Zeibright Mine, Clyde Mountain, Emigrant Gap Mining District, Nevada County, California, USAi

Regional Level Types
Zeibright Mine	Mine
Clyde Mountain	Mountain
Emigrant Gap Mining District	Mining District
Nevada County	County
California	State
USA	Country

A former Au-Cu occurrence/mine located in the NW¼ sec. 34, T17N, R11E, MDM, about 8.6 km NE of Clyde Mountain (coordinates of record)(16 miles east-northeast of Nevada City; 1 mile NW of the Blue Canyon Guard Station), on private and National Forest land (?). Discovered in 1890. Owned by the Donner Mine Camp, Incorporated 2007. MRDS database stated accuracy for this location is 500 meters.

NOTE: There are two "Zeibright" mines, one on the USGS 7.5-minute Blue Canyon quadrangle and the other on the Washington quadrangle. The deposit described here refers to that on the Blue Canyon quadrangle. This mine is considered the more significant of the two.

The mine is known to have been in operation in 1902 based on a report in the Mining and Scientific Press (1902). The name was derived from the first mine owners, F. Zeitler and W.F. Englebright. From 1918 to 1934, the Zeibright Mine was operated by the Bear Valley Mining Company. According to records filed in the Online Archive of California (http://oac.cdlib.org/), the mine was subsequently owned and operated by the Empire Star Mines Company and Newmont from 1934 to the 1950?s. It was worked extensively during the 1930?s when large tonnages of low-grade ore were mined. These tonnages included 10,285 in 1934, 129,866 in 1936, and 260,479 in 1939. There were approximately 200 employees in 1939. In 1940, a tailings dam failed (this facility was possibly at the Omega Diggings, about three miles northwest of the mine), which caused suspension of mining and milling, although development of ore bodies continued.

For many years, the mine property has been operated as a camp for youth groups. A clean-up operation at the property was ordered by the U.S. EPA in 2006 to remove lead and arsenic contamination at the site?s former assay building. (http://www.epa.gov/compliance/resources/newsletters/cleanup/cleanup29.pdf)

The Zeibright Mine is situated within the metasedimentary terrane of the Lower Paleozoic Shoo Fly Complex. The ore deposit consists of a quartz vein-dike complex that is emplaced in slate wallrock. The vein complex reportedly is nearly perpendicular in orientation and averages about 20 feet in width. On his economic geology map of the Colfax folio, Lindgren (1900) showed two north-trending quartz veins very near the deposit at the Zeibright Mine. The vein complex at the Zeibright Mine may be of similar strike. It appears to be part of a regional group of northerly trending veins that extends from Blue Canyon northward through the Washington and Graniteville mining districts.

According to Logan (1941), the ore is present in an ?impregnated dike? that carries bands of quartz on both walls; there was no ore outside the dike. Besides native gold, the ore deposit contains auriferous pyrite, chalcopyrite, and pyrrhotite. Concentrations of the sulfides are not known, but are assumed to be low. MacBoyle (1919) reported an ore shoot that extended at least 400 feet down-dip and had a length on the vein of about 160 feet.

Mineralization is a Mesozoic deposit (Mineral occurrence model information: Model code: 273; USGS model code: 36a; Deposit model name: Low-sulfide Au-quartz vein; Mark3 model number: 27), hosted in Ordovician-Devonian slate of the Shoo Fly Complex and Mesozoic aphanitic volcanic rock. The ore body is tabular and 6.1 meters thick. The dike is 20 feet thick with bands of quartz. Controls for ore emplacement include ore shoots in quartz veins formed along fractures in the metamorphic country rock. The genetic relationship of the mineralization to the dike is not certain. No specific local alteration was reported, although there is a vague reference by MacBoyle (1918) to the slate wallrock being "lightly changed at contact with the ledge." Local rocks include Paleozoic marine rocks, undivided, unit 4 (Western Sierra Nevada) and/or Tertiary pyroclastic and volcanic mudflow deposits, unit 9 (Cascade Range).

Regional geologic structures include the Melones Fault Zone.

Commodity information: Ore materials: native gold and auriferous sulfides (pyrite, chalcopyrite, and pyrrhotite); gangue materials: quartz, dike rock.

Workings include underground openings with a length of 301.75 meters and an overall depth of 533.4 meters and comprised of adits, stopes and a shaft. According to Logan (1941), the vein was initially developed by adits, one of which was 990 feet long. Subsequent mining was accomplished through a vertical shaft that reached 1,750 feet in 1940 (the current depth may be about 1,900 feet). Stoping at that time reached a depth of 800 feet. Amalgamation, flotation, and cyanidation processes were used at this mine.

Production data are found in: MacBoyle, Errol (1918); Logan, Clarence August (1941).

Clark (1970) estimated production at the Zeibright Mine to be in excess of $1 million (period values). There was significant production during the 1930's.

Estimated yield was $2.10 to $3.00 (period values) Au/ton; sulfides at $12 to $14/ton.

Other Databases

Link to USGS MRDS:	10007621

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References