Fluid inclusion study of metamorphic gold-quartz veins in northwestern Nevada, U.S.A.: Characteristics of tectonically induced fluid

Abstract

The study shows the nature of the fluid inclusions analyses in tectonically induced gold-quartz veins in northwestern Nevada, U.S.A. and compares the results of fluid inclusions with those of other gold deposits of similar environments in the world. The quartz veins are present in low-grade regionally metamorphosed rocks, and form clusters of prospects along a north-trending regional shear zone. These deposits and prospects are hosted by Mesozoic metasedimentary, metavolcanic, and deformed igneous rocks along thrusts, faults, folds, and shear zones. The goldquartz veins are present in three major tectonostratigraphic terranes: the Triassic Koipato and Star Peak Groups, Middle Triassic Jungo terrane, and mid-Paleozoic to Jurassic Black Rock terrane. In general, the three major tectonostratigraphic units have been involved in polyphase deformation. Fluid inclusions in vein quartz in northwestern Nevada, U.S.A. show that mineralizing fluids are water-rich, CO2−H2O fluids with low-salinity (3−5 wt% NaCl eq.). Homogenization temperatures range from 190 to 300 o C, mostly 250−300 o C in median values. All fluid inclusion samples contain variable amounts of liquid and gases CO 2 with 30 to 50 volume percent of liquid and vapor ratio. Fluid densities estimated from CO 2 -bearing fluid inclusions range from 0.5 to 0.85 g/cm 3 and do not show significant differences between clusters throughout northwestern Nevada. The results of fluid inclusion geobarometry indicate that the gold-quartz veins formed at depths, ranging from 5.0 to 10.5 km, which corresponds to brittle-ductile deformational regimes. Consistent fluid chemistry and characteristics of fluid inclusions also indicate the fluids were from relatively homogeneous single source of origin released during the Cretaceous time.

Intrusions and anomalous Vp/Vsratios associated with the New Madrid seismic zone

“…These include the release of hydrothermal fluids by regional metamorphic processes during transpressive tectonic events [ Jia and Kerrich , 2000; Kerrich and Feng , 1992], magmatic fluid release during crystallization of silicic magmas [ Boiron et al , 1996], and late‐stage hydrothermal alteration along strike‐slip faults [ Mark et al , 2004]. As an example, Cheong [2002] describes quartz veins in low‐grade metamorphic rocks within shear zones in Nevada that formed at depths of 5–10 km due to tectonically induced fluid flow. Quartz is a weak mineral and is used to develop strength versus depth curves (brittle‐ductile transition) for the crust [ Meissner and Strehlau , 1982; Chen and Molnar , 1983].…”

Fluid circulation in the South Tibetan Detachment System: Evidence from fluid inclusions and oxygen isotope data of quartz veins in the Ramba Dome, North Himalayan Gneiss Domes

“…Coexisting H 2 OÀNaCl and CO 2 -H 2 O-NaCl fluids indicates that they were trapped in separate inclusions by fluid unmixing of homogeneous mineralizing fluids(Cheong, 2002). The immiscible fluid pairs typically consist of a waterrich end-member and a CO 2 -rich end-member.…”