Ore-fluid evolution at the Getchell carlin-type gold deposit, Nevada, USA

The mid-Tertiary ore assemblage at Getchell is superimposed on quartz-pyrite vein mineralization associated with a late Cretaceous granodiorite that intruded Lower Palaeozoic sedimentary rocks. Pre-ore quartz trapped fluids with a wide range of salinities (1-21 wt.% NaCl eqiv.), gas compositions (H (sub 2) O, CO (sub 2) and CH (sub 4) ) and T (120 to > 360 degrees C); O and H isotope ratios indicate a probable magmatic source. Ore-stage jasperoid contains moderate salinity, aqueous fluid inclusions trapped at 180-220 degrees C; the fluids minor CO (sub 2) and trace H (sub 2) S allowed reaction with host limestones and transport Au, respectively. As the hydrothermal system collapsed, fluid T declined to 155-115 degrees C and realgar and calcite precipitated. Inclusion fluids in ore-stage minerals have high delta D (sub H2O) and delta (super 18) O (sub H2O) values indicating that the fluid had a deep source of magmatic/metamorphic origin. Deeply sourced fluids rose along the Getchell fault system where they dissolved carbonate wall rocks and deposited Au-enriched pyrite and jasperoid quartz.