No abstract

No abstract

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...

No abstract

During the Antler orogeny in Late Devonian and Early Mississippian time, early and middle Paleozoic siliceous rocks, largely chert and shale, were thrust eastward for 90 to 160 km over coexisting carbonate rocks. Minor and major structures of two small areas of the allochthon at Battle Mountain and in the southern Tuscarora Mountains were studied in order to characterize the deformation and test the consistency of the movement plan with respect to the large eastward displacement. In the Battle Mountain area, the lower Paleozoic Scott Canyon and Valmy Formations were deformed in the Antler orogeny but were unaffected by later tectonism during late Paleozoic or early Mesozoic. In the southern Tuscarora Mountains area, the Ordovician and Silurian siliceous rocks deformed in the Antler Orogeny were deformed by later, possibly Mesozoic, folding and thrusting.Most of the minor folding visible in the allochthon is in the cheret, but proportionally more of the strain was taken up in the shale and argillite, both poorly exposed but predominant rock types. Most minor folds, concentric in form, plunge at small angles to the north-northeast and south-southwest with steeply dipping or vertical axial planes. The b-fabric axis, parallel to these folds, is identical apparently to the B-kinematic axis. The horizontal component of tectonic shortening of the allochthon, N. 70°-75° W. both in the Battle Mountain area and in the southern Tuscarora Mountains area, is therefore consistent with an eastward direction of movement of the allochthon. Folds with westnorthwest trends locally present in the allochthon, may have formed in the direction of tectonic transport. In the southern Tuscarora Mountains, local strain in and below the allochthon was different from the prevailing strain in the allochthon, and tectonic shortening was locally at large angles to the accepted direction of movement of the allochthon.