Aurora Mine Area

Site Name

Primary: Aurora Mine Area
Secondary: Esmeralda
Secondary: Cambridge
Secondary: Old Humboldt Mine area
Secondary: Humboldt West claim
Secondary: Humboldt East claim
Secondary: Humboldt vein
Secondary: Prospectus vein
Secondary: Martinez
Secondary: Juniata Mine
Secondary: Del Monte Mine
Secondary: Wide West Mine
Secondary: Johnson Mine
Secondary: Pond Mine
Secondary: Chihuahua Mine
Secondary: Garibaldi Mine
Secondary: Antelope Mine
Secondary: Utah Mine
Secondary: Silver Hill
Secondary: Middle Hill
Secondary: Last Chance Hill
Secondary: Aurora Mine
Secondary: Aurora Partnership Mine
Secondary: Chesca Mine

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Commodity

Primary: Gold
Primary: Silver

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Location

State: Nevada
County: Mineral
District: Aurora District

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Land Status

Land ownership: Private
Note: the land ownership field only identifies whether the area the mine is in is generally on public lands like Forest Service or BLM land, or if it is in an area that is generally private property. It does not definitively identify property status, nor does it indicate claim status or whether an area is open to prospecting. Always respect private property.
Administrative Organization: Carson City BLM Administrative District

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Holdings

Not available

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Workings

Not available

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Ownership

Owner Name: Metallic Ventures
Info Year: 2004

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Production

Not available

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Deposit

Record Type: Site
Operation Category: Producer
Deposit Type: epithermal vein, typically with little or no wallrock dissemination
Operation Type: Surface-Underground
Year First Production: 1860
Year Last Production: 1998
Discovery Year: 1860
Years of Production:
Organization:
Significant: Y
Deposit Size: L

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Physiography

Not available

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Mineral Deposit Model

Model Name: Epithermal vein, Comstock

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Orebody

Form: lenses and stringers

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Structure

Type: R
Description: A young, less than 3 Ma old, broad regional upwarp extends form the southwest of the Bodie Hills through the Bodie District to the area of the Aurora District. This upwarp may continue to the northeast, south of the Borealis mine.

Type: L
Description: Steep N-S striking faults offset the mineralized NE-striking faults.

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Alterations

Alteration Type: L
Alteration Text: Progressive weak to strong propylitic alteration with quartz-illite alteration surrounding silicification in the mineralized faults.

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Rocks

Name: Granite
Role: Associated
Age Type: Associated Rock
Age Young: Mesozoic

Name: Basalt
Role: Associated
Age Type: Associated Rock
Age Young: Tertiary

Name: Rhyolite
Role: Associated
Age Type: Associated Rock
Age Young: Tertiary

Name: Latite
Role: Host
Description: agglomerates and flows
Age Type: Host Rock
Age in Years: 15.400000+-
Age Young: Middle Miocene

Name: Latite
Role: Host
Description: agglomerates and flows
Age Type: Host Rock
Age in Years: 13.500000+-
Age Young: Middle Miocene

Name: Andesite
Role: Host
Description: agglomerates and flows
Age Type: Host Rock
Age in Years: 13.500000+-
Age Young: Middle Miocene

Name: Andesite
Role: Host
Description: agglomerates and flows
Age Type: Host Rock
Age in Years: 15.400000+-
Age Young: Middle Miocene

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Analytical Data

Not available

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Materials

Ore: Gold
Ore: Pyrite
Ore: Chalcopyrite
Ore: Bromargyrite
Ore: Naumannite
Ore: Acanthite
Ore: Electrum
Ore: Tetrahedrite
Gangue: Quartz
Gangue: Adularia
Gangue: Calcite

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Comments

Comment (Identification): This is a new record for the Aurora Mine area significant deposit. It incorporates all pertinent material from earlier records #W002908, M035801, M242411, and M233145, which may be kept in the databases as describing historic workings.

Comment (Location): The Aurora mines are scattered over an area that covers more than a square mile and include several historic mines as well as recently mined areas in the district.

Comment (Workings): Historic development was underground. Total underground workings are estimated at about 20 miles. The deepest shaft, the Del Monte, was 900 feet deep and several others were 400-500 feet deep. Workings on Last Chance Hill seldom exceeded 125 feet in depth. Mine development since 1983 has been by open pit.

Comment (Economic Factors): Historic Aurora mines having major production were: Del Monte, Wide West, Johnson, Pond, Chihuahua, Garibaldi, Antelope, Utah, and Juniata. Total recorded production from the 1930s, 1983, and 1988-1996 is estimated to have been at least 305,923 ounces of gold and more than 344,933 ounces of silver. This does not include an unknown but substantial amount of production pre-1930. A 2003 calculation reports: 30,710,500 tons grading 0.031 opt Au of bulk-minable measured and indicated resources plus 9,206,300 tons grading 0.025 opt Au bulk-minable inferred resources plus 192,152 tons grading 0.50 opt Au in underground-minable resources remaining in the Martinez & Prospectus zones.

Comment (Environment): Oxidized subduction-related continental-margin arc along western North America.

Comment (Geology): Aurora has been is the most productive district in Mineral County in historic times, accounting for 40% of the total county production. In general the ore was of low grade, though some shoots ran as high as $1000/ton. The gold: silver ratio may have been as low as 1:14. The mineralized area of the district is approximately 2 miles long. Host rocks are pre-Esmeralda andesitic to latitic agglomerates and flows.

Comment (Development): The first camp in the early 1860s was at Esmeralda, but was soon relocated to Aurora, which reached a population of 10,000 by 1864. There were 17 active amalgamation mills in 1864, the largest of which had 30 stamps. The total amount of ore handled is estimated at 670,000 tons. From 1861 to 1869, nearly $29,500,000 in gold and silver were produced from the district, mostly by the Aurora Mines Co. and the Aurora Consolidated Mining Co. The district began to decline after 1869, although it was productive intermittently until the early 1900s. From 1914 to 1918 the district enjoyed a brief revival when $1,850,000 in gold and silver were produced, chiefly by the Goldfield Consolidated Mines Co. Much of this production was probably from reworking of tailings and dump material. As late as 1940 as small production was recorded from the district, but in 1956 there was no activity. In 1973-74, St. Joe explored for porphyry copper-moly deposits in the area and inferred possible deep (5,000-15,000 ft.) mineralization. In the late 1970s Homestake drilled the Prospectus and Humboldt veins and on Last Chance Hill but failed to find a large bulk tonnage deposit. In 1981 Hanna drilled the Juniata Mine area and the new Esmeralda area, identifying only small reserves. In 1983 Hanna drilled the Prospectus Vein, intersecting ore grades at depths of 50-100 ft. Follow-up drilling by Hanna and later by Nevada Goldfields outlined reserves of 350,000 tons of ore grading/0.185 opt gold. Electra Resources was drilling the property in 1980-1981 and in 1982, Electra combined with Pacific Northwest to form Electra Northwest Resources, Ltd. to develop the mine and conducted drilling and engineering programs. Plans were to process an initial 3000 tons of ore. Electra Northwest formed a joint venture with Centennial Minerals, and began production in July 1983 at 1000-1500 tpd at what was called the Aurora Partnership Mine, developed on the Humboldt Vein. Initial recoveries averaged 0.08 opt gold from material grading 0.12 opt gold. Full scale production was planned for 1984. Mine life projected at least five years. Production at the adjacent Aurora Mine (developed on the Prospectus Vein) began in 1987 by Nevada Goldfields. As the Aurora Mine production continued, Minerex Resources, Ltd. took over operation of the Aurora Partnership Mine in 1990, followed by Electra Mining Corp in 1994. The Aurora Partnership Mine appears to have ceased production in 1996, leaving just Nevada Goldfields mine in production, and it too closed by 1999. Precious metals exploration in the Aurora area has resumed with the recent increased gold prices. In January 2004, Metallic Ventures Gold Inc. reported the start-up of its 350 ton-per-day mill at its Esmeralda property at Aurora, and poured its first precious metal bullion on February 16. However, in the third quarter of 2004, Metallic Ventures suspended all production and exploration activities at this project in the Aurora district. The project was not providing consistent positive cash flow and, in order to ensure the company has adequatefunding for its other Nevada projects, Esmeralda was placed on care and maintenance status.

Comment (Commodity): Commodity Info: Average. Au:Ag ratio of 1:5. Higher gold values found near surface decreased as silver values increased with depth.

Comment (Commodity): Ore Materials: native gold, argentiferous tetrahedrite, electrum, acanthite, naumannite, bromargyrite, chalcopyrite, pyrite.

Comment (Commodity): Gangue Materials: quartz, adularia, calcite

Comment (Deposit): The Aurora silver-gold deposits are for the most part epithermal fissure vein deposits. Veins consist mostly of finely granular white quartz, which in some places has a milky-white porcelain-like appearance. The veins are commonly composed of layers of quartz of different grain sizes, and all the veins contain cavities lined with clear quartz crystals. The veins are a series of NE-striking to east-striking anastomosing quartz-adularia veins in pre- Esmeralda volcanic rocks that are exposed in a window in an area of predominantly barren younger rocks. A few ounces of placer gold (.408 fine) were recovered from Bodie Creek in 1940-41. Anastomosing quartz-adularia veins vary in width from less than an inch to as much as 60 feet (one reference states up to 130 feet). Average width is 4 feet. Most veins are wider at intersecting faults, with horsetailing of the veins at their extremes.

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References

Reference (Deposit): Long, K.R., DeYoung, J.H., Jr., and Ludington, S.D., 1998, Database of significant deposits of gold, silver, copper, lead, and zinc in the United States; Part A, Database description and analysis; part B, Digital database: U.S. Geological Survey Open-File Report 98-206, 33 p., one 3.5 inch diskette.

Reference (Deposit): Nevada Division of Minerals, Major Mines of Nevada 1989-2004.

Reference (Deposit): Metallic Ventures Gold Inc. press releases, 1/20/2004, 11/12/04.

Reference (Deposit): NBMG Mining District Files, File 189, Press Clippings.

Reference (Deposit): Ross, D.C., 1961, Geology and Mineral Deposits of Mineral County, Nevada: NBMG Bull 58

Reference (Deposit): Hill, J.M., 1915, Some Mining Districts in Northeastern California and Northwestern Nevada: USGS Bull 594

Reference (Deposit): Ferguson, H.G., 1929, The Mining Districts of Nevada: Econ Geol, v. 24, no. 2, p 115-48.

Reference (Deposit): Green, W.R., 1962, Structural Control of Mineralization at the Aurora Mining District, Mineral County, Nevada: M.S. Thesis, Univ. of Nevada.

Reference (Deposit): Vanderburg, W.O., 1937, Recon. of Mining Districts in Mineral County, Nevada: U.S. Bur. Mines Inf. Circ. 6941, 79p.

Reference (Deposit): Koschmann, A.H. and Bergandahl, M.H., 1968, Principal Gold-Producing Districts Of The U.S.: USGS Prof. Paper 610, p.188.

Reference (Deposit): Lincoln, F.C. 1923, Mining Districts of Nevada: Reno, Nevada Newsletter Pub. Co. p.137-8.

Reference (Deposit): State Division of Mine Inspection, Dec. 1983, Directory of Nevada Mine Operations Active During Calendar Year 1983.

Reference (Deposit): Osborne, M.A., 1991, Epithermal Mineralization at Aurora, Nevada: Proceedings of the GSN 1990 Symposium, p. 1097-1110.

Reference (Deposit): NBMG, 1990, The Nevada Mineral Industry: NBMG Special Publication MI-1989-2004.

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Nevada Gold

Nevada has a total of 368 distinct gold districts. Of the of those, just 36 are major producers with production and/or reserves of over 1,000,000 ounces, 49 have production and/or reserves of over 100,000 ounces, with the rest having less than 100,000 ounces. Read more: Gold Districts of Nevada.