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.

Overview of the deep crustal seismic surveys conducted by Geoscience Australia through the Onshore Energy Security Program since its commencment in 2006 up to September 2009.

For the last 50 years, Geoscience Australia and its predecessors have been collecting onshore near-vertical-incidence deep seismic reflection data, first as low fold explosive data and more recently as high fold vibroseis data. These data have been used in conjunction with other seismic data sets by various research groups to construct depth to Moho models. The Moho has been interpreted either as a strong reflector per se, or as the bottom of a reflective band in the lower crust. However the amplitude standout of the Moho can be very much dependent on the fold of the data and applied processing sequence. Some low fold explosive data was re-processed by Geoscience Australia to enhance the Moho for comparison with recent vibroseis data, in the Mt Isa province in Queensland, and in the Southern Delamerian and Lachlan Fold Belts in Victoria. Marked improvement was achieved by time-variant band-limited noise suppression of reverberations, as well as by coherency weighted common mid point stacking. Post stack migration can also improve the clarity of the Moho, provided there is enough continuity of the data to avoid migration 'smiles'. An important consideration was amplitude scaling, with a time variant automatic gain control (AGC) employed before stack, and a weighted AGC applied after stack, in order to preserve seismic character. These results demonstrate that processing and acquisition issues need to be understood in order to assess the reflective character of the Moho and indeed to interpret its location.

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The Australian Geological Survey Organisation (AGSO) through the partnership in the Australian Geodynamics Cooperative Research Centre (AGCRC) and Kalgoorlie Consolidated Gold Mines (KCGM) completed a joint research project to image the crustal structure of the Kalgoorlie region to develop a knowledge of the shallow and deep structures, tectonics, and fluid migration pathways. The Australian National Seismic Imaging Resource (ANSIR) was contracted to acquire the seismic data. The project's objectives were to obtain a better understanding of - sub-surface geology at a regional and mine scale - provide more information on regional crustal thickness and major features - stratigraphic and structural architecture of the mineral system - timing and locations of fluid migration pathways The seismic survey obtained 25 km of 10 fold CMP (common midpoint) regional reflection seismic data along two traverses and 8 km of 10 fold CMP high-resolution reflection seismic data along another two traverses. The data are of good quality and similar to both the 1991 and 1999 Eastern Goldfields reflection seismic data to the north and south of the survey area. The major outcome of imaging the four localities included mapping the Golden Mile and Bolder-Lefroy Faults, and the Boorara Shear at depth. This new information indicates the Golden Mile Mine was fed by a suite of relatively minor faults dangling off the major crustal-scale Boorara Shear. The dangling element relates to percolation theory. The detachment surface was imaged on all seismic traverses. Thrust duplexes were interpreted above the detachment surface.

Seismic line 07GA-GC1, described here, forms part of the Isa-Georgetown-Charters Towers seismic survey that was acquired in 2007. The seismic line is oriented approximately northwest-southeast and extends from east of Georgetown in the northwest to south of Charters Towers in the southeast (Figure 1). The acquisition costs for this line were provided jointly by the Geological Survey of Queensland and Geoscience Australia, and field logistics and processing were carried out by the Seismic Acquisition and Processing team from Geoscience Australia. Seven discrete geological provinces have been interpreted on this seismic section (Figure 2). Two of these, the Abingdon and Sausage Creek Provinces, only occur in the subsurface. The upper crustal part of the seismic section is dominated by the Etheridge and Cape River Provinces, but the seismic line also crossed the Broken River Province and the Drummond and Burdekin Basins.

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Potential field data were used to constrain or support the geological interpretations of the 2006 and 2007 North Queensland seismic data. Potential field forward modelling, potential field inversions and worms of potential field data all supported the interpretations of the seismic data.

The 2008 Rankins Springs Seismic Survey was a joint initiative by Geoscience Australia and NSW Department of Primary Industries under the Onshore Energy Security Program (OESP) in the under-explored southeastern Darling Basin. Regional acquisition parameters of 300 channels, 40 m group interval and 80 m vibration point interval nevertheless allowed detailed imaging of a 3 second (TWT) thick sedimentary sequence in the Yathong Trough. Use of three 12 second vari-sweeps from truck mounted Hemi 50 (50,000 lb) vibrators provided sufficient energy to image from immediately below regolith to the Moho. The sweep frequency ranges 6 - 64, 10 - 96 and 8 - 80 Hz were chosen both for deep penetration and high resolution in the sedimentary section. In-field processing produced a high quality preliminary section on a daily basis using an iterative process of automatic residual statics calculation on a deep gate and interactive stacking velocity analysis. Both automatic statics and stacking velocity were essential for successful imaging, but velocity was more important, as initial estimates based on first arrival velocities produced a degraded section. The field seismic section clearly shows a fault bounded trough, with evidence of compressional structures in the upper part and hints of underlying older sedimentary basins. The in-field stacking velocity analysis also provided immediate evaluation of the maximum depth of the trough, namely 6 km, deeper than expected. Efficient in-field processing allows early notification to project partners of a successful survey, facilitating future planning, and provides a sound basis for streamlined subsequent processing.

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