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Boston Mine (Boston Consolidated; Esperanza), Mokelumne Hill, Mokelumne Hill District, East Belt, Calaveras Co., California, USA

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A former Au-Pb-Zn-Cu mine located in sec. 5, T5N, R12E, MDM, about 4.65 km NE of Mokelumne Hill (town) (located along Indian Creek). The property consisted of 9 claims (3 patented and 6 unpatented). Active during the 1870's, 1892-1900, 1920-1925, 1933-1935, and from 1935 to 1937. MRDS database stated accuracy for this location is 100 meters.

Mineralization is a vein deposit hosted in schist. The ore body strikes N and dips 30-40E at a width of 15.24 meters. The vein is in rocks of the Calaveras Formation, consisting locally of limestone, schist and serpentine intruded by diorite. The vein is a crushed diorite dike and contains inclusions of the host rock schist. At the 100 foot level, the vein is 40 to 50 feet thick. At the 300 foot level the footwall is a hard, black dike with marble between it and the vein. On the hanging wall to the N there is ground-up quartz with successive layers of serpentine, limestone and black schist. Zinc and copper sulfides are present. Local rocks include Paleozoic marine rocks, undivided, unit 4 (Western Sierra Nevada).

Workings include surface and underground openings with an overall depth of 204.52 meters. In 1892 surface ore was being mined. Extensive underground mining began in 1893 and a 1,000 foot shaft was completed in 1900. The shaft is inclined with levels at the 50, 100, 200, 300, 500, 700 and 950 foot levels. Most of the ore was mined at the 150 level during later operations. No deep development was undertaken. There is also a glory hole over the 50 foot level. There are numerous crosscuts, drifts, raises, etc. A small amount of work was done with little production.

Production data are found in: Clark, Wm. B. & P.A. Lydon (1962).

The total output of the mine was estimated at $1,000,000 (period values).

The average grade of the ore was $35 ton/Au (period values), with high-grade pockets encountered.

Analytical data results: 3 to 4% auriferous iron sulfides.

Mineral List

5 entries listed. 5 valid minerals.

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Crawford, James John (1894), Twelfth report of the State Mineralogist: California Mining Bureau. (Report 12): 12: 90.

Logan, Clarence August (1925), Sacramento field division: California Mining Bureau. (Report 21): 21(2): 145-146.

Logan, Clarence August (1925), Sacramento field division: California Mining Bureau. Report 21: 145.

Franke, Herbert A. & C.A. Logan (1936), Mines and mineral resources of Calaveras County: California Division Mines (Report 32): 32: 245.

Eric, J.C. (1948), Tabulation of Copper Deposits in California in: Copper in California: California Division of Mines Bulletin 144: 218.

California Division of Mines (1957), Economic Mineral Map of California No. 7.

Goodwin, Joseph Grant (1957) Lead and zinc in California. California Journal of Mines and Geology, Division of Mines (Report 53): 53(3&4): 426.

Clark, Wm. B. & P.A. Lydon (1962), Mines and mineral resources of Calaveras County, California: California Division of Mines & Geology County Report 2; [… Geological Society of America Proceedings, 1933: 312-313, 1934]: 43, 140, 245, 299 & Pl. B.

USGS (2005), Mineral Resources Data System (MRDS): U.S. Geological Survey, Reston, Virginia, loc. file ID #10028912 & 10260289.

U.S. Bureau of Mines, Minerals Availability System (MAS) file ID #0060090485.

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