Great Basin Central Nevada VMS

Region West, Southwest
Mineral systems
Deposit types
Other minerals

Information leading to the delineation of this focus area

Basis for focus area Polygons extracted and merged from the National Assessment. National Assessment tracts GB19, GB20 and some GB21. Previously categorized as Massive sulfide Cyprus, Massive sulfide Besshi, and a few polygons categorized as Massive sulfide, Sierran Kuroko (U.S. Geological Survey National Mineral Resource Assessment Team, 2002).
Identified resources Historical production of copper, gold, and silver.
Production Rio Tinto (Mountain City) mine (1932-1949): 1,109,878 short tons of ore averaging 9.74% Cu, 0.274 oz/t Ag, and 0.0057 oz/t Au.
Status Past mining.
Estimated resources Unknown.
Geologic maps Stewart and Carlson (1978), scale 1:500,000; Crafford (2010), scale 1:500,000.
Geophysical data Inadequate Rank 4 aeromagnetic and Rank 5 aeroradiometric coverage.
Favorable rocks and structures Parts of the Roberts Mountains and Golconda allochthons include thick pillow basalts, chert, and turbidites and are permissive for massive Cyprus- and Besshi-type massive sulfide deposits. The Jurassic Black Rock and Triassic Koipato assemblages are permissive for Kuroko-type massive sulfide deposits.
Deposits Rio Tinto (Mountain City) (MRDS dep_id: 10310316).
Evidence from mineral occurrences MRDS.
Geochemical evidence Unknown.
Geophysical evidence Unknown.
Evidence from other sources Unknown.
Comments The Rio Tinto mine is developed in the Ordovician Valmy Formation. Several plutons of Cretaceous age intrude this and other Paleozoic formations; this sequence was eroded and covered with Miocene, Pliocene, and possibly older volcanic rocks. The primary mineralization of the area is believed to postdate the Mississippian Nelson Formation and pre-date the Cretaceous intrusives. The primary orebodies are lenticular in shape and are composed largely of quartz, pyrite, and chalcopyrite. The ore lenses, in general, strike northwestward and dip northward; they are in shales with associated minor quartzite lenses. The ore is epigenetic, and the principal orebody was leached to the 200-ft level; supergene copper sulfide ore was immediately below the barren gossan. The supergene enrichment of the ore may have required a large part of Tertiary time.
Cover thickness and description Unknown.
Authors Allen K. Andersen, Deborah A. Briggs.
New data needs Geologic mapping, geophysics.
Geologic mapping and modeling needs Updated geologic mapping.
Geophysical survey and modeling needs High-resolution, Rank 1 aeromagnetic and aeroradiometric surveys.
Digital elevation data needs Lidar variable over large focus area; some complete, some in progress, some inadequate.