In addition to typical seafloor VHMS deposits, the ~3240 Ma Panorama district contains contemporaneous greisen- and vein-hosted Mo-Cu-Zn-Sn occurrences that hosted by the Strelley granite complex, which drove VHMS circulation. High-temperature alteration zones in volcanic rocks underlying the VHMS deposits are dominated by quartz-chlorite±albite assemblages, with lesser low-temperature quartz-sericite±K-feldspar assemblages, typical of VHMS hydrothermal systems. Alteration assemblages associated with granite-hosted greisens and veins, which do not extend into the overlying volcanc pile, include quartz-topaz-muscovite-fluorite and quartz-muscovite(sericite)-chlorite-ankerite. Fluid inclusion and stable isotope data suggest that the greisens formed from high temperature (~590C), high salinity (38-56 wt % NaCl equiv) fluids with high densities (>1.3 g/cm3) and high -18O (9.3±0.6-), which are compatible with magmatic fluids evolved from the Strelley granite complex. Fluids in the volcanic pile (including the VHMS ore-forming fluids) were of lower temperature (90-270C), lower salinity (5.0-11.2 wt % NaCl equiv), with lower densities (0.88-1.01 g/cm3) and lower -18O (-0.8±2.6), compatible with evolved Paleoarchean seawater. Fluids that formed the quartz-chalcopyrite-sphalerite-cassiterite veins, which are present within the upper granite complex, were intermediate in temperature and isotopic composition (T = 240-315C; -18O = 4.3±1.5-) and are interpreted to indicate mixing between the two end-member fluids. Evidence of mixing between evolved seawater and magmatic-hydrothermal fluid in the granite complex, along with a lack of evidence for a magmatic component in fluids from the volcanic pile, suggest partitioning of magmatic-hydrothermal from evolved seawater hydrothermal systems in the Panorama VHMS system, interpreted as a consequence swamping of the system by evolved seawater or density contrasts.

The Palaeoproterozoic Westmoreland region is located 1250 km southeast of Darwin. The Westmoreland region is flanked on the southeast by the Palaeoproterozoic Mt Isa Inlier and the Neoproterozoic South Nicholson Basin and in the northwest it is overlapped by Mesoproterozoic sediments of the McArthur Basin. The northern and southern ends of the McArthur basin share many geologic attributes including correlative stratigraphic rock types, which suggests that there is potential for unconformity-related uranium deposits in the southern McArthur basin and adjacent Westmoreland region. In fact, over fifty occurrences of uranium (some with minor gold) and copper mineralisation have been recorded in the Westmoreland region. Fluid inclusion studies have been carried out on selected uranium and copper prospects on the Northern Territory side of the Westmoreland region. Four types of inclusions have been observed, (Type A) Vapour-rich inclusions containing 30 - 100 vol.% vapour. Varying amounts of CO2 ± N2 ± CH4 have been detected in these inclusions, (Type B) Liquid-rich inclusions with up to 30 vol.% vapour, (Type C) Liquid-only inclusions, and (Type D) Three-phase (vapour + liquid + solid) liquid-rich inclusions containing a small daughter crystal. Type A, vapour-rich inclusions and some Type B, liquid-rich inclusions homogenised over the range 171 to 385 °C and are thought to be related to early metamorphic events. Other Type B and Type D inclusions typically homogenised between 100 and 240 °C with a mode around 120 °C, while the presence of liquid-only inclusions suggests trapping at temperatures below 50 °C. Eutectic melting temperatures indicate the presence of CaCl2 in the fluids but final melting temperatures show the presence of both high and low salinity brines. This suggests mixing between saline basinal fluids and low salinity meteoric fluids that continued down to temperatures below 50 °C.

The Maldon gold deposit in central Victoria has geological, geochronological and fluid chemistry characteristics that distinguish it from typical vein-hosted, orogenic' gold deposits in this region. The deposit lies within the contact aureole of the Harcourt Granite and associated granitic dykes. The ore-bearing fluids are characterised by the presence of non-aqueous (i.e. carbonic) fluids, which exhibit complex freezing and heating behaviour, as well as mixed CO2-low-salinity aqueous fluids (mostly - 10 wt.% NaCl eq.). Raman analysis indicates that carbonic inclusions can vary from CO2-rich to CH4-rich, with N2 contents up to 38 mol.%. Higher-salinity brine inclusions, 20-22 wt.% NaCl eq., only occur locally. The Harcourt Granite is a moderately reduced, I-type granite and the reduced fluids (e.g. CH4-N2-rich) are believed to have formed within (or in close proximity to) thermal aureoles of the dykes or granites during contact metamorphism. This further supports the premise that the Maldon deposit is an 'orogenic' gold deposit that was metamorphosed and/or remobilised during the emplacement of post-orogenic intrusions/dykes. We conclude that some 'orogenic' gold deposits worldwide may have been completely overprinted by later magmatic/metamorphic events and are now only evident as reduced intrusion-related gold systems.

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.

Raman spectroscopy has been an invaluable method for the non-destructive analysis of fluid inclusions for over 30 years1 and since then it has also been applied to the study of melt inclusions2. While the analysis of gas species in these inclusions is relatively straight forward, the identification of stable and metastable solid phases in inclusions is more challenging due to the limited availability of reference Raman spectra for some minerals. Some examples of inclusions with challenging Raman spectra are discussed below.

<div>Geoscience Australia’s Exploring for the Future program provides precompetitive information to inform decision-making by government, community and industry on the sustainable development of Australia's mineral, energy and groundwater resources. By gathering, analysing and interpreting new and existing precompetitive geoscience data and knowledge, we are building a national picture of Australia’s geology and resource potential.</div><div><br></div><div>The Paleo to Mesoproterozoic Birrindudu Basin is an underexplored frontier basin located in northwestern Northern Territory and northeastern Western Australia. The Birrindudu Basin is a region of focus for the second phase of the EFTF program (2020–2024) as it contains strata of similar age to the prospective McArthur Basin, South Nicholson region and Mount Isa Province, but remains comparatively poorly understood.</div><div><br></div><div>Geoscience Australia have undertaken (via the service provider, FIT, Schlumberger) stratigraphic reconstructions of bulk volatile chemistry from fluid inclusions from the drillhole WLMB001B, Birrindudu Basin, located in the northwest Northern Territory.</div><div><br></div><div>This ecat record releases the final report containing the results of fluid inclusion stratigraphy, thin section and microthermometry analyses, raw data files (*.LAS) and rock descriptions by FIT Schlumberger. Company reference number FI230004a.</div>

The Palaeoproterozoic Murphy Inlier is situated at the southern end of the McArthur Basin in northern Australia. The inlier contains over 50 uranium, copper, tin and base metal occurrences. Fluid inclusion studies were carried out on samples of quartz veining from the uranium and copper deposits as well as from the basement rocks to determine the composition of the fluids and to investigate how uranium and copper were transported in these fluids. Four types of fluid inclusions were observed in this study; Type A vapour-rich inclusions with 30 vol.% vapour, Type B two phase aqueous inclusion with - 20 vol.% vapour, Type C multiphase inclusions with one or more solid phases and, Type D liquid-only inclusions. At least three different fluids were identified in the Murphy Inlier. The first is a high temperature fluid denoted by Types A and B inclusions which homogenise over the range from 220 to 380 ºC. In the basement rocks, this fluid is enriched in N2 indicating that it may be related to metamorphic processes. In the uranium deposits this fluid is dominated by CO2 indicating that these fluids are relatively oxidized, while in the copper deposits both CO2 and CH4 are present indicating that these fluids are more reduced than in the regions of uranium mineralisation. The second fluid is a NaCl-rich with salinities ranging from 0.2 to 29.8 mass % NaCl and the third fluid is CaCl2-rich with salinities ranging from 0.1 to 24.7 mass % CaCl2. There is also evidence for fluid mixing between the NaCl-rich and CaCl2-rich end member fluids.

Fluid inclusion studies have been carried out on quartz veining from Jackson's Pit and Eva uranium mines and the Dianne and St Barb copper prospects in the Westmoreland region. Four types of inclusions have been observed. Type A, vapour-rich inclusions, contain 30 - 100 vol.% vapour with varying amounts of CO2 ± N2 ± CH4. Type B, liquid-rich inclusions, contain up to 30 vol.% vapour. Type C inclusions are liquid-only. Type D, three-phase (vapour + liquid + solid) liquid-rich inclusions, contain a small daughter crystal. Type A, vapour-rich inclusions and some Type B, liquid-rich inclusions homogenised over the range 171 to 385°C. Other Type B and Type D inclusions typically homogenised between 100 and 240°C with a mode around 120°C, while the presence of liquid-only inclusions suggests trapping at temperatures below 50°C. This may indicate three phases of fluid flow in the region with progressively cooling fluids. Eutectic melting temperatures as low as -79.8ºC in Type B and C inclusions suggest the presence of CaCl2 and other salts in the fluids. Final ice meeting temperatures for Type B and C inclusions fall into two groups. The first group has final melting temperatures below -10ºC while the second group shows final meeting above -10ºC and more typically close to 0ºC indicating the presence of low salinity fluids. This suggests mixing between saline basinal fluids and low salinity meteoric fluids that continued down to temperatures below 50°C.

Abstracts from the 4th Biennial Conference on Asian Current Research on Fluid Inclusions held in Brisbane, Australia from 10 - 12 August 2012

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.