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Cosumnes Mine (Cosumnes Melton; Melton; Middle End), Grizzly Flat, Grizzly Flat District, East Belt, El Dorado Co., California, USA

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Latitude & Longitude (WGS84): 38° 39' 53'' North , 120° 32' 0'' West
Latitude & Longitude (decimal): 38.6647222222, -120.533333333

A former lode Cu-Au-Zn-Pb-Ag-Sb occurrence/mine located in secs. 3 & 4, T9N, R13E, MDM, 3.2 km (2.0 miles) N of Grizzly Flat, just S of the Cosumnes River, on private land. Operated by the Caldor Lumber Company. Operated in the 1880's, 1894, 1928 to 1942 & 1942 to 1951. MRDS database stated accuracy for this location is 100 meters. Active during the 1880's and in 1894 as the Melton Mine; reopened in 1928 as the Middle End Mine and operated almost continuously until 1942. Operated by the Cosumnes Mines, Inc. from 1945 to 1950, when purchased by the present owner. The workings are shown in the W½NW¼ sec. 3 on USGS topo map.

Mineralization is a vein deposit hosted in diorite. The ore body strikes NNE and dips W at a thickness of 0.91 meter. Most ore was from the Main or Middle vein that dips steeply at an average of 3 feet thick. Appreciable amounts of galena and pyrite, with sphalerite, chalcopyrite, stibnite and arsenopyrite are present in the ore. Local rocks include Mesozoic gabbroic rocks, unit 2 (undivided).

Workings include underground openings comprised of a 380 foot crosscut adit and several thousand feet of drifts.

Production data are found in: Goodwin, Joseph Grant (1957).

About 10,000 pounds of Pb and some Cu were produced during the period 1928 to 1951, in addition to Au & Ag.

During the last years of production the ore contained up to $25 (period values) Au/ton with sulfide concentrates yielding $100 to $200 (period values) Au/ton.

Mineral List

8 valid minerals.

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Logan, Clarence August (1938), Mineral resources of El Dorado County: California Journal of Mines and Geology, California Division Mines (Report 34): 34(3): 265.

USGS quadrangle Sly Park, California, topo map (1953).

Clark, Wm. B. & D.W. Carlson (1956), Mines and mineral resources of El Dorado County, California: California Journal of Mines and Geology: 52(4): 413, 494.

Goodwin, Joseph Grant (1957), Lead and zinc in California. California Journal of Mines and Geology, Division of Mines (Report 53): 53(3&4): 441.

Pemberton, H. Earl (1983), Minerals of California; Van Nostrand Reinholt Press: 82, 127.

USGS (2005), Mineral Resources Data System (MRDS): U.S. Geological Survey, Reston, Virginia, loc. file ID #10030434, 10101158 & 10236224.

U.S. Bureau of Mines, Minerals Availability System (MAS) file #0060171082.

Mineral and/or Locality  
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