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Keystone group (Darwin-Keystone; Keystone Mine), Darwin, Darwin District, Darwin Hills, Inyo Co., California, USA

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A former Cu-Au-Ag-Pb-Fe mine located in secs. 19, 20, 29 & 30, T19S, R41E, MDM, 2.5 km (1.6 miles) ESE of Darwin. MRDS database stated accuracy for this location is 100 meters.

Mineralization is a vein deposit hosted in limestone. The ore body strikes N and dips 60W, at a thickness of 3.05 meters. The ore is highly oxidized and poorly exposed at 2 to 10 feet thick. It has been ex[ploited for a strike length of 40 feet underground. The mine is on folded and faulted rock of the Keeler Canyon Formation. The rocks are brown-weathering, silty limestone and blue-gray limestone. Limestone is partly altered to calc-hornfels. The dominant faults trend between N70E and E, and dip steeply. Local rocks include Carboniferous marine rocks, unit 2 (SE California Carbonate Assemblage).

Local structures include folds and faults.

Workings include underground openings. The lower workings are comprised of the Keystone adit at 626 feet in length, a 210 foot drift, 120 feet of crosscuts, a 175 foot steeply-inclined winze, plus small stopes. The upper workings include the McDonald adit, which is caved 145 feet from its portal, 135 feet of drifts, plus minor crosscuts.

Production data are contained in: Hall & MacKevett (1958): 32.

Production statistics: Year: 1941 (period 1940-1941): ^0.04 ounce Au/ton; 27.9 ounces Ag/ton; 25% Pb; 0.6% Zn; 20% Fe.

Reported: 800 tons of sorted ore shipped from the lower winze and the zone between the two workings.

Mineral List

4 entries listed. 2 valid minerals.

The above list contains all mineral locality references listed on This does not claim to be a complete list. If you know of more minerals from this site, please register so you can add to our database. This locality information is for reference purposes only. You should never attempt to visit any sites listed in without first ensuring that you have the permission of the land and/or mineral rights holders for access and that you are aware of all safety precautions necessary.


Hall, Wayne Everett & E.M. Mackevett (1958), Economic geology of the Darwin quadrangle, Inyo County, California: Calif Division of Mines Special Report 51, 77 pp.: 31-32.

Pemberton, H. Earl (1983), Minerals of California; Van Nostrand Reinholt Press: 102 (map 3-6).

USGS (2005), Mineral Resources Data System (MRDS): U.S. Geological Survey, Reston, Virginia, loc. file ID #10033982 & 10285394.

U.S. Bureau of Mines, Minerals Availability System (MAS) file ID #0060270562.

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