No abstract available

Australia contains established oil and gas provinces (Fig. 1), is politically stable, and has a fiscal regime which encourages petroleum exploration and development. These combined with infrastructure all serve to attract and maintain petroleum exploration and production investment in the established oil and gas provinces. Over the last ten years Australia has maintained 65-85% self sufficiency in oil and better than 100% sufficiency in gas as a net gas exporter through LNG. The Australian government has a new program of data acquisition in poorly explored areas and the recently announced Spatial Information and Data Access Policy requires that basic data be made available at the marginal cost of transfer, or is free if delivered via the internet. In addition, to encourage exploration in its many under-explored regions, Australia has traditionally maintained better access to geoscience and petroleum exploration data than almost anywhere else in the world. Access to petroleum exploration information has been facilitated by legislation requiring data submission and availability, and by the provision of pre-competitive studies by government agencies. This is coupled with an aggressive, globally and yearly promoted, acreage release program. Australia remains significantly under-explored and for that reason has sought to improve the very high level of access to exploration and production data that includes seismic data, well information, and regional geological studies. Ease of access is designed to attract new explorers. Australia has less than eight thousand petroleum exploration wells onshore and offshore in an area of over twelve million square kilometres and, consequently, there is considerable opportunity for further exploration. Significant discoveries of oil and gas have occurred in Australia since the 1960?s and continue to the present day. Super giant oil and gas fields have been discovered both in the southeast and northwest of Australia. Globally, Australia ranks 27 as an oil producer and 18 as a gas producer. Although under-explored, already it is assessed as containing upwards of 2% of the world?s gas reserves and 1% of the world?s oil reserves. Recently, deeper water exploration (>1200m) has occurred in Australia adjacent to major gas and oil production in the Carnarvon Basin and to major discoveries in the adjacent Browse Basin on the Northwest Shelf. Significant deep-water oil discoveries at Laverda, Vincent and Enfield, of over 200 mmbls have been made in the Carnarvon Basin, and many tens of Tcf of gas have been discovered at Gorgon and deep water fields further to the west (Longley et al 2001).

Situated just inboard of the late Neoproterozoic Australian rift margin (Tasman Line), the Broken Hill region occupies a critical position in reconstructions of Rodinia, combining an older basement (Willyama Supergroup) deformed by Paleoproterozoic-Mesoproterozoic events with a subsequent record of crustal extension, dyke intrusion and syn-rift sedimentation commencing around 827 Ma. These events not only constrain the timing and initial direction of late Neoproterozoic continental extension but provide a critical test of competing reconstructions for Rodinia in which south-central Australia is juxtaposed against western Laurentia. Contrary to some reconstructions there is no continuation of 1100-1300 Ma Grenville-age rocks into Broken Hill (SWEAT) and alternative restorations based on juxtaposition of the Broken Hill and Mojave-Oaxaca terranes along the Sonora-Mojave mega-shear (southern USA) result in misalignment of this major palaeo-transform fault with late Neoproterozoic normal faults in south-central Australia. Differences in deformational history and tectonic setting also preclude simple matching of 1.7-1.60 Ga orogenic belts in Australia and Laurentia (AUSWUS). In contrast to the southwest margin of Laurentia which was dominated by plate convergence, terrane assembly and arc magmatism throughout much of the Late Proterozoic (Yavapai and Mazatzal orogenies), the Willyama Supergroup preserves a record of 1.72-1.67 Ga intracontinental rifting and crustal extension (D1) followed by nappe emplacement and crustal thickening after 1640 Ma, culminating in the 1600 Ma Olarian orogeny (D2). Crustal thickening produced a second generation of granulite-grade mineral assemblages in the Willyama Supergroup and was superimposed on rocks initially metamorphosed under low P ? high T conditions as a result of D1 crustal thinning and associated bimodal magmatism. The resulting counterclockwise P-T-time path is evident only in the structurally higher parts of the Willyama Supergroup whereas the underlying and once more deeply buried parts of the sequence reveal evidence of decompression and metamorphism under progressively lower pressures as might be expected to occur during emplacement of a metamorphic core complex. A major mylonite zone of D1 age separates upper and lower structural levels. Validation of existing reconstructions for Rodinia requires a greater range of temporally equivalent events be present in western Laurentia than is presently recognised.

The Stuart Shelf overlies the eastern portion of the Gawler Craton. This part of the Gawler Craton is South Australia's major mineral province and contains the world-class Olympic Dam Cu-U-Au deposit and the recent Cu and Au discovery at Prominent Hill. The Stuart Shelf is several kilometres thick in places. As such, little is known of the crustal structure of the basement, its crustal evolution or its tectono-stratigraphic relationship to adjacent areas, for example the Curnamona Province in the east. There has been much effort applied to advancing our understanding of basement, mainly through the use of potential field data and deep drilling programmes; though drilling has proved very costly and very hit and miss. The Stuart Shelf area needs new data and methods to bring our knowledge of it to the next level of understanding. At a Gawler Craton seismic planning workshop held in July 2001, stakeholders from industry, government, and university stakeholders identified several criteria fundamental to undertaking any seismic survey within the Gawler Craton. These were - Location of seismic traverse across a known mineral system in order to improve understanding and enhance knowledge of the region's mineral systems. Access to surface and/or drill hole geological knowledge to link geology data with the seismic interpretation. Good coverage of potential field data, and Potential for the seismic data to stimulate area selection and exploration in the survey region.

No abstract available

The Palaeoproterozoic to Mesoproterozoic (<1850-<1490 Ma) southern McArthur Basin, Northern Territory, Australia, contains an unmetamorphosed, relatively undeformed succession of carbonate, siliciclastic and volcanic rocks that host the McArthur River (HYC) Zn-Pb-Ag deposit. Seismic reflection data obtained across this basin have the potential to revolutionise our understanding of the crustal architecture in which this deposit formed. These data were collected in late 2002 as part of a study to examine the fundamental basin architecture of the southern McArthur Basin, particularly the Batten Fault Zone, and the nature of the underlying basement. Geoscience Australia, the Northern Territory Geological Survey and the Predictive Mineral Discovery Cooperative Research Centre combined to acquire an east-west deep seismic reflection profile (line 02GA-BT1) approximately 110 km long, commencing 15 km west of Borroloola, and extending westwards along the Borroloola-Roper Bar road to the Bauhinia Downs region (Fig. 1). A short 17 km north-south cross line (02GA-BT2) was also acquired in collaboration with AngloAmerican. The seismic data were acquired through the Australian National Seismic Imaging Resource (ANSIR).

Seismic reflection, seismic refraction and portable broadband data collected within Western Australia's Yilgarn Craton, in particular the Eastern Goldfields Province, are providing detailed images of several of its highly mineralized terranes as well as new insights into the crustal architecture of the region. When the results from these seismic techniques are integrated, the results are providing a better understanding of the structure of the crust and lithosphere beneath the Yilgarn Carton, from the surface to depths in excess of 300 km.

The eighth edition of the Airborne Geophysical Survey Index presents a summary of the essential specifications of over 900 surveys held in the National Airborne Geophysical Database. Include Index Maps at 1:10 million scale for magnetic, radiometric and gravity survey coverage of Australia as at 1 May 2004.

No abstract available

Chemical modeling of gold mineralisation in the Lachlan Fold Belt shows that gold can be precipitated over a wide temperature range (from 320 to 200 ?C in this study) from CO2-bearing, low salinity, aqueous fluid flowing upwards through faults in turbiditic sequences. In agreement with field observations, the veins are predicted to be mostly quartz (> 93 vol.%) with minor amounts of pyrite, arsenopyrite and muscovite (sericite) precipitating above 230 ?C. The predicted alteration assemblage contains pyrite, arsenopyrite, calcite, muscovite (sericite), chlorite and feldspar. Varying some of the chemical characteristics of the initial fluid has resulted in the following changes to the model: Preventing the fluid from boiling stops gold precipitating below 310 ?C but has little effect on the vein mineralogy or the mineralogy of the surrounding alteration assemblage. Removing CO2 from the fluid also prevents gold precipitation in the veins below 300 ?C. The modeling also generates an alteration assemblage with a number of Ca-rich minerals as less calcium carbonate exists in this system. Removing sulfur species from the initial fluid decreases the amount of gold precipitated by more than a factor of ten, which is to be expected if sulfur ligands are the main species for gold transport. However, the vein assemblage and the lack of sulfide minerals in the surrounding alteration assemblage also suggest that sulfur species are important in this mineral system. Increasing the initial oxidation state (?O2) of the fluid inhibits gold precipitation in the veins above 260 ?C and leads to a high proportion of dolomite in the surrounding alteration assemblage. On the other hand, decreasing the initial oxidation state of the fluid lead to gold precipitation over a range of temperatures below 310 ?C but predicts that mainly graphite ? quartz precipitates in the veins and that the surrounding alteration assemblage is dominated by feldspar proximal to the veins. This style of mineralogy is not commonly observed in gold deposits in the Lachlan Fold Belt. Increasing the initial pH of the fluid inhibits the amount of minerals that precipitate in the veins, which are dominated by calcite at high temperatures and graphite at low temperatures and corresponding minor amounts of gold. The proximal alteration assemblage is dominated by K-feldspar with amphibole, biotite and epidote. This mineral assemblage is not commonly observed in these deposits. Decreasing the initial pH of the fluid allows gold to precipitate below 280 ?C but generates a proximal alteration assemblage dominated by pyrophyllite, which again is not commonly observed. The results are in agreement with the widely accepted premise that gold is transported as bisulfide complexes and that the ore-bearing fluid is typically a low-salinity, mixed aqueous-carbonic fluid with low-moderate CO2 contents (Ridley and Diamond, 2000). However, the modeling has shown that the absence of certain physico-chemical processes or fluid constituents, such as boiling or lack of CO2 may inhibit gold precipitation in some environments. Large fluctuations in ?O2 or pH will also significantly change the vein and alteration mineralogy and generally reduce the amount of gold that is precipitated. This suggests that these fluids remain rock buffered during their journey from the source to the trap site.