Comstock Lode

Site Name

Primary: Comstock Lode
Secondary: Consolidated Virginia
Secondary: Chollar
Secondary: Crown Point
Secondary: Ophir
Secondary: Savage
Secondary: Potosi
Secondary: Yellow Jacket
Secondary: California
Secondary: C & C
Secondary: Challenge & Confidence
Secondary: Hale & Norcross
Secondary: Union
Secondary: Mexican
Secondary: Gould & Curry

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Commodity

Primary: Gold
Primary: Silver
Secondary: Copper
Secondary: Lead
Tertiary: Zinc
Tertiary: Iron
Tertiary: Manganese

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Location

State: Nevada
County: Storey
District: Gold Hill) 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: numerous

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Production

Not available

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Deposit

Record Type: District
Operation Category: Past Producer
Deposit Type: vein
Operation Type: Underground
Year First Production: 1859
Discovery Year: 1859
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: V-shaped at shallower depths; tabular at greater depths

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Structure

Type: L
Description: North-south trending Comstock, Silver City and Occidental faults controlled alteration and mineralization.

Type: R
Description: North-trending anticline; regional dip to west or northwest

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Alterations

Alteration Type: L
Alteration Text: Dominant alteration assemblages affecting the host rocks in the district are summarized as follows: 1. Early widespread propylitic alteration of host hocks, not spatially associated with ore 2. Zeolite alteration superimposed on propylitic 3. Quartz-alunite alteration (high sulfidation) - erratically distributed 4. Quartz-sericite-montmorillonite-pyrite alteration peripheral to the gold-silver veins accompanying mineralization

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Rocks

Name: Granodiorite
Role: Associated
Age Type: Associated Rock
Age Young: Miocene

Name: Ash-Flow Tuff
Role: Host
Description: silicic
Age Type: Host Rock
Age Young: Miocene
Age Old: Oligocene

Name: Volcanic Breccia (Agglomerate)
Role: Host
Description: andesite
Age Type: Host Rock
Age Young: Early Miocene
Age Old: Middle Miocene

Name: Andesite
Role: Host
Description: flows
Age Type: Host Rock
Age Young: Early Miocene
Age Old: Middle Miocene

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Analytical Data

Not available

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Materials

Ore: Gold
Ore: Chalcocite
Ore: Covellite
Ore: Pearceite
Ore: Stephanite
Ore: Polybasite
Ore: Pyrite
Ore: Sphalerite
Ore: Galena
Ore: Chalcopyrite
Ore: Argentite
Gangue: Quartz
Gangue: Albite
Gangue: Adularia
Gangue: Pyrite

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Comments

Comment (Development): Placer gold was discovered at the mouth of Gold Canyon near Dayton in 1849. Placer miners followed the gold upstream to its source, several small gold-bearing lode veins in the Silver City area, but the gold gave out in the stream above what is now called Devils Gate. The outcrop of the Comstock Lode at what is now Gold Hill was found, but it was mostly barren of gold so it was ignored for several years. Eventually, in spring 1859, prospectors digging alongside the Lode unearthed the top of what later was known as the "Old Red Ledge." the ore, formed in a hanging-wall split of the main Comstock Lode, was crushed and weathered, and consisted of quartz, gold, and much dense blue-black material that turned out to be rich silver sulfide. In June 1859, a similar discovery was made a little over one mile to the northeast on vein outcroppings at the Ophir discovery site. Once the incredibly rich silver ore of the Comstock was recognized, the "Rush to Washoe" began. Virginia City became Nevada's first bonanza boom town, and the first silver-mining camp in the United States. During its main production period, from 1860 to 1880, the Comstock produced more precious metals than all of the rest of the United States and, by 1986, almost $500 million in silver and gold was dug from a roughly 3-mile-long stretch of ground along the base of Mount Davidson. The original discovery site at Gold Hill is now gone, consumed by the Gold Hill open pit mine, last operated in the 1980s by Houston Oil and Minerals Co. until the inflow of hot water brought operations to a halt. The Sutro Tunnel was engineerind to drain the mines, but by the time it had been completed, most of the main workings had reached below the level of the Sutroo Tunnel, and most of the the large boanza deposits had been mined out. Between 1859 and 1878, the Comstock Lode yielded $400 million in silver and gold. In 1872 the famous "big bonanza" was discovered at the 1200-foot level in the Consolidated Virginia ("Con-Virginia") mine. The rich ore in great quantity was found 700 feet out in the hanging-wall territory in a northeast-trending fissure that stood vertically with its roots in the footwall of the main lode. In the early 1900s, rich stopes were discovered from the 1750-foot level to the 2350-foot level. Production dropped off sharply below the 2450-foot level. Some mining continued through the 1940s and later. The south end of the Comstock Lode vein deposits in the Gold Hill area were open pit mined by Houston Oil & Minerals Company. The first discovery of ore in Virginia City was on the outcrop of the Ophir Bonanza.

Comment (Deposit): Mineralization and hydrothermal alteration of the Comstock Lode are generally associated with the north-south trending Comstock, Silver City and Occidental faults. The main fissure-fill vein ore zones are located along the Comstock fault and at intersections with mineralized cross faults. The faults localize thick veins of crushed quartz with silver sulfosalts, native silver and native gold. The main ore mineralization episode at Comstock is middle Miocene in age. Vikre (1989) also suggests that the high-sulfidation mineralization is older than the main Lode mineralization, while Hudson (1987) suggests closer time and genetic relationship of quartz-alunite alteration to main Comstock ore. Fine-grained alunite and kaolinite are common in the district, resulting from supergene processes (oxidation of pyrite, formation of low pH fluids and alteration of rocks to alunite and clays) . The quartz veins that constitute the Comstock Lode occur in and along the north-northeast-trending Comstock fault (now roughly paralleled by C Street, Virginia City's main street). The Lode is a stockwork zone of narrow, branching and interconnecting veins of brecciated quartz formed along the Comstock fault and in nearly vertical hanging-wall fractures connected with the main fault. The bonanza ores consisted of quartz and a little calcite along with sphalerite, galena, chalcopyrite, pyrite, and lesser amounts of argentite and gold. There were 10-12 parallel or coterminous bodies about 1200 feet long and 300 feet wide. Davidson Diorite is in the footwall of the Lode for most of its length. There was some significant supergene enrichment of the vein material above 500 feet. Two types of mineralization are present: 1. regionally most extensive is advanced argillic, high-sulfidation mineralization (16?15 and 14 Ma) with abundant pyrite, silica ledges, and associated alunite, but very little gold or silver. The red rocks along Geiger Grade are evidence of this type mineralization. 2. The more restricted Comstock quartz-adularia, low-sulfidation type mineralization (13.7?12.5 Ma) consisting of quartz, calcite, adularia ores with associated silver and gold mineralization. This is the Comstock orestage mineralization.

Comment (Workings): There were extensive underground workings for many miles beneath the streets of Virginia City, to depths of more than 3200 feet (1000 meters). There were three main groups of mine workings along the Comstock Lode: 1. The South End Mines. These are the Gold Hill area mines including the Overman, Belcher, Crown Point, Yellow Jacket, and Imperial. 2. The Middle Mines. These are in the general area of the ?Divide? between Gold Hill and Virginia City, and include the Best & Belcher, Gould & Curry, Chollar, Potosi, Savage, and Hale & Norcross. 3. The North End Mines. These were the major producers under the north end of Virginia City, and included the Consolidated Virginia, Mexican, and Ophir Mines.

Comment (Commodity): Ore Materials: gold, argentite, chalcopyrite, galena, sphalerite, pyrite, polybasite, stephanite, pearcite, covellite, chalcocite

Comment (Commodity): Gangue Materials: quartz, alcite, adularia, pyrite

Comment (Geology): The oldest exposed lithologies in the region are Mesozoic metasedimentary and metavolcanic rocks, which are intruded by Cretaceous granodiorite These units are unconformably overlain by Oligocene and early Miocene silicic ash-flow tuffs, thick andesite flows and associated breccias of the Miocene Alta Formation. Overlying the Alta Formation are andesite flows, breccias, and accompanying dikes and stocks of the Kate Peak Formation. The Alta Formation is the main host of orebodies in the district (Thompson, 1956) and is the unit most affected by hydrothermal alteration. The alteration assemblages are propylitic and argillic.

Comment (Identification): This is a composite record for the central portion of the Comstock Lode covering the major producing mines of the area listed in the ?other names? field. It includes all pertinent material from earlier MRDS records for the individual Comstock Lode mines M231215, M231214, M231216, M231240, M231246, M231245, M231256, M231212, M231202, M231213, M231224, M231252, and , but is not intended to replace those recrods.

Comment (Location): The mines are located along the Comstock Lode vein which runs roughly north-south on the east flank of Mount Davidson in the Virginia Range.

Comment (Economic Factors): Between 1862 and 1953, the Comstock Lode mines produced approximately 225,000 kg of gold and 7 million kg of silver. About 192 million ounces of silver and 8.3 million ounces of gold were produced from 1859 to 1986 with 80% of that production made prior to 1880. The value at time of production was about $412 million. The Crown Point Bonanza alone, found in 1871, produced $35 million. ? the ?Big Bonanza,? found in John Mackay?s Consolidated Virginia Mine, produced $105 million between 1873 and 1880.

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

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References

Reference (Deposit): Vikre, Peter G. ,1989, Fluid-mineral relations in the Comstock Lode. Economic Geology, V.84, p.1574-1613. http://www.seismo.unr.edu/ftp/pub/louie/class/453/virginia-city/virginia-city.doc
URL: http://www.seismo.unr.edu/ftp/pub/louie/class/453/virginia-city/virginia-city.doc

Reference (Deposit): WPA State Writer's Project, 1940-41, Individual Histories of the Mines of The Comstock; unpublished NBMG Open File Report.

Reference (Deposit): Stoddard, Carl, and Carpenter, J.A., 1950, Mineral Resources of Storey and Lyon Counties, Nevada: NBMG Bull. 49.

Reference (Deposit): Thompson, G.W. (1956) Geology of the Virginia City Quadrangle. USGS Special Paper 1024 C, p.64.

Reference (Deposit): Bastin, E.S., 1922, Bonanza Ores of the Comstock Lode, Virginia City, Nevada; USGS Bull 735-C.

Reference (Deposit): Vikre, Peter G. ,1998, Quartz-Alunite alteration in the Western Part of the Virginia Range, Washoe and Storey Counties, Nevada. Econ. Geology V.93, p.338 - 343.

Reference (Deposit): Special Publication No. 4

Reference (Deposit): Bonhan, H.F., 1969, Geology and Mineral Deposits of Washoe and Storey Counties, Nevada: NBMG Bull 70.

Reference (Deposit): Hudson, D. M.,1986, Comstock Lode Fieldtrip. Geological Society of Nevada

Reference (Deposit): Hudson, D. M.,1987, Summary of the Geology of the Comstock District, Nevada in Johnson, J.L. ed. Bulk Mineable Precious Metal Deposits of the Western United States. Guidebook for fieldtrips: Geological Society of Nevada, p.413-418.

Reference (Deposit): Kruse, F. A., and Huntington, J. H., 1996, The 1995 Geology AVIRIS Group Shoot: in Proceedings, 6th JPL Airborne Earth Science Workshop: Jet Propulsion Laboratory Publication 96-4, v. 1, p. 155 - 166.

Reference (Deposit): Hutsinpiller, A. and Taranik, J.V. ,1988, Spectral Signatures at Virginia City. In Schafer et al. Bulk Mineable Precious Metal Deposits of the Western United States. Symposium Proceedings. Geological Society of Nevada, p. 545-551.

Reference (Deposit): Spatz, D. and Taranik, J. ,1988, Identification and mapping of volcanic lithologies genetically or spacially associated with the precious metal deposits of the western U.S. using Landsat TM imagery. In Schafer et al. Bulk Mineable Precious Metal Deposits of the Western United States, Symposium Proceedings. Geological Society of Nevada.

Reference (Deposit): Tingley, Joseph and Tingley, Susan, 2000, Exploring East of the Summit, A Field Trip Guide to Steamboat Springs,

Reference (Deposit): Lake Tahoe, and the Comstock Area, NBMG ES-38.

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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.