Issuu

Geological Society of Australia

ABSTRACTS Number

11th Victorian Universities Geoscience Conference

IVIonash University 10th October, 1997

11TH VICTORIAN UNFS^RSITIES GEOSCIENCE CONFERENCE

Monash University 10th October, 1997

Geological Society ofAustralia, Abstract Volume 46

GEOLOGICAL SOCIETY OF AUSTRALIA ABSTRACTS NO. 46 11th Victorian Universities Geoscience Conference^ Monash University, October, 1997

ISSN 0729-01IX

@ Geological Society of Australia Incorporated 1997

Copies ofthis publication may be obtainedfromthe Geological Society ofAustralia Incorporated, 706 Wynyard House, 301 George St, Sydney, NSW, Australia, 2000

Example citation for papers in this volume: Neil, E. A. and Houseman, G. A., 1997, Can gravitational instability in the mantle produce intraplate orogeny? Geological Society of Australia, Abstracts No. 46, pp 27.

Financial support for the 1 1 t h VICTORIAN UNIVERSITIES GEOSCIENCE CONFERENCE

was generously provided by

RIO TINTO and

NORTH GEREATCENTRALMENESLTD

£sso VICTORIADIVISION

Additional financial support was provided by

The Geological Society of Australia Specialist Group in Geochemistry, Mineralogy and Petrology

Acacia RESOURCES

NORMANDY EXPLORATION LTD

STOCKDALEPROSPECnNGUMIlED (a De Beers conqjany)

PASMINCO EXPLORATION

Financial assistance for the production of this abstract volume was provided by

£sso

Conference Co-ordinator Rebecca Sproule Abstract Volume Jodie Miller and Alison Dean Organising Committee Simon Baker JanneneMcBride Emily Neil Caroline Venn TonyDonaghy CeinwinScutter SanjaVanHuet Stuart Graham NickRawlinson Mary Jane SamWatidns Caroline Read

11th VUGC1997, Monash University

IITH VICTORIAN UNIVERSITIES GEOSCIENCE CONFERENCE

8.15 - 8.45 Registration 8.45 - 9.00 Welcome and Introduction - Jim Cull Session One - ENVIRONMENTAL GEOLOGY AND HYDROGEOLOGY Session Convenors:

Dr. D.C. "Bear" Mc Phail, Monash University Dr. Jeff Taylor, Earth Systems

9.00

The geochemistry of groundwater and mine tailings in a sediment bank of the King River, Tasmania. Deborah Green (Honours), D,C, ''Bear''McPhail Monash University

9.15

The hydrogeology of a sediment bank on the King River, Tasmania. W, Cameron Hooper (Honours), Monash University

9.30

Geophysics and acid mine drainage Simon Baker (MSc), Monash University

Session Two -SEDIMENTOLOGY, PALAEONTOLOGY AND RELATED GEOPHYSICS Session Convenors:

Professor Ray Gas, Monash University

9.50

New work on the use of seismic interval velocities to map sequence boimd lateral lithology changes. Joseph Chiupka (PhD), Melbourne

10.05

Stratigraphy and correlation of the continental redbed sequence at the Kotelnich Upper Permian fossil tetrapod locality, Russia. Andre Coffa (MSc), Monash University

10.20

Geophysical modelling of aeromagnetic anomahes in the Cape Otway area. Nancy Lammens (Honours), Monash University

10.35

Karst of the Cainozoic Limestones of the Otway Basin, southeastem Australia. Susan White (PhD), La Trobe University

10.50

SeasonaUty and temperature signals from isotope and cation analyses of aragonitic mussel shells. Jessica Reeves (Honours), Melbourne University

11.05 - 11.40 Morning Tea and Posters 11.40 -11.45 Presentation by Geological Society of Australia

11th VUGC1997, Monash University

IITH VICTORIAN UNIVERSITIES GEOSCIENCE CONFERENCE Session Three - IGNEOUS , METAMORPHIC GEOLOGY AND GEOCHEMISTRY Session Convenors:

Dr. Ian Buick, La Trobe University Jeff Foster BHP Minerals

11.50

Shear Zone deformation and metasomatism at Broken Hill, New South Wales. Chris Doyle (Honours), Monash University

12.10

Torlesse conglomerate igneous clast geochemistry: Implications for terrane provenance. Alison Dean (PhD), Monash University

12.25

AppUcation of platinum group elements and lead isotope geochemistry to the study of the corrosion products of archeaological artefacts to constrain provenance. Willem Snoek (PhD), Tony Sogona and Ian Plimer, Melbourne University

12.40

Recrystallization of silica at low temperatures. MarkDomanski (PhD), La Trobe University

1.00 - 2.00 BBQ Lunch Session Four - STRUCTURE, TECTONICS AND RELATED GEOPHYSICS Session Convenors:

Dr. Paul Bons, Monash University Dave Wallace, Aberfoyle Resources

2.05

The thermal, stratigraphic and structural history of the Otway Basin in the Lome Area Alastair Ryan (Honours), Monash University

2.20

A study of small scale localisation of deformation. Hadi Sim (Honours), Monash University

2.35

The Structure and stratigraphy of the south-eastem portion of the Cerberean Cauldron. Christopher Osborne (Honours), La Trobe University

2.50

Reassessment of the Archean tectonics in the Murchison Province, Westem Australia. Benjamin Foley (Honours), Monash University

3.05

The style of faulting in the Canning Basin, Westem Australia: Implications for basin development Anthony Almond (MSc), Monash University

11th VUGC1997, Monash University

IITH VICTORIAN UNIVERSITIES GEOSCIENCE CONFERENCE

3.20 - 3,40 Afternoon Tea and Posters

Session Five - ECONOMIC GEOLOGY Session Convenors:

Dr. David Lambert, Monash University Paul Roberts, Pasminco Exploration

3.40

The Hehnut iron-nickel sulphide deposit. Tramways, Western Austraha: A unique Archean komatiite-associated deposit. Edward Curl (Honours), Monash University

3.55

Vein system and its fluid inclusion geochemistry in the Bendigo gold ore field: implications for ore fluid evolution. Xia Li (PhD), La Trobe University

4.10

Geochemistry of copper in hydrothermal brines Matt Pomeroy (Honours), Bear McPhail, and Leon Spiccia, Monash University

4.25

Compositional banding and "Chalcopyrite Disease" style textures in massive sulphide deposits. Geoff Tonkin (MSc), Monash University

4.40 Volcanic ore environments of the westem Widgiemooltha Dome, Kambalda Westem Austraha. Narelle Wolfe (Honours), Monash University

4.55 - 5.45 Poster Session and Refreshments, Tea and Coffee 5.45 - 6.15 Prize Giving 6.15 - 6.50 Drinks

7.00 Conference Dinner

11th VUGC1997, Monash University

POSTER PRESENTATIONS

Mafic/Felsic relationships: An example from the Bega Batholith, Southeastern Australia Alison A. Dean, Monash University Structure, high-grade metamorphism and stratigraphy at Thackaringa, Broken Hill, NSW. Tony Donaghy (PhD), Mike Hall, AGCRC-Monash University George Gibson, AGSO - Canberra The environmental impacts of gold mining at Woods Point, Victoria. Amanda Johnstone (Honours), Monash University Mesozoic to recent thermal history and basement tectonics of the Irian Jaya fold belt and Arafura Platform, Irian Jaya, Indonesia RichardD. Kendrick (PhD), Kevin C. Hill, PaulB. O'Sullivan, AGCRC-La Trobe University Kaspar Lumbanbatu and Ijep Saefudin - Geological Research and Development Centre, Bandung, Indonesia Microbial activity in groundwater and its effect on cyanide contamination. Samantha M.E. Meehan (PhD), The University of Melbourne Can gravitional instability in the mantle produce intraplate orogeny? Emily Neil (PhD), Monash University Mafic rocks associated with felsic intrusions - A key to understanding granite petrogenesis, SE Australia. Alvar Soesoo (PhD), Monash University Sally Malay Intrusion: A Voisey's bay analogue? Guides to magmatic Ni-Cu-Co mineralisation in the east Kimberley. Rebecca Sproule (PhD), David Lambert, Monash University Dean Hoatson, AGSO - Canberra Thermochronology and tectonics of the Bird's Head region, Irian Jaya: Apatite fission track constraints. EdySutriyono (PhD), PaulB. O'Sullivan, Kevin C Hill, La Trobe University Badgers, Cassowaries and Oddities: The extant and extinct fauna of King Island, Bass Strait Sanja Van Huet (PhD), Monash University Evidence for extended thermal activity in Broken Hill: New geochronological constraints using SHRIMP U-Pb ages. Caroline Venn (PhD), AGCRC-Monash University

11th VUGC1997, Monash University

LIST OF STUDENT PARTICIPANTS

Anthony Almond MSc candidate, Department of Earth Sciences and VIEPS, Monash University, Wellington Rd, Clayton, 3168 email: ST-tony@artemis.earth.monash.edu.au Simon Baker MSc candidate, Department of Earth Sciences and VIEPS, Monash University, Wellington Rd, Clayton, 3168 email: ST-baker@artemis.earth.monash.edu.au Joseph Chiupka PhD candidate, School of Earth Sciences and VIEPS, The University of Melbourne, Parkville, 3052. Andre Coffa MSc candidate. Department of Earth Sciences and VIEPS, Monash University, Wellington Rd, Clayton, 3168 email: ST-coffa@artemis.earth.monash.edu.au Edward Curl Honours candidate. Department of Earth Sciences and VIEPS, Monash University, Wellington Rd, Clayton, 3168 email: ecurl@artemis.earth.monash.edu.au Alison Dean PhD candidate. Department of Earth Sciences and VIEPS, Monash University, Wellington Rd, Clayton, 3168 email: ST-dean@artemis.earth.monash.edu.au MarkDomanski PhD candidate. School of Earth Sciences and VIEPS, La Trobe University, Bundoora, 3083. TonyDonaghy PhD candidate, AGCRC, Department of Earth Sciences and VIEPS, Monash University, Wellington Rd, Clayton, 3168 email: ST-donag@artemis.earth.monash.edu.au Chris Doyle Honours candidate, Department of Earth Sciences and VIEPS, Monash University, Wellington Rd, Clayton, 3168 email: St-doyle@artemis.earth.monash.edu.au Benjamin Foley Honours candidate, Department of Earth Sciences and VIEPS, Monash University, Wellington Rd, Clayton, 3168 email: ST-foley@artemis.earth.monash.edu.au Deborah Green Honours candidate. Department of Earth Sciences and VIEPS, Monash University, Wellington Rd, Clayton, 3168 email: ST-debg@arteniis.earth.monash.edu.au W. Cameron Hooper Honours candidate, Department of Earth Sciences and VIEPS, Monash University, Wellington Rd, Clayton, 3168 email: ST-hoop@artemis.earth.monash.edu.au

11th VUGC1997, Monash University

LIST OF STUDENT PARTICIPANTS

Amanda Johnstone Honours candidate, Department of Earth Sciences and VIEPS, Monash University, Wellington Rd, Clayton, 3168 email: ST-amand@artemis.earth.monash.edu.au Richard Kendrick PhD candidate, AGCRC, School of Earth Sciences and VIEPS, La Trobe University, Bundoora, 3083. email: geordk@luff.latrobe.edu.au Nancy Lammens Honours candidate, Department of Earth Sciences and VIEPS, Monash University, Wellington Rd, Clayton, 3168 email: ST-nancy@artemis.earth.monash.edu.au XiaLi PhD candidate. School of Earth Sciences, La Trobe University, Bimdoora, 3083 email: geoxl@luff.latrobe.edu.au Samantha Meehan PhD candidate. School of Earth Sciences and VIEPS, The University of Melboume, Parkville, 3052. email: smeehan@met.unimelb.edu.au EmUyNeil PhD candidate. Department of Earth Sciences and VIEPS, Monash University, Wellington Rd, Clayton, 3168 email: eneil@artemis.earth.monash.edu.au Christopher Osborne Honours candidate, School of Earth Sciences and VIEPS, La Trobe University, Bundoora, 3083 Matt Pomeroy Honours candidate. Department of Earth Sciences and VIEPS, Monash University, Wellington Rd, Clayton, 3168 email: ST-pomer@artemis.earth.monash.edu.au Jessica Reeves Honours candidate. School of Earth Sciences and VIEPS, The University of Melboume, Parkville, 3052 email: jmreeves@rubens.its.unimelb.edu.au AlastairRyan Honours candidate. Department of Earth Sciences and VIEPS, Monash University, Wellington Rd, Clayton, 3168 email: ST-ryan@artemis.earth.monash.edu.au HadiSim Honours candidate. Department of Earth Sciences and VIEPS, Monash University, Wellington Rd, Clayton, 3168 email: hmsiml@student.monash.edu.au Willem Snoek School of Earth Sciences and VIEPS, The University of Melboume, Parkville, 3052. PhD candidate,

11th VUGC1997, Monash University

LIST OF STUDENT PARTICIPANTS

Alvar Soesoo PhD candidate, Department of Earth Sciences and VIEPS, Monash University, Wellington Rd, Clayton, 3168 email: asoesoo@artemis.earth.monash.edu.au Rebecca Sproule PhD candidate. Department of Earth Sciences and VIEPS, Monash University, Wellington Rd, Clayton, 3168 email: ST-rebec@artemis.earth.monash.edu.au Edy Sutriyono PhD candidate, School of Earth Sciences and VIEPS, La Trobe University, Bundoora, 3083. email: geoed@lure.latrobe.edu.au Geoffrey "Hammer*' Tonkin MSc candidate. Department of Earth Sciences and VIEPS, Monash University, Wellington Rd, Clayton, 3168 email: ST-tonki@artemis.earth.monash.edu.au Susan White PhD candidate. School of Earth Sciences and VIEPS, La Trobe University, Bundoora, 3083. email: geosw@luff.latrobe.edu.au Narelle Wolfe Honours candidate. Department of Earth Sciences and VIEPS, Monash University, Wellington Rd, Clayton, 3168 email: nwolfe@artemis.earth.monash.edu.au Sanja Van Huet PhD candidate. Department of Earth Sciences and VIEPS, Monash University, Wellington Rd, Clayton, 3168 email: ST-huet@artemis.earth.monash.edu.au Caroline Venn PhD candidate, AGCRC Department of Earth Sciences and VIEPS, Monash University, Wellington Rd, Clayton, 3168 email: cstreets@artemis.earth.monash.edu.au

11th VUGC1997, Monash University

THE STYLE OF FAULTING IN THE CANNING BASIN, WESTERN AUSTRALIA: IMPLICATIONS FOR BASIN DEVELOPMENT ANTHONY ALMOND Monash University In 1988, AGSO acquired 640 kilometres of deep seismic data across the centre of the Canning Basin. This data consisted of three seismic lines, two running perpendicular to the strike and one running parallel to the strike of the Fitzroy Trough. Reprocessing and reinterpretation of this seismic data has allowed a structural interpretation and geodynamic model of the Canning Basin to be developed, with emphasis on basin development and the timing of extension and crustal shortening. The Canning Basin is the largest sedimentary basin in Westem Australia, covering an area of around 640,000 square kilometres. Current models of the basin indicate four main tectonic events have taken place since the initiation of subsidence in the Ordovician. Subsidence in the Canning Basin initiated in the Ordovician. Major extension and subsidence did not begin imtil the Mid-Devonian. Extension continued in the Fitzroy Trough through the Devonian and into the Carboniferous, ceasing in the Late Carboniferous. Crustal shortening took place in the Canning Basinfromthe Middle Triassic until the Early Jurassic. This shortening folded and faulted the sequences producing uplift and erosion. The crustal shortening reactivated previously extensional faults as thrust faults, producing inversion structures on some faults. The Fitzroy Trough was the most tectonically active region in the Canning Basin during the four tectonic events. The Fitzroy Trough has been previously modelled as a series of half-graben bounded by transfer faults (Drummond, et al. 1988), however recent work has cast doubt on the validity of this model. Bounding faults for the half-graben in the Canning Basin include the Fenton Fault system, Pinnacle/Beagle Bay Fault system and the Dampier Fault system. Evidence from the AGSO seismic lines has shown the Canning Basin to consist of a series of parallel halfgraben, with changes in symmetry of the half-graben along strike. Previous work has postulated that these changes in symmetry occur at transfer faults (Drummond, et al. 1988; Drummond, et al. 1991). This is not supported by evidence from seismic interpretation of the AGSO lines. Recent workfromthe Basin and Range Mesozoic rifts in North America has established that: (1) cumulative displacement on normal faults in greater near the centre of the fault and decreases toward the tips, and (2) faults lengthen as cumulative displacement increases (Schlische and Anders, 1996). Applying this model to the Canning Basin will remove the need for transfer faults as an explanation for the switching in symmetry of the half-graben. The style of faulting in the Canning Basin providesftirtherevidence for the presence of accommodation zones. A number of fault systems in the basin pinch out along strike in a manner consistent with these zones. The presence of accommodation zones instead of transfer faults to provide for the change in symmetry across half-graben has important implications for the development of the basin. Transfer or accommodation zones influence drainage development and stratigraphy, fault displacement, location and geometry. Understanding the style of faulting in the Canning Basin will have implications for the development of the basin as a whole. REFERENCES Drummond, B. J., Etheridge, M. A., Davies, P. J. and Middleton, M. F. 1988, Half-graben model for the structural evolution of the Fitzroy Trough, Canning Basin, and implications for resource exploration, APEA Journal, 28, 76-86. Dmmmond, B. J., Sexton, M. J., Barton, T. J. and Shaw, R. D. 1991, The nature of faulting along the margins of the Fitzroy Trough, Canning Basin, and implications for the tectonic development of the trough. Exploration Geophysics, 22, 111-116. Schlische, R. W. and Anders, M. H. 1996, Stratigraphic effects and tectonic implications of the growth of normal faults and extensional basins. Geological Society ofAmerica Special Paper, 303,183-203.

11th VUGC1997, Monash University

GEOPHYSICS AND ACID MINE DRAINAGE SMON F.BAKER Monash University Groundwater flow modelling in contaminated sediment containing reactive minerals is important in characterising mass loading of acid and toxic compoundsfromgroundwater discharge to surface waters. Groundwater flow is affected by heterogeneities in hydraulic conductivity and hydraulic gradient. Contaminant transport is affected by advective and dispersive processes and chemical reactions in the sediments; e.g., oxidation and reduction. This means mass loading of groimd water discharged to surface water cannot be accurately determinedfroma few point samples. The lower King River, Tasmania has received almost a 100 million tonnes of mine tailings and slagfromthe Mt Lyell Mine, Queenstown (de Bias, 1994, Locher, 1995). While current owners are ensuring present operations do not further impact natural water systems, previous contamination presents ongoing environmental problems. Concurrent with studies of the geochemistry (Green and McPhail, 1997) and hydrology (Hooper and McPhail, 1997) of a section of the King River designated Bank D, the appUcation of geophysics to further characterise groimdwater flow is being investigated. Bank D is typical of contaminated sediment banks of the King River. It consists of quartzose sediments contaminated predominantly by pyrite mine tailings and their oxidised products. Groundwater contamination in the bank consists of acid and high trace metal levels (Taylor, et al, 1996, Green and McPhail, 1997). In this study, self-potential and ground penetrating radar are used to determine the geometry of the water table, oxidation reaction front and sediment stratigraphy. Self-potential profiles of the bank are studied using copper electrodes and porous pots containing a saturated copper sulphate solution. Surface profiles and depth soundings were both conducted. There is a strong correlation between vertical potential gradient, saturated and imsaturated zones, and redox potential. The self-potential surveys of the surface of the bank appear to indicate regions of higher contaminant flow. Ground penetrating radar surveys using a 200mHz signal covered two areas of the bank. Heterogeneities in sediment banks and hardpan layering that potentially affects groundwater flow modelling (Blowes, et al., 1991) are indicated. Depth of signal penetration is low due to the high attenuation coefficient of high frequency electro-magnetic waves in water-saturated and mineral rich sediments. Locating the depth of features indicated by the reflected wave trace depends on knowing the velocity of the signal through the medium. The pulse velocity is affected by contaminant levels, mineralogy and saturation levels, all of which are highly variable in this situation. As the velocity is a variable, estimated depths of features may be inaccurate. Imaging of shallow features (< 1 m), such as the winter water table level, is also poor due to regions of saturated water above the water table (perched water tables and capillary water zone). Interaction of transmitted signal, primary reflected signal and secondary reflections make satisfactory deconvolution of the signal difficult. Geophysical techniques may provide a method of estimating fluidflowin sediment banks, determination of depth of oxidation zone for acid mine drainage and allow estimates of acid and elementfluxeswithout requiring extensive and expensive point sampling operations. REFERENCES

de Bias, A., The environmental effects of Mt Lyell Operations on Macquarie Harbour and Strahan, Australian Centre for Independent Joumalism, UTS, May, 1994. Blowes, D.W., Reardon, E.J., Jambor, J.L., Cherry, J. A., The formation and potential importance of cemented layers in inactive sulphide mine tailings, Geochimica et Cosmochimica Acta, Vol. 55, pp. 965-978,1991. Green D.K. and McPhail, D.C., The Geochemistry of Groundwater and Mine Tailings in a Sediment Bank of the King River, Tasmania, this volume, 1997. Hooper, W.C. and McPhail, D.C., The Hydrology of a Sediment Bank on the King River, Tasmania, this volume, 1997. Locher, H., Sediment Transport in the King River, Tasmania, Working Document from the Cooperative Research Centre for Catchment Hydrology 95/5, Monash University, Clayton, Victoria, Australia, 1995. Taylor, J. R., Weaver T. R., McPhail D.C., Murphy N.C., Characterisation of Mine Tailings in the King River System and Delta and evaluation of their impact on local water quality, Report of the Office of the Supervising Scientist Number 105, Mt Lyell Remediation Research and Demonstration Project, 1996.

11th VUGC1997, Monash University STRATIGRAPHY AND CORRELATION O F i m CONTINteNTALREDBED SEQUENCE AT THE KOTELMCH UPPER PERMIAN FOSSIL TETRAPOB LOCALITY.RUSSIA.

ANDREA.COEFA Monash University The Kotehiich terrestrial tetrapod locality is part of the Tatarian, the uppermost Permian stage in Russia. The locality is a sequence of redbed sediments along the westem bank of the Vyatka River near Kotelnich, and is the site of the recovery of fossil tetrapods, fish, palyno-flora, macro-flora, and invertebrates of local, regional and global significance. The site is approximately 800 km E/N/E of Moscow on the Westem Pre-UraUan Russian Platform. Most of the Upper Permian type succession in Russia, including the sediments at Kotelnich, are continental in origin. The aims of the current project are to describe the sedimentary sequence at Kotelnich, determine its depositional history and correlate the tetrapod fossil finds with other Permian localities world-wide. Ultimately, an understanding of the palaeo-environments is sought. Prior to this investigation, the sedimentary imits at Kotelnich had not been formally recognised, described or named. Traditionally, Kotelnich fossil faunas had been allocated to either the "Kotelnich-1" or "Kotelnich-2" units. However, the current investigation has assigned the Kotelnich sequence to five members and these are summarised below using a new nomenclature: Vayftyushonkov Member* Bofovikov Membar*..., ShestakovMember* Sokolovogora Member*.

Lithologv! red calcareous clay and siltstone jflimal overbank andfloodplain orange fine to medium sandstoiie aeolian single fluvial channel grey intarbedded siltstone and medium sandstone o^^ed>ank and flood plain red calcareous siltstone green coarse to medium sandstone ribbon channels (braided fluvial) and red calcareous siltstone

Unlike marine sequences, terrestrial sequences are characterised by frequent unconformities and a relative lack of useful index fossils. This makes the hundreds of Permian terrestrial fossil localities in Russia difficuh to correlate with each other and with more recently discovered Permian sequences around the world. There is still widespread disagreement concerning the correlation of the Permian, in particular the terrestrial deposits of the Tatarian. Recently, however, interest has focused on Kotelnich as a useful locality for stratigraphic correlation. Kotelnich contains a range of useful correlatives such as palyno-flora, invertebrate fossils, drill core logs and palaeo-magnetic data. This has allowed the five members at Kotehiich to be correlated to the Vishkilsky Horizon (Regional Stage) and the Vyatsky Horizon of the Upper Tatarian, Upper Permian (Gomankov, in press). REFERENCES

Gomankov, A. V. (in press, submitted June 1995) Type and reference sections of the Volga-Urals Region. Stratigraphy. Geological Correlation. * New nomenclature by V. R. Lozovskiy (person, commu.). Descriptions and stratigraphy by Coffa.

11th VUGC1997, Monash University

NEW WORK ON THE USE OF SEISMIC INTERVAL VELOCITIES TO MAP SEQUENCE BOUND LATERAL LITHOLOGY CHANGES JOSEPH CHIUPKA Melbourne University Sequence bound lateral lithology changes result from aggradational stacking of facies tracts through an episode of geologic time. The genetic environment is an equilibrium between sediment supply and relative base level. Attractive petroleum traps can exist where subsurface lateral lithology changes involve significant intervals of strata, i.e. in excess of 30 m. Exploration for such stratigraphic traps requires confident seismic mapping of the lateral changes. The ability to map such changes would also reduce the risk of over-estimating the reserves of a structural new field discovery, and the risk of drilling dry appraisal wells. Since 1955 when C.H. Dix presented equations for extracting interval velocities from reflection data, publications (e.g. Cook and Taner, 1969, Neidell et al, 1984) have appeared which attempt to use this information to explore for stratigraphic traps. However, these treat interval velocities as elemental properties - measurements which cannot be broken down into components. A statistical study of well intersections over a lithologically complex sequence shows the lack of reUability of this approach. Laboratory experiments and mathematical analysis by K. lida in 1938 show that the p-wave velocity of granular substances is a fimction of grain composition and stacking height (burial depth). C.H. Acheson built on this in 1963 to derive equations of interval velocity based on a statistical analysis of wells. His work provides an in-situ approach to separating and quantifying the velocity influences of composition (lithology) and burial depth. New statistical studies of well intersections have resulted in a lithologically parameterized approach extending from the findings of earlier workers. Its strength lies in isolating and quantifying the velocity influencing properties of each lithology in a geologically consistent manner. Results to date indicate the approach has significant reliability advantages. REFERENCES Acheson, C.H., 1963, Time-depth and velocity-depth relations in Western Canada. Geophysics, 28, 894-909. Cook, E.E., and Taner, M.T., 1969, Velocity spectra and their use in stratigraphic and lithologic differentiation. Geophys. Prosp., 17,433-448. Dix, C.H., 1955, Seismic velocities from surface measurements. Geophysics, 20, 68-86. lida, K., 1939, Velocity of elastic waves in a granular substance. Bull Earthq. Res. Inst., 17, 783-807. Neidell, N.S., Cook, E.E., Beard, J.H., and Franz, W.L., 1984, Improve prospect picks with moveout velocity analysis. World Oil, January edition, 129-142.

11th VUGC1997, Monash University

STRATIGRAPHY AND CORRELATION OF THE CONTINENTAL REDBED SEQIJENCEATTHEKOTELNICHUPFEfe LOCALlTY.RiSSIA. ANDREA. COFFA Monash University The Kotehiich terrestrial tetrapod locahty is part of the Tatarian, the uppermost Permian stage in Russia. The locality is a sequence of redbed sediments along the westem bank of the Vyatka River near Kotelnich, and is the site of the recovery of fossil tetrapods, fish, palyno-flora, macro-flora, and invertebrates of local, regional and global significance. The site is approximately 800 km E/N/E of Moscow on the Westem Pre-Uralian Russian Platform. Most of the Upper Permian type succession in Russia, including the sediments at Kotelnich, are continental in origin. The aims of the current project are to describe the sedimentary sequence at Kotelnich, determine its depositional history and correlate the tetrapod fossilfindswith other Permian localities world-wide. Ultimately, an understanding of the palaeo-environments is sought. Prior to this investigation, the sedimentary units at Kotelnich had not been formally recognised, described or named. Traditionally, Kotehiich fossil faunas had been allocated to either the "Kotelnich-1" or "Kotelnich-2" units. However, the current investigation has assigned the Kotelnich sequence to five members and these are summarised below using a new nomenclature: Mew Noinenclaltire Vanyushonkov Member* OiiTJiev Member* Shestakov Member* SokoiovogoraMember*,.

Lithology: red calcareous clay and sfltstone fluvial overbanfc m4 flood plain orangefineto medium sandstone aeolian single fluvial channel grey inteitedded siltstone and me^om sandstone overbMk and flood plain red calcareous siltstone green coarse to medium sandstone ribbon channels (braided fluvial) and red calcareous siltstone

Unlike marine sequences, terrestrial sequences are characterised byfirequentunconformities and a relative lack of useful index fossils. This makes the hundreds of Permian terrestrial fossil localities in Russia difficult to correlate with each other and with more recently discovered Permian sequences around the world. There is still widespread disagreement conceming the correlation of the Permian, in particular the terrestrial deposits of the Tatarian. Recently, however, interest has focused on Kotelnich as a usefiil locality for stratigraphic correlation. Kotehiich contains a range of useful correlatives such as palyno-flora, invertebrate fossils, drill core logs and palaeo-magnetic data. This has allowed thefivemembers at Kotelnich to be correlated to the Vishkilsky Horizon (Regional Stage) and the Vyatsky Horizon of the Upper Tatarian, Upper Permian (Gomankov, in press). REFERENCES

11th VUGC1997, Monash University

i m HELMUT mON-MCKEL SXJLPHTOE DEPOSIT^ T1IAMWAYS,WESTEBN A0STIULIA: AIJMQUE ARCHAE^ EDWARD A. CURL, BSC. Monash University Helmut is a komatiite-associated nickel sulphide orebody located in the Tramways belt of the Norseman-Wiluna belt, Archaean Yilgam Craton, 40 km SSE of Kambalda (WA). The orebody is separatedfromthe komatiite/basalt contact by 3-7 m of weakly mineralised (uneconomic) talc-carbonate altered komatiitic rock. The ore profile is up to 21m thick and is dominated by low tenor (nickel poor) matrix and disseminated iron-nickel sulphides. Its occurrence internally rather than on the komatiite/basalt contact and the lack of a significant massive sulphide zone are characteristics of the Hehnut orebody that differ significantlyfromthe typical Kambalda-style mineralisation (Gresham and Loftus-Hills, 1981). The purpose of this study is to investigate the significance of these distinctive characteristics to the origin of the Hehnut orebody and toftirtherexploration in the Tramways belt. At Kambalda, nickel sulphide deposits typically occur as linear, ribbon-like bodies at the base of a thick (< 1000 m) sequence of komatiite flows. The volcanic environments that host ore have been interpreted to represent activelyflowingpaleo lava-channels (Cowden and Roberts, 1990; Lesher and Amdt, 1995). Olivine preferentially accumulated in the lava-channel environment, resulting in rocks with higher MgO contents than in the adjacent flanking, non-channelled lava environments. Immiscible sulphide liquid also accumulated at the base of the lava channels which, together with the effects of superimposed deformation, resulted in the linear, ribbon-like morphology shown by the orebodies. The orebodies generally occupy depressions in the top of the underlying basalt unit, and most (>80 %) of the ore is in direct contact with the underlying basalt (Gresham and Loftus-Hills, 1981). The distinctive characteristics of the Hehnut orebody may be explained by two hypotheses. The first hypothesis is that the weakly-mineralised talc-carbonate altered komatiitic footwall represents an accumulation of fractionally crystallised olivine prior to sulphide saturation. This possibility is supported by the fact that the weakly-mineraUsed footwall is cumulate textured in places and that the ore textures are predominantly interstitial to relict oUvine cumulates, suggesting concurrent crystallisation of olivine and sulphide. This is consistent with relatively late stage sulphide saturation, possibly following limited oUvinefractionationto form the weakly-minerahsed footwall. The weak mineralisation in the footwall is concentrated towards the top of the unit and, based on petrography, appears to be interstitial to relict olivine grains. This could imply that the sulphides percolated downward between aheady crystallised olivine grains. This hypothesis is being tested geochemically using major, minor and trace element concentrations measured by X-Ray Fluorescence Spectrometry (XRF), and trace element concentrations determined by High Resolution-Inductively Coupled Plasma-Mass Spectrometry (HR-ICP-MS). Relative enrichment of elements that would have been incompatible in olivine {e.g., Al, Ti, Zr, Y, LREE) in the hangingwall coupled with higher MgO and lower incompatible element concentrations in the footwall could indicate thefractionationof ohvine from the komatiite lava prior to ore deposition. The second hypothesis is that the Hehnut orebody was structurally emplaced over the top of a weakly-mineralisedflankingunit by low-angle reverse faults. The results of underground mapping indicate structural movement on the contact between the ore zone and the weakly-mineraUsed footwall. The plane of the contact is, in some places, roughly coplanar with regional-scale thrust planes {e.g., Tramways thrust). Thus, movement on the low-angle faults could be assumed to be reverse. Given the limited structural and stratigraphic information provided by the minescale mapping, the degree of displacement on these faults is difficult to estabhsh. If the weakly-mineralised footwall rocks areflanking,non-ore environment rocks, their composition is anticipated to be lower in MgO and higher in olivine-incompatible elements than if they were ore environment rocks, the opposite relationship to that described for thefirsthypothesis. REFERENCES

Cowden, A. & Roberts, D. E., 1990. In: Geology of the Mineral Deposits ofAustralia and Papua New Guinea (ed Hughes, F. E.), pp. 567-581, The Australasian Institute of Mining and Metallurgy, Melboume. Gresham, J. J. & Loftus-Hills, G. D., 1981. Economic Geology, 76,1373-1416. Lesher, C. M. & Amdt, N. T, 1995. Lithos, 34,127-157.

11th VUGC1997, Monash University

TOHLISSE CONGLOMERATE IGNEOUS CLAST GEOCHEMISTRY: IMPLICATIONS FORTERRANE PROVENANCE ALISON.A.DEAN Monash University The Torlesse terrane constitutes approximately two thirds of the New Zealand land area and the majority of the total microcontinent, comprising Permian to mid/Late Cretaceous sandstone, mudstone and metamorphic equivalents (98%), with subordinate metavolcanics, conglomerate and exotic limestone (2%). In the South Island the Torlesse terrane consists of two subterranes separated by a belt of highly disrupted melange. The Rakaia subterrane comprises Permian to Jurassic sediments and represents a complex accretionary assemblage truncated tectonically prior to the amalgamation of the younger Pahau subterrane, or as a result of subsequent juxtapositioning. The Pahau subterrane comprises Late Jurassic to mid/Late Cretaceous sediments which have strong provenance links to the Rakaia subterrane indicating relationship between the two was close. Pahau deformation is consistent with a simple accretionary model. The volume of the Torlesse terrane is substantial (at least 3.5 x 10^ km^). Potential source areas were of a similar large volume, and it has been postulated that the Torlesse terrane is allochthonous and formed spatially oceanward of a continental margin with a heterogeneous Andean-like source. (Bradshaw, 1989) Detrital conglomerates within the Torlesse terrane, although volumetrically insignificant, are widespread. Petrographic and whole rock geochemical methods were employed to examine the igneous clasts (plutonic and volcanic) collected from conglomerates at three Canterbury localitites. The accumulated data allow tighter constraint of Torlesse provenance and improved determination of Mesozoic tectonic setting within the South Island region. Igneous clasts from all three conglomerates are predominantly calc-alkaline and exhibit major and trace element characteristics indicative of subduction related magmas. Multielement abundance diagrams exhibit a distinctive spiked pattern, primarily due to depletion of HPS elements and an overall LIL element enrichment. The highly felsic nature of clasts (>65wt% SiO^) indicates intrusion and extrusion occurred along an active continental margin that had attained full crustal thickness The Rakaia subterrane conglomerate igneous clasts preserve record of an extensive peraluminous 'S-type' granitic province not represented elsewhere. The deformed granodiorite clasts with distinctive low K^O values are thought to represent melted volcanic sediments, part of a thickened accretionary prism, during the final stages of subduction. Pahau subterrane conglomerate igneous clasts display features that indicate predominantly metaluminous 'I-type', possibly cogenetic volcano-plutonic provinces. The peralkaline to weakly peraluminous volcanic clasts from one Pahau subterrane conglomerate display extreme fractionation of Sr and high HPS element abundances (A-type characteristics) that could indicate a progression toward anorogenic volcanism during the waning stages of subduction, or a change to an extensional regime at some stage prior to conglomerate deposition during the Early Cretaceous. (Collins, 1982) The differences discerned provide evidence that the Torlesse detritus has undergone homogenisation but can be considered as having been derived from continental crust with a diverse and varied igneous character that exposed a spectrum of intrusive levels. The mineralogy and geochemistry of conglomerate clasts compares favourably with numerous volcano-plutonic continental provinces around the Pacific margin that are believed to represent the former Gondwana margin. When geochemistry is correlated with subsequent radiogenic isotope analyses, particularly U/Pb zircon and Rb/Sr data, the New England Fold Belt, eastern Australia appears a likely protolith. (Frost and Coombs,1989; Ireland,1992; Adams,1997) REFERENCES Bradshaw, J.D., 1989, Tectonics, 8(4), 803-820. Collins, WJ., Beams, S.D., White, A.J.R. and Chappell, B.W., 1982, Contributions to Mineralogy and Petrology, 80, 189-200. Dean, A. A., 1993, Unpublished MSc thesis, University of Canterbury, Christchurch, New Zealand. Frost, C.D., and Coombs,D.S., 1989, American Journal of Science, 289, 744-770. Ireland, T.R., 1992, Geochimica et Cosmochimica Acta, 56, 911-920. Adams, C.J., 1997, Terrane Dynamics - 97, International Conference on Terrane Geology, Abstracts, Christchurch, New Zealand.

11th VUGC1997, Monash University

MAFIC/IELSIC RELATIONSHIPS: AN EXAMPLE FROM THE BEGABATHOLITH, SOUTHEASTERN AUSTRALIA ALISON .A. DEAN Monash University. The close association between mafic, intermediate and felsic intrusives is a common feature of most granitic complexes. However, the role of mafic (mantle-derived) magmas in the generation, evolution and emplacement of felsic magmas is uncertain. The Late Silurian/Early Devonian 'I-type' Bega Batholith in southeastern Australia comprises more than 130 separate plutons (Beams, 1980), many of which include mafic dyke swarms, small parasitic mafic intrusions and mafic microgranitoid enclaves thus providing an ideal locality to investigate such relationships. Isotopic variation for intrusives along the eastern margin of the batholith have been used as evidence for limited mixing associated with underplating and late stage intrusion into the crust of mantle derived magmas (McCulloch & Woodhead, 1989). Rama Head and Petrel Point within Croajingolong National Park, 25kms southwest of Mallacoota, East Gippsland, comprise predominantly granodiorite outcrop that contains abundant microgranitoid enclaves, syn-plutonic and post-intrusive dykes, and hybrid mixtures. This plutonic complex intrudes folded Late Ordovician age metasediments and is considered the southernmost exposure of the eastern arm of the Bega Batholith. Field relationships and petrographic evidence indicate simultaneous intrusion and mingling of several fluid magmas. Significant Sr and Nd isotopic variation supports these findings and indicate the magmas may have mixed. Previous studies have ignored the numerous basaltic dykes (0.5 to ~8m in width) with well developed chill margins that cut the granite complex (~NE/SW). "^^ArP^Ar geochronology on mineral separates for two of these mafic dykes indicate Paleozoic ages. While it is accepted that basaltic dykes such as these may have provided the heat necessary to generate the granites within the Lachlan Fold Belt, their role in the modification of crustal melts is usually discounted. The possibility of such compositions being representative of a parental end member is considered for this locality.

REFERENCES

Beams, S.D., 1980, Magmatic evolution of the southeastern Lachlan Fold Belt, Australia. Unpublished PhD thesis, La Trobe University, Melbourne, Australia, 319p. McCulloch, M.T., and Woodhead, J.D., 1993, Lead isotopic evidence for deep crustal-scale fluid transport during granite petrogenesis. Geochimica et Cosmochimica Acta, 57, pp.659-674.

11th VUGC1997, Monash University

RECRYSTALLIZATION OF SILICA AT LOW TEMPERATURES

MARKDOMANSKI La Trobe University Ethnographic and archaeological evidence suggests that intentional heating of fine-grained siliceous materials in order to improve their flaking properties has been practised in many prehistoric and recent communities. Extensive mechanical testing of heated and imheated microcrystalline and macrocrystalline siliceous lithologies has demonstrated that controlled heat treatment causes a consistent marked gradual reduction in fracture toughness with increased temperature. Micro- and macro-crystalline siliceous lithologies respond differently to heat treatment. The fracture toughness of microcrystalline silica decreases rapidly with heating to an optimum temperature of 400®C; above this, heat-induced microfracturing is common. Macrocrystalline silica shows a more gradual reduction of fracture toughness with heat treatment, and temperatures as high as 600°C do not cause significant heat damage. Petrological studies have shown that there are extensive microstructural changes accompanying the heat treatment of microcrystalline siliceous lithologies. Using thin section analysis, X-ray diffraction studies and scanning electron microscopy, it was demonstrated that the poorly ordered, strongly interlocking fabric of unheated microcrystalline silica becomes more equigranular and better crystallized with thermal treatment, as a result of heatinduced recrystallization. Under the scanning electron microscope obvious microstructural changes are visible onfractured,etched surfaces of raw and heated samples of agate and flint. The unheated agate specimen is characterized by tightly packed, interlocking fibres of chalcedonic siUca. In the agate sample heated to 400°C, these fibres are transformed into more granular, equidimensional crystals of quartz, with well-defined crystal faces. A similar recrystallization is observed in the heated flint, although it is less obvious. This recrystallization can also be detected in the high angle peaks of X-ray diffractograms, and is most easily recognizable in the 212 peaks. The crystallinity indices of the raw and heated samples of agate and flint illustrate the microstructural changes which occur when microcrystalline siliceous lithologies are heated. The crystallinity of the unheated agate is 4.4; that of the agate heated to 600°C is considerably greater, 8.7. A smaller trend is shown by the flint; the index increases from 1.2 to 2.2. The recrystallization of chalcedonic silica into more granular quartz crystals may also be detectable by thin section examination under the standard petrological microscope. Heating of microcrystalline and macrocrystalline siliceous lithologies causes microstructural changes and a consistent marked reduction in their fracture toughness, which accounts for the improvement in their flaking properties.

11th VUGC1997, Monash University

STRUCTURE, HIGH-GRADE METAMORPHISM AND STRATIGRAPHY AT THACKARINGA, BROKEN HILL, NSW. TONY DONAGHYS MIKE HALL^ andGEORGE GBSOTsF ^AGCRC - Monash University, ^AGSO - Canberra The Thackaringa region, located 35km to the southwest of Broken Hill, is important for the understanding of the Broken Hill region as a whole as it contains the type localities for the Thackaringa Group, the basal sequence of the Willyama Supergroup stratigraphy. We suggest here that many of the criteria used to separate units with similar lithological associations into different stratigraphic horizons are based on invalid assumptions of protolith formation, post-depositional features - such as partial melting, metasomatism and granitic and gabbroic intrusions, and an over-simplistic stmctural interpretation. Potential exists for gross simplification of the Willyama Supergroup stratigraphy by removal of units with similar lithological associations that are structurally, rather than stratigraphically, repeated within the sequence. This has important ramifications for mineral exploration in Broken Hill as the Broken Hill Pb-Zn-Ag style of mineralisation is believed to occupy a discrete stratigraphic position (Willises a/. 1983). The outcrop in the Thackaringa region is dominated by the Thackaringa Group, previously interpreted as a 13 km thick sequence of felsic volcanics/volcanosedimentary facies with intercalated feldspar-rich sediments and minor mafic tholeiitic lavas (Willis 1984b, Willis et al 1983). The stratigraphic subdivision has been made despite the absence of reliable sedimentary structures and younging criteria, the intense nature of strain and the degree of partial melting in the region, and is based on association of key marker lithologies, particularly mafic and quartzofeldspathic gneisses. However, detailed mapping shows that some of the key marker horizons, e.g. the Ahna Gneiss and the mafic gneisses, are clearly intrusive into the surrounding lithologies and not part of the original depositional sequence. The validity of using other post depositional features to differentiate between Thackaringa Group and Broken Hill Group imits, such as degree of partial melting and minor Na-Fe metasomatism, is also questioned. Structural fabrics mapped to date are difficult to reconcile with the previous stmctural and stratigraphic interpretations (Willis 1984a, 1984b, Willis et al 1983). The identification in this study of five regional scale deformations, including two early mylonite shear fabrics, offers an altemate explanation for the present distribution of lithologies within the Thackaringa region. F^, F3 and F^ fold interference pattems observed in this study are essentially coaxial and, coupled with the development of S2 and S3 mylonite zones, have resulted in large scale transposition, gross attenuation and reorientation of lithological layering. Also, due to the potential for transposition by coaxial deformation, it is ahnost certain that at least one generation of regional isoclinal folds (F3) has not been recognised by previous workers. The F3 isoclines and S^ and S3 mylonite fabrics are subsequently refolded by the larger wavelength regional folds mapped previously as F^. This provides adequate potential for structural repetition of lithological associations previously separated as different stratigraphic imits. We would postulate that the Thackaringa Group consists of a single quartz-albite lithology (Himalaya/Lady Brassey Formation), and that other lithologies are structural repetitions of Broken Hill Group units. The results to date create doubt as to the stratigraphic validity of a large portion of the Thackaringa Group, particularly when much of this unit shares ahnost identical lithological associations with the Broken Hill Group, host sequence for the Broken Hill ore body. As considerable doubt now surrounds the validity of the type localities for the Thackaringa Group, the stratigraphic, stmctural and palaeoenvironmental interpretation of the entire Palaeoproterozoic in the Broken Hill region must be re-evaluated. ACKNOWLEDGMENTS The authors would like to thank Rio Tinto Ltd for their financial assistance on this project and permission to publish. REFERENCES Willis, 1. L., 1984a, Journal & Proceedings, Royal Society ofNew South Wales, 117, 85-97. Willis, I. L., 1984b, MSc (applied geology) thesis, W. S. and L. B. Robinson College, Broken Hill, New South Wales, Australia (unpublished). Willis, I. L., Brown, R. E., Stroud, W. J. & Stevens, B. P. J., 1983, Journal of the Geological Society ofAustralia, 30, 195-224.

11th VUGC1997, Monash University

SHEAR ZONE DEFORMATION AND METASOMATISM AT BROKEN HILL, NEW SOUTH WALES CHRIS.M.DOYLE Monash University The Willyama supergroup is comprised of an interlayered sequence of Paleoproterozoic sediments with some volcanics that have been dated as -1690 Ma (Stevens et. al, 1988). The region has subsequently undergone metamorphism up to granulite facies at around 1600 Ma (Page & Laing, 1992), with partial melting common in both pelitic and psammitic layers. The areas of study include: the Monuments area (just north of Broken Hill); the Thackaringa Pinnacles area; and the Rockwell Schist Zone, all of which are characterised by the presence of Sundown Group gneisses (metamorphosed pelitic to psammitic meta-sediments). Cross-cutting these high grade gneisses are a niunber of amphibolite - greenschist facies retrograde schist zones: the Steven's Creek Schist Zone in the Monuments area; the Thackaringa Pinnacles Schist Zone; and the Rockwell Schist Zone, which clearly show geochemical and mineralogical alteration across their strike. Shear zone formation post-dated peak metamorphic conditions, with mineral assemblages in the shear zones at lower grade than in the surrounding rocks. Reactivation of these shear zones subsequently occurred during the Delamarian orogeny (520 Ma) (Stevens et. al, 1988). Development of a regionally-extensive NE trending planar fabric (observed in field areas), is the result of at least two phases of deformation during prograde metamorphism. This resultant schistosity is, however, overprinted or re-oriented in the shears, with the observed steeply- dipping foliation defining the shear zone fabric. Measured mineral lineations coupled withfieldobservations from within the shear zones suggest the shearing was sinistral, and movement was of a predominantly dip-slip sense. Formation of these shear zones probably provided a focus for escapingfluidsduring cooling, and as such these sites are areas of intense geochemical and mineralogical alteration. Retrograde minerals within the shear zone include muscovite, biotite, staurolite, chloritoid and some sillimanite, whilst the host gneisses contain predominantly biotite, sillimanite, plagioclase, quartz, and some minor retrograde muscovite. Large gamets (up to 5cm) are a feature of both the shear zones and host rock, and appear to pre-date most foliations, dominantly a result of pro-grade metamorphism. Escapingfluidsupon cooling of large pegmatitic melts may provide afluidsource for the metasomatism in the area. REFERENCES Stevens, B.PJ., Bames, R.G., Brown, R.E., Stroud, W.J., Willis, LL., 1988. The Willyama Supergroup in the Broken Hill and Euriowie Blocks, New South Wales. Precambrian Research, 40/41,297-327. Page, R.W., Laing, W.P., 1992. Metavolcanics related to the Broken Hill orebody, Australia: geology, depositional age and timing of high-grade metamorphism. Economic geology, 87,2138-2168

11th VUGC1997, Monash University

REASSESSMENT OF THE ARCHEAK TECTONICS IN THE MURCHISON PROVINCE, WESTERN AUSTRALIA BENJAMIN! FOLEY Monash University Earlier models put forward for Archaean tectonics in the Murchison province of Western Australia have proposed that the granitoid/greenstone structural patterns result from diapiric intrusion of granitoids into greenstone sequences (e.g. Gee et al., 1981). More recently, Myers and Watkins, (1985) have suggested that these patterns are a result of fold interferences. The same controversy is common for other Archaean granitoid/greenstone terrains across the earth (e.g. conflicting interpretations of the Chinamora Batholith by Snowden and Bickle, (1976) and Ramsay, (1981)). In the past fifteen years, progress has been made in the field of structural geology in partially melted domains. In particular structures characteristic of syn-magmatic deformation are now better recognised. Using this new knowledge, this study investigates granitoid/greenstone structural relationships in the Yalgoo district within the Murchison Province. It is found that: - syn-magmatic deformation occured in the core of batholiths. This is exempUfied by magmatic fabrics and migmatitic deformation. - sub-solidus deformation (melt in shears, in between boudins) is overprinted by solid state deformation at contacts with greenstones - multiple folding in greenstones is not found in granitoids - extensional faulting relationships exist at contacts - late strike/slip faulting occurred (anastomosing shear zones) - foUations strike and dip variably within the inner parts of batholiths, and trend conformably with greenstone belts at the contacts. The fold interferences model predicts fabric overprinting granitoid/greenstone contacts in the fold hinges. This study shows that fabrics trend parallel to the contacts and do not overprint them. Therefore the fold interference model has no serious structural ground. Results from this study are consistent in many respects to the initially proposed diapiric model. They suggest granitoid/ greenstone patterns outcropping in the Yalgoo district, result from diapiric emplacement of granitoid rocks into overlying sequences of greenstone rocks. Granitoid/ greenstone pattems now observable resultfromerosion of these structures. REFERENCES Gee, R.D., Baxter, J.L., Wilde, S.A., and Williams, I.R., 1981. Crustal development in the Archaean Yilgam block, Western Austraha. Geological Society ofAustralia Special Publications^ 7,43-56. Myers, J.S., and Watkins, K.P., 1985. Origin of granite-greenstone pattems, Yilgam block, Westem Australia. Geology 13,778-780. Ramsay, J.G., 1981. Emplacement mechanics of the Chindamora Batholith, Zimbabwe. In: Diapirism and Gravity Tectonics: Report of a Tectonic Studies Group. Journal of Structural Geology, 3, 89-95. Snowden, P.A., and Bickle, M.J., 1976. The Chinamora Batholith: diapiric intmsion or interference fold? Geological Society ofLondon Journal, 132, 131-137.

11th VUGC1997, Monash University

THE GEOCHEMISTRY OF GROUNDWATER AND MINE TAILINGS IN A SEDIMENT BANK OF THE KING RIVER, TASMANIA DEBORAH K. GREEN and D.C. 'BEAR' Mc PHAIL. Monash University During the past 80 years approximately 97 million tonnes of mine tailings and 1.4 million tonnes of slag were deposited into the Queen and King River systems (Locher, 1995). This material, presently situated in overbank, river bottom and delta deposits, contains up to 5wt.% sulphide minerals. Surface and groundwater interaction with these tailings produces high concentrations and fluxes of acid and major and trace elements that are potentially toxic to aquatic life in the King River and Macquarie Harbour. We are focusing on the mode of transport and the flux of elements in the groundwater of one sediment bank along the King River (Bank D), in order to study the spatial and temporal variability of the geochemistry in the bank. Furthermore we are studying the attenuation of elements in the sediment bank by identifying their speciation in the sediment. Field work involved installation of piezometers, site description, measurement of field parameters (pH, Eh, Cl, salinity, temperature and concentrations of Fe2+, sulphate and sulphide) and sampling of sediment and groimdwater. Groimdwater was sampled in two seasons, summer and winter, in order to characterise seasonal variability. Groundwater samples were analysed for major and trace elements by Atomic Absorption Spectrometry (AAS) and High Resolution Inductively Coupled Plasma Mass Spectrometry (HR-ICP-MS), respectively. The major elements measured include Si, Al, K, Na, Mg, Ca, Fe and Mn, in addition to the following trace elements: Cu, Zn, Co, Pb, Ti, Cr, Cd, Sn, Sb, Ba, U, Ni, As and Hg. Sediment analysis involved the preparation of polished thin sections for optical microscopy, microprobe analysis, Scanning Electron Microscopy (SEM) in combination with Energy Dispersive X Ray Analysis (EDXA), and X Ray Diffraction (XRD). Given the heterogeneous nature of the sediments and high proportion of gangue minerals (i.e. silicates), selected samples were analysed by SEM and XRD after a 2-stage heavy liquid and 5-stage magnetic separation. In addition, a five-stage sequential extraction scheme was developed and performed on eight selected sediment samples, in order to determine the speciation of trace metals in the sediment. Furthermore, adsorption characteristics of the sediment were studied with respect to grainsize and extractant concentration. The major components of the groundwater are sulphate (29.8 mg/1 to 5459.6 mg/1) and iron (5.1 mg/1 to 2155.0 mgA). The most abundant trace metals include Cu (0.8 ng/1 to 14530 ^gA),Zn(13.0 ^g/lto 1850îg/l), Co( 1.1 îg/ Ito 2311.8 |ig/l) and Pb( 0.01 ^g/lto 108.01 îg/l). Distributions of aqueous species and mineral saturation states are calculated using thermodynamic modelling (computer program MINTEQA2) in order to assess the quality of water analyses and to identify within the sediment bank, possible locations of metal attenuation and release. Preliminary results of the sequential extraction indicate that clay minerals may be important in controlling the attenuation of cobalt, lead, copper and to a lesser extent zinc. Framboidal iron sulphide grains contain traces of Co, Cu, Pb, Zn and Mn and may be a significant sink and/or source of those particular metals. The results of this study will allow us to interpret in detail the interaction between water and sediment and, in combination with the study of groundwater hydrology within the bank (Hooper and McPhail, 1997), we will be able to predict accurately, mass loadings of metals to the King River and the seasonal variability between sxmraier and winter.

REFERENCES

Hooper, W.C. and McPhail, D.C., 1997. The Hydrogeology of a Sediment Bank on the King River, Tasmania, this volume, Locher, H., 1995. Sediment Transport in the King River, Tasmania, Working document from the Cooperative Research Centre for Catchment Hydrology 95/5, Monash University, Clayton, Victoria, Australia. Taylor, J.R., Weaver, T.R., McPhail, D.C. and Murphy, N.C., 1996. Characterisation and impact assessment of mine tailings in the King River system and delta. Western Tasmania, Supervising Scientist Report.

11th VUGC1997, Monash University

THE HYDROGEOLOGY OF A SEmMEOT BANKONTHEIQNGM^ TASMANIA W.CAMERONHOOPERANDD.C/'BEAR" MCPHAIL Monash University An estimated 97 million tonnes of sulphide-rich mine tailings have accimiulated in the King River and Macquarie Harbour in western Tasmania as a result of historic copper mining at Mount Lyell near Queenstown, Tasmania (Locher, 1995). Sediment banks along the river's edge are contaminated with the tailings and are a source of acid and toxic metals. Understanding the hydrogeology of the banks is necessary in assessing how much contaminant is entering the King River. Thirty mini-piezometers were installed to measure hydraulic head and conductivity in the bank sediments. Sediments were sampled during installation in order to measure porosity, grainsize and hydraulic conductivity in the laboratory. Hydraulic heads and conductivities were measured in both summer and winter to study the seasonal variability of groimd water flow. Contours of hydraulic head indicate that in the eastem half of the bank, ground water flow radiates from the north eastem comer of the bank towards the river, whereas in the westem half of the bank the contours are sub-parallel to the river and flow towards the river (Figure 1). Hydraulic gradients vary between 4.76x1 Q-^m/m in summer to 6.1x1 O W m in winter and are higher near the river (Figure 1). During the summer the hydraulic gradients point into the bank in some parts of the bank. Hydraulic conductivity is estimated to be 9.6 x 10-Ws to 2.7 x lO Ws, based on rising head tests in the field and constant-head permeameter tests in the lab and measured porosities range between 40% and 55%. Grainsize analysis indicates that the banks are composed of well sorted, fine sands and coarse silts (28|im to 154|Lim), where grainsize increases towards the downstream end of the bank. Hydraulic conductivity is proportional and porosity is inversely proportional to grainsize. Based on Darcy's Law, preliminary estimates of ground water fluxes into the river along the whole bank are approximately 4,300 1/day in summer and 12,6001/day in winter. These values are approximately an order of magnitude lower than the estimated value of92,5001/day from Taylor et al. (1996). The difference is probably because their estimate was based on measurements from only 3 piezometers and their assumption of a higher hydraulic conductivity of lxlO"^m/s. In combination with measured water compositions from Green and McPhail (1997), the results of this study allow the calculation of acid and element fluxes into the river.

Figure 1. Map of Sediment Bank D on the King River, Tasmania. Contours of hydraulic head, in centimetres referenced to an arbitrary datum, are for July 1997.

REFERENCES

Green, D.K. and McPhail, D.C.,1997. The Geochemistry of Ground Water and Sediments in a Mine Tailings Sediment Bank of the King River, Tasmania. This Volume. Locher, H., 1995. Sediment Transport in the King River, Tasmania. Working documentfrom the Cooperative Research Centre for Catchment Hydrology 95/5, Monash University, Clayton, Victoria, Australia, 160pp. Taylor, J.R., Weaver, TR., McPhail, D.C. and Murphy, N.C., 1996. Characterisation and impact assessment of mine tailings in the King River system and delta, Westem Tasmania. Supervising Scientist Report 105, Commonwealth of Australia, 122pp.

11th VUGC1997. Monash University

THE EIWIRONMENmL IMPACTS OF GOLD MINING AT WOOttS POINT, VICTORIA AMANDA JOHNSTONE Monash University Gold was mined at the Morning Star Mine at Woods Point, Victoria between 1950's and 1960's. The ore was processed by heap leaching and cyanidation. The ore consists of auriferous quartz veins with minor sulphide minerals that occur in association with lamprophyre dykes of the Woods Point Dyke Swarm. Pyrite is the most common sulphide with notable amounts of arsenopjrite, which on exposure to oxygenated waters can dissolve and release potentially toxic concentrations of arsenic into the surrounding surface waters. An example solubiUty reaction for arsenopyrite is: 4 FeAsS(s) + ISO^Cg) + 6 Hpil) = 4 FeSO,(aq) + 4H3AsO,(aq) The mine site, which is currently under investigation for reopening, consists of the underground shafts, two settling ponds, loose waste rock dumps. Water samples have been collected from the nearby creek, the settling ponds andfromsmall ponds of water about the mine site. The samples were analysed in thefieldfor temperature, pH, Eh, dissolved oxygen, electrical conductivity (EC), salinity and total dissolved solids (TDS). In the laboratory, total arsenic concentrations were measured using standard methods with UV-Vis-NIR spectrophotometry. The measured pH values range from 3.4 to 8.4 and Eh ranged from 2 to 270mv (relative to the standard hydrogen electrode). The lowest pH and highest Eh were measured for water that was seeping out of the hillside and may be ground water or near-surface water. The bottom of the pond has yellow-orange precipitate that is probably iron oxyhydroxide. TDS varied between 35mgA and 608mg/l with the lowest values obtained upstream of the settling ponds. Dissolved oxygen was greater in the upstream waters at 1 Llmg/1 and lower in the small pond at 6.5mg/l. Salinity varied from 0 ml, in the upstream waters, to 0.4 ml in the second settling pond. The temperature ranged from 6.4°C in the upstream waters to 12. PC in the setting ponds. Low concentrations of arsenic were measured in the seepage pond and in one of the settling ponds. The inferred speciation of aqueous arsenic is a mixture of arsenate (oxidized) and arsenite (relatively reduced) based on equilibrium Eh-pH diagrams. The mobility of arsenic is likely to be affected by soils and sediments. Arsenate species can precipitate as secondary minerals (e.g., scorodite^ coprecipitate with hydrous iron compounds and adsorb onto ferric oxyhydroxides, organic materials and clay (Appleton et al., 1996). The initial results of this project, as well as the results from previous testing by the Department of Water Resources, Victoria (1989) suggest that there is potential for elevated arsenic concentrations in waterways of the Woods Point area. The results of this continuing study will help in understanding the behaviour of arsenic at Woods Point and elsewhere. REFERENCES Appleton, J. D., Fuge, R. and McCall, G. J. H., 1996. Environmental Geochemistry and Health. Geological Society Special Publication^o. 113, 153-155. Department of Water Resources Victoria, 1989. Distribution and Cause of High Arsenic Concentrations in Groundwater in Central Victoria. Water Resource Management Report Series, 110,3-5.

11th VUGC1997, Monash University

MESOZOIC TO RECENT THERMAL HISTORY AND BASEMENT TBXTTONICS OFTHEIIttANJAYAFOLDBELTANDARAFU^

RICHARD D. KENDRICK, KEVIN C. HILL, PAUL B. O'SULLIVAN, AGCRC-VIEPS, La Trobe University, Melbourne, Victoria, Australia KASPAR LUMBANBATU, IJEP SAEFUDIN Geological Research and Development Centre, Bandung, Indonesia Apatite Fission-Track (AFT) analysis of 44 surface and drill-hole samples constrain the Cenozoic tectonic history of the westem Irian Jaya Fold Belt and the adjacent Arafura Platform. These samples indicate two recent periods of cooling in response to uplift and erosion; 1) Early Miocene ages consistent with regional metamorphism in Papua New Guinea (PNG), and 2) Late Miocene-Phocene dates that correlate with arc collision in northem PNG and contemporaneous island-wide deformation driven by changing plate convergence on the northem Australian margin. Results from the Digul-1 drill-hole suggest that Mesozoic rocks reached maximum temperatures prior to development of the Late Cretaceous unconformity. To the south, a Cretaceous sample from the E-2-X drill-hole shows an AFT age greater than the stratigraphic age indicating Uttle or no exposure to the elevated paleotemperatures seen in the westem Papuan Basin. These well data suggest that Late Cretaceous heating associated with the opening of the Coral Sea was limited to the Papuan Basin east of the Araftura Platform. A major lineament corridor is interpreted at the Irian Jaya-PNG boundary from combined gravity, magnetics, thermochronology and surface data. These long-lived basement stmctures which segment the fold belt and the adjacent Araftira and Fly Platforms are along trend with Proterozoic or Paleozoic shear zones in northem Austraha that can be traced across the Araftura Basin. These stmctural features are significant controls on burial history, source and reservoir rock distribution, and economic Cu-Au mineral deposits. The main phase of cooling in response to uplift, recorded by AFT ages, ranges from --4-12 Ma with Late Pliocene-Recent deformation continuing in the foreland and southernmost fold belt. These data correlate with stratigraphic andpaleogeographic data recording the initiation of orogenic compression and development of much of the fold belt in the Middle Miocene-Pliocene, followed by a subsequent period of deformation characterized by shortening and strike-slip faulting. AFT data suggest the thermal maximum of Mesozoic sediments in Eastem Irian Jaya was reached prior to the Late Cretaceous as in the successftil Kutubufieldsof PNG. Another promising generation-trapping pathway for Eastem Irian Jaya, particularly for gas, is dependent on adequate Late MiocenePliocene burial and source rock quality.

11th VUGC1997, Monash University

GEOPHYSICiUL MODELLING OF AEROBMGNETIC ANOMALIES INTHECAPEOTWAYASEA NANCY LAMMENS,BSc Monash University The aeromagnetic image of the South East Otway area shows a strong magnetic response within an area of generally low response. This entire area is covered with low susceptibility Otway Group sediments, which are ahnost certainly not the cause of the magnetic anomahes. The magnetic response therefore appears to be due to a relatively shallow basement block, within which are three strong linear anomalies (See Figure 1.0 below). A distinct boundary defines the north-western edge of the block.

Figure 1.0 Aeromagnetic image of Cape Otway area Based on the aeromagnetic results, more detailed marine and on-shore magnetic surveys were conducted over the area to accurately determine the nature of the westem boundary of the block, and to determine the nature and position of the other strong linear features. These marine surveys were conducted by placing the magnetometer in a dinghy which was towed behind a fishing boat. Surveys Unes were east-west, with a line spacing of five kilometres. To accurately position the profiles, a global positioning system (GPS) unit was used. For this study, a magnetometer, normally used for land surveys, was adapted to fit into a waterproof housing lashed to the dinghy. However this created problems as the signal could not be monitored in real time, and hence any problems occurring could not be detected until the end of each line. A major problem was found to be the orientation of the sensor with respect to the earth's magnetic field. The housing did not allow the sensor to be positioned vertically, meaning that the magnetic signal was sometimes lost. This was overcome by allowing the sensor to remain outside the main waterproof housing and be vertically positioned, giving a continuous signal. The resulting magnetic profiles clearly show the positions of the three strong north-south trending features. While further modelling is needed, preliminary analysis suggests that these linear structures are steeply dipping bodies of magnetic material, with a major fault to the west. While initial data images appear to show the magnetic intensity of each peak decreasing eastwards, this may be due to increased source/receiver separation as the ocean depth increases in that direction. There also appears to be a fourth anomaly to the east of those detected by aeromagnetics, but with much lower intensity. While further study is required, it can be concluded firstly that the technique used for marine surveys is cheap and effective, and with minor modification the magnetic signal could be monitored in real time. It can also be concluded that evidence exists of three, possibly four, steeply dipping basement structures to the south-east of Cape Otway, with a major fault extending north east to the west of the linear structures, and possibly terminating these stractures to the north. 28

11th VUGC1997, Monash University

VEIN SYSTEM AND ITS FLUID INCLUSION GEOCHEMISTRY IN THE BENDIGO GOLD ORE FIELD: IMPLICATIONS FOR ORE FLUID EVOLUTION XIALI La Trobe University The Bendigo ore field is hosted by Lower to Middle Ordovician, Castlemaine Supergroup in turbidite sedi mentary rocks comprising alternating series of black shales and greywackes. The sequence has been metamorphosed to lower-middle greenschist facies. Gold occurs dominantly in quartz veins. Six main generations of quartz veins can be distinguished in the paragenesis and veining events: (VI) Laminated veins (Au-As-Sb-Pb-Zn-Ni) (V2) Spurs (Au-Cu-Pb-Zn); (V3) Massive veins (barren, main dilation stage); (V4). Brecciation veins (Au-As) (V5). Small quartz-ankerite veinlets; and (V6) Pure quartz veinlet/pure calcite veinlets. In the three mineralised veins VI pre- or syndated the main deformation event, whereas V2 and V4 postdated the main deformation event. Three main types of fluid inclusions have been identified at room temperature as follows: Type I, two-phase, primary/secondary VCH4+LH20 fluid inclusions; Type II, two/three-phase, primary/pseudosecondary LC02±CH4(VC02±CH4+LH20 fluid inclusions with variable degree of filling, and Type ffl, VH20+LH20 inclusions grouping into three clusters (Ilia: primary/pseudoseconary, vapour-rich, with V/L=70-90/10-30; Illb: primary/pseudosecondary, liquid-rich, with V/L=15-25/75-85; IIIc: secondary, liquid-rich, with V/L=10-15/8590). Laminated veins are characterised by Type I, II, Ilia and Illb inclusions. They represent a wide range of homogenisation temperatures (Th) (220-401°C). Estimated trapping pressure (Pt) based on isochoresfiromBowers and Helgeson (1983) rangesfirom130 to 3800 bars. The bulk compositions are XCH4=0.02-0.06, XH20=0.910.96 in Type I inclusions; XCH4=0-0.04, XC02=0.02-0.16, XH20=0.83-0.97 in Type H. Gold precipitation in laminated veins was related to CH4-C02-H20-NaCl compositional inclusions. Type 11 and Illb inclusions were identified in spur veins. Inclusions homogenise in the range of 254-400 Trapping pressures arefirom667 to 3400 bars. Highest XC02 values (0.1-0.25), XCH4 (0-0.10) and a corresponding decrease in XH20 values (0.640.88) exist in this stage of gold-rich fluid. Type II inclusions with no CH4 component and type IDb inclusions occur principally in the barren, massive veins. Th and Pt rangefirom220 to 378°C, and 275 to 2800 bars, respectively. The lowest XC02 values (0.010.07) and higher XH20 (0.92-0.97) in Type 11 inclusions are obtained in the massive veins. However, secondary CH4-H20 inclusions are foxmd in the massive veins, which probably corresponds to the brecciation veining (CH4H20-C02-AU fluid activity). In the brecciation veins, Type II inclusions contain higher C02 (0.07-0.15), H20 (0.8—0.93) and minor CH4 (0-0.01). Homogenisation temperatures rangefrom220 to 350° C, and pressures from 800 to 3000 bars. Small ankerite-quartz veins dominantly host Type Illb and minor Type II inclusions with lowest Th and Pt.. In pure quartz or calcite veinlets, fluid inclusions are too small to analyse. Type Hie inclusions are usually irregular in shape, and infrequently show necking-down phenomena. They occur within all of the veins at Central and North Deborah Mines, and have the lowest Th (145 - 200 ViC) and Pt (620 bars). Salinities estimated from clathrate melting temperature for Type II inclusions and final melting temperature of ice for Type I, HI inclusions are between 1.6 and 13.5 wt % equivalent NaCl. The salinities of the late stage barren veins are slightly higher than those in the early stage mineralised veins. The occurrence of non-aqueous CH4 and C02 fluid inclusions and intense carbonate alteration indicate that low salinity, reduced, CH4 and C02-richfluidsaccompanied Bendigo gold mineralisation. Gold occurrence commonly corresponds to higher concentration of methane during the whole process of the fluid evolution. The association of gold occurrences with CH4-H20 fluid inclusions have been reported elsewhere (e.g. Guilhaumou et al., 1990). Fluid immiscibility, including boiling, occurred in the CH4-C02-H20-NaCl system and is responsible for Au deposition in mesothermal gold mineralisation. REFERENCES Bowers, T.S., and Helgeson, H.C., 1983. Calculation of thermodynamic and geochemical consequences of nonideal mixing in the system H20-C02-NaCl on phase relations in geologic system: Equation of state for H20-C02-NaCl fluids at high pressure and temperatures. Geochim. et Cosmochim. Acta, 47,1247-1275. Guilhaumou, N., Santos, M., Touray, J.C., Beny, C., and Dardenne, M., 1990. Multiphase methane-rich fluid inclusions in gold-bearing quartz as illustrated at Pontal (Goias, Brazil). Min. Mag., 54,257-266.

11th VUGC1997, Monash University

MICROBIAL ACnVITYIN GROUNDWATER AND ITS BFEECT ON CYANIDE CONTAMINATIOR SAMANTHA M.E. MEEHAN The University of Melbourne The presence of microorganisms in groundwater affects the stability and fate of contaminants in groundwater due to the organism utilising the contaminants as a nutrient source. This results in the degradation of contaminants in the groundwater. Cyanide (free and complexed) is found in groundwater at old gasworks sites and is utilised by microorganisms as a source of nitrogen and carbon. Microbes exist in groimdwater attached to colloids, which allow them to be transported with groundwater, but may be impeded by the dimensions of the organism and the colloid with respect to pore size (Alfoldi, 1988). Through microbes utilising nutrients, electrons are transfered during the process, which affects the redox potential of the water. Temperature has a profound affect on the rate of growth of microbes, with the rate of enzyme reactions increasing with rising temperature, with optimum temperatures of around ISjC or higher (Alfoldi, 1988). Thus, changes in temperature on a daily, seasonal and annual periodicity can affect the enzyme reactions. 24 hour monitoring was completed at an old gasworks site in South Australia and Tasmania. pH, redox potential (Eh), dissolved oxygen, electrical conductivity, and temperature of groundwater were monitored in bores across each site, each bore with different contamination in the samples (ranging from PAH's, ammoniacal liquors, ammonia, sulphate, cyanide, metals). Samples were taken every two hours to determine if there were any significant changes in any of these variables which could affect the persistence of cyanide in the groundwater. pH across the sites remained relatively constant. Redox potential was the most variable with some bores fluctuating from oxidising to reducing conditions, others gradually becoming less reducing. The amount of variation in redox potential is related to the type of contamination present in the groundwater, and how easily microbes can utilise the contaminants present. Temperature remained relatively constant at South Australia but varied slightly at Tasmania, and there was little variability in dissolved oxygen content, and electrical conductivity. Through biochemical reactions mediated by microorganisms, cyanide is either wholly consumed by the organism biochemically, or the microbes grow using the cyanide for its construction, or it is decomposed through biodegradation to ammonia (NH^) and carbon dioxide (CO^) (Knowles, 1976), both of which are relatively harmless in the quantities produced by this process. Rates of biodegradation in the aquifer in South Australia and Tasmania will be determined through batch tests, using aquifer material from both sites, which will be compared to control sediment samples.

REFERENCES Alfoldi, L., 1988. Groundwater microbiology: Problems and biological treatment - State-of-the-art report. Water Science and Knowles, C.J., 1976. Microorganisms and Cyanide.

40(3), p.652-680.

11th VUGC1997, Monash University

CAN GRAVITATIONALINSTABILITYM T H E MANTLE PRODUCT INTRAFLATE EMILY A. NEIL AND GREGORY A. HOUSEMAN Monash University Intraplate deformation is an interesting phenomenon, which defies the underlying assumption of plate tectonics - that lithospheric plates behave rigidly. By definition, intraplate deformation describes any deformation process on the earth, both compressional and extensional, which occurs within the plate, some distance from the plate boundaries. As one would expect, most of the present tectonic activity seen on the earth occurs at plate boundaries and it was in fact, the localisation of such deformation and tectonism at these boundaries which contributed to the initial evidence for the theory of tectonic plates. In spite of the great extent of deformation, volcanic activity, seismicity and tectonism associated with plate boundaries, tectonic plates are not as rigid as first assumed and can experience internal deformation in addition to the activity at the boundaries. It is possible that the stresses involved in producing intraplate orogeny originate at the plate boundary and are transferred through the plate to the site of the deformation. Conversely the stresses could be mantle derived and acting on the Uthosphere from beneath. The intraplate deformation would then be an expression of deeper processes occurring in the mantle. In this study we investigate the possibility of producing intraplate orogeny from forces produced by mantle activity. Low density crustal layer High density lithospheric layer

Intermediate density asthenospheric layer

'BLOB' forms as high density lithosphere drips off into lower density asthenosphere

Rayleigh-Taylor instability describes the gravitational instability of a layer of dense fluid on top of a less dense fluid. Under these conditions, even slight perturbations at the boimdary between the two layers can grow exponentially until the system overtums. Houseman et al (1981) proposed that such a process could occur in the mantle as the colder, higher density Uthosphere drops off into the lower density asthenosphere in a process that they termed 'mantle convective thinning'. We analyse the Rayleigh-Taylor instability of a three layered system: a low density, 'crustal' layer overlying a high density, 'lithospheric' layer, with these two layers overlying a third, intermediate density, 'asthenospheric' layer. We use this system to investigate the ability of downwelling lithospheric mantle of a Rayleigh-Taylor type instability to thicken a low density crustal layer above it (See Figure). All layers have Newtonian viscosity.

Results show that the downwelling lithospheric 'blob' is indeed able to thicken the low density crustal layer. In the experiments conducted, the crustal layer was thickened to between 130% and 200% the original thickness. For an initial crustal thickness of 35 km this corresponds to crustal thickening to between 45 and 60 km. The actual amoimts of thickening depend on the density and viscosity of the crustal layer with lower density, rigid crust thickening less readily. We propose that such crustal thickening in the model relates to orogenic activity in the earth's crust. Gravitational instability in the mantle is, therefore, a possible source of stress required to produce intraplate orogeny. Figure 1. Sketch showing how a Rayleigh-Taylor instability can cause crustal thickening in a three layered system.

REFERENCES

Houseman G. A., D. P. McKenzie and P. Molnar, 1991. Convective instability of a thickened boundary layer and its relevance for the thermal evolution of continental convergent belts, J. Geoph. Res., 86,6115-6132. Work reported here was conducted as part of the Australian Geodynamics Cooperative Research Centre and this abstract is published with the pemiission of the Director, AGCRC. 31

11th VUGC1997, Monash University

THE STRUCTURE AND STRATIGRAPHY OF THE SOUTH-EASTERN PORTION OF THE CERBEREAN CAULDRON CHRISTOPHER OSBOURNE Bsc. La Trobe University The Cerberean Cauldron is located in central Victoria and formed during the Late Devonian. It is a member of the Marysville Igneous Complex. The Cerberean Cauldron formed when the country rock overlying a rising magma body collapsed along a series ofringfracturesinto the magma chamber causing the emption of the Cerberean Volcanics. The two members of the Cerberean Volcanics, the Rubicon RhyoUte and the Lake Mountain Rhyodacite, crop out in the west of the area. The ringfracturethrough which the volcanics were erupted is exposed as a series of inwardly curving, finger-like intrusions down the centre of the project area with compositions equivalent to the two members of the Cerberean Volcanics. Walhalla Group sedimentary rocks are found both inside and outside the ringfracturewhile the Koala Creek Beds are found only within the ringfracture.The area has not been looked at in detail previously and many interesting discoveries have been made, including a series a of hydrothermally altered basalts at the base of the Koala Creek Beds which may be associated with the earhest stages of cauldron development. The Koala Creek Beds occur within the project area and have been previously considered to be equivalent to the Cathedral Formation on the westem side of the Cauldron. Unlike the Cathedral Formation which has been interpreted as having afluvio-lacustrinedepositional origin (Ryan, 1992), the Koala Creek Beds are thick (>1000m) sequence deposited in a lacustrine environment. This environment formed as a result of subsidence associated with early cauldron subsidence. There are two main structural elements to the area reflected in two distinct fold types seen in the area. The first fold type occurs outside the ring fracture, within the Walhalla Group sedimentary rocks and is consistent with Walhalla Group sedimentary rocks elsewhere. The second fold type present in the area occurs within the ring fracture system. Sedimentary rocks (both Walhalla Group and the Koala Creek Beds) within the fracture have a distinctly different fold style indicating that they have undergone deformation during the formation of the Cerberean Cauldron. This type of deformation has not been recorded in other areas around the cauldron suggesting that it is most evident where the ring dyke is more curved as it is in this area. Deformation of the sediments resulted from the central cauldron block collapsing, causing sediments within tight ring fractures to be compressed due to the curved ring fracture dipping inwards.

11th VUGC1997, Monash University

POMEROY, MJ.\ MCPHAIL, D.C.^ AND SPICOA, L} ^Department of Earth Sciences, ^Department of Chemistry, Monash University The geochemistry of copper in waters and brines is an important control on the transport and deposition of copper and the solubiUty of copper minerals. Hydrothermal ore deposits (e.g., porphyry, stratiform, epithermal) are important examples of the transport and deposition of copper in hydrothermal waters and brines. Copper can exist as different aqueous species, where the predominant species depends on P, T, pH, Eh (redox) and activities of ligands such as CI- and HS-. One of the least imderstood aspects of aqueous copper geochemistry is the type and stability of aqueous copper species, especially reduced Cu(I)-chloride species. In order to identify the stoichiometrics of these species, we have measured the solubihty of cuprite (Cu^O) inpH-buffered waters (4.5<pH<8.5) with dissolved NaCl (.01m<NaCl<2m) at temperatures between 25 jC and 80 jC. Cu(I) and total copper concentrations were measured using UV-Vis-NIR spectrophotometry. Equilibrium was indicated when copper concentrations no longer changed withtime(approximately 1 week at 50; C). Cu(I) concentrations ranged between 1X10-^m and 2X10-^ and total copper concentrations ranged between 1X 10-^m and 6 X10-^. The percentage of Cu(I), relative to Cu(total), was approximately 50% to 100% and increased with decreasing pH. Copper appears to complex with some of the buffer chemicals (e.g., phthalate), based on solubiUties increasing with increased buffer concentrations and absorbance spectra. Figure 1 shows Cu(I) concentrations as afimctionof pH and salinity at 50iC. Cu(I) concentration decreases with increasing pH at all salinities, although there is a smaller decrease at higher salinities. Preliminary interpretation of the data indicates that copper in the experiments exists as several aqueous species, probably mixtures of Cu(I)- and Cu(II)-chloride, as well as Cu-phthalate in the experiments with the phthalate pH buffer. More interpretation and experiments are necessary to determine the precise nature of the aqueous species. The results of this ongoing study will allow us to predict more effectively the transport and deposition of copper in ore-forming and contaminated environments.

-1.5 [NaCl]

•

0.1m

o o

1.0 m 2.0 m

y = -1.086X + 3 . 2 8 2 r y = -0.439X + 0 . 0 6 8 r y = -0.238X-0.802 r

2 = 0.968 2 2

= 0.607 = 0.447

Figure 1. Measured solubility of cuprite at 50; C as a function of pH and NaCl concentration. The lines represent linear functions fitted to the experimental data.

11th VUGC1997, Monash University

SEASONALITY AND TEMPERATURE SIGNALS FROM ISOTOPE AND CATION ANALYSES OF ARAGONITIC MUSSEL SHELLS JESSICA REEVES University of Melbourne The shell of the freshwater mussel, Velesunio ambiguus, is composed of bricks of aragonite, periodically checked by organic-rich bands. Under cathodoluminescent microscopy the shells show a rhyttmiic fluorescence, indicative of seasonal banding, related to the manganese content of the lakefloorsediment and host water composition. Investigation of the variation of the thickness of the bricks within a 'growth band' indicate that this is most likely to be an annular phenomenon. Analysis of the variation of the dl 80, dl3C and Sr/Ca ratios across the bands compared with the temperature, salinity and composition of the host water form a seasonal signature for the modem mussel. Lake Victoria, south-west New South Wales, regulated for storage water since 1928, provides an optimal habitat for mussels. The mussels live longer and grow larger here than in naturallyfluctuatinglakes. The shells of live mussels, collected both in summer and winter were analysed for Ca, Sr and Mn content using the EM microprobe and dl80 and dl3C ratios along the axis of maximum growth, extending from the imibo to the growing edge of the shell, establishing a baseline for modem climatic and environmental variation. Collections of Holocene midden shells of the same species were exposed on the lake foreshore and barrier islands when the lake level was lowered from 27.5m to 23m (Australian Height Datum) in 1994. Bulk dl80 and dl3C ratios and Ca, Sr and Mn content were obtained from Holocene and Pleistocene samples controlled by radiocarbon dating. These values were compared to the modem analogue to infer palaeotemperature and salinity.

11th VUGC1997, Monash University

THE THERMAL, STRATIGRAPHIC AND STRUCTURAL HISTORY OF THE OTWAY BASIN IN THE LORNE ^ A , VICTORIA. ALASTAIR RYANBSc Monash University A roughly rectangular area of 10 square kilometres stretchingfromCumberland River to Lome township and extending inland to Allenvale Road was mapped at a 1:10,000 scale. Samples were taken throughout the study area for Vitrinite Reflectance (VR) and spore-pollen Thermal Alteration Index (TAI) analysis. The objectives were; to investigate in detail the structures observed by Edwards (1962), identify the stratigraphic packages present in the area, and then correlate these findings with the palaeotemperatures measured using VR and TAI to obtain information on the geothermal gradient, depth of burial, stratigraphic/structural-isothermal relationship and the relative timing of structural and thermal events. The stratigraphy of the area is dominated by Early Cretaceous Eumeralla Formation packages of massive sandstone and interbedded altemating thin sandstone/siltstone/mudstone deposits, with a smaller deposit of Tertiary sediments apparently located in the hinge of the Lome Syncline on the ridge behind the Lome township. The Eumeralla Formation deposits were laid down in a high-energy braided-river environment, (Hand 1993), and appear laterally continuous throughout the study area while the Tertiary sediments are poorly exposed and appear to consist of extraordinarily quartz-rich subangular,fineto coarse sandstone sediments that appear slightly fermginous (orange) indicating a high-energy depositional environment (probably terrestrial) with a proximal source suggesting that they were deposited in a very large channel-type deposit of a large river. VR and Apatite Fission Track Analysis (AFTA) studies by Cooper (1996), indicate that the area underwent burial to achieve temperatures of 110 to 145 degrees Celsius. AFTA results suggest that Lome possesses a unique thermal history compared to the rest of the Otway Basin. It appears that Lome has imdergone two cooling events; a Mid-Cretaceous event - 90 Ma (that it shares in conmion with the rest of the Otway Basin) as well as a Late Cretaceous event at - 70-80 Ma. Cooper (1996) hypothesized that the second cooling event was caused by a magmatic intrasion (seen at 2.0 seconds beneath shotpoint 1030 on seismic line OS88A-13), in the Torquay Embayment (Tmpp et al., 1994), and is closest to the coastline in the vicinity of Lome. Vitrinite Reflectance studies are being undertaken to examine this hypothesis. The area is stmcturally dominated by the "Lome Synclinorium", (a regional scale synclinal stmcture with smaller stmctures on its limbs running parallel to its hinge), which is represented in the study area by the Lome Syncline and St. George Anticline. Both plunge shallowly to the NE, but the Lome Syncline plunges towards 055 (NE) while the St. George Anticline plimges towards 076 (ENE), indicating that the Lome syncline may be assosciated with an older, reactivated Palaeozoic fault. Stmctural and stratigraphic mapping have shown that it is likely that the hinge of the Lome Syncline intersects the coast approximately 1.2km north of its previously believed location, suggesting that the Lome Syncline strikes at 055 as opposed to 075 (Edwards, 1962), and therefore, may have had less influence on the location and formation of Loutit Bay as proposed by Brough Smythe & Couchman (cited in Edwards, 1962: pp. 103). Support is lent to this hypothesis by the fact that mapping has also revealed that the St George Anticline actually strikes at approximately 3 degrees towards 076 (as opposed to 085 (Edwards, 1962), indicating that Edwards' statements on the geometry of the Lome stmctures are useful at only a regional scale. REFERENCES

Edwards, A.B. 1962. Notes on the geology of the Lome district, Victoria. Proceedings of the Royal Society of Victoria, 75(1), 101-20. Hand, J. 1993. The Sedimentology of the Upper Eumeralla Formation, Otway Group, Lome, Victoria. BSc (Hons) Thesis, Monash University (unpublished). Cooper, G.T. 1996. Stmctural Geology, Thermochronology, and Tectonic Evolution of the Torquay Embayment -Eastem Otway Basin. PhD Thesis, Monash University (unpublished). Tmpp, M.A., Spence, K.W. and Gidding, M.J. 1994. Hydrocarbon prospectivity of the Torquay sub-basin, offshore Yictoridi. The APEA Journal 34,479-94. 35

11th VUGC1997, Monash University

A STUDY OF SMALL SCALE LOCALISATION OF DEFORMATION

HADI M. SIM Monash University Localisation of deformation is a process in which the deformation becomes concentrated in a relatively small volume of rock and as a result, is not homogeneously distributed. Localisation of deformation is generally associated with heterogeneities in the rock. These can be either initial lithological and compositional heterogeneities or those that develop due to the deformation itself. It is important to study the localisation of deformation, for example the formation of mylonites and shear zones, because it is a common phenomenon during larger scale deformation events. Small scale localisation of deformation (centimetre to micrometre scale) is very hard to see because the microstructures left behind are easily modified or even obliterated during ongoing deformation by processes such as dynamic recrystallisation. We only see the finite state of the rock. In order to measure the deformation and to observe what is going on during deformation, deformation experiments in a transparent deformation cell were conducted using the synkinematic microscopy experimental technique. These involve deforming an organic rock analogue, in this case polycrystalline norcamphor, in a transparent deformation cell. Micro-photographs and computer images of the deforming sample were taken every five minutes. These were analysed to see where and why small scale localisation of deformation occurs. It is observed that there are "invisible" micro shear zones. They have limited life time because they evolve over time and possibly shift through the material. These zones may be associated with local diffusional mass transfer and are called "invisible" because they do not leave any trace after deformation has ceased. The result of these deformation experiments were compared to small scale localisation deformation features found in the Mt. Painter InUer of the Northern Flinders Range in South Australia to further understand the small scale localisation of deformation in rocks.

11th VUGC1997, Monash University

APPLICATION OF PLATINUM«OUP ELEMENTS AND LEAD ISOTOPE GEOCHERDSTRY TO THE SilBDY OF THE CORROSION PRODUCTS OF ARCHAEOLOGICAL ARTIFACTS TO CONSTRAIN PROVENANCE^ WILLEM SNOEK^ TONY SOGONA^ and IAN PLIMER^ ^University of Melbourne, ^Department of Classics and Archaeology The University of Melbourne Corrosion rinds on copper and copper-alloy archaeological artefacts were studied to determine whether this rind could be used, instead of the valuable metal core, to provide information relating to the provenance of the ore and the development of metallurgy in the early Bronze Age. Metal core and corrosion rind from eight corroded copper artefactsfromTell Ahmar in Syria were analysed for platinum group elements (Pd, Ft, Ir and Ru) and gold via NiS fire assay preconcentration radiochemical neutron activation analysis (RNAA), and for Pb isotopes via thermal ionisation mass spectrometry (TIMS). The Pb isotopic signature was indistinguishable for six samples, suggesting that the copper used came from a single ore deposit in Cyprus. The Pb isotopic signature for the Tell Ahmar artefacts and their associated corrosion products ranged between 2.075 to 2.085 208Pb/206Pb and 0.833 to 0.846 207Pb/206Pb, while the Cypriot Pb field ranges between 2.067 to 2.085 208pb/206Pb and 0.833 to 0.847 207Pb/206Pb. The data suggests that the corrosion products of an artefact can be used to identify the source ore deposit as both the metal and associated corrosion have the same or similar Pb isotopic signature. Additionally, synthetic artefacts were produced by smelting examples of Australian orebodies and artifically corroded in order to determine whether selected geochemical elements, ratios and isotopes could be used as tracers in provenance studies. In particular the platinum group metals, gold, silver, cobalt and nickel in the ore, smelted copper produced from the ore, and the associated corrosion were determined. The PGEs were selected for trace element studies because, although in copper ores they are only present in parts per trilUon to parts per billion range, they are chalcophile and spatially and petrologically associated with copper minerals in most ore deposits. During smelting to produce the copper, the PGEs do notfractionateand so follow the copper into the melt. Gold, silver, cobalt and nickel, like the PGEs, also partition strongly into the melt, regardless of the smelting method. The PGEs are the preferred elemental indicators to study the provenance of copper rather than base metals because base metals are less strongly, and variably, partitioned into the blistered copper melt and may also be volatilised. Preliminary investigation sugest that chondrite normaUsed PGE pattems, coupled with Pb isotopic ratios and base metal data, may be useftil in determining the provenance of archaeological artefacts.

11th VUGC1997, Monash University

MAfIC ROCKS ASSOCIATED WITH fELSIC INTRUSIONS-A KEY TO UNBERSTANDMG GRANHE PETROGENESIS, ^ ALVAR SOESOO Monash University Silurian-Devonian basaltic-andesitic dykes and equivalent plutons of the southern Lachlan Fold Belt, SE Australia, are often temporally and spatially closely related to large granitic complexes. Mafic-intermediate magmas commingling with dominant felsic magmas have produced abundant microgranitoid enclaves, partially homogenised hybrid zones and/or composite dykes. Sometimes two or three dyke generations are evident within a single felsic intrusion: (1) dykes predating the emplacement of plutons, (2) dykes more or less contemporary, and (3) dykes postdating pluton emplacement. These field relationships support the suggestion that mafic-intermediate magmas play a significant rolefromthe initial to very late stages of granitoid emplacement, and by implication mafic dykes imdoubtedly play a major role in the transfer of heat into the continental crust (providing a thermal "engine") leading to crustal melting, and they probably contribute chemical constituents to the products of this melting. Basaltic dykes in southem Lachlan fold belt rangefromtholeiitic to alkaline, including groups with both high and low TiO^ and K^O contents. Dioritic-gabbroic plutons, often consisting of several sheet-like bodies, sometimes show evidence for the influence of magma mixing processes in the presence of two generations of plagioclase (AH^Q^-JQ and An^^^) and clinopyroxene (^-Mgg^ and Mg^^^^). Resultsfromfractionalcrystallisation modelling indicate that the large compositional range of Mt. Buller rocks is not likely to reflect in situ localfractionation,but is more likely to have required deeper level polybaric fractionation. Gabbros and quartz-diorites correspond to between 25 and 50 % of decompressionalfractionalcrystallisation of a hypothetical primary magma. Mt. Buller granodiorites and granitoids demonstrate TiO^ and Sc depletion pattems, but they are highly enriched in Cr, Ni, V, and Co when compared with the calculated abundances. Granitoids may be a product of combination initialfractionationof mantle-derived basaltic magma and later mixing with evolved basaltic magma. .14 •TAae . 1 2 ->

.10 .08 FSOfV .06 -

/CFS4

.04

.02

• O •

S n o w y Bluff Tabberabbera Mt. Buller

Tambo River

.03

Figure 2. Th/Tb - Th/La plot of mafic dykes, basaltic

La C e P r N d S m Eu Gd T b D y Ho Er T m Yb Lu

Th/La

lavas, and gabbros. Three trends may indicate different mantle sources for these rocks.

Figure 1. Chondrite-normalised REE pattems of Mt. Buller, Tabberabbera, Tambo, and Snowy Bluff rocks.

Basaltic and andesitic dykes and gabbroic to tonalitic plutons within the southem LFB often exhibit "mantlelike" isotopic signatures = 0.7035-0.7045; e^^^ = +4 - +10). Together with associated felsic rocks they form apparent mixing trajectories between mantle and crustal end-members. Negative Nb- and Ti-anomalies, and dominantly calc-alkaline character of the rocks suggest the influence of subduction during Lachlan Fold Belt evolution either during or prior to the emplacement of the dykes and plutons. Chondrite-normahsed REE abundance pattems of the basaltic and andesitic rocks (Fig. 1) suggest that they relate to large variety of "classical" tectonic settings;fromisland-arc to continental (enriched) types of settings. In many cases, relative depletion in HREE is more pronounced than for island-arc type basalts. LREE enriched mafic rocks may demonstrate enriched mantle inflow or be related to continental crustal growth during Devonian. Late Devonian dykes and lavas seem to be more alkali enriched and may be related to a post-subduction magmatic stage. At least three distinct types of mantle magma sources for mafic magmas are suggested by incompatible element ratios (Fig. 2). 38

11th VUGC1997, Monash University

SALLY MALAY INTRUSION: A VOISEY^S BAY ANALOGUE? GUIDBS TO MAGMATIC NICU-CO MINERALISATION IN THE EAST iOMBERLEY. REBECCA SPROULE^ DAVID LAMBERT & DEANHOATSON^ ^Monash University, ^aGSO - Canberra The recent discovery of the Voisey's Bay Ni-Cu-Co deposit in Labrador, Canada has renewed interest in exploration for basalt-associated Ni-Cu-Co deposits. The 1845 Ma Sally Malay mafic-ultramafic intrusion located in the East Kimberley, Western Australia, displays many similarities to the Voisey's Bay intrusion, including tectonic setting, Proterozoic age, sulphide mineralogy and textures, and abundant troctolite rocks (Naldrett et al, 1996). The intrusion hosts a Ni-Cu-Co bearing massive sulphide (consisting of pyrrhotite, pentlandite, chalcopyrite and magnetite) in the postulated feeder conduit (Hoatson et al., 1997) with an indicated and inferred resource of 5.5 Mt @ 1.75% Ni, 0.66% Cu and 0.1% Co (Shedden and Bames, 1996). In this study, we present Re-Os isotopic data from the Sally Malay intrusion to determine the source(s) of the magmatic Ni-Cu-Co mineralisation, and to better understand how these metals were concentrated. The Re-Os isotopic system was employed as it provides excellent insights into the magma source reservoir and as a tracer of processes which may promote mineralisation, e.g. cmstal assimilation or hydrothermal processes. Massive sulphides from the Sally Malay intrusion have intermediate common Os concentrations (2-4 ppb) and high Re/Os ratios (---20), similar to data for low R-factor (effective mass of silicate melt with which a given mass of sulphide melt has equilibrated) massive sulphide ores from the Duluth Complex. Modelling of Ni, Cu, Re and common Os data from the massive sulphides are consistent with R-factors in the range of 200 to 300. Re-Os isotopic datafromthe Sally Malay intrusion do not form an isochron, potentially the result of variations in R-factor within the mineralised system. However, samples with only disseminated sulphides yield a Model 3 isochron of 1893 ± 57 Ma, within error of the magmatic 1845 Ma U-Pb zircon age, suggesting that these samples have remained isotopically closed. Massive sulphides yield radiogenic initial Os isotopic compositions (gOs = +1100 to +1300). Disseminated sulphide mineralisation rangesfromgOs = +450 to +470 and unmineralised troctolites and peridotites range from gOs = +60 to +369. The Os isotopic data suggest the Ni-Cu-Co mineralisation was derived from crustally contaminated mantle melts. Cmstal contamination processes are very important in ore genesis as the addition of cmstal materials to sulphide undersaturated magmas can result in sulphide saturation and the formation of an immiscible sulphide melt which can then scavenge and concentrate ore metals (PGE, Ni and Cu). Incorporating R-factor into Os-isotopic modelling and using equations developed by Foster et al. (1996) shows that the variation in the initial Os isotopic compositions in different parts of the mineralised system may be due to variable R-factor; massive sulphides appear to have experienced lower R-factor (--200) than disseminated sulphides (-500 to 800). We therefore prefer a two-stage model for mineralisation at Sally Malay which may be appropriate for other magmatic sulphide ore systems (e.g., Duluth, Noril'sk-Tahiakh, Sudbury, Voisey's Bay; Lambert et al, 1997). In this model, sulphide-imdersaturated basaltic melts assimilated older cmstal materials en-route to their mid-upper cmstal magma chambers, which promoted sulphide-saturation in conduits or staging chambers. The immiscible sulphide "proto-ore" was then entrained in the silicate magma and transported to the cmstal magma chamber where the sulphide melt was passively deposited as a result of fluid dynamic contrasts accompanying a change from a narrow, near-vertical conduit to a broader, open magma chamber. As this process resulted in low R-factor, the sulphide melt retained an old cmstal gOs value inherited from the contaminant. In contrast, disseminated sulphide ores from the Sally Malay intmsion preserve a record of higher R-factors in some portions of the magmatic system, potentially the result of more extensive/effective mixing in a replenished magma chamber. Thus, mineral exploration programs should focus on magma feeder conduits or the bases of intmsions for Voisey's Baystyle Ni-Cu-Co mineralisation.

REFERENCES Foster, J.G., Lambert, D.D., Frick, L.R., & Maas, R., 1996. Nature, 382, 703-706. / Lambert, D.D., Foster, J.G., Frick, L.R., Ripley, E.M., & Zientek, M.L., 1997. South American Symposium in Isotope Geology (Brazil), Conference Abstracts, 12-17. Hoatson, D.M, Sproule, R.A., & Lambert, D.D., 1997 (in press). AGSO Research Newsletter, 27. Naldrett, A.J., Keats, H., Sparkes, K. and Moore, R., 1996. Exploration and Mining Geology, 5, 169-179. Shedden, S.H. and Bames, G.J., 1996. Nickel '96 - Mineral to Market, AusIMMPublication, 6/96,145-155.

11th VUGC1997, Monash University

THERMOCHRONQLOGY AND TECTONICS OF THE BIRB^S HEAD REGION, IRIAN JAYA: APATITE FISSION TRACK CONSTRAINTS

EDY SUTRYONOS PAUL B. O'SULLIVAN^, and KEVIN C. HILL^ ^ La Trobe University, ^aGCRC - La Trobe University, Apatite fission track thermochronology (AFTT) has been used to reconstruct the thermal and tectonic history of rocks from the Tosem Block in the northem Bird's Head region, the Tarof-2 well in the Bintuni Basin, and the eastern Lenggum Fold Belt. The AFTT resultsfromthe Tosem Block suggest two distinct rapid cooling patterns. Dacitic and dioritic rocks cooled rapidly during the Early Miocene, probably following an episode of heating associated with hydrothermal fluids. In contrast, granite and syenite intrusions have experienced rapid Late Miocene cooling, probably associated with erosional denudation and uplift in response to obduction of the Tosem Block onto the northem Bird's Head microcontinent. The preservation of a central block of Early Miocene ages amongst the Late Miocene ages suggests that the central block was upthrust from both sides in the Late Miocene and formed a pop-up block. In the Tarof-2 well, data from Mesozoic samples deeper than -1.5 km show that the sequences were partially annealed due to exposure to paleotemperatures of up to -lOOViC. This suggests that generation of hydrocarbons from these rocks might have postdated the formation of structural traps beneath the Jurassic unconformity. Data from overlying Cenozoic rocks suggest they may have been heated to maximum paleotemperatures of <85V2C. Therefore, these rocks have not been exposed to temperatures necessary for hydrocarbon generation. The AFTT data from the Upper Miocene to Pleistocene sequences in the eastern Lengguru Fold Belt (LFB) show that multiple cooling events occurred in the provenance terrains during the Tertiary. One episode of cooling occurred contemporaneously with Eocene-Early Miocene erosional denudation and uplift, perhaps in response to the Neogene Melanesian orogeny. A subsequent cooling episode took place in the Late Miocene, contemporaneous with deformation throughout New Guinea and possibly related to the opening of the Banda sea.

11th VUGC1997, Monash University

COMPOSITIONAL BANDING AND ^CHALCOP¥RITE-DISEASE^ STYLE TEXTUKES IN MASSIVE SULPHIDE DEPOSira GEOFF "HAMMER" TONKIN Monash University It is important to distinguish between primary sedimentary and secondary tectonic features in the characterisation of both ore and deposit types. Interpreting textures and structures in massive sulphide deposits is difficult and often controversial (e.g., Yokes, 1969). Incompatible genetic and tectonic models can arisefromdiffering interpretations of structures and textures in the deposit and host formation. For example, the Wilga Cu-Zn massive sulphide deposit, located in N. E. Victoria, has been described in one interpretation as a relatively undeformed, cyclically zoned, brine-pool-style deposit (Cox et al., 1990), whereas Allen (1987) and Allen and Barr (1990) interpreted it as an isoclinally folded and sheared Kuroko-style deposit. Detailed observations of compositional banding and "chalcopyrite disease" (micron-scale blebs of chalcopyrite in sphalerite) at Wilga provide insight into the formation and deformation of the ore deposit. The formation and timing of compositional banding and "chalcopyrite disease" are both subject to varying interpretations. Sedimentation, replacement, tectonic transposition, or a combination of all three can produce compositional layering (Vokes, 1969). "Chalcopyrite disease" is thought to occur as a result of epitaxial growth of chalcopyrite with sphalerite, or alteration of sphalerite by copper richfluids(James and Vaughan, 1981; Eldridge et al., 1983). At Wilga, millimetre- to centimetre-scale pyrite-sphalerite banding is most strongly developed in the massive zinc (Py ± Sph + Cpy) ore. Compositional banding is parallel to foliation and is associated with mylonitic textures, boudinaged carbonate veins and sheath micro-folds that indicate this texture is derivedfromor modified by shearing. This hypothesis is supported by the appearance of similar banded textures in discrete shear zones that cross massive pyritic (Py + Sph & Cpy) ore. Furthermore, there are no relict primary textures such asframboidalpyrite (James and Vaughan, 1981; Eldridge et al., 1983) in the banded ore. Micron-scale blebs of chalcopyrite are common in the sphalerite-rich layers of the zinc ore, and discrete shear zones, at Wilga. The blebs are commonly associated with layer parallel grain orientation, stretching and microboudinage. In some examples a continuous gradationfromchalcopyrite lenses and streaks to a layer parallel "tail" of chalcopyrite blebs is also observed. In contrast the chalcopyrite and sphalerite in the relatively undeformed massive pyritic ores characteristically exhibits ragged intergrowth rather than "chalcopyrite disease" style textures. These features suggest that "chalcopyrite disease"-style textures at Wilga may have formed by grain-size reduction and solid-state mixing of sulphide minerals during shear. Although compositional layering in sulphide ores is often associated with deposition rather than tectonic modification of ores (Vokes, 1969) and "chalcopyrite disease" is most commonly associated withfluid-phasedeposition or alteration (James and Vaughan, 1981; Eldridge et al., 1983), both the compositional banding and "chalcopyrite disease" at Wilga are most often associated strong deformation. In the case of the Wilga deposit, both of these textures appear to be secondary tectonic features rather than primary or relict depositional textures. Without data indicating a lack of deformation it is difficult to interpret whether textures in massive sulphide deposits, such as compositional layering and "chalcopyrite disease", are related to deposition and/or deformation of the ore. REFERENCES

Allen, R. L. (1987). Subaqueous volcanism, sedimentation and geological setting of Zn-Cu-Pb deposits, Benambra, SE Australia, unpub. Phd. thesis, Monash University, 284 p. Allen, R. L. and Barr, D. J. (1990). Benambra copper-zinc deposits. In Hughes, F. E., ed., Deposits ofAustralia and Papua New Guinea, Aus. I.M.M., 1311-1318. Cox, R., Ebsworth, G. B., and Forsythe, D. L. (1990). The Wilga base-precious metals deposit, Benambra, Victoria, Australia. Terra Nova, 2, 264-272. Craig, J. R., and Vaughan, D. J. (1981) Ore microscopy and ore petrography. U.S.A., Wiley, 406 p. Eldridge, C. S., Barton, P. B., Jr., and Ohmoto, H. (1983). Mineral textures and their bearing on the formation of the Kuroko orebodies, in Ohmoto, H., and Skinner, B. J., eds., Kuroko and related volcanogenic massive sulfide deposits. Econ. Geol Mon., 5,241-281. Vokes, F. M. (1969). A review of the metamorphism of sulphide deposits. Earth Sci. Rev., 5, 99-143.

11th VUGC1997, Monash University

BADGERS, CASSOWARIES AND ODDITIES: THE EXTANT AND EXTINCT FAUNA OF KING ISLAND, BASS STRAIT^ SANJAVANHUET Monash University The extant and extinct fauna of King Island represents a geographically isolated biota subjected to repeated periods of connection and disconnection with the Australian mainland during the late Quatemary/Holocene (Jennings, 1959). It was during this time that King Island evolved its unique fauna, which includes several endemic species. The Island has also undergone a series of localised extinctions, the cause of which are, as yet, conjectural. There is some evidence to suggest that the prehistoric extinctions are related to climatic changes over the past 100,000 years and may be contemporaneous with those on the mainland (Hope, 1984; Flannery, 1990). Historically recent extinctions, (those occurring over the last 200 years) were probably caused by the arrival of European settlers (Sullivan, nd). The late Quaternary oscillations, from a glacial to interglacial climate, have been linked to changes in precipitation and temperature in southem Australia (Bowler, 1982; Galloway and Kemp 1984). Evidence for these changes can be seen in both the sediments and the fossils deposited at a number of sites on King Island (D'Costa, Grindrod and Ogden, 1993; Murray-Wallace and Goede, 1995; Van Huet pers. observ.). They are characterised by raised beaches, mass flow deposits and the development and migration of dunes. Of the areas investigated, one site is of special interest. At Pass River on the central west coast, in situ subfossil material has been recovered from each offivehorizons, preserved in superpositional order. It is anticipated that the biostratigraphic informationfromPass River will record faunal change over time. Many Late Pleistocene and Holocene sites in Australia have retumed only single facies data. Pass River may provide a rare example of an area where superposition of late Quatemary biologic events can be demonstrated. REFERENCES Bowler, J.M (1982). Aridity in the late Tertiary and Quatemary of Australia, pp. 35-45, In Barker, W.R. and Greenslade, P.J.M. eds., Evolution of thefloraandfauna of arid Australia. Frewville:Peacock Publications. D'Costa, D.M., Grindrod J., and Ogden R. (1993). Preliminary environmental reconstructionsfromLate Quatemary pollen and mollusc assemblages at Egg Lagoon, King Island, Bass Strait. Australian Journal ofEcology, 18,351366. Flannery, T.F. (1990). Pleistocene faunal loss: implications of the aftershock for Australia's past and future. Archaeology in Oceania, 25,45-55, 64-67. Galloway, R. and Kemp, E. (1984). Late Cainozoic environments in Australia, pp. 69-81, In Archer, M. and Clayton, G. eds., Vertebrate zoogeography and evolution in Australia. CarlisleiHesperian Press. Hope, J.H.. (1984) The Australian Quatemary, pp. 83-95, In Archer, M. and Clayton, G. eds.. Vertebrate zoogeography and evolution in Australia. Carlisle: Hesperian Press. Jennings, J.N. (1959) The coastal geomorphology of King Island, Bass Strait, in relation to changes in the relative level of land and sea. Records of the Queen Victoria Museum, 11. Murray-Wallace, C. and Goede, A. (1995). Aminostratigraphy and electron spin resonance dating of Quatemary coastal neotectonism in Tasmania and the Bass Strait island. Australian Journal ofEarth Sciences, 42,51- 67. Sullivan, C. (nd) King Island. Australian Schools Commission.

11th VUGC1997, Monash University

EVniENCE EXTENDED THERMAL ACTIVITY IN BROKEN HILli NEW GEOCHRONOLOGICAL CONSTRAINTS USING SHRIMP U-PB AC^S. CAROLINE VENN AGCRC- Monash UniversitY Until recently, the accepted thermal history in Broken Hill was defined primarily by volcanic activity at 1690 Ma (Page and Laing 1992), high grade metamorphism at 1640 Ma (Nutman et al 1995) and 1600 Ma (Page and Laing 1992) and lastly by emplacement of muscovite bearing pegmatites at 1560± 40 Ma (Pidgeon 1967) and 'Mimdi-Mundi' type granites at 1490 Ma (Harrison and McDougall, 1981). Following these events it appeared that there was no thermal activity until dyke emplacement at 820 Ma (Wingate et al 1997) and low grade metamorphism during the Delamerian Orogeny at 520 ±40 Ma (Harrison and McDougall 1981), suggesting that thermal and tectonic activity ceased for approximately seven hundred milhon years. However, new SHRIMP U-Pb monazite and zircon ages obtained from a granitoid body in the Mount Robe region, NW Broken Hill, reveal discrete thermal events which until now have been previously imrecorded. SHRIMP U-Pb ages from monazites were used to interpret a regional episode of granitic magmatism at 1613 ±4 Ma. Zircons obtained from sedimentary rafts within this regional granitoid reveal concordant 207Pb/ 206Pb ages at approximately 1450 Ma and 1270 Ma. Inherited zircons obtained from the overlying Lady Don Quartzite, from the base of the Adelaidean sediments, also clearly preserve these three thermal events. Coarse muscovites from within the regional granitoid body were analysed and an 40Ar/39Ar plateau age spectrum of 1387 ± 11 Ma was obtained. In addition, an extensive Ar/Ar thermochronology study is currently being undertaken throughout the Broken Hill Inlier, and ages obtained also support the presence of thermal activity during Grenville time (1100-1200 Ma) (Hartley et al 1997). Field observations of the sedimentary rafts within the granitoid and the granitoid itself suggest that the body was remelted after initial emplacement. The granitoid preserves regions of coarsely recrystallised feldspar, quartz and mica, while the sedimentary rafts within the granitoid and the surrounding metasediments are granitised and recrystallised. In thin section, micas from within the sedimentary rafts form decussate grains while quartz, opaque minerals, tourmaline and garnet exhibit foam textures with easily recognisable triple points. These textures are interpreted as resulting from the re-melting of the granitoid and local sediments. It is clearly demonstrated that the Broken Hill region was not thermally quiescent between 1490 and 820 Ma but rather remained thermally active, recording two discrete thermal events at 1450 and 1270 Ma. The extent of these thermal events and the effects of these on the Broken Hill Inlier have not been fiilly realised, nor are the tectonic implications of these events understood. However, this new data allows for a dramatic re-interpretation of the Meso and Neo-Proterozoic history of the Broken Hill Inlier.

REFERENCES Hartley, M.J., Foster, D.A. and Gray, D.R., 1997. The significance of younger thermal events in the Willyama Inliers: Using 40Ar-39Ar thermochronology. Geodynamics and ore deposits conference. Abstract volume, 117-118. Harrison, T.M and McDougall, II981. Excess 40 Ar in metamorphic rocks from Broken Hill, New South Wales: implications for 40Ar/39Ar age spectra and the thermal history of the region. Earth and Planetary Science Letters, 55,123-149. Nutman, A., Ehlers, K and Fontaine-Geary, E.L. October 1995. The age and significance of granitic melts formed adjacent to the Broken Hill ore body. Australian Crustal Research Centre, Technical Publication, 29, 38p. Page, R.W and Laing, W.P 1992. Felsic Metavolcanic Rocks related to the Broken Hill Pb-Zn-Ag Orebody, Australia. Geology, Depositional Age, and timing of high-grade metamorphism. Economic Geology, 87,2138-2168. Pidgeon, R.T 1967. A Rubidium-Strontium Geochronological Study of the Willyama Complex, Broken Hill Australia. Journal of Petrology, 8(2), 283-324. Wingate, M 1997. Broken Hill Exploration Initiative, Abstract Volume (in press). Work reported here was conducted as part of the Australian Geodynamic Cooperative Research Centre and this paper/report is published with permission of the Director, AGCRC.

11th VUGC1997, Monash University

KARST OF THE CAINOZOIC LIMESTONES OF THE OTWAY BASIN, SOUTHEASTEKN AUSTRALIA SUSAN WHITE La Trobe University The Tertiary and Quaternary limestones of the Otway Basin in southwestern Victoria and southeastern South Australia include Miocene and Oligocene marine limestones and Pleistocene calcareous dune and beach facies. These highly variable limestones of high primary porosity and high permeability show diverse karst features both in surface expression and underground, presenting particular problems with regards to the usual concepts of speleogenesis. Although there have been some studies of karst development in the Tertiary, the Pleistocene dune karst areas (White, 1994) and of some of the surface karst (Grimes, 1994), these are generally of small areas (less than 100 km^) and show some interesting contrasts in features. The Otway Basin is a large karst area where there is the potential to understand the regional patterns of karst development in particular the times taken for karst development in Pleistocene calcareous dunes. Karst development in these limestone lithologies shows substantial variation across the basin and between the different lithologies. The karst shows important differences in the number and type of cave present per volume of limestone, total passage length, passage orientation, passage size, and cave form. Substantial differences in other karst features are also evident such as the presence of the distinctive cenotes and other surficial features in some areas and yet their complete absence in otherwise similar sites. Although environmental factors such as relief and climate do not vary greatly across the basin, there are significant changes in lithology, structure and underground water conditions. The variation in karst features can be explained partly by lithological variation; especially in such highly variable karst host rock. The overall regional view can add some important insights into concepts of speleogenesis. REFERENCES Grimes, K.G., (1994). The South-East Karst Province of South Australia. Environmental Geology 23, 134 - 148. White, S., (1994). Speleogenesis in aeolian calcarenite: A case study in westem Victoria. Environmental Geology 23, 248 255

11th VUGC1997, Monash University

VOLCANIC ORE ENVIRONMENTS OF THE WEST WIDGIEMOOLTHA DOME, KAMBALBA WESTERN AUSTRALIA Narelle J. Wolfe BSc Monash University The Widgiemooltha dome is located within the Archaean Norseman-Wiluna greenstone belt of the Eastern Goldfields Province, in the Yilgam Craton, (Western Australia) approximately 60 km west-south-west of Kambalda (Gee et al, 1980). Exploration focussed on the Widgiemooltha region in 1967 after nickel/copper rich gossans were found to the north and east of the dome by Anaconda Ltd (Dalgamo, 1975). The Widgiemoolha deposits in comparison to the better known Kambalda deposits are smaller, lower in nickel tenor (nickel in 100% sulphide), have poddy distribution rather than ribbon-like bodies, are confined to smaller trough structures, and shallower depths below surface. Therefore the mineralisation environment appears to differ significantlyfromthat of Kambalda Dome. However, detailed information is not available on the immediate ore environment of nickel sulphide mineralisation nor the host komatiite succession at Widgiemooltha dome. The objective of formulating a descriptive model for ore formation will be achieved by investigating the volcanic and structural setting of the nickel sulphide deposits at the Location 1 and 2 prospects and at the Wannaway Mine. Location 1, Location 2 and the Wannaway Mine are located on the western flank of the Widgiemooltha dome where north striking, steeply west dipping komatiite flows are preserved. Specifically, answers will be sought for the following questions: Can channel andflankcharacteristics be used to distinguish mineralised from non-minerahsed environments? Are the trough-like structures associated with nickel sulphide mineralisation, volcanic or tectonic in origin? At Kambalda Dome, the komatiiteflowsare intemally differentiated into a number of zones. Vertical zonation is based on the textures observed at theflowtop or A zone, which is characterised by spinifex textures, overlying the B zone which is characterised by cumulate textures. Laterally, a single flow can be divided into channel and flanking environments (Hill et al, 1990). The channel environment is characterised by an increased thickness of cumulate to spinifex textured rock, significant nickel sulphide mineralisation, and the absence of sedimentary units. Furthermore, the channeled flow environment overlies a trough-like depression in the top of the footwall imit, thought to have originated from volcanic and/or tectonic processes. It is interpreted that these features indicate that the channel environment represents the central, most turbulent part of the flow. In contrast the flanking environment is characterised by decreased thickness of cumulate to spinifex textured rock, lack of significant mineralisation, presence of sedimentary units, and a planar basal contact. These features are interpreted to indicate that theflankingenvironment represents the lateral, more laminar parts of theflow(Hill et al, 1990). The channel environment characteristics are used in exploration to identify areas of possible nickel mineralisation. To determine whether the channel and flanking characteristics, and trough structure can be distinguished at Widgiemooltha dome, a diamond drill core logging, sampling and mapping program was undertaken. Detailed drill core logging and sampling focussed on the Location 1 and 2 prospects to document textural, mineralogical and geochemical characteristics of the komatiitic sequence. Whilst underground mapping and sampling of the Wannaway mine provided a three dimensional perspective, in addition to geochemical and mineralogical information and minor drill core work. The presence of clast-like inclusions of both the footwall and hanging wall within massive nickel mineraUsation indicate a significant role for tectonic deformation at Location 1. Good textural preservation of spinifex and cumulate textures at Location 1 provides support to textural zone thickness as an indicator of the proximity to mineralisation. The cumulate zone is abnormally thick at Location 1 compared to the more nickel-rich deposit of the Wannaway Mine. This increased thickness of the cumulate zone may be attributed to inflation of an active lava tube or channel during emplacement. Textural preservation enabled comparison betweenfieldareas indicating that each of the areas appear to have been influenced by different degrees of tectonic and volcanic processes. REFERENCES

Gee, R. D., Baxter, J. L., Wilde, S. A. & Williams, I. R., 1980. In, Archaean Geology, Proceedings oftheSecond International Symposium (eds Glover, J. E. & Groves, D. I.), pp. 43-56, Geological Society of Australia, Perth. Hill, R. E. T., Bames, S. J., Gole, S. E. & Dowling, S. E., 1995, Lithos, 34, 159-188. Dalgamo, C. R., 1975, Dordie. In, Economic Geology ofAustralia and Papua New Guinea, I. Metals (ed Knight, C. L.), pp. 83-86, The Australasian Institute of Mining and Metallurgy, Parkville.

STOCKDALE PROSPECTING LIMITED (a De Beers company)

Diamond Exploration Exploring in Australia and Asia For employment opportunities contact:

Alan Cawsey Tel: (03) 9863 5222 Fax: (03) 9863 5288 Email: alan@spLoz.au P O Box 126 South Yarra VIC 3141

The Australasian Institute of Mining and Metallurgy CM^BERSHI^ Members are drawn from all sections of the industryprivate enterprise, govemment, research, education and the support sector, including consultancies, manufacturers and suppliers. Membership of The Institute allows professionals to contribute to their profession through participation in The Institute's seminars and conferences, its many committees and Branch meetings, and through contribution to its many acclaimed publications. Membership provides opportunities for contact with and professional support from colleagues, and the interchange of infomiation on the latest industry developments. The Institute's activities are geared towards ttie achievement of professional excellence.

PmUCATION^ The Institute has a very active publishing agenda including The AusIMM Bulletin, The AusIMM Proceedings, proceedings of conferences, as well as publications which cover topics of more general interest to the membership. There are three main objectives of The AuslMM's publishing agenda. They are to benefit members by increasing and disseminating knowledge, to enhance the standing of members in the profession and in the wider community, and to contribute to the financial strength of The AusIMM by operating efficiently and profitably.

CONFERENCE

DATES ^

1997 Contract Operators' Conference 26-28 October, Brisbane OLD Field Safety & Survival Course 5-9 November, Adelaide SA Third International Mining Geology Conference 10-14 November, Launceston, TAS Mindev 97 International Mine Project Development Conference 24-26 November, Sydney, NSW 1998 1st Australian Coal Operators' Conference (COAL '98) 18-20 February, Wollongong, NSW

THE AusIMM

BULLETIN

The AusIMM Bulletin is a highly regarded source of infomiation for both management and technical staff at head office and in the field. It is read by the most influential members of the mineral and associated industries. Through its pages, readers are kept abreast of leading research, as well as the latest developments and movements in the industry.

K-

* Yes, I would like more information on: Membership Z7 Publications D Conferences U The AusIMM Bulletin

NAME: ADDRESS: Telephone: Facsimile: Retum to: The AusIMM, Marketing Department Level 3,31 Pelham Street. Carlton Vic 3053, Australia Ph: 03 9662 3166; Fax: 03 9662 3662 e-mail: marketing@ausimm.com.au