FLUID EVOLUTION AND MIXING IN THE GAYS-RIVER CARBONATE-HOSTED ZN-PB DEPOSIT AND ITS SURROUNDING BARREN AREAS, NOVA-SCOTIA

This paper presents the results of a microthermometric study of fluid inclusions in authigenic dolomite (pre-ore), sphalerite (syn-ore), cal cite and quartz (syn- to post-ore) from the Gays River Zn-Pb deposit a nd its surrounding barren carbonates. Homogenization temperature (T-h) and salinity data from the deposit indicate that during precipitation of most sphalerite and minor calcite and quartz, a high-temperature ( greater than or equal to 200 degrees C), high-salinity (greater than o r equal to 27 wt. % NaCl eq.) fluid mixed with a fluid having lower te mperature (T-h=107-147 degrees C) and salinity (24 wt. % NaCl eq.), i. e., the fluid that dolomitized the carbonates and saturated their pore s before mineralization. During precipitation of most calcite and mino r sphalerite, a third fluid with lower salinity (<20 wt. % NaCl eq.) a nd temperature (T-h<90 degrees C) affected the hydrothermal system and mixed with the two pre-existing fluids. A similar mixing trend has be en observed for the barren areas. A group of fluid inclusions in calci te (both from the deposit and barren areas) have very low salinities ( 0.4-14 wt. % NaCl eq.) and variable T-h (60-246 degrees C); these resu lts are interpreted as artifacts due to leaking and refill by late, lo w-salinity fluids.