Commonwealth Mine (Pearce Mine; Silver Ware Mine; Brockman Mine; Smith Mine; Rinaud Mine; Ritter Mine; Eisenhart vein), Pearce, Pearce District, Pearce Hills, Sulphur Springs Valley, Cochise Co., Arizona, USA
|Latitude & Longitude (WGS84):||31° 54' 4'' North , 109° 48' 56'' West|
|Latitude & Longitude (decimal):||31.90111,-109.81556|
|Other regions containing this locality:||Sonoran Desert, North America|
A former small underground Ag-Au-Mo-Cu-Pb-V-Silica mine located in the NE¼ sec. 5, T.18S., R.25E, 1/2 mile E of Pearce, on private land. Discovered by John Pearce in 1895. Produced 1895-1979. One of Arizona's major silver producers. Owned at times, or in part, by the C.O.R. Ford Corp. of Dallas, TX (1979); Commonwealth Mining and Milling Co.; Montana Tonopah Mining & Milling Co.; and the Commonwealth Development Co. Operated by GOURMET CHIEF INC. (1975). Additional names associated with this mine: Main Mine, North Mine, Hartery veins, Footwall Mine, Discovery stope.
Mineralization is irregular silver-gold halides and minor sulfo-salts with some manganese in quartz-calcite fissure veins and in fault breccia zones (on the hanging wall) in silicified Tertiary rhyolite and andesite volcanics. The ore zone is 1,219.2 meters long, 106.68 meters wide, depth to bottom of 152.4 meters, and 18.29 meters thick, striking N-S (main vein), and dipping 60E. Alteration is propylitic, silicification, and oxidation. It is more intense in and near vein fractures. Sericitic and K-feldspar alteration exists closest to the veins, with extensive argillic and propylitic alteration away from the veins. The associated rock units are the Pearce volcanics and the Brockman Andesite.
Local structures include volcanic flows that dip 35-40E. Fissure veins and fault breccia zones; N-S faults are pre-mineralization, others are post-mineralization.
Workings include a shaft(s). Two inclined shafts, 62 degrees, with extensive workings on 8 levels. The water level was at 700 feet, and a majority of mining was done above the water table, although shaft "C" was eventually sunk to 1,000 feet. There are about 20 miles of underground workings. The workings are 9,144 meters long in total and 152.4 meters deep. Over 1,000,000 tons of ore were produced from 1895 to 1942. Tailings being reworked, 1976-19, flotation methods. Intermittent shipments of tailings were made in the mid-1980'S. About 100,000 tons of tailings had been sold for use as high-silica smelter flux. It is estimated that up to a million tons of tailings remained. In addition, there are approximately 150,000 tons of mine dump material in the area that average 2.5 oz of Ag/t.
28 valid minerals.
This geological map and associated information on rock units at or nearby to the coordinates given for this locality is based on relatively small scale geological maps provided by various national Geological Surveys. This does not necessarily represent the complete geology at this locality but it gives a background for the region in which it is found.
Click on geological units on the map for more information. Click here to view full-screen map on Macrostrat.org
|Tortonian - Bartonian|
7.246 - 41.3 Ma
|Middle Miocene to Oligocene volcanic rocks|
Age: Cenozoic (7.246 - 41.3 Ma)
Description: Lava, tuff, fine-grained intrusive rock, and diverse pyroclastic rocks. These compositionally variable volcanic rocks include basalt, andesite, dacite, and rhyolite. Thick felsic volcanic sequences form prominent cliffs and range fronts in the Black (Mohave County), Superstition, Kofa, Eagletail, Galiuro, and Chiricahua Mountains. This unit includes regionally extensive ash-flow tuffs, such as the Peach Springs tuff of northwestern Arizona and the Apache Leap tuff east of Phoenix. Most volcanic rocks are 20-30 Ma in southeastern Arizona and 15 to 25 Ma in central and western Arizona, but this unit includes some late Eocene rocks near the New Mexico border in east-central Arizona. (11-38 Ma)
Reference: Horton, J.D., C.A. San Juan, and D.B. Stoeser. The State Geologic Map Compilation (SGMC) geodatabase of the conterminous United States. doi: 10.3133/ds1052. U.S. Geological Survey Data Series 1052. 
Guild, F.N. (1910), The Mineralogy of Arizona, The Chemical Publishing Co., Easton, PA.
Scott, W.A. (1916a) Commonwealth mine and mill at Pearce, Arizona: Mining and Engineering World (Chicago): 45: 187-188.
University of Arizona Bull. 41 (1916-17), Mineralogy of Useful Minerals in Arizona: 26.
Smith, L.A. (1927) The geology of the Commonwealth mine: Tucson, University of Arizona, M.S. thesis, 73 p.
Palache, C., Berman, H., & Frondel, C. (1951), The System of Mineralogy of James Dwight Dana and Edward Salisbury Dana, Yale University 1837-1892, Volume II: 24.
Galbraith, F.W. (1947), Minerals of Arizona, Arizona Bureau of Mines Bull. 153: 8, 14, 27.
Galbraith, F.W. & D.J. Brennan (1959), Minerals of Arizona: 42, 43, 64.
U.S. Atomic Energy Commission Preliminary Reconnaissance Report PRR A-P-46 (1953).
Keith, Stanton B. (1973), Arizona Bureau of Geology & Mineral Technology, Geological Survey Branch Bull. 187, Index of Mining Properties in Cochise County, Arizona: 69 (Table 4).
Howell, K.K. (1977) Geology and alteration of the Commonwealth mine, Cochise County, Arizona: Tucson, University of Arizona, M.S. thesis, 225 p.
Niemuth, N.J. (1987), Arizona Mineral Development 1984-1986, Arizona Department of Mines & Mineral Resources Directory 29, 46 pp.
Heylmun, Edgar B. (1988) Commonwealth Silver-Gold Mine, Arizona. California Mining Journal: 57(5): 14-16.
Sawyer, M.B., Gurmendi, A.C., Daley, M.R., and Howell, S.B. (1992) Principal Deposits of Strategic and Critical Minerals in Arizona, U.S. Bureau of Mines Special Publication, 334 pp.
Anthony, J.W., et al (1995), Mineralogy of Arizona, 3rd. ed.: 100, 147, 169, 182, 212-213, 234, 259, 261, 335, 372, 392, 425.
Atlas Corporation news release (1995) 9-7-1995.
Randol Mining Directory (1996/1997) U.S. Mines and Mining Companies: 133.
American Mining Handbook (1996): 242.
American Mining Handbook (1997): 277.
Arizona Bureau of Mines file data.
MRDS database Dep. ID file #10103554, MRDS ID #M030569; and, Dep. ID #10232286, MAS ID #0040030120.