Atlanta mine, Atlanta Mining District, Lincoln County, Nevada, USAi

Regional Level Types
Atlanta mine	Mine
Atlanta Mining District	Mining District
Lincoln County	County
Nevada	State
USA	Country

Sec 15 T7N R68E. Silver and gold open pit mine in silicified breccia.
Structure: Basin-and-Range-style extension produced widely spaced normal faults that clearly cut all caldera-related structures and volcanic units, including the 28 Ma Ryan Spring Formation and some Quaternary gravels. Faults and breccia zones associated with the intersection of two caldera systems; the Atlanta Fault Zone, Mine Fault, and the Gold Fault. Ore is associated with a north-south trending caldera rim fracture.

Alteration: Alteration consists of silicification (jasperoid formation) and oxidation. Adjacent to the silicified zone, intracaldera volcanic rocks are altered to illite with some pyrite. Dolomite within the caldera wall is partly recrystallized and contains barite, calcite, and disseminated hematite. Weathering of pyrite in altered rocks produced supergene kaolinite alteration, which overprints much of the mineralized area.

Tectonics: back-arc extensional cratonic basin

Commodity: Ore Materials: native gold Gangue Materials: quartz, pyrite, chert, jasper, limonite, manganese oxides, clay, alunite

Deposit: Mineralization occurs in silicified breccia and jasperoid, adjacent to a low-angle normal fault separating Oligocene ash-flow tuffs and Ordovician carbonate rocks. Potential exists for disseminated mineralization in fractured ash-flow tuffs and deep jasperoids in carbonate rocks beneath the Atlanta open pit. Prominent irregular jasperoid bodies, pods and lenses, commonly accompanied by either iron or manganese oxides, occur along the Atlanta ore zone that dips about 45 SW. In places, breccia pipes and fault zones in the dolomite overlying the Eureka quartzite are extensively silicified into drusy quartz and brecciated greenish-gray jasperoid. Commonly these brecciated, mineralized zones carry sub-microscopic gold, silver minerals, and minor amounts of uranium. The ore deposit contains brecciated fragments of limestone, quartzite, volcanic rocks, and jasperoid, cemented by quartz. Gold is submicroscopic. The Atlanta mine is situated near the intersection of two caldera systems. The older Indian Peak caldera is bounded by a fault zone that dips 70-90 degrees into the caldera, and is exposed in the Atlanta open-pit gold mine. The caldera-bounding fault is a one- to six-meter-wide breccia zone associated with tuff dikes that has accommodated over 500 m of subsidence of the caldera floor. South of the mine area, the location of Indian Peak caldera margin is constrained by exposures of Paleozoic sedimentary rocks outside the caldera and thick collapse breccias containing large blocks of Paleozoic rocks, which thin into the caldera. The Indian Peak caldera margin is truncated by the Ryan Spring caldera near the center of the district. The fault zone that bounds the Indian Peak caldera locally contains ore-grade gold, silver, and uranium mineralization within silicified breccias. Silica-pyrite mineralization is localized along the caldera-bounding fault zone and near tuff dikes within the Atlanta mine. Ore occurred in a hematite-rich silicified breccia of limestone and Tertiary volcanic rocks, along a north-south trending caldera rim fracture.

Deposit type: Hot-spring Au-Ag

Development: The Atlanta mine produced over 100,000 ounces of gold during the time period 1870-1985, mostly from an open-pit mine that was reactivated by the Standard Slag Company in a joint venture with Bob Cat Properties, Inc. in fall of 1974. Production from this operation began in 1975 and lasted through much of the 1980s. Capacity of the cyanide plant was gradually increased from 300 tpd to an average of 570 tpd in 1982. The property was listed as an active open pit mine and mill in 1983 employing a total of 45 persons. In 1996, Golden Chief Resources planned to drill eight holes on the Atlanta Gold property to test gold mineralization trending from the main Atlanta pit to the south and southeast. The property was still owned in 2001 by Golden Chief Resources, Inc. In August 2000, Franc-Or Resources Corporation announced that the Cordilleran Nevada syndicate, of which it is a forty percent partner, signed a lease agreement on the ground adjoining its Atlanta claim block in east-central Nevada. The lease will add 183 unpatented claims to the Cordilleran property, bringing the total land position to 447 unpatented claims. The lease does not include the 26 unpatented and 13 patented claims that cover the existing pit, dumps, and milling facilities

Geology: The stratigraphy of the district includes Ordovician and Silurian limestone, quartzite, and dolomite that are unconformably overlain by five Tertiary ash-flow tuffs, associated lavas, and sedimentary deposits. The oldest of these eruptions occurred about 33 Ma from a caldera approximately 35 km southeast of the district, producing rhyolite lavas and bedded tuffs of the Escalante Desert Formation in this area. The next two tuffs erupted from calderas that are partly exposed in the Atlanta district the Wah Wah Springs Formation overlies the Escalante Desert Formation, and was erupted from the Indian Peak caldera about 29.5 Ma. This formation includes andesite lavas, a voluminous crystal-rich dacite ash-flow tuff, tuff dikes that are believed to be feeders for the ash-flow tuff eruption, a granodiorite porphyry plug, collapse breccias and sedimentary deposits along the caldera margin. All members of this formation are hydrothermally altered to varying degrees. Unmineralized rhyolite ash-flow tuff of the Ryan Spring Formation overlies the Wah Wah Springs Formation.

Ore(s): Atlanta?s gold mineralization is structurally controlled, associated with caldera collapse features. Locally, gold occurs in faults and a silicified breccia zone.

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Link to USGS MRDS:	10310401

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