No abstract available

No abstract available

The Tarcoola Goldfield in central South Australia is hosted by the Palaeoproterozoic Paxton Granite and Tarcoola Formation sediments. Both of these units are intruded by narrow dykes of the Lady Jane Diorite. Crosscutting relationships and Ar-Ar dating of sericite and hornblende demonstrate that veining, alteration and mineralization occurred synchronously with intrusion of the diorite dykes at ~1580 Ma. The Lady Jane Diorite is considered to be part of the Gawler Range?Hiltaba Volcano-Plutonic event. Mineralization at the Perseverance deposit in the Tarcoola Goldfield is hosted by both granite and the lower parts of the Tarcoola Formation. Alteration intensity and mineralization are related to fracture density, suggesting the structural regime was an important control on ore location and deposition. However, at the Tarcoola Blocks mine, mineralization is hosted entirely in the Tarcoola Formation, and very high gold grades are recorded in carbonaceous horizons, suggesting chemical processes in ore deposition. Primary fluid inclusions from mineralized quartz veins are dominated by two types, a two-phase aqueous type and a three-phase H2O-CO2(l)-CO2(v)?CH4 type. Both inclusion types have salinities of <10 wt% eq. NaCl, with evidence of other salts being present. Both types have Th between ~380?C and 150?C. At the Perseverance deposit, both inclusion types occur together in single quartz grains as primary inclusions, and are interpreted to have formed from a single evolving fluid, indicating immiscibility. Pb isotopes of galena from gold-bearing mineralization are in equilibrium with K-feldspar and whole-rock samples of the Paxton Granite. This is consistent with a local source for Pb and possibly other ore components, but not all potential reservoirs were able to be tested. Variably altered and gold mineralized samples that had Paxton Granite precursors show a loss of Nd and a trend from ?Nd(1580 Ma) values of about -6.2 in slightly altered samples towards more positive ?Nd values of about -3.3 in high grade gold samples. Of the local lithologies, the Lady Jane Diorite has ?Nd(1580 Ma) values of about +0.15 and is the most probable source of the more primitive Nd isotopic components in mineralized samples. Whether the Lady Jane Diorite is a cause of mineralization at Tarcoola, or both it and the mineralization are symptoms of the same tectonothermal event at ~1580 Ma can not be resolved with the available data. The demonstrated age relationship between the diorites and mineralisation at Tarcoola, the Nd data at Tarcoola, and the presence of similar dioritic dykes in all of the known gold prospects in the Central Gawler Gold Province are strongly suggestive that such dyking was an essential ingredient in gold mineralization throughout this province.

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.

No abstract available

No abstract available

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.

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.

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).

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.