Kofa District, Kofa Mts (S.H. Mts), Yuma Co., Arizona, USA

A Au-Ag-Mn-W-Cu-Pb-F mining district located in T1-2S, R15-17W, in the southern/SW margin of the Kofa (S.H.) Mountains.

Mineralization within the district varies: (1) Spotty, but often high-grade, fine-grained, gold and silver mineralization in lensing quartz-calcite, brecciated rock, fissure veins cutting Cretaceous or Tertiary andesite and Mesozoic schist or slate. Minor copper and lead, and often considerable manganese and local fluorite. Wall rocks are strongly silicified; (2) Erratic and irregular manganese oxides in fracture zones in fragmented Cretaceous or Tertiary andesitic volcanics; and, (3) Spotty stringers, pods, and disseminated grains of scheelite, associated with quartz and iron oxides, in fracture zones in fragmented volcanics and schist.

Workings include 2 major mines and numerous prospects and small mines operated mainly in the late 1800's and early 1900's, with small, intermittent operations until 1954. Total estimated and recorded production of precious and base metals through 1974 would be some 779,500 tons of ore containing about 227,500 oz. Au, 103,700 oz. Ag, 3 tons of lead and one ton of copper. Over 1,000 oz. of placer gold were recovered. Manganese production was about 230 long tons of 27% Mn and about 94 short ton units of WO3. Total production s set at some $5,000,000 (period values).

References:
Blake, W.P. (1898) Distribution of metallic wealth in Arizona, in Report of the Governor of Arizona to the Secretary of the Interior for fiscal year ending June 30, 1898: Washington, D.C.: 19-86.

Jones, Jr., E.L. (1915), A Reconnaissance in the Kofa Mountains, Arizona, USGS Bull. 620: 164.

Thompson (1925), Arizona Mining Journal, Nov 1925: 9(12): 7.

Wilson, E.D. (1933) Geology and Mineral Deposits of Southern Yuma County, Arizona. Arizona Bureau of Mines Bulletin 134: 106-116;

A.I.M.E. Ore deposits of the western states (1933): 629.

Wilson, E.D., Cunningham, J.B., and Butler, G.M. (1934), Arizona Lode Gold Mines and Gold Mining (revised 1967), Arizona Bureau of Mines Bull. 137: 136-143.

Hewett, D.F. (1964), Veins of hypogene manganese oxide minerals in the southwestern United States, Economic Geology: 59: 1429-1472.

Keith, Stanton B. (1978) State of Arizona Bureau of Geology and Mineral Technology, Geological Survey Branch Bull. 192, Index of Mining Properties in Yuma County, Arizona: 154 (Table 4).

Hankins, D.D. (1984), Geologic setting of precious metals mineralization, King of Arizona district, Kofa Mountains, Yuma County, Arizona, San Diego State University M.S. thesis.

Anthony, J.W., et al (1995), Mineralogy of Arizona, 3rd. ed.: 225, 354.

Arizona Bureau of Mines file data.