pual Ridge, a northeast-trending volcanic structure located within a complex extensional zone between the Weitin and Djal transform faults close to New Britain and New Ireland in the eastern Manus Basin. Pual Ridge is one of several incipient sea-floor spreading ridges near the propagating tip of back-arc volcanism in the Manus Basin. If extension were to cease on Pual Ridge itself (as may already have happened) then the setting would have the character of a submarine volcanic carapace to one or more elongate plutons emplaced into older island arc crust. Extensive dredging and bottom photography confirm that vesicular dacite with negligible sediment cover is the dominant bedrock of Pual Ridge. It forms large jagged outcrops with hackly to frothy glass rinds that are susceptible to hyaloclastite fragmentation. Ropy-surfaced andesite flows are conspicuous but subordinate, and pumiceous rhyolite is a minor component. Bottom camera tows at the PACMANUS site mapped numerous chimneys up to 4m high and larger mounds, many of which are currently active as indicated by super-abundant fauna (pogonophoran tube worms, galatheid crabs, gastropods, mussels, clam shells, shrimps, small fish, fluffy bacterial mats) and by detection of a pronounced particulate and methane plume in overlying seawater. The hydrothermal

Geological Society of Australia Abstracts Number 32, Ballarat 1992

deposits extend discontinuously (interrupted by dacite pinnacles) over a 2.5 x 0.5 km zone, with the largest occurrence at least 300 m long. Attempts to dredge the deposit recovered large quantities of fresh dacite, some altered dacite, and particles of frothy dacite encrusted with Mn and Fe oxides from a large hyaloclastite mound. Small fragments of massive pyritic sulfides with anhydrite gangue were collected by the cameravideo system, probably after an observed collision with a chimney. White surfaces on many photographed chimneys suggest that anhydrite is relatively common, implying an abundance of hightemperature hydrothermal deposits. An isolated chimney was observed at another site 7 km to the northeast, where altered dacites were collected, and at a third location red-brown ferruginous muds and Mn-crusted dacites were dredged. Pual Ridge is highly prospective for additional active hydrothermal vent fields. Further exploration in 1993 is planned, and a program of manned submersible dives at the PACMANUS site and any additional discoveries is warranted in view of the potential for detailed research on this felsic volcanic setting to clarify enigmatic issues of ore genesis and of pathfinder characteristics in volcanic host rocks and lateral lower-temperature exhalite horizons in equivalent ancient mineralised environments. We thank Professor H. Sakai of Yamagata University for providing a bathymetric chart of the eastern Manus Basin and other data from the 1990 Aquarius Expedition to help plan the PACMANUS Cruise. Reference Halbach, P. and 17 others, 1989, Nature, 338:496499.

42 A 2.4

LINKING TECTONICS, METALLOGENESIS AND MINERAL EXPLORATION Michael Solomon Bureau of Mineral Resources, Canberra

Most major mineral deposit types formed in specific tectonic environments, hence recognition of the tectonic character of a region allows an assessment of the ore types likely to be present. Generally speaking, the value of the predictions increases with the level of our understanding of ore genesis. Sufficient is known about the origin of some ore types that their presence of absence may be critical in assigning a tectonic setting, and in predicting the presence of other ore types. I briefly describe some examples of the use of mineral deposits in defining tectonic settings, and of using our knowledge of tectonics to predict deposit occurrences. Diamonds: Spectacular conclusions about tectonic history come from the 5 ^ S and values obtained from diamonds in Africa and Australia (e. g. Eldridge et al. in press) which strongly imply derivation of S and C from sediment sources via pre-diamond-forming subduction. The Australian data, though only preliminary, imply pre-Late Proterozoic subduction in the Halls Creek and King Leopold fold belts, and hence the likely presence of VMS, Mn and other mineral deposits. Orogenic Tin-Tungsten Deposits: By analogy with occurrences in north and south America, Sn-W provinces in Andean-type orogenic belts are evidence of more or less coeval subduction, and they provide markers for the position of the inner (craton side) margin of subduction-related magmatic arcs. Such interpretations fit well with other evidence of subduction at the time of development of the Sn-W provinces of north Queensland and New England. They also assist in defining the tectonic setting of the Lachlan Fold Belt at about 400 Ma, confirming the westward subduction proposed by Fergusson (1987) and Scheibner (1989). Porphyry Copper-Gold Deposits: The discovery in the Lachlan Fold Belt of Late Ordovician porphyry Cu-Au deposits with similar economic mineral content to those of the southwest Pacific margin lends support to a subduction origin for the host volcanics (the Molong Volcanics), as proposed by Powell (in Veevers 1984), Scheibner (1987) and others. As the Pacific margin deposits only form after reversal of subduction polarity (Solomon 1990) there is support for a similar reversal proposed by Scheibner (1989) for the Molong Volcanics. The volcanics hosting Pacific margin deposits are calcakaline to high-K calcalkaline Geological Society of Australia Abstracts Number 32, Ballarat 1992

whereas the Molong Volcanics have a high proportion of shoshonites but whether or not this downgrades the analogy is not clear. Solomon (1990) predicted high PGE and Au for the postreversal, ore-hosting volcanics of the Pacific margin, following a two-stage melting model of Hamlyn et al. (1985), and the high Pt values recorded by Wyborn (1990) for the Molong Volcanics appear to support the analogy. The empirical finding that arc reversal is required to generate the southwest Pacific Cu-Au deposits is clearly an important exploration tool for older terranes. VMS Deposits: Stratiform, pyrite-chalcopyrite lenses in ophiolitic volcanics are recognised as evidence of sea-floor spreading because of the modern discoveries of active and fossil systems near mid-ocean ridges. The discovery of modern pyritesphalerite-galena-chalcopyrite deposits in calcalkaline volcanics of the Okinawa Trough (Halbach et al. 1989) allows tentative analogy with similar Palaeozoic deposits in eastern Australia. The Okinawa deposits appear to be forming during volcanism during rifting of continental crust behind the Ryuku volcanic arc linking Kyushu and Taiwan (Sibuet et al. 1987). The back-arc spreading and mineralization appear to be proceeding northward as volcanism in the Ryuku arc ceases, the flip-over being the location of currently forming VMS deposits. Spreading is probably induced by retreat of the subducting slab. These discoveries allow dramatic refinement of the tectonic models for the Kuroko deposits, and may lead to a better understanding of the development of the Tasmanian polymetallic VMS deposits, e. g. do the Tasmanian VMS deposits young to the north and can we predict more deposits north of Hellyer at a still higher stratigraphic level?. References Eldridge, C. S. and others, in press, Nature. Hamlyn, P. R. and others, 1985, Geochemica et Cosmochimica Acta 49: 1797-1811 Halbach, P. and others, 1989, Nature 338: 496-499 Scheibner, E., 1987, American Geophysical Union Geodynamics Series 18: 133-165 Scheibner, E. 1989, Journal and Proceedings of the Royal Society of New South Wales 122: 35-74 Sibuet, J-C. and others, 1987, Jour. Geophysical Research 92: 14,041-14,063 Solomon, M. 1990, Geology, 18: 630-633

43 Wyborn, D., 1990. Newsletter 13:8.

BMR

Research

A 2.5 DEEP SEISMIC OF THE COBAR BASIN-I: STRUCTURE AND IMPLICATIONS FOR MINERAL PROSPECTIVITY R.A. Glen 2 *, B.J. Drummond 1 , B.R. Goleby 1 , D. Palmer 2 and K.D. Wake-Dyster1 ^Bureau of Mineral Resources, Geology & Geophysics GPO Box 378 Canberra ACT 2601 AUSTRALIA Geological Survey of New South Wales, Department of Mineral Resources PO Box 536 St Leonards NSW 2065 AUSTRALIA

2

The Cobar Basin in central western New South Wales is a mineral-rich Early Devonian basin typical of those that characterise the Siluro-Devonian history of the Lachlan Orogen in southeastern Australia. In 1989, 170 line kilometres of deep seismic profiling were recorded across the Cobar Basin, with two NESW dip lines south of Cobar, and a NNE-SSW dip line west of Cobar. The last line was tied into short lines which cross the western margin of the basin. The deep seismic profiling showed that the basin is asymmetrical at depth with faulted margins. The eastdipping western margin is steeper than the moderately west-dipping eastern margin. Maximum basin thickness is around 6 km, but there are significant thickness changes, especially from south to north, which reflect the effect of synsedimentary faulting. The upper part of the basin is more folded than the lower part, with many surface folds detaching onto subhorizontal reflectors at about 1.2-1.5 km (0.5 sec) which represent detachment surfaces. The seismic profiling has therefore confirmed previous suggestions that inversion and deformation of the Cobar basin involved thin-skinned thrusting above high-level detachments: strike-slip effects were not visible on the sections. The seismic clearly imaged the generally hidden western synrift basin margin, and revealed major changes in both geometry and location of themargin between the three lines which are best resolved by the presence of one or more closely spaced, sharp, basinwards jogs. Differences in intrabasinal structure between dip lines 1 and 2 suggest the presence of a major east-

Geological Society of Australia Abstracts Number 32, Ballarat 1992

northeast oriented tear or transfer fault lying at low angles to the basin opening and closing directions. This tear coincides with the Sandy Creek Fault. It appears to have propagated into the basin from a jog in the western margin and continued right across the basin to link up with an indentor in the eastern margin just south of Cobar. Such tear faults played a prominent role in compartmentalising basin deformation and probably reflect reactivation of synsedimentary transfer structures which had a major control on the filling of the basin. Bounding and intrabasinal faults form part of a linked fault system which provides pathways for fluid flow both during basin formation, diagenesis and inversion. Such structures are m&jor exploration targets, given the strong structural control on known Cobar deposits, the syndeformational nature of some or all of the mineralisation and the concentration of deposits near the intersection of the Sandy Creek Fault with thrusts along the eastern basin margin. A contribution to the National Geoscience Mapping Accord. Published with the permission of the Director-General, New South Wales Department of Mineral Resources, and the Executive Director, Bureau of Mineral Resources, Geology and Geophysics. Geopeko, CRA Exploration Pty Ltd and Pasminco Exploration are thanked for their financial support for the seismic survey and for permission to submit this abstract prior to the expiry of the confidentiality period for the Cobar ACORP Project.

44 A 2.6 DEEP SEISMIC OF THE COBAR BASIN-II: A RAMP BASIN CONTROLLED BY A MID CRUSTAL DETACHMENT. B J. Drummond *, R.A. Glen , B.R. Goleby , K.D. Wake-Dyster and D. Palmer 1

2

1

1

2

^Bureau of Mineral Resources, Geology & Geophysics GPO Box 378 Canberra ACT 2601 AUSTRALIA Geological Survey of New South Wales, Department of Mineral Resources PO Box 536 St Leonards NSW 2065 AUSTRALIA Because the seismic data were recorded along a The Cobar Basin in central New South Wales formed in the Early Devonian and was inverted in the network of lines, some three dimensional control on late Early Devonian. It is about 100-120 km long and the crustal structure and the direction of top plate 35-45 km wide, and trends NNW-SSE. The basin fill movement is possible. The net displacement of the consists of mainly clastic material; volcanics are rare. upper crust relative to the lower crust (ie., basin Regional geological mapping and a network of opening less basin inversion) was approximately 24 seismic reflection profiles across the basin have km at an azimuth of 40° east of north. The strike of defined the basin morphology (Glen et al., 1992). The the ramp in the detachment is west of north, and is not basin is asymmetric, with the western margin steeper orthogonal to the direction of the net movement than the eastern margin. Both margins are now faulted. vector. The form of faulting along the western margin varies, In adjusting to the flexure caused by movement depending on the effects of basin inversion, from across the topography in the detachment surface, the apparently normal faults in the north and south to upper plate deformed by fracturing. Two main systems blind thrusts in the middle of the western margin. The of faults developed, one system parallel to the eastern eastern margin is defined by a series of anastomosing and western margins of the basin and the other system, strike slip and oblique slip faults. which were transfer faults, crossing the basin. Copper and gold mineralisation occurs in second The ramp detachment model is consistent with the and third order splay faults along the eastern margin. lack of volcanic material in the basin, because it Silver-lead- zinc mineralisation is presently being invokes no fault systems cutting the crust in the mined at the Elura Mine in the central northern part of region of the basin, no lithospheric thinning under the the basin. Cobar Basin, and therefore no raised geothermal The basin is cut by a major transfer, or tear, fault gradient under the basin. However, a driving which offsets the western margin and deflects the mechanism is required, and a heat source to the eastern margin. Other transfer faults are likely to be southwest is suggested. This is consistent with the present but have not been resolved with the present presence of coeval volcanics elsewhere in the Lachlan data. Fold Belt, and particularly in coeval basins to the The asymmetric nature of the basin would imply south. an extension or transtensional model in which subsidence along the western margin was controlled by This abstract is published with the permission of a normal fault, or an oblique slip fault with a normal the Executive Director, Bureau of Mineral Resources, component, which links into a detachment in the mid Geology & Geophysics and the Executive Director, to lower crust under the basin. However, the seismic New South Wales Department of Mineral Resources. data do not support such a tectonic model. The data Geopeko, CRA Exploration Pty Ltd and Pasminco show no evidence of suitable normal faults linking Exploration are thanked for their financial support for from near the surface to detachments at depth. This is the seismic survey and for permission to submit this consistent with the virtual lack of volcanics within the abstract prior to the expiry of the confidentiality period basin. for the Cobar ACORP Project. However, the seismic data do support a ramp detachment model in which the basin formed when the Reference upper crust was moved across a mid to lower crustal Glen, R.A., Drummond, B.J., Goleby, B.R., detachment. The detachment is one of the strongest Palmer, D. & Wake-Dyster, K.D., 1992. Deep reflectors seen in the seismic sections. The basin is structure of the Cobar Basin-I: Structure and perched above a ramp in the detachment which dips implications for mineral prospectivity. Geol. Soc. from about 12-16 km depth in the west of the basin to Aust. Absthis volume. about 25 km depth under the eastern side of the basin. 2

Geological Society of Australia Abstracts Number 32, Ballarat 1992

45 A 2.7

GOLD METALLOGENY FOR THE LATE PALEOZOIC OF NORTH QUEENSLAND Gregg W. Morrison*, Nicholas M. Tate and Heather J. Johns

Gold Research Group, James Cook University of North Queensland, Townsville, Q 4811 A review of the Late Devonian - Early Permian tectonic evolution of Queensland has been combined with a classification of the gold deposits of this age and an analysis of regional controls on their distribution, to produce a gold metallogenic model for the Kanimblan orogenic cycle. In the Late Devonian to Early Carboniferous, Queensland was part of the Gondwanaland margin and was an Andean or Sumatran type continental arc. The Drummond Basin was a continental back-arc extensional basin developed on the leading edge of a Proterozoic? basement salient in central Queensland. North of the salient, a rhomb shaped block, bounded by the Cape River Mylonite Zone and the Palmerville Fault, underwent sinistral transpression that deformed the enclosed continental basins and caused sinistral wrenching of the arc and forearc basin in the Rockhampton-Townsville area. Rapid anticlockwise rotation of Gondwanaland in the mid-Carboniferous initiated oblique subduction and ultimately dextral transcurrent movement in, and adjacent to, the continental margin in north Queensland. As a consequence, the continental margin became transtensional and crustal melts penetrated through reactivated basement structures, particularly in the rhomb area, from the mid-Carboniferous until the Early Permian. The gold deposits have been subdivided by their environment of formation into Epithermal, Porphyry, Plutonic and Slate Belt types. There is little convincing evidence that any of the deposits are older than 330 Ma (mid-Carboniferous) and there are vitually no occurrences in the arc, forearc and subduction complex. The Slate Belt and Plutonic deposits are concentrated in linear belts along large scale faults parallel to the regional structural grain in

A 2.8

the older flysch terraines in and north of the rhomb. The Epithermal and Porphyry deposits are most common in the rhomb area where Late Carboniferous (320 - 295 Ma) deposits concentrate close to the bounding faults and Early Permian (295 - 270 Ma) deposits occupy discrete NE trending corridors underlain by igneous bodies. The Drummond Basin is poorly mineralised except in its northeast corner where it is overprinted by rhomb structures. Some of the rhomb structures there are reactivated Basin-forming structures, but more importantly they are the locus for Late Carboniferous volcanic and subvolcanic complexes which host many of the gold occurrences. Gold mineralisation is superimposed on the Drummond Basin as it is on the other tectonic elements within the rhomb. Development of the rhomb represents midCarboniferous disruption of the established Late Devonian - Early Carboniferous continental arc. Extension and rotation attenuated the crust within the rhomb, facilitating mid-crustal dewatering and deep crustal melting. Major structures within the rhomb channelled fluids and magmas to shallow crustal levels. The Plutonic and Slate Belt deposits were localised near these structures and in the aureoles of plutons on cooling. Hydrothermal fluid evolution in equivalent magmas at subvolcanic levels and interaction with near-surface fluids localised the Porphyry and Epithermal deposits. The tectonic model has many similarities with those proposed for the Laramide and Tertiary of the southwestern United Stares and Mexico. However, the apparent restriction of gold mineralisation to the late stage transtensional regime in north Queensland is an important difference.

METALLOGENESIS RELATED TO LONG TERM TRENDS IN GLOBAL TECTONICS M.E. Barley* and D.I. Groves Key Centre for Teaching and Research in Strategic Mineral Deposits, Department of Geology, University of Western Australia, Nedlands, Western Australia, 6009.

The uneven distribution of different types of metal deposits deposits through geological time is related to the evolution of the hydrosphere-atmosphere, Geological Society of Australia Abstracts Number 32, Ballarat 1992

a secular decrease in global heat-flow and long term tectonic trends. Major peaks in the abundance of; a) metal deposits which form, or are preserved, in

46 convergent margin orogenic belts (e.g. Au, volcanogenic sulphides) in the Late Archaean (2.8 to 2.5 Ga) and past 200 Ma, and b) metal deposits associated with either anorogenic magmatism or continental sedimentation (e.g. sediment-hosted PbZn, Olympic Dam Cu-U) in the Middle Proterozoic (1.8 to 1.3 Ga), seem difficult to reconcile with the now general acceptance that plate tectonic processes have operated since the Late Archaean. This is commonly explained in terms of an evolutionary trend in global tectonics from a permobile regime in the Archaean, through a stable cratonic Proterozoic, to the operation of plate tectonics in the Phanerozoic (e.g. Meyer, 1988). However, the possible existence of long-term cyclicity in global tectonics resulting from interaction of large continental masses and mantle convection (e.g. Anderson, 1982; Gurnis, 1988) provides a tectonic framework which may resolve this problem. A review of the distribution through geological time and tectonic setting of several important groups of metal deposits indicates that rather than simply recording three distinct phases in global tectonics, temporal variations in abundance can be explained in terms of the combined influences of decreasing global heat-flow and the cyclic aggregation and breakup of large continents. The abundance of orogenic metal deposits in the Late Archaean corresponds with a period of high global heat flow with rapid growth and stabilization of cratons via accretion of magmatic arcs and related terranes. The abundance of these deposits in the past 200 Ma corresponds to the present tectonic cycle initiated following the breakup of Pangea. Although orogenic metal deposits generally have low preservation A 2.9

potential, they also occur in Proterozoic and early Phanerozoic orogens. There is increasing evidence that several Archaean cratons and Early Proterozoic orogens had aggregated to form the first large Proterozoic continents by 1.6 Ga (Hoffman, 1988; 1991). High sea-level during continental aggregation resulted in sedimentation in extensive cratonic basins, and was followed by intense anorogenic magmatism related to subsequent continental breakup. The combination of these factors produced favourable conditions for the major peaks in the abundance of sediment-hosted PbZn, Cu and U mineralization between 1.6 and 1.4 Ga. The dominance of mineralization associated with, or related to, anorogenic magmatism (PGE, Pb, U) in the Middle Proterozoic is most likely to be the result of hotter mantle upwelling beneath the first large continents. As first recognized by Sawkins (1976) the other important peaks in the abundance of sedimenthosted Pb-Zn and Cu in intracratonic basins occur in the Late Proterozoic and mid Phanerozoic. These coincide with the maximum assembly of a Late Proterozoic supercontinent (e.g. Dalziel, 1991; Hoffman, 1991) and Pangea respectively. References Anderson, D.L., 1982. Nature, 297, 391-393. Dalziel, I.W.D., 1991. Geology, 19, 598-601. Gurnis, M., 1988. Nature, 332, 695-699. Hoffman, P.F., 1988. Ann. Rev. Earth & Planetary Sci. 16, 543-603. Hoffman, P.F., 1991. Science, 252, 1409-1412. Meyer, C., 1988. Ann. Rev. Earth & Planetary Sci. 16, 147-171. Sawkins, F.J., 1976. Geology, 4, 427-430.

SEAFLOOR ACOUSTIC FACIES CONTEXT OF THE EASTERN MANUS BASIN HYDROTHERMAL SYSTEMS Melissa E. Fellows* and Keith A. W. Crook

Geology Department, Australian National University A substantial data base has been collected from the west, that extends from south of Djaul Island, in a Manus Basin, Papua New Guinea. This has facilitated complex 'braided' manner, to form the Banning Fault the construction of a well controlled seafloor acoustic in northeast New Britain and the Weitin Fault Zone on facies map. Two hydrothermally active areas have the east, which can be traced as a submarine fault, been identified in the eastern Manus Basin; Desmos through to southern New Ireland. The plate boundary Cauldron and the Pacmanus deposit. These discoveries linking them is defined by northeast trending faults can now be placed within an acoustic framework. The separating en echelon ocean floor neo-volcanic zones Manus Basin is located to the northeast of mainland in rifted island arc crust with variable young sediment Papua New Guinea and has evolved in a back-arc cover. setting since 3.5 Ma, lying athwart the boundary of facies were initially recorded for the basin the South Bismarck and Pacific plates. The eastern fromAcoustic 3.5 kHz echograms. Additional part of the basin is bounded by northeast trending, left- controlcontinuous for mapping the extent of acoustic facies came lateral transform faults: the Djaul Transform on the from supplementary criteria directly related to the

Geological Society of Australia Abstracts Number 32, Ballarat 1992

47 acoustic properties: co-registered data sets comprising SeaMARC II sidescan sonar imagery, 100 m contoured digital bathymetry and single-channel seismic refraction profiles (Taylor, 1991). Many of the echo characters types identified resembled those in Damuth & Hayes (1977) and Damuth (1980). New types were identified primarily associated with the ongoing tectonic activity in the basin. Three echo character types were associated with the neo-volcanic zone of the area; IIB' a very prolonged diffuse character, IIIC consisting of overlapping hyperbolae of varying vertex elevation and IIIC/IIB a complex character of overlapping hyperbolae overprinted by a semi-prolonged character with no subbottoms. These types of echo characters recorded the acoustic response to rough seafloor topography formed by recent neo-volcanism with minimal sediment cover. Hydrothermal deposits in the eastern Manus Basin are located within the neo-volcanic zones. The Pacmanus deposit encompasses an area of high temperature hydrothermal venting located on the northeast trending volcanic Pual Ridge, central Eastern Manus Basin. The deposit was found in a felsic setting associated with vesicular dacite (Binns et al., 1992). In contrast hydrothermal activity in the Desmos Cauldron, located to the east of the Pacmanus deposit is found within a depression associated with fresh glassy basalts (Sakai, 1990). Both hydrothermal deposits exhibit a type IIB* 3.5kHz echo character and have recorded a strong side-scan sonar reflection. These are acoustic features typically identified with young volcanic rocks with negliable sediment cover. A 2.10

Sedimented areas in the vicinity of these deposits exhibit a indistinct character with intermittent subbottoms (type IIA). The type IIB' echo character is exclusive to the youngest neo-volcanic areas in the eastern Manus Basin, which is similar to the case in the Manus Spreading Centre. The question arises of what develops from this character over time as sedimentation occurs on these neo-volcanic zones. We propose that the echo character IIIC/IIB is the resultant acoustic response. References Binns, R.A., Scott, S.D. & PACMANUS Participants, 1992: Discovery of Active Hydrothermal Sulfide Deposition Associated with Submarine Felsic Volcanism, Pual Ridge, Eastern Manus Basin, Papua New Guinea, Geol. Soc. Aus. Abstracts (this volume ) Damuth, J.E., 1980: Marine Geol., 38, 51-75. Damuth, J.E. & Hayes. D.E., 1977: Marine Geol., 24, 73-95. Sakai, H., 1990: Hakuho-Maru cruise KH90-3, Leg-2: A brief summary for SOP AC. 6pp. Taylor B. et al. 1991: Pacific Seafloor Atlas, Hawaii Institute of Geophysics University of Hawaii.

A POSSIBLE CONNECTION BETWEEN MANTLE PLUMES AND METALLOGENY Ian H. Campbell and Robert I. Hill

Research School of Earth Sciences, Australian National University, Canberra, ACT See paper A 7.6 for full abstract.

Geological Society of Australia Abstracts Number 32, Ballarat 1992

48

Geological Society of Australia Abstracts Number 32, Ballarat 1992

49

A3: ECONOMIC GEOLOGY CONVENOR: PHILLIP

SECCOMBE

KEYNOTE: A 3.1 EMPIRICISM AND CONCEPT IN SUCCESSFUL MINERAL EXPLORATION Roy Woodall WESTERN MINING CORPORATION An empiricism is knowledge acquired from experience and observations regardless of theory or scientific principles. Scientific empiricism is the use of descriptive science to develop hypotheses and exploration strategies. A concept is a thought, an idea, or theory and conceptual ore search invokes theories or ore genesis. It is fashionable to talk about exploration strategy in terms of "models" and to categorise our exploration strategies as either empirical or conceptual. However, we need to be aware that the construction and application of exploration models can narrow the vision and reduce mental agility and flexibility, especially if pursued with excessive religious zeal. Models are often dangerously linked to fads and fashions and can attract such veneration as to be a comfortable substitute for reality. Factual data collection by geologists, geophysicists and is fundamental to empirical exploration but there is no such thing as completely objective data collection or completely objective data interpretation. They both involve judgement of degrees of of relevance based on experience and beliefs. "What the evidence prevails upon the mind to believe, depends upon the mind as well as the evidence" Lasky(1948) "Geologists do much of their work intuitively in their minds based on experience so that.... exploration geology seems as much an art as a science" Adams (1985, p.273). Geoscientists are reluctant to have their exploration strategies as entirely "empirical" lest this infer their thinking and practice is unscientific. So the empirical explorer searches for a theory to demonstrate that certain observations are relevant, while the conceptualist searches for empirical evidence to justify a theory. Both aim to give their exploration strategies the cloak of integrity. Thus in practice, the Geological Society of Australia Abstracts Number 32, Ballarat 1992

distinction between the empirical and the conceptual (theoretical) becomes blurred and we thus should not expect a clear demarcation between an "empirical" exploration strategy and a conceptual exploration strategy. A conceptual model, properly used: . both constrains and promotes observations and data collection.... . promotes communication.... . aids the quantification of risk, and . identifies useful avenues of research. Never-the-less, if we express the way we organise our thoughts and develop- our exploration strategies by referring to conceptual "models" we should do so with great care. Geological theories of ore formation are extremely difficult to prove and geological time and earth processes difficult or impossible to duplicate in a laboratory. Moreover, scientific discussion concerning the evolution of planet Earth is still full of controversy, as is discussion of the processes going on within the Earth today. How less perfect is our knowledge of processes in the past. No geological research is more critical to the development of an understanding of ore formation and the development of sound exploration strategies, than meticulous, geological mapping, and core logging by mine and field geologists. Such work is however often despised by the academically inclined. Perhaps the most neglected area of documentation and conceptual thinking is research concerned with the tectonic setting of the giant mineral deposits and mineral fields, i.e. observations and theories concerned with features and events at regional and even continental scales. Exploration for nickel and gold in Australia has largely been based on empirical strategies. The average cost of discovering an economic gold deposit has been $20 million and the average cost of an economic nickel discovery $28 million. In contrast,

50 the cost of discovering an economic base metal deposit has been $274 million, or an order of magnitude greater. One contributing factor is that empirical methods of exploration: i.e. prospecting, geochemical and geophysical surveys to identify 'anomalies' and programs of pattern drilling have not been as effective in the search for base metals as in the search for gold and nickel. An Australian Company's Experience Norseman Discoveries: 1933-1949— While the development of exploration strategy on the Norseman goldfield has been firmly anchored on empirical observations in the form of detailed surface and underground mapping, there have been conceptual aspects to data interpretation. As early as 1930's concepts which evolved from the modelling experiments of Hans Cloos were relevant. Early exploration was guided by the idea of an east-dipping reef-shear with flatter sections (links) which under the reverse fault movement predicted by Cloos experiments, become zones of dilation and thus the preferred sites of maximum quartz reef formation and gold deposition. The empirical and the conceptual are interwoven into the fabric of over 50 years of successful exploration at Norseman. Kambalda Discovery: 1957-1986— It was an empiricism i.e. the recognition of the similarity in geology of the Canadian and Western Australian Archaean which aroused the initial interest in the potential of the Yilgarn Craton for metals other gold. It was conceptual thinking which recognised that nickeliferous ironstones were gossans derived from magmatic sulphides. From then on, empirical exploration i.e. the drilling of geochemical and geophysical anomalies and drilling beneath gossan outcrops dominated nickel exploration in Western Australia and resulted in discoveries which stretched from Norseman to Wiluna. Thus the successful strategies of the nickel boom were like those employed in the gold search at Norseman; they moved from the empirical to the conceptual, and back to the empirical. "the models used were a mode of travel rather than a destination" Adams (1986, p.296-7). Yeelirrie Discovery 1971— The discovery of the Yeelirrie uranium deposit was the successful culmination of an exploration programme initiated in 1968, to explore for sandstonetype uranium deposits in Australia. In common with any discovery Yeelirrie carried its own salutary lessons, not least of which being the necessity to maintain open eyes and an open mind. It strikingly Geological Society of Australia Abstracts Number 32, Ballarat 1992

illustrates the uncertainties in exploration and how a geological conceptual model may be sufficiently correct to take exploration in the right general direction yet lead to the discovery of an unexpected style of mineralisation. Olympic Dam Discovery 1957 to 1976— Western Mining began searching for a major copper deposit in Proterozoic rocks in 1957. The initial logic was strictly empirical. . look for surface indications of copper mineralisation . major copper deposits occur in Proterozoic rocks worldwide, . economic copper deposits have been found in Proterozoic rocks in Australia, and . geological mapping, geochemical stream and soil surveys and geophysical surveys should be effective, empirical prospecting techniques; By the early 1970s a line of conceptual thinking had been developed by Douglas Haynes during Doctorate research at the Australian National University. From his research came the knowledge that copper is leached from basalt during oxidation and hence the exploration concept was developed that: substantial piles of oxidised continental, thoielitic basalts could source enough copper to form a major sediment-hosted orebody. A second line of conceptual thinking was being developed in the late 1940's and 1960's by Tim O'Driscoll, while mapping the Broken Hill ore deposit, a programme which subsequently developed into Doctorate and post-Doctorate research at Adelaide University. From this research came the concept that the regional shears (lineaments) were sources and controllers of mineralisation which would be found distributed either syngenetically or epigenetically at points in and along the lineament tracks. In 1972 the ingredients of the structural lineament-ore signature was established as the paradigm for the selection of exploration targets. Two years later it was used to define targets which are now occupied by the deposits of Olypmic Dam and Century. In 1973, a third exploration scientist, Dan Evans, entered the stage. Evans asked for the opportunity to combine the conceptual ideas of the two specialists, Haynes and O'Driscoll, whom he respected. In order to lead the search for Proterozoic stratiform copper in South Australia. In July and August 1974, the small Mount Gunson copper deposit was used both by the project geophysicist Hugh Rutter, and the tectonics team of O'Driscoll and Dave Duncan, as a basis for empirical targeting. In June 1975 the first hole (RD1), was sited on a combined gravity-magnetictectonic target and his hole. Intersected the fringe of one of the world's great ore deposits. In the final analysis, the Olympic Dam deposit

51 was discovered because minds were prepared to believe in a blend of both conceptual and empirical evidence, i.e. in the power of both theory and observation, and managers were prepared to back the judgement of those scientists, even though many years of disappointment. Did serendipity play a part in the discovery of the Olympic Dam deposit? Of course it did! The Olympic Dam discovery is in keeping with the words of Pasteur. "In the fields of observation, chance favours the prepared mind\ The minds which led to this discovery were up to 40 years in preparation and the company's learning experience concerning Proterozoic copper deposits spanned 20 years.

confidence in science and ore deposit models" Woodall (1984, p. 132) What distinguishes those who can make "the act of faith, the leap beyond the unknown" from those who cannot? It is intuition. Intuition looks beyond appearances to inner meanings, relationships, interpretations possibilities. In most intuitive experience....there is an element of prophecy. Those who lack intuition are often paralysed by the search for certainty. In the final analysis it is not the exclusive possession of observations (empiricisms) or concepts (theories) that distinguishes those who discover from those who fall. What matters is what use the mind makes of the empirical and the conceptuaL.

The Road to Discovery— The road to discovery and successful exploration is neither solely paved with empiricisms nor with concepts. When empiricism is dominant we walk a more certain path. When concept, i.e. theory dominates, the path may lead to the unknown but possibly to the discovery of new ore deposit types. Earth science and ore deposit models whether empirical or conceptual: "are only relevant if they give us a sounder basis for confidence, make us bolder and more perceptive explorers, and help us to be more confident in the recognition of either the close proximity or ore or a new ore environment. But we can follow knowledge and reason just so far, then comes the act offaith, the leap beyond the sure path. Whether we are ultimately able to take that step is a test of our ultimate

References

A 3.2

Adams, S.S.,1985. Using Geological Information to Develop Exploration Strategies For Epithermal Deposits, Berger, B and Bethke, P.M., Geology and Geochemistry of Epithermal Systems. Reviews in Economic Geology, 2. pp,. 273-296. Lasky, S.G., 1948. The Search For Concealed Deposits - A Re-orientation of Philisophy Transactions of the American Institute of Mining and Metallurgical Engineers, v. 178,pp. 82-90. Woodall, R., 1984. Success in Mineral Exploration. The Joubin-James Lectures 1983. Geoscience Canada, Volume 11, Number 1, pp. 41-46. Number 2. pp. 83-90. Number 3. pp. 127-133.

THE EVOLUTION OF A NEW CONCEPT IN AN OLD AREA THE KANOWNA BELLE CASE HISTORY Kim Stanton-Cook

Chief Geologist - Australasia, Delta Gold N.L., Sydney, New South Wales Gold was first discovered in the Kanowna area, approximately 20 kilometres northeast of Kalgoorlie in Western Australia, in 1893. Gold mining in the area peaked in 1898 with the production of 152,000 ounces from vein-hosted and alluvial sources. From 1911 production became sporadic and declined rapidly before ceasing in 1946. Interest in Kanowna surged again in 1979 as the gold price rose, resulting in increased exploration activity and, in 1986, the recommencement of mining at Kanowna. Total gold production from the Kanowna area is approximately one million ounces. Exploration for additional mineralisation in the Kanowna area focussed on extending, or finding repetitions of known vein deposits and deep leads. Geological Society of Australia Abstracts Number 32, Ballarat 1992

Minor success was achieved on both fronts leading to the open-pit mine on the old Ballarat and Last Chance vein systems (Delta Gold N.L. 67.5%, Pancontinental Mining 32.5%) and the commencement, after the amalgamation of leases to form the Golden Valley Joint Venture (Delta Gold N.L. 50%, Peko Gold Ltd 50%), of mining the deep leads for heap-leach treatment at the QED operation. Using proven mineralisation concepts for the area, the GVJV employed the established techniques of soil geochemistry and RAB drilling to explore for vein and deep lead deposits. One other concept did exist in the minds of the joint venturers' geologists however; this paradigm was that the Kanowna area, because of its past production

52 and areal extent of gold occurrences, had the potential to host a major deposit. The Kanowna Belle discovery evolved as a conceptual model beginning as an occurrence of steeply dipping and narrow gold-bearing veins - the interpretation placed on RAB results obtained in 1987 and 1988. A large area (400 metres by 300 metres) of anomalous gold-in-s oil values, defined in 1989 in the area of RAB drilling, was inconsistent with the concept. Follow-up RAB drilling and the discovery RC drill hole in December 1989 led to an alternative concept - that of a flat-lying but otherwise apparently structureless body which did not fit either a vein or deep lead concept. Interpretation of deeper and more widespread drilling results throughout 1990 demonstrated an elongation of the deposit to the southwest and suggested a southern dip direction. Greater use of diamond-core drilling from mid-1990 assisted in defining the geometry of the deposit allowing further refinements of the concept. One major advance was the recognition of a strike-slip planar shear-zone, the Fitzroy Fault, and the parallelism of the main mineralised lenses to this

fault. Deeper diamond drilling, using the Fitzroy Fault as a plane of reference, provided additional data on lithology, structure, alteration and mineralisation. This included the extent of brecciation, veining and the variability of the fragmental rock compositions. Tangential concepts were proposed, based on the new information, ranging from conglomerate-hosted models to milled breccia and diatreme-related modes of genesis. Kanowna Belle is now described as a serf es of stacked lenses or shoots, striking northeast and dipping moderately to the southeast, closely related to the Fitzroy Fault. The deposit is hosted within Archaean felsic fragmentals and conglomerates intruded by felsic porphyries and is characterised by extensive sericitecarbonate-pyrite alteration with variable silicic and sodic alteration. The deposit contains, in Measured and Indicated Resources of 11.2 million tonnes at grades of 5.23g/t gold (cut to 50g/t gold) or 5.81g/t gold (uncut), approx imately two million ounces of gold.

A 3.3 THE WHITE DEVIL GOLD DEPOSIT TENNANT CREEK : RECOGNISE THE CLUES IN YOUR OWN BACKYARD! Paul Hunter1 & Bruce D. Kay2* 'White Devil Mine, Tennant Creek, N.T. 0862 Normandy Poseidon Limited, PO Box 7175, Hutt Street, S.A. 5000

2

Shallow portions of the White Devil-Black Angel ironstones were mined by prospectors from 1935 to 1951 to produce 3,141 ounces of gold. Although Peko had drilled a total of 12 holes into the system between 1957 and 1983 and obtained a significant gold intersection in one hole, further exploration was not recommended. Australian Development Limited (now Poseidon Gold Limited), acquired an option to purchase the leases in April, 1986 and the first drill hole (WDRC-1) intersected 6 metres grading 21.7 g/t Au on 30 May, 1986. Since mining commenced in August, 1987, the White Devil Mine has produced about 250,000 ounces of gold from high grade ore (1990/91 grade 22 g/t Au) at a total cost of less than $200 per ounce.

Geological Society of Australia Abstracts Number 32, Ballarat 1992

In April 1989, when only two years of resources remained to be mined, exploration drilling based on geological and magnetic information intersected a new high grade ore position ("Pinter Lodes") to the east of the current ore zone. Exploration drilling continues on these ore zones and has defined sufficient ore resources, for at least another five years production. The Tennant Creek ore deposits are characteristically small, yet very high grade and profitable. They are therefore difficult exploration targets and require persistent exploration with a strong emphasis on surface and down hole geophysics, in conjunction with geological and structural interpretation.

53 A 3.4

GEOLOGY OF THE PLUTONIC GOLD DEPOSIT WESTERN AUSTRALIA M Rowley Plutonic Resources Limited, North Sydney, N.S.W.

The Plutonic gold deposit is essentially a stratabound multiple lode system within mafic metavolcanic rocks which is partly capped by surficial gold bearing laterite. The deposit is located within the Peak Hill Mineral Field 940 km northeast of Perth in central Western Australia. Gold mineralisation was discovered in 1988 during the follow-up, by RAB and RC drilling, of geochemical anomalies indicated by rock-chip, ferruginous lag and Location Northern Lodes Pit Laterite Pit Stockpiles

Ore Type Oxide Sulphide Laterite Oxide Laterite Oxide

TOTAL An additional 4.7 million tonnes of resources grading 2.53 g/t Au were also outlined. The mine is currently wholly owned and operated by Plutonic Operations Limited. The Plutonic Mine lies within the Marymia Dome which is an Archean basement inlier within a Proterozoic belt known as the Capricorn Orogen. The Orogen formed as a result of collision between the Pilbara and Yilgarn Cratons (Myers, 1990). The Marymia Dome, a Yilgarn-type granitoid dome, contains granitoids, gneissic assemblages and two Yilgarn type greenstone belts. The Mine is located near the south western end of the northern Plutonic

Geological Society of Australia Abstracts Number 32, Ballarat 1992

soil sampling. Mining of both the primary lodes (Northern Lodes) and laterite started in June 1990. Milling of the ore commenced in August 1990. By 31 December 1990, a total of 1.57 million tonnes of ore grading 3.57 g/t Au was mined with 517,000 tonnes of ore grading 8.02 g/t Au being milled with recovery of 125,000 ounces gold. Ore reserves as at 31st December 1990 were as follows: Tonnes 1,669,000 276,000 1,910,000 372,000 432,000 599,000 5,258,000

Grade (g/t Au) 4.77

8.10

1.81 4.06 2.44 1.85 3.30

Well Greenstone belt which trends northeastsouthwest over a 50 kilometre strike length. Lithologies within this belt consist of ultramafic volcanics. tholeiitic basalts and metasediments including banded iron formation (Gee, 1987). The area around the mine is underlain by folded and faulted units of mafic and ultramafic volcanics, granitoids and minor sediments which have been regionally metamorphosed to an upper greenschist grade. The mine sequence generally strikes east-west and dips between 20 and 60 degrees northerly. The stratigraphic sequence is shown on the following table.

54 Plutonic Gold Mine Stratigraphic Sequence Unit

Average Thickness (m)

Ultramafic Volcanics

+140

Hanging Wall Unit

Mafic to Ultrafic Volcanics Mafic Volcanics Banded Zone

20 120* 1

Mineralised Units

Interbedded Mafic & Ultramafic Volcanics 26 Interbedded Mafic rocks and graphitic shale 8 70 Mafic Volcanics 3 Graphitic Shales

Footwall Units

Mafic Volcanics Mafic to Ultramafic Volcanics

60

+48

* Main mineralised unit The mafic lithologies are typically amphibolitic with a fine to coarse (often porphyroblastic) range in grain size and variable composition characterised by development of hornblende-actinolite and chlorite. The ultramafic lithologies consist of talc chlorite + carbonate schists and tremolite-chlorite bearing rocks. Metasediments are relatively minor graphitic shales, often sulphidic. A laminated siliceous sulphidic unit (known as the banded zone) at the contact between the host mafic amphibolite and the underlying maficultramafic unit is interpreted as an interflow sediment. The shales and banded zone are important stratigraphic marker horizons in the mine stratigraphy. Steeply dipping dolerite dykes ranging up to 40 metres in width intrude the mine sequence along east-west and northeast-southwest strike trends. Gold mineralisation occurs in a series of subparallel northwest-southeast striking lodes (Northern Lodes) which dip at 40°-50° to the northeast. The lodes average around 10 metres in width and often have strike and dip continuity over several hundred metres. The lodes transgress the mafic host unit being generally constrained only by the upper contact with the talc-chlorite schists and the banded zone on the lower contact. Limited extension of some of the lodes can occur for several metres into the talc-chlorite schists or into the mafic-ultramafic unit below the banded zone. Several post mineralisation structures in the Northern Lodes area have displaced or modified the lodes. Fold structures, where present, are generally open style and shallow north plunging. Minor fault structures with movement of only 1-2 metres are common. A major eastwest trending normal fault (north side down) and a northwest trending normal Geological Society of Australia Abstracts Number 32, Ballarat 1992

fault (west side down) to the south and east of the Mine respectively result in the Mine being located mainly within a triangular shaped downthrown fault block. Northwest of the Mine, a late stage northeast trending low angle (20°-30°) reverse or thrust fault has resulted in movement of a mafic sequence easterly over the top of the mine sequence. Regionally the Plutonic deposit has been interpreted to lie on the southern upright limb of an extensively faulted northeast-southwest trending overturned syncline. Although showing diffuse boundaries in the weathered zone, the lodes in fresh rock occur as well defined banded strongly siliceous sulphidic zones. The sulphides form about 5-10 volume percent of the lodes and are mainly arsenopyrite with pyrrhotite, minor pyrite and trace chalcopyrite. Lodes are also characterised by the presence of phlogopite. Interpretation of lode and host rock mineralogy and textures suggests the following sequence of events in lode development. 1. An early hydrothermal alteration (phyllicpropylitic-carbonate) and veining (carbonate-quartzsulphide) event which produced a sericite-chloritequartz assemblage with accompanying carbonate, gold, sulphide and trace tourmaline and scheelite. 2. Deformation either concurrently or following the hydrothermal alteration- veining event which resulted in the development of a strong foliation (mineralised banding). 3. Subsequent upper greenschist facies regional metamorphism which produced a recrystallisation and a coarsening in grainsize in both the host lithologies and the hydrothermal and veined zones. This resulted in growth of metamorphic phlogopite-chloriteclinozoisite-amphibole phases.

55 References Gee, R D, 1987, Peak Hill, W A, (2nd edition): Western Australia Geological Surveyor, 1:250,000 Geological Series Explanatory Notes

A 3.5

Myers, J S, 1990, Capricorn Orogen in Geology and Mineral Resources of Western Australia. Western Australia Geological Survey Memoir 3, p 197198

T H E CENTURY ZINC DEPOSIT, N O R T H W E S T QUEENSLAND John Main Chief Geologist, CRA Exploration Pty. Ltd., Gulf District

The Century zinc deposit, discovered in 1990, contains 120 MT of 10% zinc, 1.5% lead and 35 g/t silver. It is another example of a Proterozoic, shalehosted, stratabound zinc-lead deposit, similar to the McArthur River, Lady Loretta, Hilton and Mt. Isa deposits. It is located approximately 20km NNW of Mt. Isa and occurs within a gently folded shale/siltstone sequence of the Lawn Hill Formation. The deposit is bounded by faults and erosional contacts with the overlying Cambrian carbonates. The mineralised zone has a distinctive stratigraphy based upon the distribution of mineralised carbonaceous shales, dolomitic siltstones and carbonaceous mudstones. Four zones are recognised: Zone 1: Moderately to thinly banded dolomitic

Geological Society of Australia Abstracts Number 32, Ballarat 1992

siltstones and sulphide bearing, carbonaceous shales. Zone 2: Mineralised carbonaceous shale. Zone 3: Dolomitic siltstone. Zone 4: Mineralised carbonaceous shale. Each zone is characterised by regular sulphide mineral assemblages and zinc-lead-silver ratios. The mineralisation appears to transgress bedding/banding on a deposit to microscopic scale, with the sphalerite and galena composition approaching stoichiometric values. Because of weak metamorphism and minor deformation this deposit will provide an important opportunity to understand the character and genesis of this class of mineral deposit.

56

MOUNT ISA INLIER CENTURY DEPOSIT LOCATION 18'

SOUTH NICHOLSON BASIN

CARPENTARIA

CEKWY

BASIN

19

GEORGINA BASIN

tadp/ t_oretta

—

20*

-Dugald River HMdn N Nth s 1 \ \ \ \ y vMt'-lsaV/

- 214

+ /GEORGIN^ + ( BASIN ^

EROMANGA

•

Major Zinc deposit

WESTERN FOLD BELT ^ v ^ j Lawn Hill Platform V V l Leichhardt River Fault Trough

BASIN

KALKADOON-LEICHHARDT BELT

EASTERN FOLD BELT . J

Mary Kathleen zone

["--""-] Ewen Block

-•••••] Quamby-Malbon zone

1 Myolly Shelf

Cloncurry-Selwyn zone Figure 1

Geological Society of Australia Abstracts Number 32, Ballarat 1992

57 A 3.6

MINERALOGY OF THE CENTURY DEPOSIT,

NORTH QUEENSLAND

S. W. McKnight School of Mining, Geology and Materials, Ballarat University College, Victoria

Text withheld.

A 3.7 THE OSBORNE DEPOSIT: A DISCOVERY WHERE "ORE MODEL" DOGMA AND PERSISTENCE PAID OFF Tim Jauristo Placer Exploration Limited The Osborne deposit lies within the Tank Trough project area, and is situated some 130km south of Cloncurry in northwest Queensland. Gold and copper mineralization occurs within magnetite-rich Proterozoic ironstones of the Mt Isa Inlier. The Mt Isa Inlier can be subdivided into the Eastern and Western fold belts of mid-Proterozoic age separated by a basement ridge of Early Proterozoic age (Blake et al. 1990). The Osborne deposit is located near the southern end of the Eastern fold belt, within a sequence of predominantly psammitic sediments metamorphosed to amphibolite fades. As the project area is overlain by 20-40m of siltstone of the Mesozoic Wallumbilla Formation, the host unit is somewhat problematic, but may be the Mt Noma Quartzite. The Mt Noma Quartzite forms part of the Soldiers Cap Group, which host to numerous base-metal/gold deposits near the upper contact of the Mt Noma Quartzite with the overlying Toole Creek volcanics (Beardsmore et al 1988). Economic mineralization at the Osborne deposit occurs predominantly within two folded northeasterly dipping ironstone units, within an undifferentiated sequence of variably feldspathic meta-psammite, narrow intercalated biotite schist, amphibolite and pegmatite. The ironstones are comprised mostly of varying amounts of silica and magnetite with chalcopyrite, pyrite and pyrrhotite the dominant sulphide species. Geochemically anomalous C0-M0Sn-W is associated with the Cu-Au mineralization. A mineralogical zonation from west to east of pyrite-chalocopyrite through chalocopyrite-pyrite to pyhrrotite-chalocopyrite-pyrite can be observed in the upper ironstone which may represent faults. The deposit was first detected by Newmont as an

Geological Society of Australia Abstracts Number 32, Ballarat 1992

aeromagnetic anomaly in 1974 during their search for Pegmont style base metal deposits. Several shallow holes intersected weakly mineralized ironstone with a geochemical signature which didn't match that of Pegmont. A CSR/Billiton joint venture commenced exploration in 1985 on a Starra ore model (Au/Cu in Proterozoic ironstones). Initial drilling and ground magnetics confirmed the model, with thick ironstone units containing low-grade Cu and Au. Persistence by the late Bob Osborne as Project Geologist and Placer Pacific Limited (who purchased CSR's mineral interests in 1988) eventually lead to the discovery of a significant mineral deposit. Placer's doctrine of "when you're in a big system, stick to it" led to the drilling of 336 drill holes to the end of 1990, with an additional 509 drill holes to October 1991. A total diluted resource of 27mt at 1.4% Cu, 0.8%g/t Au was calculated above a cut-off of 1% Copper Equivalent in March, 1991. References Blake, D.H., Etheridge, M.A., Page, R.W., Stewart, A.J., Williams, P.R. and Wyborne, L.A.I. 1990. Mt Isa Inlier-Regional Geology and Mineralization, in Geology of the Mineral Deposits of Australia and Papua New Guinea (Ed. F.E. Hughes), pp 915-922 (The Australasian Institute of Mining and Metallurgy: Melbourne). Beardsmore, T.J., Newbury, S.P. and Laing, W.P. 1988. The Maronan Supergroup: an inferred early volcanosedimentary rift sequence in the Mt Isa Inlier, and its implications for ensialic rifting in the Middle Proterozoic of northwest Queensland. Precambrian Res., 40/41: 487-507.

58 A 38 ORE GENESIS AND EXPLORATION MODELS FOR PLATINUM-GROUP ELEMENT MINERALIZATION IN LAYERED MAFIC/ULTRAMAFIC INTRUSIONS Reid R. Keays1*' Paul R. Hamlyn 1 ' 2 and Shane J. Reeves 1 ^Department of Geology, University of Melbourne 2ORE Pty Ltd, Hawthorn, Victoria. The generation of platiniferous horizons in layered intrusions involves S-saturation of a previously Sundersaturated magma in a magma chamber. The recognition of this requirement can be used to develop exploration strategies for economic accumulations of the Platinum Group Element (PGE) in layered mafic/ultramafic intrusions. The potential of a magma to form a PGE deposit is determined by its sulphide-saturation history. Most First Stage Magmas (FSM) such as MORB are Ssaturated during ascent to the surface; as a result, they have low PGE, and high S contents. High temperature magmas (e.g. komatiites and picrites) do not become S-saturated until a late stage and as a result have much higher PGE contents than S-saturated magmas. There is strong evidence that the parental magmas to the lower portions of layered mafic/ultramafic intrusions hosting economic platiniferous horizons (Bushveld Complex, Stillwater Complex, and Great Dyke) as well as many of the mafic/ultramafic complexes (e.g Munni Munni) in the Pilbara and Kimberley regions of Western Australia were either Siliceous High Magnesian Basalts (SHMB) or boninites (Hamlyn and Keays, 1986; Sun et al., 1991). Both of these magma types have enhanced PGE contents relative to FSM; even more important, however, is that both boninites and SHMB were formed from S-undersaturated magmas. As incompatible elements, Pd, Pt and Au build up along with S and Cu during the course of fractionation of S-undersaturated magmas; however, once a magma becomes S-saturated, Pd and Pt are rapidly removed by the first immiscible sulphide droplets to separate from the magma because of their very high partition coefficients (e.g. Dpd=20,000; Peach et al., 1990). Whereas S-saturated magmas have very low Pd/S ratios, S-undersaturated magmas have relatively high Pd/S ratios. Because they contain variable proportions of trapped interstitial silicate melt, cumulates formed from these magmas preserve the Pd/S ratios of the magmas. Hence, cumulates lying below mineralized horizons have high Pd/S ratios whereas those above have low Pd/S ratios. These principles can be used in exploration for PGE mineralisation in layered intrusions as will be shown using examples from the Great Dyke, Zimbabwe (Prendergast and Keays, 1989), Munni Munni Intrusion, Western Australia (Hoatson and Keays, 1989), Stillwater Complex, U.S.A., and the Geological Society of Australia Abstracts Number 32, Ballarat 1992

Giles Complex, South Australia. Each of these intrusions exhibit markedly different PGE patterns which are attributed to different magmatic processes and timing of S-saturation in each of the intrusions. Our approach is to document PGE patterns in the entire environment rather than focusing on the immediate ore horizons as has been done in many previous studies. It thereby avoids many of the interpretative problems caused by later 'hydrothermal' redistribution of the PGE on the thin section scale resulting from the activities of late stage fluids. However, systematic variations in PGE contents and PGE/S ratios throughout layered complexes and particularly across platiniferous horizons provide extremely strong support for a 'magmatic* origin for 'Merensky type' PGE mineralization. References Hamlyn, P.R. and Keays, R.R., 1986, Sulphur saturation and second-stage melts: application to the Bushveld platinum metal deposits: Econ. GeoLy v. 81, p.1431-1445. Hoatson, D.M. and Keays, R.R., 1989, Formation of Platiniferous sulfide horizons by crystal fractionation and magma mixing in the Munni Munni layered intrusion, West Pilbara Block, Western Australia: Econ. GeoL, v. 84, p. 17751804. Peach, C.L., Mathez, E.A. and Keays, R.R., 1990, Sulphide melt-silicate melt distribution coefficients for the noble metals and other chalcophile metals as deduced from MORB: Implications for partial melting: Geochem. Cosmochim. Acta, v. 54, p.3379-3389. Prendergast, M.D. and Keays, R.R., 1989, Controls of platinum-group element mineralization and the origin of the PGE-rich Main Sulphide Zone in the Wedza Subchamber of the Great Dyke, Zimbabwe: implications for the genesis of, and exploration for, stratiform PGE mineralization in layered intrusions: in Magmatic Sulphides - the Zimbabwe Volume, Prendergast, M.D. and Jones, M.J. (eds), Inst. M.M., London, p. 43-69. Sun, S-S., Wallace, D.A., Hoatson, D.M., Glikson, A.K. and Keays, R.R., 1991, Use of geochemistry as a guide to platinum group element potential of mafic-ultramafic rocks: Examples from the West Pilbara and Halls Creek Mobile Zone, Western Australia: Precamb. Res., v. 50, p. 1-35.

59 A 3.9 USE OF CONCEPTUAL MODELS FOR GOLD EXPLORATION IN NORTH QUEENSLAND - A DECADE OF RECOGNITION AND DISCOVERY Gregg W. Morrison Gold Research Group, James Cook University of North Queensland, Townsville, Q4811 Conceptual models are often seen as the driving force for exploration in areas with minor or no previous mining history. The exploration leading to the discovery of the Olympic Dam deposit is a good example. In other circumstances, conceptual models provide a framework that encourages exploration once a key feature is recognised or an initial discovery is made. The 80's gold boom in north Queensland consisted of several cycles of recognition and discovery that prompted adoption of new or improved conceptual models that in turn stimulated exploration. When the increased gold price encouraged exploration for the metal in the 1980's many of the groups active in north Queensland had already been exploring for bulk tonnage Cu, Mo, Sn and U deposits. Kidston and Mount Leyshon, which had been evaluated as porphyry Cu prospects with recognised Au credits, gave much of the impetus to a porphyry Au exploration phase. Porphyry Au mineralisation had previously been considered by many to be subeconomic in its own right. Regional exploration focussed on porphyry-style alteration systems using airphoto reconnaissance of subvolcanic complexes followed up with prospecting and stream sediment sampling. Breccia, stockwork, vein and skarn styles of mineralisation were recognised and key examples were studied to determine controls on the distribution and origin of the mineralisation. At the same time, there was only limited interest in many of the historically significant goldfields which were perceived to have poor bulk tonnage potential. The real gold boom began in the mid 1980's. The development and initial success of Kidston broke the perception that deposits with grades less than 2g/t Au were not economically viable. About the same time, the recognition of bonanza epithermal veins at Pajingo A 3.10

led to a general reconsideration of high grade, low tonnage deposits as an exploration target. These conceptual models, together with the increased expenditures and involvement of more junior companies, led to evaluation of a complete range of occurrence types and widespread regional exploration using remote sensing and BLEG sampling. The epithermal concept was quickly expanded to include bulk tonnage targets based on the hotspring and Carlin models that were achieving such success elsewhere. The Drummond Basin was virgin territory for these concepts and there was a flurry of activity in the Broken River Province following the recognition of cinnabar in float there. Ultimately a wide range of epithermal mineralisation styles were identified, genetic links to intrusive phases were established for some deposits and the realisation emerged of the similarity in age and tectonic setting of the porphyry and epithermal deposits. The collapse of the stockmarket and subsequent decline in exploration expenditures, coupled with limited real exploration success and short life spans of the operating mines in the Drummond Basin, effectively ended the boom. Gold exploration in north Queensland, particularly the Drummond Basin, is presently in the conceptual 'doldrums'. The emphasis has shifted back to the porphyry concepts that stimulated the original exploration phase and there is greater interest in the related basemetal deposits with precious metal credits. The north Queensland gold boom was initiated and sustained by a corps of major players. Conceptual models evolved from critical phases of recognition and discovery and were not themselves the driving force for the boom.

THE GEOLOGICAL SETTING OF THE GOLDEN PLATEAU MINE, CRACOW, CENTRAL QUEENSLAND, AUSTRALIA Miles R. Worsley *, Subhash Jaireth, Gregg Morrison

Gold Research Group, Geology Department, James Cook University of North Queensland The Golden Plateau Mine occurs within the Cracow Goldfield in central Queensland, Australia. The Golden Plateau lode belongs to the adulariasericite type of epithermal gold deposit. Gold and silver mineralisation occurs mainly in steeply dipping and plunging ore shoots within an east west quartz Geological Society of Australia Abstracts Number 32, Ballarat 1992

breccia zone over an 800m strike length and has produced approximately 24 tonnes of gold. The gold deposits of the Cracow Goldfield are hosted by the Lower Permian Camboon Andesite which forms the southern portion of the Camboon Volcanic Arc, which in turn forms the eastern margin

60 of the Bowen Basin. The Camboon Andesite is unconformably overlain by marine sediments of the Lower Permian Back Creek Group. Outliers of Jurassic Precipice Sandstone lie unconformably above the Camboon Andesite on a peneplanation surface. The lodes are developed within a shallow dipping, mixed sequence of andesitic volcanics, fragmentals and tuffs. Intrusive rhyolites are spatially associated with the lodes in the eastern part of the mine. The quartz lodes are structurally controlled and ore zones occur at predictable structural sites such as intersections of major faults with lodes, lode intersections, flexures in lodes and contacts of rhyolite. Lodes have been formed in 5 successive phases of brecciation, silicification and quartz precipitation. Economic gold is associated with phases 4 and 5, with phase 4 containing a minor amount of gold (up to 4ppm) and phase 5 comprising the main ore shoots. Quartz (chalcedonic banded, crustiform banded, comb and amethystine), adularia, illite, kaolinite, calcite and siderite are the main gangue minerals accompanied by sulphides (pyrite, chalcopyrite, sphalerite and galena)

A 3.11

and tellurides (hessite, ?petzite and ?altaiite). Bornite, covellite and goethite are restricted to the zones of oxidation. Primary gold, with fineness varying between 630 and 780, forms individual grains up to 60 micron and is associated with fine grained, crystalline quartz, chalcopyrite, galena, sphalerite and hessite. Alteration assemblages associated with the Golden Plateau lodes can be divided into two distinct textural types. They are; 1) those in which the original fabric and texture are preserved and ; 2) those in which the original texture and fabric are destroyed. Texture preserved alteration assemblages may be divided into propylitic, albite dominant, K-feldspar dominant, muscovite-pyrite and silica-pyrite zones. Texture destructive alteration assemblages can be divided into chlorite-pyrite, illite-silica-kaolin and silica zones. The phases of mineralisation can be related to certain alteration assemblages and both can be related to distinct structural sites. The knowledge of the structure, alteration and mineralisation has been used to successfully target further ore zones at Cracow.

THE GOONUMBLA PORPHYRY CU/AU DEPOSITS, N.S.W. P.S. Heithersay1*, G.J. Jones^ and J.L. Walshe 3 1 Geopeko, Parkes, N.S.W. GEONZ Associates Ltd, Hamilton, New Zealand 3Geology Department, Australian National University 2

The Goonumbla porphyry copper gold province near Parks, N.S.W. is one of the most significant discoveries in the Lachlan Fold Belt. While the deposits share the important characteristics of other porphyry systems, they are different in several ways from well known Arizona or South West pacific type porphyry systems. The differences include their pronounced pipe like geometry, higher than average copper and gold grades, the close relationship of potassic alteration to mineralisation, and the focussed, multiple intrusions which form the core of each system. Copper mineralisation was known in the Parkes district since the late nineteenth century, however these are small "manto" type epidote, native copper occurrences. No evidence of any old workings occur near the main porphyry deposits. Geopeko selected the areas in 1971 following an appraisal of the Lachlan Fold Belt with emphasis on recently available regional aeromagnetic data. Initial field mapping led to the discovery of the subeconomic Endeavour 7 lead-zinc skarn in 1974. This gave sufficient impetus to further explore the host volcanics by regional scout drilling along roads and tracks in Geological Society of Australia Abstracts Number 32, Ballarat 1992

concert with regional mapping and geophysics. In 1976 one of these scout holes interested disseminated copper mineralization associated with weak potassic alteration in "andesite" was drilled. Subsequent work defined a discrete intersected 254m@ 0.6% Cu and 0.6g/t Au. Further exploration located 10 porphyry centres including Endeavour 27 and Endeavour 26 North. The Endeavour 26 North porphyry copper-gold deposit is the largest of the deposits which occur within the Goonumbla Volcanic Complex. The complex is interpreted to have been a shoshonitic stratovolcano of late Ordovician age that developed on a marine substrate which subsequently emerged above sealevel, and developed a caldera that was eventually breached. Geochemically and complex is characterised by initial ratios of 86Sr/88Sr which range between 0.70404 and 0.70464 and ratios of 207Pb/204Pb which range between 15.47 and 15.58. Two samples returned eNd values of 6 and 6.62. These data indicate that the magmas were derived from primitive source rocks that had been geochemically enriched at some time. The lack of evidence for crustal contamination weighs against contemporaneous

61

subduction in a sedimentary environment that is dominated by quartz-rich greywacke. A scenario is preferred in which Cambrian arc-material is recycled to provide suitably enriched source material during incipient rifting in the Late Ordovician. The deposits are confined to a circular structure within the Goonumbla Volcanic Complex. On the basis of geophysical and geological information this feature is interpreted to mark the limit of the summit caldera. Intrusions that are co-magmatic with the volcanism appear to have lost their volatiles and evolved at moderate to high pressure along an 'anhydrous' olivine fractionation path. Intrusions associated with mineralization have contained their volatiles and evolved at a higher level along a 'hydrous' fractionation of plagioclase-biotite fractionation path. The porphyry depsoits (Endevours 22, 26N, 27) are unusual in that they have pipe-like geometries and occur as satellites around the parent Endevour 31 stock which is only weakly mineralized. Fluid from the parent stock were focussed twoards its contact and channelled up conduits along with residual melt. The mineralization consists of successive generations of monzonite to quartz monzonite porphyries and related mineralization, which have focussed on the same conduits to form the present orebodies. The earliest alteration assemlage associated with the first porphyry (QMP1) is a biotite, magnetite anhydrite assemblage with minor chalcopyrite (stage 3) which records fluid inclusion temperatures between 500 and 600°C and salinities around 70 Wt% NaCl equiv. Redox conditions determined by fluid-mineral equilibria suggest that biotite formation was no more than 1 to 2 log units below the HM buffer and generally consistent with the condition of fH2S = fSC>2 as indicated by sulphur isotope studies as well as the sphene/rutile/quartz/anhydrite buffer. Peak hydrothermal conditions were attained in stage 4 of the paragenesis with vapour homogenization temperatures A 3.12

between 470° and 1090° C with peaks at 580° and 760°. Salinities range between 50 and 80% NaCl equiv and vapour rich inclusions coexist suggesting phase separation. At these temperatures and redox states, magnetitie is the stable iron oxide however as it is not observed at this stage, copper and sulphur must be sufficient to always maintain bornite saturation. These constraints suggest an increase in the copper and sulphur content of the fluids from stage 3 to stage 4 as the system heats up. This increase in temperature is sufficient to account for the dissolution of the secondary biotite formed in stage 3. Stage 5 represents the main mineralizing event at Endevour 26N leading to the devlopment of the main stockwork zone. The mineralogy at this stage is quartz, bornite, anhydrite, sericite and minor chalcopyrite, digenite, hematite and rutile. Temperatures by this stage had declined to around 400° to 600° and fluid inclusions show evidence of boiling. The gradual decrease in overall salinity can be explained by phase separation at constant pressure in the vicinity of 300 to 500 bars. The waning hydrothermal system was reactivated post stage 5 by the emplaceemnt of second mineralizing porphyry, QMP2. This intrusion partly digested previously formed mineralization. This prograde event may have prevented influx of meteoric waters and the pervasive development of quartz sericite alteration. A consequence of this is that features indicative of fluid-melt separation such as crenulate quartz layers and vein-dykes are preserved. These magmatic hyrothermal features form stage 6 exhibit a Th range from 440° to 980°C with a peak around 700°C, some 200° higher than Stage 5. This is consistent with a renewed magmatic hydrothermal event. QMP2 generated its own paragenetic sequence which shows an overall decrease in temperature without a major change in salinity. This paragenetic cycle is significantly less mineralized than QMP1 related paragenetic sequence.

DISCOVERY AND GEOLOGY OF THE LAKE COWAL, NSW GOLD DEPOSIT M.C. Love GEOPEKO, Clarke and Alluvial Streets, PARKES N.S.W.

An important new gold district has been discovered at Lake Cowal 35km north north east of West Wyalong in central New South Wales. The Endeavour 42 prospect is the only prospect investigated to any degree and has an indicated resource of 20,000,000 tonnes @ 1.6g/t gold, and an inferred resource of 10,000,000 tonnes @ 1.5g/t gold. The discoveries at Lake Cowal are the result of an Geological Society of Australia Abstracts Number 32, Ballarat 1992

exploration programme commenced in 1980. The programme was designed specifically to locate and explore new porphyry copper gold districts of the Goonumbla type within the Lachlan Geosyncline. Area selection parameters were empirically based on our knowledge of Goonumbla. Lake Cowal was one of the districts selected. It was virtually unexplored and almost totally covered by a poorly consolidated lake

62 bed sequence which ranges in thickness from less than 1 metre to greater than 100m. The exploration programme relied heavily on aeromagnetics, gravity and the extensive use of reconnaissance drilling for geological and geochemical definition. Several prospects, including a large copper prospect, Endeavour 39, were discovered soon after granting of tenure and were the focus of exploration for a number of years. Endeavour 39 was subsequently interpreted as the root zone of a porphyry copper system, and that economic Goonumbla style copper-gold deposits might be associated with small, high level plugs marginal to and especially along strike from the Endeavour 39 prospect. Exploration to the north of Endeavour 39 and the eventual discovery of the Lake Cowal gold district had to await the partial drying of the ephemeral Lake Cowal in 1988. Endeavour 42 is located within a substantial low grade, north south trending gold anomaly 7.5km in length and up to 2km wide. To date three other centres of gold mineralization have been recognised within the anomaly. The gold anomaly is situated immediately north and along strike from the large

(4km x 2km), low grade (0.25% Cu) Endeavour 39 porphyry copper prospect. Several other large low grade porphyry copper prospects have also been located in the area. Endeavour 42 is hosted by a sequence of intermediate, mostly latitic volcaniclastics and lavas which are intruded by diorite and monzodiorite. These rocks are currently interpreted as being Late Ordovician in age and form part of a larger volcanic and intrusive complex tentatively named, the Lake Cowal Volcanics. Gold mineralization occurs primarily within a series of dilatant and to a lesser extent shear quartz±pyrite±chalcopyrite±sphalerite±carbonate±kfeldspar veins which vary from a fraction of a millimetre to several centimetres in width. Most of the gold is extremely fine and is situated marginal to sulphide grains. The lg/t gold contour indicates that gold mineralization is best developed within a series of elongate, vertical north south striking pods. These pods are confined to an area 600m in diameter and are known to extend at least 300m below the surface.

A 3.13 SYNCHRONOUS DEFORMATION, ALTERATION AND AU-MINERALISATION IN THE TEMORA SHEAR ZONE HOSTED ADVANCED ARGILLIC SYSTEM

A.H. Allibone Department of Geology, James Cook University, Townsville, Q4811

Advanced argillic alteration occurs in epithermal, porphyry and shear zone hosted environments, where it is commonly associated with economic Au and Ag mineralization. Little is known about the relative timing and origin of alteration, deformation and mineralisation in advanced argillic systems. Previous work at Temora has suggested a porphyry or epithermal environment (Suppel et al. 1986, Thompson et al. 1986). Alteration and mineralisation at Temora is hosted by a 300m wide, NNW striking shear zone characterised by shallow plunging slickenslides and

steeply dipping, ENE striking quartz fibre veins containing shallow plunging fibres, indicative of dominantly strike slip movement. The shear zone cuts an interlayered package of plagioclase, amphibole porphyritic volcanic rocks, volcanogenic lithic sediments and minor siltstones. Intimately related plagioclase, amphibole porphyritic plugs of intermediate to evolved composition and trachytic dikes cut the associated volcano-sedimentary package. Hypogene alteration types, their mineralogy and paragenesis are summarised in Table 1:

oldest

Primary

propylitic qtz-illite qtz-bearing -pyrite peripheral

plagioclase amphibole magnetite quartz

albite chlorite illite carbonate epidote smectite

quartz illite pyrite ±sudoite leucoxene

quartz kaolinite pyrite ±sudoite rutile

adv. arg. qtz-absent core peripheral quartz alunite pyrite pyro rutile

adv. arg. = advanced argillic, pyro = pyrophyllite, qtz =quartz

quartz pyrite rutile

illite pyro

youngest

adv. arg. core

pyro alunite pyrite rutile

pyro alunite pyrite diaspore kaolinite rutile

Peripheral propylitic alteration is separated from quartz-bearing and quartz-absent advanced argillic Geological Society of Australia Abstracts Number 32, Ballarat 1992

63 Peripheral propylitic alteration is separated from quartz-bearing and quartz-absent advanced argillic alteration in the core of the alteration system by quartz-illite-pyrite alteration. Both quartz-bearing and overprinting quartz-absent advanced argillic alteration are internally zoned (Table 1). Propylitic, quartz-illitepyrite and quartz-bearing advanced argillic alteration overprint undeformed protolith rocks, unlike quartzabsent advanced argillic alteration which forms syndeformational boudinage infill and foliated overprint on older alteration types, locally preserving a flattened plagioclase porphyritic texture. Au-Ag mineralisation is confined to the core quartz-pyrite alteration zone which is associated with a background 0.2-0.5ppm Au grade. Higher Au grades appear associated with deformed vein-like pyriteenargite zones and younger undeformed pyrite-enargite stylolites containing Au-Ag alloys and Au-tellurides. Crosscutting relationships indicate pyrite-enargite stylolites are intimately associated with syndeformational quartz-fibre veins which are coeval with or post-date quartz- absent advanced argillic alteration. Textures and crosscutting relationships indicate fluids responsible for quartz-absent advanced argillic alteration, quartz-fibre vein growth and pyrite-enargite

A 3.14

stylolites were tightly focussed in an active brittle shear zone. Mapping suggests fluids associated with older alteration types were focussed around a narrow fault, the precursor to the observed shear zone. Development of the competent quartz-pyrite core partitioned subsequent deformation into the adjacent quartz-kaolinite and alunite assemblages resulting in intense development of quartz-absent advanced argillic assemblages around the margins of quartz-pyrite zones. Localised brittle fracturing of the quartz-pyrite core allowed access for mineralising fluids unlike narrow, peripheral, barren quartz-pyrite zones where deformation was partitioned into adjacent pyrophylliterich quartz-absent advanced argillic alteration. Thus both alteration and mineralisation occured synchronous with brittle deformation at high crustal level and therefore Temora is not a deformed older porphyry or epithermal system. References Suppel, D.W. et al. 1986: Geological Survey of N.S.W. quarterly notes 64. Thompson et al. 1986: Economic geology: 81, 732738.

EVAPORITES AND BROKEN HILL -NEW CONCEPTS IN AN OLD AREA Ian R. Plimer School of Earth Sciences, The University of Melbourne, Parkville Vic 3052

The Broken Hill Block, NSW, comprises highly deformed high metamorphic grade rocks of the Willyama Supergroup and pre-, syn- and post-tectonic intrusives. Deposition, intrusion and extrusion of clastic sediments, felsic and mafic volcanic, carbonate sediments, granite and submarine hot spring precipitates occurred at 1690±5 Ma (Page and Laing, in prep.). The Broken Hill orebody comprises a number of horizons of sulphide rocks of unusual composition. Intercalated with and stratigraphically equivalent to the sulphide rocks are quartz-rich horizons enriched in zinc (gahnite, sphalerite), manganese (spessartine), iron (oxides, silicates), boron (tourmaline) and lead (plumbian microcline) and calc-silicate rocks enriched in barium and tungsten. Although Broken Hill has been fertile territory for the testing of new ore genesis concepts, the consensus opinion is that the ore deposit formed in a rift or half graben as a result of precipitation from submarine hydrothermal springs. Hydrothermal activity was coincidental with sudden deepening and an elevation in the geothermal gradient. This elevated geothermal

gradient is probably the result of the intrusion of large quantities of mafic melt into the pile of wet sediments and may possibly also be the result of the emplacement of granite into the pile of wet sediments. Recent geochemical studies (Slack et al., 1989, Plimer, in prep.) and geological studies in the adjacent Olary Block (Cook and Ashley, 1991) suggest that continental evaporites were an integral part of the Willyama Supergroup. This paper reports the presence of meta-evaporites at the top of the Thackaringa Group and the base of the Broken Hill Group. Following deposition of continental evaporites at or near sea level, the area underwent sudden deepening, an increase in the rate of clastic and chemical sedimentation and an elevation of the geothermal gradient which resulted in the circulation of a mixed magmatic-seawater fluid through the pile of volcanics, clastic and evaporitic sediments. The passage of circulating hydrothermal fluid through evaporites would have resulted in a supersaline tungsten-boron- and halide-bearing mixed fluid which, upon sudden P-T-X change, precipitated sulphide and associated rocks of unusual composition.

64 A 3 15

SODIUM BICARBONATE-RICH BRINES, DENISON TROUGH: POTENTIAL ORE FLUIDS? Hugh K. Herbert * and H. Roy Krouse 1

2

Agricultural and Mineral Research Branch, Chemistry Centre (WA), Department of Mines, Western Australia Department of Physics, University of Calgary, Calgary, Alberta, Canada 1

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Sodium bicarbonate-rich brines are presently restricted to the Early Permian Aldebaran Sandstone and Freitag Formation intervals of the Denison Trough and adjacent Comet Platform . However, dawsonite distribution establishes a much wider former lateral and stratigraphic range for the soda brines. Extensive stable isotope investigations suggest that the brines represent modified Permian meteoric waters, most likely sourced within the Reids Dome Beds, which appear to have evolved by diagenetic modifications involving the precipitation of mixedlayer illite- smectite, quartz, kaolinite, carbonate, muscovite-illite, and occasionally barite. The product brine is rich in Na+ HCO -, and CI" and impoverished in Mg +, Ca +and K+ Compartmentalisation of the Aldebaran Sandstone and Freitag Formation, accompanying graben inversion in the Triassic, is considered to have initiated hyperfiltration and chemical osmotic processes that may largely have controlled the chemical character of the brines, their origin and distribution, the direction of groundwater flow, and permeability distribution. Localised development of large hydraulic heads in areas of high geopressure, coupled with superimposed thermal fluxes associated with Tertiary magmatism, is likely to have promoted 3

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hydraulic fracturing, with attendant depressurisation and possible adiabatic expansion in response to CO2 degassing; loss of CO2 to the system facilitated carbonate deposition and led to the evolution of the brine from being bicarbonate-rich to chloride- plus sulphate-rich. Where analysed, the soda brine is precious metal anomalous, as are many associated dilitant carbonate veins. These features accord with experimental evidence which demonstrates that precious metals are extremely soluble in sodium bicarbonate-rich brines containing traces of arsine, stibine or hydrogen sulphide. Calculations show that, at geologically reasonable flow rates for 103 to 106 years, a fluid pass of 109 tonnes would need to precipitate only 3ppb Au to generate a 106 tonne deposit at 3ppm. Given the combination of appropriate structural plumbing systems, reactive lithology and/or open space, and superimposed thermal regimes to set up and sustain focussed convective fluid flow, soda brines of the Denison Trough have had the potential to produce a number of significant precious metal ore bodies. These observations are discussed with reference to epigenetic gold mineralisation in the Clermont District of central Queensland.

A 3.16 MOBILIZATION OF THE PLATINUM GROUP ELEMENTS BY LOW TEMPERATURE FLUIDS: IMPLICATIONS FOR MINERALIZATION IN RED BED ENVIRONMENTS Reid R. Keays *, Malcolm W. Wallace and Victor A. Gostin 1

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department of Geology, University of Melbourne Department of Geology and Geophysics, University of Adelaide

Virtually all of the world's platinum group element (PGE) production is derived from the mining of Cu-Ni sulphides in mafic and ultramafic rocks and is generally believed to have formed as a result of high temperature magmatic processes. As the bulk of PGE production comes from rather unique geological environments in South Africa and the U.S.S.R., there is clearly a need to develop new conceptual for PGE ore deposits. Examination of the Late Proterozoic Acraman meteorite impact ejecta horizon and its host shales in the Adelaide Geosyncline has provided strong evidence that oxidized, low temperature fluids

are capable of generating PGE-bearing mineralization. The Acraman ejecta horizon was formed when middle Proterozoic dacitic volcanics in the Gawler Ranges, central South Australia, were impacted by a very large (c. 4 km) meteorite, the resulting impact structure now represented by Lake Acraman, a 30 km diameter salina. Debris from the impact was blasted for many hundreds of kilometres, some falling into the shallow sea of the gulf-like Adelaide Geosyncline, some 300 km to the east of the impact site. The 600 million year old Bunyeroo Formation hosting the impact horizon consists of deep-shelf maroon and

65 green clay shales, with minor concretionary carbonates. The ejecta horizon varies from 0 to 40 cm in thickness and consists of basal layers composed of poorly sorted, angular, and pebble sized fragments set in a mud matrix overlain by a sandy layer. The largest clast found to date is 40 cm in diameter. All of the clasts and most of the sand sized grains appear to have been derived from a pink to red porphyritic volcanic rock, similar to that currently exposed at the Gawler Ranges impact site. The ejecta horizon is enveloped by green shales that range in thickness from a few millimetres to several metres. Metal enrichment along the horizon is highly variable. Metal enrichment is lowest and the PGE's exhibit chondritic ratios where the green shale envelop is narrowest. Sections of the ejecta horizon with a significantly wider green alteration envelope are variably enriched in Cu. In these situations, both the ejecta horizon and the green shales that envelope it have strong PGE enrichments (Ir up to 2.0 ppb, Pt up to 270 ppb) relative to the host red shales (average red shale background is 0.019 ppb Ir and 0.89 ppb Pt); Cu and Pt are well correlated with each other and the PGE exhibit strong non-chondritic ratios. Thin green shale layers at other stratigraphic positions in the red shale sequence (and unrelated to any evidence of a meteoritic contribution) are also enriched in Cu-V-Zn-Ni as well as Ir (0.73 to 0.45 ppb) and Pt (3.1 to 314 ppb). In addition, isolated green reduction spots in the red shales have PGE enrichments. All thin green shale horizons and green reduction spots analyzed, regardless of their

stratigraphic position, have relatively high levels of Ir and other PGE. Whereas the ejecta horizon clearly has a meteoritic component in it, elevated Cu-V-Zn-Ni values and enhanced, non-meteoritic PGE values in Cu-rich sections of the ejecta horizon, it's green shale envelope, other thin green shale horizons and green reduction spots suggest that the elevated values are due to low temperature transport. It is suggested that the ejecta horizon was an aquifer for low Eh fluids derived from deeper in the sedimentary basin; these fluids reduced ferric iron in the red shales to ferrous iron which was removed in solution, leaving the shales with their green colour. Mixing of the reduced fluids flowing along the aquifer with oxidized fluids circulating in the red shales, from which they had leached Au, Cu, PGE, and other elements, caused metal deposition. The discovery of significant PGE mobility by low temperature oxidized fluids indicates that economically important accumulations of the metals might be anticipated in environments in which such solutions entered low redox environments. Examples of such environments are provided by red-bed copper and rolltype uranium deposits. Reference Wallace, M.W., Gostin, V.A. and Keays, R.R., 1990, Acraman impact ejecta and host shales: Evidence for low-temperature mobilization of iridium and other platinoids: Geology, v. 18, p. 132-135.

A 3.17 STRESS MAPPING - THE CALCULATION OF STRESS FIELDS DURING DEFORMATION AND THE PREDICTION OF SITES OF HYDROTHERMAL FLUID FLOW. John Ridley Key Centre for Strategic Mineral Deposits, Department of Geology, University of Western Australia, Nedlands, WA 6009 The formation of a hydrothermal ore deposit requires the focussing of fluid flow in the crust through well defined pathways. Mass balance calculations considering likely sources of ore components (e.g. Kerrich, 1986; Cox et al., 1991, for mesothermal gold deposits) show that focussing into a large ore deposit must be over several kilometres lateral or vertical distance. Large ore deposit require the development of large-scale fluid focussing systems, and the understanding of the controls on deposit location requires a consideration of the controls on fluid flow in the crust. The fundamental control on the direction of fluid flow is the hydraulic head. Fluid flow will always be

down a gradient in hydraulic head. Sites of focussed fluid flow must therefore be sites of reduced hydraulic head, which at any depth plane, will be sites of relatively low fluid pressure. Controls on fluid flow at shallow crustal levels, at which fluid pressures can be considered to be hydrostatic', have been discussed, for instance, by Forster and Smith (1990). The prediction of fluid flow at deeper levels in the crust, at which fluid pressures are close to 'lithostatic', requires different approaches. Stress mapping is the calculation of the variations in rock stress in a terrain under an imposed regional stress field. Spatial variations in stress are an automatic consequence of regional stress acting on a

66 rheologically inhomogeneous rock sequence - due to stress-guide and stress-refraction effects. Both variations in bulk rock rheology, and the presence of discontinuities (faults, fractures, and shear zones) may influence the stress field. Mathematical, analytical solutions can be used to predict stress fields around inhomogeneities of simple geometry, but, in general, their prediction in complex geological terrains requires numerical computational techniques. This is the basis of stress mapping. The use of stress mapping as a tool for prediction of potentially mineralised sites was demonstrated for epithermal gold deposits by Holy land (1990a) and mesothermal deposits by Holyland (1990b). Oliver et al (1990) used the technique to explain variations in the intensity of metasomatic alteration in a metamorphic terrain. These studies indicate the importance of the mean rock stress (l/3(ai+a2+(J3)) as the stress parameter controlling fluid flow. The reasons why mean stress variations control large scale hydrothermal fluid flow at deeper structural levels can be understood through consideration of controls on fluid pressure at depth in the crust. At temperatures at or above the brittle-ductile transition, fluid pressures will be generally buffered at 'a little below* lithostatic (rock) pressures (cf. Etheridge et al., 1983). If fluid pressures are significantly less than 'lithostatic', there will be a tendency for pore space to close up, hence increasing fluid pressure. If fluid pressures reach or surpass 'lithostatic', permeability will be high, hence promoting upward drainage of fluid, and decreasing fluid pressure. Local extreme variations in fluid pressure are expected during seismic activity (e.g. Sibson, 1987), or because of variations in fluid production, e.g. through metamorphic or igneous processes. These are, however, considered unlikely to have a significant effect on the large-scale fluid focussing indicated as important in the formation of many ore deposits. If fluid pressure is buffered to be an approximately constant high proportion of lithostatic pressure, variations in mean rock stress will be mirrored by variations in fluid pressure. The magnitude of variations in mean rock stress will be of the same order as the regional deviatoric stress (e.g. StromgSrd, 1973), hence at a specific depth, lateral variations of

up to a few hundred bars are expected (Hanks and Raleigh, 1980). That such pressure variations will give rise to effective focussing of fluids can be seen by order-of-magnitude calculations. A difference in fluid pressure of 150 bars over a 1 km horizontal distance will give a horizontal gradient in hydraulic head approximately equal to the vertical gradient if fluid pressures are close to lithostatic. If permeability is isotropic, fluid flow will be at 45° to vertical, towards the zone of lower mean stress. A model of fluid focussing into zones of low mean rock stress is consistent with a number of characteristic features of deeper-level hydrothermal deposits. 1) Low mean stress will develop in a wide variety of structural sites, hence allowing for the wide variety of structural settings of deposit observed. 2) A zone of low mean stress is predicted to be simultaneously a zone of fluid focussing and of low effective pressures. Low effective pressures been inferred for many hydrothermal deposits from the presence of abundant extension veins, often in unfavourable orientations relative to the maximum principal compressive stress (e.g. Sibson et al., 1988). References Cox, S.F., Wall, V.J., Etheridge, M.A. & Potter, T.F., 1991, Ore Geol. Rev. 6: 391-423. Etheridge, M.A., Wall, V.J. & Vernon, R.H., 1983, J. Metamorphic Geol., 1: 205-226. Forster, C. & Smith, L., 1990, MAC Short Course on 'Crustal Fluids', Handbook, vol. 18, 1-47. Hanks, T.C. & Raleigh, C.B., J. Geophys. Res. 85: 6083-6085. Holyland, P.W., 1990a, Proc. Pacific Rim Congress, Queensland, pp 337-341. Holyland, P.W., 1990b, Third Int. Archaean Symp Perth, Extended Abstracts Vol., pp 347-349. Kerrich, R., 1986, Econ. Geol. Res. Unit, Univ. Witwatersrand, Johannesburg, Information Circular 183, 34pp Oliver, N.H.S., Valenta, R.K. & Wall, V.J., 1990, J. Metamorphic Geol., 8: 311-331. Sibson, R.H., 1987, Geology, 15: 701-704. Sibson, R.H., Robert, F. & Poulsen, K.H., 1988. Geology 16: 551-555. Stromg&rd, K.E., 1973, Tectonophysics 16: 215-248.

67 A 3.18

AN INVESTIGATION OF MINOR SULPHIDE OCCURRENCES IN THE LOWER DEVONIAN BUCHAN CAVES LIMESTONE, VICTORIA D. C. Arne *, P. Cromie , J. A. Webb and J. R. Richards 1

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Geotrack International, P.O. Box 4120 , University of Melbourne, Parkville, Vic. 3052 ^Department of Geology, University of Melbourne, Parkville, Vic. 3052 Department of Geology, La Trobe University, Bundoora, Vic.3083 Research School of Earth Sciences, Australian National University, Canberra, ACT 2601 ]

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Six minor sulphide occurrences hosted by the samples from southeast New South Wales associated Lower Devonian Buchan Caves Limestone have been with Silurian magmatic activity and are consistent investigated. The results of these investigations allow with derivation of lead from the Lower Devonian new constraints to be placed on possible models of Snowy River volcanics which directly underlie the sulphide mineralization. Buchan Caves Limestone. Sulphides and associated phases are hosted by both . The Buchan sulphide occurrences show features dolostone and limestone lithologies along stylolitized characteristic of both Mississippi Valley-type and bedding planes, crosscutting fractures, low angle stratiform ore deposit types, implying a similarity to minor faults and in cavities. Mineralization was the epigenetic zones of Irish carbonate-hosted base closely associated with minor structures of inferred metal deposits. However, the sulphide occurrences at Tabberabberan age (Middle Devonian) and appears to Buchan are associated with minor compressional have post-dated these. The mineralogy of the structures, suggesting that a simple correlation with occurrences is simple and characterized by the the extensional tectonic setting of the Irish deposits is following paragenesis which reflects the increasing not applicable. An alternative genetic hypothesis is oxidation state and pH of the mineralizing fluid: iron proposed involving the circulation of hot, saline fluids sulphide (including pyrite pseudomorphing marcasite) through the Snowy River Volcanics during regional - galena+sphalerite - sparry dolomite+barite - heating coeval with or at some time after the calcite+fluorite. Tabberabberan Orogeny. The sulphur isotope composition of sulphides varies from -32.1 to +4.1 %c , with iron and base References metal sulphides forming two distinct populations around -25%o and 0 %o , respectively. A single barite Cochrane G.W. 1982. Copper-lead-zinc and barium deposits of Victoria. Geological Survey of Victoria sample gave a sulphur isotope composition of +22.4 Bulletin 61. %o , similar to that estimated for Lower Devonian Cromie P. 1990. Base metal occurrences of the seawater. Fluid inclusions in fluorite and calcite Buchan Caves Limestone, Victoria, Unpublished homogenize at temperatures in the range 160 to 212°C B.Sc. Thesis, University of Melbourne. and have average salinities of approximately 10 wt. % O'Shea P.J. 1980. Mineral potential of the Snowy NaCl eq. Sphalerite contains up to 1.81 wt. % iron River Volcanics and Buchan Caves Limestone. which correlates with colour, and up to 1.43 wt. % Geological Survey of Victoria Report 63. cadmium. Lead isotope data for three separate galena samples differ significantly compared to data for galena A 3.19 THE WOODCUTTERS PB-ZN OREBODIES: DEFORMED EPIGENETIC MINERALIZATION, N.T. AUSTRALIA Serge Smolonogov* and Brian Marshall Department of Applied Geology, University of Technology, Sydney, N.S.W. Woodcutters mine is approximately 70 km SSE of Darwin. It exploits Pb-Zn-Ag mineralization comprising a series of orebodies which are stratabound, and in part stratigraphically controlled, by a Lower Proterozoic carbonate-pelite sequence Geological Society of Australia Abstracts Number 32, Ballarat 1992

deposited within the Pine Creek basin. The mineralization consists of the "3" and "5" systems (Wand E respectively), which occupy culminations along two adjacent N-S trending antiforms and are intimately related to N-S trending faults. The latter

68 have a strike-length exceeding 1km, have a vertical extent of at least 800m (Nicholson et al. 1990), are believed to be basinal growth faults, and have controlled the emplacement of monchiquitic dykes. Regional metamorphism (lowermost greenschist facies) and deformation (Di) have formed a moderately well-developed cleavage (Si) which approximates the hinge surface of regional folds (F\). Taube (1984) and Nicholson et al. (1990) interpreted the main mineralization episode as post-Di whereas Smolonogov (1989) advocated a pre-Di model. Evidence is here presented in support of epi-diagenetic (?) mineralization modified by syn-kinematic mechanical and chemical remobilization. At mine-scale, the ore is stratigraphically controlled by a sequence of dolomitic carbonate rocks, 17m thick, over- and under-lain by carbonaceous pyrite-bearing slate. The culmination-hosted orebodies have saddle, inverted wishbone and poddy geometries in vertical E-W sections. As progressively mapped during open-cut extraction, 3 South orebody (201,800 t grading 6.77% Pb, 13.45% Zn, and 127 ppm Ag Bolger 1986) had an asymmetrical inverted wishbone geometry. Ore attenuated and then terminated on the W limb, whereas on the E limb it passed into partially fault-controlled ore, which in turn gave way to uneconomic pyritic "feeder" mineralization. A postDi replacement model is opposed by the W-limb mineralization which, for the existing geometry, would require that ore-bearing fluids flow down-dip from sights of low to high mean stress! The bulk of the 3 south orebody consisted of banded Pb-Zn-Fe mineralization comprising layers variously dominated by galena, sphalerite, pyrite or Pb-As sulphosalts, further interlayered with uncommon tourmalinite horizons. The banding where the mineralization front is locally discordant to bedding, is seen to preserve sedimentary grading and the thickness and continuity of sedimentary lamination; it is mimetic through replacement. Banding is overprinted by cleavage (Si) and elongation lineation (L e ). The resulting microfabrics show preferred distribution and preferred dimensional orientation of sulphide grains and aggregates, and pressure fringes, developed on pyrite, of less competent sulphides and gangue. Replacement of Si-

Geological Society of Australia Abstracts Number 32, Ballarat 1992

L e , as opposed to overprinting by S i - L e , is inconsistent with the distribution and relative behaviour of the sulphides reflecting their established rheological properties (e.g. Marshall & Gilligan 1987); it is also inconsistent with changes in cleavage morphology between the original and replaced parts of a single layer. Other features indicative of deformation and remobilization of pre-Di mineralization include: brecciation and localized recrystallization of concordant fine grained layers of pyrite; boudinaging of interlayered sulphide and unreplaced metasediment; and galena-sphalerite piercements into slate at fold noses. Post-Si recrystallization and vein-style remobilization are seen as diffuse-margined patches of coarse grained undeformed galena in finer grained deformed ore, and as cross-cutting quartz-carbonatesulphide veins with internal fabrics apparently unrelated to L e . Mine-, meso-, and microscale relationships suggest that fault-focussed mineralizing fluids emplaced the massive sulphide by replacement of favourable carbonate horizons, perhaps during diagenetic evolution, before the hostrocks were significantly folded. Internal and limited external remobilization accompanied regional metamorphism and deformation, during which the ore layer attained its inverted-wishbone geometry. Late metahydrothermal veins cross-cut the Sl-Le fabric. The ore genesis is therefore protracted and spans diagenesis, deformation and regional metamorphism. References Marshall, B. & Gilligan, L.G., 1987, Ore Geology Reviews 2: 87-132. Nicholson, P.M., Higham, I.M., Ormsby, W.R., Smith, S.R. & Tunjic, J.A., 1990, Woodcutters Joint Venture Report (unpubl.). Bolger, C.R. 1986, Woodcutters Joint Venture Report (unpubl.). Smolonogov, S., 1989, B.App.Sc. Thesis, University of Technology, Sydney (unpubl.). Taube, A., 1984, Aus. I MM. Darwin Conf. Notes: 347-356.

69 A 3.20 EXHALITES ASSOCIATED WITH BROKEN HILL-TYPE MINERALISATION: GENETIC IMPLICATIONS AND EXPLORATION POTENTIAL. J.M. Parr Department of geology, University of Newcastle, NSW 2308. Broken Hill-type deposits are characterised by stratabound Pb-Zn-Ag sulphide orebodies associated with a wide variety of lithologies of exhalative origin. Typically, the ores are hosted in thick successions of pelitic and psammopelitic metasedimentary rocks of both volcanic and sedimentary parentage and were deposited in rapidly subsiding rift-related palaeoenvironments (Plimer, 1986). Examples of early Proterozoic Broken Hill-type deposits are found in the Broken Hill Block (NSW), the Bergslagen Province (central Sweden), Aggeneys and Gamsberg (South Africa), and possibly southeast Colorado and Arizona (e.g. Plimer, 1986; Sawkins, 1989). The mineralised rocks include Pb-Zn, Zn-Pb, Cu-Zn, Cu- Fe-Zn-Pb sulphide rocks, scheelite (-molybdenite) rocks, magnetite-calc- silicate rocks and magnetite-quartz rocks. Exhalites associated with the mineralisation include siliceous, manganiferous, ferruginous, zincian, barian, calcareous and boron-rich rocks which formed in the silicate, oxide, carbonate and sulphide fapies. They are frequendy stacked and are found interbedded with, or directly along strike from, the sulphide orebodies. The early- to mid-Proterozoic terrains in which many Broken Hill-type deposits are hosted, have been subject to high grades of metamorphism and inhomogenous deformation (e.g. granulite facies at Broken Hill). As a result, subtle changes in the depositional environment of the ores and exhalites are often masked. Pre-metamorphic REE signatures may therefore help to determine the physical and chemical environment in which these rocks formed. The 0.6 Mt Pb-Zn-Ag Pinnacles deposit is the second largest Broken Hill- type deposit in the Willyama Supergroup, after Broken Hill itself (Stevens et al., 1988). At the Pinnacles the stratabound massive sulphide ores consist of a major Pb lode (10% Pb, 2.5% Zn, 420 g/t Ag) and several thinner and less continuous Zn lodes (3.5% Pb, 7.511.5% Zn, 100 g/t Ag) which are located in the hanging wall and footwall to the main Pb lode. The mine sequence rocks include several stratabound exhalite horizons including garnetites and quartzbearing garnetites, quartz-gahnite rocks, garnetgahnite-quartz-bearing horizons, garnet-quartzmagnetite rocks and quartz-magnetite rocks. REE concentrations of the exhalites show a wide variety of normalised patterns which cannot be accounted for by regional metamorphic effects. Anomalous REE patterns are restricted to the mine

Geological Society of Australia Abstracts Number 32, Ballarat 1992

sequence: unmineralised pelites have unaltered, flat NASC normalised REE profiles. In the mine sequence, pelites and exhalites exhibit concentrations apparently independent of mineralogy, for example garnet-rich rocks do not have expected HREEenrichment and LREE depletion, instead they have variable Eu anomalies (Eu/Eu* range 0.30 to 1.76) and inconsistent fractionation trends (La/Lu range 0.99 to 9.98). However a more systematic variation in the REE data can be recognised related to the stratigraphy of the deposit. REE concentrations in the footwall of the deposit generally have negative Eu anomalies and LREE > HREE, whilst exhalites in the hanging wall of the deposit generally have zero or positive Eu anomalies and less LREE-enriched patterns. This stratigraphic variation, coupled with similar control of 8 3 4 S data, suggests that the REE data either represent syndepositional hydrothermal REE concentrations, or an episode of post depositional, pre-metamorphic hydrothermal alteration. The exploration potential of exhalite horizons as indicators of massive sulphide deposits is important. Several studies have recently investigated REE variations in terms of ore genesis (e.g. Graf, 1977; Taylor and Fryer, 1980; Whitford et al., 1988; Lottermoser, 1989) but few have explored the variations of REE concentrations within a deposit. REE data from the Pinnacles deposit suggests that, whilst many different concentrations are associated with the exhalites, there is a systematic change from footwall to hanging wall rocks reflecting changes in temperature, f(>2 and pH of the hydrothermal (oreforming) fluids. These observations may be applied to exhalites in other metallogenically fertile areas. References Graf, J.J., 1977, Econ. Geol., 72, 527-548. Lottermoser, B.G., 1989. Mineral. Dep., 24, 92-99. Plimer, I.R., 1986, Trans. Geol. Soc. S. Afr., 89, 5773. Sawkins, F.J., 1989, Geology, 12, 451-454. Stevens B.P.J., Barnes, R.G., Brown, R.E., Stroud, W.J. and Willis, I.L., 1988, Precamb. Res., 40/41, 297-327. Taylor, R.P. and Fryer, B.J., 1980, Can. J. Earth Sci., 17, 901-926. Whitford, D.J., Korsch, M.J., Porrit, P.M. and Craven, S.J., 1988, Chem. Geol, 68, 105-119.

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A 3.21

THE STRUCTURAL CONTROLS ON MINERALISATION AT RENISON TIN MINE, WESTERN TASMANIA. Paul A. Kitto & Ron F. Berry CODES Key Centre, University of Tasmania.

The Renison Tin Mine in Western Tasmania is hosted by subareal to shallow marine, Late Precambrian to Early Cambrian Success Creek (Corbett et al.t 1987) and shallow marine Early Cambrian Crimson Creek Formations (Kitto, 1990) within the Early Palaeozoic Dundas Trough. The deposit occurs on the north-east limb of a broad southeast plunging monocline which in turn constitutes a major horst block bounded to the north-east by the Federal Bassett Fault ,(FBF), and to the south-west by the Argent Fault. The dominant brittle deformation structures at Renison, together with the FBF, include the Blow Fault, that occurs west of and sub-parallel to the FBF, and a series of east-west inter-connecting Transverse Faults. The Transverse Faults bound a complex series of minor horst and grabens. The carbonate replacement and vein styles of cassiterite mineralisation were structurally controlled by the complex nature of brittle faulting that focused the mineralising fluids into dilatent fault zones. A detailed study of kinematic indicators on the mineralised faults has determined the stress field during mineralisation (Kitto,1990; Kitto and Berry,1991). Four phases of brittle deformation (Devonian to Tertiary) were determined based on style and relative ages of fault striations. The first generation fibre growths have a mineralogy consistent with host veins suggesting contemporaneous brittle deformation and mineralisation. No striations predating the mineralisation were observed. The initial brittle deformation, (BD1), at Renison produced a normal-dextral orientation of striations grooves and undulations on fault surfaces with modelled stress tensors predicting a near vertical maximum compressive stress and near horizontal minimum compressive stress trending 84°. This stress regime was unique to Renison and initiated the FBF along a pre-existing monocline as a principal graben boundary fault-couple linked by minor antithetic normal faults. The Argent, Blow and Transverse Faults were also initiated by this BD1 event together with the complex system of horst and grabens bounded by the Transverse Faults. The syn-Devonian normal faulting at Renison contrasts with the NE-SW compressional structures related to the Taberraberran Orogeny throughout the rest of western Tasmania. The major horst structure bounded by the FBF and Argent faults resulted from the modification of a Devonian monocline by the

Geological Society of Australia Abstracts Number 32, Ballarat 1992

forceful emplacement of an asymmetrical northwest trending Devonian granite ridge. The FBF was propogated as a double fault structure on the eastern most margin of the granite subparallel to the -500m , -1000m and -1500m granite contours.The FBF offsets the monoclinal mine sequence by upwards of 700m in the immediate mine area. The Blow Fault Complex was initiated subparallel to the FBF over an apothysis in the -500m granite contour and forms the western most boundary to economic cassiterite mineralisation at Renison. Local uplift in the C2 direction and 15% N-S extension of the mine horst occurred upon the eastern margin of the intruding granite and resulted in the production of the Transverse Faults subparallel to the east-west trending section of the -500m and -1000m granite contours. As the granite related stress field decayed a regional Taberraberran dextral wrench, (BD2), reactivated earlier BD1 fault structures and produced a dilational jog in the FBF as a consequence of differential displacements on the Transverse Faults. A sigmoidal overprint on the Transverse Faults by the BD2 wrench facilitated the formation of the largest carbonate replacement orebodies within dilational areas adjacent to the convex flexures. The listric extensional Transverse Faults acted as basal detachments to a system of linked synthetic and antithetic displacements that formed a complex series of N-S oriented horst and graben structures in a plane perpendicular to (J3. These horst and grabens show maximum extension, (>20%), to the south directly above an apophysis in the -500m granite contour. These fault structures controlled carbonate replacement in the updip dolomite horizons distal to the FBF. The intimate association of brittle deformation structures, granite topography (Leaman,1991) and granite geochemistry (Bajwah et.al., in press) suggest that the forceful intrusion of a late stage Sn-rich granite occurred immediately beneath Renison during in the Devonian. The granite intrusion not only prepared the overlying carbonate rich sediments structurally but also supplied the source of fluids responsible for the carbonate replacement and vein styles of cassiterite mineralisation. References Bajwah Z. U., White A. J. R., Kwak T. A. P. & Price R. C., (in prep.).The Renison Granite Western Tasmania: A penological and geochemical

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investigation of hydrothermal alteration. Kitto P. A. & Berry R. F., 1991. A history of Corbett K. D. & Lees T. C., 1987. Stratigraphic brittle deformation and related mineralisation at and structural relationships and evidence for Renison Tin Mine, Western Tasmania.//! Bureau Cambrian deformation at the western margin of of Mineral Resources, Geology and Geophysics the Mount Read Volcanics, Tasmania. Australian Record No. 1990/95. SGEG Ore Fluids Journal of Earth Sciences 34, pp45-68. Conference, Canberra. Kitto P. A., 1990. The history of brittle deformation Leaman D. E., 1990. Renison mine lease gravity and reactivation at Renison Tin Mine, Tasmania. survey. Consultant report (unpubl.). Mine report (unpubl.). A 3.22 THE ORIGIN OF BRECCIA-HOSTED URANIUM DEPOSITS IN CARBONACEOUS METASEDIMENTS OF THE IBERIAN PENINSULA: STABLE ISOTOPE STUDIES OF THE FE DEPOSIT, SALAMANCA PROVINCE, SPAIN R. A. Both * and A. Arribas 1

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Department of Geology and Geophysics, University ofAdelaide, Adelaide Directorate-General for Science, Research and Development, Commission of the European Communities, Brussels, Belgium 2

The upper Proterozoic/lower Cambrian schistgraywacke complex (CEG) of the Iberian Peninsula hosts several important uranium deposits, characterized by their occurrence in fracture and breccia zones and by the mineral association pitchblende + carbonates + adularia + Fe sulfides. The Fe mine, in Salamanca province, is not only the largest known deposit of this type but also the most important uranium deposit in Spain, with current reserves in excess of 16,000 tonnes of U3O8. Primary mineralization occurs as narrow veins occupying fractures and in cavities as finely laminated sediments showing a variety of geopetal textures. Three stages of primary mineralization, separated by episodes of fracturing and brecciation, are recognized. The early stage commenced with chloritization of wallrocks in narrow zones adjacent to fractures, followed by deposition of an assemblage dominated by ankerite and iron sulfides. The second (main) stage mineralization is the most important for uranium and consists mainly of pitchblende, carbonates, iron sulfides and adularia. The final stage was characterized by repeated episodic deposition of carbonates, iron sulfides, pitchblende and coffinite as layered cavity-filling material. Chlorite compositions and fluid inclusion data show that wallrock alteration and ore deposition took place over a temperature range of approximately 280° to less than 60°C, probably to sub-surficial temperatures in the final stage of mineralization. U/Pb studies have dated the uranium mineralization at 35 ± 2 Ma (Saint-Andre and Arribas, 1987), indicating formation during the Pyrenean phase of the Alpine Orogeny. Calculated 8 0 H 2 0 values of the ore1 8

Geological Society of Australia Abstracts Number 32, Ballarat 1992

forming fluid range from approximately 14.5 per mil for early stage to near zero per mil for late stage fluid. 8 C values vary between -7.3 and -9.6 per mil for early and main stage carbonates and show a sharp progressive decline to -23.6 per mil at the end of the final stage. 8 S values of sulfides also decrease from the early stage (around -10 per mil) to later stages (down to -51.3 per mil). The combined geological evidence suggests deposition of the ore from a hydrothermal system that formed in response to the effects of Alpine tectonics on the Hercynian basement. Meteoric water descended via steeply dipping faults and as well as undergoing extensive isotope exchange with, also leached uranium and other components from, the metasediments of the CEG, particularly carbonaceous slates. The fluid was probably expelled towards the surface through the fracture and breccia system by seismic pumping. The episodic nature of the mineralization may have been controlled by fault movements that initiated brecciation and release of fluid pressure, leading to ore deposition in fractures and cavities. 13

34

Reference Saint-Andre, B. de, and Arribas, A., 1987, U-Pb systematics and the age of vein-like uranium deposits in metasedimentary rocks: the case of the Fe orebody, Salamanca (Spain): NATO Advanced Institute "Geochemistry of Hydrothermal Ore Forming Processes", Salamanca, January 1987.

72 A 3.23

A FLUID INCLUSION STUDY OF MINERALIZATION AT CORONATION HILL, NORTHERN TERRITORY, AUSTRALIA. T.P. Mernagh1*, J.F. Leckie 2 , D.P. Carville2, R.K. Valenta 3 , and L.A.I. Wyborn 1 . ^Bureau of Mineral Resources, G.P.O. Box 378, Canberra A.C.T. 2601, Australia 2 Newmont Australia Ltd., 339 Coronation Drive, Milton, Qld. 4064, Australia Department of Earth Sciences, Monash University, Clayton, Vic. 3168, Australia

3

Fluid inclusions in quartz and carbonate veins in diamond drill core samples from Coronation Hill, Northern Territory, Australia were investigated by microthermometry, laser micro-Raman spectroscopy and isotope analysis. Four different types of fluid inclusions were observed in both the quartz and carbonate veins. Vapor rich inclusions are by far the most abundant and contain between 25 and 100 volume percent vapor. Two phase aqueous inclusions containing approx. 5 vol. percent vapor are often found coexisting withvapor-rich inclusions. Some show evidence of necking and their shapes vary from irregular, to rounded to negative crystal but consistent liquid/vapor ratios were usually observed within single microfractures. One-phase liquid inclusions which occur near the vapor-rich inclusions indicate that healing of the inclusions continued at low temperatures (<100°C) after the vapor phase had nucleated. Finally, there are some very rare inclusions with one or more solid phases and typically less that 10 vol. percent. They often contain accidentally trapped solids and are of secondary origin. The majority of fluid inclusions homogenize at temperatures around 140°C. Primary inclusions are characterized by very high salinities with an average value of 26.3 equivalent wt % CaCl2- The salinity and high calcium content of the brines was confirmed by micro-Raman spectroscopy. Several solids, including calcite and hematite, were also identified by Raman microprobe studies of the inclusions at low temperatures and room temperature. However, the laser

A 3.24

Raman microprobe did not detect any gases in the vapor phase of the fluid inclusions. Material for isotopic analysis was obtained from quartz and carbonate veinlets in both mineralized and unmineralized zones of the deposit. The fluids in the quartz veins have 5 1 8 0 values ranging from -2.7 to 8.3%o. Fluids from the carbonate veins have 5 1 8 0 values ranging from -1.8 to -5A%c. These values are incompatible with magmatic or metamorphic origins for these brines and indicate that they are derived from meteoric water. The evidence from fluid inclusions indicates that uranium, gold and platinum-group metals were all transported in the same highly oxidized, low pH and very calcium rich brine travelling downward in the ore zone. Mineralization occurred at around 140°C and the fluid inclusion data show no significant temperature variations throughout the deposit. Vapor only fluid inclusions provide evidence of effervescence or boiling which probably resulted from the sudden fluid pressure fluctuations caused by brittle fracturing associated with the mineralization. Gold/PGE mineralization is more widespread and possibly results from an increase in solution pH to feldspar buffered values around pH 5. Uranium mineralization is restricted to zones at or below the Early Proterozoic-Middle Proterozoic unconformity and is thought to result from reduction of the oxidized fluid by mixing with a reduced fluid occurring in this region. The reduced fluid is thought to originate from carbonaceous units in the Koolpin Formation.

HYDROTHERMAL DEPOSITS OF FRANKLIN SEAMOUNT, WESTERN WOODLARK BASIN, PAPUA NEW GUINEA R.A. Binns1*, G.E. Wheller1, S.D. Scott2, Yu.A. Bogdanov3, A.P. Lisitsin3 and SUPACLARK Participants J

CSIRO Division of Exploration Geoscience, North Ryde, New South Wales ^Department of Geology, University of Toronto, Toronto, Canada 3 Institute of Oceanology, USSR Academy of Sciences, Moscow, USSR During the SUPACLARK cruise in April 1990, 1987, 1990). No venting or hydrothermal deposits seven long-duration dives with "Mir" manned were found at Dobu Seamount, an andesite-rhyolite submersibles were conducted to three submarine structure on rifted continental crust 70km ahead of the volcanic targets in the western Woodlark Basin that westwards-propagating Woodlark spreading axis, and had been defined as prospective for hydrothermal only diffuse low-temperature venting with formation activity by earlier PACLARK cruises (Binns et al., of manganiferous crusts on basaltic lavas was observed Geological Society of Australia Abstracts Number 32, Ballarat 1992

73 on the floor of East Basin at the transition from seafloor spreading to continent rifting (Fig. 1). The third target was Franklin Seamount, a young submarine basaltic andesite volcano with rare occurences of sodic rhyolite located on the neovolcanic zone of the spreading axis very near its propagating tip, where complexly-shaped spires and mounds of FeMn-Si oxide up to several metres thick and 100-200 metres in extent are widely distributed. Some are venting a 20-30 deg C, mildly acid, clear fluid which is a base metal-containing mixture of seawater and a 270-350 deg C hydrothermal end-member similar to those calculated for mid-ocean black smokers, but which lacks reduced sulfur. Inactive barite-silica chimneys with sparsely disseminated sulfides occur in a caldera at the seamount summit. Similar material may underlie some Fe-Mn-Si deposits. The yellow-orange to red-brown Fe-Mn-Si deposits consist mainly of a Si-bearing Fe-oxyhydroxide phase. Although there are no present faunal concentrations near active vents, microstructures of these deposits indicate that biogenic processes were important in the earlier stages of their origin. Silica filaments of microbial origin forming the original constructions became overgrown or replaced by hydrothermal Feoxyhydroxide. Bright green nontronite crystallised in internal patches and veinlets, and locally formed also where relatively reduced fluids reached deposit surfaces. Manganese oxides developed as replacements and cavity-fillings at oxidation fronts in the outer portions of the hydrothermal constructions. Manganese also deposited with Fe in black external crusts on older constructions. Similar crusts coat the baritic chimneys and occur on lava surfaces up to a hundred metres from the hydrothermal deposits. Trace element geochemistry of the Fe-Mn-Si deposits is partly influenced by

basaltic contaminant. Among hydrothermal components, Co, Ni, and Mo are prominently correlated with Mn, and the deposits contain anomalous As, Sb, and Hg. The baritic deposits are particularly rich in Ag (to 545 ppm) and Au (to 21 ppm), and contain significant As, Sb, Hg, Zn, Cu, and also Pb both as galena and rare cerussite. The silver occurs within disseminated pyrite spheroids and anhedra of colloidal origin, partly as submicron-sized Sb sulfosalt inclusions. The site of Au has not been determined. Fluid inclusions in barite suggest formation from a higher temperature (ca. 250 deg C) fluid slightly more saline than seawater. No massive sulfide deposits have been found, but vent fluid chemistry suggests that stockworks probably occur within the underlying volcanic pile. The Franklin Seamount occurrences confirm that seafloor hydrothermal activity can be associated with submarine volcanism where accretional spreading propagates into a continental margin environment, a setting that may have numerous ancient analogs. They support an exhalative origin for iron formations associated with ancient volcanic sequences, the chemistry of which may constitute a useful pathfinder to base metal and precious metal ores. The discovery of ore-grade Au and Ag in baritic chimneys at Franklin Seamount suggests targets for land-based exploration. References Binns, R.A., Scott, S.D. & PACLARK Participants, 1987, Proc. Pacific Rim Congress (Aus. Inst. Min. Metall.) 1:525-529 Binns, R.A., Scott, S.D. & PACLARK Team, 1990, Geol. Soc. Aust. Abstracts 25:14

Fig. 1: Bathymetry of the western Woodlark Basin and location of "Mir" submersible dives. Geological Society of Australia Abstracts Number 32, Ballarat 1992

74 A 3.25

CONDITIONS OF GOLD MINERALIZATION IN LAU BASIN BACK-ARC SULFIDES

P.M. Herzig *, M.D. Hannington , Y. Fouquet , U. von Stackelberg and S. Petersen 1

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2

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Institute of Mineralogy and Economic Geology, Aachen University of Technology, D~5100 Aachen, Germany Geological Survey of Canada, Ottawa K1A OE8, Canada IFREMER, Centre de Brest, F-29263 Plouzane, France Federal Institute for Geosciences and Natural Resources, D-3000 Hannover, Germany 2

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Bulk chemical analyses of poly metallic sulfides recovered from the Valu Fa Ridge in the southern Lau Basin (S.W. Pacific) have revealed gold contents of close to 1 oz per ton with an average of 3.1 ppm Au (n=75). These samples contain the highest gold concentrations yet reported from hydrothermal precipitates on the modern seafloor. Native gold has been identified in the most gold-rich samples (>15 ppm Au), representing thefirstdocumented occurrence of native gold in seafloor sulfides. This finding allows to specify in detail the timing and conditions of gold precipitation in seafloor hydrothermal systems. The gold-bearing assemblages are dominated (4085%) by Fe-poor sphalerite with less barite, and minor chalcopyrite, bornite, tennantite, galena, pyrite, Pb-As sulfosalts, and opaline silica. High gold concentrations are associated with elevated contents of As (1100-6600 ppm), Sb (85-280 ppm) and Pb (0.012.1 wt.%). About 85% of the gold is found as codepositional inclusions in massive sphalerite; the remainder occurs along grain boundaries or within chalcopyrite and tennantite and is rarely grown onto barite. Individual gold grains reach up tp 18 microns in diameter, but most are between 1 and 5 microns. The gold is generally of high purity, containing less than 10 wt.% Ag. Analyses of fluid inclusions in sphalerite and barite indicate that rapid precipitation of gold occurred at

about 230-250°C, following a drop in temperature from at least 280-300°C. The Fe content of sphalerite with gold inclusions is uniformly low (0.3-1.5 mole% FeS) and indicates high aS2 conditions at the time of gold deposition. The application of solubility models suggests that gold transport in the Lau Basin vent fluids was due largely to aqueous sulfur complexing [AU(HS) -]. 2

Vent fluids sampled in the Lau Basin have characteristics which point to a higher oxidation state and a lower redox buffering capacity compared to typical mid-ocean ridge fluids. The abundance of FeObearing minerals and immiscible sulfides in mid-ocean ridge basalts is largely responsible for the low a02 and strong redox buffering capacity of the resulting hydrothermal fluids. In contrast, vent fluids in the Lau Basin and other back-arc hydrothermal systems are derived from the high-temperature reaction of seawater with more felsic lavas having a lower abundance of FeO-bearing minerals. The evolved fluids are more oxidizing and may become saturated with gold following a relatively small amount of conductive cooling, mixing with seawater, or oxidation of H2S. Furthermore, earlier subseafloor boiling and precipitation of sulfides may have played an important role in separating gold from base metals in the ascending hydrothermal fluids and producing high grade gold mineralization at the seafloor.

A 3.26 THE RELATIONSHIP BETWEEN STRUCTURE, FLUID FLOW PATTERNS AND ORE SHOOTS IN A MESOTHERMAL SHEAR ZONE HOSTED GOLD DEPOSIT J.M.A. Hronsky and J.R. Ridley* Key Centre for Research and Teaching in Strategic Mineral Deposits Geology Department, University of Western Australia Within mesothermal shear zone hosted gold deposits, zones of high-grade mineralization (i.e. oreshoots) characteristically represent a relatively small proportion of the mineralized surface. Understanding of fluid flow patterns within these shear zones is important, not only for determining mechanisms of formation of these ore-shoots but also for constraining general aspects of the larger-scale syn-mineralization plumbing system. Integrated structural and Geological Society of Australia Abstracts Number 32, Ballarat 1992

geochemical studies have been carried at the Lancefield gold deposit, in the Archaean Yilgarn Block of Western Australia, in order to constrain the relationship between structure, patterns of fluid flow and the formation of ore-shoots. Gold mineralization at Lancefield is hosted by two brittle-ductile, dextral-reverse oblique-slip shear zones; Main Lode and West Lode. Both lode-hosting shear zones are localized by graphitic interflow

75 sedimentary units within a mafic sequence. The lode zones have a moderately (30-50°) dipping, sheet-like morphology which is characterized by low-amplitude warps and buckles. The distribution of mineralization is controlled by these warps and buckles, with specific parts of the lode surface in particular orientations hosting ore-shoots. The major ore-shoots in both lodes are associated with segments of the lode that are predicted as dilatant, given the inferred slip vector. Individual ore-shoots may be isolated from each other on the same lode surface. Although the Lancefield lodes are surrounded by concentric alteration haloes within their mafic wallrocks, the following evidence suggests that fluid flow was strongly channelized within the lode-hosting shear zones. 1. Gradients in alteration zonation within the mafic wallrocks are steep in a direction perpendicular to the lode. 2. Elements with limited solubility in Archaean gold fluids (e.g. Lesher et al., 1991), including Fe, Mg and Ca, are significantly added to ore-shoots within the lode but are effectively immobile within mafic wallrock alteration zones. 3. In contrast with large relative volume increases within lode-hosted ore-shoots, alteration within the mafic wallrocks is approximately isovolumetric 4. The 8 C of carbonates in altered mafic selvedges to the lodes closely reflects the 8 C of adjacent lode, which varies systematically from about -11 %o adjacent to less-mineralized zones to - 4%o adjacent to high grade lode. This indicates that the fluids responsible for wallrock alteration zones infiltrated outwards from a central conduit, defined by the lode zones, and that there is no significant fluid flow which "by-passes" the lode. The following geochemical and mineralogical criteria indicate that the ore-shoots are zones of higher fluid flux than flanking, less-mineralized parts of the lode-hosting shear zone. 1. Gresens analysis suggests a several hundred percent volume increase within the ore-shoots relative to less-mineralized (< 0.5 ppm Au) lode. This also confirms that the ore-shoots are dilatant zones. 2. There is a mixing trend in 8 C data from values as light as -11 %o in less-mineralized lode to values of about -4%o in the high grade ore-shoots. This trend is interpreted as reflecting mixing of relatively heavy carbon (introduced by the ore fluid) with light carbon from the wallrock (from either graphite or carbonates in equilibrium with graphite), and implies higher effective fluid/rock ratios within the ore-shoots. 3. Significant occurences of dolomite-ankerite are restricted to the vicinity of the ore-shoots, whereas calcite is the dominant carbonate in less-mineralized lode. Dolomite-ankerite replaces chlorite in a reaction 1 3

1 3

1 3

Geological Society of Australia Abstracts Number 32, Ballarat 1992

which indicates that the fluid in equilibrium with the ore-shoot asemblage has higher CO2 - activity than that in equilibrium with more distal parts of the lodes. The discontinuous nature of ore shoots, together with evidence for higher fluid flux within them, imply that much of the fluid focussed in ore-shoots must have passed through less-mineralized parts of the lode conduit. This constraint, coupled with the association of higher CC>2-activity assemblages with the ore-shoots, implies that a significant proportion of the ore-fluid does not react, for kinetic reasons, with the wallrock lining its conduit. Phase separation has been implicated as the most likely gold deposition mechanism at Lancefield (Hronsky et al., 1991). Dilatancy within the oreshoots implies that they were zones of relatively low mean rock-stress. Localized zones of lower mean rock-stress are likely to be zones of relatively lower fluid pressure, and movement of fluid into such zones is therefore a mechanism for inducing phase separation and facilitating gold deposition. It is concluded that fluid flow during mineralization at Lancefield was strongly channelized within the planes of the lode shear zones hosting the lodes, with only restricted infiltration into the flanking wallrocks. Within the lode-hosting shear zones, structurally controlled zones of dilatancy strongly focussed fluid flux. Reduction in fluid pressure within these zones facilitated gold deposition via the process of phase separation. The strongly channelized flux of ore fluid inferred by this study has implications for larger scale models of hydrothermal systems. It suggests that ore-fluids may retain a coherent identity for significant pathlengths, and therefore supports models for mesothermal gold mineralization which invoke onepass fluid flow through significant vertical intervals of crust (e.g. Groves et al., 1990). This research has been supported by Western Mining Corporation. Jon Hronsky is the recepient ot a Postgraduate Industry Research Award. The authors have benefitted from discussions with David Groves, Neal McNaughton and Ed Mikucki. References Groves D.I., Barley M.E., Cassidy K.F., Fare R.J., Hagemann S.G., Ho S.E., Hronsky J.M.A., Mikucki E.J., Mueller A.G., McNaughton N.J., Ridley J.R. & Vearncombe J.R.,1990. Proceedings -3 I. A.S. Hronsky J.M.A., Mikucki E.J., McNaughton N.J. & Groves D.I., 1991. B.M.R. Record No. 1990/5 Lesher C.M., Phillips G.N., Groves D.I. & Campbell I.H.,1991. Proceedings - Brazil Gold '91.

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HYDROTHERMAL ALTERATION AND GEOCHEMISTRY AT THE WAIHI EPITHERMAL AU-AG DEPOSIT, NEW ZEALAND. Keenan Jennings University of Auckland, New Zealand

The Waihi vein system is a world class epithermal Au-Ag deposit located at the southern margin of the Coromandel Volcanic Zone (CVZ), a major metallogenic zone within the North Island of New Zealand. This study characterises the alteration mineralogy and geochemistry associated with the goldbearing system, and compares it to active geothermal systems (eg. Browne and Ellis, 1970; Browne, 1978; Hedenquist, 1986). Block-faulted greywackes and argillites of Manaia Hill Group form the basement to the CVZ, cropping out as upstanding blocks to the north of the peninsula but becomes progressively downfaulted to the south. No basement is exposed in the Waihi district. A thick sequence of volcanic and locally intrusive units unconformably overlies the basement, forming the Coromandel Group. Compositions range from basaltic andesites to rhyodacites; hypersthene and plagioclase- phyric andesite lava flows, breccias, and tuffs are the dominant rock-types (Skinner, 1986). Pre-existing basement faults appear to control regional faulting in the peninsula. North-northwest trending faults are downthrown to both the east and west, while ENE-trending faults show consistent downthrow to the south, resulting in the thickening of the volcanic pile. The peninsula is bounded to the west by the Hauraki Graben, a major continental rift (Hochstein et al, 1986). Mid to Late Miocene Coromandel Group andesites form the oldest rocks exposed at Waihi, and host the vein systems of Martha Hill and nearby Union and Gladstone Hills. The rocks are hydrothermally-altered two- pyroxene quartz andesites which form uniformly textured porphyritic flows intercalated with tuffs, laminated mudstones, and siltstones dipping 40° to the southeast. The Early Pliocene Black Hill hornblende dacite unconformably overlies altered Coromandel Group rocks, occurring as a strongly porphyritic biotite-bearing dacite with prominent plagioclase and pyroxene inclusions. Late Pliocene to Early Quaternary rhyolitic ignimbrites in turn unconformably overlie Black Hill hornblende dacite, while Late Quaternary ashes, erupted from the Taupo Volcanic Zone to the south, blanket the region to a depth of 1-2, m (Brathwaite et al, 1986). Faults bounding the Waihi area trend NNE and N-S. Veins at Waihi are structurally controlled, with the dominant NE strike conforming to regional fault patterns. The vein system extends over a maximum strike length of 1600 m (Martha Vein) and has an Geological Society of Australia Abstracts Number 32, Ballarat 1992

overall width of 500 m. The vertical extent of veining is about 700 m (Brathwaite et al, 1986). Vein outcrops are confined to the immediate pit area, and the vein system as a whole plunges within the host rock andesites to the northeast under a thick ignimbrite cover. The principal gangue minerals present in the Waihi vein system are, in decreasing order of abundance, quartz + calcite + adularia ± illite. Mineralogical and textural evidence suggests that for most of the life of the geothermal system the fluids were saturated with respect to quartz. Pyrite is ubiquitous within veins and impregnates wallrocks, and is commonly the only sulfide present, while rare marcasite coring pyrite grains and arseniferous and auriferous pyrite have been recognised (Jennings, 1991). Sphalerite occurs in minor amounts, and commonly contains disseminated inclusions of chalcopyrite. Galena is restricted to deeper levels and is intimately associated with other sulfide phases. Electrum is the principal gold- bearing phase, and occurs as inclusions within pyrite, chalcopyrite, and sphalerite, and as free grains in quartz (Brathwaite et al, 1986). Limonite and Mn-oxides are common supergene minerals. Primary growth textures within the Waihi vein system are dominated by crustiform bands, reflecting episodic pulses of hydrothermal fluids. In the upper part of the system, banding varies from planar to botryoidal, comprising microcrystalline quartz, chalcedony, and ultra-fine grained sulfides. Deeper in the system, the quartz is generally fine-combed to microcrystalline, and is characterised by densely packed subhedral to anhedral crystals. Banding is more crudely developed, with individual laminae ranging from centimetres to tens of centimetres in thickness. Brecciation and cementation of wallrock and older vein material are the most common secondary textures. They are dominated by angular monolithic clasts of silicified rock supported by a matrix of quartz veins and comminuted rock fragments. Less commonly, "jigsaw" breccias occur, where individual rock clasts can be fitted together. Such features are interpreted as resulting form hydraulic fracturing, and are important in defining areas of high permeability and variable pressure gradients, as possible sites for mineralisation. A simplified paragenetic sequence of veining

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consists of: stage I wallrock silicification and hairline and fluid chemistry within an epithermal system by veining; stage II bulk infilling of fissures by barren analogies to active geothermal systems (eg. Browne, quartz and calcite; stage III fine comb quartz and 1978; 1989). chalcedony with metal sulfides and precious metals; Temperature: Illite is the dominant clay mineral in stage IV transparent comb quartz and amethyst, locally the quartz-adularia alteration zone and indicates with late milky calcite. The (inferred) primary temperatures >220° C (Browne, 1989). Where illite is mineralogy of andesites hosting the vein system at interlayered with chlorite or smectite, temperatures Waihi consists of dominant euhedral plagioclase range from 140° to 230° C. In general, the basal (labradorite-andesine), rare quartz phenocrysts, spacing of illite (which indicates the degree of hypersthene, and augite. The groundmass is interlayering) decreases towards veining, a feature also hyalopilitic, with flow-banded microlaths of described at the active Wairakei (Steiner, 1968) and plagioclase and microlites of mafic minerals. Broadlands-Ohaaki (Browne, 1978) geothermal Petrography and X-ray diffraction (XRD) systems. Chlorite is commonly interlayered with techniques were employed on samples obtained from smectite at <200° C, whereas smectite occurs as a drillcores, and have resulted in the recognition of three discrete phase at temperatures <140° C. Thus the distinct types of alteration. These are: i) chlorite type; prominent zonation of clay minerals around major ii) interlayered clay type (divisible into smectitic, veins (ie. fluid conduits) suggests steep thermal chloritic, and illitic subtypes); iii) quartz-adularia gradients. Such steep gradients indicate shallow levels of alteration where conductive heating is minimal, and type. The hydrothermal minerals that replace primary is consistent with shallow- level thermal gradients in phases in each alteration type are summarised in Table active geothermal systems. However, if silica deposition on the fracture surface occurred, isolation of 1. Figures 1 and 2 show the spatial distribution of the wallrock from the circulating fluids may result alteration minerals in drillcores. Chlorite-altered rocks (Fournier, 1985). Pulses of fluids may then cause occur in isolated pods and at stratigraphically higher heating and cooling without achieving chemical or levels, distal from intense veining. By contrast, the thermal equilibration in the wallrock, and thus result most intensely altered (quartz- adularia) rocks occur in sharp contrasts in intensity of alteration. adjacent to veins, forming an alteration envelope that Permeability: The presence of isolated little altered ranges from 10 m to 40 m wide. In between these blocks within the vein system at Waihi indicates that "end-members" are interlayered clay types. The primary permeability was low. At Waihi, the composition and extent of interlayered directly reflects presence of adularia infers high permeability. This coincides with intense silicification around vein haloes the proximity to veins. Rock samples selected as representative of the (ie. in quartz-adularia altered rocks). By contrast, alteration suite defined above were analysed by X-ray primary feldspar (An 40-55) persists in rocks most fluorescence (XRF) and neutron activation (NAA) in distal from areas of veining and infers low order to characterise the geochemical changes that permeability away from fluid conduits (cf. Browne, 1978). occurred during hydrothermal alteration. Fluid Composition: Mineralogical and fluid Major element patterns are dominated by addition of silica (90%) and potassium (>300%). By contrast, inclusion evidence (Jennings, 1991) indicate the calcium (-84%) and sodium (-34%) are strongly hydrothermal fluids were hot (220° C - 270° C) and depleted. These chemical patterns mirror the gassy (up to lm CO2), but were of low apparent progressive alteration of plagioclase to adularia and salinity (<2 wt. % NaCl equiv.), and near-neutral pH illite, and silicification of the rock. Most other major (5.5). These features are characteristic of alkalielements are relatively immobile. The apparent chloride fluids observed in active geothermal systems. Hydrothermal activity at Waihi occurred during the immobility displayed by Fe infers that iron released from the breakdown of pyroxenes is immediately taken Late Miocene, initiated by the emplacement of a plutonic to sub- volcanic intrusive during extensional up in pyrite and chlorite. Trace element patterns show elevated values for ore tectonism. Heating of groundwaters led to the elements (Sb, Au, As, Cu, Pb, and Zn). Arsenic development of a convection cell and imparted a weak appears to be the most sensitive element in regional alteration characterised by smectite clays + determining regional alteration haloes around vein chlorite + calcite + pyrite from the low temperature structures. No widespread Au anomaly is observed, breakdown of ferromagnesian phases (Table 1). and thus As (and to a lesser extent Sb) provides the Alteration was essentially isochemical. Fluid flow best pathfinder to delineate mineralisation at Waihi was restricted to pre-existing channels (joints and faults) and this low primary permeability inhibited (Jennings et al, 1990). regional alteration. The temperature of The identification of key hydrothermal minerals pervasive can be used to infer various aspects of paleohydrology alteration, as deduced by the clay mineralogy, was less Geological Society of Australia Abstracts Number 32, Ballarat 1992

78

than 140° C With continued dilation, expansion of fractures allowed more fluid throughflow. Deposition of quartz on these fractures led to regular crustiform banded textures, and formed thick veins (up to 30 m). Intense wallrock alteration adjacent to these veins is characterised by quartz + adularia + illite + chlorite + calcite + pyrite. Further from the vein contact, the alteration assemblage comprises interlayered clays + quartz + calcite + chlorite + pyrite. Cessation of activity probably resulted from the cooling of the heat source at depth and/or the decline of extensional tectonism, leading to sealing of the system. Temperatures fell to below 170° C (Jennings, 1991) as amethystine quartz deposited. Uplift and erosion of the top 200 - 300 m of the system occurred, and subsequent burial by ignimbrites and ash has occurred in the last 2 million years. This work is based on the author's M.Sc. thesis completed at the University of Auckland under the supervision of P.R.L. Browne and D.S. Clarke. I would like to thank S.F. Simmons for many stimulating discussions and for assistance on all aspects of the work. Cyprus Minerals (N.Z.) Ltd. sponsored this study, and the New Zealand Geological Society provided financial assistance through a Student Bursary Award. References Brathwaite, R.L., McKay, D.F., and Henderson, S. 1986 The Martha Hill Gold- silver Deposit, Waihi. Volcanism, Hydrothermal Systems, and Related Mineralisation, Proc. Symposium 5th Int. Vol. Cong., February, 1986, University of Auckland. Browne, P.R.L. 1978 Hydrothermal Alteration as an

Aid in Investigating Geothermal Fields. Geothermics Spec. Iss. 2: 564-570. Browne, P.R.L. 1989 Hydrothermal Alteration and Geothermal Systems. Unpubl. Course Notes, Geothermal Institute, University of Auckland. Browne, P.R.L. and Ellis, A.J. 1970 The OhaakiBroadlands Geothermal Field, North Island, New Zealand. Jour. Vole. Geothermal Res. 6: 213-215. Fournier, R.O. 1985 The Behaviour of Silica in Hydrothermal Solutions, in Geology and Geochemistry of Epithermal Systems Eds. B.R. Berger and P.M. Bethke. Reviews in Economic Geology, Vol. 2: 45-63. Hedenquist, J.W. 1986 Mineralisation Associated with Volcanic-related Hydrothermal Systems of the Circum- Pacific Basin, in Trans. 4th CircumPacific Energy and Mineral Resources Conference Ed. M.K. Horn: 513-52. Hochstein, M.P., Tearney, K., Rawson, S., Davey, F.J., Davidge, S., Henrys, S., and Backshall, D. 1986 Structure of the Hauraki Rift, New Zealand. Jour. Roy. Soc. New Zealand Bull 24: 333-355. Jennings, K., Browne, P.R.L., Clarke, D.S., and Brathwaite, R.L. 1990 Aspects of Hydrothermal Alteration at the Waihi Epithermal Au-Ag Deposit, New Zealand. Proc. 12th New Zealand Geothermal Workshop, University of Auckland: 237- 242. Jennings, K. 1991 Hydrothermal Alteration and Geochemistry at the Waihi Epithermal Au-Ag Deposit, New Zealand. Unpubl. M.Sc. Thesis, University of Auckland, Auckland. Skinner, D.N.B. 1986 Neogene Volcanism of the Hauraki Volcanic Region, in Late Cenozoic Volcanism in New Zealand Ed. I.E.M. Smith. Roy. Soc. New Zealand Bull 23: 21-47. Steiner, A. 1968 Clay Minerals in Hydrothermally Altered Rocks at Wairakei, New Zealand. Clay and Clay Mins. 16: 193-213.

[TABLE 1: Replacement series of primary mineral phases observed at Wathi

lltfilti'-VJSfTCrl^^H Chiontic Zone

1 HTTm f ^ i ^ w l Mfr/.Tft smectite subzone

chlorite subzone

illite subzone

complete alteration tocal + ad + ehl±yi

ad 4- cai • ill + qtz

Ouartz-Adulana Zone

„

Quanz Ptagjoclase

-

weak to» strong chl + cai

Octhpyroxene ,

completely altered to chl + opaq ± cai ±2°qtt

chl + opaq • cai • qtz Becoming increasingly difficult to distinguish destroyed due tofeexturaldestrocoon

Qinopyroxene'

Weak rim and fracture strong to complete Generally completely altered to a sub-opaque destroyed alteration 10 chl • py alteration to chi + opaq chloride clay with associated opaques (mainly py) + qtz + cai • qtz

Magnetite

pyrite ± titanite

Apatite

•

Groundmass

devitrification 10 smccobc clay

pyrite ± titanite

pyrite ± titanite

pyrite ± titanite

ill + ad + qtz + cai (see text)

pyrite ± titanite

m

interlayered sm + chl (sm>chl)

interlayered chl + sm ill interlayered with chl mosaic qtz • ad • chl (chl > sm). or sm + mosaic qtz • ill • ad GcneraJ stability sequence: glass < onhopyroxene < magnetise < clinopymxeoe < piagioclase < apatite < quartz. | id - adularia. cai - calcite, chi - chlorite, ill«illite, sm « smectite, ooaq « opaques, py « pyrite, qtz « Quaitz.

Geological Society of Australia Abstracts Number 32, Ballarat 1992

79 DOWNHOLE DISTRIBUTION OF z

DOWNHOLE DISTRIBUTION OF

ALTERATION MINERALS :W 7A

ALTERATION MINERALS :W 14

o

A

0 a

H A H W hw y ^

I•I k

A V

a

'i if-

u n CJ

a

r

—

=

2

c

o

*

A[ H ^ y <j 9

« CLAYS AS A PERCENTAGE OF TOTAL CLAYS

CLAYS AS A PERCENTAGE OF TOTAL CLAYS

LEGEND MINERAL ABUNDANCE

ALTERATION (

| Chtonte Type

(T~| S m e c t i t e I 2

|.

Chlorite

| j?

^

lllite

] |

O

^

^ 0 U i o

§ § Guartz - Adulana Type flq

Kaolinite Type

|

Veins

LITHOLOGY

Figure 1 (W7A) and Figure 2 (W14) showing the downhole distribution of alteration minerals. Clays are semi-quantitat'rvely estimated.

Major Moderate Minor Trace Sampie

C-S

Chlonte - smectite

l-S

lllite - s m e c t i t e

I—C

lllite - c h l o r i t e

TECTONIC FEATURES Undifferentiated breccia

y ! j Undifferentiated ignimorite - > t Welded ignimorite S j P I

Pumiceous ignimorite Lithic turf

5 g

Tuff b r e c c i a

|3 =

l*!^ F l o w - t o p b r e c c i a

j a" I =

C a r b o n a c e o u s bed t^-Fj M a s s i v e p h y n c arvoesite

j * ^ M u d s tone b r e c c i a 5>] S h e a r zone Tricon eo (no c o r e recovery)

A n d e s i t i c ruff Sheared andesite

A 3.28

HOST ROCK GEOCHEMISTRY AND ALTERATION IN THE PALAEOZOIC MOUNT AUBREY EPITHERMAL GOLD DEPOSIT, NSW S. Hopf Department

of Geology, University of Newcastle, NSW 2308

The Mount Aubrey deposit is located in the Lachlan Fold Belt 30km NE of Parkes in a gently dipping sequence of andesitic and basaltic lavas of Devonian (?) age. Welded rhyolitic ignimbrite (Dulladerry Rhyolite ?) occurs at the top of the sequence and is underlain by fine-grained amygdaloidal ophitic basaltic lavas (minimum thickness 60m)

Geological Society of Australia Abstracts Number 32, Ballarat 1992

containing augite and labradoritic plagioclase. Strongly altered porphyritic augite-bearing andesitic flows (at least 200m thick), with intercalated tuffaceous and basaltic layers, lie below the basalt. A set of EW-trending, steeply dipping veins which contain quartz pseudomorphs after bladed calcite crop out in the mine area.

80 Alteration styles in basalt and andesite are similar: igneous plagioclase is commonly replaced by albite and adularia (less often by illite, epidote and calcite), and mafic minerals are typically pseudomorphed by chlorite (±sphene). In andesite, the groundmass displays varying degrees of silicification and chloritisation. Veining is abundant in basalt and less common in andesite. Vein minerals include quartz, calcite (typically bladed) and minor illite, epidote and pyrite. Finely disseminated pyrite and chalcopyrite occur in both rock types; galena is also present in minor amounts in andesite. Native gold occurs as minute (micron sized) grains in quartz veins which originated from hydraulic fracturing in the upper basaltic portions of the system. Gold was mined from late 1990 to February 1991 and in this period an estimated 120 OOOt of ore @ 3.3g/t Au were recovered. The temperature of the hydrothermal fluid is estimated to have been in the range 230- 280°C, based on chlorite thermometry and the presence of epidote (Browne, 1978). The fluid pH (slightly alkaline) was controlled by the chlorite/pyrite buffer, and additionally in andesite, by the adularia/muscovite buffer. This is in accordance with the fact that aH2 and aH2S values calculated from chlorite compositions plot close to the chlorite-pyrite boundary. The stable existence of epidote indicates that a low oxygen fugacity (0.5 to 7 log fo2 units below the hematitemagnetite buffer) must have prevailed throughout the system. Least altered basalt is characterised by low Si02 and K2O (0.2-0.5wt%) and relatively high AI2O3 (above 16wt%) and MgO (above 7wt%) contents. Hydrothermal alteration has resulted in a redistribution of Na, Ca, and to a lesser extent K and Fe, accompanied by silicification and strong hydration. Andesite typically has higher K2O contents than basalt. Major element changes in andesite are related to the removal of Ca during the alteration of igneous calcic plagioclase. Three main types of feldspar replacement have been recognised: Na exchange for Ca (albite type), Na and K for Ca (albite-illite-adularia type), and K for Ca (illite-adularia type). Most trace elements appear to have remained relatively constant during alteration (e.g. Cr, Ni, Sc, Yb, V, Zn) with the

Geological Society of Australia Abstracts Number 32, Ballarat 1992

exception of Ba, Rb, Sr and Li which have been mobilised. Ba and Rb are enriched in zones with high K contents, Sr correlates with Ca, and Li is typically enriched in all altered samples. The andesitic lavas have calcalkaline affinities as indicated by their position in an AFM diagram, moderately high K2O contents and light rare earth element (REE) enrichment. In contrast, the basalts are transitional in character: a tholeiitic affinity is suggested by their position in an AFM plot and their relatively straight REE trends, however, high plagioclase and AI2O3 contents indicate that they may be high-alumina basalts. In a spidergram (Pearce, 1983), andesite displays a spiked pattern with enriched Sr, K, Rb and Ba due to crustal contamination. The patterns of basalts are similar to those of andesite but show less enrichment of Sr, K, Rb and Ba indicating a lower degree of crustal contamination. This is supported by preliminary lead isotope data which show that the mantle component in the basalts is stronger than in the andesites. The andesite trace element patterns show a striking similarity to those of the Ordovician Boggy Plain Supersuite which is thought to have formed from a gabbroic layer with shoshonitic affinities (Wyborn et al., 1987). It is concluded that the andesites formed in an island arc setting from a shoshonitic source which was modified due to crustal contamination. The basalt, which is clearly related to the andesites on field relationships, is thought to have originated from a more mantle dominated source in a young marginal basin which had probably not fully opened. References Pearce, J.A., 1983. Role of the Sub-continental lithosphere in magma genesis at active continental margins. In Hawkesworth C.J. and Norry M.J.,eds. Continental Basalts and Xenoliths, pp. 230-249. Shiva Publications, Orpington, UK. Wyborn, D., Turner, B.S. & Chappell, B.W., 1987. The Boggy Plain Supersuite: A distinctive belt of I-type igneous rocks of potential economic significance in the Lachlan Fold Belt. Aust. J. Earth Sci. 34:21-43.

81 A 3.29

STABLE ISOTOPE EVIDENCE FOR MULTIPLE SOURCES OF COMPONENTS IN LODE-GOLD DEPOSITS OF THE EASTERN GOLDFIELDS PROVINCE, WESTERN AUSTRALIA N. J. McNaughton 1 *, M. Gebre-Mariam1, S. D. Golding 2 , David I. Groves,1 S.G. Hagemann1 and J.M.A. Hronsky1

1

Key Centre for Strategic Mineral Deposits, Department of Geology, University of Western Australia, Nedlands 6009, Western Australia. 2 Department of Geology and Mineralogy, University of Queensland, St Lucia 4075, Queensland

Lode-gold deposits of the Yilgarn Block occur in a wide spectrum of lithologies that have been metamorphosed from granulite to sub-greenschist facies. Proximal alteration assemblages broadly correlate with the metamorphic grade of the host rocks (Mueller & Groves 1991; Witt 1991), and ore fluids appear to have a relatively uniform chemistry, in particular X ^ q 2 = 0.1 - 0.2 and low salinity (Ho et al. 1990). Mineralization temperatures vary from about 250 C to over 650 C and P-T conditions appear to reflect a crustal depth range of >15km, suggesting that the lode-gold deposits form a depth continuum (Groves et al. 1991). Structurally, the deposits form in second- and third-order faults and shear zones that appear spatially and, in places, geometrically related to major deformation zones (Eisenlohr et al. 1989). Lodegold mineralization occurs as shear zone deposits, telluride-rich lodes, laminated quartz veins, quartz vein sets and stratabound deposits (Groves et al. 1990). Deeply-derived ore fluids and giant hydrothermal systems are inferred from the depth-continuum model. The stable isotope compositions of the deeply-derived ore fluids are expected to be buffered by rocks at the source and possibly by fluid conduits at high temperature (Barnicoat et al. 1991). These rock types, however, are inferred to be isotopically heterogeneous, potentially explaining the observed isotopic heterogeneity in the ore fluids based on analyses of ore-related minerals (Golding et al. 1989). In particular, the highly variable of the higher temperature ore fluids most proximal to source regions require variable rock and low fluid:rock ratios (e.g. McNaughton et al. 1991; Barnicoat et al. 1991). The published data for ore fluids consistently have the C-0 isotopic character of 'metamorphic waters' (i.e. water derived from, or in isotopic equilibrium with, metamorphic rocks), but do not uniquely support isotopic buffering from heterogeneous sources at high temperature. A number of other different processes or fluid sources are allowable (see Golding et al. 1989). Recent work on deposits within greenschist to subgreenschist terrains, the shallowest part of the inferred depth-continuum, indicates textural and mineralogical parameters characteristic of both mesothermal and epithermal styles of mineralization (Gebre-Mariam et

al. 1991; Hagemann et al. 1991; this volume). Given the shallow crustal levels of these deposits, it is possible that surface-water was involved in the hydrothermal systems, a proposition that can be tested by fluid inclusion and H-C-0 stable isotope studies of gangue minerals within veins and proximal alteration. All lode-gold deposits hosted by lower greenschist to lower amphibolite facies rocks in the Eastern Goldfields Province have ore fluid 5 ^ 0 values which overlap the normal range of metamorphic waters. The calculated 5 1 8 0 of ore fluids for Wiluna and Racetrack, two deposits hosted by sub-greenschist facies rocks, are about +l%e> and -3%o SMOW, respectively. These are the most 1 8 0 -depleted waters so far determined for Archaean lode-gold deposits in Western Australia, and implicate contributions from surface-water. The 5 ^ 0 of Archaean seawater should have been the same as modern seawater (i.e. 0%o SMOW) if hydrothermal systems at mid-ocean ridges allowed oceanic crust to buffer the 8 ^ 0 of the oceans. The 5 o f meteoric water, if analogous to modern meteoric water, should have varied from 0%o SMOW to lighter values at high latitude and/or altitude. The Racetrack ore fluid 5180 strongly suggests a major contribution from Archaean meteoric water with < 0 %c SMOW. Preliminary C-0 isotopic modelling suggests that ore fluids from the Province are mixtures between surface water (nominally with 5 ^ 0 = 0%o SMOW, except for Racetrack where a lighter, meteoric water is required) and heterogeneous deeply-derived fluids. The modelling is dependent on a knowledge of the isotopic compositions of the deeply-derived fluids, and to a lesser extent on the CO2 content of the heated surfacewater. Utilizing various estimates for the isotopic compositions of 'deeply-derived' fluids, the ore fluids in many deposits contain no or negligible surfacewater, whereas some of the major gold camps in the Province are interpreted to contain significant surfacewater. These include not only the upper crustal deposits at Racetrack and Wiluna, but also shear/faultzone related lodes at Lancefield and Kalgoorlie. These preliminary conclusions are model-dependent and are currently being tested by 8D studies.

82 References Barnicoat, A.C., Fare, R.J., Groves, D.I., and McNaughton, N.J., 1991, Syn-metamorphic lodegold deposits in high-grade Archean settings: Geology, in press. Gebre-Mariam, M., Groves, D.I., Ho, S.E., McNaughton, N.J. and Vearncombe, J.R., 1991,The Archaean lode-gold deposit at Racetrack, near Kalgoorlie, Western Australia: a transitional mesothermal - epithermal hydrothermal system: 25 yrs SGA Anniv. Meeting. Source, Transport and Deposition of Metals, Nancy, in press. Golding, S.D., McNaughton, N.J., Barley, M.E., Groves, D.I., Ho, S.E., Rock, N.M.S., and Turner, J.V., 1989, Archaean carbon and oxygen reservoirs: their significance to fluid sources and circulation paths for Archaean mesothermal gold deposits of the Norseman-Wiluna Belt, Western Australia. Econ. Geol. Monograph 6, 376-388. Groves, D.I., Barley, M.E., Cassidy, K.F., Fare, R.J., Hagemann, S.G., Ho, S.E., Hronsky, J.M.A., Mikucki, E.J., Mueller, A.G., McNaughton, N.J., Perring, C.S., Ridley, J.R., and Vearncombe, J.R., 1991, Sub-greenschist to granulite-hosted Archaean lode-gold deposits of the Yilgarn Craton: a depositional continuum from deep-sourced hydrothermal fluids in crustal-scale plumbing systems: In Glover, J.E., and Ho, S.E. (eds), The Archaean: Terranes, Crustal Processes and Metallogeny, Geol. Dept & Univ. Extension, Univ. West. Aust., Publ. 22, in press. Groves, D.I., Knox-Robinson, C.M., Ho, S.E., and Rock, N.M.S.,1990, Nature and setting of primary gold deposits: In Ho, S.E., Groves, D.I., and Bennett, J.M. (eds), Gold Deposits of the Archaean A 3.30

Yilgarn Craton, Western Australia: Nature, Genesis and Exploration Guides. Geol. Dept & Univ. Extension, Univ. West. Aust. Publ. 20, p. 2-18. Hagemann, S.G., Groves, D.I., McNaughton, N.J. and Vearncombe, J.R., 1991, The geological setting of the Wiluna lode-gold deposits, Western Australia: The highest crustal-level endmembers of an Archean-gold deposit continuum. In: Ladeira, E.A. (ed.), Brazil Gold '91: The Economics, Geology, Geochemistry and Genesis of Gold Deposits. Balkema, Rotterdam, 649-656. Hagemann, S.G., Ridley, J.R., Groves, D.I. and McNaughton, N.J., 1991, The Archaean lode-gold deposits at Wiluna, Western Australia: examples of fluid mixing at shallow crustal levels: this volume. McNaughton, N.J., Cassidy, K.F., Dahl, N., de Laeter, J.R., Golding, S.D., Groves, D.I., Ho, S.E., Mueller, A.G., Perring, C.S., and Sang, J.H., 1991, The source of ore components in lode-gold deposits of the Yilgarn Block, Western Australia: In Glover, J.E., and Ho, S.E. (eds), The Archaean: Terranes, Crustal Processes and Metallogeny, Geol. Dept & Univ. Extension, Univ. West. Aust., Publ. 22, in press. Mueller, A.G., and Groves, D.I., 1991, The classification of Western Australian greenstonehosted gold deposits according to wallrockalteration mineral assemblages: Ore Geology Reviews, v.6, p. 291-331. Witt, W.K., 1991, Regional metamorphic controls on alteration associated with gold mineralization in the Eastern Goldfields Province, Western Australia: implications for the timing and origin of Archean lode gold deposits: Geology, in press.

A FLUID INCLUSION STUDY OF AURIFEROUS QUARTZ VEINS -- HILL END GOLDFIELD, NSW, AUSTRALIA Jianchun Lu & Philip K. Seccombe Department of Geology, The University of Newcastle, NSW 2308, Australia

Auriferous quartz veins in the Hill End goldfield, NSW, Australia, comprise bedding-parallel vein sets and a variety of extension, fault-controlled and cleavage-parallel veins which are hosted by a multiply deformed, Late Silurian slate-metagreywacke turbidite sequence. Highest gold values are recorded in steeply pitching ore shoots developed in E-dipping, beddingparallel veins and intersecting, NE-trending extension veins (leader veins'), close to the hinge of the regional Hill End Anticline. Bedding-parallel veins and leader veins consist of as many as four generations of quartz, accompanied by phyllosilicates, carbonates, gold and minor sulphides. Fluid inclusions in quartz, either from beddingparallel veins or from leader veins indicate a similar Geological Society of Australia Abstracts Number 32, Ballarat 1992

range in homogenisation temperatures (Th) from 120°C to 350°C (Figs. 1 and 2). Within this range, Th data demonstrate five maxima in the temperature intervals 120-150°C, 150-190°C, 200-250°C, 250280°C and 290-350°C, indicating that the two styles of veins were formed during similar events and are the products of the same episodes of fluid activity. Th of primary inclusions identified in first generation quartz (1-Q) in the principal beddingparallel quartz veins and Au-bearing leader veins range from 290°C to 350°C, consistent with metamorphic temperatures in the study area. Three generations of secondary fluid inclusions have been identified in 1-Q. Group A secondary inclusions are confined to sealed cracks parallel to the laminations of the principal

83 quartz veins and consist of liquid-rich inclusions with two ranges of gas-liquid ratios, 2-5% and 5-10%. Inclusion shapes comprise negative crystal cavities or polygonal and ellipsoidal outlines. Inclusion size is generally in the range 5-10 |im, but may reach 15 |im. Group A inclusions define two Th ranges, 190-250°C and 250-300°C. Group B inclusions are confined to sealed cracks which are perpendicular to and/or oblique to the vein laminations. Some inclusions of this group have a similar range in Th (200-258°C) and characteristics to those of group A, but others display a lower gas ratio and lower Th of around 150-190°C. Group C inclusions are distributed along postmineralisation cracks and are characterised by a low gas ratio of less than 2%, low homogenization temperatures (100-150°C), irregular shape and a wide variation in size from 3-5 |im to >20 |im. Fluid inclusions are poorly developed in second generation quartz (2-Q). Only a few sparsely distributed primary inclusions are observed. They are identified by negative euhedral and ellipsoidal shapes, gas ratios of 2-10% and a relatively small size (3-10 |im). Th for 2-Q primary inclusions is around around 200-260°C. Several small secondary inclusions have been identified, located in cracks around the edges of quartz grains and give a Th range of 150-200°C. Fluid inclusions are undeveloped in the third generation quartz. By contrast, in the fourth generation quartz (4-Q), well developed inclusions are characterised by uneven distribution, a range in shape including negative euhedral, polygonal and ellipsoidal forms, and wide variation in size, gas ratio and gas content. Some liquid-CC>2 bearing inclusions are identified in 4-Q. Homogenization temperatures (Fig. 3) for 4-Q inclusions are relatively constant (140210°C). Some Th measurements in the range 220350°C from 4-Q, possibly represent the preservation of 1-Q and 2-Q-stage inclusions from disrupted, laminated vein fragments. Laser Raman microprobe analysis reveals that the gas composition of the fluid inclusions varies in the different generations. In 1-Q quartz, H20(g) and N2 dominate in the primary inclusions, CH4 and CH4+H20(g) are the principal species present in Group A and Group B secondary inclusions, but H20(g) is the only major phase in group C secondary inclusions. In 2-Q quartz, the gas phase composition is dominated by CH4 and CH4+H20(g). Gas phase composition in 4-Q quartz varies both with depth in the vein system and also from the earlier to later stages of 4-Q quartz deposition. The earlier stage of 4Q quartz, associated with conformable and discordant chlorite and calcite veins in the footwall of the

Geological Society of Australia Abstracts Number 32, Ballarat 1992

principal laminated veins, contains fluid inclusions characterised by H 2 0 ( g ) and CH4+H20( g ). Later stage 4-Q quartz, accompanied by calcite in the crest of the major anticline, contains fluid inclusions characterised by CO2 as the dominant gas phase. Some liquid-CC>2 bearing inclusions have been identified in this material. Some of the group A and group B secondary fluid inclusions in 1-Q, and the primary inclusions in 2-Q, contain a tabular, or acicular solid phase, identified by Laser Raman analysis as muscovite. This mineral is unlikely to represent a daughter phase; rather a solid inclusion that has controlled the location of fluid trapping. All the inclusion fluids are characterised by a low salinity of around 0.1 to 3.6 wt% eNaCl, which is consistent with fluid derivation from a metamorphic source. Gold was deposited during and after the development of the crack-seal laminations in the veins. At least three episodes of gold mineralisation have been identified. The first two episodes occurred soon after the formation of 2-Q quartz and 3-Q quartz respectively. Minerals associated with the gold include phyllosilicates (muscovite and chlorite), sulphides (pyrite, pyrrhotite, minor arsenopyrite, sphalerite and galena), and minor carbonates (mainly calcite). The mineralising fluid is characterised by a low salinity and low CO2 concentration, but an elevated CH4 content, reflecting a relatively reduced environment. Fluid inclusions developed during the first two stages of gold deposition indicate a Th range of 190-260°C. The latest episode of gold mineralisation occurred after the main stage of laminated vein formation and during, or soon after the deposition of 4-Q. In the earlier stages of this final phase of gold deposition, the fluid was characterised by low CO2 and relatively high CH4 concentrations, however, in the later stage the situation reversed and high CO2 and low CH4 contents prevailed, reflecting a change in the geochemical environment toward oxidising conditions. It is concluded that, whereas the quartz veins formed over a protracted period corresponding to the peak of metamorphism and deformation, gold mineralisation occurred after the major phase of quartz deposition, but during and after the development of the laminations. The mineralising fluids represent metamorphic fluid and gold was probably mobilised and extracted by this fluid from either the local host rocks or from deeper within the underlying volcanic rock sequences.

84

Figure 1. Histogram of Th data for fluid inclusions in quartz from a laminated, bedding-parallel vein, Hill End.

Figure 2. Th distribution for fluid inclusions in quartz from a leader vein, Hill End.

Figure 3. Th distribution for fluid inclusions in 4-Q quartz-chlorite veins, Hill End.

Geological Society of Australia Abstracts Number 32, Ballarat 1992

85 A 3.31 ISOTOPE STUDIES FROM THE MILPARINKA-TIBOOBURRA DISTRICT, NWNEW SOUTH WALES: AGE RELATIONSHIPS AND INDICATIONS FOR THE SOURCE OF GOLD O. A. R. Thalhammer Institute of Geological Sciences, Mining University Leoben, Austria The Milparinka-Tibooburra District, situated in the northwestern corner of New South Wales, ca. 380 km north of Broken Hill, is marked by the occurrence a discontinuous series of possibly basement rocks. The Warratta and Mt Poole Inliers, that are particularly considered in this contribution, are mainly built up by multiply deformed and low-grade metamorphosed metasediments, the Wonominta Beds (Warris 1967); subordinately, intercalations of felsic volcanics and intermediate to mafic dykes appear, preferentially within the Mt Poole Inlier. The metasediments, particularly within the Warratta Inlier, characteristically contain quartz-veins which are structurally controlled. Locally, veins in dark, laminated, pyriterich slates bear gold and small amounts of sulfides. This was the reason for gold mining activities in the last century (Barnes 1975). Detailed structural investigations have shown that auriferous quartz-veins have been formed syntectonically during early stages of the development of an axial plane cleavage Si. Moreover, vein textures indicate that mineralized veins have developed by hydraulic fracturing and filling in repeted increments, the crack-seal mechanism (Ramsay 1980). Geochemical studies have shown that auriferous veins are accompanied by an alteration zone, which is characterized by a considerable loss of most of the major elements, whereas K, Rb, Au and S have been added to the host rocks in immideate vicinity to the veins during their formation. Altered metasediments closest to mineralized veins have the highest Au-values reaching 45 ppb. Mass balance calculations on the basis of silica revealed that the amount of Si released during deformation (i.e. cleavage development) and alteration was not sufficient to form the quartz veins. Sulfur isotope data, 5 S-values lie in the range of -0.9 to +10.0%o show good agreement between the isotopic composition of vein sulfides, and that of the surrounding metasediments and interbedded 34

Geological Society of Australia Abstracts Number 32, Ballarat 1992

igneous rocks. Furthermore, 8 S-values are rather close to 0%o. This indicates that the source of sulfur is either magmatic or, that the mineralizing fluids were rich in H2S. In the latter case it can be assumed that S has been derieved from sulfates and sulfides of a volcano-metasedimentary sequence, whereby sulfate ions have been reduced to H2S with a total S S around ±0%c. The isotopic composition of the lead from vein sulfides and vein gold cluster with their 207/204 vs. 206/204 ratios marginally below, but still very close to the Cumming and Richard (1975) Model 3 growth curve (Fig.l). The Pb-isotopic composition of sulfides within the host rocks deviates slightly in its 207/204 vs. 206/204 ratios from the growth curve (Fig.l). These features indicate a crustal derivation of the lead. Pb-model ages revealed an age around 500 Ma, which coincides fairly well with K-Ar datings. The latter have been carried out on synmetamorphic micas from unaltered host rocks, from altered rocks and from host rock inclusions within auriferous veins, revealing an age around 440 Ma. As a consequence, a maximum age for the formation of auriferous quartz veins within the Warratta Inlier, around 500 Ma, and a duration of vein development in the range of ca. 60 Ma can be proposed. 34

34

References Barnes, R.G., 1975, NSW Geol. Surv.: 92-101 Cumming, G.L. & Richards, J.R., 1975, Earth Planet. Sci. Let. 28: 155-171 Hart, S.R., 1984, Nature 309: 753-757 Ramsay, J.G., 1980, Nature 284: 135-139 Warris, B.J., 1967, Ph.D. thesis, Sydney Univ. (unpubl.) Zartman, R.E. & Doe, B.R., 1981, Tectonophys. 75: 135-162

86 Pb-isotopes

0.5

§ 15.6

OA

2

0.2 cV

0.3

L F B

—

*

Hartal

PY2

M

o 15.4

18.0

'

'

18.4 206/204

1

I I 18.8

Fig.l Isotopic composition of leads from the Warratta Inlier in the 207/204 vs. 206/204 diagram. Reference growths curves are from Cumming and Richards (1975) (C & R), and from Hart (1984). M and O refer to the ends of the mantle and orogene growths curves, respectively, according to Zartman and Doe (1981). Py-1 and Py2 are vein sulfide samples, Au represents vein gold, S are sulfides from the host rocks, and LFB is a mean of samples from the Lochlan Foldbelt (Richards 1991, pers. comm.) A 3.32 A REGIONAL STUDY OF LATE STAGE GOLD BEARING FLUIDS IN SHEAR ZONES FROM THE BENDIGO, FIDDLER'S CREEK AND STAWELL GOLDFIELDS, VICTORIA, AUSTRALIA N. Green , A. Changkakoti and T.A.P. Kwak 1

2

1

1 Department of Geology, La Trobe University, Bundoora, Victoria 3083 P.O. Box 6639, 600 St. Kilda Road, Melbourne 3004 2

Gold is intimately associated with quartz in many high grade, low tonnage deposits throughout the world. This paper attempts to provide an integrated approach to the question of whether the gold and quartz were transported in a common solution or several solutions over time. The study is concerned with three separate deposits in different structural settings: Bendigo, Fiddler's Creek and Stawell. In Bendigo, gold occurs in the more deformed, recrystallized sections of the laminated reefs and in the sheared outer sections qf the saddles. It replaces relict graphite fragments in more iron rich ankerites. Structurally the system is relatively simple with numerous episodes of opening and closing of the veins on a micro and macro scale. Quartz which predate gold mineralization have typical metamorphic oxygen and hydrogen isotopic signatures, while the sulphur and carbon isotopic values of sulphides and carbonates associated with gold show magmatic signatures. In Fiddler's Creek, gold-bearing quartz veins occur Geological Society of Australia Abstracts Number 32, Ballarat 1992

within a strongly deformed zone. Like Bendigo, the veins are both laminated and massive, but there are no saddle reefs. Higher grade sections of the reefs are graphite rich. Gold occurs in strongly recrystallized areas and replaces relict graphitic fragments. It also occurs in pyrite, sphalerite and galena. Oxygen and sulphur isotopic values are similar to Bendigo. In Stawell, gold mineralization occurs in a more complex structural environment with up to six deformations. Gold deposition is only related to one of the late stage phases. It occurs within laminated reefs in turbidites and in veins in mafic volcanics. It is associated with arsenopyrite and recrystallised quartz. It is believed that gold in deposits of this type was introduced late in the structural history during brittle ductile deformation which increased the permeability of the vein systems. It is important to note that the relatively uniform quartz veins are merely channelways for the gold fluids.The origin of these late gold bearing fluids is not known at this stage.

87 A 3,33 THE ARCHAEAN LODE-GOLD DEPOSITS AT WILUNA, WESTERN AUSTRALIA: EXAMPLES OF FLUID MIXING AT SHALLOW CRUSTAL LEVELS. S.G. Hagemann, J.R. Ridley, D.I. Groves, and N.J. McNaughton Key Centre for Strategic Mineral Deposits, Department of Geology, The University of Western Australia, Nedlands, WA 6009, Australia The Wiluna lode-gold deposits of Archaean age are and type 3 are low temperature (Th = 105° to 335°C; developed in the Wiluna strike-slip fault system, in mean 185°C), moderately saline (<15.0 eq.wt% NaCl) the northern part of the Norseman-Wiluna Belt, H20-NaCl inclusions. Isochores for type 1 inclusions Western Australia. The major host rocks are very low yield pressures of 1.5 to 2.5kbar whereas isochores for grade (prehnite-pumpellyite facies) ultramafic and type 2b inclusions yield pressures of <lkbar at the mafic lavas with abundant preserved primary igneous estimated temperatures of mineralization. textures. Gold mineralization and hydrothermal Dolomite and calcite from hydrothermal breccias in alteration of the host rocks is spatially associated with auriferous fault zones and proximal alteration zones the Wiluna strike-slip fault system and occurs in have consistent 5 C and S 0 values of about hydrothermal breccias, shear veins, and veins with 4.5%o PDB and 10 %o SMOW, (n=6 and 10), comb- and cockade-textured quartz. Importantly, the respectively. At the estimated formation temperature ore zones are controlled by structural inhomogeneities of 250±50°C, the H2O in equilibrium with these in the principal displacement faults and in subsidiary carbonates would have 8 0 = 1±2%o Compared to structures. The major controls on ore shoot other ore-fluid data from mesothermal gold deposits of localization within the lode deposits are intersections the Yilgarn Block, the Wiluna deposit has the lowest of planar elements. 5 0 of any deposit so far studied. The only realistic Hydrothermal alteration is strongly developed in mechanisms to achieve 8 0 values below about the hanging-wall of the fault zones, although local 2%oSMOW are via the influx of surface waters alteration pockets in the footwall, in deeper sections of (seawater and/or meteoric water), or by equilibration of the mines, have been recorded. Alteration zonation is the ore fluid with 0-depleted rocks at low fluid-togenerally asymmetric, and varies in width up to 50 m. rock ratio. The initial Pb isotopic composition of the The alteration zonation grades outwards from intensely Wiluna system, based on the least-radiogenic Pbbrecciated quartz-dolomite±fuchsite±sericite to less isotope ore of eight pyrites from the gold brecciated quartz-dolomite±fuchsite±chlorite to strain- ores, fallscomposition within distinct field defined by deposits free chlorite-calcite rocks. Disseminated pyrite, from the northernthe Norseman-Wiluna Within this arsenopyrite and/or stibnite, and traces of chalcopyrite region there is no correlation with belt. hostrock and tetrahedrite, occur within several meters of the composition or metamorphic grade. Iteither is inferred that fault zones. Gold is present principally as minute Pb for all deposits, including Wiluna, is largely flakes in arsenopyrite and stibnite, and rarely as free derived from a geographically distinct, sub-greenstone gold in quartz. Repeated brecciation and cementation reservoir, and probably represents previously depleted of the mafic-ultramafic protoliths within the inner ore- lower-mid crust. zone suggest that the development of the strike-slip The ore fluid composition at Wiluna can be fault system and hydrothermal alteration were contemporaneous and occurred after prehnite- modelled as a mixture between surface water and deeply sourced fluids which equilibrated with deeper pumpellyite facies metamorphism. Primary fluid inclusions are trapped in: (1) gold- crustal rocks along the transcraton fault zones which bearing shear veins and hydrothermal breccias acted as conduits for these ascending fluids. The representing an early stage of mineralization with type deposits are considered respresentative of the upper 1 and 2a fluid inclusions, and (2) gold-bearing stibnite portions of the vertically extensive continuum of veins and breccias, and cockade textured quartz Archaean hydrothermal gold-bearing systems because representing a late stage mineralization with type 2b of the inferred input of surface water, and the styles of and 3 fluid inclusions. Type 1 are carbonic inclusions mineralization are intermediate between those that are containing up to 15 mole% CH4 whereas type 2a are normally described from mesothermal and epithermal mixed, low salinity (<4.8 wt% NaCl) CO2-H2O gold deposits. inclusions with homogenization temperatures of 270° to 370°C (mean 300°C). Type 2b are low temperature (Th = 145° to 335° C; mean 250°C), low salinity (<6.4 eq.wt% NaCl) CC>2-H20-NaCl fluid inclusions, 1 3

1 8

1 8

1 8

1 8

18

Geological Society of Australia Abstracts Number 32, Ballarat 1992

88 A 3.34 INITIAL LEAD ISOTOPE COMPOSITIONS OF ARCHAEAN LODE-GOLD DEPOSITS: A RECORD OF ARCHAEAN CRUSTAL-SCALE HYDROTHERMAL SYSTEMS AND CRATON-SCALE SOURCE HETEROGENEITIES Neal J. McNaughton *, David I. Groves and Walter K. Witt 1

1

2

Key Centre for Strategic Mineral Deposits, Department of Geology, University of Western Australia, Nedlands 6009, Western Australia. Geological Survey of Western Australia, Kalgoorlie 6430, Western Australia.

l

2

Archaean lode-gold deposits of the Yilgarn Block, Western Australia, are hosted in sequences that have been metamorphosed from sub-greenschist to granulite facies. Most deposits have P-T conditions of mineralization broadly compatible with metamorphic P-T conditions, corresponding to mineralization over a range of crustal depths of >15km (Groves et al., 1991; Witt 1991). Despite this large range in P-T conditions of mineralization, the deposits form a coherent group with the following common characteristics (from Groves et al., 1991): (i) they are epigenetic and structurally controlled, typically in late (or reworked earlier) shear/fault zones; (ii) they are 'gold-only' with high Au enrichment factors, significant enrichments in Ag, As, Sb and W, and low enrichments in Cu, Zn and Pb; (iii) alteration assemblages are characteristically enriched in C02, S, K (+Rb, Ba), with an overall volume increase being common; and (iv) lateral alteration zoning around quartz veins or shear zones is on the 0.1 to 10 m scale, whereas vertical zonation, where present, is on the >100 to 1000 m scale. The absence of significant vertical metal zonation and the consistent relationship between alteration mineralogy and metamorphic grade of wallrocks (Mueller and Groves, 1991; Witt 1991) imply fluid infiltration into, and mineralization within, heated wallrocks. Lode-gold mineralization in the Yilgarn Block was broadly coincident with late-Archaean metamorphism and granitoid magmatism, with most greenschisthosted deposits postdating peak metamorphism, whereas most amphibolite-hosted deposits were synmetamorphic (see Groves et al., 1991). In the ca. 2.70 Ga Norseman-Wiluna Belt, the emplacement of most intrusive bodies occurred at 2.69 to 2.66 Ga with peak metamorphism towards the end of this period (see McNaughton et al. 1990). The timing of lode-gold mineralization was ca. 2.63 Ga at Kambalda in the Norseman-Wiluna Belt (Clark et al. 1989), and at Griffin's Find in the Southern Cross Province (Barnicoat et al. 1991), where peak metamorphism was contemporaneous. On the mining camp scale in the NorsemanWiluna Belt, there is not an exact coincidence between the initial Pb isotopic compositions of ore fluid, as determined from the least-radiogenic Pb isotopic compositions of ore-related sulphides, and those for Geological Society of Australia Abstracts Number 32, Ballarat 1992

spatially-associated minor felsic intrusive rocks (Perring & McNaughton 1991). However, on a more regional scale (>104 km ), there is a gross similarity between the initial Pb isotopic compositions of regional granitoids and ore fluids for the lode-gold deposits, irrespective of host rock composition and metamorphic-grade setting of individual deposits. Furthermore, the regional granitoids show craton-scale systematic variations in initial Pb isotopic compositions, extrapolated to the time of mineralization, from north to south within the belt (McNaughton et al.1991), and reconnaissance data for syngenetic sulphide deposits and greenstone volcanic rocks suggest that the upper crustal rocks show a similar spatial variation in initial Pb isotopic ratios. Importantly, the lode-gold deposits show parallel spatial variations in the initial Pb isotopic ratios of their ore fluids, implicating a ubiquitous and dominant Pb component from mid- to upper-crustal sources. On the >100 km scale, ore fluid Pb is essentially homogeneous within the central zone of greenstone belts in any major portion of the Norseman-Wiluna Belt, but becomes more radiogenic towards some regional granitoid batholiths, implicating a greater Pb contribution from these batholiths or their source regions. Consideration of U/Pb and Th/U in the crustal source regions for ore fluid Pb indicates that there was a systematic northward increase in metamorphic grade due to a » 2 . 7 Ga metamorphic event in the sub-greenstone basement to the Norseman-Wiluna Belt and/or the crustal Pb sources had a complex pre-2.7 Ga age structure from north to south. The initial Pb isotopic data confirm a deep source for ore fluids which formed Archaean lode-gold deposits in the Yilgarn Block, and potentially offer a window into the nature of crustal source regions in the same way as initial isotopic ratios elucidate the nature of granitoid source regions.The observed Pb isotope structure of the Norseman-Wiluna Belt is similar to that recorded in younger convergent margin settings (e.g. Gunnesch et al. 1990), lending support to the convergent-margin tectonic model of Barley et al. (1990). 2

89 Acknowledgements 1990, Lead isotope variations across the Central Peruvian Andes. Econ. Geol., v. 85, p. 13841401. The authors acknowledge useful discussions with members of the Key Centre at UWA, and support of McNaughton, N.J., Cassidy, K.F., Dahl, N., de Laeter, J.R., Golding, S.D., Groves, D.I., Ho, the isotope facilities by ARC, MERIWA, UWA and S.E., Mueller, A.G., Perring, C.S. and Sang, Curtin University of Technology. J.H., 1991, The source of ore components in lode-gold deposits of the Yilgarn Block, Western References Australia: In Glover, J.E., and Ho, S.E. (eds), The Archaean: Terranes, Crustal Processes and Barley, M.E., Eisenlohr, B.N., Groves, D.I., Perring, Metallogeny, Geol. Dept & Univ. Extension, C.S. and Vearncombe, J.R., 1989, Late Archean Univ. West. Aust., Publ. 22, in press. convergent margin tectonics and gold McNaughton, N.J., Cassidy, K.F., Groves, D.I. and mineralization: a new look at the NorsemanPerring, C.S.,1990, Constraints on the genesis of Wiluna Belt, Western Australia: Geology, v. 17, primary gold deposits: Timing of mineralization: p. 826-829. In Ho, S.E., Groves, D.I., and Bennett, J.M. (eds), Barnicoat, A.C., Fare, R.J., Groves, D.I. and Gold Deposits of the Archaean Yilgarn Craton, McNaughton, N.J., 1991, Syn-metamorphic lodeWestern Australia: Nature, Genesis and gold deposits in high-grade Archean settings: Exploration Guides. Geol. Dept & Univ. Geology, in press. Extension, Univ. West. Aust. Publ. 20, p. 221Clark, M.E., Carmichael, D.M., Hodgson, C.J. and 225. Fu, M., 1989, Wall-rock alteration, Victory gold Mueller, A.G. and Groves, D.I., 1991, The mine, Kambalda, Western Australia: processes and classification of Western Australian greenstoneP-T-XC02 conditions of metasomatism: Econ. hosted gold deposits according to wallrockGeol. Monogr. 6, p. 445-459. alteration mineral assemblages: Ore Geology Groves, D.I., Barley, M.E., Cassidy, K.F., Fare, R.J., Reviews, 291-331. Hagemann, S.G., Ho, S.E., Hronsky, J.M.A., Perring, C.S.v.6,andp. McNaughton, N.J., 1991, The Mikucki, E.J., Mueller, A.G., McNaughton, NJ., relationship between Archaean gold mineralization Perring, C.S., Ridley, J.R. and Vearncombe, J.R., and spatially associated minor intrusions at the 1991, Sub-greenschist to granulite-hosted Kambalda and Norseman gold camps, Western Archaean lode-gold deposits of the Yilgarn Craton: Australia: lead isotope evidence: Mineral. a depositional continuum from deep-sourced in press. hydrothermal fluids in crustal-scale plumbing Witt,Deposita, W.K., 1991, Regional metamorphic controls on systems: In Glover, J.E., and Ho, S.E. (eds), The alteration associated with gold mineralization in Archaean: Terranes, Crustal Processes and the Eastern Goldfields Province, Western Metallogeny, Geol. Dept & Univ. Extension, Australia: implications for the timing and origin Univ. West. Aust., Publ. 22, in press. of Archean lode gold deposits: Geology, in press. Gunnesch, K.A., Baumann, A. and Gunnesch, M., f

POSTER SESSION A 3.35 STRUCTURAL CONTROLS, ALTERATION HISTORY AND GENESIS OF ARCHAEAN GOLD DEPOSITS AT CORINTHIA-HOPES HILL NEAR SOUTHERN CROSS, WESTERN AUSTRALIA Erik J.M. Bloem * J.R. Ridley ' D.I. Groves , T.J. Jackson & N.M. Edwards 1

1

1

1

2

2

Key Centre for Teaching and Research in Strategic Mineral Deposits , University of Western Australia, Nedlands, WA 6009 ^Broken Hill Metals N.L., P.O.Box 90, Southern Cross, WA 6426

The Corinthia and Hopes Hill lode-gold deposits, near Southern Cross in the Southern Cross Province, Yilgarn Block, Western Australia, produced about 2500 and 4500 kg Au, respectively. They are sited along the Fraser's-Corinthia shear-zone which follows the regional granitoid-greenstone contact north of Geological Society of Australia Abstracts Number 32, Ballarat 1992

Southern Cross and trends about 320° for 30 km. The mineralized zone is located along and adjacent to a lithological contact. The host rocks to the western side of the zone consist of tremolite-chlorite-talc schists, after komatiitic ultramafic rocks, and mafic to ultramafic amphibolites, consisting of magnesio- and

90 actinolitic hornblende and plagioclase (An37-59%). To the east, adjacent to the regional granitoid, the host rocks are biotite-muscovite-chlorite-quartz schists. Whole-rock and trace-element studies are in progress to determine the parentage of these micaceous schists. At both deposits, mineralization is sited in a wide ductile-brittle deformation zone. The rocks are strongly foliated and in part mylonitic. The foliation strikes parallel to the deformation zone. Folded quartz veins, both sub-horizontally and sub-vertically boudinaged quartz-veins, boudinaged banded iron formation (BIF) and boudinaged aplitic dikes indicate a strong flattening component perpendicular to the granitoidgreenstone boundary. The geometries of tight to isoclinal folds, and crenulation of the foliated biotitemuscovite-chlorite-quartz schists, also indicate late shortening perpendicular to the granitoid-greenstone contact. The strong flattening component is possibly related to syn-tectonic diapiric intrusion of the surrounding granitoids. Despite the dominant flattening, rotated porphyroblasts and a displaced aplite dike at Corinthia show an overall sinistral movement on the ductile-brittle deformation-zone. The mineral assemblages indicate that the regional metamorphic grade was low- to mid- amphibolite facies, in agreement with the studies of Ahmat (1986). In particular, amphibole-plagioclase thermometry in mafic amphibolites yields temperatures of 600°C (±75°), using the calibration of Blundy and Holland (1990), and garnet-biotite assemblages in biotitemuscovite-chlorite-quartz schists suggest temperatures of 580°C (±25°), using the calibration of Hodges & Spear (1982), for peak metamorphism. Three types of quartz veins have been recognized: non-mineralized, boudinaged and folded quartz veins, non-mineralized, non-deformed, foliation-parallel quartz veins and mineralized quartz-pyritepyrrhotiteichalcopyrite iarsenopyrite veins. The non-mineralized, boudinaged and folded quartz veins (up to 20 cm thick) that are restricted to amphibolites and tremolite-chlorite-talc schists usually display an inner alteration halo of apatite or diopside and calcite, and an outer alteration halo consisting of biotite, chlorite and pyrrhotite which are all locally overgrown by tschermakitic or actinolitic hornblende. Some scheelite occurs parallel to the main foliation and, in places, is present at the margin of the quartz veins. Primary fluid inclusions from these veins, with a degree of filling ranging from 0.4 to 0.9, contain carbonic fluids with Xch4 up to 0.8 (Bloem & Brown, 1991). Isochores for the mixed CO2-CH4 fluids yield pressures of 3.5-4.5 kbars (Bloem & Brown, 1991), assuming their trapping during peak metamorphism at 580°-600°. The non-mineralized, non-deformed, foliationparallel quartz veins (0.5 to 10 m wide) have rims of actinolitic hornblende and some carry minor amounts Geological Society of Australia Abstracts Number 32, Ballarat 1992

of molybdenite. These foliation-parallel veins have a close structural relationship to the boudinaged and folded quartz veins, but are interpreted to be slightly younger. The overprinting of the strong foliation by the alteration assemblages together with the close relationship between foliation and boudinaged and folded quartz veins, indicates that veining and associated alteration took place late in the regional metamorphic event. Gold mineralization is closely associated with the quartz-pyrite-pyrrhotitelchalcopyrite ±arsenopyrite veins that trend parallel to the shear-zone, with minor mineralization related to pyrite-filled fractures. These veins and fractures cross-cut earlier non-mineralized, sulphide poor veins in the biotite-muscovite-chloritequartz schists, but appear to have an axial-planar relationship to folds in the schists, indicating that they are broadly synchronous with the flattening deformation. In contrast to the fluid inclusions in the non-mineralized, boudinaged and folded quartz veins in amphibolites, fluid inclusions from the mineralized veins commonly contain aqueous inclusions with moderate to high salinities (Bloem & Brown, 1991). The structural relationship between the nonmineralized, boudinaged and folded quartz veins in amphibolites and the mineralized quartz-pyritepyrrhotite±chalcopyrite ±arsenopyrite veins is still unresolved, but the latter appear to be of similar age as the non-mineralized, foliation-parallel quartz veins described above. These reconnaissance studies indicate that gold mineralization was broadly coincident with flattening and minor strike-slip deformation in a major deformation zone along a granitoid-greenstone contact. Metasomatic assemblages in gold-related wallrock alteration are broadly compatible with peak metamorphic assemblages in host schists and amphibolites, although they are most likely slightly retrograde. Acknowledgements Broken Hill Metals N.L. is thanked for their financial support and access to mine data. E.B. is the recipient of OPRS and UWA scholarships and the Dr. Schurmann Fund for a field work supporting grant. The study is supported by a MERIWA grant. References Ahmat A.L., 1986. Metamorphic patterns in the greenstone belts of the Southern Cross Province, Western Australia. Geol. Surv. West. Aust., Prof. Paper 19,1-21. Bloem E.J.M. & Brown P.E., In press. Fluid Inclusion evidence from amphibolite facies lode gold deposits: variations on the greenschist theme. In: Geological Society of America Abstracts with Programs, Vol. 25, no. 5, sept. 1991.

91 Blundy J.D. & Holland T.J.B., 1990. Calcic amphibole equilibria and a new amphiboleplagioclase geothermometer. Contrib. Mineral. Petrol 104, 208-224. Hodges K.V. & Spear F.S., 1982. Geothermometry, A 3.36

geobarometry and the A12Si05 triple point at Mt. Moosilauke, New Hampshire. American Mineralogist, Vol. 67, 1118-1134.

GEOCHEMISTRY OF BLACK SLATES AND ITS RELATIONSHIP WITH GOLD MINERALIZATION IN CHEWTON, VICTORIA, AUSTRALIA Z. Gao* and T.A.P. Kwak Department of Geology, La Trobe University, Bundoora, Vic 3083

Gold-bearing quartz veins in the Chewton area of Central Victoria, is hosted by the Lower Ordovician turbidite sequence composed of grey to black slates, sandstones and greywackes. At the Wattle Gully mine where native gold occurs in association with sphalerite, galena, chalcopyrite, arsenopyrite, pyrite, ankerite and dolomite, gold values are found to be the highest where the veins cross-cut the black slates. The black slates have undergone varying degrees of hydrothermal alterations. The unaltered or fresh slates

which occur away from the gold-bearing veins are composed primarily of muscovite, quartz, minor chlorite, albite and pyrite. The alteration assemblage (c) in the slightly altered slates include siderite, and pyrite, whilst the highly altered slates (Assembladge a) are composed of adularia, muscovite, chlorite, ankerite, arsenopyrite and pyrite. The Alteration assemblages is shown below, however, all phases are not always present as shown, particularly assemblage a.

DDISTANCE FROM VEINS

a

Siderite Ankerite Adularia Muscovite Chlorite Pyrite Asenopyrite Gold Sphalerite Galena Chalcopyrite

b ••

c mmm

— —

(Not always observed)

— —

-

(Very close to veins)

0 ~10cm

(Only in one sample) (Only in one sample) (Only in one sample) , (Minor, in sphalerite or in carbonate porphyblasts) -50m -5 m

Geochemical analyses of the black slates show decrease in the concentration of Si02, Na20, FeO and MnO, and an increase in AI2O3, Fe203, K2O, CO2, S, As, Ba, Rb, Sc, Cr and Au concentrations in the altered samples. Au is found to correlate positively with AI2O3, Fe203, S, K2O, and As, and negatively with Si02The increases in K2O and lithophile trace elements and the loss in Na20 are consistent with the Geological Society of Australia Abstracts Number 32, Ballarat 1992

development of adularia or muscovite. The increase of S and CO2 are explained as the introduction of hydrothermal fluid and fluid/rock interaction products. The good correlation between Au and the major and some trace elements indicates that these elements can be used in the Au exploration in the Ordovician black slates in the study area and possibly in the BendigoBallarat slate belt.

92 A 3.37

EXPLORATION FOR SAPPHIRE IN THE GLEN INNES / INVERELL AREA.. P G L Harlow

Ipswich Grammar School, Ipswich This paper touches on the history of mining and References discusses in detail the past, present, and suggested future, exploration techniques, and the models upon Cant, Mrs T., Photograph. 1915. which they were based, for sapphire in the Glen Innes Cas, R.A.F., and Wright, . V., 1987. Volcanic Successions - Modern and Ancient. Allen & / Inverell area. Unwin, Sydney. The basaltic model suggested by numerous authors Coenraads, R.R., 1988. New England Orogen ( eg. MacNevin, 1972 ) for the origin of the sapphire Tectonics and Metallogenesis, ed J.D. Kleeman. is discussed along with the exploration techniques that University of New England, Australia. derived from it. Coenraads, R.R., Sutherland, F. L., and Kinney, The more recent acidic volcaniclastic models P.D., 1990. Mineralogical Magazine 54, 1, 1990. proposed by other authors (eg. Lishmund and Oakes, Lishmund, S.R. and Oakes, G.M., 1983. New South 1983, and Pecover, 1987 ) are discussed and the Wales Geological Survey - Quarterly Notes 53, 23 -27. exploration techniques that have derived from them are MacNevin, A.A., 1972. New South Wales mentioned. Geological Survey - Records 14 (1), 19 - 35. The author's (Harlow, 1990) volcaniclastic model for the deposition of the sapphire is discussed. The Mumme, I.A., 1988. The World of Sapphires. Mumme, Sydney. New south Wales Mining consequences of this model in terms of the types of Reports. geophysical and field sampling techniques that may be NewWardens South Wales Geological Survey Reports implemented are discussed in detail. Further the Various 1900-1989. application of this model to the extraction and Oilier, C.D., and Schmidt, P.W., 1988. New England treatment of sapphire bearing material and the location Orogen Tectonics and Metallogenesis. ed. J.D. of prospective areas is covered. Kleeman. University of New England, Australia. Finally the similarities of volcaniclastic breccia Pecover, S.R., 1987. New South Wales Geological sapphire deposits to volcaniclastic diamond deposits is Survey - Report GS 1987 / 058 Stellar Mining N.L., 1971. Quarterly Reports, mentioned. EL372, Burraga area (unpubl.) (GS 1971 / 1972). Young, P., 1991. Personal Communication.

A 3.38

BALLARAT WEST AREA F L Hunt

PO Box 203, Eltharn, VIC, 3095 In an informal report of May 1983, F.L. Hunt and D.M. Ransom described to Directors of Eastern Copper Mines NL several areas of exploration at Ballarat West. The author has considerably extended the concepts expressed in this report. It is shown that a discordant body of quartz and sulphide intermixed with slates and sandstones appears to exist. The recorded body width typically exceeds 8 metres, and a volume exceeding 650,000 tonnes is probable although never drilled. Three drawings are displayed, allowing examination of the above, and placing this body in the context of past gold mining generally at Ballarat West Geological Society of Australia Abstracts Number 32, Ballarat 1992

- both alluvial and quartz. Lessons from past mining history are important for future development. These lessons can be derived from some 60 exhibits relating to gold production from Ballarat West to be displayed at the Fine Art Gallery, Ballarat, for 5 weeks commencing about the date this Convention opens.

93

A 3.39

ON THE SEDIMENTATION-REWORKING GENESIS OF SOME STRATIFORM COPPER DEPOSITS Renmin Hua

Department of Earth Sciences Nanjing University, Nanjing 210008, China Taking the Dongchuan-type copper deposit, Yunnan Province, China as an example, the author proposes a "sedimentation-reworking" origin for some sediment hosted stratiform copper deposits, especially those occurring in the carbonate rocks (mainly dolomite). According to the new idea, orebodies were not directly deposited in the dolomite where they are hosted. Instead, copper was preliminarily concentrated in the detrital rocks beneath or nearby the host rock. During or after diagenesis, copper was mobilized and leached by

A 3.40

hydrothermal solutions derived from the interstitial water of sediments under the high geothermal gradient of rift environment. Copper was thus transported from the source bed to the (algal) dolomite where sulfur was produced by the reduction of sulfates. The copper sulfides (mainly pyrite) by Clbearine solutions. It is suggested that the CI orebodies at Mount Isa deposit, the ores in KatherineDarwin area, and those at San Angelo,Texas, are also example of the sedimentation-reworking genesis.

IRON FORMATIONS, CHEMICAL SEDIMENTS AND BASE METAL MINERALISATION AT BROKEN HILL, NEW SOUTH WALES W.R. Leyh, D.F. Larsen and I.D. Oppy Pasminco Miningt Broken Hill

In the Broken Hill Block thick sequences of highly variable and deformed metasediments, quartzofeldspathic gneisses and amphibolites contain many intercalations of lode rocks that host a broad spectrum of economic and sub-economic Pb, Ag, Zn, W, Cu, Co and Au mineralisation. Four general associations of stratiform base metal mineralisation are here recognised (compare with Barnes, 1988). They are: 1. Quartz-magnetite/quartz-pyrite iron formations (Sisters type). 2. Quartz-gahnite/garnet quartzite (Broken Hill type). 3. Calc-silicate/amphibolite (Corruga type). 4. Layered calc-silicate (Ettlewood type). It is suggested that these associations are linked genetically, based upon a number of common features including the presence of: (a) iron formations, (b) distinctive lode rocks, and (c) related alteration assemblages (Figure 1). Examples of the various associations occur in a number of different stratigraphic positions within the Willyama Supergroup although the majority of occurrences are restricted to the Thackaringa Group and Broken Hill Group (Figure 2a). The stratiform Geological Society of Australia Abstracts Number 32, Ballarat 1992

mineralisation has a strong spatial association with a range of magnetite bearing metasediments. Some metasediments are closely associated with or grade into at least two types of predominantly oxide to oxidesilicate facies iron formation. These are locally termed quartz- magnetite (QM) and banded iron formation (BIF) (Richards, 1963; Stanton 1972,1976). The iron formations are in turn closely associated with a wide range of compositionally variable but distinctive lode rocks including quartz-gahnite and garnet quartzite and tourmaline rich rocks. Many of these are interpreted as chemical sediments and have been mapped as subfacies of quartz magnetite iron formation (Leyh and Larsen, 1983). Although closely spatially related and chemically very similar to the lode rocks hosting the 300 million tonnes Broken Hill orebodies, no direct facies relationship of the BIF to lode rocks hosting ore has yet been observed (Figure 2b). The alteration zones are enriched in one or more of the following minerals; chlorite, biotite, quartz, garnet, iron sulphide and magnetite (Leyh and Larsen, 1983). Some of the minerals within these zones occur in a number of diverse forms and the zones including the chemical sediments occur in a wide range of country rocks. An exhalative and/or sub-sea floor chemical origin for the lode rocks, sulphide

94 mineralisation and iron formations is favoured on the basis of: 1. General concordance with lithological layering and presence of internal layering. 2. Stacking of compositionally distinctive elongate, tabular ore lenses. 3. Distinctive mineralogy and chemistry. 4. Intimate association of sulphide, lode rock, iron formations and magnetite bearing metasediments. 5. Often sharply defined lateral and vertical variability of the iron formations and lode rock sub-facies at all scales. 6. Presence of distinctive enveloping alteration zones at some deposits. A comparison of host rock sequences with iron formation, lode indicators and associated mineralisation suggests major differences in the overall depositional environment of the base metal deposits. However, mineralisation processes are clearly related because of the links established through the iron formation/ chemical sediment model. This model incorporates a broad spectrum of mineralisation from pyritic Cu with minor Pb + Zn ± Co in the lowest unit of the Mulculca Formation and overlying Thackaringa Group through to Pb + Ag + Zn ± W mineralisation at the top of the Broken Hill Group (Figure 2a). Minor Au occurrences are also known throughout the sequence. Because of their wide regional distribution in several separate stratigraphic positions the iron formations, related lode indicator

Geological Society of Australia Abstracts Number 32, Ballarat 1992

rocks and intimately associated sulphides appear to have formed at various stages over a protracted time interval throughout the period of deposition of Willyama Supergroup as defined by the New South Wales Geological Survey (Stevens et. al. [1980], Willis et. al. [1983]). This focuses attention on additional exploration targets for a wider range of commodities lower down in the Willyama Supergroup apart from the 'typical' Broken Hill types which have been much explored for in the past. References Barnes, R.G., 1988, Geological Survey of New South Wales, Bull. 32 (1, 2). Leyh, W.R. and Larsen, D.F., 1983, in Broken Hill Conference, 1983, AusJMM - Conference Series 12:133-156. Richards, S.M., 1963, University of New England Ph.D. Thesis (unpub). Stanton, R.L., 1972, Economic Geology, 67:11281145. Stanton, R.L., 1976, Inst. Min. Metall. Transactions, B33-B46. Stevens, B.P.M., Stroud, W.L., Willis, I.L., Bradley, G.M., Brown, R.E., and Barnes, R.G., 1980, Geological Survey of New South Wales, Records 20 (l):9-32. Willis, I.L., 1989, Broken Hill Stratigraphic Map, Geological Survey of New South Wales. Willis, I.L., Brown, R.E., Stroud, W.I., and Stevens, B.P.J., 1983, Jour. Geol. Soc. Aust., 30:195-224.

95 F I G U R E ASSOCIATIONS

-

STRATIFORM

X

MINERALISATION

-

BROKEN

HILL

BLOCK

ASSOCIATION

IRON FORMATION FACIES

LODE TYPES

ALTERATION

HOST LITHOLOGIES

EXAMPLES

MINERALISATION

Sisters Type

Oxide: qtz-magnetite 'Silicate: qtz-chlorite qtz-garnet qtz-amphibole Sulphide: qtz-pyrite qtz-pyrite-po massive base metal sulphides

- garnet quartzite - quartz gahnite - blue quartz - tourmaline rich rocks

- chlorite - biotite - sericite

Variable, includes: metasediments, quartzofeldspathic (albitic) gneiss, basic gneiss. Diss, magnetite common.

1. Tors Tank 2. Iron Blow 3. Copper King 4. Pinnacles 5. Razorback 6. Sisters 7. Copper Blow 8. Bald Hill 9. Pyrite Hill

Py,Cu,(Co,Mo) Py.Cu,(Zn,Pb,Au) Py.Cu Py,Pb,Zn,Ag,(Co) Py.(Cu) Py.Cu,Co Py.Cu,Au Py.Cu,Co Py.Co

Broken Hill Oxide-Silicate: BIF (laminated qtz-mag-garType apatite) Silicate : BIF (laminated qtz-gar±mag)

-garnet quartzite - quartz gahnite - garnet banding - blue quartz - lode pegmatite - tourmaline rich rocks

- garnet - quartz - sericite - biotite

Variable, includes: metasediments, quartzofeldspathic (Potosi) gneiss, basic gneiss. Diss, magnetite common but variable.

10. Numerous Pb,Zn,Ag,(Cu,W,Au) including: with Po,Py Allendale, Southern Cross, Great Western, Little Broken Hill, Windy Ridge, etc. 11. Broken Hill

Corruga Type

Rare qtz-magnetite with calc-silicate

- calc-silicate breccia - garnet quartzite - quartz gahnite - blue quartz - lode pegmatite - tourmaline rich rocks

- siln. - quartz veining - biotite - garnet - chlorite - epidote

basic gneiss (garnetiferous), feldspathic gneiss, metasediments

12. Corruga 13. Esmeralda 14. Maybe11 15. Yuba North

Ettlewood Type

Rare layered qtz • magnetite in calc-si1icate

- calc-silicate - laminated graphitic siltstone - blue quartz - tourmaline rich rocks

- local skarns

Variable, includes: metasediments, basic gneiss, feldspathic gneiss

16. Lakes Nob W,Zn,(Pb.Ag,Cu) 17. Bomangaldy Hill 18. Bald Hill

|AAA|

Amphibolite

|00°|

Spotted psammopelite Pelite(disseminated magnetite)

Generolised strotigrophic sequence of the Broken Hill Block (after Willis, 1989.) | I -18 | Strotigrophic location of mineral occurences listed in Figure I.

[*»*[

Geological Society of Australia Abstracts Number 32, Ballarat 1992

Diogrammotic strotigrophic column of the upper part

Psommite

of the Broken Hill Group showing distribution of

Undifferentiated metosediments

and Banded Iron Formation.

Banded Iron Formation

W,Zn,(Pb,Ag,Cu)

Broken Hit! orebodies, (e g ( b ) = B lode), lode rocks

96 A 3.41

THE CHARACTERISTICS OF THE FLUID INCLUSION IN MINEROGENETIC QUARTZ FOR SOME TYPES OF GOLD DEPOSITS IN CHINA Li Li*, Zheng Chao, Yu Zhikai and Mao Dongqing

Shenyang Institute of Gold Technology, P. R. China It's a fresh topic to do research on the fluid produced in this stage only has little native gold. 2. The quartz produced in the middle stage of the inclusions of gold deposits in china. We have got some succeed in this area. The research has been done mineralisation period. The quartz is grey or whiteto determine the minerogenetic temperature and grey; not very much clear; the grain size varies is 0.1pressure of the Gold deposits and consist of the fluid 5.5 mm. It is stringerly inserted in the quartz produced inclusion in some famous gold minerogenetic regions, in the early stage or closes the quartz. The paragentic for example, Liaodong, Western Henan (Xiao qin ling) mineral combination are mainly fine pyrite, and Eastern Shandong of China. It is useful to chalcopyrite, sphalerite, calena etc. In some gold determine the formation of the deposits, the fields, such as Sanshandao in the area, arsenopyrite is minerogenetic material resources and the mineralized found sometimes. fluid of gold deposits. Limited by instruments and 3. The quartz produced in the late stage of the techniques, the research is not popular in china. mineralisation period. It's colourless clear, fine Fluid inclusion in quartz, which has close relation grained. The grain size varies in 0.01-0.06 mm, with mineralisation in quartz vein and altered rock mainly. It is paragenetic with carbonates and a little types of gold deposits, is mainly studied in this paper. sulfide. The physical-chemical environment where gold is It is not all equal in different gold fields of the dissolved, removed and deposited is studied from the characteristics of fluid inclusions in quartz which has research of the fluid inclusion. And then the close relationship with mineralisation in the area. For mineralisation principle can be drawn. example, in ling long gold field, the fluid inclusions Eastern Shandong is one of the very famous gold in the quartz which produced in the early stage include minerogenetic regions, more than 50 gold deposits air-liquid facies mainly; next is fluid inclusion of have been found in the region, and more than 90 liquid facies; the inclusion of CO2 is rarely. The ratio percent of them are rich-gold deposits which include of air to liquid in volume varies in 20-40%. The gold-quartz deposits (58%), altered rock of gold inclusion sizes vary in 2.5-10% mainly; some of them deposits (29%) skarn gold deposits (9%) and gold are more than 10 pi big. There are a good number of placer deposits (4%). there are old layer, complex inclusions in the quartz; the arrangement is irregularly. geologic structure, frequently vulcanism and tensive The shapes of the inclusion are long circle or metamorphism in the area, which are good conditions elliptical. The homogeneous temperature varies in for gold re-movement and mineralisation, the types of between 335-350°C. quartz in the gold deposits include mainly all kinds of The inclusions in quartz produced in main quartz, which present in drusy block, chalcedony and mineralisation period present in shape of elliptical opal and so on, Drusy quartz is mainly found in circle mainly. Some of them are long prism or minus crystal hole. crystal. The grain size not equal usually varies in 5In quartz vein gold deposits, most quartz present in 15|LI. The great grain size is more than 50|i big. The veins or crystalline blocks; some present in drusy, main facies are liquid-air. There are not only clear chalcedony is rarely met The crystal forms of quartz liquid facies. the percentage of inclusion of C02 are mainly hexagonal prism, plus rhombohedron and increases with apparently, which reaches 10%. Ratio miners rhombohedron; triangle can be met as well. All of the air to liquid in volume varies in 25-50%. The quartz in the gold deposit is produced in multirange homogeneous temperature varies in the rang of 280and multistage, the quartz produced in different stages 315°C mainly. has different crystal forms; grain size; mineral There are not many inclusions in quartz produced combinations and relationships with gold. in the late stage. And most the of them are liquid 1. The quartz produced in the early stage of the facies. There are few liquid-air facies inclusions in the mineralisation period^re milk white coloured, clear, stage. And no inclusion of CO2 is found in the stage. massive structured; the grain size varies in 5-45 mm; The grain size is not more than 3%. The recrystallised quartz can be met sometimes. Usually, homogeneous temperature varies in 220-280°C. From quartz presents in great vein (different in altered rock all above as we know that the variation of the stages deposit). The Paragenetic mineral combination are in the main mineralisation period can be drawn from pyrite, wolframite scheelite, siderite etc. The quartz the characteristics of the inclusions. From the begin to Geological Society of Australia Abstracts Number 32, Ballarat 1992

97 the end of the period. The percentage of the inclusions of liquid facies increases obviously, the rate of air to liquid in volume decreases gradually. And the grain size of the inclusions has an increasing trend. In Jiaodong gold field, except H2O , C02^2 H2,CH ,Ca2,Mg2,Cr,F-,HC0 -,S04 -, there are F e , C u , P b , Zn ,in the inclusions as well. The inclusions composition in the quartz of the field shows that the percentage of H2O is much more than that of CO2, which indicates that the minerogenetic material is migrated in liquid facies. And the infiltration and substitution take place under the same conditions. The percentage of N2 is low, while the ratio of CO2+H2+CH4 to N2 is high. It indicates the high percentage of CO2 and CH4. And it indicates the change of the physical-chemical characteristics of the minerogenetic fluid. The ratio N a / K is low, which indicates the same geological environment. The percentage of CI" is much more than that of F", and there is a high percentage of SO4 " at the same time, which shows in some sense that there is a quantity of mineralized agents in the fluid. It makes gold dissolved, removed, and deposited. It can be drawn from above that gold may be migrated in the forms of AuFeCU- AuAlCU [Au(S203)2] " and [Au(HS)2]~. Xiaoqinling is another famous gold minerogenetic region in China. The mineralized type is Au-sulfidequartz vein. More than a thousand Au-quartz veins have been found around granite erupted in Yanshan movement. The quartz present in vein which are limited by fault structures. The facies of the inclusion in the quarts of the region are air, liquid, air-liquid, multifacies and inclusion of CO2. Three of them, multi facies, CO2 facies and air-liquid facies, has a close relationship with mineralization. Their grain size is mostly great, colour is less and clear. The shapes are long-circle, )

4

2+

+

2

3

2+

2+

2+

+

2

2

A 3.42

long prism, and so on. Dongchuang gold deposit is located in the region. The homogeneous temperature of the inclusions in the quartz, which have a closely relationship with main mineralisation period, is limited to 200-260°C. The compositions of the inclusions produced in minerogenetic period shows that there is high percentage of CO2 ,CH4, K+, Na+ H2O, and SO4 etc. Which indicates that gold is removed in fluid. The big ratio of N a + / K and Cl'/F", and the high percentage of Na and CI", and multi-facies inclusion indicates that the minerogenetic fluid is a weak alkaline clorinate-bicarbonate liquid which has a high percentage of Na and K ,but it has a low percentage ofCa + and Mg .According to Moixinc, a Russian geologist, this type of fluid is found in different types of quartz vein deposits. In the fluid, gold may be removed in the forms of [ AUCI4 ]", [ AuS2 ]', etc. Above all, some types of gold deposits in china have some same characteristics of fluid inclusion in quartz produced in minerogenetic period. They are: 1. The main face of the fluid in conclusion is airliquid facies. 2. The grain size of the inclusions is great mostly. There is big ratio of air to liquid, which usually reaches 10-40% in volume. Heated, they usual change into air facies, a little of liquid facies. 3. The homogeneous temperature is concentration. It varies between 200-400°C. 4. The percentage of H2O, CO2, Na , CI' in the fluid is high, the K+ and F" is low. Usually there is some of SO4 ". It indicates that minerogenetic material is removed in liquid to be carbonates of weak alkaline. Gold is removed by complex of CI" and S. Gold deposit are formed in appropriate conditions. 2

+

+

+

2

+

2+

+

2

NUGGET FACTOR-GREEN FACTOR IN PLACER GOLD EVALUATION: THE AMERICAS* PERSPECTIVE ON COARSE GOLD TAILS AND FINE GOLD TAILINGS AND AUSTRALIA'S TALES OF GROWTH AND MOBILITY. Michael W.Milner 182 Gough Ave., Toronto, Canada M4K 3P1

Large and small particles of gold occur in both hypogene and supergene facies of mineralized zones. These contribute in the surficial environment to placers primarily by mass wasting and secondarily by fluvial processes. Basal gravels and bedrock crevices of narrow, proximal montane placers preferentially retain coarse Geological Society of Australia Abstracts Number 32, Ballarat 1992

gold with sorting and preferential downstream migration of fine gold occurring by during fluvial transport. Primary paystreaks produced during entrenchment of low density, high relief drainage remain intact, during landscape maturation, as relict placer paystreaks, in valley centre positions. Recycling and either concentration, remobilization or

98 dispersion can occur during fluvial rejuvenation, depending on the depth of entrenchment, the gradient of the stream, and the amount of storage on slopes and in terraces, to produce intervals of discontinuity in pay streaks. Local variation in grade along basal paystreaks is produced by inhomogenieties in the bedrock strath and in channel and gravel characteristics which preferentially trap placer gold. Fluvial concentrations of well sorted, fine gold within the gravel section in more distal reaches of the placer occurs near the paystreak with sorting or preferential entrainment of fine gold particles at the youthful valley stage or during sporadic scour in the mature valley paystreak. These variations involve different principles relevant to the proximity of intermediate reaches and the grade of the distal reaches of the paystreak. "Nugget factor" incorporates the uncertainty of placer evaluation, pertaining to both coarse gold and patchy concentration of coarser gold in basal placers. It makes the definition of placer ore zones difficult if not impossible in the reaches near the proximal end and those of intervals of inhomogeneous bedrock. Granulometry of small samples in exploration and evaluation of montane placers can aid in identifying paystreaks and marginal facies that can be used to determine ore and to predict metallurgical recovery. High latitude, high relief montane placers in the Americas have coarse mean sizes, high degree of sorting and coarse tails. Low latitude, low relief placers in the Americas are characterised by fine gold and more homogeneous concentrations characteristic of jungle placers where lode and lateritic facies are concentrated by residual processes with minor fluvial sorting, produce homogeneous zones amenable to drill evaluation. Relatively low latitude, low relief eluvial and alluvial placers in Australia are characterised by large nuggets, disseminated grains and "dissolved" paleoplacers that may reflect optimum geomorphic and geochemical conditions for the growth of nuggets by descending solution in the supergene zone, the ascending remobilization of gold in the zone of lateritization, and the horizontal remobilization of gold in paleochannels. Recycling and migration of gold in the physical

Geological Society of Australia Abstracts Number 32, Ballarat 1992

state is significant in that eluvial placers include characteristically worn placer forms that likely represent long term lag and geomorphic recycling of some grains. Biological transport upwards by ants and termites to the illuvial zone in residual placers and downwards by gravity, inflow and ultimately piping, through deep openings related to taproots, and deep soil structure are predictable. "Green factor" encompass the costs of mining and recovery as it relates to acceptable environmental practice. It is a matrix of present and possible future mining methods, land use, potential by-product clay and aggregate, and water management for mining and post mining use. Cumulative effects of placer mining may be environmentally positive and have to be anticipated early in mine planning. Mining methods are in part controlled by the certainty of grade and the depth of overburden. Open pit methods for deep overburden and strip methods for shallow cover have both different costs and perceptions of environmental impact. These costs vary greatly if late decisions are made to mine beneath tailings or spoil piles. Reprocessing of tailings is similarly dependant on commitments to land reclamation. The combination of the excessive clays of "low relief residual placers" and the poorly sorted, fine gold population present difficult conditions for normal, gravity recovery; tailings losses are great and reworking of the tailings is the rule. Blending auriferous tailings with ore to produce enhances liberation and recoveries is also a consideration in reclamation plans. Auriferous tailings, in places reflecting losses in excess of 50%, may be free of the initial recovery problems and amenable to both drill evaluation and extraction by either old or new technology both because of the homogenization produced by handling during the first attempt at exploitation and the diagenetic effects in the tailings. In the ideal state of strong nugget factor and weak green factors strip mine testing becomes an exploration and evaluation method; the planned environmental impact is positive and the effected area is returned to the natural or industrial system with minimum effort

99 A 3.43

GOLD MINERALISATION IN THE STAWELL ZONE, WESTERN VICTORIAIMPLICATIONS FOR EXPLORATION P.J. O'Shea AND K. Inan Geological Survey of Victoria, Melbourne

The Stawell zone in western Victoria is a structural zone bounded by major thrusts, extending from the western side of the Grampians to the Avoca Fault zone in the east. Primary gold mineralisation is hosted by Cambrian turbidites and volcaniclastics, with minor amounts hosted by Devonian granites. Mineralisation is sulphide-rich, and located in quartz vein systems which are structurally controlled by northeast striking east vergent thrusts developed throughout the zone. A model for primary gold mineralisation is proposed which involves the leaching of gold and other metals from volcanics, together with quartz and sulphur from the turbidites, by hydrothermal fluids sweated out of the turbidite pile during regional metamorphism. Subsequent granite intrusion is thought to have provided a high thermal gradient which led to metamorphic/magmatic fluid mixing, boiling of gold rich fluids and precipitation of ore grade concentrations A 3.44

of gold in suitable structural traps. Based on the above model a number of exploration criteria have been identified as important for defining primary gold mineralisation targets in the Stawell zone. These include definition of reverse fault zones, lineament intersections, granite proximity, presence of volcanics and favourable lithologies. An integrated study of geology, geophysics and Landsat has identified sixteen target areas outside of existing goldfields. References Inan, K., 1990 Ararat 1:100 000 map. Economic geology notes. Geological Survey of Victoria Unpublished Report 1990/45, 81 pp. Wilson, C.J.L., Thomas M. Will, Cayley, R.A. and Chen, S. Geological framework and tectonic evolution in Western Victoria, Australia. In press.

REGIONAL GEOPHYSICS OF THE MATHINNA - ALBERTON GOLDFIELD, NORTHEAST TASMANIA M.J.Roach

Centre For Ore Deposit And Exploration Studies, The University of Tasmania. Gold mineralisation in the Mathinna - Alberton to gold occurrences. An interpretation based on a Goldfield occurs within quartz veins which crosscut combination of gravity and magnetic data indicates the the Siluro-Devonian Mathinna Beds turbidite sequence. following: The distribution of gold occurrences defines a clear 1. The low density, non-magnetic granitic rocks of NNW trending lineation which passes through the the Blue Tier and Scottsdale Batholiths underly the centre of a narrow zone of sediments separating the entire goldfield at a maximum depth of approximately Devonian Scottsdale and Blue Tier Batholiths. 4 km. Mining in the region commenced with the 2. Subsurface sheet-like bodies of dense, magnetic discovery of alluvial gold in the 1850's and proceeded granodiorite, similar to the exposed Pyengana Pluton, sporadically through until the 1930's. The majority of parallel the line of gold deposits. These bodies have reefs were rich in gold, but only thin and of limited thicknesses between 1 and 2 km and intrude to within strike extent. The largest mine in the field was the a few hundred metres of the surface at a number of New Golden Gate Mine which produced 7895 kg of locations. gold form ore with an average grade of 25 g/t 3. The concentration of gold deposits near the town (Williams et al., 1989). Little modern systematic of Mathinna occurs near the intersection of major exploration has been conducted in Mathinna - Alberton NNW and EW striking structures. area Structural features are the dominant control on the Regional geophysical data was used to define the localisation of gold mineralisation within the gross structure of the goldfield and in particular, the Mathinna Alberton area. The underlying granitoid form of the adjacent granitoids and their relationships intrusives however provide a possible heat source to Geological Society of Australia Abstracts Number 32, Ballarat 1992

100 drive the hydrothermal systems which deposited the gold and also perhaps the addition of magmatic fluids. Williams, E. et al., 1989, Mid Palaeozoic deformation, Granitoids and Ore Deposits, in Fluid inclusion and isotopic studies are in progress to Geology and Mineral Resources of Tasmania, ed. test these ideas. Burrett C.F. and Martin E.L., G.S.A. Special Publication No. 15. References A 3.45

PLATINUM-GROUP ELEMENTS IN THE GREAT SERPENTINE BELT OF NEW SOUTH WALES: A PRELIMINARY STUDY K. Yang * and P.K. Seccombe

Department of Geology, The University of Newcastle, NSW 2308, Australia The Great Serpentine Belt in the New England within chromite, (iii) associated with silicate Fold Belt delineates the Peel Fault, a major Paleozoic inclusions in chromite and (iv) within interstitial suture separating a subduction sequence of the Central silicates. The PGE level of harzburgite is the lowest of the Block to the east from a fore-arc basin sequence of the Tamworth Belt to the west. The rock association in silicate rocks, and their patterns exhibit a small the belt comprises a dismembered ophiolite, differentiation favouring enrichment of IPGE with represented by a lower sequence of tectonised respect to PPGE. This differentiation, which is quite harzburgite and a upper magmatic sequence comprising distinct from that observed in the chromitites and the overlying rocks of the magmatic sequence, implies ultramafic cumulate, gabbro, dolerite and basalt. Whole rock analyses reveal that chromitites in the that the IPGE are more inert than PPGE during partial ophiolitic association are the main host for platinum melting of the upper mantle, due to the fact that either group elements (PGE), with the level of all six IPGE are more compatible in mafic silicates (Naldrett elements (ranging from hundreds of ppb to a few ppm) and Barnes, 1986), or PPGE have higher solubility in being about 1 to 2 orders of magnitude higher than basic melts (Amosse et al, 1990) that may have been that of the silicate-dominated rocks. Two types of derived by partial melting of upper mantle. The PGE chromitite occur in this belt, podiform chromitite in pattern reflects the residual nature of the harzburgite. tectonised harzburgite and banded (stratiform) Cumulate and gabbro from the magmatic sequence chromitite within ultramafic cumulate. For CI- show PGE patterns opposite to those of the chondrite normalised PGE patterns, the podiform harzburgite, defined by an increase from IPGE to chromitite is enriched in Ir-group PGE (IPGE: Ir, Os, PPGE, similar to that for banded chromitite within the and Ru), similar to other podiform chromitites such as cumulates. The PGE pattern of positive slope for the those of Troodos, Cyprus (Prichart and Lord, 1990), magmatic sequence is expected if PPGE are more Bay of Islands, Newfoundland (Edwards, 1990), and mobile during partial melting, as evidenced by the California and Oregon (Page et al, 1986), but the relatively depleted PPGE in harzburgite. banded chromitite is enriched in Pt-group PGE Within the cumulates and chromitites, the sulphide (PPGE: Rh, Pt, and Pd), like the typical stratiform mineralogy is dominated by heazlewoodite, millerite chromitites of the Bushveld Complex (Von and pentlandite. This assemblage, and some textural Gruenewaldt et al, 1986) and Stillwater Complex observations that relate the sulphides to the (Talkington and Lipin, 1986). The difference in PGE development of ferritchromit alteration rims on patterns implies that the two types of chromitites chromite and fracture infillings within chromite, originated by different processes. suggest that they reequilibrated at low temperatures PGE minerals are found in both styles of under hydrothermal conditions, and no longer represent chromitite and the mineral assemblage of each type primary sulphides segregated from basaltic magma. reflects the whole-rock PGE pattern. The identified PGE probably experienced remobilisation as well, but PGE minerals in podiform chromitite are laurite only to a limited extent, so as not to greatly influence (RuS2), probable erlichmanite (OsS2) and irarsite their primary distribution, since samples of the same (IrAsS), and an Os-Ru alloy. Platinum, palladium, lithology with differing degrees of serpentinisation and alloys of Pd with Hg, Pb, or Cu, and Rh with Sn and deformation have similar levels and distribution Cu, and cooperite (PtS) have been located in banded patterns of PGE. chromitites. All of these phases are extremely small Weighted-average PGE abundance of the magmatic (<10 microns) and occur as (i) isolated inclusions in sequence the residual harzburgite indicates that, chromite, (ii) associated with sulphide inclusions compared and with CI- chondrite, the source rocks in the Geological Society of Australia Abstracts Number 32, Ballarat 1992

101 upper mantle were depleted overall in PGE before the reference to the composition of magmatic sulfide ores. Forschr. Mineral., 64, 113-133. partial melting event that generated the upper magmatic sequence. This depletion could result from Page N.J. et al, 1986, Platinum-group element resources in podiform chromitites from California (i) an anomalously low PGE content in the source and Oregon. Econ. Geol., 81, 1262-1271. region because of inhomogeneity of the upper mantle, Prichard H.M. & Lord R.A., 1990, Platinum and or (ii) prior episodes of partial melting in the upper palladium in the Troodos Ophiolite Complex, mantle leading to depletion in the source region. Cyprus. Can. Mineral28, 607- 618. Talkington R.W. & Lipin B.R., 1986, PlatinumReferences group minerals in chromite seams of the Stillwater Complex, Montana. Econ. Geol., 81, 1079-1186. Amosse J. et al, 1990, Experimental study of the Von Gruenewaldt G. et al, 1986, Platinum-group solubility of platinum and iridium in basic silicate elements - chromitite associations in the Bushveld melts-implications for the differentiation of Complex. Econ. Geol., 81, 1067-1079. platinum-group elements during magmatic processes. Chem. Geol., 81, 45-53. Naldrett A.J. & Barnes S.J., 1986, The behaviour of platinum group elements during fractional crystallisation and partial melting with special

Geological Society of Australia Abstracts Number 32, Ballarat 1992

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Geological Society of Australia Abstracts Number 32, Ballarat 1992

103

A4: GEOLOGY OF ENERGY RESOURCES CONVENOR: GREG SMITH KEYNOTE: A 4.1 SEDIMENT SUPPLY, TECTONISM, AND SILICICLASTIC DEPOSITIONAL SYSTEMS AND SEQUENCES William E. Galloway The University of Texas at Austin, Department of Geological Sciences, Austin, Texas, U.SA. 78713 The complex interplay of sediment supply, tectonism and eustatic sea-level change in time and space determines the sequence stratigraphy of a basin fill. Regional depositional episodes, and their resultant genetic stratigraphic sequences, may be further punctuated by relative sea-level change events, producing the well-known depositional sequences. This lecture will focus on (1) sediment supply as a key variable and (2) application of process sedimentology (rather than stratal geometry) as the basis for facies analysis and reservoir prediction in the context of process- and facies-defined depositional system tracts within genetic stratigraphic sequences. This approach is prefaced on several observations (Fig. 1). 1. The fundamental array of coastal-plain and marine depositional systems found within a sequence is the product of the interplay between sediment supply and process regime. Sediment supply has three components: volume, textural composition, and geographic distribution. Basin process regime includes wave and tidal energy fluxes, geostrophic currents (of whatever origin and depth), and gravitational potential. Response times for regimesediment interactions range from hours to a few thousand years. 2. Changes in rate of total sediment input determine the time/space distribution of progradation, aggradation, and retrogression/transgression of depositional system tracts.

Geological Society of Australia Abstracts Number 32, Ballarat 1992

3. Pattern of sediment supply (point vs. line source; dip- vs. strike-fed) localizes depocenters, defines lateral depositional system tracts, and influences the stratal architecture within sequences. 4. Texture of sediment supply (gravel/sand/mud) plays a major role within many depositional systems by influencing channel geometry and stability, relative impact of wave vs. tidal energy flux, erosional vs. depositional character of the shoreline, and, perhaps most importantly, subaqueous depositional slope. Subaqueous slope, in turn, is a primary control on the frequency and magnitude of resedimentation events leading to shelf-platform bypassing and development of slope systems. 5. The depositional systems array is modified by relative sea-level change and differential structural growth. Relative sea-level change most importantly influences the efficiency of shelf-platform storage vs. bypass. It also influences parasequence stacking pattern and superimposes disjoint facies across stratal discontinuities. Differential structural growth disrupts stratal/facies continuity and provides local sediment sources, sinks, or bypass zones. The fundamental reservoir attributes - volume, areal pattern and distribution, vertical stacking, interconnectedness, and diagenetic history - are predictable within the context of a well-understood depositional systems array and its tectonic/eustatic overprint.

104

Basin Process Regime • Terrestrial energy fluxes • Wave energy flux • Tidal energy flux • Geostrophic flows • Gravitational potential

Sediment Supply • Volume • Texlural composition • Geographic distribution of Input

Depositional System Array

Modified By Differential Structural Displacement (Depositional and (Shelf storage vs. shelf bypass) preservationa! continuity) • Eustasy • Regional uplift/subsidence • Basement tectonics • Gravity tectonics Relative Sea-Level Change

Potential Reservoir Attributes • Volume • Three-dimensional distribution — areal pattern and trend — vertical stacking/offset — interconnect edness/isolat ion

Geological Society of Australia Abstracts Number 32, Ballarat 1992

105

A 4.2

LARGE-SCALE SEDIMENT ARRANGEMENTS IN ALLUVIAL BASINS AND SEQUENCE STRATIGRAPHY P.E. O'Brien & A.T. Wells

Bureau of Mineral Resources, Canberra. The large-scale patterns of grain-size, composition, continued low avulsion to subsidence ratios. Motif 3 sedimentation style and palaeocurrents in an alluvial is a fining-up sequence changing from sandy braided basin fill reflect slope-discharge relationships in the stream deposits to muddy sinuous and anastomosing river systems flowing through the basin which in turn stream deposits and lakes. This change is brought reflect climate, basin tectonics, hinterland geology and about by a rise in relative base level, either by an topography, basin base level and the time scale over increase in subsidence or by a relative rise in sea level. which river systems are allowed to adjust to changes. This is not an exhaustive list of possible successions The influence of sea level change on alluvial that could be found in fluvial deposits but the sedimentation depends on whether the basin is in close approach could be used as a basis for genetic enough contact with the sea for it to influence base packaging for fluvial sediments analogous to systems level. Base level rises propagate up a river system by tracts in sequence stratigraphy. migration of a backwater effect and falls by upstream The origin of any occurrence of one of these motifs migration of nick points. Alluvial sedimentation at a in a particular basin should be deduced from local point will only reflect these changes if the backwater evidence. In the Clarence-Moreton Basin, climate effect or nick point has sufficient time to reach it. changes were minimal during deposition so most Our study of the alluvial Bundamba Group in the sedimentation changes reflect tectonic influences. Clarence-Moreton Basin of eastern Australia has Likewise, most baselevel changes were tectonically suggested a number of facies successions or motifs induced but one unit was deposited in response to a that may represent standard behaviour by fluvial major second order eustatic sea level rise. A basement depositional systems in response to change. Motif 1 is lip to the basin probably prevented sea level falls a coarsening-up sequence featuring an increase in playing any part in deposition but a rise of sufficient sediment maturity. It represents aggradation of the magnitude was able to produce a backwater effect in system to near grade after a rise in relative base level. the basin. Motif 2 is a change from conglomeratic to fine grained sediments caused by the retreat of steep basin sides and

A 4.3

HOW WELL DO THE SEA-LEVEL CURVES COMPARE WITH THE CLIMATE RECORD L. A. Frakes* and A. A. Krassay

Department of Geology and Geophysics, University of Adelaide, South Australia The relationship between sea level and the state of the global climate is well established for the last few hundred thousand years, with highstands corresponding closely in time to interglacial intervals and lowstands to glacial periods. Farther back in the record the relationships are not so clear, at least partly because climate changes are more poorly dated than are the proposed changes in sea level. The most detailed dating of sea level change (Haq et al.,1987) recognizes megacycles, supercycles and cycles in the Mesozoic and Cenozoic. These have periods of hundreds of m.y., several tens of m.y., and a few m.y., respectively. There is only fair agreement Geological Society of Australia Abstracts Number 32, Ballarat 1992

between megacycles (and the broad trends in sea level curves of Vail et al.(1977) and Hallam (1984)) and a recent compilation of global climate history (Frakes, Francis and Syktus, 1992). Major peaks in sea level correlate reasonably well with the warm modes in the late Cretaceous-early Tertiary and the Cambrian, although not so well with warmth in the midPalaeozoic and in the latest Palaeozoic-early Mesozoic. Marked lowstands in the early Ordovician, early Devonian and the Triassic are apparently not accompanied by any evidence of cool intervals. The late Ordovician-early Silurian glacial time saw quite high stands of sea level. On the other hand, the late

106 Palaeozoic glacial interval did feature a falling sea level. It would appear that either tectono-eustasy sometimes played an overriding role in causing sea level to stand at a high level while climates were cool, or coolings at times did not result in the construction of significant amounts of polar ice and hence sea level did not fall noticeably due to glacio-eustasy. Generally poor correspondence exists between sea level and climate at both the supercycle and cycle level, but examples can be found showing good correlation, as for example in the Pliocene cooling in parallel with falling sea level. Again, the problem here may relate to poorer age control on climate fluctuations as compared with that for sea level change. A 4.4

References Frakes, L.A., Francis, J.E. and Syktus, J.I., 1992. Climate Modes of the Phanerozoic, Cambridge University Press. Hallam, A., 1984. Annual Rev. Earth Planet. Sci., v. 12, p. 205-243. Haq, B.U., Hardenbol, J. and Vail, P.R., 1987. Science, v. 235, p.l 156-1167. Vail, P.R., Mitchum, R.M. Jr., and Thompson, S. Ill, 1977. Amer. Assoc. Petrol Geol. Memoir 26, p. 83-97.

THE APPLICATION OF CARBONATE SEQUENCE STRATIGRAPHY IN A THRUST-FAULTED TERRAIN: STRETCHING THE LIMITS?

Thomas Bernecker* and John A. Webb Department of Geology, La Trobe University, Bundoora, Vic., 3083, Australia The concept of sequence stratigraphy has enjoyed a age. In order to establish valid sequence stratigraphy positive response from geologists over the past five for the entire study area these thrust sheets have been years. It proved to be a successful tool in hydrocarbon considered first, and then correlated with other thinner exploration, but is also generally relevant for the and stratigraphically incomplete slices and slivers. interpretation of sedimentary basin histories. Most Overall, sequence stratigraphy in the Mungana area has published examples focus on well exposed or well to cope with the following problems: drilled sedimentary successions, many of which are (1) Different thrust sheets often display different technically undisturbed (i.e. Sarg, 1989; Vail, 1987). facies types of identical age. A recent attempt to apply carbonate sequence (2) Thrusting and associated diagenetic and stratigraphy in a Palaeozoic terrain with limited metamorphic processes (i.e.: dilation, recrystallization) outcrop and strong tectonic overprint showed the obscured many internal sediment textures. validity of this concept (Van Steenwinkel, 1990). (3) Sequence boundaries and maximum flooding However, carbonate sequence stratigraphy is challenged surfaces are difficult to locate, because no Type 1 when the sedimentary pile has been subject to intense sequence boundaries are present, and the deepest water thrust-faulting. This presentation tries to outline some facies are sometimes hard to identify. constraints and even limits of this concept, when (4) If sedimentation was controlled by applied to a technically complex terrain. syndepositional tectonic activity, some facies types The Chillagoe Formation is an example of a may actually be diachronous. thrust-faulted carbonate dominated sequence at the In general, the Chillagoe Formation consists of western margin of the Hodgkinson Basin in North dominant limestones with intercalated chert and minor Queensland. Although heavily dissected by thrust siliciclastics and basalt. Litho- and microfacies faults, detailed mapping of the Mungana area revealed analysis distinguished shallow marine sediments from the existence of several marker beds. These, in deeper water deposits, thus a subdivision into combination with conodont biostratigraphy, can be Highstand Systems Tracts (HST) and Transgressive used to identify time intervals within each thrust slice, Systems Tracts (TST) appears possible. In the and so construct a stratigraphic framework for the Mungana area a number of microfacies give evidence entire formation. for sedimentation during low sea level stands: the Late In the Mungana study area the complete Chillagoe Llandoverian segment of the Chillagoe Formation is Formation is represented on only two thrust sheets of typically represented by a rich shallow marine coral approximately 500 m thickness, ranging from Early association, which appears to be related to the Silurian (Llandoverian) to Early Devonian (Emsian) in existence of a submarine basaltic high. A prominent, Geological Society of Australia Abstracts Number 32, Ballarat 1992

107 30-50 m thick shoal facies, consisting of peloidal grainstones is developed in the Pridolian. At the same time an extensive restricted shallow marine environment developed behind these shoals, typified by abundant megalodont bivalves, stromatoporoids and cortoid grains. A final shallowing sequence is terminated by the influx of siliciclastic material during the Early Emsian (Bernecker & Webb, 1990). It is suggested that the Chillagoe Formation consists of two complete and, one incomplete sequences, responding to sea-level variations. However, the proposed palaeo-bathymetry curve needs to be tested against other mid-Palaeozoic strata. It can then be decided how dependent deposition was on eustatic sea-level changes, on regional tectonic movements, or on the combination of the two. A 4.5

References Bernecker, T. and Webb, J. A., 1990, Abstracts, 13th International Sedimentological Congress, Nottingham, U.K.: 30. Sarg, J.F. ,1988, SEPM Special Publication, No 33: 155-181. Vail, P.R., Mitchum, R.M., JR., Todd, R.G., Widmier, J.M., Thompson, S., Ill, Sangree, J.B., Bubb, J.N. and Hatlelid, W.D., 1977, American Association of Petroleum Geologists Memoir, 26: 49-212. Van Steenwinkel, M. ,1990, Sedimentary Geology, 69: 259-280.

SEISMIC IMAGING OF PLEISTOCENE DEEP-SEA CYCLOTHEMS: IMPLICATIONS FOR SEQUENCE STRATIGRAPHY R.M. Carter & L. Carter 1

2

James Cook University, Townsville 2New Zealand Oceanographic Institute, DSIR, Wellington 1

Plate collision along the New Zealand Alpine approximately 50 cyclothems have been deposited Fault since the late Miocene has provided an abundant since the late Pliocene, i.e. each cyclothem supply of terrigenous sediment to a starved late corresponds to two contiguous oxygen isotope stages. Cretaceous rift-basin, the Bounty Trough. During the Each cyclothem also corresponds to the offshore late Neogene, alternating pulses of terrigenous conformity of a single 5th or 6th order sequence, with (glacial) and biopelagic (interglacial) sediment were the lower portion marking a lowstand systems tract, deposited in the trough in the form of deep-sea and the upper biopelagic part representing cyclothems, in sympathy with the fluctuating transgressive and highstand systems tracts. Therefore, glacial/interglacial position of sea-level. Individual as a single sequence is traced seawards it passes from cyclothems range up to 15 m in thickness, have been unconformity-bounded shelf and shelf-margin directly imaged by both 3.5 kHz and single airgun cyclothems, to slope sediments which include thick profiling, and are particularly conspicuous on the conformity-bounded cyclothems or autocyclic canyon continental slope and in areas of the trough under the deposits, to thin conformity-bounded deep-sea influence of overbank turbidite deposition from the cyclothems on the distal rise, and finally to biopelagic Bounty Channel. On the abyssal Bounty Fan, sediment and/or red clay on the abyssal plain. A 4.6 DEPOSITIONAL SYSTEMS OF TROUGH-FILL, SEAWARD OF THE GREAT BARRIER REEF D.Johnson A 4.7 SEQUENCE STRATIGRAPHY OF THE TERTIARY SUCCESSION IN THE PORT CAMPBELL EMBAYMENT OF THE OTWAY BASIN, VICTORIA. P.A. Arditto B.H.P. Petroleum, 120 Collins Street, Melbourne, Victoria The Tertiary succession in the vicinity of Port Campbell offers a unique opportunity to demonstrate the principles of sequence stratigraphy as a tool in basin analysis. The coastal cliffs in this region provide some of the best outcrop exposures of Tertiary Geological Society of Australia Abstracts Number 32, Ballarat 1992

sequences, within easy access of Melbourne, and also display a variety of depositional environments. The presence of both marine and non-marine age-diagnostic flora and fauna provide excellent age control within this succession.

108 Onshore water bore and petroleum exploration wells (some fully cored and many wireline logged) have allowed detailed subsurface correlations from outcrop sections. Recent good quality offshore reflection seismic data together with a number of offshore petroleum exploration wells allowed an integrated approach to sequence analysis with the ability to tie outcrop sections into well logs and seismic data. The stratigraphic nomenclature used here is that of Abele et al (1988). Three distinctive stratigraphic sequences are recognised using the criteria of Vail et al. (1977). The lowermost sequence is Palaeocene to Middle Eocene in age and comprises a siliclastic succession traditionally recognised as the Pebble Point Formation, overlain by the Pember Mudstone which is in turn overlain by the Dilwyn Formation. The middle sequence is late Middle Eocene to Early Oligocene in age and comprises a lower siliclastic succession and an upper carbonate succession collectively known as the Nirranda Sub Group. Locally this Sub Group is divided, in ascending order, into the Johannna River Sand, the Browns Creek Clay, the Castle Cove Limestone and the Glen Aire Clay. The youngest sequence is Late Oligocene to Middle Miocene in age and mainly comprises carbonates recognised in ascending order, as the Clifton Formation, the

Gellibrand Marl and the Port Campbell Limestone. This study concentrates on the first two sequences and has demonstrated that they are contained by sequence boundaries which are regional unconformities recognizable as seismically mappable events. The internal components of these genetic sequences can be separated into the Lowstand Wedge/Transgressive Systems Tract, the Condensed Interval, and the Highstand Systems Tract based on outcrop studies, wireline log character and seismic stratal patterns. This systematic approach for analysing the sedimentary rock record has allowed construction of a unified physical and temporal stratigraphic framework which transcends the existing local stratigraphic nomenclature and promtes a better understanding of depositional processes in the basin. References Abele, C., Kenley, P.R., Holdgate, G., & Ripper, D. 1988, Otway Basin in Geology of Victoria (Eds., Douglas, J.G. and Ferguson, J A.) Victorian Division, Geol. Soc. Aust. Inc. 272-303. Vail, P.R., Mitchum, R.M. & Thompson, S. 1977, The depositional sequence as a basic unit for stratigraphic analysis. American Association of Petroleum Geologists, Memoir 26: 53-62.

A 4.8 LITHO-STRATIGRAPHY AND SEQUENCE STRATIGRAPHY OF A MIDCRETACEOUS SHELF ENVIRONMENT IN THE GULF OF CARPENTARIA A.A. Krassay * and L.A. Frakes Department of Geology & Geophysics, University of Adelaide, South Australia Cretaceous sediments are exposed intermittently as mesas and plateaux along the western and southwestern margins of the Gulf of Carpentaria in northern Australia and consist of an undeformed clastic platform sequence resting on a Precambrian basement complex. These dominantly marine sediments are Aptian to Albian in age and are coarse grained, high energy, shelfal equivalents of the upper Gilbert River Formation and the Rolling Downs Group (Wallumbilla Formation, Toolebuc Formation, Allaru Mudstone and Normanton Formation (Mackunda Formation in Eromanga Basin)) in the central part of the Carpentaria Basin and the northern part of the Eromanga Basin (Burgess, 1984). The bulk of the sequence comprises sandstones and conglomerates along with thin bioturbated mudstones which often cap fining-upward cycles. Deposition of these units occurred in an inner-shelf, storm-dominated setting as indicated by the presence of HCS, abundant cross-bedding and intense bioturbation throughout

Geological Society of Australia Abstracts Number 32, Ballarat 1992

much of the sequence. The presence within the sequence of numerous conglomeratic lags and disconformities, often able to be correlated over large distances, indicates that reworking of initially deposited strata between and during successive transgressions was an important process. Unfortunately biostratigraphic age control is rather poor due to the sparse palaeontological information available overall for the sequence. The basal and middle strata yield rare benthic foraminifera and palynomorphs whilst indeterminate plant fossils and poorly preserved marine, molluscan macrofossils (Skwarko, 1966) are relatively common throughout the sequence but are of little use in dating individual units or their bounding disconformities. Regional correlation is therefore based primarily on detailed lithological analysis, sedimentary style and the stratigraphic position of small fining-upward and coarsening-upward cycles relative to bounding disconformities.

109 In the absence of any known local tectonic controls on sea level and sedimentation the extent of the Aptian and Albian seaways in the region were controlled in a broad sense by eustasy and more locally by basement topography in the form of irregularly distributed, highstanding Precambrian terrains. Haq et al (1987) document a time of rising sea level following the mid-Cretaceous low (type 1 sequence boundary) in the early Aptian with a continuous rise in sea level through the Albian and into the early Cenomanian. Although the present data agree in general with their sea level curve, the limited biostratigraphic age control coupled with the very A 4.9

small thicknesses of the units involved means that an allostratigraphic approach (Walker, 1990) to stacking 'parasequences sets' and 'parasequences' may be of more use than classical sequence stratigraphic analysis for this region. References Burgess, I.R., 1984, The Apea Journal 1984: 7-18 Haq, B.U., Hardenbohl, J. and Vail, P.R., 1987, Science 235: 1156-1167 Skwarko, S.K., 1966, B.M.R. Bull. 73 Walker, R.G., 1990, /. Sed. Petrol. 60: 777-786

SEQUENCE STRATIGRAPHIC ANALYSIS OF THE PERMIAN SUCCESSION IN THE WESTERN BOWEN BASIN, QUEENSLAND; IMPLICATIONS FOR HYDROCARBON EXPLORATION V. Ziolkowski , C.R. Fielding *' M. Wilkinson & J .J. Draper 1

1

2

3

Dept. of Geology & Mineralogy, University of Queensland, Queensland 4072 AGL Petroleum Pty. Ltd., P.O. Box 1010, Brisbane, Queensland 4001 Dept. of Resource Industries, P.O. Box 194, Brisbane, Queensland 4001

1

2

3

Recent literature on sequence stratigraphic analysis of sedimentary successions has concentrated on the study of passive continental margins, resulting in the development of somewhat idealised models for sequence architecture in sedimentary basins (Van Wagoner et al. 1990). This paper aims to establish a sequence stratigraphy based upon extensive outcrop and subsurface data for a basin formed in a retroarc setting, the Bowen Basin of Queensland. Analysis of Permian sequences in the western part of the basin (cratonic margin) has revealed a complex interplay between tectonic and eustatic effects, reflecting the evolution of the basin from a back-arc extensional trough to a true, retroarc foreland basin through time. The sequence architecture in the Denison Trough shows considerable departure from conventional models of sequence development based fundamentally on passive margins. According to conventional models, in passive margin development siliciclastic sediment dispersal is unimodal, impinging on a continental shelf and slope of infinite capacity which are subsiding in a predictable fashion about a continental margin hinge point. High frequency eustatic cycles can readily be separated from this passive tectonism, and resultant systems tracts carry a recognisable signature. Such systems tracts can therefore be assigned to various phases of a simple, sinusoidal eustatic cycle (Van Wagoner et al., 1990). In the case of retroarc foreland systems, the cratonic margin hingepoint is unpredictably mobile 9

Geological Society of Australia Abstracts Number 32, Ballarat 1992

and cannot readily be defined due to the presence of active faulted margins, movement of depocentres through time and consequent uplift and erosion. Foreland basins also exhibit bimodality of sediment provenance, as early stage sediments shed from the craton are later overwhelmed by material derived from the evolving orogen. Depocentres become progressively restricted or isolated from the open marine systems of the forearc. According to sequence stratigraphic models, platform sediments can only accumulate during highstands, while lowstands are recorded by erosion. In foreland systems, however, it can be demonstrated that major regressive pulses occur during active tectonism. These regressions cannot be considered to be in phase with eustatic cyclicity, and must be treated as composites of the two independent controls. Analysis of Permian sequences in the Denison Trough has revealed a complex interplay between tectonic and eustatic effects, as might be expected in a retroarc situation. The Permian section has been divided into seven major cycles, each bounded by unconformities or correlative conformities. Some cycles are internally composed of more than one sequence. The earliest phase of development of the western Bowen Basin in Early Permian times involved limited crustal extension and the formation of a series of grabens and half-grabens. These early sub-basins were infilled by mainly continental, alluvial clastic sediments (Cycle 1, corresponding to Facies

110 Assemblage 1 of Fielding, this volume). Cycle 1 was progressively terminated by a widespread marine transgression, coinciding with a transition from extensional subsidence to a more regionally uniform phase of thermal subsidence. Much of the late Early to early Late Permian section (Cycles 2-5, corresponding to Facies Assemblage 2 of Fielding, this volume) is of marine aspect, deposited in a realm of dominantly thermal subsidence with periodic, mainly subtle compressive structuring. The subtle, progressive growth of positive structures through this time is particularly apparent on a local scale, where wireline log correlations show unconformities over structural highs that pass laterally into conformable surfaces downdip. This feature is particularly significant in that studies based only on wells drilled on structural highs in such situations would lead to the establishment of spurious sequence boundaries. Late in the Permian period, a resurgence of arc volcanism occurred at the eastern basin margin, together with uplift of the volcanic terrain and the onset of significant compressive deformation. From this time onward, the Bowen Basin behaved as a true retroarc foreland basin. The deformation, which peaked during Triassic times (see Kassan, this volume), involved the propagation of large thrust sheets westward across the eastern half of the basin and inversion of former graben-bounding faults in the Denison Trough. In the initial stages of tectonic resurgence, much of the Bowen Basin was infilled by major, axially (north

Geological Society of Australia Abstracts Number 32, Ballarat 1992

to south) prograding clastic wedges (Cycles 6 and 7, corresponding to Facies Assemblage 3 of Fielding, this volume). These systems ultimately spilled over westward across the Springsure Shelf into the Galilee Basin. By latest Permian times, alluvial plain conditions had become established across much of the basin, conditions which persisted into Triassic times (see palaeogeographic maps presented by Fielding et aU 1990). Detailed analysis of the Permian sequence in the Denison Trough has revealed a complex interplay between tectonic and eustatic controls, which has only been possible with the aid of closely-spaced well data. This study has demonstrated that the sequence architecture of compressive margin basins may be considerably more complex than that of passive margins, and may not conform to the idealised models of Van Wagoner et al (1990). References Fielding, C.R., Falkner, A.J., Kassan, J. & Draper, J.J., 1990. Permian and Triassic depositional systems in the Bowen Basin. In: J.W.Beeston (compiler), Proceedings, Bowen Basin Symposium 1990, Mackay, Geol.SocAustr. (Qld), 21-25. Van Wagoner, J.C., Mitchum, R.M., Campion, K.M. & Rahmanian, V.D., 1990. Siliciclastic sequence stratigraphy in well logs, cores and outcrops. AAPG Methods in Exploration Series No. 7, 55pp.

Ill SEQUENCE STRATIGRAPHY OF PERMIAN SILICICLASTICS IN THE FITZROY TROUGH, CANNING BASIN, WESTERN AUSTRALIA P.E. O'Brien*, J.F. Lindsay, M.J. Jackson, J.M. Kennard, P.N. Southgate & M.J. Sexton. Bureau of Mineral Resources, Canberra. As part of a larger study of the Canning Basin, the Bureau of Mineral Resources is studying the sequence stratigraphy and sedimentology of Permian siliciclastic rocks in the Fitzroy Trough to develop a better understanding of the reservoir and seal facies within them. These rocks exhibit two contrasting styles of sequence development; the earliest Permian consisting of sequences that are difficult to correlate and relate to conventional interpretations and overlying units that more closely conform to published models. The Early Permian Grant Group contains two to five major sequence boundaries with up to 100 m of relief on them. Large channel features are common. Lowstand and transgressive systems tract deposits are thick tabular interbedded sandstone and mudstone units and channel fill deposits that include thick poorly sorted sandstone bodies and mudstones and coarseningup deltaic sediments. Highstand systems tracts feature glaciomarine mudstones, shallow marine sandstones, sandy braid delta and fluvial braidplain deposits. A facies widespread in all systems tracts is massive to indistinctly bedded sandstone, associated in places with large-scale synsedimentary folds. This facies is interpreted as the result of catastrophic floods produced by rapid draining of englacial and proglacial lakes. Above the Grant Group, Permian rocks have sheetlike geometries so that their sequence stratigraphic characteristics are deduced more from detailed well subdivision and correlations rather than features on seismic lines. The Poole Sandstone rests on a low relief sequence boundary cut into the Grant Group. Its lowest part is a sheet-like transgressive systems tract A 4.11

of cross-bedded, shallow marine sandstone 1 to 30 m thick that passes eastwards into deltaic and fluvial sediments (Nura Nura Member). This sandstone passes abruptly upwards into siltstones and minor shales with a well defined flooding surface. Above the flooding surface, the Poole Sandstone consists of stacked parasequences 2 to 7 m thick. Each parasequence comprises mud chip breccias marking each minor flooding surface overlain by swaley cross-bedded sandstone that passes up into shoreface and beach deposits. The parasequences show a general upward trend to shallower facies with shoreface and beach sediments predominating in the upper part of the Poole. These highstand sediments are truncated by a sequence boundary overlain by cross bedded fluvial sandstone (Christmas Creek Member) that is the lowstand to transgressive systems tract of the next sequence. Above the Poole Sandstone, the Noonkanbah Formation consists of a least three sequences of fine grained marine clastics arranged in fining-up parasequences 3 to 25 m thick that can be correlated for tens of kilometres using wireline logs. The contrast between the conventional sequence stacking patterns of the Poole Sandstone and Noonkanbah Formation and the chaotic Grant Group reflects changes in basin tectonics and palaeoclimate. Grant Group deposition was strongly conditioned by rapid basin subsidence and the presence of major ice sheets adjacent to and sometimes in the basin. The change to the overlying sequence patterns reflects the decay of thermal subsidence in the Fitzroy Trough and the disappearance of the Permian ice sheets.

A NEW STRATIGRAPHY FOR THE ILLAWARRA COAL MEASURES, SOUTHERN SYDNEY BASIN A C Hutton1*, W J Bamberry2 and B G Jones1 1

Department of Geology, University ofWollongong, Wollongong NSW 2 Department of Minerals and Energy, Singleton, NSW

The presently accepted stratigraphic nomenclature for the Southern Coalfield of the southern Sydney Basin, was ratified by the Standing Committee on Coalfield Geology of NSW in 1970. The nomenclature was extended to include the previously defined Southwestern Coalfield in 1980. A recent detailed study of the Southern Coalfield, based on a comprehensive geological database was compiled from 30 measured sections and 600 drill hole Geological Society of Australia Abstracts Number 32, Ballarat 1992

lithologs (many of which were relogged where core was available), indicated that the previous stratigraphic nomenclature needed revision. The published stratigraphy of the Illawarra Coal Measures was based on the sequence in the Illawarra area where it is thinner than in the northern part of the coalfield and also lacks the significant lateral facies changes that are apparent in the norn and west. Thus a revision of the accepted terminology is proposed and

112 tentative correlations with the Western Coalfield are given. Recommended revisions include: i. the four latite members identified by Carr (1983) should be included in the formal definition of the Pheasants Nest Formation of the Cumberland Subgroup; these latites are restricted in occurrence to the coastal areas centred on and south of Wollongong; ii. the Marrangaroo Conglomerate, previously only recognised in the Western Coalfield, extends into the western part of the Southern Coalfield and this unit should now be formally recognised in the Southern Coalfield stratigraphy; iii. the Tongarra seam splits in the central western part of the Southern Coalfield; this has not previously formally recognised; iv. the Allans Creek Formation contains two carbonaceous to coaly intervals separated by interbedded claystone, siltstone and sandstone; the definition should be revised to account for this; A 4,12

v. the Sydney Subgroup contains several pallid * claystone1 layers, derived from tuffaceous detritus; three claystone layers are laterally persistent and can be recognised over much of the Southern Coalfield; these should have member status as follows: i. Farmborough Member, formerly known as the s sandstone band' in the Wongawilli Coal; ii. Huntley Member, formerly known as the Nolan band' in the Bargo Claystone; and iii. the unit informally called the Burragorang Chert should be formerly recognised the Burragorang Member; vi. The clastic interval between the Bulli Coal and the Balgownie seam is dominated by sandstone over much of the coalfield and should be recognised formerly as the Loddon Sandstone Member. Reference Carr, P.F., 1983, Proc Linn. Soc. NSW, 106:287-297

EARLY DEVONIAN SEQUENCE STRATIGRAPHY FROM BUCHAN AND BINDI, EASTERN VICTORIA John A. Webb Department of Geology, La Trobe University, Bundoora, Victoria 3083.

Across eastern Victoria there a number of outcrops of an Early Devonian carbonate/ mudstone sequence 13 km thick. The largest and best exposed of these are a synclinal area at Buchan and a downfaulted block at Bindi. The sequences at both localities are closely comparable with respect to stratigraphic sequence and age (as determined by well preserved conodont faunas; Mawson 1987), but differ in thickness, presumably reflecting different subsidence rates. The basal formation, the Buchan Caves Limestone, is of ?Lochkovian - mid Pragian age, and lies disconformably over the predominantly terrestrial Snowy River Volcanics. Separating the two is a thin, discontinuous clastic unit with occasional freshwater fossils. The Buchan Caves Limestone was deposited initially under restricted, probably intertidal conditions, as shown by the presence of cyanobacterial mats and a low diversity fauna dominated by gastropods. The upper part of this formation was deposited in deeper, subtidal conditions, as it contains a more diverse fauna with corals and open water forms like nautiloids. The Buchan Caves Limestone records a major transgression that extended over much of eastern Victoria; this must have been initiated by regional subsidence, but may also record a eustatic sea level rise. Geological Society of Australia Abstracts Number 32, Ballarat 1992

Overlying the Buchan Caves Limestone is a deeper water marl/mudstone unit, the Taravale Formation, with a predominantly open shelf fauna, including a moderately diverse conodont and ammonoid assemblage. The Taravale Formation varies greatly in thickness between Buchan and Bindi, but represents approximately the same time interval at both localities. Within the Taravale Formation at Buchan is a lensoidal unit, the Murrindal Limestone, which represents a reef/mud mound, behind which was a protected lagoon. An apparently similar unit of the same age (early Emsian), the Shanahan Limestone, is present at Bindi, but is less well exposed. The concepts of sequence stratigraphy can be readily applied to the carbonate/mudstone sequence at Buchan and Bindi. The Buchan Caves Limestone and the basal part of the Taravale Formation form a Transgressive Systems Tract, with the maximum flooding surface located within the Taravale Formation (late Pragian). The middle portion of the Taravale Formation and the Murrindal and Shanahan Limestones represent the Highland Systems Tract (early Emsian). The top of the Murrindal Limestone is a Type 2 sequence boundary, as it shows no evidence of subaerial exposure or erosion. The section of the

113 Taravale Formation that overlies the Murrindal Limestone forms part of another Transgressive Systems Tract that extended into the late Emsian.

A 4.13

References Mawson, R., 1987, Palaeontology 30: 41-87.

LATE DEVONIAN REEFS OF THE CANNING BASIN: A SUBSURFACE SEQUENCE STRATIGRAPHIC PERSPECTIVE

P.N. Southgate *, J.M. Kennard, M.J. Jackson, P.E. O'Brien, J.F. Lindsay and M.J. Sexton. Bureau of Mineral Resources, Canberra, ACT. In order to assist petroleum exploration in the Canning Basin the Bureau of Mineral Resources is presently interpreting and integrating subsurface seismic, well and biostratigraphic data from the Lennard Shelf and adjacent Fitzroy Trough. This part of the Canning Basin hosts the Late Devonian, MedaBlina reef trend, the target of major oil exploration activity during the 1970's and 1980's and the Blina Oil Field. In this area play concepts have been based on reef models generated by Playford and co-workers and information from the Devonian of Western Canada. The outcrop model uses lithostratigraphic facies analysis techniques to subdivide the reef complex into basinal, fore-reef, reef and backreef facies. Although minor oscillations in sea-level are interpreted from low-relief karst associated with the FrasnianFamennian boundary, the general picture that emerges from the outcrop studies is one of backstepping reef complexes during the Frasnian (Pillara Cycle) and advancing reef complexes during the Famennian (Nullara Cycle). Minor terrigenous clastics occur within the carbonates and locally conglomerate may dominate. By extending the database into the subsurface we have identified an additional suite of sediments not represented in the outcrop. Our sequence interpretation has divided the reef complex into eight third order sequences each of which contains deposits attributable to lowstand, transgressive and highstand systems tracts. Five sequences are present in the Pillara Cycle and three in the Nullara Cycle. Each reef sequence is characterised by reciprocal lowstand-highstand sedimentation; lowstand clastic-rich sediments restricted to the basin, and highstand carbonate sediments across the platform and platform margin. The outcropping reef complexes are dominated by platform and platform-margin sediments. Lowstand deposits have been subdivided into three depositional systems; basin floor fan, slope fan and prograding complex. The basin floor fans form extensive sheets, tens of kilometres across and 20-60 ms twt (approx. 40-100 m) thick, that onlap the basal Geological Society of Australia Abstracts Number 32, Ballarat 1992

sequence boundary basinward of the platform margin. Their upper surfaces are commonly defined by reflectors with high impedance contrasts. The fans are interpreted to have been deposited during periods of relative sea-level lowstand when the platform was exposed, and to comprise terrigenous sands fed by incised river systems, the proximal deposits of which are locally preserved on the platform (eg. conglomerates in Meda 1 and Yarrada 1, and outcropping conglomerate at Mt Behn and the Van Emmerick Range. The slope fans form thick wedges above the basin floor fans and pinch out against the platform slope. They generally have a mounded seismic character, and locally display distinct "gull wing" reflectors that indicate channel - levee complexes within the mounds. The flanks of the mounds display subparallel reflectors interpreted as distal turbidite aprons. The slope fans consist of siltstone, shale and minor sandstone. The upper surface of the slope fan is delineated by a prominent downlap surface. The prograding complex forms a thick progradational and aggradational lens which onlaps the basal sequence boundary at or near the platform margin, and downlaps basinward onto the slope fan. In places this downlap surface climbs basinward suggesting the presence of shingled turbidites at the toe of the prograding complex. The prograding complex is commonly the most volumetrically important depositional system within the reef sequences, and is characterised by well-defined sigmoidal clinoforms. This depositional system has been penetrated in several wells; the distal portion of the prograding complex consists of calcareous siltstone and minor sandstone, and proximal portions comprise micritic pelletal carbonates. Highstand reefal carbonates are volumetrically minor compared to their lowstand deposits, but have been intersected in many wells. Transgressive deposits are generally below seismic resolution. The highstand deposits display oblique progradational geometries at the platform margin, parallel reflectors across the platform, and downlap onto the prograding complex.

114 They comprise back-reef, reef and fore reef carbonates. Our sequence interpretation has not only identified new play concepts in this part of the Canning Basin, but has also led to the resolution of problems associated with the present lithostratigraphy. Lowstand fans represent a new play concept along the northern portion of the Fitzroy Trough. Potential reservoirs are provided by turbidite sand sheets within the basin floor fans, and sand channels flanked by levee complexes within the slope fans. Potential source rocks and seals are provided by interbedded shales and distal deposits of the overlying and underlying prograding complexes. Up-dip pinchouts of the fans provide a stratigraphic trap. Since many of the Frasnian fans occur at considerable depth (> 2s twt), Famennian fans are considered to offer the best

potential for hydrocarbons. Analogs of this play are the lowstand fans of the North Sea and Gulf Coast. The present lithostratigraphic nomenclature is both cumbersome and inconsistent in its useage. Sequence stratigraphic subdivision provides a means of linking facies and formations into genetically related mappable units. For example, we are now able to genetically link five diachronous lithostratigraphic units that occur near the contact between the Nullara Cycle and the overlying Fairfield Group. Our Famennian 2 sequence comprises three systems tracts: lowstand clastics (Clanmeyer Formation), transgressive calcareous shales (May River Shale), and highstand carbonates (variously referred to as the Windjana Limestone, Nullara Limestone or Gumhole Formation).

A 4.14 FACIES ANALYSIS OF PERMIAN MARINE SHELF, DELTAIC AND COASTAL PLAIN DEPOSITS IN THE WESTERN BOWEN BASIN, QUEENSLAND; IMPLICATIONS FOR RESERVOIR DESCRIPTION Christopher R. Fielding Dept. of Geology & Mineralogy, University of Queensland, Queensland 4072 The Permian succession in the Denison Trough, Trough from the western basin margin repeatedly on the western side of the Bowen Basin, comprises a during this time. During Late Permian times, there series of units of mainly marine shelf to coastal aspect was a resurgence of arc volcanism at the eastern (Fig. 1). These intervals have been subjected to a margin of the basin, uplift of the volcanic terrain and detailed facies analysis involving both outcrop and the onset of significant compressive deformation. In the initial stages of tectonic resurgence, much subsurface data, leading to the recognition of a series of recurrent facies and facies associations. The of the Bowen Basin was infilled by major, axially purpose of this paper is to summarise the major facies (north to south) prograding clastic wedges (Facies associations and their component facies, and to provide Assemblage 3), which spilled over westward across the a sedimentological framework for the sequence Springsure Shelf into the Galilee Basin. By latest stratigraphic analysis reported by Ziolkowski et al. Permian times, alluvial plain conditions had become (this volume). established across much of the basin, and persisted The earliest phase of development of the western into the Triassic period (Kassan, this volume). Bowen Basin involved limited crustal extension and The thrust of the present paper is the definition the formation of grabens and half-grabens. These early of recurrent lithofacies associations and component sub-basins were infilled by mainly continental, facies within the late Early to early Late Permian alluvial clastic sediments which now comprise the Facies Assemblage 2. coal-bearing Reid's Dome beds (Fig. 1). A series of facies associations are recognised and Accumulation of the Reid's Dome beds (Facies reconciled to environments within the marine shelf and Assemblage 1) was progressively terminated by a coastal realm. Facies are recognised on the basis of marine transgression, coinciding with a transition lithology, sedimentary structures, relationships to from extensional subsidence to a more regionally other facies and contained body and/or trace fossils. uniform phase of thermal subsidence. The facies scheme is designed to be applicable to both Much of the late Early to early Late Permian outcrop and core. While it is therefore based on section (Facies Assemblage 2) comprises a succession features visible in core, there are strong geometrical of offshore shelf to coastal facies (Fig. 1), accumulated connotations to each facies arising from observations in a realm of dominantly thermal subsidence. Coarse on good outcrop exposure. Consequendy, each facies clastic wedges prograded eastward into the Denison has distinct reservoir properties (including geometry, Geological Society of Australia Abstracts Number 32, Ballarat 1992

115 poroperm, etc.), an observation which has some value in hydrocarbon exploration across the area. The following facies associations are recognised; 1. Offshore Shelf (below storm wave base) mainly siltstone and sandy siltstone, mostly strongly bioturbated. 2. Transition Zone (between storm and fairweather wave base) - as above with minor interbedded sandstone, hummocky cross-stratified (HCS), variably bioturbated. 3. Shoreface (between fairweather wave base and low tide level) - mainly sharply-bounded sandstone beds, with lesser fine-grained horizons, HCS, minor bioturbation. 4. Foreshore (between low and high tide level) amalgamated, quartzose sandstones with flat and lowangle lamination, mainly minor bioturbation. 5. Tidal Inlet and Delta - erosively-based, crossbedded sandstones, modest Skolithos bioturbation. 6. Distributary Channel - thick, erosively-based, cross-bedded sandstone, rare bioturbation. 7. Lower Delta Plain Interdistributary Bay/Backbarrier Lagoon - thinly interbedded sandstone and siltstone, abundant wave-generated structures and small-scale HCS, coal and carbonaceous shale, PERIOD EPOCH

fc

Differing sub-sets of the recognised facies occur in the various formations (Fig.l). Some units such as the Ingelara Formation, which represent major transgressive events, are dominated by facies of Associations 1 and 2. Others show a more complete cross-section of facies. Some facies, such as amalgamated shoreface sands (delta front of major deltaic complexes), occur in specific situations. The overall aspect of coastal and inner shelf sequences within the described interval can be said to be wave-dominated and probably microtidal, with tidal flux affecting sediment dispersal only in lower delta plain channels and inlets. In areas of significant fluvial outflow, deltas are of wave-fluvial interactive type with minor tidal influence. The activity of tides during this period implies physical connection with the palaeo-Pacific Ocean, presumably through gaps in the temporarily inactive magmatic arc east of the Bowen Basin. DEPOSITIONAL ENVIRONMENT

UNIT

Rewan

Alluvial

Group

Z

Bandanna

2 cr tu

B l a c k Alley

CL

variable bioturbation. 8. Upper Delta Plain Interdistributary Lake mainly thinly interbedded sandstone and siltstone, current-generated structures dominant, minor bioturbation, coal and carbonaceous shale.

Fm

Deltaic

Shale

R e s t r i c t e d Marine to ? L a c u s t r i n e

ID

Peawaddy

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< —1

Catherine

Sst

Shoreline & Nearshore Shelf

Ingelara

Fm

Offshore

Upper Aldebaran S s t / Freitag z < 2

L.Aldebaran

>-

<

ID

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Cattle Creek Fm

J

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Sst^"

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\

\

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R e i d s Dome beds

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Deltaic, with a s s o c i a t e d shoreline systems

/

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Offshore Shelf J with > Deltaic ^Mafine influence S j | n f l u e n c e s

_J

Alluvial & Lacustrine

Figure 1 - Stratigraphic table for the Permian sequence in the Denison Trough, showing broad depositional settings.

Geological Society of Australia Abstracts Number 32, Ballarat 1992

116 A 4.15 BROWN COALS & RESERVOIR SANDS: RESPONSES TO RELATIVE SEA LEVEL CHANGES & TERTIARY COASTAL ONLAP, GIPPSLAND BASIN. G.R. Holdgate* Department of Earth Sciences, Monash University, Victoria. Marine ingressions into the brown coal fields of Gippslands' Latrobe Valley have been interpreted from occurrences of marine foraminifera and dinoflagellates in the interseam clays and reservoir sands (Holdgate & Sluiter, 1991). Quantitative coal seam pollen data (Sluiter, 1984) recognises stratigraphically equivalent changes in the palynology around the times of interseam development. Field work has now demonstrated the association of erosional disconformites within the coal seam sequence to sulphur highs and interseams, and proposes a regional coal lithotype stratigraphy can be influenced by relative sea level changes. Brown coal moisture content decreases towards the marine boundaries and reflects compaction factors of up to 30% by volume to accommodate the loading by shoreface reservoir sands. Conclusions from the above with regard to relative sea level changes and Tertiary coastal onlap are:. palynological dating constrains some 14 OligoA 4.16

Miocene marine ingressions to 12 "Vail-type" condensed sections. . significant portions of time are taken up by the interseam sediments with correlative disconformites in the coal seams. . between disconformites, most coal accumulated during "Vail-type" transgressive systems tracts, and most reservoir sands formed during the high stand systems tracts. . coal lithotype sequences tend to lighten upwards during each transgressive interval. . high stand systems tracts are poorly represented in the Latrobe Valley coastal plain swamps. References Holdgate, G.R. & Sluiter, I.R.K., 1991, Geol. Soc. Aust. Spec. Publ. 18:137-157. Sluiter, I.R.K., 1984, Ph.D. Thesis, Monash University (unpublished).

RELATIONSHIP OF COAL FACIES WITH SEA LEVEL IN THE BASS BASIN Peter Baillie Department ofResources and Energy, P.O. Box 56, Rosny Park, Tasmania 7018

The Bass Basin is a Late Mesozoic Cainozoic intracratonic basin, trending northwestsoutheast between Victoria and northern Tasmania, consisting of up to 16 km of non-marine and marine sediments and volcanics ranging in age from Late Jurassic (?) to Recent. The main stratigraphic units in the basin are the Upper Jurassic (?) - Lower Cretaceous non-marine Otway Group, the Upper Cretaceous - Upper Eocene coal-bearing Eastern View Group, the Upper Eocene marginal-marine Demons Bluff Formation and the Oligocene - Recent marine Torquay Group. The Eastern View Group (EVG) is up to 8 km in thickness, consisting of interbedded sandstone, siltstone, mudstone, coal and volcanics. An unconformity of possible regional extent ("M. diversus Unconformity") has been used to informally divide the EVG into two units. The lower unit comprises dominantly finer-grained sediments of Late Geological Society of Australia Abstracts Number 32, Ballarat 1992

Cretaceous to Early Eocene (Lower M. diversus Zone) age, while the overlying upper EVG is richer in coals and more sandy than the lower division. Although all EVG coals are vitrinite rich (usually > 80 per cent), there are significant differences between lower EVG and upper EVG coals. In general, upper EVG coals have more detrovitrinite than telovitrinite, whereas in lower EVG coals these macerals are present in roughly equal proportions; in addition, upper EVG coals are richer in exinite and poorer in inertinite than lower EVG coals (Smith, 1986). Upper EVG coals occur in seams up to 25 m in thickness and generallly have sharp upper and lower contacts, together with low ash and/or clay contents. The apparent absence of rooted sediments and seat earths suggests that the coals are allochthonous and may have originated largely from floating bogs or swamps. Although the absence of marine

117 dinoflagellates indicates that the coals are of freshwater levels of Paleocene times. Greatest coal development origin, sedimentological evidence and boron trace in the basin took place during Upper M. diversus and element geochemistry indicates that the coals formed P. asperopolus Zone times (48-51.5 Ma) when global in very close proximity to the sea (Baillie and Bacon, sea levels were at the highest levels of the entire 1989). Cainozoic era. In contrast, coals of the lower EVG are much less abundant and have a different log character. They References are generally thinner than those of the upper division; gamma ray counts are usually higher indicating greater Baillie, P.W.; Bacon, C.A. 1989. Integrated Sedimentological Analysis: The Eocene of the ash and/or clay contents, and upper and lower Bass Basin. APEA J. 29(1): 312-27. bounding surfaces are not as sharp. It is probable that these coals originated as swamp forests or bogs in a Baillie, P.W.; Tingate, P.R.; Stuart, W.J. 1991. Reservoir development and diagenesis in the Bass delta system (Baillie et al. 1991). Basin, Tasmania. APEA J. 33(1): 85-100. It is considered that sea level was a primary Smith, G.C. 1986. Bass Basin geology and petroleum control on coal formation. The relative absence of exploration, in Glenie, R.C. (ed,).Second Southcoals in the lower EVG may be a function of the Eastern Australia Oil Exploration Symposium.: lower water tables related to the comparatively low sea PESA Symp., Melb.: 257-84. A 4.17 CORRELATION OF THE ILLAWARRA COAL MEASURES, SOUTHERN AND WESTERN COALFIELDS, SYDNEY BASIN A C Hutton Department of Geology, University of Wollongong, Wollongong NSW The Illawarra Coal Measures has been a significant influence on industry and the economic viability of the Southern Coalfield (centred on Wollongong) and the Western Coalfield (centred on Lithgow) of the Sydney Basin since coal was first discovered last century. An understanding of the stratigraphy of the two areas received much attention initially but because of the relatively simple geological structure of the sequences in the two coalfields, emphasis was given to mining problems rather than rather than to what could perhaps be described as academic studies. Consequently, those familiar with the two coalfields accepted that the two sequences were correlatives. Indeed although many correlations were made, few were based on detailed geological fieldwork and consequently none was universally accepted. Many of the problems relating to existing correlations have been outlined (Hutton, 1990). With increased costs relating to fully cored holes, many companies have turned to open holes with accompanying geophysical logs. The latter provide an ideal tool for correlation provided that earlier nonlogged holes, especially those containing the type sections, can be slotted in to sections. Arditto (1987a, b, c) was the first to use logs in basin wide studies. One of the significant findings of his studies was the recognition that unit boundaries could be identified and matched with lithological boundaries in core. In a more recent publication, Arditto (1990) undertook a sequence stratigraphic Geological Society of Australia Abstracts Number 32, Ballarat 1992

analysis of the Late Permian succession in the Southern Coalfield and addressed among other things, a correlation problem relating to the Wongawilli Coal in the northeastern part of the coalfield. It can be argued that geophysical logs provide an easy, efficient and useful tool for characterising coal measures sequences in the southern Sydney Basin and that correlation between the Southern and Western Coalfields, based on geophysical logs, is not only logical but overcomes the difficulties associated with handling, deterioration or loss of core. Correlations using geophysical logs also provide detailed information on the coal seams (such as thinning of the Wongawilli seam towards the northern part of the Southern Coalfield) and the clastic interseam sediments, especially vertical and lateral facies changes (such as northerly thickening of the interseam unit between the Bulli Coal and Balgownie Coal Member and a change in the nature of the Balgownie seamWongawilli Coal clastic interval) and the identification of tuffaceous layers, commonly referred to as 'claystone' bands. References Arditto, P.A., 1987a, Proc. 21st Adv. Sydney Basin Newcastle Symp., 11-17 Arditto, P.A., 1987b, Proc. 21st Adv. Sydney Basin Newcastle Symp.,99-105 Arditto, P.A., 1987c, £*/?/. Geophys., 18:355-366

118 Arditto, P.A., 1990, Aust. J. Earth Sci., 38: Hutton, A.C., 1990, Proc. 24th Adv. Sydney Basin

A 4.18

COAL

COMPOSITION

Newcastle Symp., 17-24

AND

SEQUENCE

STRATIGRAPHY

Claus F. K. Diessel Department of Geology, The University of Newcastle, N.S.W. 2308 There have been several attempts to explain the depositional patterns of coal measures in sequence stratigraphic terms, although in none of these cases was much consideration given to the composition of coal seams in relation to their inferred sequence stratigraphic status. This paper discusses two examples of coal seams which cap upward coarsening, regressive marine rock units formed above a marine flooding surface. One example is the Bayswater Seam from the Wittingham Coal Measures in the Hunter Valley, the other is the Borehole Seam from the Newcastle Coalfield. Both coal seams represent backbarrier strandplain deposits situated on drawn-out beach sandstones which grade downward into offshore siltstones and bioturbated laminites. The similarity in lithofacies, the order of superposition and interpreted palaeo-environmental setting suggest that the two seams share the same sequence-stratigraphic position at or near the top of a parasequence, possibly within a transgressive systems tract. This interpretation is based on the widely held assumption that each parasequence begins with a marine flooding surface along which a landward shift of facies has occurred. The comparatively rapid retrogradation of the strandline is followed by a period of relaxation during which the strandline progrades seaward and most of the sedimentation, including peat accumulation, takes place. In this scenario the formation of coal occurs within the context of a marine regression. However, when coal composition is taken into account, more complex relationships become apparent, as is demonstrated by the two above mentioned coals and other seams. The salient points are listed below: 1. The Bayswater Seam contains downlapping tuff bands within a 5 km long section, which demonstrate that the coal is time-transgressive, i. e. its peat has followed the prograding barrier beach (= Archerfield Sandstone) by occupying remnant lagoons, washover fans, and other emergent features of the backbarrier. Tuff-derived claystone bands in the Borehole Seam have been correlated over a 25 km long section down palaeo-slope. No downlapping has been found, but the seam appears to be part of an onlapping trend that reversed the progradation of the underlying Waratah Sandstone. Geological Society of Australia Abstracts Number 32, Ballarat 1992

2. The Bayswater Seam is subhydrous because of a low H/C ratio in comparison to the Borehole Seam. 3. The pyrite content of the Bayswater Seam is generally low when compared with the Borehole Seam which has elevated pyrite contents near its floor and roof, the latter cosisting of bioturbated shale. 3. Within the generally high inertinite content of the Bayswater Seam inertodetrinite is particularly common. There is no botanical reason for this unusual composition, since both its vitrinite-rich and inertinite-rich portions contain similar average proportions of the main palynomorphs. The high concentration of inertodetrinite must therefore be related to unique circumstances in the depositional environment in which the peat, formed from a largely arborescent vegetation, was frequently exposed to oxidative decay. The Borehole Seam has a comparatively high vitrinite content and high degree of gelification which is indicative of a generally high groundwater table and frequent inundation during its peat stage. 4. The vertical distribution of optical properties in the Bayswater Seam is consistent with coal formation under regressive conditions shown by the decreasing intensity of vitrinite fluorescence towards the seam roof. In contrast, vitrinite fluorescence in the Borehole Seam increases towards the seam roof, which is typical of coals formed under a regime of marine transgression. These observations are consistent with the nature of the roof sediments of the Bayswater and Borehole seams, which consist of fluvial/overbank and lagoonal deposits, respectively. The contrasting properties of the two seams suggest that, in spite of the similarity of their respective palaeo-environmental settings, the two seams occupy different positions within the sequence stratigraphic model. The Bayswater Seam follows the prograding strandline as an integral part of the highstand systems tract which begins with the underlying barrier beach complex of the Archerfield Sandstone. The Bayswater Seam therefore caps the parasequence and conforms to the preferred model in the sequence stratigraphic literature. Conversely, the Borehole Seam ushers in a new parasequence, a genetic position it shares with other transgressive coals, such as the Greta Seam in the Hunter Valley or the

119 Katharina Seam in the Ruhr Basin. A 4.19

TECTONICS AND SEDIMENTATION IN THE MAE MOH COAL BASIN, NORTHERN THAILAND *

Colin R.Ward and P.R. Evans Department of Applied Geology, University of New South Wales, Kensington, N.S.W. The Mae Moh Basin is one of a number of NNESSW trending intermontane sedimentary basins of Cainozoic age in northern Thailand, separated by elevated ridges composed of Palaeozoic and Early Mesozoic strata of the Sukothai Fold Belt. The disposition of these basins reflects regional tectonic grain set up by the transpressional convergence of the Asia, Southeast Asia and Indo-Australia Plates during the Late Cretaceous and Cainozoic. The Shan-Thai block, a rhombic-shaped area flanked by the Red River Fault zone to the north, the Uttradit Suture to the east and the complex of the Mae Ping and Three Pagodas Faults to the south, was rolled in this convergence between the Indo-Australia Plate and the China sector of the Asia Plate. The rolling action appears to have been accommodated by strike-slip motion along marked fracture zones within the rhomb, producing deformation analogous to that in a collapsing stack of books on a shelf (bookshelf tectonics). The Mae Moh Basin lies on one such fracture zone between two "books" of Permo-Triassic strata, and is thought to have been formed where relative motion between the basement blocks was transferred from one fault to another. The basin is filled by a fluvio-lacustrine, coalbearing sequence of Early to Middle Miocene age, overlain by a gypsiferous red-bed succession and capped, in the south, by Quaternary sediments and basaltic lava flows. The overall Tertiary succession is up about 750 m in thckness. It includes a basal sandy unit of fluvial origin, the Huai King Formation, overlain by a thick sequence (Na Khaem Formation) made up mainly of grey-brown calcareous lacustrine mudstones, with a number of minor grey-green claystone beds, several gastropod-bearing shelly horizons, and five separately identified coal seams. An interval of red-brown, partly silty mudstones, the Huai Luang Formation, overlies this sequence, with further coaly sediments occurring above the red-beds in the central part of the basin. The basin itself has a rhombic outline, defined by

Geological Society of Australia Abstracts Number 32, Ballarat 1992

the surrounding areas of basement rock. It is divided into two graben-like blocks, separated by a sedimentdraped basement ridge. The strata are cut by a northsouth trending normal fault pattern, with many of the faults possibly being listric on to the basement beneath. Two unconformities are recognized within the sequence, based on interpretation of seismic reflection data. The coal in the Na Khaem Formation is classed as a vitrinite-rich lignite, with around 32% in-situ moisture and a virtrinite random reflectance of around 0.4%. Three main coal seams are exposed by mining in the northern half of the basin, with each being up to about 30 m in overall thickness. Further towards the northern end of the basin, however, these seams are split into several separate beds by muddy lacustrine sediment. The coal in the main seams usually rests directly on lacustrine mudstone and is mostly overlain by further grey-brown or in some cases by grey-green mudstone deposits. The main seam plies thus appear to represent peats deposited in blanket mires across a slightly submerged lake-fill surface, with clastic sediment input coming mainly from the northern end of the basin. Intra-seam bands of calcareous shell fragments are common in the coals in the central part of the basin, but clay-rich bands become more common in the north towards the split seam area. The organic matter of the coal also contains a high proportion of calcium, apparently held mainly in exchangeable carboxylate form, and thus even without dilution by siliciclastic sediment the coals tend to give relatively high ash yields. Ash composition varies across the basin, however, reflecting dilution of the calcareous organic matter with abundant intra-seam shell debris, found in the central area, by muddy sediment introduced to the lake from rivers entering the basin in the north. A similar trend also appears to be developed towards the southern end of the basin, suggesting clastic input to the peat-forming mire from both ends of an enclosed lake system.

120 A 4.20

THE SEQUENCE ASSOCIATED WITH THE ALBIAN MAXIMUM FLOODING SURFACE IN AUSTRALIA, OR THE GREAT ANTEDILUVIAL FLOOD

G.C. Smith , B.E. Messent andR.A. Henderson tBHP Petroleum Pty Ltd, Melbourne Vic 3000 Geology Department, James Cook University of North Queensland, PO 4811, Townsville, Qld. 1

2

1

The Albian records one of the most widespread maximumfloodingsurfaces (MFS) ever deposited over the Australian continent. The various sedimentary environments represented by this marine incursion event are identifiable in all of the basins around the northern, western and south-western margins of the continent and over much of the Eromanga Basin. Probable equivalents are recognisable in parts of the Canning, Eucla and Great Australian Bight Basins. Truly this was a Great Antediluvial Flood which covered vast areas previously emergent. The sedimentary environments are typically starved and range from proximal shallow inland seas (eg euxinic mudstones of the Toolebuc Formation in the Eromanga Basin), to more distal radiolarian marine siltstone (eg Windalia Radiolarite in the Carnarvon Basin) and radiolarian claystones culminating inplaces in nodular phosphate beds (eg within the Darwin Formation, Southern Bonaparte and Money Shoal Basins) and oceanic warm water limestones (eg within the Darwin Formation, on the Sahul Platform). The precise age of these and associated units is difficult to determine because the varying sedimentary environments yield different fossil assemblages (eg radiolarians, forams, nannofossils, dinoflagellates, acritarchs, spore-pollen, belemnites and ammonites) and the occurrence of some species are more or less controlled by palaeoecology. Moreover, fine correlation between the biozones based on the different groups is not well established. The palynological zones (Helby et al, 1987) suggest some diachroneity from Aptian to Albian (roughly west to east) but they are somewhat provincial. The belemnite and ammonite data in the Bonaparte Basin especially in the succeeding highstand marine shales (Henderson, 1990), contain cosmopolitan species which indicate a more tightly constrained age of late Albian and this is A 4.21

2

consistent with nannofossil dating of the Toolebuc Formation in the Eromanga (Shafik, 1985). The event is commonly recognisable on seismic data. Marked impedance contrasts are produced by the lithological changes, going upwards from the thin lowstand and transgressive system tract sediments, through the MFS units and the downlap surface of the succeeding progradational highstand systems tract. These produce one of the most pronounced seismic events recognised all around the Australian margin and commonly referred to as "the base Albian seismic marker". The units associated with this MFS are extremely significant for petroleum exploration in most basins where they occur. The lowstand units can form major reservoirs (eg the Barrow Island oilfield with reserves of about 270 million barrels). The transgressive systems tracts units can form non-net or thief zones, while the MFS units together with the overlying thick highstand marine shales provide extensive regional seals and potential source rocks which cover vast areas of offshore and onshore Australia. Finally, the highstand units herald the building of the continental margin sequences around much of Australia. References Helby, R., Morgan, R. & Partridge, A.D. 1987. A palynological zonation of the Australian Mesozoic. Association of Australasian Palaeontologists Memoir 4, 1-94. Henderson, R.A., 1990. Late Albian ammonites from the Northern Tertiary, Australia. Alcheringa 14, 109-148. Shafik, S., 1985. Calcareous nannofossils from the Toolebuc Formation, Eromanga Basin, Australia. BMR Journal of Australian Geology and Geophysics 9, 171-181.

PRECISE RESERVOIR GEOMETRY MODELLING K R Johnson

KRJA Systems, 210 Glen Osmond Road, Fullarton, SA, 5063 The problem of using computer mapping to model techniques which satisfy conventional methodology as the geometries of complex reservoirs has been well as providing a fast and accurate assessment of addressed by combining a variety of spatial mapping reservoir volumes. This work has led to the evolution Geological Society of Australia Abstracts Number 32, Ballarat 1992

121 of OIL VIS ION, a 3-D Mapping and Modelling GIS tailored for the Oil & Gas industry. It is based on the ENVISAGE Software Engine which is a highly structured CAD-like package for the creation and modelling of spatial data and can be readily configured to meet specific requirements. In summary, the following steps are used to achieve the volumetric models: 1. Seismic interpretations form the primary input along with the downhole geological data relating to reservoir and other formations. These data can be captured direct into the system or loaded from industry-standard formats. These data are stored and displayable in 3-D in both space and time windows. 2. The Spatial Database containing the Seismic data and the Well Database with the downhole geology form the foundation for mapping the seismic data into interpreted structure models and thence modelling the detailed reservoir geometry of production formations. The seismic time data is gridded in conventional fashion and these surfaces form the control horizons from which the reservoir geometry and extent are established. Experimentation with large scale triangulations of the seismic data instead of grids is also proving successful. 3. A velocity model (usually a grid model) is applied to derive the depth models. The database has concurrent storage of the time and depth values and this allows direct instant switching between time and depth views of the data. 4. The Fast Triangulation coupled with gridding methods allows geologically accurate surfaces to be formed from the seismic reflectors. From these surfaces of the top and base of porosity, accurate definition of hydrocarbon limits can be created and stored. 5. The 3-D data structure allows all data to be stored and dynamically displayed in its true geological view. With the geological database loaded, the well information is also shown in full geological view allowing the well data and the structural data to be reconciled. The geological database is also used to store the net pay, porosities and saturation and other relevant

Geological Society of Australia Abstracts Number 32, Ballarat 1992

data. All these data can be displayed against the well log strings, usually colour-coded by reservoir name. The geological database can be established directly from the well picks of the interactive well log analysis system. 6. Reservoir Geometries can be accurately defined. Surfaces such as formation tops and bases, faults and unconformities can be intersected as grids or triangulations allowing accurate pinchout lines and wedge effects to be easily and precisely mapped. These techniques can be applied with equal ease to convex, tight-sand reservoirs, stratigraphic traps, or complex fault/unconformity controlled structures. With the use of various manipulative routines for dealing with the interaction of geological surfaces, including fault surfaces, it is possible to establish a unique configuration of each reservoir body, even though it may be bounded by a variety of surfaces. 7. Accurate Reservoir Volumetrics are provided from the Net & Gross Sand geometric models. These models are built interactively and can be queried graphically to establish the reserves and all the reserve calculations are stored in the database for later recall and reporting. Successive assessments and reviews can be maintained to establish reserve histories. The link between the graphics and the reserve inventories is permanently established for graphical interrogation. Any of the surfaces or isopach bodies can be contoured and the contours will honour all defined and established discontinuities, including wedge-edges, where different surfaces meet. Instant geological validation of the reservoirs is made easy by the 3-D visualization capabilities of the software. 8. The Extensive CAD functionality of OILVISION allows unlimited flexibility in creating the sub-surface geology. Faulting, including reverse thrusts, is handled without problem. All information can be graphically presented as standard Hydrocarbons-in-Place reports, along with drafting of high quality contour plots.

122 A 4.22

SEDIMENTOLOGICAL ANALYSIS CAN EXPLAIN THE EVAPORITE/HYDROCARBON ASSOCIATION John K Warren NCPGG and APCRC, University of Adelaide

Evaporites overlie carbonates that enclose an estimated one-half of the world's known petroleum reserves. About 70% of the world's giant oil fields in carbonate rocks have a relationship to evaporites and all of the giant gas fields in thrust belts possess an evaporite seal. The association among evaporites, carbonates, and hydrocarbons is more than accidental as evaporites constitute less than 2% of the world's platform sediments. The partnership persists for various reasons. Bedded ancient evaporites overlying or up-dip from porous sediments set up effective seals to any underlying potential reservoirs. Sedimentological signature in these seals can often be used to establish the local paleotopography of both the seal and the immediately underlying strata. Evaporite seals are tight even under high stress and typically embody capillary entry pressures in excess of 1000 - 1500 psi, hence thin evaporite units can support tall oil columns. Evaporites tend to flow rather than fracture under conditions of tectonically-induced stress so that under subsurface conditions where shale and mudstone seals tend to fracture and leak, even thin evaporite beds retain their continuity as both top and lateral seals. The contact between an underlying reservoir and an evaporite seal is typically knife sharp. Abrupt contacts are due to the very different conditions that were required to deposit thick subaqueous evaporite sequences (except sabkha seals) compared to the underlying, often marine, reservoir rock (e.g. a reef) as the units are separated in time and location, by Walther's Law the contact is typically sharp. This contrasts to many shale and micrite seals where the seal facies is a lateral time equivalent to the reservoir. This lateral continuity and time-equivalence of nonevaporite reservoir-seal environments often leads to a uneconomic transitional zone of silty sand that contains non-recoverable oil and gas, and separates the sand reservoir from the shale seal (e.g. floodplain shales sealing barrier island and deltaic reservoirs). The subsurface movement of pore waters leaches evaporites from many carbonate and siliciclastic matrices and so creates areas of secondary porosity. Evaporite diagenesis can also release large quantities of magnesium-rich brine and so form sucrosic dolomite, an excellent potential reservoir, in adjacent limestones. Thick, buried halite units are often remobilized into salt domes, which in turn creates potential Geological Society of Australia Abstracts Number 32, Ballarat 1992

reservoirs in the subadjacent sediments. Producing or potential reservoirs associated with salt structures have be found in the northwest shelf of Australia, in the Amadeus basin, Central Australia, in southern Russia, the North Sea, southern France, and the Atlantic Seaboard of Canada. Traps in many of these salt structure provinces are created by anticlinal closure over salt walls, diapirs, salt pillows, and turtle structures, as well as fault-line and unconformity traps lying above and adjacent to salt structures. Some oil traps in Germany even occur below mushroom-shaped diapirs where the salt acts as both trap and seal. Salt structures are most often found in active rifts or along previously rifted continental margins. These were regions of initial restriction and high geothermal gradients, followed by sediment dumping atop thick bedded evaporites. Not all salt structures still contain salt; fossil salt structures outcrop along the rift axis of the Adelaide Geosyncline in South Australia and in the Amadeus Basin in Central Australia. These structures were most active in the Proterozoic and influenced sedimentation patterns at various times in their flow history. The salt has long since been flushed from the structures, although they still contain extensive but small Cu-Pb-Zn mineralized pods similar to those forming aureoles about active salt structures in the Gulf of Mexico. An association may even exist between some evaporite depositional settings and source rock formation. Evaporites and evaporitic carbonates are by definition deposited in arid environments lacking fresh water, hence sediments, do not contain a high proportion of organic matter derived from higher plant debris. Rather, the elevated salinities and general environmental stress means the organics are often derived from algae and zooplankton. Most modern evaporites are deposited adjacent to, or within, areas of high algal productivity and accumulation. Thus evaporitic source rocks - often laminated carbonates are more likely to be oil-prone than gas-prone. Hypersalinity encourages anoxia due to inherent oxygen and carbon dioxide depletion in a brine, a reflection of decreased gas solubility in this highly saline water. Subsequent diagenetic regimes in some ancient evaporitic settings, such as rifts, intrashelf basins, and collision basins, are conducive to the preservation of this organic matter until it reaches the zone of catagenesis.

123 A 4.23

STOCHASTIC MODELLING OF SEDIMENTATION SYSTEMS: SOME IMPLICATIONS FOR SUBSURFACE GEOLOGY John C. Tipper

Department of Geology, Australian National University, GPO Box 4, Canberra, ACT 2601 Sedimentation systems are usually rather simple in concept. It is a quite straightforward exercise, for instance, to outline what fluvial sedimentation is and to describe its model facies patterns. Yet within any one system there will usually be sufficient spatial heterogeneity and temporal variability to ensure that its many possible realisations are quite varied, and it will thus never be a simple matter to predict from any general sedimentation model just what the actual stratigraphic record produced in a particular set of circumstances is likely to be. Stochastic sedimentation models seem to be the key to progress here, rather than models that are inherently deterministic. Deterministic modelling can be extremely useful in showing the variety of possible realisations that any one sedimentation system might have, and so a deterministic approach is often sensible in the initial stages of any modelling exercise. Deterministic models are thus, for instance, very appropriately used to show how the gross patterns of basin fill change with variations in subsidence rate, sediment supply and sea-level change. Deterministic models cannot, however, readily incorporate spatial heterogeneity and temporal variability (except at very considerable computational expense), and so they are less appropriate for detailed work. As spatial heterogeneity and temporal variability can readily be built into stochastic models, it is stochastic models that should be preferred. An illustration of this is given here in

A 4.24

the context of basin fill modelling, specifically in developing models that reproduce the substantial incompleteness of the stratigraphic record and which can thus better guide subsurface correlations. All stratigraphic successions must be expected to be incomplete, and this incompleteness is inevitably a function of the time-scale over which it is measured (Sadler, 1981). Stochastic models of sedimentation systems explain this phenomenon rather well (Tipper, 1983; Strauss & Sadler, 1989), but deterministic models of sedimentation systems give quite unrealistic estimates of completeness. This paper analyses one of the deterministic models commonly used for basin fill calculations and shows that the rock successions that it predicts are quite unlike any that are really found. Not only are they unrealistically complete, but that completeness is also independent of the measurement time-scale. An alternative stochastic model (Tipper, 1991) is then analysed and shown to produce successions that are realistic. References Sadler,P.M., 1981,/. Geol. 89: 569-584. Strauss,D. & Sadler,P.M., 1989, Math. Geol 21: 3759. Tipper,J.C., 1983, Nature 302: 696-698. Tipper,J.C., 1991, Expl. Geophys. 22: 397-400.

BASIN ANALYSIS: A HIDDEN DILEMMA Mike F. Middleton

Department of Exploration Geophysics, Curtin University of Technology Quantitative basin analysis has currently achieved a high level of popularity with the availability of a considerable variety of PC based programs. A very common application for petroleum well data is the combination of (i) burial history (including compaction effects), (ii) thermal maturity (based on vitrinite reflectance) and (iii) hydrocarbon generation (incorporating various chemical kinetic-based generation algorithms). This type of basin modelling is often referred to as geohistory modelling (Falvey and Middleton,1981). A common dilemma, the recent heat pulse, which results from the application Geological Society of Australia Abstracts Number 32, Ballarat 1992

of this type of basin modelling technique is reviewed in this paper. Geohistory analysis was applied to the Phoenix 1 and 2 wells in the Bedout Sub-basin, on the North West Shelf to demonstrate the "interpretation" of a recent, and unexplained, heat pulse. Some observed petrophysical data from the wells are shown in Tables 1 and 2. It should be noted that the wells are about 10km apart, the stratigraphic sequence is very similar in both wells, and the BHT data from both wells are almost identical. The porosity and thermal conductivity data in Table 1 were

124 measured on sandstones. Geohistory modelling was carried out on Phoenix 1, and the results (Table 3) indicated that a good match to the observed vitrinite reflectance data was achieved by using a constant heat flow of 1.1 Heat Row Units (46 mW/sqm). Table 3 shows that while the model matches the vitrinite reflectance data fairly well, the calculated maximum temperature and the observed temperature are in considerable conflict. Further, if the modpl heat flow were increased, the observed and calculated vitrinite reflectance would not match. The simplest, and obvious, model that satisfies both the vitrinite reflectance and the temperature data is a very recent heat pulse, such that the vitrinite reflectance has not yet had time to adjust to the increased temperature: thus, the recent heat pulse scenario. This behaviour is seen elsewhere on the North West Shelf, in the Canning Basin and in the Eromanga Basin. The recent heat pulse hypothesis, however, while a convenient explanation to the dilemma, does present significant problems. Essentially, for the temperatures to rise recently at bottom hole depths from 105°C to 146°C, the mean heat flow through the basin would have to rise from about 1.1 HFU to about 1.6 HFU in less than a million years. This increase of heat flow, when viewed from a lithospheric perspective, would imply the development of an incipient rift, as described by Falvey (1974) and McKenzie (1978). This clearly is not happening, and another explanation of the temperature discrepancy must be sought. The observation from Table 1 that both porosity and thermal conductivity are decreasing with increasing

depth indicates that the lithologies in the well are not behaving petrophysically in a way consistent with the "hidden" geohistory model asumptions, i.e. porosity decreases with depth and thermal conductivity increases with decreasing porosity. The petrophysical data suggest that the sedimentary sequence may have undergone a late diagenetic episode, rather than a late heat flow pulse. In the case of a late diagenesis pulse, a decrease of porosity by replacement of pore space with amorphous silica will decrease the bulk thermal conductivity of a sandstone (normally 4 to 5 SI units) to a value approaching that of a shale, which is about 1.5 SI units (see Table 2). A late change of thermal conductivity, induced by diagenesis, will have the same effect on temperature within the wells as a change in heat flow. The increased thermal conductivity will produce a thermal blanketing effect which will increase temperature without increasing heat flow. Hence, the temperatures near the base of the well will rise, without regional thermal doming and rift development, which make the late increase in heat flow (=late heat pulse) a technically unsupported and unattractive explanation of the present dilemma. References Falvey, D.A., 1974. APEA J. 14:95-106. Falvey, D.A. & Middleton, M.F., 1981. Ocean. Acta. 4: 103-114. McKenzie, D., 1978. Earth Planet. Sci. Lett. 40: 2532.

Table 1. Data from the Phoenix 1 and 2 wells DEPTH(m) TEMPERATURE(C) POROSITY(%) K(SI) VR(%) 1860 77 4.2 0.38 3460 118 17 2.9 0.56 4580 125 10 2.7 0.65 4880 146 4 0.71 K=thermal conductivity; VR=vitrinite reflectance Table 2. The Thermal Conductivity of Samples Measured from the Phoenix 1 and 2 Wells; K=thermal conductivity. WELL Phoenix 1 Phoenix 1 Phoenix 2 Phoenix 2 Phoenix 2

DEPTH(m) 3469 4369 4315 4316 4316

Geological Society of Australia Abstracts Number 32, Ballarat 1992

LITHOLOGY sandstone sandstone sandy shale sandstone shaley sand

K(SI units) 2.9 2.9 1.7 2.5 1.7

125 Table 3. Results of Geohistory & Vitrinite Reflectance Modelling of the Phoenix 1 Well; constant heat flow=l.l HFU assumed. DEPTH(m) I860 3640 4880 A 4.25

OBS TEMP 77 118 146

OBS VR 038 0.56 0.71

CALC MAX TEMP 48 81 105

CALC VR 034 0.53 0.72

THERMAL MATURATION MODELLING: A SCIENCE, AN ART OR A CRAFT? N. J. Russell

Division of Exploration Geoscience, CSIRO Intsitute of Minerals, Energy and Construction, North Ryde, N.S.W. Some pitfalls and problems that beset would-be basin modellers can be illustrated using a commercial, one-dimensional (ID) basin modelling software package, BASINMOD, which provides options for the compaction correction of paleoburial or geohistory plots, transient or steady- state heat flow calculation of paleotemperatures, and kinetic modelling of vitrinite reflectivity, apatite fission track analysis (AFTA), Rock- Eval Tmax and hydrocarbon generation data. BASINMOD is regarded as a robust software package inasmuch as its modelling algorithms are based on well-documented material published in the literature. In general, the more sophisticated the modelling software, the greater is the array of options available to bewilder the hapless modeller. Like most basin modelling software, BASINMOD allows the option of user-input or default values for the various parameters. However, the user is required to select between algorithm options for different modelling operations, e.g. linear or exponential compaction correction, transient or steady- state heat flow calculations, IFP (French Petroleum Institute) or LLNL (Lawrence Livermore National Laboratory) kinetics, etc. In common with most deterministic (numerical) basin modelling software, BASINMOD models paleotemperatures, hydrocarbon generation and thermal maturation indices in terms of first-order reaction kinetics, in which the first-order reaction rate is described by the Arrhenius equation. However, Snowdon (1979) questionned the extrapolation of laboratory- generated kinetic data, derived from shortduration, high temperature, pyrolysis, to longduration, low-temperature, geological processes. Furthermore, Price (1983) and Stannage (1988) disputed the use of first-order reaction kinetics to describe petroleum generation, arguing that such reactions are more likely to be controlled by multiorder reaction kinetics, that reach an equilibrium limit Geological Society of Australia Abstracts Number 32, Ballarat 1992

in a finite time. This led to the concept that vitrinite reflectivity provides a direct measure of maximum paleotemperature, i.e. that it consttutes an absolute maximum paleogeothermometer (Barker, 1983; Price, 1983, Barker & Palewicz, 1986, Barker, 1989, Barker & Goldstein, 1990); a concept that has been rejected by other authors (Waples, 1983; Lerche et al., 1984). The inadequacies of the Lopatin (1971)/Waples (1980) time-temperature index (TTI) method for modelling thermal maturity have been discussed in the literature (Lerche et al., 1984; Wood, 1988; Waples et al., 1991b). Burnham and Sweeney (1989) concluded that the classical form of the Arrhenius equation, combined with an appropriate, empirically-defined, activation energy distribution, provides the best way to model thermal maturity, in general, and vitrinite reflectivity, in particular. They reject the use of modified forms of the Arrhenius equation (Toth et al., 1981, Lerche et al., 1984; Armagnac et al., 1988; Armagnac et al., 1989; Cao & Lerche, 1989) as having little theoretical basis. Waples et al. (1991b) have emphasized the need for adequate, reliable vitrinite reflectivty data against which to test the plausibilty of geological models. There are problems associated with the reliabilty and interpretation of these data (Jones et al., 1972; Bostick & Foster, 1975; Dow, 1977); not least of which is the phenomenon of vitrinite reflectance suppression in hydrogen-rich environments (Hutton & Cook, 1980; Newman & Newman, 1980; Price & Barker, 1985). The slope of a linear trend, plotted on a semilogarithmic vitrinite depth/reflectance diagram, is a function of the maximum paleoheat flow density. Increase in the latter yields an increase in the logarithmic vitrinite depth/reflectance gradient, i.e. increase in logarithm of reflectivity with increase in depth. The vitrinite reflectance surface intercept is a function of the depth/reflectance gradient and thickness

126 of section lost by erosion. Sensitivity analysis, i.e. determination of how sensitive a modelling operation is to variation in input data, is regarded as an integral part of basin modelling (Waples, 1991b). BASINMOD software provides a sensitivity matrix analysis option for optimizing the heat flow density and thickness of eroded section to achieve a best fit between the observed and calculated vitrinite depth/ reflectance profiles. Examples taken from Australian sedimentary basins, e.g. Bowen, Clarence -Moreton and Sydney Basins in eastern Australia, and the North West Shelf of Western Australia, illustrate the way in which paleoburial and paleothermal trajectories can be constrained and the validity of the various geological models can be tested. The Bowen and Sydney Basins provide excellent opportunities to explore the effects of thin skinned thrust tectonics, resulting in relatively rapid sedimentary burial by tilting, folding and overthrusting, as well as those of the transient heating associated with localized igneous intrusive activity. In the Bowen Basin, the highest regional coal ranks and youngest AFTA ages are associated with the overthrust zone in the eastern central part of the basin; however, locally, the regional pattern is perturbed by igneous intrusions in the northern part of the basin (Mallett et al., 1990). In the Sydney Basin, the highest current surface heat flows and coal ranks are recorded in the southeastern part of the basin (Facer et al., 1980); deep (> 2 km) burial or high heat paleoheat flow densitiies have been invoked to account for these high coal ranks. Recently, Middleton (1991) proposed that the main period of uplift occurred in response to mantle/lithospheric rebound in the Early Jurassic/Early Cretaceous, rather than the previously-postulated Late Cretaceous thermal doming, prior to seafloor spreading in the Tasman Sea. He suggested that the paleomagnetic overprinting and high coal ranks in the east of the basin may be attributed to high paleoheat flows provided by a hypothetical basic igneous intrusion intruded at 10-15 km beneath the coastal plain in the Late Cretaceous during continental breakup. There is a regional eastward increase in vitrinite reflectivity, and decrease in AFTA ages, for surface rocks in the Clarence-More ton Basin; modelling of depth/ reflectance profiles in this basin tests the need to invoke a Late Cretaceous heating event associated with continental breakup (Russell 1991). Perhydrous coals in the Sydney Basin and marine sediments of the North West Shelf provide examples of the influence of vitrinite reflectance suppression on thermal maturation modelling. Clearly, attempts to fit calculated vitrinite reflectivities to "suppressed" vitrinite depth/ reflectance profiles will result in underestimations of paleoheat flow density, paletemperature and the level of thermal maturity of Geological Society of Australia Abstracts Number 32, Ballarat 1992

organic matter with respect to oil and gas generation. The laser Raman micro- beam technique for oil exploration (RAMBOE) promises to provide a microfluorometric method for correcting for the effects of vitrinite reflectance suppression and an independent index of both organic matter thermal maturty and type for finely-disseminated carbonaceous material, e.g. Wilkins et al., 1991a, 1991b. Whilst unique solutions may not be found (Waples, 1991a), geologically implausible models can be rejected and a range of plausible geological models delineated. Although underpinned by well-documented, robust, scientific hythotheses, there is considerable scope for craft or art, perhaps even black art, in an intuitive approach to basin modelling. A good example is the Law et al. (1989, 1990) interpretation of kinky vitrinite depth/reflectance profiles associated with overpressuring in low-permeability, gas-bearing sequences in Rocky Mountain foreland basins, USA. and its subsequent criticism by Waples (1990). Clearly, a well-developed sense of imagination is required, provided that it is tempered by experience and a concept of the boundary between science, on the one hand, and science ficton or fantasy, on the other. References Armagnac, C., Bucci, J., Kendall, C.G.St.C., & Lerche, I., 1989, In: Thermal History of Sedimentary Basins, Naeser, N.D., & McCulloh, T.H. (Eds.), Springer-Verlag, New York, 217-. Armagnac, C., Kendall, C.G.St.C., Kuo, C., Lerce, I., & Pantano, J. J. Geochem Explor., 30, 1-28. Barker, C.E., 1983, Geology, 11, 384-388. Barker, C.E., 1989, In: Thermal History of Sedimentary Basins, Naeser, N.D., & McCulloh, T.H. (Eds.), Springer-Verlag, New York, 73-98. Barker, C.E., & Goldstein, R.H., 1990, Geology, 18, 1003-1006. Barker, C.E., & Pawlewicz, M.J., In: Paleogeothermics, Buntebarth, G., & Stegena, L. (Eds.), Springer-Verlag, Berlin, 79-93. Bostick, N.H., & Foster, J.N., 1975, In: Petrographie de la matiere organique des sediments et relations avec la paleotemperature et le potentiel petrolier, Alpern, B. (Ed.), Int. Colloq., Paris, September 1973, CRNS, 13-25. Burnham, A.K., & Sweeney, J.J., 1989, Geochim. Cosmochim. Acta, 53, 2649-1657. Cao, S., & Lerche, I., 1989, Petrol. Geol., 12 (3), 325-351. Dow, W.G., 1977, Geochem. Expl7, 79-99. Facer, R.A., Cook, A.C. & Beck, A.E., 1980, Int. J. Coal Geol., 1, 1-17. Hutton, A.C., & Cook, A.C., 1980, Fuel, London, 59,711-714. Jones, J.M., Murchison, D.G., & Saleh, S.A., 1972, In: Advances in Geochemistry, von Gaertner, H.R., & Wehner, H. (Eds.), 1971, Pergamon

127 Press, Oxford, 601-612. Law, B.E., Nuccio, V.E., & Barker, C.E., 1989, AAPG Bulletin, 73 (8), 999-1009 & 74 (6), 948949. Lerche, I., Yarzab, R.F., & Kendall, C.G.St.C., 1984, AAPG Bulletin, 1704-1717. Lopatin, N.I., Isvest. Akad. Nauk SSSR, Ser. Geol, 1971,3,95-106. Mallett, C.W., Russell, N.J., & McLennan, T.P.T., Proc. Bowen Basin Symp., Mackay, September 1990, 15-20. Middleton, M.F., Proc. 8th. Gondwana Symp., Hobart, Jume 1991 (In Press). Newman, J., & Newman, N.A., 1982, N.Z. J. Geol. & Geophys., 25, 233-243. Price, L.C., 1983, J. Petrol., Geol., 6 (1), 5-38. Price, L.C., & Barker, C.E., 1985, J. Petrol Geol, 8(1), 59-84. Russell, N.J., 1991, In: BMR Bulletin 241 (In press). Snowdon, L.R., 1979, AAPG Bulletin, 63 (7), 11281138 Stannage, W., 1988, J. Petrol Geol., 11 (4), 415428.

Toth, D.J., Lerche, I., Petroy, D.E., Meyer, R.J., & Kendall, C.G.St. C., 1981, In: Adavance in Organic Gechemistry, 1981, John Wiley & Sons, New York, 588-596. Waples, D.W., 1980, AAPG Bulletin, 64 (6), 916926. Waples, D.W., 1983, Colorado School of Mines Quarterly, 78 (4), 15-30. Waples, D.W., 1990, AAPG Bulletin, 74 (6), 946947. Waples, D.W., Kamata, H., & Suizu, M., 1991a, AAPG Bulletin (In press). Waples, D.W., Suizu, M., & Kamata, H., 1991b, AAPG Bulletin (In press). Wood, D.A., 1988, AAPG Bulletin, 72 (2), 115-134. Wilkins, R.W.T., Wilmshurst, J.R., Hladky, Ellacott, M.V., & Buckingham, C.P., 1991a, NERDDP End of Project Report, 78 pp. Wilkins, R.W.T, Wilmshurst, J.R., Russell, N.J., Hladky, G., Ellacott, M.V., & Buckingham, C.P., 1991b, Org. Geochem. (In press).

A 4.26 PARAMETERS OF TIME AND HEAT IN ORGANIC MATURATION: A CASE STUDY FROM THE BUCHAN LIMESTONE C.E. B a r k e r

1

y. Bone, ' and C.R Dalgarno, 1

3

* Department of Geology and Geophysics, University of AdelaideSouth Australia U.S. Geological Survey, Denver, Colorado 80225 U.SA. 3 Geological Survey of Victoria, Melbourne, Victoria f

2

It has long been established that there is a minimum time during which temperature must be elevated for organic material in sediments to mature into the oil/gas window. This work is based, in part, on models of thermal maturity that use measured vitrinite reflectance and the computed rock temperature profile from heat flow equations. These results can now be tested by a new technique using reequilibrated fluid inclusions in metamorphosed cements (Barker and Goldstein, 1990). Microthermometry of the reequilibrated fluid inclusions is used here to indicate the peak temperature reached in rocks adjacent to dykes. The test of thermal maturity models involves measuring peak temperature and vitrinite reflectance, and comparing them to the computed temperature, heating time, and thermal maturity. The expected vitrinite reflectance profile should be comparable to the measured values. Because peak temperature and vitrinite reflectance are measured, the influence of heating time in modeling thermal maturity can be clearly assessed. This paper considers a Tertiary dyke that has intruded the Devonian Buchan Caves Limestone, near Geological Society of Australia Abstracts Number 32, Ballarat 1992

Murrindal, Victoria. Samples were taken from one bed at increasing horizontal distance from the near-vertical dyke margin. Regional background measurements were made on samples far removed from the intrusions. Vitrinite was sparse in these samples adjacent to the dyke, and reflectance measurements was not practical on this maceral. However, fracture- and pore-lining bitumen (meso-impsonite), showing a well developed mosaic structure, is common in these samples. The bitumen has a reflectance of about 2.4 to 2.7% (equivalent to about 2.0% vitrinite reflectance-Jacob, 1975). Bitumen reflectance showed little change up to 6 m away from the dyke contact. This thermal maturity level suggests a peak temperature of over 200°C was reached during metamorphism. Other studies of fluid inclusions trapped in lead-zinc deposits indicate similar paleotemperatures were widespread throughout the Buchan trough. Although these sample limitations negate a test of vitrinite-reflectance based thermal-maturity models at this site, it is important to note that bitumen was present in the Buchan Caves Limestone when the Tertiary dyke intruded. Thus, oil generation and

128 temperature in calcite and its comparison to the vitrinite reflectance geothermometer: Geology, v. 18, p. 1003-1006. Jacob, H., 1975, Mikroskopphotometrische Analyse References naturlicher fester Erdolbitumina, in, Alpern, B., ed., Petrographie Organique et Potentiel Petrolier. Barker, C.E., and Goldstein, R.H., 1990, A fluid Coll. int., CNRS, Paris, p. 103-113. inclusion technique for determining maximum

subsequent formation of meso-impsonite occurred before the Tertiary dyke intruded the Buchan Trough.

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RODDA BEDS, EASTERN OFFICER BASIN: ANATOMY OF A LEAN NEOPROTEROZOIC PETROLEUM SOURCE ROCK David M. McKirdy *, Stephen D. Pell ' and Michelle Smyth 1

1 3

2

department of Geology & Geophysics, University of Adelaide, Adelaide, SA 5001 CSIRO Division of Exploration Geoscience, North Ryde NSW 2113 Present address: Research School of Earth Sciences, Australian National University, Canberra, ACT 2

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3

2601

The Rodda Beds comprise a monotonous succession of grey, calcareous and dolomitic siltstones with subordinate beds of limestone, sandstone and pebble conglomerate. Maximum thickness of the sequence is >1.35 km in the Munyarai Trough. An outer marine shelf to upper slope environment is envisaged for these sediments which display evidence of slumping and mass flow. They are for the most part organically-lean (TOC = 0.05-0.35%), although thin potential source beds containing oil-prone lamalginite (TOC = 0.4-1.5%) have been identified in core from 5 drillholes. Contributors to the lamalginite include large spinose acritarchs (Jenkins et al., 1991). Kerogen type (hydrogen index = 53-244) and carbon isotopic composition (8 CPDB = -33 to -23 %o) are decidedly non-uniform. Rock-Eval Tmax data, kerogen H/C atomic ratios and lamalginite reflectance and fluorescence colours indicate levels of thermal alteration ranging from immature on the Murnaroo 13

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Platform to overmature below 2.8 km depth in the Munyarai Trough. Oil shows are associated with the sequence in Ungoolya-1 and also occur in the underlying Murnaroo Sandstone at Lake Maurice West-1. Elsewhere petrographically recognisable bitumen (in part thucolitic) provides further evidence of widespread oil generation in the Rodda Beds. Marine carbonate in the lower Rodda Beds at Murnaroo 1 and Observatory Hill-1 is isotopically heavy (mean 8 CPDB = +5 %o) and appears to record a relatively short-lived (and perhaps local) episode of enhanced preservation and burial of organic matter in sediments flooring the Early Ediacaran ocean. 13

Reference Jenkins, R.J.F., McKirdy, D.M., Foster, C.B., O'Leary T. & Pell, S.D., 1991, Geol. Mag. (submitted)

SEQUENCE STRATIGRAPHY OF A COAL SEAM Michelle Smyth * and Michael Buckley 1

2

CSIRO Division of Exploration Geoscience, PO Box 136, North Ryde, 2113, Australia CSIRO Division of Mathematics and Statistics, PO Box 218, Lindfield, 2070, Australia

J 2

Coal is an extremely finely layered sedimentary rock, the heterogeneous nature of which is obvious at both macroscopic and microscopic levels. Correlations are being established between coal petrography and coal properties critical to coalbed methane drainage, such as permeability. Preliminary results indicate that vitrite-rich coal is 10 x more permeable than inertiteGeological Society of Australia Abstracts Number 32, Ballarat 1992

rich coal in the Bulli seam, Sydney Basin (Lincoln Paterson, pers. comm. 1991, CSIRO Division of Geomechanics). Microlithotype analyses provide precise and detailed information on the abundance and location of vitrite-rich and inertite-rich layers in coal seams, particularly where sequential analyses are carried out.

129 This paper presents the results of a statistical analysis of sequentially recorded microlithotypes through the Bulli Coal, Sydney Basin. A Markov Chain model is found to fit well to the data. The model explains not only the order of the bands in the seam which corresponds to transitions between different states in the Markov Chain, but also to thickness of the bands which corresponds to transitions from one state back to itself. If fracturing and permeability depend on the type, order and

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thickness of bands, the locations of atypical, thick bands in seams may be critical. Parameters of the model - state transition matrices - are estimated from the data. This is done separately for each of the five macroscopically identified plies in the seam. The model is to be used in predicting the natural fracturing behaviour of the coal for methane drainage, by characterizing the structure of the microlithotype sequences through the coal.

PETROLOGY AND PALYNOLOGY OF CATTAMARRA COAL, PERTH BASIN, WESTERN AUSTRALIA K. K. Sappal* and A. Islam School of Applied Geology, Curtin University of Technology, Perth Western Australia

The Cattamarra Coal Measures of Jurassic age subcrop and outcrop over a 5 to 10 km wide north trending strip along the Hill River Fault zone in the Northern Perth Basin. The present configuration of the four coal deposits associated with the coal measures is structurally controlled as a consequence of post depositional faulting, folding and erosion, Kristensen and Wilson (1986). The coal samples of a 30 metre interval from the CRA Bore hole No.CPCHl have been studied for their petrology and palynology. Like Collie coal, the Cattamarra coal predominandy consists of banded, dull banded and dull coal types with minor bands of bright, bright banded and fusain types, Sappal (1987). The coal is high in vitrinite and intertinite content, with low exinite and predominance of alginite. The mineral matter content in the coal is higher than the Collie coal. The palynological analysis of coal samples and the associated sedimentary rocks correlates the interval with the upper part of the Corollina torosa Opel zone and dated Pliensbachian to Toracian. Based on methods of Whitaker (1984) and Van Der Zwan (1990) for palynodebris analysis the interval has been divided into four distinct palynofacies, which in stratigraphic order are lower back swamp, tidal flat, an upper back swamp and delta flat. Mutually exclusive occurrences of acanthormorph and sphaeromorph acritarchs in the

Geological Society of Australia Abstracts Number 32, Ballarat 1992

coal measures indicate their environmental preferences. The acanthomorphs occur in open brackish environment while the sphaeromorphs favour closed fresh water swamps. The petrological and palynological study of coal and associated sediments supports that the coal measures were deposited during a regressive phase of a marine transgression possibly in a delta type depositional environment. References Kristensen, S.E., and Wilson, A.C., 1986. A review of the coal and lignite resources of Western Australia. Proc. 13th Congr Min & Met. Inst. 2: 87-97. Sappal, K.K., 1987. Petrography of Collie Coal, Collie Basin, Western Australia. WAMPRI Report 26: 202. Van der Zwan, C.J., 1990. Palynostratigraphy and palynofacies reconstruction of the Upper Jurassic to lower most cretaceous of the Draugen Field, Offshore Mid Norway, Rev. Paleobot Palynol. 62: 157-186. Whitaker, M.F., 1984. The usage of palynostratigraphy and palynofacies in definition of Troll Field Geology. In: Offshore Northern Seas - Reduction of Uncertanities by Innovative Reservoir Modelling. Norsk Petroleums forening Art G6: 46.

130

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PETROLOGY AND GEOCHEMISTRY OF TERTIARY COALS IN WEST ACEH BASIN, SUMATRA, INDONESIA Hadiyanto1*' A.C. Hutton1, CJ. Boreham2

1

Department of Geology, University ofWollongong, P.O BOX 1144, Wollongong NSW 2500. 2 Bureau of Mineral Resources, GPO BOX 378, Canberra ACT 2601

West Aceh Basin is a typical Indonesian Tertiary technically active forearc basin resulting from the collision between the Indo-Australian and Asian plates. Coal measures sequences were deposited in this basin between the Oligocene and Plio-Pleistocene. Coal petrography and geochemistry have been applied to evaluate the evidence of liquid hydrocarbons produced from these coals and the petroleum generation within this basin. Petrographic studies show that most of the coals are rich in vitrinite with vitrinite content generally in the range of 65 - 90% whereas liptinite content is variable, ranging from 5 - 35% (Figure 1). Inertinite is usually present but seldom comprises more than 5% of the coals. Detrovitrinite is dominant over both telovitrinite and gelovitrinite. The vitrinite reflectance varies from 0.20 - 0.80%. The Rock-Eval data reveal that most of the coals are immature which Tmax values within the range of 370 - 460 C . HI values are variable between 140 455 whereas OI values are in the range of 10 - 150. TOC exhibits a gradual increase with increasing coal rank with the values ranging from 35 -75%. In

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Geological Society of Australia Abstracts Number 32, Ballarat 1992

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addition, Tmax values increase as vitrinite reflectance increases (Figure 2). Gas chromatography analyses of the saturates extracts from the coals showed a homologous series of straight-chained alkanes ranging from n-C14 to n-C33. In general, traces show a decrease in the relative amounts of compounds, with carbon numbers beyond n-c21, as vitrinite reflectance increases. Comparative studies relating type and rank of the coals to the pyrolysis products indicate there is good correlation between maceral composition and rank to the oils produced from the coals, both qualitatively and quantitatively. The amount of oils produced increases as rank increases (Figure 3). Some liptinite and vitrinite macerals make a significant contribution to the type and the amount of hydrocarbon products. Suberinite and cutinite have a positive correlation with waxy-hydrocarbons produced by pyrolysis. Exudatinite and bitumen show a positive relationship with nhydrocarbons up to n-C21. In general, there is a tendency for the amounts of gas to increase as rank decreases.

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ORGANIC PETROLOGY OF PERMIAN COAL, VASSE SHELF, PERTH BASIN, WESTERN ASUTRALIA. B. Santoso* and K.K. Sappal School of Applied Geology, Curtin University of Technology, Perth, Western Australia.

Coal seams of economic significance and restricted to a stratigraphic interval of lower Permian age, occur in the Vasse Shelf, southern Perth Basin, Western Australia. The coal bearing sediments described as the Sue Coal Measures are widespread in subsurface over a length of 17 kms, at depths between 180 m and 450 m, Kristensen and Wilson ( 1986). The area is faulted block/graben lying between the Bunbury Trough to the east and the Dunsborough Fault to the west. The coal samples of a 230 m interval from the CRA borehole No.CPCH 1 have been studied for their petrology. The coal predominantly consists of dull, dull banded, and bright banded, with minor bands of banded and bright types. The coal has a high content of inertinite and vitrinite with low exinite and mineral matter. The mineral matter is dominated by pyrite and clay which are usually associated with inertinite and vitrinite. Coal ash ranges from 5% to 49%; specific energy varies from 17-31 MJ/kg; bed moisture ranges Geological Society of Australia Abstracts Number 32, Ballarat 1992

from 6% to 20%; volatile matters are 23%; sulphur contents vary from 0.5% to 1.4% and chlorite is about 0.01 % on a dry basis. The maximum reflectance of vitrinite of is between 0.58% to 0.63%. So, based on these values, the Vasse Shelf coal is of sub-bituminous A rank of the ASTM Classification. The environment of deposition postulated for the coal measures is essentially point bar deposits whereas, the depositional environment of coal is mixed consisting of dry forest moor to open moor conditions. Reference Kristensen, S.E. and Wilson, A.C., 1986. A review of the coal and lignite resources of Western Australia. Proc. 13th. Congr. Min.&Met. Inst. 2, 87-97.

132 A 4.32

ORGANIC PETROLOGY OF HILL RIVER COAL, PERTH BASIN, WESTERN AUSTRALIA N. Suwarna* and K.K. Sappal

School of Applied Geology, Cur tin University of Technology, Perth, Western Australia. Coal samples for the study were taken from the Gairdner Range of the Hill River Area. The range occupies the Hill River Shelf of North Perth Basin, and is located approximately 225 kms north of Perth. The area is bounded by the Lesueur - Peron Fault in the west and the Warradarge Fault in the east. Six core samples from Jurassic Cattamarra Coal Measures containing splits G1 to G5 were examined for lithotype and maceral analyses. Predominantly, the coal consists of banded, dull banded, and dull lithotypes with minor bright, bright, bright banded, and fusainous types, with a few clastic beds. Maceral analyses indicate that the coal is rich in vitrinite content, within the range of 50% - 73%, and inertinite content within the 10% - 25% range. Exinite content is relatively low and it ranges from 7% - 14%. Mineral matter is dominated by clay and A 4.33

pyrite, ranging from 4.5% - 36% and ash content of the coal has a range of 12% - 37 %. The maximum reflectance of vitrinite varies from 0.33% - 0.51%, indicating that the rank of coal corresponds to the sub-bituminous B rank of the ASTM classification. On the basis of lithotype and petrographic indices gained from diagnostic macerals (Diessel, 1986), depositional environment for coal and coal measures is postulated to be an upper delta type. Reference Diessel, C.F.K., 1986. The correlation between coal facies and depositional environments. Advances in the Study of the Sydney Basin, Proc. 20th Symp., Univ. Newcastle,pp. 19 - 22.

PALAEOGEOGRAPHY AND SEQUENCE STRATIGRAPHY

J. Bradshaw, M.T. Bradshaw, J.E. Blevin, G.E. Wilford and R.P.Langford. Bureau of Mineral Resources, G.P.O. Box 378, Canberra, A.C.T., 2601, Australia The BMR-APIRA Palaeogeographic Maps Project has produced a series of palaeo-environmental maps for Australia for seventy time slices covering the period from the Cambrian to the Recent. The second phase of the study, the BMR-APIRA Phanerozoic History of Australia Project, has supplemented the original "map" view of the continent with a grid of regional cross-sections based on well, seismic and outcrop data. The poster shows the integration of the seven Cainozoic palaeogeographic time slice maps with seismic from regional cross-sections in the offshore Canning, Carnarvon and Otway basins. The seismic lines show a series of sedimentary packages that include thick prograding units in the Cainozoic. The same pattern is repeated in several locations along the western and southern margins of the Australian continental shelf. Similar prograding sequences have been recognised in many places around the world producing the characteristic "sedimentary signature of the Neogene" as recognised by Peter Vail and related to cycles of eustatic sea level change as shown on the chart developed by Haq, Hardenbol and Vail (1987). In these Australian examples there is a close

Geological Society of Australia Abstracts Number 32, Ballarat 1992

correlation between the palaeogeographic maps for each of the respective time slices in the Cainozoic with the seismic packages. Periods suggesting low sea level from the palaeogeography correlate with thick prograding sedimentation on the continental margin (Cainozoic time slice 5). Conversely periods of high sea level on the palaeogeographic maps correspond to coastal onlap on the continental margin sequences (Cainozoic 1,2,4,6 & 7). Within single time slice intervals, two or more different sequences can be identified. A major time break in the Oligocene was produced by erosion of the underlying sequences during the rapid sea level fall at the end of Cainozoic time slice 3. This episode is represented by the sparseness of deposition on the palaeogeographic map, and corresponds to an unconformity or thin sequence at the base of the thick prograding units on the seismic sections. Reference Haq, B.U., Hardenbol, J. & Vail, P.R., 1987 -Chronology of fluctuating sea levels since the Triassic. Science, 235, 1156-1167.

133

A5: SEDIMENTOLOGY AND VOLCANOLOGY CONVENOR:

R.A.F.

CAS

A 5.1 VOLCANICLASTIC MEGATURBIDITES IN DEEP MARINE BASINS • THE LATERAL EQUIVALENTS OF SUBAERIAL IGNIMBRITES? EXAMPLES FROM THE PALEOZOIC OF SOUTHEASTERN AUSTRALIA. R.A.F. Cas*, R.L. Allen and D. Hutton Department of Earth Sciences, Monash University, Clayton, Victoria, Australia, 3168. Sedimentation units up to tens of metres thick of texturally juvenile volcanic quartz, feldspar crystal and pumice debris are common in the deep-marine turbidite and hemipelagic fills of some Paleozoic basins in the Lachlan Fold Belt of southeastern Australia. These basins were either ensialic or adjacent to significant landmasses, and were associated with regionally extensive, felsic volcanic activity. The Cambrian Mt. Read Volcanics lie in the eastern margin of the Cambrian Dundas Trough in Tasmania and were previously interpreted as being a subaerial to marine ignimbrite-lava-sedimentary succession. The Volcanics are subdivided into a Central Volcanic Complex (CVC) and a Western Sequence (WS), which are considered to be lateral equivalents. The CVC is dominated by volcaniclastics, coherent lavas, intrusive porphyries, and only minor ambient sedimentary intervals. The WS consists of interbedded volcaniclastics, porphyries and abundant ambient sedimentary rocks of deep-water affinity (hemipelagic mudstones, turbidites). Contrary to previous work, this study has found no evidence of ignimbrites or of subaerial conditions in the CVC. Rocks that were previously interpreted as ignimbrites contain abundant pyroclastically fragmented debris, but there is no evidence of welding. Crystal rich units consist of varying mixtures of first cycle, angular to euhedral fragments of volcanic quartz and feldspars, indicative of rhyolitic to dacitic sources. Pumice rich units are dominated by fine lapilli size, angular to blocky-shaped pumice clasts, finer pumice shreds and shards, and minor crystal fragments. Depositional units are up to tens of metres thick, massive to diffusely laminated, and often have graded, laminated tops or an overall crude grading. Individual units are either crystal rich, or pumice rich, or grade from crystal-rich at the base to pumice rich at the top. The detritus is overwhelmingly juvenile volcanic debris, although intraclasts of bedded mudstone up to 25m in length, and small lithics also occur.

Geological Society of Australia Abstracts Number 32, Ballarat 1992

Sedimentation units are often amalgamated, producing thicknesses of hundreds of metres of volcaniclastics in places. In the WS the volcaniclastic sedimentation units are more readily definable because they are intercalated more regularly with ambient sedimentary intervals. Sedimentation units are up to 50m thick, and are often amalgamated producing intervals over 100m thick in the basinal succession. The sedimentation units mostly have crystal-rich bases, and are hydraulically graded, passing gradationally upwards into pumice and shard rich intervals. They have sharp bases which may be erosive or conformable, they are massive with planar stratification in the upper parts of some units, and they may be crudely size graded. Mudstone intraclasts occur in the bases of some units. Similar, very thick, massive sedimentation units of juvenile pumice or volcanic crystal debris also occur in the Tyndall Group and the base of the Dundas Group, which are laterally equivalent to and overlie the Mt Read Volcanics. These volcaniclastic sedimentation units contain varying proportions of rounded volcanic lithics, indicating derivation from the shore zone, or a subaerial environment. Such clasts also occur rarely in the CVC units. Similar, regionally extensive, excessively thick sedimentation units of juvenile crystal rich volcanic debris, occur within the 8,000m thick turbidite fill of the Siluro-Devonian Hill End Trough in central New South Wales. Cas (1979, 1983) noted that many sedimentation units in the Merrions Tuff were up to 60 m thick but some appeared to be over 100m thick. Many sedimentation units extend over the full preserved 3,400 square kilometre extent of the Formation. Local concentrations of fossiliferous limestone, suggest passage through shallow marine environments of the depositional agent. Similar facies occur in the Turondale Formation, the Bay Formation and the Winburn Tuff, and have also been documented in the hanging wall successions of Kuroko massive

134 sulphide deposits in the Miocene Green Tuff Belt of Japan. In all the successions discussed the sedimentation units are characterised by great thickness, massive to diffusely stratified interiors, variably normally graded and laminated tops, and sharp to erosive bases, often with intraclasts. These features all suggest mass-flow emplacement. The volumes of detritus represented by the sedimentation units of the Merrrions Tuff, and inferred from the preserved thicknesses of other units are at least an order of magnitude greater than the associated ambient epiclastic turbidites. There is no evidence of a hot state of emplacement such as welding or columnar jointing. Furthermore, in most cases the deposits have closed frameworks of crystals or pumice in their basal parts, fine ash or clay size matrix occurring in the graded top. The depositional agents were therefore not hot or cold pyroclastic flows, which are characteristically rich in a fine ash component, but appear to have been exceptionally large-scaled turbidity currents. The large volumes of finely fragmented angular crystal debris as well as the finely fragmented pumice aggregates, indicate a pyroclastic mode of fragmentation. Each sedimentation unit appears to be a compositionally homogenous grain assemblage, suggesting little or no time elapsed between eruption and deposition, and no mixing of multiple source matrials occurred. The implied volumes of pyroclastic detritus involved (calculated to be at least 1000 cubic kilometres for the Merrions Tuff, with individual sedimentation units involving up to 150 cubic kilometres) are dimensionally comparable only with subaerial ignimbrite forming scale eruptions. The juvenile volcaniclastic sedimentation units

found in the deep-water basin successions of the Paleozoic Lachlan Fold Belt are therefore interpreted to have resulted from large volume subaerial(-shallow marine) pyroclastic flow forming eruptions. The pyroclastic flows then flowed from air into water and transformed into water supported mega-turbidity currents. During eruption, subaerial flow, interaction with seawater, and subaqueous flow, significant elutriation of the original fine ash fraction occurred. Some flows entrained fluvial and shoreline clasts and transported them into deeper water, and some had enormous erosive capacity judging from the size of the enormous intraclasts present in some sedimentation units. As proposed by Cas and Wright (1991), such facies are not the deposits of subaqueous pyroclastic flows, but water-transformed pyroclastic flows or largescale turbidity currents. They do however, almost certainly herald contemporaneous large scale pyroclastic eruptions from subaerial or shallow marine centres. References Cas, R.A.F. 1979. Mass-flow arenites from a Paleozoic interarc basin, New South Wales, Australia: Mode and environment of emplacement. Jour. Sed. Petrology, 49, 29-44. Cas, R.A.F. 1983. Submarine 'crystal tuffs': their origin using a Lower Devonian example for southeastern Australia. Geol. Mag., 120, 471486. Cas, R.A.F & Wright J.V. 1991. Subaqueous pyroclastic flows and ignimbrites: an assessment. Bull. Volcanology, 53, 357-380.

A 5.2 SUB-VOLCANIC FACIES ANALYSIS WITHIN AN INTRUSIVE BRECCIA AND IGNEOUS COMPLEX (HOSTING THE MT. LEYSHON GOLD MINE, NE QLD.). P.J. Wormald Department of Geology, James Cook University, Townsville, Qld. Recent work (Wormald et al., 1991) has suggested that the Mt. Leyshon breccia complex should be reinterpreted as a number of intrusive breccia and igneous phases (Fig. 1). A protracted structural history dominated in the later stages by strike-slip faulting is preserved within the breccia complex. The complex has been divided into brecciated basement, main pipe breccia and an interactive magma/breccia sequence. The main zone of gold mineralisation is hosted within the Mt. Leyshon breccia, its partially brecciated margins and porphyry phase IV. Post- mineralisation basalt dykes represent the last intrusive event. Many relationships, such as the strongly preferred orientation Geological Society of Australia Abstracts Number 32, Ballarat 1992

of breccia/igneous units relative to pre and postintrusion faults, suggest active fault control on breccia/magma emplacement. Detailed mapping and drill-core logging has lead to the development of a graphic analysis system for interpreting and representing sub-volcanic facies relationships (Fig. 2). A graphic analysis of 14 drillholes has been completed within the ore zone. This allows documentation of fragmentation progressions, magma/breccia interaction, composition and fragment size variations and the construction of fence diagrams (controlling facies geometry). A key factor in breccia interpretation is the style and type of any associated

135 alteration mineral assemblage. It constrains the number of brecciation episodes and the extent of development of a given breccia. Integration of the above approach with outcrop mapping (of facies characteristics and unit geometry) and structural analysis is providing new insights into understanding the mechanisms of breccia formation. The graphic logging approach also provides a visual technique for understanding the distribution and controls on gold mineralisation. The facies relationships present within drill-hole MLD 277, passing from basement granite through main pipe breccia, the Mt. Leyshon breccia and porphyry phase IV are illustrated graphically in Figure 2. Fragment size variations are shown for the Mt. Leyshon breccia and tuffisite dykes only. The polymict Mt. Leyshon breccia zones occur as narrow anastomosing regions breaking up the pre-existing "stratigraphy". It is predominantly a fragment supported breccia with a small rock flour matrix component and abundant open space. An assemblage dominated by quartz - chlorite - carbonate - sulphide ± gold is present as matrix replacement and cavity infil SEE PAGE 222 FOR A

alteration (represented by a darkened background on the graphic log). Large blocks of pre-existing stratigraphy (from 1-20 metres in size) maintain their previously developed potassic or phyllic alteration assemblage and appear to havesuffered only limited transport. A preliminary model for the development of the Mt Leyshon breccia involves magmatic emplacement during extension related to the wrench system noted above. Initial tectonically formed crackle-rubble fragmentation provides ground preparation for the development of narrow polymict breccia zones. These polymict zones appear to develop by magmatic gas release in the zones of maximum extension often focused along reactivated earlier breccia/basement contacts. References Wormald, P.J., Orr, T.O.H. and Hodkinson, LP., 1991, World Gold '91 conference volume, AusI.M.M., Cairns, p.223-232. COMPANYING FIGURE

A 5.3 DEPOSITIONAL CONTROLS AND CHARACTERISTICS OF SUBAQUEOUS BEDDED VOLCANICLASTICS OF THE LOWER DEVONIAN SNOWY RIVER VOLC ANICS. Stuart W. Bull and R. A. F. Cas Department of Earth Sciences, Monash University, Clayton, Victoria, 3168, Australia. The Snowy River Volcanics are a succession of Lower Devonian volcanics and volcaniclastic rocks which outcrop in a 110 km long, north-south trending synclinal depression in eastern Victoria termed the Buchan Rift (VandenBerg, 1988). Although some regional studies have been carried out (e.g. Cochrane and Sampson, 1947; Ringwood, 1955; Fletcher, 1963), only one (Orth et al., 1989) attempts to document the palaeoenvironmental setting of the SRV, and this study is restricted to the uppermost part of the stratigraphy. Work conducted by Klicker (1984) and the authors demonstrates that a substantial part of the Snowy River Volcanics succession in the southern end of the belt (termed the Mt Johnson Member) represents a relatively deep, quiet marine enclave within the largely subaerial volcanic pile. Although surface outcrop is poor, the Mt Johnson Member is intersected by seven diamond drill holes, allowing a detailed analysis of the constituent sediment sequences. "Normal" sedimentation is represented by a mudstone facies which consists of interbedded black mudstones and turbiditic siltstones. However, this fine-grained deposition was periodically Geological Society of Australia Abstracts Number 32, Ballarat 1992

interrupted by the emplacement of thick, amalgamated volcaniclastic mass-flow sequences. Six mass-flow sequences are defined, and two types can be recognized according to their overall bedding thickness and grainsize profile. Upward thinning and fining sequences are characterized by thickly bedded basal deposits of juvenile, magmatically fragmented pyroclastic debris, emplaced as cold, water-supported mass-flows. These are interpreted to be essentially syn-eruptive, arising either from flow transformation as pyroclastic flows ingested water upon entering the sea, or from immediately post-eruptive slumping of unreworked pyroclastic debris ponded at the shoreline. These juvenile deposits are overlain by intervals of thinner bedded mass-flows, which are of a similar provenance, but are considerably depleted in fines. The second type of mass-flow sequence, the complex bedding thickness sequences, has a basal zone of bedded, fines-depleted mass-flow deposits, with juvenile deposits in the mid to upper portions. These mass-flow sequences are interpreted to have arisen either from volcanic eruptive events which did not initially deposit primary pyroclastic debris

136 subaqueously, or from epiclastic events which eroded previously erupted unconsolidated volcaniclastic debris. The depletion of fines in much of the volcaniclastic debris within the Mt Johnson Member indicates that it was subjected to a degree of epiclastic reworking. Since this cannot have occurred in the deep, quiet marine host environment, it indicates an external source for the parental magmatic eruptions. The eruptions probably occurred in an adjacent subaerial hinterland drained by an alluvial/fluvial/deltaic or fan-deltaic system. This system would have been a natural site for ponding and storage of freshly erupted debris and would have allowed the complex interaction between eruptive and epiclastic events which appear to have been responsible for the mass-flow sequences. References Cochrane, G. W. and Sampson, H. R., 1947. The geology of the Nowa Nowa-South Buchan area,

A 5.4

Victoria. Proc. Roy. Soc. Vic., 60: 92-122. Fletcher, K., 1963. The Snowy River Volcanics west of Buchan, Victoria. Proc. Roy. Soc. Vic., 76: 169-179. Klicker, T. M., 1984. Sedimentology, palaeovolcanology and mineralization in an associated bedded volcaniclastic and intrusive complex, Devonian Snowy River Volcanics, Bruthen-Buchan area, Eastern Victoria. B. Sc. (Hons.) thesis, Monash University, (unpubl.). Orth, K., Cas, R. A. F. and Wright, J. V., 1989. Facies analysis and facies associations in the recognition of volcanic centres in silicic terranes: An example from the Early Devonian of Australia. Aust. J. Earth Sci., 36: 167-188. Ringwood, A. E., 1955. The geology of the Snowy River district, East Gippsland. Proc. Roy. Soc. Vic., 67: 67-74. VandenBerg, A. H. M., 1988. Chapter 4, SilurianMiddle Devonian. In: Douglas J. G. and Ferguson J. A. (Editors.). Geology of Victoria. Victn. Div. geol. Soc. Aust: 103-114.

THE PASSAGE OF A SUBAERIAL PYROCLASTIC FLOW INTO WATER: A PROTEROZOIC EXAMPLE FROM THE PINE CREEK INLIER, N.T. Elizabeth A. Jagodzinski and Ray A.F. Cas Department of Earth Sciences, Monash University.

The Pul Pul Rhyolite is a Formation of the El Sherana Group, which outcrops in the southeast of the Pine Creek Inlier, an Early Proterozoic terrane in the Northern Territory. It is a bimodal volcanic suite consisting predominantly of acid volcanics and associated intrusives and volcaniclastics, with minor mafic volcanism and mafic intrusives. In the area southeast of Coronation Hill, the Pul Pul Rhyolite is dominated by quartz-feldspar bearing rhyolitic ignimbrites which form a succession - 700 m thick. Most of the ignimbrites are welded, with attenuated pumice clasts defining eutaxitic textures on the macroscopic scale, and plastically deformed shards and pumice shreds forming welding textures microscopically. Horizons of lithics within the sequence represent lithic concentration zones formed at the base of separate pyroclastic flow units. One horizon of lithics - 2 0 m thick, is clast supported, containing lithic boulders up to 2 m in diameter, and is interpreted to be a ground layer formed at close proximity to vent. The top ignimbrite unit is nonwelded and hosts discontinuous lenses of volcanic sandstone and pebble conglomerate, interpreted to represent local sediment filled fluvial gullies formed between ignimbrite eruptions. These have a mixed basement and contemporaneous pyroclastic deposit Geological Society of Australia Abstracts Number 32, Ballarat 1992

source. A coherent rhyolite lava overlies the ignimbrites in the southeast, and the sequence is intruded by several geochemically distict acidic porphyry stocks and dykes. Facies of the Pul Pul Rhyolite were deposited subaerially, and the association of facies suggests a proximal environment of deposition; either an intracaldera or a proximal outflow sequence. The Pul Pul Rhyolite is overlain by subaqueous sediments of the Big Sunday Formation (also of the El Sherana Group). The sediments consist of planar to cross laminated tuffaceous siltstones which interbed upsection with coarser-grained sandstone intervals. The sandstones have the definitive features of turbidites such as graded bedding, sharp bases with load casts, and internal structural divisions consistent with the Bouma sequence. Upsection they become more proximal in character, with coarser-grained, amalgamated sandstone beds, and more A-B or A-C Bouma sequences dominating over B-C. The tuffaceous siltstones are interpreted to result from the continuous supply of fine-grained material from the underflow of a river draining into a basin. The introduction of turbidite beds, becoming more proximal in character upsection, suggests the whole sequence formed as the river mouth or delta prograded

137 into the basin. Thick (20-50m) massive crystal-rich volcanic sandstone beds overlie the subaerial welded ignimbrites and fluvial epiclastics of the Pul Pul Rhyolite, and are conformably overlain by the subaqueous sediments of the Big Sunday Formation. Their stratigraphic position is consistent with having been deposited at the shoreline of the basin containing the overlying tuffaceous sediments. The facies forms a laterally extensive horizon beneath the Big Sunday Formation, but is best exposed in an across strike section along the South Alligator River, where a thicker accumulation of the facies, forming a buttress unconformity against a vertical wall of ignimbrite, suggests a palaeovalley or canyon fill. The facies is massive apart from rare, diffuse stratification, with no features indicative of tractional deposition, such as planar or cross stratification. The lowermost unit has a fine-grained, stratified basal shear zone. The main body of the sandstones lack any grading or sorting features, but the uppermost unit fines upward and is planar laminated at the top. These features are consistent with deposition by mass flow, probably a high density debris flow or grainflow, with the fining upward, laminated flow top consistent with some degree of turbulence and sorting and sedimentation of grains due to mixing of water with the more expanded or fluidised flow top. The facies contains angular crystals and lithics (quartz 48%, feldspars 22%, dolerite 7%, metamorphic fragments 9%, plutonic fragments 11%, chert 2%) which show no evidence of rounding or reworking, in a granophyric to locally spherulitic groundmass. The composition and texture of the crystal population is similar to that of the underlying ignimbrites, suggesting it also has a pyroclastic origin. The extraordinary thickness of the facies also suggests it is the product of contemporaneous pyroclastic eruption . Normal epiclastic turbidites rarely exceed thickness of a few metres (Cas & Wright, 1991). Significant ash loss must have occurred during formation of the crystal-rich facies which contains 50-60% crystals and lithics, compared with 10-25% crystals and lithics in the subaerial ignimbrites. In the palaeovalley area, the facies displays some very unusual features. There are two horizons which contain clasts of ignimbrite which are extremely irregular and wispy in shape. Macroscopically the ignimbrite clasts show evidence of welding, with fiamme flattened to form eutaxitio textures.

Geological Society of Australia Abstracts Number 32, Ballarat 1992

Microscopically the ignimbrite clasts contain shards but they are poorly preserved and do not provide definitive evidence of welding. The clasts have the same crystal population as the host crystal-rich sandstone, implying a genetic association. The base of the upper sandstone unit consists of a diffuse mix of crystal-rich sandstone and what appears to be welded ignimbrite, or crystal-rich sandstone containing pumice clasts aligned to form a pseudoeutaxitic texture. The pumice-bearing facies has a greater proportion of ashy matrix (60%) compared to the crystal-rich sandstone (40%). The boundaries between the two facies are extremely irregular and gradational with the ignimbrites showing an increase in crystal content toward their margins. The crystal-rich facies is interpreted to have formed in response to a pyroclastic flow entering water. Winnowing of fine ash occurred during phreatic explosions triggered by the pyroclastic flow entering the shoreline, and perhaps further ash loss occurred as the flow transformed from a gas-supported pyroclastic flow to a water-supported high density debris flow. The model of pyroclastic flows entering water and disintegrating is supported by the random occurrence of irregular ignimbrite clasts and the diffusely bound patches of ignimbrite, interpreted to be remnants of the original pyroclastic flow, where winnowing of fine ash has not been as effective. The implication of welding in these ignimbrite patches suggests the pyroclastic flow was undergoing deposition by agglutination as it reached the shoreline. Outside of the palaeovalley, the crystal-rich facies shows no sign of the ignimbrite relicts, indicating the ash component of the pyroclastic flow was more efficiently winnowed. This suggests the flow may have been channelled by the palaeovalley, and spread along the shoreline of the basin (lake?). Ash winnowing processes may have been more effective along the shoreline where the flow spread out allowing more efficient interaction with water. Final deposition after the flow disintegrated at the shoreline, was by resedimentation as a water-supported slurry of pyroclastic debris, the solidified relics of the original pyroclastic flow, and patches of ripped up shoreline. References Cas, R.A.F. & Wright, J.V., 1991, Bull. Volcanol 53: 357-380.

138 A 5.5 LATERAL VARIATIONS IN A MIDDLE SILURIAN VOLCANICLASTIC APRON: THE INTER-RELATIONSHIP OF THE GOOBARRAGANDRA VOLCANICS AND THE BLOWERING FORMATION OF SOUTHEASTERN N.S.W. K. A. Dadd Department of Applied Geology, University of Technology, Sydney, P.O. Box 123, Broadway, N.S.W. 2007. The Middle Silurian Blowering Formation and emplaced within the source region of the dacite. The major difference between the Goobarragandra Goobarragandra Volcanics of the southeastern Lachlan Fold Belt comprise dacitic volcaniclastic rocks, lesser Volcanics and Blowering Formation is their coarse- and fine-grained non-volcaniclastic sedimentary depositional facies. The Goobarragandra Volcanics rocks, and rare mafic flows. The Blowering consists of massive ash-flow tuff, re-deposited debris Formation crops out in the Tumut Synclinorial Zone, flow units, some with limestone olistoliths, and to the west of the Mooney Mooney Fault System minor bedded and graded dacitic turbidites. Finewhereas the Goobarragandra Volcanics occur further grained rocks are only a minor component. Units east in the Young Anticlinorial Zone where they have deposited from pyroclastic flows occur in the east been intruded by the Young Granodiorite. Basden et whereas re-deposited and turbidite facies are found al. (1987) interpreted the two structural zones as further west implying a lateral change from subaerial distinct terranes that amalgamated in the Late Silurian. to submarine conditions. The Blowering Formation However gross lithological and geochemical comprises mostly re-deposited mass flow dacitic similarities between the Blowering Formation and volcaniclastic rocks, pebble conglomerate, sandstone Goobarragandra Volcanics suggest that they have a and siltstone with minor limestone-bearing boulder similar source and imply a para-autochthonous conglomerate and rare mafic flows. The rocks relationship between the two zones by the Middle accumulated in a submarine environment with the Silurian. percentage of fine-grained sedimentary rocks increasing Dacitic volcaniclastic rocks in both the to the west. Goobarragandra Volcanics and Blowering Formation The S-type nature of the volcaniclastic rocks and are crystal-rich with crystals of quartz, plagioclase, the Young Granodiorite indicate that the Young biotite and garnet. Lithic clasts include biotite-rich Anticlinorial Zone was underlain by crust of schist, fine-grained amphibolite and rare sedimentary substantial thickness. The Blowering Formation and rocks. Pumice is noticeably absent and both units are western parts of the Goobarragandra Volcanics were characterised by the presence of quartz megacrysts up most likely deposited in a marginal basin west of a to 15 cm long. Volcanic material in both units show magmatic complex that developed in continental crust. S-type characteristics and on most geochemical variation diagrams they overlap considerably. The References Young Granodiorite has a similar geochemistry and mineralogy to the volcaniclastic rocks, including Basden, H., Franklin, B.J., Marshall, B. & Waltho, quartz megacrysts and xenoliths of similar A.E., 1987, Am. Geophys. Union, Geodynamics composition to the lithic clasts in the volcaniclastic Series 19:57-66. rocks, and is probably their intrusive equivalent, ANALYSIS IN SUBMARINE VOLCANIC SEQUENCES: LESSONS BEING LEARNT IN THE MOUNT READ VOLCANICS, CAMBRIAN, WESTERN TASMANIA A

5 6

F A C I E S

J. McPhie CODES, University of Tasmania, Hobart, Tasmania The Mount Read Volcanics (MRV), western hydrothermal alteration is intense. Volcanosedimentary Tasmania, comprise compositionally and texturally formations MRV provide evidence for diverse, Mid-Late Cambrian lavas and volcaniclastic emplacementofin the a submarine setting, below storm rocks. The volcanics have been affected by regional wave base. Intercalated basaltic lavas are pillowed, and deformation and metamorphism, and locally hyaloclastic breccias are associated with rhyolitic, Geological Society of Australia Abstracts Number 32, Ballarat 1992

139 basaltic and andesitic lavas. Widespread massive sulphide mineralisation for which these volcanics are famous worldwide, also suggests deposition in a "relatively deep" submarine setting. The research reported here concerns reconstruction of the original facies architecture of the MRV. Careful elucidation of emplacement processes of these altered and deformed volcanics has proven to be critical in meeting this aim. The rules of stratigraphic analysis designed for studies of sedimentary basins are linked to sedimentary transportation and deposition processes that are not entirely applicable in volcanic terrains. Facies analysis of sedimentary systems strongly emphasizes the influence of the environment of deposition on the resultant facies. That relationship is far more tenuous and difficult to predict in volcanic sequences. In fact the reverse is commonly true: volcanic facies play a major role in physically modifying environments (e.g. elevation, gradient, relief, drainage patterns in subaerial environments, shape and position of shorelines, water depth in subaqueous settings). In sequences that include primary volcanic rocks, lateral facies variations in many cases reflect contrasting emplacement processes rather than marked changes in the depositional environment. Facies geometry in particular is strongly influenced by mode of emplacement. For example, silicic lava domes construct topography that may be infilled later by pyroclastic flow deposits. As a result, two contrasting but coeval facies are juxtaposed or interleaved in the context of a single environment of deposition. Even where sedimentary environments and processes are well established, nearby volcanism, especially explosive volcanism, has the potential to create abnormal sedimentation rates and upset drainage patterns to a degree where the usual predictions of facies analysis break down. Very large volumes (10 k m 3 ) of pyroclastic debris may be released instantaneously, interrupting or terminating ambient sedimentation. Locations of both intrabasinal and extrabasinal source areas for successive influxes may fluctuate dramatically. A variety of vigorous volcanic erosion processes accompany the emplacement of some pyroclastic deposits. Volcanic deposits range far more widely in physical properties such as density, porosity, permeability, chemical stability and resistance to erosion than most sediments. Some are emplaced at temperatures very much higher than ambient. Significant primary dips (e.g. in fallout deposits) and syn-depositional unconformities (e.g. in surge deposits) are actually characteristic of some modes of emplacement. The shapes and dimensions of lava flows are strongly controlled by discharge rate and magma composition; the sedimentary substrate is however important in influencing whether lavas

Geological Society of Australia Abstracts Number 32, Ballarat 1992

remain discrete surface flows, mix with the sediment to produce peperite, or burrow into the sediment (invasive flows). In the northern MRV the principal volcanic facies represented are: 1. Silicic, intermediate and mafic lavas. Coherent lavas occur at many localities and at all levels in the stratigraphy e.g. rhyolite in the Southwell Subgroup; Hellyer Basalt; dacite and andesite in the Que-Hellyer Volcanics. 2. A variety of eruption-correlated, juvenile volcaniclastic deposits. Two main sorts of subaqueous, juvenile, volcaniclastic mass-flow deposits occur. One is dominated by relatively dense lava clasts, and is related to the emplacement of lava flows and domes. The other sort is pumiceous, and evidently produced by explosive silicic eruptions. 3. Largely conformable, syn-sedimentary intrusions. Occurrences of coarse quartz-feldspar porphyry display diverse contact relationships, implying that some are intrusive sills emplaced into unconsolidated sediments, some are coherent and brecciated lava flows, and that some may have erupted explosively, contributing porphyritic clasts and discrete crystals to a variety of mass flow-emplaced volcaniclastic deposits. These facies are interbedded with a sedimentary facies association comprising black mudstone and/or graded bedded sandstone of mixed volcanic and metasedimentary Precambrian basement provenance. Given this selection of facies with which to work, an attempt has been made to predict the facies geometry in simplest circumstances (Fig. 1). Volcanic facies that are strictly extrusive, produced in large volumes, erupted infrequently, emplaced rapidly and widespread provide a "framework" for reconstructing the facies architecture. Massflow-emplacedpumiceous volcaniclastic facies are the obvious first choice. A distinctive "key" facies association that includes units of this type occurs in the upper part of the northern MRV. The three main components of this association are (Fig. 2a): Volcaniclastic Facies A — bluish-grey, pumiceous sandstone and pumice breccia characterised by wispy, sparsely feldspar-porphyritic relic pumice (now composed of sericite or chlorite). Intervals of Facies A range from a few tens of metres to greater than 100 m in thickness. Thinner sections comprise a single graded sedimentation unit; thicker sections are made up of a small number of graded units. Lithic breccia at the base is polymictic, although locally it is dominated by basaltic lava clasts. Volcaniclastic Facies B — crystal-rich volcaniclastic sandstone and mudstone characterised by coarse (1 cm commonly), round quartz and more abundant, prismatic feldspar (2-4 mm). Coarsely porphyritic (round quartz and euhedral feldspar),

140 formerly glassy (now sericite) lenses and wisps are an additional characteristic component; these may have originally been entirely pumiceous although vesicular microtextures are only sporadically preserved. Volcanic lithic clasts are relatively minor. Facies B is a texturally complex mixture of the juvenile volcanic particles described above, and non-volcanic mud that closely resembles black mudstone elsewhere in the sequence. Parts of some sections include apparently coherent, coarse quartz-feldspar porphyry that is locally flow banded or brecciated. The internal organization of Facies B is complicated; multiple sedimentation units are present and in general, are massive rather than graded. Field relationships and some drillholes show that Facies B and coherent, coarse quartz-feldspar porphyry are spatially, and probably, genetically related. Sedimentary Facies C — black, laminated or massive, commonly pyritic mudstone. Facies C (mudstone) is recurrent, and appears below, between, in (as intraclasts) and above the two other facies. Facies A is an example of the type of pumiceous volcaniclastic unit predicted to be voluminous, rapidly emplaced, and regionally widespread. It was probably generated by explosive silicic magmatic eruptions from a nearby basin-margin or extrabasinal, shallow water or subaerial source. Facies B may be a case involving extrusive and syn-sedimentary intrusive processes. Whether or not explosive fragmentation processes (magmatic and/or steam driven) were important has yet to be determined. An intrabasinal source is considered likely in view of the close association between Facies B and extensive bodies of coherent, at least partly intrusive, compositionally and mineralogically similar, coarse quartz-feldspar porphyry. Because such an origin is complex, this facies may prove troublesome as a tool in correlation. However, in combination with Facies A and C (black mudstone), it has so far been extremely useful because it is readily distinguished in the field and appears to be unique in the northern MRV. The key association (Facies A, B and C) has so far enabled correlations over 13 km from north of Hellyer to Sock Creek South. The potential for such an association to be regionally extensive prompted attempts to establish its southerly limits. Preliminary results suggest the possibility that the association extends for another 30 km south (White SpurHowards Road area). If correct, the association defines a region that at least temporarily shared essentially the same provenance, sedimentation processes and environment of deposition. Eruptive volumes implied for the volcaniclastic facies are of the order of several tens of cubic kilometres, comparable to smallmedium magnitude pumiceous pyroclastic flow deposits that are common in subaerial silicic volcanic terrains. Geological Society of Australia Abstracts Number 32, Ballarat 1992

The key association described above is part of the Dundas Group (Corbett 1989). However, associations of similar character occur in other formally-defined formations of the MRV including the Central Volcanic Complex. In fact, the Rosebery-Hercules massive sulphide ore body is hosted by a feldsparbearing pumice breccia-black mudstone-quartz-rich volcaniclastic sandstone facies association (Fig. 2b) with remarkable correspondence to the key association in lithofacies, emplacement processes, interpreted depositional setting (Allen and Cas, 1990), and provenance. Regardless of any potential for a direct correlation of these two, the similarity suggests that volcanosedimentary sequences in the MRV are just as prospective for massive sulphide mineralisation as are the lava-dominated parts. Such associations also offer a means of eventually establishing correlations along the length of the belt that will constrain the relative ages of the known ore deposits. Study of emplacement processes of diverse volcanic facies present in the MRV has helped define the basic outline of the facies architecture: (i) lavas and related volcaniclastic deposits (autobreccia, hyaloclastic breccia, and redeposited equivalents) occur separately or in clusters within more extensive volcanosedimentary sequences; (ii) pelagic mudstone and turbidite sandstone of mixed or Precambrian provenance are the record of background sedimentation; (iii) the substrate provided by these sediments was relatively weak and of low density so that some lava remained embedded below the surface, and surface flows commonly foundered, enveloped by peperite; (iv) background sedimentation was episodically interrupted by emplacement of pumiceous and/or crystal-rich mass flows generated by explosive eruptions. Finally, this analysis is revealing that the sea floor hydrothermal systems responsible for the massive sulphide mineralisation operated in a wide variety of volcanic hosts and settings within the MRV. References Allen R.L. & Cas R.A.F., 1990, Tenth AGC Hobaru GSA Abs 25: 31-32 Brathwaite R.L., \914yEconGeol 69: 1086-1101 Corbett K.D., 1989, GSA Spec Pub 15: 86-116

141 LAVAS mafic

•

silicic

may "burrow" into sediment substrate

high discharge rate, simple

• •

strongly constructional

low discharge rate, compound !

MASS-FLOW VOLCANICLASTIC FACIES •

source may be extraor intrabasinal

•

may correlate with an eruption, or result from redeposition LAVA-DERIVED

PUMICEOUS

V: yl "•'•S\

© small volume, limited extent, multiple

® large volume, widespread, uncommon

0

© clasts produced by explosive eruption

by-product of lava effusion

/ SYN-SEDIMENTARY •

INTRUSIONS

complex geometry in detail : concordant, stratabound vs. crosscutting extrusive —

burrowing ± re-sedimentation

Fig. 1: Cartoon sketches showing the contrasts in geometry of volcanic facies emplaced by different processes. (a) HIGH POINT - HELLYER

(b) HERCULES -ROSEBERY

Fig. 2 : Stratigraphic logs of (a) the key facies association in the northern MRV; based on DDH HP2; (b) the host sequence of the Rosebery-Hercules massive sulphide ore body showing the subdivisions recognised by Brathwaite (1974). Quartz is abundant in the lower part of the "hangingwall pyroclastics", whereas the pumice-rich "footwall pyroclastics" and the upper part of the "hangingwall pyroclastics" are dominated by feldspar.

Geological Society of Australia Abstracts Number 32, Ballarat 1992

142 A 57

INTERACTION BETWEEN VOLCANISM AND SEDIMENTATION IN THE SILURO-DEVONIAN WOLLONDILLY BASIN C. J. Simpson School of Earth Sciences, University of Melbourne, Victoria

The Wollondilly Basin records a Siluro-Devonian extensional event in the northeastern Lachlan Fold Belt in NSW and was the site of large influxes of siliciclastic and volcaniclastic detritus between the Late Silurian and the Late Devonian. The volcanic component of the basin covers an area of approximately 1350 km and constitutes the Bindook Volcanic Complex. The Wollondilly Basin is at least 150 km long and is bounded in the west by the Taralga Fault, whilst the eastern margin is largely obscured by Permo-Triassic rocks of the Sydney basin. The oldest rocks in the Wollondilly Basin are Late Silurian quartz turbidite deposits, allochthonous limestone blocks and in situ limestone and shale sequences. Shallow marine lagoonal to biostromal limestone and shale (Carr et al 1980) were deposited adjacent to the eastern margin of the Wollondilly Basin. Localised quartz sand influxes also occur near the eastern margin but were more widespread in the western part of the basin producing thick turbidite deposits. Rocks of quartzose provenance were derived from exposed Ordovician quartzose strata on the basin margins and were emplaced into the basin on a semicontinuous basis throughout its history. Shelf carbonate accumulation and siliciclastic sedimentation were interrupted during the Early Devonian by the development of silicic volcanoes to the east of the basin and consequent input of large volumes of volcaniclastic detritus into shallow water adjacent to the southeastern basin margin. A subsequent shift in the locus of volcanism resulted in the development of a thick pile of subaerial pyroclastic rocks and lavas that are best developed in the northern half of the basin. The youngest rocks in the Wollondilly Basin are Late Devonian shallow marine to fluvial, quartzose sedimentary rocks that unconformably overlie the Late Silurian to early Devonian succession. This paper is concerned only with the Early Devonian portion of the Wollondilly Basin succession in which a complex interaction between silicic volcanism and quartzose sedimentation can be documented. The distribution of primary volcanic, volcaniclastic and non-volcanogenic sedimentary rocks reflects a dynamic interplay between explosive volcanic activity on the eastern basin margin, drainage patterns on the basin margins and contemporaneous uplift associated with volcanism and/or the Early Devonian tectonism in this area (Fergusson and Vandenberg 1990). Furthermore, it is the Early 2

Geological Society of Australia Abstracts Number 32, Ballarat 1992

Devonian part of the succession that records the change from marine to non-marine depositional environments within the basin. The earliest indication of volcanic detritus in the Wollondilly Basin is restricted to the southeast margin and is preserved at the base of the Tangerang Formation, which is the oldest unit in the Bindook Volcanic Complex. Input of pyroclastic detritus probably occurred from the disruption of pyroclastic flows entering the sea or from prograding river deltas draining the volcanoes. This resulted in localised accumulations of shallow marine volcaniclastic rocks which pass laterally and/or vertically into intervals of either pure quartz sandstone or sedimentary rocks of mixed volcanic/quartzose provenance. The large volumes of pyroclastic detritus, rapidly emplaced into the basin, are preserved as thick shallow marine massflow beds that form marker horizons within this part of the sequence. Periods of lower volcanic input allowed contemporaneous reworking of the volcanic material by tide-generated currents that operated in the southeast part of the basin. Reworking of this volcanic material formed a thick (700 m) pile of well bedded and cross-bedded shelf sandstone within the continuously subsiding basin. Gradual emergence of the southeastern part of the Wollondilly Basin is indicated by the development of localised prograding deltaic sequences of volcanic provenance, followed by extensive erosion of the shallow marine succession. A close association between volcanic products and quartzose sedimentary rocks continued during the nonmarine history of the Wollondilly Basin; steady input of quartzose detritus derived from Ordovician rocks exposed on the western basin margin was periodically interrupted by catastrophic emplacement of silicic pyroclastic deposits. The quartzose sediment was deposited in the basin as a thick sequence of predominantly fluvio-lacustrine quartz sandstone and shale. Several ignimbrite-forming eruptions from vents mdst likely located in the northern part of the basin temporarily overwhelmed the fluvial systems. Inter-eruption periods were characterised by removal of easily eroded volcanic lithologies, redeposition of reworked volcanic material and reinstatement of the fluvio-lacustrine quartz sandstone and shale regime. References Carr P.F., Jones B.G., Kantsler A.J., Moore P.S. and

143 Cook A.C. 1981. The geology of the Bungonia district, New South Wales. Proceedings of the Linnean Society of New South Wales 104, 229244.

Fergusson C.L. and Vandenberg A.H.M. 1990. Palaeozoic thrusting in the eastern Lachlan Fold Belt, southeastern Australia. Journal of Structural Geology 12, 577-589.

A 5-8 ERUPTIVE DRAINAGE STRUCTURES WITH IN SITU BOULDER MILLINGA MODEL FOR LOCAL DERIVATION OF CERTAIN CONGLOMERATES PROVIDED BY TOOMBA FLOW QLD. E .J. Heidecker Department of Geology and Mineralogy, University of Queensland, St Lucia, Queensland Rounded boulders surround pits in angular talus along basalt walls, the cliffed edges of Toomba Flow, north Queensland. Pits along a basalt wall in Dalrymple National Park are commonly 3 metres deep. Some piles of boulders are opposite caverns extending into pebbly leads below the basalt flow. Mixed with the boulders are siliceous pebbles common in the sub-basaltic leads, but not present in nearby Fletcher Creek. These boulders are not river milled. They are being generated within piles of blocky scree and contain pebbles derived from sub-basaltic springs rather than rivers. Plunge-pool milling is not involved as adjacent walls are not scoured by falling water. Several months after the heavy rains of January 1991 groundwater was still issuing from the toe of a wall at Dalrymple towards a fan of rounded boulders. During pluvial events water dammed by the basalt flow erupts, or breaks out, along the wall. Violent flow from beneath pits is indicated by smoothing of fissures and joint intersections. Aprons of large

KEYNOTE:

A 5.9

boulders about the pits point to groundwater flows sufficient to agitate and thus mill large boulders. Boulders forced out of the pits appear to have rolled back down sloping aprons, to be agitated and milled once more. Elsewhere milled volcanic cobbles and pebbles appear to have been generated rapidly and locally. Volcanic cobbles in Upper Devonian tuffaceous sandstone are rounded, though extremely tough and derived locally from the western part of the Burdekin Basin, north Queensland. Radiometric dates suggest that these volcanic cobbles are apparently slightly younger and thus contemporaneous with surrounding sediments. Rounding of such tough cobbles was surprisingly rapid. Boulder formation along Toomba Flow provides a model for groundwater milling during eruptive flow episodes. Rounded cobbles which are tough, locally derived, and rapidly formed are thus a line of evidence for large flows of groundwater during Devonian volcanicity in the Burdekin Basin.

RECENT DEVELOPMENTS IN CLASTIC SEDIMENTARY FACIES ANALYSIS Christopher R. Fielding

Department of Geology and Mineralogy, University of Queensland, Queensland 4072 Fades models for clastic depositional systems were established as summaries of the essential characteristics of particular sedimentary environ-ments. Since the 1960's, when the first modern facies models were published, sedimentologists have given considerable attention to the development, refinement and testing of such models. Walker (1984) proposed that "type" facies models should act as a norm, a framework for future

Geological Society of Australia Abstracts Number 32, Ballarat 1992

observations, a basis for hydrodynamic interpretat-ion and a predictive tool. As the understanding of natural depositional systems tends towards a certain maturity, however, it has become apparent that many if not most of the established "type" facies models are overgeneralised or inadequate in some other way. Furthermore, the improvements in understanding of sedimentary sequences that have come with the concepts of sequence stratigraphy have necessitated a

144 reappraisal of the rigid application of Walther's Law of Facies. This paper proposes that "type" facies models in their traditional form are redundant, and suggests strategies for modernisation. The level of development of facies models varies for different depositional systems, as indeed does the degree of consensus. Fluvial environments, which are among the most intensely studied systems, have been regarded as among the best understood. A variety of facies models have been proposed and adopted for different fluvial styles, most of which are based upon simple, vertical sequence criteria (Rust & Koster, 1984; Walker & Cant, 1984). Some of these, such as the classical "fining-upward cycle" for meandering streams, have been shown to be hopelessly inadequate (Jackson, 1978, 1981). Facies models for lacustrine systems have only come about in the recent past (Eugster & Kelts, 1983), and perhaps for this reason are more durable. Likewise, glacial facies models are both more recent and more reliable (Eyles & Miall, 1984). Volcaniclastic models are for the most part quite generalised (Lajoie, 1984), although substantial advances have been made in the recent past (Cas & Wright, 1987). Facies models for aeolian systems are in an initial stage of development, and cannot be regarded as formal proposition (Brookfield, 1984). In coastal systems, facies models for deltaic systems have been established for some time, and are based upon a combination of vertical sequence character and lithosome geometry (Miall, 1984). Models for non-deltaic coastlines are similarly wellestablished (Reinson, 1984) and detailed. Few reliable criteria have been established, however, to distinguish between deltaic and non-deltaic coastal sequences. Furthermore, geologists are yet to fully come to terms with the differences between deltas dominated by coarse, as opposed to fine-grained sediment. Facies models for marine systems have perhaps attracted the greatest controversy. Shelf systems are still poorly understood in terms of facies architecture, and there is a lack of consensus on matters of process vs. product Deep marine deposits have been intensely studied, and as with fluvial systems an earlier notion of one simple model has evolved into an acceptance of several models for differing styles of submarine fan and apron (Stow, 1986). Major uncertainties still exist over the validity of submarine fan models, however (Shanmugam et al, 1985). Many type facies models are inadequate to fulfill their intended roles, mainly because insufficient information is incorporated into models. Those models based fundamentally on vertical sequence analysis are especially weak, and have only limited usefulness. Some facies models are based upon a severely limited database, and there is a general lack of consistency in style and application between the various models. It is becoming increasingly desirable Geological Society of Australia Abstracts Number 32, Ballarat 1992

to incorporate facies geometry data into models, to increase their predictive value particularly in resource exploration applications. There is a need for a standardised format to facies models, a greater level of detail incorporated into models, and a system whereby a sequence of unknown origin may be objectively interpreted. It is suggested that certain diagnostic criteria are established for each major depositional system. If neccessary, a hierarchical classification of depositional systems could be adopted. Models should be presented in a form that allows researchers to readily access critical data. The degree of uncertainty associated with different models should be clearly stated, together with some measure of reliability of the established diagnostic criteria. References Brookfield, M.E., 1984. Eolian Sands. In: Ed. R.G.Walker, 1984, 91-103. Cas, R.A.F. & Wright, J.V., 1987. Volcanic Successions. Allen & Unwin, London. Eugster, H.P. & Kelts, K., 1983. Lacustrine chemical sediments. In: Ed. A.S.Goudie & K.Pye, Chemical Sediments and Geomorphology, Academic Press, London, 321-368. Eyles, N. & Miall, A.D., 1984. Glacial Facies. In: Ed. R.G.Walker, 1984, 15-38. Jackson, R.G., 1978. Preliminary evaluation of lithofacies models for meandering alluvial streams. In: Ed. A.D.Miall, Fluvial Sedimentology, Can.Soc.Petrol.Geol.Mem. 5, 543-576. Jackson, R.G., 1981. Sedimentology of muddy, finegrainedchannel deposits in meandering streams of the American Middle West. J.Sedim.Petrol. 51, 1169-1192. Lajoie, J., 1984. Volcaniclastic Rocks. In: Ed. R.G.Walker, 1984, 39-52. Miall, A.D., 1984. Deltas. In: Ed. R.G.Walker, 1984, 105-118. Reinson, G.E., 1984. Barrier-Island and associated Strand-Plain Systems. In: Ed. R.G.Walker, 1984, 119-140. Rust, B.R. & Koster, E.H., 1984. Coarse Alluvial Deposits. In: Ed. R.G.Walker, 1984, 53-69. Shanmugam, G., Damuth, J.E. & Moiola, R.J., 1985. Is the turbidite facies association scheme valid, for interpreting ancient submarine fan environments? Geology 13,234-237. Stow, D.A.V., 1986. Deep Clastic Seas. In: Ed. H.G.Reading, Sedimentary Environments and Facies (2nd Edn.), Blackwell, Oxford, 399-444. Walker, R.G. (Ed.), 1984. Facies Models (2nd Edn), Geoscience Canada Reprint Series 1,317pp. Walker, R.G. & Cant, D.J., 1984. Sandy Fluvial Systems. In: Ed. R.G.Walker, 1984, 71-89.

145 A 5.10 FLUVIAL ARCHITECTURE AND SEDIMENTOLOGY OF THE LATE JURASSIC-EARLY CRETACEOUS STRZELECKI AND OTWAY GROUPS. Andrew Constantine Department of Earth Sciences, Monash University, Victoria 3168 The Otway and Gippsland basins are two WNWtrending extensional rift basins which form the eastern extremity of a complex rift system which propagated along the length of the southern Australian margin during the Late Jurassic-Early Cretaceous as a precursor to the post-Middle Cretaceous break-up of Antartica and Australia. The Otway and Gippsland basins are separated by the Morning ton High, a Paleozoic basement high several 10's of km wide. Consequently, the Late Jurassic-Early Cretaceous fill of each basin has been referred to as the Otway and Strzelecki Groups respectively. During the Late Jurassic-Early Cretaceous, inexcess of 2500 metres of predominantly volcaniclastic fluvial sediments were deposited in both the Gippsland and Otway basins. Sedimentological analysis has identified 9 architectural elements based on a combination of 23 lithofacies. Lithofacies associations indiactes 4 depositional environments are present: (1) high-energy active tract, (2) overbank, (3) floodplain and (4) lacustrine. Stratigraphic subdivision indicates fluvial patterns changed throughout this period in response to a combination of changing basin tectonics, provenance, and possibly climate. Initial Late Jurassic-early Neocomian syn-rift sediments were derived from Paleozoic metasediments and granites exposed along the rift margins, and deposited by alluvial fans off active fault scarps into

assymetrical sub-basins. Further basin subsidence during the early Neocomian led to the deposition of a thick sequence of lacustrine and floodplain sediments, with locally thick coal accumulations, traversed by variably-sinuous, multi- to single channel, mobile sheet fluvial channels. Block rotation at the end of the early Neocomian resulted in an influx of coarse bed load sediment transported by a low-sinuosity sheetflood to mobile channel system, which became increasingly more suspension-laden. A marked change in channel pattern is evident in the late Neocomian with thick sequences of sand deposited from moderateto low-sinuosity, mobile- to sheet flood systems. During the Aptian, laterally accreting macroforms and thick floodplain sequences, more typically associated with moderate- to high sinuosity rivers, are common. Similarly, do wnstrean-accreting macroforms, more typically associated with lowsinuosity systems, are also present suggesting the sediments were deposited by a variably sinuous, multito single channel, mobile sheet fluvial system with both bed load and suspension transport of sediment. Sediments deposited during the ?late Aptian-early Albian (Otway Group), however, were aggraded from a broad, multi-channel, multi-storey, sheet flood system dominated by downstream accreting macroforms. Floodplain and lacustrine development was extensive within inactive tract areas of the rift valley.

A 5.11 VOLCANICLASTIC LACUSTRINE FACIES OF THE LATE DEVONIAN ROCKFIELDS MEMBER, BROKEN RIVER PROVINCE, NORTH QUEENSLAND Simon C. Lang ** and Christopher R. Fielding 2 1 Geological Survey of Queensland 2Department of Geology and Mineralogy, University of Queensland. Introduction. The Rockfields Member is a thick sequence of dominantly alluvial plain channel sandstones, floodplain siltstones and associated crevasse splay sandstones (Lang and Fielding, 1991). The member lies at the base of the Late Devonian Bulgeri Formation, a 3500 m thick, dominantly nonmarine clastic wedge, in the Broken River Province, north Queensland. The clastics were derived from erosion of the surrounding Precambrian to early Palaeozoic basement rocks, and from uplifted areas of Ordovician to Middle Devonian siliciclastic and Geological Society of Australia Abstracts Number 32, Ballarat 1992

carbonate sedimentary rocks. Numerous short intervals occur within the Bulgeri Formation where local contemporaneous acid to intermediate volcanism provided the dominant source material, mainly in the form of reworked, unconsolidated, volcanic ash. These reworked tuff intervals are described and interpreted in this paper, and their significance to regional geology is discussed. Description. The fine-grained floodplain deposits of the Rockfields Member contain many reworked tuff intervals. These intervals are laterally extensive (> 15

146 km), up to 6 m thick, and composed mainly of fine to coarse silt-grade ash (mainly glass shards, volcanic quartz, and feldspar), and detrital muscovite. The shards are replaced by zoisite, clinozoisite, chalcedony, and lesser calcite. The thickest interval, referred to informally as the "green reworked tuff bed" (GRTB) lies in the upper part of the Rockfields Member (Fig. 1). The lower part of the GRTB is marked by a dark green, structureless bed with angular tuff clasts (lithofacies Tm, Fig. 1), overlain by a normally graded bed containing accretionary lapilli up to 10 mm in diameter (lithofacies Ta, Fig. 1). The upper part of the GRTB comprises interbedded conglomeratic and fine-grained tuffaceous intervals, with lithic clasts ranging up to cobble-grade (70 mm in diameter). The clasts are mainly rhyolite lava, and fragments of green, fine-grained tuff similar to the matrix, although there are also large feldspar crystals and a few metamorphic rock clasts. The coarse clasts are randomly distributed in the fine-grained matrix, or confined to scour fills and thin, normal and reverse-graded beds. The volcanic clasts are commonly subrounded, but many are angular, especially the fine- grained tuff clasts. The upper part of the GRTB is variably structureless, laminated or thin bedded, and ripple cross-lamination, and wave-formed micro-ripples occur in places. Scoursurfaces are common, and usually occur at the base of graded beds. Plant fragments and rhizoliths occur at the southwestern margin of the GRTB. Paleoflows were to the east or northeast, consistent with the enveloping fluvial channel sandstones (Fig. 1). These sandstones contain rip-up-clasts of green tuff, diluted by the overwhelming supply of non- volcanic detritus. A striking feature of the Rockfields Member is the pervasive soft- sediment deformation, and in the GRTB this includes convolute laminations, water escape structures, flame structures, clastic dykes and sills, ball and pillow structures, slumping, brecciation, and microfaults. The soft-sediment deformation occurred during and after deposition, but before consolidation. Interpretation. The reworked tuffs not only contain primary sedimentary structures indicative of deposition from suspension in a body of water, but also current and wave action features typical of relatively shallow water. The lateral extent of some of these intervals,

Geological Society of Australia Abstracts Number 32, Ballarat 1992

and the presence of plant fragments and rhizoliths suggest a shallow floodplain lake depositional setting (Fig. 1), similar to other non-volcanic floodplain intervals described by Lang and Fielding (1991). The base of the GRTB may have been deposited as a primary airfall tuff, but the upper part was largely reworked by traction currents and waves. The pervasive soft-sediment deformation was probably caused by a variety of factors including compaction, liquefaction and de-watering, slumping, and possibly seismic shocks. The reworked tuff intervals are evidence of Late Devonian acid to intermediate volcanism in the region. This is significant, because no Late Devonian volcanics are known to occur in the surrounding area. Lang & others (1990) suggested that similar green tuffs in the Late Devonian Vanneck Formation in the Burdekin Basin, 200 km to the east, were related to a now largely denuded volcanic pile in the northern part of the Drummond Basin. The accretionary lapilli of the GRTB could have been delivered via an ash clouds emanating from volcanism in the Drummond Basin to the southeast. However, the pebble to cobble- grade volcanic clasts, the angular nature of some of the material, and the paleocurrent data indicate a more proximal source to the south or west. The conclusion is that Late Devonian volcanics (or more likely their subvolcanic equivalents) are yet to be recognised in the surrounding Lolworth-Ravenswood and Georgetown Province. Given the association of gold mineralisation with Late Devonian volcanism in the Drummond Basin, the recognition of such rocks could have important implications for future exploration strategies in the region. References. Lang, S.C. and Fielding, C.R., 1991: In Miall, A.D. and Tyler, N. (Eds), Soc. Econ. Paleontol. MineralSpec. Publ. in press. Lang, S.C., Gunther, L.M., and Rich, N., 1990: ProcPac. Rim. Congr. 90, The Australas. Inst, of Min. and Metal., Melbourne, Australia, 3: 631640.

147 INTERPRETED DE POSITIONAL ENVIRONMENT

j r n m s i

MEAN GRAIN SIZE I PALEO- COLOURS UTHOFACIES M C VC G P fflflBHM

CY ST UF F

REFERENCE

•—•3

Grey

LOW SINUOSITY FLUVIAL CHANNEL

St.Sh

o 0

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9

— -

:

-i

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REWORKED TUFF IN FLOODPLAIN LAKE

Gm

CC Hi CO

2

/

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1

Light Olive Green

Dark Olive Green

Tuffaceous

sediment

Accretionary

lapilli

Y

Glass

shards

ng

Normal

grading

rg

Reverse

^

Trough

—

Flat

grading cross-bedding lamination

Ripple

St

PRIMARY AIR FALL TUFF INTO FLOODPLAIN LAKE

Tm

Dark Grey

Fl.Sr

FLOODPLAIN LAKE

Grey

St.Sh

LOW SINUOSITY FLUVIAL CHANNEL

cross-lamination

-AA.

Wave

JnL

Convolute

7~ w JJ

Figure 1 : Section through the "Green Reworked Tuff u p p e r m o s t U n i t C , R o c k f i e l d s M e m b e r , in B r o k e n River t y p e s e c t i o n , 7 2 1 - 7 2 6 . 8 m .

A 5.12

* ©

Fl.Sr &

Light Olive Green

*

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Water

escape

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dyke

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structures or

sill

structures balls

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directions readings

Bed",

CONGLOMERATE-DOMINATED TROPICAL FAN-DELTAS (PLEISTOCENE) IN A COLLISION ZONE, THE MARKHAM VALLEY, PAPUA NEW GUINEA Keyu Liu* and Keith A. W. Crook Dept. of Geology, The Australian National University

Coarse-grained fan-deltas are currently the focus of intense sedimentological research (Nemec and Steel, 1988; Colella and Prior, 1990) due to the growing realization of their tectonic implications and potential as petroleum reserviors. The Leron Formation in the Markham Valley (146°30'; 7°), Papua New Guinea is composed of an over 1000 m coarsening and thickening upwards sediment sequence of conglomerates, sandstones and mudstones (Fig. 1). Based on detailed sedimentary facies analysis and regional tectonic synthesis, it is interpreted as fandeltas prograded into a tropical lacustrine environment. The lake or intramontane basin, about 80 km long and 20 km wide, was formed by the collision between the Finisterre Terrane (a Cainozic island-arc) and the Australian plate about 1 million years ago (Liu and Crook, 1991). Fifteen lithofacies have been recognized (Table 1) Geological Society of Australia Abstracts Number 32, Ballarat 1992

and they are grouped into four facies associations. Facies Association I consists mainly of Facies PLM, RLFS, HCSS with subordinate Facies BM, IGS, XHPS and CCH. Facies Association II is composed predominantly of Facies IGS, XHPS, SSC and IGC with minor Facies PLM, BM and CCH. Facies Association III is dominated by Facies UGC, NGC, MSM, UMS and CCN with minor Facies SSC. Facies Association IV is coposed almost entirely of Facies UGC with ubordinate Facies NGC and UMS. At least another 500 m of Facies Association IV occurs above the measured section and is not shown in Fig. 1. The facies organization suggests they are "shelf-type" fan-deltas of Ethridge and Wescott (1984) with Facies Associations I, II, III and IV corresponding to prodelta shelf sediments, delta front deposits, distal subaerial fan/distal plains and proximal alluvial fan, respectively.

148 The characteristics of the facies organization of these conglomerate-dominated tropical fan deltas are similar to those described by Wescott and Ethridge (1980,1983) from Jamaica. But other unique features associated with these fan deltas related to the particular tectonic setting and climate are: (1) a very thin prodelta shelf mudstones, (2) a very narrow subaerial/subaquaceous transitional zone (shoreface), (3) a very pronounced coarsening- upwards trend and (4) extremely high chemical precipitation. Recognition of different types of carbonate concretions such as Facies CCH and CCN can be very useful in differentiating subaqueous from subaerial environments in such sparsely fossiliferous strata.

References Colella, A. and Prior, D. B., 1990. Coarse-grained Deltas, IAS sp. No: 10. Ethridge, F. G. and Wescott, W. A., 1984. CSPG Memoir 10, p. 217-235. Liu, K. and Crook, K. A. W., 1991. Proceedings of GEM 91, PNG, AusIMM, p. 8-16. Nemec, W. and Steel, R. J., 1988. Fan Deltas, Blackie and Sun Ltd. Wescott, W. A. and Ethridge, F. G., 1980. AAPG Bulletin, v. 64, p. 374-399. Wescott, W. A. and Ethridge, F. G., 1983. Sedimentology, 30: 235-247. LITHOFACIES DESCRIPTION

CODE

LITHOFACIES

PLM

Plane laminated mudstone

Grey to dark grey, poorly indurated, sometimes sheared, plane laminated mudstone, normally 10 to 200 cm thick, can be as thin as 1 cm or up to 400 cm

BM

Black mudstone

MSM

Massive sandy mudstone Ripple laminated fine sandstone Hummocky crossstratified sandstone Inverse-graded sandstone

Black, organic material-rich, massive to plane laminated mudstone with abundant lignite, normally 2 to 10 cm thick Grey, yellowish to reddish, poorly sorted, poorly indurated, massive sandy mudstone with fsu to vcsu sand pockets or lenses Light grey, moderately well indurated, small ripple to plane laminated vfsl to fsl sandstones with convoluted bedding and loading structures, 5 to 100 cm thick Light grey, moderately well indurated, hummocky cross-stratified vfsl to fsl sandstones with distorted lamination, individual beds about 20 to 100 cm thick Grey, relatively well indurated, massive to plane laminated sandstone inversely graded from vfsu to msu sandstones with csu grains or pockets at the top, the lower part normally plane laminated with the top part sometimes dominated by distorted lamination, about 50 to 200 cm Well indurated, inversely and then normally graded vfsu to csl sandstones with a massive, distorted and rarely cross laminated middle part, a plane to ripple laminated upper 1/6 and a massive to plane laminated lower 1/2, 40 to 200 cm thick Grey to yellowish, poorly sorted, poorly indurated massive sandstone with variable grain sizes from fsl to csu, about 10 to 100 cm thick Very well indurated, horizontally to trough/planar tabular cross-stratified, medium to small pebble msl to csu sandstones, normally inverse-graded, 50 to 400 cm

RLFS HQSS IGS

INGS

UMS XHPS

ggO |QQ fsJ30 U3Q 0Q-| QQfSj

Inverse and then normally graded sandstone Ungraded massive sandstone Cross to horizontal stratified pebbly sandstone Well stratified sandy conglomerate Inverse-graded conglomerate Normal-graded conglomerate Ungraded conglomerate Carbonate concretion horizon Carbonate concretion nodules

Well indurated, horizontally to rarely cross-stratified very sandy small to large pebble conglomerate, predominantly inverse-graded with minor component of ungraded beds Relatively well stratified, clast supported, inversely graded large pebble to cobble conglomerate, 2 to 5

m

Normally graded, clast-supported large pebble to cobble conglomerate, 2 to 4 m with increasing pebbly sandstone lenses upwards Massive to crudely stratified very large pebble to cobble clast-supported conglomerate with occasional outsized boulders, 4 to 10 m thick Light grey to white, well indurated, thin (0.2 to 2 cm) carbonate concretion horizon capping on top of Facies PLM or RLFS White, grey to reddish irregular shaped carbonate nodules, normally forming relatively thick horizons (2 to 20 cm) capping sandy mudstone (MSM)

TABLE 1 Fifteen sedimentary facies recognized from the measured sequence. Grainsizes are according to KSEPL grainsize comparator (e.g. vfsl: very fine sandstone (lower/finer))

Geological Society of Australia Abstracts Number 32, Ballarat 1992

149 MCS (mm)

4

0

-6 0

M l II I I I I I I

0 200 400 600 I ... I ... I... I 4

0 111 "

-6 0 " "

Facies Association IV

1

Proximal fan

subaerial

— UGC MSM

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fan

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front

Facies Association I Prodelta/shelf sediments LEGEND Snails

Mudstone F ? m Sandstone »• •• •• 1 Cong I. Plane lam.

^

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CD Carbonate concretion

«=5 Lignite u

W

Bioturbation Coarsening

f u?warSfs

K V ^ Hummocky cross strat. Trough cross bedding

Fig. 1 Part of measured fan-delta sequence showing four Facies Associations (I, II, III and IV) and various Facies discussed in text; MPS, Maximum clast size

Geological Society of Australia Abstracts Number 32, Ballarat 1992

150

A 5 13 THE DEPOSITIONAL ENVIRONMENT AND PROVENANCE OF THE GRAMPIANS GROUP, GRAMPIAN RANGES, WESTERN VICTORIA. Merren A. Jones and Ray A.F. Cas Department of Earth Sciences, Monash University, Clayton, VIC The Grampians Group is a thick (6200 m to 13000 m; Spencer-Jones, 1965; Atkinson, 1976) ?Late Silurian-Early Devonian quartz sandstone sequence that outcrops in the Grampian Ranges, Western Victoria. The group is predominantly composed of quartz-rich sandstones (98% quartz) with minor siltstones and pebble sandstones units. The area of the study extends from Halls Gap to Mafeking, and includes both the Mt William and Serra Ranges. The area encompasses the stratigraphy of the Red Man Bluff Sandstones (units 3-5), the Silverband Formation and the Mt Difficult Sandstones of Spencer-Jones (1965). Nine distinct facies were defined using the lithofacies code of Miall (1978). Facies Gm (massive to crudely stratified gravel), St (trough cross-bedded sand), Sp-Sl (low angle planar cross-bedded), Sm-Sh (massive to faintly laminated), Sh (horizontally laminated), Shn (normally graded horizontally laminated), Sr (rippled), Sd (deformed), and Fsc (massive to laminated muds) were each recognised within the sequence. The facies were grouped into four main facies associations. Determination of the depositional environment of the Grampians Group is extremely difficult due to a general absence of body fossils, the great thickness of the component facies of the sequence, an apparent absence of any regular systematic arrangement of sets of sedimentary structures, and because the dominant sedimentary structures of facies are not diagnostic of any particular environment of deposition. However, the abundance and combination of the major facies suggest deposition in a marginal or nonmarine environment (Heckel, 1972), and minor features of the sequence such as desiccation cracks, convolute bedding, and overturned beds are probably more consistent with a fluvial rather than marine origin. Palaeocurrent roses for individual outcrops were characteristic of fluvial deposits with unimodal palaeocurrent distributions in 80% of cases. Conversely the absence of marine fossils, hummocky cross-stratification, flaser and lenticular bedding, and tidally induced structures (such as mud drapes on the foresets of cross-bedded units, winnowed pebble horizons or herringbone cross-stratification) are inconsistent with a marine origin for the Grampians Group. Tubular cylindrical structures approximately 2-3 mm (range 2 mm-1 cm) in diameter and between 10 Geological Society of Australia Abstracts Number 32, Ballarat 1992

cm and 50 cm in length were present in all horizontally laminated, trough and planar cross-bedded sandy facies of the Mt William Range (units 3 and 5 of the Red Man Bluff Sandstones). The structures were first identified by Talent and Spencer-Jones (1963), who identified them as animal(?) burrows, possibly of the type Skolithos. Skolithos are generally believed to be indicative of intertidal and nearshore environments. Five possible origins were postulated for the structures. Plant roots, fluid escape structures and weathering processes were discounted as likely origins for the structures on the basis of the morphology of the structures and the manner in which they cut across bedding. It would also seem unlikely that the structures are the product of diagenetic processes since their presence and density varies between individual beds of apparently similar permeability. The structures share a large number of characteristics with known Skolithos deposits. However in the absence of supporting shallow-marine or tidal evidence their identification remains too ambiguous to conclude a shallow marine-tidal environment of deposition for the rocks of the Mt William Range. On the basis of all the evidence presented a fluvial origin for the sedimentary rocks of the Grampians Group is concluded. The great thickness of the component facies of the sequence and absence of any regular systematic arrangement of sets of sedimentary structures distinguishes the Grampians Group from established facies models developed from both modern and ancient successions. It is proposed that the most significant difference between these deposits and the Grampians Group (and a number of Proterozoic and Early Paleozoic sandstone successions to which the Grampians Group is analogous (e.g. Mississagi Formation, Long, 1978) is the absence of abundant land plants. The first occurrence of land plants occurred, during the Silurian. The absence of prolific land vegetation probably resulted in increased denudation and runoff rates, larger floods, the dominance of bedload channels and the production of river beds with high width to depth ratios (Schumm, 1968; Long, 1978). The absence of land vegetation would also have had a significant effect on the style of river that deposited the Grampians Group. Schumm (1968) suggested that the development of a meandering stream in the absence of vegetation would be hindered by a lack of cohesive banks and increased runoff. An

151 absence of well defined fining up cycles, lack of extensive mudstone units (vertical accretion deposits) and absence of lateral accretion surfaces (characteristic of the lateral migration of point bars in a channel) within the area of study supports a braided rather than meandering interpretation. A three phase model is proposed for the deposition of the Grampians Group within the field area, which roughly stratigraphically corresponds with the broad formational subdivisions of the Grampians Group by Spencer-Jones (1965). The sediments of phase 1 (Red Man Bluff Sandstones; Associations 1 and 2 and minor 3) and 3 (Mt Difficult Sandstones; Association 1 and 4) were deposited by an areally extensive braided stream system. The transition from the first to second phase of deposition (Silverband Formation; Association 3) is characterised by a gradational decrease in the overall thickness, grainsize and apparent energy conditions of the system. This may suggest that either; conditions became more ephemeral, the basin was filling up, or avulsion of the main channel occurred away from this area of deposition. The characteristics of the sediments suggest they were deposited by a series of large floods in the distal parts of a flood plain, marginal to sandy overbank deposits. Deposition on the alluvial mudflat was discontinuous and at least periodic exposure and drying out occurred. The contact between the second and third phases of sedimentation is sharp, indicating an abrupt change in the conditions of deposition, presumably controlled by avulsion or tectonics. The sedimentary rocks of the Grampians Group are predominantly a mature to supermature, medium to fine grained quartz arenite derived from a metasedimentary source rock. While there is no direct evidence for the sediments of the Grampians Group

A 5.14

being derived from an older sedimentary source rock (i.e. overgrowths on rounded quartz grains, fragments of mudstones or siltstones), the high concentration and rounding of quartz, implied high rates of sedimentation, thickness of the deposit, and the compositionally restricted, largely ultrustable and texturally rounded to well rounded heavy mineral assemblage, all suggest the sediments to be at least second cycle. Palaeocurrent data suggests the source of the sediments is to the west of the Grampian Ranges. It seems probable that the sediments were eroded from the quartz-rich metasediments (e.g. Glenelg River beds) of the Glenelg Metamorphic Complex. Some of the quartz may also have been derived first cycle from granites (e.g. Wando Granodiorite) or from schists (e.g. biotite schists of the northwest of the Complex) which outcrop within the presumed source area. References Atkinson, P.L., 1976, Unpublished Honours Thesis, LaTrobe University. Heckel, P.H., 1972, Society of Economic Palaeontologists and Mineralogists, Special Publication 16, 226-286. Long, D.G.F., 1978, Canadian Journal of Earth Science 15, 190-206. Miall, A.D., 1978, Canadian Society of Petroleum Geologists, Memoir 5, 597-604. Schumm, S.A., 1968, Society of Economic Palaeontologists and Mineralogists, Special Publication 31,19-29. Spencer-Jones, D., 1965, Geological Survey of Victoria, Memoir 25, Dept. Mines. Talent, J.A., and Spencer-Jones, 1963, Proceedings of the Royal Society of Victoria, 76, 1-11.

SEDIMENTOLOGICAL RESPONSE TO FORELAND DEFORMATION: THE TRIASSIC OF THE BOWEN BASIN Jochen Kassan Department of Geology and Mineralogy, University of Queensland, Q 4072

The Bowen Basin is part of a larger retro-arc foreland basin complex, which occupies a North-South elongate area in eastern Australia, parallel to the New England Foldbelt. The basin fill comprises Permian continental and marine sediments and Triassic continental sediments. Because of its economic significance for coal and hydrocarbons, the Permian part of the succession has been subject of intense study (see Fielding 1992, Ziolkowski et al. 1992, both this volume). The Triassic part of the basin fill, however, has not undergone systematic examination

Geological Society of Australia Abstracts Number 32, Ballarat 1992

since initial work by the BMR in the early to mid seventies. As part of this work, Jensen (1975) revised the stratigraphy of the Triassic and proposed the scheme adopted in the current study (Fig 1.). This study examines the sedimentology of the Triassic succession in the southern part of the basin. It documents the influence of the structural development of the area on sediment composition and dispersal patterns. The Triassic was the time of major fold-thrust deformation in the Bowen Basin, culminating during

152 the conglomerates in this well and have been correlated to possible source areas in the New England Foldbelt. Palaeocurrent directions in this area for the Clematis Group reveal diversion of a major southward flowing braided drainage system to the southwest. Small areas of detailed study show a reversal of drainage directions during early Clematis times on the western margin of the basin (Kassan & Fielding 1991). This is interpreted to reflect tectonic warping of the floodplain during deposition of the unit, probably resulting from reactivation of prexisting faults in a compressive regime. The influence of contemporaneous deformation on sediment accumulation in the Triassic of the Bowen Basin can also be demonstrated on selected reflection seismic records from throughout the basin. An integrated approach, utilising data from seismic records, wireline logs, drilllcore and outcrop, allowed to study the evolution of Triassic deposition in the Bowen Basin, and examine it in context with the structural development of the area.

the ?late Middle Triassic and sediments were accumulated contemporaneous with deformation. This is evident on seismic lines as well as from detailed study of drill core and laterally extensive outcrop sections. Influence of coeval structural deformation on the deposition of clastic sediments is evident at three different scales. At the largest scale, encompassing basinwide characteristics of the sediment dispersal, isopach maps provide information on the relative position of depocentres in time and space. Isopach maps were constructed from the well information available and supplemented with seismic data. A marked asymmetry of individual stratigraphic units is evident, with a steeply dipping eastern flank and a much shallower western margin. Similar geometries have been observed from other foreland basins and are considered characteristic for this type of basin. At the largest scale sediment distribution is controlled by the depth and geographical position of the foredeep and its subsidence rate. On a more local scale, examples of direct influence of tectonism on the nature and dispersal of sediments are abundant. In the eastern and central parts of the study area polymictic conglomerates and conglomeratic sandstones can be found at various stratigraphic levels from the Late Permian Baralaba Coal Measures to the Middle Triassic Moolayember Formation. In excess of 300 metres of conglomerates have been penetrated in the Moolayember Formation in GSQ Taroom 16. Four mutually exclusive clast populations can be petrographically differentiated in

References Jensen, A.R. 1975 Permo-Triassic Stratigraphy and Sedimentation in the Bowen Basin, Queensland Bur. Min. Resources Aust. Bull. 154 Kassan, J & Fielding, C.R. 1991 Triassic Depositional Environments in the Southwest Bowen Basin Proceedings 25^ Symposium on Advances in the Study of the Sydney Basin p. 154161

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Fig. 1 Triassic stratigraphy of the Bowen Basin ('Outcrop' after Jensen 1975 ), absolute time scale approximate only.

Geological Society of Australia Abstracts Number 32, Ballarat 1992

153 A 5.15 SEDIMENTOLOGY OF THE LATE PROTEROZOIC ACRAMAN IMPACT EJECTA HORIZON, SOUTH AUSTRALIA Malcolm W. Wallace 1 *, Victor A. Gostin 2 and Reid R. Keays1

2

1 Geology Department, University of Melbourne, Parkville, Victoria, 3052, Australia. Geology Department, University of Adelaide, GPO Box 498, Adelaide, SA 5001, Australia.

Australia's largest meteorite impact structure, in the Gawler Ranges of South Australia is linked to a widely dispersed ejecta blanket in late Proterozoic sediments of the Adelaide Fold Belt and the Officer Basin. The ejecta horizon occurs within the red and green shales of the Bunyeroo Formation (of the Adelaide Fold Belt) and Lower Rodda Beds (of the Officer Basin). The nature of these shales (widespread distribution, large stratigraphic thickness, almost total absence of sandy material, fine scale lamination) is most compatible with a relatively deep water environment of deposition. The ejecta consists predominantly of normally graded, acid volcanic clasts ranging from boulder (up to 30 cm) to fine sand-silt size. The most common and widespread ejecta sequence found in the Adelaide fold belt is, from base to top: a) breccia; b) sandy mustone; and c) graded sand. A characteristic feature of the sequence is the virtually perfect normal grading of clasts. However, in many outcrops, this sequence variably modified by a number of processes, including reworking, slumping etc. Based on the following observations, we believe that this normally graded sequence represents the primary ejecta fallout: 1. The normally graded sequence is very widespread and occurs throughout the Adelaide fold belt. 2. The sequence displays virtually perfect sorting and normal grading, as would be expected if the ejecta had been subject to suspension settling through the marine water column. 3. The normally graded sequence invariably contains a sandy mudstone layer which directly overlies the basal breccia. Such near perfect sorting of clasts, combined with

the presence of a sandy mudstone unit are not expected products of normal deep water depositional processes (e.g. mass flow -turbidites, debris flows etc., or storm wave processes). Clast size analysis of the primary fallout sequence indicates two distinct grain size populations are present (gravel and sand size). These two populations may be products of sorting by transport through the atmosphere or fragmentation processes during impact or subsequent transport. Superimposed and commonly obliterating this primary sequence are a number of sedimentological processes which appear to have occurred either during the latter stages of, or after the deposition of the ejecta. These include mass flow and storm reworking processes. The following sequence of events is used to explain the above observations: 1. Initial impact, debris ejected into the atmosphere, massive seismic event with consequent disruption and slumping of muds in adjacent marine basins. 2. Ejecta enters water column, hydrodynamic settling through water column, gravel size material deposited first. 3. Deposition of suspended host muds, together with continued settling of coarse sand to produce sandy mudstone. 4. Continued hydrodynamic settling of sandsize material to produce graded sand unit (several hours after ejecta initially entered water column, assuming 200 m water depth). Storm waves produced during massive atmospheric disruption reach site of deposition during latter stages of sand deposition, producing hummocky and trough cross-stratification.

A 5.16 SM-ND ISOTOPIC EVIDENCE FOR THE PROVENANCE OF SEDIMENTS FROM THE ADELAIDE FOLDBELT AND SOUTHEASTERN AUSTRALIA WITH IMPLICATIONS FOR CRUSTAL GROWTH MODELS S.P Turner J.D. Foden, M. Sandiford and D. Bruce Department of Geology and Geophysics, University of Adelaide, GPO Box 498, SA, 5001 In South Australia the Late Proterozoic Adelaidean and Cambrian Normanville and Kanmantoo Group sediments were depositied in basins formed adjacent to the Archaean to Early-Mid Proterozoic Gawler Craton. These were subsequently deformed and uplifted by the Geological Society of Australia Abstracts Number 32, Ballarat 1992

Cambro-Ordovician Delamerian Orogeny to form the Adelaide Foldbelt. In using the Adelaide Foldbelt to address models for lithospheric growth we need to answer: do the sedimentary sequences merely reflect reworking of the cratonic material to the west or was

154 there crustal growth through new additions from the mantle? Does the Kanmantoo reflect further erosion of the craton, reworking of the Adelaidean, or a foreland basin with its sediments derived from a source converging from the east? Likewise the Ordovician sediments to the east in Victoria may well represent detritus eroded off the Adelaide Foldbelt and contiguous parts of Antarctica but might themselves contain a contribution from volcanic detritus. The robustness of the Sm-Nd isotopic system during sedimentary and metamorphic processes allows it to be used to investigate these questions because eNd and Nd depleted mantle model ages reflect those of the source regions of the sediments. Preliminary data shows the Adelaide Foldbelt sediments have a range of eNd values similar to average upper crust yet when compared with the eNd evolution paths for Archaean and Early-Mid Proterozoic meta-igneous or metasedimentary rocks of the Gawler Craton it is apparent that they do not simply reflect erosion and redeposition of this cratonic material. Either they were derived from a different, unrecognised, more juvenile source or alternatively they represent mixtures of Gawler Craton detritus with a more primitive, mafic volcanic component. Supporting the second hypothesis is the broad range of eNd values that decay from maxima at the base of both the Adelaidean and the Normanville/Kanmantoo. These two basal maxima A 5.17

are correlated with input from the Wooltana/Depot Creek and Truro volcanic episodes respectively. The Kanmantoo sediments have Nd model ages similar to the upper Adelaidean yet generally lower eNd which may indicate an origin through further erosion from the Gawler Craton. Samples from the Glenelg River Complex in western Victoria can, isotopically, be correlated with either the Adelaidean or the Kanmantoo. However, sediments from the Ordovician and Silurian further to the east are isotopically indistinguishable from those analysed from South Australia and western Victoria have much higher K20/Na20 consistent with their being reworked from the Adelaide Foldbelt/Glenelg River provinces. Overall, Nd model ages form a curvilinear trend decreasing with depositional age but flattening out to -1.8 Ga after 2 Ga consistent with other studies that have shown that recycling of older crustal material has increased since 2 Ga. However, in detail, the Adelaidean and Kanmantoo sediment data still reflect mixing with a primitive component and new crustal additions are clearly manifested by mantle-derived mafic and felsic magmatism that occurred during the Delamerian Orogeny. Therefore our data lend support to models of crustal growth that combine recycling of older crustal material with new additions from the mantle during both orogenesis and episodes of extension related sedimentation.

THE RECOGNITION AND EFFECTS OF DIAPIRIC STRUCTURES IN THE NORTH EAST AMADEUS BASIN, CENTRAL AUSTRALIA. Martin Kennedy * Department of Geology and Geophysics, University ofAdelaide, Adelaide SA.

Salt movement within the Gillen Member of the Bitter Springs formation had a dramatic effect on the subsequent late Proterozoic stratigraphy of the north eastern Amadeus Basin. Later folding during the Devonian Alice Springs Orogeny and erosion has exposed sections through these salt structures providing a rare opportunity to observe the effects of diapiric growth on local fades and structure, effects commonly only seen via seismic reflection methods. Three previously undescribed diapir like structures were mapped in detail at; 1) Halfway Dam, 9 km S.E. of Ringwood Station ( lat. 23° 55', long. 135° 00', type section of the Olympic Formation ), 2) 3 km west of Dead Horse Waterhole (lat. 23° 46', long. 135° 09') and 3) south of Benstead Creek (lat. 23° 36', long. 134° 16'). Salt movement began shortly after deposition of Gillen Member evaporites, affecting the deposition of the overlying Loves Creek Member and later Geological Society of Australia Abstracts Number 32, Ballarat 1992

formations. Early salt pillowing stages thinned sediments over the crest of these structures while thickening flanking sediments in salt withdrawal basins. A previously unrecognised, lithologically distinct, 900m sequence was measured in one such salt withdrawal basin adjacent to the Mt. Benstead Creek structure. Continued movement of salt toward the dome structurally influenced adjacent strata by piercempnt of overlying units (diapirism), drag folding with local overturning, and migration of the salt withdrawal basin toward the dome by means of normal faulting. Uplift of areas above the dome during pulses of salt movement created local unconformities and shed wedges of pebble sized mass-flow diamictites into the anoxic starved basinal facies of the overdeepened salt withdrawal basins. In cross sectional outcrop pattern these structures appear asymmetric with an oversteepened or mushroomed flank showing well

155 developed diapiric features. The opposing flanks of laterally persistant. Regional stratigraphic these salt structures show gently onlapping sediments, interpretations based on local outcrop relationships apparently not as affected by salt movement. Hank will provide misleading conclusions if the occurence geometries at Mt. Benstead Creek and Dead Horse and influence of local salt structures is not accounted Waterhole are complicated by later (Alice Springs for. Orogeny) thrust faults directed through the cores of these incompetant salt structures obscuring the References original diapiric geometry. Previous work conducted on the Late Proterozoic Field B., 1991 Glacial Facies of the Late Proterozoic Olympic formation. In Korsh R.J. and Kennard stratigraphy in the north-east of the basin has described J.M. (Editors) Geological and Geophysical laterally variable thickness changes within units and Studies in the Amadeus Basin, Central Australia. regionally paraconformable relationships between Bureau of Mineral Resources, Australia. Bulletin units with local angular unconformities. Thickness 236. changes and angular relationships have been used as a M.J., Oaks R. Q. and Shaw R.D., basis for dividing up the sequence and assigning Freeman Stratigraphy of the late Proterozoic Gay lad formation status. They have also been interpreted as Sandstone, northeastern Amadeus Basin , and evidence for tectonic movements, such as the recognition of an underlying regional Olympic and Souths Range Movements (see Freeman unconformity. In Korsh R.J. and Kennard J.M. et al. 1991, and Field 1991). This study shows (Editors) Geological and Geophysical Studies in the Amadeus Basin, Central Australia. Bureau of however, that at least some of these angular Mineral Resources Australia. Bulletin 236. stratigraphic relationships and depositional thickness changes occur adjacent to salt structures and are not A 5.18

SEDIMENTOLOGY AND STRATIGRAPHY OF THE REYNELLA SILTSTONE MEMBER, ELATINA FORMATION: A LATE PROTEROZOIC GLACIGENIC SEQUENCE IN THE ADELAIDE GEOSYNCLINE. I.A. Dyson School of Earth Sciences, Flinders University of South Australia, Bedford Park SA. 5042

The Reynella Siltstone Member of the late Proterozoic Elatina Formation is widespread throughout the western Adelaide Geosyncline of South Australia. This dominantly gritty red siltstone facies is particularly well exposed in the coastal cliffs of the Marinoan type section at Hallett Cove near Adelaide. Here it attains a thickness of about 110 metres and displays a wide range of lithofacies types not seen at other localities. The Reynella Siltstone Member does not occupy a regionally consistent stratigraphic position within the Elatina Formation, nor is it identified in all sections of the Formation (Preiss, 1987). Recent studies (Dyson, 1986, Dyson and von der Borch, 1986) concentrated on the nature of the limestones and channelized units and presented palaeoenvironmental interpretations that suggested the Reynella Siltstone Member to have been deposited in a glacio-fluvial to glacio-lacustrine environment. Repeated cycles of glacioeustaic exposure resulted in direct glaciation by grounded ice and subsequent periglacial weathering. The preferred interpretation is that fine-grained diamictites suggest large concentrations of ice rafted sediment deposited in a Geological Society of Australia Abstracts Number 32, Ballarat 1992

glaciomarine environment. Suspension deposition, ice rafting, density underflow, highly variable traction current activity and sediment gravity flow were operative some distance from a grounded marine ice margin. The lack of storm-derived sedimentation suggests that floating ice and an extensive ice shelf had a significant damping effect (1949) to be a distant echo of Elatina glaciation in the Adelaide Geosyncline, a description which has been borne out by this study. Glacigenic sediments of the Reynella Siltstone Member in its type section at Hallett Cove consist of a series of thick diamictites interbedded with minor cross-bedded sands, conglomerates and limestones. A basal fine-grained grayish-red diamictite disconformably overlies a thick (2m) fine-to-mediumgrained, pale yellowish brown sandstone. Basal granule layers define what appears to be swaley cross stratification. The sandstone in turn overlies with possible disconformity the fine-grained, grayish green sandstones of the Wilmington Formation. The diamictites, often massive in texture, appear to be arranged into a number of crude upward-coarsening sequences. Each sequence consists of a diamictite, often gritty towards the base and fining upwards, often

156 grading into diamict-free mudstones. It is in turn compositions of these carbonate units show a close values (range overlain with an erosive contact by medium-grained and consistent clustering. The sandstones displaying planar cross-bedding and coarse- 2.11 to 7.15% PDB) is typical of marine limestones. grained angular conglomerates that show horizontal The high negative 5180 values (range -14.50 to -21.26% PDB) suggest an origin under glacial planar stratification and inverse grading. These coarse-grained shallow water facies, conditions and/or a digenetic effect. The interpreted as cross-bedded tidal sands and subaqueous pseudomorphs are contained within the lower orange gravity flows are typical of marine areas subject to brown zone of the limestones that contain microbial glacio-isostatic recovery after glacial retreat or eustatic tufa and display rhythmic lamination of possible tidal sea level fall. Rhythmites and ripplecross laminae, origin. It is suggested that the crystals are relicts of often of the herringbone type, are associated with the ikaite (CaCC>3, 6H2O), the cold water analogue of sandstones which are interpreted to be of tidal origin. aragonite with respect to the stable form calcite in These rhythmites have been interpreted by Williams seawater. The association with microbial tufa is (1989) as having been deposited by ebb tidal jets. The consistent. Ikaite found in present day fjords where observation of a large tidal channel (approximately columns containing the crystals have grown over 100 metres wide, 2 metres thick) displaying low angle springs that issue from the floor of the fjord epsilon cross stratification and thin cycles of (Shearman et al., 1989). Tufa deposition during the rhythmite, ripple cross-laminae and thin bedded Pleistocene is typical of lacustrine high stands (pers. comm. L. hardie, 1989). diamicite supports this interpretation. The vertical transition from diamictite to Sequence stratigraphic analysis of the Reynella mudstones free of ice rafted debris is a typical facies Siltstone Member suggests that the base is marked by change suggesting withdrawal of a glacial source and a a sequence boundary or combined sequence glacioeustatic sea level rise during an interglacial or boundary/transgressive surface. The sequence postglacial period. The origin of diamictic muds can boundary is represented by shoreface incision and is be complex. Lithofacies of this type may form either overlain by thick, fine-grained sandstones at the top of by rapid ice-proximal deposition of fines from the Reynella Siltstone Member are disconformably meltwater stream plumes or by slow ice-distal overlain by shallow marine and estuarine sediments of deposition of pelagic or hemipelagic muds. An ice- the Seacliff Sandstone. The Seacliff Sandstone is an distal origin is favoured from the underlying incised valley fill and its base is interpreted as a Wilmington Formation that crops out at Marion sequence boundary. Rocks. The activity of subaqueous gravity flows Interpretation of the sequence stratigraphy is associated with glacio-marine sedimentation is limited by the lack of 3-dimensional data, the base of characteristic of sea level lowstands. Sediment gravity the Elatina formation displays a regional unconformity flows may have been triggered by rapid sedimentation in the central Flinders Ranges (Lemon and groatin, of coarsed-grained material delivered to the shelf by 1990). Adjacent to diapirs, the Elatina Formation is subglacial meltstreams. characterised by a major flucial incision and may Higher in the sequence, massive diamictites of the represent incised valley fills of galcigenic sediment. Reynella Siltstone Member appear to be overlain Distally the base of the Elatina formation appears as a conformably by limestones, previously interpreted to correlative conformity. Detailed sequence analysis of be palaeosols (Dyson and von der Borch, 1986). the Elatina Formation (Dyson and von der Borch, in Some limestones contain abundant sand-sized material prep) on a regional scale will help to identify sequence and display convoluted parallel lamination. The boundaries and glacial/interglacial cycles. interbedded limestones and fine-grained clastics pass upwards into a thick sequence of massive siltstones References and fine grained sandstones that contain abundant diamict. The Seacliff Sandstone overlies this unit Dyson, I.A., 1986, Geol. Soc. Aust. Abs. 15,232 with a sharp erosive base and consists of interbedded Dyson, I,A. and von der Borch, C.C., 1986, One day geological excursions of the Adelaide region. dolostones, mudstones and sandstones arranged into a Geol Soc. Aust., 17-40. series of stacked upwards-coarsening cycles. Lemon, N.M. and Gostin, V.A., 1989, Geol. Soc. The occurrence of interbedded fine-grained clastics Aust. Spec. Pub. lb, 149-163. and limestones suggests deposition during post-or D., 1949, Trans. R. Soc. S. Aust. 73, 117inter-glacial cycles when the shelf was starved of Mawson, 121. terrigenous material. The orange-yellow limestones Preiss, W.V., 1987, Bull. geol. Surv. S. Aust., 53 appear to cap upwards-shallowing cycles (ca 5m thick) D.J., McGougan, A., Stein, C. and Smith, and are associated with stromatolites and possible Shearman, A.J., 1989, Bull. Geol. Soc. America, 101, 913evaporite pseudomorphs (Dyson and von der Borch, 917. 1986). The stable carbon and oxygen isotope Williams, G.E., 1989, J. Geol. Soc. London, 146, t

Geological Society of Australia Abstracts Number 32, Ballarat 1992

157 97-111.

A 5.19 SILURIAN - DEVONIAN CARBONATE RAMP DEPOSITION AT THE WESTERN MARGIN OF THE HODGKINSON BASIN, NORTH QUEENSLAND Thomas Bernecker* and John A. Webb Department of Geology, La Trobe University, Bundoora, Vic. 3083, Australia The Chillagoe Formation is the oldest limestone dominated sedimentary sequence in NE Australia. Previous studies interpreted many of the limestones as allochthonous blocks, originating from the collapse of a carbonate shelf (Green, 1990). Recent detailed mapping of the Mungana area found evidence for an intact sedimentary sequence which has been extensively dissected by a complex thrust system. The delineation of five marker horizons and conodont biostratigraphy established a valid stratigraphic framework on each thrust sheet. Interpreting depositional environments in the study area is complicated by strong diagenetic and tectonic overprinting which often obscures sedimentary textures. However, careful microfacies analysis has allowed the Chillagoe limestones to be assigned to palaeo-depositional environments ranging from shallow marine restricted to open marine and hemipelagic. Almost at the base of the Chillagoe Formation is a spectacular example of shallow marine carbonate deposition in a unique Llandoverian basalt/boundstone association, which proved to be an excellent marker bed throughout the study area. On top of a 20-35 m thick basalt horizon, encrusting tabulate corals and stromatoporoids alternate with bioclastic wackestones over a thickness of 12 m. These organisms grew well within wave energy conditions, but were periodically covered with carbonate detritus. Much of the Wenlockian and Ludlovian is represented by extensive megalodont bivalve wackestones, which commonly comprise algal derived peloidal material, branching stromatoporoids (Amphipora) and rugose corals {Tryplasma). Such an assemblage is indicative of shallow marine restricted environments, an interpretation supported by the corresponding conodont fauna.

Geological Society of Australia Abstracts Number 32, Ballarat 1992

Although a variety of coral species exist in the Chillagoe Formation, a true reef facies cannot be recognized. Coral blooms are mostly confined to small patches ('coral gardens'); the main evidence for carbonate buildups in the study area are sporadic occurrences of stromatactis, a feature generally associated with mud mounds (Wallace, 1987). Most of the limestones are characterized by a high percentage of matrix (lime mud) indicating that low energy conditions prevailed during sedimentation. Moreover, a lot of micritic material was transported towards deeper marine environments, because no shelf break (reef) barred the offshore sediment transport from the proximal shallow areas. The variety and distribution of limestone facies, the lack of distinct reef-buildups as well as the mud (micrite) dominance correspond with sedimentation patterns on a gently dipping carbonate ramp, where the change from shallow to deeper marine environments is typically gradational. Carbonate accumulation was terminated during the Emsian when uplift of the western hinterland caused a prominent influx of terrigenous material (Bernecker & Webb, 1990). Consequently the ramp sediments were covered with siliciclastic deposits and also deeply eroded along submarine canyons.

References Bernecker, T. and Webb, J. A., 1990, Abstracts, 13th International Sedimentological Congress, Nottingham, U.K.: 30. Green P.M., 1990, Queensland Government Mining Journal, 91: 357-366. Wallace, M. W., 1987, Journal of Sedimentary Geology, 57: 695-700.

158 A 5 20 A SHALLOW WATER SILURIAN-DEVONIAN LIMESTONE-CHERT ASSOCIATION WITHIN THE HODGKINSON BASIN, NORTH QUEENSLAND John A. Webb* and Thomas Bernecker Department of Geology, La Trobe University, Bundoora, Victoria, 3083 Bedded Palaeozoic biogenic cherts arefrequerntlyof deep water origin, being composed predominantly of radiolaians and generally interbedded with siliclastic turbidites (Jones and Murchey 1986). However, under particular circumstances Palaeozoic biogenic cherts accumulated in shallow marine environments, as illustrated clearly by the Early Silurian-Early Devonian Chillagoe Formation. The Chillagoe Formation occurs along the western margin of the Hodgkinson Basin in north Queensland, and consists predominantly of limestones, with intrecalated chert and minor basalt and siliclastics. Although recently proposed to be a deep water deposit (Green 1990), detailed mapping and facies interpretation has shown that the Chillagoe Formation represents a long-lived shallow water carbonate ramp environment (Bernecker and Webb, this volume). Within the carbonate sequence there are two main chert horizons, both of which can be traced for severals kilometers. The lower unit, Llandoverian in age, is underlain by limestones containing conodont faunas typical of outer shelf, open ocean conditions. The chert series consists of interbedded chret and mudstone layers, sometimes showing fining upwards sequences. In the upper chert beds, spicules become progressively more abundant. It seems likely that these cherts formed as a result of storms periodically reworking the radiolarian ooze and clay accumulating in moderately deep water on the outer shelf, at the same time

introducing sponge spicules from onshore shallower water areas. The second chert unit is Ludlovian-Pridolian in age, and is generally underlain by peloidal wackestones/grainstones and overlain by crinoidal grainstones or peloidal wackestones, all containing faunas indicative of inner shelf, shallow water conditions. This chert is laminated, lacks mudstone interbeds, and consists almost entirely of sponge spicules. It appears to have accumulated in extensive shallow lagoons with restricted circulation, perhaps confined behind pelsparite shoals during a sea level lowstand. The sponges probably grew around the edges and perhaps also on the floor of the lagoon. The Chillagoe Formation cherts indicate that biogenic silica accumulation can occur in shallow water carbonate environments, provided that the water can become silica saturated, and there is a nearby source of abundant silica. These shallow water siliceous deposits, particularly those on the outer shelf, could act as source areas for siliceous turbidites which deposit bedded cherts in deeper water. References Jones, D.L. and Murchey, B. 1986. Ann. Rev. Earth Sci., 14: 455-492. Green, P.M. 1990. Qld. Govt. Min. J. 91:357-366.

A 5.21 PERITIDAL CARBONATE CYCLES IN THE EARLY DEVONIAN LILYDALE LIMESTONE , CENTRAL VICTORIA Raia Wall* & John A. Webb Department of Geology, La Trobe University, Bundoora, Victoria, 3083 The Lilydale Limestone is one of several small carbonate lenses deposited during the Early Devonian around the margins of the Melbourne Trough. Located at Lilydale, 30 km east of Melbourne, it is approximately 220 m thick and 1.2 km long, and overlies the Humevale Siltstone. It is in turn overlain by the Cave Hill Sandstone. A quarry covers much of the area of the limestone deposit, presenting some excellent exposures of the section. Except in areas affected by dolomitization, primary features in the Geological Society of Australia Abstracts Number 32, Ballarat 1992

sequence are well preserved. The sequence is typified by a series of lithologies that may represent shallowing upwards cycles from subtidal to supratidal environments. Within the subtidal limestones, micrite is not a common constituent - turbulence has produced well washed biosparite grainstones, floatstones and rudstones, composed of crinoids, red and green algae, gastropods, brachiopods, stromatoporoids, and rugose and tabulate corals. Some of these grainstones were cemented on

159 the sea floor by marine fibrous calcite with a cloudy, brownish appearance. Many of the subtidal units consist of floatstones/rudstones fining upwards to biosparite grainstones, which are interpreted as stormgenerated beds. The shallowing sequences may reach the supratidal zone before inundation by the next cycle, and there is occasional evidence of exposure, including mud cracks and, rarely, pendant cement (suggesting a vadose cementation environment). Microbial mats with well preserved fenestral fabrics feature in the supratidal zone. Fine, early formed calcite crystals line the bases of the fenestral cavities as a crystal silt. These shallower water lithologies, however, represent only thin units within the overall shoaling upwards sequences, that preserve intertidal biosparite grainstones as the dominant lithology. The presence of cyanobacteria is evident in the intertidal deposits as

A 5.22

oncoids, bored rims on skeletal grains, and even completely micritized grains. The Lilydale Limestone is composed of a large number of shallowing upwards cycles, which appear to be determined by changes in eustatic sea level, and therefore offer the potential to construct s third order sea level curve for the Early Devonian. This curve can then be compared with sea level curves for the Early Devonian constructed from elsewhere in the world (Talent, 1989). References Talent, J.A. , 1989, Transgressive - regressive pattern for the Silurian and Devonian of Australia. In Pathways in geology; essays in honour of E.S. Hills (ed. R.W. LeMaitre).

MODERN COOL-WATER CARBONATE/SILICICLASTIC OPEN PLATFORM SEDIMENTS, LACEPEDE SHELF, SOUTHERN AUSTRALIA. Yvonne Bone** and Noel P. James

1Department of Geology and Geophysics, University of Adelaide, Adelaide, South Australia, 5000 2Department of Geological Sciences, Queens University, Kingston, Ontario, Canada, K7L 3N6 The Lacepede Shelf is a 130km x 190km embayment approximately mid-way along the extensive southern margin of Australia. This open platform is covered by waters that seasonally show a marked temperature gradient from average surface temperatures of 18°C to 10°C at 100m, and which is constantly swept by oceanic swells that move the loose sediments, even in water depths of over 100m. It can be subdivided into 4 zones:- (1) strandline, (2) shelf plain, (3) shelf margin and (4) deep shelf edge and slope. A steep shoreface characterises most of the strandline, with the high-energy, predominantly quartzose sediments containing a high proportion of relict particles. This coastal area includes the mouth of the River Murray - Australia's largest drainage system. The River Murray no longer delivers large volumes of sediment on to the platform although it has done so in the past, especially during low-stands. The shelf plain is remarkably flat, only dropping from 40m to 70m over a distance of up to 120km. This flat bathymetry is locally disrupted by sea-floor rises, reflecting the underlying rugged terrain of deformed Precambrian and Early Paleozoic bedrock in the north and Tertiary limestones and Quaternary dunes in the south. It is a mosaic of subtly different facies composed of mainly coarse-grained, palimpsest sediments. These sediments reflect the complex Geological Society of Australia Abstracts Number 32, Ballarat 1992

interaction of modern flora and fauna, numerous high stands of sea-level over the last 80,000 years, modern mixing of sediments from relatively recent highstands and the afore-mentioned terrigenous load delivered during low-stands. The resultant carbonate bioclasts are dominated by bryozoans and bivalves, although coralline algae are locally prolific, particularly around sea-floor highs, and gastropods, forams, echinoids and serpulids are minor but ubiquitous. The shelf margin is a gentle incline from 70m to 140m. The sediments are mainly modern carbonate, consisting of uniform, clean, coarse to medium sands fromed from the remains of the in-situ, diverse suite of delicate to robust bryozoans that inhabit this environment. Subaqueous dunes of abraded particles of these are common. The deep shelf edge and slope, ca. 140-350m, is the habitat of a more restricted bryozoan assemblage, producing progressively finer grained sediments with depth. These muddy sediments veneer relict coarsegrained, bryozoan/coral-rich, lowstand, late Pleistocene sediments. Below 350m deposits are pelagic and/or ^deposited. Study of this cool-water open platform has resulted in the development of a model which offers an alternative for the interpretation of older platforms that formed when large reefs were not present.

160 A 5 23 MODERN CARBONATE MUD IN LAKE REEVE, VICTORIA: SOME COMPARISONS WITH THE COORONG Richard A. Davis, Jr. Department of Geology, University of South Florida , Tampa, Florida, USA Lake Reeve is a coastal barrier lagoon which has Mg calcite is present in two small lakes within the been essentially deprived of terrigenous sediments for landward adjacent Pleistocene barrier; no dolomite was up to 4000 years. During that period there has been detected. Although Lake Reeve and the Coorong share no significant tidal or marine influence. Rainfall is seasonal with annual evaporation 2.5 times the many common conditions and both produce abundant precipitation. Much of the lagoon is intermittent and carbonate mud, there are striking contrasts in important characteristics of the environments and their dries up during the summer. These conditions, plus the abundance of photo- carbonate sediments. Mineral composition of the Coorong includes abundant dolomite and the apparent synthetic organisms, have resulted in widespread carbonate mud accumulation throughout most of Lake source of the source of the magnesium and calcium is Reeve. The mud is up to 30 cm thick in some parts different. These cations come from older beach ridge of the lagoon and is typically in the form of <2 complexes in the Coorong. In Lake Reeve they micron crystallites. Most of the carbonate is low-Mg are postulated to come from the open ocean via tidal calcite wity some local occurrence of aragonite. High- pumping and setup in the Southern Ocean. A 5.24 DIAGENESIS OF SANDSTONES IN THE PERMIAN SEDIMENTARY SEQUENCE OF THE DENISON TROUGH, BOWEN BASIN, QUEENSLAND: IMPLICATIONS FOR HYDROCARBON EXPLORATION R. Ahmad*, J. C. Tipper, R. A. Eggleton, and J. L. Walshe Basin Research Group, Department of Geology, The Australian National University, GPO Box 4, Canberra, ACT 2601. The diagenetic characteristics of the Permian sandstones from the Denison Trough have been investigated by means of petrography, SEM, XRD, and Electron Microprobe. A large number of sandstone samples were obtained from the Boreholes GSQ Eddystone 4 and GSQ Eddystone 5 from the southern Denison Trough (Fig.l). The Borehole GSQ Eddystone 5 encountered a 1000 m thick Permian sedimentary sequence of eight formations, in ascending order, the Reids Dome Beds, Cattle Creek Formation, Aldebaran Sandstone, Freitag Formation, Ingelera Formation, Peawaddy Formation, Black Alley Shale, and the Bandanna Formation. The Borehole GSQ Eddystone 4 encountered a 1250 m thick Permian sedimentary sequence comprising all of the above formations with the exception of the Black Alley Shale and the Bandanna Formation. The lithology of these sedimentary formations generally varies among sandstone, siltstone, mudstone, shale, and some thin layers of skeletal limestone. Sandstones, however, constitute the bulk of the Permian sedimentary sequence, and they have undergone intense diagenetic alterations. The sandstones are mostly fine to medium grained, Geological Society of Australia Abstracts Number 32, Ballarat 1992

poorly to moderately sorted, and their compositions vary among litharenite, sublitharenite, feldspathic litharenite, and subfeldspathic litharenite. They were derived from dual sources such as recycled orogenic and continental craton interior. XRD analysis of the bulk sediments show the presence of quartz, Na-plagioclase, K-feldspar, micas, calcite, dolomite, ankerite, siderite, dawsonite, gypsum, pyrite, analcite, chlorite, kaolinite, illite (I), smectite (S), and I/S interstratified clay minerals in these sandstones. Thin section petrography and SEM investigations reveal that a large number of diagenetic events have occurred in these sandstones. These diagenetic events include: compaction; decompaction; dissolution of feldspars and recrystallization to smectite, I/S and kaolinite; illitization of smectite and I/S; recrystallization of chert, formation of overgrowth quartz; formation of authigenic chlorite; primatry pore-filling and replacement of matrix materials, quartz and feldspars by calcite; pore-filling by dawsonite; replacement of calcite by ankerite, siderite and dolomite; and the formation of framboidal pyrite. Among these diagenetic events, compaction, dissolution of feldspars, primary pore-filling and

161 replacement of matrix materials by carbonates, and the formation of overgrowth quartz are the dominant ones that control the diagenetic evolution of these sandstones, thereby controlling their reservoir quality. Among these major diagenetic events, dissolution of feldspars has contributed to the creation of secondary porosity, whereas the others have caused a large-scale reduction of the porosities in these sandstones. The pore-filling and replacement of the matrix materials and different detrital grains by carbonates is the single most important diagenetic factor, controlling the porosity reduction during the post-depositional history of these sandstones. The major sources of ions responsible for the formation of the authigenic carbonate mineral phases are the dissolution of thin limestone layers occurring at certain stratigraphic levels, dissolution of fossil shell fragments, feldspars, volcanic rock fragments, trapped seawater, and possibly the input of CC^-rich meteoric water. The thin section porosity in the sandstones varies

Geological Society of Australia Abstracts Number 32, Ballarat 1992

from about nil to 8%, and the minus-cement porosity varies from about 0.5% to 7%. The modal % carbonate content in the sandstones varies from <1% to up to 58%, and generally bears an inverse relationship with the porosity. The carbonate content, mostly authigenic carbonates, is significantly higher at three distinct stratigraphic levels in both boreholes, generally in the Reids Dome Beds, Cattle Creek Formation, and the Bandanna Formation sandstones. These high contents of carbonates as pore-filling and replacement of matrix materials in the above three stratigraphic levels form "seals" that have created stratigraphic compartments in the Permian sedimentary sequence, and thereby may have controlled greatly the reservoir quality of these sandstones. The carbonate seals seem relatively late in the diagenetic history of these sandstones. Their existence may have important implications for hydrocarbon exploration in the Denison Trough.

162

Figure 1. Map showing the locations of the Boreholes GSQ Eddystone 4 and GSQ Eddystone 5 in the Denison Trough, Bowen Basin.

Geological Society of Australia Abstracts Number 32, Ballarat 1992

163

A 5.25 DETRITAL SYNSEDIMENTARY DOLOMITE WITHIN COOL-WATER CARBONATE SEDIMENTS, LACEPEDE SHELF SOUTHERN AUSTRALIA Yvonne Bone1*, Noel P. James 2 and T. Kurtis Kyser3 ^Department of Geology and Geophysics, University of Adelaide, Adelaide, South Australia, 5000 2 Department of Geological Sciences, Queens University, Kingston,Ontario, Canada, K7L 3N6 Department of Geology, University of Saskatchewan, Saskatoon, Saskatchewan, Canada, S7N OWO

3

Modern carbonate sediments on the Lacepede Shelf, South Australia, contain up to 25% dolomite. This dolomite occurs as either single rhombs or as clusters of rhombs, with the rhomb size being up to 0.5mm. The colour ranges from transparent to yellow to light orange through to dark red. Some of the rhombs are sharply-edged crystals, others are slightly abraded and yet others are so abraded that they are almost rounded particles. The abraded aggregates are cemented together by high-Mg calite and in some cases also have loosely cemented, pristine, unabraded crystals attached peripherally. XRD analyses show that all the dolomite is Ca-rich (-43 mole % MgC03) and probe analyses show that it is Fe poor and variably zoned in respect to Mn. This zonation is spectacularly revealed under cathodoluminescence. Sr isotopes suggest precipitation from modern sea-water. Crystals from the site with the highest concentration of dolomite have a 14 C

age of 28,000 BP, re-affirming the age suggested by the Sr isotope value. Stable carbon and oxygen values are similar to those for dolomite precipitated

from sea-water. The crystal size, cathodoluminescent signature, composition and geochemistry show that this dolomite is unrelated to the nearby Modern Coorong and the underlying Tertiary dolomites. The dolomite occurs in variable amounts in the quartzose bryozoan-bivalve rich sediments, which are a Modern/relict Late Pleistocene mixture,that veneer the flat shelf. The higher dolomite concentrations (5-25%) occur in the sediments with the higher relict component. It is interpreted as having initially formed during the Late Pleistocene, a period of fluctuating sea-level on the Lacepede Shelf, within mildly reducing sediments just below the sediment-water interface. The abraded nature of much of the dolomite suggests re-working, whilst the sharply-edged crystals may result from Modern, epitaxial precipitation on buried, older dolomite nuclei. Synsedimentary, detrital dolomite of this type could be interpreted as post depositional in ancient limestones. The Lacepede Shelf example offers an alternative inteipretation.

POSTER SESSION A 5.26

RECOGNITION OF DOLOMITIC CARBONATE MICROFACIES IN THE HOLOCENE BIRD LAKE, COORONG REGION, SOUTHEAST SOUTH AUSTRALIA: A STATISTICAL APPROACH R. Ahmad

Department of Geology, The Australian National University, G.P.O. Box 4, Canberra, ACT 2601. The Bird lake is located at Latitude 36°25'50" S and Longitude 139°48,30" E in the Coorong region of southeast South Australia (Fig.l). Dolomitic carbonate sedimentation has been taking place in the lake during the Holocene. Based on the physical, mineralogical, and biological characteristics of the surface sediments, three carbonate microfacies have been recognized at the lake surface. These are: Microfacies A - Dolomitic carbonate mudstone wackestone, Microfacies B - Skeletal carbonate Geological Society of Australia Abstracts Number 32, Ballarat 1992

packstone, and the Microfacies C - Organic-rich carbonate wackestone (Fig.l). A large number of physical and geochemical parameters were measured in the core- sediment samples obtained from three different borehole sections in the lake. These data were used to perform R- and Q-mode cluster analyses using computer programs. The R-mode cluster analysis produced cluster diagrams that show the interrelationships / associations among the physicochemical/geochemical variables. The Q-

164 mode cluster analysis using the same variables produced cluster diagrams that show the interrelationships / associations among the samples for each borehole section. Based on the associations among the sediment samples, appearing in the Q-mode cluster diagrams, together with the fossil contents indicate the presence of three different facies within the Holocene sedimentary sequence in the Lake. These are: Facies I: Pre-lagoonal pond carbonate packstone, Facies II Lagoonal carbonate wackestone - packstone dolomitic mudstone, and Facies III: Lacustrine dolomitic mudstone. Facies I represents gray to olive gray, very weakly consolidated carbonate packstone, containing aragonite and low-Mg calcite. Facies II consists of very light gray to greenish gray, very weakly consolidated to unconsolidated carbonate wackestone - packstone - mudstone that contain aragonite, low- and high-Mg calcite, protodolomite and dolomite. The Q-mode cluster analyses have been able to indicate the presence of three microfacies (IIA IIC) within this facies representing depositional

Geological Society of Australia Abstracts Number 32, Ballarat 1992

environments such as protolagoon, ephemeral lagoon, and a lagoon - lake transitional stage respectively. Facies III is represented by the lacustrine, very light gray to white carbonate mudstone - wackestone. Qmode cluster analyses of the physicochemical / geochemical variables show the presence of two microfacies (IIIA - IIIB) within this facies. The carbonate minerals present in these microfacies are aragonite, low- and high-Mg calcite, and protodolomite/dolomite. Microfacies IIIA contains relatively more abundant dolomite and high-Mg calcite than the Microfacies IIIB. The mole% MgCC>3 in the lattice varies from 39 to 42% in the protodolomite, and 42 to 49% in the dolomites. The dolomites are microcrystalline and disordered to partly ordered. Hydrogeochemical data as well as the physical evidences suggest that the dolomites have formed as a result of direct chemical precipitation from the lake water having Mg/Ca ratio > 3 and pH > 7 caused by CC>2-degassing and plant photosynthesis.

165

INOEX

ELE VATlON(m) 4

r -

Grovel

O

Road

carbonate lakes Dolomitic carbonate mudstone wackestone of Microfaoes A if

Skeletal ca'bonate packstone

m 0f m.c.'Ofac.es B y alLLU Marginal flat, orQanic-rich £ 5 3 carbonate wackestone of Mtcrofaces C Modern turner dune sands Calcrete

Figure 1. Geological map of Bird Lake, showing carbonate facies/microfacies distribution and location of the Boreholes C65.4, C65.3 and C65.2, the Pit, and the piezometers.

Geological Society of Australia Abstracts Number 32, Ballarat 1992

166 A 5 27 HOLOCENE EVAPORITE AND DOLOMITIC CARBONATE SEDIMENTATION IN HALITE LAKE, SALT CREEK AREA, COORONG REGION, SOUTH AUSTRALIA R. Ahmad * and P. B. Hostetler 1

2

1Department of Geology, The Australian National University, G.P.O. Box 4, Canberra, ACT 2601. School of Earth Sciences, Macquarie University, North Ryde, N.S.W. 2109. The Halite Lake is located near Salt Creek in the minerals present in this microfacies include aragonite, Coorong region, southeast South Australia. It has hydromagnesite, dolomite, and low-Mg calcite. The evolved as a result of the post-Pleistocene rise in sea Microfacies IIB lies at the top of the Holocene level. Evaporite sedimentation has been taking place sequence, and is generally capped by about 10 cm thick layer of halite salt. This microfacies consists in the lake during the Holocene. A number of carbonate microfacies occur both in predominantly of carbonate sediments that include the present depositional surface and also in the light gray to yellowish gray, pelletal packstone. Holocene sedimentary sequence in the lake (Fig.l). Carbonate minerals present in this microfacies are Four microfacies have been recognized in the surface aragonite, dolomite, hydromagnesite, and low-Mg sediments; Microfacies A - pelletal carbonate calcite. Sediments of the gypsum dominated Microfacies wackestone and halite at the lake centre, Microfacies B - pelletal carbonate packstone of the inner lake margin, IA and IB were deposited during the early phase of evolution of the lake during which it maintained Microfacies C - skeletal/pelletal carbonate packstone of the lake shore outer lake-margin, and Microfacies D connection with the Open Coorong Lagoon such that - pelletal/skeletal carbonate wackestone of lake the summer evaporation of the lake water maintained an equilibrium with the precipitation of gypsum. The marginal flat. Physical, chemical, and the bilological criteria carbonate sediments of the Microfacies IIA and IIB indicate that four microfacies occur within the were deposited in the lake basin with its progressively Holocene stratigraphic section of the lake. more restricted connection with the Coorong Lagoon Microfacies IA lies at the bottom of the Holocene due to the build up of a sand barrier on the western sequence followed stratigraphically upward by the side of the lake. The dolomites present in the Holocene sequence are Microfacies IB, IIA, and IIB respectively. Sediments of the Microfcies IA consist of alternately laminated, microcrystalline, containing 4 1 - 4 5 mole% MgC03 light coloured, crystalline prismatic gypsite and dark in the lattice, and are partly ordered to ordered. gray, pelletal carbonate wackestone that contains Hydrogeochemical investigations in the lake over a aragonite and trace amounts of dolomite. The number of years show that the salinity (TDS) of the Microfacies IB consists predominantly of crystalline, lake surface water varies from 73,000 ppm to 365,000 prismatic gypsite with alternate thin layers of dark ppm, and the Mg/Ca ratio varies from 19 to 254. The gray, micritic, pelletal carbonates that contain dolomites have formed as a result of direct inorganic aragonite, dolomite, and trace amounts of precipitation from the lake water with high Mg/Ca hydromagnesite. Microfacies IIA consists of poorly ratio and elevated pH. laminated carbonate wackestone at the bottom and followed upward by packstone. The carbonate 2

Geological Society of Australia Abstracts Number 32, Ballarat 1992

167

fSV^S Marginal flat carbonate mudstone

Skeletal Carbonate Pelletal Modern carbonate wackestone grainstone barrier a n d haUte packstone sands

m

Pleistocene $ calcrete

Figure 1. Geological map of Halite Lake, showing carbonate and ^vaponte facies/microfacies distribution and the locations of Piezometers C2.1, and C2.2A and B. Vertical scale of ttfe cross-section is exaggerated.

Geological Society of Australia Abstracts Number 32, Ballarat 1992

168 A 5.28 TURBIDITE FACIES AND DEPOSITIONAL ENVIRONMENTS OF THE PRECAMBRIAN LABOUCHERE FORMATION, PADBURY GROUP,W.A. D.McB. Martin Key Centre, Dept. of Geology, University of Western Australia, Nedlands 6009, WA. Introduction The Padbury Group was deposited in one of three sub-basins of the Early Proterozoic Nabberu Basin. This basin unconformably overlies the northern margin of the Yilgarn Craton, and is unconformably overlain by the Middle Proterozoic Bangemall Basin. The Nabberu Basin can be subdivided, from east to west, into the Earaheedy, Glengarry, and Padbury Subbasins respectively (Fig. 1) (Hall and Goode, 1978). The Glengarry Sub-basin is the oldest of the three, and consists of a southern siliciclastic-dominated shelf sequence which thickens northwards into a volcanogenic trough sequence (Gee, 1979). Shallowwater shelf sediments of the Earaheedy Group unconformably overlie the eastern margin of the Glengarry Sub-basin (Bunting et al., 1977; Hall and Goode, 1978). The Padbury Group unconformably overlies the western margin of the Glengarry Subbasin, and has been correlated with the lower formations of the Earaheedy Group (Bunting et al., 1977; Hall and Goode, 1978). The western margin of the Padbury Sub-basin was thrust eastward during the emplacement of the 1.7 - 1.8 Ga Gascoyne Province (Bunting et al., 1977; Gee, 1979). Definition of the Padbury Group is controvercial. Bunting et al. (1977) placed the base of the Padbury Group at the disconformable contact between the Labouchere and the Horseshoe Formations (Fig. 1). Gee (1979) revised this definition on the basis of the identification of an unconformity at the base of the Wilthorpe Conglomerate which he designated as the base of the Padbury Group (Fig. 1). Elias and Williams (1980) place the basal contact of the Padbury Group at the base of the Horseshoe Formation. In this paper, preliminary results of a detailed stratigraphic and sedimentological study of the Labouchere Formation, aimed at resolving this controversy, are presented. The study area is centred around the type sections of the Labouchere Formation at Mt. Labouchere, and the Wilthorpe Conglomerate east of Wilthorpe Gold Mine (Fig. 1). Stratigraphic setting of the Labouchere Formation Detailed mapping during the present study has shown that the Labouchere Formation unconformably overlies the Horseshoe Formation, and is conformably overlain by the Robinson Range Formation (Fig. 1). Although the Wilthorpe Conglomerate unconformably overlies the Narracoota Volcanics and Thaduna Greywacke of the Glengarry Group southeast of the study area, stratigraphic and palaeocurrent data indicate Geological Society of Australia Abstracts Number 32, Ballarat 1992

that this unit is a proximal facies of the Labouchere Formation. The Wilthorpe Conglomerate and Labouchere Formation are therefore part of the same genetic stratigraphic sequence. The base of this sequence, known as the Padbury Group, is defined as the unconformity at the base of the Labouchere Formation. The Labouchere Formation can be further subdivided into three coarsening-upward intervals and one fining upward interval (Fig. 1). The upward-fining Wilthorpe Conglomerate is the uppermost interval in the Labouchere Formation and is gradationally overlain by the Robinson Range Formation. Facies associations of the Labouchere Formation General statements The 4000 m thick Labouchere Formation consists predominantly of medium- to coarse-grained sericitic quartz wacke, and sericitic siltstone and mudstone. Medium- to coarse-grained super-mature quartz arenite beds occur at the base of coarsening-upward intervals which are characterised by an upward increase in quartz wacke grain-size. A thin discontinously outcropping bed of banded iron formation approximately in the middle of the formation, forms a local marker horizon. The Wilthorpe Conglomerate consists of matrix- to weakly clast-supported pebble to boulder conglomerate. A unit of mafic to ultramafic volcanic rocks, with a possible maximum thickness of 1300 m, also occurs within the formation. The exact stratigraphic position of this unit is not certain at present, due to structural complexities created by the eastward emplacement of the Gascoyne Province. However, volcanism appears to have occurred in a distal environment with respect to the quartz wacke and conglomerate facies. Previous authors have described the Labouchere Formation as consisting of shallow-water sericitic siltstones and sandstones, and mature quartz arenites (Bunting et al., 1977; Gee, 1979) "that are not related in any way to greywacke turbidites" (Gee, 1979, p. 59). However, siliciclastic lithofacies within the Labouchere Formation indeed display characteristics indicative of deposition from turbidity currents, and can be arranged into facies classes according to the classification scheme for deep-water sediments proposed by Pickering et al. (1989). These characteristics include all elements of the Bouma (1962) turbidite sequence. Facies class A This facies class contains the coarsest sediments in

169 the Labouchere Formation, and is best developed in the Wilthorpe Conglomerate. The conglomerates consist of poorly-sorted, rounded to well-rounded veinquartz, with chert and minor quartzite clasts in a matrix of coarse to very-coarse sericitic quartz wacke. In the type area at Wilthorpe, clasts reach a maximum size of 1 m. Individual conglomerate beds fine-upwards to very-coarse wacke, displaying normal coarse-tail grading and planar stratification. Fining-upward cycles are occasionally capped by thin siltstone beds which become reworked as intraformational clasts at the base of the overlying conglomerate. Massive, disorganised pebbly quartz wackes and reverse-graded conglomerates are also common. This facies is interpreted to have been rapidly deposited by grain-by-grain settling from high concentration turbidity currents. Planar stratification is indicative of bedload transport after deposition. Facies class B This class is represented by the super-mature quartz arenite marker beds which are developed at the base of coarsening-upward intervals. These arenites are massive, medium- to very coarse-grained, well-sorted, and silica cemented. Primary sedimentary structures are largely obliterated by secondary silicification, but lowangle trough cross-stratification at the top of finingupward cycles is quite common. Thin planar bedding is also occasionally preserved. Deposition is interpreted to have occurred by initial rapid settling from high-concentration turbidity currents derived from a mature unconsolidated source area, followed by bottom current reworking. Facies class C Facies class C consists of sericitic quartz wacke and siltstone lithofacies, and can be described using the classic Bouma (1962) turbidite (Ta,b,c,d,e) sequence. The predominant facies associations consist of incomplete Ta, Ta-b, and Ta-c sequences. The Ta and Ta-b cycles are medium- to very coarse-grained with erosional bases. The Ta-c cycles are usually flat-based, although bottom marks such as flute casts, transverse scours, longitudinal ridges and furrows, and groove casts are locally preserved. Wackes within the Ta-c cycles are medium- to coarse-grained, and fine-upward to ripple- and wavy-laminated siltstones with minor mudstone. This facies also displays abundant evidence of liquefaction, sediment loading, and dewatering. Basal Ta units were deposited by grain settling from suspension, followed by tractional bed load transport to produce the Tb and Tc units. Facies class D This facies consists of thinly-bedded, graded sericitic siltstone to mudstone. Cycles are predominantly planar and ripple laminated, with minor convolute and wavy lamination. Thin, lenticular units of fine-grained, normally-graded quartz wacke are also common. Suspension settling from low concentration Geological Society of Australia Abstracts Number 32, Ballarat 1992

turbidity currents, followed by bottom current reworking and minor sediment creep is interpreted. Palaeocurrents Preliminary palaeocurrent data indicate that there are three modes within the Labouchere Formation, each associated with the various facies classes. The conglomerates and quartz wacke turbidite sediments were transported predominantly off the Yilgarn Craton towards the north, and sub-parallel to the craton margin towards the east. The super-mature quartz arenites were transported towards the south from a source area that is probably now covered by the Bangemall Group. This mode is also occasionally represented in the quartz wackes. Lateral variations in thickness of individual stratigraphic units are consistent with these transport directions. Discussion and conclusions Palaeocurrent directions, as well as vertical and lateral facies distributions (Fig. 2) are consistent with the interpretation of a fan-delta to submarine fan system prograding off the Yilgarn Craton towards the north. Thickening of conglomerate and siltstone dominated facies towards the Yilgarn Craton (Fig. 2) is interpreted as being indicative of a fault-controlled ponded basin margin. Fan-delta conglomerates of facies class A are interpreted to pass basinward into predominantly sandy lobe facies of class C and silty lobe-fringe facies of classes C and D. Outcrop does not permit an accurate interpretation of the proximal environment to the mature quartz arenites, but these sediments may have been shed from a winnowed environment developed on the distal end of a tilted fault block. Acknowledgements This research was funded by Dominion Mining Limited, and permission to publish these data is gratefully acknowledged. References Bouma, A.H. (1962): Sedimentology of some flysch deposits: a graphic approach to facies interpretation. Elsevier, Amsterdam. Bunting, J.A., Commander, D.P. and Gee, R.D. (1977): Preliminary synthesis of lower Proterozoic stratigraphy and structure adjacent to the northern margin of the Yilgarn Block. West. Australia Geol Surv. Ann. Kept., 1976, 43-48. Elias, M. and Williams, S.J. (1980): Robinson Range, Western Australia. West. Australia Geol. Surv. 1:250 000 geological series - explanatory notes. Gee, R.D. (1979): The geology of the Peak Hill area. West. Australia Geol. Surv. Ann. Rept.y 1978, 55-62. Hall , W.D.M. and Goode, A.D.T. (1978): The Early

170 Proterozoic Nabberu Basin and associated iron Pickering, K.T., Hiscott, R.N. and Hein, FJ. (1989): formations of Western Australia. Precambrian Deep marine environments: clastic sedimentation Research, V. 7,129-184. and tectonics. Unwin Hyman, London.

Figure 1: Regional setting and stratigraphy of the Labouchere Formation in the study area. NW

Mt. LABOUCHERE *

WILTHORPE *

SE

. — _. B

>

:

7

:"

iv." m I

A

im

B

•

•

C

|. -

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1

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| 500 m.

Figure 2: Palinspastically reconstructed section showing the approximate vertical and lateral distribution of turbidite facies in the Labouchere Formation. See text for description of facies. Geological Society of Australia Abstracts Number 32, Ballarat 1992

171

A6: PALAEONTOLOGY

CONVENORS: NEIL ARCHBOLD & DAVID BRIGGS

A 6.1

MULTIVARIATE STATISTICAL METHODS IN PALAEOECOLOGY AND PALAEOBIOGEOGRAPHY _J Guang R. Shi Department of Geology, University of Melbourne, Parkville, Vic 3052

Multivariate statistical methods are techniques by which many variables from a number of samples are analyzed simultaneously. These methods have been widely and successfully applied to community ecology and increasingly attract attentions of palaeoecologists because of their power to detect and objectively describe the patterns of variation between and within communities. Numerous multivariate methods have been developed in community ecology, not all of them can be readily applied to palaeoecology or palaeobiogeography. The purpose of the abstract is to summarize some of the major multivariate methods which have been used and proven to be successful in palaeoecology. Data collection and treatment— Multivariate methods can be grouped into two major categories: classification and ordination. The former usually refers to cluster analysis, and ordination is sometimes called gradient analysis. Both reguire a data matrix as input, which consists of M samples (sites, i.e. a single locality or a composite record from several adjacent localities) and N variables (taxa in palaeoecological context - species or genera). The preparation of a data matrix is essential and critical in all multivariate analyses as the choice of numerous multivariate methods largely depends on the nature of the data being studied. Two most commonly used types of data in palaeoecology and palaeobiogeography are binary (presence/absence) data and quantitative (abundance) data. Choice between the two types of data to large extent depends on the scale of the study, but in general binary data are usually preferred in large scale analysis of continental and intercontinental distributional data such as global palaeo-biogeographical study and abundance data are considered to be more suitable for local and regional palaeoecological study such as recognition of assemblages or communities. A problem often arises when abundance data (counts of specimens) are used, i.e. the distribution of the data Geological Society of Australia Abstracts Number 32, Ballarat 1992

may vary considerably from normality partly due to differential preservation and sampling error. The skewness of the raw data may be moderated by logarithmically transforming the data matrix before the analysis is proceeded. Missing values and outliers (entries with extreme values) are another problem often encountered in preparing a data matrix. Data entries with missing values can either be deleted or given estimated values calculated from other entries. Outlying entries, in my opinion, should better be excluded from initial quantitative analysis to avoid, if any, uninterpretable results, and the outliers can be later reallocated to core groups defined by cluster analysis through calculating their discriminant scores (see Shi and Waterhouse, 1990b). Cluster analysis (CA)— Cluster analysis is a form of classification technique in which the objects of study are divided into discrete groups, which will hopefully reflect the major patterns of variation in the data . There are two types of cluster analysis. Nonhierarchical CA simply divides the objects into groups without showing the relationships between the groups (for details see Gauch, 1982). This is particularly useful when a large heterogeneous data is being studied, because the method can look at the redundancy of the data and detect possible outliers. Hierarchical CA arranges objects in a hierarchical order so that the mutual (hierarchical relationships between objects become apparent. Divisive hierarchial CA treats all objects as one group and divide successfully the group into smaller groups based on their mutual similarities. Agglomerative hierarchical CA starts with all objects and cluster them successfully into groups until all objects are assembled in one group. This method is most commonly used in ecology and has several clustering techniques (Single-Linkage, CompleteLinkage, Minimum Variance, and Average Linkage). Detailed discussions of these techniques can be found in Clifford and Stephenson (1975) and Pielou (1984),

172 among many others. The Unweighted Pair Group Average Linkage is perhaps the best known and most widely used and appears to give a most reliable and consistent result (Shi and Waterhouse, 1990a). Ordination— Unlike CA in which objects under study are forced into discrete groups, the basic goal of ordination is to reduce the dimensionality of the raw data and to attempt to represent the relationships of objects in a reduced, usually two or three dimensions, scatter diagram so that major trends or patterns in the data can be observed more easily than studying the raw data alone. The ordination methods do not assume discontinuity in the data, but if discrete groups exist in the data they should be revealled by the ordination methods. This is not to say, however, that ordination is always better that CA; the two methods are complimentary and show different aspects of the data, and are strongly recommended to be combined in use to draw a more regorous conclusion. The combination of the two approaches will also provide a cross check to the results obtained by each method alone. Six ordination methods are most widely used in community ecology and palaeoecology, of which principal components analysis (PCA) is the best known and earliest technique. Mathematically, PCA is carried out by a process called eigenanalysis, which consists of a series of transformation of (N) original variables (taxa) to reduce the original N dimensionality to a fewer (preferably 2 or 3) simplified axises (principal components), which account for most of the variation in the data and may imply importance of certain environmental parameters. Principal component loadings of taxa on a particular principal component indicate the relative importance of the taxa to the component and can be used as coefficients of taxa to calculate discriminant scores of outliers, by which these outliers can then be related to core groups recognized by CA (see for example in Shi and Waterhouse, 1990b). PCA takes a covariance or correlation matrix as input and normally requires normality for the input data. Principal coordinate analysis (PCO) is a method closely related to PCA but can take a variety of similarity matrices as input in which the data are not necessarily normally distributed. Polar ordination (PO) starts with a similarity or distance matrix, from which two endpoints must be chosen as axises, and all other objects are then placed in the two-axis coordinate system based on their similarities to the two endpoints. Reciprocal averaging (RA) or correspondence analysis is a moderfication of PO; it involves iterative calculation of estimated

Geological Society of Australia Abstracts Number 32, Ballarat 1992

sample and taxa scores until both sets of scores stablize. The four ordination methods described above (PCA, PCO, PO, and RA) sometimes produce scatter diagrams in which the objects under study appear in an arched pattern along the first axis, i.e.. Arch Effect. This effect makes interpretation of the scatter diagrams difficult. Detrended correspondence analysis (DCA) is specifically designed to overcome this effect. Nonmetric multidimensional scaling (MDS) makes no assumption about the normality of the data and thus appears to be particularly useful in palaeoecology in which the normality of data is usually hardly met, but the method is computationally demanding and requires that the number of axises must be chosen before the analysis actually starts. Inappropriately chosen number of the axises may lead to a totally uninterpretable result. Comparisons and testing of multivariate statistical methods— Although numerous multivariate methods have been developed, there are relatively rather few studies that compared these methods. At present there is no general conclusion as to which method is best. The choice of methods depends on the type of the data and the scale of the study. It may be suggested that CA and at least one of the ordinations methods described above be employed for a detailed quantitative study. The reliability and consistency of multivariate methods may be tested by following approaches: (a) applying several methods to the same data set and compare results; (b) applying the same method t, if possible, to different groups of fossils and compare the results; and (c) comparing results derived from multivariate analyses with those obtained by independent methods such as sedimentary approaches and parsimony analysis of endemicity (Rosen and Smith, 1987). References Shi, G.R. and Waterhouse, J.B. 1990a. A quantitative study of four regosochonetid genera. In D.I. MacKinnon, D.E. Lee, and J.D. Campbell (eds), Brachiopods Through Time. A.A. Balkema, Rotterdam, p. 57-62. Shi, G.R. and Waterhouse, J.B. 1990b. Sakmarian (Early Permian) brachiopod biogeography and major associations as related to terrane drift. In D.I. MacKinnon, D.E. Lee, and J.D. Campbell (eds), Brachiopods Through Time. A.A. Balkema, Roterdam, p. 355-365.

173 A 6.2 LATE LOCHKOVIAN-PRAGIAN SILICIFIED FAUNAS AND CONODONT BIOSTRATIGRAPHY OF THE GARRA LIMESTONE AT WELLINGTON, NSW George A. Wilson Earth Sciences, Macquarie University, NSW 2109 Conodont faunas from several hundred samples on stratigraphic sections through the Lochkovian-Pragian sequence at Wellington, central New South Wales, indicate assignment of the lower part of the Garra Limestone (at Wellington) to the pesavis Zone. Marine transgression in this area across the Cuga Burga Volcanics is thus documented from the Eurimbula-Cumnock area farther south. A substantial part of the remaining 1000+m of shallow water (and even supratidal) carbonates at Wellington can be assigned to the sulcatus Zone; the kindlei and pireneae zones are also represented by a dearth of diagnostic forms has resulted in imprecision in definition of the zonal boundaries. No conodonts have been obtained from the upper, presumably early Emsian part of the sequence. In common with a number of other Late Lochkovian sequences in eastern Australia, Central Asia and Alaska, the pesavis Zone faunas include the unusual form Kimognathus alexeii\ it is more abundant than other species, such as the forms of Pedavis that one might otherwise use in making approximate alignments with the pesavis Zone. The A 6.3

entry of Eognathodus sulcatus eta morph is taken as a marker for the pesavis-sulcatus boundary; significantly, Kimognathus alexeii does not occur in this or younger horizons. The belief that the rich sponge, rugosan, brachiopod and trilobite faunas previously described (c.200 spp.) from the Wellington area extend down from the sulcatus Zone into the Lochkovian (delta and pesavis zones) is not supported by the new conodont data. Discovery of two previously overlooked sequences (each aggregating more than 100m) of richly fossiliferous silicified horizons - just above and below the Lochkovian-Pragian boundary, and a further sequence several hundred metres higher - has added greatly to knowledge of the Wellington faunas, especially as regards trilobites, dacryoconarids and brachiopods. The last, including more than 50 species not previously recorded from Australia will, when documented, make the Wellington Early Devonian faunas one of the most diverse in the world, and of pivotal importance in global biogeographic analysis for that time-interval.

DEVONIAN CHITINOZOAN BIOSTRATIGRAPHY OF EASTERN AUSTRALIA Theresa Winchester-Seeto Earth Sciences, Macquarie University 2109, Australia.

Chitinozoa have been recovered from numerous localities in eastern Australia, but most importantly from closely sampled sequences through the Garra Limestone in central New South Wales, the Taravale Formation in eastern Victoria, and the Shield Creek Formation and Broken River Group in northern Queensland. These span most of the interval late Lochkovian to Givetian, i.e most of the Early and Middle Devonian. Chitinozoan assem-blages are delineated and analysed in the context of the conodont framework elaborated by Mawson (1987), Mawson et al (1988), and Wilson (1989). A preliminary biozonation is presented for eastern Australia, and compared with the results of studies of the same interval in Europe and northern Africa. Three of Paris' (1981) seven biozones based on sequences in southwest Europe can be identified in the early Devonian of eastern Australia. Departures may be due Geological Society of Australia Abstracts Number 32, Ballarat 1992

to provinciality of a number of species in the European biozonation, or to little understood effects of environment on chitinozoan distributions. References Mawson, R., 1987, Palaeontology, 30:257-297 Mawson, R., et al., 1988, Can. Soc. Pet. Geol., 111:425-527 Paris, F., 1981, Mem. Soc. geol. mineral de Breagne, 26:1-412 Wilson, G.A., 1989, Cour. Forsh.-Inst. Senck 117:117-171

174 A 6.4

EARLY AND MIDDLE DEVONIAN ATRYPID BRACHIOPODS FROM UKALUNDA AND THE BROKEN RIVER, NORTH QUEENSLAND Glenn A. Brock Earth Sciences, Macquarie University, NSW 2109

Atrypid brachiopods occur in enormous abundance and great taxonomic diversity in eastern Australian Devonian sequences. They are especially diverse and well preserved in the calcareous shales of the Ukalunda Beds (Emsian, perbonus to serotinus zones) and the carbonates, calcareous shales and mudstones of the Broken River Group (late Emsian to early Frasnian, serotinus to asymmetricus zones). For instance, 18 species of atrypids occur in the early to middle Givetian (ensensis-varcus zones) portion of the Papilio Formation in the Broken River area. Atrypids have been assumed to be remarkably provincial; the predominance of the following European (and a few South China) species of Atrypidae and Palaferellidae in Australia is therefore surprising: Desquamatia (Desquamatia) peshienesis (Grabau), D (Synatrypa) subzonata (Biernat), A 6.5

D. ([Independatrypa) magna (Grabau), D. (/.) zonata (Schnur), Kerpina vineta vineta Struve, Spinatrypina {Spinatrypina) streblo Chen, Carinatina plana (Kayser), Gruenewaldtia latilinguis (Schnur) and the cemented form Davidsoniaverneuili BouchardChantereaux. Only 4 new species have been discriminated- of the genera Atrypa {Kyrtatrypa), Atryparia, Spinatrypa and Spinatrypina {Spinatrypina). The genera Atryparia, Desquamatia (Independatrypa), Kerpina, Gruenewaldtia and Davidsonia are reported from Australia for the first time. In addition there are several species of Coelospiridae and Notanopliidae from the Papilio Formation and Lissatrypidae from the Bracteata Mudstone. Preliminary discussions of atrypid biofacies, systematics and biogeography are given.

LATE MIDDLE AND EARLY LATE DEVONIAN (GIVETIAN-FRASNIAN) FAUNAS FROM CHITRAL, NORTH-WEST PAKISTAN Richard J. Morante Earth Sciences, Macquarie University, NSW 2109

On the basis of new collections made by J.A. Talent et al.y 39 species and two subspecies of brachiopods are documented from the late Middle to early Upper Devonian (Givetian and Frasnian) of the Shogram Formation, Chitral, north-west Pakistan. Dating of the faunas has been underpinned by conodont studies by P.D. Molloy, with additional work by R. Mawson. Taxa previously described but taxonomically reassigned are: Petrocrania (Craniella) cf. obsoleta (Goldfuss), Schizophoria cf. kutsingensis (Grabau), Douvillina asiatica (Reed), Productella chitralensis (Reed), Spinulicosta pamirica (Reed), Cyphoterorhynchus ponderosa (Reed), Spinatrypa chitralensis (Reed), Athyris gentilis (Reed), Sulcathyris asiatica (Reed), ?Sulcathyris triplesoides (Reed), Sulcathyris hudlestoni (Reed), Cyrtospirifer murchisonianus transversus subsp. nov., Cyrtospirifer pariricus Reed and Cyrtospirifer parilis (Reed). In addition, the following taxa are reported for the first time from the Shogram Formation: Nervostrophia sp., Retichonetes sp., Yunnanella cf. abrupta var. globosa Tien, Atrypa (Planatrypa) sp., Spinatrypina cf. robusta Copper, Athyris cf. oscarensis Veevers, Sulcathyris cf. gastra Du rkoop, Cyrtina sp., "Eosyringothyris" cf. trapezoidalis Brice et all Geological Society of Australia Abstracts Number 32, Ballarat 1992

Cyrtospirifer crassiplicatus crassiplicatus Brice, C. crassiplicatus cyrtinaeformis Brice, C. cf. lebedianicus Nalivkin, C. triplisinosus (Grabau), Cyrtospirifer cf. verneuili echinosus Lyashenko and Dichospirifer thyla-kistoides Brice. Additionally, three species of trilobites, two of gastropods, and three of tentaculitids are described. The faunas are from a terrane (part of the Talent et al. Pamir Block) separated from the Kohistan Terrane by the ophiolitic 'Northern Suture' and this in turn from Indo-Pak continental block by the 'Main Mantle Thrust'. They are nevertheless remarkably similar to the less well preserved faunas from the Ali Masjid Formation of the South Khyber region of the Northwest Frontier Province, an area that was indubitably part of the Indo-Pak Block. This similarity is consistent with contiguity or proximity during Middle and Late Devonian times. The Chitral faunas contrast with contemporaneous faunas from South China, Soviet Central Asia and Siberia; there is much greater similarity with faunas from northwest Australia. Similarities to faunas of former Gondwana blocks in Iran (Elburz) and southern Afghanistan (Dasht-e-Nawar and Robat-e-Pai) are obvious.

175 A 6.6 SILURO-DEVONIAN CONODONT BIOSTRATIGRAPHY AND SILICIFIED SHELLY FAUNAS IN THE CUMNOCK-LARRAS LEE AREA, NSW John R. Farrell School of Education, Macquarie University NSW 2109 Mapping of an area including the type section of the Garra Formation near The Gap, between Cumnock and Larras Lee in east-central New South Wales has shown large areas previously shown as Garra Formation or Late Devonian Catombal Group to be Late Silurian and very Early Devonian units including a time-equivalent or perhaps extension of the Camelford Limestone. A brief account is given of the stratigraphy and faunal and floral content of pre-Garra and Garra stratigraphic units, together with brief discussion of piercement structures, with Late Devonian sediments, occurring in a contorted area of Garra Formation adjacent to the Eurimbla Thrust where Garra Formation has apparently been thrust over Late Devonian Catombal Group. The presently unnamed Late Silurian clastic sequence NE of The Gap includes carbonate intervals with silicified horizons yielding low diversity brachiopod faunas. A progress report on brachiopodconodont faunas from this sequence will be presented. Some 150 samples collected stratigraphically through the often poorly bedded Camelford Limestone (c. 575 m. thick) has yielded earliest Devonian conodonts and numerous silicified faunas. A progress report on these will also be given.

A 6.7

A sequence of 64 silicified horizons of the Garra Formation (c. 830 m. thick) yielded in excess of 16,700 specifically or generically determinable fossils assigned to 121 taxa. Though 16 of these appear to be new, only 10 are formally named (Farrell, in press). Computer-analysis of the specifically identifiable silicified brachiopods and mollusks of the faunas has shown clustering into three communities; a fourth, non-silicified community is discernible in the highest part of the sequence. The Garra Formation is diachronous, the basal portion of the Garra Formation (latest Lochkovian pesavis Zone) at Wellington to the north correlating with only the highest horizons at The Gap. In its type area north of The Gap, the Garra Formation is delta Zone, approximately the time-equivalent of the richly fossiliferous limestones with well-documented faunas at the base of the Mandagery Park Formation at Manildra. References Farrell, J.R., in press, Palaeontographica abt., A.

EASTERN AUSTRALIAN SILURIAN AND DEVONIAN ALGAL FLORAS John Johnstone Earth Sciences, Macquarie University, NSW 2109

Apart from the floras of allochthonous blocks (mostly Early Devonian - Lochkovian) in the Nubrigyn Formation of east-central NSW (Johnson, 1964), and a brief paper on some Silurian forms (Bischoff,1988), the algal floras of numerous Silurian and Devonian carbonate sequences of eastern Australia have been neglected. The floras are in fact remarkably diverse. Forms similar in external morhology to Lancicula Maslov 1956 are widely distributed. Cup angle, cup shape and filament arrangement are used in distinguishing species and genera; there was to much reliance on total filament number in previous taxonomy. Australian forms previously referred to

Geological Society of Australia Abstracts Number 32, Ballarat 1992

Lancicula include charophytes and non-siphonous algae. Australian Silurian and Devonian algae will be exemplified by florules from Cowombat Plain (latest Silurian, eastern Victoria), the Garra Limestone (Early Devonian, east-central NSW), and the Shield Creek Formation (spanning the Lochkovian-Pragian boundary) and the Broken River Group (Emsian to Givetian) of North Queensland. The Arch Creek Limestone Member of the Shield Creek Formation, for instance, consists of 8 genera and 9 species, 2 of the genera and 4 of the species are new. These florules are typically associated with crinoids, corals, brachiopods, and molluscs in environments inferred to

176 Bischoff, G., 1988, Neues Jahr. Geol. Palaont. Mont., 3:129-140 Johnson, J.H., 1964, Palaeontology, 38:98-108

have been shallow tropical to subtropical. References A 6.8

THE DEVONIAN SUCCESSION AT RAVINE (SNOWY MOUNTAINS), NSW. Mario Biasutti Earth Sciences, Macquarie University, NSW 2109

The Byron Range Group at Ravine is a well exposed and instructive example of a transgressive/regressive cycle. The basal member of the group, the Milk Shanty Formation has the appearence of typical red beds consisting of haematite stained conglomerites, litharenites, quartz rich sublitharenites and red-purple siltstones. These rocks are interpreted as being deposited in a terrestrial fluvial environment. The contact between the Milk Shanty Formation and the overlying Lickhole Formation is conformable. Three distinct units are recognised in the Lickhole Formation: 1. a relatively thin unit just above the contact with the red beds ranges from a sub-litharenite with minor carbonate through a dolomitised fine grained quartzose siltstone to a grey shaly siltstone; 2. a thick sequence of blue grey biomicrite interspersed at irregular intervals by nodules and flaggy layers of biomicrudites; 3. a sequence of well bedded fissile mudstone. Fossils in the first and third units are typical of very A 6.9

shallow marine conditions while the second unit is palaeontologically similar to the Buchan Caves Limestone in Victoria and the Taemas-Cavan Limestones near Wee Jasper, NSW. These units are interpreted as being deposited in marine conditions initially increasing in depth followed by an interval of shallowing. Conformably overlying the Lickhole Formation is the Round Top Formation consisting of interbedded fine red-purple siltstone and fine sandstones. These mark a return to terrestrial deposition. This cycle of transgression and regression is fixed in time by conodont biostratigraphy. Conodonts recovered throughout the Lickhole Formation include a number of shallow water pandorinellinid and ozarkodinid species. The appearence of Polygnathus dehiscens abyssus Mawson, P. nothoperbonus Maw son and P. perbonus Philip relatively high in the section signals both deeper water and that deposition of the Devonian succession at Ravine occurred during the dehiscens-perbonus Zones in the early Emsian.

MIDDLE CAMBRIAN TRILOBITES FROM ALLOCHTHONOUS BLOCKS IN THE MURRAWONG CREEK FORMATION, N.S.W. Terrence R. Sloan Earth Sciences, Macquarie University, NSW 2109

Trilobites from allochthonous limestone blocks of Middle Cambrian age from the Murrawong Creek Formation within the Gamilaro terrane of the Southern New England Orogen include a new genus of alokistocarid and a new species of Opsidiscus. Other taxa include: Diplagnostus sp., Linguagnostus cf. perplexus Robison 1964, Phalagnostus cf. scanicus (Tullberg 1880), Hypagnostus parvifrons (Linnarsson 1869), Peronopsis quadrata (Tullberg 1880), Utagnostus cf. trispinulus Robison 1964, Helepagetia bitruncula Jell 1975, Pagetia pollosta Jell 1975, P. Geological Society of Australia Abstracts Number 32, Ballarat 1992

salebra Jell 1975, P. whitehousei Jell 1975, Fuchouia cf. labda Opik 1982, Sunia cf. idica Opik 1982, Kootenia sp.A, Kootenia sp.B, Anomocarella cf. comus (Walcott 1906), Maotunia cf. distincta (Resser & Endo 1937), Modocia cf. typicalis (Resser 1938), Eosoptychoparia kochibei (Walcott 1911) and Quebecaspis cf. breviceps Rasetti 1944 as well as several unidentified pygidia. The trilobite faunas provide useful data on a former carbonate platform margin - one for which no outcrop tracts have survived.

177 A 6.10 INTERNATIONAL GEOLOGICAL CORRELATION PROGRAMME 328: PALAEOZOIC MICROVERTEBRATE BIOCHRONOLOGY AND GLOBAL MARINE/NONMARINE CORRELATION - NEW EVIDENCE FOR CORRELATION OF PALAEOZOIC FISH BETWEEN CENTRAL AUSTRALIA AND THE CANNING AND GEORGINA BASINS Gavin C. Young1 and Susan Turner^ 1

Bureau of Mineral Resources, PO Box 378, Canberra, ACT 2601 Queensland Museum, PO Box 300, South Brisbane, QLD 4101

2

Preliminary recognition of fish remains in the basal beds of the Pertnjara Group, Parke Silts tone (Young 1988), has led to the discovery of two new Devonian fossil fish sites in the western Amadeus Basin, central Australia. The older horizon contains natural moulds of fish plates belonging to the Wuttagoonaspis fauna. The younger is a sequence of purple-red mudstones with an in situ bone bed near the base containing numerous thelodont scales (Turinia sp.) associated with rarer pieces of bone, crossopterygian fish teeth, shark and acanthodian? scales. One or more younger beds have yielded wellpreserved bones including placoderm spinal plates (IGroenlandaspis), crossopterygian scales, skulls and teeth - laniary teeth of onychodontids, palaeoniscoid and/or acanthodian sculptured bone and lungfish remains, tooth plates, skull fragments and scales. This site on the westerly edge of the Amadeus Basin is thus closest to the type location of Turinia australiensis Gross 1971, which came from a borehole

A 6.11

at Wilson's Cliffs in the Canning Basin, W.A. The turiniid thelodont scales from the new site also resemble those from the Cravens Peak Beds of western Queensland and the Mulga Downs Group of western NSW (Turner et al. 1981). The co-occurrence of macro- and microvertebrate remains at the new locality will assist in correlation of similar non-marine occurrences, for example the fauna from the Aztec Siltstone, south Victoria Land, Antarctica (Turner & Young 1991 in press). References Young, G.C., 1988. BMR Jl. Aust. Geol & Geophys . 10 , 363-376. Gross, W., 1971. Palaont. Z. 45, 97-106. Turner, S., Jones, P.J., Draper, J.J. 1981. BMR Jl. Aust. Geol.& Geophys. 6, 51-69. Turner S. & Young, G.C., 1991 (in press). Antarctic Science.

AUSTRALIA'S EARLIEST ORNITHISCHIAN DINOSAURS: FOOTPRINT EVIDENCE FROM THE EARLY JURASSIC OF QUEENSLAND Tony Thulborn

Department of Zoology, University of Queensland, St. Lucia, Queensland 4072, Australia Natural casts of seven small footprints have been identified on a single weathered block derived from the Precipice Sandstone (Lower Jurassic) of the Carnarvon Gorge, south-east Queensland. The footprints are attributed to ornithopod dinosaurs (Bipedal plant-eaters of the suborder Ornithopoda, order Ornithischia) and are referred to the ichnogenus Anomoepus. They appear to be most similar to the ichnospecies Anomoepus gracillimus, originally defined on footprints from the Lower Jurassic of the north-eastern United States. This identification is consistent with the presumed age of the Precipice Sandstone, since Anomoepus or closely related ichnotaxa are common in Early Jurassic sediments of the United States, Europe and southern Africa but have never been identified with certainty in Triassic sediments. The tracks described here were made by at least four Geological Society of Australia Abstracts Number 32, Ballarat 1992

dinosaurs, all estimated to have been about 30cm high at the hip and less than 1.3m in total body length. In their size and body proportions these animals probably resembled the small plant-eating dinosaur Fabrosaurus (Lesothosaurus), from the Lower Jurassic of southern Africa. Tracks of two animals are sufficiently complete to provide estimates of walking speeds between 0.68 and 0.80 m/c (2.4 and 2.9 km/h). These footprints are the earliest evidence for the existence of ornithischian dinosaurs in Australia. The discovery of at least seven footprints on a single small slab implies that vertebrate tracks may be locally abundant in the Precipice Sandstone. And the identification of the tracks as Anomoepus certainly hints at the existence of a more substantial ichnofauna. Anomoepodid tracks are major components of Early Jurassic ichnofaunas in the

178 north-world's richest and most diversified footprint the existence of both these ichnofaunas was first from the Connecticut Valley, and over 70 have been betrayed by discoveries of anomoepodid tracks. described from Lesotho. It may be significant that A 6.12

MIDDLE PALAEOZOIC EXTINCTION EVENTS: QUEST FOR ISOTOPIC SIGNATURES

John A. Talent *, Ruth Mawson , Anita S. Andrew^, P. Joseph Hamilton^, and David J. Whitford 1

1

2

Earth Sciences, Macquarie University, NSW 2109 CSIRO Exploration Geoscience North Ryde 2113

1 2

t

The global extinction event at the FrasnianFamennian boundary (Kellwasser Event = KE) has long been recognised, but there are at least five other sharp cut-backs in generic diversity (c.40-50%) that can be discriminated during Silurian and Devonian times. These are: 1. Approximating the Llandovery-Wenlock boundary at the top of the amorphognathoides Zone (Amorphognathoides Event = AE). 2. Very late in the Ludlow (Pentamerid Event = PE). 3. At about the beginning of the late Emsian (Emsian or Dalejan Event = EME). 4. In the late Eifelian just above the base of the kockelianus Zone (Eifelian Event = EFE). 5. In the late Givetian at the base of the upper varcus Zone (Stringocephalid Event = SE). These events are clearly expressed in brachiopod, conodont and coral data. The first is most clearly expressed by a c. 90% global 'wipe-out' in conodonts, the second by abrupt decimation of conodonts and pentamerid brachiopods [the latter readily discriminated in the field in Late Silurian carbonate sequences], and the fifth by a dramatic wipe-out of large stringocephalid brachiopods, globally important as A 6.13

rock-builders immediately prior to the extinction event. Events 3 to 5 were of such importance that, despite the large number of new brachiopod genera in the late Emsian and Middle to Late Devonian, the rate of gradual increase in generic diversity between each extinction event was not sufficient to offset the consequences of recurrent decimation. In a pilot study using sC values on whole rock and brachiopods across the EFE, a sudden increase of s6 permil correlates with a 46% extinction of late Eifelian brachiopod genera. Global extinction events at the K/T and P/T boundaries are associated with decreases in s C of similar magnitudes, consistent with a reduction in organic productivity. The increase in s C values at the EME, is similar to that recognised by others for the "Kellwasser" Event (KE) at the Frasnian-Fammenian boundary, and may be related to blooming of phytoplankton concomitant with shelly fauna extinction. Whole rock and brachiopod shell sampling of other carbonate sequences through the EFE and EME intervals, underpinned by conodont data, reveals the same isotopic anomalies. The results of detailed work on these and the AE interval will be reported. 13

1 3

EARLY DEVONIAN-EARLIEST CARBONIFEROUS STRATIGRAPHY AND CONODONT BIOFACIES:BROKEN RIVER AREA, NORTH QUEENSLAND Ruth Mawson & John A. Talent Earth Sciences, Macquarie University, NSW 2109

A suite of 34 stratigraphic sections and about 200 spot-samples from the predominantly carbonate units of the Broken River region of northern Queensland has enabled discrimination of Early Devonian-earliest Carboniferous conodont biofacies especially during the interval late Lochkovian to early Frasnian, inversus to at least asymmetricus zones. The late Lochkovianearly Pragian Shield Creek Formation has conodont Geological Society of Australia Abstracts Number 32, Ballarat 1992

faunas of the pandorinellinid and simple cone biofacies. Conodont biofacies are more complex in the Broken River Group. The stratigraphy can be viewed in terms of a simple model with mixed carbonate and siliciclastic shelf sequences flanking an eastnortheasterly oriented submarine valley down which predominantly non-carbonate sediments (the Burges

179 Formation), but including allochthonous blocks and debris-flow deposites, were funnelled. Four sections through carbonate in the northern or Pandanus Platform provide an impression of the conodont biofacies spectrum from nearshore, generally massive carbonates (often associated with fenestral fabrics) through to areas where autochthonous carbonate slope environments pass downslope into allochthonous deposites. Twenty sections through offshore carbonate shoal (Dosey Shoal), relatively protected embayment (Papilio Embayment) and other environments in the southern or Dosey-Craigie Platform, including nearshore carbonate ramp environments resembling those of the Pandanus Platform, complete the picture of shallow marine carbonate and calcareous clastic lithofacies and their associated conodont biofacies in this region during the late Emsian and most of the Middle Devonian. There are no indubitable hemipelagic or pelagic carbonates in the area. Low diversity conodont faunas with prominence of simple cones and pandorinellinids occur in the shallow water nearshore carbonate ramps and offshore shoals

A 6.14

(Lomandra, Dosey, Lockup Well and Chinaman Creek limestones and Spanner Limestone of the Papilio Formation), though with conodonts usually absent in the oolitic facies and rare (icriodid biofacies) in the algal/stromatoporoid/coral limestones of the early Frasnian Stanley Limestone Member of the Mytton Formation. Polygnathids increase in abundance with depth, especially in the vicinity of the change from mainly autochthonous to predominantly allochthonous carbonates; icriodid numbers increase through time. Maximum taxonomic diversity of polygnathids and icriodids occurs in the lagoonal mixed carbonateterrigenous facies (Papilio Formation) in the southwest of the area. Late Devonian-Early Carboniferous sequences in the region consist predominanly of clastics but include marine transgressions, sometimes with carbonate intervals. Conodonts from these are very shallow water bispathodid assemblages; alignment with palmatolepid-polgnathid and siphonodellid sequences at Mt. Podge and in the Star Basin is therefore imprecise.

C O N O D O N T C H R O N O L O G Y AND P A L A E O C O M M U N I T Y S E Q U E N C E IN T H E T A E M A S L I M E S T O N E (EARLY D E V O N I A N , E M S I A N ) , N.S.W. Catherine E. Humphrey Earth Sciences, Macquarie University NSW 2109

Silicified faunas have been documented from the Taemas Limestone in its type area in the TaemasHume Park area of NSW, principally from the Warroo and Receptaculites Limestone members. Because of taxonomic diversity and elegance of preservation, these faunas, especially the brachiopods, bivalves, gastropods, trilobites, ostracodes, and fish, have attracted international attention. Acid-leaching of several hundred samples obtained from bed-by-bed stratigraphic sections through all 6 members (formerly given formational rank) of the

Geological Society of Australia Abstracts Number 32, Ballarat 1992

Taemas Limestone has yielded a sequence of conodont faunas that provide chronological underpinning for these famed faunas and, as well, has produced an abundance of distributional data for the conodonts and silicified taxa. Many of the latter are new. Analysis of these data reveal a community 'sequence' tied to changes in carbonate lithologies. Of special interest are data on the evolution of polygnathid conodonts through the 4 conodont zones, dehiscens to serotinus, represented in the Taemas Limestone.

180 A 6.15 MOLONG PLATFORM AND HILL END TROUGH (NSW) IN THE EARLY DEVONIAN: A PATTERN OF PLATFORM EXPOSURE AND RECIPROCAL CARBONATE SEDIMENTATION OFFSHORE Ruth Mawson & John A. Talent Earth Sciences, Macquarie University, NSW 2109 Prior to recent conodont studies, correlations advocated for the extensive tract [100+ km] of Garra Limestone in east-central NSW fluctuated remarkably. We now have evidence from autochthonous sections for continuous carbonate sedimentation through at least 5 conodont zones, delta to dehiscens (Mawson et al, 1989; Sorentino, 1989; Wilson, 1989; Mawson, Talent & Farrell, unpub. data) and infer from the ages of allochthonous carbonates in the Hill End Trough to the east, that carbonate sedimentation persisted on the Molong Platform for possibly 3 more, perbonus to serotinus zones. Sampling through carbonate sequences offshore in the Hill End Trough [Tolga, Red Hill, Nubrigyn, and Cunningham formations] in pursuit of data about the Lochkovian-Pragian and Pragian-Emsian boundaries has produced results consistent with a pattern of reciprocal sedimentation: development of carbonate fans within the Hill End Trough correlative 'time-wise' with regressive events on the adjacent carbonate platform. The latter are expressed as units of massive or poorly bedded limestones, often with fenestral fabrics testifying to sabka-type sedimentation. Fossils are typically infrequent in such intervals: rare, coarsely recrystallized trochiform gastropods, huge bivalves sometimes demonstrably fossilized by leaching of shell carbonate followed by laminar sedimentation within the moulds - and a disheartening dearth of conodonts apart from rare, simple cones. In the past, the prevalence of such massive, poorly fossiliferous units in the Garra outcrop tract has been a major cause of the lack of a coherent stratigraphy for the carbonate complex as a whole. The western Hill End Trough carbonate intervals A 6.16

include megabreccias, allochthonous blocks hundreds of metres in length, and allodapic limestones. Hemipelagic limestones are rare but of special interest because of relative abundance of conodonts and, especially in one sequence, three-dimensional graptolites. Large scale carbonate-fan accumulations, lithologically very similar to that represented by the Red Hill Fan (pireneae Zone) [derived from the Molong Platform] occurred on the flank of the Capertee High. An example of these is the Jesse Limestone at Limekilns. A closely sampled sequence through this unit showed it to be entirely late Emsian, serotinus Zone, but to include blocks of shallow water carbonates as well as richly fossiliferous blocks of dehiscens Zone limestones (especially rich in conodonts), inferred to have been eroded from an ajacent platform — presumably exposed by marine regression. The dehiscens and perbonus intervals have not been identified in autochthonous sequences on the Capertee High, though perbonus Zone carbonates occur in association with allochthonous blocks of shallow water limestone at Flirtation Hill, Mudgee, obviously derived from the Capertee High. References Mawson, R., et al., 1988, Can. Soc. Pet. Geol., 111:485-527 Sorention, L., 1989, Cour. Forsh.-Inst. Senck., 117:81-115 Wilson, G.A., 1989, Cour. Forsh.-Inst. Senck 117:117-171

MORPHOLOGICAL PLASTICITY IN CAMBRIAN TRILOBITES. Nigel C. Hughes Queensland Museum, PO Box 300, South Brisbane, Queensland 4101.

Trilobites are one of the few groups which permit assessment of morphological variability at the species level during the earliest Phanerozoic. An investigation of over 2500 specimens of the Sunwaptan trilobite Dikelocephalus from the St. Lawrence Formation of Wisconsin, Minnesota and Iowa has revealed a previously unsuspected degree of morphological Geological Society of Australia Abstracts Number 32, Ballarat 1992

plasticity within an Upper Cambrian trilobite species. Extensive collecting has formed the basis for a new study of well-localised specimens of Dikelocephalus covering a wide size range (transverse pygidial width varies from 0.5 to 20.0 cm). All specimens from this formation must now be regarded as a single morphospecies D. minnesotensis, and twenty-six

181 species have been suppressed. The validity of biostratigraphic zonations of the Sunwaptan based on species of Dikelocephalus is clearly doubtful. Variation in D. minnesotensis is partitioned into two'components; one ontogenetically-related, the other ontogenetically-independent. Both show a mosaic pattern of inter-populational variation. Slight heterochronic shifts are responsible for some differences between populations, but most characters appear to vary independently. The remarkable degree of morphological plasticity within D. minnesotensis contrasts with low levels in Ordovician or Devonian species. It supports the idea that the degree of developmental canalization was A 6.17

reduced in the Cambrian, and predicts that other Cambrian species should be similarly variable. By demonstrating marked intraspecific developmental flexibility within Cambrian trilobite species, this study provides new evidence that genetic systems were less strongly canalized duing the Cambrian than in later times. This difference may provide an explanation for the extraordinarily high rates of appearance of new taxa during the Cambrian explosion. Reference Hughes N.C., 1991. Geology 19: 913-916.

REVISED AGES FOR EARLY CARBONIFEROUS MARINE INVERTEBRATE ZONES OF EASTERN AUSTRALIA J. Roberts *, PJ. Jones and T.B.H. Jenkins 1

2

3

1Department of Applied Geology, University of New South Wales, Kensington, NSW Bureau of Mineral Resources, Geology & Geophysics, Canberra ACT 3Department of Geology & Geophysics, University of Sydney, Sydney, NSW 2

The palaeontological basis for ages of marine invertebrate zones in eastern Australia (Roberts, 1975) has been reassessed to provide an up to date biostratigraphic framework for the calibration of the Carboniferous-Early Permian succession of eastern Australia by SHRIMP ion microprobe (Roberts et al., 1991). It takes into account Riley's (1990, 1991) work on Visean ammonoids, new work on Visean conodonts from eastern Australia by Jenkins et al. (in press) which gives four Visean conodont zones, and suggestions by Brunton (1984) that a greater emphasis be placed on ages indicated by brachiopods. Riley's proposal of a new ammonoid zone (Bollandites-Bollandoceras Zone) below his revised Beyrichoceras Zone and his reallocation of a critical Australian ammonoid (B. trevallynense) to Bollandites have removed the ammonoid evidence, previously questioned by Jenkins (1974), for the late Visean age of the australis Zone. Cosmopolitan conodonts from the australis Zone directly indicate its early Visean age (Jenkins et al., in press) and leave no room for any significant temporal hiatus at its base above the late Tournaisian Scaliognathus anchoralis Zone. The apparent absence in Queensland of the australis Zone is attributed to a paucity of brachiopods, there being abundant early Visean conodont faunas in the principal sections. The Pseudopolygnathus cf. nodomarginatus Zone (Jenkins, 1974) is now regarded as part of the S. Geological Society of Australia Abstracts Number 32, Ballarat 1992

anchoralis Zone. The ages of other Visean Zones are governed by the occurrence of Gnathodus bilineatus, a cosmopolitan conodont, in the barringtonensis Zone, signifying as Asbian and Brigantian age (V3b-V3c). Foraminifera and calcareous algae suggest ages for the elegans (Vlb-V2a) and tenuirugosa (V2b-V3b) Subzones. The top of the latter is taken at the top of V2b to accommodate the fortimuscula Zone in V3a. The Levipustula levis Zone contains earliest Namurian (Elc-E2a) conodonts at its base and, from SHRIMP zircon data, extends into the Permian (Roberts et al., 1991). References Brunton, C.H.C., 1984. 9e Congr. Int. Strat. Geol Carb., Compte Rendu 2: 35-46. Jenkins, T.B.H., 1974. Palaeontology 17: 909-924. Jenkins T.B.H., Crane D. & Mory A.J., in press. Alcheringa. Riley, NJ., 1990. Newslet. in Strat. 21: 149-156. Riley, N.J., 1991. Courier Forsch.-Inst Senkenberg 130: 133-143. Roberts, J., Claoue-Long, J. & Jones, P.J., 1991. Proc. 25th Newcastle Symp. Univ. Newcastle. 3843. Roberts, J., 1975. J. Geol Soc. Aust. 22: 1-32.

182

mp %

V3b

nia

4

barringtonensis

16

P! b

B2 —

a 15

ASBIAN 116

B1

fortimuscula

GF10 14

V3a

3

HOLKERIAN

z<

EAST AUSTRAL BRACHIOPODS

P2

FORAMS

GERMANY my

GF9

V2b

13

P4 >

V2a

12

Vlb

Via

11

CHADIAN

c Z< £2 <

b

a

IVORIAN

Ily

GF7

10

Ha

GF6 GF5

9

IIP

GF4 GF3

1

australis

|

cuichoralis *s. Gnathodus sp A burlington— 8 ensis G. semiglaber •S3 oo

G. punctatus O GF2 U.isosncnacrenulata sol H Yl a HASTARIAN L crenulata 6 sandbergitemnstriata duplicata Tnlb I GF1 sulcata LATE TERTIARY OSTRACOD BIOSTRATIGRAPHY OF THE SORRENTO GRABEN, VICTORIA, AUSTRALIA. z

oc D

A 6.18

Tn

2

GF8

ARUNDIAN

tenuirugosa Delepinea aspinosa <s

BRIGANTIAN

AMMONOIDS j

BRITISH ISLES

BELGIUM

V3c

EAST AUSTRAL. CONODONTS

ZONES

STAGES

c

7

M. T. Warne Victorian Institute of Earth and Planetary Sciences, Department of Geology, La Trobe University, Bundorra, Victoria, 3083. Within the late Tertiary succession of rocks from determined by comparison with the distribution of the Geological Survey borehole Nepean 1, the timing planktonic foraminifera. Represented among these of past ostracod migrations into the region have been migrations are the first local appearances of ostracod Geological Society of Australia Abstracts Number 32, Ballarat 1992

183 species which have lithological ranges extending from offshore marine facies in which fossil plankton are abundant to nearshore normal or marginal marine facies in which fossil plankton are rare. Of a number of local first appearances that have been determined, the following are the most significant. The first appearance of Cytherella auricula Chapman.— The earliest appearance of the ostracod Cytherella auricula occurs in the Nepean 1 borehole sequence between the intervals 429 metres and 255 metres. Here the rock is a clayey siltstone of late Early Miocene to early Middle Miocene age (G. sicanus to G. peripheronda planktonic foraminiferal zones). This ostracod species is common in mid shelf clay and silt facies throughout the Middle and Late Miocene. It is rare in carbonate or clastic sand facies. The first appearance of Ponticocythereis militaris McKenzie— The first appearance of Ponticocythereis militaris also occurs in the Nepean 1 borehole sequence between the intervals 429 metres and 255 metres, (late Early Miocene to early Middle Miocene; G. sicanus to G. peripheronda planktonic foraminiferal zones). This species is common throughout the late Tertiary and Quaternary in inner to mid shelf clastic silt and sand facies. It is rare in clay and carbonate facies. The first appearance of Actinocythereis dampierensis Hartmann — Actinocythereis dampierensis makes its first appearance within the Nepean 1 section between the intervals of 247 metres

and 181 metres (predominantly clastic sand or silt facies' of Late Miocene age; G. acostaensis to G. conomiozea planktonic foraminiferal zones). This species occurs abundantly in clastic sand and silt facies throughout the late Tertiary and Quaternary. The first appearance of Osticythere spp— Species belonging to the genus Osticythere Hartmann make their first appearance within the Nepean 1 borehole sequence at 175 metres (late Late Miocene glauconitic and ferrigunised sand; G. conomiozea planktonic foraminiferal zone). Species of this genus are common in.latest Miocene to Recent clastic sands and silts. When they are associated with a relatively high diversity fossil ostracod fauna they indicate a coastal lagoon depositional environment. When they are the predominant ostracod within a low diversity fauna they indicate an estuarine depositional environment. The first appearance of Mutilus pumila Hartmann- Mutilus pumila makes its first appearance within the Nepean 1 section at 142 metres. Here the rock is a fine clastic sand of late Early Pliocene age (G. viola planktonic foraminiferal zone). Unfortunately, earlier Early Pliocene ostracod faunas are sparce within the Nepean 1 section, so the first appearance of Mutilus pumila cannot be accurately gauged from this section. However this species makes its first appearance within the rock sequences of the Lakes Entrance Platform, Gippsland Basin, Victoria, at the base of the Jemmys Point Formation near Kalimna. (early Early Pliocene, G. crassaformis planktonic foraminiferal zone).

POSTER SESSION A 6.19

CAMBRIAN PALAEONTOLOGY AND BIOSTRATIGRAPHY OF THE WIRREALPA, AROONA CREEK AND RAMSAY LIMESTONES OF SOUTH AUSTRALIA Glenn A. Brock1 & Barry J. Cooper2 1 Earth Sciences, Macquarie University, NSW 2109 Department of Industry, Trade and Technology, GPO Box 1264, Adelaide, South Australia 5001

2

The last major transgression in South Australia during the Cambrian resulted in the deposition of the Wirrealpa and Aroona Creek Limestones in the Flinders Ranges and the Ramsay Limestone on Yorke Peninsula. These formations have traditionally been assigned a lower Middle Cambrian (Ordian sensu Opik, 1967) age based on lithostratigraphic interpretation and determination of trilobites (e.g. Daily, 1956, 1990). Acetic acid dissolution of samples collected from these three stratigraphically equivalent formations has

Geological Society of Australia Abstracts Number 32, Ballarat 1992

yielded a moderately diverse array of non-trilobite shelly fossils. These include poriferans, coelosceritophorans, palaeoscolecidans, ^conodontomorphs', hyolithelminthes, hyoliths, mollusks, inarticulate brachiopods and a number of problematic sclerites and plates. These taxa, combined with descriptions of new trilobite species (Bengtson, et al., 1990) and new data from regional sequence stratigraphy (Gatehouse et al., 1990; Gravestock, in press) indicate that a late Early Cambrian age (equivalent to the Toyonian Stage of the Russian

184 Daily, B.D., 1990, Geol. Soc. Aust., Spec. Pub., 16:215-229 Gatehouse, C.G., et al., 1990,10th Aust. Geol. Con., References Abstracts, A10:192-193 D.I. in press, In Geology of South Bengtson, S., et al., 1990, Mem. Assoc. Aust. Gravestock, Australia, SADME. Palaeon.,9:\-?>(A A.A., 1967, BMR, Geol. & Geophys., Bull, Daily, B.D., 1956, In El Sistema Cambrico, su Opik,114:133-170. paleogeographica y el problema de su base. Report Int. 20th Geol. Cong., pp. 91-147.

Platform) is more appropriate for these formations.

A 6.20 MIDDLE CAMBRIAN NON-TRILOBITE SHELLY FAUNA FROM ALLOCHTHONOUS BLOCKS IN THE MURRAWONG FORMATION, NSW Michael J. Engelbretsen & Glenn A. Brock Earth Sciences, Macquarie University NSW 2109 Allochthonous limestone blocks of Middle Cambrian age (spanning the Floran-Undillan Stages) from the Murrawong Creek Formation, Tamworth district, NSW, have produced rich phosphatic, silicified and epidote coated faunas; The surprisingly diverse trilobite fauna, often occurring as tightly packed coquinas, is discussed elsewhere (T.R. Sloan, this symposium). The non-trilobite taxa are abundant

Geological Society of Australia Abstracts Number 32, Ballarat 1992

and taxonomically diverse: a profusion of hyolithids and brachiopods (17 inarticulates and 4 articulates), mollusks (Latouchella, Helcionella, Yochelcionella, Pelagiella), chancelloriids, a new genus of cnidarian, a protoconodont (Amphigeisina), and diverse problematic plates.

185

A 7: PETROLOGY

CONVENOR: RICHARD PRICE A 7.1

ND-ISOTOPIC EVIDENCE FOR ULTRA-DEPLETED MANTLE IN AN EARLY PROTEROZOIC BACK-ARC SETTING : IMPLICATIONS FOR MANTLE EVOLUTION W.J. Sivell * and M.T. McCulloch l

1

2

2

Faculty of Science and Technology, University of Western Sydney, Nepean, Kingswood 2747, Australia Research School of Earth Sciences, The Australian National University, Canberra 2601, Australia

It is widely recognised that the upper mantle has been progressively depleted in incompatible elements as a result of the episodic formation of continental crust. Some parts of the mantle are more depleted than others because of differential crustal extraction. In an attempt to assess the extent of depletion in the early Proterozoic mantle, and possible implications of this for the survival time of mantle heterogeneities produced in the late Archaean, initial N d / N d ratios have been determined on mafic volcanics from the early Proterozoic Harts Range Meta-igneous Complex (HRMC) in the eastern Arunta Inlier of central Australia. The HRMC comprises mainly concordant mafic amphibolite bodies (up to 2000m thick) occurring within laterally extensive interlayered pelitic, calcareous and quartzose schists of the Irindina Supracrustal Assemblage. The HRMC-Irindina sequence was deposited in a (failed) latitudinal ensialic rift, and overlies a basement terrain (the Strangways Orogenic Belt) which formed during an earlier phase of crustal extension « 1800 Ma. The minimum age of the HRMC is constrained by the 1748 -4 Ma emplacement age (Cooper et al. 1988) of a megacrystic granitoid gneiss that intrudes both the cover sequence and the major detachment zone along which the basement and cover were juxtaposed. Initial N d / N d ratios for the least contaminated 1.76 Ga HRMC mafic volcanics range from 8]sjci = +8.2 to +6.9. These are the highest values yet reported for Proterozoic igneous rocks. They far exceed values proposed for the isotopic evolution of the depleted mantle at this time and imply a long-term (> 1.0 Ga) highly depleted mantle source. These highly depleted compositions in the early Proterozoic are compatible with further depletion of an already partially depleted Archaean (2.7 - 2.8 Ga) mantle source having 8jsfd (2.7) - + 4 and /Sm/Nd 0.17. A 2.6 Ga age is a reasonable minimum estimate. This is because the low /Sm/Nd 143

1 4 3

=

1 4 4

144

values of possible sources resulting from older depletions do not require large Sm/Nd fractionations (i.e. very small degrees of partial melting) in order to generate the rare earth element distributions of the HRMC tholeiites. Near chondritic Sm/ Nd ratios measured in the HRMC basalts require moderate to low-degree (~ 10%) partial melts of the proposed source, consistent with their low Al/Ti and Ca/Ti ratios. The HRMC source could represent the residuum after extraction of late Archaean tonalites and must have been convectively/chemically isolated from the bulk of the evolving Archaean - early Proterozoic depleted mantle for at least 900 Ma. This provides first-order evidence that major periods of continental growth, such as occurred in the late Archaean, resulted in long-lived, pronounced heterogeneities in the Earth's upper mantle. Exceptional depletion of the upper mantle and its subsequent long-term preservation may reflect unique conditions of layered mantle convection operative during the late Archaean. McCulloch and Bennett (in press) have suggested that mantle convection, following a period of major crustal formation at 2.6 - 2.7 Ga, was restricted to the uppermost - 400 km of the mantle (above a strong upper mantle transition zone). This effectively isolated deeper, more primitive asthenosphere from upper mantle which had been highly depleted by continental extraction. It is unlikely, however, that ultra-depleted portions of the upper mantle produced during the late Archaean would have survived intact much beyond the early Proterozoic. The onset of asthenosphere-dominated magmatism in the Harts Range was apparently related to extension, triggered by subduction beneath an early Proterozoic Cordilleran-style plate margin. Geochemical features of the HRMC rocks (e.g. Nb/Th, Th/Pb, Nb/Pb and La/Yb ratios intermediate between those of mid-ocean ridge basalts and island arc tholeiites) typify back-arc basin basalts. There is also strong support for a close temporal and spatial kinship 147

144

186 of the HRMC with an active early Proterozoic convergent plate margin, since mafic-felsic Entia orthogneisses structurally underlying the cover sequence have pronounced Cordilleran-margin chemical affinities. The HRMC tholeiites are closely analogous to "continental" basalts from the Columbia River Plateau erupted in an ensialic setting behind the Cascade arc. A 7.2

References Cooper, J.A., Mortimer, G.E. & James, P.R., 1988, PrecambrianRes. 40/41: 217-231. McCulloch, M.T. & Bennett, V.C., in press, Geochim. Cosmochim. Acta.

TRACE ELEMENT PARTITIONING AND MANTLE METASOMATISM T.H. Green *, J. Adam and S. Sie 1

1

2

School of Earth Sciences, Macquarie University, NSW 2109 CSIRO Division of Exploration Geoscience, North Ryde, NSW 2113 1

2

Enrichment of trace elements in localized regions 925-1050~C on Nb, Ta enriched basanite and tholeiitic of the mantle has been ascribed to the movement of andesite and a trace element (Rb, Ba, Sr, Zr, Y, Nb, nephelinitic or carbonatitic melts into these regions. It Ta, La, Sm, Ho and Lu) doped silicate carbonatite mix has been further suggested (D.H. Green and Wallace, have been combined with proton microprobe analysis 1988) that LILE and HFSE might be decoupled, with of trace element contents of the phases produced. This mantle enrichment of both element groups through resulted in determination of partition coefficients for alkaline silicate melts, but only LILE enrichment key LILE (Rb, Ba, Sr, Y) and HFSE (Zr, Nb, Ta) through advent of carbonatitic melts. It was proposed between amphibole and clinopyroxene and silicate or that the key residual mineral controlling this difference carbonatitic liquids. The values obtained (D's) are was pargasitic hornblende, since Ti partitioned given in Table 1. strongly into this mineral. Recent high pressure experiments at 10-30kb and Table 1 Selected partition coefficients b = basanite; t.a. = tholeiitic andesite; c = carbonatite Run Nos

1389, 93,95

1388

1409

1422

1380

1379

1402,3 1389

1402,3 1401

20 10001050 Comp b osition %H 0 10 %F

20 1050 b

10 1000 b

20 950 t.a.

20 925 t.a.

10 925 t.a.

25 1000

25 1000

8 2

10

10 5

10 5

Rb Sr Ba Y Zr Nb Ta

0.37 0.31 0.48 0.37 0.21 0.07 0.07

8 2 amph 0.20 0.44 0.65 0.55 0.33 0.09 0.09

0.12 0.59

<.3 0.08

-

-

<.25 0.15

P(kb) T(°Q 2

-

0.46 0.32 0.40 0.87 0.27 0.09 0.09

-

1.8 0.52 0.34 0.37

0.42 0.15 0.03 0.02

D (Nb, Ta) for amphibole/silicate liquid pairs (-0.1 - 0.4) are much lower than commonly applied in geochemical modelling (eg D Nb = 0.8 - 1.0 has been used - Pearce and Norry, 1979; McDermott and Geological Society of Australia Abstracts Number 32, Ballarat 1992

-

0.35 0.33 0.03 0.02

c ~1 -

0.28 0.04 0.01 0.22 0.23 0.06 0.13

20 1050 b

c

10

~1

cpx (0.01) 0.09 (0.007) 1.1 0.22 0.01 0.02

0.004 0.025 0.006 0.22 0.29 0.01 0.03

_

_

30 1025 • b 10

_

mica 5.8 0.22 2.9 <1 0.13 0.14 0.14

Hawkesworth, 1991), but are close to measured phenocryst/matrix pairs for D Ta (0.2 - 0.4 for basalt to mugearite - Lemarchand et al, 1987). Thus models of melting or crystal fractionation involving

187 amphibole and indicator trace elements such as Nb, Ta will need revision, where inappropriate D values have been used. Addition of F to silicate systems markedly lowers D values especially in more silicic compositions, and may be important in modelling trace element variation in fractionating A-type granite, generally believed to contain significant F (Eby, 1990). D values given in Table 1 confirm that carbonatitic melts are expected to be more enriched in LIL than silicate melts, and accordingly will have a greater

effect in any metasomatic process contributing these elements to a particular region of the mantle. However the values also show that carbonatitic melts in equilibrium with pargasitic hornblende do not significantly decouple the HFSE from silicate melts at 20-25kb pressure. This is evident from similar partition coefficients for hornblende/silicate liquid or carbonatitic liquid pairs. One evident difference is that hornblende/carbonatitic liquid partitioning will fractionate Nb and Ta, but this will not occur for hornblende/silicate liquid equilibria.

(D hbl-carb / D hbl-carb = 0.42; D hbl-sil / D hbl-sil = 1.0) Nb Ta Nb Ta Thus metasomatism of mantle by "ephemeral carbonatitic melts" would be expected to cause an increase in the Nb/Ta ratio of the mantle it affects. Unfortunately this is not a discriminatory effect, as garnet, clinopyroxene and Ti-rich minerals residual in the source region for carbonatitic or nephelinitic melts will also fractionate Nb and Ta. However, contrasting partition coefficients between amphibole/ clinopyroxene and silicate/carbonatitic liquids allow identification of other marker geochemical ratios which may provide an indication of whether a silicate or carbonatitic melt was responsible for mantle metasomatism. Thus relative to primitive mantle ratios (Sun and McDonough, 1989) Ba/Nb should increase and Sr/Nb remain unchanged for carbonatitic

A 7.3

metasomatism, while Ba/Nb and Sr/Nb should decrease for silicate liquid metasomatism. References Eby, G.N., 1990, Lit ho s 26: 115-134 Green, D.H. & Wallace, M.E., 1988, Nature 336: 459-462 Lemarchand, F., Villemant, B. & Calas, G., 1987, Geochem. Cosmochim Acta 51: 1071-1081 McDermott, F. & Hawkesworth, C., 1991, Earth Planet. Sci. Lett. 104: 1-15 Pearce, J.A., & Norry, M.J., 1979, Contrib. Mineral Petrol 69: 33-47 Sun, S. & McDonough, W.F., 1989, Geol. Soc. Spec. Publ. 42: 313-345.

MANTLE TERRANES: GEOCHEMICAL, GEOPHYSICAL AND GEOCHRONOLOGICAL DISTINCTIONS Suzanne Y. O'Reilly1*, W.L. Griffin 2 and Y. D. Chen1 1 School of Earth Sciences, Macquarie University , Sydney, NSW 2109 2Division of Exploration Geoscience, CSIRO, North Ryde NSW, 2113

Four mantle domains within the spinel lherzolite stability field have been characterized geochemically using a large sampling base of xenoliths entrained in basaltic rocks. Regions sampled are from eastern Australia and eastern China; xenoliths analysed range from spinel lherzolite (metasomatized to varying degrees) to granulites and pyroxenites (frozen basaltic magmas and cumulates thereof). Three regions of eastern Australia define isotopically distinct domains in eNd/ 87 Sr/ 86 Sr space. The most comprehensive data set, from western Victoria, shows a wide spread of values from around eNd=6.5 , 8 7 Sr/ 8 6 Sr= .703 extending in a mixing hyperbola to extremely "enriched" values (eNd= -8, 87 8 7 Sr/ 8 6 Sr= .716). The NSW and Qld domains Geological Society of Australia Abstracts Number 32, Ballarat 1992

trend off the mantle array towards high 8 7 Sr/ 8 6 Sr values but define separate fields. Additional constraints for models of geochemical evolution are provided by the isotopic characteristics of suites of granulites and pyroxenites. Many of these formed within the mantle by crystallization of melts with a crustal isotopic signature. These melts formed within a mantle volume already metasomatized and imprinted with "subduction-type" isotopic signatures. This ties in with eastern Australia's tectonic history which has involved multiple rifting and collision episodes during the Phanerozoic. Xenoliths from the Nushan (China) region show a high degree of modal metasomatism. However, these xenoliths shows no pronounced 8 7 S r / 8 6 S r

188 enrichment;this must reflect the addition of fluids with a primordial or, at least, mantle-array isotopic signature. Calculations of oxygen fugacities and determination of the ages of lithospheric tectonic events from zircon geochronology support the isotopically determined domain concept. Data from xenoliths are also crucial in interpreting remotely-sensed (geophysical) information on the lithospheric mantle including thermal, magnetic, seismic, gravity, electromagnetic properties. Measurements of acoustic velocities of mantle xenoliths (O'Reilly et al., 1990) and characterization of thermal states have allowed realistic modelling of seismic profiles to define the fine structure of the crust-mantle boundary and lower crust/upper mantle stratigraphies in cratonic and non-cratonic lithosphere sections. Results show that the thermal profiles of

lithospheric sections must be known to model Vp profiles realistically. In addition, the conventional use (by seismologists) of dunite as a generalized mantle wall-rock results in overestimates of mantle Vp. The variable anisotropy (up to 10%) in acoustic velocities measured in moderately foliated mantle rocks may account for enigmatic seismic reflectors in mantle regions, especially at boundaries of large-scale tectonic blocks. Integration of petrologic, geochemical and geophysical data can provide a holistic models for the structure and evolution of different lithospheric domain. Many significant mantle events appear to be coupled to tectonic episodes observed in crustal layers. This methodology can be used to identify large continental blocks with contrasting chemical and physical properties relevant to the formation and preservation of diamonds.

A 7.4 CONTRASTING BEHAVIOUR OF SR, ZR AND TI DURING MANTLE METASOMATISM: A PROTON MICROPROBE STUDY A. Greig1*, I.A. Nicholls1 and S.H. Sie 2 ^Dept Earth Sciences, Monash University, Clayton, Victoria, 3168. CSIRO, Division of Exploration Geosciences, North Ryde, NSW, 2113

2

Incompatible trace element concentrations of clinopyroxenes in spinel peridotite xenoliths from the Western Districts of Victoria have been determined by proton and electron microprobe analyses. The bulk rock geochemistry of these xenoliths suggests they represent the residues left after varying degrees of partial melt extraction from a source with an original composition similar to MORB source (O'Reilly and Griffin). Using a model composition of N-MORB source mantle (Wood), it can be calculated that clinopyroxene in a spinel lherzolite of this composition should have about 90 ppm Sr, 50 ppm Zr and 17 ppm Y. In contrast, clinopyroxenes from Mt. Porndon commonly have much higher Sr and sometimes higher Zr than expected for primitive mantle compositions, indicating they have been enriched in these elements. Three styles of enrichment are found in these clinopyroxenes: TYPE A: systematic core to rim enrichment in Sr, Zr, Ti, Na and Y in a single clinopyroxene grain, which is consistent with inward diffusion of these elements from an incompatible element enriched melt or fluid on the grain boundary (Griffin et al.); TYPE B anhydrous xenoliths with clinopyroxenes which show enrichment only in Sr (320 ppm) and depletion in both Zr (7 ppm) and Ti (0.05%); TYPE C: deformed phlogopite bearing Geological Society of Australia Abstracts Number 32, Ballarat 1992

harzburgites have clinopyroxenes which show extreme enrichment in Sr (up to 800 ppm) and Zr (up to 420 ppm), with some enrichment in Na20 (2.6%) and Y (37 ppm), but depletion in Ti02 (0.1%); The contrasting behaviour of the incompatible elements is shown by a plot of Ti02 against Zr, where two distinct trends are seen. One trend shows Ti02 decreasing from 0.7% to 0.1 % while Zr decreases from 50 to 5 ppm, which may be due to increasing degrees of partial melt extraction, while the other trend shows Zr increasing from 130 to 420 ppm while Ti02 remains uniformly low at around 0.1%. Clinopyroxenes from the latter trend are also distinctly more enriched in Sr (500 - 800 ppm) compared to the other clinopyroxenes (60 - 320 ppm). All three styles of enrichment are believed to be due to metasomatism by melts. Clinopyroxenes in some peridotites adjacent to Al-augite suite veins show enrichment in Sr, Ti and Zr which has probably been caused by melt infiltrating from the veins (Greig et al.). TYPE A clinopyroxene also shows core to rim enrichment in these elements with rim compositions similar to those in clinopyroxenes adjacent to such veins, and thus may also have been metasomatised by basaltic melt infiltrating from a vein. The preservation of zoning suggests the metasomatism occurred shortly before entrainment in the host magma. Bodinier et al.

189 have shown that melts will undergo chromatographic fractionation of elements according to their compatibility with increasing distance from a vein, and can ultimately cause cryptic metasomatism. As Sr is more incompatible than Zr and Ti, this process may also be capable of causing the enrichment in Sr, but not Ti and Zr found in clinopyroxenes from anhydrous xenoliths showing TYPE B enrichment. The extreme Sr, high Na and low Ti contents of clinopyroxenes from harzburgites showing TYPE C enrichment are perhaps most consistent with metasomatism by a sodic carbonatite melt, which may also explain the presence of Cr-diopside layers in these xenoliths (Green and Wallace). The high Zr contents of these clinopyroxenes suggests that such melts may also A 7.5

cause enrichment in Zr. References Bodinier. J.L. et al., 1990: J. Pet Green, D.H. and Wallace, M., 1989: Nature 361, 541543. Greig, A. et al., 1991: in Proc. 7th Australian Conference on Nuclear Techniques of Analysis, Melbourne University, in press. Griffin, W.L. et al., 1989: Geochim Cosmochim. Acta 53, 561-567. O'Reilly, S.Y. and Griffin, W.L., 1988: Geochim Cosmochim. Acta 52, 433-447. Wood, D.A., 1979: Geology 7, 499-503.

CARBONATITE METASOMATISM: OBSERVATIONS AND IMPLICATIONS G.M. Yaxley*, D.H Green and A .J Crawford University of Tasmania, PO Box 252C, Sandy Bay, Tasmania, 7005.

A suite of unusual magnesian spinel lherzolite to spinel wehrlite nodules from western Victoria display the predicted characteristics (Green and Wallace, 1988) of metasomatism by an ephemeral carbonatite melt. Petrographically, they contain accessory apatite. Some samples retain clear evidence of replacement of the primary mineralogy during decarbonation reactions involving dolomitic melt. These reactions have pushed the major element geochemistry of the nodules towards unusually high Ca0/Al203 and Na20/Al203 values. Extreme LELE enrichment is decoupled from Ti abundances, which remain apparently unaffected by the metasomatic process. Nd-Sr isotopic data suggest a petrogenetic relationship between the metasomatic process and the Tertiary-Recent undersaturated mafic volcanism which hosted the xenoliths. Recent experimental studies in the system peridotite-C02-H20 (Wallace and Green, 1988) have established the existence of a window in PT space in which a sodic dolomitic carbonatite melt can coexist in equilibrium with pargasitic lherzolite at depths >90km. Analogy with natural carbonatites, as well as experimental determinations of the partitioning behaviour of trace elements between silicate phases and carbonatite melt (Sweeney et. al. in prep), suggest that the carbonatite would exhibit extreme LILE enrichment, but would not transport significant Ti. Thus, a model is proposed in which carbonated, highly undersaturated silicate melts ascend from the subcontinental asthenosphere into the pargasitic amphibole stability field. Crystallization of pargasite results in production of a sodic dolomitic carbonatite melt in equilibrium with pargasite-rich lherzolite or Geological Society of Australia Abstracts Number 32, Ballarat 1992

harzburgite mantle. We argue that segregation and upward migration of such a melt would result in it crossing the univariant decarbonation reaction 4Enstatite + Dolomite = 2Forsterite + Diopside +2C02 at around 21 kbar whereupon reaction of the carbonatite with lithospheric wall rock phases (particularly orthopyroxene) would occur, converting the wall rock spinel lherzolite to a LILE-enriched, Tidepleted pargasite+apatite-bearing magnesian wehrlite mineralogy (Green and Wallace, 1988). This model is supported by experimental reversals of the postulated natural metasomatic process, run at PT conditions within the carbonatite melt window in the peridotite-C02-H20 system (Wallace and Green, 1988). These involved addition of excess CO2 to the synthetically prepared compositions of two representative wehrlite nodules, resulting in production of Na20-bearing dolomitic carbonatite melts in equilibrium with a refractory harzburgitic or lherzolitic residue. This technique demonstrates that the compositions of the nodules are consistent with addition of a Na-bearing dolomitic carbonatite to a refractory lithosphere, and allows estimates of the composition of the metasomatic carbonatite to be made. References Green, D. H. and Wallace, M. E. (1988); Mantle metasomatism by ephemeral carbonatite melts; Nature 336,459-462. Sweeney, R. J. and Green, D. H. (1991) Trace and minor element partitioning between garnet and

amphibole and carbonatitic melt; in prep. Wallace, M. E. and Green, D. H. (1988); An

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experimental determination of primary carbonatite composition; Mztare 335,343-346.

A POSSIBLE CONNECTION BETWEEN MANTLE PLUMES AND METALLOGENY Robert I. Hill* and Ian H. Campbell

Research School of Earth Sciences, Australian National University, Canberra, ACT Laboratory, numerical, and geological 'studies lead to the suggestion that mantle plumes have played an important role in the development of the continents, and, by implication, may have played a significant role in continental metallogeny. This comes about because, although mantle plumes transport through the Earth <10% of the mantle heat ultimately lost at the surface, the temperatures associated with mantle plumes are higher than those of the convecting mantle. Ascent of this high temperature material can result in the production of large volumes of basaltic melt, the generation of komatiites and picrites, regional-scale crustal metamorphism and partial melting, and uplift leading to extension and even continental rifting. Mantle plumes result from the rise of buoyant material from a thermal boundary layer (or layers) within the Earth. A new plume starts with a largevolume spherical head trailing a narrow pipe-like conduit or "tail". Laboratory simulations have been used to estimate that a new plume initiating at the core-mantle boundary will attain a diameter of about 1000 km before flattening within the upper mantle (Griffiths and Campbell, 1991). For the modern Earth, flattening results in the emplacement into the uppermost mantle of a disc of hot material 1500-2500 km in diameter and 100-200 km thick having an average temperature 50-100°C greater than that of the convecting upper mantle. Hot source material rising up the centrally-located tail initially spreads out across the top of the plume head; however, following head emplacement and plate movement the surface expression of the tail may move away from the area underlain by the head to produce a hotspot track. Ascending tail material may be up to 250°C hotter than the uppermost convecting mantle (McKenzie and Bickle, 1988). Thermally-driven mantle plumes thus comprise a mode of convection distinct from that of plate tectonics, which is driven by the negative buoyancy of cold oceanic lithosphere (Davies, 1988). Observation shows that these two modes of convection operate largely independently (Stefanick and Jurdy, 1984), and that distinct differences in the magmatic records of the igneous provinces resulting from each mode are those Geological Society of Australia Abstracts Number 32, Ballarat 1992

expected from consideration of the dynamics of subduction versus plume ascent (see Campbell and Hill, 1988). Thus, ascent of a new plume head introduces into the uppermost mantle an approximately circular thermal anomaly -2000 km across. Uplift of up to -1000 metres can result in important crustal extension, and may even trigger continental break-up in favourable circumstances (Hill, 1991; see also Houseman and England, 1986). Decompression melting within a rising plume head can result in the production of large volumes of basaltic liquids, including komatiitic and picritic varieties derived from the hot material ascending within the plume tail (Campbell et al, 1989; Campbell and Griffiths, 1991). Although the mechanism of lithosphere removal is not understood at present, geological and penological evidence is interpreted as showing that hot plume head material can ascent to sufficiently close to the base of the crust to initiate, after a time delay of up to several tens of millions of years, large-scale partial melting of pre-existing continental crust (Campbell and Hill, 1988). In particular, we have interpreted the Late Archean geological evolution of the Eastern Goldfields Province of Western Australia in terms of the starting plume model (Campbell and Hill, 1988; Campbell et al., 1989). Zircon U-Pb geochronology shows that, in the Norseman-Kambalda-Kalgoorlie region, basaltic volcanism which began about 2715 Ma (million years) ago and which includes komatiitic sequences having an age of 2702 Ma was replaced by felsic volcanic and granitic magmatism 2687±3 Ma ago. This episode of crustally-derived magmatism, although voluminous, was of short duration, perhaps about 5 Ma. It was followed closely by a second period of much less important mafic magmatism, and by later crustally-derived magmatism extending to ages of -2600 Ma. Both the magmatic sequence of early basaltic volcanism followed after a time gap by major crustally-derived felsic magmatism, and then an extended period of later crustally-derived magmatism, as well as ,the fundamentally bimodal (basalt plus granodiorite-granite) nature of magmatism, differ significantly from that of clear subduction-related

191 provinces such as the Sierra Nevada and Peninsular Ranges batholiths of western North America, where compositionally diverse (gabbro-diorite-tonalitegranodiorite-granite) magmatism commonly is continuous for periods of several tens of millions of years. The geological record can be used to estimate that, on average, each piece of crust will pass above a plume head approximately every 1000 Ma. Mantle plumes are thus a potentially important cause of crustal reworking, and may have played a significant role in the development of the apparent episodicity of continental orogenesis inferred from the geochronological record. Mantle plumes may play both a direct and an indirect role in metallogeny. A direct role is envisaged for deposits hosted by plume-derived magmas, with the best examples being komatiite-hosted nickel (e.g., Agnew, Kambalda) and ultramafic-hosted platinum group element (PGE) deposits (e.g., Bushveld, Norilsk, Stillwater). A link between kimberlites (and thus diamonds) and hotspots has been suggested by Crough et al (1980), and layered-intrusion-hosted gold deposits such as that of the Skaergaard (likely the product of melting within the Iceland hotspot) may be another example of plume-related ore bodies. Most plume-related metallogeny is likely to be related only indirectly to the causative plume, and to result because the structural and thermal reworking of the crust above a plume (particularly above a plume head) may produce favourable conditions for the concentration of economically-important elements. For example, most of the gold deposits of the Eastern Goldfields province of Western Australia, an area that we consider to be a plume head province, have resulted from deposition within large-scale hydrothermal systems capable of scavenging gold from large volumes of crust (e.g., Phillips et al, 1987). Although there is still debate as to whether the heat driving these hydrothermal systems is of metamorphic or magmatic origin, we infer that the ultimate source for the heat (and more specifically, the temperature gradients driving fluid flow) was the head of a Late Archean mantle plume. Similarly, the ultimate source of the heat responsible for at least some of the later Tertiary gold deposits of the Basin and Range province

Geological Society of Australia Abstracts Number 32, Ballarat 1992

of western North America may be the head of the Raton plume (Suppe et al, 1975), which we infer to have risen beneath the southern Arizona - New Mexico border region -32 Ma ago. We infer also that at least some VMS-type deposits (e.g., Teutonic Bore in Western Australia) are plume-linked because the basaltic intrusion inferred to have driven the oreforming fluids resulted from melting within a mantle plume. Finally ,we note the possibility that the unusually high temperatures that may be attained within the crust above mantle plumes (particularly plume tails) may be sufficient to bring organic-rich sediments within the gas- or oil-generation windows. The oil and gas fields of southeastern Queensland, which are associated spatially with a line of volcanic constructs suggested to mark a mantle plume track (Wellman and McDougall, 1974), provide one possible example. References Campbell, I.H. & Griffiths, R.W., 1991, Earth Planet. Sci. Lett. 99: 79-93 Campbell, I.H. & Hill, R.I., 1988, Earth Planet. Sci. Lett. 90: 11-25 Campbell, I.H., Griffiths, R.W. & Hill, R.I., 1989, Nature 339: 697-699 Crough, S.T., Morgan, W.J. & Hargraves, R.B., 1980, Earth Planet. Sci. Lett. 50: 260-274 Davies, G.F., 1988, J. Geophys. Res. 93: 1045110466 Griffiths, R.W. & Campbell, I.H., 1991, Earth Planet. Sci. Lett. 99: 66-78 Hill, R.I., 1991, Earth Planet. Sci. Lett. 104: 398416 Houseman, G. & England, P., 1986, J. Geophys. Res. 91: 719-729 McKenzie, D. & Bickle, M.J., 1988, J. Petrol. 29: 625-679 Phillips, G.N., Groves, D.I. & Brown, I.O., 1987, Can. J. Earth Sci. 24: 1643-1651 Stefanick, M. & Jurdy, D.M., 1984, J. Geophy. Res. 89: 9919-9925 Suppe, J., Powell, C. & Berry, R., 1975, Amer. J. Sci. 275A: 397-436 Wellman, P. & McDougall, I., 1974, Tectonophysics 23: 49-65

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193 A 7.7

COMPARATIVE GEOCHEMICAL EVOLUTION OF THE SOUTHERN AFRICAN, SIBERIAN AND AUSTRALIAN CRATONIC LITHOSPHERES W.L. Griffin 1 *, C.G. Ryan1, J.J. Gurney2, and N.V. Sobolev3

ICSIRO Division of Exploration Geoscience, North Ryde, NSW 2113, Australia 2Dept. of Geochemistry, Univ. of Cape Town, Rondebosch 7700, South Africa 3Inst, of Geology & Geophysics, Academy of Sciences, Novosibirsk, USSR Published Nd model ages on garnets indicate Archean ages for peridotite-suite diamonds from both Siberian (SIB) and southern African (SA) kimberlites. Comparison of major- and trace-element patterns in diamond inclusion (DI) garnets and spinels from these two areas shows many similarities, and some important differences. Garnet DI populations are dominated by subcalcic pyropes in both areas, but calcic garnets are relatively more common in S A. Garnet DI show a similar large range of TNi (850-1500°C) in both areas. They also show similar patterns of depletion in Zr and Y, and enrichment in Sr, with decreasing Ca/Cr. However, DI garnets from SIB show higher median Cr values, but lower median mg, than similar garnets from SA. Chromite is an abundant DI phase in SIB, and less common in SA. DI chromites from both areas show a similar range of Cr/Al, but those from SIB are lower in median mg and higher in Zn. Comparison of garnets from diamondiferous kimberlites shows several significant differences between SA and SIB. Concentrates fron? both areas contain significant proportions of subcalcic garnets, but extremely subcalcic (<2% CaO) garnets appear to be more common in SIB. The concentrates show a similar range of TNi, but the distributions in SIB are strongly weighted toward lower TNi compared with high-grade pipes from SA; this suggests a lower average heat flow through the Siberian craton. SIB concentrate garnets show higher Cr (maximum and average values) at any TNi than SA concentrates. They also have higher Cr/Mg, and lower median mg, than SA garnets. SA concentrate garnets have significantly higher median Zr and Y values than those from SIB, even when the subcalcic garnets are excluded. Finally, significant (>5 ppm) levels of Sr are common in subcalcic concentrate garnets from SIB, but rare in SA. Comparison of the DI and concentrate data suggests that the SA lithosphere is lower in Cr and Cr/Mg, and higher in mg, Zr and Y than the Siberian lithosphere, and may contain a lower proportion of highly subcalcic harzburgite. The differences in Cr and mg existed prior to Archean diamond formation; the differences in Zr, Y, and possibly average Ca content were established after diamond formation. These differences may be related to other Geological Society of Australia Abstracts Number 32, Ballarat 1992

significant differences between kimberlites in the two cratons. The maximum, and perhaps mean, diamond grades of Siberian kimberlites apparently are higher than those of SA kimberlites. Siberian diamonds are typically octahedra with little evidence of resorption, while SA diamonds typically are dodecahedra, and have lost up to 50% of their mass by resorption. Krichterite and other metasomatic minerals occur in many SA pipes, but apparently are rare in Siberian ones. Finally, garnets from Siberian garnet peridotite xenoliths show lower Fe3+/Fe than similar garnets from SA kimberlites (Luth et al., 1989). We suggest that: (1) Early Archean processes were similar in the SA and SIB lithospheres, leading to depletion in most LIL and HFSE elements, a high proportion of harzburgite to lherzolite, and enrichment in Sr (and LREE) in very subcalcic garnets. (2) The differences in major-element composition (Cr, mg) were established in very early Archean time, and do not reflect simple differences in degree of depletion. (3) The SA lithosphere was "refertilized" following diamond formation, by metasomatic processes which have affected the Siberian lithosphere little if at all. (4) Effects of these processes include introduction of Zr, Y and Ca; reduction in the proportion of harzburgite to lherzolite; and stripping of Sr and LREE from subcalcic garnets, (5) The same process may have raised the oxygen fugacity of the SA lithosphere, leading to resorption of diamonds either in the mantle wall rock, or in later kimberlites which have been buffered to the oxidation state of the mantle wall-rock. The few Australian DI studied to date are of the eclogitic or lherzolitic parageneses, and do not allow detailed comparisons with concentrate phases. Garnet concentrates from Argyle and Ellendale contain very low proportions of subcalcic garnets and harzburgitic spinels. The lherzolitic garnets are at least as enriched in LIL and HFS elements as those from South African kimberlites. These observations suggest that the deep lithosphere beneath most of WA has undergone less original depletion than the SA lithosphere, and similar levels of refertilization. Depleted harzburgite/dunite comprises much of the lower part of the lithosphere beneath SIB, and of a well-defined layer between 140160 km depth in SA. Such rocks are generally rare in the WA lithosphere; where present, as in parts ofthe

194 Yilgarn and North Kimberley provinces, they commonly lie at shallower levels, in the graphite stability field. Paleogeotherms at the time of intrusion were "cratonic" in the Kimberley province,

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but elevated (ca 45 mW/m 2 ) beneath the Ellendale field; this is consistent with the craton-margin setting of the latter area.

SAMPLES OF A MOHO MAGMA CHAMBER, FOR NEWER BASALTS, NEWLYN, WESTERN VICTORIA F.L. Sutherland1*, J.D. Hollis1, W.D. Birch 2 and L.R. Raynor 3 1 Mineralogy Section, Australian Museum, SydneyE 2Mineralogy Department, Museum of Victoria, Melbourne 3deceased

Abundant xenoliths of pyroxenites, some granulites and metaperidotites occur in a Quaternary (?) explosion crater near Newlyn. Cumulate textured rocks (over 80%) include websterites, clinopyroxenites (± olivine, spinel), wehrlites and gabbros. Websterites are characterised by cpx (Mg41-44 Ca40-43 Fel4-18), opx (Mg71-75 Fel4-18 Ca2-3) and spl (Mg48-50 Fe48-50 Ti2) and the clinopyroxenites by cpx (Mg42 Ca49 Fel8) and spl (Mg43 Fe55 Ti2). Gabbros contain cpx (Mg34-44 Ca44-48 F e l l ) subordinate opx (Mg64-66 Fe33-35 Cal) and sodic to calcic plagioclase (Ca39-56 Na42-60 Kl-2). Olivines are 'iddingsitised' in wehrlites and metaperidotites. Cr diopside-spinel lherzolites show cpx (Mg48-49 Ca44 Fe8) and opx (Mg84) and where preserved olivine is Mg85-90. They represent partly metasomatised mantle wall rocks. Rare granulites contain garnet and amphibole relics. Analysed cumulate rocks give norms appropriate to ne- to hy-normative olivine basalts and the host basalt is olivine tholeiite (Fig.l). The more mafic cumulates show higher Ni (to 276ppm), Cr (to 629ppm) and Sc (to 55ppm) than more feldspathic rocks which show higher Zr (47-315ppm), Sr (737881ppm) and Nb (6-57ppm). 'Xenolith in xenolith' relationships between the metaperidotites, wehrlites and pyroxenites show that

Geological Society of Australia Abstracts Number 32, Ballarat 1992

the first two rocks were 'iddingsitised1 by introduction of the pyroxenites. The latter may contain gabbroic layers. The suite suggests cumulates formed near the crust-mantle boundary at around 7-10kb. Twopyroxene temperatures (1000-1100°C) appear unequilibrated to the geotherm established nearby from garnet metapyroxenites (Griffin et al. 1984), at Gnotuk-Bullenmerri maars (Fig.2). The Newlyn cumulate suite differs from hydrous and garnet-bearing re-equilibrated suites at Bullenmerri and Anakie. It is a sample of young magma bodies at the MOHO below the newer basalts. The cumulates, in retaining un-equilibrated igneous crystallisation temperatures, resemble xenoliths from the Pinacate basalt field, Sonora, Mexico (Gutman, 1986). The crust-mantle igneous underplating may be directly responsible for the hot advective geotherm nearby at Bullenmerri and indirectly bear on the occurrence of diamonds in the region. References Brey, G.P. & Kohler, T., 1990, J. Petrol., 31:135378 Griffin, W.L., Wass, S.Y. & Hollis, J.D., 1984, J. Petrol., 25:53-87 Gutman, J.T., 1986, Aw. Miner., 71:1076-84.

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GPa -0-6

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Bui I en mer r i — G not u k f i e B rey & Koh ler 1-4 1 9 9 0 T P *

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THE LITHOSPHERE OF EAST AND WEST ANTARCTICA FROM XENOLITHS IN BASALTS: IMPLICATIONS FOR THE PACIFIC RIM John A. Gamble*, Richard J. Wysoczanski* & Martin A. Menzies^ 2

1Department of Geology, Victoria University, Wellington, New Zealand. Department of Geology, Royal Holloway & Bedford New College, Univ. of London

Intraplate volcanism in the Ross Sea Embayment and Marie Byrd Land (MBL) is associated with lithospheric extension which, arguably, was linked to a waning mantle plume which rifted Antarctica from SE Australia and New Zealand. Since mid Miocene times intraplate volcanism in the Ross Sea Embayment and MBL has produced voluminous outpourings of intraplate magmas ranging from tephrite basanite to phonolite, trachyte and peralkali rhyolite, the evolved magmas building complex, caldera topped, volcanic shields. Many of the small tephrite basanite scoria cones which are satellitic to the major (evolved) stratovolcanoes have entrained rich xenolith assemblages en route to the surface. These Geological Society of Australia Abstracts Number 32, Ballarat 1992

xenoliths include supracrustal rocks (mainly granitoids), layered ultramafics (which represent the crystallised contents of lithospheric magma chambers), granulites (considered to represent the lower crust) and peridotites (lithospheric mantle). As such they represent incomplete sections through the lithosphere beneath the vent and may include both mantle and crustal samples. In the Ross Sea Embayment, xenoliths have been collected from 15 sites normal to the front of the Trans Antarctic Mountains (TAM). Lower crustal xenoliths are dominated by granulites which vary from felsic (plagioclase dominated) to mafic (opx + cpx ± olivine dominated) types. Garnet is a significant

196 constituent in granulite xenoliths from the foothills of the TAM whilst olivine typifies samples from McMurdo Sound (eg Ross Island) and garnet is absent. An unusual suite of phlogopite (± pargasite) bearing pyroxenite xenoliths occurs at Foster Crater in the foothills of TAM and these are thought to be interleaved with the granulites. Mantle xenoliths include spinel lherzolite, harzburgite and dunite with a variety of textures ranging from protogranular to porphyroclastic. A variety of pyroxenites, many with cumulus igneous textures, are also recorded. Both the peridotites and the pyroxenites commonly contain amphibole (pargasite in lherzolites, kaersutite in the pyroxenites) which may assume major proportions in the pyroxenites. Phlogopite is also present Contrasts between the major element, trace element and isotopic geochemistry of granulites from the TAM and the McMurdo Sound areas have led to the suggestion of a major lower crustal discontinuity paralleling the TAM front. In MBL xenoliths have been collected from localities in the Executive Committee Range (ECR),

the USAS Escarpment, the Fosdick Mountains and Mount Murphy. The xenoliths span the broad compositional range recorded in the Ross Sea Embayment suites with mantle peridotites, granulites, layered ultramafics and supra crustal granitoids all represented. Petrographically, however, there are important distinctions. For example, phases such as phlogopite and pargasite are absent from the peridotites which are mainly protogranular spinel lherzolites. The MBL granulites are cpx, spinel ± olivine and amphibole bearing, with no opx and garnet. Chemically, the granulites from the southern end of the ECR (Mount Sidley vents) are distinctive from those of the northern ECR, USAS escarpment and Mt Murphy. The Mount Sidley samples have an enriched or alkaline magmatic affinity, contrasting with the depleted tholeiitic affinity of those from the other areas. This paper will compare and contrast the xenolith data from our studies on the Antarctic plate(s) with data from New Zealand and SE Australia.

KEYNOTE: A 7.10 DEVELOPMENT OF ARC SYSTEMS IN THE WESTERN PACIFIC: RESULTS FROM THE 1989 *90 OCEAN DRILLING PROGRAM Richard J. Arculus Department of Geology and Geophysics, University of New England, Armidale, N.S.W. 2351 The major portion of island arc systems in the western Pacific are deeply submerged. Although the general bathymetry is reasonably well known, it is only recently that localised sonar swath mapping has been undertaken whereby the detailed geomorphology can be revealed. Rock samples obtained in field context have been hard to recover, but the highly successful Deep Sea Drilling Project legs in the Philippine Sea and transect across the Mariana arc inspired a renewed campaign of direct sampling by deep-diving submersible, and sustained drilling in a number of arc systems in the past 2 years, under the aegis of the international Ocean Drilling Program (ODP). A number of remarkable petrologic and tectonic discoveries have been made as a result of these efforts, many of which have clear relevance for understanding the structural and geochemical evolution of ancient collision margins. Some of the most significant observations made during specific legs are: Leg 125 — forearcs of the Mariana and Bonin systems. Major features of the development of these arcs are : (i) the near-continuous protrusion alongstrike, under tensional conditions, of serpentinite with entrained blocks of variably serpentinised harzburgite Geological Society of Australia Abstracts Number 32, Ballarat 1992

and dunite, on the trenchward side of the forearc highs; (ii) existence of 3 major pulses of boninite series rocks in the forearc of the Bonin system (mid-Eocene; mid-Oligocene, and mid-Miocene) correlative with inception of the Mariana-Bonin system and subsequent forearc rifting episodes; (iii) clear and persistent geochemical distinction between ash sequences derived from a subaerial arc culmination to the west of the forearc and the boninite series forming the forearc basement, implying isolation of the respective magma sources in the mantle; (iv) development of a mineralised stockwork in boninite series rocks at the base of one of the Bonin forearc sites. Leg 126 — backarc-forearc transect of the Bonin system. Major observations are that : (i) the prominent forearc Bonin Trough was the product of mid-Oligocene forearc rifting, with the generation of a boninite-related igneous basement; (ii) highly volatilerich and vesiculated basaltic magmas are being erupted in water depths > 2000m in the actively spreading backarc rift. Legs 127 - 128 — the backarc basin of the Japan Sea. (i) recovery of lower- to mid-Miocene basement of dolerites and basalts in the eastern part of the Japan Sea (Yamato Basin); (ii) penetration of

197 interlayered shallow-to-deep water sediments and altered rhyolitic tuffs in a Kuroko-style failed rift of the Yamato Rise continental fragment; (iii) documentation of a major pulse of explosive volcanism in the neighbouring Japanese arcs in PlioPleistocene time. Leg 131 — the accretionary prism of the Nankai Trough. This leg achieved the first successful penetration through the sedimentary wedge and decollement into the subducted oceanic crust of the Philippine Sea Plate. Numerous in-situ and postcruise studies have targeted the tectonic relations, fluid chemistry and fluid flows within the accretionary prism. Leg 134 — collision zone of the twin-ridge dUntrecasteaux Zone (DEZ) with the Vanuatu arc and the intra-arc basin. The variable subduction behaviour of the DEZ and consequences for the tectonic development of the forearc are distinctive. For example, the northern ridge of the DEZ (mid ocean ridge basalt basement) is being subducted with relatively little disturbance of the forearc, whereas subduction of the southern ridge of the DEZ (andesite basement) results in accretion of portions of the ridge to and deformation of the forearc. Variations in sediment type and thickness within the intra-arc basin appear to reflect in part, the collision history of the DEZ with the arc. Leg 135 — Lau Basin and Tonga arc. Major results are : (i) the Lau Basin is older than previously thought (> 5.6 Ma) with "basin and range"-type extension preceding spreading and the creation of new basaltic crust; (ii) absence of any consistent spatial or temporal variation in the chemistry of Lau Basin rocks; (iii) recovery of a thick sequence of pre-late A 7.11

Eocene high-Si dacite tuffs, welded tuffs and lava flows forming the basement of the Tonga forearc. These units may well be correlative with the extensive late Cretaceous siliceous volcanic rocks of the present northeast Australian margin. There is a possibility that fragments of Australian crust are now dispersed through the various rises and intervening back arc basins, as far east as the Tonga-Kermadec arc system. A particularly important feature of a number of the intra-oceanic arcs of the western Pacific, is the prevalence of tensional tectonics at many periods of development of the backarc-arc-forearc systems. Despite the location of these systems at overall convergence sites in a plate tectonic framework, the absence of transmission of compressive stress from the subducting to over-riding plate is characteristic of the Bonin and Mariana systems in particular. Nevertheless, it is clear that periods of tension can alternate with those of compression. The widespread occurrence of actively serpentinising outcrops of upper mantle materials in the Mariana-Bonin forearcs may provide important clues for understanding the development of serpentinite bodies in arcs such as the Solomons. For example, the serpentinite outcrops of the eastern Solomons may well have formed in a forearc tensional regime prior to a subduction polarity reversal, and subsequent uplift of the Solomons. Finally, we know now that boninite series magmatism was ubiquitously developed along the full length of the Mariana-Bonin system at the time of its inception in the mid-Eocene. Initiation of this subduction system resulted from changes in the vectors of plate motion, and appears to have required the cannibalisation of preexisting transform fault(s).

PETROLOGY AND GEOCHEMISTRY OF BACK-ARC BASIN BASALTS FROM LAU BASIN SPREADING RIDGES AT 15, 18 AND 19°S T.J. Falloon *, A. Malahoff L.P. Zonenshain and Y. Bogdanov 1

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1Department of Geology, University of Tasmania, Hobart 2Department of Oceanography, University of Hawaii at Manoa, Honolulu, Hawaii 3Institute of Oceanology, The USSR Academy of Sciences, Moscow 117218, U.S.S.R. Fresh back-arc basin lavas were recovered during five dives of the submersible 'Mir' during the 1990 cruise of the research vessel 'Akademik Mstislav Keldysh' to the Lau Basin. Three dives were conducted on the central spreading center of the 'King's Triple Junction' (KTJ) in the northeastern part of the Lau Basin east of Niuafo'ou Island at approximately 15°S. Andesitic lavas were associated with an extinct sulphide chimney field on one of the dives. The lavas from the KTJ can be divided into types I and II based Geological Society of Australia Abstracts Number 32, Ballarat 1992

on their similarities to N-MORB and the BABB magma type of Sinton and Fryer (1987) respectively. One dive each was made on the Central Lau Spreading Center (CLSC) at 18°S and the Eastern Lau Spreading Center (ELSC) at 19°S. Lavas sampled during the dive on the CLSC were associated with active hydrothermal sulphide chimneys occurring at the base of a collapsed caldera structure on the central volcanic axial high. Sampled lavas from both the CLSC and ELSC are all of type I geochemistry.

198 The results of the 'Keldysh' 90 cruise are integrated with previous work to evaluate the geochemical characteristics of the Lau Basin crust as a whole and geochemical zonation models for back-arc basin development. An important part of this review of Lau Basin basalt geochemistry is the recognition of boninites and rocks of boninite affinities which occur at off-ridge locations throughout the Lau Basin. The boninites are suggested to occur during the initial stages of development of new spreading ridges associated with episodes of ridge jump or the propagation of back-arc spreading ridges into arc crust. Hf-Th-Ta systematics of the Lau Basin lavas are used to identify unmodified mantle source compositions and possible subduction-related enriched components. Unmodified mantle source compositions range from D-, N-, E-MORB to OIB. All Lau Basin lavas show some evidence of enrichment by a A 7.12

H20±LILE±LREE-enriched component which is suggested to be a slab derived hydrous fluid. The slabderived fluid is not homogeneous in composition and is suggested to reflect the presence or absence of a subducted sediment component. The sampled lavas from the KTJ confirm the uniqueness of the BABB magma type of Sinton and Fryer (1987) and, as a result, a broad classification of back-arc basin magmas is developed which incorporates original unmodified mantle source composition and the presence of an H 0±LILE±LREE-enriched slab-derived fluid. 2

Reference Sinton JM, Fryer P (1987) Mariana Trough lavas from 18°N: implications for the origin of back arc basin basalts. J Geophys Res 92: 12782-12802

PETROGENESIS AND TECTONIC SIGNIFICANCE OF THE HELLYER BASALT, MOUNT READ VOLCANICS, W TASMANIA Anthony J. Crawford * and David J. Whitford 1

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1 Geology Department, Univ of Tasmania ^CSIRO Exploration Geoscience N Ryde t

The economically important Cambrian Mount Read Volcanics (MRV) belt borders the western margin of the Precambrian Tyennan Region in western Tasmania. A detailed geochemical study of leastaltered lavas and shallow intrusives, with emphasis on basaltic to andesitic compositions, has been carried out to determine the primary magmatic affinities and tectonic setting of eruption of the Mount Read Volcanics, to aid in internal correlations within the belt, and to provide 'starting material' estimates for mineralization-related alteration studies. The Central Volcanic Complex (CVC) dominates the main N-S trending section of the MRV and includes medium- to high-K andesites (La/Yb)N = 5 12 (av. 8.1) and more felsic rocks (CVC Group 1), but also a suite of high-K, more P205- and LREEenriched (La/Yb)N = 1 0 - 2 6 (av. 16.7) hornblendephyric andesites (CVC Group 2), many of which appear to be intrusive into CVC Group 1 rocks. The CVC is overlain by greywackes (Animal Creek Greywacke in the northern section of the belt) that are dominated by detritus from Precambrian pelitic metamorphics, but also contain large red detrital chromite grains with Cr/(Cr+Al) values of 0.82-0.95, indicating derivation from boninitic rocks in the W Tasmanian ophiolites. Immediately above the Animal Creek Greywacke in the northern section of the MRV are the QueHellyer Footwall Andesites, plagioclase-phyric Geological Society of Australia Abstracts Number 32, Ballarat 1992

medium-K calc-alkaline lavas with geochemical features essentially indistinguishable from the CVC Group 1 andesites. The uppermost lavas in the MRV are the Hellyer basalts; these have correlates in the Lynchford basalts in the south of the belt. The Hellyer basalts were erupted in a submarine environment and include abundant primitive olivine+ chromite+cpx-phyric basalts and subordinate more evolved basalts and andesites; olivine is only preserved as inclusions in cpx phenocrysts. Chromites in the Hellyer basalts have Cr/(Cr+Al) values of 70-85, and cpx phenocrysts have Mg' values from 93.9 - 86 in the more primitive basalts and very low Na20 contents (<0.15%), indicative of lowpressure crystallization from near-primary magmas. Olivine inclusions preserved in some cpx phenocrysts are Fo86-90 but are probably re-equilibrated with their hosts. Wholerock K20/Na20 values of the often glassy Hellyer basalts are invariably <1 due to alteration during low-grade metamorphism. However, careful study of melt inclusions in the cpx phenocrysts in one of the most LREE-enriched basalts shows all have K20/Na20 values > 2, suggesting shoshonitic parental magmas. Key compositional features of the Hellyer Lynchford basalts include: 1: abundant primitive lavas with >8% MgO, and exceptionally magnesian cpx phenocrysts Mg' = 93.988), implying olivine (now serpentinized) as

199 magnesian as Fo93. 2: typical 'arc magma1 depletions in Ti, Zr etc, indicating that their source mantle had suffered processing in a 'supra-subduction zone' environment . 3: rapid variations in the degree of enrichment or depletion of LILE, from low-Ti (0.30.4% TiC>2) basalts with Ti/Zr values around 90 and (La/Yb)N = 6, to exceptionally LREE-enriched higher Ti (0.5-0.9% Ti02) shoshonitic basalts with (La/Yb)N commonly > 100 (up to 500 times chondritic La in a basalt with 11% MgO). 4: wholerocks and cpx separates have initial (500Ma) epsilon Nd values of +1 to -1, and initial Sr ratios around 0.7080 in both the most LREE-enriched and least LREE-enriched compositions, suggesting derivation of the entire spectrum of basalt compositions from an isotopically similar source.

A 7.13

The presence in sediments beneath the Hellyer basalts of chromites unambiguously derived from the ophiolite allochthons demands that the Hellyer basalts are post-collisional. The Mount Read Volcanics were erupted in a series of extensional basins formed probably in the late Middle to Upper Cambrian, following an arc-continent collision during which allochthonous mafic-ultramafic complexes were overthrust westwards on to a Late Precambrian passive margin. Post-collisional relaxation rifting, involving increasing extension with time, led initially to production of a medium-K calc-alkaline suite dominated by andesites and more felsic lavas (CVC and Que - Hellyer Footwall Andesites). Increasing extension allowed passage to the surface of the Hellyer basalts accompanied by minimal fractionation.

TRACE CU, U AND AG MINERALISATION IN THE LAKE BOGA GRANITE, NORTHWESTERN

VICTORIA.

W. D. Birch and D. A. Henry Dept of Mineralogy and Petrology, Museum of Victoria The Lake Boga Granite, of Devonian age, is the sourcehas not yet been traced. Rare chlorargyrite northernmost granite outcrop in Victoria and forms part crystals indicate that a primary source of Ag exists of the Terricks Range, a group of residual hills within the granite. The assemblages suggest a multiprotruding through the sediments of the Murray Basin. stage process involving oxidation of primary sulphides The granite, which has been exposed entirely by and dissolution of fluorapatite, followed by reaction quarrying, is very heterogeneous. While it is generally with Cl-bearing solutions in an 'arid-environment' coarse-grained with large orthoclase phenocrysts, oxidised zone. especially at depth, aplitic layers, pegmatoidal veins andclots, and miarolytic cavities are common in the References uppermost levels. The granite is distinguished chemically and mineralogically by relatively high P, Birch, W.D., Mumme, W. G., and Segnit, E. R., 1988, Ulrichite - a new coppercalcium uranium Cu and U contents, expressed by the presence of large phosphate from Lake Boga, Victoria, Australia. fluorapatite crystals, and a suite of secondary uranium Australian Mineralogist, 3(4), 125-131. minerals including saleeite, torbernite and the new Henry, D. A., and Birch, W. D., 1988, Sampleite and species ulrichite (Birch etal, 1988). Copper for these associated minerals from theLake Boga granite and other secondary phosphates such as quarry, Victoria, Australia. Australian turquoise,chalcosiderite, libethenite, pseudomalachite Mineralogist, 3(4) 135-148. and sampleite is derived from disseminated patches of chalcopyrite (Henry & Birch, 1988). The primary U

Geological Society of Australia Abstracts Number 32, Ballarat 1992

200 A 7.14

CHANNELLED FLUID FLOW AT STEPHEN CROSS QUARRY, QUEBEC, CANADA

I. Cartwright *' N.H.S. Oliver ' and T.R. Weaver 1

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department of Earth Sciences, Monash University, Clayton, Vic 3168. ^Department of Earth Sciences, University of Waterloo, Waterloo, Ontario N2L 3G1, Canada. Stephen Cross Quarry (SCQ) lies within the Gatineau domain of the Central Metasedimentary Belt (CMB) of the Grenville Province of Quebec (WynneEdwards, 1972). The CMB consists of a diverse assemblage of Grenville Supergroup metaigneous and metasedimentary lithologies which have undergone polycyclic deformation and metamorphism. The CMB underwent regional metamorphism during the Ottawan Orogeny at 1040-1070Ma (Easton, 1986) with peakmetamorphic conditions in the Gatineau domain varying from amphibolite to granulite facies (~4kbar and 650-700°C; Indares and Martignole, 1984). Just after the peak of the regional metamorphism, marbles and calcsilicates at SCQ underwent metasomatism associated with the intrusion of the Wakefield syenite (Hogarth and Steacy, 1986). At SCQ the regional calcite + diopside ± quartz ± dolomite ± phologopite mineralogies are replaced by calcite + periclase + forsterite + brucite + serpentine assemblages, and calcsilicates comprise wollastonite + calcite. Brucite and serpentine typically form polycrystalline aggregates which overgrow, and hence postdate, the periclase and forsterite. Within 10m of most, but not all, syenite-marble contacts, skarns (typically diopside + spinel + calcite, anorthite + diopside + grossular + calcite, and wollastonite + diopside + grossular + calcite assemblages) are developed. The mineral assemblages in the skarns, calcsilicates, and marbles indicate that metasomatism occurred at 710-815°C with fluids of XH2O >0.9. Marbles >40m from the marble-syenite contact have calcite (Cc) 8 0 values of 20-24%o. Closer to the contacts 8 0(Cc) values in the marbles are as low as 9%o, suggesting that these rocks have interacted with fluids in isotopic equilibrium with the syenites (8 0(Cc) = 9-12%o). On the tens of metres scale fluid flow was channelled, resulting in: a) skarn zones not being developed at all contacts; and b) variable 8 0 vs distance profiles in different regions of the quarry. 1 8

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Geological Society of Australia Abstracts Number 32, Ballarat 1992

Quantitative one-dimensional modelling of fluidhosted advective-diffusive transport suggests that these profiles may have been formed in 0.1-1 Ma with horizontal fluid fluxes (volume of fluid per unit area per unit time) of 2 . 8 x l 0 " to 2.8xl0" m /m /s (8.8xl0" to 8.8xl0- m /m /year). For a wide range of horizontal pressure gradients (3P/3z = 10 to 10^ Pa/m), permeabilities calculated from these fluxes are 2 . 8 x l 0 ' to 2 . 8 x l 0 - m for times of O.lMa and 2.8xl0" to 2.8xl0" m for times of IMa. These fluxes and permeabilities correspond to porosities of 10~ to 10~6 if fluid flow was along the grain boundary, or 10" to 10"^ if fluid flow was hosted in microcracks. In many of the marbles, the brucite and serpentine clots have been deformed; in these rocks, brucite often also occurs in veins. Calcite in these marbles contains bright irregular linear zones under cathodoluminesence which are interpreted as recrystallized calcite veins. These deformed marbles generally have lower 8 0(CC) values than adjacent less-deformed marbles, suggesting that they represent fluid flow channels. These data suggest that fluid flow was probably crack hosted, and that channelling of fluids occurred due to deformation. References Easton, R.M.,1986, In: The Grenville Province, (ed. Moore, J.M., Davidson, A., & Baer, A.J.), GeoI .Ass. Can. sp. pap. 31: 127-174. Hogarth, D.D. & Steacy, H.R., 1986, Can. Geophys. Union Fieldtrip Guidbook 17, 16pp. Indares, A. & Martignole, J., 1984, Can. J. Earth Sci. 21: 853-863. Wynne-Edwards, H.R., 1972, In: Variations of Tectonic Styles in Canada, (ed. Price, R.A. & Douglas, R.J.W.), Geol. Ass .Can. sp. pap. 11: 263-334. n

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201 A 7.15 PETROGENESIS OF AN EVOLVING PSAMMO-PELITIC MIGMATITE: AN EXAMPLE FROM THE WONGWIBINDA METAMORPHIC COMPLEX, EASTERN AUSTRALIA T.R. Farrell Department of Geology, University of Newcastle, N.S.W.

The Wongwibinda Metamorphic Complex, in the southern New England Fold Belt, is a small, lowP/high-T migmatite-bearing terrain associated with the Abroi Granodiorite, a member of the Hillgrove Plutonic Suite. Psammo-pelitic migmatites from the complex display evidence of progressive development during prograde metamorphism in two phases of deformation. The first set of leucosomes is parallel to Si, and the second is largely discordant to host rock layering. Migmatite development culminated late in D2 with the generation of small granitoid bodies and the emplacement of the Abroi Granodiorite. First generation (Di) leucosomes are generally thin, occur sub-parallel to Siand are quartz-rich. Two distinct types are present: thin vein-like leucosomes (< 5mm thick) with very high length/width ratios (100200), and thicker leucosomes (up to 50mm thick) which are boudinaged in Si and commonly have a pod-like or lenticular shape. The former are typically closely spaced, have relatively constant modal compositions (qtz 45-50%, pig 35-40%, kfs 5- 12%, bio 1-8%), and become progressively thicker with increasing degree of migmatisation. The lenticular leucosomes are interpreted to be early Di features because of their strong but variable extension in Si. They are frequently linked by thin quartz-rich veinlets, and contain variable amounts of quartz (45-90%) and feldspar (pig 4-50%, kfs 0-17%). The first generation leucosomes were folded during D2 and crosscut by a second generation of thicker, coarser grained, variably deformed "granitic" leucosomes. Compositionally, these later leucosomes range from leuco-adamellite, with sub- equal proportions of plagioclase and Kfeldspar, to biotite-granodiorite (up to 13% bio). Both leucocratic and biotite-rich D2 leucosomes show differing structural relationships; early leucosomes are folded about S2, whereas late stage leucosomes are relatively straight and lie parallel to S2. Leucocratic leucosomes usually have very sharp discordant boundaries, irrespective of the timing of their formation, whereas biotite-rich leucosomes may show either diffuse margins and ghost fabrics concordant

Geological Society of Australia Abstracts Number 32, Ballarat 1992

with Si in the host schist, or very sharp boundaries. Coarse grained pegmatitic varieties are relatively straight, occur parallel to the axial surfaces of F2 folds, have sharp discordant boundaries and are interpreted to be late D2 features. Di and D2 leucosomes are geochemically distinct. As a consequence of their quartz-rich compositions Di leucosomes are strongly depleted in a wide range of trace elements (eg. Rb, Ba, Hf, Th, Zr, Y, LREE) with respect to their host rocks, whereas D2 leucosomes lack the global trace element depletion shown by Di leucosomes. Discordant leuco-adamellite D2 leucosomes have higher Zr, Ba and HREE, and slightly lower LREE, Th, V, Sr, Zn and Cr contents than the host rock suggesting that they may represent fractionated melts. In contrast, biotite-rich leucosomes display incompatible element contents which are remarkably similar to those of the host rock. The chemistry and structural relationships indicate that Di leucosomes formed under sub-solidus conditions. Firstly, their mineralogy deviates significantly from minimum melt compositions, and secondly they are typically extended in Si, implying solid state deformation during Di. Their depleted incompatible trace element compositions are not consistent with an anatectic origin. Conversely, the textural relationships suggest that D2 leucosomes formed by anatectic processes. The biotitegranodiorite leucosomes with gradational margins are interpreted to be partial melts that have not segregated from their source area but have frozen in situ (sensu lato). This can account for the presence of vague internal structures which are continuous with Si in the host rock, and the remarkable similarity of the trace element composition of the host and leucosome. Leuco-adamellite leucosomes are thought to be partial melts that formed at deeper levels and intruded upwards into the overlying migmatites. Their depleted Th and LREE contents suggest that they may represent the fractionated residuum from which a fluid-rich, highly evolved meltfractionhas separated.

202 A 7.16

ON THE ORIGIN OF PERALKALINE GRANITES Allan J R White

Department of Geology, LaTrobe University, Bundoora, Victoria 3083. Peralkaline granites are those in which chemical known as the "plagioclase effect". To explain composition the granite magma had molecular AI2O3 pantellerites, Carmichael & McKenzie (1963) / (Na20 + K2O) < 1 such that there were more alkalis discussed this effect for fractional crystallization in the than could be accommodated in the feldspars in which system Di-Ab-An : when the liquid reaches the Di-Ab AI2O3 / (Na20 + K2O) = 1. This means that the join where there is a speudo eutectic at 95Di-5Ab the rock crystallizes peralkaline mafic minerals such as liquid leaves the binary join, calcic plagioclase not early aegirine augite or aegirine and later alkali albite crystallizes, and the melt phase becomes amphibole such as arfvedsonite. Peralkaline granites peralkaline. At the high temperatures and low H2O are also hypersolvus: only one feldspar, an alkali activities necessary to form hypersolvus granites, the feldspar, crystallizes although normally, this initially mafic mineral crystallizing from a metaluminous homogeneous feldspar subsequently unmixes to coarse granite will be clinopyroxene (usually very Fe rich by perthite. The two important problems for the origin this stage), and it is suggested that continued fractional of these granites are i) how they became peralkaline crystallization allows the plagioclase effect to operate and ii) why they are only have one feldspar. For all if the one feldspar is sufficiently sodic. The production granite types it has been found that there are equivalent of peralkaline granite magma by this process is also volcanic rocks with the same chemical compositions consistent with the occurrence of large crystals of and hence there are the same problems with the origin dioside-hedenbergite in trachytes which have a of peralkaline rhyolites (comendites and pantellerites). peralkaline groundmass containing aegirine augite or All hypersolvus granites are not peralkaline and hence aegirine (Ewart, pers.comm 1991). the two problems are not related. The limited field in which plagioclase resorption In normal granite magmas, plagioclase and K- takes place and the conditions necessary for a magma feldspar co-precipitate down to the solidus. For to become peralkaline, virtually preclude an origin by equilibrium crystallization to produce only one partial melting. It is concluded that peralkaline feldspar, a haplogranite melt in the system Q-Or-Ab- granites are produced by the fractional crystallization An-H20 melt must lie within that region of this of magmas in which the temperature is high enough system where there is complete resorption of for the field of plagioclase resorption to be relatively plagioclase feldspar by a peritectic-like reaction. For large and the activity of H2O in the magma is low Si02 saturated systems, the resorption region can only enough (and temperature high enough) to precipitate be reached at low activities of H2O and is small: the clinopyroxene rather than hornblende enabling the resorption region is most extensive at high Bowen effect to render the melt phase peralkaline. temperatures (Nekvasil, 1990). These data indicate that These are the conditions that operate in the production peralkaline granites are produced from high of pantellerites by fractionation from trachytes temperature magmas having low activities of H2O. (Carmichael & McKenzie, 1963), and some Cordierite granites thought to have been produced peralkaline granites may be produced in this way. But by partial melting of sediments, have high AI2O3 / it is suggested that any high temperature granitic (Na20 + K2O + CaO) not because of high AI2O3 but magma having low H2O activity may fractionate to because of low Na20 and CaO and the problem is why produce a peralkaline magma. A-type granites are one are the latter elements low. On the other hand, the example. Other magma types may also become low AI2O3 / (Na20 + K2O) of peralkaline granites peralkaline. Compositions that do this are discussed. results from low AI2O3 and the the problem here is: why is AI2O3 low ? Bowen (1945) found that in the References system Ab-Ne-Wo, pure albite fails to crystallize in liquids containing a Ca-bearing component but more Nekvasil, 1990, Amer. Min. 75, 560 calcic plagioclase forms instead. The resulting liquid Bowen 1945, Amer. J. Sci. 243A/75) leaves the plane of the system and becomes depleted in Carmichael & McKenzie 1963, Amer. J. Sci. 261, 382. A1 with respect to Na: it becomes peralkaline. This is

Geological Society of Australia Abstracts Number 32, Ballarat 1992

203 A 7.17

GRANITOID GENESIS IN THE CHAELUNDF COMPLEX, NORTHEASTERN NEW SOUTH WALES: IMPLICATIONS FOR THE PETROGENESIS OF A-TYPE GRANITES OF THE NEW ENGLAND BATHOLITH B. Landenberger & W J . Collins

Department of Geology, University of Newcastle, Shortland, NSW. 2308, Australia The Chaelundi Complex in the New England Fold Belt, northeastern New South Wales, comprises an older I-type suite and a younger A-type suite of granitoids which are both Triassic in age. The A-type suite is dominated by a leucoadamellite that is mineralogically and geochemically similar to the Triassic group of post-orogenic leucoadamellites, which constitute the youngest group of intrusives in the New England Batholith. However, the suite is compositionally extended, ranging from a quartz monzonite (66% S1O2) to leucoadamellite (76% Si0 2 ). Relative to the enclosing I-type Chaelundi Granodiorite (67-70% Si02), the A-type suite is distinguished by higher alkali and high-field strength element contents, and lower CaO and MgO. AI2O3 contents are also high, resulting in corundum normative values of 0.2%-0.6%. The mafic end member, the quartz monzonite, is characterized by sodic plagioclase (Anll-An31), relatively Fe-rich biotite (Mg# 30), hornblende (Mg# 35), ferrohypersthene (Mg# 35). Derivation of the leucoadamellite from the quartz monzonite is achieved by 60% fractionation, involving removal of

A 7.18

plagioclase, K-feldspar and orthopyroxene, with minor hornblende and ilmenite. Trace element and REE data support this degree of fractionation, with the Eu/Eu* value of 0.08 for the leucoadamellite, which is fairly typical for the New England leucoadamellites (Shaw & Hood, 1981). Microxenoliths of augite, hypersthene and calcic plagioclase also occur at Chaelundi, and intact enclaves of a high-K, high-Al basalt are present in a similar body of quartz monzonite at Woodlands, 30km to the northwest. Although these enclaves are clearly magmatic, and have a mantle origin, they also have REE patterns that are comparable to patterns for both the A- and I-type granitoids present at Chaelundi. This is consistent with a source of previously underplated basalt of similar composition, melting to generate the granitoid magmas. References Shaw, S.E. & Flood, R.H. 1981. The New England Batholith eastern Australia : geochemical variations in time and space. Journal of Geophysical Research 86:10530-10544

DISTRIBUTION, GEOCHEMISTRY AND ORIGINS OF THE YOUNGEST LAVAS OF HEARD ISLAND, SOUTHERN INDIAN OCEAN G.E. Wheller1* and J. Barling2 J

CSIRO Division of Exploration Geo science, North Ryde, New South Wales 2 Max-Planck Institut fur Chemie, Mainz, Germany

Heard Island is an historically-active, composite, intraplate volcano with young well-formed scoria cones and associated basaltic lava flows in many places around its present coastline (Fig. 1). Located on the northern part of the submarine Kerguelen Plateau in the southern Indian Ocean, 400 km SSE of the Kerguelen Islands, Heard Island is the youngest manifestation of the hotspot which may have been responsible for the opening of the Indian Ocean, the construction of the Kerguelen Plateau/Broken Ridge and the Ninetyeast ridge, and widespread contamination of the Indian Ocean asthenosphere. Geological Society of Australia Abstracts Number 32, Ballarat 1992

Heard Island consists essentially of two modern cones, Big Ben (the larger) and Mt Dixon built over an uplifted Late Miocene-Early Pliocene marine sequence of volcanics, volcanoclastics and calcareous sediments. Approximately 2745 m high asl, Big Ben is about 20 km in diameter at sea-level. It is capped by Mawson Peak, an impressive symmetrical cone which rises 500 m above a summit plateau lying within a semicircular ridge 5-6 km in diameter. Mt Dixon is about 706 m high asl and 5 km in diameter. It lies at the end of a narrow peninsula formed mainly of older, but compositionally-related, trachytic volcanics. Rapidly

204 retreating glaciers lie over 80 % of the island. The volcanic products exposed on the island form a moderately potassic basanite, alkali basalt, hawaiite and trachyte sequence which is similar to the products of many other oceanic island volcanoes. Big Ben lavas, however, display geochemical and petrographic evidence for a high rate of magma recharge and extensive magma mixing compared to those erupted from Mt Dixon which appears to have formed as a result of slow magma recharge and protracted fractional crystallization. Strontium, Nd, and Pb isotopic and UTh radionuclide differences indicate that the two cones tap different magma sources. The young volcanic products on the island include lavas erupted from the main edifices of both Big Ben and Mt Dixon as well as numerous ash cones and small lava fields formed around their flanks. A prominent plinian trachytic pumice deposit also crops out in one place. Some of the flanking cones and lava fields are being eroded by the sea and additional young cones and lavas probably existed beyond the present coastline. Since its first recorded sighting in 1833, four eruptions are known to have occurred on Heard Island, each localized around Mawson Peak. The most recent was first observed in January 1985 and resulted in the formation of a deep crater 50 m across at the summit of Mawson Peak and a pahoehoe lava flow about 8 km long between the summit crater and Cape Arkona.

The same spatial, petrographic, geochemical and isotopic characteristics which distinguish the older products of Big Ben and Mt Dixon are also reflected in the young lavas (Fig. 2). This indicates that both cones are potentially active and demonstrates the isolated and localized nature of their respective magmatic plumbing systems. Moreover, the Mt Dixon young lavas, in particular, display a wide and continuous range in compositions from alkali basalt to trachyte. This suggests that the modern magma chamber feeding Mt Dixon is compositionally heterogeneous and that different parts of it are liable to erupt. Consequently, relatively explosive eruptions of trachytic material, as well as less explosive eruptions of basaltic material, could occur from Mt Dixon in future as a result of its present magmatic regime. Some of the young cones and lavas from both Big Ben and Mt Dixon display field evidence for having formed either before or during the last glacial maximum on Heard Island at the end of the Pleistocene. Most, however, have clearly formed since the glaciation retreated. Because the young volcanic products appear to represent a significant surge in volcanism on Heard Island it is interesting to speculate on what triggered it. One possibility is the release of lithostatic pressure as a result of the progressive reduction in glacial load on the island up to 10 Ka ago.

South Barrier

Plateau 0

1

2

3

5

6

7

8

9

50 Fig. 1 Map of Heard Island showing locations of young volcanic cones and the 1985 lava flow. Geological Society of Australia Abstracts Number 32, Ballarat 1992

10km

73°53

205

20

Recent

15

P \

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Lavas

•

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A

Mt Dixon

1985 V flow Big

Ben

old

lavas

Mt Dixon old l a v a s 0

40

45

50

55

60

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S i 0 (wt %) 2

Fig. 2. Si02-Mg0 plot of Heard Island volcanics showing compositional ranges of the young lavas. A 7.19 GEOCHEMICAL AND ISOTOPIC STUDIES OF PROTEROZOIC MAFIC DYKE SWARMS IN CENTRAL AUSTRALIA Jian-xin Zhao *, Malcolm T. McCulloch , and Alfredo Camacho ^ 1

1

1

^ Research School of Earth Sciences, Australian National University, Canberra 2N.T. Geological Survey, Alice Springs, NT 0871, Australia Mafic dyke swarms of middle to late Proterozoic samples and their respective mineral separates are used age occur in central Australia, as the result of post- for isochron regression and the age results are listed tectonic continental extension events (Parker et al. below: 1987). Among them, the Stuart Dyke Swarm (SDS) in the Arunta Block, the Kulgera Dyke Swarm (KDS) in the eastern Musgrave Block and mafic dykes in the Amata area, central Musgrave Block have been investigated in terms of major, trace and rare earth elements and Sm-Nd isotopic compositions. Rocks of the KDS, the SDS, and to a lesser extent, the dolerite dykes in the Amata area are relatively unmetamorphosed and undeformed with ophitic textures being clearly preserved. The SDS and KDS appear to represent the last magmatic intrusions in each block which predate the onset of the Amadeus Basin sedimentation. Sm-Nd isotopic analyses for a number of dolerite Geological Society of Australia Abstracts Number 32, Ballarat 1992

206 Table: Summary of Sm-Nd mineral isochron data for mafic dyke swarms in central Australia Sample

Points

Assemblage

Age (Ma) (±2a)

Initial £Nd

Model

MSWD

1061±36 1049±94

-7.8±0.8 -6.6±2.2

3 1

1.10 0.57

Kulgera Dvke Swarm, eastern Musgrave Block 1-3 6 3cpx+2plag+TR 1121±42 1-3 4 3cpx+TR 1076±49

+0.5±1.3 +1.0±1.6

3 1

1.71 1.00

Dolerite dykes in the Amata area, central Musgrave Block 87-497 3 cpx+plag+TR 790±40 87-504 3 cpx+plag+TR 797±49

+4.1±0.9 +2.5±1.2

1 1

0.3*7 0.02

Stuart Dvke Swarm, southern Arunta Block 89-506 6 3cpx+2plag+TR 89-474 3 cpx+plag+TR

The consistent age results from two samples of the SDS are substantially older than the Rb-Sr mineral isochron age of 897±9 Ma as previously reported by Black et al. (1980) for the SDS. The 1121±42 Ma age for the KDS sample is slightly older, however, the removal of the two less precise plagioclase data (due to extremely low REE abundance) from regression reduces the age to 1076±49 Ma, which is consistent with both its Rb-Sr WR-mineral -mesostasis isochron age of 1054114 Ma reported by Camacho et al. (1991) and the above Sm-Nd age for the SDS. Considering the immobile nature of REE during low-grade metamorphism and the Model One nature of the isochrons, the above Sm-Nd ages for both swarms are interpreted as the crystallization age of the dykes. These ages are also similar to the Rb-Sr isochron ages of the Beda Volcanics at the base of the Adelaide Geosyncline and the Gairdner Dyke Swarm in the eastern Gawler Craton, both of which are considered as representing the earliest phase of intracratonic extension associated with the formation of the Adelaide Geosyncline (Parker et al., 1986). The two spatially widely separated samples from the Amata area give consistent, but surprisingly younger ages. These ages could record either another episode of magmatism, or a later metamorphic event in the Musgrave Block. However, the consistency of the two ages, the intact magmatic textures displayed by the two samples, combined with its unique geochemical features distinctive from either the KDS or the SDS indicates the first case is preferred. It is tempting to note that these ages are consistent with UPb zircon ages of 802110 Ma obtained for the Rook Tuff in the Adelaide Geosyncline (Fanning et al 1986). Major and trace element data for the SDS and KDS show tholeiitic affinities with pronounced depletion in Nb, Zr, Ti, Y and high contents of MgO. Their HREE patterns are relatively flat (GdN/YbN = 0.91-1.28), with slight but variable enrichment in LREE (LaN/Smn = 1.22-2.19). In comparison, the

SDS is higher in MgO and lower in Sr than the KDS. Three samples of the SDS yield a range of e(1061 Ma) values from -5.12 to -7.45, which appear to be correlated with Nd concentrations and l^Sm/M^Nd ratios, three samples of the KDS have remarkably identical 8(1076 Ma) values of +0.11 to +0.54, which are much higher than those of the SDS. Four samples taken from the Amata area, central Musgrave Block display smooth, negatively sloped REE patterns with LaN/SmN = 1.18-1.47 and GdN/YbN = 1.46-1.62. Their corresponding e(800 Ma) values range from +2.55 ~ +4.27, whilst the e(1076 Ma) values, from +3.65 - +5.15. These features displayed by the Amata rocks are clearly distinctive from those of the KDS, suggesting a different source and petrogenesis. Combined geochemical and isotopic evidence indicates that the parental magma of the SDS was derived by partial melting from a chemically refractory, but isotopically evolved subcontinental lithospheric mantle source, which was subsequently contaminated by continental crust material during crystallization. The contemporaneous KDS has similar geochemical features to the SDS, however, its magma sources appear to be more depleted in terms of Nd isotopes. At this stage it is still difficult to envisage the possible source components and processes of magma genesis for the KDS. However, it is tempting to note that the more positive e(T) value of the KDS could be related to a much younger subcontinental lithosphere under the Musgrave Block than that under the Arunta Block. The unique features such as extremely low HFSE and high La/Nb and Zr/Nb displayed by both swarms, especially the SDS (La/Nb - 9 and Zr/Nb - 65) cannot be explained by crustal contamination. We explain these features as due to the lithosphere having been previously metasomatised by HFSE-depleted slabderived fluids/melts during earlier stage subduction processes (e.g. 1.7-1.8 Ga for Arunta Block). The much younger dolerite dykes in the Amata area, central Musgrave Block are related to a depleted

207 Geophys. J. Int., 107 (in press). asthenospheric mantle source with individual rocks being variably contaminated by crustal material during Fanning, C.M., Ludwig, K.R., Forbes, B.G., & Preiss, W.V., 1986. Geol. Soc. Aust. Abstr. 15: crystallization. 71-72. Parker, A.J., Rickwood, P.C., Baillie, P.W., Boyd, References D.M., Freeman, M.J., McCenaghan, M.P., Murray, C.G., Myers, J.P. & Pietsch, B.A., Black, L.P., Shaw, R.D. & Offe, L.A., 1980. J. 1987. Geol Assoc. Can. Spec. Pap. 34: 401-417. Geol. Soc. Aust. 27: 151-155. Camacho, A., Simons, B. & Schmidt, P.W., 1991. A 7.20

CHEMICAL ZONING IN SMALL VOLUME BASALTIC VOLCANOES IN THE AUCKLAND VOLCANIC FIELD, NORTHERN NEW ZEALAND: EVIDENCE FOR SUB-CRUSTAL FRACTIONATION PROCESSES. Ian E.M. Smith Department of Geology, University of Auckland, Private Bag, Auckland, New Zealand.

The Auckland Isthmus contains 48 discrete eruption centres within an area of about 400Km2 known as the Auckland volcanic field; the tectonic environment is appropriate to intraplate volcanism. These volcanoes consist of small volume (<lKm DRE) monogenetic eruption sequences of phreatomagmatic tuffs, Hawaiian to Strombolian cinder beds and associated lava flows. The field has been active for about 140Ka and the most recent eruption occurred about 1400AD. Rock types of the field are petrographically simple. Olivine and less commonly clinopyroxene (diopside-augite) occur as phenocrysts in a groundmass of plagioclase, clinopyroxene minor olivine and ubiquitous accessory Fe-Ti oxides; nepheline as a minor interstitial phase is common. The rocks of the Auckland volcanic field constitute an association of alkali basalt, basanite and nephelinite; intermediate and silicic rocks are absent. Transitional basalt and minor tholeiite are found in the youngest and most voluminous centre - Rangitoto Island. Recognition of trends in the composition of erupted magmas with time are hampered by the difficulty of dating young mafic volcanic rocks. However, in four well exposed centres (Crater Hill, Motukorea, Lake Pupuke, Mount Wellington), stratigraphically controlled suites of samples show clear compositional trends. In each case the trend is 3

Geological Society of Australia Abstracts Number 32, Ballarat 1992

toward increasing silica under-saturation from top to bottom of the eruption sequence. Correlated with this is a decrease in Si02, mafic major and trace element abundances and Mg number, and an increase in total alkali content and incompatible trace elements. These trends are continuous through the deposits of each of the eruption centres and are sub-parallel but distinct in each case. For each of these centres the stratigraphically highest samples show highest Si02 (in the range 43-48 wt.%) and Mg number, and are alkali basalts or basanites; stratigraphically lower samples are basanite to nephelinite. The clear compositional trends within individual centres are interpreted to have resulted by eruption from a compositionally zoned magma column or chamber. The process which produced the zoning is most likely fractional crystallisation but the trends cannot be explained by shallow level differentiation involving observed phenocryst phases. Rather the process requires the extraction of mineral phases which would only occur near the liquidus at pressures >10Kb. The proposed model is one of partial melting of an asthenospheric plume, ponding and fractionation of the resulting magmas at the asthenosphere/lithosphere boundary and rapid ascent of a zoned magma column. The distinct compositional trends observed in each Auckland centre suggests that each eruption involves a discrete melting event.

208 A 7.21 DISTRIBUTION AND NATURE OF MESOZOIC AND EARLY-MID TERTIARY ("OLDER VOLCANICS") MAGMATIC ACTIVITY IN VICTORIA I.A. Nicholls1* and R.A. Day 2 1 Department of Earth Sciences, Monash University, Clayton, Victoria 2 ANSTO, Lucas Heights, MSW Mesozoic and Palaeocene-Miocene mafic to intermediate magmatic activity in Victoria occurred in at least 15 provinces, distinguishable by age and the geochemistry of volcanic products (Day, 1983). Jurassic activity (-190-160 Ma), associated with the early stages of rifting and separation of Australia from Antarctica, produced strongly alkaline volcanic rocks (nephelinites to phonolites - Dundas Tableland province western Victoria), and small dykes and diatremes very rich in mantle and crustal xenoliths, e.g. the Meredith "kimberlitic" (melilitite) breccia pipe. The major group of dominantly basaltic rocks referred to as the Victorian "Older Volcanics" forms at least 14 provinces. Available radiometric age ranges for these provinces span the period Late Cretaceous (95-85 Ma - Poowong province) to mid-Miocene ((2217 Ma - Melbourne province). Volcanic activity within these provinces was initially related to crustal extension leading to the opening of the Tasman Sea (-80-60 Ma) and the Southern Ocean (commencing -55 Ma), and later to the continued northward motion of Australia over mantle thermal anomalies (e.g. Sutherland, 1991) The Older Volcanics include a very broad range of primitive basaltic types, from strongly silicaundersaturated nephelinites to oversaturated quartz tholeiites, with high MgO, Ni and Cr contents and mg values. Representatives of most of these types contain mantle-derived ultramafic xenoliths. This suggests that the dominant controls on compositional varation were degree of melting (<5 to -15%) of broadly lherzolitic mantle sources (with both phlogopite and garnet, as residual phases over much of this melting range, controlling ratios such as K/Al and Ca/Al) and perhaps depth of magma segregation. Six provinces show stratigraphic evidence for increasing alkalinity with time, suggesting decline in

Geological Society of Australia Abstracts Number 32, Ballarat 1992

degree of melting as the associated mantle heat sources waned. Volumetrically minor less primitive lava types, including some hawaiites and the mugearites and basaltic icelandites, are probably related to more mafic parent magmas by fractionation of mainly olivine and Ca-clinopyroxene. The only clearcut systematic variation in chemistry over the - 8 0 Ma life of the provinces is a gradual decline in maximum mgvalue from - 7 0 to 60. This suggests an increase in the degree of fractionation undergone by mantle-derived magmas in traversing a gradually increasing thickness of lithosphere. The Mesozoic-Recent volcanic provinces of south eastern Australia (including the 5 Ma - 5000 years BP "Newer Volcanics" province of South Australia and Victoria) provide a magnificent example of long-term magmatism and complementary evolution of a volume of sub-continental mantle via the generation, transport and eruption (or shallow crustal intrusion) of magmas and associated fluids. At present, detailed study of the earlier history of this system is hampered by a lack of isotopic data on volcanic rocks and ultramafic xenoliths. Further geochemical studies of the Mesozoic volcanic rocks and the "Older Volcanics", similar in scale to recent detailed investigations of the "Newer Volcanics", are therefore urgently needed. References Day, R.A., 1983. Petrology and geochemistry of the Older Volcanics, Victoria. Ph.D. thesis (Unpubl.), Monash University, 372 pp. Sutherland, F.L., 1991. Cainozoic volcanism, Eastern Australia: a predictive model based on migration over multiple "hotspot" magma sources. The Cainozoic in Australia: A re-appraisal of the evidence (Eds.: M. A. J. Williams, P. De Deckker, A. P. Kershaw). Geol. Soc. Australia, Spec. Publ. No. 18, pp. 15-42.

209 A 7.22 THE BROCKMAN RARE-METALS DEPOSIT, HALLS CREEK MOBILE BELT, WESTERN AUSTRALIA: GEOCHEMISTRY OF THE HOST TRACHYTIC VOLCANICS. Wi*. Taylor *, G. Esslemont , R. Page , N.M.S. Rock and D.I. Chalmers 1

1

2

1

3

Key Centre for Strategic Mineral Deposits, Univ. of Western Australia, Nedlands, W.A. 6009. Bureau of Mineral Resources, Canberra, A.C.T. 2601. Multi-Metal Consultants Pty Ltd, 133 Edwards St, Perth, W.A. 6000.

J

2

3

The Brockman rare-metals deposit, located in the Proterozoic Halls Creek Mobile Belt of N.W. Australia, contains economic concentrations of niobium (>0.4 wt% Nl^Os), zirconium (>1 wt% Z1O2), hafnium, heavy rare earth elements (HREE), yttrium and gallium. The ore horizon, informally known as the Niobium Tuff, is a fluorite-bearing ashflow tuff that occurs as the basal unit of a sequence of trachytic lava and volcaniclastic units (the Upper Brockman Volcanics). The Niobium Tuff has a SHRIMP ion-microprobe U-Pb zircon age of 1870±4 Ma. The highest topographic features in the Brockman deposit area comprise -20 volcanic edifices or "domes" of -0.1 to 2.5 km^ size which are composed predominantly of subaerial and subaqueous trachyte lava flows, later trachyandesite flows and sills, and minor tuffaceous units. They are surrounded by extensive volcaniclastic deposits. The Brockman volcanics have been affected by low-grade metamorphism but volcanic units display excellent preservation of primary volcanic features including pillow lavas, pillow breccias, scoriaceous and laharic deposits, and columnar jointed flows. The volcanic environment is analogous to some Tertiary shallowmarine intra-plate volcanic settings. The Upper Brockman trachytes and trachyandesites are characterized by silica-saturated compositions with low TiC>2, P2O5, CaO, and K+Na/Al <1. Igneous differentiation can be modelled by crystal fractionation of the least evolved trachyandesite but high, and possibly unrealistic, degrees of crystallization are required to achieve the highest enrichments. Three evolutionary stages are recognized (see Fig.l): (1) the

trachyandesite-to-trachyte stage (-80% crystallization) characterized by strongly compatible behaviour of Sr, Ba, Eu, P and Ti which can be modelled by anorthoclase, clinopyroxene, Ti-magnetite and apatite fractionation; (2) the trachyte-to-enrichedtrachyte stage (-90% crystallization), characterized by incompatible element enrichments, and (3) the final Niobium Tuff stage (-98% crystallization) which is characterized by extreme enrichment in F, Nb, Ga, Y, HREE and depletion of the light rare-earth elements (LREE) (see Fig. 2). REE modelling of stages (2) and (3) requires fractionation of a small amount (<0.5%) of a highly LREE-selective phase, e.g. allanite, although such a mineral has not been found as a phenocryst in the Niobium Tuff or trachytes. Alternatively, other magma chamber processes such as upward segregation of an immiscible fluorine-rich melt fraction, which strongly partitions the HREE, could lead to the observed enrichments and LREE/HREE fractionation. Stages (1) to (3) are in the reverse order of the stratigraphic sequence seen in the field suggesting that magmatic differentiation led to development of a chemically stratified magma chamber which "unloaded" from the top down during eruption. Fractionation of calcic feldspar and high magmatic fluorine contents (which result in low magma viscosities and hence more efficient fractionation) are considered to be significant factors leading to high incompatible element enrichments in the Brockman volcanics.

210

6000 A Niobium Tuff o Enriched Trachyte O Trachyte • Trachyandesite

1000 E

Q_ Q.

/ /

J

(3)

f o

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100

200

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10000

Figure 1. Plot of Nb versus Zr showing enrichment stages (1) to (3)

10000

• Niobium Tuff o Enriched Trachyte • Trachyte • Trachyandesite

g 1000 ~o

c

o

sz 0

1 o o

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10

i i i i i i—i 1 1 1 , 1 , ]— La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu

Figure 2. REE plot for showing behaviour of REE elements from least to most enriched

Geological Society of Australia Abstracts Number 32, Ballarat 1992

211

A 7.23

AMPHIBOLITE FACIES METAMORPHISM OF A COMPOSITE IGNEOUS BODY, SOUTH VICTORIA LAND, ANTARCTICA T. .i.Aslund -, *, C. R. .i.Walcott ; and D. Craw 1

2

2

^ Department of Earth Sciences, Monash University, Victoria. Geology Department, University of Otago, New Zealand. 2

The Dromedary gabbroic complex, which is part of the basement sequence of south Victoria Land, is located approximately 70km south of the Dry Valleys, Antarctica. The complex is 2X5km, intrudes Koettlitz Group metasediments and has undergone amphibolite facies metamorphism. It comprises a deformed outer zone and a relatively undeformed, variably recrystallised inner region. On the basis of metamorphic mineralogy, the complex can be divided into 4 groups, the western, central and eastern zones, and the foliated marginal zone (FMZ) (Aslund, 1990). In the western zone igneous textures are preserved. Primary orthopyroxene is partially replaced by cummingtonite and clinopyroxene is typically rimmed with hornblende. The central zone is characterised by polycrystalline aggregates of cummingtonite rimmed with hornblende. Large (16cm across) almandine-rich garnets are locally abundant. Within less metamorphosed portions of the central zone, olivine coronas (olivine/orthopyroxene/ Ca-amphibole) are apparent. The eastern zone comprises polycrystalline aggregates of pale green, relatively Mg-rich calcic amphibole enclosing igneous plagioclase. Lithologies of the FMZ are biotite-rich, quartz-bearing, and contain metamorphic clinopyroxene in places. The presence of relict igneous plagioclase results in a lenticular appearance. The composition of relict igneous phases from the respective metamorphic zones suggests that each zone, with the exception of the FMZ, is characterised by a distinct igneous mineral assemblage (see table 1). This implies original rock composition strongly influenced the subsequent metamorphic character. Relict plagioclase compositions from the FMZ indicate the original rock was gabbroic. The abundance of biotite and quartz in these rocks suggests significant water, K2O and Si02 were present during recrystallisation. Thus, two styles of amphibolite facies metamorphism can be distinguished. One was essentially isochemical and is characterised by replacive textures (western, central and eastern zones). The other, probably later, event was associated with metasomatism and

Geological Society of Australia Abstracts Number 32, Ballarat 1992

localised development of foliation (FMZ). Three groups of related structures are identified in the Dromedary massif and are thought to relate to 3 'phases of deformation (Walcott, 1990). Amphibolite facies metamorphism coincides with the second phase of deformation (D2). Intrusion of the Dromedary complex occurred prior to D2. The pervasive L2 lineation developed within Koettlitz Group metasediments is relatively steep (-50 E-SE). During the latter stages of D2, the Dromedary south high strain zone (DSHSZ), which is a major E-W trending ductile shear zone, developed between Dromedary complex and a neighbouring granite pluton. Within this zone a more shallow lineation (0-30SE) overprints the steep lineation (Walcott, 1990). Comparison with structural styles observed in the Dry Valleys (Cox, 1989) suggests development of the shallow lineation is related to intrusion of a large granite body, the Bonney pluton. Conceivably, intrusion of the Bonney pluton also resulted in the introduction of significant volumes of K2O- and Si02-rich fluids which caused metasomatism within the FMZ during D2. In summary, the Dromedary complex was intruded just prior to D2. Slow subsolidus cooling resulted in the development of corona microstructures in olivine gabbro. Isochemical amphibolite facies metamorphism occurred in the early stages of D2. Steep lineations formed in the surrounding metasediments at this time. Local development of shallow lineations, and an influx of fluids associated with intrusion of the Bonney Pluton occurred in the latter stages of D2, resulting in metasomatism within zones of high strain. 1

References Aslund, T., 1990, unpubl. M.Sc. thesis, University of Otago. Cox, S. C., 1989, unpubl. M.Sc. thesis, University of Otago. Walcott, C. R., 1990, unpubl. M.Sc. thesis, University of Otago.

212 A 7.24

EARLY EXTRATERRESTRIAL IMPACTS AND THE ARCHAEAN CRUSTAL RECORD A.Y. Glikson Canberra, A.C.T. Australia

The Archaean crustal record contains evidence for clustered major igneous episodes involving deep upwelling and adiabatic fusion of the mantle and associated crustal anatexis. U-P, zircon studies allow precise definition of principal age clusters about 3.5, 3.0, 2.7 Gyr and several less well dated episodes, followed by protracted thermal fluctuations in infracrustal high-grade metamorphic zones, interpretations of these events in terms of internal dynamics of the Earth are difficult to reconcile with current understanding of silicate rheology and thermal behaviour in a continuously convecting mantle regime. A triggering of major magmatic episodes by mantle rebound response to intermittent extraterrestrial mega-impacts, postdating the @3.85 Gyr late heavy bombardment of the moon, is required by the frequency/size distribution of the asteroid flux and the cratering history of the moon, and is supported by converging lines of direct and indirect evidence: (1) identification of major impacts from microtektite and distal ejecta horizons marked by iridium anomalies; (2) the temporal relationships between some of these horizons and volcanic activity; (3) The distinctly episodic nature of major Archaean igneous events as identified by precise U-P, zircon age data; (4) geochemical and experimental evidence for deep mande derivation and rapid ascent of diapirs required to generate peridotitic komatiites; (5) considerations based on the major discrepancy between the present-

day volume of continental crust and the volume of sial expected to result from continuous accretion in a plate tectonic regime. The impact history of the Archaean Earth has been largely obscured by (1) outpouring of voluminous basic and ultrabasic lavas, inundating shock-deformed crust and extending beyond the perimeters of impact excavated basins; (2) gravity subsidence and downfaulting of terrestrial maria, accounting for the rare exposure of sub-greenstones basement, and (3) extensive recrystallization and obliteration of impact features in high grade metamorphic terrains. Geochemical and isotopic data suggest a heterogeneous basement, including (a) basic materials whose anatexis gave rise to Na-rich felsic magmas and (b) quartzofeldspathic and anorthositic rocks, evidenced by zircon xenocrysts, giving rise to more fractionated magmas. Isostatic subsidence and anatexis of impact-triggered volcanic piles and of underlying impacted basement would produce comagmatic plutonic and volcanic suites within periods of about 3 0 x 1 y e a r s , controlled by postimpact convection cooling in the underlying mantle. Repeated post-tectonic thermal/magmatic fluctuations occur principally in high grade terrains, possibly reflecting disturbances related to distal impact events. Broad age zonation of Archaean terrains suggests endogenically driven lateral accretion of the maria accumulations according to plate tectonic patterns.

Table 1: W-zone

Central zone

E-zone

FMZ

cumm+hbld+gnt +fsp An 33.46

Mg-rich hbld+ fsp An45

bi+qz+/-cpx+ fsp An38-43

An59-84 cpx+opx+(bi+ amph)

An 50-60 ol+cpx+opx+bi+ (amph)

An

cpx-f(opx)

An52-70

original lithology

anorthosite, minor gabbronorite

olivine-ferrogabbro

gabbronorite, minor anorthosite

mixture?

whole rock geochemistry

tholeiitic

alkaline

tholeiitic

dominantly tholeiitic

metam. mineral cummingtonite + assemblage hornblende relict igneous phases: plagioclase others

Geological Society of Australia Abstracts Number 32, Ballarat 1992

68-80

213

A 7.25

THE BROKEN HILL OXIDISED ZONE W. D. Birch1* and A. van der Heyden2

department of Mineralogy and Petrology, Museum of Victoria, Victoria. ^Minerals Mining and Metallurgy Ltd, Broken Hill, N.S.W. While the oxidised zone of the Broken Hill (NSW) orebodies is recognised as being extremely complex, previous models have been either overly simplified, or confined to selected near-surface gossan exposures. Mineralogical studies have generally been confined to the more spectacular species for which Broken Hill is reknowned. More recent investigation of the oxidised zone in the Kintore and Block 14 Opencuts has revealed considerable mineralogical complexity in previously unrecorded secondary assemblages. These fall into four broad associations, involving over 80 species, some of which are new. These include carbonates and silicates rich in Zn and Cu; phosphates rich in Fe and/or Pb; sulphates of Cu and Zn; and arsenates of Pb, Fe, Cu and Zn (Birch, 1990). Most of the secondary minerals are derived by oxidation of the primary ore in '3 lens', consisting of galena and sphalerite, with minor chalcopyrite and arsenopyriteloellingite in a quartz-spessartine gangue. They occur as crusts or aggregates of microcrystals in seams in garnet sandstone or in etch cavities in quartz-rich lode rocks. Less significant suites occur in vuggy patches of iron- manganese oxides. Mineralogical relationships, particularly in the As-rich association, are often complex, with widespread pseudomorphism,

endomorphism, overgrowths, condensed crystallisation sequences and compositional zonation. Many of the species lie in solid solution series involving up to 5 or more elements, including REEs (Y and Ce). This textural complexity reflects the overall history of the Broken Hill oxidised zone, for which a simple paragenetic model cannot be generated. However, the mineralogy does offer scope for investigating the relationships between temperature, pH and crystal chemistry for selected species, such as the polymorphs mawbyite and carminite (Pring et al., 1989), and the Pb As-dominant members of the alunite- jarosite group. References Birch, W. D., 1990, Minerals from Kintore and Block 14 opencuts, Broken Hill, New South Wales; a review of recent discoveries including tsumebite, kipushite and otavite. Australian Mineralogist, 5(4), 125-141. Pring, A., McBriar, E., and Birch, W. D., 1989, Mawbyite, a new arsenate of lead and iron related to tsumcorite and carminite, from Broken Hill, New South Wales. American Mineralogist, 74, 1377-1381.

A 7.26 INTERACTION OF MAFIC INTRUSIVES WITH METEORIC AND METAMORPHIC FLUIDS, MARY KATHLEEN, QUEENSLAND N.H.S. Oliver*, I. Cartwright, T. Aslund Victorian Institute of Earth and Planetary Sciences, Department of Earth Sciences, Monash University, Clayton, 3168, Australia Geochemically and mineralogically extraordinary metamorphosed scapolitic mafic intrusive rocks are very abundant in the Proterozoic Corella Formation - a metamorphosed evaporite-carbonate sequence in the Mount Isa Inlier. These rocks are important in that the mass transfer involved is a major part of the total mass transfer in a belt of rocks with widespread mineralization. Furthermore, unravelling the history and nature of the mass transfer places important constraints on syn-intrusive and later regional metamorphic fluid migration systems. The metadolerite/metagabbro bodies are characteristically lensoidal in plan, 50 to 1000m wide and up to 5 km long, elongate in the regional Geological Society of Australia Abstracts Number 32, Ballarat 1992

foliation. Dykes are more abundant than sills. Timing criteria and radiogenic isotope data indicate that they intruded at around 1740 Ma, coeval with equally abundant granitoids, some 200 Ma before the regional metamorphism and deformation. In some bodies, the only leucocratic mineral present is sodic Cl-rich scapolite (dipyre); in others the scapolite/plagioclase ratio varies regularly throughout the bodies, with fairly common zonation towards scapolitic margins. The scapolite occurs as folded (early) or planar (late) veins, recrystallized cm-size clumps, and as evenly distributed granularrecrystallized grains. Co-existing with the scapolite and sodic plagioclase are Cl-bearing amphibole with or

214 without Cl-biotite, and sphene with relict ilmenite or magnetite. The most extremely altered samples contain scapolite+ amphibole+sphene only. Overall, scapolite-bearing metadolerites typically contain in excess of 1 wt. % CI, up to 2 % in the most altered samples. The mineral assemblages and the scapolite compositions (typical equivalent anothite content An32, around 3 wt. % CI) indicate that the rocks were in equilibrium with highly saline NaCl-H20-CC>2 fluids during the regional metamorphism and possibly at earlier stages. Observation of fluid inclusions in related quartz veins and comparison with published experimental data suggests that the coexisting fluid had NaCl molalities in excess of 20. Given the amount of chlorine contained in these abundant mafic rocks, interaction between the rocks and evaporitederived fluids appears most likely. Regionally, the metasomatic effects of syn-granite contact metamorphism and later regional metamorphism can be discerned by fairly clear overprinting relations. Commonly scapolitic exo- and endo-skarns are well developed around and within the granites, indicating extensive fluid exchange between the granites and their calc-evaporitic wallrocks during intrusion. For the mafic meta-intrusives, however, it has proven much more difficult to determine the timing of scapolitic alteration. Microstructural data indicate that the growth of scapolite predominantly pre-dated and partly postdated the development of the syn-regional metamorphic foliation. We have conducted whole-rock geochemical and stable isotopic analyses on selected metadolerite bodies to attempt to define the relative roles of syn-intrusive and synmetamorphic hydrothermal activity within these bodies, as it is quite possible that at least some of the mass transfer occurred during an early phase of synintrusive hydrothermal activity. Samples containing plagioclase and Cl-poor amphibole, with rare relict clinopyroxene, show 5 ^ 0 whole-rock values of 5.7 to 6.0%©, typical of unaltered continental tholeiites. With a few exceptions, scapolite-bearing samples have considerably enriched

8 0 values, ranging from 7.0 to 10.1 with the highest values recorded adjacent to zones of intense veining and albitic alteration in the boundary zones with the surrounding metasediments. These values are inferred to represent partial or near-complete equilibration of the dolerites with saline regional metamorphic fluids. Several values to as low as 5 0 3.5%o have been recorded: these also occur in scapolitized rocks but these rocks are not mineralogically distinct from other scapolitic rocks with 8 0 > 7.0%o, and thus reflects a hitherto unrecognised rather cryptic phase of stable isotopic depletion. Whole rock geochemical changes associated with the scapolitization are also large. Intensely scapolitized samples have gained Na, Al, Ca, and CI at the expense of Fe, Mg, Mn and many of the trace elements. However, we cannot presently correlate particular whole rock geochemical shifts with the stable isotopic shifts. For example, one rock with 5 18q = 3.5%o has effectively the same bulk composition as a rock with 5 0 = 7.8%o; likewise rocks with similar isotopic composition may show distinctive geochemistries. Overall, the data suggest two major phases of hydrothermal activity - a syn-intrusive phase which involved interaction of partly meteoric fluids with the dolerites, and a metamorphic phase, both of which probably involved major mass transfer due to the high fluid salinity and fairly extensive fluid/rock interaction. The cryptic nature of the oxygen isotopic depletions suggest geochemical decoupling between oxygen and the chlorides responsible for mass transfer during initial syn-intrusive alteration, or complex overprinting of the early alteration during synmetamorphic alteration. Decoupling is a common feature of mass transfer in a multi-element infiltration system, but our results counter-intuitively suggest that oxygen travels at a slower rate than NaCl in highly saline fluids. Further work is underway! 1 8

1 8

1 8

1 8

POSTER SESSION A 7.27

A NEW PB-AS MEMBER OF THE ALUNITE-JAROSITE FAMILY FROM THE OXIDISED ZONE AT BROKEN HILL, NSW. W. D. Birch Department of Mineralogy and Petrology, Museum of Victoria, Victoria

Pb-dominant members of the alunite-jarosite family of minerals (Scott, 1987) are widespread in the oxidised zone at Broken Hill. They are amongst the earliest formed species, usually occurring as Geological Society of Australia Abstracts Number 32, Ballarat 1992

microcrystalline yellowish to greenish brown encrustations on lode rocks, and upon which later species such as pyromorphite, mimetite, adamiteolivenite and bayldonite crystallise. They are also

215 found in vuggy iron and manganese oxides. The minerals can be described by the general formula PbA 3 (X0 4 )2(OH) 6 , where A is Fe 3 + or Al, and X is As, P or S. While most of the Broken Hill minerals in this family can be given an accepted species name, such as beudantite, corkite or hidalgoite, a new solid solution series has been established, defined by A=Fe 3+ and X varying from As to P, with S virtually absent. The As" endmember is the analogue of philipsbornite (A=A1) and has recently been approved as a new species. It forms yellowish brown

A 7.28

rhombohedral and pseudo-octahedral crystals up to 5 mm high. A full description including the name, will be published late in 1992. References Scott, K. M., 1987, Solid solution in, and classification of gossan-derived members of the alunite-jarosite family, northwest Queensland, Australia. American Mineralogist, 72,178-187.

CHARACTERISTICS OF THE MESOZOIC SHOSHONITE SERIES IN EASTERN CHINA Kerong Chen Department of Earth Sciences, Nanjing University, Nanjing 210008, China

Recent studies have revealed that the shoshonite is an important type of the Mesozoic terrestrial volcanic and widely distributed in the eastern part of China, especially along the Tanlu Fault and the Lower Yangtze fracture zone. According to the studies of shoshonite rocks at Southern Shandong Province, Luzong area and the Lishui basin, it is recognized that the shoshonite in Eastern China possesses not only the general features of, but also some special

characters differing from the typical shoshonite rocks in the other areas of the world. Shoshonite in eastern China includes more acidic-intermediate rocks than mafic rocks, and the alkaline basaltic rocks such as leucite basalt is found. These characteristics are considered as the reflection of a special geotectonic setting which is the combination of a continent margin background and a rift-like pull-apart fracture zone.

A 7.29 DATING THE CRATONIC LOWER CRUST BY SHRIMP: A U-TH-PB ISOTOPIC STUDY ON ZIRCONS FROM LOWER CRUSTAL XENOLITHS FROM KIMBERLITE PIPES Chen Y. D. 1 , O'Reilly, S. Y. 1 , and Kinny, P. 2 1 School of Earth Sciences, Macquarie University, Sydney, NSW, 2109, Australia ^Research School of Earth Sciences, The Australian National University, Canberra, ACT, 2601, Australia We here report first time an U-Th-Pb isotopic study of zircons from a suite of lower crustal (probably also upper mantle) xenoliths from some kimberlitic pipes at Calcutteroo, South Australia by using the ion microprobe SHRIMP established at Research School of Earth Sciences of Australian National University. In particular, zircons from a xenolith of eclogitic composition were first time found and dated. Xenoliths found from the Calcutteroo kimberlitic pipes included spinel lherzolite, eclogite, mafic and quartzofeldspathic granulites with the mafic granulite predominant. The importance of those xenoliths is Geological Society of Australia Abstracts Number 32, Ballarat 1992

that they are extremely rare occurrence of samples of lower crust and upper mantle from a tectonic environment of eastern margin of the Australian Craton. Petrological, geothermobarometric and geochemical studies on those xenoliths (Pearson et al., 1990) have acquired significant information on the composition and stratigraphy of the lower crust and upper mantle of the region but not the timing. Seven mafic to felsic granulite xenoliths were previously dated by whole rock Rb/Sr and Sm/Nd techniques and about 2200 Ma was suggested by the isochron approach as the formation age of those mafic to felsic granulite xenoliths (McCulloch et al., 1982). In the

216 present study, we separated and dated zircons from from the quartzo-feldspathic granulite xenoliths three xenolith types: eclogite (1 xenolith), mafic (1 broadly coincides with the development duration of the xenolith) and quartzofeldspathic (3 xenoliths) Willyama metamorphic complex occurring in South Australia and New South Wales; this indicates that the granulites. Zircons from three quartzofeldspathic granulite distribution of Willyama complex is more extensive than presently exposed and is southwards extended to xenoliths gave bimodal age distribution: 1700-1400 Ma and 600-350 Ma. Zircons from a mafic granulite beneath the region of Calcutteroo. The different, xenolith have ages mostly clustered between 800 and younger ages found in all xenolith types indicate that 700 Ma with subordinate number of spot analyses several later episodes of mantle-derived magma being younger (530-480 Ma). Zircons from the intrusion and regional metamorphism has occurred in eclogite xenolith range in age from 600 to 300 Ma. the region and significantly contributed to the growth The immediate significance of these zircon growth and evolution of the lower crust. ages is that they invalidate the previous Rb/Sr and Sm/Nd isochron ages. It is plainly shown here that References the those different types of xenoliths were not cogenetic in the sense that a whole rock isochron age McCulloch, M. T., Arculus, R.J. Chappel, B.W. and Ferguson, J., 1982, Nature, 300:166can be regressed through them. More importantly, the zircon data indicate that the Pearson. 169 N.J., O'Reilly, S.Y. and Griffin, W.L., formation of lower crust (also upper mantle) of the 1991, Eur J. Mineralogy, 3: 293-322 region is the result of time integration and multipleepisodes. The 1700-1400 Ma age of the zircons found A 7.30 DEEP KAOLINIZATION IN MEDIUM-GRADE MET AMORPHICS OF THE MOUNT LOFTY RANGES, SOUTH AUSTRALIA J.L.Keeling ** S.G.McClure , M.D.Raven and P.G.Self 1

1

2

2

2

Department of Mines & Energy, South Australia CSIRO -Division of Soils, Adelaide 2

Narrow zones of deep kaolinization in amphibolitegrade, metamorphic rocks in the Williamstown area, 50km northeast of Adelaide, are a source of commercial kaolin. Deposits of high-grade ore are mined currently at Williamstown for refractories and at Birdwood for use in white cement manufacture and industrial fillers. The kaolin mineralogy of 4 deposits, Williamstown, Birdwood, Cromer and Springton, was examined as part of an investigation into the nature and origin of the kaolinization. At all deposits, the host rocks show some evidence of metasomatic or hydrothermal alteration. However, Williamstown is the only deposit where metasomatic/hydrothermal processes appear to be directly responsible for kaolin formation. Here, depth of kaolinization exceeds 100m with kaolinite replacing massive sillimanite and, to a lesser extent, Na-rich muscovite and kyanite. Sillimanite replacement is by dissolution and epitaxial growth of pseudo-hexagonal kaolinite crystals which form lath-shaped aggregates elongated parallel to the c-axis of sillimanite. At Birdwood, high-grade kaolin zones are found as irregular bodies within a folded, 30m thick, kaolinized quartz-mica schist. High-grade kaolin ore formed mainly in the hinge zones of open D2 folds and is often associated with remnant sericitic alteration, evidence of pyrite mineralisation and in some areas] Geological Society of Australia Abstracts Number 32, Ballarat 1992

gold-bearing quartz veins. The kaolinite is massive, well-crystalline and comprises sheets of crystal aggregates mixed with coarse crystal stacks. Kaolinization of the schist unit extends below overlying quartzite to depths of 50m. Deep weathering, enhanced by an acidic environment resulting from the oxidation of pyrite, is interpreted as driving the extensive kaolinization. Increased groundwater movement in fractured fold hinge zones, acidic conditions and some tectonic mobilisation of quartz, appear to be important controls in the distribution of high-grade kaolin bodies. The Cromer and Springton deposits are characterised by a high proportion of halloysite in the kaolin ore. The deposits form zones of intense kaolinization within a broad area of weathered schist bedrock. Cromer is a series of discontinuous, steeply dipping orebodies, less than 25m wide, which can be traced along strike for over 1.5km. The narrow kaolin zones contain stringers and pods of coarse rutile, and are cut by thin quartz veins, but there is little evidence of the original, pre-kaolin, mineralogy. The Springton deposits retain a strong schistose fabric and include remnant coarse talc in a matrix of dehydrated halloysite and coarse kaolinite. The kaolin minerals formed mostly by alteration of mica and feldspar and, less commonly, sillimanite.

217 A 7.31

THE PETROLOGY AND GEOCHEMISTRY OF ERUPTIVE VENTS IN THE MONARO VOLCANIC PROVINCE, SOUTHEASTERN N.S.W. I.C. Roach*, K.G. McQueen and M.C. Brown

School of Resource and Environmental Science, University of Canberra, Belconnen, A.C.T. 2616. The Monaro Volcanic Province (MVP) is a Tertiary lava field composed dominantly of alkali basalts, with minor nephelinite, basanite and doleritic flows, erupted from numerous small vents and fissures. Regional and small-scale geological mapping of the province by students and staff from the University of Canberra has revealed more than 55 volcanic plugs and vents between 51 and 34 Ma in age. The plugs range from approximately 10 m to over 50 m in diameter and show varied topographic expression from small, low outcrops to prominient peaks and remnants standing over 100 m above the surrounding basalt plains. One small maar has also been found near the base of the volcanic sequence. Criteria used for distinguishing plugs include shape and form, compositional difference from enclosing basalt, grainsize, the style of jointing and presence of abundant mantle and crustal xenoliths. Eruption sites in the MVP are aligned in linear patterns and appear to have been controlled mainly by major NNW-trending wrench faults and reactivated Ntrending faults in the Palaeozoic basement. Although widely distributed, exposed plugs are concentrated near the center of the province in the area of the present divide. Three large flows of titanaugite-phyric dolerite extend over 400 km 2 in the northern part of the province. These are at three closely spaced levels and represent a useful marker in the volcanic stratigraphy. Several plugs of similar composition have been mapped in the vicinity of these large flows. Many flows within the sequence show deep weathering profiles (some with bauxites) which combined with the spread of ages for the flows and plugs suggests a sporadic style of eruption. Breaks between eruptions may have lasted as long as 3 Ma. Tertiary lacustrine sediments, coals, hyaloclastites and reworked Tertiary gravels are also interlayered with the flows. The plug rocks can be grouped according to mineralogy, the presence and types of contained xenoliths and geochemistry. They include nephelinites, nepheline basanites, alkali dolerites which show aphanitic, porphyritic or gabbroic textures. The main type is a predominantly aphanitic, peridotite-xenolith bearing rock which may be slightly vesicular. Nephelinite plug rocks usually contain glomerophyric or porphyritic olivine and titanaugite in

Geological Society of Australia Abstracts Number 32, Ballarat 1992

a ground mass of euhedral titanaugite, opaques, nepheline, apatite and/or zeolites. Basanite and alkali basalt plug rocks contain similar phenocrysts of olivine and titanaugite together with plagioclase (An50-60) phenocrysts (<5% in basanite, >5% in alkali basalt) in a ground mass with titanaugite, opaques, plagioclase, apatite and zeolites. Mantle xenoliths and xenocrysts are common in the finer grained plug rocks and range from spinel lherzolites (ol>cpx>opx>sp) to dunites and wehrlites. Xenocrysts derived from disaggregated xenoliths take the form of anhedral crystals of olivine, diopside, spinel and hypersthene, the latter normally surrounded by a thick reaction corona of olivine and opaques. Kaersutite is also an important phase in the finer grained plug rocks, occurring in some where there are no other mantle or crustal xenoliths. Crustal xenoliths include 2-pyroxene granulites, granite and vein quartz, indicating sampling at different levels. The mantle xenolith assemblage suggests a relatively shallow magma source at around 40-50 km depth. Doleritic and gabbroic plug rocks have no preserved xenoliths but exhibit similar mineralogy to the finer grained plugs. In some cases, titanaugite phenocrysts in the plugs are rimmed by aegirine, which also ocurs in the mesostasis, consistent with an Na-rich final stage melt. Work to date on the geochemistry of the plug rocks indicates that most are towards the more alkalirich end of the compositional spectrum found in the flows (Fig. 1). Some show marked enrichment in incompatible elements. Larger plugs appear to have undergone some chemical changes related to posteruption, cumulate processes. The MVP as a whole appears to show a continuous trend of compositions from alakali basalts through basanites to nephelinites. REE patterns show intraplate basalt trends, with strong enrichment in LREE and lesser enrichment in HREE relative to chondritic values. K and P contents are typical of apatite-rich alkali basalts. Reference Kesson, S.E., 1972, Basic alkaline rocks. Ph.D. Thesis, Aust. Nat. Univ. Canberra, Unpubl.

218 • •

O Alkali Basalt-AB • Nephelinite Pluc

Basanite - B Basanite Plug

A Nephelinite - N 4 Teschenite Pluc

O

CM

a*

Si02 wt%

A 7.32 SM-ND ISOTOPIC STUDY OF MANTLE-CRUST INTERACTION IN THE HARTS RANGE META-IGNEOUS COMPLEX: IMPLICATIONS FOR THE ORIGIN OF ANORTHOSITES W.J. Sivell * G.E. Mortimer^ and M.T. McCulloch^ 1

faculty of Science and Technology, University of Western Sydney, Nepean, Kingswood 2747, Australia Research School of Earth Sciences, The Australian National University, Canberra 2601, Australia 2

Within the pre-1748 Ma rift-related Harts Range Meta-igneous Complex (HRMC), eastern Arunta Inlier, well-layered leucoamphibolite-anorthosite suites are emplaced at discrete stratigraphic levels.These rocks possess a wide range of £Nd values, ranging from +6.4 to -4.4, and showing an upward stratigraphic progression from high (mantle-like) to lower (crust-like) values. Host HRMC metatholeiites also display systematic isotopic variation from very high £Nd values (ENd = +8.2 to +6.9) in basal amphibolites (reflecting an ultra-depleted mantle source) to lower values (ENd = +6.3 to -1.8) for amphibolites in the upper parts of the sequence. The stratigraphically-controlled shift in Nd-isotopic values for the mafic and felsic suites is accompanied by increasing La/Yb, Ba/Nb, Rb/Nb, La/Nb and K/P ratios, together with decreasing Zr/Nb and Ti/Yb. These compositional changes provide clear evidence of increasing crustal involvement in sequentiallyemplaced HRMC magmas. The HRMC tholeiites assimilated 0-30% lower Geological Society of Australia Abstracts Number 32, Ballarat 1992

crustal components, chiefly by combined assimilationfractional crystallization (AFC)-type processes. Maximum crustal contamination occurred in layered zones where isotopic heterogeneities between mafic and felsic rocks are preserved on less than a metre scale, indicating variable, intimate interaction of crustal and mantle melts. The most contaminated, highly fractionated tholeiites possess very low Zr/Nb ratios (anomalously low Zr) implying that contamination was by moderate to low degree partial melts of sialic crust with residual zircon. Extensive crustal assimilation imparted to these mafic rocks distinctive geochemical signatures thought to characterize plagioclase-rich lower crust residual after granitoid (upper crust) extraction (e.g. high Al, Eu/Eu*, Ab + An and K/Rb, and low Rb/Sr, Rb/Nb). HRMC leucoamphibolites (eNd = +6.4 to 1.6) and anorthosites (eNd = -0.6 to -4.4) represent plagioclase-rich cumulates derived from mantle melts variably contaminated by large degree crustal melts that equilibrated with garnet-bearing lower crustal

219 mineral assemblages. Anorthositic gneisses contain up to 80% of this isotopically evolved (Archaean) crustal component, while leucoamphibolites from lower and upper layered zones (lower in the HRMC sequence) contain 5-20% and > 50% respectively. This is confirmed by the high Sm-Nd model age (2200 Ma) for the anorthosites, which exceeds that of their host amphibolites. The presence of mafic layers in all felsic units, and of ultramafic cumulates in one (multiple intrusive) anorthosite band, indicates that these rocks are at least partly of mantle origin. The mantle component is cogenetic with the highly depleted source of the HRMC tholeiites. Generation of these hybrid magmas took place in large, periodically replenished magma chambers via meltingassimilation-storage-homogenisation (MASH)-type processes. The early Proterozoic HRMC anorthosites (-leucoamphibolites) show features akin to both mantle-derived Archaean stratiform anorthosite complexes (e.g. presence of interlayered ultramafic cumulates and plagioclase with An 65-90) and typical mid-Proterozoic massif-type anorthosites of probable lower crustal origin (e.g. clear isotopic evidence for massive crustal involvement in upper units and some Fe Ti oxide, V and P-rich layers). They represent a transitional style of anorthosite-producing magmatism which progressed from increasing crustal contamination of mantle-derived melts (lower leucoamphibolites) to bulk mixing of mantle magmas with (dominant) lower crustal melts (upper anorthosites). Their (likewise progressively contaminated) host HRMC tholeiites were sourced in ultra-depleted upper mantle that must have evolved in long-term (-1 Ga) convective isolation during the late Archaean. Like the preservation of this ultra-depleted A 7.33

mantle source, the change from mantle to crustdominated magmatism recorded in the HRMC anorthosites (i.e. a transition from Archaean-style to more Proterozoic-style anorthosite genesis) reflects mantle geodynamic and crustal growth conditions unique to the Archaean-Proterozoic boundary. The HRMC tholeiites formed in an ensialic backarc setting. They are closely analogous to "continental" basalts from the Columbia River Plateau erupted in an ensialic setting behind the Cascade arc. Isotopic signatures of the Harts Range anorthosites and amphibolites provide the first evidence for pre-rift Archaean sialic basement in the eastern Arunta Inlier. At the onset of HRMC rifting, small volume, lowdegree (10%) mantle melts (lower amphibolites) possessed insufficient heat to extensively melt the intruded crust so that mantle isotopic values were largely preserved in mafic magmas, while the isotopic compositions of early-formed felsic cumulates indicate unsustained, erratic mixing of basalt magma with only small amounts of crustal melt. By contrast, large volume, higher degree (initially more magnesian) partial melts of the mantle (upper amphibolites) in the more mature rift readily assimilated fusible crustal components. A major sustained transition from ACF to MASH-type processes took place when a thermal regime conducive to extensive lower crustal melting was established, partly in response to high magmatic flux and crustal pre-heating in the back-arc regime. This facilitated bulk mixing of mantle and crustal magmas, and major anorthosite production. Ridge subduction or sinking of a detached lithospheric slab possibly perturbed asthenospheric convection, changing the thermal structure in the supra-subduction zone upper mantle wedge.

ORIGIN OF SAPPHIRE IN EASTERN AUSTRALIAN BASALTS: INFERRED FROM INCLUSION STUDIES J.F. Guo , S.Y. O'Reilly and W.L. Griffin 1

1

2

1 School of Earth sciences, Macquarie University, NSW 2109 Division of Exploration Geoscience, CSIRO, North Ryde, NSW 2113

2

Sapphires (gem-quality corundum) are associated with Cainozoic basalts and their equivalent pyroclastic rocks in Eastern Australia. Economic deposits of sapphire have resulted from the weathering of these basalts and pyroclastic rocks with subsequent alluvial and diluvial concentration, e.g., the Inverell-Glen Innes region of NSW, the Anakie-Rubyvale region of central Queensland and the Lava Plains of northeastern Queensland. The heavy mineral concentrate from the present-day alluvial deposits cutting through basaltic lavas and/or pyroclastic sequences in the Inverell- Glen Geological Society of Australia Abstracts Number 32, Ballarat 1992

Innes region mainly consists of sapphire, zircon, spinel and ilmenite with so-called "ironstone" also present. This heavy mineral association is almost a duplication of the "non-cognate" megacryst suite in the nearby alkalic basaltic rocks, comprising feldspar, Mg-Fe spinel, ilmenite, zircon, apatite and corundum. Sapphire occurring in basalts is apparently not in equilibrium with the host rock and commonly shows reaction with the magma, resulting in etched and rounded surfaces and sometimes with a thin rim of black spinel. It often shows igneous characteristics:

220 strong growth zoning parallel to the C-axis and complex intergrowths of euhedral crystals. Other minerals may have also grown along with sapphire such as anorthoclase, Na-rich pyroxene, biotite, apatite, zircon, ilmenorutile and columbite (Stephenson, 1976; Aspen et al., 1990; this study). In the present study, more than a thousand individual sapphire fragments from areas worldwide (including eastern China and Thailand) have been examined for inclusions. The recognized mineral inclusions through the application of electron microprobe and proton microprobe include zircon, albite, sulphide, spinel, Kfeldspar, columbite, pyrochlore and some U-, Th- and REE-rich minerals. It appears that columbite, albite and zircon are the most common mineral inclusions in sapphires from basaltic terrains. Preliminary analyses of columbites showed that they are of very distinctive compositions: high TiC>2, low MnO and Ta205, low but constant MgO. Comparisons of these data with columbites occurring in granites and granitic pegmatites (low TiC>2, variable MnO and Ta205 and non-MgO) formed a sharp contrast. Precise proton microprobe analyses of zircon inclusions also exhibited distinctive features: high U, Th, Hf and Y, making it distinguishable from zircons in kimberlites, basalts, granitoids and from alluvial zircons which were the, previously-believed, indicator minerals in prospecting sapphire. U-Pb dating of the zircon inclusions using the SHRIMP ion probe shows a constant relationship between the apparent ages of zircon inclusions in sapphires and the age of the basalt A 7.34

from which sapphires were recovered. It also showed that within each basaltic provinces, the U-Pb age of zircon inclusion are not distinguishable from the ages of the basaltic eruption interval. However, the real timing of zircon crystallization may be much older than the determined values (Guo et al., in preparation). The mineral inclusions and their unique compositions provide constraints for the chemical environment of the original source of the sapphire and are strong evidence against the hypothesis that the host corundum might have crystallized out of basalts at high pressure. It is envisaged that the host corundum may be formed through the interaction between a quite evolved composition and silicaundersaturated magmas, carbonatitic or very mafic (?). The present host basalts represent volatile-rich alkalic magmas which ascended rapidly to the Earth's surface, providing a suitable transport mechanism for the heavy, deep-seated corundum. As a result, corundum may be found in both basaltic lavas and the relevant pyroclastic sequences. References Aspen, P., Upton, B.G.J. & Dickin, A.P., 1990, Eur. J. Mineral 2: 503-517 Guo, J.F., O'Reilly, S.Y., Griffin, W.L. & Kinny, P., 1991 (in preparation) Stephenson, P.J., 1976, Abstracts of the 25th International Geological Congress, 2: 602-603, Sydney

A STUDY ON QUANTITATIVE CRYSTAL OPTICS Zhu Zhongyi

Department of Geology, China University of Geosiences(Wuhan),Wuhan,P.R.China Quantitative crystal optics is a branch of crystal optics which studies the law of qyantitative changing of crystal optic parameter (brightness and color etc.) under different polarization sets. Based on law of crystal optics: A =OB *sin [2(a)*sin (R*7C/X)...[l]; I=K*A [2]; where A is amplitude under cross polarization; OB is radius of max-amplitude; a is angle between upper and lower Nicol; R is aberration; X is wave length of incident light; I is brightness; K is a coefficient of brightness. Under cross polarization,when section of crystal is 2

2

2

2

2

Geological Society of Australia Abstracts Number 32, Ballarat 1992

rotating a cycle image are four blacks. Actually,when long axis or short axis of ellipse of indicatrix parallel upper Nicol or lower Nicol,there is a brightness; is not all black. If angle between long axis of ellipse and Nicol is considered, [l],[2]can change as follows: I=K*OB *sin 2(a-f^)*sin (R*7i/X)+V...[3]; 2

2

2

where I is general brightness; K is a coefficient of brightness; OB is radius of max-amplitude; a is a rotating angle; ¥ is an angle between long axis of ellipse and Nicol of E-W; R is aberration;

221 X is RGB general wave length; V is a brightness of background, move item, I-V=K*OB *sin 2(a+^)*sin (R*7c/X); roots, I-V=K*OB*sin(2a+2 F)*sin(R*7i/X); If I-V=Y, and sin(R*;c/X) is no change, so general amplitude A is K*OB*sin(R*n/X); then have: Y=A*sin(2a+2¥) [4]; change form, Y=a* sin2a+b*cos2 F [5]. This formula is basis of measurement of optical fabric analysis. If we measure many values of brightness and rotating angle on table,we can calculate angle between long axis of ellipse of indicatrix and E-W axis,and maximum general amplitude.Because, tg(2Y)=b/a,so ¥=0.5arctg(b/a) [6]; A= ( a+b) ' , so A =a +b [7]. Opcical fabric instrument is based on formulae 2

2

2

x

v

1 2

2

2

2

Geological Society of Australia Abstracts Number 32, Ballarat 1992

[5],[6],[7]. For example,fabric analysis operating is: 1)in 0°,120°,240° gain three scanning images 2)insert the plate then in 0°, 120°,240° gain three scanning images 3)rotating E-W axe of universiral stage 30° in 0°, 120°,240° gain three scanning images 4)insert the plate then in 0°, 120°,240° gain three scanning images Analysis of 12 scanning images, uniaxial indicatrix can be claculated.. References William,D.Nesse, 1986,Introduction to Optical Mineralogy, New York :p38 David Shelley, 1985,Optical Mineralogy (second edition),Elsevier: 106-117 Emmons,R.C.,1943,The Universal Stage, Geological Society of America Memoir 8 :p205

222

SEE WORMALD, PAGE 134 FOR ACCOMPANYING TEXT

median frogment size ( ^ t Leyshon breccio)

3 tooo

m o n pipe breccia (43-102m)

L(G,S,D,M,E,P) Mr. Leyshon breccia (GRANITE RICH)

*m

9

M t Leyshon breccia (MAIN PIPE BRECCIA RICH)

A

( Lore Dyke)

L(G,M,D,E) L(M,S,D,G) I (G,M) L(G,S,D,M) Mr Leyshon L(G) (GRANITE RICH) L(G) + L(G,D)

KEY A-late dyke T - t u f f l s l t e dyke PPIV-porphyry phase IV L-Mt.Leyshon breccia E - e a r l y dyke M-maln pipe breccia O-dolerlte G-granlte S-metasedlment

Figure 1. Schematic east-west cross-section. Note: 1. The three main components of the breccia complex, basement (metasediment, granite, rhyolite and dolerite dykes), main pipe breccia and an interactive magma/breccia sequence (porphyry phases I-IV, Mt. Leyshon, Mt. Hope and tuffisite dyke breccias, early and late dykes). 2. position of drill-hole MLD 227 illustrated in Fig. 2. 3. for the sake of clarity syn to post breccia faults are not shown. 4. steeply dipping, chaotic antler-like geometry of the main pipe breccia. 5. complex variation and gradation between main pipe breccia sub-facies. 6. gross textural differences between Mt. Leyshon and Mt. hope breccias compared to the main pipe breccia 7. interfingering and intrusive nature of the tuffisite dykes. 8. largely in situ basement blocks.

(M.S) fragment types, In decreasing order Contacts Intrusive igneous intrusive breccia G i fM r n L ( M G,D,

Mr Leyshon br«ccia (MA,NP,PE:

S,E)

BRECCIA RICH)

L(M,G,S,E)

LIM.D.G) "Rl — LIM)

Figure 2. Graphic log of inclined drill-hole, MLD 227. Note: 1. diagram represents a diamond drill-hole, inclined at 50 degrees towards the east. 2. fragment size variations are only shown for zones of Mt. Leyshon breccia (represented by a darkened background) and tuffisite dykes (stippled). 3. larger blocks of granite, dolerite and main pipe breccia have suffered only limited transport.

223

A8: STRUCTURAL GEOLOGY CONVENOR: VINCE MORAND A 8.1

FRACTALS IN GEOLOGY

Bruce E. Hobbs* and Alison Ord CSIRO Division of Geomechanics, P.O. Box 54, Mt Waverley Vic 3149, Australia Two important observations concerning the geometry of rock masses, namely, an element of irregularity that suggests description in terms of statistical parameters, and scale invariance, which means that the geometry can be repeated at a number of scales, are the hallmarks of the fractal nature of such structures. If one views rock systems as fractal objects then their irregularities and somewhat chaotic orientation patterns and spatial distributions are seen as resulting from well defined rules of fractal geometry that have their origins in well founded physical laws. The irregularity and scale invariance follow directly " X

COn y = z

from the physical processes that formed the rock in the first place or were responsible for its subsequent metamorphism. The three dimensional geometry of rock systems is accurately reproduced using the iterated function system (ifs) concepts introduced by Barnsley and Demko (1985). Such concepts have been explored in depth for two dimensions in Barnsley (1988), but the concepts are readily extended to three dimensions. In this approach the rock geometry is represented by a system of affine transformations which have the form

• ll

a

12

a

13

" X "

a

21

a

22

a

23

y

- 31

a

32

a

33 -

z

a

a

tl

+ h

Lt J 3

(11=1,2, ..., N) where each affine transformation is applied to map space into itself according to specified probabilities. Suitable forms of the coefficients produce geometries which duplicate those of natural rock systems. An example is given in Figure 1 where seven affine transformations have been used to generate a complicated fold system. Many of the attributes of natural fold systems are present here including commonly observed irregularities in layer thickness. The development of fractal geometry in structurally complex rock masses arises from the interaction of processes during deformations that are described by at least three differential equations namely, the laws of motion, the constitutive equation describing the deformation process and the flow rule. Conditions under which perfectly regular as opposed to fractal geometries form are discussed together with the

Geological Society of Australia Abstracts Number 32, Ballarat 1992

relationships between the physics of these processes and the form of the ifs codes. The approach can be extended to describe the geometries of all natural rock systems and other examples are presented which duplicate joint and lineament systems, ore grade distributions and metamorphic microstructures. References Barnsley, M.F. (1988). Fractals Everywhere. Academic Press, 396 pp. Barnsley, M.F. and Demko, S. (1985). Iterated Function Systems and the Global Construction of Fractals. Proc. Roy. Soc. Lond., A39, 243-275.

224

Figure 1. Fold system produced by 7 affine transformations.

A 8.2

STRESS AND STRAIN ASSOCIATED WITH A FAULT EMBEDDED IN A DUCTILE MEDIUM Terence D. Barr* and Gregory A. Houseman

Department of Earth Sciences, Monash University, Clayton, Victoria, 3168

Most studies of deformation associated with faulting assume that the crust is a brittle, elastic medium containing one or more discrete faults. As the medium deforms, elastic strain increases until slip occurs on one of these faults. This approach is valid for deformation in the upper crust on short timescales, but fails below the brittle-ductile transition where much of the deformation that occurs is ductile. Also, on timescales of thousands to millions of years, deformation in the upper crust can extend hundreds of kilometers away from major faults; the entire crust is, in effect, deforming ductilely at these timescales. Therefore, the study of a fault in a ductile medium has many important geologic applications. We look in detail at the behavior of an externally stressed ductile medium in which a discrete fault is embedded. The two goals of this paper are 1) to look Geological Society of Australia Abstracts Number 32, Ballarat 1992

at the deformation of the material in the vicinity of the fault and the consequent deformation of the fault itself, and 2) to examine the manner in which a fault propagates into a ductile medium. We develop here a finite element model of a two-dimensional non-linear viscous medium with the embedded fault represented as an internal boundary. The fault is given a yield criterion, and the boundary conditions on the fault are adjusted in an iterative manner to correspond to the fault being locked or unlocked. This model allows for large strains (>100%) and a variable fault geometry. With increased deformation, strain is localized around the fault and in particular at the fault tip. This localization in strain increases with an increase in the non-linearity of the viscous rheology. The actual partitioning of strain between the ductile deformation of the bounding medium and slip along the fault

225 depends on the strain rate of the system and the yield criterion of the fault; with higher strain rates or a

A 8.3

lower yield criterion, more of the strain occurs as slip along the fault.

EXPERIMENTAL MODELLING OF TRANSCURRENT SHEAR ZONES AROUND RIGID BODIES L. B. Harris Department of Geology, University of Western Australia, Nedlands 6009 WA.

Experiments have been carried out to investigate the development of shear zones around rigid bodies in order to draw comparison with both the evolution of "mobile belts" around cratons and shear zone formation around granitoid bodies in granitegreenstone terranes. Models consisted of a 1 cm thick sand layer (upper, brittle crust) overlying silicone putty (lower, ductile crust); with both being supported isostatically on a bath of honey. "Rigid objects" were formed by the addition of a thin additional sand layer in localised areas. The models were subjected to uniaxial compression by an advancing plate attached to a stepper motor controlled screw-jack. A strain rate of 1 cm/h was used, with experiments lasting up to 8 hours. Experiments were carried out with both free and partially constrained margins. Conjugate shear zones developed in the sand layer, initiating tangential to rigid bodies, along with zones of reverse and thrust movements onto the bodies at a high angle to the shortening direction.. Through-going transcurrent shear zones were developed where a clear path was possible around the rigid objects, thereby varying slightly the angles between conjugate sets from that found in isotropic media. En echelon folds, rotating into parallelism with the displacement direction in high strain zones, develop in underlying silicone layers. Changes in the vertical component along transcurrent shear zones without a substantial change in strike were observed due to differences in the relative positions of rigid bodies. Uplift occurs when a line between the centres of two bodies makes a small angle with the maximum compression direction, with extension developed between two bodies aligned perpendicular to the shortening direction. As one body

Geological Society of Australia Abstracts Number 32, Ballarat 1992

is translated past another along a transcurrent shear zone, changes from transpression to parallel wrenching to transtension can be observed. Geologically therefore, several deformation "phases" and structures in both tensile and compressive regimes may form and mutually overprint each other within a single deformation event. Where the density contrast between sand and silicone layers was lowered by the addition of ethyl cellulose to the sand, shear zones initiated around the rigid objects but at a late stage, some shear zones cut across the bodies. Whilst uplift took place in addition to transcurrent motion along a shear zone of constant strike away from a rigid body, no vertical component was seen where the shear zone cut the body. From these experiments, it can be seen that: (i) a complex network of anastomosing shear zones develops during regional compression, with a large variation in the angles made by shear zones to the bulk shortening direction; (ii) shear zones nucleate along the margins of rigid bodies; (iii) large changes in the vertical movement component can occur within a transcurrent shear zone due to the proximity of rigid bodies or where a structure cross-cuts bodies of different composition; (iv) these models provide an understanding of progressive deformation within shear zones, indicating the extreme changes in deformation regime with time for a given locality due the movements of adjacent bodies; (v) a study of analogue models can aid the interpretation of field and aeromagnetic data and provide insights into the localisation of dilatant zones as an aid mineral exploration.

226 A 8.4

CONTROLS ON FLUID PUMPING DURING DEFORMATION Alison Ord and Nick Oliver 1

2

CSIRO Division of Geomechanics,Victoria ^Department of Earth Sciences, Monash University ,Victoria J

The dynamic nature of earthquakes is easily comprehended when the earth's surface ruptures. However, although an association between episodes of fault slip and hydrothermal vein systems is recognised (Sibson, 1987, 1989), the dynamic nature of the rock deformation/fluid flow interaction is not well understood in detail. Conceptually, seismic and dilatancy pumping are dynamic mechanisms for moving fluids around according to differing stress regimes, and therefore patterns of contours of hydraulic head, changing as deformation of the heterogeneous body of rock continues (Sibson et al., 1975; Etheridge et al., 1983 Cox and Etheridge, 1989; Oliver et al., 1990) However, it is important to emphasize here that the above authors have addressed the role of pore fluid pressure rather than hydraulic head in their discussions. We aim here to address specific aspects of this problem by the use of numerical modelling techniques in examining the behaviour of various physical models in a fully coupled fluid flow-deformation system. Initial models include dilational jogs and high-angle reverse faults with and without imposed gravity. More complex models are aimed at describing the rapid and extreme perturbation of head at one point at depth in homogeneously permeable crust with initial quasi-static fluid, and then with a fault plane extending from the surface to the base of the model. The next stage is to impose these designs on a crust of inhomogeneous permeability and dynamic fluid flow. 'Movies' of the instantaneous stress regime, volume change and fluid flow, and of the finite volume change and fluidflowdemonstrate the dynamic A 8.5

nature of these interactive phenomena. The aim here is to test the models proposed for understanding the association of earthquakes and goldbearing quartz vein deposits in a rigorous manner, and to constrain the time and length scales of metamorphic fluid flow in mid-crustal rocks. References Cox, S.F. and Etheridge, M.A. (1989). Coupled grain-scale dilatancy and mass transfer during deformation at high fluid pressures: examples from Mount Lyell, Tasmania. Journal of Structural Geology, 11: 147-162. Etheridge, M.A., Wall, V.J. and Vernon, R.H. (1983). The role of the fluid phase during regional metamorphism and deformation. Journal of Metamorphic Geology, 1: 205-226. Oliver, N.H.S., Valenta, R.K., and Wall, V.J. (1990). The effect of heterogeneous stress and strain on metamorphic fluid flow, Mary Kathleen, Australia, and a model for large scale fluid circulation. Journal of Metamorphic Geology„ 8: 311-331. Sibson, R.H., Moore, J. and Rankin, A.H. (1975). Seismic pumping - a hydrothermal fluid transport mechanism. Journal of the Geological Society of London, 131: 653-609. Sibson, R.H. (1987). Earthquake rupturing as a mineralising agent in hydrothermal systems. Geology, 15: 701-704. Sibson, R.H. (1989). High-angle reverse faulting in northern New Brunswick, Canada, and its implications for fluid pressure levels. Journal of Structural Geology, 11: 873-878.

ANTARCTICA, TWO SUPERCONTINENTS, A HANDFUL OF OCEAN BASINS, AND A BUNCH OF TERRANES Ian W. D. Dalziel , and Eldridge M.,.Moores 1

1

2

Institute for Geophysics, University of Texas, 8701 Mopac Boulevard, Austin, TX 78759-8397 Geology Department, University of California, Davis, CA 95616-8605.

Given its position as the keystone of the Gondwana supercontinent, even a global view of the Antarctic continent has tended to be somewhat selfcentered. Serious consideration of the idea that North America and East Antarctica/Australia were contiguous in the late Precambrian changes that situation irrevocably. Geological Society of Australia Abstracts Number 32, Ballarat 1992

The enigmatic Transantarctic Mountains may represent the thermally rejuvenated margin of a Neoproterozoic rifted continental boundary, and the Ross embayment may have originated as a failed rift system at that time. The late Precambrian Beardmore orogeny and the Cambrian Ross-Delamerian orogeny may reflect oblique separation of a major continent

227 (?Laurentia) even as Gondwana amalgamated along Neoproterozoic to Cambrian sutures. Alternatively, the Ross-Beardmore orogens may be extensions of the collisional Gariep orogen of Namibia-South Africa. The "outboard" terranes of the Transantarctic Mountains and the allochthonous terranes of North Victoria Land and southeastern Australia could have originated during conversion of the rifted margin into a convergent one, after initiation of the Pacific Ocean basin. Distinction between the East Antarctic/Australian and Laurentian trilobite faunas could be explained by rapid spreading in the Pacific while Iapetus (between Laurentia and South America) remained narrow. Paleomagnetic data indicate that the Pacific was 9,000 km wide by the end of the Cambrian, while the proto-Appalachian and protoAndean margins were a maximum of 1,700 km apart. Between the Cambrian and the end of the Paleozoic A 8.6

Laurentia made an "end run" around South America while Gondwana oscillated over the South Pole. Break-up of the Gondwana supercontinent, whether plume-driven or not, for the most part followed Neoproterozoic sutures. The opening of the Southwest Indian and South Atlantic ocean basins are almost a mirror image of the proposed opening of Iapetus and the Pacific in the early Paleozoic, perhaps reflecting the influence of deep cratonic keels. Separation of minor continental fragments such as Madagascar, the Falkland Islands block, and the Ellsworth-Whitmore block follow patterns similar to those suggested for the displaced late Precambrian to early Paleozoic terranes. The Scotia arc between Antarctica and South America forms a model for the initiation of arc magmatism in the embryonic Pacific and Iapetus ocean basins following the amalgamation of Gondwana.

THE POSSIBLE ROLE OF FLEXURAL-SLIP FOLDING MECHANISM IN THE DEVELOPMENT OF NATURAL CHEVRON FOLDS FROM THE BENDIGOCASTLEMAINE AREA, VICTORIA T.J. Fowler * & C.N. Winsor Geology, La Trobe University College of Northern Victoria, PO Box 199, Bendgio, Victoria, 3550

The Bendigo-Castlemaine goldfields are located in a north-trending belt of strikingly continuous chevron folds in thinly-bedded Early to Middle Ordovician turbidites. These folds present an opportunity to investigate the role of flexural slip in the development of chevron folds and to compare our conclusions with those of others involved in examining this problem (e.g. Chappie & Spang 1974, Johnson & Page 1976, Behzadi & Dubey 1980, Tanner 1989). Well-exposed examples of folds were examined for bedding parallel slip planes identified by bedding parallel laminated quartz veins showing fold axis (approx.) normal fibres or fibre casts, or bedding surfaces showing striated slickensides or brecciation. No duplex structures were found. The bedding slip planes ("movement horizons" or Tanner 1989) were found to be irregularly and sometimes widely spaced (1 cm to > 20 m apart), longitudinally discontinuous (typically traceable for only a few tens of metres parallel to the fold axes) and typically thin (mms to a few cms thick - the thicker "bedding veins", "legs" and "backs" are rare in comparison). The detailed location of slip planes is stratigraphically controlled in the same manner described by Tanner (1989) and they show greater degree of discontinuity than lithological units. Slip directions are typically roughly normal to the fold axis but include some anomalous orientations. The small total area of slip plane and the narrow Geological Society of Australia Abstracts Number 32, Ballarat 1992

width of the veins along them suggests that the overwhelming majority of these slip surfaces represent minor flexure slip components developed late in the folding history. The anomalous slip directions may related to late stage reactivation. The slip planes are most common nearest the hinge and may be folded in the hinge zone. We suggest that these surfaces formed as a result of increased shear strain rates at incompetent - competent layer boundaries accompanying fold shape modification particularly at the hinge during fold development. The fold shape may have changed from concentric to chevron or conjugate to chevron as suggested in the models of Johnson & Honea (1975). Relicts of earlier conjugate fold median segments are rarely preserved as low amplitude gentle folds between steeply dipping planar limbs. The much rarer thick bedded-veins (backs and legs) associated with later saddle and neck reef may have formed at an earlier stage of folding or may even proceed folding since they are more continuous and traceable across fold hinges. References Behzadi, H. & Dubey, A.K. 1980. Variation of interlayer slip and time during flexural folding, J. struct, geol 2, 453-457. Chappie, W.M. & Spang, J.H. 1974. Significance of

228 layer-parallel slip during folding of layered Johnson, A.M. & Page, B.P. 1975. A theory of concentric, kink and sinusoidal folding and of sedimentary rocks. Geol. soc. am. bull. 85, monoclinal flexuring of compressible elastic 1523-1534. multilayers, Part IV. Tectonophysics 33, 97Johnson, A.M. & Honez, E. 1975. A theory of 143. concentric, kink and sinusoidal folding and of monoclinal flexuring of compressible elastic Tanner, F.W.G. 1989. The flexural slip mechanism. J. struct, geol. 11, 635-655. multilayers, Part III. Tectonophysics 27,1-38. A 8.7

STRAIN DISTRIBUTION AND FOLD INTERFERENCE IN OBLIQUE CONTRACTION: COBAR BASIN John V. Smith* and Brian Marshall

Department of Applied Geology, University of Technology - Sydney, Broadway, N.S.W., Australia. Smith (1991) developed a qualitative model of DI The Cobar Basin, according to Glen (1985, 1990), was inverted in an oblique contractional folding based on experimental work with wet tissue (transpressional) regime during the late Early paper which suggested convergence at 60° to the Devonian. Three major structural zones were margin rather than the 30° suggested in previous work recognised in terms of the varying intensity, geometry (Glen, 1990). These experimental results have been and orientation of structures. In the regional Di analysed quantitatively to demonstrate the patterns of event, Zones 1 and 2 underwent NE-SW compression strain in coherent obliquely convergent deformation of but experienced different kinematic histories due to layered material above a detachment. A distinct, but partitioning of deformation. Zone 1, along the eastern coherent, boundary between high strain adjacent to the edge of the former basin, suffered high strain and margin (comparable to Zone 1) and low strain away developed a positive flower structure above a basement from the margin (comparable to Zone 2) is shown to wrench fault, whereas Zone 2 (to the west of Zone 1) be a natural consequence of this style of deformation underwent low strain and shortened parallel to the be imposed on layered materials. compressional direction above a flat detachment. Glen In further experiments orthogonal shortening was considered that the Myrt Fault, or the axis of the Myrt applied normal to the earlier displacement direction. Syncline where the Myrt Fault is blind, forms an Strain distribution in the first phase of deformation abrupt boundary between Zones 1 and 2. controlled the fold interference resulting in a pattern Detailed investigation across western Zone 1 and analogous to that observed in the Cobar region. eastern Zone 2, in the region north of CSA mine Glen (1991) noted that all the major mineral where the Myrt Fault is not emergent, has shown that deposits in the Cobar district, except Elura, occur in there is no abrupt boundary. Rather, Di fabric Zone 1 indicating a strong influence of contractional elements vary progressively, both in orientation and structures on mineralisation. As the structural zones intensity (decreasing from east to west), over a few are slightly oblique to the basin trend the major kilometres. This suggests that Zones 1 and 2 are deposits, including Elura, lie near the eastern margin coherent and should be kinematically compatible of the basin indicating the influence also of basinduring the Di event. On a larger scale, coherent forming processes on mineralisation. behaviour is supported by the non-emergence of much of the Myrt Fault. The implications of coherence References between Zones 1 and 2 are that strain must vary smoothly across the boundary, that the boundary is Glen R.A. 1985, Basement control on the deformation not a strain discontinuity and that substantial strikeof cover basins: an example from the Cobar district in the Lachlan Fold Belt, Australia. Journal slip motion on the Myrt Fault is insupportable. of Structural Geology, 7: 301-315. Interference patterns resulting from fold R.A. 1990, Formation and inversion of superposition during D change progressively from Glentranstensional basins in the western part of the distinct variation of bedding strike in Zone 1 and Lachlan Fold Belt, Australia, with emphasis on eastern Zone 2 to dome and basin folding in western the Cobar Basin. Journal of Structural Geology, Zone 2. This change is a consequence of the Di strain 12: 601-620. distribution. In the east, F! folds are tight and the Glen R.A. 1991, Inverted transtensional basin setting redistribution of minor Fi folds around steeply for gold and copper and base metal deposits at plunging F2 folds was recorded. Cobar, New South Wales. BMR J. Aust. Geol. 2

Geological Society of Australia Abstracts Number 32, Ballarat 1992

229 Geophys12: 13-24. Smith J.V. 1991, Kinematic modelling of oblique

A 8.8

divergence and convergence: Cobar, Australia. Tectonophysics, in press.

AGE RELATIONSHIPS BETWEEN GRANITE INTRUSION, METAMORPHISM, AND DEFORMATION IN THE MOUNT ISA INLIER K.A. Connors * and R.W. Page 1

2

department of Earth Sciences, Monash University, Clayton, Victoria 3168 Bureau of Mineral Resources, Geology and Geophysics, Canberra, ACT 2601

2

The Sybella Batholith forms an extensive granitic complex in the western Mount Isa Inlier and intrudes early Proterozoic metavolcanic and metasedimentary units of the Haslingden Group and older basement gneisses. The batholith and country rocks have been metamorphosed, multiply deformed, and metasomatized during a complex tectonic history. Previous U-Pb geochronology studies of zircon from the Sybella Batholith using conventional techniques resulted in two distinct age groups: 1671±8 and 1668+ -21 Ma in the two northern plutons and 1610±10 Ma for the southern Queen Elizabeth Pluton (Page & Bell 1986). The present study involved reanalysis of the original sample from the Queen Elizabeth Pluton and a second sample from this pluton using the SHRIMP ion microprobe (Research School of Earth Sciences, the Australian National University). Both metagranite samples produced concordant results (1655±4 Ma and 1660±5 Ma - error 95% confidence level) which unequivocally document the igneous crystallization age of this metagranite. This is in good agreement with the previous conventional U-Pb age of the northern plutons and suggests that all three plutons of the batholith are the same age. Zircons from two pegmatites, one that is overprinted by E>3 deformation and a younger one that postdates deformation, were also analysed. Both pegmatites contain high-U zircon populations that have complex U-Pb systematics as a result of alteration and Pb loss. From the older pegmatite, a concordant group of zircon analyses defines an age of 1554±10 Ma which we interpret as the age of pegmatite emplacement. The majority of data for the younger pegmatite is highly discordant and indicates multi-stage Pb loss. However, replicate analyses of a few less altered zircon grains are near concordant, and cluster in 2 0 7 2 0 6 with an apparent age of 1500±30 Ma. This is interpreted as a minimum age for pegmatite emplacement. These ages indicate that neither pegmatite is genetically related to the Sybella 26

a

P 5 /

P 5

Geological Society of Australia Abstracts Number 32, Ballarat 1992

Batholith. These new age determinations provide some constraints for the timing and duration of deformation and metamorphism in the Mount Isa Inlier. The older pegmatite, dated at 1554 Ma, is overprinted by intense development of S3 and L3 and has quartz microstructures (i.e. relict granoblastic textures overprinted by grain boundary migration) that demonstrate annealing followed by further deformation, therefore indicating emplacement pre-(to syn)-metamorphism. Timing relationships with respect to D2 are obscured by D3 , however pegmatites of similar mineralogy are folded by F2, therefore suggesting that the 1554 Ma pegmatite intruded pre-D2. Furthermore, the structural and metamorphic evidence for progressive deformation indicates that the metamorphic peak (sillimanite facies to partial melting) was reached soon after D2 and that D3 faulting and shearing followed quickly (Connors & Lister submitted). Therefore, even if the pegmatite postdates D2 it is unlikely to be significantly younger. In this latter case, it is likely that the pegmatite was emplaced near the peak of metamorphism as the result of partial melting related to the high heat flow during this event. The undeformed, younger pegmatite provides a minimum age of roughly 1500 Ma for the end of regional metamorphism and deformation. Thus at least the metamorphic peak, D3 and subsequent deformation phases occurred between 1554 and -1500 Ma, however if the older pegmatite is overprinted by D2 then prograde metamorphism (and D2) also occurred within this period of roughly 54 Myr or less. This interpretation agrees with previous Rb-Sr and K-Ar studies which document the cooling/uplift history. The evidence outlined above demonstrates that regional low pressure-high temperature metamorphism and associated deformation occurred more than 100 Myr after emplacement of the Queen Elizabeth Pluton and the rest of the Sybella Batholith. Thus the pluton was not emplaced during this regional period of crustal a

a

a

a

a

230 shortening as postulated by Page & Bell (1986) based on previous geochronology results, nor did it contribute to the high heat flow during low pressurehigh temperature metamorphism. Age relationships instead suggest that the entire batholith was emplaced during extension and rift-related sedimentation and felsic volcanism as proposed by Wyborn et al. (1988). A 8.9

References Connors, K.A. & Lister, G.S. submitted to Journal of Structural Geology. Page, R.W. & Bell, T.H., 1986, Journal of Geology 94, 365-379. Wyborn, L.A.I., Page, R.W., & McCulloch, M.T., 1988, Precambrian Research 40, 509-541.

GEOPHYSICAL CONSTRAINTS ON STRUCTURE AND ALTERATION IN THE SOUTH ALLIGATOR VALLEY, NT R.K. Valenta1* L.A.I. Wyborn 2 and M. Morse 2 1

Department of Earth Sciences, Monash University 2 Bureau of Mineral Resources

A multidisciplinary study of the geology of Early to Mid-Proterozoic rocks in the South Alligator Valley has allowed detailed investigation of structure, alterationand mineralization, and the geophysical expression of these features. The following observations can be made from the synthesis of structural mapping, alteration mapping and geochemistry, deposit-scale mapping, and magnetic and radiometric data: 1) The area has experienced a complex structural history involving early ductile deformation followed by dextral strike-slip faulting. Unconformity-related U-Au-Platinoid orebody geometries and positions are systematically related to the geometry of the strikeslip system. 2) There is a regional sodium depletion associated with mineralization, suggesting that the late fault system provided the pathways for large scale flow of mineralizing fluids. 3) Individual deposits have a distinctive highUranium radiometric signature, which can be differentiated from Uranium-rich granites by the fact that the granites have a higher Thorium response.

KEYNOTE: A 8.10

4) Both magnetic and radiometric data can be used to provide form surface information in areas of relatively poor exposure. The Koolpin formation contains high susceptibility iron formations which are expressed in the magnetic data, while the arkosic Mundogie sandstone has a distinctive potassium-rich signature in radiometric data. 5) Magnetic and radiometric data have also been used to map patterns of alteration and contact metamorphism. In the main zone of mineralization between the Rockhole and Coronation Hill deposits, hematite alteration of the Koolpin Formation has resulted in a loss of magnetic signature. On the other hand, contact metamorphism of the pelitic Masson Formation near the Cullen Granite has resulted in an increase in susceptibility and a high magnetic response. In summary, magnetic and radiometric data have provided important constraints on the distribution of structures and lithologies, as well as on the nature and distribution of some metasomatic and metamorphic features.

FLUID FLOW RELATED TO FAULTING IN DIFFERENT TECTONIC

ENVIRONMENTS

R.H. Sibson* Department of Geology, University ofOtago, P.O. Box 56, Dunedin, New Zealand Hydrothermal vein systems developed within the seismogenic upper crust record the passage of substantial volumes of aqueous fluid through faults and allied fracture networks. Vein textures suggest that fluid flow through the fractures is generally episodic. One may look, therefore, for mechanisms linking the intermittent flux of fluids through faultfracture systems to the earthquake stress cycle Geological Society of Australia Abstracts Number 32, Ballarat 1992

accompanying incremental fault slip. Stress cycling around a seismogenic fault extends through a response zone with dimensions comparable to characteristic rupture size (Sibson, 1989). For ruptures occupying the full depth of the continental seismogenic zone, stress cycling may extend laterally for perhaps 10-15 km, but the highest amplitude effects occur adjacent to causative faults and may be locally exaggerated in the

231 vicinity of jogs and other fault irregularities. The complete earthquake stress cycle involves processes operating on several different time-scales. Slow accumulation of shear stress through the interseismic period lasts tens to perhaps many thousands of years. The rapid drop in shear stress during seismic rupturing takes place over a period of a few seconds at any one place, while the period of postseismic adjustment (corresponding to the aftershock phase) may last for days to many years depending on the size of the rupture. Three main mechanisms are envisaged whereby fracture permeability and fluid flow are coupled to the cycles of shear stress accumulation and release accompanying incremental seismic slip. Fluid redistribution may arise from: (1) recurring changes in mean stress accompanying cyclic fault loading; (2) localised postseismic redistribution around rupture irregularities, especially dilational jogs which act as suction pumps and, (3) postseismic discharge of fluids from overpressured portions of the crust through faultvalve action when ruptures breach permeability barriers. Low-stress hydrofracture dilatancy may develop prefailure in association with extreme faultvalve action. While other forms of prefailure dilatancy may also occur, particularly within the fault zone itself (NUT, 1975), there is no strong field evidence for extensive high-stress microfracture dilatancy of the kind described from laboratory experiments on the brittle failure of intact rock (Brace et al., 1966) which formed the original basis for the seismic pumping mechanism (Sibson et al., 1975). While all three of the main recognised processes may contribute to the development of fault-related mineralisation, they operate to differing extents in different tectonic regimes, and at different levels of the crust. The most favoured sites for fault-related hydrothermal mineralisation appear to be near the top and bottom of the seismogenic zone (Sibson, 1990). Epithermal mineralisation tends to be localised in

dilational irregularities within the top kilometre of extensional/transtensional fault systems, where sudden fluid pressure reductions resulting from slip transfer across the irregularities may trigger episodes of boiling and mineral precipitation (Sibson, 1 9 8 7 ) . Recurring fluid movement in response to cyclic fault loading may also contribute to disseminated epithermal mineralisation within intensely fractured portions of the uppermost crust flanking major faults. In contrast, many mesothermal Au-quartz vein systems appear to have developed through fault-valve action near the base of the seismogenic zone on steep reverse or reverse-oblique faults within compressional/transpressional fault systems (Sibson et al., 1988; Cox et al., 1 9 9 1 ) . A characteristic common to these different settings is that mineralization tends to be localised at structural sites where increments of slip lead to abrupt reductions in fluid pressure. Within the earthquake stress cycle, the aftershock phase of stress and fluid-pressure readjustment likely represents the main period for an episode of mineral deposition. Fluid pressure reductions induced by rupturing thus play a key role effecting mineral precipitation, though the precise mechanism varies in different tectonic environments. References Brace, W.F., Paulding, B.W., & Scholz, C.H., 1966, J. Geophys. Res. 7 1 : 3 9 3 9 - 3 9 5 6 . Cox, S.F., Wall, V.J., Etheridge, M.A., & Potter, T.F., 1991, Ore Geol Rev. - in press. NUT, A., 1 9 7 5 , Pure Appl. Geophys. 113: 1 9 7 - 2 0 6 . Sibson, R.H., 1 9 8 7 , Geology 15: 7 0 1 - 7 0 4 . Sibson, R.H., 1989, J. Struct. Geol. 11: 1-14. Sibson, R.H., 1990, Min. Assoc. Can. Short Course Handbook Vol. 18: 9 3 - 1 3 2 . Sibson, R.H., Moore, J.McM., & Rankin, A.H., 1 9 7 5 , / . Geol. Soc. Lond. 131: 6 5 3 - 6 5 9 . Sibson, R.H., Robert, F., & Poulson, K.H., 1988, Geology 16: 5 5 1 - 5 5 5 .

A 8.11 FAULT AND SHEAR ZONE MINOR- AND MICRO-STRUCTURES AND FABRICS ASSOCIATED WITH LARGE SCALE THRUSTING IN THE TALISKER AREA OF THE SOUTHERN FLEURIEU PENINSULA, SOUTH AUSTRALIA T. Flotmann, P.R. James, T. Johnson and J. Rogers Department of Geology and Geophysics,University of Adelaide, Box 498, Adelaide, 5001, South Australia. Detailed mapping and section construction has revealed multiple contractional faults of regional extent, supporting a thin-skinned tectonic model recently postulated for the southern Mt. Lofty Ranges of the Adelaide Fold-Belt. Ductile strain fabrics and rotational criteria suggest strain localization within Geological Society of Australia Abstracts Number 32, Ballarat 1992

NE-trending shear zones of up to 100 metres thickness. Slip vectors on fault planes show consistent NW directed (present day coordinates) reverse slip displacement. The shear zones are mostly bedding parallel and concentrate along (and define?) major lithostratigraphic boundaries, but also occur

232 within individual lithologies. Variation of strain intensity and geometry across shear zones has been estimated using aspect ratio and orientation variations of clastic fragments, phosphatic nodules and from subellipsoidal pressure fringes around pyrite grains. Early and synkinematic quartz vein arrays in shear zones suggest mutual interdependance of elevated pore pressures and shear strain localization within fault zones. The quartz veins record different stress geometries in shear-zones and country rocks. Subsequent (possibly near contemporaneous) shortening has produced the major folding of both beds and fault /shear zones. Some faults have reactivated with dip-slip reverse-sense displacement. Bedding has

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deformed to grossly non-cylindrical doubly plunging folds with plunge variations between moderate N to S directions occuring on the metre scale. Noncylindricity of the folds reflects the style of the preexisting nonplanar stratigraphy. Intense buckling of minor early veins provides an excellent marker for the variation in the intensity of the later type of deformation geometry. Complex late-kinematic vein sets indicate continued high fluid pressures and hydrothermal fracturing in a changing stress regime. Reevaluation of the structural relationships as demonstrated on balanced sections has important implications for the previously published stratigraphy of the area.

YARRAMYLJUP FAULT ZONE: EASTERN BOUNDARY OF GLENELG RIVER COMPLEX AND POSSIBLE CRUSTAL SUTURE IN WESTERN VICTORIA G M Gibson School of Applied Science, University of Southern Queensland

The subvertical Yarramyljup Fault Zone (YFZ) separates crustal provinces with different structural, metamorphic and intrusive histories. The western province, represented by the Glenelg River Complex (Fig. 1), is an extension of the South Australian Cambro-Ordovician Delamerian Fold Belt into Victoria and comprises a diverse assemblage of multiply-deformed (D1-D4) slates, phyllites, amphibolites, pelitic schists and calc-silicate rocks intruded by 480-500Ma I- and S-type granites (Wells, 1956; Richards & Singleton, 1981; Foden et al., 1990). Most granite emplacement occurred during the D2 deformation and was accompanied by tight to isoclinal folding, high temperature - low pressure metamorphism and south west-vergent thrust faulting such that progressively deeper crustal levels of the complex are exposed towards the northeast. Syn-D2 metamorphism gave rise to successive biotite, garnet, staurolite and andalusite metamorphic zones adjacent to the Wando Granodiorite (Wells, 1956), and at deeper crustal levels to migmatite and sillimanite - K feldspar assemblages. Metamorphic isograds are undeformed and trend NW-SW, parallel to the Wando Granodiorite contact and the regional D2 axial plane schistosity. Peak metamorphic conditions (650oC; 3-4 kbars) are comparable to other parts of the Delamerian Fold Belt. The eastern province comprises low grade slates and metabasites which (beneath an unconformably overlying cover sequence of (?) late Silurian-earliest Devonian quartz-rich sediments (Grampians Group) and silic volcanics (Rocklands Rhyolite)) are probably continuous with Cambro-Ordovician volcanogenic

Geological Society of Australia Abstracts Number 32, Ballarat 1992

sediments and volcanic rocks making up the Stawell Zone farther east. The Stawell Zone also incorporates metamorphosed late Proterozoic basaltic rocks and has been variously interpreted as part of the Delamerian (eg. Wilson et al., 1991) and Lachlan Fold Belts (eg. Gibson & Nihill, 1991); its eastern boundary is defined by the Avoca Fault Zone (AFZ) (Wilson et al., 1991). Evidence that the YFZ is a major structural discontinuity and the more likely boundary between the Delamerian and Lachlan Fold Belts includes the following: (1) where exposed in Yarramyljup Creek, the YFZ juxtaposes low grade slates against sillimanite grade schists, indicating a significant component of dip slip and/or strike-slip motion along the presently defined eastern boundary of the Glenelg River Complex; (2) the YFZ defines the eastern limits of Delamerian (Cambro-Ordovician) magmatism in Victoria; granites in the Stawell Zone give 400 Ma ages (Richards & Singleton, 1981) similar to that of the 410 Ma Rocklands Rhyolite; (3) the Stawell Zone, in common with other parts of the Lachlan Fold Belt, is characterised by east-vergent folds and thrust faults whereas their counterparts in the Glenelg River Complex and Delamerian fold Belt are west-vergent (Jenkins, 1990; Gibson & Nihill, 1991); and (4) the YFZ approximates the western limits of lower Palaeozoic shallow marine-fluviatile sedimentation (Grampians Group) in Victoria and thus may lie along, or close to, the western margin of the riftrelated trough in which these sediments are thought (Spencer-Jones, 1965) to have been deposited.

233 An analogous crustal boundary (Lanterman) Fault Zone) can be identified in Antarctica (northern Victoria Land) (Fig. 1); it marks the trace of a Palaeozoic collision zone and separates multiply-deformed, high temperature-low pressure metamorphic rocks and associated Cambro-Ordovician granites (Wilson terrane) from a terrane (Bowers terrane) in which low grade Cambro-Ordovician metasediments and basic metavolcanic rocks are intruded by 400 Ma granites (Borg et al., 1987). The AFZ is better equated with the Leap Year Fault, both structures defining the western limit of a chevron-folded and thrust-imbricated quartz-rich turbidite sequence floored by Cambrian volcanics (Lachlan Fold Belt versus Robertson Bay terrane).

References Borg, S. G. et al. (1987): A. J. Sci.y 287: 127-169. Fanning, C. M. (1991): Rept., 1991/6, Geol. Surv. Victoria (unpubl). Foden, J. D. et al., (1990): Geol Soc. Aust. Spec. Publ., 16: 465-482. Gibson, G. M. & Nihill, D. N. (1991): Tectonophysics (in press). Jenkins, R. J. F. (1990): Geol. Soc. Aust. Spec. Publ., 16: 396-420. Richards, J. R. & Singleton, O. P. (1981): Jl. Geol. Soc. Aust., 28: 395-421 Wells, B. E. (1956): Proc. R. Soc. Vict., 68: 85-110. Wilson, C. J. L. et al., (1991): Tectonophysics (in press). Spencer-Jones, D. (1965): Mem. Geol. Surv. Vict., 25.

A 8.13 T H E PITFIELD-AVOCA FAULT SYSTEM: T H E L O C U S OF A C R Y P T I C - D I S C O N T I N U O U S G R E E N S T O N E IN C E N T R A L - W E S T E R N V I C T O R I A

BELT

WRH Ramsay 1 *, JM Stanley 2 , M Hughes 1 , V Morand1 and RP Carroll1 1 Department of Geology, Bailor at University College 2 Geophysical Research Institute, University of New England

The Pitfield Fault is a north-south trending fault located within quartz-rich turbiditic sediments of Cambro?-Ordovician age in central western Victoria. Much of the fault is now obscured by Tertiary basalt flows. It has been traced from 7 kms south of Pitfield, in a northwards direction for a total of some Geological Society of Australia Abstracts Number 32, Ballarat 1992

15 kms. It is proposed that the Pitfield Fault is the southern extension of the Avoca Fault a major discontinuity which separates rocks of the BendigoBallarat structural zone to the east from the Stawell zone to the west. Geomorphological evidence for the Pitfield Fault

234 comprises a meridionally aligned valley-system, now partially filled with Tertiary basalt flows, into which has been incised the strongly linear Woady Yallock River. Reprocessed aeromagnetic data indicate a distinctive linear magnetic feature trending 010° and located some 2 km west of Scarsdale. The anomaly has an amplitude of 15 nT and is indicative of a slab-like magnetic body within sediments. A series of eastwest magnetic ground traverses reveals an anomalous north-trending zone, some 300 m wide. The magnetic susceptibility of the source material varies from 0.0026-0.0013 SI units and a model involving a series of steeply east-dipping fault slices of mafic-ultramafic material within quartz-turbiditic sediments is proposed to account for the magnetic response. Structural evidence for the Pitfield Fault is contained within deformed lower Palaeozoic quartz-rich sediments found within a north-trending zone of the Devils Kitchen area, some 6-8 km south-east of Linton. Here a prominent zone of polydeformed metasediments grades eastwards into a -0.25 km wide zone of strongly sheared metasediments. The polydeformed zone is characterised by north-south striking subparallel bedding (SO) and cleavage (SI), now cut by a NNE striking, steeply dipping, spaced cleavage (S2), axial planar to F2 folds. At the mesoscopic scale these F2 folds are close to tight, subhorizontal, asymmetrical, with NNE-SSW trending fold axes, easterly vergence, and a west-dipping enveloping surface. Within the shear zone, both bedding and S1 are transposed into a strong S2 cleavage-crenulation cleavage in pelitic metasediments and a spaced cleavage in silty rocks. F2 folds are tight to isoclinal and plunge steeply NNE. Quartz veining is prominent with veins parallel to S0/S1, some isoclinally folded with S2 as axial plane and most showing boudinage. A generally steep stretching lineation on S2 and on quartz veins, has a variable pitch within both surfaces - a feature typical of mylonitic stretching lineations. Asymmetrical foliation boudinage indicates strong east-west compression and west over east movement, which is also indicated by discrete steeply westdipping reverse faults within the shear zone. To the south of Devils Kitchen within the Pitfield Plains various mine dumps contain a variety of rock types including polydeformed sediments, alluvial quartz pebbles and cobbles, and angular and water-worn metabasite and metaperidotite samples. In addition an inclined drillhole at Glenfine South mine intersected some 9 m true width of metavolcanics contained within a black shale, siltstone, and quartzwacke-siltstone sequence. To the north within the Avoca Fault, deformed and thermally metamorphosed volcaniclastic sediments occur near Homebush. Geological Society of Australia Abstracts Number 32, Ballarat 1992

The Pitfield metabasites (greenstones) vary from fine grained to variolitic quench-textured lavas of tholeiitic affinity (FeO*/MgO 1.18 - 1.64) to olivine cumulates (MgO 33 wt%, FeO*/MgO 0.41). Primary mineralogy in the lavas is dominated by plagioclase, clinopyroxene, opaque oxide, whilst cumulate mineralogy comprises olivine and intercumulus poikilitic clinopyroxene, and opaque oxide. Alteration minerals include tremolite/ actinolite, chlorite, epidote, sphene, minor carbonate, serpentine and quartz. The Homebush occurrence comprises mineralogically layered samples containing biotitequartz-feldspar-oxide and green pleochroic actinolitic hornblende-plagioclase-quartz-opaque oxide believed to represent original bedding. SI is subparallel to this layering whilst a low angle crenulation cleavage cuts the layering. Chemically the Pitfield metabasites have MgO 7.4-8.6 wt%, moderate Ti02 (0.98-1.18 wt%), and variable large-ion lithophile element concentrations indicative of alteration. The remarkably constant Ti/Zr, Zr/Y and Ti/V contents of the lavas (average 80, 3.3 and 23 respectively, n=4) are comparable both with the Heathcote tholeiites at Ti02 - 1 . 1 wt% and typical low-K, N-type MORBS. In sympathy with Heathcote and Mt Wellington Cambrian tholeiites and modern back arc basin basalts, the Pitfield metabasites have Zr/Nb ratios 13-25 and moderately enriched LREE levels with (La/Yb)N ratios > 1. The Pitfield Fault is regarded as the southern extension of the Avoca Fault, and they collectively comprise a supracrustal fault system traced for approximately 110 km. Discontinuous greenstone occurrences are inferred to lie within the fault system. According to current emplacement models for Victoria with east-directed thrusting and thrusts ramping up from a mid or upper crustal greenstone layer underlying the Cambro?-Ordovician metasediments, the Pitfield-Avoca greenstone occurrences would mark the hanging wall of this major thrust system. Geochemical characteristics of greenstones from Heathcote, Pitfield, Mt Ararat, Stawell, and Mt Dryden contain a community of features indicative of extrusion on, or within, thin or thinning crust. In contrast, extrusives from the Mt Stavely Volcanic Complex with elevated LILEs and strongly enriched LREE patterns, are closely comparable with Andeanstyle volcanism associated with thickened sialic crust. Assuming that the Mt Stavely Volcanic Complex has not been transported significant distances from its site of origin, then the eastern margin of the Late Proterozoic-Cambrian continental crust lay immediately east of the present location of the complex. The Pitfield-Avoca Fault System represents one of a number of seaboard-directed thrust systems originating from a decollement zone at some 15-20

235 km depth and containing within it, slices of Cambrian? thin mafic crust.

This abstract was supported by the Ballarat University College Director's research seeding grant programme and by analytical facilities through the courtesy of Dr C Wilson, University of Melbourne.

Acknowledgements

A 8.14 STRUCTURAL, IGNEOUS AND TECTONIC IMPLICATIONS OF THE COOLAC SERPENTINITE/YOUNG GRANODIORITE BOUNDARY, SOUTHEASTERN N.S.W. Brian Marshall* and Brenda J. Franklin Department of Applied Geology, University of Technology, Sydney, N.S.W. The Coolac Serpentinite Belt (CSB) is the easternmost linear tract of several tracts of serpentinite which occupy the portion of the Lachlan Fold Belt (LFB) between the Gilmore Fault Zone (GFZ) and the Mooney Mooney Fault System (MMFS). The age and emplacement history of the CSB and its relationship to the other serpentinite bodies are contentious (Stuart-Smith 1990a; Basden 1990; Warner etal. 1991). According to Ashley et al. (1979), Basden (1990), and Warner et al. (1991), the CSB is part of a Silurian ophiolitic suite, whereas Stuart-Smith (1991) suggested that it is an Alpine-type body emplaced as a tectonic slice within the MMFS. Its field relationships have bearing on the Tumut Trough and on the involvement of thin-skinned tectonics in this central portion of the LFB. The Young Granodiorite (YG) is a regionally extensive S-type batholith of Late Silurian age that parallels the CSB for more than 50 km along its eastern margin, but northward, between Coolac and Young, transgresses the CSB and is shallowly discordant to the regional strike. Field relationships show that the YG intruded the CSB subsequent to emplacement of the CSB as a subvertical sheet along the eastern margin of the Tumut Synclinorial Zone. Although usually steep, the intrusive contact is, in places, very shallow and irregular, this most probably reflecting the inherited local geometry of the serpentinite body. Intrusive contacts, against which there are welldefined chilled and hydrothermally altered margins of YG, locally give way to approximately co-eval tracts of mylonitized granodiorite, in which S-C fabrics in the adjacent CSB commonly show a related east-sideup component of movement. However, on shear zones within the CSB away from the faulted contact, and in places adjacent to intrusive YG, S-C relationships record an intense sinistral event. This is consistent with a sinistral event preceding upthrust and intrusion of YG against the CSB. On the western

Geological Society of Australia Abstracts Number 32, Ballarat 1992

boundary of the CSB a sinistral movement is also recorded, but this post-dates the late Silurian upthrust event (Stuart-Smith 1990b) and probably reflects reactivation. The mixed intrusive/mylonitized boundary relationships of the YG upthrust against the CSB are consistent with emplacement of the granodiorite at a high crustal level by surge tectonic processes (Hollister & Crawford 1986; Warner et al. 1991). Recent interpretations of the LFB have focussed on thin-skinned thrust-tectonic (flake tectonic) models in which much of the LFB comprises east-verging imbricate plates allochthonous above mid- to lower crustal detachments (e.g. Gray et al. 1991; Glen 1991). Interpretations of the Tumut region have featured the GFZ and MMFS as the steeply dipping portions of either west-verging (Basden et al. 1987) or dominantly east-verging (Glen 1991; Stuart-Smith 1991) listric reverse faults. However, irrespective of vergence, any interpretation involving thrustemplacement of the CSB against the YG is inconsistent with the field relationships and is rejected. If a thrust-tectonic model is applicable, the imbricate architecture was probably established before the Silurian when, at least in the Tumut region, the structural style changed, possibly in response to different displacement vectors, such that steeply dipping portions of thrust-faults were reactivated. The development, upward migration and intrusive fault emplacement of the YG against the CSB reflect the components of E-W extension and shortening which accompanied the change. References Ashley, P.H., Brown, P.F., Franklin, B.J., Ray, A.S. & Scheibner, E., 1979, J. Geol. Soc Aust. 26: 45-60. Basden, H. 1990, Geology of the Tumut 1:100 000 geological sheet 8527, New South Wales Geological Survey, Sydney. Basden, H., Franklin, B.J., Marshall, B. & Waltho,

236 A.E., 1987, Am. Geophys. Un. Geodyn. Ser. 19: 57-66. Glen, R.A., 1991, Geol. Soc. Aust. Abstr. 29: 21-22. Gray, D.R., Wilson, C.J.L. & Barton, T.J., 1991, Geology 19: 574-577. Hollister, L.S. & Crawford, M.L., 1986, Geology 14: 558-561. Stuart-Smith, P.G., 1990a, Record 1990/78, Bur.

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Miner. Resour, Aust. Stuart-Smith, P.G., 1990b, J. Struct. Geol 12: 621638. Stuart-Smith, P.G., 1991, BMR J. Aust. Geol. & Geoph. 12: 35-50. Warner, P.J., Marshall, B. & Franklin, B.J., 1991, Aust. J. Earth Sci.

THE NATURE OF INTRAPLATE OROGENY AS ILLUSTRATED BY THE ALICE SPRINGS OROGEN IN CENTRAL AUSTRALIA

R.D. Shaw 1 , P. Zeitler 2 ' 3 , L.P. Black 1 ,1. McDougall 2 & P.R. Tingate 4 ' 5 1 Bureau of Mineral Resources, GPO Box 378, Canberra, ACT, 2601, Australia 2Research School of Earth Sciences, The Australian National University, GPO Box 4, Canberra, ACT, 2601, Australia 3Present address: Department of Geological Sciences, Williams Hall 31, Lehigh University, Bethlehem, PA 18015-3188, USA 4University of Melbourne, Melbourne, Victoria, Australia. 5Present address: National Centre for Petroleum Geology & Geophysics, GPO Box 498, Adelaide, South Australia, 5000, Australia. An excellent example of an orogen developed in the interior of a plate is the basement-involved thrust belt which became the boundary between the basement Arunta Block and the Amadeus Basin in central Australia during the Devonian-Carboniferous Alice Springs Orogeny. The orogen is the result of high regional compressive stresses that reactivated a Proterozoic suture, the Redbank Zone. These compressive stresses are presumed to have originated at the northern and southern margins of the Australian plate and to have been transmitted to the plate interior with the lithosphere acting as a stress guide. The stratigraphic record suggests that thrustgenerated uplift was episodic and points to compressive tectonic movements in the mid-Devonian (Emsian), possibly in the early Late Devonian (Frasnian), in the latest Devonian (Fammenian), reaching at peak in the mid-Carboniferous (Namurian?). Rb-Sr and 4 0 Ar- 3 9 Ar geochronological results are consistent with episodic thrust activity. A

Geological Society of Australia Abstracts Number 32, Ballarat 1992

Rb-Sr TR age of 415+50 Ma for the generation of hydrated mylonite in the Redbank Zone suggests initial thrust reactivation may have occurred as early as Silurian. Results of 4 0 A r . 3 9 A r and apatite fission track analysis indicate that cooling on exhumation at the thrust-front continued until about 300-320 Ma. Data from 4 0 A r . 3 9 A r and apatite fission track analysis are readily explained in terms of a model for the Alice Springs Orogeny of slow cooling, with some limited sedimentary burial, followed by rapid uplift and exhumation. The thermal input during the Orogeny was severely limited. Geophysical evidence shows that the Redbank Zone cuts through the crust to mantle depths. As a consequence of the thick-skinned nature of this controlling structure, crustal shortening may have been as low as 20%, consistent with uplift models derived from Rb-Sr and 40 Ar-39Ar data.

237 A 8.16 THE EFFECT OF PROTEROZOIC REGIONAL EXTENSIONAL SHEAR ZONES ON THE GEOMETRY OF GRANITE-GREENSTONE BELTS: OBSERVATIONS FROM THE QUADRILATERO FERRIFERO, BRAZIL Stephen Marshak1*' Fernando F. Alkmim2, and Hanna J. Evangelista2 1 Department of Geology, University of Illinois, Urbana, Illinois, USA Departamento de Geologia, Universidade Federal de Ouro Preto, Ouro Preto, Minos Gerais, Brazil

2

Archean granite-greenstone belts typically possess domes of crystalline rocks separated by deep troughs ("keels") containing a deformed and metamorphosed supracrustal sequence of greenstone and overlying platform marine strata. The origin of such terranes has long been a mystery. One popular model considers the structural geometry displayed by granitegreenstone belts to be a reflection of vertical tectonic processes unique to the Archean. Field work in the Quadrilatero Ferrffero (QF), at the southern end of the Sao Francisco craton, suggests an alternative explanation for this geometry. In the QF, the greenstone (Nova Lima Group) and the platform sequence (Minas Supergroup) were deposited in an asymmetric basin that initiated during Late Archean rifting and continued to subside during Early Proterozoic, presumably due to thermal subsidence of stretched continental lithosphere. The first phase of deformation and metamorphism recorded in the rocks of the QF reflects the closing of this basin during the Lower Proterozoic Transamazonian orogeny (Marshak and Alkmim, 1989). As a result of this event, Nova Lima and Minas strata were affected by development of major NNW-verging folds and faults. We propose that a previously unrecognized period of crustal extension in Middle Proterozoic juxtaposed this pre-deformed supracrustal sequence against hot basement brought up in the footwall of normal faults. The extension involved movement on both trans-crustal low-angle normal faults and on local high-angle normal faults. In this context, the "keels" of the present granite-greenstone terrane are narrow asymmetric grabens into which pre-deformed rocks dropped during the extensional event. The style of Proterozoic extension recorded in the QF differs from that displayed in Cenozoic rifts and classic Cordilleran core-complex terranes. Most

Geological Society of Australia Abstracts Number 32, Ballarat 1992

notably, the contact between basement and supracrustal rocks in the QF is marked by a pronounced metamorphic aureole. Strata above the shear zone contain biotite, kyanite, staurolite, andalusite, cordierite, and sillimanite, minerals that are absent away from the contact. Petrographic analysis indicates that this metamorphism is syn- to posttectonic with respect to hanging-wall down movements. We can demonstrate that this aureole is not a result of later intrusion, for basement rocks at the contact are older Archean gneisses. In many localities, sheared granitoid occurs at the contact. This granitoid appears to have formed when water that was derived from metamorphism of metasediments was introduced to the hot dry basement brought up along the shear zone. Finally, fabric relationships suggest that the basement underwent active diapiric flow to form regional domes at a late-stage during the extensional event (earlier extensional shear fabrics are tilted and overprinted by hanging-wall down shear movements that are radial to the domes). If the features displayed in the QF are representative of features in other granite-greenstone belts, then our observations suggest that the present structural geometry of such belts reflects the cumulative effects of alternating contractional and extensional tectonics. Special tectonic processes unique to the Archean or Early Proterozoic need not be called upon to explain the development of granitegreenstone belt geometry. The manifestation of the processes, however, may reflect the different thermal structure of a younger earth. References Marshak S., & Alkmim, F.F., 1989, Tectonics 8: 555-571.

238 A 8 17

MICROSTRUCTURE OF A METAMORPHIC CORE COMPLEX: THE NORTHERN SNAKE RANGE Anja-Karina Pahl and Gordon S. Lister

VIEPS, Dept of Earth Sciences, Monash University, Wellington Rd., Clayton Vic. 3168 The lower plate of the northern Snake Range Metamorphic Core Complex (MCC) contains a strongly deformed sequence of quartzites and schists with mineral parageneses ranging from amphibolite to greenschist facies. The dominant mesoscopic foliation is mylonitic, and is associated with a strong east-west mineral elongation lineation. This mylonitic foliation is defined on the microscopic scale by mica fish and associated C-surfaces throughout the Range, and by parallel quartz ribbon grains in parts of some units in the eastern part of the Range. The metamorphic tectonites were deformed in a large ductile shear zone and there is considerable debate as to the role of crustal scale pure shear and simple shear during their evolution. This study provides evidence that both pure shear snd simple shear occur simultaneously at the microscopic and mesoscopic scale. Detailed analysis of quartz c-axis fabrics using a digital universal stage (designed by one of the authors) show a variety of patterns including both symmetric and asymmetric type I and type II crossed-girdles. In all fabric skeletons produced, grains with different microstructures occupy distinct sections of the fabric pattern. Symmetric skeletons with an "hourglass" appearance have a central partial girdle orthogonal to the mylonitic foliation. The asymmetric appearance of some type II crossed-girdles arises due to a greater intensity of c-axes along one arm of the fabric skeleton compared with the other. This girdle could define a local flow plane oriented at a small angle to the C-surfaces. Domains of symmetry and asymmetry are juxtaposed against each other. For example, stretched pebbles without oblique subgrains (i.e relict quartz ribbons) occur alongside zones in which subgrain formation (or rotation recrystallization) of quartz produced a grainshape foliation oblique to C-surfaces. Asymmetric fabric patterns attest to the non-coaxiality of deformation in the latter domains. However because the sense of shear is not always consistent throughout a thin-section, whole slide analysis over regions of synthetic and antithetic shear may give rise to an apparent "overprinting" effect of asymmetries. This could lead to either incipient or relict symmetry in some patterns. It is also possible that the zones of plainly symmetric fabric are relict from an earlier stage in the evolution of the MCC, when rocks were subject to pure shear as the crust (uniformly?) stretched, as suggested by previous workers. However, if this is Geological Society of Australia Abstracts Number 32, Ballarat 1992

true, fabrics and microstructures have survived to a remarkable degree given the temperatures and amount of strain to which the rocks were subject in the later parts of the deformation history. It might be expected in this case that the domains of pure shear be replaced by "annealed" foam textures, or other evidence of static heating. They are not, although some domains of foam textured quartz have been recognized. Otherwise, the microstructures in domains which produce both symmetric and asymmetric fabrics are typical of dynamic recrystallization during deformation under decreasing temperature conditions. For example, dynamic recrystallization with subgrain formation (and associated undulose extinction) is superimposed upon older tabular and globular quartz grains which had triple point junctions. Note that in some regions, equant quartz overprints or at least coexists with rotated subgrains of previously larger grains which have been recrystallized. Further, there are also generations of oblique grainshape foliations at successively lower angles to the C-surfaces, indicating that the finite strain clock may have been "reset" by episodic recrystallization. Clearly, models which suggest that uniform simple shear takes place in the ductile shear zone associated with MCCs (eg. Wernicke, 1985) must be questioned in the light of these observations. The shear zone in the northern Snake Range has transected well defined stratigraphy and deformation has been partitioned so that boudinage of strata has taken place. Shear sense and the degree of non-coaxiality vary systematically around these structures, so that zones of simultaneous pure shear and simple shear coexist on scales varying from millimetres to hundreds of metres. This can be seen not only in the microstructures and fabrics, but in the mesoscopic monoclinic folds and kinkbands in the quartzites, as well as in shearbands and extensional crenulations in the schists. It is thus very difficult to argue a case for anything but simultaneous pure shear and simple shear occuring in the ductile shear zone associated with MCCs. This work was supported by the Australian Research Council grant "Continental Extension Tectonics " (Lister, Houseman and Gleadow). Reference Wernicke, B.P. (1985) Uniform sense normal simple shear of the continental lithosphere. Can. J. Earth Sci. 22, 108-125.

239

POSTER SESSION A 8.18

STRUCTURAL AND METAMORPHIC ASPECTS OF A NAPPE DEFORMED BY MANTLED GNEISS DOMES, NEW HAMPSHIRE, U.S.A. Rebecca Askew Victorian Institute of Earth and Planetary Sciences Monash University, Clayton, Victoria, 3168.

A number of 'mantled gneiss domes' occur within the Northern Appalachian Fold Belt. Such domes are present in many deeply eroded mountain belts, including the Alps, Caledonides and the Canadian Cordillera. In the Appalachians the gneiss domes are overlain by Mid-Ordovician (465 Ma, Aleinikoff & Moench 1985) metavolcanics which are unconformably overlain by Siluro-Devonian metasediments. These 'mantling' rocks have been thickened by nappe scale recumbent folding and thrusting (D2) prior to deformation into a series of elongate, en-echelon domal structures (D3) cored by leucocratic calc-alkaline gneiss of Late Ordovician age (455-440 Ma, Naylor 1987). Metamorphic isograds commonly wrap around the domes and the grade of metamorphism increases toward the centre of the dome. Isotopic and geologic data show that the formation of the domes took place during Acadian deformation (380 Ma; e.g. Harrison 1986). Metamorphic studies of assemblages in rocks mantling the domes during dome emplacement suggest pressures of 8.5 kbar (25 km) for pre-doming conditions, and 5.5 kbar (17 km) for post-doming conditions, giving a total displacement for the dome core of about 8 km (Tracy & Robinson 1980). D2 produced a penetrative sub-horizontal, spaced cleavage (S2) parallel to the axial plane of recumbent folds. In addition, a strong SE-SSE trending stretching lineation was developed in suitable lithologies. S2 is well developed in both the outer (upper) regions of the Ordovician gneisses and the overlying Ordovician-Devonian sediments. Di is in evidence as inclusion trails within pre-D2 staurolite and garnet porphroblasts, as rare mesoscopic tight folds refolded by F2, and by the spaced nature of the S2 cleavage. A large; tabular pre-D2 granodiorite body intrudes the area at the level of the Devonian sediments. This Di deformation affects rocks up to at least Devonian in age and cannot therefore be related to Taconian Deformation (480-450 m.y.) but must be a previously undocumented Acadian fabric. D3 is associated with the heterogeneous development of upright folds and crenulations locally progressing into a sub-vertical differentiated cleavage. The development of D3 is strongly domainal in both its intensity and orientation. Although regionally this Geological Society of Australia Abstracts Number 32, Ballarat 1992

deformation has a doubly plunging non-coplanar geometry, the orientations of F3 and S3 are closely associated with individual domes, and vary only from one dome to the next. This may be a result of shortening during doming or shortening overprinting domal structures, in which case the event of dome formation would correspond to D3, and the upright structures would correspond to D4. A number of models pertaining to the formation of mantled gneiss domes in areas of pre-thickened overburden are proposed to explain the rise, geometry and distribution of the domes. Currently the most favoured model is one in which rapid thickening of fairly dense pelitic and volcanic units overlying less dense gneissic/granitic basement gives rise to an unstable gravity profile and a perturbed geotherm. This allows plastic rise of the basement into domal culminations, or into the core of synchronous antiforms. The tectonic regime accompanying this deformation is highly problematic. Some domal structures now known to be core complexes have in the past been described as mantled gneiss domes: e.g: the Albion Mountains of Southern Idaho (Armstrong, 1968; Crittenden etal., 1980) Many core complexes have formed through extension of the crust following thickening of the crust: e.g. North American Cordillera (e.g. Coney & Harms, 1984), Basin and Range Province (e.g. England et al., 1985), Papua New Guinea (e.g. Davies and Warren, 1988). In nearly every case, ductile structures now known to be related to crustal extension were first ascribed to crustal shortening (Miller, 1991). Are the nappes and subhorizontal foliation and lineation the manifestation of extensional collapse at ductile levels, or a product of convergent tectonism with associated low angle thrusting and thrust parallel shear failure? Is the doming which overprints this deformation associated with further extension and tectonic denudation resulting in uplift, or with the diapiric rise of basement made plastic through thickening?

240 References Aleinikoff, J. N. & Moench, R. H. (1985), Geol. Soc. Am. Abstr. Progr17: 1. Armstrong, R. L. (1968), Geol. Soc. America Bull., 79: 1295-1314. Coney, P. J. & Harms, T. A. (1984), Geology, 12: 550-554. Crittenden, M. D. J., Coney, P. J. & Davis, G. H. (1980), Cordilleran metamorphic core complexes. Memoir 153: 480. Davies, H. L. & Warren, R.G., (1988), Tectonics, 7: 1-21. England, P. C., Sonder, L. J., Christiansen, R. L. & Wernicke, B. P. (1985), Continental Extensional

Tectonics, Abstracts with Program. University of Durham. Geological Society of London. Harrison, T. M. (1986), Geol. Soc. Am. Abstr. Progr., 8: 22. Miller, E. L. (1991), The geometry of naturally deformed rocks, Abstracts with Program. Zurich, Switzerland. Geol. Inst. ETH. 39-40. Naylor, R. S. (1987), Northeastern Section of the Geological Society of America, Centennial Field Guide. (Roy, D. C.) Boulder, Colorado, The Geological Society of America, Inc. 5: 243-246. Tracy, R. J. & Robinson, P. (1980), The Caledonides in the USA, IGCP Proceedings, Project 27. (Wones, D. R.) Virginia Polytech Instit. Geological Sciences. Memoir no.2: 189-196.

A 8-19 THE ROLE OF NON-UNIFORM BEDDING-PARALLEL SLIP ON FOLD NUCLEATION AND GROWTH FROM EXPERIMENTAL MULTILAYER DEFORMATION C.N. Winsor*

& T.J. Fowler

Geology, La Trobe University College of Northern Victoria, PO Box 199, Bendgio, Victoria, 3550 The significance of localized inhomogeneity in the nucleation of folds, fold shape evolution and the development of layer parallel voids is investigated using multilayers of plasticine and putty, deformed in a compression box. These experiments support previous investigations by Behzadi & Dubey (1980), Watkinson (1976), Ghosh (1968), wherein folds were initiated slowly, but increases rapidly until the fold locks-up and limb thinning-hinge thickening occurs. The initiation of chevon folds in our experiments follows a path through sinusoidal buckles-concentricchevron folds identified previously, however, inherent heterogeneity assists nucleation. In some cases the ideal fold shape is modified by anisotropy, however localised regions of easy slip may locally inhibit initiation by aiding layer parallel slip. Although plasticine does not provide a complete analogue to rock deformation (McClay 1976), due to variable deformation mechanism, within certain limitations it can give insight into the effects observed in rocks particularly at the scale of observation. Our experiments support observations made of chevron folds within the Ballarat Slate Belt and may assist in developing an explanation for their localization at a mesoscale. Local finite stress, strain,

strain rate and lithological differences as well as other factors can be important, however the localization of particularly mesoscopic folds may be effected by bedding parallel heterogenity either of a sedimentalogical or structural nature. An association between folds, zones of axial plane dilation and gold mineralisation has been inferred in the Ballarat Slate Belt. Our investigation suggest that an earlier localized heterogeneity has exerted an influence on the nucleation of chevron folds and may have assisted the location of dilation zones at the mesoscale. References Behzadi H. & Dubey A.K. 1980. Variation of interlayer slip in space and time during flexural folding. J. struct, geol. 4, 453-457. McClay K.R. 1976. The rheology of plasticine. Tectonophysics 33, T7-T15. Ghosh, S.K. 1968. Experiments of buckling of multilayers which permit interlayer gliding. Tectonophysics 6, 207-249. Watkinson, A.J. 1976. Fold propagation and interference in a simple multilayer unit. Tectonophysics 34, T37-T42.

J 4

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241 A 8.20

TECTONIC EVOLUTION OF THE SOUTHERN ADELAIDE FOLD BELT A STRAIN AND BALANCED-SECTION APPROACH T Flotmann and P.R James Department of Geology and Geophysics, University of Adelaide, Box 498, Adelaide, 5007, South Australia.

The tectonothermal evolution of the southern Adelaide Fold Belt has been regarded as simple "thickskinned" superposed folding and orogenic contraction homogeneously distributed through the Adelaidean and Kanmantoo Supergroup sediments Upright, subhorizontal regional folds are traceable over considerable strike lengths, and have long east to southeast dipping normal limbs and short usually steep to overturned western limbs, with occasional thrust faults. Recent "thin-skinned" models involving intense strain partitioning with large-scale displacement on intermediate to low angle thrust faults have been presented, and have highlighted problems only soluable by detailed mapping of strain geometry and

A 8.21

kinematics. These include the lack of a recognised thrust system so common to similar foreland fold and thrust belts, the sigmoidal shape to the belt, the apparently inverted and often telescoped character of the metamorphic facies, and finally the uncertain age, unusual thickness and the contentious nature of the basal contact, of the Cambrian Kanmantoo Group. In this paper we present preliminary evidence to test these models and investigate the specific problems by combining a structural field mapping programme with a detailed finite-strain and kinematic study. Restored and balanced cross sections will be presented which provide initial data on the architecture and evolution of the fold belt.

A REVIEW OF CRUSTAL LINEAMENTS AND RINGS IN SOUTHEASTERN AUSTRALIA R.C. Glenie Geological Consultant, Melbourne

The surface of Earth is blemished by traces of extensive linear and circular features, generally referred to as lineament zones and structural rings. These faint scars are the visible mark of megastructures of primordial origin and can provide a record of subsequent episodic events involving energy releases from deep-seated subcrustal phenomena. Previous studies by O'Driscoll (1980, 1981, 1982, 1986, 1989, 1990) indicate global lineament belts and continental lineament corridors are surface expressions of fundamental sutures through the lithosphere to upper mantle layers. Major and minor lineament nets occur with four preferred directions ~ Tethyan (WNW) and Laurasian (ENE) primaries each with its orthogonal (NNE & NNW) - across continental blocks and their shelves, and in places are distinguishable along ocean floors. Not so well known are the more subtle crustal rings of huge dimension that also can be discerned on continents. The many lineaments and newly recognized rings in the southeastern quadrant of Australia are observable on O'Driscoll's selected ingredient plots of various published maps, particularly those showing boundaries of geological units. The assessment of their Geological Society of Australia Abstracts Number 32, Ballarat 1992

subsurface structure will require intensive geophysical investigation. From evidence to date in the region, resurgent lineament movement through geological time accounts for an origin of some giant structural rings in terms of stress-strain ellipsoids; this tectonism is often associated with igneous activity. Others may be reflections of buried relicts of cryptoexplosion cratering; either from the volcanic outgassing of rising hot-spot plumes (geoblemes) perhaps also related to lineament intersections, or by the impact of asteroid-size meteorites (astroblemes) at apparent random locations. This review identifies between 15 and 20 circular to slightly elliptic rings, with most diameters of 100 to 500 km, and in some cases with an overlap indicating relative age. They cumulatively encircle at least 45% of the surface area of the region. An excellent example of a structural ring is revealed across the Palaeozic rocks occupying the Melbourne Trough. Appropriately called the Cerberean Ring (E.S.T. O'Driscoll, pers. comm.), it is centred northeast of Marysville in the cauldron subsidence of 25 km diameter, named the Cerberean Caldron by Hills (1959), with which it must have

242 genetic connection. The ring is a nearly perfect circle of diameter 180 km with its perimeter showing as a real physical feature similar to that indicated by a lineament trace, and may likewise represent a narrow zone of crustal mobility, in this case curvilinear. The exact nature of this zone of weakness circumscribing the ring is enigmatic. The ring encompasses a large part of the trough, including most of the Upper Devonian acid lavas/ash flows and their related (mainly S-type) granitic magmas such as the Strathbogie and Tynong massifs which are roughly in apposition inside the northern and southern periphery. The ingredient map shows that pairs of WNW and NNE lineaments, part of a network first noted by Hills (1956) then developed in detail by O'Driscoll (op. cit.) with additions by Campbell (1989), meet the ring tangentially; lineaments and ring appear to be directly related. The ring may represent a now truncated, interference dome that has been formed by the movement of these sets of conjugate parallel lineaments. The remarkable symmetry of the structure apparently results from even matching of the crossdirectional forces. The effect of another major NNE lineament, which bisects the ring, is as yet undetermined, but it had a vital controlling influence on the central location and construction phases of the caldron. The sinusoidal exposures of folded and eroded Lower Palaeozoic marine sedimentary rocks in the Melbourne Trough show outlines of both left and right sigmoids relating to the tangential WNW and NNE lineament sets. The combined lateral shearing effect of these sets, augmented by those of NNW and ENE lineaments, may determine the configuration of Middle Palaeozoic nonmarine sedimentary outliers in the Mount Howitt Province. The interpretation of a periodic resurgence of lineament and ring forces in the region is sustained by features such as the distribution of Early Tertiary basic volcanic rocks around the ring and by the circular record pattern of recent microearthquake epicentres. It is clear that revision of some tectonic processes, commonly attributed to evolution of the southeastern Australian region, will need to be modified in terms of lineament tectonics and with reference to ring structures. For example, the essential mechanism involved in formation of the Great Escarpment of eastern Australia (Oilier, 1985) might be found by

Geological Society of Australia Abstracts Number 32, Ballarat 1992

morphotectonic study of lineaments transecting the continental margin. The global distribution pattern of lineaments and their associated rings show that they are derived from ancient and often persistent tectonic systems. Their existence perhaps gives credence to the theory of an expanding Earth and to a dominating role for vertical tectonics, and poses problems for many of the tenets of tectonic plate dynamics including the basis for deduced past orientation of continents. They also offer new insight to the mechanics of mountain building and granite emplacement. References Campbell, I.B., 1989. In Le Maitre, R.W. ed. Pathways in Geology - Essays in in Honour of Edwin Sherbon Hills, Melbourne (Blackwell Scientific): 280-303. Hills, E.S., 1956. Journal of the Geological Society of Australia 3: 1-15. Hills, E.S., 1959. Geologischen Rundschau 47(2): 543-561. O'Driscoll, E.S.T., 1980. Tectonophysics 63: 397417. O'Driscoll, E.S.T., 1981. Mineralium Deposita 168: 85-101. O'Driscoll, E.S.T., 1982. Journal of the Petroleum Exploration Society of Australia 1: 1-31. O'Driscoll, E.S.T., 1986. In Reading, H.G., Watterson, J. and White, S.H. eds. Major crustal lineaments and their influence on the geological history of the continental lithosphere. Philosophical Transactions of the Royal Society, London A 317,195-218. O'Driscoll, E.S.T., 1989. In Le Maitre R.W. ed. Pathways in Geology - Essays in Honour of Edwin Sherbon Hills, Melbourne (Blackwell Scientific): 247-267. O'Driscoll, E.S.T., 1990. In Hughes, F.E. ed. Geology of the mineral deposits of Australia and Papua New Guinea. The Australasian Institute of Mining and Metallurgy Monograph 14: Vol.1, 33-41. Oilier, C.D., 1985. In Morisawa, M. and Hack, J.T. eds. Tectonic Geomorphologyt Allen & Unwin: 3-25.

243 A 8.22

PROGRESSIVE DEFORMATION DURING MID-PROTEROZOIC THRUSTING IN THE EASTERN ALBANY MOBILE BELT, WESTERN AUSTRALIA L.B. Harris, M.J. Pascoe and W. Witham Department of Geology, University of Western Australia, Nedlands 6009 WA.

This contribution describes the deformation of pegmatites crosscut all previous structures. Drag along granulite facies gneisses of the Albany Mobile Belt, the margins of these shear zones results in a warping metasediments of the Mount Barren Group and of the foliation, producing a very gentle fold with an Proterozoic overprinting on Archaean granite - axis plunging towards 150°. A set of NW striking Kgreenstones of the Yilgarn Block in the eastern sector feldspar, quartz and biotite pegmatites crosscut older of the Albany Mobile Belt near its boundary with the structures and are controlled by brittle-ductile shear Fraser Mobile Belt. zones. Geochronological studies indicate that all the Discrete, NW directed thrusts and reverse shear above events took place in a relatively short time-span zones cross-cut Archaean granites, gneisses and at -1190 Ma and were ,associated with dextral greenstones near the northern margin of the belt (eg transpression in the central and western parts of the Calyerup Creek greenstone belt). Reverse shear zones Albany Mobile Belt where foliations trend E-W. partially reactivate Archaean foliations (with The Mount Barren Group is a sedimentary formation of lower grade mineral assemblages along succession at the junction of the Albany and Fraser them than in the host rock). Shear zones locally Mobile Belts. Although basal units unconformably flatten in dip, cross-cutting Archaean foliations. overlie the Archaean granite - greenstone terrain near Quartz veining along flats contains minor Au Ravensthorpe, the remainder of the Mount Barren mineralisation due to remobilisation of low-grade Group has been thrust to the north-west over basement Archaean mineralisation. The Proterozoic overprint in gneisses forming fold and thrust nappes. Exposures Archaean gneisses increases southwards (ie. towards of quartz -muscovite-chlorite schist, quartzite and quartz mylonite near the base of the Mount Barren the mobile belt). The structure of gneisses of the Central Domain is Group contain a shallowly SE dipping foliation with a strongly developed, steeply pitching, mineral best seen in the Bremer Bay area. Mafic dykes and K-feldspar pegmatites folded elongation lineation. The asymmetry of minor NW during the first deformation stage form mesoscopic, verging folds folding the foliation (with axes submoderately to gently inclined, tight to isoclinal folds perpendicular to the mineral lineation, although (Fa), that plunge moderately to gently to the west curvature is common) along with the formation of southwest. The second stage of folding is represented shear bands at a low angle to the foliation indicates by a generation of recumbent to gently inclined NW directed thrusting of metasediments onto the centimetric to metric scale folds (Fb) that plunge Yilgarn craton. The foliation is also folded by tight, gently toward the southwest folding Fa. The general generally SW verging folds whose axes lie subsoutheast vergence of Fb folds indicates that the parallel to the mineral elongation lineation. Local Bremer Bay region is situated on the overturned limb changes in vergence of these folds are observed along with "eye-shaped" closures of sheath folds. These of a regional recumbent structure.The third stage of folding (Fc) comprises metric to hectametric, upright structures have been interpreted as forming during to steeply inclined open folds which plunge gently to intense non-coaxial deformation at the base of a thrust the southwest. The axial surface of these folds dips to nappe. Early formed folds have rotated into the southeast and a weak biotite foliation is developed parallelism with the movement direction. Folds parallel to the axial plane. Localised increases in resemble those developed within a thrust regime with plunge ocur towards interpreted high strain thrust a dextral wrench component. The superposition of several phases of folds and zones. Three phases of mafic dykes are recognised, the associated axial planar fabrics can be observed within first pre-dating folding, along with two syn-tectonic higher levels. Isoclinal folds folding lithological dolerite dyke generations: the first being folded by Fb layering in quartzites and quartz-muscoviteichlorite folds, the second intruding along axial surfaces of Fc schists (whose foliation is axial planar) have been structures.Dyke intrusion suggest 'relaxation' or tight to isoclinally refolded by a second generation that in turn have been refolded by a third generation of SW collapse phases in the development of the orogen: Dextral (strike ~125°±15°) and sinistral (strike plunging, upright to NW verging folds. A fourth ~020°±15°) centimetre and metre scale shear zones generation of SE plunging folds is locally seen containg plagioclase, quartz and orthopyroxene refolding all previous structures with an axial planar Geological Society of Australia Abstracts Number 32, Ballarat 1992

244 crenulation cleavage. A thick sequence of white quartzites, with a basal section of alternating conglomerate beds and quartzite, has been thrust over mica schists (verified on th ebasis of S/C and C/C' relationships within the basal shear zone to the quartzite nappe). Minor folding is rare in the quartzite nappe, and where observed, folds verge to the NW and resemble the third generation structures in schists. Pebbles have been highly deformed, flattened in the cleavage plane within which they are A 8.23

highly elongated, with steeply pitching long axes. In the eastern exposures of the Mount Barren Group, large-scale recumbent folding of quartzites and schists has been overprinted by upright and open, SSW trending folds. Metamorphic grade here is in the staurolite zone of the amphibolite facies. Deformation within the nappes may therefore be correlated with deformation stages recognised in the gneissic basement in the eastern Albany Mobile Belt.

THREE PHASES OF FOLDING IN AN INLIER IN THE BUSHVELD COMPLEX, SOUTH AFRICA. B. Mortimer Department of Geology and Applied Geology, University of Natal, King George V Avenue, Durban, 4001, Republic of South Africa.

The Crocodile River Fragment is a 1000km inlier in the Bushveld Complex, South Africa. The succession in the fragment comprises clastic sediments, carbonates and banded ironstones of the Transvaal Sequence, originally deposited towards the centre of the Transvaal Basin. A structural investigation of the area has resulted in a new interpretation involving a Fi anticline refolded by two events (F2 and F3). A tectonic model is proposed for the fragment on the basis of the new information. A number of opposing theories regarding the exact tectonic development of the fragment and hence its relationship with the Bushveld Complex have been put forward. The most recent is that of Hartzer (1989), who interpreted the large-scale structure in the fragment as a single anticline in the southern half, and two anticlines in the northern half, separated by a syncline to which he assigned a different age. Only the single antiform in the southern half was interpreted as being refolded. In the current study, stereographic projection of structural data obtained from suitable sub-domains within the northern half of the fragment indicates that the deformation results from at least three folding events. This is supported by both detailed mapping and qualitative field observations. The first event, Fi, has an axis originally orientated north-south, which has been affected by east-west cross-folds (F2). A third event (F3) has folded the entire structure about a southerly-plunging axis trending southwest-northeast, such that the two anticlines described by Hartzer (1989) are actually the limbs of the same F3 fold (Figure 1). This allows better correlation between the northern and southern parts of the fragment since it implies the existence of 2

Geological Society of Australia Abstracts Number 32, Ballarat 1992

only one anticline in both regions, which have the same origin. This anticline represents original basinal updoming (Fi) in response to a sub©horizontal maximum stress, at a time when the sediments were still continuous with those in the rest of the basin. As a result, the basic structure is such that the sediments dip towards the perimeter of the fragment. At approximately 2200ma (SACS,1980), pressure during intrusion of the Bushveld Complex caused a change in the principal stress direction, and the associated increase in temperature caused the degree of deformation to increase. The existing fold axis underwent shortening (F2). This shortening is responsible for the development of a broad synform in the centre of the fragment and the apparent separation of the two antiforms. The final folding event (F3) probably coincided with a later phase of intrusion of the Bushveld Complex, during which time the entire structure folded about a plunging axis causing overturning and tight folding in areas of compression. Figure 2 summarizes the tectonic development. Reference Hartzer (1989). Stratigraphy, structure and tectonic evolution of the Crocodile River Fragment. S. Afr. J. Geol.92 (2), 110-124. South African Committee for Stratigraphy (SACS) (1980). Stratigraphy of South Africa. Part 1 (Comp. L.E. Kent). Lithostratigraphy of the Republic of South Africa, South West Africa/Namibia, and the Republics of Bophuthatswana, Transkie and Venda. Handbk. Geol Surv. S. Afr. 8, 690pp.

245

Figure 1. Simplified fold axis map of the Crocodile River Fragment using the outcrop distribution of the Black Reef Formation (quartzite) as a marker horizon.

Figure 2. Schematic block diagrams showing the development of folding in the Crocodile River Fragment in terms of Fi, F2 and F3.

Geological Society of Australia Abstracts Number 32, Ballarat 1992

246 A 8 24 THE STRUCTURAL GEOLOGY OF THE TREPHINA GORGE AREA, A BASAL PART OF THE ARTLUNGA NAPPE COMPLEX, CENTRAL AUSTRALIA: IMPLICATIONS FOR THE TECTONIC DEVELOPMENT OF THE NORTHERN MARGIN OF THE AMADEUS BASIN David Selley CODES, University of Tasmania, Sandy Bay, TAS. The complex structural style of the northern margin of the Amadeus Basin has long been recognised as being characteristic of a southerly propagating fold and thrust belt (Forman and Milligan, 1967). The tectonic evolution of this region has, however, in recent years become a topic of considerable controversy. While most researchers (Forman and Milligan, op. cit.; Wells et al., 1967, 1970; Teyssier, 1985; Shaw, 1991; Shaw et al, 1991; Stewart et al., 1991) attribute major structures along the northern margin to the DevonoCarboniferous Alice Springs Orogeny, Ding et al., 1989 consider that an inconsistency in structural style between crystalline basement and basal, Upper Proterozoic basin lithologies, and the overlying Palaeozoic succession is evidence for an Upper Proterozoic orogenic period. An event they named the Arltunga Orogeny. The Trephina Gorge Area is a critical area for the understanding of the tectonic development of the northern margin of the Amadeus Basin. It is situated 80km to the east of Alice Springs and represents a basal portion of the Arltunga Nappe Complex. Lithologies include basement rocks of the Arunta Complex and an Upper Proterozoic cover sequence which involves basal Amadeus Basin sediments: Heavitree Quartzite, Bitter Springs Formation and the unconformably overlying Areyonga Formation. A complex structural style is displayed within Basement, Heavitree Quartzite and Bitter Springs Formation. The vergence, geometry and distribution of early fold generations, juxtaposition of exotic and autochthonous stratigraphic sequences and the partitioning of strain throughout the area, can be explained in terms of a southerly propogating fold and thrust belt ( D j ) . Two mechanisms of thrust emplacement have been identified; a primary phase, which involved considerable shortening within basement and cover rocks, giving rise to a present thickness almost twice that of the pre-orogenic sequence, and a secondary phase, which involved gravity sliding above detachments within the uppermost portion of the tectonic stack. Two episodes of westerly directed reactivation of a middle level detachment surface (D2 & D3) have produced high amplitude, steeply inclined to recumbent, tight to isoclinal folds. These structures have resulted in repeated refolding of overlying thrusts Geological Society of Australia Abstracts Number 32, Ballarat 1992

and early isoclinal, recumbent fold generations developed during D i . As with the major thrusting episode, the effects of these deformations are restricted to lithologies stratigraphically lower than the Areyonga Formation. Thus D1-D3 involve structures which are characteristically thin-skinned in style. Subsequent tilting, steep normal faulting and apparent strike-slip faulting has modified D1-D3 structures and deformed the Upper Proterozoic and Palaeozoic sequences overlying the Bitter Springs Formation. The recognition of an angular unconformity at the top of the Bitter Springs Formation and the absence of D1-D3 within the Areyonga Formation and younger strata, leads the author to conclude that the thin skinned structures exhibited throughout the Trephina Gorge Area developed during an Upper Proterozoic phase of orogenesis. References Ding, P., James, P. R., Sandiford, M., 1989. Late Proterozoic deformation and the evolution of the northern margin of the Amadeus Basin. Geol. Soc. Aust. Abstract 24: 34-35 Forman, D. J., Milligan, E. N., 1967. Regional geology and structure of the north-eastern margin of the Amadeus Basin, Northern Territory. Bur. Miner. Resour., Geol. Geophys. Aust., Report 103 Shaw, R. D., 1991. The tectonic development of the Amadeus basin, central Australia. Bur. Miner. Resour., Geol. Geophys. Aust., Bull. 236: 429-462 Shaw, R. D., Korsch, R. J., Wright, C., Goleby, B. R., 1991. Seismic interpretation and thrust tectonics of the Amadeus Basin, central Australia, along the BMR regional seismic line. Bur. Miner. Resour., Geol. Geophys. Aust., Bull. 236: 385-408 Stewart, A. J., Oaks, P. Q., Deckelman, J. A., Shaw, R. D., 1991. 'Mesothrust' versus 'megathrust' interpretations of the structure of the northeastern Amadeus Basin, central Australia. Bur. Miner. Resour., Geol. Geophys. Aust., Bull. 236: 361-384 Teyssier, C., 1985. A crustal system in an intracratonic tectonic environment. J. Struct. Geol., 7: 689-700 Wells, A. T., Ranford, L. C., Stewart, A. J.,

247 Cook, P. J., Shaw, R. D., 1967. Geology of the north-eastern part of the Amadeus Basin, Northern Territory. Bur. Miner. Resour., Geol. Geophys. Aust. Report 113

Wells, A. T., Forman, D. J., Randford, L. C., 1970. Geology of the Amadeus Basin, central Australia. Bur. Miner. Resour., Geol. Geophys. Aust. Bull. 100.

A 8.25 THE ROLE OF GRANITIC MAGMATISM IN THE FORMATION OF METAMORPHIC CORE COMPLEXES IN THE D'ENTRECASTEAUX ISLANDS, EASTERN PAPUA NEW GUINEA E. J. Hill 1 , S. L. Baldwin 2 and G. S. Lister 3

2

1 Department of Earth Sciences, Monash University, Clayton, Victoria Researcfi School of Earth Sciences, Australian National University, Canberra 3 Victorian Institute of Earth and Planetary Sciences, Melbourne, Victorai

The D'Entrecasteaux Islands of eastern Papua New Guinea lie in an area of active continental extension at the western end of the Woodlark Basin sea floor spreading system. Domes of metamorphic basement are bounded by broad mylonitic shear zones (several 100 metres thick) and faults, and cored by multiply deformed, high grade metamorphic rocks (reaching eclogite and granulite facies). The shear zones consist of intensely deformed, transposed and retrogressed (amphibolite facies) equivalents of the core zone rocks. Complex intersections between numerous shear zones resulted in the domal shape of the metamorphic basement (Hill, 1990). The basement is overlain by faulted ultramafic rocks and recent volvanics and sediments. Approximately 30-40% of the basement rocks in the D'Entrecasteaux Islands consist of undeformed and deformed granodiorite. Emplacement of the plutons post-dates all pre-shear zone deformation and there is a clear relationship both spatially and chronologically between granitic plutonism, shear zone deformation and the exhumation of high grade metamorphic rocks. Bouguer anomalies around the D'Entrecasteaux Islands confirm that there is a broad spatial correlation between the high grade metamorphic rocks and the intrusion of large bodies of granodiorite. K/Ar and ^^Ar/^^Ar analyses on hornblende, muscovite, biotite and K-feldspar indicate that the plutons are Pliocene to Pleistocene age and cooled extremely rapidly (>100°C/Ma). Estimates of depth of emplacement of granodiorites are 4-5 kbars. At least two major episodes of granodiorite intrusion can be delineated on the basis of structural and geochronological relationships. Older plutons (Ar/Ar cooling ages of approx. 3.5 - 4.0 Ma) were emplaced prior to, or at the onset of shearing and contain pervasively developed mylonitic shear zone fabrics. Younger plutons (Ar/Ar cooling ages of approx. 1.5 - 2.0 Ma, U/Pb zircon age 2.1 Ma), which are largely undeformed except for localised crosscutting shear zones, were emplaced late during Geological Society of Australia Abstracts Number 32, Ballarat 1992

shearing. Previous workers have suggested that granodiorite forms the core of the domes and that the geometry of the domes is directly related to the spatial arrangement of the plutons (Davies & Ives, 1965; Oilier & Pain, 1980; Davies & Warren, 1988). However, most outcrops of granodiorite found in the basement are not located in the centre of the domes. For example, a large pluton of granodiorite, the Omara pluton (covering an area of approximately 150 km^), lies in a relatively low topographic area between two of the basement domes. Minor outcrops of granodiorite are also found in the cover rocks which overlie the basement. The upper boundary of the Omara pluton dips around 0° to 10°, suggesting that the pluton may be a sheet-like body. The pluton boundaries are discordant with structures in the host rocks, including the domebounding shear zones which intersect the pluton boundaries at angles of around 30° or more. The plutons do not appear to be strictly related to the geometry of the shear zones, and it is therefore considered unlikely that the granodiorite caused the shearing of the basement. There is no evidence of deformation in the outer margin of the Omara pluton or boundary - parallel deformation in the nearby country rocks; this indicates that the intrusion of the Omara pluton was essentially a passive process and not diapiric as suggested by Oilier & Pain (1980). Furthermore, the orientation of the stretching lineation and asymmetric microstuctures in the mylonitic shear zone rocks indicate that movement on the shear zones which bound the domes is not radial. However, there is undeniably an important temporal and broad spatial relationship between the granodiorite plutons and topographically elevated areas of exhumed high grade metamorphic basement. A model is proposed in which extension of the crust, related to nearby sea floor spreading and rifting in the Woodlark Basin and graben formation in Goodenough Bay and the Trobriand Basin, was accommodated by

248 movement on normal shear zones and allowed localised exhumation of high grade metamorphic basement in the D'Entrecasteaux Islands. The prodution of large quantities of granodiorite magma must be the result of localised heating associated with continental extension, for example by basaltic underplating. It is proposed that the large quantites of granodiorite magmas introduced into the crust during extension caused inflation of the crust resulting in localised surface uplift. References Davies, H.L. & Ives, D.J., 1965. The geology of Fergusson and Goodenough Islands, Papua New Guinea. Bureau Mineral Resources Australia,

Geological Society of Australia Abstracts Number 32, Ballarat 1992

Report, 82 Davies, H.L. & Warren, R.G., 1988. Origin of eclogite-bearing, domed, layered metamorphic complexes ("core complexes") in the D'Entrecasteaux Islands, Papua New Guinea. Tectonics, 7, 1-21. Hill, E.J., 1990. The nature of shear zones formed during extension in eastern Papua New Guinea. Proceedings of the Pacific Rim Congress 90, Australian Institute of mining and metallurgy 537548. Oilier, C.D. & Pain, C.F., 1980. Active rising surficial gneiss domes in Papua New Guinea. Journal of the Geological Society of Australia, 27, 33-44.

249

A9: ENGINEERING GEOLOGY CONVENOR: PETER

THORNTON

KEYNOTE: A 9.1 ENGINEERING GEOLOGY AND ENVIRONMENTAL CONTROL IN PROJECTS ADJACENT TO THE WORLD HERITAGE AREA, TASMANIA FJ.Baynes Consulting Engineering Geologist, Tasmania A number of developments adjacent to the World Heritage Area in south-west Tasmania have been subject to intense environmental scrutiny to ensure that any impacts are minimised. The developments involve major earthworks and/or rock excavation in forested mountainous terrain that has often been subject to the influence of glaciation and is underlain at relatively shallow depths by Palaeozoic rock, The developments are associated with the extractive industry and hydro power development.

2,000,000m3 of varied construction materials for dam construction. * The location and excavation design of two power stations. * The investigation, design, construction and rehabilitation of over 20 kilometres of roads. * The assessment of the potential for leakage of a dam on a karst foundation.

The usual relationship between the engineering geological model and the investigation and design of Case histories are detailed to illustrate the way in the project has another important function to perform, which timely engineering geology can form an that of ensuring acceptable environmental intrinsic part of environmental impact assessment and management. The role of the engineering geologist in control. The case histories include: the process of environment management of heavy civil and mining projects is considered and it is suggested * The analysis of the effects of production that the engineering geologist is well placed to exert a blasting in an operating quarry adjacent to a positive influence on major developments. karst system. * The search for and development of A 9.2

VICTORIAN COASTAL VULNERABILITY STUDY R.W.Buckley

Coastal Investigations Unit, Port of Melbourne Authority, Victoria. Current scientific opinion indicates that the worlds climate will undergo change within the near future due to the Greenhouse Effect. Estimates for a rise in mean sea level have been made assuming a Business-asUsual scenario, ie, only a minor decrease in the current rate of greenhouse gas emissions. These indicate the global mean sea level will rise by 8-29cm by the year 2030 and 21-7 lcm by the year 2070 (Warrick & Oerlemans, 1990). Unfortunately, current models are unable to predict detailed regional variations in climatic patterns which also have a vital impact on Geological Society of Australia Abstracts Number 32, Ballarat 1992

coastline stability. Following the Victorian Governments draft strategy policy statement on the greenhouse effect (Roper, 1989), the Coastal Investigations Unit was funded in 1990 to conduct a study to investigate the impact of projected greenhouse mean sea level changes on the 3000km coastline of Victoria. Assessment of greenhouse changes on the Victorian coastline and subsequent identification of areas of high potential vulnerability to these changes was both qualitative and quantitative. Qualitative

250 assessment was based on site visits and information derived from aerial photography, maps and reports on Victorian coastal geomorphology, coastal processes and wave climates. Quantitative assessment was undertaken through numerical modelling of 21 typical shore normal profiles for a 0.3m and 0.5m rise in mean sea level. Profile sites were selected so that they were representative of geomorphic units along the Victorian coast. Results provide an indication of the magnitude of beach erosion during the next fifty years (see Table 1). The impact of greenhouse changes on the coastline will vary depending on such factors as coastal geomorphology, coastal processes, wave climate and rate and magnitude of any sea level rise. As a general model, physiographic response to a rise in sea level was taken from Bird (1988). Delineated by physiographic type, the following locations (not listed in priority order) were identified as areas which may suffer significant impacts due to greenhouse changes: 1. SANDY BEACHES - Middle Park, Brighton, McCrae, Somers, St. Leonards, Swan Island, narrow sections of the beach from Aspendale to Cairum, Henty Bay area Portland, Bridgewater Bay, Port Fairy, Lome, Grantville and the majority of beaches in the Gippsland Lakes. Structures built on the beach such as yacht clubs, life saving clubs, bathing boxes and boat sheds are at risk from increased wave attack. 2. SANDY BARRIERS - Melbourne Water Corporation Metropolitan Sewerage Farm at Werribee, Cheetham Salt Works at Werribee, Avalon and Point Henry, Ninety Mile Beach fronting Bunga Arm and Jack Smith Lake, Ewings Morass and low lying sections of the barrier fronting Comer Inlet. 3. ESTUARIES - Lake Connewarre, Lower Barwon River, Snowy River, Andersons, Shallow & Sydenham Inlets & Belfast Lough, Port Fairy. 4. MUDFLATS - Swan Bay, north east Corner Inlet and low gradient mudflats in north, west and eastern sections of Western Port. 5. SWAMPLANDS - Carrum Swamp and low lying sections adjacent to the Gippsland Lakes, especially Lake Wellington and the

Geological Society of Australia Abstracts Number 32, Ballarat 1992

Mitchell River Silt Jetties. 6. CLIFFS - soft Tertiary sedimentary cliffs at Sandringham, Beaumaris, Torquay to Fairhaven and Pebble Point to Warrnambool and the calcarenite cliffs Portsea to Sorrento, and Warrnambool. In general, impacts on cliffs will be slower than on the more dynamic, variable landforms hitherto listed. This study has identified coastal sites that are potentially vulnerable to greenhouse changes. Results indicate that the largest recession rates are for ocean beaches west of Cape Otway, due in part to the relatively fine beach sand and the more severe Southern Ocean wave conditions. Shoreline recession rates will also be of significance in parts of Port Phillip Bay and the Gippsland Lakes. This is due to the generally narrower beach zone at these locations compared to the ocean beaches. The Government now has the chance to develop policy, planning and management practices that will minimise future economic, social and environmental costs resulting from greenhouse changes. Acknowledgments This study was funded by the Greenhouse Unit, Department of Conservation & Environment and conducted by personnel of the Coastal Investigations Unit. Permission to publish this paper by the Port of Melbourne Authority is acknowledged. References Bird, E.C.F. 1988, Physiographic indications of a sealevel rise, in G.I.Pearman(ed.) Greenhouse: Planning for Climate Change. Commonwealth Scientific & Industrial Research Organisation, Melbourne, pp. 60-73. Roper, T. 1989, The Greenhouse Challenge: The Victorian Government's Response. A Draft Strategy for Public Comment. Ministry for Planning & Environment. Warrick, R.A. and Oerlemans, H. 1990, Sea Level Rise, in J.T.Houghton, G.J.Jenkins and J.J.Ephraums (eds.) Climate Change. The IPCC Scientific Assessment. Intergovernmental Panel on Climate Change. World Monetary Organisation, United Nations Environment Programme.

251 TABLE 1 - SUMMARY OF NUMERICAL MODELLING OF BEACH RECESSION DISTANCES DUE TO MEAN SEA LEVEL RISE LOCATION

RECESSION OF BEACH BERM DURING NEXT 50 YEARS (METRES) 0.3m Rise in 0.5m Rise in Sea Level Sea Level South Australian Border to Cape Otway 3-15 5-28 Cape Otway to Point Lonsdale 2.5-9 4-13 Port Phillip Bay 2.5 - 4.5 3.5 - 8.5 Gippsland Lakes 4 3 Wilsons Promontory to New South Wales Border 2-5 3.5-7 NB. Variation of recession distances within sections of the coast is due to site specific factors. A 9.3 INTRODUCING THE VOLUME "THE ENGINEERING GEOLOGY OF THE MELBOURNE REGION" J.L. Neilson and W.A. Peck 1

2

^Geological Survey of Victoria, Department of Manufacturing and Industry Development. ^Geology and Geological Engineering School, Department of Transport and Resource Engineering, R.MJ.T. The continuing growth of the Melbourne urban region, with associateddemands for building construction and infrastructure development meansthat there is an ongoing requirement for geological and geotechnicalinformation across this region in order to assist sound decisionmaking and optimal cost-effective developments. There is an extensive amount of geological and geotechnicalinformation on the Melbourne region. Some of this is published indiverse places and much of it is unpublished in the files ofindividuals, consultants, semi-government and government authorities.The Victoria Group of the Australian Geomechanics Society iscompleting a major project of recording, integrating and documentingthis data in the form of a volume entitled "The Engineering Geology ofthe Melbourne Region". The basic method of the book is to present inconcise form on account of the geological units of the Melbourneregion and their distribution which integrates their geological natureand geotechnical properties. Much new information from engineeringprojects will be brought together and made known publicly for thefirst time. The authors of the book are more than 30 widely experiencedengineering geologists and geotechnical engineers from government,semi-government, academic and private bodies; individual workers andconsultants are included. Though they are specialists in either thegeological or the geotechnical engineering field, the authors all haveawareness of the Geological Society of Australia Abstracts Number 32, Ballarat 1992

field which is not primarily their own. The content of the volume is shown below: 1. Introduction 2. Geological setting of Melbourne: geological structure stratigraphy, groundwater and geomorphology. 3. Geological hazards and problems for engineering, including reaction soils, slope stability, seismicity, groundwater and corrosivity. 4. Geological units, e.g. Silurian, Werribee Formation (Tertiary). Each unit is described in terms of geology and geotechnical engineering by both a geologist and an engineer to yield a comprehensive description. 5. Construction materials, e.g. crushed rock, clays and building stones. 6. Special engineering issues, e.g. tunnels, rock anchors and basement construction. 7. Consolidated references, locality index and glossary. The book is aimed at a readership of engineers, geologists, buildingsurveyors, planners, building contractors, architects and students.lt will not remove the need for site investigation but make it moreeffective as the paper will explain. The comprehensive data will helpwith questions of land use, ground problems and constructionmaterials. The publisher is A.A. Balkema, Rotterdam, and

252 the book will appear inMarch, 1992. Enquiries should be directed to the AustralianGeomechanics Society

A 9.4

through the Institution of Engineers, Australia,at 191 Royal Parade, Parkville 3052.

THOMSON SADDLE DAM: GEOLOGICAL CONSIDERATIONS IN DAM STABILITY P.N. Thornton1* and P. Styles2 1 Golder Associates Pty. Ltd., formerly Board of Works Coffey Partners International Pty. Ltd., formerly Melbourne Water

2

The Thomson Dam was constructed by the Melbourne and Metropolitan Board of Works (now Melbourne Water) as part of the final stage of a major augmentation of the water supply of the City of Melbourne. The Main Dam is a 165 m high earth and rock fill dam on the Thomson River in Gippsland. The associated Saddle Dam is 36 m high and also of earth and rock fill construction. They create a reservoir that holds more than 1.1 megalitres of water which is fed into Melbourne's Water supply via some 37 kilometres of tunnel. The geology of the dam site is complex and had a major impact on design and construction. As an example this paper focuses on the affect of the geology on the stability of the Saddle Dam. The dam site is located on Early Devonian Norton Gully Sandstone consisting of interbedded siltstone and sandstone. To the west is the Middle Devonian Baw Baw Batholith consisting of biotite granodiorite to adamellite. The eastern margin of the batholith is less than 1 km west of the Saddle Dam and there is a zone of contact metamorphism which extends under the Saddle Dam. These rocks are folded into a series of anticlines and synclines with axial planes generally striking north-south. The major folds are the Thomson Syncline and Beardmores Anticline. Under the Saddle Dam folding becomes tighter and more complex than under the Main Dam. At the site, folding of the siltstone and sandstone has resulted in the formation of bedding faults and thrust faults which are generally continuous sub planar features of low shear strength. Also common are sub vertical cross faults which strike at right angles to the fold axes and rotational or scissor faults. The combination of folded and faulted bedrock and steep topography has resulted in slope movement being a common feature in the Thomson River valley. Areas of instability identified during the investigation and construction of the Main Dam were the: • Ski Jump Landslide, a wedge failure which required the removal of about 250000 cubic metres of disturbed material. • Core Trench Landslide, caused by the river undercutting bedding and requiring the removal of about 1 million cubic metres of material Geological Society of Australia Abstracts Number 32, Ballarat 1992

from the dam foundation. Synclinal Landslide, caused by the Thomson Syncline which plunges at about 12 degrees being undercut by the Thomson River. Construction of haul roads reactivated this slide which involved some 500000 cubic metres of material and required the placement of a major area of stabilising rock fill. Also evaluated in considerable detail was the stability of the ridge forming the right abutment of the Main Dam and in turn the downstream side of the Saddle Dam. It was postulated that preferential erosion of the east limb of the Thomson Syncline had created an imbalance of masses across the syncline which could result in movement to the east along a bedding plane fault. Extensive investigations ultimately provided sufficient information on the geology and geotechnical properties of the area to indicate there was sufficient factor of safety provided the Saddle Dam axis was moved upstream and drainage adits were extended. These major stability issues were considered and resolved as construction proceeded. However it was not until 1987 and after construction was completed that the stability of small scale features underlying the Saddle Dam was reviewed. During the winter of 1987 rising reservoir levels resulted in rising piezometric levels under and downstream of the Saddle Dam and seepage downstream. An overall re-evaluation of the Saddle Dam was then undertaken which included consideration of potential failure modes utilising features of the structural geology. Additional investigations and re-evaluation of the available geological data were carried out. This data included comprehensive geological mapping of the Saddle Dam foundations, detailed borehole logs and information resulting from the installation of further groundwater monitoring points. The re-evaluation identified five areas as possible failure mechanisms that warranted evaluation by two and three dimensional stability analyses. Two were wedges formed by a combination of bedding and a near vertical fold couple. The third was a wedge caused by a variable plunge on an axis of a syncline. Analysis carried out by the Board of Works and the dam •

253 designers, the Snowy Mountains Engineering Corporation, indicated that these three areas all had acceptable factors of safety. The fourth area was an upstream dipping wedge formed by a combination of bedding, a synclinal axis and faulting. The fifth area was a wedge formed by a combination of low angle bedding and a prominent fault. The bedding dipped toward the upstream side of the dam at an angle which decreased from about 27 degrees under the dam core to below 10 degrees in the vicinity of the upstream rock fill face and "daylighted"

Geological Society of Australia Abstracts Number 32, Ballarat 1992

just below the toe of the rock fill. Both wedges were found to have factor of safety of less than 1.5 which was judged insufficient for long term stability. A stabilising rock fill was subsequently added to the upstream side of the Saddle Dam to improve the factor of safety to that required. The stability investigations carried out for the Saddle Dam after construction was complete illustrate the importance of having detailed as constructed records of the geology of projects such as the Thomson Dam.

254

Geological Society of Australia Abstracts Number 32, Ballarat 1992

255

A10: HYDROGEOLOGY CONVENOR: RICHARD

KEYNOTE: A 10.1

EVANS

APPLICATION OF FIELD-SCALE TRACER TESTS IN THE EVALUATION OF SOLUTE TRANSPORT BEHAVIOUR David L. Rudolph

Waterloo Centre for Groundwater Research, University of Waterloo Waterloo, Ontario, Canada, N2L 3G1 As the awareness of the potential ramifications of groundwater contamination continues to develop, engineers and scientists are being compelled to provide a clear understanding of the behaviour of dissolved contaminant species in the subsurface. Prediction of the fate and persistence of a given solute in various hydrogeological regimes is a primary objective in problems related to the long-term quality of urban groundwater supplies and in the containment of hazardous waste. The problem of predicting the transport behaviour of many contaminants and specifically organic compounds, becomes progressively more complex with the realization that these contaminants are considered toxic at exceedingly low concentrations. The accuracy of our predictive capability, therefore, requires a thorough understanding of the processes that influence the transport and mixing of these solutes in different groundwater environments. Typically, the strategy adopted to predict solute migration has been to measure the critial physical and chemical parameters that are believed to control transport through either local, in- situ measurements, or through laboratory testing of small samples taken from the site under consideration. These data are generally introduced into some mathematical simulator which is then used to predict the movement of the solute. Recently, it has been observed by many investigators that predictions of solute transport that are based on the small-scale measurements of the physical parameters, seldom, if ever accurately reproduce the field-scale observations. This has generally been attributed to the heterogeneous nature of the geologic sediments that cannot be captured by a reasonable number of point measurements. In order to gain further insight into the nature of solute migration at the field-scale, contaminant hydrogeologists have designed controlled field experiments where specific solute species are Geological Society of Australia Abstracts Number 32, Ballarat 1992

introduced into the undisturbed porous medium and their movement monitored in detail as they migrate through the natural flow field or through a flow field artificially created in-situ. These experiments are referred to as natural-gradient and forced-gradient tracer tests respectively. By injecting a known mass of solute at a given time into a carefully monitored or controlled groundwater velocity field, the transport and mixing evolution of the solute can be observed and quantitatively evaluated. The mathematical simulator can be calibrated to match the tracer cloud at various points in time and thus, physical parameters more representative of the porous medium at the field-scale can be determined (Mackay et al., 1986). Alternatively, the movement of the tracer cloud can be analyzed by the method of moments, Aris (1956), such that the solute transport parameters, specifically dispersivity, can be inferred from the location and shape of the tracer cloud. This approach has been applied by Freyberg (1986), and recently by Garabedian et al (1991), in sand and gravel deposits. Tracer tests have been conducted in fractured clays and in unsaturated sand deposits among other settings and have even involved the release of dense, nonaqueous phase liquids. In this presentation, the main strategy behind these large-scale tracer tests will be discussed with reference to several examples in different hydrogeologic settings. Some of the major observations from these tests will be presented along with an overview of specific conclusions and insights that have been derived from them. The question of practicality and future direction in this area will also be considered. References Aris, R., On the dispersion of a solute infa fluid flowing through a tube, Proc. R. Soc. London,

256 a non-reactive tracer, Water Resour. Res., 27(5), Ser. A, 235, 67-78, 1956. 911-924, 1991. Freyberg, D.L., A natural-gradient experiment on solute transport in a sand aquifer: 2, Spatial Mackay, D.M., D.L. Freyberg, P.V. Roberts and J.A. Cherry, A natural gradient experiment on solute moments and the advection and dispersion of nontransport in a sand aquifer, 1: Approach and reactive tracers, Water Resour. Res., 22(13), overview of plume movement, Water Resour. 2031-2046, 1986. Res., 16(5), 901-907, 1980. Garabedian et al., Large-scale natural gradient tracer test in sand and gravel, Cape Cod, Massachusetts, 2: Analysis of spatial moments for A 10.2

CAMPASPE VALLEY CONJUNCTIVE USE STUDY A 10.2 M. Dudding *' F. Chiew and A.Brinkley 1

2

1

1 Investigations Branch, Rural Water Commission of Victoria Dept. of Civil and Agricultural Engineering, University of Melbourne

2

INTRODUCTION The Campaspe Deep Lead is a high yielding source of good quality water, with current usage in the northern section of approx 9000 Ml/year. Large scale Deep Lead development was initiated during the 1982-83 drought and the resultant increased pumping stabilised rising Deep Lead pressures around pumping sites. This extraction also had an effect on the shallow aquifer (Shepparton Formation) due to increased deep drainage. The extent of Deep Lead control is not as great in dryland areas, where Deep Lead pressures are rising at up to 20 cm/year and Shepparton Fm. watertables are also rising at up to 20 cm/year. The irrigation region watertable "mound" is spreading into dryland areas, also posing considerable salinity risk. The Conjunctive Use Study is to form a basis for community discussion of options and implementation of an operational groundwater extraction scheme. The objectives of the study are: * To fully assess, both technically and economically, the merits of conjunctive use of groundwater and surface water * To determine the optimum yield and sustainability; and to monitor yield and water quality of the Deep Lead resources * To obtain salinity benefits by enhancing drainage to the Deep Lead from the Shepparton Formation * To devise a strategy which seeks to conjunctively manage the available surface water and groundwater resources to ensure their long term sustainability and efficient use THE CONJUNCTIVE USE STUDY A 30 day pumping test conducted to determine the optimum yield and resource sustainability of the Deep Lead. The Production Bore at Elmore was pumped at 160 litres/sec, extracting a total volume of 414 Megalitres (Ml). The Deep Lead water quality stabilised after two weeks of pumping and Deep Lead transmissivities Geological Society of Australia Abstracts Number 32, Ballarat 1992

ranged generally from 900 - 1300 m2/day. At one site, a vertical hydraulic conductivity of 3.8 - 4.3 mm/day was calculated. The varying shallow aquifer response to Deep Lead pumping in this area points to preferred pathways providing the dominant recharge mechanism to the Deep Lead. The following options were considered for conjunctive use: 1. Borefield sited at Barnadown and water pumped to Bendigo. 2. Borefield sited at Elmore and water pumped to the CID No 1 channel or the Campaspe River. 3. Borefield sited on southern edge of CID and water pumped to the Campaspe River. 4. Incentives to encourage a greater volume of extraction from private bores in the CID. RESULTS The pumping of Deep Lead groundwater into the Campaspe River will result in an increase in the total Campaspe River Salinity. Current Campaspe River salinity of 500EC will increase on average by 19 EC under option 2 and by 38 EC to 174 EC under option 3. Pumping of this groundwater, however, will result in reduced baseflow to the Campaspe River. This is the most significant benefit apart from the sale of groundwater. Only option 3 and 4 have an impact on baseflow volumes. The only area of increasing demand for water in the Campaspe region is the urban sector (Bendigo), which is expected to pay approximately $500/ML to meet the current excess demand over supply. The costs of supplying additional water to Bendigo under options 2,3, and 4 are all less than $500/ML, meaning that the project is financially viable through resource costs alone. CONCLUSIONS The benefits of Deep Lead Pumping are to: * Provide an additional water resource to urban or rural users. * Assist in controlling water tables in dryland areas.

257 * Reduce groundwater baseflow into the Campaspe River. The disbenefits of Deep Lead Pumping are to: * Increased salinity of irrigation water. * Increased salt loads in the Murray River caused by groundwater pumped into the Campaspe River.

In summary: * Significant benefits, in terms of water supply to Bendigo, have been identified. * An inexpensive supply of groundwater has been identified for private development. * Salinity benefits, whilst hard to accurately define, are very real.

A 10.3 OPTIMAL GROUNDWATER PRODUCTION USING GENERAL-PURPOSE OPTIMISATION SOFTWARE N.P. Merrick1* and R.C. Harwood 2 department 2

of Applied Geology, University of New South Wales, Kensington, NSW. Groundwater Technology Australia Pty Ltd, Kings grove, NSW.

Allocating limited resources to competing users is an age-old problem which is common to every walk of life. Mathematical programming techniques have long been used to solve general problems of this type by establishing optimal operating rules which achieve some stated objective. When groundwater is considered as a limited resource, the competing users are the bores (or their owners) and the operating rules are the volumes of water pumped from each bore over a period of time. The objective is usually to minimise cost but a physical surrogate of cost will often suffice. This paper shows how the groundwater production problem can be solved by invoking the commercial software package called GAMS (Brooke, et al., 1988) which is essentially a high-level programming language linked to optimisation routines. The user needs to know how to formulate the problem as an optimisation problem, but does not need to know anything about the mathematics of optimisation. Suppose that a borefield consists of N production bores which pump groundwater according to a demand pattern Dt(t = l,2, T) defined over a period of T days. On any one day t, the output Qnt from any one bore n (n = 1, 2, ..„, N) is taken to be constant. At each bore there are constraints on installed pump capacity (P n ), available drawdown (s n ) and perhaps required drawdown (r n ). The aim is to find optimal values for Q n t which minimise cost, or a surrogate measure of cost such as average drawdown, while satisfying the demand schedule. If the groundwater system can be represented by an analytical model with linear drawdown behaviour, such as a confined or leaky aquifer, then the drawdown constraint at bore n on day t may be written as: N r

t

n - X X ^nmdQmd m=l d=l

Geological Society of Australia Abstracts Number 32, Ballarat 1992

^

where a n ^ is the drawdown produced at bore n due to pumping bore m at unit rate (1 m3d _1 ) during day d. The pump capacity constraint is:

Qnt^Pn The demand constraint is:

N

X Qnt - ^ t n=l A specific industrial borefield in the Botany Basin near Sydney operates three production bores over a 28day cycle. The demand is generally 700 m 3 d _1 except for a 3- day period when 1000 m 3 d _1 is required, and on alternate weekends the plant shuts down for two days. Available drawdown is about 9 m and installed pump capacities range from 720 to 840 m 3 d _1 . Because the present modus operandi withdraws water in excess of requirements, the company wished to know the optimal pump rate for each bore on each day of the 28-day period, not only under normal conditions but also for periods when one bore might be out of action. The problem has been solved using the linear programming (LP) option within the GAMS software package. A key advantage of GAMS is that constraints are specified algebraically without having to write the full set of equations. In this case there are 84 unknowns defined by 280 equations. Solutions have been found for a number of scenarios. In each case, the optimal solution is to pump each bore at a constant rate during the period of normal demand, and to pump at a different constant rate during the period of peak demand. The results for some of the scenarios are summarised in Table 1.

258 Scenario 1 examines the case in which all three bores are available for production. Scenarios 2-4 consider the impact of having each bore in turn unavailable for use.

Scenario 5 looks at the special case where the third bore is reserved for days of peak demand only,

Table 1 : Optimal Pump Rates Scenario:

1

2

3

4

Normal supply (m\i~ 335 0 327 Q1 205 365 361 0 Q2 286 0 373 339 Q3 209 Peak supply (m 3 d _1 ) 436 426 Q1 180 0 574 579 0 Q2 412 564 0 Q3 403 421 Average drawdown (m) s 3.88 3.86 3.91 3.87

Because GAMS is general-purpose software, it can be applied to any problem which can be formulated as an optimisation problem. In particular, it holds great promise for providing assistance in practical groundwater supply and dewatering decision-making.

A 10.4

5

335 365 0 276 443 281 3.88

Reference Brooke, A., Kendrick, D. and Meeraus, A., 1988, GAMS: A users guide. The Scientific Press, California, 289p.

MINE DEWATERING OPERATIONS AT MORWELL OPEN CUT J Schaeffer1, B Llewellyn1, P Wood1 and R Friday2 1

Geoengineering Division, SECV, Morwell, Victoria 2 Golder Associates Pty Ltd, Hawthorn, Victoria

Morwell Open Cut produces approximatey 14 million tonnes per annum of brown coal for power generation in the Latrobe Valley of South Eastern Australia. To maintain the stability of the mine floor and batters two major underlying aquifer systems, within the sediments of the Tertiary Latrobe Valley Group, require depressurisation. These aquifer systems are referred to as the Ml and M2 Aquifers. The Ml Aquifer system is the shallower, occuring at depths between 2 m and 20 m below the base of the open cut. This aquifer contains up to 3 discrete sand bodies which vary in thickness up to 6 m. The M2 Aquifer system occurs at depths between 60 m and 150 m below the base of the open cut and consists of a number of separate sand bodies, of which the top 6 are presently being depressurised. The M2 Aquifer sands are generally thicker, coarser and more transmissive than the Ml Aquifer sands. The separators (aquitards) between the M2 Aquifer sand bodies are also less ligneous than those of the Ml and consist of weathered volcanics, silty clays and minor ligneous clays and coals. Geological Society of Australia Abstracts Number 32, Ballarat 1992

Both aquifer systems require significant depressurisation to prevent heave of the open cut floor, excessive batter movements and flooding. Pumping from these aquifers commenced in the 1960's and an extensive dewatering network has been developed. Pumping from the Ml Aquifer peaked at 350 L/s in 1970 and from the M2 at 1000 L/s in 1975. Current total pumping yields are approximately 100 L/s (Ml) and 650 L/s (M2). Aquifer pressures have been lowered by up to 130m over the last thirty years. Since 1989 a drilling program has been carried out to refine the hydrogeological model for Morwell Open Cut as the mine develops further to the west and south-west. Significant variations in aquifer stratigraphy, including the occurrence of thick sequences of weathered volcanics, the identification of a clay unit above the top M2 sand, and the identification of discrete sand bodies within the Ml Aquifer system are now leading to different approaches to dewatering. The new data is also enabling more accurate predictions of piezometric pressure trends and pumping requirements for the new South East Field,

259 and as overburden is progressively dumped back into the miife. This paper summarises the revised hydrogeology at Morwell Open Cut, the effect of dewatering on mine

A 10.5

development and stability, and the use of groundwater models in the determination of future pumping requirements.

G R O U N D W A T E R P R O C E S S E S IN T H E B A S A L T PLAINS OF S O U T H W E S T E R N VICTORIA B.S. Mann 1 *, D.A. Stanley 1 , P.F. Bolger 1 and J.Nolan 2 1 Groundwater Section, Rural Water Commission of Victoria 2Gutteridge, Haskins and Davies, Melbourne, Victoria.

The hydrogeology and salinity processes beneath the northern Basalt Plains of southwestern Victoria are governed by the interactions of local and regional flow systems. The two major aquifer systems within the region are the unconfined to semi-confined shallow system comprised of fractured basalts and scorias belonging to the Pliocene to Recent Newer Volcanics, and the underlying confined system consisting of Palaeocene to Pliocene-aged, non-marine to marine clastic sediments which comprise the Eastern View and Moorabool Viaduct Formations. Ordovician basement rocks outcropping along the southern slopes of the Central Highlands and forming the northern edge of the Basalt Plains acts as an unconfined fractured rock aquifer. These basement units have a localized influence on both the volcanic and the sedimentary aquifer systems along the highland/plains boundary zone. Basement structure contours show that a major graben trends northwest-southeast within the region and apparently terminates to the south against an extensive subsurface ridge of Devonian granite. Drilling in the vicinity of Lismore and Derrinallum townships indicated that the graben does not extend south of the granite ridge. The northern part of the graben joins a narrow channel which represents the palaeo-drainage system to the north. A thick sequence of Tertiary sediments was deposited within the confines of the graben. To the north, a restricted, very coarse grained fluvial deposit (up to pebble and cobble size), now covered by Newer Volcanics lavas, comprises the Langi Logan Deep Lead and delineates the major fluvial system supplying clastic material to the graben. Further to the south, in the central zone of the graben, the Tertiary sediments become finer and range from thin, fine to medium sands interbedded with thick silty clays and minor lenses of brown coal. Palynylogical age determinations indicated a Palaeocene to Early Eocene age for the graben sediments, and they have been subsequently assigned Geological Society of Australia Abstracts Number 32, Ballarat 1992

to the Palaeocene to Miocene Eastern View Formation. A second Deep Lead deposit identified immediately north of the granite ridge comprises coarse grained, very angular reef quartz, suggesting that these sediments were deposited close to their source and are probably limited in areal extent. These deposits have also been included in the Eastern View Formation. Thin deposits of gravels, sands and brown coals overly the Eastern View Formation in the northern parts of the area, while to the south calcareous sands and clays predominate. These strata, dated as Pliocene in age, are included in the Moorabool Viaduct Formation and represent a lateral facies change from non-marine to marine deposition during a late Tertiary marine transgression-regression cycle. The Eastern View Formation sediments comprise an extensive regional aquifer system which, in the southern parts of the study area, is capped by a thin aquitard formed by the Moorabool Viaduct Formation. The variation in lithology and thickness with the Eastern View Formation sequence indicates a wide range of hydraulic conductivities and transmissivities for the aquifer system. Piezometric data and estimated transmissivities were used to construct a flow net for the Eastern View Formation grater than 30 mm/year in the northern part of the study area, with discharge of the same order in the south. This is consistent with the observation bore data which demonstrates upwards discharge of the Eastern View Formation aquifer into the overlying New Volcanics. The proximity of the discharge zones in relation to the granite ridge indicates the importance of basement structure upon the potentiometry of the Eastern View Formation aquifer. Where the Eastern View Formation sediments abut elevated basement rocks, lateral groundwater flow is restricted and forced upwards into the overlying Newer Volcanics. The Newer Volcanics form two major aquifers within the study area in terms of both groundwater resources and salinity. They can be subdivided on the basis of lithology and weathering characteristics into

260 an earlier , widespread "First Phase" and a younger, more locally distributed Second Phase'. The lower parts of the "First Phase" volcanics represent the initial valley flows which filled existing streams and generally subdued the pre-volcanic topography, probably during the Early to Middle Pliocene. The "lower Fist Phase is characterized by relatively fresh basalts of variable thickness, with a high degree of fracturing and vesicularity, with a welldeveloped and laterally extensive weathering horizon at the top. The upper parts of the 'First Phase' basalts were emplaced over the existing volcanic terrain, which further subdued the topography to form the typical 'plains' landscape seen today. These 'upper First Phase' basalts consist primarily of massive, sense basalts with a low degree of fracturing and the development of a major weathering horizon at the top, which represent the general deep clayey soils typical of the "plains' country. The distinction between the lower and upper units of the First Phase basalts can be readily seen on neutron logs which reflect the higher porosity of the lower unit. Moreover, the highest yielding water intervals within the First Phase basalts are invariably associated with the lower unit. The lower unit comprises the major regional fractured basalt aquifer system, capped by aquitards consisting of weathering horizons (at the top of both the lower and upper units). The upper unit of the First Phase basalts itself may be considered as a leaky semi-confining layer, 1

A 10.6

which restricts downwards drainage to the lower First Phase unit. The 'Second Phase' basalts have been emplaced directly upon the upper First Phase volcanics and generally form unconfined aquifers. Scoriaccous horizons in the vicinity of volcanic cones act virtually as porous media aquifers, while the blocky 'stony rise' basalts form a fractured rock aquifer. The weathered surface of the upper First Phase basalts restricts vertical seepage, so that lateral throughflow is the dominate groundwater movement in the Second Phase Volcanics. This lateral flow discharges at the edges of scoria cones and lava flows, giving rise to the formation of shallow saline lakes and streams within and close to the margins of the Second Phase volcanic terrain. The enhanced evaporation of already brackish groundwaters concentrates salts which eventually find their way into the regional basalt aquifer (lower First Phase unit). The regional Tertiary sedimentary groundwater system, in conjunction with the more localised Second Phase basaltic groundwater system, both have important influences upon the regional New Volcanics (lower First Phase) groundwater system, and hence land salinization. This influence is characterised by upwards discharge on a regional scale (Tertiary sedimentary aquifer) and regional-local discharge from the Second Phase volcanics onto the flatter plains country of the First Phase volcanics.

CHLORINE-36 DATING OF VERY OLD GROUNDWATER IN THE GREAT ARTESIAN BASIN, AUSTRALIA M.A. Habermehl *, T. Torgersen and F.M. Philips 1

2

3

^Bureau of Mineral Resources, Geology and Geophysics, Canberra, A.C.T., Australia ^Department of Marine Sciences, University of Connecticut, Groton, CT, U.S.A. Geoscience Department and Geophysical Research Center, New Mexico Institute of Mining and Technology, Socorro, NM, U.SA. 3

Chlorine-36 dating of very old groundwater in the Great Artesian Basin has enabled the interpretation of rates of movement of the artesian groundwater in the Lower Cretaceous-Jurassic aquifers of most of the Great Artesian Basin, and produced a broadscale pattern of groundwater ages for the Basin. The Great Artesian Basin occupies 1.7 x 10 km or about one-fifth of Australia, and consist of a multilayered confined aquifer system, with aquifers occurring in continental quartzose sandstones of Triassic, Jurassic and Cretaceous age. The intervening confining beds consist of siltstone and mudstone; a thick argillaceous sequence of sediments of marine origin and Cretaceous age forms the main confining 6

Geological Society of Australia Abstracts Number 32, Ballarat 1992

2

unit. Recharge occurs mainly in the eastern marginal zone, and large-scale regional groundwater movement is generally towards the southwestern, western and southern margins. Minor recharge takes place in the western margin, and that water moves in a southeasterly direction. Regional groundwater movement and residence times have been determined by basin- wide hydrogeological studies, including the simulation of the regional groundwater hydraulics by computer-based numerical models. The inferred groundwater flow patterns, and the Basin's hydrodynamics have been confirmed by isotope hydrology studies, including C and C1 analyses. 14

36

261 Chlorine-36 analyses comprise the measurement of which occurs at a very low ratio to stable chloride of several parts in 10 1 4 in environmental samples, using Accelerator Mass Spectrometry. The half-life of chlorine- 36 is 3.01 x 10 5 years, giving a potential dating range of more than 2 million years. Chlorine-36 and carbon-14 isochrones are in good agreement with ages obtained from hydrodynamic data, and show residence times from several thousand years near the marginal recharge areas to more than 1.0 x 10 6 years near the centre of the Basin. Groundwater flow patterns and the continuing recharge by meteoric water from geological to modern times have been c o n f i r m e d by e n v i r o n m e n t a l isotope and hydrochemical studies. Groundwater in the most widely exploited pressure aquifers in the Lower Cretaceous- Jurassic sequence generally contains water of the chemical Na-HCC>3-Cl type, and these ions contribute more than 90 % of the total ionic strenght of solutes in the main basin area. Evolution of the groundwater chemistry along the flowlines is characterized by the removal of Na and K by reconstitution reactions involving kaolinite, a Nasmectite and illite. In the southwestern part of the Basin the groundwater is characterized by Na-Cl-S04 type water, and the two regional groundwater flow directions show different hydrochemical characteristics, with the westwards flowing water being of the NaHCO3-CI type and the eastwards flowing water being of the Na-Cl-S04 type. These flows, within the same aquifer meet and mix, and are directed towards the main discharge area near the Basin's southwestern margin. Natural discharge occurs from flowing artesian springs in these areas. Groundwater surface temperatures of wells tapping aquifers in the Lower Cretaceous- Jurassic sequence generally range from about 30° to 100°C. It is suggested that the flow conditions in the Basin have been largely unchanged during the last 1-2 x 10^ years, and that the recharge areas have been operating similar to the present. The western part of the Basin has operated as a distinct separate flow system from the main part of the Basin, with its own

recharge area and its own geochemical evolution. In the northwest-central region of the Basin occurs an area with young 36 C1 ages, and groundwater in this area must have originated from a source region towards the northwest. This additional recharge area was more active over the last 0.5 x 106 years than at present, as indicated by the 36 C1 results. As radiotracers retain a memory of the history of the groundwater in an aquifer system, it is possible to evaluate, using 3 6 C1 data, whether flow within the Great Artesian Basin aquifer system has been in a steady-state or has changed its flow rate, recharge and direction over the mean residence time or age of the groundwater in the system. The use of radiotracer methodologies for the delineation of groundwater residence times or ages has been shown to be a valuable addition to the interpretation of potentiometric data and for the understanding of the geochemical evolution of the groundwater. It is clear that all these factors contribute to a better groundwater resource evaluation in the Great Artesian Basin. References Allan, G.L., Fifield, L.K., Bird, J.R., Smith, A.M., Ophel, T.R., & Habermehl, M.A., 1991, International Hydrology & Water Resources Symposium, Perth Bentley, H.W., Phillips, F.M., Davis, S.N., Habermehl, M.A., Airey, P.L., Calf, G.E., Elmore, D., Gove, H.E., & Torgersen, T., 1986, Water Resources Research, 22:1991-2001 Calf, G.E., & Habermehl, M.A., 1984, Isotope Hydrology 1983:397-413 Habermehl, M.A., 1980, BMR Journal of Australian Geology and Geophysics, 5:9-38 Herczeg, A.L., Torgersen, T., Chivas, A.R., & Habermehl, M.A., 1991, Journal of Hydrology 126: 225-245. Torgersen, T., Habermehl, M.A., Phillips, F.M., Elmore, D., Kubik, P., Jones, B.G., Hemmick, T., & Gove, H.E., in press, Water Resources Research

A 10.7 M I X I N G OF G R O U N D W A T E R W I T H I S O T O P I C A L L Y DISTINCT SIGNATURES IN S H A L L O W DEVONIAN O I L - B E A R I N G F O R M A T I O N S IN S O U T H W E S T E R N O N T A R I O , CANADA. Tamie R. Weaver*, Shaun K. Frape, and John A. Cherry Institute for Groundwater Research, University of Waterloo Waterloo, Ontario N2L 3G1, CANADA The Devonian Dundee and Detroit River Group Formations of southwestern Ontario lie on the easternmost flanks of the Michigan Basin, to the west of the Algonquin and Findlay Arches in the Precambrian Geological Society of Australia Abstracts Number 32, Ballarat 1992

basement. The Devonian formations in this region are the uppermost formations in a Paleozoic sedimentary sequence including Cambrian sandstones, Silurian carbonates, shales and evaporites, and Devonian

262 This survey has also established that at least one major episode of mixing of groundwater from different formations has occurred in response to the preproduction hydrogeological system. In regions where the oil-bearing formations have been largely uninvestigated or where production practices such as fresh-water flooding have been limited, high salinities and anomalously low 8 H values indicate that brines have migrated from the deeper Silurian evaporites and have mixed with groundwater in the overlying Devonian formations. In order to replicate the low values and constant 8 ^ 0 in these regions, a third component is required in the mixing model. Given the isotopic signatures in this hydrogeological region, the third component is most probably water recharged under glacial conditions, depleted in both ^H and It is hypothesized that a large influx of Siluriansignature brines to the Devonian system may have occurred in response to glacial unloading in this region, simultaneously mixing with glaciallyrecharged groundwater. In regions of higher oil production this high-salinity signature appears to have been diluted by more recently recharged meteoric water. The Silurian signatures of stable isotopes in sulphate even in low-salinity Devonian groundwater indicates that the influx of Silurian brines to the Devonian occurred regionally. Consequently, the groundwater currently present in the Devonian oil-bearing formations of southwestern Ontario indicates that mixing has occurred on two scales: locally as a result of oil production practices since the 1860's; and regionally, possibly as a result of deglaciation in the region. Both types of mixing are most clearly defined by determining the major ion and stable isotope signature in groundwater from these formations.

carbonates and shales. The Paleozoic sequence is overlain by a 15-40 m thick sequence of Pleistocene clayey tills across the entire study area. Throughout the Michigan Basin, carbonates and sandstones within this sedimentary sequence bear significant quantities of oil and gas. Oil production from the Devonian oil-bearing formations in southwestern Ontario has occurred since the 1860's and has included practices such as oil-field flooding with fresh water and reinjection of oil-field brines. These production practices have increased the complexity of the fluid input history to the Devonian hydrogeological system in the region and have altered the groundwater chemistry of this system. Also, liquid waste injection to the lower Devonian formations occurred during the 1960's and 1970's, introducing fluids with different chemistry and densities to the Devonian sequence. In addition to these anthropogenic influences on the flow regime and groundwater chemistry of the Devonian sequence, fluxes to and from the formation in response to variations in the natural hydrogeological system have occurred on a geological timescale. One of the major events likely to have altered the flow regime is the deglaciation of southwestern Ontario during the late Pleistocene. A survey of the groundwater chemistry in the Devonian system of southwestern Ontario has determined the extent to which the flow regime and groundwater chemistry have been affected by petroleum-production practices. Stable isotopes in water are an effective tracer, distinguishing water with a glacial origin from water recharged during climatic conditions similar to the present. Low tritium values in the Devonian oil-bearing system indicate that leakage through abandoned boreholes, and forced oilfield flooding are not occurring in this system at present. Consequently, the meteoric water in the system must have been introduced prior to the 1950's. A 10.8

2

MICROCOMPUTER MANAGEMENT OF GROUNDWATER RESOURCES IN THE SALINAS VALLEY, CALIFORNIA Philip Hall and Matt Zidar 1

2

^Principal hydrogeologist, Earthware of California, Laguna Niguel CA 92677 Principal hydrologist, Monterey Water Resources Agency, Salinas, CA The Monterey Water Resource Agency is responsible for the management of water resources in the Salinas Valley, California. The area covers 4400 square miles and groundwater is used to irrigate 210,000 acres, producing $1.4 billion per year in crop revenue. Groundwater also supplies drinking water for some 200,000 people in the valley. The valley has been broken down into four Geological Society of Australia Abstracts Number 32, Ballarat 1992

hydrogeologic units, the Upper valley, the Forebay, the Pressure and the East side aquifers. Some of the shallower aquifers are unconfined and are subject to nitrate contamination. Some of the deeper aquifers near the coast are subject to sea water intrusion. Five years of drought, various agrochemical pollution problems, and sea water intrusion along the coast have lead the Agency to implement a

263 groundwater management plan utilizing computers. As a first step, water well records are being entered into a Database Management System (DBMS) (Geobase). Then these records are used to create geological cross sections, contour and isopach maps of various aquifers. Water quality is also plotted up with time on maps for the different aquifers. The data is being interfaced through a GIS system to other agencies in Monterey so that property boundaries, roads and other features can be included. Initially, the Agency is using PC based systems but plans to move up to workstations in the near future.

I—f i

sz _

ri ii ii ii ir

The portability of data and programs is, therefore, of great importance. A number of computer models are being used by the Agency to manage the groundwater resources. These range from simple graphic analytical models which are used for quick estimates of the impact of new wells, to the USGS finite difference models for more precise management of multi-layered aquifers on a local wellfield basis. A combined surface water/ground water finite element model is being developed for the basin wide management strategy.

!

i

m.

E3.

_E9_

MONTEREY WATER RESOURCES AGENCY PROJECT.

SALINAS VALLEY

DATE:

SEPT

SITE:

GEOLOGIC C R O S S S E C T I O N C - C"

1991

P R E P A R E D BY

P.L.HALL

E a r t h w a r e of

California Figure ' SECN 1

MONTEREY WATER RESOURCES AGENCY PROJECT:

TOP OF ISO FOOT

DATE:

SEPT

SITE

DISPERSED WELLFIELD

AQUIFER

1991

Geological Society of Australia Abstracts Number 32, Ballarat 1992

P R E P A R E D BY: P L

HALL

Eartnware o f Call f o r m Figure ' 3-D 1

264

MONTEREY WATER RESOURCES PROJECT:

AGENCY PREPARED BY. P.L .HALL

SALINAS VALLEY

DATE

SEPT. 1990

SITE

DISPERSED WELLFIELO

Earthware of California

F i g u r e : STIFF

KEYNOTE: A 10.9 WHERE DO HYDROGEOLOGISTS COME FROM? A NORTH AMERICAN PERSPECTIVE ON THE EDUCATION OF GROUNDWATER SCIENTISTS AND ENGINEERS. Ronald V. Nicholson Waterloo Centre for Groundwater Research, Department of Earth Sciences University of Waterloo, Waterloo, Ontario, CANADA, N2L 3G1 Education in hydrogeology within North America occurs almost exclusively at the graduate level with students entering the programmes from classical geology backgrounds or water resource training in Civil Engineering. More recently, students with undergraduate degrees in other fields of science and engineering are pursuing hydrogeology at the graduate level. Those with a classical undergraduate degree in geology often must make up lower level courses in mathematics and obtain additional undergraduate credits in groundwater hydrology and low temperature geochemistry. With the required course work in the graduate program, few students can meet all requirements for the M.Sc. degree in less than two years. There has been a developing awareness that specialized programmes in hydrology, generally, and hydrogeology, specifically, are needed at the undergraduate level and there has been a move at some universities in this direction. However, the process to this end is not as simple as one might expect. Indeed, the position of hydrology as an "Earth Science" may be one reason for the slow adaptation of such programmes. The difference in the general philosophy of classical geology education and that required for hydrogeology may be at the root of this matter Geological Society of Australia Abstracts Number 32, Ballarat 1992

Farvolden and Cherry, 1991). The technical issues that are faced by hydrogeologists today, whether as an acting professional or as research scientist or engineer, are highly interdisciplinary in nature (Nash et al, 1990). The physics of flow and mass transport must often be integrated with the principles of geochemical interactions and microbiologic activity that are finally described mathematically for predictive purposes. It is evident that the classical education in geology is insufficient to address these issues, yet it is recognised that the Earth Sciences play a key role in any hydrogeological phenomenon that is encountered. How then do we find a compromise to include a core of geology yet allow sufficient space in the curriculum for other required courses in mathematics, chemistry, physics and engineering? First and foremost we must recognise hydrology and hydrogeology as important and distinct disciplines that deserve individual programmes within Earth Science departments and not just as fragmented "addons" to already crowded curricula. A strong basis in sciences and mathematics must provide the needed foundation for the integration of a core of earth science courses including a number that form a nucleus of hydrology. Some case histories in hydrogeology will

265 be examined to understand the broader issues and the educational background required to deal with them. References Farvolden, R.N. and J.A. Cherry, 1991. Are geology departments prepared for the 21st century?

A 10.10

Geology, May, pp. 419. Nash, J.E., P.S. Eagleson, J.R. Philip and W.H. van der Molen, 1990. The education of hydrologists (Report of an IAHS/UNESCO Panel on hydrological education), Hydrol. Sci. /., 35 (6): 597-607.

ASSESSING T H E PERMEABILITY OF COAL BEARING STRATA IN SOUTH AFRICA C A Jermy & A Van As Department of Geology & Applied Geology, University of Natal Durban, South Africa

A number of coal mines in South Africa have been experiencing roof failure due to water and gas pressure in the overlying strata. Although this problem has been studied in America and Australia, very little work has been carried out locally. In an attempt to gain some knowledge of the underlying forces at work a large scale geotechnical testing programme of coal bearing strata has been undertaken. This paper presents the results of a preliminary set of experiments which have been carried out to assess the permeability of the strata. A permeameter based on the design of Ohle (1951) has been used to measure permeabilities in the range 10~2 to 10~7 millidarcies (mD), using nitrogen and methane as the test fluid. This apparatus, in contrast to the modified Hoek cell (Daw, 1971), allows permeability determinations to be made on samples at atmospheric pressure, rather than at higher pressures. A detailed investigation of the properties of coal bearing strata in South Africa (Jermy & Ward, 1988, Jermy & Bell, 1990) have identified twenty four sedimentary facies types which can be readily identified in borehole core from a number of coalfields. These facies have widely differing geotechnical properties which obviously influence the design and development of coal mines. The most stable strata belong to the fine grained arenaceous facies, with the coarse grained arenaceous facies being slightly less stable. In contrast, poor roof and floor conditions exist in argillaceous rocks, which deteriorate rapidly on exposure, with consequent reduction of strength and potential instability. In addition to the properties of the strata, the movement of water and methane gas through the sediments appears to play an important

Geological Society of Australia Abstracts Number 32, Ballarat 1992

role in causing roof falls in some coal mines. The methodology used to determine the permeability of the sediments involved cutting borehole core into discs approximately 20mm thick, and carefully cleaning them in order to prevent any clogging of the pores. Once dried at 105°C, each sample was placed in the permeameter and gas allowed to flow into it at a constant pressure. The flow rate of •gas was monitored at the low pressure end of the permeameter, by means of a bubble flow meter, until it reached equilibrium. A number of such determinations were made on each sample using different gas inlet pressures; which ranged from 25 to 1000 kPa, depending upon the sample facies type and the gas employed. Once one set of tests had been carried out using nitrogen, the sample was re-tested using methane as the permeating fluid. Sufficient time was allowed to ensure that all the nitrogen had been replaced by the methane prior to any further permeability determinations being made. A number of safety precautions were adhered to when using methane, and a hand held methanometer was employed to ensure that there was no build up of the gas in the laboratory during testing. A total of 350 permeability measurements have been made on 75 samples from seven facies types. Each set of measurements has been plotted as a graph of the reciprocal of the mean pressure versus the coefficient of permeability, and the straight line fitted to the results extrapolated back to zero reciprocal mean pressure. The value of the permeability at the intersection is the equivalent liquid permeability of the sample (ASTM, 1985). Table 1 summarises the results of the permeability determinations.

266 Table 1. Permeability of coal bearing strata. Permeability (mD) Methane

Facies Number

Description

5 7 8 9 11 18 23

0.001-0.014 Ripple cross laminated sandstone 0.06-0.12 Fine grained feldspathic sandstone Cross laminated fine grained feldspathic sandstone 0.005-0.025 0.02-0.11 Medium grained feldspathic sandstone 0.1-0.65 Coarse grained feldspathic sandstone 0.005-0.01 Beaufort mudstone 0.01-0.08 Mixed coal and mudstone

Nitrogen

Because of the inherent variability of sedimentary rocks there is a wide range of permeabilities for each facies type. This variability was noticeable not only between the same facies taken from different depths in the boreholes, but also in adjacent samples taken from the same facies type. Since the sample discs used in this testing programme were cut parallel to the bedding, any minor argillaceous parting or subtle change in pore size would have a significant effect on the measured permeability. The permeability of the sediments to methane is lower than the permeability to nitrogen, with samples showing a reduction of between 5 and 56%. This reduction is higher than would be expected due to the difference in molecular diameter or adsorption of the gas on the sediment pore surfaces. Further tests are being carried out using the Ohle cell with mine water as the permeating fluid, and using a modified Hoek cell, in order to monitor the permeability under different stress conditions. This data will allow calculations concerning the movements of fluids underground to be performed, and lead to a better understanding of how the mining induced stresses act as a driving force for the flow of water and methane into mine workings. A 10.11

0.001-0.01 0.04-0.10 0.005-0.02 0.01-0.09 0.1-0.45 0.002-0.005 0.005-0.047

Acknowledgements This research has been partially funded by a University of Natal research grant. References ASTM. 1985. Standard test method for permeability of rocks by flowing air. Method D4525-85, Annual book of ASTM standards. Vol 04.08 Daw, G.P. 1971. A modified Hoek-Franklin triaxial cell for rock permeability measurements. Geotechnique. 21. 89-91 Ohle, E.L. 1951. The influence of permeability on ore distribution in limestone and dolomite. Economic Geology. 46. 667-706 Jermy, C.A. & Ward, J.R. 1988. The application of geotechnical testing to the mining of coal. SANGORM Symposium: Rock Mechanics in South Africa. Mbabane, Swaziland. 267-272 Jermy, C.A. & Bell, F.G. 1990. A survey of some engineering properties of coal bearing strata from South Africa in relation to the stability of roof rocks in coal mines. 6th International Congress of the International Association of Engineering Geology. Amsterdam. 4. 2601-2609

IDENTIFICATION OF NUTRIENT LEVELS IN GROUNDWATER WITHIN THE MURRAY DARLING BASIN, AUSTRALIA John Nolan and Greg Hoxley 1

2

Gutteridge Haskins and Davey Pty. Ltd. Rural Water Commission of Victoria The groundwater resources of the Murray-Darling authorities in the states of Victoria, New South Basin are variably distributed. The two major regional Wales, South Australia and Queensland. It has aquifer systems are the Great Artesian Basin in the included general state database information as well as north and the Murray Groundwater Basin to the south. information from specific site monitoring. The This study deals with the nutrients in groundwater of spatial distribution of information reflects the the Murray Groundwater Basin. Nutrient data was respective bore densities and variable groundwater obtained from water and environment protection quality reporting requirements. In the semi-arid l

y

2

Geological Society of Australia Abstracts Number 32, Ballarat 1992

267 regions the data is sparse, thus, the results in these regions are at best qualitative. High Nitrate levels in drinking water can cause methaemoglobinaemia, particularly in infants. As result routine monitoring of nitrate levels in groundwater has been carried out by state authorities since 1970. A variety of methods have been adopted for the reporting of nitrate, for example; As (NO3-N) As NO3 As NO x In this study all values have been converted to molecular equivalent values as NO3-N. Expressed in this form, groundwaters are considered to be nitrate rich when the concentration exceeds 10 mg/1. All bores sampled with nitrate levels above this value have been identified. Phosphate levels in groundwater are generally very low as a result of attenuation, reaction with iron and adsorption in soils. As the levels are well below those likely to cause concern in drinking water, phosphate concentrations in groundwater in the Murray Basin are not routinely monitored. Little information on phosphate concentrations in groundwater exists for the basin. In New South Wales 287 bores were found with recorded nitrate levels above 10 mg/1. Of these bores, 92% were less than 50 m deep. Often there was good correlation of nitrate with Total Dissolved Solids, indicating that there is a consistent ionic balance in these waters. There is, thus, high nitrate groundwater in areas of high groundwater salinity. Phosphate concentrations were found to range between 0.02 mg/1 and 0.18 mg/1 as total phosphate. In Victoria 520 bores were recorded as having nitrate above 10 mg/1. These bores are generally concentrated in areas of high groundwater salinity or areas of intensive irrigation. From the data available there is a significant difference in nitrate concentration in the Victorian Riverine Plain between urban and agricultural land. Urban areas appear to have nitrate levels 2 to 3 times higher than the irrigated agricultural areas. In some locations, more intense monitoring of nutrients has been undertaken. The Shepparton Phase A groundwater pumping scheme has had an extensive chemical testing program underway for a number of years. In the groundwater pumped as part of this scheme the mean phosphate concentration is 0.1 mg/1 and the mean nitrate concentration is 2.9 mg/1. At these concentrations the estimated nutrient load that enters the surface drainage system as a result of pumping (hence into the Murray River) is 13 tonnes of nitrogen and 0.5 tonnes of phosphorus per year. In a one-off sampling program across Victoria, bores with potential to discharge to surface water were sampled and analysed for nitrate and phosphate (total as well as reactive). The nitrate concentrations varied between 0 and 11 mg/1 while total phosphate ranged Geological Society of Australia Abstracts Number 32, Ballarat 1992

between 0 and 1.4 mg/1. There does not appear to be a relation between the nutrients and any other single ionic species in solution. The implications of these concentrations for surface water nutrient loads has not yet been fully assessed. In South Australia, monitoring for nutrients is sparse and usually directed at localities known to be at risk. Of the bores monitored only nine recorded nitrate levels above 10 mg/1. There is evidence that deeper aquifer systems near the Murray River may contain significant concentrations of phosphate, but the degree of interaction with the Murray River of these systems has not been firmly established. As a result of the review of the available information the following conclusions have been reached: The evidence available indicates that within the Murray-Darling Basin, shallow aquifer nitrate concentrations have increased significantly in irrigation areas and around urban (rural) development. The significance of point sources as against distributed sources resulting from land use changes has not been established. More detailed monitoring is required to establish the differences. Over the next 30 years, groundwater pumping for watertable control may increase than annual nitrogen load to the Murray River from less than 20 tonnes per year up to 700 tonnes per year. Action relating to nutrients in groundwater in the Murray Basin should include the following: Maps of nitrate concentrations should be prepared for individual aquifers commencing with the shallow systems. Effort should be concentrated in the alluvial valleys where recharge is significant and in the arid areas where data is currently sparse. Nutrient monitoring should include temporal as well as spatial elements. Anomalous nutrient values should be further investigated. Guidelines for the location and construction of nutrient intensive activities (such as piggeries or wastewater treatment plants) should be developed. The monitoring of such activities should be increased. Investigations to determine the source of nitrates in groundwater in dryland areas should be initiated. Having characterised the nutrient distributions, a more detailed assessment of stream-aquifer interactions should be made to re-assess the current and likely nutrient loads into streams in the Basin.

S

268 A 10.12 EARTH SCIENCE, COMPUTERS AND THE ENVIRONMENT : THE 'HYDROGEOLOGY OF THE MURRAY-DARLING BASIN PROJECT EXAMPLE

1

R.Brodie, R.Cooper & A.Tucker Groundwater Branch, Bureau of Mineral Resources, Canberra ARC/INFO was trialled in 1990. The GIS is a Soil and water degradation is the major graphical interface to the ORACLE database, environmental problem confronting Australians today. allowing spatial analysis of borehole data with In the Murray Basin, soil and surface water other available information - surface geology, salinisation threatens export producingagriculture and geophysics, topography etc. The incorporation generates costs to the environment, domestic water of remotely sensed data, derived from Bureau supply and irrigation. image processing facilities is being The salinity problem is groundwater related, investigated. requiring the study of the regional groundwater system * Groundwater Modelling: The finite difference of the Murray-Darling Basin, a task shared by several groundwater modelling package MODFLOW state andfederal agencies. The Bureau of Mineral has been modified for variable density flow. Resources (BMR) Groundwater Branch is involved in Graphics software to display model input and the compilation of two major products of the research output parameters have been established to aid program - the Murray Basin Hydrogeological Map calibration. A database with a forms and menu Series, a basin wide coverage of 1:250 000 scale maps interface has been developed to allow rapid and showing groundwater features, and a regional consistent changes to be made to model input numerical model aimed at predicting salinity risk. parameters. Computer technology has impacted dramatically on the delivery of these products, from initial data * Data Presentation: The maps are prepared using collection, through integration and interpretation to an Intergraph Computer Assisted Mapping final information presentation. Within the System. This system allows data to be Groundwater Branch this includes; assembled for final presentation using screen * Data Storage & Query: An ORACLE-based based techniques, when the assembly is relational database has been designed and complete the map information is processed and implemented to accommodate the historical negatives are produced ready for plate making record of water bores and investigative drilling by the printer. The mapping system is also in the Murray Basin. Subsets of data on used to plot subsets of map and model output downhole stratigraphy, aquiferparameters, as required. palynology, head and water chemistry may be The challenge faced today is the successful linking retrieved. of these powerful tools, not only to each other, but to * Data Integration & Interpretation: The utility of people involved in the compilation of the groundwater the geographical information system, maps and models. A 10.13

DEVELOPMENT OF AN INTEGRATED DATA COLLECTION AND PROCESSING SYSTEM FOR GROUNDWATER MONITORING AROUND LATROBE VALLEY MINES G. Reinsch & C. Daniels Mine Planning and Geotechnical Division, SECV, Morwell, Victoria. Information collected from more than 1500 individual instruments monitoring aquifer pressures, groundwater levels and earth- movements is used extensively in the design and operation of large brown coal mines in the Latrobe Valley. The effective use of this data has required the development and Geological Society of Australia Abstracts Number 32, Ballarat 1992

implementation of an information management system embracing the collection of data through to its ultimate integration into design packages used in stratigraphic and hydrogeological modelling and geotechnical analyses. Instrument monitoring procedures were

269 enhanced with the installation of a borehole telemetry system. Data from this and other collection systems are then efficiently transferred into a technical database which provides storage, validation and reporting facilities. Through customizing of the

database all relevant data may then be utilized for project modelling and assessment. Experience gained from this development work can be applied to suit a variety of other monitoring schemes.

A 10.14 HYDROGEOLOGICAL INVESTIGATIONS FOR DRYLAND SALINITY MANAGEMENT PLANS Susan Ryan Centre for Land Protection Research Department of Conservation and Environment, Bendigo Salinity Management Plans are currently being prepared for the Campaspe, Loddon, Avoca and Avon Richardson Catchments, of Northern Victoria. The plans are being devised by local community groups, with the assistance of several government agencies. Representatives from the Dept. of Conservation and Environment, Dept. of Agriculture and Rural Water Commission have formed technical working groups to provide advice to community groups. The technical working groups consist of a wide variety of specialists, such as hydrogeologists, agronomists, soil scientists, biologists, foresters and engineers. Salinity is primarily a groundwater problem and its management requires a detailed understanding of groundwater processes. The dynamics of a groundwater system are influenced by factors such as climate, geology, landforms, soils and vegetation. Salinity was caused by the dramatic change in vegetation bought about by European agricultural practises. Native vegetation was replaced with lower water using crops and pastures. This resulted in greater recharge to groundwater systems, rising watertables and groundwater discharge in low lying areas. Consequently, one of most the important objectives in dryland salinity management plans, is to lower watertables by increasing plant water use. This will only be achieved with the support of landholders. Hence, any alternative landuse practises must be economically viable. To lower watertables, whilst maintaining economically viable landuse, requires a detailed local understanding of hydrogeology, within these catchments. Hydrogeological investigations, for the plans, have included collation of geological, geomorphic, groundwater monitoring and climatic data. In addition land salinisation and groundwater recharge areas have been mapped. The catchments lie on the boundary between the Western Uplands and the Murray Basin Plains. Groundwater systems are influenced by both the fractured rock aquifers of the Uplands and the unconsolidated aquifers of the Murray Basin. Salinity is associated with both types of groundwater systems. Geological Society of Australia Abstracts Number 32, Ballarat 1992

There is about 28000 ha of land salinisation, across the four catchments, and there are large areas at risk from salinity. Stream salinity is a particularly important issue. High stream saltloads are generated in the Uplands, because of groundwater discharge from fractured rock aquifers. This affects both downstream users and wetlands areas. In order to provide a framework for broad scale planning, the catchments has been divided into land management units, within which similar salinity control options might apply. The units have been defined primarily by geology, physiography, soils, climate, landuse and groundwater systems. The usefulness of the land management unit concept, can be illustrated by a comparison of characteristics, between the Sedimentary Hills and the Wimmera Sedimentary Rises land management units. Sedimentary Hills are associated with intermediate and local fractured rock groundwater systems, and are used primarily for grazing and forestry. The aquifer is exposed or covered by thin skeletal soils on hill crests. The soils on the crests are much more permeable than the deeper clayey soils of the slopes. Thus crests form easily identifiable recharge areas, and are priority areas for salinity control measures. Such measures could include establishment of high water using pastures and tree planting. Soils in these areas are acidic and consequently are prone to aluminium toxicity. Hence aluminium tolerant pastures ( e.g. some varieties of phalaris and cocksfoot) are recommended for recharge control. W'immera Sedimentary Rises form a gentle landscape, used for cropping and grazing and are characterised by more regional groundwater systems. There is less variation in soil water properties throughout the landscape compared to Sedimentary Hills, and preferential recharge areas are difficult to define. Consequently, landuse changes must be widespread, and both cropping and pasture salinity control options need to be developed. One salinity control option is lucerne, which is a high water using pasture. Within Wimmera Sedimentary Rises, lucerne

270 can be used for both recharge control, in the upper landscape, and as a means of drawing down watertables, in the lower landscape. To assist in the development of salinity control options, trial and demonstration sites have been established throughout the state. The sites are situated in a variety of hydrogeological settings, and are

Geological Society of Australia Abstracts Number 32, Ballarat 1992

monitored to assess the effectiveness of a range of options. The community groups, of these four catchments, are currently developing management strategies for each land management unit based on the results of these investigations. These strategies will be further refined as more information becomes available.

271

A l l : ENVIRONMENTAL GEOLOGY CONVENOR:

KEYNOTE: A 11.1

ANTHONY

LANE

GEOLOGY- A KEY COMPONENT IN UNDERSTANDING AND MANAGING OUR ENVIRONMENT J.P. Trudinger Director, Dames & Moore

Geological processes have shaped our world. Despite man's efforts to shape the world to meet his own requirements, geological processes continue to dominate among the dynamic forces that affect our landscape and our living environment, and to impose serious constraints to man's activities. Processes such as volcanic eruption, earthquakes, weathering, leaching and erosion, solute and sediment transport, precipitation and sedimentation are of fundamental importance to our understanding of environmental dynamics. The same processes impact on man's activities and his works. The geological record contains a wealth of data which can help us to put into perspective man's activities and their effects. Gross changes in atmospheric composition and major climatic changes have occurred throughout geological history and many of the consequent ecological changes have been documented. Similarly over a much shorter timescale, studies of the recovery of ecosystems damaged by natural events in recent geological history provide a basis for us to predict how nature will respond to maninduced perturbations. Geology and its expression in landforms and surface soils, combines with climate and biogeography to determine the earth's ecology. The same physical factors determine the capability of land to support artificial ecosystems of agriculture and forestry. Understanding of geological processes and their products is therefore essential to the practice of environmental planning in general and land use planning in particular. The importance of geology for understanding and managing the environment leads to the concept of environmental geology as an applied discipline within the broad science of geology. Equally, however, environmental geology can be viewed as a branch of ecology. The nutrient cycles, the carbon cycle, the hydrologic cycle and the cycling of energy within an ecosystem - all involve geological as well as Geological Society of Australia Abstracts Number 32, Ballarat 1992

biological processes. The specific applications of environmental geology include most of the issues of environmental concern such as desertification, catchment management, coastal erosion, salinisation, and waste disposal. In addition, environmental geology is one of the key disciplines required in the environmental assessment of development projects. With continued growth of the human population and its consumption of resources, with increasing pressure for sustainable development and with recognition of the need to remediate past environmental damage, the infant discipline of environmental geology can be expected to grow until it becomes the most active discipline within the earth sciences. Tertiary education institutions need to plan now for the demands which this will impose. As the discipline of environmental geology is quite new, there are as yet few undergraduate courses aimed at producing graduates qualified in this area. Courses in engineering geology contain much of the course work required for training in environmental geology. There is scope for a four year course of training in both engineering and environmental geology. Also, three year degree courses in environmental geology and in engineering geology could be designed with man common units. The desirable components of a syllabus in environmental geology include advanced geomorphology, hydrogeology and hydrochemistry together with an emphasis on Quaternary geological studies. A selection of appropriate non-geological subjects should be available including ecology, pedology, oceanography, meteorology and waste management.

272 A 11.2

BREACHES OF ENVIRONMENTAL LAWS AND SITE REHABILITATION: PENALTIES AND LIABILITIES R A North

Corrs Chambers Westgarth, Solicitors, Brisbane, Queensland Any activity undertaken by man has an effect on legislators and regulators are paying greater attention his environment. It is for man in his wisdom to to ways of encouraging compliance. Site strive to balance the benefit of his activities against rehabilitation can no longer be left to the conclusion of a mining project. Progressive rehabilitation is the environmental impact they have. Without mineral and petroleum production man required. Frequently compliance with environmental would not have moved as he has done in the 20th laws is a condition of the mining title. Failure to Century. This has not been without cost. Mineral comply with environmental laws may lead to loss of and petroleum production, processing and the mining title as well as the penalty prescribed by transportation have produced their own forms of the mining laws. There is a growing trend under Australian environmental impact. Legislators and regulators are reflecting man's environmental laws to impose strict liability for a increasing concern with his environment. breach and to impose personal liability on officers, Environmental Impact Statements have long been a particularly directors. The Paper will review certain Australian requirement for Australian mining projects and site rehabilitation requirements have been conditions of legislation to illustrate the trends in site rehabilitation requirements and how they are imposed, how personal approvals to mine for many years. Apart from setting more rigorous and higher liability is imposed and how the opportunity to defend environmental standards for resource projects, a prosecution is restricted. A 11.3

REHABILITATION OF A DISUSED SITE IN LEEDS, U.K. F.G.Bell and A.W.Bell 1

2

department of Geology and Applied Geology, University of Natal, Durban, South Africa White Young Consulting Group, Leeds, England 2

From the early part of this century light industrial foundry work has taken place in the southern part of the city of Leeds. Over the years various plots of land were developed to suit the needs of the factories existing at the time. With the advancement of casting and machining technologies, as well as economic changes generally, many of these buildings became redundant and some were subsequently demolished, often only to ground level. An additional problem associated with many of these sites is that of ground contamination. The latter need not only present a hazard to the construction of foundations but it can also mean hazardous conditions for operatives to work in. Hence it is necessary to establish whether or not precautionary measures are required. One such old foundry site (Fig.l), which is the subject of this account, required rehabilitation in order to make it available for light industrial development. Accordingly a desk study was undertaken in order to establish as accurately as possible the previous usage of the site, as well as to gain some data regarding the site conditions. It revealed a plan of the last layout of buildings on the site, indicating areas where Geological Society of Australia Abstracts Number 32, Ballarat 1992

manufacturing took place. These areas represented areas of potential underground hazards in that manmade obstructions and both ground and groundwater contamination may be present. The site exploration programme consisted of a number of boreholes, sunk by light cable and tool rig, to a maximum depth of 12.5 m below ground level. These were supplemented by the excavation of trenches and pits. The subsurface exploration confirmed the presence of a number of underground obstructions (Fig.2) and in fact some of the boreholes had to be sunk from the bases of pits dug through rubble and old foundations. The exploration revealed some two to four metres of made ground overlying a layer of sand with gravel, the maximum thickness of which was six metres. The made ground consisted of ashes, cinders, slag, foundry sand and brick rubble. Depending on the position within the site either mudstone or siltstone, belonging to the Coal Measures, occurred beneath the sand with gravel. Both rock types were highly weathered. Standard penetration tests were carried out within the sand with gravel, indicating N-values increasing from as low as 8

273 (loosely packed) to 32 (densely packed). The degree of compaction tended to increase with depth and most of the sand with gravel was medium dense (angle of friction 35° to 40°.) Groundwater levels were recorded in boreholes at the beginning and end of each working day. The water table tended to occur at 3.5 or 4.0 m below the surface. Samples of made ground and groundwater were taken for chemical testing to try to determine the degree of contamination. The pH values obtained from testing the made ground ranged from 4.2 to 9.1, with most materials being alkaline. Total sulphate concentrations were very high in some samples of rubble fill and would warrant the use of sulphate resistant cement in foundations. More sophisticated chemical testing was undertaken to determine the concentrations of lead, cadmium, arsenic, copper, nickel, zinc and chloride across the site since their levels could be a cause of concern in relation to industrial redevelopment or landscaping. In general, the concentrations of these materials within made ground were below levels likely to represent problems. For an old industrial area their occurrence in most cases surprisingly was only in trace amounts. However, elevated concentrations of magnesium were found in certain locations on site (eg. over 0.9% at two locations). These were due to the fact that part of the site was used for a munitions factory during the Second World War. In reworking the site dust from such material could cause irritation to the eyes. Accordingly it was recommended that eye protection should be worn and that good eye wash facilities be available on site. Concentrations of

phenol high enough to permeate plastic water service pipes were present in some foundry sands. Any piping involved in subsequent redevelopment which would come in contact with such deposits therefore would have to be either phenol resistant (eg. made of uPVC) or laid in trenches backfilled with clean sand. Minor oily contamination was exposed at two locations in trenches but the volumes were not large enough to be significant. Small fragments of asbestos (chrysotile) sheeting were scattered across the site and within the fill. Although this type of material is low risk and does not generally release dangerous dust, it would be better to remove it rather than crush and recompact it with fill during redevelopment. A scheme for rehabilitation of the site was then developed which involved bulk excavation of the material on site. The depth of excavation across the site would have to be varied in relation to the location of known obstructions. Specifications for the handling and selection of the excavated ground, and its re-use as compacted backfill, incorporating the above recommendations, were also included. Re-using the made ground as rubble fill and compacting it in lifts would cost £200 000. However, although this would rehabilitate the site as a landscaped open space amenity it would not necessarily be suitable for subsequent building development. It therefore was further recommended that if the site was to be used for such development, then the most economic method of enhancing the ground carrying capacity after backfilling would be by using vibrocompaction. Vibrocompaction would cost £500 000.

Fig.l. General view of the site prior to the site investigations.

Geological Society of Australia Abstracts Number 32, Ballarat 1992

274

Fig.2. Old foundations and vaults revealed in trenches.

A 11.4

ARSENIC IN THE VICTORIAN ENVIRONMENT David Welsh1*, Michael Jones 2 and Geoff Clarke 2

* Environmental Unit, Minerals Group, Department of Manufacturing and Industry Development, Melbourne, Victoria. NSR Environmental Consultants Pty Ltd., Burwood Rd., Hawthorn, Victoria.

2

A resurgence in gold mining activity in Victoria in the latter part of the 1980's increased community concerns about the possible mobilization and fate of arsenic and its effect on humans, stock, flora and fauna. In response to these concerns the Department of Manufacturing and Industry Development contracted NSR Environmental Consultants Pty Ltd to examine the distribution, extent and likely fate of arsenic in the Victorian environment. Despite the occasionally substantial concentrations of arsenic in the country rock and soils from the gold mining regions of the state, the concentration of arsenic in surface waters was generally low. Elevated levels of arsenic were found in some groundwaters in the vicinity of past mining activity, but these were considered to be due to the arseniferrous nature of the geology. Some stream sediments contained elevated levels of

Geological Society of Australia Abstracts Number 32, Ballarat 1992

arsenic for up to 20 km below tailings dumps, but the effects on aquatic biota tends to be more localised. Fish sampled downstream of a historic mining region were found to contain arsenic within acceptable limits. Arsenic chemistry is complex, involving transformations between four oxidation states and interactions with solids and organic matter. The toxicity of arsenic depends on its speciation, with inorganic arsenic (III) compounds being the most toxic. Unlike mercury, bioaccumulation of arsenic in aquatic organisms does not appear to take place to any great extent. The Department of Manufacturing and Industry Development is continuing to develop strategies for the protection of the environment from the possible effects of mining activity. Comments on the speciation and mobilization of arsenic near past and present gold mining areas will be provided.

275 A 11.5

MT. TAYLOR KINGSTON GOLD MINE: SITE RECOVERY PROJECT R J Morphet1*, R G Friday1 and R J Parker2

2

^Golder Associates Pty Ltd, Brisbane Golder Associates Pty Ltd, Melbourne

Open cut and underground gold mining activities took place at Mt Taylor Kingston (south east of Brisbane) from the 1930's to the 1950"s (Fig. 1). Between 1955 and 1967 residues from oil reprocessing operations were disposed of in the "Northern Pit" and it is possible that waste from other industrial processes may also have deposited on the site. The "Main Open Cut" was used as a municipal rubbish dump during the period 1968 to 1973. The site was then developed fro residential and commercial uses (Envirotest 1990). In 1987 residents complained of sludge material oozing onto their properties and, following a series of studies, the decision was made by the Queensland Government (1990) to accept the remedial option involving purchase os selected properties and capping and landscaping of the area. The authors were involved in developing a design for the proposed capping system to meet the design objectives of: •

Forming a separating layer (barrier) between any contaminated materials beneath the site and the surface • Minimising infiltration and subsequent percolation of water through contaminated materials, and • Reducing groundwater mounding in the vicinity of Mt. Taylor, thus limiting groundwater contact with contaminated materials. Application of hydrogeological and geotechnical analyses and the preparation of computer models was integral in the development, assessment and optimisation of the capping design. The geology and structure was re-evaluated and computer models were established to assist in evaluating drainage and capping options for the area. HELP (Hydrological Evaluation of Landfill Performance), Schroder et al (1988) was used to calculate volumes of water passing through the multi-layered barrier and drainage systems. The results

from this were input into a second model, AFPM (Aquifer Flow in Porous Media), a series of Golder Associates Pty Ltd groundwater programme packages. The AFPM model was calibrated using measured groundwater levels and permeability information from boreholes around the project site and then used for assessing the lowering of steady state groundwater levels produced by capping of Mt. Taylor. A range of capping measures was decided upon (Fig 2) and the recovery project was completed in September 1991. These capping options took account of the primary objectives along with the need to accommodate risks associated with each part of the site, to require minimal maintenance, allow public access and, in places, to achieve a stable surface over waste material.

References Envirotest. Review and Assessment of Hazardous Waste Investigations, Kingston, Logan City, May 1990. Envirotest/IAER, Griffith University, Report prepared for the Minister of Police and Emergency Services. Golder Associates (1990), Kingston Site Recovery Project, Design Report, Report 90638145(E) prepared to the Administrative Services Department, November, 1990. Marlon-Lambert, J.R., Manuel, P.J., Friday, R.G. (1981). The Development of a General Groundwater Computer Modelling Package. Civil Eng. Trans. Inst. Engrs. Aust. Vol. CE23 No.4, Nov. 1981, pp. 264-271. Schroeder, P.R., Gibson, A.C. and Smolen, M.D. (1988). Hydrologic Evaluation of Landfill Performance (HELP) Model: EPA/530-SW-84010, Municipal Environmental Research Laboratory, U.S. Environmental Protection Agency, Cincinnati, OH 1984. _

SEE PAGE 282 FOR ACCOMPANYING FIGURES

276 A 11.6

MODELLING OF THE SUBSURFACE ENVIRONMENT USING STRATA3: CASE STUDIES IN ENVIRONMENTAL GEOLOGY. A.S. Stenning* and S.P. Bentley Division of Civil Engineering, University of Wales, Cardiffi South Wales, U.K.

Strata3 is a P.C. based computer program account in decision making by planners, developed jointly at the University of Wales, Cardiff developers, resource exploiters, conservationists and and Wallace Evans Limited (Engineering and engineers. The second case study looks at the use of Environmental Consultants). The program uses spatial Strata3 as an aid in the assessment of pollution and data inputs obtained from a variety of sources contamination hazards at an old gasworks situated including geological surveys, existing geological adjacent to Cardiff Bay. There is a proposal before maps and sections, site investigations and geophysical Parliament to construct a barrage across the mouth of surveys; means are also provided to allow geologists Cardiff Bay and impound the waters of the rivers Taff and other users to input their knowledge of the area. and Ely. The creation of this 300 hectare freshwater* Strata3 combines the data inputs and uses lake will cause a permanent rise in the surrounding triangulation and gridding techniques to create a 3- groundwater levels. The gasworks study aimed to dimensional layered geological model of the subsurface investigate the distribution and concentration levels of environment for the area defined by the data. Program contaminates in the estuarine alluvium under the site routines permit the model created by Strata3 to be and to assess the implication of the water table rise in interactively interrogated on the computer screen via a terms of transport mechanisms. Such environmental wide range of easy-to-use functions which include audits generate a vast quantity of chemical data which geological cross sections, geological maps and in a tabulated form is difficult to appreciate and assess. perspective views. Upper layers can be stripped away The Strata 3 program was used to construct models of to obtain maps and views of any surface defined within the contamination by each chemical. Within these the model. In addition to visual images the program contamination models all the routine functions of the can provide detailed numerical information, that program still operated. is, precise measurements can be made of the internal structure of the models, contour and isopachyte maps References can be requested by simple keystrokes and a precis of any borehole or other record can be displayed in a Carr, J.R., 1990, UVKRIG: A Fortran program for universal kriging, Computers and Geosciences, corner of the screen. Hardcopy output to any working Vol. 16, No. 2:211 -236 scale is also provided via a range of plotters and David, M. 1977, Geostatistical ore reserve printers. This paper describes the development of estimation, Elsevier Scientific Publishing Strata3 and highlights methods used to create the Company: 364p Davis, J.C., 1986, Statistics and subsurface models, it also demonstrates the use of data analysis in geology, 2nd edition., John Wiley Strata3 for geological mapping and environmental and sonsInc: 646p impact assessment with respect to two case studies in Journel, A.G. & Huijbregts CH.J., 1978, Mining the U.K.. The first of these case studies considers an Geostatistics, Academic Press: 600p environmental geology mapping exercise of 530km Jones, T.A., Hamilton, D.E. & Johnson, C.R., 1986, of coastal wetlands around the Severn Estuary. Part of Contouring geologic surfaces with the computer, this work involved the collection of all available Van Norstrand Reinhold: 314p geotechnical investigation reports and the abstracting Raper, J., 1989, Three dimensional applications in geographic information systems, Taylor and of a proportion of the borehole records into a projectFrancis: 189p specific ORACLE database. A linking program enabled Strata3 to read that data held in the database Watson, D.F., 1982, ACORD: Automatic contouring of raw data, Computers and geosciences, Vol. 8, necessary to build a subsurface model. The overall aim No. 1: 97 - 101 of the project was to demonstrate the means and the benefits of taking earth science information into t

2

Geological Society of Australia Abstracts Number 32, Ballarat 1992

277 A 11.7

PROTECTING OUR INESTIMABLE EARTHLY HERITAGE E.B. Joyce1* and E.M. McBriar2* 1 Department of Geology, University of Melbourne 2South Australian Museum, Adelaide

Geological features and sites must be assessed to determine their significance in terms of uniqueness or representativeness, and scientific or educational value; they can be classed as important at local, regional, national, international or world heritage level. In this discussion techniques of assessment used by the Divisional subcommittees of the Geological Society of Australia Inc. in Australia, nationally by the Australian Heritage Commission, and internationally by UNESCO are compared and contrasted, and the problems of protecting our geological heritage are considered E.B. Joyce is Convener of the GSA's Standing Committee on Geological Monuments. This Committee exists to provide liaison between the Divisonal Subcommittees working on geological conservation, and to report to the Society regularly on such activities. The Committee through its convener is also currently engaged in a project to assess geological sites of national and international significance in Australia, drawing on the detailed work carried out by each Division (Cochrane and Joyce 1986). In November 1990 E.B. Joyce was requested by the chairman of a UNESCO working group on geological sites to attend a meeting in Paris to consider a list of sites of possible World Heritage significance in Australia, New Zealand, the Pacific Islands, Papua New Guinea and Antarctica. Lists were prepared for each of these areas, drawing on the work of local geologists (Joyce 1991a). For example, the Geological Society of New Zealand provided information on its major geological sites. The list for Australia was compiled from the work already undertaken by the Society (Cochrane and Joyce 1986), and from subsequent comments from Divisional Subcommittees. A brief report on the meeting later appeared in the Australian Geologist (Joyce 1991b), and a full report to UNESCO by the chairman of the working group is expected to be available shortly. The experience involved in assessing geological sites at local, regional, national and world level will be discussed, and practical ways of carrying out such assessment will be considered (Joyce in press). The compilation and publicising of global lists may give rise to misunderstanding, as the list may be seen as the initiation of a formal nomination for World Heritage listing. An attempt will be made to explain what the drawing up such lists actually involves. E.M. McBriar is Convener of the Geological Geological Society of Australia Abstracts Number 32, Ballarat 1992

Monuments Subcommittee of the GSA in South Australia, and was the main Australian representative at the recent First International Symposium on the Conservation of Our Geological Heritage held at Digne, France in June 1991 (McBriar in press). The Australian and State Governments, acting through their heritage legislation (Bilney and others 1981), and professional geologists working through the GSA (for example, McBriar and Mooney 1988) are ensuring that outstanding examples of earth history in this country are conserved. The most important of these geological monuments are being listed on domestic and, more recently, global inventories. Of eight Australian World Heritage properties, three appeared on a recent UNESCO list of sites of world geological significance (Joyce 1991b). A further three properties - The Great Barrier Reef, Kakadu National Park and Western Tasmanian Wilderness National Parks - might also be considered for this list for their significant geological features. Four South Australian sites are on the current UNESCO list - Ediacara, Lake Callabonna, Lake Acraman (and one of its fall-out sites), and Victoria Fossil Cave at Naracoorte. Of these only the last falls within a National Park and has a legal Management Plan. Management Plans need to be prepared for the other sites, and this should be done before further publicity is given to these sites. Problems involved in protecting such remote sites were discussed at the recent international meeting on geological heritage (McBriar in press). References Bilney, E., Chisholm, A. and Thorne, J. (eds), 1981. The Heritage of Australia. The Macmillan Company of Australia and the Australian Heritage Commission. Cochrane, R.M. and Joyce, E.B., 1986. Geological Features of National and International Significance in Australia. A report prepared for the Australian Heritage Commission, May, 1986. Federal Committee for Geological Monuments, Geological Society of Australia Inc., 43pp + 6 appendices. Joyce, E.B., 1991a. Pacific and Antarctic areas, World Heritage List, Geological Sites. Unpublished document prepared for the Meeting of the World Heritage Working Group Task Force on a Global Inventory of Geological and Fossil Sites held in Paris, 11-13 February, 1991. 10pp. and 2 maps. Joyce, E.B., 1991b. World Heritage and Australian

278 Symposium on the Conservation of Our Geological Features. (Conference Reports), The Geological Heritage, 11-16 June, 1991, at DigneAustralian Geologist, Newsletter No. 79, pp. 26. Les Bains, France. Joyce, E.B., (in press). Assessing the Significance of Geological Heritage Sites: from the Local Level to McBriar, E.M. and Mooney, P.A., 1988. Geological Monuments in South Australia Part 7, Geological World Heritage. First International Symposium on Monuments Subcommittee of the S.A. Division the Conservation of Our Geological Heritage, 11of the Geological Society of Australia Inc., 66pp. 16 June, 1991, at Digne-Les Bains, France. + figs and plates. McBriar, E.M., (in press). Australian Initiatives in Earth-Science Conservation. First International A 11.8

PROTECTING SIGNIFICANT GEOLOGICAL FEATURES IN VICTORIA, SOUTH AUSTRALIA AND QUEENSLAND R.L. King *, E.M. McBriar * and P. Harlow * 1

2

3

1 Geological Survey of Victoria, Melbourne 2South Australian Museum, Adelaide 3Ipswich Grammar School, Queensland Over the past fifteen years voluntary Subcommittees of the Geological Society of Australia Inc. in all parts of Australia have worked on the identification, documentation, evaluation and conservation of geological sites of significance (Joyce 1988). This review of geological conservation studies in Victoria, South Australia and Queensland illustrates the problems and successes of the work. R.L. King is Convener of the Geological Conservation Subcommittee of the GSA in Victoria, where a study is underway on the young volcanic features of central and western Victoria. Nearly 400 volcanoes are known, but an earlier listing by the Subcommittee (Joyce and King 1980) mentioned only some twenty-five volcanoes. The Society's Victorian Subcommittee, in conjunction with the Landscape Committee of the National Trust of Australia (Victoria) has received a substantial grant to survey the scoria and tuff volcanoes which are currently under threat from quarrying. A consultant has been employed, under the direction of a joint Subcommittee/National Trust steering committee, to survey and evaluate the young volcanic features in Victoria, and make recommendations for their conservation. During the progress of this study, the consultant has prepared material for several substantial descriptive signboards which the local council has erected recently in the Camperdown township area. In a related study a consultant sponsored by the Geological Survey of Victoria has reviewed known and possible sources of scoria and tuff, and assessed future needs in Victoria. E.M. McBriar is Convener of the Geological Monuments Subcommittee of the GSA in South Australia, where seven volumes of documentation (for example, McBriar and Mooney 1988)) have now been issued, with a total of 214 files, some of which Geological Society of Australia Abstracts Number 32, Ballarat 1992

describe more than one geological monument so that the total number of sites to date is approximately 273. To increase the protection that may be afforded under the S.A. Planning Act 1982 the South Australian Division has adopted the practice of advising Local Governments of the geological monuments in their jurisdiction. This has allowed Councils to include these sites in their Supplementary Development Plans. The Subcommittee also actively comments on development proposals which affect geological sites and amongst its successes has been the protection of Halletts Cove, south of Adelaide. Assistance to other organisations with the preparation of descriptive signs has been part of the Subcommittee's work. Many sites have been entered on the Register of the National Estate in Canberra, and more recently nominations have been made to the S.A. register of State Heritage Items and Areas. In addition, attention is given to seeing that information on geological sites is included in the various scientific databases in South Australia, and each published report is lodged in the State Library of South Australia. P. Harlow is Convener of the Subcommittee for the Preservation of Geological Monuments in Queensland, where a permanent geological reserve has recently been set-up at Toowoomba. This crown reserve will be administered by the local council, in conjunction with the Society. Further reserves of this type are planned. Interest in re-opening sites where access is no longer available is an increasing concern in countries such as the United Kingdom. In Queensland, a fossil site at Ipswich (Willmott 1984), buried years ago to prevent damage from collecting, is now a local council environmental park, and is being considered for re-excavation to allow further geological study.

279

References Joyce, E.B., 1988. Looking after scientific sites in Australia - a decade of work by the Geological Society of Australia. Geol. Soc. Aust. Abstr., 21, 215-216. Joyce, E.B. and King, R.L., 1980. Geological Features of the National Estate in Victoria. An inventory compiled for the Australian Heritage Commission, Victorian Division, Geological

Society of Australia Incorporated (x + 208 pp). McBriar, E.M. and Mooney, P.A., 1988. Geological Monuments in South Australia Part 7, Geological Monuments Subcommittee of the S.A. Division of the Geological Society of Australia Inc., 66pp. + figs and plates. Willmott, W.F., 1984. Geological sites in Brisbane, nominations for the Brisbane Conservation Atlas, Geological Society of Australia Incorporated, Queensland Division, 55pp.

POSTER SESSION

A 11.9

RECLAMATION OF COLLIERY SPOIL HEAPS AT BARNSLEY, YORKSHIRE. F.G.Bell 1 and A.W. Bell 2 1

Department of Geology and Applied Geology, University of Natal, Durban, South Africa 2 White Young Consulting Group, Leeds, England

The term "derelict" is frequently used to describe land which has been spoiled by the extraction of minerals or other industrial operations. Generally the area is left in an unsightly state and is of little use without undergoing some form of rehabilitation. Some of the worst dereliction in the United Kingdom has been associated with mining activities, especially of coal since this has been the most extensively worked mineral. Spoil heaps represent the most notable form of dereliction associated with subsurface coal mining. They are particularly conspicuous and can be difficult to rehabilitate into the landscape. Furthermore well over half the collieries operational in 1960 have now closed. Such dereliction contributes towards urban blight in that it tends to influence population migration and deters the establishment of new industry. In order to counteract such trends, affected areas need to be restored to sufficiently high standards to create a pleasant environment. Two old colliery spoils heaps at WharncliffeWoodmoor near Barnsley, Yorkshire, are provided as examples of reclamation to improve the local amenity and to provide a site for light industrial development. The site consisted of two distinct areas, namely, a western area comprising 19 ha of agricultural land, and the area containing the spoil heaps occurred on the eastern part. The latter covered 29.5 ha and contained two spoil heaps, one 45 m in height, the other 25 m high, and a large area occupied by old tailings ponds, as well as pithead buildings and stock grounds. The smaller heap and pithead buildings were separated from the main heap and tailings ponds by a canal which carried compensation water from a local reservoir to the river Dearne. As a consequence the canal had to be Geological Society of Australia Abstracts Number 32, Ballarat 1992

diverted prior to reclamation work commencing. The larger spoil heap had an estimated volume of 3 000 000 m 3 and consisted mainly of shale, some of which had been burnt. The smaller spoil heap to the north of the canal was composed of similar material and its volume was less than 2 000 000 m 3 . Spoil had been spread over other areas and had been tipped over some of the tailings ponds. However, there was no evidence of burning in this spoil. The dominant mineral in the unburnt shaley material was quartz. Illite was the most important clay mineral, with kaolimite usually averaging less than 5 or 10%. Mica and chlorite tended to occur in similar amounts to that of kaolinite. Feldspars, sulphates, pyrite and' carbonate occurred in trace amounts. The coarse discard of which spoil heaps are made, contains other material in addition to shale. As run-of-mine material it reflects the various rock types which are extracted during mining operations. Hence it contains various amounts of coal which have not been separated during the preparation process and in old tips there may be appreciable proportions of coal. Those discards with relatively high coal contents frequendy are burnt in part or are still burning. This is a result of spontaneous combustion of carbonaceous material, frequently aggravated by the oxidation of pyrite. It can be regarded as an atmospheric oxidation (exothermic) process in which self-heating occurs. The moisture content and grading of spoil are important in this respect. An increase in free moisture at relatively low temperatures increases the rate of spontaneous heating. In material of large size air can cause heat to be dissipated whilst in fine material the air remains trapped which means that burning ceases

280 when the supply of oxygen is consumed. Consequently ideal conditions for spontaneous combustion exist when the grading is intermediate between these two extremes. Hot spots may develop under such conditions. What is more the rate of oxidation generally increases as the specific surface of the particles increases. The moisture content of the spoil material tended to increase with increasing content of fines. It is also influenced by the permeability of the material, the topography and the climatic conditions. Generally it fell within the range 6% to 13%. The bulk density of the unburnt spoil showed a wide variation, with most of the material having values between 1.5 and 2.5 Mg/m 3 . Low densities were mainly a function of low specific gravities. These obviously were influenced by the relative proportions of mudrock, sandstone and coal in the waste. In particular, the higher the coal content, the lower is the specific gravity. As far as the particle size distribution of the coarse discard was concerned, it fell mostly within the sand range although significant proportions of gravel and cobble size were present. At placement, coarse discard consists mainly of gravel and cobble size but subsequent weathering reduces particle size. However, once buried within a tip, coarse discard undergoes little further reduction in size. Although the pyrite content of a spoil heap is in trace amount, nonetheless its presence can have a significant effect. Pyrite breaks down rapidly under the influence of weathering to produce ferrous sulphate and sulphuric acid. Oxidation of pyrite within tip waste depends on access of air which, in turn, is influenced by particle size distribution, moisture content and degree of compaction. However, although oxidation products may be formed, they may be neutralized by alkaline materials in the waste material. If this is not the case and waste material is acidic, then it will probably be deficient in plant nutrients and so would require careful treatment if vegetation is to be established. In fact there was little vegetation cover over the tipped areas, that which did occur being found at the base of spoil heaps. However, the results of pH tests on the waste material gave values around 6.5 to 6.8. Hence the material was only very slightly acid. The site investigation included the production of topographic plans of the site from aerial photographs and sinking boreholes in the old tailings ponds and spoil heaps. The tailings ponds appeared to be quite stable, so that their level could be raised by covering with waste material during the reclamation process. Reclamation of a colliery spoil heap is essentially a large scale exercise in earthmoving. The first part of the reclamation work involved stripping over 1 000 000 m 3 in order to reduce the height of the

Geological Society of Australia Abstracts Number 32, Ballarat 1992

spoil heaps. The purpose of the levelling was to achieve a pleasant contoured landform within the site, related to the topography of the adjoining land. This was brought about not only by reducing the height of the spoil heaps, but also by regrading and rounding off the steeper slopes. The other areas such as those occupied by the pithead buildings, as well as the tailings ponds, were buried by spoil. These areas were also sloped. In this way a gently sloping ridge, valley and hill were created on the site. This work unfortunately encountered problems with hot spots. These were normally around 600°C but at some locations temperatures were as high as 900°C. The heat often caused engines on the scrapers to cease and rescue of both operator and machine often proved hazardous. In addition the types on scrapers frequently melted. Where levelling was still in progress and hot spots were present it was decided to only remove a layer of 300 mm in thickness and then compact the waste with a vibratory roller. This reduced the temperature by about 50% after two hours. Levelling could then commence again. When hot spots were found in areas where the tip material had been lowered to its finished level, 450 mm of clay was spread and compacted on top of the hot spot. Then a layer of shale was spread and compacted over the clay. Boreholes were sunk into these hot spots to determine whether or not they were cooling. Those spots where the temperatures had not dropped within a year were enclosed by an injected curtain wall of pulverized fuel ash which extended down to original ground level. Spontaneous combustion may give rise to subsurface cavities in the spoil, the roofs of which may be incapable of supporting a person. Fortunately no such cavities were met with on this site. Drains, in the form of open ditches containing pipes and filled with gravel, were constructed after levelling was completed and led into existing streams. An open ditch was also placed around the site to catch any surface run-off. The next operation involved harrowing the waste, after which lime was applied at 7.5 tonnes per hectare. Once liming was complete, subsoil and then topsoil was applied. This was obtained from the agricultural land on the western part of the site. Fertilizers were spread over the ground prior to seeding. Part of the site was developed for a large bakery and most of the rest was used as a golf course. The latter was mainly grassed, although a large number of trees were planted on the course. Trees were also planted to enhance the character of the landscape, to reduce erosion on steeper slopes and to screen parts of the site. In all, some 20 000 trees were planted over a three year period. The area now represents a source of employment and a popular local amenity rather than an unpleasant eyesore.

281 A 11.10

REHABILITATION OF A SAND QUARRY D. Sceney and A. Wissenden

Environmental Unit, Minerals Group Department of Manufacturing and Industry Development, Victoria. The poster display shows several stages of the rehabilitation work undertaken by the Environmental Unit of the Department of Manufacturing and Industry Development, Victoria at a site in the Strezlecki Ranges in South Eastern Victoria. The site was formerly a sand quarry producing a granitic filter sand for dam construction. Rehabilitation was not carried out satisfactorily in the first instance with large areas left in an as worked state. The Strezlecki Ranges form a high plateau South East of Melbourne. Once densely forested the area is now largely cleared and used for grazing and horticulture. Average rainfall in the area exceeds 1000mm per annum. There have been a number of important elements in the rehabilitation of the site. Stabilization of the land form has been a significant concern due to the steep and loose slopes left by poor waste dumping practices and serious erosion in areas of exposed sand and clay. These problems have been addressed in three ways. Firstly areas of major erosion were repaired and drainage

Geological Society of Australia Abstracts Number 32, Ballarat 1992

redesigned to avoid a recurrence of this problem. Secondly soil spreading and conditioning and extensive tree and pasture planting was done. Finally rubble drains and simple flow control structures made of hay bales and car tyres have been used to obviate further erosion. Topsoil respread at the site has been stockpiled for several years. Soil viability has been of concern and an effort was made to condition the soil by the addition of nutrients and fertilizers so as to achieve good results with pasture grass species. So far germination and growth appear to be good although weed competition is intense. Trees were planted as tube stock and appear to be much less sensitive to soil type. Growth has been good even where planting has occured in pure clay. This is attributed to the choice of local species and the high rainfall of the area. Rehabilitation of the site is now complete and a large part of the land will be available for grazing within the next 12 to 18 months.

282

SEE MORPHET ET AL. PAGE 275 FOR ACCOMPANYING TEXT FIGURE I.

SITE PRIOR TO RECOVERY

^

J

LEGEND •

GROUNDWATER

[ M ]

FIGURE 2.

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ONSITE

OBSERVATION BOREHOLES

/

SITE CAPPING FEATURES FOLLOWING RECOVERY

LEGEND LANDSCAPING

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| •

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|

1 I 1 I I I I I I I I I J

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RETAINED

Li

283

A12: GEOPHYSICS

CONVENOR:

GREG

HOUSEMAN

A12.1 MAGNETIC PROPERTIES OF THE CRATONIC LOWER CRUST AND UPPER MANTLE NJ. Pearson * D.A. Clark and S.Y. O'Reilly 1

1

2

1

School of Earth Sciences, Macquarie University, Sydney NSW 2109, Australia. Div. Expl. Geosciences, CSIRO, North Ryde NSW 2113, Australia. 2

Xenoliths in basaltic and kimberlitic rocks near the eastern margin of the Australian craton (EMAC) and across the south-western margin of the Kaapvaal Craton, southern Africa, provide direct evidence of the nature of the lower crust and upper mantle beneath these two cratons. The lower crustal suite xenoliths are dominated by mafic rock types and include mafic granulites (garnet-2 pyroxene granulites, garnet-clinopyroxene granulites, kyanite-bearing granulites), eclogites and garnet websterites. Mantle-derived xenoliths comprise garnet lherzolites, garnet websterites and rare spinel lherzolites. The mafic and ultramafic xenoliths have distinctive oxide mineralogies which significantly influence the magnetic properties. Fe-Ti oxides (ilmenite, hemoilmenite, pseudobrookite) and rutile occur as discrete grains in both the garnet-clinopyroxene granulites and garnet-2 pyroxene granulites, but are absent in the kyanite granulites. Detailed SEM studies have also revealed the presence of exsolved Fe-Ti oxides in clinopyroxene. Cr-spinel of variable composition is the dominant oxide phase in the mantle-derived ultramafic xenoliths. All rock types are characterized by low magnetic

susceptibility , although the garnet granulites are significantly higher than the kyanite granulites and unserpentinized ultramafic xenoliths. Spinels (< 0.1 vol%) ranging in composition from 80-90 mol% magnetite to end-member magnetite dominate the susceptibility of the more magnetic samples. Chromian spinels with low Curie temperatures are also present in some samples but would not make a substantial contribution to the magnetization of these rocks at elevated temperatures. The xenoliths carry an essentially monocomponent remanence that represents the TRM acquired during cooling. Enhancement of susceptibility at high temperatures, immediately below the Curie point, is negligible and cannot explain the "missing magnetization" of the lower crust that is interpreted from MAGSAT data. Thermal demagnetization shows that much of the remanence is carried by magnetite-rich spinels with Curie temperatures above 500°C. These grains should acquire substantial viscous remanence parallel to the ambient field at elevated temperatures in the lower crust. This should account for at least some of the missing magnetization.

A12.2 GEOPHYSICAL CHARACTERISTICS OF THE LITHOSPHERE AND THEIR IMPLICATIONS FOR THE FORMATION MECHANISM OF THE EROMANGA BASIN IN CENTRE-EASTERN AUSTRALIA S. Zhou Department of Geology and Geophysics, University of Adelaide. The Eromanga Basin, a major Mesozoic intracratonic basin in centre-eastern Australia, is characterised by flat-lying sediment structures on regional scales; high surface heat flow; low magnetic Geological Society of Australia Abstracts Number 32, Ballarat 1992

and gravity anomalies; non-seismic reflection from the upper crust (the Thomson Fold Belt) and strong reflection from the lower crust; relatively shallow depth of the Moho and thin magnetic crust.

284 Seismic investigations have suggested that the Eromanga Basin is situated on a rifted back-arc setting, which was probably related to a possible low-angle subduction beneath the eastern Eromanga Basin and thrusted into upper mantle at the Westgate Trough from the east (Finlayson, 1990). The subduction processes could be associated with ductile movements along the middle crustal detachment zone. The lower crustal reflections of the region are very likely to have been caused by a combination of multiple intrusive underplating and ductile deformation associated with the movements of the crustal detachment zone. From the study of both MAGSAT and aeromagnetic anomalies of the Eromanga Basin region, it has been suggested that the crust of this region is thinner or composed of less or nonmagnetized rocks than surrounding areas (also see Johnson et al., 1986; O'Reilly et al., 1988). Prominent positive anomaly patterns in the western Eromanga Basin are believed to be associated with igneous intrusions of Devonian to Carboniferous age. From the analysis result of the Curie point depths of this region, the magnetic crust beneath the basin is on the order of 13-23 km in thickness. This indicates a high thermal gradient in the crust, which is generally consistent with the observed surface heat flow in the region. Obtained geothermal gradients (corrected for the cooling effect of drilling mud circulation) in the Eromanga Basin vary extremely between 30 and 80 C/km. Combining thermal conductivities (2.0 2.2 W/m/K) of the sediments (Gallagher, 1987) of the basin, yields surface heat flow in the range of 70 160 mW/m 2 . Heat flow above a background value of about 75 - 80 mW/m 2 has been attributed to lateral variations in heat production in the basin basement (Gallagher, 1988), which are attributed to granite intrusions. However, it has been shown in this study that surface heat flow can be influenced greatly by groundwater movements in the aquifer system of the basin. Numerical experiments indicate that groundwater movements not only alter thermal gradients at discharge and recharge zones but also create an apparent heat flow anomaly, which is not associated with basal heat flow but an indication of the aquifer structure. As a result, the artesian water movements in the Eromanga Basin must have complicated the thermal regime in the basin. Thermal studies have revealed that the thermal history of the basin is rather complicated. However, thermal contraction of the crust may have followed early intrusive events, since the present high thermal state of the basin has been attributed to a recent thermal event (<10 Ma) in the crust (Pitt, 1986; Kantsler et al.,1983; Duddy, 1987). Gravity anomaly analysis of the basin region has played a critical role in delineating the driving load for basin subsidence during this study. By removing the Geological Society of Australia Abstracts Number 32, Ballarat 1992

effects of surface sediment load and the flexure of the lithosphere under the surface load, a residual gravity map has been produced, which clearly identifies the areas of internal loads responsible for possible basin subsidence. These loads are represented by relatively high positive anomalies of residual gravity, which are believed to have resulted from large scale granite intrusions during the late Palaeozoic. These loads are situated within the Simpson Desert, Cooper, Adavale and Galilee Basins, which gives an indication that these basins probably formed as a result of early intrusive orogenic events. Cooling of these intrusive bodies and their likely metamorphism afterwards led to further isostatic subsidence for the development of basins of younger age. By correlating deep seismic velocities with crustal rock types on the basis of published laboratory tests on crustal rocks (Mueller, 1977; Meissner, 1986; O'Reilly and Griffin, 1990), the crust beneath the central Eromanga Basin could consist of four different rock types: the top layer (on average < 5km) is represented by sediments aged from the late Palaeozoic to the Mesozoic with velocity less than 5.6 km/sec; the second layer with a velocity zone from 5.6 to 6.3 km/sec (the Thomson Fold Belt less than 20 km thick on average) may be composed of granites and lowgrade gneisses or metasediments and metavolcanics; the third marked by the velocity from 6.3 to 7.0 km/sec may represent high-grade metamorphic rocks such as amphibolites and granulites; the bottom layer just above the Moho boundary and with a velocity range from 7.0 to 8.0 km/sec probably consists of a high proportion of ultramafic rocks and eclogites. In addition, a crustal density distribution has been constructed on the basis of empirical relations between the commonly observed P-wave velocity and rock density (Dooley, 1977). The result indicates once again that the bottom layer (less than 4 km thick on average) just above the Moho has a high density from 3 to 3.4 g/cm 3 and could be composed of high-grade granulites, eclogites or ultramafic rocks like lherzolites and pyroxenites. This is also supported by the result of pressure-temperature modelling of the crust in comparison with the P-T diagram for metamorphic facies (Meissner, 1986) as well as the results of residual gravity analysis. It is very likely that deep crustal metamorphism from granulite to eclogite played a significant role in inducing basin subsidence. In addition, based on the derived densities for central and eastern Australia, overburden pressures relative to the central Eromanga Basin were constructed, and reveal that the crust (above 40 km depth) of the basin is subjected to deviatoric compression from surrounding areas and the deeper part (below 40 km) is however subjected to deviatoric extension. This suggests that the effect of lithospheric flexure associated with sediment load probably played

285 a certain role in the development of the Eromanga Basin sequence. References Finlayson, D., 1990, BMR Bulletin, 232. Johnson, et al., 1986, poster paper given at 4th IKC, perth. O'Reilly, et al., 1988, BMR record 21. Gallagher, K., 1987, Explor. Geophys., 18, 381-392. Gallagher, K., 1988, PhD thesis, ANU. Pitt, G. M., 1986, Geol. Soc. Aust. Special Publ. 12,

KEYNOTE: A12.3

323-351. Kantsler et al., 1983, APEA 23, 75-92. Duddy, I. R., 1987, Technical Report of NERDDP Project No. 720. Mueller, S., 1977, Geophys. Mono. 20, Am. Geophys. Union. Meissner,R., 1986, The Continental Crust, - A Geophysical Approach, Academic Press. O'Reilly, S. Y. & Griffin, W. L., 1990, BMR Bulletin 232. Dooley, J. C., 1977, BMR J. Aust. Geol. Geophys 2, 1-5.

GEOLOGICAL MAPPING USING AIRBORNE GEOPHYSICS -

NEW FRONTIERS D F Pridmore

World Geo science Corporation, Perth Airborne geophysics, principally airborne magnetics and radiometrics is becoming far more widely used in mineral exploration and resource assessment as a tool for detailed geological mapping, relative to its traditional application of target detection and regional studies. Image processing has played a dominant role in widening the application areas of airborne geophysics, although advances in acquisition, processing and navigation technologies have all had some impact. The ease with which the eye can resolve both fine and coarse information from an appropriately stretched image reduces both the level of skill and effort required to interpret the data. Image processing is now used to measure the effectiveness of developments in acquisition, processing and navigation. The pivotal role played by image processing is quite remarkable considering that the technology, as applied to airborne geophysics, is only 5 years old. New frontiers in airborne geophysics which, when developed, will give the technology even wider application are: Interpretation: Interpretation of airborne geophysical data has lagged well behind acquisition and processing methodologies. "Stick and circle" interpretations must be replaced by structural and lithological maps where the geological history is inferred from airborne data and supported with critical ground investigations. The lack of even a basic rock property data base and theoretical modelling software that can simulate realistic three dimensional geologic environments are major impediments to more effective interpretation. Data and Image Processing: Filtering and levelling techniques prior to image processing are especially useful in isolating and enhancing fine structure in the data. Significant geological features often have only Geological Society of Australia Abstracts Number 32, Ballarat 1992

subtle expression and quite specific processing is required to allow the interpreter to interrogate the data for such features. Good communication between geophysicists processing the data and geoscientists interpreting the data is important. The subjective process of extracting information from a data image is very poorly understood, and given the importance of image processing, urgently requires investigation. For instance, the ability of the observer to distinguish a subtle linear on a greyscale image depends on the wavelength of the feature, the geological environment of the linear and undoubtedly a number of other variables. Images are typically generated by interpolating the measurements onto a regular grid. At least half of the primary data is ignored in this process. As a result the maximum presentation scale of an image is l/(line spacing in metres x 125), too small for detailed work. This problem , present in almost all gridding algorithms, is a major limitation of image processing. Data Acquisition: Lowering noise levels in the data, both in geophysical measurements and aircraft position increase the area of application of airborne geophysics. The current noise floor of 0.1 to 0.5nT in airborne magnetic surveying limit, the sensitivity to lithotypes with equivalent magnetite concentrations in excess of approximately 2,000 ppm. Many wackes and acid volcanics sequences cannot be mapped with current airborne magnetic technology. Data Integration and Digital Data Bases: The image processor, through judicious use of graphics and raster planes, can superimpose data sets which are conventionally overlain on a light table. However, the image processor can integrate data sets in a far more effective manner through utilising the variables of hue, saturation and intensity in colour space. Superimposing Landsat TM data with aeromagnetics

286 is a powerful display tool for structural analysis; locating geochemical and potassium radiometric responses in the vicinity of strike faults defined by magnetics is important in gold exploration. Display and data base technologies have evolved to the point where integration of digital data bases can be done on a routine basis. Geological craft is required to make this technology work more effectively for mapping. Recent advances in airborne electromagnetics

A12.4

(AEM) including the development of digital systems with large bandwidth, offer the potential for a new airborne mapping technique that resolves silicate lithologies through differential weathering in the regolith. Development, driven by an understanding of geological problems to be solved will ensure exciting growth of airborne geophysical technology.

THE FORESHOCK SEQUENCE AT TENNANT CREEK IN 1987 Emmanuel Bouniot, Trevor Jones and Kevin M c Cue Australian Seismological Centre, Bureau of Mineral Resources, GPO Box 378, Canberra, ACT, Australia

Three magnitude 5+ earthquakes shook the Tennant Creek region of the Northern Territory between 5 and 9 January 1987 and aftershocks continued throughout the year. The total moment release in 1987 was equivalent to that of a single magnitude 6.3 earthquake. On 22 January 1988 these earthquakes proved to be foreshocks when three magnitude 6 + earthquakes occurred along with a 35 km long thrust fault scarp. Three portable seismographs were installed near Tennant Creek by 21 January 1987 and fifty aftershocks to March 1987 were located with an accuracy of just a few kilometres. The plotted foci outline a dipping fault coincident with the

A12.5

Kunayungku fault, the westernmost of three fault segments comprising the prominent fault scarp formed on 22 January 1988. Modelling of a 200 Nms"2 gravity anomaly in the focal region reveals a fault bound intrusion extending to within one km of the surface. We conclude that stress was attracted to the competent volcanic intrusive rock until some asperity in the intrusion failed in January 1987. No triggering mechanism has been identified. Failure propagated through 1987, until January 1988 when a much greater rupture in the less competent country rock occurred

EARTHQUAKE HAZARD IN THE CANBERRA REGION Marion Michael-Leiba Australian Seismological Centre, BMR

Australia's national capital, Canberra, is not aseismic. During the period January 1982 - October 1991, 15 tremors with magnitudes ML 1.0 - 2.4 occurred at distances up to 20 km from the Canberra GPO. Several of these micro-earthquakes were heard and felt. Canberra lies within a broad belt of earthquake epicentres extending from Newcastle in the north to Bass Strait in the south. The Dalton-Gunning zone, 60 km north of Canberra, is assessed as the highest earthquake hazard area in eastern Australia (Gaull, Michael-Leiba and Rynn, 1990). The larger earthquakes in this zone are also felt in Canberra. Canberra's earthquake hazard (Gaull, Michael-Leiba and Rynn, 1990) has been assessed to be higher than that of Melbourne or Sydney, lower than Adelaide, and approximately equal to that of Perth, Western Geological Society of Australia Abstracts Number 32, Ballarat 1992

Australia. In Canberra, there is a 10% chance of experiencing at least Modified Mercalli (MM) intensity VI in a 50 year period. At this intensity, objects may fall off shelves, plaster crack, and people run outside in fright. The corresponding intensity for the DaltonGunning zone (Gaull, Michael-Leiba and Rynn, 1990) is MM VII, at which some structural damage may occur. References Gaull, B.A., Michael-Leiba, M.O. and Rynn, J.M.W., 1990. Probabilistic earthquake risk maps of Australia. Australian Journal of Earth Sciences, v. 37, pp. 169-187.

287 A12.6

SEISMIC WAVE ATTENUATION IN DUNITE AT HIGH SUB-SOLIDUS TEMPERATURES: AN EXPERIMENTAL STUDY Ian Jackson*, M.S. Paterson and J.D. Fitz Gerald Research School of Earth Sciences, Australian National University, Canberra

One of the principal features of seismological models for the Earth's interior is a zone of low wave velocities and high attenuation in the upper mantle at depths of 100 - 250 km. The existence of this regionally variable zone is commonly attributed to the presence of a small fraction of aqueous fluid or partial melt. However, fluid-absent conditions with high sub-solidus temperatures may be sufficient. A detailed mechanistic understanding of the observed attenuation and velocity dispersion (frequency dependence) would be of value, not only in the interpretation of the seismological observations but also in helping constrain the rheology of the asthenosphere. To this end we have developed a machine which provides for the study of both shear modulus dispersion and internal friction in geological materials through the observation of forced torsional oscillations of low frequency (10 -1000 mHz) and strain amplitude (<10"6) under conditions of high pressure (to 300 MPa) and temperature (to > 1000°C). Here we report measurements on cylindrical specimens of an olivinerich rock from Aheim, Norway which contains, in addition to olivine, about 10% pyroxene and 5-10% of hydrous silicate phases dominantly clinochlore, serpentine and talc. In order to separate aspects of the mechanical behaviour associated with the olivine aggregate from those attributable to the hydrous phases and/or their dehydration products, the specimens were either previously fired under controlled oxygen fugacity at 1200 C for 24 hours in order to effect complete dehydration within the olivine stability field, or simply oven-dried at 110°C. Linearity of the mechanical behaviour has been demonstrated by the amplitude independence of the results for the strain amplitude range 10"® and by the quantitative consistency between the observed modulus dispersion and that calculated from the

Geological Society of Australia Abstracts Number 32, Ballarat 1992

measured internal friction through the Kramers-Kronig relations of linear theory. Both the pressure dependence at room temperature, and the temperature dependence at 300 MPa, of the shear modulus and internal friction have been investigated. Much of the variation of the shear modulus (Fig. 1(a)) is attributed to changes of crack porosity associated with changes in pressure and temperature and with in situ dehydration. Temporal evolution of towards a lower asymptotic value over periods of hours of exposure to given conditions of high pressure and temperature is tentatively attributed to the gradual diminution of enhanced anelastic relaxation associated with regions of decaying stress concentration at asperities on cracks and/or grain boundaries. At the highest pressures and temperatures achieved in this study, 300 MPa and 1000 C, marked dispersion of the shear modulus, amounting to 5% between periods of 3 and 100 s, and concomitant strong internal friction (Fig. 1(b)), varying with oscillation period T approximately as 0 . 0 1 a r e observed. The energy dissipation appears to be concentrated within, rather than at the boundaries between, the olivine grains. These results provide the clearest indication yet that solid-state, probably intragranular, anelastic relaxation in ultramafic rocks gives rise to losses comparable with those observed seismologically in the Earth's upper mantle, although the mechanistic basis for the observed anelasticity remains to be established. 0

Reference Jackson I, Paterson M S and Fitz Gerald J D. Geophys. J. Int. (in press)

288

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Temperature / °C Fig.l Temperature dependence of shear modulus and internal friction Q"1 for Aheim dunite compared with the results of previous studies at atmospheric pressure.

Geological Society of Australia Abstracts Number 32, Ballarat 1992

289 A 12.7

ADVANCES IN GEOPHYSICAL BORE LOGGING IN THE LATROBE VALLEY W.Wood *, R.Moss , Z.Smith 1

1

2

Uine Planning and Geotechnical, State Electricity Commission of Victoria, P.O. Box 195, Morwell, Victoria 3840 Datcol, 141 Princes Highway, Trafalgar, Victoria 3825

1

2

Since around 1975 the State Electricity Commission of Victoria (SECV) has routinely employed geophysical bore logging to enhance and optimise stratigraphic and groundwater information from operational and investigative boreholes in the Latrobe Valley coal fields. The principal technique used was, for a number of years, natural gamma, supplemented on occasions with electric and other logs. Although natural gamma readily distinguishes brown coal from sand and sand from clay where these lithologies are relatively pure, it soon became apparent that near identical traces could at times be recorded in quite different lithologies. For example, a signature typical of inferior coal could easily be confused with that of ligneous sand while ligneous clay and clayey sand might also be difficult to differentiate with confidence where no material samples or other indicators are available. Although conventional neutron and density logs could probably overcome this problem, the combination of unstable borehole conditions and A 12 8

abundant aquifer systems which characterise the Latrobe Valley Coal Measures effectively precluded the use of strong radioactive sources. The SIROLOG gamma gamma system, which employs a very weak (5 millicurie) source, was trialled and subsequently proved to be capable of significantly better lithological discrimination than could be achieved using natural gamma methods. in the Latrobe Valley since 1986. In-house software has been developed to permit greater flexibility in display and manipulation of the digital output, and this has also assisted in achieving a higher level of confidence in the reliable interpretation of geophysical logs. The SIROLOG system records a broad spectrum of radiation wavelenghths and therefore has the inherent capacity, through the application of selective windows, filtering and correlations, to indicate more subtle parameters such as variations in coal quality and clay mineralogy. This potential is yet to be actively explored.

SEAFLOOR ELECTRICAL CONDUCTIVITY AND OCEAN CURRENTS FJE.M.(Ted) Lilley *, Jean H. Filloux and Ian J. Ferguson ' 1

2

1 3

1R.S.E.S., Australian National University, Canberra, A.C.T. Scripps Institution of Oceanography, San Diego, U.S.A. 3 now at University of Manitoba, Winnipeg, Canada 2

The movement of sea water in the magnetic field of earth causes electric currents to flow both in the sea water and in the material beneath the seafloor. The process is one of motional electromagnetic induction. Ocean currents thus generate a possible source-field for the electrical exploration of the seafloor. For four months over the summer of 1983/84, a set of electric and magnetic field instruments of Jean H. Filloux of Scripps Institution of Oceanography in California operated on the floor of the Tasman Sea between Australia and New Zealand. The electrical signals due to the movement of sea water in the East Australian Current were remarkable, and immediately evident. The amplitude of the signals was of order tens of iiV.m" , and the time-scale of variation tens of days. Recent analysis of the data has now also revealed 1

Geological Society of Australia Abstracts Number 32, Ballarat 1992

magnetic signals due to the same movement of sea water. The amplitude of the magnetic signals is of order tens of nT, and these signals have been extracted from a strong background of ionospheric origin by using "remote-reference" data. The remote-reference sites have been another seafloor site remote from the East Australian Current, and also the Canberra Magnetic Observatory of the Bureau of Mineral Resources. Together, the magnetic and electric signals enable the determination of a "leakage factor" of 0.06 ± 0.01, which controls the fraction of electric current flowing in the material beneath the seafloor. This quantity in turn enables the determination of seafloor conductance, which is the electrical conductivity of the seafloor material integrated from the ocean bottom down to the depth where the material becomes highly resistive.

290 The seafloor conductance thus determined for two sites on the Tasman Abyssal Plain is 910 ± 150 S. This value agrees well with calculations of the conductance of the known sedimentary column, 1200 m in thickness, which underlies the sea water. The agreement is pleasing, and carries the conclusion that

beneath the sedimentary column the seafloor must be resistive, and of correspondingly low porosity. This particular case history has implications for the wider use of the method in other areas of active ocean current.

POSTER SESSION A 12,9

SURFACE FAULTING AND EARTHQUAKE RECURRENCE IN AUSTRALIA J. R. Bowman *, A.J. Crone , M.N. Machette , J.R. Prescott and K. Tanaka 1

2

2

3

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Australian Seismological Centre, Bureau of Mineral Resources, Canberra U.S. Geological Survey, Golden, Colorado, USA Department of Physics and Mathematical Physics, University of Adelaide Abiko Research Laboratory, Central Research Institute for Electrical Power Industry, Abiko, Japan 2

3

4

Earthquakes in 'stable' continental interiors (SCI) are rare relative to those along plate margins, but they can cause widespread damage because of low regional attenuation and because the population and buildings are usually ill prepared for severe ground motion. Past earthquake-hazard assessments of SCI have relied on statistical analyses of seismicity because geological data on the behaviour of seismogenic faults were virtually nonexistent. Worldwide, only ten historical SCI earthquakes have formed surface ruptures, and five of these have occurred in Australia since 1968. In addition to these historical events, there are reports of as many as eight prehistorical scarps in Australia. Considering the increasing number of such reports from Australia and abroad in recent years, a systematic search of SCI would probably show that prehistoric ruptures are more common than previously thought. Geological studies of the scarps from the 1988 Tennant Creek,. NT and the 1986 Marryat Creek, SA earthquakes show that the recurrence intervals for surface-rupturing earthquakes on these faults are several tens of thousands of years or more. At Tennant Creek, dating of eolian sand using thermoluminescence and electron-spin resonance A 12.10

methods indicates that the penultimate faulting event occurred more than 60,000 years ago. At Marryat Creek, the lack of topography associated with the scarp and the moderately developed soil exposed in two trenches indicate that the recurrence of surface-faulting events is measured in at least tens of thousands of years. In both cases, the historical earthquakes reactivated ancestral faults that probably formed in Proterozoic time. Earthquake hazard assessments of SCI are hindered by an incomplete inventory of fault scarps, poor knowledge of the behaviour of seismogenic faults, and the aseismic character of some seismogenic faults. If recurrence intervals of tens of thousands of years or more typify SCI faults, then, on a human scale, the hazard posed by a single fault is small. On the other hand, if many faults are present, then the hazard would be proportionally greater. Better hazard assessments in SCI might result from statistically computing a composite recurrence interval for all faults in a region and using this interval to evaluate the probability of a specific site being affected by a damaging earthquake.

UNDERPLATING OF THE SOUTHERN NEW ENGLAND OROGEN ? D. M. Finlayson* & C. D. N. Collins Bureau of Mineral Resources, Geology & Geophysics, Canberra

The central and southern parts of the Australian east coast are regarded as rifted margins formed during the opening of the Tasman Sea (Shaw, 1990; Symonds et al., 1988). The earlier development of the eastern Australian craton margin has been described by Geological Society of Australia Abstracts Number 32, Ballarat 1992

Coney et al.(1990) and Korsch et al.(1990). Mechanisms for rifting have been proposed involving large-scale delamination of the crust and underplating (Lister & Etheridge, 1989; Lister et al., 1988). Determination of crustal and upper mantle velocities

291 provides some information on possible processes. Wide-angle reflection and refraction seismic studies indicate that two velocity models are appropriate for the structure of the crust and upper mantle under the southern New England Orogen. Under the southern part of the New England Batholith crustal velocities increase gradually from 5.5-6.03 km/s at the surface to 6.45 km/s near a distinct Moho at 34-35 km depth, suggesting that rocks of granitic composition make up a large part of the crust. Under the northern part of the New England Batholith there is a (? mafic) sill-like feature at 21-24 km depth with a velocity maximum of 6.7 km/s. The crustal velocities are significantly less than those of the Lachlan and Thomson orogens underlying the Bowen-Gunnedah-Sydney Basin system just to the west of the New England Orogen (typically > 6.3 km/s at >10 km depth) and of terranes in the northern New England Orogen. In areas with similar granite geochemistry and inferred to have similar evolutionary process (e.g. southwestern U.S. Peninsular Ranges Batholith), there are contrasts with the New England Batholith with high velocity mafic rocks (inferred ophiolite basement) at quite shallow (10 km) depths (Mooney & Weaver, 1989). Under the southern New England Orogen an upper mantle velocity of 7.7 km/s is determined, the lowest yet interpreted for any region of continental Australia. This upper mantle velocity persists down to about 45 km depth and then increases to 8.08 km/s at 60 km. This again contrasts with upper mantle velocities

0

Woolbrook

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SOUTH

under the adjacent Lachlan and Thomson Orogens (typically >8.04-8.15 km/s), and with the southwestern U.S. batholiths (about 8.2 km/s). Low velocity material in the mantle under New England could be the residue from geochemical differentiation within the mantle during I-type plutonism, or be underplated material emplaced during the formation of the Tasman Sea Basin and the subsequent uplift of eastern Australia. Other rifted margins, such as the southern Australian margin with Antarctica (Veevers & Eittreim, 1988), may exhibit a similar deep crustal velocity structure. References Coney P. J. et al., 1990. J. Struc. Geol. 12, 519-543. Korsch R. J. et al., 1990. Bur. Miner. Res., Geol. & Geophys. Bull 232, 35-52. Lister G. S., & Etheridge M. A. 1989. In: Intraplate Volcanism, Camb. Uni. Press, 297-313. Lister G. S. et al., 1988. Geol. Soc. Aust. Abstracts 21, 252-253. Mooney W. D., & Weaver C. S. 1989. Geol. Soc. Am. Mem. 172, 129-161. Shaw R. D. 1990. Bur. Miner. Res., Geol. & Geophys. Bull 232, 53-66. Symonds P. A. et al., 1988. Geol. Soc. Aust. Abstracts 21, 393-394. Veevers, J. J., & Eittreim, S. L., 1988. Aust. J. Earth Sc. 35, 355-362.

Deepwater

300 km Warwick

NORTH

Figure 1. Velocity model of the crust and upper mantle across the southern New England Orogen (Velocities in km/s).

Geological Society of Australia Abstracts Number 32, Ballarat 1992

292 A 12.11 THE THERMAL STRUCTURE OF MANTLE PLUMES Gregory A. Houseman Department of Earth Sciences, Monash University, Clayton, VIC 3168, Australia Mantle plumes are key elements of the plate observed. In addition, the solutions show elongate tectonics theory, introduced to explain the seamount- cold downwelling features on the upper surface of the island chains whose age increases linearly with layer, analogous to subduction zones. These solutions for R = 6 x 10 and (I = 0.5 are distance from a presently active source characterised by elevated topography and heat flow, positive gravity strongly time-dependent. There are frequent blob-like instabilities associated with both hot upwelling and geoid anomalies and volcanism. Mantle plumes are also implicated in continental rifting, where the regions and cold downwelling regions. On the lower same uplift signature can cause active extension in the boundary layer, these instabilities take the form of relatively weak continental lithosphere. It is well blob-like thickenings of the hot boundary layer which known that plumes must originate from a hot thermal grow rapidly and become the focus for the new boundary layer but at present it is not yet clear upwellings. However, these incipient plumes usually whether this boundary layer is at the base of the form on one of the hot rising sheets near an mantle, implying a single circulation system for the established plume, and they are swept along the sheet entire mantle, or whether the mantle circulation and soon merge with the nearby established plume. system may be separated into two layers by a change On the upper surface the effect of the plume in chemical composition at around 680 km depth. In instabilities can be characterised as movement of the two layer model the plumes originate at the base individual hotspots along a trend aligned with the of the upper mantle and the circulation is primarily dominant hot sheet structure on the base of the layer. driven by heating from below. The hot spots appear to merge, to split into two and Numerical experiments of thermal convection in a to increase or decrease in intensity. The time 3-D plane layer with constant viscosity and a dependence is difficult to describe in words, but is best component of basal heating (Houseman, 1990) shown using video animations produced from the demonstrate a class of thermal structures analogous to computer output. The net effect of the many blob-like mantle plumes. These hot, upwelling structures form instabilities that occur is to produce a continual a network of sheets on the base of the layer, but the rearrangement of the details of the convection cell upwards flow is most intense at the nodes of this boundaries without having a major impact on the long network where the sheets join together in triple- or wavelength features of the convective circulation quadruple-junctions. Above these locations the hot which are otherwise relatively stable. A zone of hot plumes impinging on the upper surface produce upwelling or cold downwelling, once established, is approximately axisymmetric temperature, heat flow, likely to remain so for many overturn times. surface uplift and extensional stress anomalies. The The phenomenon described by Griffiths and relatively minor deviations from axisymmetry of the Campbell (1990) of large new plume heads produced surface uplift trace the connecting ridges of hot mantle by instability of the basal thermal boundary layer has on the base of the layer. not been observed in these experiments, probably The two major factors influencing the formation of because of the relatively low Rayleigh number used thermal plume structures are the Rayleigh number R, here (6 x 10 ). If the Rayleigh number were increased (ratio of buoyancy forces to viscous dissipative forces) by one or two orders of magnitude then the form of and the heating mode number (i, defined as the ratio of the time-dependence described above might develop internal heating : (internal + basal heating) into the type of isolated plume head described by (Hd/(F+Hd)}. For Rayleigh numbers up to about Griffiths and Campbell (1990). Comparable 10 , the experiments show that when the basal calculations with such high Rayleigh numbers are heating component is less than about 25% of the total beyond the capacity of presently accessible computers. heating, stable thermal plumes are effectively not These experiments don't provide a definitive answer present in the flow. The flows are strongly time- to the question of whether the mantle is layered or not, dependent and dominated by localised downwelling mainly because of the relatively unconstrained structures. The relatively diffuse upward return flow influence of physical effects, such as temperature in the layer is slightly enhanced by the minor basal dependent viscosity and compositional buoyancy, heating, but it cannot be associated with the plume- which have not been included in the calculations. like phenomena described in the first paragraph. However some constraints are obtained: Firstly, the However, when basal heating constitutes 50% of the presence of long-lived thermal mantle plumes such as total heating, strong plume-like structures are Hawaii implies something greater than 30 or 40% of 5

5

6

Geological Society of Australia Abstracts Number 32, Ballarat 1992

293 the surface heat flow is input through the base of the layer. Secondly, a flux based Rayleigh number of about 107 is indicated by observational constraints on the magnitude of surface uplift above mantle plumes (less than about 1 km). The first constraint appears to favour a layered mantle but it is possible that this conclusion can be avoided, either because the actual Rayleigh number is significantly greater than that used in these calculations, or because temperature-dependent viscosity permits mantle plume-like structures even

with a relatively small amount of basal heating. These possibilities are not easily tested using presently available computers. References Griffiths, R.W. and Campbell, I.H., Earth Planet. Sci. Lett., 99, 66-78, 1990. Houseman, G.A., Geophys. J. Int., 102., 15-24, 1990.

A 12.12 COMPUTER MODELLING OF THE STRUCTURE AND TECTONIC EVOLUTION OF THE CANNING BASIN H.W.S. McQueen and J. Braun Research School of Earth Sciences, Australian National University, Canberra In common with most Australian sedimentary basins, the Canning Basin in northern Western Australia has been moulded by several distinct tectonic events over a long history. The basin has been the subject of renewed scientific investigation since, in 1988, the Bureau of Mineral Resources collected three deep reflection seismic lines along and across the Fitzroy Trough, aimed principally at unveiling the morphology of the deepest parts of the basin and the structures in the underlying crust and upper mantle (Drummond et al., 1989). As part of a co-operative project between the BMR and the Geodynamics Group of the Research School of Earth Sciences, we have analyzed the seismic data in combination with new high resolution aeromagnetic data as well as existing gravity, well and shallow seismic data in an effort to improve our understanding of the tectonic and structural development of the basin. The Canning Basin lies at the intersection of an number of distinct crustal blocks including the Archaean Pilbara Block, and the Proterozoic Paterson Province, Arunta Block and Halls Creek Province and its sediments therefore overlie several major ancient crustal sutures. Some of these crustal boundaries may be responsible for features visible in artificial illumination images of basin scale gravity anomalies. Other features of the gravity field appear to reflect major bounding faults in the Fitzroy Graben. Extension and subsidence appears to have begun around the Ordovician and may have been continuous right through into the Permian, with the depocentre migrating between the different sub-basins. The southern Willara and Kidson sub-basins received early sediments, while the majority of the sediment in the deeper Fitzroy Trough in the north was deposited during an episode of fault controlled crustal extension from the late Devonian to late Carboniferous. This behaviour can be understood in terms of a model of Geological Society of Australia Abstracts Number 32, Ballarat 1992

lithospheric deformation and healing under the influence of fluctuating extensional stresses on a timescale comparable to the conductive cooling time (Braun, 1991). The deep seismic lines confirm the proposed asymmetric character of the Fitzroy Trough (Begg, 1987; Drummond et al., 1988), limiting the range of acceptable models, and provide a framework for more specific models of the deformation in some parts of the basin. They have not, however, completely resolved the nature of the deep crustal movements which accommodated the graben development. We have investigated several alternative models of the lithospheric deformation along the basin cross section marked by BMR line 3. The most straightforward interpretation of the deep seismic line is that this part of the basin changed polarity from asymmetrical extension on a southward dipping fault to extension on a northward dipping fault at some time between the late Ordovician and early Devonian. We have reconstructed the kinematics of this picture and discuss the dynamic implications. The distribution of strain in the mantle lithosphere which accompanies the crustal faulting also has major implications for the overall subsidence of the basin, particularly in the later stages and we compare models of offset extension zones with one of long term steady extension as explanations for the relatively weak signal of a distinct thermal sag phase in the basin. The latter explanation presently seems most likely in the light of available data. References Begg , J., 1987, APEA 27(1), 137-151. Drummond, B.J., M.A. Etheridge, P.J. Davies, and M.F. Middleton, 1988, APEA 28(1), 76-86 Drummond, B.J., D.M. Finlayson, H.J. Harrington,

294 C. Wright and the Explosion Seismology Group, 1989, BMR Research Symposium 1989 extended A 12.13

abstracts. Braun, J., 1991, J. Geophys. Res., in press.

ATTENUATION OF STRONG EARTHQUAKE GROUND MOTION IN TASMANIA Marion Michael-Leiba

Australian Seismological Centre, BMR which approximates the instrumental magnitude In Tasmania, strong earthquake ground motion calculated using Michael-Leiba and Malafant (1989) to attenuation can be described by the formula: half a magnitude unit or better, for hypocentral distances in the range 20 - 240 km, for 25 out of 28 I = 4.94 + 1.45 ML - 3.61 log R measurements of isoseismal radii of the 14 where I is Modified Mercalli intensity, R is earthquakes. hypocentral distance in kilometres (assuming a focal depth of 10 km) and ML is Richter magnitude based References on southeastern Australian attenuation (Michael-Leiba and Malafant, 1989). The standard error from 29 Everingham, I.B., McEwin, A.J. and Denham, D. 1982. Atlas of isoseismal maps of Australian measurements on 14 earthquakes (Everingham et al, earthquakes. Bureau of Mineral Resources, 1982: McCue et al, in prep) with instrumentally Geology and Geophysics, Bulletin 214. determined epicentres and Richter magnitudes in the B.A., Michael-Leiba, , M.O. and Rynn, range ML 2.5 - 6.0, is 0.5 intensity units. This linear Gaull, J.M.W., 1990. Probabilistic earthquake risk maps formula is satisfactory for hypocentral distances in the of Australia. Australian Journal of Earth Sciences, range 20-240 km. It tends to overestimate intensities v. 37, pp. 169-187. for isoseismal radii outside this range. McCue, K.F., et al, in prep. Atlas of isoseismal maps The Tasmanian formula gives intensity estimates of Australian earthquakes, part 3. Bureau of 0.6 - 0.7 intensity units higher than the southeastern Mineral Resources, Geology and Geophysics bulletin. Australian attenuation function of Gaull, MichaelMichael-Leiba, M. and Malafant, K., 1989. Leiba and Rynn (1990). Attenuation and the ML scale in southeastern Rearrangement gives an intensity-based magnitude Australia. In: Michael-Leiba, M. (compiler). formula for Tasmania: Seismicity of the Australian plate and its margins. Bureau of Mineral Resources, Geology & ML = 2.49 log R + 0.690 I - 3.41 Geophysics, Record 1989/6. A 12.14

ELASTICITY OF OLIVINE AND ITS HIGH-PRESSURE POLYMORPHS AND THE COMPOSITION OF THE TRANSITION ZONE Sally Rigden

Ian Jackson Gabriel Gwanmesia and Robert Liebermann 2

2

Research School of Earth Sciences, Australian National University, Canberra Centerfor High Pressure Research and Department of Earth and Space Sciences, State University of New York, Stony Brook, New York, USA 1

2

There is continuing debate over the bulk mineralogical composition of the mantle, whether chemical stratification occurs and what this implies for layered versus whole-mantle convection. As much of the evidence bearing on these problems is indirect (seismology, geochemistry, petrology) it is important to develop methods of testing different chemical Geological Society of Australia Abstracts Number 32, Ballarat 1992

models. Measurement of the physical properties, particularly the elasticity, of mantle minerals at high pressures and temperatures is critical in this regard as it allows the construction of models for the variation of velocity with that can be compared with seismic results. Until recently, such measurements have been precluded because samples of high-pressure phases of

295 sufficient size were unavailable. Interest in the influence of phase transformations in the (Mg,Fe)2SiC>4 system on seismologically observed mantle structure has intensified with the advent of a novel seismic imaging technique (Shearer, 1991). Although the global velocity discontinuites in the vicinity of 400 and 670 km depth are widely agreed to be a result of transformations in this system (olivine (a) to modified spinel (p), and spinel (y) to perovskite + magnesiowustite) at least in part, the existence of a discontinuity at -520 km which might be related to the (5-y phase transformation in the (Mg,Fe)2SiC>4 system is more controversial. This discontinuity has been observed fairly widely in long period seismic reflection studies and is strikingly evident in Shearer's stacked seismograms, but is rarely seen in short period or refraction studies. Recent developments in high pressure synthesis (Gwanmesia et al, 1990) and ultrasonic interferometry ( Niesler and Jackson, 1989; Rigden and Jackson, 1991) have made it possible to make measurements on small, sintered polycrystalline specimens. The pressure dependence of elastic wave velocities of hotpressed, elastically isotropic polycrystals of the P and y (Fig 1) phases of magnesium orthosilicate (Mg2SiC>4) has been determined to 3 gigapascals at room temperature (Gwanmesia et al, 1990; Rigden et al, 1991). By combining the new results with data for the olivine (a) phase, velocity profiles are calculated for the M2Si04 (M=Mg, Fe) component of the mantle to -600 depth (Fig 2). As a result of the similarity between the elastic properties of the P and y

Geological Society of Australia Abstracts Number 32, Ballarat 1992

phases, it is unlikely that any seismologically observable velocity discontinuity in the region of 520 km can be attributed to the M2Si04 component; however, the contrast in impedance (density x velocity) might be sufficient for the p - y transformation to be observed in long period seismic reflection studies near normal incidence. Furthermore, for any reasonable values of temperature derivatives of the P and y phases, the velocity gradients in the transition zone are steeper than would be expected for adiabatic compression of likely mantle compositions. This is particularly striking for shear waves and could be related to gradual recovery of a shear velocity deficit associated with anelastic relaxation concentrated at depths shallower than 400 km where the geotherm more closely approaches the mantle solidus. References Gwanmesia, G.D., R.C. Liebermann and F. Guyot 1990. Geophys. Res. Lett., 17, 1331-1334. Gwanmesia, G.D., S.M. Rigden, I. Jackson and R.C. Liebermann, 1990. Science, 250, 794-797. Niesler, H. and I. Jackson, 1989. J Acous. Soc. Amer. 86, 1573-1585. Rigden, S.M. and I. Jackson, 1991. J. Geophys. Res. 96, 9999-10006. Rigden, S.M., G.D. Gwanmesia, I. Jackson and R.C. Liebermann, 1991. Proceedings of the 4th USJapan Seminar, High-Pressure Research: Applications to Earth and Planetary Sciences. Shearer, P.M., 1990. Nature, 344, 121-126. y

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500

600

Figure 2: Calculated acoustic velocity profiles for (Mgo.9,Feo.i)2SiC>4 (short-dashed lines: latm velocities; long-dashed line: pressure corrected only; solid lines: corrected for P and T along a HOOT adiabat using a range of plausible temperature derivatives of elastic moduli). Geological Society of Australia Abstracts Number 32, Ballarat 1992

297 A 12.15 THE MAGNETIC ANOMALY MAP OF AUSTRALIA C.Tarlowski, P.Milligan and F.Simonis Bureau ofMineral Resources, Geology and Geophysics, CanberraAustralia. The Bureau of Mineral Resources has been routinely acquiring airborne magnetic surveys over the land area of Australia since 1951 to record and map anomalies in the earth's magnetic field attributable to geological structures and lithologies. In forty years, over four million line kilometers of survey data have been flown, while the technology of survey practice has passed through various stages of development. Important among these was the introduction of digital data acquisition techniques in the early 1970's. The majority of the land area has now been covered with so-called reconnaissance surveys at 1600 m line spacing and at a flying height of 150 m. Much of the remainder - particularly the inland sedimentary basins is covered by surveys of lower specifications, leaving only very limited ares unsurveyed. While the data quality varies with instrumentation and survey parameters, it is almost everywhere good enough to provide a useful synoptic view of magnetic anomaly patterns which can be expected to give important new insights into the geology and tectonics at a continental scale. The technical difficulties in combining hundreds of separate surveys into a uniform grid of values are considerable, however. These problems include significant temporal variation in the geomagnetic field itself over this period, and the fact that surveys have never been designed to ms^sure accurately anomalies of wavelength in access of about 100 km. This leads to difficulties in reconcilling adjacent survey areas with each other and with the broad goemagnetic field variations over Australia, as recorded, for example, by BMR's recent AWAGS (Australia-wide array of geomagnetic stations)

experiment. Furthermore, much of the early aeromagnetic surveys data does not include absolute measurments of the total magnetic field values. Use of the latest computer technology for processing and presentation of these data also necessitates digitizing early non-digital data with considerable labour. Located profile datafromtape archives are being regridded using a minimum curvature techniques to 15 second of arc centres (about 400 m). The gridded data were merged on a 1:250 000 sheet basis by minimizing the discrepancies on the boundaries between adjacent surveys and reducing remaining misties through Laplacian smoothing. The resulting maps contain reliable short-wavelength anomaly information of the order of 60 km or less which is attributable to the surfuce and near-surface geology. The poster shows progress with the Australian compilation up to the end of 1991. The project will lead to a completed digital grid and published anomaly maps using latest colour presentation technology in the course of 1992. It is proposed to extend the compilation by cooperating with institutes compiling similar data for other southern continents to produce a magnetic anomaly map of (reconstructed) Gondwana in due course. References Teskey,D.J.,Dods,S.D. and Hood,P.J., 1982, Compilation techniques for 1:1 Million magnetic anomaly map series, Curent Research, Part A, Geological Survey of Canada, Paper 82-lA,351358.

A 12.16 PRECAMBRIAN TIDAL RHYTHMITES AND THE EARTH'S PALAEOROTATION George Williams Department of Geology & Geophysics, University of Adelaide, Adelaide, South Australia An important recent development in geochronometry has been the recognition of tidal rhythmites - sequences of laminated, fine-grained sandstone, siltstone and mudstone displaying cyclic variations in lamina thickness and grain size that indicate a strong tidal influence on sedimentation. Such tidal rhythmites are now known from the Late Geological Society of Australia Abstracts Number 32, Ballarat 1992

Proterozoic, as well as from Phanerozoic and modern deposits. The study of tidal rhythmites has rejuvenated geochronometry, which had reached an impasse about ten years ago because of difficulties in interpreting palaeontological data, and expanded its application to include the Precambrian. This presentation illustrates

298 Proterozoic rhythmites in Australia and their implications for the geochronometry of the EarthMoon system. Tidal rhythmites can provide valuable data on palaeotidal periods, the Earth's palaeorotation and the ancient lunar orbit. The periodicities recorded by tidal rhythmites usually can be ascribed to tidal pattern and type, thus avoiding some of the uncertainties associated with palaeontological data. In addition, rhythmite sequences may span many years - the longest continuous sequence so far obtained is about 60 years in the Late Proterozoic Elatina Formation, South Australia - thus enhancing the reliability of the identified cycles. Such a long rhythmite record also permits the determination of long-term palaeotidal periods that cannot be obtained from palaeontological data. Rhythmites of laminated siltstone and very finegrained sandstone from the Late Proterozoic (-650 Ma) Elatina Formation and Reynella Siltstone Member in South Australia record a wide range of palaeotidal cycles that provide unique information on the Earth's palaeorotation and the past lunar orbit (Williams, 1988, 1989a-c, 1990, 1991). These rhythmites evidently were deposited in littoral settings ranging from estuarine to upper and lower delta slope and distal ebb-tidal delta. Periodic changes in the thickness of semidiurnal and diurnal laminae, and of conspicuous fortnightly groups of such laminae (lamina-cycles), reflect variations in the amount of fine clastic material entrained and deposited by tidal currents in response to periodic changes in the velocity and range of palaeotides. Stratigraphic series of lamina and lamina-cycle thickness measurements obtained from drill core of the 10-m-thick rhythmite member of the Elatina Formation at Pichi Richi Pass contain strong periodicities that are evident visually or revealed by Fourier spectral analysis. These data represent an unsurpassed palaeotidal record. Supplemented by observations from the Reynella Siltstone Member of the Elatina Formation at Hallett Cove, they give palaeotidal and palaeorotational values (Table 1) that are more accurate and numerous than values previously obtained for any geological interval. The Late Proterozoic (650 Ma) year contained 13.1 ± 0.1 lunar months and 400 ± 7 solar days, and the Late Proterozoic lunar month 30.5 ± 0.5 solar days. The periods of the lunar apsides (perigee) and lunar nodal cycles were then 9.7 ± 0.1 and 19.5 ± 0.5 years, respectively. The mean Earth-Moon distance of 58.28 ± 0.30 Earth radii at 650 Ma, determined by applying Kepler's third law to the value of 13.1 ± 0.1 lunar

Geological Society of Australia Abstracts Number 32, Ballarat 1992

months/year, gives a mean rate of lunar retreat of 1.95 ± 0.29 cm/year over the past 650 Ma. This mean value is only about half the present rate of lunar retreat of 3.7 ± 0.2 cm/year obtained by lunar laser ranging (Dickey et al., 1990). The implied increasing mean rate of lunar retreat since 650 Ma is consistent with increasing tidal dissipation in the oceans as the Earth's rotation slows. The Late Proterozoic rhythmites provide additional information of importance to palaeogeophysics (Williams, 1990). The values for days/sidereal month and sidereal days/year at 650 Ma suggest virtually no overall change in the Earth's moment of inertia I since that time: ///o = 0.998 ± 0.018 for solar/lunar retarding couples acting on the Earth (j3) = 1/5.5, and I/Io = 1.005 ± 0.018 for p = 1/3.7. These results appear to rule out significant Earth expansion since 650 Ma. The rich palaeotidal record of the Elatina Formation also indicates that southeastern Australia faced an open ocean in Late Proterozoic time. Furthermore, the strong signatures of the diurnal inequality, half-yearly tidal cycle of solar declination, and annual sea-level oscillation in the Late Proterozoic rhythmite data imply a significant obliquity of the ecliptic at 650 Ma. The study of other tidal rhythmites, particularly those of early Precambrian age, may further advance our understanding of the Earth's palaeorotation and the ancient lunar orbit. For example, very thin, cyclic microbanding in Early Proterozoic (-2500 Ma) ironformation (Weeli Wolli Formation) in the Hamersley Basin, Western Australia, although commonly regarded as annual-climatic increments, may well be of fumarolic origin related to fortnightly earth tides (Williams, 1989c, 1990). Through study of such ancient rhythmites, sedimentology promises to illuminate the evolving dynamics of the Earth-Moon system over much of geological time. References Dickey, J.O. et al., 1990. Eos (Trans. Am. Geophys. Un.) 71: 475. Williams, G.E., 1988. Climatic Change, 13: 117y

128.

Williams, G.E., 1989a. J. Geol. Soc. London, 146: 97-111. Williams, G.E., 1989b. Eos (Trans. Am. Geophys. Un.), 70: 33 & 40-41. Williams, G.E., 1989c. Episodes, 12: 162-171. Williams, G.E., 1990. Phys. Earth, 38: 475-491. Williams, G.E., 1991. Canad. Soc. Petroleum Geologists Mem., 16 (in press).

299 Table 1. Late Proterozoic (650 Ma) and modern tidal and rotational values

Parameter

Late Proterozoic

Modern

solar days/lunar month solar days/sidereal month lunar months/year sidereal months/year lunar apsides cycle (years) lunar nodal cycle (years) solar days/year sidereal days/year length of solar day (hours) Earth-Moon distance (/?e) lunarretreatrate (cm/year)

30.5 ± 0.5 28.4 ± 0.5 13.1 ± 0.1 14.1 ± 0.1 9.7 ± 0.1 19.5 ± 0.5 400 ± 7 401 ± 7 21.9 ± 0.4 58.28 ± 0.30 1.95 ± 0.29 (650-0 Ma)

29.53 27.32 12.37 13.37 8.85 18.61 365.24 366.24 24.00 60.27 3.7 ± 0.2 (laser ranging)

*Values indicated by tidal rhythmites of the Late Proterozoic Elatina Formation and Reynella Siltstone Member, South Australia (Williams, 1988,1989a-c, 1990, 1991). The rhythmite data also display strong semi-annual and annual periods.

A 12.17

DECONVOLUTION OF VERTICAL SEISMIC (VSP) DATA Marianne Windhofer* and Christopher Juhlin

Curtin University of Technology, Department of Exploration Geophysics Deconvolution is a process commonly used to improve the resolution of seismic data. It is generally used for removing multiple energy and wave shaping. Processing of Vertical Seismic Profile (VSP) data was done with the VSP processing package WELLPRO. This processing package has been provided to the Seismic/Lithology project by Robert Stewart of the University of Calgary. A deconvolution operator is calculated that will zero the phase and increase the frequency content ("spike") of the first break signature of the downgoing wave. For calculating the operator a standard Wiener-Levinson algorithm is used. The user of WELLPRO has control

A 12.18

over the processing parameters, window length and operator length. The results from the deconvolution are highly dependent upon the choice of these parameters. When applying deconvolution on VSP data these parameters will differ from those used on surface seismic data, in particular the applied decon operator length. On VSP data, our research shows the best deconvolution results when using an operator length which is the same as the window length. In contrast, on surface data the operator length is generally 1/4-1/8 the window length from which it is calculated. This poster shows different operators and the results when applied on VSPs.

GEODYNAMIC MODELLING OF THE CAINOZOIC EPEIROGENY OF THE EAST MIDLANDS SHELF, BRITAIN. J. M. Wood* and G. A. Houseman Department of Earth Sciences, Monash University, Clayton, Victoria.

This study represents the results from geodynamical simulation of epeirogenic processes acting on the lithosphere of the East Midlands, England, during the Cainozoic. Apatite fission track Geological Society of Australia Abstracts Number 32, Ballarat 1992

analysis with tectonic and thermal history interpretation, carried out by P. Green of Geotrack International (Green 1989) revealed that surface rocks in the area were at maximum palaeotemperatures in

300 the early Tertiary. The heating was probably due to Mesozoic burial, and the sediments were subsequently brought to the surface by up to two kilometres of erosion. We have applied epeirogenic models of erosion and flexure to the area in an attempt to model its geological history. Erosion is simulated using an erosion rate (Lambeck & Stephenson 1986) dependent on surface height: e(t)=h(t)/te where te is a time constant and h(t) is the time dependent elevation. The thermal lithospheric energy balance is initially in steady-state, the lithospheric geotherm given by using constant temperature top and base, and with an exponentially decreasing radiogenic heat source. Isostatic and potential energy balance are maintained at all times. For an initial surface elevation of 500 metres the results show that observed erosion of up to two kilometres would occur if a low erosion rate (te=10 m.y.) was applied throughout the Cainozoic. With an initial erosion rate of 50 m/m.y. the surface erodes to an elevation of about 150 metres (isostatically compensated) in 60 m.y., giving a cumulative erosion of about 1900 metres of stratigraphy. The model begins with a surface temperature gradient of 31°C/km, for the area, that decreases by about 3°C/km during the 60 m.y. The observational data shows that current and palaeotemperature gradients, near the surface, are about the same (Green 1989). The fairly slow erosion rates used produce the observed erosional uplift of buried material; alternatively, similar results are obtained if the model assumes short periods of fast erosion interspersed with periods of no or slow erosion. Simplified elastic flexural modelling of the Southern North Sea basin, utilising the Cainozoic A 12,19

sediments as a distributed load upon the chalk, indicate flexural bulge uplifts of up to about 50 metres located at the East Midlands shelf. The amount of uplift and location of uplift depends on the elastic lithospheric thickness and the distribution of the load; a wider load reduces the amplitude of the uplift and moves the location of the forebulge maximum away from the centre of the load - a thicker elastic lithosphere moves the location of the forebulge maximum away from the load's centre. These simple models don't include the effects of sediment compaction, topography of the surface prior to flexure, or the position of sea-level. The second order effects of load modification due to emergence of the forebulge above sea-level will also be examined. Flexure, although contributing slightly to East Midlands uplift today, is not primarily responsible for the amount of emergence seen now in the area, or that implied during the Cainozoic. We have developed a semi-analytical solution for flexure subject to in-plane force with a distributed load. The effects of in-plane compression or extension on uplift are negligible. However, there are important implications for interpretation of transgression/ regression sequences in the sedimentary record. References Green, P.F., 1989, Thermal and tectonic history of the East Midlands shelf (onshore UK) and surrounding regions assessed by apatite fission track analysis. Journal of the Geological Society, London. 146 : 755-773. Lambeck, K. and Stephenson, R. , 1986, The postPalaeozoic uplift history of SE Australia. Australian Journal of Earth Sciences 33 :253-270.

THE ENIGMATIC LATE PROTEROZOIC GLACIAL CLIMATE: THE LOW PALAEOLATITUDE OF LATE PROTEROZOIC GLACIATIONS George Williams , Phillip Schmidt and Brian Embleton 1

2

3

Dept. of Geology and Geophysics, University of Adelaide, SA 5000 CSIRO Division of Exploration Geoscience, North Ryde NSW 2113 CSIRO Division of Exploration Geoscience, Floreat Park, WA 6014 1

2

t

s

Late Proterozoic glaciation between 800 and 600 Ma is the most puzzling climatic event in Earth history. Low palaeolatitudes (< 30°) of glacial deposition are indicated by numerous palaeomagnetic investigations of Late Proterozoic glaciogenic deposits; most studies indicate glacial deposition between 0° and 12° palaeolatitude (see McWilliams & McElhinny, 1980; Embleton & Williams, 1986; Schmidt et al., 1991). A positive fold test on a softGeological Society of Australia Abstracts Number 32, Ballarat 1992

sediment slump fold in the Elatina Formation, which is part of the Marinoan glacial succession in South Australia, confirms the primary nature of the remanence (Schmidt et al., 1991). Palaeomagnetic evidence for coeval glaciation in high palaeolatitudes has not been forthcoming; areas such as the North China Block occupied high palaeolatitudes (up to 62°) during the Late Proterozoic yet afford no evidence of glaciation (Zhang & Zhang, 1985).

301 Fossil permafrost horizons displaying periglacial seasonal freeze-thaw structures in Late Proterozoic glaciomarine basins indicate frigid, strongly seasonal palaeoclimates near sea level (Williams, 1986). Preserved sand-wedge structures imply mean annual air temperatures as low as -12° to -20°C or lower, and a seasonal temperature range of ~40°C or more (mean monthly air temperatures ranging from < -35°C in midwinter to +4°C in midsummer). Palaeomagnetic and palaeoclimatic data thus present the enigma of frigid, strongly seasonal climates near sea level in preferred low palaeolatitudes. Indeed, the Late Proterozoic glacial climate is one of the major paradoxes in contemporary Earth science, calling into question basic tenets of palaeomagnetism and palaeoclimatology. The presence of unglaciated areas in high palaeolatitudes and the evidence for strongly seasonal climates in low palaeolatitudes during the Late Proterozoic militate against the idea of global (pole to pole) glaciation. Possible explanations of preferred glaciation and strongly seasonal climates in low palaeolatitudes (Williams, 1975; Embleton & Williams, 1986) include: (a) the axial geocentric dipole model of the Earth's magnetic field is invalid for that time interval; and (b) a reversed climatic zonation and marked seasonality prevailed because of a large obliquity of the ecliptic (> 54°) in Late Proterozoic time. Discrimination between these two

Geological Society of Australia Abstracts Number 32, Ballarat 1992

hypotheses requires palaeogeophysical data that are independent of both palaeoclimate and palaeomagnetism. It may be significant, therefore, that palaeotidal data for the Elatina Formation (Williams, 1988, 1989a-c) are consistent with both a low palaeolatitude of deposition and a substantial obliquity of the ecliptic at that time (Williams, 1990). References Embleton, B.J.J. & Williams, G.E., 1986. Earth Planet. Sci. Lett., 79: 419-430. McWilliams, M.O. & McElhinny, M.W., 1980. J. Geol., 88: 1-26. Schmidt, P.W., Williams, G.E. & Embleton, B.J.J., 1991. Earth Planet. Sci. Lett., 105: 355-367. Williams, G.E., 1975. Geol. Mag., 112: 441-465. Williams, G.E., 1986. Precambrian Res., 32: 233242. Williams, G.E., 1988. Climatic Change, 13: 117128. Williams, G.E., 1989a. J. Geol. Soc. London, 146: 97-111. Williams, G.E., 1989b. Eos (Trans. Am. Geophys. Un.), 70: 33 & 40-41. Williams, G.E., 1989c. Episodes, 12: 162-171. Williams, G.E., 1990. J. Phys. Earth, 38: 475-491. Zhang, H. & Zhang, W., 1985. Precambrian Res., 29: 65-75.

302

Geological Society of Australia Abstracts Number 32, Ballarat 1992

303

A13: REMOTE SENSING CONVENOR: JOSEPH LEACH A 13.1

THE USE OF TM IMAGERY TO MAP RECHARGE AND DISCHARGE ZONES IN THE GRENVILLE AREA OF CENTRAL VICTORIA. Joseph HJ. Leach Remote Sensing Unit, Ballarat University College.

This study's brief was to investigate the contribution that remote sensing could make to whole farm planning by providing information on recharge and discharge zones. The study area is approximately 30 Kms south of Ballarat and consists of an area about 15 Kms on a side centered on the drainage channel between ML Mercer and the Enfield state forest Basalt from Mt. Mercer covers the south of the region. Mt. Mercer is a roughly circular basalt sheild surrmounted by a small scoria cone. The major rock types in the area are Lower Ordivican slates and sandstones. These underlie the volcanics and form the majority of the ground base. While there is little outcrop in the study area, their coverage can be recognised by the lighter soils which contrast to the heavier black soils of the volcanics. They are tightly folded, slightly metamorphosed, and heavily fractured. Upper Pliocene non marine gravels and sands occur in the region. These are mainly exposed as hill cappings and probably represent the remains of sand dune deposits associated with the tertiary marine transgression into the Port Campell embayment to the south. They are often iron cemented and are always extremely porous. In the study area they are confined to the region of the Enfield State Forest and their occurance and extent are difficult to map. The climate is cool temperate with an average rainfall from 650 to 700mm. While most of the rainfall is in winter, the main growth periods are in autum and spring since the winters are generaly too cold and wet. The regional drainage is to the south with the main drainage system being the Yarrowie River. The groundwater conditions were investigated using bore hole data from the RWC. While the results are generalised because of the relatively poor coverage of bore holes in the area, these logs were able to give standing water level and total dissolved solids. Lithological logs were also used to determine the general nature of the aquifers. Geological Society of Australia Abstracts Number 32, Ballarat 1992

The groundwater mainly moves through unconfined, fractured basalt aquifers. There are some perched aquifers which are confined by weathering surfaces within the basalt and there is also an unconfined aquifer within the fractured paleozoic rocks. The amount of total dissolved solids varies from less than lOOOmg/litre (slightly saline) up to 5000 mg/litre (moderately saline). As expected, the potentiometric surface reflects a subdued version of the surface topography. In 1869 a map was prepared for the Victorian Geological Survey showing proposed mine extentions along the Durham Lead in the Mt. Mercer region. This map clearly shows the major east west drainage system as an area of discharge. The area was also flown in 1948 and in these photographs the floors of the gullies are marked by extensive dark areas, indicating water logged ground. The sensor used for the majority qf this investigation was the Landsat Thematic Mapper (TM). It was decided that resorces should be put into getting seasonal coverage of the study area to investigate the variations in plant behavior over the year. This seems to be the first study to apply multi-temporal imaging to a salinity investigation in Victoria and the results suggest that the technique should be used more often. The seasons chosen for the study were summer, when plant activity would be at a minimum, and spring, when plant growth would be maximised. The main strength of seasonal (or multi-temporal) data is that it is able to show the variations in plant response and soil moisture at varying times of the year. The model we are using for discharge zones is as follows: 1. In summer such zones will be areas where there is relatively green vegitation because of the continuing avaliability of water, even if the water is moderately saline. This is contrasted to the extreme water stress experienced by the surrounding pasture over much of the summer. 2. In spring, discharge zones will show relatively

304 poor plant growth both because of the stress of salinity and the water logged condition of the ground. This will be contrasted with the surrounding pasture which will be showing a maximum growth response. There will also be a larger discharge zone in the spring than in the summer since the seasonal recharge will be higher. This additional recharge will mark an area which may not be effected by salinity yet but which would be at risk if there were further rises in the water table. The model we are using for recharge zones is as follows: 1. In summer these areas will not be easily distinguishable from their surroundings since the whole area will be dry and only minimal recharge will be occuring. 2. In spring these areas will show a reduced plant response, relative to the surrounding pasture, since the higher water infiltration will mean that less is available to the surface plants. This reduced response A 13,2

will be differentiated from that of the saline discharge by geographical considerations. The area was investigated using ratios, PC analysis, and the "greeness index" of Kauth and Thomas (1976). The resultant images enabled the mapping of both major and minor recharge zones as well as various levels of discharge. The study demonstrated that seasonal imagery is a major tool in environmental monitoring, especially in relation to salinity. References Kauth, R.J. & Thomas, G.S., 1976, "The Tasselled Cap - a graphic description of the spectoraltemporal development of agricultural crops as seen by Landsat. Proc. Symposium on Machine Processing of Remotely Sensed Data, Purdue university, West Lafayette, Indiana, 4B41-4B51.

THE REGIONAL SETTING OF THE MURRAY TRENCH USING NOAA-AVHRR IMAGERY Patrick Halewood Ballarat University College

The Murray Trench is a shallow trough cut by the Murray River as it passes through the Mallee tract of northern Victoria. The trench, consisting of terrace sets formed in the Quaternary Coonambidgal Formation, has a maximum width of 40-50 km, and is often less than 15 km wide. Even though it is a narrow feature, the trench has a significant influence on groundwater movement between the surrounding shallow Tertiary aquifers of the Murray-Darling Basin, and the Murray River. This project aimed to identify large scale structures that may affect the distribution and movement of groundwater in the Murray Trench and adjacent Tertiary aquifers, using the data obtainedfrom the NOAA-9 satellite. The NOAA-AVHRR scanner aquires data in five spectralb ands during its two day-time passes, and in three bands during its two night-time passes. All bands have a pixel size of 1.1 km. The section of the electromagnetic spectrum recorded in each band are: Bandl: 0.55-0.68 microns. Band2: 0.725-1.1 microns. In these two bands the scanner is recording reflected solar radiation. This data can only be recorded during the day. Band3: 3.55-3.93 microns. Band4: 10.3-11.3 microns. Band5: 11.5-12.5 microns. These three sections of the spectrum consist of Geological Society of Australia Abstracts Number 32, Ballarat 1992

thermal infrared radiation (TIR) emitted by all matter. The amount of TIR emitted by an object is approximately proportional to its radiant temperature. Factors affecting the emission of TIR from the Earth's surface include the physical properties of the material on or below the surface eg composition; the slope and aspect of the surface (only significant during the day and early evening); soil moisture; land cover and surface roughness. The data set used was a day/night pair recorded on the 9/2/88. The data was processed to provide grey scale images of both day and night TIR, false colour composites, vegetation index, principal component, and apparent thermal inertia images. Two sets of features are apparent on the night TIR images: a NNE trending set of lineaments, anda NW trending series of lunate (concave to the SW) structures. Neither set could be seen on images of the day-time data, indicating that any topographic expression of the lineaments is not the cause of their temperature contrast with the surrounding sediments. Loghlin (1990) outlines a number of geological situations that can cause features such as those seen on the TIR images. Groundwater build-up against a fault crossing an aquifer is one possibility. NNE trending basement structures are common in this area (e.g. Danyo Fault, Neckarboo Ridge, Willandra Trough), and many of the NNE lineaments, seen on the images, correlate well with the locality of these faults. Due to

305 this correlation other NNE lineaments are believed to represent previously unknown faults. Not all known faults in the area have corresponding thermal anomalies (e.g. the north striking Tyrell Fault), indicating these faults do not have the same effect on groundwater flow as the ones identified on the images. The lunate features correspond with the direction and distribution of Pliocene strandlines. These strandlines have different thermal properties than the surrounding sediments, probably due to grainsize and/or A 13.3

compositional differences rather than due to the presence of groundwater. Reference Loughlin W.P., 1990. Geological exploration in the western United States by use of airborne scanner imagery, in Remote Sensing! an Operational Technology for the Mining and Petroleum Industries. Inst. Min. Metal., London.

THE APPLICATION OF AIRBORNE RADIOMETRIC CLASSIFICATION TECHNIQUES TO SALINITY STUDIES IN WESTERN VICTORIA. P. A. McDonald* and G. R. Pettifer

Geological Survey of Victoria, Department of Manufacturing and Industry Development. Airborne radiometric surveys are used to determine the distribution of the naturally occurring radioactive elements potassium (K), thorium (Th) and uranium (U) over the ground and have long been used for qualitative geological mapping purposes in mineral exploration. Airborne radiometrics also has the potential for soil and regolith mapping. Radiometrics uses a sodium iodide crystal detector and a gamma-ray analyser to measure gamma rays emitted from K,Th and U isotopes and their daughter products within in situ rocks and soil and transported soils. The radiometric method samples an area with a diameter of approximately twice the flying height of the aircraft and soil depths of up to thirty centimetres. Gridded airborne radiometric data was analysed and presented using modern image processing techniques on the ERMAPPER (Version 2.0) image processing software. Using radiometrics, the soils were classified into

Geological Society of Australia Abstracts Number 32, Ballarat 1992

regions with a unique radiometric signature (ie. K, Th and U content). Soil type is important for groundwater recharge and soil salinity, it follows that radiometrics may also be useful for groundwater and salinity studies. Applied research over known salinity and groundwater recharge areas was undertaken to evaluate the utility of radiometrics. The potassium content of the soil predominantly reflects the amount of clay within that soil. Therefore, the soil's potassium signature is of primary interest in groundwater investigations. Soils with high contents of potassium indicate potential areas of poor groundwater recharge and also salinization of the groundwater. Soils with low potassium contents (low clay), indicate potential groundwater recharge zones. The methodology and ground truthing of airborne radiometrics for soil classification is discussed.

306 A 13 4

THE USE OF TM IMAGERY IN TERRAIN UNIT MAPPING OF THE BALLARAT REGION E.B. Joyce1 and Joseph HJ. Leach2* ^School of Earth Sciences, University of Melbourne. ^Remote Sensing Unit, Ballarat University College.

Regolith maps have recently been developed in Australia as a regional study tool. Trial maps have been prepared for the the Hamilton sheet area in Western Victoria and adjacent Southeastern South Australia (Oilier and Joyce 1986). As well, engineering terrain evaluation maps have been prepared by the CSIRO for a number of regions in Australia using the PUCE program(Grant 1975). One of these was conducted over the study area (Grant 1972). While both of the Victorian maps were prepared using a range of data types including geological, soil, land evaluation, topographic maps, and air photographs; neither made significant use of remote sensing. A 1973 study of Landsat MSS hardcopy data includes the Ballarat area (Joyce 1974). The Ballarat area has been used in the present study as a suitable test area to both evaluate Landsat TM imagery for terrain unit mapping, and to allow an historical comparison with the image interpretation of 1973. An area in Central Victoria was studied as part of a NASA project in 1973 using ERTS-1 paper prints of Bands 4,5,6, and 7 at 1:1000000 scale. The area extended from Port Phillip Bay across the coastal and volcanic plains and into the central highlands of folded Paleozoic sediments and granites which included deep weathering profiles. A series of interpretive overlays showing trend lines, drainage, and geomorphic regions, including major geological boundaries, was prepared by the first author with contributions from student classes at the University of Melbourne (Joyce 1974). This historical study was used as a test base against which the spectral improvments of the TM instrument and the capabilities of digital image processing could be evaluated. The scale of the study has meant that full use of the increased resolution of the TM instrument could not be utilised except over small test areas where it was used to map drainage. The capabilities of TM which were of particular interest were the clay response of Band 7 which was used to show differential weathering profiles over the basalt, and the thermal response of Band 6 which was used to determine the physical condition of the rock as well as depth of soil cover. These bands have already been identified as important components in any physical terrain mapping project using remote sensing (Leach and Mallett 1988). The new study was able to prepare thematic maps of major drainage systems, geological structure, and Geological Society of Australia Abstracts Number 32, Ballarat 1992

apparent weathering on the basis of Landsat TM imagery using the 386/Vista microBRIAN image analysis system at the Ballarat University College, Remote Sensing Unit. The value of such image interpretation was evaluated and comparisons made with the use of MSS hardcopy and the procedures used in the Hamilton study. It is clear that the increased spectral range of the TM instrument allows a much finer division of regolith units, even when considered at the same scale. In addition, the availability of digital image processing increases the certainty with which regolith units can be mapped. Thus the current study was able to divide the basalt plains around Ballarat into four broad units. These were: 1.Older basalt plains, characterised by deep weathering, 2. Younger basalt plains, which show a higher response on Band7, 3.The Gordon Basalt Plains, characterised by intensive cultivation, and 4.Rocky Outcrops, which include stony rise features, flow margins, and regions exposed along stream courses. This is also true of geological structure. A north west/south east trend which was only minimally sketched in the early study has, after the application of high pass and directional filters, been recognised as the major structural element in the area. However, the major conclusion is that the greatest value of satellite imagery still lies in its ability to provide a synoptic view unavailable fromother sources. References Grant, K. (1972). Terrain classification for engineering purposes of the Melbourne Area, Victoria. CSIRO Aust. Div. of Appl. Geomechs. tech. Pap. No.ll. Grant, K. (1975). The PUCE Programme for Terrain Evaluation for Engineering Purposes 11. Principles. CSIRO Aust. Div. of Appl. Geomechs. Tech. Pap. No. 15. Joyce, E.B. (1974) Evaluation of Available ERT"-1 Imagery for the production of a Geomorphic Map of Southeastern Australia. School of Geology, University of Melbourne, pp 13. Leach, J.H.J. and Mallett, C.W. (1988) "A SatelliteBased Investigation of the Significance of Surficial Deposits for Surface Mining Operations, Geotechnical Applications of Remote Sensing and

307 Remote Data Transmission, ASTM ST- 967, A.I. Oilier, C.D. and Joyce, E.B. (1986) Regolith Terrain Johnson and C.B. Pettersson Eds. American Units of the Hamilton 1:1000000 Sheet Area, Society for Testing and Materials, Philadelphia, Western Victoria. BMR Record 1986/33. pp 55 1988, pp.122-137. plus map. A 13.5

MAPPING MICROCRACKS AND ROCK JOINTS AUTOMATICALLY USING DIGITAL IMAGE ANALYSIS S J D Cox ' , T J Green * & M W Jessell 1

2

3

1

WlEPS, Dept of Earth Sciences, Monash University, Clayton, Victoria, 3168 CSIRO Division of Geomechanics, PO Box 54, Mt Waver ley, Victoria, 3149 3 Geology Dept, University of Melbourne, Parkville, Victoria, 3052

2

Fractures have important effects on the mechanical and transport properties of rock on all scales. For example: joints and faults are a dominant feature of shallow crustal rock masses and provide the main control over fluid permeability; and the formation and growth of microcracks is the main cause of weakening and rupture of rock loaded at low to moderate temperatures and pressures. An accurate characterization of the distribution of fractures in terms of their density, size, orientation and relative locations is therefore a prerequisite for an analysis of rock behaviour in terms of processes. We have used digital image analysis to generate fracture maps from a variety of samples. These are based on (i) black-and-white and colour photographs taken of cliff faces and road cuttings in the Grampians, from sandstone and granite outcrops, and (ii) photographs and micrographs of polished surfaces prepared through rock cores which have been partially fractured in laboratory compression tests. The photographs are then digitised for analysis by a desktop computer (Fig. 1). The initial stage of analysis involves: (i) removal of noise with a 3x3 median filter; (ii) smoothing the image by convolution with a 7x7 Gaussian filter mask; (iii) enhancement of linear features by convolution with a 7x7 Laplacian mask; (iv) thresholding at a user defined level to generate a binary

Geological Society of Australia Abstracts Number 32, Ballarat 1992

image of background and potential cracks; (v) shrinking and thinning the particles to further reduce background noise and accentuate linear features; (vi) manual separation of overlapping or intersecting features; (vii) generation of a table of best-fitting ellipses to these candidate-cracks. This data is further processed in the following sequence: (vii) rejection of those particles whose size is below a selected threshold, and with a minor/major axis ratio above a selected value; (viii) classifying particles lying within specific relative orientation and separation bands into sets; (ix) generation of a final fracture map by linear regressions through these sets, weighted according to the size and slenderness of the candidate cracks. The product is vector map of linear fracture segments (Fig. 2), which can be used to generate the statistics required. The methods have been verified by comparison with the results of conventional mapping techniques. Although the results of the image analysis initially gives a 2D representation, compared with the full 3D that can be obtained from field mapping, this data can be compiled more rapidly and by combining statitics from images taken from intersecting planes the 3D representation can be recovered. Furthermore the increased amount of information increases the validity of statistical measures.

308

Figure 1. Initial image of crack array as scanned into computer.

A 13.7

GEOLOGICAL APPLICATIONS AND LIMITATIONS OF AIRBORNE MULTI-SPECTRAL SCANNERS; THEIR AVAILABILITY, COST EFFECTIVENESS AND FUTURE R.A. Agar* GEOSCAN Pty. Ltd., 24 Outram Street, West Perth, WA.

Multi-Spectral Scanning devices have extended their range from having been orbiting satellite-borne, multi-purpose systems with a limited spectral resolution via a small number of broad recording bands and low (^30m) ground resolution to airborne systems Geological Society of Australia Abstracts Number 32, Ballarat 1992

6005

which provide greatly enhanced spectral and spatial resolution and the ability to record data in specific wavelengths for specific applications. Focussing our attention on geological applications, the nature of geological work demands

309 that all remote sensing systems are applicable to both mapping and targetting problems. An ideal system would be capable of discriminating surface mineralogy and hence lithology without recourse to extensive field work, while at the same time being relatively cheap, readily available and easy to use. The extent to which this has and can be achieved is not just a problem of developing the technology. There are astronomical climatological, botanical, geomorphological, educational and economic barriers to be brought down before it can become as universally used as a hammer or lens. Astronomical and climatological factors severely restrict the operations of an airborne multi-spectral scanner (AMSS) and indirectly affect the cost of operations. Botanical and geomorphological criteria at present limit the applications of AMSS systems although with better directed research they could be turned to advantage. Educational limits are merely the same problem faced by all new technologies and will be overcome in time but in the meantime, still impact on the economics of AMSS operations. The limited operational life of AMSS systems, their high cost and relatively limited use up to present, place a high premium on their use which in itself is a deterrent to potential clients. However, AMSS systems have been used to great

effect in a number of geological applications. Both regional mapping (at 1:50,000 scale for example) and detailed mapping (1:5,000 scale) have been successfully carried out using AMSS data. Mineral mapping is now also becoming an accepted use of such data which is consequently finding increased use in metals exploration where identification of specific alteration minerals is crucial to optimising target selection. Similar procedures are used in both industrial mineral exploration, the search for oil and gas and also for geothermal resources. In each of these examples, it can be demonstrated that exploration utilising AMSS data is both cost and time efficient, yet all currently operating AMSS systems around the world are under-utilised. If AMSS technology is to progress therefore, it is not newer and better instruments with higher spectral and spatial resolution that are immediately needed, but a greater understanding of its applications by field geologists, a greater and lower cost of data, and improved quality of data to allow ease of manipulation on field based image processing systems. When these conditions are satisfied, then development of remote sensing technology will become industry rather than research driven and will inevitably lead to instruments with improved spectral and spatial resolutions.

A 13.8 A REMOTE SENSING STUDY OF KIMBERLITE AND LAMPROITE PIPES USING GEOSCAN AIRBORNE MULTISPECTRAL SCANNER IMAGERY: EXAMPLES FROM THE KIMBERLEY, WESTERN AUSTRALIA. A. Hatch , W.R. Taylor *, and R.A. Agar 1

1

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Key Centre for Strategic Mineral Deposits, Univ. of Western Australia, Nedlands, W.A. 6009. GEOSCAN Pty Ltd, 24 Outram St, West Perth, W.A. 6005. Infrared remote sensing imagery from airborne exploration may not be successful. The aim of this multispectral scanners (e.g. GEOSCAN AMSS Mks I study is to at least partly remedy this situation by: (i) and II) have proved useful in identifying surficial determining the cause of SWIR reflectance anomalies mineralogical anomalies associated with alteration over selected kimberlite and lamproite bodies from the zones surrounding mineral deposits. In applications to Kimberley region; (ii) investigating the degree to diamond exploration, there has been some success in which the anomalies are kimberlite/lamproite specific identification of anomalies arising from kimberlite and versus site specific; and (iii) determining what spectral lamproite pipes using clay-mineral-sensitive bands in and mineralogical differences exist between kimberlite the 1.9-2.5 |im portion of short-wave infra-red (SWIR) and lamproite pipes. Detailed on-ground verification studies investigated spectrum and image enhancement treatments based on band ratios, e.g. GEOSCAN AMSS Mk 1 SWIR band on-pipe and outwash SWIR AMSS anomalies associated with the Aries kimberlite pipe, and ratios 9/8, 7/8 and 6/8 have been successfully applied in distinguishing the diamondiferous Aries kimberlite anomalous areas lying to the east of the large Walgidee Hills lamproite intrusion in the Noonkanbah pipe (Phillips Range, central Kimberley). With limited spectral resolution in the SWIR, lamproite field, as well as several other lamproites. GEOSCAN Mk I data is not mineral specific and, Sample collection took into account the relative with little on-ground mineralogical information proportions of surface materials present in a available for Australian kimberlites and lamproites, representative ~ l m site (i.e. rock, soil, organic generalized application of these techniques in diamond matter and vegetation), and sites were carefully selected 1

2

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Geological Society of Australia Abstracts Number 32, Ballarat 1992

310 to avoid disturbed areas. Laboratory reflectance spectra were obtained over the range 0.4-2.5 urn using an IRIS spectroradiometer at the CSIRO Divison of Exploration Geoscience. Data reduction and GEOSCAN Mk I AMSS simulations were performed using the CSIRO PC-Spectra package. Reflectance spectra of surface materials were remixed in their observed proportions for each site also using PC-S. Clay mineralogy was investigated with standard XRD techniques and moisture contents of soils were measured by weight loss at 65°C and 110°C. The Aries pipe and outwash zone AMSS anomaly is defined by low 6/8 and high 9/8 band ratios; the other band ratio, 7/8, shows little variation. The intensity of the 6/8 ratio correlates with depth of the 2.2 nm feature in the reflectance spectra of aluminous clays suggesting that the SWIR anomaly in this case arises from a low content of aluminous clay rather than enhanced magnesian clay. XRD results confirm that the soils from the SWIR anomalous areas are quartz-sand dominated with a relatively small clay component comprising kaolinite rather than montmorillonite or nontronite that might be expected from kimberlite weathering. Thus the SWIR anomaly over the Aries pipe appears to be due to a thin covering of well-drained, sandy overburden that covers the pipe and comprises the outwash zone. The material is probably derived from the surrounding sandstone

country rocks. For the Walgidee Hills intrusion, AMSS SWER anomalies were not satisfactorily detected in the laboratory spectra. They occur in an area of channelways that drain the eastern margin of pipe so that the extent of the anomaly may show seasonal variations depending on the material transported during the wet season. An important mineralogical feature of all on-pipe lamproite-derived soils is the presence of mica as a significant component. SWIR anomalies associated with the kimberlite and lamproite bodies studied show a high degree of site specificity and in the case of the Aries kimberlite pipe the anomaly does not directly relate to the weathering/alteration products of kimberlite. Discriminant analysis techniques based on laboratory spectra, however, indicate that off-pipe and on-pipe sites for the kimberlite and lamproite pipes investigated can be distinguished with >90% accuracy. These results suggest that better targeting of kimberlites and lamproites can be achieved by (i) image enhancement techniques that are specifically designed for the particular terrain under investigation; (ii) development of a larger kimberlite/lamproite spectral database incorporating mica spectra in particular; and (iii) a clearer understanding of the weathering and erosional process within each specific terrain.

POSTER SESSION A 13.9 THE APPLICATION OF LANDSAT TM DATA TO GROUNDWATER INVESTIGATIONS IN THE NEWER VOLCANICS PROVINCE OF WESTERN VICTORIA Patrick Halewood Ballarat University College

The moisture content of vegetation and soils has a strong effect on their spectral reflectances. As little rain falls during summer in western Victoria, the main source of moisture for vegetation in the area, apart from irrigation, is near-surface and discharging groundwater. Landsat TM data was processed to emphasise the distribution of non-stressed vegetation during the middle of summer, thus indicating the distribution of groundwater discharge, as well as to aid geological mapping. The two areas investigated are Mount Rebecca and the Wool Wool/Mount Warrion region. The techniques used to process the raw data were: (i) n-based ie 6 channel principal components analysis (PCA), selective PCA and Crosta technique, (ii) ratiobased ie vegetation ratios such as the normalised Geological Society of Australia Abstracts Number 32, Ballarat 1992

difference vegetation index (NDVI) (TM4TM3/TM4+TM3), the infrared index (TM4TM5/TM4+TM5), the moisture stress index (TM5/TM4) and an index that compares the surface temperature with the NDVI (TM6/NDVI). The n-based techniques allowed improved geological discrimination, while the ratio-based techniques emphasised the distribution of healthy vegetation and soil moisture. Mount Rebecca is a low basalt cone consisting of multiple, radial lava flows, erupted 2 to 3 mya. A small scoria accumulation occurs at the crest of the cone. The main features identifiable on the images of this area are the subcircular cone and the series of swamps and shallow lakes occurring along the contact of the Mt. Rebecca flows witE the surrounding basalt

311 flows and alluvial/lacustrine deposits. The presence of flows, along with a poorly developed drainage system, these lakes and swamps during the middle of summer allow a high percentage of rainfall to infiltrate to the indicates they are being "fed" by groundwater subsurface. The images of this area clearly indicate the discharging from local aquifers, possibly being different lava flows and pyroclastic deposits. recharged near the crest of the cone. These aquifers Groundwater discharge can be seen along the contact may be fractured basaltflows,or scoria layers confined between the stoney rise flows and the surrounding by overlying impervious lavas in a similar fashion to volcanic and alluvial deposits. Springs discharging Mt Shadwell, a scoria cone near Mortlake. below bordering lakes can also be identified. The The Wool Wool/Mt. Warrion area consists mostly distribution of the discharge zones indicates the radial of young (<100,000 yrs) "stoney rise" type flows. flow of groundwater from east of Mt. Warrion in all These flows have irregular, blocky surfaces, with directions, especially south and south-east. shallow soil development. The blocky nature of these

A 13.10 THE XP-1 "CURLEW" - A LOW COST SYSTEM FOR HIGH RESOLUTION, LARGE SCALE AIR PHOTOGRAPHY. Joseph H J. Leach Remote Sensing Unit, Ballarat University College. Kites are the earliest aeronautical devices devised by man. Prior to the advent of aircraft, they were used for signalling, meterological sounding, and even military observation. Kites have been developed which can lift a man and have flown to altitudes of over 12,000 ft (Eden 1991). Under the right conditions they are extremely stable and cost nothing to fly. The Remote Sensing Unit at BUC became interested in Kites as a means of carrying out low cost, high resolution air photography over small, restricted targets. Such targets as small erosion gullies, and initial salt scalds in pastures were found to be difficult to study even in high resolution conventional air photography. Other methods of lofting cameras to low altitudes, such as helium balloons (Mims, 1990), were still considered too expensive for repeated use. As a result we constructed the XP-1 "Curlew". This is a kite lofted camera platformw hich provides single shot stereo photography for no more than the price of thefilmand processing. Although it is limited by weather, its potential applications include any investigation where cost is a factor and repeated air photography is required over a small area. The main module of the Curlew consists of a 1.3m box kite with ripstop nylon sails and two wooden camera mounts fixed centrally between the top and bottom cell struts. The cameras used are Konica Zup80RCs which have an inbuilt intervalometer and can be preprogrammed for any photographic sequence prior to flight. This was felt to be a less costly solution than remote control. These are 35mm cameras which also adds to the low cost and Geological Society of Australia Abstracts Number 32, Ballarat 1992

operational ease of the system. Each of the cameras can be offset from the vertical so as to provide a one shot stereo capability. Initially we used a delta design with the cameras located on a suspended annular mount. However, there proved to be a very narrow operational margin between a wind speed insufficent to lift the cameras and the high speed instability of the delta design. This meant that there was only a five knot range in which the system would work. The box kite design was used as a fix for this problem. Box kites are very stable in moderate to strong winds, even though they do not have the same lifting power in light winds. To operate the Curlew in light winds the box kite can be "chained" with a 2.4m delta. In stronger winds the box kite is used on its own. This arrangment gives a 15 to 20 knot operational wind range. The upper limit being determined by the strain to which yoi are willing to subject the system components. However, weather, particularly the avaliablity and strength of the wind, still remains the main operational restriction on the system. Other include the avaliablity of free space awayfromtrees and power lines. Demonstration experiments are now under way in soil erosion, archeology, beach protection, crop and pasture monitoring, and general interest photography. The system has a very low operating cost and may be of particular interest to developing countries who have a tradition of kite technology and also have a real need for remote sensing to monitor their natural resources. References Eden, M., 1991, "The Sky's No Limit. Popular

312 Science. Vol.239, No.l, pp66-71. Mims, F.M., 1990, "The Amateur Scientist" A 13.11

Scientific American (October), pp92-95.

GEOLOGY OF THE BALLARAT REGION: A DETAILED AIRBORNE SURVEY Robert Carroll and Joseph H.J. Leach

Remote Sensing Unit, Ballarat University College. This paper gives some preliminary results from a project which aims to carry out a structural analysis of the Ordovician basement of the Ballarat region (approximating the Ballarat 100,000 sheet) using detailed airborne magnetics and radiometrics as well as satellite imagery. DATA PROCESSING The project has been based on a detailed geophysical survey carried out by Austirex P/L for Conzinc Riotinto Australia Ltd. (CRA). The data include both magnetic and radiometric data (Potassium, Uranium, and Thorium) within approx. 600,000 records. The data cover an irregular area which roughly corresponds to the "Ordovician Window" around Ballarat and were supplied as raw and levelled flight line data. These were manipulated using ECS and MicroBrian software. The data were gridded at various mesh values and thresholds for viewing at different scales and levels. The limits of the data, essentially flight line seperation, allow a maximum resolution grid of 50m. This is comparable to Landsat TM data which has a ground resolution of 30m. The mesh was transferred to MicroBrian for image processing with differential thresholding being used to carry the full dynamic range of the data. This resulted in two sets of raw magnetic data; a compressed full data image and an image with a narrow threshold range to enhance features in the magnetically flat palaeozoic. The image products produced include various colour composites of radiometric and magnetic data, pseudo-colour versions of the magnetic data, and magnetic images with both high pass and directional filters imposed. RESULTS In the Creswick/Linton area a strong north/south (from 0 to 10 degrees) trend is evident in the palaeozoic. These features are sharply defined, narrow magnetic highs and may represent either dykes or iron oxides deposited along fault planes. The radiometrics in the same area show east/west offsets of around lOKms. In contrast, the Enfield Region shows a prominent linear magnetic low trending almost due north/south. This is a broad feature with diffuse boundaries. The very different nature of the feature means that it is probably not related to the Creswick Geological Society of Australia Abstracts Number 32, Ballarat 1992

lineaments even though it has a similar trend. This feature may be the result leaching along a major fault zone. Palaeo-valleys in the region, marked by magnetically distinct valley flow basalts, show pronounced linear segments in various directions. These may be the trace of faults no longer evident in outcrop. All of this evidence suggests that the region is more structurally complex than currently recognised. Valley flows across the region show either extreme high or low magnetic values. The bimodal nature of their return probably represents the influence of magnetic reversals and may be useful as collaborative evidence in dating. Most of the major eruption points are magnetic lows, indicating eruption during a reversed epoch, with Mt. Buninyong being a prominent exception. The volcanoes in the Creswick region show an interesting radiometric zoning. In particular, there seems to be Thorium enrichment in the volcanic shields. No obvious explanation for this observation is currently available. Two granitoid plutons exist in the extreme west of the study area. These are the Flagstaff Hill Granite and the Chepstow Granodiorite. These two differ markedly in their magnetic and radiometric properties even though they are virtually conterminous. The Chepstow Granodiorite is a topographic low and a magnetic high. Radiometrically it is low in Potassium and Uranium and high in Thorium. The Flagstaff Hill Granite is a topographic high with a pronounced aureole and contains pegmatites and graphic granite. Geophysically it is variable with marked boundary effects which may be due to its aureole. Generally it is a magnetic low containing local magnetic highs. It is a Uranium and Potassium high, especially towards the western edge of the data set. The granite body is cut by two magnetic lineaments trending at 300 degrees which corresponds to the strike of Aplite dykes in the Ararat region. This paper presents a preliminary survey of features visible in the imagery. Detailed modelling of magnetic traverses is currently underway to characterise the observed features with particular reference to structural features.

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A14: COMPUTERS IN GEOLOGY CONVENOR: ANDREW WALTHO A 14.1 COMPUTER SYSTEMS IN BROWN COAL EXPERIENCES FROM THE LATROBE VALLEY R.Gaulton*, W.Wood, G.Simpson, A. Bell Mine Planning and Geotechnical, State Electricity Commission of Victoria, P.O. Box 195, Morwell, 3840 The active utilisation of computer technology in brown coal geological work has expanded rapidly over the past few years. As a result, significant speed and efficiency gains in data management and geological modelling have been achieved. This has been timely, as substantial staffing reductions within the organisations geological services have coincided with a stronger focus on the need to maintain a high level of support to key operational and mine planning functions. Although continuing to develop into new and promising areas, the implementation and utilisation of new technology has met with a number of problems, many of which relate to the need to achieve effective interfacing between various hardware and software systems. Hardware in use includes small laptop machines, used in field data acquisition, benchtop PC's, graphics workstations and powerful mainframe computers, all of which are required to accept,

process, enhance, or format data at some point in the flow of information. In parallell, a range of commercial packages ranging from very complex geological modelling/mine scheduling software to simple PC routines are employed to interact with more specialised programs developed in-house to meet local needs. The State Electricity Commission experience has shown that system compatibility is a vital consideration and therefore an issue which needs to be addressed at an early stage. This is very pertinent to the geological and mining arenas where there tends to be a good deal of functional diversity accompanied by the need to integrate separate, but hopefully complementary, systems. The importance of this consideration is also heightened by the increasing number of proprietary mining and geological software packages appearing in the marketplace.

A 14.2 USE OF INDICATOR KRIGING AND 3D GEOLOGICAL MODELLING FOR ORE RESOURCE ESTIMATION AT MARVEL LOCH OPEN PIT GOLD MINE, WESTERN AUSTRALIA N. Schofield * and P.J. Rolley 1

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FSSI Consultants (Australia) Pty Ltd, Sydney, N.S.W. ^Reynolds Yilgarn Gold Operations Ltd, Southern Cross, W.A. ]

The Marvel Loch open pit operations are situated in the Archaean Southern Cross Greenstone Belt, approximately 240 kms west of Kalgoorlie. The geology of the Southern Cross belt is summarised in Griffin (1990), and of Marvel Loch in Rolley and Baxter (1990). The geological features that impact upon an ore resource estimation are as follows: Geological Society of Australia Abstracts Number 32, Ballarat 1992

* Stratigraphic succession of metapsammites, metapelites and ultramafics. * Intrusion of ultramafic and pegmatitic dykes. * Early deformation including upright folding. * Development of a steeply west dipping mylonitic shear zone, 20° to bedding. * Development of heterogenous strain in the stratigraphic units cross cut by the mylonitic

314 panels chosen to model a deposit depends on the drill hole density and the size of the selective mining units. Rock density was modelled separately from gold grade using lithology and depth information. The IK model was then reported against production for two cutoff grades for periods of 14 months and 4 months, and for a number of production benches. The model was also compared against contoured exploration cross sections, longitudinals and plans, and production GC plans to determine the spatial interpolation of the model. This IK model in fact showed good correlation with known geological and structural mineralisation controls and honoured the grade boundaries identified by GC drilling. The reliability of each panel estimate of recoverable resource was classified on the basis of the number and spatial distribution of the data used to generate each estimate. The initial project involved verification of the RC, DDH and grade control (GC) drilling data for errors in Finally, the previously stoped tonnes and grade the geological logging and drillhole survey data, and were proportionaly removed from the panels affected, assay bias, and to validate the data entry. This process and the model reported to present pit surface. This involved six months of work compared to the three model was then used for pit optimisation (utilising months for the estimation of the ore resource. Whittle 4D) and mine design and scheduling. Geological interpretation onto cross sections, plans In summary, wire framing played an important role and longitudinal sections of the lithologies, faults, in helping to isolate the different geologic and weathering profiles, alteration and major quartz lodes statistically important populations of samples for were then 3D wire framed using Minex-3D. This analysis and modelling. Indicator kriging provided a enabled domainal classification of the data set, by useful tool for the mapping of gold grade within the lithological host, weathering profile, and alteration. different mineralisation types, and the estimation of The sampling was composited into two metre recoverable resource. The combined strengths of these down hole composites for data analysis. The tools allowed the building of a model which captured statistical analysis of samples from different the important broad geologic features of the mineralisation types supported the classification of the mineralisation and the detailed spatial structure of the mineralisation into different domains. Comparison of gold grade necessary for the reliable estimation of the statistics of paired RC, DDH and GC composites reserves. indicated some important differences between the samples generated by different drilling methods. References However, these differences were not consistent across Griffin, T.J., 1990, Southern Cross Province, in the all mineralisation types. Geology and Mineral Resources of Western Indicator correlograms (Srivastava and Parker, Australia: West Australian Geological Survey, 1988) were used to characterize the spatial structure of Memoir 3:60-77. the different populations of gold grade corresponding Journel, A.G., 1983, "Non-parametric Estimation of to the different mineralisation types. Correlograms Spatial Distibutions", Math. Geology, Vol.15, tend to provide a more robust measure of spatial No.3, pp445-468. structure than the traditional variogram. Correlograms Rolley, P.J., and Baxter, J.L., 1990, Marvel Loch were produced for 12 indicators in three directions Gold Deposit, in Geology of the Mineral Deposits (azimuth, east, and downhole (-60°) or vertical). of Aust. and P.N.G.:AusIMM, Monograph No. Indicator kriging (IK) (Journel, 1983; Verly and 14:297-300. Sullivan, 1985) was used to infer the recoverable Srivastava, R. and Parker, H.,1988, "Robust measures resource on a panel by panel basis within the different of spatial continuity", in Third International zones of gold mineralisation. IK was preferred over Geostatistics Congress, (Armstrong, M.et al, ed.), other kriging methods because it permits explicit D. Reidel, Dordrecht, Holland. accounting for different spatial continuity at different Verly, G.W.and Sullivan, J., "Multigaussian and Probability Krigings - Application to the Jerrit levels of gold grade. This is very important for grade Canyon Deposit.", Mining Engineering, Vol.37, mapping in many gold deposits. A panel is a regular No.6, pp568-574. volume (usually rectangular) that comprises usually more than 30 selective mining units. The size of the shear zone. * Development of post mineralising faults 30°50° to Si, with both strike slip and dip slip movement. * Tertiary lateritisation developing a 100 m thick weathering profile, with consequent remobilisation of gold. Economic mineralisation is discontinuously developed over 1.3 kms of strike length, 150 m of width, and at least 400 m depth. The exploration data set comprises RC drillhole coverage to 60 m or 110 m depth and surface or underground diamond drilling from 120 m to 400 m depth at various drill densities. The underground diamond drill hole sampling is strongly spatially clustered.

Geological Society of Australia Abstracts Number 32, Ballarat 1992

315 KEYNOTE: A 14.3

GEOLOGICAL CONTROL IN COMPUTER-BASED RESOURCE ESTIMATION A.A. Cram

Engineering Computer Services, 500 Moss Vale Road, Bowral, NSW . 2 1/2 D techniques - e.g., seam or vein The economic assessment of mineral deposits modelling, and potentially involves a number of phases from initial . 3 D techniques using a 3D block model. assessment through to detailed orebody evaluation and subsequently to estimation of bench or slope grades in 2 1/2 D techniques normally make the assumption an operational mine. Obviously the nature and quantity of information varies significantly from one that the variation of grade over the thickness of the orebody is not of concern - that is the average grade extreme to the other. Information used for assessment may be generally provides adequate information - this assumption being valid of "thin": deposits which are to be mined as a classified into:a) geological interpretation which may include single face. 2 1/2 D methods will normally involve information gathered from similar geological some form of selection of the orebody limits - either from inspection of core samples or geophysical logs environments, in the case of coal, or, grade optimisation methods in the case of gold or nickel. With this technique the b) remote sensing information and geologists interpretation of seam or vein correlations c) geological samples at a variety of densities e.g. plays an all important role. 3D modelling techniques vary in emphasis between soil samples through to drill hole data. Obviously geological interpretation plays a major geological control and the pure mathematical part during the early phases of assessment and it manipulation of drill hole samples. One important logically flows that computerised assessment factor in this emphasis is the ratio of the borehole techniques must be able to effectively utilise this spacing to the width of the structures (or domains) contained within the orebody. Geological control information. Even in an operational mine the importance of takes a number of forms in 3D modelling - varying geological control varies according to the type of from the interpretation of spatial extent of ore zones to orebody. The method of modelling coal seams is examination of variograms to determine modelling distinctly different those techniques used for a massive parameters e.g., anisotropy. In most 3D modelling an accurate estimation of sulphide deposit. For coal seams significant reliance is placed on the correlation of seam intercepts from metal content can be made with a variety of grade holes which are widely spaced in relation to the seam interpolation techniques. However, only too (i.e., orebody) thickness. The use of geological frequently a valid grade distribution can only be interpretation in this case is justified on the experience achieved with proper geological control. Both geological control and geostatistical analysis gained in the past, compared to the coast of reliance only on samples from a very dense drill hole pattern. play important roles in orebody modelling and it is Ore body modelling techniques may be generally essential that both disciplines by adequately implemented in computerised modelling processes. classified into two methods

A 14.4

DIGITAL PHOTOGRAMMETRY OF FAULT SURFACES M.WJessell , P.Schwarze ' S.J.D.Cox ' , & W.Power 1

1

1 2

1

Dept of Earth Sciences, Monash University, Clayton, VIC, 3168 CSIRO Division of Geomechanics, PO Box 54, Mt Waverly, Victoria, 3149 The mechanical and transport properties of rock contacting asperities. Analysis of the effect of abutting masses are often dominated by the behaviour of surfaces must therefore make some assumption as to discontinuities, such as faults and joints. Deformation the configuration of asperities on the surfaces, and of these is controlled by local interactions between both the height and spatial distributions of these J

2

Geological Society of Australia Abstracts Number 32, Ballarat 1992

316 asperities need to be considered. Most existing data on asperities is derived from stylus profilometry, where a stylus is dragged across the rock surface and the height variations are measured for two-dimensional profiles. Stylus profilometry suffers from significant drawbacks: i) that the profile will in general miss the highest peaks and lowest troughs on a surface, ii) only two-dimensional profiles may be made, so that the question of the anisotropy of the shape and positioning of asperities is difficult to address and iii) the technique generally has a different precision and accuracy in directions perpendicular and parallel to the rock surface. In this study we are using a new, microcomputer

A 14.5

based, analytical technique to assess a number of aspects of rock surface characterisation over a wide range of scales. The technique is based on the use of overlapping stereo-pairs of images, and the automated matching of equivalent positions in the two images. The apparent displacement from one image to the other can be used to calculate topographic relief relative to some fixed reference point The analytical techniques of digital photogrammetry are in themselves already well developed so we have concentrated on procedures which allow us to assess the accuracy of the resulting digital elevation models, and their implementation on an inexpensive, general purpose, desktop computer system.

LIMCO - A COMPUTER BASED LITERATURE COMPILATION OF DIAMOND INDICATOR MINERALS AND A NEW APPROACH FOR ASSESSING DIAMOND PROSPECTIVITY R. R. Ramsay Key Centre for Strategic Mineral Deposits, University of Western Australia, Nedlands, Perth, 6009, Western Australia

Diamond crystallises at depths of greater than 150 km in the upper mantle and is a potential xenocryst in magmas. Diamondiferous magmas, expressed as volcanic to subvolcanic intrusions, also contain other mantle-derived xenolithic minerals such as olivine, pyrope-garnet, chrome-rich spinel, enstatite, chromediopside, and magnesian ilmenite. These minerals are usually more abundant than diamond in the host and their dispersion haloes are used to locate primary diamondiferous sources, via diamond indicator mineral sampling. None of these minerals, however, is restricted to the diamond stability field, and as such they only indicate that a source of mantle xenoliths is present. Diamond prospectivity can be determined by recovery of polyminerallic xenoliths to establish the pressure and temperature regime sampled. In many localities containing diamond indicator minerals, however, these rocks may be difficult to recover. As such, schemes developed to assess diamond prospectivity can involve either detection of mineral compositions intimately associated with diamond (Sobolev, 1977; Gurney, 1984; Botkunov et al., 1987), or detecting geothermal regimes based on the distribution of trace elements in specific minerals (Griffin et al., 1989). The problems with these schemes is that they require recovery of specific minerals, and assume relatively uniform upper mantle conditions. It is also difficult to determine whether results from different minerals (eg garnet and spinel) actually demonstrate consistent source sampling as the

Geological Society of Australia Abstracts Number 32, Ballarat 1992

group/rock type boundaries are not developed from the same data. LIMCO is a computer-based compilation of published mineral analyses from localities containing mantle xenoliths. The data files currently contain 1810 garnet, 455 spinel, 663 orthopyroxene, 1673 clinopyroxene, and 885 ilmenite analyses representing both crustal and mantle-derived xenoliths. Analyses in LIMCO are screened using morphological, mineralogical and geochemical features into groups reflecting both their mineral association - rock type and mineralogical Katies'. Each mineral from a xenolith is thus classified into an internally selfconsistent rock type 'fades' - termed lithotype. Most analyses in LIMCO can be assigned to the following lithotypes: a. Peridotite - subdivided with increasing pressure into plagioclase, spinel, garnet, and diamond facies. b. Pyroxenite/eclogite - subdivided into granulite (plagioclase), spinel, garnet, and diamond facies. c. Megacryst - subdivided into those derived from localities dominated by either spinel peridotite or garnet peridotite xenoliths. d. Others - including crustal metamorphic and MARID (mica, amphibole, rutile, ilmenite, diopside xenoliths). Mineral compositions in each groups have been characterised to produce a hierarchical graphical scheme based on cation/oxide or cation/oxide ratio plots with

317 fields allocated for source rock origin. Following the discovery of a source of mantle xenoliths, representative selections of isolated mineral grains can be analysed and their origins determined. Features regarded as indicators of high diamond prospectivity include: a. A predominance of minerals from garnet peridotite; including garnet, and/or spinel, and/or orthopyroxene with compositions indicating depleted rocks known to be significant hosts for diamond. b. Spinels (Mg-Cr-rich) with both low TiC>2 suggesting an absence of Ti-metasomatism, and low /O2 (<QFM) suitable for diamond crystallisation and preservation. c. A relatively minor component of asthenospheric-derived megacryst minerals associated with oxidising (>QFM) crystallisation conditions. A 14.6

In addition to assessing diamond prospectivity, the classification provides evidence of which crustal and upper mantle rocks have been sampled, and indirectly, the geothermal regime in which the host magma was generated. References Botkunov, A. I., Garanin, V. K., Krot, A. N., & Kudryavtseva, G. P., 1987, Internat. Geol. Rev. 29:163-177. Griffin, W. L., Cousens, D. R., Ryan, C. G., Sie, S. H. & Suter, G. F., 1989, Contrib. Mineral Petrol 103:199-202. Gurney, J. J., 1984, In; Glover, J. E. & Harris, P. G. (eds) Kimberlite occurrence and origin. UWA Geol. Dept. & Ext. Public. 8:143-167. Sobolev, N. V., 1977, Deep-seated inclusions in kimberlites and the problem of the composition of the upper mantle. AGU. Washington. 279p.

EDUCATING GEOLOGISTS IN THE USE OF COMPUTERS C A Jermy

Department of Geology & Applied Geology University of Natal Durban, South Africa Computer experience is becoming increasingly experience with each of the programs a number of important to today's geology students, and it is the projects are set, ranging from a simple task like role of universities to provide this knowledge. The preparing a Curriculum Vitae, to developing a Department of Geology, University of Natal, Durban, spreadsheet model to plot the Mohr- Coulomb and has for a number of years been teaching an Hoek-Brown failure criteria for data obtained from introductory course in computing to its second year triaxial testing. Once sufficient experience has been students, and following this up with more gained on these packages classical statistical problems geologically oriented studies during the senior years of are solved using Statgraphics, and geostatistical study. The courses are designed to illustrate the use of problems investigated with Geo-Eas. A typical computers as problem solving tools, with the students geostatistical project would be to investigate the being encouraged to work through the examples plume of leachate from a landfill site, or predict the manually, where appropriate, in order to understand the properties of a construction site from a limited number techniques concerned, prior to using the computer to of geotechnical measurements. Spatial data is readily manipulated and displayed check their solution. The department currently has a laboratory with 16 AT class machines fitted with math using Surfer, a simple-to-use package which grids and co-processors, available for undergraduate use. A contours data, as well as allowing grid mathematics to number of other machines including a 25MHz '486 are be performed. A typical project would be to grid and accessible for post graduate students to carry out contour the roof and floor of a coal seam, using data obtained from borehole logs; subtract the two grids to specialised projects. The introductory course, which consists of 26 provide a graphical representation of the variation in lectures and 13 practical periods, is aimed at students the coal seam thickness, and calculate the volume of who have not had much exposure to computers during coal present within the grid coordinates provided. The their schooling. It provides a brief overview of the companion program, Grapher, may then be used to history of computing, computer terminology, and an construct a cross section through the coal seam, as introduction to MS-DOS and hard disk management. required. The effect of using different gridding The course then proceeds to use a number of standard algorithms may also be easily demonstrated by the contoured output of Surfer to that computer programs to illustrate word processing comparing from a thorough geostatistical investigation (WordPerfect), data management (dBase III+) and obtained spreadsheet modelling (Quattro Pro). In order to gain of the same data using Geo-Eas. Senior students Geological Society of Australia Abstracts Number 32, Ballarat 1992

318 studying engineering geology are encouraged to create their own spreadshet models to solve particular problems that are set as course work. They are also introduced to a number of programs that carry out stability analysis for plane and wedge failure of rock slopes, as well as rockfall analysis and soil slope stability analysis. Stresses around underground excavations are also investigated using boundary element methods, in an attempt to illustrate the importance of orientation of the underground opening, the sequence of excavation, and the interaction between the rock and the excavation. Stereographic data is plotted, contoured and analyzed using the Dips program from Toronto University. Specialised projects have also been

initiated which involve the computer modelling of ore deposits from borehole information provided by a number of mining organisations. Programs such as Geomodel and PC Xplor have been donated to the department in order to allow the students to gain an insight into this type of work. Because of the length of time it takes to enter all the raw data into the programs before any useful modelling may be started, it is expected to spread this type of project over a number of years. The aim of these courses in the use of computers in geology and engineering geology is to ensure that our graduates leave the university with a thorough grounding in computers and the use of commercial and specialised geological programs.

POSTER SESSION A 14.7

GEOLOGICAL AND MINE MODELLING OF THE BALLARAT GOLDFIELD John Duke

Senior Geologist, ECS Mining Consultants, P.O. Box 160 Bowral N.S.W. 2576

Years of painstaking compilation and interpretation of geological and mining data from the historic Ballarat gold mines, is being computer databased. As work progresses, three dimensional models are then being generated to help target exploration drilling. Underground mine workings have been digitised as centrelines, profiles and stope outlines. These have then been wireframed to create a true 3D model of the workings. Stopes, drives and shafts have been entered with unique identifiers so that they can be colour coded and selectively displayed in 2D sections and 3D views. Interpreted geological control structures have been modelled using an open wireframing technique. The majority of the gold mineralisation is hosted by an irregular network of quartz veins that occupy 45 degree westerly dipping reverse faults that are known locally as "leatherjackets" because of the presence of a tough leathery fault pug. The larger leatherjacket structures occupy the steeply dipping eastern limb of the First

Geological Society of Australia Abstracts Number 32, Ballarat 1992

Chance Anticline. Trends of mineralisation on these geological control structures, depicted by stopes and previous drillhole intersections, have been used to target deep exploratory drilling. This work is being carried out by staff of Joint Venture partners Geopeko and Ballarat Goldfields Pty. Ltd in the township of Ballarat in Victoria, situated directly over the old underground mine workings. A Sun Sparc IPC high resolution colour graphics workstation is being used to run the MINEX-3D software package written and supported by ECS in Bowral N.S.W. ECS has assisted the joint venture partners by providing graphics images created by its latest solids modelling and dynamic 3D rotation software. By using graphics techniques including hidden line removal, directional illumination and depth shading, the complex Ballarat gold mine models are presented as clearly defined and enhanced images.

319 A 14.8

COMPUTER APPLICATIONS IN RESOURCE MODELLING AT THE CSA MINE, COBAR, NSW M. Erickson *, J. T. Carswell , N. Schofield and B. J. Larkin 1

1

2

2

Cobar Mines Pty Ltd FSSI Consultants (Australia) Pty Ltd 1

2

Copper and lead-zinc ore at the CSA occurs in up to sixteen subvertical lenses which are characterised by their short strike length, variable width and irregular grade distribution. Intensive definition drilling is required to provide the high level of selectivity necessary to mine this style of mineralization efficiently. The CSA Mine does not rely on a single integrated mining software package but recognises that a combination is needed to perform all the functions required by the technical staff and imposed by the style of mineralization. A commercial package, Surpac, is used in conjunction with customised software written by specialists in fields such as geostatistics. This poster presentation describes the methods used at the CSA Mine in the areas of data acquisition and processing, ore definition, reserve estimation and mine planning. Procedures to be presented include: 1. The electronic capture of drill core logging information. A small, relatively inexpensive unit manufactured by Psion is in use. Logging data is quickly and simply transferred to a PC as text files through an RS-232 cable. 2. Assay data collection. Assay results are entered by laboratory staff and transferred electronically via the Banyan Vines network for loading into Surpac. 3. Manipulation of data within Surpac. Plotting of A 14.10

sections and plans of assay data and geology, digitizing of ore outlines, compositing of assay data and some mine planning functions are carried out. 4. The use of customised geostatistical software for orebody modelling. Multiple Indicator Kriging is used for ore selection and grade estimation. The benefits of indicator kriging include the ability to create grade distribution maps for a range of cut-off grades, which assists in stope design. The indicator method enables more accurate modelling of the spatial continuity of higher grade zones and also facilitates geological input to block modelling for each grade class. 5. The use of AutoCAD in mine planning. Customised AutoCAD routines enable ore lens outlines and stopes to be manipulated in 3-D and sectioned in any orientation. The geostatistical block model can be loaded into AutoCAD and stope designs performed interactively using the colour coded grade blocks to optimize grade recovery. 6. Metal accounting and reconciliation. A Lotus 12-3 spreadsheet is used for a weekly reconciliation which compares actual production with reserve estimates.

COMPUTER-AIDED RESTORATION OF DEFORMED FOSSILS: METHOD AND APPLICATION. Nigel C. Hughes and Peter A Jell

Queensland Museum, PO Box 300, South Brisbane, Queensland 4101. Tectonic deformation limits the palaeobiological 1990). A new method for strain removal based on information that can be retrieved from fossils and can existing computer software has been applied to Middle result in serious taxonomic error. Several techniques Cambrian trilobites from the Kashmir and Spiti have been used to restore the original shape of valleys of the Indian Himalaya. Images scanned onto deformed fossils but none have proved satisfactory. into an Apple Macintosh were manipulated using Most methods are time consuming or involve commercially available image processing software. specialist equipment not widely available. Recently The resulting reconstructions were then tested using computer-aided reconstructions have been performed on strain vectors identified by Principal Components both mainframe and microcomputers which provide a Analysis. Results suggest that specimens previously quick and convenient method for restoring the shape of assigned to eight species belonging to five genera in deformed fossils (Cooper, 1990; Hughes and Rushton, fact represent a single morphospecies. The revised Geological Society of Australia Abstracts Number 32, Ballarat 1992

320 taxonomy suggests that the supposed taxonomic References distinctness of Kashmir and Spiti faunas is largely the R.A., 1990. New Zealand Journal of Geology result of stratigraphic miscorrelation. Most of the Cooper, and Geophysics. 33: 321-332. Cambrian within the Tethyan belt of the Indian Hughes, N.C. & Rushton, A.W.A., 1990. Himalaya is of middle Middle Cambrain age and shares Palaeontology. 33: 429-445. faunal affinities with north China and north Vietnam. A 14.11

GEOLOGICAL AND GEOPHYSICAL DATA INTEGRATION IN A GIS: STRUCTURAL APPLICATIONS FROM THE 51 MILE WELL AREA, EASTERN GOLDFIELDS, W.A, Mark S. Rattenbury and Alan J. Whitaker BMR Geology and Geophysics, GPO Box 378, Canberra, ACT 2601.

In regions of relatively sparse and weathered outcrop, such as the Archaean Eastern Goldfields Province, geological interpretation based only on surface data of complexly deformed rocks can be difficult and equivocal. Employing airborne geophysical techniques increases the reliability of geological mapping and interpretation beyond surface outcrop constraints, and is being used for current BMR mapping in the Eastern Goldfields. Since most mineral exploration in the Eastern Goldfields is targeted at ore deposits within the Archaean maficultramafic metavolcanics, commonly associated with faulting, knowledge of the geometry of the metavolcanics is crucial. Aeromagnetics, used in conjunction with surface geology, is particularly effective in constraining that geometry. The 51 Mile Well area in the Mount Ida region has been covered with a detailed aeromagnetic and radiometric survey flown for Shell in 1985 as part of a gold tenement exploration programme. The tenement has been relinquished and the data is available on open file. The geology of the same area has been recently mapped as part of the BMR's current Eastern Goldfields project. The geological map data is stored digitally as a series of covers which include geological boundaries, faults, structural measurements, and mineral occurrences, as well as cultural, hydrological and topographic features. The aeromagnetics and radiometrics can be integrated directly on computer with any combination of the geological covers thus providing a powerful tool for analysing the structural geometry of the 51 Mile Well area beyond the surface outcrop constraints. The aeromagnetics in particular has delineated strong banding within the eastern belt of gneisses. Sympathetic but less intricate banding is also evident in the radiometric data. The more strongly magnetised bands have relatively low radioactivity and correlate with concentrations of interlayered amphibolites within the gneisses. The amphibolite Geological Society of Australia Abstracts Number 32, Ballarat 1992

banding has a continuity in length and a constancy in width that was not realised during mapping, and supports mineralogical evidence that the amphibolites were intercalated in a sedimentary environment as volcanic tuffs or flows. Numerous east-west trending faults, apparent in the aeromagnetic images, displace the gneiss banding but do not displace the gneiss-metavolcanic contact (the Ballard Shear), and are not apparent in the western metavolcanic belt. The consistent orientation with sinistral displacement suggests the faults may be Riedal R* shears to brittle dextral strike-slip of the Ballard Shear. The position of the Ballard Shear is well constrained by a marked drop in total radioactivity and a change to complex magnetic anomaly patterns from the gneisses to the maficultramafic metavolcanics. The ultramafic metavolcanics have strong positive magnetic anomalies whereas zones of weak magnetisation correlate with metabasaltic lithologies. Olivine cumulates, peridotites, and komatiites cannot.be easily discriminated by the aeromagnetics, however. The fold hinge of the south-plunging Kurrajong Anticline is well defined by interlayering of these contrasting lithologies. Within the hinge area, the aeromagnetics reveals various structural complexities in the mafic-ultramafic stratigraphy, some of which were tentatively identified from geological mapping. These structures include a number of low angle faults which cut through and imbricate the stratigraphy, forming local duplexes and thrust ramps. Thus a fourfold deformation sequence has been determined from the integration of detailed airborne geophysics with conventionally mapped geology in the 51 Mile Well area; D1 comprising low angle thrusting and very tight to isoclinal folding, D2 upright shallow plunge folding (the Kurrajong Anticline), D3 ductile sinistral shearing (the Ballard Shear), reactivated as a D4 brittle wrench system with an overall dextral shear.

321 A 14.12 A RESOURCE MODELLING OF THE CENTURY ZINC-LEAD DEPOSIT, NORTH QUEENSI AND Andrew Waltho CRA Exploration Pty Limited, P.O. Box 1559 Mount Isa QLD 4825 Century, located approximately 250km northnorthwest of Mount Isa, is one of several significant, shale hosted zinc-lead deposits in the western fold belt of the Mount Isa Inlier (Figure 1). The deposit occurs within a gently folded interlaminated shale-siltstone sequence within the upper portion of the Proterozoic Lawn Hill Formation. Mineralisation comprises fine laminae of sphalerite, pyrite and galena occurring within carbonaceous shales. The deposit is bounded to the south and north by normal faults (Magazine Hill and Nikkies Faults - Figure 2), and to the east and west by erosional contacts with unconformably overlying Cambrian limestones and dolomites of the Thorntonia Limestone. A significant normal fault (Pandoras Fault - Figure 2) divides the deposit into a northern and southern zone. The mineralised zone has a distinctive, well established stratigraphy across the entire deposit, based on the distribution of mineralised carbonaceous shales, and several distinct, unmineralised dolomitic siltstone and carbonaceous mudstone horizons, which are used to define four units (Figure 2): Unit 1: Moderately to thinly interlayered dolomitic siltstone and variably mineralised carbonaceous shale horizons (top of Zone 1 defined by the first occurrence of stylolitic layering in dolomitic siltstones) Unit 2: Mineralised carbonaceous shale (up to five metres thick) Unit 3: Dolomitic siltstone horizon (up to approximately five metres thick, the lower one to three metres of which is characteristically unmineralised) Unit 4: Mineralised carbonaceous shale sequence containing distinct, unmineralised massive carbonaceous mudstone, and dolomitic siltstone horizons. Each of these units is characterised by distinctive, regular sulphide mineral assemblages and corresponding zinc-lead-silver ratios across the entire deposit, although gradual grade variations occur. Computer data management and modelling techniques are used routinely at Century. All computer facilities used in conjunction with the project, including the primary project database and computer deposit models, are available to geologists and engineers on site. All drill hole collar and downhole survey information, summary geological logs, assay, Geological Society of Australia Abstracts Number 32, Ballarat 1992

mineralisation specific gravity, and geotechnical engineering data are managed using Paradox database software running on MS-DOS personal computers. This provides a simple, flexible means of managing a constantly increasing volume of information, as well as satisfying all basic reporting needs. Data can analysed using Paradox itself, or exported to other packages such as spreadsheets for further analysis. The ability to export data in a number of formats has proved extremely useful in providing consultants with data in a familiar, readily useable form. Database structures and reports were developed entirely by geological personnel involved with the project. It is also worth noting that computer based information recording techniques employed at Century are a direct extension of manual data management methods used for the project. ECS Minex-3D software, running on a Sun Sparcstation, is used for all routine plan and section production, geological and resource modelling. Data used in modelling is transferred directly from the project's Paradox database. Computer models of the deposit allow ongoing assessment of the effects of new information on the overall understanding of the deposit as exploration proceeds, and detailed modelling of geological structures. The principal advantage of computer based resource modelling is the ease with which new ideas relating to the deposit can be evaluated. Minex-3D provides the ability to apply rigorous geological control in resource estimation. Current deposit models were constructed by generating initial synthetic grids of major geological boundaries (including boundaries between mineralised sequence zones noted above), based on intersections of each geological unit in drill holes, which were then used as the basis for manually digitised "wire-frame" outlines on 50 metre spaced north-south sections. The initial synthetic grids were especially useful in compensating for the effects of "off-section" drill holes (i.e. displacement of boundaries through drill hole information being projected from up to 25 metres each side of any section). Wire framing, in turn, allowed features too complex to be represented by gridded surfaces alone to be faithfully represented in the completed model. Upper and lower bounding surfaces of completed wire frame volumes were then used to re-generate more realistic grids of geological boundaries to enable data to be readily presented as contours in plan, something

322 which could not be achieved using wire frames alone. Wire framed volumes allow Z-grid control to be applied during geostatistical analysis and resource estimation, which effectively allows data searches to follow geological outlines by varying the orientation of the Z axis of the search ellipse, removing the effects of folding and faulting. Three dimensional display capabilities within Minex-3D, including the ability to rotate models of geological features in real time, contribute positively

to geologists' abilities to assess the overall significance of specific structural features within the deposit. CRAE's experiences with computer based, information management and deposit modelling provide an excellent example of how this technology can be applied to enhance personnel effectiveness, through reducing time spent on routine tasks, in the ongoing assessment of a major mineral deposit.

CENTURY DEPOSIT LOCATION

• Major Zinc d«po«!t WESTERN FOLD BELT Lown HHI Platform Lotohbordt Rtv«r Poult Trough Ew«n Block Ytfch Myolly Shtlf

KALKADOON—LEJCHHAROT BELT EZ3 EASTERN FOLD BELT f- >J\ Mory Kothl««n *on« I'v'.-j Quomby-Malbon zont Clonourry-Sohiryn zono

CENTURY DEPOSIT CROSS SECTION A - B

(47400mE)

(south)

(north)

A

B

0

metres

500

MINERALISED ZONE E 3

Cambrian limestone

Hangingwall dolomitic siltstone At shale unit

Sandstone unit

Footwall shale tc siltstone unit

Geological Society of Australia Abstracts Number 32, Ballarat 1992

Unit 1 Unit 2 Unit 3 Unit 4

323 A 14.13

A COMPUTER SIMULATING MODEL OF CLASTIC SEDIMENTATION AT BOTH CONTINENTAL MARGIN AND INLAND BASIN SETTINGS. S. Zhou Department of Geology and Geophysics, University of Adelaide

A program called SEDFIL (modified from the old version of SEDPAK initially developed by the basin research group in the department of Geological Sciences, University of South Carolina, also see Helland-Hansen et al., 1988; Strobel et al., 1989), is an interactive computer simulation which produces simple models of sedimentary geometries by infilling a two-dimensional basin from either one side or both sides with transported clastic sediments. The modeled geometries of clastic sediments evolve through time and respond to various processes that include thermoinduced subsidence, fault controlled basement movements, eustatic sea level changes and varying sediment inputs. Also included in the model are sediment compaction, both local isostatic and regional (i.e. flexural) response to sediment loading as well as treatments of extensional (both vertical and nonvertical) faults within the basin. In this simulation model, sediment deposition is expressed by creation of new surfaces above previous ones. The thickness of deposited layers are reduced by both erosion and compaction while their surfaces move vertically in response to tectonic change and surface loading. The actual simulation is divided into a series of equal time steps in which sediment is deposited as an array of en-echeloft columns that mark the top of the previously depositional surface. The volume of the sediment deposited in each time step is expressed as a 2-D cross section and is derived from two right-angle (sand and shale) triangles, whose areas

Geological Society of Australia Abstracts Number 32, Ballarat 1992

are a 2-D expression of the quantity of the sediment deposited at that time step. Each column in the array is filled by both marine sediments (up to sea level) and alluvial sediments (to a surface determined by an "alluvial angle" that is projected back from shore to landward intersection with the previous surface). The main propose of SEDFIL is to mimic geological processes involved in clastic sediment deposition in various settings through large spans of time. The program is designed to study the effects of changes in tectonic, depositional and eustatic parameters upon evolving sedimentary geometries. Acknowledgement The original program was kindly given by Prof. Chirstopher Kendall of the University of South Carolina to Dr. Gabor Korvin of the department of Geology and Geophysics of the University of Adelaide for his research project "Geophysical modelling of sedimentary basins funded by the Adelaide University grants # 184 and #1181 for 1988 and 1989. References Helland-Hansen et al., 1988, J. Math. Geology, v. 20, no., 7, 777-802. Strobel et al., 1989, Computers & Geosciences, vol., 15, no. 8, 1279-1290.

324

Geological Society of Australia Abstracts Number 32, Ballarat 1992

325

A15: GEOLOGICAL DATABASE MANAGEMENT CONVENOR: DAVID RICHARDS

A 15.3

MINERALOGICAL AND GEOLOGICAL REFERENCE DATABASES IN THE MUSEUM OF VICTORIA. D. A. Henry* andW.D. Birch

Department of Mineralogy and Petrology, Museum of Victoria, Victoria The Department of Mineralogy and Petrology at & PhD batches) have been completely computerised. the Museum of Victoria has developed six databases to Databases for the Museums rock and tektite store and rapidly retrieve information on its large collections have been commenced. Two reference databases have also been developed geological collections. The powerful TITAN database system, developed by Knowledge Engineering Ltd, on the TITAN system. VICREF, a bibliography of runs on a 386 processor with Xenix (UNIX) operating Victorian mineralogy (1000 references) and VICLOCS system. TITAN has a very flexible design facility, a geographic database of Victorian mineral locations allowing text retrieval in all fields specified by the (2400 records). In addition the Department utilises MINERAL designer and no constraints on the size of the data (CSIRO/Aleph), MINABS, and Phillips Ltd's TOTAL fields. DIFFRACTION DATABASE to provide rapid and up The Museum's mineral (42,000 specimens), meteorite (300 specimens) and photographic to date mineralogical information. collections (2000 slides) and the University of Melbourne's research collections (400 Honours, MSc A 15.4

GDB - VICTORIA'S GROUNDWATER DATABASE A.J. Brinkley and B.J. Kingsbury Rural Water Commision of Victoria

Groundwater is a valuable resource which is used by many Victorians. Town water supplies, agriculture, mining, commerce and manufacturing depend on the provision of groundwater. Like surface water, it can be depleted and polluted. The Rural Water Commission of Victoria (RWC) is responsible for managing Victoria's groundwater. It undertakes research, investigations and monitoring; issues licences to construct water bores; licences drillers; and authorises the extraction and use of groundwater. Information gathered from new and existing bores, both government and privately owned, is essential in properly managing groundwater resources. This information needs to be as reliable, accessible and upto-date as possible to efficiently manage the resource for the benefit of the entire community. To meet this objective, the RWC is developing a complete statewide Groundwater Database (GDB). The GDB will combine the data and facilities of the Geological Society of Australia Abstracts Number 32, Ballarat 1992

existing, separate databases and provide for extra information such as geological logs, pollution analyses, geophysical logs and pumping data. The GDB project, however, consists of more than just a database. It is about collecting, collating, processing and interpreting groundwater information as efficiently as possible. Work practice issues such as regional data entry and processing are being addressed, as well as provision for interfaces between the GDB and external applications. These applications include geological logging, hydrograph plotting and watertable contouring. GROUNDWATER DATA The new GDB will store records from approximately 110,000 bores throughout the state. This includes construction, waterlevel, chemical and geological information. This data represents an extremely valuable asset, when one considers the effect

326 groundwater management (using this data) has on Victoria's prosperity. The total replacement cost of this data is over 100 million dollars. GDB CLIENTS Data from the GDB will be used by the RWC to investigate groundwater resources, to manage salinity and to advise landholders via the Groundwater Enquiry Service. The provision of data to external users will be streamlined. Consultants, educational institutions, other private and public sector organisations and the general community will benefit from the increased availability of data. IMPLEMENTATION The implementation of the GDB will occur in two stages Stage 1 of the GDB will include: * Data entry screens for Bore Location and Construction details, Waterlevels, Annual Maintenance, Field Chemistry and Driller's Logs. * Software to graph groundwater levels upon entry of waterlevel data. * On-line enquiries for all old and new bore numbers. * Registration screens for new bore numbers. * Customer information.

A 15.5

Stage 2 of the GDB will include: * Detailed extraction/enquiry facilities. * Laboratory chemical analyses * Geologist's logs, geophysical stratigraphic logs. * Management reporting facilities. * Pump and metering data

logs,

DATABASE SOFTWARE AND HARDWARE The GDB is being developed using the INGRES RDBMS and WINDOWS/4GL applications development tools. The development is occurring on a network of X-terminals located in the Systems Development area. The GDB application, when complete, will operate on a network of X-terminals, PCs and character terminals for Investigations* Diversions and Regional users. The X-windows environment will be initially available at Head Office and Tatura, with other regions using character terminals for data entry and enquiry. The windows system, designed to create an intuitive, mouse driven, "point and click" environment, enables users to access the GDB in one "window" of the terminal, while running other applications (e.g. modelling, contouring, etc.) in other "windows".. Groundwater enquiry screens will be created, enabling users to access composite data in seconds for telephone enquiries. Greater efficiency will occur in all facets of data entry, validation, processing and extraction.

REGIONAL RESOURCE EVALUATION AND AREA SELECTION USING GEOGRAPHIC INFORMATION SYSTEMS M.C. Aubrey and K.M. Chan Technical & Field Surveys Pty Ltd

Most computer applications in the mining industry are applied to detailed activities, such as orebody modelling, mine planning and geophysical data presentation. The objective of the paper is to demonstrate the practical applications of cost-effective Geographic Inform-ation Systems (GIS) technology in the initial stages of developing exploration strategy. With the increasing power of desk top computers and the availability of inexpensive, easily used GIS software, this approach is no longer confined to specialised research departments of large companies. The paper discusses the use of GIS techniques to analyse the continental distribution of metallic minerals in relation to major structural trends and to Geological Society of Australia Abstracts Number 32, Ballarat 1992

assist the process of regional area selection. Area selection in mineral exploration relies on the ability to correlate information from a variety of disparate, often spatially-related, datasets into a single conceptual hypothesis. In the past this has been accomplished by interpreting each set of data separately and then overlaying interpretation results to seek coincident, or anomalous, ingredients. This approach tends to bias the result in favour of the most prominent anomalies in each dataset. Favourable loci for mineralisation are, however, more often reflected by individually subtle expressions in several datasets which aggregate to produce a potentially significant anomaly. It is, therefore, preferable to combine basic data, rather than

327 interpreted information, in order to retain the subtleties in the data. GIS provides the mechanism to achieve this aim. The key to successful data correlation is the ability to convert the various data sets into a uniform format, so that data from a variety of different sources can be directly integrated. Attribute data related to mineral occurrences, exploration activities and sample results are commonly stored in tabular databases with geographic coordinates as one of the attributes. Graphic display of these data, as well as geological and structural maps, is achieved by digitising the data into a vector map analysis system. Other data sets, such as geophysical and remotely-sensed data, are more effectively displayed in raster format for image analysis. GIS provides the bridge for correlating between vector, raster and tabular data sets. To demonstrate this methodology, continental distribution is presented, at global and national scales, using lead-zinc mineralisation as a focus. The distribution is analysed by parameters, such as host age, stratigraphy and lithology, element associations, structural controls and resource size and type. Regional area selection, based on the employment of large mineral deposit and prior exploration data sets, associated with structural and stratigraphic and remotely-sensed data, is illustrated by a case study in north-western Tasmania.

KEYNOTE: A 15.6

References Aubrey M.C., 1975; An integrated recording and retrieval system for mineral exploration data. A.M.F. Proc. Geoscience Information Sem. Aubrey M.C., 1981; The construction of a computerised mineral exploration database. A.M.F. Proc. Geoscience Numeric & Bibliographic Data Sem. Aubrey M.C., 1982; Applications of remote sensing in the mineral and petroleum sectors. Sem. Remote Sensing for Decision Makers, Univ. NSW. Aubrey M.C., 1984; Computer-assisted area selection - or micros in mineral exploration. Earth Resources Foundation, Proc. Sem. Computers in Exploration. Aubrey M.C., 1986; The distribution of mineralisation; An analytical procedure using a geographic information system. 3rd Int. Conf. on Geosci. Information, Adelaide. O'Sullivan, K.N. 1986; "Computer enhancement of Landsat, magnetic and other regional data", 13th CMMI Congress, Singapore. Tassell G.W., Aubrey M.C., 1984; Computer-assisted analysis of Landsat and geological data - A new approach to regional exploration. 7th Australian Geological Convention, Sydney.

GEOLOGICAL INFORMATION IN MINERAL EXPLORATION T M Porter CRA Exploration Pty Limited, Adelaide, South Australia.

".. all experience is an arch wherethrough Gleams that untravelled world whose margin fades For ever and for ever when I move." TENNYSON - Ulysses In mineral exploration, no region is ever fully explored. The information from preceding projects and phases of exploration provides an 'arch' through which, to the perceptive, new opportunities 'gleam'. Such information is generally timeless, and may be used to good effect repeatedly for differing purposes, targets and theories. Successful mineral exploration involves two key elements, namely: * the application of the necessary knowledge, experience and intellect to the development of concepts, and, * the collection, collation and interpretation of information to test those concepts. Geological Society of Australia Abstracts Number 32, Ballarat 1992

The key to both steps is 'information'. Where appropriate information already exists, it must first be located, collated and then supplemented by additional data collected anew in the field. To effectively access, integrate and apply both 'new' and 'existing' information, it is necessary to have efficient systems to provide 'reference' and 'source' information, as well as a means of 'manipulating' the information to reach conclusions. These three aspects of information systems are separate, each has a different emphasis and should not be confused one with the other. They apply equally to document and computer based systems. 'Reference' and 'source' systems together constitute 'database management'. In both, the the scrupulous integrity, completeness and correctness of the information is of paramount importance, with lesser emphasis on the system itself. In contrast however, for systems employed in the 'manipulation, interpretation and display' of information, the prime

328 consideration is in the utility of the system. Reference systems rely upon the data being consistent, correct and comprehensive so that the user may confidently and reliably locate the required information, if it exists. The contribution of the system is in the validation, maintenance and management of the database and the eloquence of the retrieval functions. The more databases that must be searched and the greater the inconsistency between each, the greater the probability that the required data will not be located. Geoscience information is commonly descriptive, containing complex detail, nuances, abstractions and meanings that may be deduced by others with insight or complimentary knowledge. It is not just tables of numbers. Consequently it is essential that these characteristics are preserved intact within the 'source' database and are not lost in the processes of standardisation, coding or 'computerisation'. Care must be taken that the integrity and value of the information held in 'reference' and 'source' databases is not sacrificed by the current primitive stage of evolution of the computerisation to which these databases are increasingly entrusted. Similarly resources that might be expended on the building of 'reference' and 'source' databases should not be squandered following computing 'fashions' in the erroneous perception that rapid changes in technology are taking place. As Australia and the rest of the World is progressively more intensively explored and as geoscience knowledge expands, the relative importance of these three different aspects of information systems is changing. Forty years ago, when modern mineral exploration was in its infancy, the 'manipulation and interpretation' of new data was the prime consideration. Today it is essential that existing

A 15.7

information is not ignored, and as a consequence, 'reference' and 'source' databases have assumed far more prominence. The value and cost effectiveness of such database systems resides in the comparative cost of managing and accessing existing information versus the cost of collecting that data anew. Virtually all modern discoveries in Australasia have been detected through the application of available 'existing information'. In some cases the existing data pointed directly to the deposit, while in others the discovery arose by both formulating concepts and pursuing clues derived from the available information. As the more obvious outcropping deposits are discovered, exploration must employ methods which are more intellectually challenging and information dependant. As the cost of gathering the necessary data increases, access to comparatively cheap, existing, reliable data grows more attractive. Although Australia is not endowed with any more minerals than other comparable areas on the Earth's surface, the mining legislation which, over the last forty years, has encouraged and supported exploration, provides the nation's mineral industry with an international advantage. One of the cornerstones of this legislation has been the requirement that the information generated by exploration under title is the property of the State, and is available to the public upon relinquishment of title. The resultant data that has accumulated would now cost tens of billions of dollars to replicate. This resource, utilised in conjunction with the base geological data provided by State geological surveys and the BMR, and supported by the experience embodied within the international geological literature, should, if properly managed and utilised, underpin the future of the Australian mining industry.

THE NATIONAL EARTH SCIENCES REFERENCE DATA BASE AND ASSOCIATED INFORMATION SERVICES G R T Hudson1 *and D A Tellis2 1

Australian Mineral Foundation, Adelaide 2 Consultant, Adelaide

The Australian Earth Sciences Information System (AESIS), developed and maintained by the Australian Mineral Foundation (AMF), in cooperation with the Bureau of Mineral Resources, the State Geological Surveys and Departments of Mines/Minerals and Energy, CSIRO, the National Library of Australia, the Australian Geoscience Information Association and many companies, is a unique national reference system covering published and unpublished Australian Geological Society of Australia Abstracts Number 32, Ballarat 1992

geoscience documented information over the full spectrum of the earth science and resource subjects. It covers from exploration geology, geophysics, geochemistry and other geological disciplines, through mining and extractive metallurgy, to mineral economics, energy, environmental protection, policy and legislation and all aspects of the infrastructure associated with the mineral, petroleum, coal and extractive industries. AESIS commenced in 1976, but

329 coverage goes back to 1965 and beyond, especially for open-file exploration reports. In addition to managing the national earth sciences reference data base AMF has developed extensive information services for the geosciences over the last 19 years. The services cover computer-based search services having access to national and international systems, current awareness and selective dissemination of information (SDI) services, an informative book review programme, document delivery through a well developed library with special collections, and consulting services for development of systems in the geoscience information field. The document delivery service includes a book shop specializing in publications of many major overseas learned societies and institutions. Of particular importance is the on-line public availability of AESIS Australia-wide through the GEOPAC suite of data bases on INFO-ONE Internationals computing network. A series of hardcopy products on a range of topics are and have been produced from AESIS and remain the most popular outputs from the data base. AESIS has also

been used to provide special indexes to publications of the Geological Society of Australia, the Australian Society of Exploration Geophysicists, The Australasian Institute of Mining and Metallurgy, the Australian Mining Industry Council, the Bureau of Mineral Resources and many State Geological Surveys. A particular feature of these indexed products is the multiple approaches provided to any particular sub-set through 7 associated indexes covering: subject, locality, author, map sheet, mine/deposit/well names, stratigraphic names, and journal/serial names. In keeping with its approach to information transfer AMF conducts a range of intensive workshop courses for leading edge developments and methods over the full spectrum of geoscience and resource disciplines for both individual and organizational needs. Overall, through AESIS, its Information Services, Bookshop and Education services, AMF has advanced access to geoscience information and knowledge in Australia by orders of magnitude over the last two decades.

A 15.8 EXPLORING IN HYPERSPACE: GETTING MORE OUT OF YOU EXPLORATION DATABASE C.A. Laughton Laughton Consulting Services The search or exploration for non-renewable resources entails extensive research at both the generative and exploration stages, in the development of ideas and the techniques for their implementation. The research requires both systematic, methodical examination of all the relevant information and the creation of new concepts, with the most successful ideas originating with unconventional thinking. Electronic databases are now essential for storage of the exponentially increasing volume of data that comprises the information source, and the majority employ structured database management systems with linear retrieval mechanisms that generally need the use of skilled intermediaries (particularly for high precision and recall). Both aspects negate the potential of those information sources to stimulate creativity through cognitive browsing. The mind is inherently associative in nature, a function not well served by linear retrieval systems, and controlled by established patterns. To be truly creative in the problem solving sense requires stimulation by apparently unrelated concepts, to allow restructuring of those patterns. Exploration of unstructured databases in hyperspace allows the creation of linkages between information nodes, Geological Society of Australia Abstracts Number 32, Ballarat 1992

analagous to the neural networks of the brain, giving rise to the possibility of providing those random inputs. Full-text databases are essential to maximize the possibility of providing those inputs during browsing, with searching by natural language queries desirable, to facilitate the use by the explorationist (researcher) who must do the browsing. A single natural language query can achieve the same effect as a complete Boolean search strategy. With company databases not subject to copyright restrictions, recent text generally already available in electronic format through the use of word-processors, and scanners capable of tackling previous hardcopy formats, it is incumbent on database managers to assess the added value of full-text hypermedia databases, in the form of increased potential for exploration success.

330 Hobart, February, 1990. Geological Society of References Australia, Abstracts No.25. Ray, Kenneth and Driscoll, James, R. 1990 New de Bono, Edward 1970 Lateral thinking: A textbook of directions for microcomputer-based hypertext creativity. Ward Lock Education. Reprinted 1984, systems. Database, August 1990, pp.60-64. Penguin Books, Harmondsworth, England. Hutchinson, R.W. 1990 Unconventional thinking and Woodall, R. 1984 Ingredients of successful exploration. AMIR A Annual conference, 6 earth science. In 'R.L. Stanton symposium - New September, 1984 frontiers in ore deposit and exploration studies', pp.21-22. 10th Australian Geological Convention,

POSTER SESSION A 15.9 MANAGING GROUNDWATER DATA AT THE RURAL WATER COMMISSION OF VICTORIA A.J. Brinkley Rural Water Commission of Victoria Introduction— The Rural Water Commission of Victoria (RWC) is a public business authority whose primary mission is to sell water and related services, like salinity mitigation and water management, throughout rural Victoria for beneficial purposes. Included in this brief is the responsibility for the management and investigation of groundwater resources within the state. The RWC conducts monitoring and research, administers regulations covering groundwater drilling and authorises and manages the extraction and use of groundwater. A staff of approximately 35 professionals (geologists and engineers) and 30 technical/support staff are directly involved in groundwater related functions. These staff, other departments, consultants, community groups and the public are some of the clients making use of groundwater data provided by the RWC. A significant collection, collation and processing effort is required to obtain effective data to support this work. Existing databases at the RWC were developed several years ago using outdated technology, supporting only fragments of the whole groundwater research, investigation and management function. A completely new Groundwater Database (GDB) is currently being implemented to address the shortfalls of the four existing systems and to enable additional, valuable datasets to be accessed by staff and clients. Current Requirements— The new GDB is designed to: * Document the history of individual boreholes, especially Government-drilled observation bores (treated as tangible assets). * Store all geological, hydrogeological and associated data considered to be of relevance to Geological Society of Australia Abstracts Number 32, Ballarat 1992

the RWC. * Record technical details of all bores licensed for groundwater extraction. * Form a basis for RWC groundwater investigation and management. * Assist external agencies and the public in inquiries. Computing Environment— The RWC's integrated information technology strategy is to have all computing operating in a network of PCs, Unix workstations and X-terminals. The OSF/Motif XI1 standard has been adopted as the workstation and Xterminal GUI. To support technical applications, the INGRES RDBMS was purchased. It is this system, together with the INGRES Windows/4GL development and applications tools running in an XI1 GUI environment which form the basis of the GDB. Managing Data— The GDB project addresses other issues besides the location of the data. It also concerns work practice changes aimed at collecting, processing and interpreting the data as efficiently as possible, with the ultimate goal being the effective provision of services to all internal and external clients. Significant efficiencies have been introduced to streamline this entire process. These include: * using a single, unique identifier for all bores. Up to three types of bore numbers were previously used within the RWC. Facilities have been created to enable enquiry on old numbers (temporary bore numbers, exploration bore numbers and departmental bore numbers) * generating new bore numbers on a "just in time" basis. For example, a geologist requests a group of five bores be drilled for a certain

331 project. Once this is approved, he GDB allocates the new bore numbers, which are passed onto the geologist and drilling staff. Basic project information is stored against the bore number. This obviates the allocation of large blocks of numbers and also eliminates "orphan" data, (e.g. chemical data, which sometimes arrives with a temporary identifier and no official bore number) * reducing the numbers of reporting forms. This is especially relevant when recording drilling details. Numerous paper-based formats existed for private and government drilling. This has been reduced to one consistent form, reflecting a normalised, non-redundant structure. Data entry screens closely resemble the paper form, promoting higher standards of data entry. A 15.10

* locating data entry screens amongst field data collection staff in regional offices. Efficiencies occur when field staff are convinced to "own" the data. By entering data directly from field sheets to the GDB, time-consuming double handling of data through keypunch coding sheets is eliminated. Future Directions— Once the basic issues of data storage and work practices have been addressed, the RWC will be strongly positioned to expand its ability to capture and process data efficiently. The next step is the integration of bar code geological logging, datalogger, and geophysical logging applications and groundwater models. While this is all existing technology, its integration with the GDB project will create a user environment which will assist the RWC in meeting its objectives.

COMPUTERISED GEOLOGICAL FIELD DATA MANAGEMENT IN QUEENSLAND - SIX YEARS OF REGMAP I.W. Withnall*, K.G. Grimes, S.C. Lang & M.P. Thornton Geological Survey of Queensland

Reconnaissance mapping of Queensland at 1:250 000 scale was completed in the early 1970 s with the support of the Bureau of Mineral Resources. In 1984 the GSQ took over the responsibility of revising this geological mapping database. It was apparent that the field notes made during the first pass mapping could be useful when revising the maps. If the notes were sufficiently detailed, it might not be necessary to revisit many areas, and field work could thus be better directed. However, it was found that these notes, if preserved and available, required considerable work to retrieve selected and meaningful data and this often precluded their use. It was a lot easier to start more or less from scratch, using only the published maps and synthesis reports as a basis. It was also desirable to take advantage of modern technology to rapidly retrieve, manipulate, and analyse the large amount of data collected as part of the more detailed second generation mapping, not only by individual geologists working on their own data, but also by groups of geologists being able to pool data. Another requirement was to make the field data compatible with geographic information systems (GIS) which were looming on the horizon. After some experimentation and examination of systems used by other organisations, REGMAP was successfully trialed in 1986 and thereafter adopted for use by all geological mapping teams. REGMAP uses standardised field notebooks (Figure 1). Data collected at each outcrop are divided into three basic types of information, site, structure, and lithology. The site f

Geological Society of Australia Abstracts Number 32, Ballarat 1992

information records where the outcrop occurs spatially (map sheet, AMG coordinates etc.) and geologically (stratigraphic unit, tectonic unit, and age). The orientation of various structural fabrics and palaeocurrents are recorded. The major part of the database, the description of the rocks themselves, the lithological data, was the most difficult to adapt to a computerised system, because it is largely descriptive. For the system to overcome user resistance, it could not depend on too many codes, and had to be flexible enough to cope with the complete range of geological situations. The concept behind the system we adopted is that the description of each rock type at a field site can be broken down under a number of data types (see Figure 1). The data type field is the key to the flexibility of the system, avoiding the restrictions imposed by fixed fields or 'tick-the-box' forms. The geologist decides what types of data need to be recorded, aided by a prompt list of common data types and their four-letter codes. New data types can be addled to the system at any time to meet specialised needs. The description field for each data type can contain as many lines as required and is essentially free text. The information is structured by the use of a special data type called LITH, with a rock name in the description field. All subsequent data are taken to refer to that LITH until a further LITH is entered. The system is explained fully in the Field Manual (Lang & others, 1990). At present we use FOXBASE as the database management system and have developed a range of

332 programs to produce various kinds of selective retrieval and output. A User Manual explaining their use is available (Grimes & others, 1990). Within the next year or so, the database will be transferred to ORACLE as part of MERLIN, the corporate GIS of the Department of Resource Industries. Since 1986, data from all our field programs has been recorded using REGMAP and the database now contains data from over 25 000 field stations from about twenty 1:100 000 map sheet areas. The system was quickly accepted by all geologists as a field recording system, and has resulted in major changes to work practises in both the field and the office. The system is now proving its worth as many of the initial projects are in the final write-up stage, and data describing attributes of particular rocks or units can be selectively retrieved without tedious manual searching of notebooks. It is particularly useful for searching the data of staff who have resigned before writing up their work. Output in graphical format is also aided, e.g. stereo and rose plots, scatter plots of palaeocurrent data etc. Automatic plotting of structural data onto our final maps will also be possible. It also has great potential for 'training' in remote sensing interpretation and this has already been tested successfully by integretating

REGMAP and geophysical data in the Charters Towers area. In addition to its use by GSQ, the joint BMRGSQ party in Cape York is using the system. The BMR now intends to use REGMAP in projects outside Queensland, initially in the Lachlan Fold Belt and Macarthur Basin. Interest has been shown by the Northern Territory Geological Survey and DSIR in New Zealand, and some universities. Another advantage of REGMAP is that raw data can be easily distributed to other users, in particular the exploration industry, and a marketing strategy for REGMAP data is being developed. References Lang, S.C., Withnall, I.W. & Grimes, K.G., 1990, Department of Resource Industries, Queensland, Geological Mapping Manual 1. Grimes, K.G., Withnall, I.W., Lang, S.C., Murphy, P.R., & Thornton, M.P., 1990, Department of Resource Industries, Queensland, Geological Mapping Manual 2.

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333

A16: HISTORY OF GEOLOGICAL SCIENCES CONVENOR: DAVID

BRANAGAN

KEYNOTE: A 16.1 JAMES COOK (1777) TO CHARLES GOULD (1869) MARITIME EXPLORERS TO GEOLOGICAL SURVEYOR MAINLY IN VAN DIEMENS LAND Max Banks University of Tasmania Cook's surgeon, William Anderson, made a single, the first, geological observation on rocks on the coast of van Diemens Land late in January, 1777. A little over eighty years later, in July 1859, Charles Gould arrived in Tasmania to take up appointment as first Geological Surveyor of Tasmania and began a decade of very productive work. Anderson's observation was recorded as a single footnote in a voluminous work, Gould's work appeared in Parliamentary Papers supported by geological maps and in papers to learned societies. In the period 1777 to 1869 the rate of acquisition of geological knowledge in V.D.L. increased, but quite irregularly. Considerable increase in knowledge of coastal rocks and of rocks on Bass Strait islands accrued from about 1792 to 1804 in a period of active maritime exploration by the English (eg. Flinders) and more especially the French (D'Entrecasteaux, Baudin). A few interpretations were attempted. New information on both coastal and inland rocks accrued slowly until about 1836. Robert Brown, surgeon and naturalist, was an active contributor in 1803-4 with observations , specimens later described or commented upon by English palaeoontologists and some penetration into the interior. A. W. Humphrey, His Majesty's Mineralogist to N.S.W. (which included V.D.L.), was not so active. Between early 1836 and late 1842 visiting ships brought scientists such as Charles Darwin, J. B. Jukes and surgeons with the Ross Antarctic expedition, such as M'Cormick. These stayed varying amounts of time, some of it well away from Hobart Town. Another burst of acquisition of geological knowledge and interpretations resulted. This burst was rendered even more profitable by the sojourn in and travels through V.D.L. of P. E. von Strzelecki (1840 - 1842) despite the pre-Huttonian cast of Strzelecki's interpretation. The work of these visitors was recorded in expedition volumes, papers to learned societies and books and so became more readily accessible than most of that done Geological Society of Australia Abstracts Number 32, Ballarat 1992

between about 1803 and 1836. The founding of the Tasmanian society by Sir John Franklin and the activities of the Royal Society of V.D.L. which succeeded it provided meeting places for those interested in the natural sciences, and media for the publication of their observations and interpretations. Between 1843 and 1859 the rate of acquisition of geological information slowly increased. Prominent among the members of the Royal Society was surgeon Joseph Milligan, who, inter alia, published four papers on the coal basins of V.D.L. in the first volume of the Papers and Proceedings of the Royal Society in 1851. It is notable that prior to the arrival of Charles Gould in 1859, only three people with formal training in geology had worked in V.D.L. Two of these, Bailly and Depuch, were with the French expedition under Baudin, the other, J. B. Jukes came much later. Even Darwin, although acknowledged as a geologist by the time he reached Hobart Town, had acquired his skills and knowledge after his formal education ceased. The name "Tasmania" was formally adopted in 1853 to replace "Van Diemens Land." By this time gold had been "discovered" in Victoria (1851) and in V.D.L. (Feb. 1852). Prospecting got under way in earnest in Tasmania. A little later the colonial government commenced a series of actions which led to the appointment of Charles Gould as first Geological Surveyor and his arrival in Tasmania in July 1859. His exploratory work and geological surveying over the next decade were reported to the public in Parliamentary Papers and papers to learned societies. He produced a corpus, greater in bulk and significance than the sum of previous work on the island, one with lasting effects. Gould's initial contract was for six years during which time he was to produce a book on the geology and a geological map of Tasmania. The contract was a bait; the Government really wanted a Mineral Explorer. His contract, renewed several times, was not renewed beyond about mid-1869. Gould did

334 not fulfil the terms of the original contract but there is evidence that he did produce a map and much of the book. Three points emerge from this study. The first is that even at the time of Darwin's visit in 1836 and certainly by the time of Gould's appointment a body of factual information was available as well as some interpretation and synthesis. This knowledge with much of that added by Gould has been subsumed into or rendered obsolete by later literature and thought. But not all of it has! The second point is that the sequence of developments in the history of geology in V.D.L. to 1869 parallels that elsewhere in Australia. An early phase of maritime exploration was followed by a phase of relatively slow accumulation of information derived from work by inland explorers and prominent visiting naturalists and geologists. The next phase, and last one relevant here, was one of a Government appointment. In Tasmania as in several other colonies, this appointment was of relatively short duration. The third point concerns the change in availability A 16.2

of the geological information. The early phase was one of publication, after some delay, in reports of maritime explorations. After settlement the information was preserved in intergovernmental documents, official reports to the British or V.D.L. goverments and a little disseminated in papers in overseas journals, mainly British. Information accrued by prominent visitors in the 1830's and 1840's was published in expedition reports in a systematic fashion, in papers to learned societies and in books; in most cases te delay was considerable. The advent of the Tasmanian Society and the Royal Society of V.D.L. allowed local publication, in some cases of reports commissioned by the Government, and usually with little delay. Gould's results were published to some extent almost immediately in local newspapers, more fully and after a shortish delay as Parliamentary papers, and some were published in local and overseas journals. In general the public availability of the information increased and the delay in making it accessible decreased.

THE ETHERIDGE / BROWN CORRESPONDENCE : AN INSIGHT INTO SOUTH AUSTRALIAN GEOLOGY IN THE LATE NINETEENTH CENTURY Barry J. Cooper Department of Industry, Trade & Technology, GPO Box 1264, Adelaide, SA. 5001

This paper discusses the perspective provided by a suite of letters to H.Y.L. Brown (Government Geologist of South Australia) from his palaeontological consultant, R.L. Etheridge Junior (Australian Museum, Sydney) between 1891 and 1899. The geological horizons of South Australia in the late 19th century were vastly different from today. Not only was the geological database very limited and the number of geologists very few, but an activity, far more critical than now, was the search for fossils. These contributed to basic geological understanding and provided a correlation with well known sections in Europe. Hence the need for H.Y.L. Brown, who never specialised in palaeontology, to seek assistance. In addition to Brown, prominent South Australian geologists during the 1890s included: R. Tate ( Professor of Natural Sciences, University of Adelaide), J.J. East (S.A. School of Mines & Industries) and W. Howchin (part-time consultant, lecturer, amateur palaeontologist). Tate was pre-eminent in palaeontological research, and was supported in vertebrate research by South Australian Museum Director, E.C. Stirling. The letters, under consideration here, provide surprisingly candid comment on the tensions that Geological Society of Australia Abstracts Number 32, Ballarat 1992

existed amongst the small Adelaide geological community. A dividing line developed during this period between those who supported Tate (including East and Stirling) and those who had difficulties working with him (Brown and Howchin). Brown, began seeking palaeontological advice from his former associate at the Victorian Geological Survey in preference to Tate soon after Etheridge returned to Australia in 1887. Etheridge quickly established contact with many Australian geologists at this time and soon understood the antagonisms developing among Adelaide geologists. He counselled and supported Brown thus: 7 would not pressure Tate for the fossils were I you. He is a queer man and easily offended(1) At the same time Etheridge was aware that he was competing with Tate with his palaeontological investigations in South Australia : ".... please send reference or geological information that you may have on the matter... J want to be up along sides with Tate & Co(2) He also lent a sympathetic ear to others who faced difficulties with Tate: 7 heard from Howchin all about his troubles with Tate: (3)

335 In 1893, these underlying tensions were briefly publicised in the Adelaide press when both Tate and Etheridge differed in their age determinations of the Leigh Creek Coal Measures. Brown, solicited by Etheridge, wrote formally to Tate (4) in order to resolve the matter. Neither Tate nor Brown were interested to debate scientific issues in public. In 1896-7, Brown consulted Etheridge with regard to the classification of Tertiary strata in South Australia (5). Later in 1899, Etheridge was asked to identify Tertiary fossils from the Murray River cliffs (6). In both these instances, Etheridge wisely used the most recent published papers of Tate and counselled Brown to do the same. The Etheridge/Brown correspondence provides tangible evidence of the personal constraints on Adelaide-based geologists in the late nineteenth century, constraints that persisted over the ensueing decades. Today, such tensions are less likely to be recorded in writing. In 1924, long after Tate's death, his student, H. Basedow, vividly described the antagonisms that then continued between himself and Howchin (7).

The letters also provide an indication of the longlasting relationship that was developing between Sydney and Adelaide geologists. This is exemplified by Etheridge's request for Brown to support the appointment of T.W.E, David to the Chair of Geology at the University of Sydney in 1891 (8). This liaison blossomed in such a way that Sydney graduates were appointed to most new geological positions created in Adelaide at the University and at the Department of Mines between 1901 and 1920. References (1) Letter from Etheridge to Brown, dated 18.5.91 (2) Ibid, dated 12.5.91 (3) Ibid, dated 9.8.97 (4) Letter from Brown to Tate, dated January 3,1894 (5) Letter from Etheridge to Brown, dated 9.8.97 (6) Ibid, dated February 2,1899 (7) Basedow, H. 1924. The collapse of mining in South Australia : a tragedy in geology. Webb & Son, Adelaide. (8) Letter from Etheridge to Brown, dated 2.1.91

A 16.3 NEWCASTLE COLLIERIES PAST PROSPERITY, PRESENT DERELICTION, FUTURE HAZARD? G.H. McNally Department of Applied Geology, UN.S.W.

Coal has been mined in the Newcastle area for nearly 200 years, and the problems of ground movements above old workings and of derelict mining land have been a matter of concern to the local residents and their representatives since the late 19th century. Present day and potential problems are largely associated with more recent shallow workings in the western and southern suburbs of Newcastle. In general these areas remain derelict, but the pressures of urban expansion and land price increases have lead to residential and other development in places. In particular, the construction of the F3 freeway west of Newcastle and the reconstruction of the Pacific Highway south of Swansea have necessitated extensive reclamation of abandoned shallow colliery workings. More of this can be expected in future decades. Mining at Newcastle commenced in 1801 in the vicinity of the present city centre, using convict labour. The working methods were haphazard, and some later subsidences have been attributed to this. Systematic mining was initiated by the Australian Agricultural Company (AA Co.) in 1831. The company's leases covered most of the inner suburbs of Newcastle, but operations were concentrated close to the harbour. During the 1830s the activities of small Geological Society of Australia Abstracts Number 32, Ballarat 1992

scale miners in the Lake Macquarie and MinmiMaitland areas, west and southwest of the AA Co. leases, were tolerated but by the late 1840s the company monopoly was being challenged by the brother James and Alexander Brown (among others). The dominance of the A A Co. was revoked by the British government in 1847, ushering in two decades of rapid mining expansion (Turner, 1982; Branagan, 1972; Ellis, 1969). This first coal boom, which was based on the growth of steamship traffic and (later) rail locomotion, saw the establishment of mining villages at Lambton, Wallsend, Minmi and elsewhere along the western and southern boundaries of the AA Co. land. Where the earlier mines had exploited the Nobby's and Yard Seams, these newer collieries worked the lower and higher quality Borehole Seam close to its crop line. Further expansion in the 1870s followed this coal southward and west, while in the Burwood area the Victoria Tunnel Seam was the main source. Later still the Great Northern Seam was worked along the western and eastern shores of Lake Macquarie, but such was the attractiveness of the Borehole Seam that as late as the 1900s seventeen of the 26 operating collieries in the Newcastle area were working this coal

336 (Danvers Power, 1912). As might be expected, problems associated with abandoned shallow (here taken to mean less than 30m of cover) colliery workings vary considerably with local geology, age and mining practice, but include: -Cratering or sink hole formation at the surface, due to shaft or mine roadway intersection failure, or along the trace of open subsidence cracks, -Discharge of saline, acid and toxic mine waters, -Seam fires propagated by air flowing down surface cracks (and in turn generating more cracks and renewed subsidence), and -Possible slope instability in excavations adjacent to subsidence-fractured overburden, or soft foundations on filled ground (mainly drift portals and waste dumps). The most widely used mining systems used in Newcastle collieries up to about the 1950s were bordand-pillar, principally variations on the Welsh Bord' method, and hand-worked pillar and longwall extraction. The Welsh Bord system employed long rectangular pillars which were partially extracted by driving tunnels (bords or rooms) parallel to the shorter dimension. Eventually the pillar was reduced to a series of parallel remnants (or 'fenders') 30 to 50 m long by 5-10 m thick with 5-7 m wide voids between them. A later system of bord and pillar mining made use of square pillars, which were split twice to create four smaller 'stooks' at each corner of the original block. Alternatively, the pillars could be progressively

A 16.4

stripped (or 'lifted') until all its coal had been removed and the roof fell in. The different systems of mining thus produced different pillar layouts on abandonment, ranging from complete pillar removal, roof collapse and void closure, to robust pillar stumps supporting large broadly arched areas of roof with 'ballrooms' in between. The redevelopment of areas of Newcastle left derelict by coal mining will present a major challenge to geologists and engineers over the next decades. Where this work differs from other types of geotechnical investigation is the importance attached to understanding the site's mining history, since direct inspection of the old workings is either impossible or extremely difficult. At the very least such an understanding will reduce the cost of investigation, but more importantly it will make the interpretation of drillhole and geophysical data easier and more effective. References Branagan, D.F. (1972). Geology and Coal Mining in the Hunter Valley, 1791-1861 Newcastle History Monograph No. 6. Danvers Power, F. (1912). Coalfields and Collieries of Australia Critchley Parker, Melbourne. Ellis, M.H. (1969). A Saga of Coal Angus and Robertson, Sydney. Turner, J.W. (1982). Coal Mining in Newcastle, 1801-1900. Newcastle History Monograph No. 9.

AN UNEXPLOITED RESOURCE: GEOLOGISTS' PERSONAL ARCHIVES Margaret R Dwyer Archives, University of Sydney NSW

This paper draws attention to the value of unpublished records of Australia's geologists; its focus is the personal archives,often termed "private papers", of individual geologists, as distinct from records of an institution, association or company. The potential value of transferring personal archives to an archival repository to be preserved for the use of future generations is illustrated by reference to the University Archives1 collection of papers of Tannatt William Edgeworth David, Professor of Geology and Physical Geography at the University of Sydney from 1891 to 1924. The collection is arranged in 57 archival series; a selection is given in Table 1. Most record David's research, especially his geological surveys in Australia, notably in the Hunter River Valley NSW where David and G A Stonier discovered the South Maitland coalfield in 1886; also David's Geological Society of Australia Abstracts Number 32, Ballarat 1992

expeditions to Antarctica in 1907-09 and to the Pacific Ocean coral atoll Funafuti in 1897-98. In the arrangement of David's archives, novel as well as standard procedures have been used; they are designed to facilitate access to the records and reduce their rate of decay. In many folios of David's lecture notes, the chemical bonds maintaining the structure of cellulose had so broken down that the papers smelt strongly of pyruvic acid and disintegrated on handling; the information has been preserved in photocopies on especially durable paper buffered with calcium carbonate. Key criteria for selecting documents to be preserved for posterity in an archival repository are uniqueness and those properties adding to the value of the document as a piece of evidence. Such properties include signature or other property identifying the

337

author of the document, date and context of use, continuity of custody, identity of former custodians. The authenticity of David's experiences during his ascent of Mt Erebus and trek of some 1700 kilometres to the Magnetic South Pole described in his field notebooks is not in doubt The various drafts of letters in David's hand, addressed to the Royal Geographical Society of Australasia, Commander-in-Chief (Royal Navy) Australia Station and NSW Government regarding the coral boring expeditions to Funafuti, are a valuable research source, a marked contrast to documentation in this computer era.

Correspondence, such as letters written by Douglas Mawson to David, can have considerable monetary value in the marketplace if sold individually or in small lots. The integrity of the T W Edgeworth David's archives adds greatly to the research value of individual documents in the collection, Few papers of David's successors at the University are in an archival repository. Experience leads to the conclusion that rich resources for the interpretation of Australia's geological heritage and other purposes would become available if systematic survey principles were applied to geologists' private papers.

Table 1. SELECTED LIST OF SERIES III THE UNIVERSITY OP SYDNEY ARCHIVES' COLLECTION OF PERSONAL ARCHIVES OF TANNATT WILLIAM EDGEWORTH DAVID SER NO

SERIES

TITLE

01 Research - British Antarctic Expedition 1907-09: ascent Erebus /Magnetic Pole journey - scripts authored by David

DATE RANGE SHELF METRE 1908/undated

0.1

0 4 Research - British Antarctic Expedition 1907-09/other - naps/plans

C1907-1931

0.02

05 Research - British Antarctic Expedition 1907-09 - field notebooks

1908-1909

0.1

10 Research - Funafuti (Tuvalu) Coral Boring Expeditions 1897-98 correspondence authored by David

1897-8, 1901 0.01

11 Research - Funafuti (Tuvalu) Coral Boring Expeditions 1897-98 - drafts of letters/ianuscripts ascribed to David

1897-1900/nd

0.03

12 Research - Funafuti (Tuvalu) Coral Boring Expeditions 1897-98 - field

1897-1898

0.1

notebooks/working papers, lostly handwritten or annotated by David 13 Research - Funafuti (Tuvalu) Coral Boring Expeditions 1896-98 - correspondence 1895-1914

0.1

15 Research - Funafuti (Tuvalu) Coral Boring Expeditions - photographs (albuain) cl898 (nd) soie with annotations/ other records

0.04

16 Research - fossil fauna in rocks of the Adelaide series, South Australia letters received/ letters sent (drafts, copies)

1928-1934

0.1

19 Research - fossil fauna in rocks of the Adelaide series, South Australia working papers/field notebooks - David/Yorke D M

1929-33/nd

0.2

20 Research - glaciation/ Ice Ages: Snowy Mts field trips 1905-07/other naps/ working papers/ field notebooks

1905-29/nd

0.2

2 3 Research - coalfields New South Wales - plans/ nuierical data/ working papers C 1 8 9 0 - 1 9 2 8

0.2

25 Research - Miscellaneous field notebooks

1882-1932

1.4

31 Research - addresses given by David - scripts/notes

1895-1923

0.1

1894-1933

0.3

1904-1923

0.05

43 Australasian Association for the Advanceient of Science/ related bodies correspondence/ other records

1910-1928

0.1

45 Australian Governient - Australian Imperial Forces field notebooks/ other records

1914-1920

0.45

1901-1934

0.06

1916-1919

0.05

1883-1934

0.1

32 Research - Miscellaneous correspondence 33 Research / other - diaries

46 Personal 47 Personal

- letters received - diaries

51 Miscellaneous - letters authored by David - originals/ copy/ drafts

G e o l o g i c a l S o c i e t y of A u s t r a l i a Abstracts N u m b e r 32, B a l l a r a t 1 9 9 2

338

Geological Society of Australia Abstracts Number 32, Ballarat 1992

339

All: GEOLOGICAL EDUCATION CONVENORS: LLOYD HAMILTON AND GABOR MARKOVICS A 17.1

CURRENT ISSUES IN GEOLOGICAL EDUCATION L. H Hamilton

Dept Applied Geology, QLD Uni of Technology, Brisbane, Queensland Problems in geological education are becoming focussed at the High School level where enrolments have dropped over the whole country to an alarming extent. The trend is continuing. This has flow-on implications at the Tertiary level where enrolments also seem to be dropping. It also tends to imply that something is wrong at the junior or Lower Secondary School level. Geology is a compulsory part of science at this level but at Upper Secondary level students exercise a choice on the subjects they select. This could directly reflect the general attitude of the community, or possibly it might be related to reduced entry level requirements of junior Earth Science teacher's courses and reduced emphasis of geology in these courses. This in turn would also reflect the general community's attitude to geology and teaching, fortunately there still appears to be fun in Geology at the Primary level at some places but unfortunately at others geology is being taught. The need to improve the general community's attitude to geology and raise awareness is well known to at least some of our more enlightened colleagues. It was the main aim of GAP, the Geological Awareness Program. It is increasingly important that the public sees the relevance of geology to world issues and to their own lives. The evolution of geological utilization must be emphasised with respect to new developments in environmental science and the expansion of traditional geological endeavours. Government intervention is currently a strong issue in geological education. The Dawkins Report

Geological Society of Australia Abstracts Number 32, Ballarat 1992

has resulted in hasty mergers and shotgun marriages. One result is the loss of geological teaching at the level between that of the TAFE Colleges and the Universities. Rationalization of departments is still feared by some but on the positive side has stimulated closer collaboration between certain departments. The Viviani Report in Queensland is expected to result in depressed future enrolments in High Schools. Curriculum matters are also of concern. The lag between syllabus writing and implementation is protracted. In NSW a student electing to do physics and chemistry is prohibited from studying geology, yet to study geology at Tertiary level physics and chemistry are required. Similar problems occur in some other States. To help overcome the disadvantage of studying geology at school The University College of Southern Queensland now allows students to sit for an examination to gain exemption from certain geological units in first year. This has had good results so far. Public education awareness is still the main problem in geological education today and emphasis needs to be placed on the relevance factor generally and the fun factor in educational institutions. High school enrollments give us a good barometer of educational needs. We must act now before we loose even the barometer. There is hope in the work of the Geological Education Subcommittees and in the formation of a Specialist Group in Geological Education.

340 A 17.2

ENVIRONMENTAL GEOLOGY, VALUE JUDGEMENTS AND EDUCATION Bronte Nicholls Muirden Matriculation College, Adelaide

Geology is a science that covers most aspects of the interactions between Earth Systems. A wide range of environmental problems can be defined and understood using geological principles. McGowran (1991) states that "Acceptable decisions on the future of the environment require an understanding of the environment, which means research and education in a very wide range of sciences. And that range, in turn, includes geology as an essential, central component". For individuals to make informed decisions on environmental issues, they need first to be exposed to the "factual" information surrounding the subject concerned Personal experience and "feelings" cannot be ignored as a major force in determining values. As Judith Wright (1970) says "There is no stronger force than emotion....For it is feeling that establishes values, and if we are ever going to move from economic values to a reassertion of ecological values, our feelings and sympathies must be engaged first". A shift in feeling towards conservation and away from economic factors is clearly evident in our society, particularly in the mining versus conservation debate. An example of this would be the proposed Coronation Hill Joint Venture. Media presentation of this debate focussed mainly on the ecological issues concerned, while information regarding the mining operation itself and it's likely economic benefits was largely ignored. This limited and subjective coverage of the proposed venture, coupled with the strong environmental concerns held by todays society, resulted in many people making poorly informed value judgements. Comments such as "what will happen to the rainforests" and "what measures are there to

KEYNOTE: A 17.3

contain radioactivity" are evidence of this lack of information. It is the "feeling" aspect of value determination that cannot be measured or easily changed. A child brought up in a mining town will place a different value on mining to a child reared in the suburbs of a capital city. These different life experiences and the influences of parental values will give the child much of the feeling aspect of their own value determination. It is the role of the educator to present a balanced view on controversial issues such as mining, land degradation and the use of fossil fuels. If the media or other groups have presented a certain point of view on an issue, then the educator may need to search for other viewpoints that also need to be presented to their students. Some strategies could include inviting speakers to address the class, providing written material from a wide range of sources or setting a research assignment. Rational debate based on a combination of factual evidence and personal feelings can then lead to the individual developing a balanced value judgement on an issue. Through geological education, students can gain an understanding of Earth processes, materials, structures and history and by a balanced teaching approach, this knowledge can be used by the student to develop their own value judgement of an environmental issue. References McGowran, B. (1991) "Greenhouse and Geology" SASTA Journal No 91/2:35-36 Wright, J. (1970) "Conservation as an emerging concept" Occas. Publ. No 2

GEOLOGICAL EDUCATION AND THE ROLE OF THE GEOLOGICAL COMMUNITY I. F. Clark

Department of Geology, University of South Australia Public ignorance about science in general, and surface, are dependent on its resources and are about key concepts of the geological sciences in surrounded by its awesome beauty. Surely the story particular, inhibits effective action on problems behind these things should be a legitimate part of relating to environmental change, land use, sustainable everyone's education. development and many other areas that concern the Most geoscientists agree that geology/earth science whole community. We spend our lives on the Earth's is relevant to, and should be part of the school Geological Society of Australia Abstracts Number 32, Ballarat 1992

341 curriculum. The majority of schools leavers in Australia have not studied a year long or even a semester long course in geology/earth science. Many have never been taught geology/earth science topics even in basic science courses. How do we change this situation? Do we need to? What is the role of geoscientists? These are some of the questions that we have to answer. The situation is not unique to Australia. The same questions have been asked in USA and other countries.

A 17.4

A number of solutions have been proposed. Some of these proposed remedies will be suitable to Australia, others will need to be adapted and we need to develop some that are our own. There is no single program that will solve our problems, there is no consensus on where to start. The current concern for the environment may give us the opportunity to develop programs for formal and informal education. We need to cooperate, coordinate our activities and patiently move forward.

INITIATIVES IN ENVIRONMENTAL EDUCATION FOR THE GEOLOGY AND GEOLOGICAL ENGINEERING COURSES AT THE ROYAL MELBOURNE INSTITUTE OF TECHNOLOGY J.C. Brumley Senior Lecturer, Geological Engineering, RMIT.

The Applied Geology and Geological Engineering courses offered at RMIT are designed to give students the skills required for employment in the construction, mining, petroleum and environmental industries. The courses are responsive to changing requirements in Industry. During 1990 and 1991 significant course developments have occurred to meet the demand for graduates with environmental awareness and the skills required to contribute tothe resolution of environmental problems that have arisen from industrialisation in Australia and overseas. The course developments are also designed to support a new degree in Environmental Engineering, which is being introduced by the Faculty of Engineering in 1992. The paper will describe the course developments that have occurred, and discuss them in relation to career opportunities and to the environmental objectives of the Institution of Engineers, Australia. At first year level, a new subject was introduced in 1991 to develop an early awareness of environmental issues. The subject, entitled "Environmental Issuesin Engineering", provides an introduction to Environmental Impact Assessment, Sustainable Development, community consultation, waste management and specific examples of environmental issues in geological engineering practice. The Institution of Engineers policy on Sustainable Development and its Code of Environmental Practice are used to illustrate the professional significance of environmental issues. This knowledge provides an excellent basis for integrating environmental considerations into all relevant aspects of the student's subsequent studies. In this way, environmental considerations become a natural part of the engineering design process, to be considered equally with the "normal" factors such as costs and geotechnical Geological Society of Australia Abstracts Number 32, Ballarat 1992

conditions. The most important development from an employment point of view has been the introduction of a third year subject dealing specifically with "Land Contamination". The subject complements the sister subject of Hydrology and provides specific training in both local and regional land contamination problems. A number of students have already gained employment with Consultants involved in cleaning up contaminated industrial land and with Government Departments working on regional land salinity problems. Post-graduate research is also proceeding on remediation techniques for cleaning contaminated land sites. Feedback from both students and employers has been very positive concerning these new course initiatives. RMIT is also taking up the challenge of providing undergraduate training specifically in environmental engineering. This new degree will be introduced in 1992. The course is structured on a major/minor basis with students selecting appropriate minor subjects from either Chemical, Civil or Geological Engineering and from other courses at RMIT. This new course has provided a unique opportunity to bring together environmental skills from each of these disciplines in a mutually supportive manner. A close association has always existed between the disciplines of Civil Engineering and Geological Engineering and it is now rewarding to see similar links emerging between Geological Engineering and Chemical Engineering. Areas of mutual interest converge on activities concerning waste disposal in landfills, industrial land contamination and the general dispersion and attenuation of pollutants in the lithosphere. In addition to applying their skills in a professional capacity, it is intended that these course

342 development initiatives will also help graduates to contribute to community awareness in environmental

A 17.5

matters,

CONTINUING EDUCATION FOR EARTH SCIENCE GRADUATES IN THE MINERALS AND PETROLEUM INDUSTRIES Geoff Hudson and David Pollard Australian Mineral Foundation

The investment of human resources in exploration and development of our mineral and petroleum resources is a critical factor in maintaining and improving Australia's position in increasingly competitive world markets. It is important that the costs of human resources development are integrated into strategic plans and capital budgets. The development of professional staff starts at university, with the scientific and engineering basis for the various professions, and is continued after entry to the workforce by on-the-job experience supplemented by a variety of more formal training. Once working in the industry, graduates very quickly learn a range of things not taught in university, and a need for some further formal learning often becomes apparent in some areas. Categories which could be identified include: bridging courses for subjects not covered, or not adequately covered, at university; in-depth technical courses where greater specialized knowledge is required; management skills courses to help to deal with the increasing financial and human resource management responsibilities. It is possible to acquire additional knowledge by self study, using Distance Learning techniques involving printed material, computer systems and sohpisticated communication systems made possible by satellites. Universities offer postgraduate degrees which may be taken on campus or by a variety of remote methods. Short courses are available which cover a comprehensive range of topics. All of these methods have some advantages and disadvantages, and the balance of time and money spent against the useful rewards will depend on different factors in each case. The reward of a Graduate Diploma or Masters Degree may be worth the disclipine and hard work for some, but unnecessary for others who can acheive their objectives in ways more compatible with their other commitments. The changes imposed on the tertiary education sector by the Federal Government have done little to rationalise the earth sciences scene. There are more institutions with university status, and Key Centres at

Geological Society of Australia Abstracts Number 32, Ballarat 1992

some of them, both factors which should encourage more understanding, and greater excellence, in earth sciences. However the introduction of market philosophies into the funding of tertiary courses, encouraging for them to compete for students, consulting and other sources of income, has resulted in a need to devote more effort to staying afloat. Universities are offering short courses to people in industry as revenue raising exercises as well as education services. Unlike AMF courses, these are usually restricted to the available staff or visitor expertise. The AMF Career Path Development plan allows such courses to be fitted in to a longer term perspective. The Australian Mineral Foundation has been presenting short courses by the leading experts in fields related to petroleum and minerals exploration and development since 1973, and the Syllabus of courses is now structured to provide Career Path Development plans for various professionals working in those industries. This is a framework of course topics which are updated and repeated at regular intervals, and permits planning of continuing education to provide a balanced range of relevant courses extending over a period of 10 or more years after graduation. Courses can be taken at introductory/refresher level, intermediate and advanced levels. The AMF Career Path Development plans provide the framework for such programs, and it is easier to see where AMF and other courses best fit for individual staff. AMF courses are mostly designed as workshops, and allow ample opportunities for applications. An important feature of is the interaction with course leaders, and with other participants working in similar situations. Comprehensive notes are provided, and these are backed up by the AMF Information Services facilities. AMF continues to present courses, seminars and conferences which do not necessarily fit into individual Career Path Development plans, within an overall philosophy of responding to the needs of industry with practically oriented programs.

343 A 17.6 WHAT DO ANCIENT EUCALYPTS AND VOLCANOES HAVE TO DO WITH GEOLOGY EDUCATION? THE USE OF WILSON BOTANIC PARK, BERWICK AS A RESOURCE FOR SCIENCE TEACHING Neville Green1* and Robert Hill^ 1

Institute of Education, University of Melbourne, Parkville 2 Plant Science, University of Tasmania, Hobart

Wilson Botanic Park is being developed as a botanic garden and educational resource area that has several important features that make it rather unique. The park is being developed in a Tertiary volcano which was quarried for basalt until 1983. An excellent sequence of Older Basalts, ash and fluvio-lacustrine muds, sands and brown coal are exposed in the quarry. The fossil mud layers contain many organically preserved plant fossils and pollens, and captures a stage in the transition from a rainforest dominated landscape to open woodlands dominated by Eucalyptus. The overlying basalts have been dated by isotopic methods at 22Ma. which enables us to put a minimum age on the deposit. The park will have native grasslands, woodlands and a rainforest similar to those found in North Queensland and Tasmania today. The rainforest will be growing over the fossil sequence, enabling students to see the extant and ancient plants together. A laboratory and field station is being set up to aid both student groups and the general public in the understanding of plant fossils and the evolution of Australian vegetation, especially in the middle Tertiary. The educational potential of the site is unlimited and many areas of junior science and V.C.E. geology,

A 17.7

biology, geography and environmental science can be covered both at the park and in kit type reference material. Students can construct a data base of fossil characteristics, geology, geomorphology and soils of the area which could be used to build up a picture of the environment at the time of the volcanism and sedimention. A number of questions can be asked including; (1) What are the characteristics of the environment, both past and present? (2) What physical processes were involved in the volcanic eruptions and the subsequent climatic change? How would plants cope with such catastrophic events? (3) How do people respond to catastrophic events like the eruptions of Mt. Pinatubo and Mt St Helens? A series of practical exercises are being developed that include geological-topographic mapping and interpretation, fossil and extant plant identification and the preparation of a herbarium and pollen reference collection. The combination of plant ecology and evolution with continental drift and climatic change provides an interesting interactive approach that combines many disciplines. Computer applications include the construction of a data base and spreadsheet of fossil leaf and pollen characteristics that could be compared with living species.

ROADSIDE GEOLOGY AS A RESOURCE IN PROMOTING GEOLOGY A.T. Grenfell* School of Geology, Queensland University of Technology George St, BRISBANE Q. 4000

Major roadcuts and pronounced and spectacular physiographic features along, or close to, Highway 1 in SE Queensland form the basis for a booklet which has been developed to promote the earth sciences within the general community. It is intended that road travellers and tourists would be the major audience; educational institutions at chiefly the secondary level could well be interested in the geological aspects which are addressed The booklet is the result of an educational project in which the clear aim was to stimulate interest in geology and its relevance to everyday life, rather than focus unduly on the geological history and current Geological Society of Australia Abstracts Number 32, Ballarat 1992

interpretations of the tectonic development of the region. Emphasis is placed on communicating the fundamental principles of geology at a level appropriate to people who have little or no previous geological knowledge. The text and photographs of the booklet are therefore supported by simplistic schematic models which illustrate aspects such are volcanic activity, shoreline processes, structural deformation, and landscape evolution. These are generally conveyed using sequential diagrams which have been drawn using computer graphics packages. The nature of the geology in the region is such that some segments of Highway 1 are comparatively

344 monotonous geologically or contain relatively little of interest, given the major objective of promoting earth science in the general rather than the geological community. Along other segments of the highway, however, geological features or aspects of a relevant or spectacular nature are somewhat more clustered. Accordingly, the geological maps presented are simplified regional maps, together with localised geological maps at a larger scale for features of particular interest. These are preferred to routine strip geological maps for the section of Highway 1 involved. In addition, the structure of the booklet attempts to reflect this uneven distribution of geological features by encompassing a topic-based A 17.8

approach, focussing on aspects such as the Glasshouse Mountains, gold mining at Gympie, resource management, the evolution of the large sand islands, beach erosion and shoreline management, and the Tweed Volcano. Not only does the self-guiding programme includes aspects which centre on the relevance of geology to everyday life and the need for a balance between mining and conservation; it also attempts to extend the information presented beyond the geological base by incorporating related social and cultural aspects. These include the mining history of some towns and aboriginal legends which relate to specific physiographic features.

EXCURSION GUIDES - A NEW APPROACH William G. Shackleton * and Mary-Anne N. Binnie

Department of Geology, University of South Australia Salisbury Campus, South Australia For some time there has been a demand, particularly from teachers, for a geological excursion guide providing information on individual locations of geological interest throughout South Australia. The authors felt that the new style used in their Geological Excursion Guide to South Australia (Shackleton and Binnie, 1990) would be of more value to teachers who have to prepare excursions for a wide range of student ages and abilities. These new format guides are data bases, not prescriptive materials. They encourage development of tailor-made excursion booklets which suit particular topics, or areas, or styles of teaching. The Guide is divided into two parts. The first part, a booklet, contains an introduction to the use of the guide, a list of geological locations and regional and district location maps. The second part is made up of separate fact sheets, which may be purchased individually, each describing the geology of one location. The Location List is a serial list of geological locations and excursion fact sheets, the title of each generally includes geological features and geographical locations. The relevant regional location map is also given which makes the selection of suitable excursion stops a relatively easy task. The Regional Location Maps section includes an index map of South Australia showing the areas covered by the following regional location maps. These latter are based on the RAA of SA road maps. Each map shows the position of each geological stop and the relevant excursion fact sheet. On the reverse of these maps is a list of the stops and fact sheets, including grid references. Regional maps have been subdivided into smaller districts each with a corresponding District Location Geological Society of Australia Abstracts Number 32, Ballarat 1992

Map so that finding a particular location is made easier. These maps may be copied for inclusion in individually prepared excursion guides. The second part of the Guide consists of excursion fact sheets each of which describes the geology of one location. The front page contains district and detailed location maps and labelled sketches or photographs of the outcrop or feature. The back page contains an outline of the purpose in stopping at that location, a detailed description of the feature and a discussion of the regional significance, if relevant. Information about facilities such as parking, toilets and shopping is also included as is a list of relevant maps and other publications. The fact sheets are printed on card and are copyright free. The main advantage of this type of guide is that teachers and others are able to design their own excursions. They can do this by selecting the fact sheets relevant to the topic being studied and presenting them in an order which suits the teacher and students rather than that selected by an author of a comprehensive excursion guide. Each fact sheet is a separate publication and users need only purchase those sheets which they consider relevant. A teacher can photocopy the required number of each selected fact sheet (and district location map if desired) for the class. This format allows the users to compile their own sequence, add material and develop particular emphases - equally successful for biology, geography and environmental studies. Examples of geological and biological fact sheets will be shown, together with an example of a tailor-made excursion guide using these techniques.

345 Reference

Excursion Guide to South Australia. South Australian College of Advanced Education, Adelaide.

Shackleton, W.G. & Binnie, M.N., 1990, Geological

A 17.9 TERTIARY GEOLOGIC EDUCATIONA COMMENT ON TWO APPROACHES TWO SYSTEMS D.A. Gust School of Geology Queensland University of Technology, Brisbane, Queensland. Approaches to geologic education in tertiary institutions are many and reflect the goals of the institution as well as the participants in the program. Amongst this diversity it is possible to identify two end member approaches - neither of which is ever attained in its pure form. Although these approaches may employ similar teaching methods, lectures, practical work, and field studies, their ultimate goals are quite different. This paper explores some of the differences between these approaches and is unabashedly a comment derived from personal experience and not rigourous scientific analysis. One approach to geologic education seeks to produce "professional geologist" at the end of a three to four year period of study immediately ready to take their place in industry whereas the other approach integrates the study of geology into a broader context of human knowledge. The "professional" versus the "humanistic/liberal arts" approaches are best developed in public institutions of technology and private liberal arts universities, respectively. In the first case, students enrol believing that their study will lead directly to employment as a professional in an area specifically related to their study. They question the value of knowledge that isn't perceived to be relevant to their employability. A 17.10

Course development is sensitive to this issue with the development of specialised "service subjects" and rigid formalised programs of study. Freedom of choice and the chance to explore other subjects/disciplines are limited. This perception that education and employability are linked is heightened as institutions complete and attempt to rank their performance. A "humanistic/liberal arts" approach promises no definite professional employment regard but encourages the development of a well-rounded nonspecialist capable of pursuing many careers. Students are not "fast-tracked" into a career but are given the opportunity to sample some of the breadth of human knowledge, ideas and opinions. Specialisation is developed at the graduate/post graduate level or within industry. The relevance and value of this approach is often questioned by industry but is important in a broader societal context This paper examines these approaches using examples of geologic education from Australia and American tertiary institutions. Its intent is to comment on their underlying philosophies, their mechanisms, and their ultimate result. Its purpose is not to decide which is the better approach; this task is better left for debate in the public forum

EARTH SCIENCE AND THE PRINTED MEDIA Dawn Hendrick

USQ Press, University College of Southern Queensland, Toowoomba Many authors have acknowledged that the declining interested them sufficiently in the past. The aim of numbers of students entering Tertiary Geology this paper is to give an appraisal of the information departments is due to a lack of Earth Science education available to teachers of Earth Science at any level, in secondary schools. Studies by Stutchbury and through the printed media. Requests were made to 30 Australian Carter have shown that Secondary School Science Teachers under training do not have to be qualified in organisations, listed in "Australian Books in Print" as Geology even though they may be required to teach it. having some connection with Earth Science, for them Once appointed to a teaching position it is unlikely to provide a copy of their regular newsletter/factsheet that they would want to expend vast amounts of time or equivalent which could be used as a reference for a and energy learning about a subject which has not paper to be presented at this gathering. A similar Geological Society of Australia Abstracts Number 32, Ballarat 1992

346 request was made to 18 overseas organisations to which 6 have replied to date. The response overall was encouraging and illuminating. The price of Geological Textbooks is like that for other subjects, on a never-ending spiral upwards. The majority of texts are written overseas and therefore subject to sales tax and exorbitant freight charges. The notable exceptions are "Perspectives of the Earth" published by ANU Press at $39.95 and "Earth Science: The Study of Geology and Astronomy" by Philip Harlow, an Earth Science Teacher at Ipswich Grammar School which retails for $14.00. The alternatives to textbooks are journals, fact sheets or articles in professional magazines. The majority of journals are published by learned societies specialising in one aspect of the Earth Sciences, for example the New Zealand Journal of Geology and Geophysics. Two societies with grave concerns about the future of Earth Science at secondary and tertiary levels of education are the Geological Society of Australia (GSA) and the Australasian Institute of Mining and Metallurgy (AusIMM), both of whom produce publications which are suitable for teachers wishing to increase their knowledge base. The "Rocks and Landscapes" Series compiled by members of the Queensland Division of the GSA introduces the geology of certain areas of Queensland in easy-to-understand language accompanied by simple maps and figures. Available from the Department of Resource Industries in Brisbane, these guides range in price from $4 to $6. The GSA Newsletter "The Australian Geologist" published quarterly includes a variety of articles dealing with topical issues. The reviews section at the back of each issue provides a valuable insight to new publications as they become available. The Monograph Series published by the AusIMM includes some very specialised works, however two recent publications would make extremely valuable contributions to any school library. Monographs 14 and 17 both discuss various geological aspects of the economic deposits in Australasia although their respective prices may be somewhat prohibitive. Information sheets are available from a number of sources covering a wide variety of topics. The Department of Mineral Resources in New South Wales provided examples which described the three

Geological Society of Australia Abstracts Number 32, Ballarat 1992

main rock divisions and a longer one on prospecting equipment. The Australian Mining Council produces "Mineral Facts" Sheets which give excellent accounts of the different mineral commodities extracted throughout Australia. The Earth Exchange which incorporates the Minerals and Energy Information Centre in New South Wales provided a series of handouts which included articles on Earthquakes, Who Discovered Gold and The Story of Fossil Fuels. They also produce a magazine called "ITAM" (Introduction to Australia's Minerals) which is distributed at no cost through sponsorship from the various companies featured in the magazine. ITAM 3 published in June 1990 featured Gold. A similar sponsorship scheme results in the publication of "GeoNews" by the E. de C. Clarke Geological Museum at the University of Western Australia. Two excellent publications from overseas are "Arizona Geology" (which replaced "Fieldnotes" in July 1988) produced by the Arizona Geological Survey. This is a quarterly newsletter and research publication featuring some excellent articles on introductory geological concepts. At US$5.00 per year the surface mail subscription rate is most reasonable. A little more expensive and specialised in its approach is "Episodes" the quarterly journal of the International Union of Geological Sciences at US$24.00 per year (airmail). A large number of other specialised groups produce newsletters but these rarely contain information at an introductory level for teaching purposes. Finally there are articles in scientific magazines which in the case of "Nature" and "Scientific American" tend to be rather too specialised for general use in schools. "Australasian Science Mag" published quarterly by the USQ Press in Toowoomba is a magazine designed for students of Years 11 and 12, which has over a number of years featured articles on several different aspects of Earth Science. Recent articles include the Somersby Fossil Dig, Mt Leyshon Gold Deposit, Weipa Bauxite Deposit, Land Degradation - A Geological Perspective. References Stutchbury, R.J. & Carter, R.M. 1990 A Review of the Position of Geology in the K-12 Curricula of the Australian States. GSA, Sydney.

347 A 17.11 AUSTRALIAN MINING INDUSTRY COUNCIL-SPONSORED PRACTICAL GEOSCIENCE SHORT-COURSES FOR PRIMARY AND SECONDARY TEACHERS (IN THE ACT) Phil Smart and Dianne Stuart 1

2

^Head of Department of Geology and Gemmology, ACT Institute ofTAFE 2Education Consultant, Australian Mining Industry Council Since 1990 the Australian Mining Industry Council (AMIC) has arranged funding for the ACT Institute of TAFE to conduct two short practical geoscience courses for local primary and secondary teachers each year. The curriculum outlines were formulated in consultation with AMIC's resident education consultant and the ACT Education Department's Science Consultants in the Curriculum Unit. It was agreed to limit the class size for each course to 15 so that a "hands-on" practical approach could be adopted. At their first class, both primary and secondary teacher groups are given an opportunity to influence the scope of their respective courses. They are asked to select preferred topics from a given listing of possibilities. The AMIC funding includes a visit to an underground mining operation in both courses Woodlawn for the primary teachers and the CSA, The Peak and/or Elura mines in Cobar for the secondary teachers. Science backgrounds of the primary teachers range from minimal high school biology and/or chemistry (many years ago) to more recent strong backgrounds at the tertiary level. The Secondary teachers are mostly science specialists required to teach geology as part of multi-strand science courses to Yr 10 level. Some teach Earth Science courses to Yr 12 level. The group can include geography, economics and language teachers who feel that geoscience and mining could be effective vehicles for covering certain aspects of their respective curricula. Only a very small number of the teachers have previously studied geology at a tertiary level. These short courses, which comprise 8 weekly two-hour sessions followed by a weekend mine visit,

Geological Society of Australia Abstracts Number 32, Ballarat 1992

are conducted out of school hours and the major reasons given for enrolling in the program are:* genuine interest in geology or earth science * lack of confidence/limited ability to teach practical geoscience at primary or secondary level * interest in learning more about local geology Some primary teachers have expressed a more general concern that insufficient emphasis is placed upon appropriate practical science education in initial and in-service training. In the ACT 5 out of 17 senior colleges and private schools offer courses in geology and some of these teachers with Earth Science degrees have done the course to increase their familiarity with the geology of the local region. The classes have such a positive outcome that AMIC will continue funding of the program. It is anticipated that the ACT Education Ministry will grant formal recognition to successful participants. Teachers are very appreciative of quality and instantly usable in-service courses and recognition of such courses is long overdue. Another positive outcome is that the ACT Education Department has called upon the ACT Institute of TAFE to conduct one-day in-service "Geoscience Activity Workshops" for both primary and secondary teachers, as part of its professional development program for teachers in the ACT. As a result of this AMIC initiative geoscience is being taught more practically and enthusiastically in a greater number of schools in the ACT region. Greater use is also being made of geoscience as a vehicle for teaching other aspects of school curricula.

348 A 17.12

GEOLACT: A GEOSCIENCE EDUCATION LIAISON NETWORK IN THE A.C.T.

D.J. Perkin , K.G. McQueen *, W. Mayer and TJ. Munson 1

2

2

3

1Bureau of Mineral Resources Geology and Geophysics, Canberra, A.C.T. 2University of Canberra, Belconnen, A.C.T. Australian National University, Canberra, A.C.T. collect their own rock and mineral sets for class GEOLACT (Geoscience Education Organisations use. Liaison of the ACT) is an organisation set up in A field trip for teachers to the Woodlawn mine. May 1990 on the initiative of some members of the Preparation of guides to geological sites, written Education Subcommittee of the A.C.T. Branch of the for teachers and students, as well as Geological Society of Australia. The group consists compilation of a consolidated bibliography of of about 12 scientists and educators working to all available geological excursion guides for the establish links between professional geoscientists region. and educational organisations in the A.C.T. with the Short talks and presentations to schools by aim of providing a network of support, particularly members of the group. for science teachers attempting to teach geology in Judging of the Geoscience and Environmental schools and secondary colleges. section of the A.C.T. Schools Science Fair Canberra is well endowed with geoscience and presentation of awards. organisations, including the BMR, CSIRO, three GEOLACT meets formally about three times a geology departments in two universities, a TAFEbased geoscience group, AMIC, a branch of the year to plan activities. A short newsletter and list of Geological Society of Australia, a branch of the contact names, addresses and phone numbers is Australasian Institute of Mining and Metallurgy and periodically circulated. Our activities are also offices of several major mining companies. advertised in the A.C.T. Science Teachers' Surprisingly, little of this geoscience expertise has Newsletter. Through the group's efforts an filtered down to Canberra schools, and only six of expanding network of contacts is developing the 19 government and private colleges currently offer between interested geoscience professionals and a Geology or Earth Science course to Years 11 and school teachers at the primary, secondary and college 12. GEOLACT is helping to address this problem levels. More work needs to be done however. by providing contacts, assistance, advice and The establishment of this liaison network is resources to assist teachers in presenting geology as showing promising signs of success, although its effectiveness is clearly proportional to the amount a vital and relevant science subject. of effort put in by the geoscience profession. Perhaps Activities to date have included: A field trip for teachers around the A.C.T. to GEOLACT could provide a model for the setting up demonstrate suitable sites for class excursions of similar networks between geoscientists and school and to indicate areas where teachers could teachers in other regions. 3

Geological Society of Australia Abstracts Number 32, Ballarat 1992

349 A 17.13

HOW TO BUILD A SECONDARY EARTH SCIENCE DEPARTMENT. Phillip G L Harlow Ipswich Grammar School, Ipswich

This paper gives a few suggestions to the Donation was as good as winning the lottery. The Queensland Times. p2, 30 July 1988. Secondary Science teacher who is thinking about establishing an Upper Secondary Earth Science Greenhouse Education Grant. Ipswich Grammar School Environmental Group. 1990. Department These include: Harlow., P.G.. Designing Successful Earth Science Excursions. The Queensland Science Teacher, a) How to convince the Principal that he/she June 1991, Vol 17, No 2. needs an Earth Science Department. I., Personal Communication. 1990. b) How to raise money to establish and maintain Lapa, Scamp, K.. Science in the Primary Share and Grow the Department. Program (Lismore Schools). The Queensland c) Places to go to obtain materials and equipment. Science Teacher, November 1990, Vol 16, No 4. d) Places to go and people to see to obtain Science Pupils Strike,it Lucky. The Queensland expertise in Earth Science. Times. pi, 19th April 1989. e) What to write to obtain a successful syllabus. Scott, W., Kenmore State High School Newsletters. 1990. f) What are the potential rewards in establishing a UMIAC Seminars (Annual). Queensland Mining new Department. Industry Council. References Dobos., S.K., Supply of Penological Microscopes. University of Queensland. 1989. A 17.14

EARTH SCIENCE IN PRIMARY SCHOOLS Wolf Maya* University of Canberra

Children of primary school age have an enormous curiosity about the physical landscape that surrounds them and about earth materials and processes. During short visits to primary schools over many years it has become apparent that young children are fascinated by minerals and rocks and have a keen interest in the significance and origin of landforms, particularly in their local areas. The children were particularly attracted by the variety and the different properties of minerals. They enjoyed handling these and making, what were for them, surprising discoveries. Of greatest interest were the variety of colours; that some minerals were soft enough to cut and others hard; that many could be split into ever thinner sheets; that some were transparent enough to see through, like windows; that some could be used like crayons to draw pictures in different colours; and that one of them could even be tasted and eaten. Their interest in the landscape of their local area prompted many questions about the formation of hills, Geological Society of Australia Abstracts Number 32, Ballarat 1992

about volcanoes and earthquakes, about rivers and floods and about finding and mining precious stones and other minerals. They were particularly pleased in having rocks and minerals identified, which they had themselves collected, and were very interested in finding out how these had formed. As few primary schools have adequate resources to introduce children to earth science, many of them learn little about it at a time when they appear to be most curious to learn. A visit by a local geologist to a school may, for many of them, be the only opportunity to find out a little about how the earth works and what it is made of. This paper presents some approaches to introducing aspects of earth science to primary school children. It also encourages geologists to offer shorts visits to their local primary school. The Education Committees in the various States could play an important role in a scheme organising such school visits.

350 A 17.15

A BRIEF LOOK AT SOME GEOLOGICAL SOFTWARE FOR SCHOOLS Darold E Klindworth Yarra Valley Anglican School, Ringwood, Victoria

Computers have not in my experience yet realised their potential in many classrooms. This is partly due to lack of access to computers and the lack of programs that fit comfortably into teaching programs. This paper looks briefly at some of the possibilities that exist. The first programs I met were simple ones designed as an aid to the identification of rocks or mineral samples. Some of the students were even able to write such programs. Then Prologic published 'Geological History* and 'Geologists at Work' in the mid-80's. These programs dealt with geological cross sections. The student was able to build up a section layer by layer. They could choose the rock type, the time span it was to represent and/or tilt or fold beds. They could also choose to interpret the events required to produce a sequence generated by the program. Print outs are available of the sections studied. 'Geologists at Work' was a better buy. It involved some economic geology by introducing coal seams. Its biggest advantage was it's ability to print out two cross sections at 90 degrees to each other and the map to go with the sections. This provided a three dimensional view of the work. In my opinion this is a useful program and it is available in both Apple and IBM formats. 'Mining Your Business - Strike It Rich' is a mining simulation program. It requires students to carry out an exploration program with a budget. The debt is not to go over $600 million. Once a suitable deposit is found then more money is required to run the mine. Machinery is purchased and machinery breaks down. The price of Aluminium varies as the simulation proceeds. The task is to make a profit (surprise!) in ten years. It can be surprising difficult to survive for the ten years! 'Volcanoes' is an American production that simulates the monitoring of volcanoes in a region. It is designed for two or more players who are each given a section of country to study and a budget to work to.

Geological Society of Australia Abstracts Number 32, BaUarat 1992

The researchers are able to use a variety of methods to study their areas. Some of the tools are infared surveys, tilt meter surveys, gas emission analysis and historical records of eruptions. If an eruption is considered possible then each player is able to adjust the warning levels for the concerned areas. If eruptions are correctly predicted players ratings improve and so do their budgets. If finances do become a problem then there is always the trip to the casino to top up a bit. How many real life scientists would like such a chance. There are a lot of skills required in this program. Sadly, today it seems very slow when compared with the new generation of programs which have the advantage of much larger memories to work with. One must not over look the Sim series of programs. 'SimEarth' is a complex program requiring a Mac or IBM equivalent to operate. It models the Earth or other planets along the GAIA Theory. It enables one to tinker with components of the atmosphere,the biosphere and the geosphere. You can even try to Terraform Mars or Venus. Green house modelling is quick and harmless to the experimenter. The geological events are massive. The volcanic eruptions that you can place where and when you like make the Mt. Pinatubo eruption look like a grade two project. Meteors can strike and earthquakes can rift land masses or build mountain ranges. I find it an interesting 'software toy' that looks at Earth Science as a whole. Its very popular relation "SimCity' allows the player to manage a city from the ground up. For our purposes it is interesting because you can try to manage San Fransisco or Tokyo through an earthquake. Science and society come together in a game that is interesting to many students. There is certainly scope for comprehensive programs that involve students in an active way. The level of sophistication that programs like the Sim programs indicates to me at least that the medium still has a lot of potential as a learning tool.

351 A 17.16

VOCATIONAL AND TECHNICAL EDUCATION IN GEOSCIENCE WITH EMPHASIS ON GEOPHYSICAL EXPLORATION James A. Madonna Mining Extension, University of Alaska Fairbanks Fairbanks, Alaska, USA

Universities and colleges in three countries Australia, Canada and the United States, recognized the need to establish and reorganize geoscience programs at the vocational and two-year technical levels. To accomplish this goal, a cooperative study with industry in one state or province from each country was initiated. These include 1) Tasmania, Australia, 2) British Columbia, Canada and 3) Alaska, United States. Over one hundred mineral exploration companies and private consultants cooperated in the study by providing information regarding their specific

training needs for support personnel, the data gathered has been used to identify training areas for semiskilled, skilled and technical personnel in geophysics, including, but not limited to, geological skills, geophysical skills, surveying skills, environmental skills, and computer skills. With areas of major educational need defined for geophysical exploration, educational models have been developed for the three levels of training. The depth of each level of education and the training objectives for the work force at each level will be discussed.

A 17.17 THE PACSCHOOL INFOLINE - ELECTRONIC MAIL BULLETIN BOARD SERVICES PROVIDING GEOLOGICAL EDUCATION RESOURCES M.P. Thornton Geological Survey of Queensland.

The PACSCHOOL INFOLINE project was an education initiative of the PACIFIC RIM 90 Congress of the Australasian Institute of Mining and Metallurgy. PACSCHOOL INFOLINE used a special area of Telecom's Keylink electronic mail and bulletin board service administered by the Queensland Department of Education. PACSCHOOL INFOLINE was designed to bring the "real" world of geoscience into the classroom using electronic media technology. The system allowed Queensland schools to interact with current geoscientific information and visiting international experts whilst performing structured projects relevant to their curriculum. The schools were able to dial in and scan various Earth Science projects specially prepared by science lecturers from Queensland University of Technology, Kelvin Grove Campus, and mail enquiries for further information back to the system. The projects were designed to provide incentive for participants to develop research skills, improve their knowledge and contribute to discussions with a strong emphasis on solving problems. A trial of the system, involving several schools using a project on Earthquakes, was run in OctoberNovember 1989. Modifications were made for the main project, run in April- June 1990, using three topics: Sea Level Changes, Volcanoes, and The Impact of Mining. A menu driven system was provided for easier access by the schools. Each of the three project boards contained general project

Geological Society of Australia Abstracts Number 32, Ballarat 1992

information and a number of other files containing details of project activities, other resources and sources of information. A mailbox was attached to each topic for questions to be forwarded to the administrator. Mailboxes were monitored and questions were forwarded to specialist geoscientists for responses. The responses were returned to the school mailboxes of the enquirers and copies of both questions and answers were posted on the relevant project boards for other participants to see. The contents of all boards and mailboxes are retained by the author in both digital and hardcopy form. Grenfell (1990) reported the PACSCHOOL activities to science teachers at CONASTA90 (Conference of the Australian Science Teachers Association) and CONSTAQ90 (Conference of the Science Teachers Association of Queensland) providing operation details of PACSCHOOL INFOLINE and a summary of the educational tasks and the benefits of such a system to educators. He also produced a simulation program on disk for demonstration purposes. At least nine schools accessed the system and another six expressed interest in using the system. The Geological Society of Australia, Queensland Division, offered to assess any projects based on PACSCHOOL INFOLINE which were sent in before the end of June 1990 and to award prizes. One project was received from Albany Creek State High School. In July 1990, a meeting was called by the

352 administrator of PACSCHOOL INFOLINE to which representatives of industry, academia, government, and secondary educators, were invited as potential contributors to a permanent "Infoline". This meeting discussed feedback from PACSCHOOL INFOLINE; the potential for a permanent service; the demand or need for such a service; the costs of running a permanent system of boards and mailboxes; and what could be done to promote the service. The following resolutions were endorsed: 1. That PACSCHOOL INFOLINE should be maintained beyond July 1990 to allow promotion, further feedback and a study of the feasibility of establishing a permanent service. 2. That such a permanent service be called GEOINFOLINE. 3. That the Geological Society of Australia, Queensland Division be approached to fund the temporary continuation of PACSCHOOL INFOLINE and, subject to such funding being approved, that they appoint a chairperson to form a committee of interested parties to perform the tasks mentioned in point 1 above. The PACSCHOOL INFOLINE system was maintained from July to October 1990 by the Society for further promotion and demonstration. By the end of the trial period, a number of conclusions had been made regarding the questions asked at the July 1990 meeting: 1. There is a lack of knowledge amongst teachers of the Keylink system: - some do not know it is available. - some do not know where their facility is.

- most do not know how to use it. 2. The market is limited if only Earth Science is catered for - the PACSCHOOL INFOLINE projects were designed to include Geography students and some Economics students as well as being topical and interesting enough to appeal to most students. 3. The total cost of running the computer facilities for the period was reasonable but a more efficient approach would need to be taken in any future venture of this type. Boards should not be limited to projects only but should include topical information, bulletins from bodies providing geoscience activities and current geological news items which would be of interest to students. A number of boards would be provided by a central administration with only one mailbox. Each board would be funded by its provider or sponsors and their mail would be collated and forwarded by the administrator who would also place new material on the boards at regular intervals. Considering these factors it was decided not to continue the project but to monitor developments in the use of the Keylink service with a view to initiating a permanent GEOINFOLINE service at some future time. References Grenfell, Dr A., Simpson, A., Broadfoot, J., & Tulip, D., 1990, Australasian Science Magazine 4:54-57.

POSTER SESSION A 17,18

THE ROLE OF GEOLOGICAL EDUCATION IN CONSERVATION I. F. Clarkl*and P. R. James 2 ^Department of Geology ..University of South Australia Department of Geology and Geophysics, University of Adelaide

2

In Australia Earth Science education is not commonly part of the school curriculum. Consequently the majority of the population is unaware of the geological significance of many of the features which are central attractions in our National Parks. This ignorance has resulted in degradation and sometimes destruction of important outcrops. One example is the complete removal of the Ediacaran Fauna fossil assemblage from Brachina Gorge in South Australia. Geological Society of Australia Abstracts Number 32, Ballarat 1992

Education of the public will overcome such problems but to be successful education must include both formal and informal modes. It must also involve input from the geological community. One such mode is the development of geological interpretive materials for sites of significance which are part of popular tourist itineraries. Geologists and geological organisations must work with National Park authorities and tourist organisations to coordinate the development of such materials.

353 A 17.19

WHEN AND WHY DO STUDENTS BECOME INTERESTED IN GEOLOGY Phillip G L Harlow Ipswich Grammar School, Ipswich

This paper interprets the results of a survey of Primary and Secondary school children undertaken in Queensland. The survey took the form of a questionnaire with 12 multiple choice questions and eight questions where students had to rank their opinion on a scale of 1 to 10. The survey included the total populations of six primary and five secondary schools randomly selected from city, town, and country areas. The survey was designed to test the basic knowledge of, attitudes to, and interest of, school children to geology. In addition it gives an indication of the age when children first start forming opinions about geology and geologists. The results give an overview of attitudes among children to geology and geologists and has significant implications for the teaching of geology in Schools and for the recruitment of students to the geosciences at Secondary and Tertiary levels.

Australian Geologist, Newsletter 64, p 5. Emerson, D. W., 1990 Address to Australian Institute of Geoscientists. Enrollments Statistics. Board of Secondary School Studies. Queensland. 1988- 1991. Ewart, A. 1990 Personal Communication. Hamilton, L. 1987 Letter to the Editor. The Australian Geologist, Newsletter 62, p 8. Key to Course Codes and TE Cut-off. 1990 Courier Mail. Newspaper. Meeting Australia's Skill Needs. 1987 Australian Government Publishing Service, Canberra. Student Information Guide 1991. Universities Admissions Center (NSW & ACT). Lidcombe. Stutchbury, R., 1990 Submission to the Education Minister, Queensland. July,. Sydney Tertiary Geology Department Chairmen. 1990 Letter to the Prime Minister. Viviani, N., 1990 The Review of Tertiary Entrance in Queensland.. Worden, J., 1990 Test out. University of the South Queensland..

References Adamson, C. Letter to the Editor. 1987 The

A 17,20 COMPUTER ANIMATION AND MULTIMEDIA PRESENTATION SOFTWARE AS AN AID TO LECTURES AND WORKSHOPS IN TERTIARY AND FURTHER GEOLOGICAL EDUCATION PR James & I Clarke 1

2

Department of Geology and Geophysics, University of Adelaide 2Department of Geology, Salisbury Campus, University of South Australia 1

An inexpensive and "off the shelf microcomputer and direct presentation (video/datashow) hardware system has been used to develop and display lectures, tutorials, seminars and workshops in structural geology at undergraduate University level. Using the presentation software "Powerpoint" (© Microsoft Corp.), a series of topics covering the broad range of introductory structure and deformation concepts (stress, strain, folds, fractures, fabrics etc) is available and currently in use. The hardware and software system has a number of advantages making it a useful (though not exclusive) adjunct to standard lecturing techniques. These advantages include, very simple updating of lectures and slide manipulation, clear and professional visual presentations, readily available handout material and finally availability and rapid review of the lecture Geological Society of Australia Abstracts Number 32, Ballarat 1992

material by the audience via floppy disc. The software is also ideal for the demonstration and display of the geometric and kinematic principles of geological structures. Real-time manipulation of simple figures allows the illusion of unsophisticated motion eg. development of progressive strain or displacement on fractures. More sophisticated three dimensional geometries such as rotational faults and superposed folds and fabrics may be produced as graphic images and imported to the presentations. Further advancements of the system under development include, the importation of scanned images including maps, figures, diagrams, graphs and ultimately colour slides. A new software aquisition to the system (Macromind Director, © Macromind Inc.) also is aiding the development of fully animated scientific multimedia presentations.

354 A 17,21 EVIDENCE FOR SEA LEVEL RISE AT POINT LONSDALE 1988-1991 N.W. Schleiger 1 Astley Street, Montmorency , 3094 Monitoring of the heights on the sea wall at Point,Lonsdale of the Blue-banded Periwinkle, Nodilittorina unifasciata, and the filamental green alga, Enteromorpha intestinalis, together with the sand demonstrates that the sea level has been rising gradually over the 28 months* period. (Alternatively the Point Lonsdale area could be slowly subsiding). Nodilittorina is an air breather and has to be regularly splashed by sea water to remain in its position. Its profile persistently rising trends in its maximum and minimum heights on the wall over the period., Enteromorpha rises on the sea wall each spring and

has successively shown higher maxima each year. A rising sea level could also account for the continual depletion of beach sand which occurs in response to seasonal winds and the tidal cycle. However, today the beach sand is slower to regenerate because of the protection of the sea wall. Activities described herein require constant measurement and a graphical analysis in relation to wind direction and tide height. Such activities could be good for student projects whether individual or as a group.

A 17.22 THE E. DE C. CLARKE GEOLOGICAL MUSEUM AN EDUCATIONAL RESOURCE FOR THE WHOLE COMMUNITY Georgina M.I. Rockett E. de C. Clarke Geological Museum, Department of Geology, The University of Western Australia, Nedlands 6009 The common perception of a university geological museum would probably be a dusty room with cabinets and drawers full of research specimens - a service to the research efforts of the department, not a place to visit and enjoy if you had no geological knowledge. The redesigned E de C Clarke Geological Museum at The University of Western Australia maintains a large research collection, but is also targeted at the community as a whole, particularly high school students. The Museum was officially reopened on 25th August 1989 after two years of fund raising and renovations. Importantly, the new museum is more than just a room full of static displays as it has developed activities and worksheets that focus on aspects of geology for use by visiting groups. The Museum is using its resources to teach geology to the community as a whole. The Geology Department recognized the need for a museum with a strong educational bias because few schools in Western Australia teach geology as a formal subject, and as a consequence most first-year university students are unaware of the potential of the science before commencing their degree. The Museum reaches the general public and school students through its displays and through on-going projects. Geological Society of Australia Abstracts Number 32, Ballarat 1992

1) The displays. These are targeted primarily at the general public and high school science students. However, the scientific information can be enjoyed by a wide cross-section of the community, from primary school students to geologists. The text of the exhibits was written in conjunction with a Senior Science Teacher and the Science Education Consultant from the Curriculum Department at the Ministry of Education, and the displays have been designed to relate to both geology units and other science units taught at high school. The E de C Clarke Geological Museum is not only a geological museum; it is a science museum. The bright and easily read displays include; • Plate tectonics The history of the atmosphere Colour in minerals/gemstones The crystal systems Properties of minerals • The story of diamonds The story of gold Economic resources of Western Australia A marine aquarium: today's sea creatures are tomorrow's fossils Fossils: the remains of ancient life

355 Was Gingin under a sea 100 m deep? A world-wide catastrophe 66.5 million years ago The tower of time. 2) Activities and worksheets. A visiting school group may undertake a number of activities based around sets of minerals, rocks, and fossils from the Museum collection. As with the displays, these activities have been designed to relate to both high school geology units and to geology-related objectives within other science units. Teachers' notes and student worksheets are provided for these visits. The Museum Staff are constantly developing new activities to accommodate the requirements of teachers, and are encouraging teachers to design their own workshops using the Museum's resources. Activities provided for upper primary students include: • Reassembling the world - a felt map of the world is used to show the movement of continents over time. • Construct-a-saur - a group prepares a small presentation about a chosen dinosaur, such as where it lived, what it ate, what it looked like, size, weight etc. • Mineral house - using a cut-away picture of a modern house, the children identify everyday objects which have been produced from industrial minerals. For high school students: • Year 8 Sedimentation and sedimentary rocks - after observing a suspension settle, the students relate types of sedimentary rock to position within a river profile. • Year 9 Earthquakes and Volcanoes match volcanic rocks and earthquakes to plate margins using a map of the world. A set of volcanic rocks is provided. • Year 10 Mineral separation techniques - separate a mineral sand into four fractions using a Frantz Magnetic Separator. For senior high school students, the activities are designed around objectives within TEE subjects: • Biology The present is the key to the past - by studying a fossiliferous limestone and using physical characteristics of the fossil animals and plants, the students reconstruct the environment of deposition. Chemistry Mineral identification using physical properties, identify Geological Society of Australia Abstracts Number 32, Ballarat 1992

minerals, and relate the properties to the composition and atomic structure. Physics Polarising microscopelight and its use in studying thin sections of rocks. Although developed principally for education of school students, many of these activities have been enjoyed by a range of visitors including naturalist clubs, senior citizens, and groups of disabled. 3) Travelling displays. The Museum has a number of portable displays designed to travel to venues outside the Museum. Titles include: The present as the key to the geological past. Geology: A Multidisciplinary and Environmental Science. Pictures and Patterns in Geology. Landsat: Information from the sky. 'Geology: A Multidisciplinary and Environmental Science' was produced in May 1990 and has since travelled to the main foyer of the Ministry of Education Building, a geological symposium at U.W.A., two country libraries, ten metropolitan libraries and to CONSTAWA (Conference of the Science Teachers Association of Western Australia). 'Landsat: Information from the sky' was set up as a display in the International Mining Centre at Digital Corporation in West Perth which is a venue for information exchange amongst members of the mining industry. 4) Display of student work. The Museum has an on-going offer to schools to display class projects in the foyer area. A show-case and display boards are supplied, and students can supplement their project material using the museum collection. One such student project was awarded a prize in the 1987 R&I Bank Awards for Museum Education. 5) Supply of resources to teachers. The Museum has a supply of a wide variety of rocks, minerals and fossils for donation to schools. Donors to the collection include GSA members, mining companies, rock collectors and gem suppliers. Over 25 schools in Western Australia have requested and received sets of specimens for class sets since they became available late in 1990. This considerable response to our offer indicates that it is often a lack of resources rather than enthusiasm that inhibits the teaching of geoscience units in the schools. In addition, through the generosity of organisations involved with the mining and exploration industry, the Museum has collected a large library of information booklets and pamphlets which can be donated to schools or made available to students when they visit the Museum. The Museum keeps teachers in touch with its developments, and with the resources that are available

356 to them from the Museum through its twice-yearly publication "GeoNews". 6) Educating teachers. There is plenty of scope within the WA school curriculum through which to teach geoscience principles, however teachers do not appear to be making the best use of these opportunities, mainly because most teachers have little knowledge of the subject, and little confidence to teach it. A professional development course is currently being designed to inform science teachers of the facilities available from the Museum. In May 1991, the Museum presented two workshops at CONSTAWA, which showed fun and interesting ways to teach geoscience concepts in the classroom. The workshops were entitled Touch the Earth - Geology in Science' and 'So You Don't Teach Geology?'. The Museum Staff also encourage the teacher-training lecturers from the different institutions to bring their students to the Museum as part of their course. 7) Links with other organisation involved with geology education. There are a number of groups within WA interested in promoting geoscience education. The Curator has been involved in the development of curriculum material with the Vocation and Education Sub-committee of the Geological Society of Australia (W.A. Branch). Through this, a comprehensive package of resource material for the year 9 'Geology' unit was produced along with resource material to assist in the teaching of the year 8 unit 'Forces in Nature' and the year 10 unit 'Mining, Chemistry and Industry'. The Museum is a member of the Geoscience Education Liaison Committee, which is a lobby group interested in promoting geoscience education in Western Australia. 8) Links with the community. After reopening, the Museum received requests from members of the general public who wished to become involved in its running and promotion. The Friends of the Museum was formed to provide support to the Museum through

Geological Society of Australia Abstracts Number 32, Ballarat 1992

a variety of activities. The group currently supports the Museum by: Staffing the Museum on Sundays. Collecting, sorting, bagging and labelling specimens for donation to schools. It also runs regular activities for the benefit of the Members, including: A fossil hunt, and other geological excursions. A Geo-car Rally. A family barbeque and beachcombing day to learn about the foreshore environment. A priority in the future development of the Museum is regarded to be the designing of effective exercises tailored to cover as wide a range of school units as possible to further the teaching of geology at all levels in the school curriculum. To achieve this effectively, we intend to employ an experienced science teacher to work with the Curator in developing activities, work-sheets and additional information, as well as running professional development courses for teachers to encourage them to teach earth science related objectives. Through this, it is intended to develop a situation where the teachers will bring their class and do the teaching themselves, the Curator will then only be required as a facilitator. A measure of the success to date of the education programme must be the constantly increasing number of school groups using the Museum. In 1991, the Museum will have received almost thirteen-hundred students in organised school groups, and over fivehundred people in other community groups. Geology is the study of our planet Earth and the E. de C. Clarke Geological Museum is a science museum which aims to introduce the wonders of the Earth to as many students and members of the public as possible.

357

A18: ECONOMIC GEOLOGY- CORPORATE CONVENOR: A 18.1

ROSS FARDON

CORONATION HILL - CASE STUDY AND IMPLICATIONS FOR OTHER PROJECT DEVELOPMENTS C E Palethorpe, D P Carville, J F Leckie, C F Moorhead and J G Rayner Newcrest Mining Limited

The Coronation Hill gold-palladium prospect is located in the valley of the South Alligator River (latitude 13°35*S, longitude 132°36'E), about 80 kilometres east of Pine Creek in the Northern Territory. Coronation Hill was one of thirteen sites in the South Alligator Valley at which uranium was mined between 1955 and 1964 after initial discovery by the Bureau of Mineral Resources in 1953. Most of the mines were operated by United Uranium No Liability. The Sleisbeck mine 25 kilometres south of Coronation Hill was operated by North Australian Uranium Corporation and the group of mines at Rockhole about 20 kilometres to the north-west of Coronation Hill was operated by South Alligator Uranium No Liability. The uranium mine at Coronation Hill produced about 26,000 tonnes of ore averaging 2.6kg/t U3O3 with an estimated average gold grade of 10.4 g/t gold. Gold was commonly associated with the uranium mineralisation and was recovered at the gravity treatment plant at El Sherana. Gold was also recorded in 1986 by Pacific Gold Mines Limited by treating the tailings from the Moline and Rockhole uranium leach plants at a CIP plant at Moline. With the completion of uranium contracts in 1964 mining in the South Alligator Valley ceased.

Geological Society of Australia Abstracts Number 32, Ballarat 1992

Exploration for uranium continued in the area during the 1960s and 1970s with no success. The Coronation Hill Joint Venture (BHP Gold Mines Limited 45 percent, Pioneer Minerals (Gold) Pty. Ltd. 45 percent, Norgold Limited 10 percent) carried out the first exploration specifically targetted at gold in 1984 with the drilling of five vertical drill holes which indicated high potential for a substantial gold resource at Coronation Hill with no associated uranium. The Joint venture has subsequently drilled about 25,000 metres of diamond drill holes at Coronation Hill alone. Analytical results from 1985 drilling established that platinum and palladium were associated with gold. An indicated resource of 3.49 Mt at 5.12 g/t Au, 0.21 g/t Pt and 0.56 g/t Pd has been calculated using a 1 g/t Au cut off. The Coronation Hill prospect and other abandoned uranium mines in the South Alligator Valley are within the 47.5 square kilometre Kakadu Conservation Zone which is surrounded by Stage III of Kakadu National Park. In October 1989 the Australian Government decided to refer the proposed mining project to the Resource Assessment Commission to reassess environmental impacts of he project. The enquiry reported to goverment early in 1991. The enquiry outcome, and the implications of this inquiry will be addressed by this paper.

358 A 18.2

THE ROLE OF GOVERNMENT GEOLOGICAL ORGANIZATIONS IN RELATION TO THE MINERAL EXPLORATION INDUSTRY J N Cramsie Director, Geological Survey of New South Wales

Government geological organizations have number of very important roles to play in supporting and encouraging the mineral exploration industry. These roles are: • providing basic geological, peophysical, and mineral resources information to form a foundation and framework for information • advising Governments on development of legislation and policies so that mineral exploration and development can proceed under favorable conditions The view of the mineral industry and other clients and customers is that the most important function of Government geological organizations is the compilation and development of a good framework of geological, geophysical and mineral resources maps, and that more resources need to be allocated for these mapping programs. Programs of geophysical and mineral resources mapping are also very highly regarded The importance of a good framework of geological and mineral resources maps and databases has been highlighted in recent years, in the Woods review of the Bureau of Mineral Resources, in organization reviews on the New South Wales and Victorian Geological Surveys, and in representations from the minerals industry to Governments. The most important direct beneficiary for most Government geological organization products is the mineral exploration industry. These products, and the advice provided by the Surveys, have a positive influence on the mineral industry by increasing the level, effectiveness of exploration, and contributing to greater access to land for exploration and mining. In New South Wales the provision of highly geoscientific maps and reports has boosted exploration activity in a number of identifiable commodity areas and prospective regions, notably in the Broken Hill and Cobar areas. Good geoscientific information enables companies to operate more effectively by identifying areas likely to have greater potential, and also by limiting duplication of previous exploration activity.

Geological Society of Australia Abstracts Number 32, Ballarat 1992

The mineral industry has become increasingly concerned at the shortfall in the total national effort in geoscientific mapping. The major program of geological mapping of the Australian continent took place during the 1960's and 70's, with most of Australia being mapped at reconnaissance level. The mapping momentum was maintained in some States, either by continuance or upgrading of the reconnaissance mapping, or more detailed mapping in areas of high exploration potential. The Bureau of Mineral Resources and some other States reduced their focus on standard series geological mapping. In summary, the level of geological mapping in Australia falls well short of what is required. Recognizing the need for a new focus on geological mapping and the industries concerns, the States and the Commonwealth have initiated the National Geoscience Mapping Award involving cooperative mapping projects of mutually agreed high priority. The Australian Minerals and Energy Council (which is the Council of Commonwealth and State Ministers) endorsed this Award in principle at its meeting in August 1990. The Bureau of Mineral Resources and the Surveys are redeploying staff and resources into Accord projects. Over 100 person-years of work were invested in joint Commonwealth States Accord projects during 1990/91. A further increase of 15% is planned in 1991/92. However, resourcees currently allocated to Accord projects fall well short of those necessary to complete a second generation of geoscientific mapping of the Australian continent within the target timetable of 20 years. Government geological organizations have a major contributioon to make to the Australian mineral industry. To ensure that their contributions are minimized, they must upgrade the quality of geological and mineral resources mapping and information, they must make this information available more effectively, they must take advantage of new technology, and they must work cooperatively with the mineral industry and other institutions.

Author A Adam 186 Agar 308, 309 Ahmad 160, 163, 166 Alkmim 237 Allen 133 Allibone 62 Andrew 178 Arculus 196 Arditto 107 Arne 67 Arribas 71 Askew 239 Aslund 213 Aubrey 326

B Baillie 29, 116 Baldwin 247 Bamberry 111 Banks 333 Barker 127 Barley 45 Barling 203 Barr 224 Baynes 249 Bell, A. 313 Bell, A.W. 272, 279 Bell, F.G. 272, 279 Bentley 276 Bernecker 106, 157 Berry 70 Biasutti 176 Binnie, M.N. 344 Binns 72 Birch 34, 194, 199, 213, 214, 325 Black 236 Blevin 131 Bloem 89 Bogdanov 39, 72, 197 Bolger 259 Bone 127, 159, 163 Both 71 Bouniot 286 Bowman 290 Bradley 22 Bradshaw, J. 131 Bradshaw, M.T. 131 Braun 293 Brinkley 256, 325, 330 Brock 174, 183, 184 Brodie 268

Index Brown 217, 334 Bruce 153 Brumley 341 Buckley 128, 249 Bull 135 Burchfiel 6

C Caluzzi 37 Camacho 205 Campbell 47, 190 Carey 16 Carey, S.W. 5 Carroll 233, 312 Carswell 319 Carter, L. 107 Carter, R.M. 107 Cartwright 200, 213 Carville 72, 357 Cas 133, 135, 136, 150 Cayley 23 Chalmers 209 Chan 326 Changkakoti 86 Chao 96 Charsley 30 Chen, K. 215 Chen, Y. D. 187 Cherry 261 Chiew 256 Clark, D.A. 283 Clark, I. F. 340, 352, 353 Clough 32 Collins 203 Collins, C. D. N. 290 Coney 24 Connors 229 Constantine 145 Cooper 183, 268, 334 Cox 307, 315 Cram 315 Cramsie 358 Craton 193, 215, 283 Crawford 25, 189, 198 Cromie 67 Crone 290 Crook 39, 46, 147

D Dadd 36, 138 Dalgarno 127 Dalziel 8, 226

360 Daniels 268 Davies 1 Davis, R.A. 160 Day 208 Dewey 11 Diessel 118 Dongqing 96 Draper 109 Drummond 43, 44 Dudding 256 Duke 318 Dwyer 336 Dyson 155

E

Edwards 89 Eggleton 160 Embleton 300 Engelbretsen 184 Erickson 319 Esslemont 209 Evangelista 237 Evans 119

F

Falloon 197 Farrell 175, 201 Fellows 39, 46 Ferguson 289 Fergusson 24, 26, 28 Fielding 109, 114, 143, 145 Filloux 289 Finlayson 290 Fitz Gerald 287 Flotmann 231, 241 Foden 153 Fouquet 74 Fowler 227 Frakes 105, 108 Frankel 36 Franklin 31, 235 Frape 261 Friday 258, 275

G

Galloway 103 Gamble 195 Gao 91 Gatehouse 32 Gaulton 313 Gebre-Mariam 81 Gibson 232 Glen 21, 43, 44 Glenie 241 Glikson 212

Golding 81 Goleby 43, 44 Gostin 64, 153 Graham 31 Gravestock 32 Green, A. R. 12 Green, D.H 189 Green, N. 86, 343 Green, T.H. 186 Green, T.J. 307 Greig 188 Grenfell 343 Griffin 187, 193, 219 Grimes 331 Groves 45, 81, 87, 88, 89 Guo 219 Gurney 193 Gust 345 Gwanmesia 294

H

Habermehl 260 Hackman 30 Hagemann 81, 87 Hale wood 304, 310 Hall 262 Hamilton 178, 339 Hamlyn 58 Hannington 40, 74 Harlow 92, 278, 349, 353 Harris 225, 243 Harts Range 218 Harwood 257 Hatch 309 Heidecker 143 Heithersay 60 Henderson 26, 28, 120 Hendrick, D. 345 Henry 34, 199, 325 Herbert 64 Herzig 40, 74 Hill, E. J. 247 Hill, R. 47, 190, 343 Hobbs 223 Holdgate 116 Hollis 194 Hopf 79 Hostetler 166 Houseman 224, 292, 299 Hoxley 266 Hronsky 74 Hronsky 81 Hua 93 Hudson, 328, 342 Hughes 180, 233, 319 Humphrey 179

Hunt 92 Hunter 52 Hutton 111, 117, 133

I Inan 99 Islam 129

J Jackson 89, 111, 113, 287, 294 Jago 32 Jagodzinski 136 Jaireth 59 James, N.P. 159, 163 James, P. R. 231, 241, 352, 353 Jauristo 57 Jell 319 Jenkins 181 Jennings 76 Jermy 265, 317 Jessell 307, 315 Johns 45 Johnson, D. 107 Johnson, K R 120 Johnson, T. 231 Johnstone 27 Johnstone, D.W. 36 Johnstone, J. 175 Jones, B G 111 Jones, G.J. 60 Jones, M150, Jones, T.286 Jones, P.J. 181 Joyce 277, 306 Juhlin 299

K Kassan 151 Kay 52 Keays 58, 64, 153 Keeling 216 Kennard 111, 113 Kennedy 154 Key 30 King 278 Kingsbury 325 Kitto 70 Klindworth 350 Korsch 27, 36 Krassay 105, 108 Krouse 64 Kwak 86, 91 Kyser 163

L Landenberger 203 Lang 145, 331 Langford 131 Larkin 319 Larsen 93 Laughton 329 Le Grand 5 Leach 303, 306, 311, 312 Leaman 28 Leckie 72, 357 Leitch 26, 28, 36 Leyh 93 Li 96 Liebermann 294 Lilley 289 Lindsay 111, 113 Lisitsin 72 Lisitsyn 39 Lister 238, 247 Lithosphere 283 Liu 147 Llewellyn 258 Loutit 12 Love 61 Lu 82

M Machette 290 Madonna 351 Main 55 Malahoff 197 Mann 259 Marshak 237 Marshall 31, 67 Marshall, B. 228, 235 Martin 168 Mawson 178, 180 May 12 Mayer 348, 349 McBriar 277, 278 McClure 216 McCue 286 McCulloch 32, 185, 205, 218 McDonald 305 McDougall 236 McKirdy 128 McKnight 29, 57 McNally 335 McNaughton 81, 87, 88 McPhie 138 McQueen 217, 293, 348 Menzies 195 Mernagh 72 Merrick 257 Messent 120

362 Michael-Leiba 286, 294 Middleton 123 Milligan 297 Milner 97 Molnar 5 Moores 226 Moorhead 357 Morand 28, 233 Morante 174 Morphet 275 Morrison 45, 59 Morse 230 Mortimer 218, 244 Moss 289 Munson 348 Muravev 39

N Neilson 251 Nicholls, B. 340 Nicholls, I.A. 188. 208 Nicholson 264 Nolan 259, 266 North 272

o

O'Brien 105, 111, 113 O'Reilly 187, 219, 283 O'Shea 99 Offler 29 Oliver 200, 213, 226 Oppy 93 Ord 223, 226 Orth 34

P PACMANUS 41 Page 209, 229 Pahl 238 Palethorpe 357 Palmer 43, 44 Parker 3, 275 Parr 69 Pascoe 243 Paterson 287 Pearson 283 Peck 251 Pell 128 Perkin 348 Petersen 74 Pettifer 305 Philips 260 Plimer 63 Pollard 342 Porter 327

Powell 29 Power 315 Prescott 290 Pridmore 285

Q R Ramsay, J. G. 15 Ramsay, R. R. 316 Ramsay, WRH 233 Rankin 32 Rattenbury 320 Raven 216 Rayner 357 Ray nor 194 Reeves 58 Reinsch 268 Richards 67 Ridley 65, 74, 87, 89 Rigden 294 Roach 99, 217 Roberts 181 Rock 209 Rockett 354 Rogers 231 Rolley 313 Rowley 53 Rudolph 255 Russell 125 Ryan, C.G. 193 Ryan, S. 269

S Sandiford 153 Santoso 130 Sappal 129, 130, 131 Sceney 281 Schaeffer 258 Scheibner 21 Schleiger 354 Schmidt 300 Schofield 313, 319 Schwarze 315 Scott 72 Seccombe 82, 100 Self 216 Selley 246 Sexton 111, 113 Shackleton 344 Shaw 236 Shi 171 Sibson 13, 230 Sie 186, 188

Simonis 297 Simpson 142 Simpson, G. 313 Sivell 185, 218 Skilbeck 36 Sloan 176 Smart 347 Smith, G.C. 120 Smith, I. E.M. 207 Smith, J.V. 228 Smith, Z. 289 Smolonogov 67 Smyth 128 Sobolev 193 Solomon 42 Southgate 111, 113 Stanley 233, 259 Stanton-Cook 51 Stawell 86 Stenning 276 Stevens 25 Stuart 347 Styles 252 SUPACLARK 72 Sutherland 194 Suwarna 131

T

Talent 178, 180 Tanaka 290 Tarlowski 297 Tate 45 Taylor 209 Taylor, W.R. 309 Tellis 328 Thalhammer 85 Thorne 22 Thornton 252, 331, 351 Thulborn 177 Tingate 236 Tipper 123, 160 Torgersen 260 Trudinger 271 Tucker 268 Turner 153 Turner, S. 177

u

V

Valenta 72, 230 Van As 265 van der Hey den 213 Vandenberg 21, 29, 34

Vanderhor 39 von Stackelberg 74

W

Wake-Dyster 27, 36, 43, 44 Wall 158 Wallace 64, 153 Walshe 60, 160 Waltho 321 Ward 119 Warne 182 Warren 122 Weaver 200, 261 Webb 67, 106, 112, 157, 158 Wells 105 Wheller 72, 203 Whitaker 320 White 202 Whitford 178, 198 Wilford 131 Wilkinson 30, 109 Williams, G. 297, 300 Wilson, G.A. 173 Winchester-Seeto 173 Windhofer 299 Winsor 227 Wissenden 281 Witham 243 Withnall 331 Witt 88 Wood, J. M. 299 Wood, P. 258 Wood, W. 289, 313 Woodall 49 Wormald 134 Worsley 59 Wyborn 72, 230 Wysoczanski 195

Y

Yang 100 Yaxley 189 Young, G. C. 177

z

Zeitler 236 Zhao 205 Zhikai 96 Zhongyi 220 Zhou 283, 323 Zidar 262 Ziolkowski 109 Zonenshain 39, 197

364

s

365

SUBJECT INDEX A A-TYPE 203 ACOUSTIC FACES 46 ACRAMAN IMPACT EJECTA HORIZON 153 ADELAIDE FOLD BELT 153, 241 ADELAIDE GEOSYNCLINE 155 AIR PHOTOGRAPHY 311 AIRBORNE GEOPHYSICS 285 AIRBORNE RADIOMETRIC CLASSIFICATION 305 ALBIAN MAXIMUM FLOODING SURFACE 120 ALGAL FLORAS 175 ALICE SPRINGS OROGEN 236 ALLUVIAL BASINS 105 ALUNITE-JAROSITE FAMILY 214 AMADEUS BASIN 154, 246 AMPHIBOLITE 211 ANORTHOSITES 218 ANTARCTICA 195, 226 ARC SYSTEMS 196 ARCHAEAN 212 AROONA CREEK 183 ARSENIC 274 ARTLUNGA .I.NAPPE 246 AS 214 ATRYPID BRACHIOPODS 174 AUCKLAND VOLCANIC FIELD 207 AUSTRALIA 193

B BACK-ARC 74, 185 BACK-ARC BASIN 197 BACK-ARC SPREADING CENTRES OF THE WESTERN PACIFIC 40 BALANCED-SECTION 241 BALLARAT 29, 92, 312 BALLARAT GOLDFIELD 318 BALLARAT REGION 306 BASALT PLAINS 259 BASALTS 195 BASE METAL 39, 93 BASIN ANALYSIS 123 BASS BASIN 116 BEAUFORT 23 BENAMBRAN UPLIFT 36 BENDIGO 86 BENDIGO-CASTLEMAINE 227 BENDING 8 BINDI 112 BIOCHRONOLOGY 177

BIOSTRATIGRAPHY 173, 175, 182, 183 BIRD LAKE 163 BLACK SLATES 91 BLOWERING FORMATION 138 BO PARAMETER 29 BORE LOGGING 289 BOWEN BASIN 109, 114, 151, 160 BRINES 64 BROCKMAN RARE-METALS DEPOSIT 209 BROKEN HILL 63, 69, 93, 213, 214 BROKEN RIVER 174, 178 BROKEN RIVER PROVINCE 145 BROWN COAL 116,313 BUCHAN 112 BUCHAN CAVES LIMESTONE 67 BUCHAN LIMESTONE 127 BUCHAN RIFT 34 BUSHVELD COMPLEX 244

c

CAMPASPE VALLEY 256 CAMPBELL EMBAYMENT 107 CANNING 177 CANNING BASIN 111, 113, 293 CARBONATE 157, 159, 180 CARBONATE CYCLES 158 CARBONATE MUD 160 C ARB ONATITE 189 CATTAMARRA 129 CENTURY 55, 57, 321 CHAELUNDI COMPLEX 203 CHARLES GOULD 333 CHEVRON FOLDS 227 CHEWTON 91 CHITINOZOAN 173 CHITRAL 174 CHLORINE-36 260 CLASTIC SEDIMENTATION 323 CLIMATE RECORD 105 COAL 111, 116, 117, 118, 128, 129, 130, 131, 265, 313 COASTAL PLAIN 114 COASTAL VULNERABILITY 249 COBAR 319 COBAR BASIN 43, 44, 228 COMPUTER ANIMATION 353 COMPUTERS 317 CONJUNCTIVE USE STUDY 256 CONODONT 173, 175, 178,179 CONSERVATION 352 CONTINENTAL MARGIN 323 COOLAC SERPENTINITE 235 COORONG 160,163,166

366 COPPER 60, 93, 199 CORINTHIA-HOPES HILL 89 CORONATION HILL 72, 357 COSMOLOGY 16 CRACOW 59 CRUST 13, 283 CRUSTAL SUTURE 232 CRYSTAL OPTICS 220 CUMNOCK-LARRAS LEE 175 CURLEW 311 CYCLOTHEMS 107

D

D'ENTRECASTEAUX ISLANDS 247 DAM STABILITY 252 DATA MANAGEMENT 331 DATABASE 325, 328, 329 DEEP SEISMIC 43, 44 DELTAIC 114 DENISON TROUGH 160 DEVONIAN SUCCESSION 176 DEWATERING 258 DI AGENESIS 160 DIAMOND INDICATOR MINERALS 316 DIAPIRIC STRUCTURES 154 DINOSAURS 177 DOLOMITE 163 DOLOMITIC CARBONATE 163,166 DUNITE 287

E

E. DE C. CLARKE GEOLOGICAL MUSEUM 354 EARTHQUAKE 286, 294 EARTHQUAKE RECURRENCE 290 EAST MIDLANDS SHELF 299 EASTERN GOLDFIELDS 81, 320 EDUCATION 339, 340, 341, 342, 343, 345, 348, 351, 352, 353, 354 ELASTICITY 294 ELATINA FORMATION 155 ELECTRICAL CONDUCTIVITY 289 EMPIRICISM 49 ENGINEERING GEOLOGY 249, 251, 341 ENVIRONMENT 271, 274, 276, 340, 341 ENVIRONMENTAL CONTROL IN PROJECTS ADJACENT TO THE .I.WORLD HERITAGE AREA 249 ENVIRONMENTAL LAWS 272 EPIGENETIC 67 EPITHERMAL 76, 79 EROMANGA BASIN 283 ERUPTIVE DRAINAGE STRUCTURES 143 ERUPTIVE VENTS 217 ETHERIDGE 334 EVAPORITE 63, 122, 166

EXCURSION GUIDES 344 EXHALITES 69 EXPLORATION 327, 351, 358 EXTENSION 6 EXTINCTION EVENTS 178 EXTRATERRESTRIAL IMPACTS 212

F

FACIES ANALYSIS 114, 138, 143 FAN-DELTAS 147 FAULT 224, 231 FAULT SURFACES 315 FAULTING 230 FIDDLER'S CREEK 86 FISH 177 FITZROYTROUGH 111 FLEURIEU PENINSULA 231 FLEXURAL-SLIP FOLDING 227 FLUID FLOW 65, 74, 200, 230 FLUID INCLUSION 72, 82, 96 FLUID PUMPING 226 FLUIDS 64, 86, 87 FOLD INTERFERENCE 228 FOLD NUCLEATION 240 FOLDING 244 FORELAND DEFORMATION 151 FORESHOCK 286 FOSSILS 319 FRACTALS 223 FRACTIONATION 207 FRAMPTON VOLCANICS 36

G

GARRA LIMESTONE 173 GEOCHEMISTRY 25 GEODYNAMIC MODELLING 299 GEOGRAPHIC INFORMATION SYSTEMS 326 GEOLACT 348 GEOLOGICAL SOFTWARE 350 GEOPHYSICS 99 GEORGINA BASIN 177 GIPPSLAND BASIN 116 GIS 320 GLACIAL CLIMATE 300 GLACIGENIC SEQUENCE 155 GLEN INNES 92 GLENELG RIVER COMPLEX 232 GOLD 21, 40, 45, 52, 53, 59, 60, 61, 62, 74, 76, 79, 81, 82, 85, 86, 87, 88, 89, 91, 96, 97, 99, 275 GOLDEN PLATEAU MINE 59 GONDWANA 26 GOOBARRAGANDRA VOLCANICS 138 GOONUMBLA 60 GOVERNMENT 358

367

GRAMPIANS GROUP 150 GRANITE-GREENSTONE BELTS 237 GRANITES 202 GRANITIC MAGMATISM 247 GREAT ARTESIAN BASIN 260 GREAT BARRIER REEF 1 GREAT SERPENTINE BELT 100 GREENSTONE BELT 233 GREENSTONES 34 GRENVILLE AREA 303 GROUNDWATER 257, 259, 260, 261, 262, 264, 266, 268, 310, 330 GULF OF CARPENTARIA 108 GUNNED AH BASIN 27

HHALLS CREEK 209

HEARD ISLAND 203 HELLYER 198 HILL END 82 HILL END TROUGH 180 HILL RIVER 131 HODGKINSON BASIN 157 HUNTER-BOWEN OROGENY 26 HYDROCARBON 122 HYDROGEOLOGISTS 264 HYDROGEOLOGY 268,269 HYDROTHERMAL 46, 65, 72, 76, 88 HYDROTHERMAL SULFIDE 41

IIGNIMBRITES 133

ILLAWARRA 111, 117 ILLITE CRYSTALLINITY 29 INCLUSION STUDIES 219 INITIAL LEAD ISOTOPE 88 INLAND BASIN 323 INTRAPLATE OROGENY 236 INTRUSIVE BRECCIA 134 INVERELL 92 INVERTEBRATE 181 IRON FORMATIONS 93

JJAMES COOK 333 JOINTS 307

KKANOWNA BELLE 51

KAOLINIZATION 216 KENYA 30 KIMBERLEY 309 KIMBERLITE 309 KIMBERLITE PIPES 215

KRIGING 313

L

LABOUCHERE FORMATION 168 LACEPEDE SHELF 159, 163 LACHLAN FOLD BELT 24 LACHLAN OROGEN 21 LAKE BOG A GRANITE 199 LAKE COWAL 61 LAKE REEVE 160 LAMPROITE 309 LATROBE VALLEY 268, 289 LAU BASIN 197 LAYERED 58 LEAD 214 LEAD67 LILYDALE LIMESTONE 158 LIMCO 316 LINEAMENTS 241

M MAE MOH COAL BASIN 119

MAFIC 58 MAFIC DYKE 3, 205 MAGMA CHAMBER 194 MAGNETIC ANOMALY MAP 297 MANTLE 47, 185, 186, 187, 188, 190, 283, 292 MANTLE PLUMES 292 MANTLED GNEISS DOMES 239 MARINE SHELF 114 MARKHAM VALLEY 147 MARVEL LOCH 313 MARY KATHLEEN 213 MATHINNA - ALBERTON GOLDFIELD 99 MELBOURNE REGION 251 MELBOURNE TROUGH 29 METALLOGENESIS 42,45 METALLOGENY 47, 190 MET AMORPHIC CORE COMPLEX 238,247 METAMORPHIC FLUIDS 213 METAMORPHISM 211 MICROCRACKS 307 MIGMATITE 201 MILPARINKA-TIBOOBURRA 85 MINE MODELLING 318 MINERAL EXPLORATION 49 MODELLING 225 MOHO 194 MOLONG PLATFORM 180 MONARO VOLCANIC PROVINCE 217 MORWELL OPEN CUT 258 MOUNT AUBREY 79 MOUNT ISA 229 MOUNT LOFTY RANGES 216 MOUNT READ VOLCANICS 138, 198

368 MOUNTAIN BELTS 6, 11 MOUNTAIN BUILDING 5 MT. LEYSHON GOLD 134 MT. TAYLOR KINGSTON 275 MULTILAYER DEFORMATION 240 MULTISPECTRAL SCANNER 308, 309 MURRAWONG CREEK FORMATION 176, 184 MURRAY DARLING BASIN 266, 268 MURRAY TRENCH 304

N

NAPPE 239 ND 153, 185, 218 NEW ENGLAND OROGEN 27, 28,290 NEW HAMPSHIRE 239 NEWCASTLE COLLIERIES 335 NEWER 310 NEWLYN 194 NOAA-AVHRR 304

O

OCEAN BASINS 226 OCEAN CURRENTS 289 OCEAN DRILLING PROGRAM 196 ODP1 OFFICER BASIN 128 OLDER VOLCANICS 208 OLIVINE 294 ONTARIO 261 ORE MODEL 57 ORE RESOURCE ESTIMATION 313 ORGANIC MATURATION 127 ORNITHIS CHI AN 177 OROGENIC BELTS 8 OSBORNE DEPOSIT 57 OSTRACOD 182 OTWAY 145 OTWAY BASIN 107

P

PACIFIC 16 PACSCHOOLINFOLINE 351 PALAEOBIOGEOGRAPHY 171 PALAEOCURRENTS 29 PALAEOECOLOGY 171 PALAEOGEOGRAPHY 131 PALAEOLATITUDE 300 PALAEOROTATION 297 PALYNOLOGY 129 PANGAEA 16 PERALKALINE 202 PERMEABILITY 265 PERSONAL ARCHIVES 336 PERTH BASIN 129, 130, 131

PETROLEUM SOURCE ROCK 128 PHILLIP ISLAND 34 PHOTOGRAMMETRY 315 PINE CREEK INLIER 136 PITFIELD-AVOCA FAULT 233 PLACER GOLD 97 PLATINUM-GROUP 58, 64, 100 PLUTONIC 53 POINT LONSDALE 354 PRECAMBRIAN TECTONICS 3 PRIMARY SCHOOLS 349 PRINTED MEDIA 345 PROTECTING SIGNIFICANT GEOLOGICAL FEATURES 278 PUMICE 133 PROVENANCE 150, 153 PYROCLASTIC FLOW 136

Q QUADRILATERO FERRIFERO 237 R

RAMP BASIN 44 RAMP DEPOSITION 157 RAMSAY LIMESTONE 183 RAVINE 176 RECLAMATION 279 RED BED 64 REEDY CREEK 22 REEFS 113 REGMAP 331 REHABILITATION 272, 281 REMOTE SENSING 309 RENISON TIN MINE 70 RESERVOIR DESCRIPTION 114 RESERVOIR GEOMETRY 120 RESOURCE ESTIMATION 315 RESOURCE EVALUATION 326 RESOURCE MODELLING 319, 321 REYNELLA SILTSTONE MEMBER 155 RIFT 30 RINGS 241 . ROADSIDE GEOLOGY 343 ROCKFIELDS MEMBER 145 RODDA BEDS 128

s

SALINAS VALLEY 262 SALINITY 269 SALINITY STUDIES 305 SALT CREEK AREA 166 SAPPHIRE 92, 219 SEA LEVEL 116 SEA LEVEL RISE 354 SEA-LEVEL CURVES 105 SECONDARY EARTH SCIENCE

369

DEPARTMENT 349 SEDIMENTARY BASINS 12 SEDIMENTATION SYSTEMS 123 SEDIMENTOLOGY 145 SEISMIC 287, 299 SEISMIC IMAGING 107 SEISMIC REFLECTION 27, 36 SEQUENCE 120 SEQUENCE STRATIGRAPHY 105, 106, 107, 108, 109, 111, 112, 113, 118, 128, 131 SERPENTINITE 31 SHEAR ZONES 74, 86, 225, 231, 237 SHELLY FAUNA 184 SHORT-COURSES 347 SHORTENING 6 SHOSHONITE SERIES 215 SHRIMP 215 SIBERIA 193 SILICICLASTICS 103, 111, 159 SILVER 76, 199 SITE RECOVERY 275 SITE REHABILITATION 272 SM 153, 218 SNAKE RANGE 238 SNOWY RIVER VOLCANICS 135 SODIUM BICARBONATE 64 SOFTWARE 353 SOLUTE TRANSPORT 255 SORRENTO GRABEN 182 SOUTH AFRICA 265 SOUTH ALLIGATOR VALLEY 230 SOUTH VICTORIA LAND 211 SOUTHERN AFRICA 193 SR 188 STABLE ISOTOPE 81 STAWELL ZONE 23, 29, 37, 99 STEPHEN CROSS QUARRY 200 STOCHASTIC MODELLING 123 STRAIN 224, 228 STRATA3 276 STRATIGRAPHY 111 STRESS 224 STRESS MAPPING 65 STRUCTURAL GEOLOGY 15 STRZELECKI 145 STUDENTS 353 SUBMARINE VOLCANIC 138 SULPHIDE 67 ^ SUPERCONTINENTS 226 SURFACE FAULTING 290 SYDNEY BASIN 111, 117

T TAEMAS LIMESTONE 179 TALISKER AREA 231 TASMANIA 28

TECTONICS 15, 25, 29, 30, 42, 45, 103, 119, 293 TEMORA SHEAR ZONE 62 TENNANT CREEK 286 THERMAL MATURATION 125 THOMSON SADDLE DAM 252 THRUSTING 28, 231, 243 TI 188 TIDAL RHYTHMITES 297 TM 303, 306, 310 TOOMBA FLOW 143 TRACE ELEMENT 186 TRACER TESTS 255 TRACHYTIC VOLCANICS 209 TRANSITION ZONE 294 TREPHINA GORGE 246 TRILOBITES 176, 180 TRURO VOLCANICS 32 TURBIDITE FACIES 168

U UKALUNDA 174 ULTRAMAFIC 58 UNDERPLATING 290 UPPER MANTLE 31 URANIUM 71, 199

V VAN DIEMENS LAND 333 VASSE SHELF 130 VOLCANIC ARC 36 VOLCANICLASTICS 133, 135, 138

w

WEST ACEH BASIN 130 WHITE DEVIL 52 WILSON BOTANIC PARK 343 WILUNA 87 WIRREALPA 183 WOLLONDILLY BASIN 142 WONGWIBINDA METAMORPHIC COMPLEX 201 WOODCUTTERS 67

X XENOLITHS 195, 215 XP-1 311

Y YARRAMYLJUP FAULT ZONE 232 YOUNG GRANODIORITE 235

370

z ZINC 67 ZIRCONS 215 ZR 188