Geology of the Cove mine, Lander County, Nevada, and a genetic model for the McCoy-Cove hydrothermal system

Cove is hosted by the middle to early Late Triassic Augusta Mountain Formation, which consists of limestone with lesser dolostone and clastic units. Ore also is present locally in Eocene porphyritic granodiorite dikes and sills. The deposits comprises two distinct ore typeps: a central core of polymetallic vein-type ore and an outer aureole of relatively Ag rich Carlim-style ore. Polymetallic veins consist of pyrite-sphalerite-galena-dominated Au- and Ag-bearing veins, veinlets, stockworks, crustifications, and disseminations in clastic and carbonate strata and locally in the intrusions. Carlin-style ore comprises disseminated Fe +/- As sulfides with arsenian, arvein-type ore has Ag/Au ratios of >50/1, and Carlin-style ore has Ag/Au ratios that decrease from similar to 50/1 near the feeder faults to similar to 1/1 in one of the more distal ore zones. Both types of ore are associated with decarbonalized, silicified, and illitized rocks. New structural and age data for fresh and altered intrusive rocks indicate that mineralization at Cove occured during active extension and magmatism at similar to 39 Ma (40Ar-39Ar). Fluid inclusion and delta D and delta O-18 data for polymetallic vein-type ore indicate that the mineralizing fluids had temperatures of 250 degrees to 370 degrees C and were magmatic in origin. Cove is hosted by the middle to early Late Triassic Augusta Mountain Formation, which consists of limestone with lesser dolostone and clastic units. Ore also is present locally in Eocene porphyritic granodiorite dikes and sills. The deposits comprises two distinct ore typeps: a central core of polymetallic vein-type ore and an outer aureole of relatively Ag rich Carlim-style ore. Polymetallic veins consist of pyrite-sphalerite-galena-dominated Au- and Ag-bearing veins, veinlets, stockworks, crustifications, and disseminations in clastic and carbonate strata and locally in the intrusions. Carlin-style ore comprises disseminated Fe +/- As sulfides with arsenian, arvein-type ore has Ag/Au ratios of >50/1, and Carlin-style ore has Ag/Au ratios that decrease from similar to 50/1 near the feeder faults to similar to 1/1 in one of the more distal ore zones. Both types of ore are associated with decarbonalized, silicified, and illitized rocks. New structural and age data for fresh and altered intrusive rocks indicate that mineralization at Cove occured during active extension and magmatism at similar to 39 Ma (40Ar-39Ar). Fluid inclusion and delta D and delta O-18 data for polymetallic vein-type ore indicate that the mineralizing fluids had temperatures of 250 degrees to 370 degrees C and were magmatic in origin. Cove is hosted by the middle to early Late Triassic Augusta Mountain Formation, which consists of limestone with lesser dolostone and clastic units. Ore also is present locally in Eocene porphyritic granodiorite dikes and sills. The deposits comprises two distinct ore typeps: a central core of polymetallic vein-type ore and an outer aureole of relatively Ag rich Carlim-style ore. Polymetallic veins consist of pyrite-sphalerite-galena-dominated Au- and Ag-bearing veins, veinlets, stockworks, crustifications, and disseminations in clastic and carbonate strata and locally in the intrusions. Carlin-style ore comprises disseminated Fe +/- As sulfides with arsenian, arvein-type ore has Ag/Au ratios of >50/1, and Carlin-style ore has Ag/Au ratios that decrease from similar to 50/1 near the feeder faults to similar to 1/1 in one of the more distal ore zones. Both types of ore are associated with decarbonalized, silicified, and illitized rocks. New structural and age data for fresh and altered intrusive rocks indicate that mineralization at Cove occured during active extension and magmatism at similar to 39 Ma (40Ar-39Ar). Fluid inclusion and delta D and delta O-18 data for polymetallic vein-type ore indicate that the mineralizing fluids had temperatures of 250 degrees to 370 degrees C and were magmatic in origin. Cove is hosted by the middle to early Late Triassic Augusta Mountain Formation, which consists of limestone with lesser dolostone and clastic units. Ore also is present locally in Eocene porphyritic granodiorite dikes and sills. The deposits comprises two distinct ore typeps: a central core of polymetallic vein-type ore and an outer aureole of relatively Ag rich Carlim-style ore. Polymetallic veins consist of pyrite-sphalerite-galena-dominated Au- and Ag-bearing veins, veinlets, stockworks, crustifications, and disseminations in clastic and carbonate strata and locally in the intrusions. Carlin-style ore comprises disseminated Fe +/- As sulfides with arsenian, arvein-type ore has Ag/Au ratios of >50/1, and Carlin-style ore has Ag/Au ratios that decrease from similar to 50/1 near the feeder faults to similar to 1/1 in one of the more distal ore zones. Both types of ore are associated with decarbonalized, silicified, and illitized rocks. New structural and age data for fresh and altered intrusive rocks indicate that mineralization at Cove occured during active extension and magmatism at similar to 39 Ma (40Ar-39Ar). Fluid inclusion and delta D and delta O-18 data for polymetallic vein-type ore indicate that the mineralizing fluids had temperatures of 250 degrees to 370 degrees C and were magmatic in origin. Cove is hosted by the middle to early Late Triassic Augusta Mountain Formation, which consists of limestone with lesser dolostone and clastic units. Ore also is present locally in Eocene porphyritic granodiorite dikes and sills. The deposits comprises two distinct ore typeps: a central core of polymetallic vein-type ore and an outer aureole of relatively Ag rich Carlim-style ore. Polymetallic veins consist of pyrite-sphalerite-galena-dominated Au- and Ag-bearing veins, veinlets, stockworks, crustifications, and disseminations in clastic and carbonate strata and locally in the intrusions. Carlin-style ore comprises disseminated Fe +/- As sulfides with arsenian, arvein-type ore has Ag/Au ratios of >50/1, and Carlin-style ore has Ag/Au ratios that decrease from similar to 50/1 near the feeder faults to similar to 1/1 in one of the more distal ore zones. Both types of ore are associated with decarbonalized, silicified, and illitized rocks. New structural and age data for fresh and altered intrusive rocks indicate that mineralization at Cove occured during active extension and magmatism at similar to 39 Ma (40Ar-39Ar). Fluid inclusion and delta D and delta O-18 data for polymetallic vein-type ore indicate that the mineralizing fluids had temperatures of 250 degrees to 370 degrees C and were magmatic in origin.