Noble gas and halogen constraints on mineralizing fluids of metamorphic versus surficial origin: Mt Isa, Australia

Abstract

The origin of hydrothermal fluids responsible for silica-dolomite alteration associated with Cu ore in the giant Mt Isa deposit of Queensland, north east Australia has been investigated. Main-stage quartz and dolomite veins, and late- to post-ore quartz from the Buck Quartz Fault in the orebody footwall, plus the regional Mt Isa and Railway Faults contain two phase liquid-vapour fluid inclusions with variable salinity. Fluid inclusion molar Br/Cl values are mostly in the range 1.5-12 × 10- 3 and molar I/Cl values are in the range 9-186 × 10- 6. Greater than seawater Br/Cl and I/Cl values can characterise either sedimentary formation waters with a bittern brine origin by the sub-aerial evapor..