The wide-angle reflection seismic survey coincident with regional transect through Northern Yilgarn focused on the Leonora-Laverton Tectonic Zone, Western Australia was carried out to supplement deep seismic reflection studies. The major objectives were to collect high-density refraction information for offsets up to 60 km, to carry out a comparative study of near-vertical and wide-angle recordings of vibroseis energy at various offsets within the Leonora-Laverton tectonic zone and to obtain velocity information for upper crust. The survey deployed 120 short period recorders with spacing of 500 m. Acquisition parameters used for wide-angle reflection experiment were selected to fit into conventional reflection survey. The same vibrations were recorded in both surveys simultaneously. The major challenge in processing the Vibroseis data is to manage the huge volume of data. The processing of data includes several steps: sorting into receiver and source gathers, cross-correlation with reference sweeps and summing original seismic traces to form single source point traces, producing seismograms from individual traces and finally creating seismic record section from separate seismograms. The major step in processing and interpretation of data is to analyse recorded wave fields on the basis of seismological criteria prior to seismic velocity modelling. Seismic velocity models developed by using forward and inverse travel modelling software will supplement geological interpretations for this complex region and allow an estimation of its crustal composition.

No abstract available

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.

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.

No abstract available

The Antarctic region has profoundly affected the global climates of the past 50 million years, influencing sea levels, atmospheric composition and dynamics, and ocean circulation. A greater understanding of this region and the Antarctic cryosphere is crucial to a broader understanding of the global climates and palaeoceanography at all scales. Much of the information obtained during the last two decades derives from studies of sedimentary sequences drilled in and around Antarctica.