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A description of the deposit, whose ores are dominated by magnetite, chalcopyrite, pyrite, carbonate, quartz and apatite hosted by brecciated and strongly K-feldspar altered metavolcanics with a potassic alteration halo, leads to the proposal that the deposit formed where mafic and felsic magmas of the c.1530 Ma Naraku batholith mingled, driving volatile exsolution. Extreme fluid overpressuring resulted, confirmed by an impermeable carapace formed by regional sodic and sodic-calcic alteration. The eventual failure of this seal led to the flow of high-energy fluids transporting clasts upward and grinding them, to form hydrothermal breccias. Mixing of basinal and magmatic fluids accompanied ore precipitation, although the source of the metals remains unclear. In the upper portions of the deposit, most ore was precipitated as hydrothermal infill between clasts of K-feldspar altered metavolcanics, whereas at greater depths the more prolonged interaction between fluids and rocks formed both infill and replacement-style ores., A description of the deposit, whose ores are dominated by magnetite, chalcopyrite, pyrite, carbonate, quartz and apatite hosted by brecciated and strongly K-feldspar altered metavolcanics with a potassic alteration halo, leads to the proposal that the deposit formed where mafic and felsic magmas of the c.1530 Ma Naraku batholith mingled, driving volatile exsolution. Extreme fluid overpressuring resulted, confirmed by an impermeable carapace formed by regional sodic and sodic-calcic alteration. The eventual failure of this seal led to the flow of high-energy fluids transporting clasts upward and grinding them, to form hydrothermal breccias. Mixing of basinal and magmatic fluids accompanied ore precipitation, although the source of the metals remains unclear. In the upper portions of the deposit, most ore was precipitated as hydrothermal infill between clasts of K-feldspar altered metavolcanics, whereas at greater depths the more prolonged interaction between fluids and rocks formed both infill and replacement-style ores.

The role was investigated of deeply sourced fluids, either as separate phases or from melts, in the genesis of Au deposits, based on observations at the Sunrise Dam mine in Western Australia. The thick laminated ‘D3’ quartz veins comprise two mineral assemblages, preferentially aligned muscovite-tourmaline-dolomite-rutile-apatite, often associated with pyrite Au, and open space and brecciated quartz, including clasts of quartz from the surrounding rocks. Mineral chemical and textural relationships were used to distinguish the types of fluids that were present during multiple episodes of fluid-flow and deformation. Apatite data from the D3 laminated veins indicated that a primitive, ‘carbonatite-like’ fluid was present just prior to pyrite-dolomite-Au precipitation, and may have been critical in transporting the Au from deep in the crust. This was confirmed by fluid-inclusion evidence for extreme X(CO2) fluids and Sr isotope evidence for both a primitive and crustal fluid reservoir., The role was investigated of deeply sourced fluids, either as separate phases or from melts, in the genesis of Au deposits, based on observations at the Sunrise Dam mine in Western Australia. The thick laminated ‘D3’ quartz veins comprise two mineral assemblages, preferentially aligned muscovite-tourmaline-dolomite-rutile-apatite, often associated with pyrite Au, and open space and brecciated quartz, including clasts of quartz from the surrounding rocks. Mineral chemical and textural relationships were used to distinguish the types of fluids that were present during multiple episodes of fluid-flow and deformation. Apatite data from the D3 laminated veins indicated that a primitive, ‘carbonatite-like’ fluid was present just prior to pyrite-dolomite-Au precipitation, and may have been critical in transporting the Au from deep in the crust. This was confirmed by fluid-inclusion evidence for extreme X(CO2) fluids and Sr isotope evidence for both a primitive and crustal fluid reservoir.

The extended abstracts cover the relationship between magmas, their associated fluids, and the roles they play in ore deposition in the porphyry-epithermal environment, their evolution in magmatic-hydrothermal systems, and the geological fingerprint of these processes. The contents are: Lindgren's legacy, by Baker T.; Textural and paragenetic evidence for the source of higher-grade ore in some porphyry Cu-Au deposits, by Morrison G.W.; Chlorine-water evolution in arc-magmas, by Cleverley J.S., Willan R.C.R. & Yardley B.W.D.; Fluid inclusions in porphyry Cu-Au deposits, by Fu Bin et al.; Exploration, geology and mineralisation at Oyu Tolgoi, by Forster C.N. et al.; High-sulphidation Cu-Au mineralisation in the Ertsberg district, by Pollard P.J. & Taylor R.G.; Structural and hydrothermal features of the Gunung Bijih Cu skarn, by Clarke G.W.; Similarities between porphyry-related systems at Wanagon Gold and Big Gossan, by Prendergast K.; Geological setting of hydrothermal systems in the Seongsan district, by Bowden C.D.; Alteration, paragenesis and vein textures at Vera-Nancy, by Mustard R. et al.; and Mineral resource estimation of epithermal gold veins, by Dominy S. et al., The extended abstracts cover the relationship between magmas, their associated fluids, and the roles they play in ore deposition in the porphyry-epithermal environment, their evolution in magmatic-hydrothermal systems, and the geological fingerprint of these processes. The contents are: Lindgren's legacy, by Baker T.; Textural and paragenetic evidence for the source of higher-grade ore in some porphyry Cu-Au deposits, by Morrison G.W.; Chlorine-water evolution in arc-magmas, by Cleverley J.S., Willan R.C.R. & Yardley B.W.D.; Fluid inclusions in porphyry Cu-Au deposits, by Fu Bin et al.; Exploration, geology and mineralisation at Oyu Tolgoi, by Forster C.N. et al.; High-sulphidation Cu-Au mineralisation in the Ertsberg district, by Pollard P.J. & Taylor R.G.; Structural and hydrothermal features of the Gunung Bijih Cu skarn, by Clarke G.W.; Similarities between porphyry-related systems at Wanagon Gold and Big Gossan, by Prendergast K.; Geological setting of hydrothermal systems in the Seongsan district, by Bowden C.D.; Alteration, paragenesis and vein textures at Vera-Nancy, by Mustard R. et al.; and Mineral resource estimation of epithermal gold veins, by Dominy S. et al.

The Predictive Mineral Discovery Cooperative Research Centre (PMD*CRC) in Australia has been developing new technologies for modelling the complexities of geochemical thermodynamics and geochemistry in general. Some applications to mineral exploration in greenstone terrains are demonstrated, with examples of fluid-rock interaction, the role of intrusions, outflow above buried deposits, dispersion haloes and forward modelling of geophysical signatures. The core to the new models is the web-enabled thermodynamic database FreeGs, while the operating software HCh can be used for temperatures of 0-1 000 degrees C and pressures up to 500 MPa, extending potential to the P-T realm of lode gold and iron-oxide-copper-gold deposits as well as porphyry copper-gold systems., The Predictive Mineral Discovery Cooperative Research Centre (PMD*CRC) in Australia has been developing new technologies for modelling the complexities of geochemical thermodynamics and geochemistry in general. Some applications to mineral exploration in greenstone terrains are demonstrated, with examples of fluid-rock interaction, the role of intrusions, outflow above buried deposits, dispersion haloes and forward modelling of geophysical signatures. The core to the new models is the web-enabled thermodynamic database FreeGs, while the operating software HCh can be used for temperatures of 0-1 000 degrees C and pressures up to 500 MPa, extending potential to the P-T realm of lode gold and iron-oxide-copper-gold deposits as well as porphyry copper-gold systems.

Liberation of Fe and K by widespread postmetamorphic albitisation of country rocks was one of the likely contributing processes in the formation of both barren and mineralised magnetite+/-chalcopyrite ironstones with biotite, gold, haematite, clinopyroxene, actinolite and apatite in the Cloncurry district of the Proterozoic Mount Isa block. Whole-rock geochemical data indicate nearly immobile Al, Ga +/- Ti, Zr during transformation of a variety of least altered rocks toward albitite. The data indicate that the addition of Na from a brine to the rock accompanied the loss of Fe, K, Ba, Rb +/- Ca, Sr, Co, V, Mn, Pb and Zn from those altered rocks and enrichment in the brine, but that Cu was not systematically stripped from a variety of wall rocks during albitisation. Conversely, the formation of metasomatic ironstones, the immediate hosts to some Cu-Au ores, involves addition of most of the same elements that were lost during albitisation. Precipitation of sulphides in the Cu-Au deposits was the result of mixing of Cu-bearing brine, of ultimately magmatic origin, but modified extensively via albitisation, with S-bearing fluids or reaction of the brine with S-bearing rocks. When Cu was absent from the initial magmatic fluid, barren ironstones may have been the result., Liberation of Fe and K by widespread postmetamorphic albitisation of country rocks was one of the likely contributing processes in the formation of both barren and mineralised magnetite+/-chalcopyrite ironstones with biotite, gold, haematite, clinopyroxene, actinolite and apatite in the Cloncurry district of the Proterozoic Mount Isa block. Whole-rock geochemical data indicate nearly immobile Al, Ga +/- Ti, Zr during transformation of a variety of least altered rocks toward albitite. The data indicate that the addition of Na from a brine to the rock accompanied the loss of Fe, K, Ba, Rb +/- Ca, Sr, Co, V, Mn, Pb and Zn from those altered rocks and enrichment in the brine, but that Cu was not systematically stripped from a variety of wall rocks during albitisation. Conversely, the formation of metasomatic ironstones, the immediate hosts to some Cu-Au ores, involves addition of most of the same elements that were lost during albitisation. Precipitation of sulphides in the Cu-Au deposits was the result of mixing of Cu-bearing brine, of ultimately magmatic origin, but modified extensively via albitisation, with S-bearing fluids or reaction of the brine with S-bearing rocks. When Cu was absent from the initial magmatic fluid, barren ironstones may have been the result.

A mineral systems approach can be used to understand the formation of Au deposits, based on geodynamic history, architecture, fluid sources and reservoirs and metal transport and depositional mechanisms. The most important periods for Au production were the Late Archaean for greenstone- hosted deposits, the Palaeoproterozoic for iron oxide-Cu-Au and lode deposits and the Phanerozoic for porphyry and epithermal deposits. The deposits and provinces are commonly associated with cratonic margins, cross-arc structures, tears in slabs and trans-crustal structures. The nature of the fluid reservoirs in the mantle and the forces that drove fluid release may have been a common theme in the genesis of Au deposits. Research priorities are discussed in relation to Au deposition mechanisms., A mineral systems approach can be used to understand the formation of Au deposits, based on geodynamic history, architecture, fluid sources and reservoirs and metal transport and depositional mechanisms. The most important periods for Au production were the Late Archaean for greenstone- hosted deposits, the Palaeoproterozoic for iron oxide-Cu-Au and lode deposits and the Phanerozoic for porphyry and epithermal deposits. The deposits and provinces are commonly associated with cratonic margins, cross-arc structures, tears in slabs and trans-crustal structures. The nature of the fluid reservoirs in the mantle and the forces that drove fluid release may have been a common theme in the genesis of Au deposits. Research priorities are discussed in relation to Au deposition mechanisms.

Models were developed to compare and couple thermally and mechanically driven fluid flow. In models in which high basal heat flow is coupled with extensional deformation, the effects of the deformation dominate flow regimes, rather than the thermal structure. A model with initial heating and fluid flow established large convection cells with basement fluid circulation, prior to deformation being incorporated. The convection cells are effectively destroyed by extension at geologically reasonable strain rates, with surface fluids driven downward and meeting remnants of the decaying convection deep in the system. This simulation provides a possible solution for mixing of near-surface and deep fluids in unconformity-related U deposits and Olympic Dam-style iron oxide Cu-Au deposits. Geological models for shale-hosted base metal deposits, such as Mount Isa Zn-Pb, involve transitions from active rifting to blanketing by mineralised sag-phase shales, requiring reduction or cessation of extension with time. This is simulated by stopping the deformation component of the coupled model and allowing the heating and fluid-flow parts to continue. Exhalative or other near-surface ores are likely to form when extension ceases and the thermal structure becomes the driver of fluid flow., Models were developed to compare and couple thermally and mechanically driven fluid flow. In models in which high basal heat flow is coupled with extensional deformation, the effects of the deformation dominate flow regimes, rather than the thermal structure. A model with initial heating and fluid flow established large convection cells with basement fluid circulation, prior to deformation being incorporated. The convection cells are effectively destroyed by extension at geologically reasonable strain rates, with surface fluids driven downward and meeting remnants of the decaying convection deep in the system. This simulation provides a possible solution for mixing of near-surface and deep fluids in unconformity-related U deposits and Olympic Dam-style iron oxide Cu-Au deposits. Geological models for shale-hosted base metal deposits, such as Mount Isa Zn-Pb, involve transitions from active rifting to blanketing by mineralised sag-phase shales, requiring reduction or cessation of extension with time. This is simulated by stopping the deformation component of the coupled model and allowing the heating and fluid-flow parts to continue. Exhalative or other near-surface ores are likely to form when extension ceases and the thermal structure becomes the driver of fluid flow.

The DeGrussa (Cu-Au) ore body on the margins of the Yilgarn Craton in the Bryah Basin was successfully identified using organic soil, vegetation and groundwater with multi-element anomalies associated with the buried ore. Primarily, the anomalies are caused by weathering and vertical dispersion through thin (2-10 m) transported cover and vegetation cycling of Au and Cu located a few metres below the surface. Aqua regia extractions of soils and vegetation, and MMI-M extraction of soils were effective by providing strong, coherent multi-element anomalies at relatively close spacing (50 m). Conversely, portable XRF analysis was less effective at this site as the elemental concentrations were too low. Gold, As and Cu in groundwater were present in anomalous concentrations, but inconsistently so at larger sample spacing (100s of metres). When compared to regional hydrogeochemistry (e.g. more than 1000 m spacing), Au, As, Cu, Pd and Pt element concentrations in the DeGrussa groundwater were elevated in a broad, general area along strike potentially identifying additional targets. Weathering, hydraulic lift by vegetation and hydromorphic dispersion are the mechanisms responsible for metal migration at the DeGrussa site., The DeGrussa (Cu-Au) ore body on the margins of the Yilgarn Craton in the Bryah Basin was successfully identified using organic soil, vegetation and groundwater with multi-element anomalies associated with the buried ore. Primarily, the anomalies are caused by weathering and vertical dispersion through thin (2-10 m) transported cover and vegetation cycling of Au and Cu located a few metres below the surface. Aqua regia extractions of soils and vegetation, and MMI-M extraction of soils were effective by providing strong, coherent multi-element anomalies at relatively close spacing (50 m). Conversely, portable XRF analysis was less effective at this site as the elemental concentrations were too low. Gold, As and Cu in groundwater were present in anomalous concentrations, but inconsistently so at larger sample spacing (100s of metres). When compared to regional hydrogeochemistry (e.g. more than 1000 m spacing), Au, As, Cu, Pd and Pt element concentrations in the DeGrussa groundwater were elevated in a broad, general area along strike potentially identifying additional targets. Weathering, hydraulic lift by vegetation and hydromorphic dispersion are the mechanisms responsible for metal migration at the DeGrussa site.

The Bismark deposit, northern Chihuahua, is one of several base metal-rich high-temperature, carbonate-replacement deposits hosted in northern Mexico. Previous fluid inclusion studies based on microthermometry and PIXE have shown that the Zn-rich, Pb-poor deposit formed from a moderate salinity magmatic fluid. New LA-ICP-MS analysis was carried on the same fluid inclusion population and data reveal overall lower concentrations of Pb in the ore fluid (av. 285 ppm) than previously indicated by PIXE analysis (av. 713 ppm). Chemical modelling tested the following ore deposition processes: cooling; fluid-rock reaction at constant temperature; cooling and simultaneous fluid-rock interaction. Results show that gangue and ore minerals are best reproduced by fluid-rock interaction and simultaneous cooling. Simulations strongly indicate that ore deposition was mainly driven by a pH increase due to neutralisation of acidic ore fluid (pH 3.9) with limestone. Modelling results do not support the hypothesis of a temperature decrease as the principal ore-forming process., The Bismark deposit, northern Chihuahua, is one of several base metal-rich high-temperature, carbonate-replacement deposits hosted in northern Mexico. Previous fluid inclusion studies based on microthermometry and PIXE have shown that the Zn-rich, Pb-poor deposit formed from a moderate salinity magmatic fluid. New LA-ICP-MS analysis was carried on the same fluid inclusion population and data reveal overall lower concentrations of Pb in the ore fluid (av. 285 ppm) than previously indicated by PIXE analysis (av. 713 ppm). Chemical modelling tested the following ore deposition processes: cooling; fluid-rock reaction at constant temperature; cooling and simultaneous fluid-rock interaction. Results show that gangue and ore minerals are best reproduced by fluid-rock interaction and simultaneous cooling. Simulations strongly indicate that ore deposition was mainly driven by a pH increase due to neutralisation of acidic ore fluid (pH 3.9) with limestone. Modelling results do not support the hypothesis of a temperature decrease as the principal ore-forming process.

World-class Neoarchaean gold deposits of the eastern Yilgarn can be zoned with respect to alteration assemblages, but in many cases fluid pathways are poorly understood. Results of detailed core logging, SEM mineral mapping of alteration assemblages and microprobe analysis of biotite and apatite show that the East Repulse deposit is vertically zoned with relatively oxidised sulphate-rich alteration (anhydrite, celestine and/or barite) in the footwall of the deposit, sulphide-rich alteration (pyrite/magnetite with minor barite and celestine) in the core of the deposit and relatively reduced sulphide-only assemblages (pyrite/pyrrhotite with minor pentlandite, millerite, and cobaltite) in the hanging wall of the deposit. Gold was identified as inclusions in pyrite and associated biotite, implying a link between biotite-pyrite alteration and gold mineralisation. The trend of decreasing F in biotite and apatite with decreasing depth is consistent with an hypothesis that oxidised F- and K-bearing fluids were focused along subvertical pathways beneath the deposit, within or subjacent to granitoid dykes. The biotite-apatite geothermometer shows that these fluids were relatively hot (480+/-60 degrees C) at the time of alteration. These relatively high-temperature, oxidised, F- and K-bearing fluids may have been derived from a proximal magmatic source., World-class Neoarchaean gold deposits of the eastern Yilgarn can be zoned with respect to alteration assemblages, but in many cases fluid pathways are poorly understood. Results of detailed core logging, SEM mineral mapping of alteration assemblages and microprobe analysis of biotite and apatite show that the East Repulse deposit is vertically zoned with relatively oxidised sulphate-rich alteration (anhydrite, celestine and/or barite) in the footwall of the deposit, sulphide-rich alteration (pyrite/magnetite with minor barite and celestine) in the core of the deposit and relatively reduced sulphide-only assemblages (pyrite/pyrrhotite with minor pentlandite, millerite, and cobaltite) in the hanging wall of the deposit. Gold was identified as inclusions in pyrite and associated biotite, implying a link between biotite-pyrite alteration and gold mineralisation. The trend of decreasing F in biotite and apatite with decreasing depth is consistent with an hypothesis that oxidised F- and K-bearing fluids were focused along subvertical pathways beneath the deposit, within or subjacent to granitoid dykes. The biotite-apatite geothermometer shows that these fluids were relatively hot (480+/-60 degrees C) at the time of alteration. These relatively high-temperature, oxidised, F- and K-bearing fluids may have been derived from a proximal magmatic source.

This study illustrates that combined portable X-ray fluorescence (pXRF) and portable X-ray diffraction (pXRD) analysis can be performed on a large set of complex geological samples and the techniques complement each other. It also shows the viability and usefulness of currently underused portable XRD analysis. pXRD analysers can provide data comparable to modern lab-based instruments and the novel, innovative and unique convectional sample chamber of the Olympus Terra analyser is ideally suited for analysis of minerals with preferred crystallographic orientation such as mica-group minerals, chlorites, and amphiboles. Samples studied here are from a diamond drill hole at the closed Brukunga pyrite mine, South Australia. A small amount (less than 5-10 g) of sample is required for coupled pXRF-pXRD analysis that can be performed in less than 15 minutes for both measurements. This analysis, therefore, offers rapid and low-cost characterisation of materials for mineral exploration and the mining industry and delivers elemental and mineralogical information of high quality where appropriate QA/QC protocols are followed. The integrated data can then be used to constrain lithologies and contacts between various units, hydrothermal alteration and ore types., This study illustrates that combined portable X-ray fluorescence (pXRF) and portable X-ray diffraction (pXRD) analysis can be performed on a large set of complex geological samples and the techniques complement each other. It also shows the viability and usefulness of currently underused portable XRD analysis. pXRD analysers can provide data comparable to modern lab-based instruments and the novel, innovative and unique convectional sample chamber of the Olympus Terra analyser is ideally suited for analysis of minerals with preferred crystallographic orientation such as mica-group minerals, chlorites, and amphiboles. Samples studied here are from a diamond drill hole at the closed Brukunga pyrite mine, South Australia. A small amount (less than 5-10 g) of sample is required for coupled pXRF-pXRD analysis that can be performed in less than 15 minutes for both measurements. This analysis, therefore, offers rapid and low-cost characterisation of materials for mineral exploration and the mining industry and delivers elemental and mineralogical information of high quality where appropriate QA/QC protocols are followed. The integrated data can then be used to constrain lithologies and contacts between various units, hydrothermal alteration and ore types.

The amphibolite-facies metabasaltic rocks of the Mine Mafic Package at Plutonic Gold Mine, Western Australia, contain an estimated endowment of 10 500 000 oz Au. A preliminary study based on portable X-ray fluorescence (pXRF) analyses identified a geochemical stratigraphy which strongly controlled the location of Au mineralisation. The present study incorporates a significantly larger pXRF dataset and presents the data in a three-dimensional framework. This dataset allows an investigation of the mineralogy of Au mineralisation with varying geochemical associations across the deposit. Historically, high As content in the mill feed resulted in poor metallurgical performance. Seamless data integration of the pXRF dataset allows for recognition of the different styles of Au mineralisation based on Au/As ratios, and visualisation of the distribution of these different mineralogical associations in three dimensions. This work enables us to predict better the As concentration of underground ore blocks, and to be proactive in optimising the mill configuration to improve metallurgical performance. (Authors.), The amphibolite-facies metabasaltic rocks of the Mine Mafic Package at Plutonic Gold Mine, Western Australia, contain an estimated endowment of 10 500 000 oz Au. A preliminary study based on portable X-ray fluorescence (pXRF) analyses identified a geochemical stratigraphy which strongly controlled the location of Au mineralisation. The present study incorporates a significantly larger pXRF dataset and presents the data in a three-dimensional framework. This dataset allows an investigation of the mineralogy of Au mineralisation with varying geochemical associations across the deposit. Historically, high As content in the mill feed resulted in poor metallurgical performance. Seamless data integration of the pXRF dataset allows for recognition of the different styles of Au mineralisation based on Au/As ratios, and visualisation of the distribution of these different mineralogical associations in three dimensions. This work enables us to predict better the As concentration of underground ore blocks, and to be proactive in optimising the mill configuration to improve metallurgical performance. (Authors.)

The Late Archaean deposit has a resource of about 10 000 000 oz of Au and is characterised by extreme structural complexity resulting from a protracted deformation history with evidence of structural reactivation and multiple phases of Au mineralisation. Early Group I orebodies are hosted within shallow- to moderately dipping NW-trending shear zones and occur in foliation parallel veins within a strong penetrative fabric. Group II orebodies occur within steeply dipping shear zones and are characterised by veins and breccias, and Group III and IV orebodies comprise mainly stockwork veins. Two main fluid inclusion types have been recognised, low-salinity CO2-H2O inclusions and CO2 inclusions. CO2-H2O inclusions are more common in the early Group I orebodies, the fluids having been trapped under high P-T conditions during D3. CO2-H2O inclusions in later Group II and III ore bodies were trapped predominantly within the two-phase field at temperatures below 300 degrees C and pressures of about 1 kbar. CO2 inclusions crosscut the early CO2-H2O inclusions and are the dominant type in Group II, III, and IV structures. They probably represent a major late influx of separately sourced fluid during D4 and were trapped at lower pressure conditions than the earlier CO2-H2O fluids. The combined structural and fluid history suggests that the early CO2-H2O fluid ponded beneath moderately dipping shear zones during late D2/early D3, and that fluid pressures increased to near- or supralithostatic conditions. Shear failure along these structures resulted in widespread precipitation of moderate-grade Au mineralisation from the CO2-H2O fluid. Continued deformation and exhumation modified P-T-X conditions, and cooling of the host rocks to below 300 degrees C resulted in the CO2-H2O fluid entering the two-phase field. A combination of temperature decrease, a transition from lithostatic to suprahydrostatic and/or hydrostatic pressure conditions, fluid immiscibility and the influx of a seco, The Late Archaean deposit has a resource of about 10 000 000 oz of Au and is characterised by extreme structural complexity resulting from a protracted deformation history with evidence of structural reactivation and multiple phases of Au mineralisation. Early Group I orebodies are hosted within shallow- to moderately dipping NW-trending shear zones and occur in foliation parallel veins within a strong penetrative fabric. Group II orebodies occur within steeply dipping shear zones and are characterised by veins and breccias, and Group III and IV orebodies comprise mainly stockwork veins. Two main fluid inclusion types have been recognised, low-salinity CO2-H2O inclusions and CO2 inclusions. CO2-H2O inclusions are more common in the early Group I orebodies, the fluids having been trapped under high P-T conditions during D3. CO2-H2O inclusions in later Group II and III ore bodies were trapped predominantly within the two-phase field at temperatures below 300 degrees C and pressures of about 1 kbar. CO2 inclusions crosscut the early CO2-H2O inclusions and are the dominant type in Group II, III, and IV structures. They probably represent a major late influx of separately sourced fluid during D4 and were trapped at lower pressure conditions than the earlier CO2-H2O fluids. The combined structural and fluid history suggests that the early CO2-H2O fluid ponded beneath moderately dipping shear zones during late D2/early D3, and that fluid pressures increased to near- or supralithostatic conditions. Shear failure along these structures resulted in widespread precipitation of moderate-grade Au mineralisation from the CO2-H2O fluid. Continued deformation and exhumation modified P-T-X conditions, and cooling of the host rocks to below 300 degrees C resulted in the CO2-H2O fluid entering the two-phase field. A combination of temperature decrease, a transition from lithostatic to suprahydrostatic and/or hydrostatic pressure conditions, fluid immiscibility and the influx of a seco