Eureka Mining District, Eureka County, Nevada, USAi

Regional Level Types
Eureka Mining District	Mining District
Eureka County	County
Nevada	State
USA	Country

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13 mile by 1 to 2 mile wide district. Skarn replacement with weathering to 250m.

Structure: compound thrust faults, perhaps in front of deep Roberts Mountains Thrust to west; later block faulting Complex faulting in limestone and dolomite, major structures are all pre-ore

Alteration: Ore is oxidized to 1000 feet depth.

Commodity: Ore Materials: argentiferous and auriferous galena, pyrite, sphalerite, arsenopyrite, plumbojarosite, wulfenite, azurite, malachite, arsenopyrite, tetrahedrite, scorodite, anglesite, cerussite, smithsonite, bindheimite, mimetite, hemimorphite, auriferous pyrite, native gold, cerargyrite, molybdenite, cerussite, native gold, anglesite, wulfenite Gangue Materials: quartz, halloysite, goethite, calcite, dolomite, aragonite, siderite, hematite, pyrite, limonites, iron oxides,

Deposit: Deposits are replacement veins, chimneys, irregular masses and bedded deposits in Cambrian limestone along fissures and above a thrust fault in the richest area. Igneous rocks are a small quartz monzonite stock and quartz porphyry dikes of early Cretaceous age; intrusive and extrusive andesite of middle Eocene age; and rhyolite plugs and flows of middle Oligocene age. There are abundant sulfide minerals, but the bulk of the production was from oxidized ores. The Eureka Consolidated property contained the Champion & Buckeye claims on the south side of Ruby Hill, which were the richest of five mineralized blocks in the district. Water is found at the 2500 foot level in the underground workings, below which sulfide ore occurs. Some ore occurred as pods, replacement veins and irregular replacement bodies in brecciated zones at intersections of faults and fissures, and associated with a system of caves.

Deposit type: Polymetallic replacement

Development: Silver was discovered in 1864 and the Diamond Springs District was founded. Silver strikes were made in 1864 by prospectors from Austin proved uneconomical to work because of the high lead content of the ores. Ore was shipped to England and Wales for smelting until 1869, when the first of sixteen successful smelters was constructed and the smelter emissions gave Eureka the nickname "Pittsburgh of the West." Eureka grew in size and mining productivity during the middle 1870s when the Eureka & Palisade Railroad was extended south from the Central Pacific to Eureka. By 1878, Eureka had a population of about 9,000, second largest city in Nevada. Fifty mines produced lead, silver, gold, and zinc that fed the smelters, which could process a total of more than 700 tons of ore a day. By 1879, mining had reached well below the water table, and the increased cost of pumping the water out of the mines began to make mining deeper less profitable. Eureka mining production peaked in 1882, but tailed off rapidly after 1885 and by 1891 the major mines had been shut down. Eureka continued to be an important producing district, at least through 1957, though output in later years fluctuated widely, with no production as recently as 1952-53. The district was one of major producers in the west of lead, silver and gold from 1869-90; since this time there has been production every year until 1952. Only zinc was produced only after 1942 until the Ruby Hill (Archimedes) gold deposit was discovered. There are important deep reserves of sulfide lead, zinc and silver, carrying gold, but the water problem has prevented development of these resources.

Geology: Ore occurs in the upper plate of the Ruby Hill thrust, at intersection with Ruby Hill normal fault (N 40 deg W) in limestones with late Mesozoic deformation.

Ore(s): Ruby Hill Thrust Fault

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Mineral List

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90 valid minerals.

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