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Iron Duke Mine, Hunter Valley Mountain, Hunter Valley District, West Belt, Mariposa Co., California, USA

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A former lode Au mine located in sec. 4, T4S, R16E, MDM, 2.4 km (7,800 feet) SSE of Hunter Valley Mountain (coordinates of record), in the headwaters area of Temperance Creek (¼ mile SE of the Oaks & Reese Mine). Operated in 1865, 1934-1935 and 1938-1941. MRDS database stated accuracy for this location is 500 meters.

Mineralization is a vein deposit (Blue Lead vein), hosted in rocks of the Amador group (chert, andesite, greenstone, tuff and Late Jurassic slate). Thye ore body strikes N30-35W and dips 61NE at a thickness of 1.22 meters and a length of 457.2 meters. The Blue Lead vein is intersected by cutter veins at angles of 45 to 90 degrees. The cutter veins ar hosted in greenstone. Controls for ore emplacement included junctions of cutter veins with main vein, and the cutter vein themselves. Local rocks include Jurassic marine rocks, unit 1 (Western Sierra Nevada and Western Klamath Mountains).

Workings include underground openings with a total length of 205.74 meters and an overall depth of 60.96 meters. A single compartment, 200 foot deep, shaft is inclined at 61 degrees. There is a 2,500 foot long drift driven S on the 185 level to the cutter vein. A secondary drift is 100 W W, plus a 30 foot raise. There is a 75 foot drift on cutter vein 3. A 35 foot shaft is partly caved. Shallow surface workings ar near Specimen Hill.

Production data are found in: Bowen, O.E., Jr. & C.H. Gray, Jr. (1957).

Total production was $21,800 (period values). During the sinking of the shaft, a small pocket yielded 190 ounces of Au. One pockset in the secondary drift yielded $524 (period values). $16,000 (period values) of Au was taken from Specimen Hill workings. $3,800 (period values) was mined from a small stope at the junction of the Blue Lead vein and cutter vein at 104 feet, plus $2,000 (period values) from the raise on cutter vein No. 2. Sulfide concentrates yielded about $50 (period values) Au/ton.

Mineral List

3 entries listed. 3 valid minerals.

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Laizure, Clyde McK (1928), Mariposa, Madera Counties: California Journal of Mines and Geology, California Mining Bureau (Report 24): 24(2): 133.

Bowen, O.E., Jr. & C.H. Gray, Jr. (1957), Mines and mineral deposits of Mariposa County, California: California Journal of Mines and Geology (Report 53): 53(1&2): 113-114.

USGS (2005), Mineral Resources Data System (MRDS): U.S. Geological Survey, Reston, Virginia, loc. file ID #10076870 & 10115227.

U.S. Bureau of Mines, Minerals Availability System (MAS) file ID #0060430132.

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