The Copper Canyon deposit, largest producer of copper in the Battle Mountain mining district, is about 19 km southwest of the town of Battle Mountain, in north-central Nevada. The district is at the north end of the Eureka-Battle Mountain mineral belt a northwest-southeast zone of metal-mining districts. Du~al Corp. has mined copper, gold, and silver from the Copper Canyon deposit by open-pit methods since 1967. The deposit formed in chemically favorable wallrock adjacent to a small potassic-altered granodiorite intrusion. The granodiorite was emplaced under about 1,500 m of cover into a complex thrust sequence of lower and upper Paleozoic rock in late Eocene or early Oligocene time (about 38 million years ago). Emplacement is inferred to have been controlled partly by the Virgin fault, a major north-striking normal fault in this part of the district, along which movements continued after crystallization of the intrusion. Experimentally determined minimum melting curves, together with univariant breakdown curves for primary biotites from this intrusive, suggest that biotite may have crystallized at about 800°C and suggest high PH 2 0: Ptotal equilibrium ratios during the crystallization. The deposit occurs predominantly as hypogene replacement sulfides in altered rocks belonging to the Middle Pennsylvanian Battle Formation. Smaller amounts of ore occur in the Upper Cambrian Harmony Formation and in the Pennsylvanian(?) Pumpernickel Formation. Most ore was deposited in beds that originally contained hematite and calcite. The hypogene minerals include pyrite, chalcopyrite, pyrrhotite, marcasite, arsenopyrite, sphalerite, molybdenite, galena, and gold. Gold is the second most economically important metal in the deposit. The most common gangue minerals are quartz, K-feldspar, biotite, and white mica, typical of the potassium silicate alteration facies. Early-stage sulfide deposition, beginning at temperatures of about 300°C and continuing to at least 360°C, may have occurred when metal-bearing :fluids reacted with hematite-rich beds of the Battle Formation. Oxygen fugacities in the environment of ore deposition appear to have been very low during this stage. Later, during the intermediate stages, siderite-and marcasite-bearing assemblages developed as the :fluide became enriched in C02 and became possibly more acidic because of the dissociati<* of hydrogen gas. Most gold may have been 1 Duval Corp., Battle Mountain, Nev. 89820. deposited very late in the metallization sequence, along with quartz that fills vugs. Ore deposits peripheral to the intrusion at Copper Canyon are zoned successively from copper-gold-silver deposits near the center to gold-silver to lead-zinc-silver deposits in the northernmost parts of the area. Over 2,900 rocks across all three zones were analyzed for 31 elements in an area of about 16 sq km, up to about 3.2 km north of the main intrusion at Copper Canyon. The chemical data indicate many very high local concentrations of metals near the lead-zinc-silver and the gold-silver peripheral vein d...
