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3 EXPLORING AN ANCHIENT LANDSCAPE: THE FLINDERS DIAMOND PROJECT

Kevin J A Wills Tiger International (Australia) Pty Ltd

The Flinders Diamond Project area of 5,522 square kilometres is located in the Southern Flinders Ranges between Hawker and Port Augusta. The Project lies near the G2 gravity lineament and contains the densest known concentration of diamond localities and positive indicator mineral results in South Australia. The recent phase of diamond exploration has been carried out by Tiger International (Australia) Pty Ltd, a subsidiary of Tiger International Resources Inc, which is a Canadian public company listed on the Vancouver Stock Exchange. Tiger has spent a total of $1.3 million on the project area since April 1998. Tiger is managing two joint ventures, one with the Springfield Syndicate (informal name) consisting of Jim Allender, Tony Le Brun and Ian Youles, and the other with Amity International of Perth consisting of Jeff Moore and Lynda Frewer. Current plans are to vend the project into a new Australian Public company to be called Flinders Diamonds Limited. The new company’s objective will be to find South Australia’s first diamond mine.

Knowledge of landscape evolution and regolith distribution is a very important aspect of the Flinders Diamond Project. To meet its objective, exploration is focussing on locating new kimberlites. From the eight diamond localities and numerous kimberlitic indicator minerals located to date, it is anticipated the some of the kimberlites in the project area will contain macrodiamonds.

Worldwide, kimberlites have usually been located by initial reconnaissance kimberlitic indicator mineral sampling and then detailed follow up of secondary dispersion trains in the regolith to locate primary sources. Geophysics, particularly magnetics, has been successful in some areas (eg Ellendale). However, in the Flinders Project area surface concentrations of maghemite make magnetic identification of kimberlitic targets very difficult. Also, the surface expression of kimberlites is often complicated by regolith cover. As kimberlites are normally soft they tend to form depressions that become disguised by other materials. The project area has been reconnaissance regolith mapped at 1:100,000 scale by Perth-based geomorphologist Dr Richard Russell. This work has aided kimberlitic indicator mineral sampling and our general understanding of the area’s landscape evolution.

The regolith mapping has been very useful for the following purposes:

Definition of areas where cover is over 25 metres deep leading to avoidance in current exploration.

Choice of areas where drainage sampling should lead to shallow buried Kimberlites. Selection of areas where drainage sampling is likely to be inappropriate and where undercover drilling should be a more effective technique. Understanding Tertiary geomorphological evolution, as influenced by uplift and faulting, and in particular the understanding of likely sediment transport directions over time and their associated sedimentary deposits. Identification of likely source areas where indicators have been found in Permian and Tertiary sedimentary basins. In conjunction with individual grain abrasion textures, the likely distance to kimberlitic sources. In this case, the effects of weathering and sedimentary transport must be taken into consideration. For instance, chrome diopside may be present in a buried kimberlite pipe, but due to in situ chemical weathering may not even reach the surface. Also, chromite, particularly high-chromium chromites which indicate a high diamond potential, is very soft and is unlikely to travel more than a few hundred metres in a creek bed.

Application of the above knowledge has led to the identification of numerous targets for future exploration of the Flinders Diamaond Praoject area. These include the following: Regionally, 90 clusters of kimberlitic indicator anomalies have been identified by previous exploration research and Tiger’s recent exploration. Many of these clusters need to be resampled to obtain new mineral grains so the chemistry of their indicators can be determined. This will enable a ranking of the best targets for more intense follow up sampling. In the Springfield Basin area, the diamondiferous Permian conglomerate at Diamond Ridge has produced 196 diamonds to date and over 22,000 kimberlitic indicator minerals; mostly chromite and pyrope garnet. Other basal conglomerates also contain indicator minerals and three assemblages thought to represent at least three different kimberlite sources have been identified. At the Calabrinda Basin, of probable Tertiary age, large numbers of poorly abraded picroilmenites, chromites and one microdiamond are highly suggestive of a separate nearby primary source. In the catchment of the Springfield Basin, 27 positive indicator anomalies (35%) were located from a first- pass survey of 77 samples. These were followed up by three additional phases of indicator mineral sampling. This work led to six prospects with on-source results. Work at these prospects has consisted of geological mapping, detailed regolith mapping, griding, ground magnetics and soil sampling for incompatible kimberlitic trace elements. At three prospects (KA12A, KA12B and KA113), results were encouraging and undiscovered kimberlites are suspected. At the Hut Hill Prospect surface sampling and undercover drilling has led to a situation with abundant on- source picroilmenite and, immediately uphill, an interesting magnetic target.

4 It is concluded that follow up of these numerous targets in 2000 is likely to lead to the discovery of several new kimberlites. Some of these are expected to contain diamonds, and it is hoped that at least one will contain diamonds in economic quantities.

5 EXPLORATION USING GOLD AND BASE-METAL PATHFINDERS IN CALCAREOUS SOILS

Antonio Belperio and Hamish Freeman Minotaur Gold NL 1A Gladstone St Fullarton SA 5063

Exploring under cover traditionally has required extensive and expensive drilling through the cover sediments(RAB, Aircore) to locate areas of anomalous mineralisation in bedrock. Calcrete and calcareous soil sampling of surficial cover at a variety of spatial scales provides a far more cost effective way of locating mineralisation even where bedrock is masked by over 100m of regolith. The technique has been used extensively by Minotaur in its exploration programs over the northern and southern Gawler Craton, the Adelaide Geosyncline and the Curnamona Craton. It is particularly useful at the regional, greenfield exploration stage where prospect scale targets can be generated from large tenements. Gold, copper, arsenic, silver, lead and zinc have all been utilised as pathfinders with various degrees of success. Incremental increase in sample density can be used to delineate robust, coherent anomalies at the surface that provide a direct guide to bedrock drill testing. Thus once calibrated for local response, surface sampling of calcareous soils can result in major cost savings through eliminating regional drilling programs to top of bedrock and guide deeper bedrock drilling directly into prospect scale targets.

Exploration for gold on the northern Gawler Craton has been particularly successful, with bedrock mineralisation recorded beneath all significant gold-in-calcrete anomalies on Minotaur’s Commonwealth Hill tenements (southwest of Coober Pedy) drilled to date. Regional sampling on a 1km offset grid has highlighted numerous (40+) regions of anomalous Au (>8ppb) amongst general background levels of 1-5 ppb. Infill sampling of anomalous regions at 200m and 50m sampling density has revealed robust, coherent anomalies peaking at typical values of 30 to 80 ppb Au. Aircore grid drilling has confirmed that in many instances, anomalous mineralisation at top of masked bedrock directly mimics the gold in calcrete anomalism at the surface, to the extent that in the latest programs, aircore drilling was successfully eliminated. RC drilling into bedrock has encountered primary mineralisation with typical intercepts such as :

Comet Prospect RCCM 1 14m @ 2.33 g/t Au from 28m (incl 1m @ 8.74 g/t Au) Mars Prospect RCMR1 12m @ 0.60 g/t Au from 32m Aurora Tank RCAT13 20m @ 0.46 g/t Au from 116m (incl 1m @ 3.3 g/t Au) Birthday RCBD44 40m @ 0.05 g/t Au from 60m

Arsenic is not always present in soils with the Au, and where present, has been documented to disperse further within the surficial regolith. Copper and zinc pathfinders have not produced any success to date with erratic surface concentrations suggesting significantly wider dispersion and/or variable uptake by other regolithic components.

On the southern Gawler Craton and on the southern Curnamona Craton, background levels of 1-3 ppb Au has necessitated a lower (0.1 ppb) detection limit be utilised at the regional exploration level, reverting to conventional analysis at the infill stage. An identical process of successive infill sampling generates similar coherent anomalies that have led to discoveries of primary Au mineralisation in bedrock. An example is the discovery by Acacia Resources in joint venture on Minotaur’s Caralue Bluff tenement of the Waddikee Prospect where a coherent gold- in-calcrete anomaly peaking at 40 ppb has returned bedrock intercepts of up to 21m @ 0.49 g/t Au from initial RC drilling. On Mutooroo, infilling to 50m spacing reveals a calcareous soil Au response that mimics interpreted structural and lithological controls in the subsurface.

Both lead and silver are strongly elevated in calcareous soils over base metal mineralisation. In particular, lead produces excellent anomalous signal to background response and coherent anomalism over a number of geological terranes await drill testing. Typical background levels of 4 to 10 ppm Pb contrast with anomalous regions peaking in the hundreds of ppm. However, the use of Pb pathfinder requires particular care where a transported component is present within the calcareous regolith being sampled as these can easily contaminate the results.

6 LAND SURFACES AND 'LATERITES' IN SOUTHERN SOUTH AUSTRALIA

BOB BOURMAN SCHOOL OF ENVIRONMENTAL AND RECREATION MANAGEMENT LEVELS CAMPUS, UNIVERSITY OF SOUTH AUSTRALIA MAWSON LAKES BOULEVARD, MAWSON LAKES, S.A. 5095 [email protected]

Ferruginous and aluminous rich crusts, sometimes associated with weathered, mottled and bleached materials, loosely regarded as 'laterite' by many have a widespread distribution in southern Australia, although commonly their collective area of coverage is not as widespread as indicated on many geological maps. Critical to the interpretation of 'lateritic' materials is their association with landsurfaces. In recent times there has been conflict about the interpretation of lateritic materials, specifically about their antiquity and their use as morphostratigraphic and palaeoclimatic indicators.

Views include the possibility of the preservation of Mesozoic 'laterite' in a subaerial environment and in pristine condition for some 200 Ma, that it can be used as an excellent morphostratigraphic marker over widespread areas, and that it indicates widespread formation on a subdued land surface during humid and torrid tropical conditions. Ferricrete crusts are relatively rare in many areas, and are often absent above pallid and/or mottled zones, suggesting the erosional truncation of former complete 'laterite profiles'. However, perhaps the crusts had never developed. An alternative suggested to a former uniform blanket of 'laterite' over large areas, is that different types of ferricretes, mottled and bleached zones may have developed in specific sites in response to local environmental conditions. Stratigraphic evidence suggests that ferricrete development, mottling and bleaching was an on-going process throughout the Mesozoic and Cainozoic.

Ferricretes appear to be younger than underlying 'companion materials' and are not mono-genetically related to them. Diverse forms of ferricrete appear to have developed in different palaeo-environments through the operation of a range of processes. For example, some have formed by the in situ weathering transformation of pre existing iron-rich minerals. Some other ferricretes developed as a result of the transport, accumulation and cementation of ferruginous materials such as pisoliths and fragments of mottles.

The chemical and mineralogical characteristics of 'lateritic' materials in southern Australia reflect various modes of formation. Different facies of ferricrete (vermiform, pisolitic, nodular vesicular to massive, slabby and ferruginised bedrock and ferruginised sediments) display differing chemical and mineralogical compositions that reflect environmental conditions during formation. Consequently the view is taken that the detailed characteristics of the different ferricrete morphologies represent 'tape recordings' of their epigenetic histories, the unravelling of which may be accomplished by careful study of their attributes.

Evidence of different facies of ferricrete having formed coevally in different parts of the same landscape and the occurrence of identical ferricretes on landsurfaces of disparate ages, restricts the usefulness of ferricretes as morpho-stratigraphic markers, except in the coarsest sense. No direct indication of age derives from ferricrete morphology, chemistry or mineralogy, as similar ranges of weathering and ferruginous materials occur on both lowland and summit surfaces. However, ferricretes with the greatest mineralogical diversity (e.g. hematite, goethite, maghemite, gibbsite, boehmite and kaolinite) appear to have more complex histories of evolution than do ferricretes and mottles with simple iron oxide mineralogies (e.g. goethite in ferruginised clastic sediments, and hematite in mottles).

In some cases there is the progressive exposure of inherited weathering features such as kaolinised and mottled zones, which become modified by present day weathering processes through exposure, hardening and disintegration at the surface where iron-rich segregations have accumulated and formed lags during landscape downwasting and planation surface development. Lateral transport often plays an important role in these situations.

7 CONTROLS OF PLACER GOLD DEPOSITION IN THE VICTORIAN GOLD PROVINCE

Martin J Hughes1,2, Stephen P Carey2 and Peter G Dahlhaus2

1Martin Hughes and Associates, PO Box 148N, Ballarat North VIC 3350 (for correspondence) 2Geology Department, University of Ballarat, PO Box 663, Ballarat VIC3353

Reactivation of north-striking Palaeozoic faults, and of faults which strike ENE to WSW (which formed during Gondwana breakup in the Jurassic), was important in controlling the formation and distribution of secondary gold deposits in the Victorian gold province of the West Victorian Uplands. These reactivated faults controlled: (i) uplift of the West Victorian Uplands, (ii) the distribution of deep chemical weathering, duricrusts, and associated secondary gold, (iii) the limits of late Miocene – early Pliocene marine incursions in the Otway Basin and Murray Basin, adjacent to the uplands, (iv) deposition of coarse clastics in palaeodrainages of the uplands, and (v) the generation of important gold palaeoplacers and placers of the region (Phillips and Hughes, in press 1999). These fault controls were important from before late Eocene uplift (Carey and Hughes 1997) to at least the mid-Pliocene (Smith et al. 1997).

Deep chemical weathering in the Victorian gold province of the West Victorian Uplands produced a Mesozoic regolith, which was uplifted in the mid-Cretaceous (Table 1). This regolith was then mostly eroded when a Palaeogene palaeoplain formed on which the first important gold palaeoplacers, those of the White Hills Gravel, were deposited. The precursors to some major modern valleys, e.g. Loddon River, were probably initiated before this time, because these valleys contain remnants of Permian sediments at their base. A second deep weathering event formed the Norval Regolith, which was superimposed on Palaeozoic rocks and the White Hills Gravel. This event produced deep pallid zones of kaolinite and local bauxite in Victoria, and may been associated with supergene enrichment of gold; bauxite and nickel laterite may also have formed in Tasmania (Hughes et al. 1998). The lateritic weathering was probably terminated by late Eocene uplift of the West Victorian Uplands, rather than by climatic change (Hughes et al. 1999).

The second and most important group of gold palaeoplacers, those near the base of the Loddon River Group (which include the “deep leads”), formed as a response to rapid erosion and down-cutting of valleys immediately following the late Eocene uplift. The Loddon River Group includes diverse sediments which filled palaeovalleys of the uplands, and which post-dated the White Hills Gravel but pre-dated the basalt flows of the Newer Volcanics. These palaeoplacers, like those of the earlier White Hills Gravel, were deposited directly on Palaeozoic bedrock. The palaeovalleys of these palaeoplacers were then back-filled with sand, lignite and clay of the Renmark Group because of rising sea level in the Oligocene (e.g. in the lower Loddon valley). A local palaeoplain, the Mologa Surface, formed on both the Renmark Group and older rocks in the southern Murray Basin (present Loddon Plain) in the mid to late Miocene as the sea retreated from the basin. The Renmark Group of the Loddon plain, lower Loddon valley and adjoining areas, which includes the northern extension of the second group of gold palaeoplacers present in the partly correlative Loddon River Group of the uplands to the south, was extensively eroded at this time. On-going studies indicate that equivalents of the Renmark Group are extensively preserved farther south in the Loddon valley, i.e. upstream within the uplands, where they included economically very important palaeoplacers at the base of the Loddon River Group (e.g. Creswick).

Coarse fluvial clastics of the Calivil Formation (at the base of the Wunghnu Group of the Murray Basin) were then deposited on the Mologa Surface (Macumber 1991), where they overlie the Renmark Group and older rocks. The Calivil Formation as defined here from the type section of Macumber (1991) in bore Calivil 2 does not contain any important known palaeoplacers, contrary to interpretations of Macumber (1991) and others. The Calivil Formation appears to be mostly confined to north of the uplands. The reason for this is uncertain, but is possibly because uplift and associated erosion of the uplands were entirely concentrated along older faults which bound the uplands adjacent to the Murray Basin (e.g. north of Bendigo). The late Miocene – early Pliocene marine and fluvial sands of the Parilla Sand and Moorabool Viaduct Formation then formed in the Murray Basin and northern Otway Basin, respectively. The upper Calivil Formation reportedly interfingers with the base of the Parilla Sand (Macumber 1991), consistent with the young age for the Calivil Formation interpreted here.

A third period of lateritic weathering associated with a brief period of high rainfall produced the Karoonda Regolith of the Murray Basin and an equivalent regolith in the Otway Basin; these formed on the Parilla Sand and Moorabool Viaduct Formation as the sea retreated. Reactivation of north-striking Palaeozoic faults and of the faults along the northern and southern boundaries of the uplands adjacent to the basins (e.g. Enfield Fault) was again important in the late Miocene and Pliocene. Uplift as great as 150 m south of Ballarat (Taylor et al. 1996) resulted in capture of “deep lead” palaeoplacers of the Loddon River Group at Ballarat, and erosion of south- flowing palaeoplacers of similar age in the Trunk – Pitfield and Mount Mercer “lead” systems to the south (Hughes et al. 1998). A third group of sub-economic gold palaeoplacers and economically important placers formed, and only the earliest of these palaeoplacers were buried by the Newer Volcanics.

8 Most of the important placers and palaeoplacers of the West Victorian Uplands are therefore thought to have formed over relatively brief periods of time following individual uplift events in the uplands.

REFERENCES

Carey SP and Hughes MJ 1997, Three generations of gold-bearing fluvial systems at Ararat, Victoria. Geological Society of Australia Abstracts 47, p 4

Hughes MJ, Carey SP and Kotsonis A 1999, Lateritic weathering and secondary gold in the Victorian gold province. New approaches to an old continent, Proceedings of Regolith 98, CRC LEME, Kalgoorlie 2-9 May 1998, p155-172

Hughes MJ, Kotsonis A and Carey SP 1998, Cainozoic weathering and its economic significance in Victoria. VICMIN 98: AIG Bulletin 24, p 135- 148

Macumber PG 1991, Interaction between ground water and surface systems in northern Victoria, Dept. of Conservation and Environment, Victoria, 345 pp.

Phillips GN and Hughes MJ, in press 1999, Gold chapter, Geology of Victoria.

Smith M, Hughes MJ and Carey SP 1997, “White Hills Gravel” of Bamganie–Dereel: Calivil Formation gold leads overlain by Moorabool Viaduct Formation. Geological Society of Australia Abstracts 47, p 28

Taylor DH, Whitehead ML, Olshina A and Leonard JG 1996, Ballarat 1: 100 000 map geological report. Geological Survey of Victoria Report 101

TABLE 1 Timing of events related to secondary gold, Stawell zone to Melbourne zone (West Victorian Uplands). Volcanics: OB Otway Basin, BG Ballan Graben, M Melbourne region, OV Older Volcanics, NV Newer Volcanics. Major uplift: a mid-Cretaceous uplift, b late Eocene (?) uplift of West Victorian Uplands c uplift south of Enfield Fault, Steiglitz Plateau, Murray Basin margin Alluvial gold: 1 White Hills Gravel palaeoplacers, 2 Loddon River Group palaeoplacers (including “deep leads”), 3 Placers.

9 Remote Sensing techniques in Palaeochannel research with a focus on hyperspectral imagery.

Vicki Stamoulis

Primary Industries and Resources South Australia, 101 Grenfell St, Adelaide, SA 5000

An unusual linear feature was observed on a series of hyperspectral surveys (HyMap) over the Gawler Craton in South Australia. Initial analysis on remote sensing data such as NOAA and DEM showed that this feature was due to a Tertiary palaeochannel, a tributary to the Kingoonya. Stratigraphic evidence from drill data verified the existence of the palaeochannel. These findings were presented on a poster for the “Exploring Ancient Landscapes” workshop held by PIRSA in December 1999. Exactly what feature associated with the palaeochannel that the HyMap data was highlighting needed to be further researched. All the VNIR bands were processed. The spatial and spectral data was reduced and 15 endmember spectra were collected. A library file was created and 3 of these endmembers with distinct absorption features were identified. Their abundance and distribution was plotted as an RGB and the following conclusions were made. A high concentration of poorly crystalline kaolinite was associated with the Gawler Range volcanics. One of the spectral responses coincided with the green vegetation growing along modern drainage. The third endmember occurred in high proportions in the area of the palaeochannel. Field work is necessary to groundtruth the findings. However, the spectral response of this endmember was identified as a mixed pixel of stressed grass/nontronite. Research on this dataset is ongoing, but so far has shown that there is a correlation between groundwater and landform. Whether this method is scene dependent is yet to be established.

10 Tertiary palaeochannels and their significance for mineral exploration in the Gawler Craton region, SA

Baohong Hou1, Larry Frakes2, Neville Alley3, Andrew Rowett3…

1. Department of Geology and Geophysics, the University of Adelaide, Adelaide SA 5005 / Mineral Resources Group, Primary Industries and Resources of South Australia, GPO Box 1671, Adelaide SA. 5001 2. Department of Geology and Geophysics, the University of Adelaide, Adelaide SA 5005 3 Mineral Resources Group, Primary Industries and Resources of South Australia, GPO Box 1671, Adelaide SA. 5001

Tertiary palaeodrainage systems on the northwest Gawler Craton incise into sediments and deeply weathered basement, and the sedimentary sequences deposited in the systems are dated as Eocene and Miocene. The Eocene sequence is mainly composed of fining up channel fills consisting of clastic (fluvial) and carbonaceous (overbank/lacustrine) deposits. These are laterally equivalent to a series of coastal sequences consisting of lowstand, transgressive and highstand deposits. In contrast, the Miocene sequence is dominated by mud-rich deposits, indicating that the through-flowing Eocene rivers were replaced by chains of shallow lakes and abandoned channels. Late Miocene sediments in the lakes / channel segments contain gypsum, are dolomitic and reflect increasingly evaporitic environments. Regoliths, characterised by silcrete, calcrete and ferricrete, mainly formed on the top of channel sediments; gypcrete is found near to lacustrine deposits

Sedimentological evidence is combined with that of other geological and geophysical sources derive a general reconstruction of Tertiary palaeochannel architectures and environments. The environmental setting is interpreted as a marginal marine, estuarine and fluvial / alluvial plain complex; the range of subenvironments includes barrier, lagoon / tidal flat, estuary mouth, estuary funnel, estuary channel, alluvial channel, freshwater swamps, overbank, and lacustrine. Freshwater swamp/forest facies were generallylocated adjacent to various highstand estuary facies. Carbonaceous sand, silt, mud and lignite, representing channels, floodplains and well vegetated swamps, were widely deposited from the upper reaches of palaeochannels to coastal areas of the Eucla Basin during the Eocene. Non-vegetated lacustrine or overbank mudplain environments were common during the Miocene. Sea level fluctuations and climate change significantly influenced erosion and sedimentation in the main (Garford and Tallaringa) palaeodrainage systems.

Over the Cainozoic period, sediments weathered from mineral-bearing surface rocks of the Gawler Craton were carried by rivers discharging into the coastal Eucla Basin. These palaeochannel fills therefore are a potential source of valuable commodities, given traces of gold, diamonds, uranium, and heavy minerals have been recovered/identified in sediments deposited by these river systems. Additional studies of these palaeodrainages include gold mineralisation during regolith formation, the history of groundwater, and the significance of clay mineralisation.

Detailed mapping of these buried Tertiary palaeochannels has been accomplished by application of geological, geophysical, remote sensing, and digital topographical methods, and including drilling information. The task is difficult because channels are often associated with underlying Palaeozoic trough sediments and/or deeply weathered basement. Studies of channel architecture and their relationships to tributaries will assist in identifying where placer / secondary geochemical deposits may occur and provide important clues for tracing these back to their lode deposits on the Craton.

11 OPTICAL LUMINESCENCE DATING OF QUATERNARY DUNES AND ITS IMPLICATIONS FOR MINERAL EXPLORATION: GREAT VICTORIA DESERT, SOUTH AUSTRALIA.

1D.J. Huntley, 2J.R. Prescott, 3M.J. Sheard and 4M.J. Lintern 1. Physics Department, Simon Fraser University, Burnaby, Canada 2. Department of Physics and Mathematical Physics, University of Adelaide SA 3. Regolith Terranes, Minerals Group, PIRSA, Adelaide SA 4. CRC Landscape Evolution and Mineral Exploration, Adelaide SA

As part of a programme to evaluate methods of sampling from the regolith for the purposes of mineral exploration, we have determined optically stimulated luminescence ages for samples of quartz extracted from dune sediments at sites in the Barton and Ooldea Ranges (near the Transcontinental Railway) of the Great Victoria Desert (western Gawler Craton). The method presupposes that the luminescence clock has been reset by exposure to sunlight during deposition of the sediment. This expectation is normally fulfilled in Australian dune systems and the present determinations appear to be no exception.

For a dune in the Barton Range, an age of 74±8 ka is found for a sample from an auger hole some 2 m below the dune crest; and ages of 106±8 and 184±14 ka, 1.3 m apart vertically, from the face of a borrow pit near the base of the same dune, about 10 m below the crest and just above the swale. A pilot swale age for the Barton site suggests that the age is probably beyond the range of luminescence dating at about 250 ka for this location.

Near Immarna Siding in the Ooldea Range, a site 0.7 m below the present (eroded) dune surface gave an age of 22±3 ka and two samples in the same dune, 1 m apart and some 5 m lower than the previous sample, gave ages of 192±14 and 212±15 ka. The latter site was about 2.3 m above the level of the swale.

The ages must be regarded as unexpectedly old and indicate long-term stability of the dune field pattern, a conclusion that has been drawn by Pell et al. (1999) on different grounds. Establishing the age of the dunes is significant in the context of regolith geochemistry; in particular, in the sampling of calcrete for anomalous gold signatures which may have been geochemically transported into the regolith. The dune or swale sand must be older than any calcrete formed in it. Since the terrain over the Gawler Craton is unevenly covered with dunes, it is important to know whether the dunes themselves have been in position long enough for the calcrete formed in them to acquire a gold signature and whether sampling these materials is likely to prove advantageous.

REFERENCE

Pell, S.D., Chivas, A.R. and Williams, I.S., 1999. Great Victoria Desert: development and sand provenance. Australian Journal of Earth Sciences, 46:289-299.

12 REGOLITH AND LANDFORM EVOLUTION OF THE FORBES REGION, NSW

Roslyn Chan and David Gibson, CRC LEME / AGSO

Exploring Ancient Landscapes Workshop Adelaide, December 10th, 1999

Recent regolith-landform mapping in the Forbes region of NSW has elucidated the evolution of the regolith and associated landforms (Gibson and Chan, 1999a,b). This understanding has been integrated with results from regolith-landform mapping in the Bathurst region (Chan, 1998, 1999), regional palaeodrainage investigations (Gibson and Chan, 1999c), and interpretations from palaeomagnetic and apatite fission track data (Pillans et al., 1999; O’Sullivan et al., in press) to take the regolith-landform history of the Forbes region back to the Carboniferous.

The Forbes region extends from higher elevation and relief (up to 300 m) terrain with dominantly in-situ regolith from the Parkes to Grenfell areas in the east, to lower elevation and relief (mostly less than 9 m) terrain, towards Condobolin and West Wyalong in the west with dominantly alluvial sediments and some in-situ regolith. The northwest flowing Lachlan River and its tributaries have had a major influence on the development of the landforms and associated regolith that are presently in evidence.

Weathering since the Early Carboniferous, as preserved at North Parkes mine (palaeomagnetic data), has been interrupted by two major periods of deposition and erosion (apatite fission track data): 1. burial by several kilometres of sediments in the Late Carboniferous to Late Permian, and vigorous erosion in the Late Permian to Early Triassic; 2. burial by 0.5 to 1 km of sediments in Late Jurassic to Late Cretaceous, and vigorous erosion in the Late Cretaceous to Early Tertiary. Remnants of these sediments are found on the Canobolas Divide between the Macquarie and Lachlan River catchments as outliers of the Surat Basin.

The rate of weathering is dictated by bedrock properties, depth to the water table and groundwater chemistry – both present and past. The competence of the bedrock dictates the topography, such as the resistant bedrock residuals with pediment sheetwash of the Booberoi Hills east of Wyalong. Less resistant bedrock weathers to erosional plains and rises, often with a transported and residual veneer, such as the highly and deeply weathered granite around West Wyalong and to the north.

Rapid uplift and erosion of the southeast highlands at around 95 Ma (O’Sullivan et al., 1996) resulted in a west- northwest palaeoslope across central NSW. Northerly flowing rivers on the Surat Floodplain migrated to flow northwest to west and evolved into the palaeo-Lachlan River and its tributaries (Chan, 1998). The trunk palaeo- Lachlan River and some tributaries superimposed their courses across the structure of the underlying rocks after erosion of the overlying sediments. Others, such as the palaeo-Bland Creek, established their courses in either newly eroded or exhumed strike-controlled valleys, with a network of palaeotributaries, for example the Wyalong Palaeovalley (Lawrie et al., 1999). The palaeo-Lachlan River and palaeo-Bland Creek eroded wide valleys in variably competant bedrocks in the Early Tertiary resulting in an irregular palaeotopography. Time transgressive erosion occurred by knickpoint retreat and valley widening.

This erosional palaeotopography was alluviated by thick sediments (up to 140m) of Miocene to Pleistocene age (Martin, 1991) forming two sequences, the Lachlan and Cowra Formations, separated by an erosional hiatus (Williamson, 1986). Local hill tops remain today as islands in a sea of sediment. Previously weathered and hydrothermally altered bedrock in the valleys would have been preserved by this alluviation, and weathering may have accelerated during and after deposition of the sediment. Deep leads were formed in the alluviated steeper headwaters within the erosional domains, such as at Parkes and Grenfell, and also in valleys buried by Lachlan River sediments, such as at Forbes.

Alluviation was probably due to two independent time transgressive mechanisms: 1. rising base levels due to the filling of the Murray Basin, and 2. change to a drier climate affecting vegetation, sediment balance, and discharge in the upper catchment.

In the Holocene, aeolian sand deposition occurred, and sand is present as small dunes, mostly on the alluvial plains, and as wedges built up on the western sides of steep ridges. Most of the sand is probably locally derived from the modern Lachlan floodplain. Aeolian sand associated with the Wyalong palaeovalley may have been derived from these eroded old sediments, and have caused the evulsion of the previously northeasterly flowing drainage towards the southeast. There is some evidence from possible remnants of source bordering dunes to the east of Lake Cowal that there may have been a more extensive palaeo-Lake Cowal.

13 The balance between erosion and deposition along the Lachlan River has probably varied considerably over time. Presently, the river is incising upstream of Eugowra-Gooloogong with terraces up to 40 m above river level, and actively alluviating downstream, although there are large areas of stagnant alluvial plains away from the Lachlan River.

This understanding of the regolith and landform evolution of the Forbes region is enhanced by a more detailed definition of the 3 dimensional distribution of regolith materials. A map of the depth to slightly weathered bedrock (Gibson & Chan, 1999b) was generated from the NSW Department of Water Resources water bore database and mineral exploration drill holes. Detailed logging and laboratory analyses of drill hole material is required to ascertain the transported–saprolite interface. High-resolution airborne geophysics datasets (magnetic, gamma-ray spectrometric, and electrometric) have helped to delineate many sub-surface and near-surface features, such as palaeochannels containing detrital maghemite gravels in the Wyalong area (Lawrie et al., 1999). Palaeochannels are significant for mineral exploration as they may contain placer deposits, and may be vectors to bedrock mineralisation. Palaeochannels are equally significant in the Forbes region for land use and the environment, as they relate to dryland salinity, biodiversity, and water resources.

REFERENCES

CHAN, R. A. 1998. Bathurst regolith-landforms. In WATKINS J.J. and POGSON D. (Cmpls.) Explanatory Notes for Bathurst 1:250 000 geological sheet, SH/SI 55-8. Geological Survey of New South Wales / AGSO.

CHAN, R.A., 1999. Palaeodrainage and its significance to mineral exploration in the Bathurst region, NSW. Proceedings of Regolith 98 Conference, Kalgoorlie, WA, May 1998. CRC LEME, Perth, 38-54.

GIBSON, D.L. & CHAN, R.A., 1999a. Regolith and landscape mapping and evolution. In LYONS, P. and WALLACE, D. (Eds), Forbes 1:250 000 Geological Sheet: Field conference guide: geology and metallogenesis of the Parkes-Grenfell-Wyalong-Condobolin region, NSW. AGSO/GSNSW. AGSO Record. 1999/20

GIBSON, D.L. & CHAN, R.A., 1999b. Forbes 1:250 000 Regolith Landforms (1:250 000 map scale). CRC LEME, Perth.

GIBSON, D.L. & CHAN, R.A., 1999c. Aspects of palaeodrainage in the north Lachlan Fold Belt region. Proceedings of Regolith 98 Conference, Kalgoorlie, WA, May 1998. CRC LEME, Perth, 23-37.

LAWRIE, K.C., CHAN, R.A., GIBSON, D.L. & DE SOUZA KOVACS, N., 1999. Alluvial gold potential in buried palaeochannels in the Wyalong district, Lachlan Fold Belt, New South Wales. AGSO Research Newsletter, 30, 1-5.

MARTIN, H.E., 1991. Tertiary stratigraphic palynology and palaeoclimate of the inland river system in New South Wales. In WILLIAMS, M.A.J. et al. (eds), The Cainozoic in Australia: a reappraisal of the evidence. Geological Society of Australia, Special Publication No 18, 181-194.

O'SULLIVAN, P. B., FOSTER, D.A., KOHN, B.P., and GLEADOW, A.J.W., 1996a. Tectonic implications of Early Triassic, and middle Cretaceous denudation in the eastern Lachlan Fold Belt, NSW, Australia. Geology 6. 563-566.

O'SULLIVAN P.B., KOHN, B.P., PILLANS, B., GIBSON, D.L. & PAIN, C.F., in press. Long-term landscape evolution of the Northparkes region of the Lachlan Fold Belt, New South Wales: constraints from fission track and paleomagnetic data. Geology, in press.

PILLANS, B., TONUI, E. & IDNURM, M., 1999. Palaeomagnetic dating of weathered regolith. Proceedings of Regolith 98 Conference, Kalgoorlie, WA, May 1998. CRC LEME, Perth, 237-242.

WILLIAMSON, W.H., 1986. Investigation of the groundwater resources of the Lachlan Valley alluvium. Part 1: Cowra to Jemalong Weir. Water Resources Commission of New South Wales, Hydrogeological Report 1986/12.

14 REGOLITH GEOCHEMISTRY AND STRATIGRAPHY OF THE CHALLENGER GOLD DEPOSIT

M. J. Lintern1 and M. J. Sheard2

1Cooperative Research Centre for Landscape Evolution and Mineral Exploration CSIRO Exploration and Mining c/o PIRSA, GPO Box 1671, ADELAIDE, SA 5001, Australia. 2Regolith Terranes Team, Geological Survey Branch, Mineral Resources Group, PIRSA, GPO Box 1671, ADELAIDE SA 5001, Australia.

The Challenger Gold Deposit lies in the northern Gawler Craton, South Australia, 750 km NW of Adelaide, and 140 km NW of Tarcoola. A 1.5 km traverse (the regolith line) was chosen for the study of geochemical dispersion and regolith stratigraphy across three zones of mineralisation (Zones 1, 2 and 3) and various landforms in the Challenger area. The principal mineralisation (Challenger I or Zone 1) outcrops on the flank of a low rise. Zone 2 mineralisation occurs about 400 m to the south east of Zone 1. Kelpie, or Challenger II (Zone 3), is located beneath about 20 m of sediments, presumed to be mostly Tertiary in age, about 800 m to the SE of Zone 1. Other zones of mineralisation occur in the area, but were not studied. Mineralisation is associated with silica and arsenopyrite alteration in the Archaean Christie Gneiss, a garnet-rich paragneiss consisting of plagioclase, perthitic K-feldspar, quartz, cordierite, garnet, biotite, and trace graphite.

Deep weathering of the Christie Gneiss has led to the development of a clay-dominated saprolite of variable thickness (but averaging about 30 m) that contains abundant relict quartz. The upper regolith (designated as 0– 6 m) is dominated by silicification (silcrete) and calcrete development, with comparatively small quantities of ferruginous material occurring mainly as ferruginous granules (lag) on the surface. The area is of low relief and dominated by a shrubland of bluebush (Maireana sedifolia), with pockets of mulga (Acacia sp.) flourishing in thin (< 2 m) aeolian dunes.

Thirty holes were specially drilled along the regolith line in order to study the upper regolith in detail. The lower regolith was sampled to about 60 m, using cuttings from pre-existing drill holes, at intervals along the regolith line that correspond with the upper regolith samples. A series of eight, 3 m deep pits were excavated along the regolith line to enable detailed examination of the relationship (i) between silcrete and calcrete, and (ii) between silcrete/calcrete and mineralised saprolite. In addition to the drill cuttings and pits, sampling and analyses of calcrete, silcrete, lag and vegetation was undertaken using a suite of 50 major and minor elements, XRD and SEM.

Results and recommendations are summarised (from Lintern and Sheard, 1998a) below: 1. Stratigraphic studies recognised two regolith units, in situ and transported. The in situ unit consists of Archaean basement rocks deeply weathered to saprolite. The transported unit consists of mainly fluvial deposits (up to 25 m thick) of presumed Tertiary age. Exploration strategies should aim to recognise the different units due to their quite dissimilar genesis, mineralogy and geochemical signatures, including anomaly thresholds. 2. Distinguishing between transported and in situ regolith has been demonstrated to be important from the geochemical sampling perspective. The light REE (Ce, La, Pr, Sm and Nd) appear to be able to be used to discriminate between transported and in situ regolith. 3. The elements in the regolith associated with mineralisation at the Challenger Gold Deposit fall into two broad groups: sulphide-related (Ag, As, Bi, Cd, Cr, Cu, Fe, Mo, S, Se, ?W and Zn) and alteration-related (Ba, Cs, K, Rb, Tl). The use of these elements as pathfinders is dependent on the sample medium to be used and the regolith setting. 4. Calcrete is ubiquitous and is recommended by far as the best sample medium for Au exploration in the in situ unit providing broad, high-contrast anomalies. Gold is by far the superior element to analyse for in calcrete but Cu and As are also useful. Drill cuttings, silcrete, soil, lag, and vegetation are alternative sample media that could be used, but further investigations are required to test the limits of their effectiveness. The use of near-surface calcrete for exploration over transported overburden is less clear, but is unlikely to be effective when the transported overburden is thick, except possibly on a regional basis. 5. Silcrete lag has been demonstrated for the first time to be a potential sample medium for Au. In areas where calcrete is absent, silcrete or soil are recommended as surficial sampling media (Lintern and Sheard, 1998b). 6. Gypsum was associated with mineralisation in the weathered in situ upper regolith. 7. Non-precious opal (potch) was identified in siliceous palaeochannel materials. Although precious opal was not encountered, there is a high potential for precious opal to occur in this environment. It is recommended that regolith settings similar to those found at Challenger are explored for opal.

REFERENCES Lintern, M.J. and Sheard, M.J., 1998a. Regolith studies related to the Challenger Gold Deposit, Gawler Craton, South Australia. Geochemistry and stratigraphy of the Challenger Gold Deposit. CRC LEME Restricted Report 78R / Primary Industries and Resources. South Australia. Report Book, 98/10, (2 Volumes. 95 pp + Appendices [un-numbered] or as CD-ROM version). Lintern, M.J. and Sheard, M.J., 1998b. Silcrete – a potential new exploration sample medium. Department of Primary Industries and Resources, South Australia. MESA Journal, 11:16-20.

15 Acknowledgments: Financial and in-kind support provided by the Gawler Joint Venture (Resolute Ltd and Dominion Mining Ltd) was gratefully received. CRC LEME is supported by the Australian Cooperative Research Centres Program.

16 GEOCHEMISTRY AND DISTRIBUTION OF SURFICIAL REGOLITH MATERIALS AT THE CHALLENGER GOLD DEPOSIT

Dwayne Povey School of Engineering (Applied Geology), University of South Australia, Mawson Lakes, SA, 5095.

BACKGROUND The lateral distribution of gold and a wide range of other elements in surficial regolith close to Au mineralisation, have been investigated at the Challenger exploration site in the western Gawler Craton, South Australia (750km NW of Adelaide). Following the initial exploration and discovery of Challenger by calcrete sampling, this study examines other sample media in the area that may provide additional avenues for sampling in the absence of calcrete. The objective of this study was to determine the most suitable and applicable exploration tool to locate mineralisation in surface regolith, in arid to semi-arid terrains of inland Australia.

A range of landforms and surficial features occur within the surface regolith at Challenger – including clay pans, calcrete plains, silcrete and ferricrete cappings, all over weathered basement and transported materials (alluvium, colluvium and low dunes). Topographic inversion is a feature of the landscape at Challenger with duricrusts of ferricrete, silcrete and calcrete now forming topographic highs (Lintern and Sheard, 1998a, 1998b).

METHODS The lag, soil and calcrete have been investigated mineralogically and geochemically. The area investigated covered a 3x3 km region, and the results have been plotted and assessed at 1:5,000 mapping scale. A square grid 300x300 m, allowed 140 sample sites within the investigation area. An additional 50 sample sites included specific areas of interest that were not covered in the initial pass of sampling. A more detailed petrology and description accompany these sites. The sampling method involved using a one metre square frame that was lain out and the contents swept up to be sieved into two size fractions (2-6 mm & >6 mm). A soil sample was then taken inside the frame to provide information as another sample medium. Calcrete samples previously collected by the Gawler Joint Venture, were deemed to be suitable for broader scale elemental geochemical reanalysis. Landscape and site features were photographed and described, to aid in the interpretation of materials geochemistry. Sample preparation involved washing, removal of calcrete from lag samples and weighing all samples. These were then analysed through a commercial laboratory for 51 elements.

RESULTS The results are plotted on a series of maps displaying: regolith, total lag distribution, lag type abundance, depth of transported cover, and geochemistry. When these new maps are used in conjunction with the known major regolith terrain boundaries (i.e. in situ vs transported) an interpretation of the various dispersion patterns can be made. Results have indicated the premium surface sample medium for Au exploration to be calcrete. Nevertheless, coarse and fine lags and the soils may provide a restricted element suite that may aid exploration in the absence of calcrete.

Challenger mineralisation exists at the surface, consequently, materials forming in that location encapsulated gold and other elements during their formation. Ensuing erosion, stripped and redistributed duricrust (ferricrete and silcrete) materials, whereas more recent calcrete and soil have remained largely in place, however, there is a dispersion halo associated with calcrete and soil materials that extends south from the area of mineralisation ~500 m into transported regolith.

Key words: Challenger, regolith, calcrete, silcrete, ferricrete, lag, geochemistry, South Australia.

REFERENCES Lintern M.J. and Sheard M.J., 1998a. Regolith Studies related to the Challenger Gold Deposit, South Australia. Cooperative Research Centre for Landscape Evolution and Mineral Exploration. CRC LEME Restricted Report 78R / Primary Industries and Resources. South Australia. Report Book, 98/10, (2 Volumes. 95 pp + Appendices [un-numbered].

Lintern M.J. and Sheard M.J., 1998b. Silcrete – a potential new exploration sample medium. Department of Primary Industries and Resources, South Australia. MESA Journal 11, 16-20.

Acknowledgments: This project was supported by Regolith Terranes, Mineral resources Group of Primary Industries and Resources, South Australia and Cooperative Research Centre for Landscape Evolution and Mineral Exploration, in conjunction and cooperation with the Gawler Joint Venture who provided data assistance, in-field accommodation and logistic support.

17 REGOLITH STRATIGRAPHY ABOUT THE CHALLENGER GOLD DEPOSIT, SOUTH AUSTRALIA

Simon E. van der Wielen

University of South Australia, School of Engineering, Department of Applied Geology, Mawson Lakes, SA 5095. Home: 11 Blue Wren Court, Highbury, SA 5089. Ph: 08 8263 7046.

An investigation of regolith stratigraphy using geological logging, petrology, geochemical, computer three dimensional modelling and infra-red spectroscopy (PIMA) techniques was carried out over the Challenger Gold deposit.

The regolith stratigraphy comprises a mixture of in situ and transported regolith that exhibit various styles of overprinting. In situ regolith outcrops from just southwest of the deposit and extends past the northeast corner of the study area, forming a rectangular body. Transported regolith thickens with distance from in situ outcrop and is thickest 2 km south of the field area where over 100 m of sediments have been drill intercepted in an inferred palaeochannel.

Results from 300 geochemical samples taken from 40 different drillholes have been graphically represented as: histograms, line plots (depth vs elemental abundances), box and whisker plots, and scatter plots, as well as being statistically analysed. As with Lintern and Sheard (1998) study, it was found that light rare earth elements (La, Ce, Eu, Nd, Pr and Sm) can be used to distinguish between in situ and transported regolith, where light rare earth elements have significantly lower concentration in transported regolith when compared to in situ regolith.

Eighty-five drillholes were analysed using Portable Infra-red Mineral Analyser (PIMA). PIMA measures reflected radiation of rocks in the short wavelengths infra-red (1300-2500 nm). Kaolinites and montmorillonites are the most common minerals identified. A kaolinite crystallinity index was used to distinguish between in situ and transported regolith. Silicification does not appear to effect the kaolinite crystallinity index.

Three dimensional modelling of regolith stratigraphy, kaolinite crystallinity, topography and Au geochemistry was carried out using Mine Visualisation Systems (MVS) software. Results from 3D plume diagrams of Au drill data has shown that there was depletion of Au within the lower regolith, formation of a supergene mineralisation (some lateral dispersion) and apparent vertical dispersion of Au into transported regolith.

The Challenger Gold deposit has undergone an extremely complex evolutional history which is evident in the regolith stratigraphy, materials, landscape and geochemical dispersion patterns at the site. Results show that there were multiple phases of erosion, sedimentary deposition, supergene formation and silicification.

Key words: Digital Elevation Model (DEM), Challenger Gold Deposit, Gawler Craton, geochemistry, gold, Portable Infrared Mineral Analyser (PIMA), regolith stratigraphy, South Australia.

18 METAL GEOCHEMISTRY OF REGOLITH IN THE MT LOFTY RANGES AND ASSOCIATED ALLUVIAL FANS OF THE ADELAIDE PLAINS

Andrew K.M. Baker Department of Geology and Geophysics, Adelaide University, Adelaide SA 5000

The Glen Osmond Pb-Ag mines are located about 12 km east of Adelaide GPO in the western Mount Lofty Ranges. The Glen Osmond Slate, part of the Neoproterozoic Burra Group, hosts 30 recognised lodes of sulphide mineralisation. These lodes provided an opportunity to apply a geochemical orientation survey over an area subject to high levels of anthropogenic contamination.

Various samples including rock chips, soil, primary mineralisation, drill core and drainage samples were collected for geochemical assay. Geochemical analysis provided information on secondary dispersion around base metal mineralisation. These data enabled the identification of preferred sample media and the establishment of local geochemical thresholds.

Lead isotopic analysis provided “fingerprints” for base metal mineralisation and anthropogenic contamination. This aided in determining which sample media was least susceptible to anthropogenic influences.

The search for new mineralisation will invariably lead to exploration in areas subject to large amounts of anthropogenic contamination. To avoid poorly directed exploration expenditure any false or misleading geochemical anomalies must be identified. With this in mind, isotopic methods available exploration may provide an additional tool during the orientation stage of geochemical survey work in anthropogenically disturbed areas.

Acknowledgments: Primary Industries and Resources South Australia, Adelaide University and the Cooperative Research Centre for Landscape Evolution and Mineral Exploration are thanked for their support.

19 THE USE OF PARTIAL LEACHING EXTRACTION METHODS FOR EXPLORATION: WINDABOUT PROSPECT, SOUTH AUSTRALIA

Alison Carragher

University of Adelaide, North Terrace, Adelaide, SA, 5000

Exploration for deeply buried mineralisation is very costly, and methods such as partial extractions have recently become more widely applied in the exploration industry, to locate mineralisation buried under thick, transported overburden. The processes involved in partial leaching extraction are generally poorly understood. However, due to the cost of routine drilling into saprolite or bedrock for regional or prospect scale exploration, methods such as partial leaching are the more favoured exploration tools for deeply buried mineralisation.

The Mount Gunson Cu deposits are located approximately 130 km NNW of Port Augusta, about 60 km west of the Torrens Hinge Zone on the eastern side of the Gawler Craton. The Cu deposits are located on the same NNW trending transcontinental gravity lineament as the Olympic Dam deposit (Tonkin and Creelman, 1990) There are two distinct hosts for the Mount Gunson deposits, the sandstone breccia and sandstone of Pandurra Formation and Whyalla Sandstone, or the black shale of Tapley Hill Formation. The Mount Gunson Cattle Grid deposit is an example of mineralisation hosted by the sandstone of the upper surface of Pandurra Formation. Copper and Co mineralisation at Windabout prospect is hosted by the black shale of Tapley Hill Formation, forming a sub-economic deposit. Mineralisation at Windabout is buried by approximately 70 m of transported overburden.

Characterisation and partial leaching analysis of the soils at Windabout attempts to aid in the understanding of geochemical anomalies obtained by partial extraction methods, and in the use of partial extraction for locating mineralisation that is deeply buried beneath transported overburden.

Surface soil samples were collected along two traverses across the buried mineralisation at Windabout, continuing into areas over background. Samples were taken from 0.0-0.1 m and 0.1-0.2 m depth at each site. The sample sites were located approximately 100 m apart. Each sample was characterised according to pH, salinity, location with relation to landforms, material texture and colour. The most dominant landforms in the study area are sand dunes and swales. Clay pans are also a common drainage sink landform. Gypcrete and calcrete are common regolith materials in the area.

Sub samples of each bulk sample were totally digested and analysed for 51 elements. The samples from one sample line were then sieved using a 180 µm sieve, and sub samples from both the course and fine fractions were totally digested. Sub samples of the +180 µm and -180 µm fractions were then partially digested using 0.1 M HNO3, 1.0 M HNO3, 0.1 M EDTA, and MMI Technology solutions. A pH 5 ammonium acetate leach was also applied to these bulk samples.

Results of the total digest of the bulk samples did not indicate the presence of buried mineralisation. A close relationship with Fe was shown by most elements including Co, Cu, Mn, Pb, and Zn. The amount of Fe also seemed to be related to the clay content of the samples, such that those samples high in Fe correlated to a high clay fraction, whereas the samples with little clay were lowest in Fe.

None of the partial leaches applied to the bulk or sieved samples showed the location of the buried mineralisation. The results of the digests indicated that Fe and Mn oxides are very effective in scavenging elements from the regolith. A close association between Co and Mn was demonstrated by several of the partial leaches, but generally Cu did not show any clear relationships with either Mn or Fe.

REFERENCES

Tonkin, D.G. and Creelman, R.A., 1990. Mount Gunson Copper Deposits. In: Hughes, F.E. (Editor), Geology of the mineral deposits of Australia and Papua New Guinea. The Australasian Institute of Mining and Metallurgy. 1038-1043.

Acknowledgments: Thankyou to CRC LEME and PIRSA, especially M. Lintern and M. Sheard for their supervision. Thankyou also to AMDEL for their support; Stuart Metals NL for allowing access to the site; H. Patterson for providing drillhole information and maps; John Foden for his supervision.

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21 EOCENE COASTAL BARRIER EVOLUTION IN THE EUCLA BASIN

Jonathan D. A. Clarke and Baohong Hou 1 CRC LEME, Department of geology, Australian National University, ACT 0200 2 Department of geology, Adelaide University, Adelaide, SA 5000

INTRODUCTION A range of shoreline features occurs along the northern and eastern margins of the Eucla Basin include coastal scarps, barriers, lagoons, and estuaries. These were deposited during the latest Eocene transgression of the Eucla Basin. The complex geometry of these features and their scale (they extend along a 600 km front and are up to 200 km wide, the barrier sands reach a thickness of 100 m) strongly suggest that these features formed in more than one transgressive episode. This poster presents a testable suggestion as to how the Eocene coast barrier system evolved.

STRATIGRAPHY Two third order Eocene transgressions that reached this far inland. These were the Middle Eocene Tortachila and the Late Eocene Tuketja transgressions. The Tortachila is represented in the area by the Middle Eocene marine limestones of the Paling Member of the Wilsons Bluff Formation. The spicular Kharsta Member of the Hampton Formation, which everywhere occurs as the highest Eocene unit, overlies it.

TORTACHILA TRANSGRESSION The highstand is characterised by development of the Ooldea Range, which forms a coast barrier. A northwest- southeast trending basement high may have provided a site on which the barrier originally nucleated. Sand was supplied by the 5 major palaeorivers to the west of the Ooldea Range, and by the 8 palaeorivers directly landward of the barrier. Lagoonal sediments included low energy brackish water facies of the Pidinga, high-energy brackish facies of the Hampton, and marine facies of the glauconitic and calcareous Paling Member. Multiple beach ridges in the Ooldea Range suggest a fourth order control on barrier accretion.

Erosion of the much of the upper part of the lagoonal succession is likely during the subsequent regression. This would have removed much of the Hampton and Paling from the lagoonal area. Existing tidal channels would have been enlarged as palaeorivers extended out across the former sea floor.

TUKETJA TRANSGRESSION In WA the Tuketja transgression reached an elevation some 20-m higher than the Tortachila (Clarke 1994) and we assume a similar figures applies in the eastern Eucla Basin. Consequently the shoreline extended much further inland at this time. An erosional scarp marks the shoreline position. A new barrier system developed, forming the Barton Range. The Ooldea Range formed a chain of offshore sand islands. A J-shaped barrier (the Paling Range) formed late in the evolution of the barrier complex. This tied the Ooldea Range to the Barton Range.

Lagoonal sediments between the Ooldea and Barton Ranges and landward of the Barton Range during the Tuketja transgression consisted of estuarine sands and clays (Pidinga Formation) and spicular marine sands (Kharsta Member of the Hampton Formation. The lagoonal and barrier facies are widely preserved owing to the shift of to more arid conditions following the terminal Eocene transgression.

IMPLICATIONS Much of the stratigraphy of these units occurs in the subsurface (Figure 5), however the proposed model makes a number of predictions that can be tested by stratigraphic drilling.. It specifically predicts that the Ooldea Formation (recognisably more angular than the Hampton and lacking marine fossils) of the Ooldea Range should overlie Hampton containing sparse calcareous fossils (Paling Member equivalent). On the landward side of the Ooldea Range the spicular Kharsta Member should overlie the Ooldea Formation, but the Ooldea Formation of the Barton and Paling range should overlie the Kharsta Member.

22 RELICTS OF A CENTRIPETAL DRAINAGE SYSTEM AND THE SUPERPOSITION OF THE PRESENT DRAINAGE REGIME; AN EXAMPLE FROM THE EASTERN MUSGRAVE BLOCK, SOUTH AUSTRALIA. ALSO SOME ECONOMIC IMPLICATIONS.

Colin Conor. Geological Survey Branch, Primary Industries and Resources, GPO Box 1671, Adelaide, South Australia 5001

The Musgrave Block contains remnants of an ancient, presumably Tertiary and perhaps Miocene-Pliocene, fluvio- lacustrine centripetally drained landform; the example shown in Figure 1 is Myall Swamp from the Eateringinna 1:100 000 area. The remnant lithologies are of two types: (1) colluvial, alluvial and fluvial sediments (eg. Mangatitja Formation, Cadelga Limestone, Doonbara Formation), (2) products of the temporally related, deeply weathered profile.

The Tertiary sediments are thin and were surficial in nature. Channel infill is represented by argillites and arenites, the latter generally poorly sorted and locally conglomeratic. The observation that the clast population comprises only highly resistive material such as reworked Tertiary duricrust, or basement-derived BIF or vein quartz debris, but not the less stable quartzo-feldspathic debris, indicates that the weathering system had been long established. The playas general contain grey gypsiferous clay, overlain by coarse unconsolidated arenite with scattered, polished silcrete pebbles, which in turn is capped by dolomitic limestone and chert (the latter, formerly, frequently utilised as a stone tool-manufacturing resource).

Preservation, which presents a ‘snap shot’ in time, is due to syn-depositional silicification (silcrete) and ferruginisation (ferricrete) of certain sediments and specific parts of the weathered profile. Induration was concentrated along channels or in the small playas into which the drainage was locally focussed. The induration was a component process of the mature weathering system which also involved widespread leaching to produce kaolin or kaolin + detrital quartz assemblages from felsic precursors (ie. granites and quartzofeldspathic gneisses), and jasper, magnesite, saponitic and montmorillonitic clays from mafic to ultramafic rocks (ie. mafic gneisses and intrusives eg. Giles Complex). The depth of the weathered profile over felsic rocks is typically in the order of a few tens of metres, elsewhere ultramafics are known, from drilling, to be intensely affected to greater than 200m.

The recognition of recent river terracing, evidence for drainage flow reversals and the spatial relationship of sediments to basement structures indicated that the region was, and is, seismically active. This was dramatically confirmed in 1986 by the Marryat Creek earthquake (Richter magnitude ~6.0) which resulted in the elevation of a two sided, pop-up, thrust block; the fault scar is 13km in length with a vertical displacement approximating one metre.

The episode of Tertiary weathering is of economic importance. Exploration in the late 1960’s indicated nickel resources at Wingellina (61Mt @ 3.2% Ni) and Claude Hills (4.5Mt @ 1.5% Ni) in Western and South Australia respectively. The resources are hosted by ochre which is a leached lag derived from mafic-ultramafic bodies. Mining has continued sporadically for the apple-green, gemstone chrysoprase (cryptocrystaline nickelliferous quartz), formed by replacement of nodular magnesite in saponitic clays, or as veins in nickelliferous jasper. Both surface and mottled-zone ferricretes have been researched as potential sampling media for regional exploration; the ferricretes showed considerable base metal anomalism. Carbonate bodies developed within the ancient drainage are potential hosts for Eleura-type calcrete-uranium mineralisation. Work on both the ferricrete and carbonate sampling programs was halted due to increasing access difficulties and the former political situation concerning the mining of uranium; such difficulties are currently being resolved.

Fig.1. Myall Swamp; a partly eroded playa which represents the ancient centripetal drainage regime of the Musgrave Block.

23 The Mt. Fitton Hyperspectral Mineral Mapping Project

Anthony Denniss, Senior Applications Specialist, (NRSC, UK) Jon Huntington, Chief Research Scientist (CSIRO Exploration and Mining) Steve Hore, Geologist (PIRSA)

An international collaborative project is underway in the Northern Flinders Ranges demonstrating the benefits of mineralogical mapping with air and spaceborne hyperspectral data. The collaboration involves CSIRO Exploration and Mining, the National Remote Sensing Centre (NRSC) UK and Primary Industries and Resources South Australia. The assistance of De Beers Stockdale Prospecting (Australia), Commercial Minerals (Australia) and Integrated Spectronics (Australia) is also gratefully acknowledged. The project consists of two phases, viz:

1. processing and field-checking the airborne hyperspectral data at its maximum 5m resolution in-order to produce a new series of detailed mineral abundance maps, and 2. re-processing the airborne data, after it has been convolved spatially and spectrally to the resolution of the proposed Australian Resources and Environment Satellite (ARIES-1).

The two sets of processed data will then be used in a comparative study of the value of the new hyperspectral- derived mineral maps and the differences seen at different scales. The study area is located in the Northern Flinders Ranges of South Australia, centred approximately on the Mt. Fitton Talc deposits, approximately 750km north of Adelaide and 130km northeast of Leigh Creek. The area is detailed on the Marree (SH 54-5) 1:250,000 and the Blanchewater (6738) 1:100,000 scale geological maps. The Mount Fitton area consists of regionally metamorphosed Neoproterozoic Adelaidean sediments of the Umberatana and Wilpena Groups. Six flight-lines (four north-south and two east-west) of 96 and 128-channel HyMap™ data, spanning the 0.4-2.4 µm wavelength range, were available for the project. These wavelengths are ideal for mapping of stratigraphic units, the regolith or alteration zones containing carbonate, sulphate, and hydroxyl-bearing minerals (such as sericite, kaolinite, chlorite, talc, etc), as well as iron oxides and green and dry vegetation. The data available for most of the area were slightly different from ‘conventional’ HyMap data, as the shortwave- infrared (SWIR-2) channels between 2.1 and 2.4 µm were re-configured to a finer bandwidth of approximately 10 nm, as opposed to the conventional 18-20 nm. Part of the area was also covered with conventional 18-20 nm resolution HyMap data. The hyperspectral data were processed using the ENVI image processing package augmented by a series of special tools developed in-house at CSIRO. The data processing consisted of calibrating and atmospherically correcting all channels prior to extracting the SWIR-2 data. To date only the SWIR-2 data over the most geologically interesting, 2.1-2.4µm region, has been fully processed, however work is currently underway analysing the Visible and Near-Infrared (VNIR) data (0.4-2.0 µm). Processing consisted of reducing the data volume using the Maximum Noise Fraction transformation (MNF) prior to creating a Pixel Purity Image (PPI) to identify the spectrally most extreme materials in the area. These pixels were then visually examined using a dynamic n-dimensional scattergram tool to identify spectrally coherent mineralogical groups (clusters) from the regional noisy background. A spectral library of endmember spectra was then created representing the spectrally purest pixels (i.e., the different mineralogies) within these coherent groups. This project is still on-going and a lot of work remains to be done, including electron microprobe analysis of the mica and chlorite compositions and the acquisition of additional flight-lines of data. However the preliminary results are extremely encouraging and indicate the data are clearly mapping distinct mineral assemblages and bringing to light new geological data that will a) demonstrate the power of this new geological mapping tool and b) refine the geological understanding of this particular area.

24 LAKE LEWIS BASIN, CENTRAL AUSTRALIA: Cainozoic basin development on Proterozoic basement

Pauline English: Research School of Earth Sciences, Australian National University, Canberra, ACT, Australia, 0200

Lake Lewis basin is a hydrologically closed intermontane basin developed on the crystalline Arunta craton in central Australia. The basin is bounded to the south by the West Macdonnell Range and the Amadeus Basin, and to the north by Stuart Bluff Range of the southern margin of the Ngalia Basin. The landscape is composed of steep mountains of Proterozoic granite, gneiss and quartzite; widespread alluvial fans; a lacustrine plain; dunefields and playas. Lake Lewis itself is a 250 km2 salt lake at 550 m (AHD) elevation; the lake is fed by groundwater discharge and a centripetal array of ephemeral creeks. Rainfall in the area is around 300 mm per year, exceeded by evaporation by a factor of 10.

The structural and geomorphic grain of the area is defined by major east-west trending faults and regional-scale folds that are legacy of the Devonian - Carboniferous Alice Springs Orogeny (ASO). The over-thrusted central uplands area remained elevated above the Cretaceous marine incursions that affected much of the rest of the continent. Subaerial weathering and erosion of the Gondwanan landscape produced the mountainous bedrock relief that is extant today. In the early Tertiary, normal (extensional) movement on former ASO thrust faults resulted in crustal subsidence north of the fault-bounded ranges. In particular, mechanically unstable segments of the Redbank Thrust Zone failed in response to small changes in tectonic stress (Beekman et al., 1997). This passive tectonism and subsidence along ancient faults was contemporaneous with early Tertiary rifting between Australia and Antarctica. The crustal subsidence initiated Cainozoic basin development and was accompanied by reversal of a vast headwater drainage system of the upper Finke River in the Macdonnell Range. The captured mountainous catchment subsequently fed the evolving Lake Lewis basin to the immediate north, providing high runoff and abundant alluvium.

Up to 250 m of terrestrial sediments accumulated in contiguous basins north of the ranges. Palynological data indicate that deposition of lacustrine sediments on weathered gneiss in the area commenced by the Middle-Late Eocene (Macphail, 1996) and continued through the Oligo-Miocene although with prevalent brackish conditions represented in the stratigraphic record (Macphail, 1996). Palaeomagnetic data indicate that perennial lacustrine sedimentation continued to dominate until well into the Brunhes magnetic chron of the Quaternary (to < 0.78 Ma).

During the late Pleistocene Lake Lewis was a large lake that extended to the 560 m topographic contour. This palaeolake covered an area of 1375 km2, i.e, 5.5 times the area of the present playa. The megalake had distinctive features that included protruding granite inselbergs, fetches of the lake that lapped through gaps in quartzite ranges to the north, downwind accumulation of lake-fringing quartzose foredunes, and small satellite lakes. Impinging climatic change resulted in contraction of the lake and precipitation of a broad envelope of calcrete within the prior lake margins. Subsequent developments included excavation of deflationary landforms, groundwater outcrop at the lowered playa surface, precipitation of voluminous gypsum at the groundwater discharge zone, aeolian redeposition of evaporites, and establishment of a highly irregular playa morphology in response to groundwater control of geomorphic processes. Thermoluminescent ages for aeolian gypsum dune units indicate that major episodes of evaporite precipitation and aeolian redeposition were: >70-80 ka and 46-33 ka (Chen et al., 1995). During the late Pleistocene period of peak aridity, ~24-12 ka, landscape evolution was dominated by the establishment of regional quartzose dunefields.

Ameliorated climatic conditions since the Last Glacial Maximum are represented in the landscape by the marked impact of ephemeral surface waters on the fluvial, aeolian and playa environments. The Macdonnells induce an orographic effect on the northern monsoon system that favours precipitation in Lake Lewis basin at the expense of inland areas south of the ranges. Consequent high magnitude flood events result in episodic deposition of vast floodplains across the basin; these floodplains – along with the playas and dunefields – now dominate the landscape of the region.

References Beekman, F., Stephenson, R.A. and Korsch, R.J., 1997. Mechanical stability of the Redbank Thrust Zone, central Australia: dynamic and rheological implications. Australian Journal of Earth Sciences, 44/2: 215-226.

Chen, X.Y., Chappell, J. and Murray, A.S., 1995. High (ground) water levels and dune development in central Australia: TL dates from gypsum and quartz dunes around Lake Lewis (Napperby), Northern Territory. Geomorphology, 11: 311-322.

Macphail, M.K., 1996. A provisional palynostratigraphic framework for Tertiary organic facies in the Burt Plain, Hale, Ngalia, Santa Teresa, Ti-Tree and Waite basins, Northern Territory. AGSO Record 1996/58.

25 PALAEODRAINAGE MAPPING AT ULURU (AYERS ROCK), NORTHERN TERRITORY

Pauline English: Research School of Earth Sciences, Australian National University, Canberra, ACT, Australia, 0200.

The Dune Plains area is located between Uluru (Ayers Rock) and Kata Tjuta (The Olgas) in the Amadeus Basin in southwestern Northern Territory. The plain overlies an in-filled palaeodrainage valley that is up to 100 m deep. The present-day landscape of the area between the spectacular upstanding outcrops of bedrock is flat and blanketed with dune networks and broad sheetwash aprons of red earths. No vestige of the underlying Dune Plains palaeovalley is evident in the modern landscape.

The geology of the area is dominated by the monolith of vertically-dipping Cambrian arkose of Uluru itself and, 30 km to the west, the 36 domes of sub-horizontally dipping Cambrian conglomerate at Kata Tjuta (Sweet & Crick, 1992). Northeast of Kata Tjuta, and east of Yulara village, Proterozoic quartzite outcrops in a NW-striking ridge known as the Sedimentaries. Lake Amadeus salt lake is 50 km north of Uluru.

The presence of organic material at depth in the Uluru and Dune Plains area was first recognised following drilling for water resources for the National Park and Yulara village. Twidale & Harris (1977), Harris & Twidale (1991) and Macphail (1997) identified Late Maastrichtian and Middle-Late Eocene palynofloras in cuttings from lignitic siltstone layers sampled from between 90-66 m depths in the boreholes.

Integrated datasets including aeromagnetic and airborne gamma-ray spectrometric imagery, processed Landsat TM imagery, a digital elevation model and water-bore logs were subsequently used to complement the palynological data and reconstruct the palaeodrainage system at Uluru.

The aeromagnetic imagery reveals conjugate WNW- and ENE-striking fault networks across the region. These pervasive structures are the heritage from the Devonian-Carboniferous Alice Springs Orogeny in which the principal compressive stress direction was roughly N-S. The magnitude of the 100 million years of the orogeny is best exhibited at Uluru itself where the former horizontal disposition of the arkose was tilted vertically. The dominant WNW-strike is conspicuous in both the bedrock outcrops and the geomorphology of the region. In particular, the >200 km long Lake Amadeus - Lake Neale playa system is concordant with the WNW-trend of regional structures. The elongate Amadeus lake system follows a major fold axis of the Amadeus Basin along which Proterozoic dolomite has been exhumed. The ENE-striking aeromagnetic anomalies correspond with fractures that crosscut the regional bedrock strike. It is the ENE-trending structures that were important in the early development of the Dune Plains palaeovalley. The Dune Plains zone is floored with a variety of basement lithologies that are juxtaposed between the erosionally resilient outcrops of arkose at Uluru in the east, conglomerate at Kata Tjuta in the west, and Proterozoic quartzite of the Sedimentaries to the northwest. The recessive, fault-bounded rock types beneath the Dune Plains area include dolomites, siltstones and sandstones. Clearly, initial valley development in the area followed the strike of fault-lines and associated zones of easily eroded rock types.

Borehole data reveal a heterogeneous subsurface topography with up to 100 m vertical relief beneath the Dune Plains area (a buried 'mini-Kata Tjuta'). This uneven basement topography is attributable to differential subaerial weathering and erosion – from the late Palaeozoic to the Cretaceous – of the varied Proterozoic-Cambrian rocks. In particular, dolomite was most likely subject to dissolution processes in runoff waters derived from the adjacent mountains of Uluru, Kata Tjuta and the Sedimentaries, and in percolating acidic waters that would have preferentially infiltrated faults and fractures. By the late Cretaceous, a closed basin with several discrete depocentres was generated in weathered dolomite. Up to 40 m of sediments, including organic material, accumulated in the hollows from the Late Maastrichtian to the Middle-Late Eocene when low energy fluvio- lacustrine conditions prevailed in the area. The basin was closed to the north by a basement high in the vicinity of the present-day Yulara village. Only when the basin became in-filled with sediment above the level of this obstruction could a through-flowing river develop, with an outlet northward towards Lake Amadeus. The uppermost >60 metres of deposition in the Dune Plains palaeovalley comprises fine to coarse quartzose sands indicative of higher energy fluvial regimes after the Eocene.

Airborne gamma-ray spectrometric imagery and processed Landsat TM imagery indicate that the course of the Dune Plains palaeoriver was arcuate, from south of Kata Tjuta and with a main NNE-trending reach to the vicinity of Yulara in order to circumnavigate the eastward-protruding Sedimentaries range. Once clear of the Sedimentaries, the river course spread out – northward from the vicinity of the Yulara airport – in a deltaic plain to Lake Amadeus, coalescing with drainages flowing from Kata Tjuta and the Sedimentaries. During the late Tertiary, Lake Amadeus was greatly expanded relative to the present playa extent, possibly reaching the mid-plain position between Yulara and the modern playa.

26 Drainage became restricted and lakes contracted in central Australia perhaps by the late Miocene to Early Pliocene, with the general trend of increasing aridity during the Pliocene and Pleistocene. The Quaternary landscape of the area is dominated by calcrete bodies, broad sheetwash aprons around outcrops, and curvilinear and reticular dune networks. The buried Dune Plains palaeodrainage valley and underlying fractured bedrock make up a complex aquifer system that is a major source of water supply for the inhabitants and tourists of this World Heritage Area.

REFERENCES Harris, W.K. and Twidale, C.R., 1991. Revised age for Ayers Rock and the Olgas. Transactions of the Royal Society of South Australia, 115 (2), 109.

Macphail, M.K., 1997. Palynostratigraphy of Late Cretaceous to Tertiary basins in the Alice Springs district, Northern Territory. Australian Geological Survey Organisation, Record 1997/31.

Sweet, I.P. and Crick, I.H., 1992. Uluru and Kata Tjuta: a geological history. Australian Geological Survey Organisation, Canberra, 27 pp.

Twidale, C.R. and Harris, W.K., 1977. The age of Ayers Rock and the Olgas, Central Australia, Transactions of the Royal Society of South Australia, 101: 45-50.

ACKNOWLEDGEMENT The Uluru palaeodrainage mapping project was carried out on behalf of the Australian Geological Survey Organisation and Uluru - Kata Tjuta National Park. The research is documented in the following publication: English, P.M., 1998. Cainozoic Geology and Hydrogeology of Uluru-Kata Tjuta National Park. Geoscience for Land and Water Management. Australian Geological Survey Organisation Monograph, 95 pp.

27 The application of geological and geophysical technology to the study of Tertiary palaeochannels draining the Gawler Craton, SA. Baohong Hou1, Larry Flakes2, Neville Alley3, Vicki Stamoulis3 and Andrew Rowett3

1. Department of Geology and Geophysics, University of Adelaide, Adelaide SA 5000 / Mineral Resources Group, Primary Industries and Resources of South Australia, GPO Box 1671, Adelaide SA 5001 2. Department of Geology and Geophysics, University of Adelaide, Adelaide SA 5000 3. Mineral Resources Group, Primary Industries and Resources of South Australia, GPO Box 1671, Adelaide SA 5001

The precise geometric definition of the Tertiary palaeochannels on the northwest Gawler Craton of South Australia is important in the exploration of placers (gold, uranium, diamonds, heavy minerals), secondary geochemical deposits (eg. uranium) and even for groundwater resources which probably occur in channel sediments. Knowledge of the concentration of minerals in the channels is also of interest as a guide to the location of bedrock minerals (eg. gold, diamonds) in the Gawler Craton.

Although series of present-day playa lakes either partially connected or isolated along current topographic lows in some cases define palaeodrainage in the Gawler Craton of South Australia palaeochannels normally show considerable displacement from these features, and other methods are required to locate them. These include interpretations from field exposures, geological and drilling data, topographic and remote sensing imagery, digital elevation models (DEM), gravity and transient electromagnetics (TEM), all of which have contributed to a systemic investigation of both shape and depth of the channels. Physical property contrasts which exist between the channel sediments and the underlying Archaean bedrock, for instance, can be differentiated by geophysical methods to locate the channel thalweg.

The palaeochannels are originally incised into the pre-Tertiary landscape, mostly weathered basement, in which Tertiary fluvial/alluvial and lacustrine sediments accumulated. The dimensions of the palaeochannels vary greatly, ranging from tens to more than100km in length, a few tens of metres to > 30km in width and depths of up to 100m. The principal direction of palaeodrainage is towards the southwest with considerable variation in places owing to low and variable gradients. Tallaringa, Garford and Kingoonya palaeodrainages spread out in a broad estuary or deltaic braid plain in their lower reaches to the margins of the Eucla Basin.

Eocene and Miocene sediments are known from the buried palaeochannels. Irregular tributaries to the major channels are also recognised. Some draining nearby known mineral deposits have potential for significant mineral concentrations.

Regolith units in the region include calcrete, silcrete, ferricrete, gypcrete, and sheetwash landscape units composed of duricrusts and red earths both in and outside the palaeochannels.

The most successful procedure for defining the palaeochannels is to use a combination of geological and geophysical methods.

Though no palaeodrainage deposits in the region have been mined yet, on-going research seeks to understand the possible presence of placer and other deposits as well as their clues for both important secondary resources and bedrock mineralisation.

28 GARFORD PALAEOCHANNEL: CLAY MINERALOGY OF MIOCENE SEDIMENTS AND THE USE OF FIELD IR IN THE SEARCH FOR COMMERCIAL CLAYS

1 2 J L Keeling and P G Self 1 Primary Industries and Resources SA, GPO Box 1671 ADELAIDE SA 5001 2 Ian Wark Research Institute, University of South Australia MAWSON LAKES SA 5095

INTRODUCTION Palygorskite (attapulgite), a fibrous magnesium aluminium silicate with commercial use in absorbents and gellants, is a common accessory mineral in Miocene lacustrine sediments in palaeodrainage channels in northern and western South Australia. Identification of commercial grades of palygorskite in the Garford Palaeochannel was aided by the use of a portable shortwave infrared (IR) analyser to test samples on-site during drilling operations. The technique proved highly effective in mapping clay mineralogy and in particular the distribution of zones containing high-grade palygorskite.

GEOLOGY Garford Palaeochannel is part of an extensive network of Tertiary palaeodrainage channels that once drained a wide region of north-western South Australia, discharging into the marine Eucla Basin. The channels remain largely intact and preserve an average 30-80 m thick sequence of fluvial channel sand deposits (Pidinga Formation) overlain by lacustrine clay and clayey dolomite (Garford Formation). Garford Palaeochannel is over 120 km in length and varies in width from 2 to 10 km. The target Miocene clays rarely exceed 20 m thickness and typically comprise poorly-ordered sandy kaolinite at the base overlain by interstratified illite/smectite and illite clays (± palygorskite), with the upper 5-15 m dominated by mixed dolomite and palygorskite (Keeling and Self, 1995). Non-clay phases present include quartz, halite and gypsum with trace amounts of goethite, garnet, amphibole, celestine, barite, microcline, albite and anatase.

QUANTITATIVE MINERALOGY The complex chemistry and mineralogy of Garford Formation sediments produced X-ray diffraction (XRD) patterns that were difficult to quantify due to overlapping peaks compounded by inadequate data on the chemistry of individual mineral phases. Specialised techniques were required to achieve quantitative analytical results. Pure end members of illite, dolomite and palygorskite were separated from selected Garford samples using fine particle sizing by centrifugation and careful acid treatment to remove unwanted phases. The pure phases were characterised and used to make standard mixtures which were analysed by high resolution XRD (step size 0.02° 2• and 5 sec count per step). The ratios of integrated areas of selected characteristic peaks for minerals were obtained for known mixtures and used to produce calibration curves for determining the amount of mineral present in the raw samples (Self et al., 1996).

Normalised results from the suite of raw samples analysed by XRD were used to test relationships between IR spectra and palygorskite concentration. For samples containing predominantly mixtures of dolomite and palygorskite there is a strong correlation between palygorskite content and the depth of the main palygorskite absorption feature at 2220 nm. For palygorskite in the presence of illite/smectite, the 2220 nm feature is distorted by the smectite Al-OH absorption at around 2210 nm. This distortion can be largely corrected to achieve a reasonable estimate of palygorskite content from field data (Keeling and Mauger, 1997). Variable moisture content proved to be an early source of error that was overcome by drying samples overnight and grinding by hand in a mortar and pestle (Keeling et al., 1995).

PALYGORSKITE FORMATION AND DISTRIBUTION Highest concentration of palygorskite was found at the interface of illite/smectite clays with dolomitic clay. Increased alkalinity of lake waters appears to have resulted in incongruent dissolution of smectite clays on the lake floor and recrystallisation to palygorskite. Thickest intersections of palygorskite are at the shallow margins of the alkaline lake where intertonging detrital and chemical sediments generated stacked sequences of high-grade palygorskite.

REFERENCES Keeling, J.L., Ferris, G.M. and Statham-Lee, L., 1995. Palygorskite investigations, Garford Palaeochannel, South Australia: results of drilling April-May, 1995. South Australia, Department of Mines and Energy Report Book 95/48. Keeling, J.L. and Mauger, A.J., 1997. Use of a field portable IR analyser in delineation of commercial grades of magnesium-rich clay at Garford, South Australia. Proceedings of the 12th International Conference, Applied Geologic Remote Sensing, Denver, Colorado, USA, 17-19 November 1997, Vol 1: 29-36. Keeling, J.L. and Self, P.G., 1995. Garford Palaeochannel palygorskite. MESA Journal 1: 20-23. Self, P.G., Keeling, J.L. and Raven, M.D., 1996. Mineralogy and physical properties of samples containing palygorskite collected during the MESA 1995 drilling programme in the Garford Palaeochannel, South Australia. CSIRO - Division of Soils report to MESA, open file envelope 8785: 156pp. 29 Salinity and pollution geochemical up-date of the Renmark to Morgan section of the River Murray and its immediate environment, Murray Basin, South Australia.

1Kiasatpur, G., 1Bone, Y. and 2Clarke, J.A.D.

1Dept of Geology and Geophysics, University of Adelaide, South Australia 2CRC LEME, Australian National University, Canberra

The River Murray is instrumental in the generation of several million/annum of agricultural products in South Australia. This industry is under threat due to salinisation and pollution of the water-way. The River Murray is sorced in high rainfall and topographically high areas in NSW and Victoria. The water within the river is already severely altered from its original pristine state by the time it reaches the SA border. Increased irrigation in the Renmark to Morgan section of the Murray Basin has led to the displacement of saline groundwater into the river itself. Similarly, increased human activity has led to an increase in the pollutant load in the river water.

Samples of water were collected from the River Murray itself, from deep and shallow irrigation bores and wood- lot bores, from adjacent lakes, swamps, seeps, waste water drains, evaporation pans and fresh rain-water. The pH and salinity of the samples were immediately recorded. The samples were treated as necessary prior to analysis for 13 elements and for their δ34S, δ13C and δ18O stable isotope values and their δ86Sr/δ87Sr ratios.

The elemental analyses were surprisingly low, with the concentration of Na (as NaCl) the only element of concern. Consequently, the total dissolved solids figure can be used as a proxy for salinity. The salinity values are much higher (141-38,000 mg/L) than those predicted for an area draining sedimentary rocks (50 – 200mg/L). This elevation of NaCl has been brought about by the raising of the water table and the influx of saline bore water in to the surficial zone and subsequent run-off. Similarly, the pH of the waters has risen to between 8 – 10 in contrast to average river water of 7. This has been bought about by the interaction of CaHCO3 derived from the carbonate aquifers and CO2. The pH level is significant inasmuch as it is one of the controlling parameters on the solvent effect of the water. A pH of approximately 7 should be the goal.

The interception scheme is achieving its goals of preventing the run-off into the river of highly saline surface water and seepage of shallow groundwater. It appears that there is likely to be increased problems in the area on the northern bank of the river due to the morphology of the river terraces allowing the inflow of saline water to the surface and from there into the river.

Some of the shallow and lagoon samples had slightly elevated Fe concentrations, but observation showed that this is due to the remains of Fe-oxidising bacteria. The highest concentrations of metallic elements were in the samples from Berrivale Winery drain, but these were much lower than the WHO recommended limits.

Overall, the present scenario appears to have slowed down from the previous frighteningly rapid-speed deterioration of the river as an uncontaminated water source. Those naturally occurring contaminants (pollutants), eg. Fe, are all within acceptable levels and so do not qualify as pollution. However, the salinity level and pH still demand urgent remedial action, otherwise the outlook for this large tract of land is that it will become a desolate tree-less salt plain.

30 TERTIARY PALAEODRAINAGE MAP OF SOUTH AUSTRALIA Paul Rogers Primary Industries and Resources South Australia, GPO Box 1671 Adelaide, SA 5001

Compilation of a map showing known Tertiary palaeochannels in South Australia was proposed at a palaeochannel workshop held at the Department of Primary Industries and Resources in March 1998. This task has been complete and the map is available from the Department as a digital colour plot (nominal scale 1:2 000 000, price $25). It is proposed to incorporate the map into PIRSA’s digital geoscientific database.

The map compiled at a scale of 1:1 000 000 in part from data published by PIRSA including 1:1 000 000 scale Tertiary palaeogeographic sketch maps accompanying 1:250 000 geological maps. Other sources of information include Rowett (1997) (Mt Lofty Ranges – St Vincent Basin) and Curtis et al (1990) (Lake Frome region). Additional interpretation of Tertiary palaeodrainage was carried out, mainly using geological mapping, digital elevation data and drillhole logs.

Palaeochannels delineated on the map are classified by the age and facies of their sediment fill (Neogene Palaeogene, marginal marine facies of the Palaeogene, Neogene and Palaeogene), and their geomorphological expression (topographic depression, topographic high, buried). A more detailed portrayal of palaeochannel stratigraphy is given in a separate chart.

Also shown on the map are palaeochannel-related mineral deposits and occurrences, selected drillholes, and type or reference sections of palaeochannel-related stratigraphic units, along with principal Tertiary basins and Precambrian geological provinces.

The map provides an up-to-date overview of Tertiary palaeodrainage which is becoming increasingly important as a source of groundwater, construction materials and sedimentary uranium, as well as being prospective for placer gold, clay minerals and other commodities. Production of the map complements the PIRSA/University of Adelaide collaborative study of Tertiary palaeodrainage in the Gawler Craton (see MESA Journal 6, pp10-11).

REFERENCES

Curtis, J.L., Brunt, D.A. and Binks, P.J., 1990. Tertiary palaeochannel uranium deposits in South Australia. In Hughes, F.E. (Ed.) Geology of mineral deposits of Australia and Papua New Guinea. Australasian Institute of Mining and Metallurgy. Monograph, 14:1631 –1636.

Rowett, A.I. 1997. Preliminary report of palaeodrainage in the St Vincent Basin and Mt Lofty Ranges. South Australia. Department of Mines and Energy. Report Book, 97/25.

31 THE STUART CREEK PALAEOCHANNEL: A SITE OF PALAEOBOTANICAL AND GEOLOGICAL SIGNIFICANCE.

Andrew Rowett Geological Survey Branch, Mineral Resources Group, PIRSA, GPO Box 1671 Adelaide, South Australia 5001

The Stuart Creek palaeochannel system is located approximately 40km south west of Lake Eyre South, within the Late Tertiary Billa Kalina Basin. The basin contains a thin flat-lying sequence including the Watchie Sandstone, Willalinchina Sandstone and Mirikata Formation. Channel sediments are represented by the Willalinchina Sandstone which consists of a pebble conglomerate overlain by medium-scale cross-bedded, largely fine to medium-grained sandstone containing minor course-grained strongly silicified quartz sandstone (Callen & Cowley 1995, Rowett & Alley 1997). Sedimentological investigations indicate that deposition occurred in a broad, shallow meandering to braided channels system. Ripple surfaces are common and rare climbing ripples occur at a few localities. Channel, bar, levee, and floodplain to lacustrine facies are recognisable.

Origin of the ?Miocene – Pliocene palaeochannel is suggested by Alley (in Rowett & Alley,1997) as being associated with subsidence in the Lake Eyre Basin or uplift along the Billa Kalina – Stuart Range axis causing erosion of a valley and deposition of the Willalinchina Sandstone in a broad channel system bordered by marginal monsoonal rainforest and drier sclerophyllous vegetation in the hinterland. The channel flowed northwards towards a depocentre in the current Lake Eyre area, and thus the Willalinchina Sandstone is related to the Lake Eyre Basin not the Billa Kalina Basin. Further subsidence in the Lake Eyre Basin causing erosion and relief inversion along Stuart Creek valley so that the silicified fossil-bearing Willalinchina Sandstone now stands above the current creek level as a series of linear outcrops and small mesas (Rowett & Alley, 1997).

Palaeobotanical investigations carried out on the Willalinchina Sandstone has identifying 145 leaf types, 47 fruit and seed types and 2 major wood type. The floristic composition indicates that a marginal monsoonal rainforest, with well defined tropical and sclerophyllous components, existed along the Stuart Creek palaeochannel during the Late Tertiary. Lobed-leaf forms comparable to the modern genera Brachychiton (Sterculiaceae), Cochlospermum (Cochlospermaceae), Orites (Proteaceae) and a serrate-margined fossil species of Callicoma (Cunoniaceae) dominated the tropical component. These plants and many others grew along the watercourses where permanent water enabled them to survive the dry season. The sclerophyllous component dominated the flora, consisting of plants with mainly linear to lanceolate leaf forms, many of which appear indistinguishable from modern Eucalyptus leaves. These plants grew on the exposed, drier plains in more open forest communities and probably on edaphically drier parts of the flood plains.

The Stuart Creek flora provides valuable information on the mid - late Tertiary distribution of Eucalyptus. The little variation in its leaf form implies Eucalyptus has existed in the Stuart Creek area for approximately 15 million years, undergoing very little apparent change in leaf morphology and therefore suggesting Eucalyptus has maintained a similar habit and ecological niche in the environment throughout this period. Rainforest plants no longer exist at Stuart Creek, their absence indicative of a changing climate and environment. As the climate became increasingly dry these plants died out to eventually become confined to the present monsoonal and tropical rainforests of northern Australia.

REFERENCES Callen, R.A. & Cowley , W. M. 1995. Billa Kalina Basin, In Drexel, J.F & Preiss, W.V (Eds), 1995. The geology of South Australia, Vol. 2, The Phanerozoic. South Australia. Geological Survey. Bulletin, 54.

Rowett, A.I. & Alley, N.F. 1997. Earthwatch’96. Vol.5. MESA Journal,. 27-29.

32 DEPTH TO BASEMENT IMAGE FROM OUTCROP AND DRILLHOLE DATA ON THE LINCOLN .1: 250 000 MAP SHEET

Michael P.Schwarz Primary Industries and Resources South Australia, GPO Box 1671 Adelaide, SA 5001

The compilation of digital geology and drill hole data for the Lincoln 1:250 000 map sheet has allowed the production of a relatively detailed depth to basement image. This has been achieved by using nodes on basement outcrop polygons as zero points for depth to basement in conjunction with depth to basement obtained from drillholes. The GIS software package, MapInfo Professional V5.0, was used to interrogate SAGEODATA (Primary Industries and Resources geoscientific database) to select all basement polygons and basement intersecting drillholes. This information was then exported to Microsoft Excel V7.0 in a MIF (mapinfo interchange format) from where it was formatted into a suitable format to use in the geophysical gridding program Intrepid. DEM (Digital Elevation Model) data was then added to the resulting grid to rectify each point to relative topographic levels. The rectified grid was then processed in ER Mapper V6.0 to create a three dimensional image.

The resulting depth to basement coverage shows a remarkably steep sided palaeochannel, running in a N-S to NE- SW direction. At the northern extent the palaeochannel connects to a roughly elliptical basin (Cummins Basin), both of which are filled with Tertiary sediments.

The addition of digital geology has provided a significant amount of constraint within the depth to basement image, enhancing detail of the Tertiary drainage systems.

33 REGOLITH IN AN URBAN ENVIRONMENT: A CASE STUDY FROM ADELAIDE, SOUTH AUSTRALIA Malcolm J. Sheard

Regolith Terranes, Geological Survey Branch, Mineral Resources Group, Department of Primary Industries & Resources, GPO Box 1671, Adelaide, S. Aust., 5001

BACKGROUND Metropolitan Adelaide was established in 1836 on a series of westward facing piedmont slopes abutting the metasediments of the Mt Lofty Ranges and bounded by Gulf St Vincent. Seasonal and Human-induced moisture changes in the soils and underlying sedimentary—saprolitic materials of this area produces shrink-swell reactions that can be very detrimental to urban structures. A shift from the ‘fire prone’ (flexible) timber dwellings to more rigid masonry buildings late last century brought the general populous and civil engineers face to face with soil heave-induced building cracking or footing failures. Soil mapping surveys in the late 1940’s and 1960’s had concentrated only on the surficial 0-1.5 m but engineering research by the late 1960’s was beginning to reveal that the root causes to lie deeper in the regolith profile. Late in 1979 the South Australian Department of Mines & Energy in collaboration with CSIRO – Division of Soils (Adelaide) commenced a 15 year study of these reactive materials (Sheard and Bowman, 1996).

INVESTIGATIONS A series of ‘Benchmark Sites’ were established across the Metropolitan area, consisting of 170 cored holes, drilled to ~10 m or bit-refusal and spaced according to known or encountered pedological, geological, geomorphological and geomechanical variability. The derived 50 mm diameter cores were logged in detail and then subjected to a series of geomechanical tests, mineralogical and chemical analyses. All cores have been retained in the PIRSA Core Storage Facility at Glenside for reference and further research work. Interpretation and synthesis culminated in a large Report containing a collection of distribution maps, cross-sections, data tables and composite log sheets. This resource has subsequentially been reinterpreted to reveal the regolith components and their impact on urban development.

REGOLITH MATERIALS & LANDSCAPE EVOLUTION Drilling and inspection of the various exposures (surficial & 3 dimensional – natural & anthropogenic) for the study by Sheard and Bowman (1996) and incorporation of the investigative data from previous surveys has revealed a number of important regolith materials and palaeo-landscape features. These include: palaeosols, palaeochannels, extensive calcrete and collapsive carbonate earths, highly reactive smectite-rich clays with concomitant reactive weathered versions (black soils), near surface saprolites deriving from the subcropping Mt lofty Ranges metasediments, and significantly organic-rich Holocene coastal marine sourced sediments.

Many of these features have required modified building design on both the small and large scales, complicated urban planning, influenced underground service installation and maintenance, and revealed the need for geo- hazard monitoring (landslips, soil creep, acid-sulphate-soil conditions and seismic liquefaction potential). Earthy carbonate accumulations (calcrete) usually collapse when loaded by a building and subsequently exposed to excess water. Many of the smectite-rich subsurface clays and surficial soils are prone to marked shrink-swell behaviour in response to moisture changes. Gilgai and severe surface cracking (in summer) are indicators of problems deeper in the profile, while trees planted too close to buildings can amplify any incipient reactivity. Some clays are capable of 20-50% volume changes and ground surface movements of 50 to 300 mm are commonly observed, making Adelaide’s soils the most reactive of any Australian capital city. These have in extreme cases, led to expensive litigation between building owners and those who constructed and/or approved the affected building.

Palaeochannels are ubiquitous within the piedmont slope deposits of the Adelaide Plains. Many carry groundwater (potable & saline) or are used as storm water drainage sinks. One large alluvial fan – alluded to by several authors prior to the 1950’s – stretches from North Adelaide to Port Adelaide, covering an area of ~50 km2 and appearing to have been created by a palaeo-alignment of the River Torrens. Deep excavations in this fan deposit can have appreciable groundwater problems.

Deep weathering of the plains bounding metasediments forming the Mt Lofty Ra. during Mesozoic—Cainozoic times has yielded saprolith and saprolite with a much reduced bearing capacity, reduced slope stability and in some places an enhanced water transmissivity. These features have significantly restricted building development and modified urban planning along the ‘Hills Face Zone’ where slopes are greater than 1:5. Slope colluvium and talus deposits associated with the major Cainozoic block faults have also provided numerous geotechnical problems for urban expansion and redevelopment.

REFERENCES Sheard, M.J. and Bowman, G.M., 1996. Soils, stratigraphy and engineering geology of near surface materials of the Adelaide Plains. South Australia. Mines and Energy. Report Book, 94/9 (Hard copy or as a CD-ROM DataPackage).

34 Acknowledgements: The original project was jointly sponsored by the S. A. Department of Mines & Energy and the Division of Soils, CSIRO. Approval to publish this derived material has been granted by the Director of Mineral Resources Group, Department of Primary Industries and Resources, SA.

35 HYPERSPECTRAL IMAGERY TO LOCATE PALAEOCHANNELS

Vicki Stamoulis

Primary Industries and Resources South Australia, 101 Grenfell St, Adelaide, SA 5000

Present day drainage patterns in the Gawler Craton in the centre of South Australia are poorly defined. They often spread out creating areas of sheetwash or draining into shallow claypans. Evidence from drillhole data suggests that some of these claypans which are connected by watercourses forming chains are remnants of the deepest parts of Tertiary palaeochannels.

Landsat TM highlights the chain patterns formed by the claypans. NOAA data is another remote sensing method which detects the temperature variation in the sediments caused by the higher moisture content. In addition to these techniques the use of DEM and other geophysical methods such as EM and gravity have been successfully applied in locating palaeochannels.

These contemporary techniques were used to support an observation made using hyperspectral data supplied by Integrated Spectronics Pty. Ltd., which was flown over the Gibraltar Rocks region in Tarcoola, which suggested the possibility of a palaeochannel. The focus of this study is the application of hyperspectral data as a remote sensing tool in research on palaeochannels.

Hyperspectral imagery measures the solar radiation reflected from surfaces in a contiguous spectrum. A wide linear feature with a uniform spectral response and texture suggested a structurally controlled spectral anomaly. Initial analysis and groundtruthing confirmed the anomaly to be related to an unusually high vegetation response. Soil samples were taken along the length, width and depth of the channel in order to establish the composition of the mixed pixel response.

In September 1983 a drilling program was carried out by PNC Exploration (Australia) Pty. Ltd. in pursuit of a uranium prospect in the area. Stratigraphic data from these drillholes provided further evidence that this was the location of a tributary of the Kingoonya Palaeochannel.

In conclusion, contemporary techniques and stratigraphic evidence support Hymap data which highlighted the surficial features resulting from the presence of a palaeochannel.

36 LANDSAT IMAGERY OF PALAEODRAINAGE IN THE GREAT VICTORIA DESERT, SOUTH AUSTRALIA

Vicki Stamoulis and Paul Rogers Primary Industries and Resources South Australia, GPO Box 1671 Adelaide, SA 5001

The Landsat image covers GILES and northern TALLARINGA 1: 250 000 areas. The main palaeochannels present on the image are Tallaringa (east), Garford (SE corner) and Meramangye (NW corner).

The geological features on this image have been enhanced using the following ratios: • red layer = sum of band ratios 4/3 and 5/7 (highlights clay and vegetation) • green layer = band ratio 5/4 (highlights areas rich in iron oxide) • blue layer = sum of bands 1 and 7 (highlights areas rich in silica).

The main geological features visible on the image include the Carnadinna Surface, Tertiary palaeochannels and Quaternary sand dunes and playa lakes: • the Carnadinna Surface is a Late Cretaceous-Palaeogene land surface on which a ferruginous duricrust with an Oligocene to Miocene palaeomagnetic age has formed. This is predominantly a yellow colour (= red + green layers) indicating abundance of iron oxide and clay, with marginal orange to red zones having a denser vegetation (mulga) cover. Pale (off-white) areas are underlain by kaolinite-rich weathered Bulldog Shale • palaeochannels are infilled with Palaeogene (Pidinga Formation) and Neogene (Garford Formation) sediments and are generally blanketed by Quaternary deposits dominated by aeolian sand. Hues are mainly magenta and cyan, highlighting clay/sand and iron oxide/sand respectively. Notable features include playa lakes (magenta) with marginal aeolian gypsum (pink), and a broad sand-veneered calcrete sheet in the Meramangye Palaeochannel (pale blue) • Quaternary longitudinal dunes of The Great Victoria Desert are indicated by red and blue colours highlighting vegetation and sand respectively.

The spectral contrast between the Tallaringa Palaeochannel and the Carnadinna Surface portrays beautifully the entire palaeodrainage system including the main channel and major tributaries. Fine drainage detail is also preserved in the Carnadinna Surface and is thought to have formed during a period of fluvial downcutting (low sea level) between the Palaeogene and Neogene phases of sedimentation (high sea level).

The image also shows strong structural control of Tertiary palaeodrainage. SW to WSW structural trends appear to be related to major thrust faults in Officer Basin sediments and underlying basement that were generated or reactivated during the Petermann Ranges (~560-550 Ma), Delamerian (~507 Ma) and Alice Springs Orogenies. Examples of these structural controls include: • Meramangye Palaeochannel in the Lake Meramangye area • Deflection in upper reach of southernmost western tributary of the Tallaringa Palaeochannel. Cainozoic reactivation of a SW structural trend has formed the drainage divide between the Meramangye and Tallaringa systems. This reactivation has caused upwarping of Meramangye tributaries in the Emu and Dingo Claypan areas, and has cut off the headwaters of the Tallaringa Palaeochannel, forming a separate small basin. The structural trend also locally controls the NW boundary of the Carnadinna Surface.

37 DEEP WEATHERING AND GOLD: THE LANDSCAPE EVOLUTION OF THE WESTERN VICTORIAN GOLDFIELDS

David H. Taylor Geological Survey of Victoria, PO Box 500, East Melbourne, Victoria 3002

The Geological Survey of Victoria is producing maps and reports outlining the landscape evolution and resulting regolith of the western Victorian goldfields (eg. Taylor & Joyce, 1996). Although the regolith is often viewed as an impediment to exploration, dispersed geochemical haloes within it, and geochemical plumes in the groundwater may enhance the expression of the narrow parent gold deposits (Giblin, 1997). The present landscape of the western Victorian goldfields dates back to the start of the Cainozoic when a deeply weathered Mesozoic landscape was severely dissected during Australia-Antarctica break-up. Several cycles of erosion following the break-up have left fluvial placer gold deposits (derived from nearby mesothermal quartz-gold reefs) scattered across the present landscape. In historical times these placers were extensively mined, but today they mainly complicate exploration as transported anomalies. The landscape evolution which produced the placers also generated a variety of bedrock regolith profilesfrom pallid clay to ferruginised saprockwhose distribution affects the sample media available. In addition, large areas of the goldfieldsan area characterised by million ounce gold depositshave been masked from any previous exploration by relatively young basalt flows that are generally only tens of metres thick but locally aggregate to over 100 m.

The first continental products recording the dissection of the Mesozoic landscape are early Cainozoic deposits of undated coarse gravel (White Hills Gravel) which lie some 300-500 m lower than Mesozoic palaeosurface remnants. The gravels were deposited as outwash and flood sheet deposits in broad, shallow valleys. The gravel consists almost entirely of resistant vein quartz, suggesting that the enclosing sedimentary bedrock was already deeply weathered for virtually the entire eroded thickness. Despite this suggestion of erosion of a completely weathered environment the newly emergent landscape is still largely preserved today and can be seen to consist of meridional strike-ridges of bedrock, separating broad shallow valleys filled with the dissected remnants of the gravel. Today the emergent bedrock ridges consist of relatively fresh bedrock but that underlying the gravels is now deeply weathered to pallid clays. The bedrock clasts within the overlying gravel, which must have been fresh at the time of high energy deposition, are similarly weathered and suggest that this deep weathering was subsequent to deposition of the gravel and focussed on the valley floors where the gravel occurs.

In the middle Cainozoic a second erosion cycle led to more channellised drainage systems inheriting the broad pre- existing valleys. The streams were of much lower energy, possibly because of increasing aridity when the circum- polar current developed as Australia and Antarctica drifted apart. The new streams gradually carved steeper, narrower valleys through the gravel back into the underlying deeply weathered bedrock. The gravel remnants are now perched about 30−80 m above these streams, with this depth of incision probably reflecting the exhumation of fresher bedrock from below the weathering front. The deposits in the new streams consist of recycled material from the earlier landscape and include weathered debris such as ironstone and pallid clay. Further concentration of gold, from both hardrock sources and earlier White Hills Gravel placers into these new channels formed the richly auriferous ‘deep leads’. As well as a major historic gold source the deep leads are the major groundwater aquifers beneath the extensive cover.

Towards the end of the Cainozoic the deep lead drainage system was effectively shutdown by voluminous outpourings of basalt. Lavas filled the valleys and in places overtopped the bedrock interfluves to completely bury the landscape and form basaltic plains which mask large areas from simple exploration. Around Ballarat there was large-scale northward divide migration caused by stream diversion. The disruption to stream base-levels caused poorly sorted outwash to be deposited around the flow margins and where close to earlier gold deposits mineralisation may be phenomenally rich in nuggetty gold—much of which is probably of supergene rather than detrital origin.

Since that time the present drainage has re-established largely as lateral streams which have started to deeply incise. High standing areas of bedrock in the early Tertiary palaeosurface have remained relatively unweathered and are uncontaminated by transported gold liberated from the Tertiary deposits. Low standing areas of bedrock exhumed from below the early Tertiary palaeosurface range from highly weathered to almost fresh and are contaminated by transported gold. Major deposits completely hidden beneath the basalt plains may express themselves as geochemical plumes in the major aquifer system of the deep leads.

REFERENCES Taylor, D.H., & Joyce, E.B., 1996. Ballarat 1:100 000 regolith-exploration map report. Geological Survey of Victoria technical record 1996/4.

Giblin A. 1997. Geochemisty of Groundwaters in the Vicinity of Stawell, Clunes, Ararat and Ballarat Gold Deposits. The AusIMM Annual Conference Ballarat, 12-15 March 1997.

38 WEATHERING:CYCLING OR CONTINUOUS? A SOUTHERN PERSPECTIVE

Graham Taylor1 & Greg Shirtliff2 Cooperative Research Centre for Landscape Evolution and Mineral Exploration 1University of Canberra, ACT 2601 2Australian National University, ACT 0200

Extensive research was recently undertaken to find the age distribution of existing weathering profiles and related ferruginous products on the Australian continent. Information was gathered from published and unpublished sources, and resulted in some important findings. The age distribution of existing weathering profiles follows an appropriate exponential increase towards the present. This corresponds to similar trends by most other geological entities on earth and can be correlated with the effect of recycling, ie destruction over time. In accordance with general theory and past assumptions a possible increase in weathering was observed during the Palaeogene, an increase much less significant than previous studies thought. There is now reasonable evidence from recent studies to suggest that such deviations from long term trends may have occurred as a consequence of increases in the potential for preservation rather than the direct influence of climate, despite the well known effect precipitation has on weathering.

A broad range of ages, from Permian to Present in significant proportions supports the concept that weathering in Australia was relatively continuous and did not occur as distinct episodes.

We acknowledge the University of Canberra Research Committee for supporting the project.

39 Evaporites as cement: the precipitation of gypsum from the dying Lake Bungunnia into Late Cenozoic calcareous sequences, Murray Basin, South Australia.

1Thomas, B., 1Bone, Y. and 2Clarke, J.A.D.

1Dept of Geology and Geophysics, University of Adelaide, South Australia 2CRC LEME, Australian National University, Canberra

A maximum Pleistocene age (∼0.6 Ma) has been assigned to surface and sub-surface gypsum cements occurring in the Norwest Bend Formation and Upper Morgan Limestone, in the western Murray Basin. The gypsum cement post-date the draining of Lake Bungunnia and the formation of the Murray River Gorge.

The chemical and morphological diversity exhibited by the gypsum forms indicate a variety of genetic processes. Three main gypsum facies can be distinguished by their facies, which are indicative of the environmental conditions in which they formed:- (1) Bedded gypsum crusts (selenite) and gypsum nodules with fibrous to lenticular crystals which occur as discrete horizons along sections of the River Murray cliffs. (2) Massive crystalline gypsum containing piokilitic solid inclusions of clastic material, indicating formation below the surface, with long periods of stable brine conditions allowing for extraordinarily large crystal growth. (3) Aeolian seed gypsum dunes derived from the deflation of gypsum sand from modern playa lakes.

Sulphur and strontium isotopes, fluid inclusion microthermometry studies, and geochemical analysis (XRD) and (XRF) were used to interpret the brine conditions under which the different gypsum facies formed. The final melting temperatures for fluid inclusions indicate that brine salinities and compositions were similar to brines derived from evaporates sea-water. They also indicate that the gypsum crusts formed from less saline water than the fluids involved in the formation of the selenite and gypsum nodules.

The δ34S values of the gypsum crusts are similar to those for gypsum derived from sea-water (values of +17.9‰ to +20.2‰). This suggests that marine waters were the dominant S source.

However, the Sr isotope ratios negate this, as a signature of the lacustrine “sea-water like” brine chemistry resulting from only fluids derived from either marine transgressions or weathering of connate salts from marine strata is not possible. There has been a terrigenous component as well. Sulphur and Sr isotope ratios of the gypsum crust indicate that they were predominantly derived from the dissolution of the aeolian gypsum dunes by meteoric water, with a sea-spray aerosol component.

The demise of Lake Bungunnia indicated the onset of aridity in South Australia. The draining of this mega-lake may have been responsible for the gypsum cements and the aeolian gypsum dunes from which they are derived.

40 The Miocene Macroflora of Stuart Creek, South Australia.

Michael R. Whyms1, David R. Greenwood1 and Andrew Rowett2

1. School of Life Sciences and Technology (S008), Victoria University of Technology, PO Box 14428, MCMC Melbourne Vic.8001 2. Mineral Resources Group, Primary Industries and Resources of South Australia, GPO Box 1671, Adelaide SA. 5001

The interior of the Australian continent today is characterised by anardi climate with highly Tertiary palaeodrainage systems on the northwest Gawler Craton incise into sediments and deeply weathered basement, and the sedimentary sequences deposited in the systems are dated as Eocene and Miocene. The Eocene sequence is mainly composed of fining up channel fills consisting of clastic (fluvial) and carbonaceous (overbank/lacustrine) deposits. These are laterally equivalent to a series of coastal sequences consisting of lowstand, transgressive and highstand deposits. In contrast, the Miocene sequence is dominated by mud-rich deposits, indicating that the through-flowing Eocene rivers were replaced by chains of shallow lakes and abandoned channels. Late Miocene sediments in the lakes / channel segments contain gypsum, are dolomitic and reflect increasingly evaporitic environments. Regoliths, characterised by silcrete, calcrete and ferricrete, mainly formed on the top of channel sediments; gypcrete is found near to lacustrine deposits

41 REGISTRANTS Dr Alley Neville Director, MINERAL RESOURCES PIRSA Arundell Mark North Ltd. St Baker Andrew UNIVERSITY OF ADELAIDE, Department of Geology and Geophysics /CRC LEME Benbow Mark Longlat Enterprises Pty Ltd. St Beng Daryll UNIVERSITY OF ADELAIDE, Department of Geology and Geophysics Dr Belperio Antonio MINATOUR GOLD NL Bernal Juan-Pablo AUSTRALIAN NATIONAL UNIVERSITY, Department of Geology Bishop Mark UNIVERSITY OF SOUTH AUSTRALIA, Department of Applied Geology Dr Bone Yvonne UNIVERSITY OF ADELAIDE, Department of Geology and Geophysics Dr Bourne Jenny UNIVERSITY OF ADELAIDE, Department of Geology and Geophysics Prof Bourman Robert UNIVERSITY OF SOUTH AUSTRALIA, School of Environmental & Recreation Management Brown Cathy AGSO Dr Carey Stephen UNIVERSITY OF BALLARAT, Geology Department St Carragher Alison UNIVERSITY OF ADELAIDE, Department of Geology & Geophysics /CRC LEME Chan Roslyn CRC LEME /AGSO Dr Clarke Jonathon CRC LEME/ AUSTRALIAN NATIONAL UNIVERSITY Department of Geology Conor Colin Mineral Resources Group, PIRSA Dalgarno Bob Dare David Dodds Sandy GROUNDWATER PROGRAM, PIRSA Drown Chris Adelaide Resources NL St English Pauline AUSTRALIAN NATIONAL UNIVERSITY, Research School of Earth Sciences Prof Frakes Larry UNIVERSITY OF ADELAIDE Department of Geology and Geophysics Frater Max UNIVERSITY OF SOUTH AUSTRALIA, Department of Applied Geology Gray David CRC LEME/CSIRO Dr Greenwood David VICTORIA UNIVERSITY OF TECHNOLOGY, School of Life Science and Technology Dr Gostin Vic UNIVERSITY OF ADELAIDE Department of Geology and Geophysics Dr Gum Justin Mineral Resources Group, PIRSA St Higgins Jonathon UNIVERSITY OF ADELAIDE, Department of Geology and Geophysics Dr Hou Baohong UNIVERSITY OF ADELAIDE, Department of Geology and Geophysics /MINERAL RESOURCES, PIRSA Hore Steve MINERAL RESOURCES PIRSA Hughes Martin MARTIN HUGHES & ASSOCIATES

42 Dr Jago Jim UNIVERSITY OF SOUTH AUSTRALIA, Department of Applied Geology Keeling John MINERAL RESOURCES PIRSA St Kiasatpur Goran UNIVERSITY OF ADELAIDE, Department of Geology and Geophysics Lintern Melvyn CRC LEME Mason Doug MASON GEOSCIENCE PTY LTD Major Bob Morgan Lynn O'HALLORIN HILL TAFE Morris Brian MINERAL RESOURCES PIRSA Dr Oliver Robin UNIVERSITY OF ADELAIDE, Department of Geology and Geophysics Ollier Cliff Painter Jim Mineral Resources Group, PIRSA Prof Prescott John UNIVERSITY OF ADELAIDE, Deparment of Physics St Povey Dwayne UNIVERSITY OF SOUTH AUSTRALIA, Department of Applied Geology /CRC LEME Robertson Stuart MINERAL RESOURCES, PIRSA Rogers Paul MINERAL RESOURCES, PIRSA Dr Rowett Andrew MINERAL RESOURCES, PIRSA Schwarz Michael MINERAL RESOURCES, PIRSA Sheard Malcolm MINERAL RESOURCES, PIRSA Dr Skwarnecki Marian CSIRO, CRC LEME Stamoulis Vicki MINERAL RESOURCES, PIRSA Dr Sudesh Vikas UNIVERSITY OF ADELAIDE, Department of Physics Tan Kok AUSTRALIAN NATIONAL UNIVERSITY, Department of Geology A/Prof Taylor Graham CRC LEME, UNIVERSITY OF CANBERRA Taylor David GEOLOGICAL SURVEY OF VICTORIA St Tingay Mark NCPGG, UNIVERSITY OF ADELAIDE St Thomas Brett UNIVERSITY OF ADELAIDE, Department of Geology & Geophysics Tokarev Victor UNIVERSITY OF ADELAIDE, Department of Geology & Geophysics Dr Uppill Robin GEOSURVEYS AUSTRALIA Pty Ltd St van der Wielen Simon UNIVERSITY OF SOUTH AUSTRALIA, Department of Applied Geology /CRC LEME Prof Visocekas Raphael UNIVERSITY OF PARIS, UNIVERSITY OF ADELAIDE Department of Physics Dr White Marigold MINERAL RESOURCES, PIRSA Dr Wills Kevin TIGER INTERNATIONAL (Australia) Pty Ltd St Whyms Michael VICTORIA UNIVERSITY OF TECHNOLOGY School of Life Sciences & Technology Dr Zang Wenlong MINERAL RESOURCES, PIRSA