Comstock Lode

Past Producer in Storey county in Nevada, United States with commodities Silver, Gold, Copper, Lead, Zinc, Iron, Manganese

Sections on this page

Identification information
Geographic coordinates
Site location context
Geographic areas
Public Land Survey System information
Commodities
Materials information
Alteration
Mineral occurrence model information
Host and associated rocks
Nearby scientific data
Geologic structures
Ore body information
Controls for ore emplacement
Economic information about the deposit and operations
Mining district
Land status
Ownership information
Bibliographic references
General comments
Reporter information

Geologic information

Identification information

Deposit ID	10310576
MRDS ID	M231215
Record type	District
Current site name	Comstock Lode
Alternate or previous names	Consolidated Virginia, Chollar, Crown Point, Ophir, Savage, Potosi, Yellow Jacket, California, C & C, Challenge & Confidence, Hale & Norcross, Union, Mexican, Gould & Curry
Related records	10043912

Comments on the site 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.

Geographic coordinates

Geographic coordinates:	-119.64767, 39.31129 (WGS84)
Elevation	1890
Relative position	The Comstock Lode mines are located under what is now downtown Virginia City Nevada, about 15 miles southeast of Reno, and 12 miles northwest of Carson City.

Site location context

Political divisions (FIPS codes)

Storey(county)

Nevada(state)

United States(country)

North America(continent)

Land(continent)

USGS map quadrangles

Virginia City(quadrangle 1:24,000 scale)

Carson City(quadrangle 1:100,000 scale)

Reno(quadrangle 1:250,000 scale)

Hydrologic units (watersheds)

Middle Carson(hydrologic unit)

Carson(hydrologic accounting unit)

Central Lahontan(hydrologic subregion)

Great Basin(hydrologic region)

Geographic areas

Country	State	County
United States	Nevada	Storey

Public Land Survey System information

Meridian	Township	Range	Section	Fraction	State
Mount Diablo	017N	021E	29 32		Nevada

Comments on the location information

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.

Commodities

Commodity	Importance
Silver	Primary
Gold	Primary
Copper	Secondary
Lead	Secondary
Zinc Critical	Tertiary
Iron	Tertiary
Manganese Critical	Tertiary

Comments on the commodity information

Ore Materials: gold, argentite, chalcopyrite, galena, sphalerite, pyrite, polybasite, stephanite, pearcite, covellite, chalcocite
Gangue Materials: quartz, alcite, adularia, pyrite

Materials information

Materials	Type of material
Gold	Ore
Argentite	Ore
Chalcopyrite	Ore
Galena	Ore
Sphalerite	Ore
Pyrite	Ore
Polybasite	Ore
Stephanite	Ore
Pearceite	Ore
Covellite	Ore
Chalcocite	Ore
Quartz	Gangue
Albite	Gangue
Adularia	Gangue
Pyrite	Gangue

Alteration

(Local) 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

Mineral occurrence model information

Model code	150
USGS model code	25c
Deposit model name	Epithermal vein, Comstock
Mark3 model number	16

Host and associated rocks

Host or associated

Host

Rock type

Volcanic Rock (Aphanitic) > Intermediate Volcanic Rock > Andesite

Rock type qualifier

flows

Rock unit name

Alta Formation

Stratigraphic age (youngest)	Early Miocene
Stratigraphic age (oldest)	Middle Miocene

Host or associated

Host

Rock type

Volcanic Rock (Aphanitic) > Pyroclastic Rock > Volcanic Breccia (Agglomerate)

Rock type qualifier

andesite

Rock unit name

Alta Formation

Stratigraphic age (youngest)	Early Miocene
Stratigraphic age (oldest)	Middle Miocene

Host or associated

Host

Rock type

Volcanic Rock (Aphanitic) > Pyroclastic Rock > Tuff > Ash-Flow Tuff

Rock type qualifier

silicic

Stratigraphic age (youngest)	Miocene
Stratigraphic age (oldest)	Oligocene

Host or associated

Associated

Rock type

Plutonic Rock > Granitoid > Granodiorite

Rock unit name

Davidson Diorite (actually a granodiorite)

Stratigraphic age (youngest)	Miocene

Nearby scientific data

(1)	-119.64767, 39.31129	ListMap

Economic information

Geologic structures

Type of structure	Local
Structure description	North-south trending Comstock, Silver City and Occidental faults controlled alteration and mineralization.
Type of structure	Regional
Structure description	North-trending anticline; regional dip to west or northwest

Ore body information

General form V-shaped at shallower depths; tabular at greater depths

General form	V-shaped at shallower depths; tabular at greater depths

Controls for ore emplacement

Mineralization and hydrothermal alteration of the Comstock Lode are generally associated with the north-south trending Comstock, Silver City, and Occidental faults. The high-grade bonanza oresof the Comstock Lode were associated with the Comstock Fault.

Comments on the geologic information

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.

Economic information about the deposit and operations

Operation type	Underground
Development status	Past Producer
Commodity type	Metallic
Deposit size	Large
Significant	Yes
Discovery year	1859
Year of first production	1859

Mining district

District name	Comstock (Virginia City
District name	Gold Hill) District

Land status

Ownership category	Private
Area name	Carson City BLM Administrative District

Ownership information

Type Owner-Operator

Owner numerous

Type	Owner-Operator
Owner	numerous

Comments on the workings information

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.

Comments on other 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.

Comments on 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.

Comments on the environmental information

Oxidized subduction-related continental-margin arc along western North America.

Reference information

Bibliographic references

Deposit

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

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

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

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

Hudson, D. M.,1986, Comstock Lode Fieldtrip. Geological Society of Nevada
Deposit

Special Publication No. 4
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.
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.
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.
Deposit

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

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

Lake Tahoe, and the Comstock Area, NBMG ES-38.

General comments

Subject category	Comment text
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.

Subject category

Comment text

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.

Reporter information

Type	Date	Name	Affiliation	Comment
Reporter	01-DEC-2006	LaPointe	Nevada Bureau of Mines and Geology
Editor	01-SEP-2007	Schruben, Paul G.	U.S. Geological Survey	Converted from S&A FileMaker format to Oracle. Edit checks on rocks, units, and ages with Geolex search, and other fields.

Beyond USGS

Supplemental information added by qvyshift.com. Not part of the original USGS MRDS record.

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