Comprehensive studies of the well preserved, Paleoarchean Panorama volcanic-hosted massive sulfide (VHMS) district provide for the first time definitive evidence that Zn, Pb, Cu, Mo and Ba were leached from the base of the volcanic pile and redeposited at the top in VHMS deposits. This leaching provided more than enough metal to form known deposits, implying that direct input of metal is not required. Sulfur is depleted from the base of the volcanic pile, in line with an increase in Fe2O3/FeO and hematite alteration. These data, combine with sulfur isotope data, indicate that seawater sulfate reduction was facilitated by the oxidation of rock FeO to hematite at high temperature in the H2S stability field. This is the first time such processes have been demonstrated regionally in ancient VHMS mineral systems. The data presented here require Paleoarchean seawater to be sulfate-bearing.

A metamorphic database covering the entire eastern Yilgarn Craton has been compiled from pre-existing mapping, 14,500 sites with qualitative metamorphic information, and 470 new key sites with detailed quantitative metamorphic data including P, T, temperature/depth ratio and P-T paths. The derived temporal and spatial patterns contrast with previous tectonic models and invariant crustal depth with the single prograde metamorphic event of the long-standing metamorphic paradigm. In particular, there are large variations in peak metamorphic crustal depths (12 to 31 km), and five metamorphic periods can now be recognised. &#149; Ma: Very localised, low-P granulite of high temperature/depth ratio (>50ºC/km). &#149; M1: High-P (8.7kb), low temperature/depth ratio (<20ºC/km) assemblages localised to major shear zones with clockwise isothermal decompression P-T paths. &#149; M2: Regional matrix parageneses with T ranging 300-550ºC across greenstone belts and elevated temperature/depth ratio of 30-40ºC/km throughout. Tight clockwise paths evolved through maximum prograde pressures of 6 kb and peak metamorphic pressures of 3.5-5.0 kb. &#149; M3a: An extension related thermal pulse localised on the Ockerburry Fault and post-volcanic late basins. Anticlockwise paths to peak conditions of 500-580ºC and 4.0 kb, define moderately high temperature/depth ratio of 40-50ºC/km. &#149; M3b: Multiple localised hydrothermal alteration events during a period of exhumation from 4 kb to 1 kb. Metamorphic patterns during each event have been temporally and spatially integrated with the new deformation framework (Blewett & Czarnota, 2007c) by a process of metamorphic domain analysis and using metamorphic field gradients. The continual evolution with time of fundamental metamorphic parameters throughout the entire history have been constructed as evolution curves and integrated with the deformation, magmatic, stratigraphic and mineralization history. <p>Related material<a href="https://www.ga.gov.au/products/servlet/controller?event=GEOCAT_DETAILS&catno=69771">East Yilgarn Craton Metamorphism and Strain</a> - Map.</p>

The physical properties of non-porous basement rocks are directly related to the mineralogy of those rocks. The MineralMapper3D software package originally developed by Nick Williams at the Predictive Mineral Discovery Cooperative Research Centre (pmd*CRC), Geoscience Australia, uses the physical properties of minerals to provide bounds on estimates of the abundance of specified minerals in non-porous basement rocks. This approach is applicable to both estimates of density and magnetic susceptibility derived from 3D inversions of gravity and magnetic data as well as physical measurements on specimens or down-hole derived physical properties.

No abstract available

The 2007 North Queensland seismic survey provided a new geodynamic framework and province architecture map for the North Queensland region. Coupled with this, companion geophysical studies provided new understandings of the subsurface of the region. A major focus of the geophysical investigations was the use of potential field inversions. These inversions allow for the mapping of units undercover, predict the extension of geometries away from seismic lines, and also provide a measure of alteration. The North Queensland region also allowed for the testing of both qualitative and quantitative methods to map alteration using geophysical inversions.

No abstract available

The Cobar project of the pmd*CRC utilised potential field inversions to delineate zones of alteration within the Cobar region, NSW. These zones of alteration and correlation with mineralisation is consistent with the mineral system analysis of the region, performed by the T11 Cobar project.

Geophysical inversions provide a mechanism to calculate subsurface chemical alteration in terms of alteration minerals. In the Cobar region, NSW, Australia, the base metal deposits show significant geophysical contrasts to their host rocks. These contrasts can be inverted to provide measures of the causative chemical alteration, allowing targeting for mineralisation under cover.

Regional-scale constrained potential field inversions can be used to infer rock types, alteration, and structure. This is particularly valuable when basement is obscured by younger cover. The methods outlined in this study have been applied to a 150 km ? 150 km region around the giant Olympic Dam copper-uranium-gold deposit, where abundant haematite, sulphide, and magnetite alteration produces a strong potential field response despite thick cover. The results are used to develop the first 3D map of magnetite and haematite/sulphide alteration for the Olympic Cu-Au province, and shows that the alteration around known Cu-Au mineral occurrences can be detected using coarse regional-scale inversions. The provision of a reference model in the inversion formulation permits geological observations to be introduced into the inversion process, and to be used to guide the inversion towards more geologically reasonable outcomes. This allows hypotheses regarding 3D geological architecture to be tested rigorously for compatibility with potential field data. An iterative procedure of inversion followed by updating of the reference model allows 3D maps of alteration and structure to be created that are consistent with both the known geology and observed potential field data.

South Australia's Gawler Craton is known for its high exploration potential for iron oxide copper gold (IOCG) deposits. In addition to the giant Olympic Dam deposit, relatively recent discoveries at Prominent Hill and Carapateena and a large number of smaller prospects confirm the attractiveness of the Mesoproterozoic rocks near the eastern margin of the Craton. The challenge facing explorers is the thick and extensive sedimentary and volcanic cover that overlies those prospective basement rocks. The only way to image buried rocks is by integrated analysis of remotely measured geophysical data with geological knowledge. Deep reflection seismic data provides critical information on unit depths, thickness and geometries. Interpreted profiles along the 03GA-OD1 and transverse 03GA-OD2 reflection seismic lines centred on the Olympic Dam deposit provide the best available information on the crustal-scale 3D geometries in that area. These relationships are extended throughout a 600 km east-west by 510 km north-south subset of the eastern Gawler Craton, to a depth of 25 km below surface, using geologically-constrained 3D inversion of public domain gravity and magnetic data. Including geological constraints is critical to ensure that the 3D property models recovered using the inversions are consistent with all available geophysical and geological data. Geological constraints are developed from surface mapping, seismic profile interpretations on the Olympic Dam lines as well as the 08GA-C01 and 03GA-CU1 lines in the Curnamona Craton, and 2D potential field modelling. Where knowledge of the cover rocks exists, it is included as a constraint to enhance the resolution of features at depth.