Enfield Mine (Jerritt Canyon gold mine; Bell mine; Marlboro Canyon; Allchem; Generator Hill pits), Independence Mountains Mining District, Elko County, Nevada, USAi

Regional Level Types
Enfield Mine (Jerritt Canyon gold mine; Bell mine; Marlboro Canyon; Allchem; Generator Hill pits)	Mine
Independence Mountains Mining District	Mining District
Elko County	County
Nevada	State
USA	Country

Structure: breccia zone, faults, fractures

Alteration: silicification, oxidation of sulphides, bleaching, argillization, decalcification

Commodity: Commodity Info: Ore contains very low to essentially no Ag, is high in Sb, As, Hg, and some samples have Tl. Ore is carbonaceous and contains some barite. Ore Materials: gold Gangue Materials: calcite, quartz, pyrite, oxidation products, limonite, clays, stibnite, barite, realgar, orpiment

Deposit: Fracture zone contains crystals, pods, & veinlets in brecciated footwall limestone. Ore also occurs along bedding planes usually within ten feet of the fracture zone.

Deposit type: Sediment-hosted Au

Development: Historic Sb development consisted of a 29 ft. shaft, 80ft of underground workings, and an open pit. 20 tons of antimony was produced in1918, 12 1/2 tons in 1945. The Sb mine was owned by D. Williams and D. Andrae in 1957. In the mid-1970's, FMC showed an initial interest in the area due to the occurrence of the antimony deposits as described by Lawrence in his Antimony bulletin. When gold was discovered by sampling surface exposures and drilling, FMC asked Freeport Gold Co. (later Independence Mining Co. and still later, Anglo Gold) to joint venture with them. Construction of the mine began in 1980, at a cost of about 105 million dollars. In 1983, the mine and mill together employed about 272 persons. The claim block includes 374 sections along the crest of the Independence Range where additional exploratory drilling was ongoing by 5 rigs in 1982. Producing mine since 1981-see production comments. Eventually the Alchem, Marlboro Canyon, West Generator, and North Generator deposits merged into a single multi-lobed pit area, and when open pit working became less profitable, mining of the higher-grade deeper zones took over. Additional nearby deposits were discovered in windows through the Roberts Mountains thrust. Several of these have also been mined with ore trucked to the Jerritt Canyon mill. Currently (2000) the only remaining surface mining is ongoing from the Dash pit, with most of the deposits developed by underground workings (Murray, Deep, SSX).

Geology: Fracture zone contains crystals, pods, & veinlets in brecciated footwall limestone. Ore also occurs along bedding planes usually within ten feet of the fracture zone. calcite, quartz, pyrite, oxidation products, limonite, clays, stibnite, barite Within the Generator/ marlboro Canyon deposits, ore occurs in a fracture zone 12 to 18" wide containing single crystals, pods, & veinlets of stibnite within the brecciated footwall limestone. Ore also occurs along bedding planes usually within 10' of the fracture zone. A sample of stockpiled ore contained 17% stibnite, and .5 oz silver per ton. Upper plate rocks are exposed in several windows. Jasperoids and jasperoid breccias are abundant and important in prospecting. According to company geologists, there is no way to discern a au-bearing jasperoid from a barren one. The jasperoids above the Marlboro and Generator pits are anomalous in gold as well as Sb and Ba. Outcrops of jasperoid contain abundant barite, stibnite and calcite in pods and vugs. Rocks show open-space textures with many vugs and crosscutting veinlets of drusy quartz. The E-W trending generator jasperoids show multiple brecciation or fracturing and are cut by many quartz veinlets. Barite crystals up to 0.5 in commonly fill iron-stained quartz-encrusted vugs. The Marlboro jasperoids reportedly ran 0.1-0.04 oz/t au. They cover the entire hillside n of the Marlboro pit. Jasperoids occur over, under, adjacent to, and far from the orebodies. In the generator pit, the jasperoids are mined.

Ore(s): fracture zones, bedding planes

Other Databases

Link to USGS MRDS:	10310527

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References