Metallogenic, geologic and isotopic data indicate secular changes in the character of VHMS deposits relate to changes in tectonic processes, tectonic cycles, and changes in the hydrosphere and atmosphere. The distribution of these deposits is episodic, with peaks at 2740-2680 Ma, 1910-1840 Ma, 510-460 Ma and 370-355 Ma that correspond to the assembly of Kenorland, Nuna, Gondwana and Pangea. Quiescent periods of VHMS formation correspond to periods of supercontinent stability. Large ranges in source 238U/204Pb that characterize VHMS deposits in the Archean and Proterozoic indicate early (Hadean to Paleoarchean) differentiation. A progressive decrease in - variability suggests homogenisation with time of these differentiated sources. Secular increases in the amount of lead and decreases in 100Zn/(Zn+Pb) relate to an increase in felsic-dominated sequences as hosts to deposits and an absolute increase in the abundance of lead in the crust with time. The increase in sulfate minerals in VHMS deposits from virtually absent in the Meso- to Neoarchean to relatively common in the Phanerozoic relates to oxidation of the hydrosphere. Total sulfur in the oceans increased, resulting in an increasingly important contribution of seawater sulfur to VHMS ore fluids with time. Most sulfur in Archean to Paleoproterozoic deposits was derived by leaching rocks below deposits, with little contribution from seawater, resulting in uniform, near-zero-permil values of 34Ssulfide. In contrast the more variable values of younger deposits reflect the increasing importance of seawater sulfur. Unlike Meso- to Neoarchean deposits, Paleoarchean deposits contain abundant barite, which is inferred to have been derived from photolytic decomposition of atmospheric SO2 and does not reflect overall oxidised oceans. Archean and Proterozoic seawater was more salty than Phanerozoic, particularly upper Phanerozoic, seawater. VHMS fluids ore fluids reflect this, also being saltier in Precambrian deposits.

This address was presented at the 2009 Australian Nickel Conference held in Perth, 14-15th October 2009. Geoscience Australia has recently released two web-based map sheets (at: http://www.ga.gov.au/resources/maps/minerals/index.jsp) that show the continental extent and age relationships of Archean mafic and ultramafic rocks and associated mineral deposits throughout Australia. The maps were produced in close collaboration with the State and Northern Territory geological surveys. The Archean eon (~4000 million years to 2500 million years) represents an early part of Earth's history that is noteworthy for the earliest forms of life and the widespread occurrence of unusual olivine-rich ultramafic rocks called komatiites which contain world-class deposits of nickel sulphides. The major objective of this presentation is to promote the applications of the National map, which should be of interest to those explorers searching for nickel, platinum-group elements (PGEs), chromium, titanium, and vanadium. The new map sheets, when used in association with the `Australian Proterozoic Mafic-Ultramafic Magmatic Events' map published in 2008 (GeoCat 66114; GA Record 2008/15), summarise the temporal and spatial evolution of Precambrian mafic-ultramafic magmatism in Australia. These maps provide a national framework for investigating under-explored and potentially mineralised environments, and assessing the role of mafic-ultramafic magmatism in the development of the Australian continent.

A number of Paleoproterozoic layered mafic-ultramafic intrusions in the central part of the Halls Creek Orogen of East Kimberley, Western Australia, have been explored for platinum-group elements (PGE), chromium, nickel, copper, cobalt and gold. Here we report on the halogen geochemistry of apatite and biotite in a number of these intrusions. Interstitial apatite is ubiquitous in these intrusions and, in most samples, tends to be relatively enriched in F- and OH-endmembers and relatively poor in Cl (< 20 mole %). Fluorapatite occurs in the more evolved igneous rocks and in marginal samples that apparently have been contaminated by metamorphic country rock. Cl/F ratios generally increase with bulk rock molar Mg/(Mg + Fe) ratios, as observed in other intrusions. Only a few samples show Cl-enrichment as high as that seen in the Stillwater and Bushveld complexes beneath the major stratabound PGE deposits. The most Cl-rich compositions observed occur in the upper part of the Springvale intrusion, where it is associated with troctolite, and in a single sample from the McIntosh intrusion. For the former intrusion, it is suggested that volatiles migrating out of the lower part of the mafic stratigraphy stabilized olivine at the expense of pyroxene. Associated biotite tends to be low in both Cl and F, containing no more than 10 mole % of these components. It is concluded that the East Kimberley intrusions contained a low to moderate volatile component that, during the combined processes of crystallization, degassing and fractionation of interstitial halogen-bearing minerals, was able to produce a late, mobile interstitial silicate liquid or volatile-rich fluid phase of variable Cl/F content that gave rise to most of the observed variations within any given intrusion. The exceptions include some marginal samples that appear to have been affected by country rocks, either during emplacement (assimilation) or during later metamorphism. The generally low Cl/F ratio of apatite, the lack of primary amphibole and the high background sulfur concentrations of the East Kimberley intrusions suggest that these magmas were relatively dry. The possible development of high-grade, PGE-enriched horizons by late-stage hydrothermal processes that could have mobilized significant amounts of the PGE and sulfur is considered to be of low potential.

Early formed rift architecture has a major control on the subsequent compressional and strike-slip fault systems that host the world class St Ives Goldfield in the Yilgarn Craton, Western Australia. The current topography of the faults, at both a camp and regional scale, is a reflection of the geometry of the early rifts and old basement boundaries. Early structures have been physically mapped and identified in potential field data sets, isopach thickness variations and by the distribution of dolerite and basalt units. The early rift geometry is interpreted to have been a series of early WNW-trending normal faults and breached relay ramps associated with oblique rifting along an older NNW-trending basement boundary. Strike changes on major regional faults, such as the Boulder-Lefroy Fault, correlate with the location of major early formed WNW-trending faults. These control dilational and contractional fault segments associated with several world class gold fields. Within the St Ives Goldfield a series of N-trending linking thrusts developed during D2 inversion that are bounded by WNW-trending faults. During gold mineralization these linking thrusts became contractional jogs that now host several gold ore bodies. The WNW-trending relay faults acted as transfer faults syn-gold mineralization, although only discrete segments of these transfer faults were active during gold mineralization. They transferred strain from a complex combination of block on block movement associated with thrusting and strike-slip movement on NW- and N-trending faults. The WNW-trending faults were also a focus of intrusive dykes and larger scale intrusions that are inferred to have produced the pronounced WNW-trending gravity trends in regional potential field data sets.

From 1995 to 2000 information from the federal and state governments was compiled for Comprehensive Regional Assessments (CRA), which formed the basis for Regional Forest Agreements (RFA) that identified areas for conservation to meet targets agreed by the Commonwealth Government with the United Nations. These 5 CDs were created as part of GA's contribution to the SE Queensland CRA. CD1 contains ArcView Legends and Projects, data coverages, shapefiles, all documents and reports and associated maps and figures. CD2 contains various edited versions of covers and shapefiles, original data supplied by custodians, and staff workareas. CD3 contains Landsat, Magnetics etc. images. CD4 contains DEM etc. CD5 contains integration data, miscellaneous ArcInfo grids, and ArcInfo graphic files.

The Tasman Orogen represents a long-lived accretionary orogen with numerous orogenic cycles of extension and subsequent orogeny. Although details of the orogen are controversial, it is evident that the present configuration represents the cumulate products of many orogenies including both accretion and significant rearrangement of terranes. As a result the Tasman Orogen plays host to a significant array of commodities within a myriad of deposit styles, related to a variety of tectonic regimes. It is also evident that many mineralisation styles are repeated through the different orogenic cycles, and commonly during the same parts of the orogenic cycle. For example, volcanic-hosted massive sulphide deposits form early in cycles, whereas lode gold deposits form during contractional orogenesis that terminates the cycle. The geological complexity is both an advantage and disadvantage. Although the complexity can hinder regional exploration, it offers significant potential for identifying regions where previously unrecognised mineralisation styles may be present, particularly under cover where the geology (and tectonic history) is less well constrained.

This web-enabled system allows researchers to retrieve fluid inclusion data from anywhere in the world. The concept is to build a free and widely available web-based library of fluid properties for a range of geological fluids. The database is being developed as an "open" project, which intends to bring together researchers interested in the properties of geological fluids or fluid inclusions.

Proceedings of papers presented at an industry workshop held in Perth, 20 June 2002. Edited by K.F. Cassidy

Thematic map showing the distribution and age of Australia's diamond deposits and related rock types

The Late Archaean granite-greenstone terranes of the Yilgarn Craton WA are the host to Australia's premier world-class orogenic Au deposits. The Eastern Goldfields Superterrane (EGST) within this region hosts the majority of Au deposits and is therefore data rich, with high-resolution gravity, magnetics, geological and geochemical maps and databases, augmented with a number of high-quality deep seismic reflection profiles, teleseismic and magnetotelluric studies. Research within Geoscience Australia and the Predictive Mineral Discovery Cooperative Research Centre (pmd*CRC) have integrated these data into a set of new 3D maps at a range of scales. Integration of these data in 3D space has enabled greater understanding of the giant Au mineral systems. At the craton scale a tomographic survey was deployed to investigate whether anomalous crustal and/or upper mantle velocities exist beneath the highly mineralised EGST compared to "normal" velocities beneath barren regions in the Yilgarn Craton as a whole. The resulting velocity data were spatially represented in 3D using Gocad, enabling spatial links to be drawn between dramatic velocity variations in the tomographic data and zones of mineralisation in the upper crust. At the crustal/upper mantle scale, 2D seismic reflection lines throughout the EGST have imaged crustal penetrating shear zones that are often spatially coincident with mineralised corridors. Multiple 2D seismic reflection profiles, combined with geological and potential field data, have enabled the sub-surface geometries of faults to be constructed in three dimensions, providing insight into potential fluid pathways. A 130 km long magnetotellurics survey located along the EGF01 seismic line was also used to explore the relationship between seismic architecture and the crustal/upper mantle-scale conductivity distribution. At the camp-scale, 3D technologies have greatly improved our ability to compare complex relationships between spatially referenced 2D and 3D data, leading to improved targeting. The construction and display of the 3D distribution of lithological units and complex fault arrays, as surfaces and solid volumes, has enabled the 3D geology of a region to be statistically analysed in a quantitative way that is not possible using conventional techniques. Mine- to camp-scale 3D faults, lithologies and alteration assemblages are used to define preferential zones of fluid flow and Au deposition. This process involves detailed structural analysis of mineralisation at mine-scale to determine stress vectors during mineralisation, combined with numerical modelling of preferentially orientated structures. Favourably orientated faults calibrated with known mineralisation and alteration assemblages provide a framework to statistically analyse the relationship between structural architecture, alteration signatures and mineral deposition. 3D maps provide a tool to analyse data at a range of scales and better integrate a wide range of datasets. These technologies enable spatial and temporal relationships to be compared in a more quantitative way and also provide a 3D interpretation of geology that can be statistically analysed for predictive mineral discovery.