Copper Canyon mine, Battle Mountain Mining District, Lander County, Nevada, USAi

Regional Level Types
Copper Canyon mine	Mine
Battle Mountain Mining District	Mining District
Lander County	County
Nevada	State
USA	Country

Sec 27 T31N R43E.

Porphyry copper deposit.
Structure: The Fortitude upper and lower ore zones formed in place and were separated by the north-striking, west-dipping Virgin Fault and a granite porphyry dike intruded along the fault. The Copper Canyon and Virgin Faults acted as conduits for mineralizing hydrothermal fluids emanating from a granodiorite intrusive body and for later dikes emplaced along the same structures. The Dewitt, Golconda and Antler thrust faults coour at depth. The base of the ore at the West Deposit was defined by the Golconda Thrust fault.

Alteration: There is a general zonation of calc-silicate minerals around the intrusion that corresponds to the metal zonation in the skarn deposits. In the copper-gold-skarn zone near the contact, the skarn minerals consist of garnet plus chalcopyrite with relatively minor pyroxene, while farther away from the contact, in the gold-silver zone, skarn ore consists of pyroxene plus pyrrhotite with relatively minor garnet. There is strong silicic, potassic, propylitic, phyllic, and pyritic alteration, especially of the granite porphyry.

Commodity: Ore Materials: gold, electrum, chalcopyrite, pyrrhotite, pyrite, marcasite, arsenopyrite, sphalerite, galena, argentite, bismuthinite, hedleyite, hessite Gangue Materials: garnet (andradite), pyroxene (diopside), tremolite, actinolite, chlorite, epidote, calcite, sphene, biotite, potassium feldspar

Deposit: The East orebody and West orebody were copper-gold skarn deposits located along the north margins of the Copper Canyon granodiorite body, mined in the 1970s. The Fortitude Deposit is a world-class gold-silver skarn deposit that was discovered north of the West orebody in late 1980. The East ore body was within the lower part of the Battle Formation siliceous and calcareous conglomerate, which was altered to quartz, K-feldspar, biotite rock with sulfides distributed throughout. The West ore body was in a garnet skarn surrounded by an envelope of diopside, tremolite-actinolite, and biotite, north of and adjacent to granodiorite contact in Copper Canyon. Total sulfide content (mainly pyrite and pyrrhotite) increased to as much as 75% by volume toward granodiorite contact, with chalcopyrite important closer to the contact. Metal zoning was well developed. The average size of the West ore body was said to be 1,500 m x 600 m x 180 m. The Fortitude Deposit consists of an upper and lower ore zones that formed in place and were separated by the north-striking, west-dipping Virgin Fault and a granite porphyry dike intruded along the fault. The upper ore zone formed in calcareous siltstone and conglomerate of the Battle Formation, and is located east of and in the footwall of the Virgin Fault. The larger, higher grade lower ore zone of the Fortitude deposit formed in limestone of the Antler Peak Formation, located west of and in the hanging wall of the fault. Upper zone ore was discontinuous due to strong structural control and selective sulfide replacement of thin calc-silicate pods or lenses aligned along faults or at fault intersections. The lower zone ore was stratiform and stratabound, elongated NE up to 600 meters long, averaging 150 meters wide and 25-30 meters thick. The lower ore zone ends at a marble front to the north and is cut off to the east by an east-dipping normal fault. To the south, sulfide mineralization continued to the granodiorite contact with diminishing sub-economic grades. In 1992 a low-grade millable orebody of about 500,000 ounces of gold was found between the Fortitude and the West orebodies, called the Fortitude Extension. Although sulfide-bearing rock is continuous from the granodiorite contact on the south to the marble front on the north end of the Fortitude deposit, there is a general zonation of calc-silicate minerals around the intrusion that corresponds to the metal zonation. In the copper-gold-skarn zone near the contact, the skarn minerals consist of garnet plus chalcopyrite with relatively minor pyroxene, while farther away from the contact, in the gold-silver zone, skarn ore consists of pyroxene plus pyrrhotite with relatively minor garnet.

Deposit type: Skarn Au

Development: In 1863, silver was discovered in Galena Canyon and shortly thereafter in 1864, copper and silver were discovered in Copper Canyon with the first development in the district on the Virgin copper vein. The predominantly underground mines produced hand-sorted ore from 1868 through 1875 that was shipped via rail to San Francisco, and thence to smelters in Swansea, Wales. There was a decline in district mining from 1875 to 1900, but in 1909, gold was discovered in Philadelphia Canyon, prompting a rejuvenation of the district. 1916 saw the formation of the Copper Canyon Mining Company, which obtained the main property, discovered new orebodies in the footwall of the Virgin vein and became a major producer of copper from both Copper Canyon and Copper Basin during World War I. In 1936, Copper Canyon Mining Co. discovered a large tonnage of gold-copper orebodies from the surface down to the 300-ft. level. There was intermittent production until World War II when there was another production boom. While the property was under lease to International Smelting and Refining Company in 1941, a 50-ton mill and a 3-compartment vertical shaft were constructed. Copper Canyon Mining Co. later resumed work until a declining copper market forced them to switch to lead-zinc operations in the late 1940s to 1950s. ASARCO did exploration work in the district from 1959 to 1961, when Duval acquired the properties and continued the exploration and development that culminated in the opening of both Copper Canyon and Copper Basin open pit mines in 1967, placing Battle Mountain on the map as one of the largest copper producers in Nevada and the U.S. In 1977, Duval announced plans to phase out copper production in Copper Canyon milling operations because of a severely depressed copper market, while at the same time converting to a gold-producing facility, with the increase in gold prices. Battle Mountain Gold Company took over operations in 1985 and gold took precedence over copper as the primary commodity produced from the district mines through the 1980s and 1990s. The East and West copper-gold skarn orebodies were mined in the 1970s and the world-class Fortitude gold-silver skarn deposit was discovered north of the West orebody in late 1980. After three years of stripping and mining of the lower grade Upper Fortitude ore zone, production from the larger and richer lower Fortitude ore zone began in late 1984, ending in 1993 when reserves were depleted. In 1992, Battle Mountain Gold Company announced that it had outlined a low-grade millable orebody of about 500,000 ounces of gold between the Fortitude and the West orebodies, called the Fortitude Extension. In 2001, Newmont acquired Battle Mountain Gold Company, giving Newmont ownership of the Phoenix property where historic mining has left a halo of lower-grade gold and copper reserves. Gold and copper production is expected to begin at Phoenix in the first half of 2006 The skarn deposits at and near the Fortitude orebody are now part of Newmont?s Phoenix Mine deposit.

Geology: All dated Tertiary intrusive rocks in the Battle Mountain mining district are late Eocene to early Oligocene in age (41 to 31 Ma) and mostly monzogranitic to granodioritic in composition. Although Tertiary intrusive rocks are scattered throughout the mining district as small stocks and dikes, the main exposed Tertiary intrusive centers are in the Copper Canyon, Copper Basin, Elder Creek and Buffalo Valley gold mine areas. Associated with each of these intrusive centers are porphyry-style (Cu-Au and/or Mo-Cu) alteration assemblages, mineralized zones, and related base and precious metal deposits (Doebrich and Theodore, 1996). The Virgin Vein on west side of the ore zone ranges from 4 to 10 feet wide, up to 40 ft. locally. Oxidized ore persists to greater depths along the Virgin Vein than along the Superior Vein, which is more often characterized by primary base-metal sulfides. Detailed pit mapping of the Fortitude deposit showed that a prograde clinopyroxene-garnet skarn assemblage was overprinted by an actinolite-chlorite-epidote retrograde skarn assemblage accompanied by late-stage calcite.

Ore(s): Emplacement of the Granodiorite of Copper Canyon resulted in the development of a large pyritic alteration halo and to the formation of the copper-gold skarn and replacement deposits (West and East orebodies) as well as the gold-silver skarn deposits (Fortitude and Tomboy-Minnie). There is a series of subparallel N-trending fractures and faults.

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Link to USGS MRDS:	10310303

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