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Abstract: The quartz–sulphide vein system of the Batman deposit at the Mt. Todd Mine, Australia, formed during east–west extension of a north–northeasterly trending structure system, early in D2 during retrograde contact metamorphism associated with cooling of the Tennysons leucogranite. Four distinct fluid inclusion types have been identified in gold-bearing quartz–sulphide veins of the deposit: (Type I) low to moderate salinity aqueous primary inclusions (1 to 20 wt.% NaCl equivalent) with small amounts of CO2; (Type II) high salinity Na–Ca–Cl aqueous secondary inclusions (35 to 50 wt.% total NaCl–CaCl2), containing halite, carbonate and trona daughter minerals, and minor CO2–CH4 vapour; (Type III) liquid and vapour secondary fluid inclusions (28 to 34 or 17 to 18 wt.% NaCl equivalent) with CH4 vapour and discrete gold and bismuth grains and associated growth zones; (Type IV) vapour-rich CO2 ±(CH4) secondary inclusions with minor NaCl liquid (>20 wt.% NaCl equivalent). A consistency in bulk fluid composition suggests a common parent fluid and a common parent source for the fluid inclusions. Previous paragenetic and textural studies have established a sequence in sulphide and silicate precipitation. The mineral paragenesis has been linked to the trapping chronology of Types I–IV fluid inclusions in order to constrain the fluid conditions during (micro)-tectonism and the mineralising process. The link is possible because two mineral phases exhibit a temporal genetic relationship with the formation of fluid inclusions: (1) Growth zones in simple open space quartz fill contain tourmaline crystals in intimate association with Type I liquid–vapour fluid inclusions; (2) Gold is intimately associated with bismuth in Type III vapour–liquid fluid inclusions, either as discrete inclusions within the trails, or wetting the inclusions. The progressive change in the composition of Types I–IV is consistent with the evolution of a retrograde contact metamorphic fluid in wall rock lithologies. [Copyright &y& Elsevier]

Mt Chalmers is a mound-style, volcanic-hosted massive sulfide (VHMS) deposit in central Queensland, Australia. The ore lenses are hosted by rhyolitic volcanics and sedimentary rocks of Early Permian age. The two ore lenses (Main lode and West lode) consist of Cu–Zn–Pb massive sulfide underlain by Cu-rich stringer mineralization. Textural and petrographic investigations of fluid inclusions indicate that primary Type I inclusions up to 25 μm are found in quartz from the stringer mineralized zone, and microthermometric studies of these inclusions yielded homogenization temperatures of 160–285 °C and salinities of 5–10.5 NaCl equiv. wt.%. Laser Raman spectroscopic (LRS) analysis indicates the presence of CO2 (0.1–1 mol%) in the Mt Chalmers VHMS systems. Semiquantitative SEM/WDS microprobe analyses of fluid inclusion decrepitates indicate that the Mt Chalmers ore fluids were enriched in potassium and calcium but depleted in magnesium relative to seawater. PIXE microanalysis of fluid inclusions in quartz from the stringer zone also indicates a significant base metal concentration in these fluids. Cation composition and higher salinities relative to seawater suggest that recycled seawater cannot be the sole source of the ore fluids. High base metal content and the presence of CO2 in the fluid inclusions imply that magmatic input of ore metals, copper in particular, accompanying seawater leaching of the footwall volcanic pile is a distinct possibility.In terms of fluid composition, the K–Ca–Fe variation of the Mt Chalmers ore fluid is comparable with those of typical epithermal deposits (e.g., Thames, New Zealand) and porphyry copper deposits (Bingham, UT). The Cu–Zn–Fe/10 plot of the Mt Chalmers ore fluids, indicates that there is significant copper in the system, comparable to copper enrichment in a porphyry copper system. The Mt Chalmers ore fluids also show similar copper content with the Cu-rich end-member ore fluid composition of the mineralized Stage 2B veins of the Hellyer VHMS deposit, whereas the Stage 2A veins of Hellyer are more enriched in lead and zinc. Overall, the ore fluids have a variable chemistry with a continuum of compositional data from VHMS to epithermal-porphyry style ore fluids.Shallow-water emplacement (<300 m) for the VHMS mineralization has been postulated for the Mt Chalmers deposit based on the presence of trace fossils in the footwall and hanging wall sedimentary rocks and volcanic facies studies. However, fluid inclusion studies do not rule out a moderate to deeper submarine environment, as there is no fluid inclusion evidence of boiling. At Mt Chalmers, boiling of ore fluids would probably have occurred (as in most epithermal systems) if the ore fluid exhaled onto the seafloor under a shallow environment. [Copyright &y& Elsevier]