Thursday, 5 April 2018

Gooseberry Ore from a Nevada Gold Mine near Tesla Gigafactory

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The above lump of gold ore is from the Gooseberry mine,  Ramsey District, Storey Co., Nevada, USA.

This specimen is part of my gold collection, see here

I bought it from Mike Owens, during a stay in Virginia City in 1986. Mike's Comstock Rock Shop had a small selection of gold ore specimens from the Gooseberry, complete with copies of the fire assay done by Rocky Mountain Geochemical Corp.

The dark sections of the rock are the gold bearing minerals, which the certificate of analysis shows 14.39 oz/ton gold and 478.97 oz/ton silver. The specimen weighs 28 grams, its size 4.4 x 3.2 x 2.0 centimetres.

The Gooseberry mine is 112 years old, and shares it's Nevada location with the more recent Tesla Gigafactory.

Gooseberry Mine is about four miles from the Tesla Gigafactory

Gooseberry MineA prospector discovered gold and silver at the surface in 1906, and did some trenching and surface work until 1910, when "a Fuller mining man", from back East bought a half interest and soon bought the whole property. 

The original Gooseberry Shaft was sunk at that time to a depth of 50 ft by hand. In 1928, J.D. Martin, Sr. purchased a half interest in the Gooseberry Mine from "the Fuller man," and together they operated the mine on a small scale, concentrating on development until the early 1930s when they switched from hand operation to a gas engine and air conditioning for the main shaft.

The Martin family took over the mine in mid-1930s and for 40 years sank a 70 degree inclined shaft to the 1000-ft level. Over 9000 ft of drifts were driven at 100-ft intervals with the longest at the 1000-ft level extending 2100 feet west and 1640 feet east. Despite all this development, there was no production recorded from 1906 to 1966. Most of the drift material was stockpiled in dumps at surface, with no development of stopes or vein material.

In 1974 the Martin family executed a partial sale of the Gooseberry Mine to APCO Minerals Inc. who sampled and began construction of a 350 tpd mill, shaft and plant. West Coast Oil and Gas (subsidiary of Scurry-Rainbow Oil Limited) took over the mine in 1976 and operated the mine until suspending mining operations in 1981.

Asamera Minerals purchased the mine in late 1982. Mill capacity was increased to 500 tpd by the end of 1984. Mine closed down to a skeleton crew in 1985, but reopened in 1987 and production continued throughout 1990.

The Gooseberry Mine is developed by a 1450-ft vertical shaft and drifts on the 500, 800 and 1000 ft levels. Mill capacity is 350 st/day, with 85% gold recovery. Developments include the mine, cyanide flotation process mill complex, a laboratory, heap leach pads, mill tailings and a solid waste landfill.

The USGS MRDS (United States Geological Survey Mineral Resources Data System.... catchy eh?) lists Gooseberry mine as primary - gold & silver, tertiary - copper, lead & zinc. Ore occurs in quartz-carbonate veins that range from a few inches up to 10 or more feet in width. Ore minerals are disseminated or form thin bands.

Reserves for the Gooseberry Mine in 1985 were reported to be 216,505 tons of ore grading 0.209 opt gold and 8.08 opt silver. Production from 1978-81 was 235 Kilotonnes of ore grading 0.14 opt gold and 7.18 opt silver. 1985 production was 225 kilotonnes of ore yielding 5,000 ounces of gold and , 225,000 ounces of silver. Asamera halted production after 1985 due to depressed metal prices. Past production reported: pre-1980: 36,858 kg silver and 800 kg gold; 15,551 kg silver in 1980, 4,959 kg silver in 1981, 9529 kg silver and 217 kg gold in 1983.

The Gooseberry vein is a precious-metal, epithermal, calcite-quartz vein deposited in Tertiary volcanics along the east-west trending Gooseberry fault. Propylitized rocks envelop this fault and the north-northeast trending Red Top structures. The alteration pattern suggests that the Red Top structures may contain precious-metal mineralization at depth. Ore-shoot location is controlled by abrupt change in dip, major change in strike, and intersection with northeast-trending faults. The silver-to-gold ratio increases markedly with depth. Preliminary fluid-inclusion studies indicate a temperature of deposition between 240 and 245°C, probably under non-boiling conditions and hydrostatic pressure.
From - "Wallrock alteration vein structure and preliminary fluid-inclusion studies, Gooseberry Mine, Storey County, Nevada." by Sprecher, Terry Ann. 1985

Analytical DataNevada Bureau of Mines and Geology Bulletin 70 "Geology and Mineral Deposits of Washoe and Storey Counties, Nevada" 1959 -
"...Grab samples taken from the dump at the mine were found to contain gold values ranging from .83 to 1.14 ounces per ton and silver values of 13.02 ounces to 69 ounces per ton.  Presumably these samples came from the underground workings, but it is not known how representative these samples are of the deposit." Ave. Grade in 1990 194 ozs Au/ton and 7.24 ozs Ag/ton.

The deposit consists of a nearly vertical quartz-dolomite veins that range from a few inches up to 10 or more feet in width. The veins follow an east-west zone, which is better developed at the 900-ft level than at surface. The vein can be traced for several hundred feet at the surface. Ore minerals are disseminated in numerous thin quartz veins present in vicinity of the mine with occasional areas of considerable jarosite, gypsum, and disseminated pyrite. Fissure vein, shear zone, disseminated.

Ores: Argentite, Stephanite, Tetrahedrite, Chalcopyrite, Electrum, Gold, Silver, Stephanite, Polybasite, Sphalerite, Galena.

Gangue: Dolomite, Quartz, Pyrite, Adularia, Calcite, Gypsum, Jarosite.

This specimen is part of my gold collection, see here

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