Carlin-Hardie-Pete Mine Area, Carlin Gold mine, Elko, Lynn Mining District, Eureka County, Nevada, USAi

Regional Level Types
Carlin-Hardie-Pete Mine Area	Deposit
Carlin Gold mine	Mine
Elko	- not defined -
Lynn Mining District	Mining District
Eureka County	County
Nevada	State
USA	Country

Structure: The Carlin Gold Mine is situated along the NNW-striking Carlin trend. Carlin occurs in the Lynn Window of the Roberts Mountains Thrust. Some workers believe the windows in the thrust are due to doming of the Paleozoic sediments by intrusions at depth. Carlin lies near the crest of the NNW-striking Tuscarora Mountains anticline. The regional scale Leeville fault system consists of numerous high angle fault strands that strike NNW and form an important ore-controlling feature along the eastern edge of mineralization. The greater Carlin-Hardie-Pete deposit area is generally contained within a triangular area bounded by three intersecting major fault systems: the NW-trending Castle Reef fault on the southwest, the NE-trending Hardie fault on the NE, and the NNW-trending Leeville fault on the east. Within the mine area, three sets of high angle normal faults are recognized. In order of oldest to youngest, their attitudes are 1) N60-80W, dipping steeply north, 2) N45W to N-S, dipping in either direction from 60 degrees to vertical, 3) N40-60E, dipping 50-80 degrees either NW or SE. The third (youngest) set of faults have very minor offsets and may best be described as zones of shearing or rock shattering. Igneous dikes of intermediate composition have been emplaced along some faults.

Alteration: The main alteration types present are decarbonatization, silicification, and argillization. In the main ore zone, Bakken (1990) has identified 5 mappable alteration types based on progressive carbonate dissolution (types 1, 2, and 3) and silica replacement (types 4 and 5). High grade gold is associated with type three alteration (complete carbonate removal and doubling of porosity). Jasperoids occur both along bedding planes and as fault fillings discordant to bedding. The discordant jasperoids average around 1 m thick and most often occupy structures striking N40-70E and dipping steeply south. Alteration and mineralization patterns tend to center around these jasperoid bodies.

Tectonics: Antler Orogenic Belt

Commodity: Ore Materials: native gold, electrum Gangue Materials: cinnabar, orpiment, stibnite, tennantite, getchellite, tetrahedrite, galena, sphalerite, chalcopyrite, covellite, chalcocite, molybdenite, kaolinite, sericite, barite, scheelite, fluorite, calcite, dolomite, carbonaceous materials, illite, pyrite, realgar, native arsenic

Deposit: The main Carlin deposit contains four ore zones: West, Main, South Extension, and East. The west ore zone contains a tabular vein-like body, striking about N60W and dipping 60-70N. It extends horizontally for about 335 m and reaches a maximum width of 9 m. The main ore zone contains a series of irregular orebodies along a zone 914 m long trending S60W on the southwest side of Popovich Hill, as well as several large connected sheet-like orebodies trending approx. E-W for about 460 m and dipping 30-35N along the south side of the hill. The south extension ore zone occurs in extensively shattered carbonate rocks along closely spaced normal faults trending N40-50E, or at intersections of these faults with older N-S faults. The east ore zone contains two principal orebodies along a zone that begins at the south side of Popovich Hill and continues for 730 m to the northeast. Gold values of 0.2 - 0.6 ppm are ubiquitous throughout hydrothermally altered rocks in the Popovich Formation above the orebodies hosted by Roberts Mountains Formation. No gold tellurides have been found in Carlin ores. Radtke (1985) states that gold in unoxidized ores occurs: 1) as coatings or thin films on pyrite, 2) sporadically distributed on surfaces of amorphous carbon grains, 3) in association with organic acid(s) as a gold-organic compound, 4) as native gold, 5) dispersed as particles of native gold in realgar or in solid solution in realgar, and 6) in solid solution is sparse grains of elemental arsenic. Bakken (1990) found no such gold "films" or "coatings" on pyrite. She determined that gold is present in three habits: 1) as discrete particles that vary from 50-200 angstroms in diameter that are encapsulated primarily in pyrite, but also in cinnabar and quartz, 2) as free gold particles up to 1000 angstroms in diameter that are associated with 1m illite, and 3) within as-rich pyrite, probably as a lattice component.

Deposit type: Sediment-hosted Au

Development: In 1907, small-scale gold placer mining began along Lynn Creek and continued intermittently to the 1980s. Also in 1907, a series of narrow auriferous quartz veins were discovered approximately 1.5 km north of the Carlin orebodies. These veins were developed as the Big Six mine, which achieved maximum production of about 500 ounces of gold between the years 1935 and 1936. The Morning Glory prospect was located during the 1920s in a quartz-barite-stibnite vein 1.5 km east of the Carlin orebodies. Gold was associated with stibnite and antimony oxide minerals along a NW-trending shear zone, but no production is recorded. Based on an exploration model developed by the USGS, Newmont Mining Corp. chose the Lynn Window for detailed exploration in 1961. Mapping and sampling along the Roberts Mountains Thrust began in the spring of 1961, followed by claim staking in October and November of that same year. Exploration drilling began in July 1962, with the first ore intercept encountered in the third drill hole in September 1962. When gold production began in May 1965, reserves of 11 million tons grading 0.3 ounces of gold per ton had been delineated. Carlin was idled in 1987 after producing nearly 4 million ounces of gold. Satellitic orebodies to Carlin have been and continue to be developed and mined within a few hundred meters of the original Carlin orebodies. These include the Carlin West Ore Zone, Island, Hardie Footwall, Fence, Peregrine (Perry), Pete, Castle (Castle Peak), and Crow orebodies. As of 2003, Newmont Mining Corp.'s Pete Mine is in production. Pete is a four-phase project that will eventually mine roughly 100 million tons of rock, including gold ore. Pete will be the largest of three open pits that together comprise the Pete Mine. The Pete Pit will provide near-surface oxide ore for heap leaching, although in a later phase, there will be carbonaceous ore for the roaster. The Castle Pit is oxide, and Crow Pit is refractory ore. The Pete Pit will have a life of 8 to 10 years, and contains 700,000 ounces of gold reserves. Crow has 100,000 ounces of gold reserves, while Castle has 30,000 ounces of gold. Development drifting from the Carlin East underground mine to the new Leeville project also serves as a platform for further exploration drilling (2004).

Geology: Five types of unoxidized ore are differentiated by Radtke (1985) on the basis of mineral content, chemical composition, and associations of the gold: 1) normal ore, 2) siliceous ore, 3) carbonaceous ore, 4) pyritic ore, and 5) arsenical ore. The hydrothermal system responsible for the formation of the Carlin deposit likely operated over a period of at least 100,000 years. Radtke (1985) favors a hot spring model in which gold was deposited at shallow levels via boiling of the hydrothermal fluid. Kuehn (1989) suggests that gold deposition occurred at much greater depths (>3 km) based on stable isotope and fluid inclusion work.

Ore(s): High angle normal faults and their intersections apparently were channel ways for hydrothermal solutions. Most of the known orebodies occur in the upper 250 m of the Roberts Mountains Formation, principally within a unit consisting of interbedded dark gray, medium bedded, bioclastic limestone and thinly laminated, silty dolomitic limestone. A small amount of ore at the east end of the east orebody occurs in calcareous shale of the upper plate. High grades of gold probably are linked to increased permeability due to decarbonatization.The Roberts Mountains Thrust does not appear to localize ore either at the Carlin deposit or elsewhere in the district.

Other Databases

Link to USGS MRDS:	10310467
Link to USGS MRDS:	10270827

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