Black Rock Mines (Black Rock group; Black Magic prospects), Limestone Gulch, Copper Mountain District (Clifton-Morenci District), Shannon Mts, Greenlee Co., Arizona, USA
A former surface and underground Mn mine on 9 unpatented claims, located in the NE¼NE¼ sec. 19 and the SE¼SE¼ sec. 20, T4S, R30E, 2.2 miles N of Clifton, on BLM-administered land. This mine is located ¼ mile N of Limestone Gulch in an unnamed wash. The wash is located ¼ mile NE of the mouth of Limestone Gulch. Discovered in 1906 by Del M. Potter, who owned the property from 1906 to 1949. Produced 1951 - ?. Owned by Matt and Ed Danenhauer; N. T. Jackson; Ernest W Foote: Danenhauer Business Service (1956). Past operators included Gordon S. Buttorff; Tom U. Wolfe; Manganese Valley Mines Inc; Mines Contracting Inc; Danenhaver Brothers; and United States Manganese Corporation (Brock and Schuster).
Mineralizaton is an irregular ore body hosted in the Longfellow Limestone. The ore zone is 45.72 meters long, 22.86 meters wide, and 10.67 meters depth to top with a thickness of 15.24 meters, striking NE and dipping 45NW (strike and dip are estimated). An associated rock unit is the Precambrian granite-granodorite complex. Manganese occurs within a relatively thick bed of chert in the Longfellow Limestone. Ore bodies border a large fault between the contact of chert and the limestone. Ore concentration was secondary enrichment of the fracture zone, replacement of limestone wall rock, and, in general, erratic mineralization of the chert bed proportional to the intensity of the fracturing. Alteration was replacement of the limestone and crushed chert particles in brecciated areas. The upper contact of chert and limestone is very irregular. Most ore exposures are located on the canyon walls, 20 to 40 feet above the bed of the gulch. At the mouth of the canyon, the erratically mineralized chert bed is about 50 feet thick. 0.1 mile further up the wash, ore-bearing chert beds are exposed to lengths of 150 feet.
Where fracturing was moserate, manganese minerals were deposited in the fractures and replaced part of the limestone walls. In brecciated areas, the manganese minerals replaced the crushed chert particles and formed high-grade pockets. Manganese ore is primarily located in the chert bed rather than in the limestone wall rock or granite beds.
Area structures include a NE-trending large fault between limestone and Precambrian granite that comprises massive bluffs overlooking the San Francisco River.
Tectonic component is deeply sunken limestone fault blocks east of the Copper King Massif with a vertical throw of about 3000 feet.
Workings included a 40 foot adit, a 50 foot deep vertical shaft, a 27 foot deep shaft with 13 feet of drifts, 4 open cuts, several small open prospect pits, and small mill on the San Francisco River. Mining consisted of opening up small veins or ore lenses on the sides of the canyon walls and scraping out ore. 1952 assay values ranged from 12-48% Mn.
ReferencesLindgren W. (1905) The Copper Deposits of the Clifton-Morenci District, Arizona. USGS Professional Paper 43: San Francisco River Geology Comments.
Farnham, L.L., Stewart, L.A., and Delong, C.W. (1961), Manganese Deposits of Eastern Arizona, US Bureau of Mines Information Circular 7990: 101-102.
Bennett (1975) Geology and Origin of the Breccias in the Morenci-Metcalf District, Greenlee County, Arizona, MS thesis, University of Arizona, 153 pp.
Arizona Department of Mineral Resources file data, Black Rock Mines.
MRDS database Dep. ID #10109875, MRDS ID #M800416; and Dep. ID #10234833, MAS ID #0040110022.
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2 entries listed. 1 valid mineral.
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