Basement controlled basin architecture and fault geometries in the Mount Isa Western Succession. SEG 2004: Predictive Mineral Discovery Under Cover; extended abstracts. Centre for Global Metallogeny, University of Western Australia Publication, 33, p.419.

Final Report 3D Geological models of the eastern Yilgarn Craton Project Y2

Final Report Camp- to Deposit-Scale Alteration Footprints in the Kalgoorlie-Kambalda Area Project Y3

This dataset shows the approximate flight paths (lines) and centres of the aerial photography in relation to the Cocos Islands. This data is used to establish and map the approximate coverage and location of orthophotos over the island. Two shape files were created, one to describe the flight lines the other to describe the photo centers.

A compilation of datasets gathered for the Central Gawler Gold subproject was released at the Gawler Craton: State of Play 2004 conference held in Adelaide on 4 - 6 August 2004. This presentation gives examples of some of the more recent datasets available in the data compilation, such as new AEM, Crystalline basement, Gravity, Magnetics, and worm layers.

Knowledge of the spatial and temporal relationships between fluid flow, the generation of structures, and crustal architecture is essential to understanding a mineral system. In regions dominated by cover, such knowledge strongly depends on interpretation of potential field data. Forward modelling and inversion of cross-sections, based on solid geology maps, provide valid approximations of 3D crustal geometries but reliability of interpolation decreases away from section planes. Models of crustal architecture are more rigorously produced by 3D inversion. Inversion programs derive physical property distributions that reproduce potential field observations consistent with a set of model parameters and geological constraints. The inversion techniques used in this study are based on the potential field inversion software, MAG3D and GRAV3D, developed at the University of British Columbia-Geophysical Inversion Facility (UBC-GIF). These programs have largely been used at the deposit-scale, but we modified the approach and settings for use at a regional-scale. The volume of crust chosen for study, centred on the Olympic Dam deposit, is 150 kmx 150 kmy 10 kmz. It comprises Archaean granulites, Palaeoproterozoic orthogneiss and metasediments (including BIFs), and early Mesoproterozoic felsic and mafic intrusives and extrusives. Zones of Fe oxide alteration are distributed throughout the upper parts of the crustal volume. Because a buffer is required to minimise edge effects, the volume for inversion is expanded to 198 kmx 198 kmy 18 kmz, discretised into 1 kmx 1 kmy 0.5 kmz cells. A series of trial inversions were run on a desktop PC with a 2.0 GHz processor and 2 GB of RAM. The initial trials were designed to investigate the feasibility of doing regional-scale inversions and to show where development of methods and support software were needed. For tractable computation, it is necessary to split each volume into a number of overlapping tiles that can be processed independently then rejoined. Even so, runs took up to 40 hours. The time elapsed can be substantially reduced if processing is performed as a distributed application across a network with each PC dedicated to a single tile. The inherent non-uniqueness of potential field inversion means that, even after some models have been rejected on 'geo-logical' grounds, a number of models consistent with the solid geology and 2D cross-section forward modelling, inter alia, will remain. Tests that prove or disprove the models may be devised, but actual physical testing may not be practical. However, we can make probabilistic determinations of the distribution of Fe oxide alteration, which may be used to map likely fluid pathways and guides to Fe oxide Cu-Au ore. Such predictions are amenable to testing through current exploration practice.

The Olympic Cu-Au province is an early Mesoproterozoic (~1570-1600 Ma) metallogenic belt along the eastern margin of the Gawler Craton, containing the Olympic Dam and Prominent Hill iron oxide Cu-Au (IOCG) deposits. Almost entirely concealed by cover, the province extends over 500 km from the Moonta-Wallaroo district through the Olympic Dam district to the Mt Woods Inlier. Based on the criteria below, and open-file company data, we propose extensions of the province to the Peake and Denison Inlier, Coober Pedy Ridge, and Mabel Creek Ridge. Guides for high-level style IOCG Hiltaba Suite felsic and mafic intrusive complexes - pancake-like intrusions emplaced at high crustal levels, which we view as symptoms of elevated heat flow around 1590 Ma that also drove hydrothermal fluid flow; mafic/ultramafic intrusive magmatism and mantle-like Sm-Nd- and S-isotopic signatures are less obvious at the sub-economic prospects than at Olympic Dam. - Regional host sequence composition - Palaeoproterozoic metasedimentary rocks of diverse composition are favourable as fluid source(s), buffers and traps; rock types include oxidised meta-arkosic units, feldspathic argillites/siltstones, carbonates and BIF. - Gawler Range Volcanics - Their presence in a district is a plus for preservation of high-level IOCG mineralisation; volcanic/maar/diatreme centres have been best documented at Olympic Dam and are not recognised at the sub-economic prospects. - Major fault networks - A major set striking NW to WNW, and dipping NE in Olympic Dam district, partly controlled hydrothermal fluid flow at ~1570-1600 Ma; a conjugate NE-striking set may be in part younger. Some of these faults probably developed during during the Kimban (~1700-1730 Ma) and/or Neil (~1850 Ma) compressive orogenies. - Regional to district scale alteration - Extensive alteration zones of magnetite, K-feldspar, actinolite, pyrite, apatite, carbonate, quartz, and minor chalcopyrite, producing magnetic-gravity anomalies; a first-order guide to the possible presence of high-level IOCG mineralisation. Regional high-temperature brines were sourced from, and/or reacted with, metasedimentary rocks but direct magmatic-hydrothermal or leached igneous contributions cannot be ruled out. - Local (deposit) scale alteration & mineralisation - Zones of abundant hematite, sericite, chlorite and carbonate are spatially and temporally associated with Cu-Fe sulfides, pyrite, fluorite, barite, and REE minerals. These oxidised alteration zones may be either above or lateral to magnetite alteration, with highest grade Cu-Au mineralisation predicted within hematitic alteration, near (10's to 100's of metres) the transition to magnetite alteration. Guides for deeper-level style IOCG (e.g., parts of Moonta-Wallaroo district & Mt Woods Inlier): - Regional host sequence composition, regional structure and intrusive associations are likely to be similar to those of high-level style IOCG, but the following regional characteristics will differ. - Volcanics coeval with mineralisation (e.g., Gawler Range Volcanics) will not be preserved if IOCG deposits have been exhumed. - Host structures - Shear zones and other brittle-ductile (rather than brittle) structures will be the dominant host structures, although tectonic-hydraulic breccias may be present if strain rates and/or fluid pressures were high (e.g., Ernest Henry style breccias). - Regional alteration - Dominated by albite-actinolite ± clinopyroxene ± magnetite rather than K-feldspar rich; additionally, magnetite-biotite alteration with minor to significant chalcopyrite-pyrite-REE mineralisation is common in deeper-level style IOCG systems, particularly in zones proximal to sulphide mineralisation. - Local (deposit) alteration - Magnetite-biotite-K-feldspar-bearing proximal alteration assemblages in felsic host rocks; intermediate to mafic host rocks will contain less feldspar and more Fe-Mg silicate alteration (e.g., amphiboles, chlorite) and carbonate.

The Gawler Craton is a complex Archaean to Mesoproterozoic terrane. Defining the age-range of the geology in different areas of the craton is vital to understanding its geological history and aiding mineral exploration. Recent SHRIMP U-Pb results from the Mount Woods Inlier and the Central Gawler Au province clarify the age of magmatic events, and gives an insight into the extent, and significance of the ~1590 Ma Hiltaba Suite. Further to this, the U-Pb dating has helped constrain the age of mineralisation in several areas. Data from felsic and mafic igneous rocks from the Mount Woods Inlier show a predominant age-range of ~1590 Ma to ~1580 Ma. However, ~1708 Ma granite has also been identified. Along with inherited zircon spectra, the older granite may have important implications for unravelling the pre-Hiltaba history of the Mount Woods Inlier and its relationship to other Australian Proterozoic cratons. As high-grade metamorphic rocks are common in the Mount Woods Inlier, the significance and timing of their metamorphism have also been examined. The age of magmatism in the Central Gawler is similar to the Mount Woods Inlier, with ~1590 Ma to ~1580 Ma igneous activity dominating. However, felsic igneous rocks of the Barns prospect (Adelaide Resources) are significantly older at ~1690 Ma. Mafic dykes from this area have also been dated, and although a similar age was returned, the zircons analysed may represent the age of the host rock into which the dyke has intruded. Granites and sedimentary rocks from the Tarcoola goldfield returned ages around 1590-1580 Ma and 1730-1715 Ma. Granitoid from the Weednanna prospect (Aquila Resources) has a Hiltaba age of ~1590 Ma.

This paper was presented at the World Diamond Conference, Perth, 22-23 November 2004.

Presented at the Society of Economic Geologists (SEG) 2004: Predictive Mineral Discovery Under Cover Conference, Perth, September 2004. The paper discusses a web-based information and mapping system for defining nickel sulphide metallogenic and prospective provinces. The system contains information on regional geology, mineral occurrences and deposits, resources, and age of mineralisation for most Precambrian nickel sulphide deposits. The three basic criteria used to delineate the metallogenic provinces are: same style of mineral system, similar age, and spatial contiguity of geology