Richmond-Eureka mine (Ruby Hill mine), Ruby Hill, Eureka Mining District, Eureka County, Nevada, USAi

Regional Level Types
Richmond-Eureka mine (Ruby Hill mine)	Mine
Ruby Hill	Hill
Eureka Mining District	Mining District
Eureka County	County
Nevada	State
USA	Country

Alteration: Zones of silicification, jasperoid development, and limestone decalcification (decarbonization) guided ore formation.

Tectonics: Central Nevada Fold Belt

Commodity: Commodity Info: Mercury is retorted from process metal sludge. Ore Materials: gold, electrum Gangue Materials: quartz, limonite, hematite, pyrite, cinnabar, barite, various sulfide minerals

Deposit: Archimedes is a Carlin-style sediment-hosted gold deposit in carbonate rocks. The ore is a mixture of jasperoid and decalcified limestone exhibiting strong structural controls. Micron-size gold is associated with oxidized pyrite sites and is strongly fracture controlled. Deeper portions of the east Archimedes resource are sulfidic, and root-zones include retrograde-altered base metal skarn and marble hosts. The mineralized area closely adjoins a Cretaceous porphyry intrusive and may be genetically linked to it, as both base metal-related adularia and the intrusive yield similar radiometric ages. Some evidence suggests the presence of a younger cross-cutting Au-As-Hg system superimposed on the earlier base-metal system and associated with Oligocene magmatism. The West Archimedes deposit is about 780 m long, plunging gently S60?E and covered by 15 to 150 m of partially cemented calcareous alluvium. The deposit is subtabular to ovate in cross section, branching locally at structural intersections. The orebody has a central elongated lens of higher grade jasperoid ore enclosed by a more tabular envelope of lower grade decalcified limestone ore.

Development: The initial discovery sample was collected in 1991 by a geologist working under contract to Homestake from a pit north of the old Holly Extension mine dump. The first hole was drilled in the orebody in 1992, and an economic deposit was indicated by mid-1993. The Archimedes orebody was discovered by rock-chip sampling and subsequent geochemical soil anomaly and drilling. Stripping of the Archimedes deposit began in early 1997, and the first gold was poured on November 6,1997. By year?s end, the mine had reached expected production of 3,500 tons per day, of which about 2,600 tons of lower-grade ore is heap leached, while 900 tons of higher-grade material is sent to the mill. The stripping ratio is 7-to-1 and anticipated production is between 105,000 and 110,000 troy ounces of gold annually. Exploration in 1998 continued in the immediate area to identify other shallow oxide deposits as well as a deep drilling program designed to further define a zone of high grade sulfide mineralization discovered 1,500 feet below the West Archimedes open pit. By 2005, Barrick reported that thecurrent project will be an open-pit, heap leach operation exploiting the East Archimedes deposit, a deeper continuation of the ore mined previously at Ruby Hill. Permitting has been secured and the two-year, approximately $75-million construction phase is underway. The project is expected to enter production in early 2007 and has reserves of 1.0 million ounces at December 31, 2005.

Geology: The primary host rock of the Archimedes deposit is thin to thick bedded cherty limestone of the early Ordovician Goodwin Limestone of the Pogonip Group. minor hosts are micritic to shaley limestone of the early Ordovician Ninemile Formation also of the Pogonip Group, and early Cretaceous quartz porphyry. Archimedes satellite deposits are hosted by fine- to coarse early to middle Ordovician limestone and chert of the Antelope Valley Limestone, also of the Pogonip Group. The West Archimedes deposit is a more stratigraphically controlled offshoot of the East Archimedes deposit, a steeply-plunging, oxidized, gold-bearing jasperoid breccia adjoining the quartz-feldspar porphyry intrusive.

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Link to USGS MRDS:	10310484

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