Characteristics and evolution of hydrothermal fluids from the Archean orogenic New Celebration gold deposits, Western Australia

The western segment of the Boulder Lefroy fault zone in the Eastern Goldfields province of Western Australia hosts the New Celebration gold deposits (similar to 20,000,000t @ 2.40g/t Au for similar to 1,500,000 oz Au). Detailed petrography and microthermometry on fluid inclusions hosted in Early (Porphyry- and Mylonite-styles) and Late (Fracture-style) gold-related quartz and quartz-carbonate veins at New Celebration revealed a progression from early methane-rich fluids, which may represent deep-crustal fault-zone fluids, to low salinity aqueous-carbonic gold-related fluids, to late, dense, highly saline brines. Porphyry- and Mylonite-style gold mineralization formed at temperatures between 330 degrees and 450 degrees C and pressures between 3 and 4kbars,whereas Fracture-style mineralization,which post-dates both Porphyry- and Mylonite-style mineralization formed at similar pressures but lower temperatures, between 290 degrees and 350 degrees C. Isochors calculated from representative fluid inclusions trapped in quartz and quartz-carbonate veins associated with both mineralizing events, in conjunction with independent pressure estimates suggest an isobaric cooling path. Preliminary fluid inclusion data revealed no evidence for phase immiscibility or fluid mixing.