The Maldon gold deposit in central Victoria lies within the contact aureole of the Harcourt Granite and associated granitic dykes. The ore-bearing fluids are characterised by the presence of CH4-rich fluids, which exhibit complex freezing and heating behaviour, as well as mixed CO2-low-salinity aqueous fluids. Raman analysis indicates that the CH4-rich inclusions from Maldon contain 30 to >70 mol.% CH4 (and <40 mol.% N2) and have highly variable ratios of CH4/CO2, ranging from 0.12 to 15.6. The presence of graphite in the CH4-rich inclusions indicates either accidental trapping of the solid phase at high temperature or post-trapping changes (i.e. incomplete reactions). Higher-salinity brine inclusions only occur locally. The Harcourt Granite is a moderately reduced, I-type granite and the reduced fluids are believed to have formed within (or in close proximity to) thermal aureoles of the dykes or granites during contact metamorphism. We conclude that the Maldon deposit is an 'orogenic' gold deposit that was metamorphosed and/or remobilised during the emplacement of post-orogenic intrusions/dykes. The late-stage magmatic fluids and retrograde metamorphic fluids have produced many of the features associated with other well documented reduced intrusion-related gold systems. This suggests that some 'orogenic' gold deposits may have been completely overprinted by later magmatic/metamorphic events and are now only evident as reduced intrusion-related gold systems.

The concentration of sulfur in fluids associated orogenic gold deposits is important for understanding the transport of gold species but still remains poorly defined. In this study Raman spectroscopy has been used to obtain the concentrations and fugacities of H2S in individual fluid inclusions from the Archean, sub-amphibolite facies Missouri gold deposit in Western Australia. Type III, vapor-rich (XH2O < 0.4) fluid inclusions from the Missouri gold deposit were shown to contain highly variable CO2/CH4 ratios (0.01 to 1.9) and H2S fugacities of up to 1.6 MPa. The calculated values of H2S are consistent with the location of fluids within the general pyrite stability field next to the pyrite-pyrrhotite reaction boundary. This is in accord with the quartz(-plagioclase)-biotite-carbonate-pyrite alteration assemblage that occurs adjacent to the quartz veins at the Missouri deposit. Geochemical modelling was used to investigate how the concentration of H2S was affected by the fCO2/fCH4 ratio of a fluid in equilibrium with the pyrite-pyrrhotite alteration assemblage. Overall, the highest H2S concentrations are predicted for 'reduced-fluids' near the CH4 apex of the H2O-CH4-CO2 ternary diagram. Comparisons with the measured H2S concentrations show that the CH4-CO2¬-Pyrite-Troilite equilibrium could be the controlling factor on the H2S concentration of the fluid; other processes could have affected some inclusions which contain higher than predicted H2S concentrations. These are mostly restricted to the population of water-poor (XH2O < 0.1), essentially CH4-CO2 inclusions.

No abstract available

A compilation of abstracts of talks and posters presented at the Broken Hill Exploration Initiative (BHEI) 2003 conference at Broken Hill, 7-9 July 2003.

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

The poster/panel summarises result of preliminary fluid flow and chemical modelling in the Frome Embayment

As part of the North Pilbara NGMA Project, AGSO (now Geoscience Australia), together with Newcastle University and the Geological Survey of Western Australia (GSWA), have been conducting a research program to document the geological setting, characteristics and genesis of Au deposits of the North Pilbara Terrane. This record summarises some results of this research program. This research has concentrated on turbidite-hosted lode Au deposits in the Indee and Nullagine areas as well as basalt and ultramafic-hosted deposits in the Mt York-Lynas Find area. In addition to these areas, AGSO's research also concentrated on epithermal deposits in the Indee area, and less detailed studies were undertaken on lode Au deposits at Gold Show Hill and Klondyke. This research program was designed to complement recent (e.g., Neumayr et al. [1993; 1998] on the York deposits and Zegers [1996] on the Bamboo Creek deposits) and ongoing (e.g., D. Baker, University of Newcastle] at Mt York-Lynas Find) programs conducted at the other institutions. This Pilbara Gold Record is supported by an extensive GIS dataset, providing many new digital data sets, including a number of variations of the magnetics, gravity, and gamma-ray spectrometry. A solid geology map, and derivative maps, mineral deposits, geological events, and Landsat 5-TM provide additional views. This data set complements the 1:1.5 Million scale colour atlas (Blewett et al., 2000).

Presented at the Evolution and metallogenesis of the North Australian Craton Conference, 20-22 June 2006, Alice Springs. The southern Arunta region contains a number of small (<5 Mt) Zn-Cu-Pb (Ag-Au) deposits. Although none of these deposits are economic, they do indicate a moderate level of base-metal potential for this region. Most of these deposits are located in the Strangways Range, which forms part of the Aileron Province. These deposits were classified as Oonagalabi-type deposits by Warren & Shaw (1985), citing similarities in metal assemblages, alteration assemblages, and host units, and interpreted as volcanic-hosted massive sulphide (VHMS) deposits. More detailed geological mapping and geochemical and geochronological data suggest that the Oonagalabi group should be subdivided further into three types, the Utnalanama-type, the re-defined Oonagalabi-type and the Johnnies-type (Hussey et al., 2005). <p>Related product:<a href="https://www.ga.gov.au/products/servlet/controller?event=GEOCAT_DETAILS&amp;catno=64764">Evolution and metallogenesis of the North Australian Craton Conference Abstracts</p>

Poorly exposed Paleoproterozoic sandstones and siltstones of the Killi Killi Formation record developement of a large turbidite complex. Killi Killi Formation sediments were eroded from the uplifted ~1860 Ma Nimbuwah and Hooper Orogens as indicated by detrital zircons with sediment deposition at ~1840 Ma. Facies analysis, isopach maps and detrital zircon populations, combined with Sm-Nd data from the Tanami region and Halls Creek Orogen, confirm the previously suggested correlation of the Paleoproterozoic successions in the Eastern zone of the Halls Creek Orogen and the Tanami region. Detrital zircons from the Aileron Province suggest the turbidite complex extends into the Arunta region, however, high metamorphic grade precludes direct facies comparisons in the Arunta region. Portions of the turbidite complex in the Tanami region are dominated by mudstones, consisting of low-density turbidites and associated hemipelagites, that potentially acted as a redox boundary to gold-bearing fluid. Gold prospectivity in turbiditic systems is increased within these mudstone sequences with the potential for further gold discoveries.

Legacy product - no abstract available