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.

Deposits of the iron oxide copper-gold (IOCG) family are diverse in composition, ranging from relatively reduced magnetite-rich to hematite-dominated oxidized styles that may contain major uranium resources. These variations reflect an interplay between multiple hydrothermal fluids with different properties and the varied host lithological settings, each of which ultimately relate to differences in the tectonic evolution of IOCG provinces. - Early Mesoproterozoic and late Paleoproterozoic terranes of southern Australia host the 7.7 Bt Olympic Dam Cu-Au-U deposit as well as numerous lesser known IOCG±U deposits and prospects. They represent the spectrum of magnetite- to hematite-dominated IOCG deposit styles. Magnetite-rich styles of IOCG alteration and mineralization occur in the eastern Gawler Craton and western Curnamona Province. These styles developed at mesozonal to epizonal crustal levels between ~1610 Ma and ~1575 Ma when the terranes were subject to low pressure - high temperature metamorphism and compressional deformation. Magnetite-rich alteration was spatially and temporally associated with high-temperature A-type granitoids of the Hiltaba Suite and with mafic magmas, although the magnetite-forming fluids show major chemical and isotopic contributions from non-magmatic sources. Magnetite-rich alteration varies between IOCG districts and includes biotite-albite or albite-clinopyroxene-actinolite or K-feldspar. Generally minor quantities of chalcopyrite, gold, pyrite and rare pyrrhotite occur in magnetite-rich alteration. - Higher grade IOCG ±U mineralization is associated with hematite-rich alteration (± sericite, chlorite, carbonate) which generally overprinted magnetite-rich assemblages and formed at epizonal crustal levels prior to ~1575 Ma. In the Olympic Dam district uplift and exhumation inferred between ~1595 Ma and ~1575 Ma resulted in superposition of hematitic ±U mineralization on magnetite-rich alteration. Brittle deformation structures and the temporal and broad spatial association of hematitic alteration with bimodal volcanism and alkaline mafic magmatism are consistent with an extensional setting, although supporting data are not yet comprehensive. - The switch from syn-orogenic mesozonal magnetite-rich IOCG formation to post-orogenic epizonal hematite-rich IOCG mineralization is suggested to reflect a change from compressional to extensional tectonism at ~1595-1590 Ma. Contrary to propositions of an 'anorogenic' setting for the Olympic Dam deposit, back-arc settings have been advocated recently. However, several features including the composition of the Hiltaba Suite and co-magmatic volcanics are inconsistent with typical backarc settings. Alternatively, intracontinental orogenesis was closely followed by extension and uplift. A possible driver was convective removal or delamination of thickened lithospheric mantle, triggered by convergence at distant plate margins. This model reconciles magma compositions and timing of volcanism with a switch from compression to extension.

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.

No abstract available

Physical property measurements provide a critical link between geological observations and geophysical measurements and modelling. To enhance the reliability of gravity and magnetic modelling in the Yilgarn Craton's Agnew-Wiluna greenstone belt, mass and magnetic properties were analysed on 157 new rock samples and combined with an existing corporate database of field measurements. The new samples include sulphide ore, serpentinised and olivine-bearing ultramafic host rocks, granitoid, and felsic and mafic volcanic and volcaniclastic country rock. Synthesis of the data provides a useful resource for future geophysical modelling in the region. Several rock types in the region have sufficiently distinct physical properties that a discriminant diagram is proposed to facilitate a basic classification of rock types based on physical properties. However the accumulation of emplacement, metamorphic, hydrothermal and structural processes has complicated the physical properties of the rocks by imposing duplicate and sometimes opposing physical property trends. The data confirms that massive sulphide and ultramafic rocks have the most distinctive mass and magnetic properties but with variability imposed by their complex history. Sulphide content imposes the strongest control on densities, but can only be identified when comprising > 10 vol. % of the rock. The pyrrhotite-rich Ni-sulphide assemblages generally have similar magnetic properties to the host ultramafic rocks, but can have much lower susceptibilities where the thermal history of the rocks has favoured development of hexagonal pyrrhotite over monoclinic pyrrhotite. In ultramafic rocks that contain < 10 vol. % sulphides, density and susceptibility are primarily controlled by serpentinisation, with olivine breaking down to serpentine and magnetite in the presence of water.

Hyperspectral airborne images from the Eastern Fold Belt of the Mount Isa Inlier, were validated as new tool for the detection of Iron oxide Cu-Au (IOCG) related alteration. High resolution mineral maps derived from hyperspectral imaging (4.5m/pixel) enables the recognition of various types of hydrothermal alteration patterns and the localisation of fluid pathways. Four different types of hydrothermal alteration patterns were identified with the hyperspectral mineral maps: (1) Metasomatic 1: White mica mineral maps were applied to map the spatial distribution of regional sodic-calcic alteration in metasedimentary successions of the Soldiers Cap Group in the Snake Creek Anticline. (2) Metasomatic 2: Alteration zoning is evident from albitised granites, assigned to the Williams-Naraku Suite, along the Cloncurry Fault show characteristic absorption features in the shortwave infrared range (SWIR) and can be detected with white mica mineral maps (white mica composition, white mica content, white mica crystallinity index).

An integrated package comprising geological, structural, geophysical, geochronological and geochemical data. The GIS encompasses the outcropping and covered portions of Palaeoproterozoic and Mesoproterozoic rocks straddling the NSW-SA border (the Broken Hill, Euriowie, Olary, Mount Painter and Mount Babbage Inliers). The GIS features recent data collected by the Broken Hill Exploration Initiative.

Globally, iron-oxide Cu-Au deposits are a prime exploration target given the super-giant status of Olympic Dam, the type example. The most commonly identified primary ingredients for these deposit types are granites, mafic igneous rocks and oxidised host sequences (e.g., Hitzman 2000). The deposits are also characterised by sodic-potassic and potassic alteration which can be significant on a regional scale. Deposits in the Tennant Creek, Cloncurry and Olympic Dam regions are the three main examples of iron-oxide Cu-Au deposits in Australia: all are Proterozoic. A continent scale-spatial analysis of their regional setting reveals some common elements and suggests that these deposit types are unlikely to be found in the Archaean or the Phanerozoic of Australia. In all three cases, intrusive rocks occur in proximity, but whether the metals come direct from these or are leached from the country rock is unimportant to this analysis. The nearby granitic rocks are all fractionated, and show evidence of release of late stage magmatic fluids. Chemically these granites are a very specific type: all strongly oxidised, metaluminous, high temperature, high Ca granites that formed as a result of well above average geothermal gradients from crustal sources. These granites contain anomalously high concentrations of K, Th and U. Such granites are not found in the Archaean and rare equivalent Phanerozoic granitic types are of an order of magnitude smaller in size. This analysis shows that the known Australian deposits occur in regions of present-day anomalously high heat flow. Heat production is enhanced by high concentrations of K, Th and U in the nearby granites, particularly in the Olympic Dam and Cloncurry areas. Such elevated heat production may have resulted in anomalously long-lived hydrothermal cells and enhanced the metal leaching process. The large areal extent of the alteration zones in these two areas may also be a result of this fundamental crustal anomaly. Mafic igneous rocks are common in the vicinity of known Australia deposits, and might be another essential ingredient of an efficient Fe-Ox Cu-Au mineral system. They are regarded as an additional source of Cu for leaching. The regions with known deposits are dominated by oxidised rock packages containing hematite?magnetite. These oxidised packages are regarded as essential to maintaining the high redox state of the metal-bearing fluids. Elsewhere where similar granites intrude reduced packages, particularly those bearing graphite, Cu deposits are rare. Where oxidised host packages are not intruded by granites these deposit types do not occur. Equivalent oxidised host packages intruded by granites are not common in the Australian Archaean or Phanerozoic.

No abstract available

Gold deposits in the Archaean Eastern Goldfields Province in Western Australia were deposited in greenstone supracrustal rocks by fluids migrating up crustal scale fault zones. Regional ENE-WSW D2 shortening of the supracrustal rocks was detached from lower crustal shortening at a regional sub-horizontal detachment surface which transects stratigraphy below the base of the greenstones. Major gold deposits lie close to D3 strike slip faults that extend through the detachment surface and into the middle to lower crust. The detachment originally formed at a depth near the plastic-viscous transition. In orogenic systems the plastic-viscous transition correlates with a low permeability pressure seal separating essentially lithostatic fluid pressures in the upper crust from supralithostatic fluid pressures in the lower crust. This situation arises from collapse in permeability below the plastic-viscous transition because fluid pressures cannot match the mean stress in the rock. If the low permeability pressure seal is subsequently broken by a through-going fault, fluids below the seal would flow into the upper crust. Large, deeply penetrating faults are therefore ideal for focussing fluid flow into the upper crust. Dilatant deformation associated with sliding on faults or the development of shear zones above the seal will lead to tensile failure and fluid-filled extension fractures. In compressional orogens, the extensional fractures would be sub-horizontal, have poor vertical connectivity for fluid movement and could behave as fluids reservoirs. Seismic bright spots at 15-25 km depth in Tibet, Japan and the western United States have been described as examples of present day water or magma concentrations within orogens. The likely drop in rock strength associated with overpressured fluid-rich zones would make this region just above the plastic-viscous transition an ideal depth range to nucleate a regional detachment surface in a deforming crust.