Comstock Lode, Virginia City, Comstock Mining District, Storey County, Nevada, USAi

Regional Level Types
Comstock Lode	Lode
Virginia City	City
Comstock Mining District	Mining District
Storey County	County
Nevada	State
USA	Country

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It started as a placer gold operation until the blue heavy sticky stuff made mining difficult (someone later found out that the "bad" stuff was extremely rich silver ore). The ore bodies were so wide that the square set mining method was invented by Philip Deidesheimer of the Ophir mine.

The Comstock was also the home base for Samuel Clemens for several years (later better known as Mark Twain - American novelist and humorist).

The silver deposit was discovered in 1859 and became the impetus to create the Nevada Territory and a few years later the State of Nevada.

Structure: North-south trending Comstock, Silver City and Occidental faults controlled alteration and mineralization. North-trending anticline; regional dip to west or northwest

Alteration: 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

Commodity: Ore Materials: gold, argentite, chalcopyrite, galena, sphalerite, pyrite, polybasite, stephanite, pearceite, covellite, chalcocite Gangue Materials: quartz, calcite, adularia, pyrite

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 a 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 1,200 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 of 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.

Deposit type: Epithermal vein, Comstock

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 the spring of 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 the rest of the United States combined 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 engineered 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 1,200-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 1,750-foot level to the 2,350-foot level. Production dropped off sharply below the 2,450-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.

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.

Ore(s): 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 ores of the Comstock Lode were associated with the Comstock Fault.

Commodity List

This is a list of exploitable or exploited mineral commodities recorded from this region.

Mineral List

Mineral list contains entries from the region specified including sub-localities

46 valid minerals.

Rock Types Recorded

Rock list contains entries from the region specified including sub-localities