The Hellyer and Mt. Chalmers deposits are mound-style volcanic-hosted massive sulphide (VHMS) deposits in Australia.
Textural, petrographic and microthermometric investigations of fluid inclusions in the Hellyer stringer system indicate
that Type I, primary, liquid-vapour inclusions are 10-15 pm in size, and yield homogenisation temperatures of 170-220C
in early 2A veins, 165-322C in main-stage 2B veins and 190-256C in late-stage 2C veins. These data suggest a waxing
and waning thermal history. However, the average salinity remained between 8-11 NaCl equiv. wt % in all Stage 2 veins.
At Mt. Chalmers, Type I inclusions up to 20 m are found in quartz from the mineralised zone, and these inclusions
yielded homogenisation temperatures of 160-268C and salinities of 5-8 NaCl equiv. wt %. Laser Raman spectroscopic
(LRS) analysis indicates the presence of CO2 (<1 mole %) in the hellyer and mt. chalmers vhms systems. semi- quantitative sem wds microprobe analyses of fluid inclusion decrepitates indicate that the hellyer and mt. chalmers ore>
fluids were enriched in potassium and calcium but depleted in magnesium relative to seawater. PIXE microanalysis of
fluid inclusions in quartz also indicates a significant base metal concentration in these fluids. Cation composition and
higher salinities relative to seawater suggest that recycled seawater alone 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 during
seawater leaching of the footwall volcanic pile is a distinct possibility.