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This report provides details of the West Musgrave airborne magnetic, radiometric and elevation survey, carried out east of Warburton in Western Australia. The survey area partially covers the Scott (SG52-6) 1:250,000 map sheet and the Cooper (SG52-10) 1:250,000 map sheet and covers an area of over 46,000 line kilometres. The survey was flown for Geoscience Australia and was undertaken by Fugro Airborne Surveys Pty Ltd.

The basement beneath Australia's offshore basins was the cradle for sediments involved in oil and gas formation. Knowledge of basement depth, boundaries and evolution provides clues to the petroleum potential of Australia's sedimentary basins. The problem is finding the right combination of geophysical techniques to define basement offshore, and knowing what adjustments to make to reduce unwanted effects in definition. Geoscience Australia's Alexey Goncharov outlines his team's exciting new basement and crustal studies that are tackling the problems.

The Archean Pilbara granitoid-greenstone terrane (GGT) has been the focus of numerous studies on Archaean geology, especially the classic dome-and-basin area around Marble Bar in the east Pilbara. This area has been used as evidence for different tectonic processes, i.e. that vertical tectonics or diapirism was a cause for Archean deformation. This paper provides evidence to support regional horizontal (plate-interaction) stresses as being largely responsible for the compressive deformation of the Pilbara GGT, at least from ca. 3.2 Ga. The relative chronology of meso-to macro-scale structural elements are presented for a number of selected areas across the Pilbara GGT. These locally identified events are correlated with a regional (Pilbara-wide) structural framework of deformation events that are constrained by geochronological and stratigraphic controls. The dome-and-basin geometry characteristic of the east Pilbara was established after 3.2 Ga, and was successively modified by repeated orthogonal extensional and compressive (subhorizontal) events. The result has been a locally complex development of polyphase structural elements with consistent overprinting relationships that can be correlated across much of the Pilbara from 3.2 Ga. Diapirism did not cause these deformation elements, although it may have modified them.

This talk was presented at the Gawler Craton 2002: State of Play conference held in Adelaide, December 2002.

The Harris Greenstone Belt in the central Gawler Craton of South Australia has potential for Archaean Ni-Cu-PGE sulphide and Archaean-Proterozoic lode-Au mineralising systems. This map is a preliminary interpretation of the Precambrian basement geology based on aeromagnetics, gravity, and diamond drilling. It highlights the extensive distribution of poorly exposed Archaean komatiites and associated rocks (green) that have a strike extent of at least 300 km. The regional pattern of linear komatiitic sequences associated with ovoid granitic plutons and province-wide shear systems, is very similar to the economically important Eastern Goldfields Province in the Yilgarn Craton, Western Australia. The ca. 2520 Ga Lake Harris Komatiite in the central Gawler Craton of South Australia is the first documented komatiite outside the West Australian Craton and the easternmost occurrence of such primitive ultramafic rocks in Australia. The steeply dipping ultramafic sequence consists of komatiite cumulates, high- to low-Mg komatiite, komatiitic and tholeiitic basalt, and pyroxenite cumulates. The komatiitic rocks display a range of quenched and cumulus textures defined by the different habits of olivine and its alteration products. Trace sulphides form very small (0.01-0.2 mm) single-phase disseminated grains and coarser disaggregated grains. Thick ponded lava lake and distal composite sheet flow facies have been identified in the magmatic environment. Systematic whole rock and mineral chemical trends indicate that despite the effects of recrystallisation and re-equilibration during amphibolite-facies metamorphism, the original magmatic geochemical profiles are largely preserved. The whole-rock data for the Lake Harris Komatiite does not show any obvious Ni depletion during fractionation but indicate a strong olivine control in dominantly S-undersaturated environments. The Lake Harris Komatiite has chemical and initial Nd isotope characteristics similar to typical Al-depleted Archean komatiites.

Copper-gold mineralisation in the Moonta-Wallaroo district of the south-eastern Gawler Craton is associated with regionally extensive magmatism and Na-Fe-K metasomatism, typical of Fe-oxide Cu-Au mineral provinces worldwide. In the Moonta-Wallaroo district, early widespread albite+/-actinolite+/-magnetite alteration is closely associated with magmatic fluids from granites of the Hiltaba Suite (ca. 1600 Ma) infiltrating the metasedimentary Wallaroo Group host rocks. Zones of biotite-magnetite alteration, often in highly foliated structural zones, also formed at this time and are associated with minor Cu mineralisation. Dating of monazite and titanite associated with magnetite-bearing alteration shows a strong temporal link with Hiltaba magmatism. Copper mineralisation is most closely associated with later chlorite-quartz-hematite-kfeldspar veining and alteration which overprints, replaces and demagnetises the early magnetite-bearing alteration. Latest stage alteration occurs as kaolinite-quartz and quartz-carbonate-hematite epithermal style alteration and veining, most notably along the Alford Shear Zone on the southern margin of the Tickera Granite. This late argillic alteration is also seen as a late overprint in the Wheal Hughes mine at Moonta. Drill targeting has historically often been of magnetic anomalies, but alteration paragenesis suggests that magnetic lows due to de-magnetising copper-bearing fluids may be better drill targets.

New Pb isotope analyses from the Curamona Terrain

Geology of the B Lode, A Lode and 1 Lens on CML7, Broken Hill, N.S.W. - Richard Tully BSc (Hons) thesis, La Trobe University

The Australian Bureau of Statistics March quarter data indicate further deterioration in Australian mineral exploration keeping current expenditure levels well below recent levels. Despite this, indicators including increased mineral company floats in 2002 on the back of new discoveries, improved gold prices, increased activity especially by juniors, and prospects for improved metal prices in 2003-2004, present the most positive outlook for mineral exploration since 1997. However, a period of sustained increases in metal prices is required for a significant rise in exploration levels. Exploration is focussed in the Yilgarn Craton, the Tanami Province, the Gawler Craton, the Musgrave Province, and the Murray Basin. The Ashburton province is an emerging gold province and much of the Northern Territory is under tenement for diamonds. Discoveries continue to be made but increased greenfields exploration, especially in areas under cover, is needed to exploit Australia's potential. New government geoscience programs, especially regional pre-competitive geophysical surveys, are playing an important role in helping to unlock that potential. Originally published in The AusIMM Bulletin No. 5 September/October 2002, pp 36-42.