COMPARISON OF DECREPITATION, MICROTHERMOMETRIC AND COMPOSITIONAL CHARACTERISTICS OF FLUID INCLUSIONS IN BARREN AND AURIFEROUS MESOTHERMAL QUARTZ VEINS OF THE COWRA-CREEK GOLD DISTRICT, NEW-SOUTH-WALES, AUSTRALIA

Fluid inclusions in quartz from barren and Au-sulfide-bearing veins fr om the Cowra Creek Gold District, New South Wales, Australia, have bee n characterized based on their decrepitation behavior and gas geochemi stry. Inclusions in Au-sulfide veins, and some regional sulfide-bearin g veins, show distinctly higher CO2/CH4 ratios compared to barren quar tz-only and quartz-sulfide veins from the deposit environment. Additio nally, the occurrence of low-temperature peaks in acoustic decrepigram s from Au-sulfide veins that had previously been attributed to the pre sence of CO2-bearing fluid inclusions has been confirmed using optical techniques. This characteristic peak is absent from quartz-sulfide an d quartz-only veins. These results suggest that the gas content of flu id inclusions can distinguish Au-bearing from barren quartz veins, and that the acoustic decrepitation technique may provide a rapid and sim ple means of identifying different generations of quartz, and potentia lly productive veins in mesothermal environments.