A former small surface and underground Cu-Ag-Mo-Au-Pb-Zn mine located on 5 patented claims in the NE¼NW¼ sec. 9, T24S, R16E, on the NE slopes of Mount Washington, on a southern tributary of San Antonio Canyon, 2½ miles SW of Duquesne (Washington Camp), on the east slopes of the Patagonia Mountains, on National Forest land. Discovered 1908 by Dennis Coughlin. Produced 1912-1955. Previous owners/operators include the Miami Copper Co.; Beyerle (1927); the Santo Nino Mining Co. (1926-1931); Young & Gardner (1943); Santo Nino Lessees (1954-1955); the Havalena Mining Co. (1910-1912); A. De La Ossa (1958); and, W.S. Talcott (1959). Owned by the Southern Copper Mining Co., New York (1959). Operated by Utah Construction and Mining Co., Utah International (1970).
The country rock of the area is a fresh gray quartz monzonite with very conspicuous joints. The principal joints strike north to N.10W. and dip 60º to 70ºW., and the secondary joints dip 0º to 10ºN.
Prominent fractures, both mineralized and unmineralized, are found in the mine and on the surface above the mine. The fractures strike N.45º to 50ºE. and dip 60ºN. to vertical. Where mineralized, the fractures may contain pink, feldspathized quartz monzonite, light cream-colored aplite, or pyrite- and chalcopyrite-bearing vein quartz. Where unmineralized, the fractures contain as much as 5 feet of white or limonite-stained gouge and breccia.
The principal ore-bearing formation is a pink feldspar-rich medium-grained granitic rock. The contact between the pink feldspar rock and the gray quartz monzonite country rock is gradational and very irregular and suggests that the feldspar has replaced the quartz monzonite. The principal body of the feldspathized rock is a roughly sheet-like body that averages only a few feet in width, strikes N.10ºW., and dips 70ºW. The maximum thickness observed was about 20 feet, but pocketlike extensions or apophyses extend out from the main mass for more than twice that distance.
Pyrite and chalcopyrite are disseminated through most of the feldspathized rock and for several feet into the adjacent quartz monzonite. Large and small vugs and pockets of massive and terminated quartz are scattered irregularly throughout the feldspathized rock.
Molybdenite is found principally in pockets and lenses that are as much as 10 feet in maximum dimension and are located at irregular intervals in the feldspathized rock. Observed molybdenite pockets were associated with conspicuous joints. The high-grade molybdenite is disseminated for 2 to 3 inches out into the rock surrounding the joints.
Workings included development on 7 levels. The stoped area was about 200 feet long, more than 200 feet high, 30 to 40 feet wide on the stope level, and 5 to 6 feet wide in the upper levels. Worked sporadically from the early 1900's-1955.
References:
Schrader & Hill (1915), Mineral deposits of the Santa Rita and Patagonia Mountains, Arizona, USGS Bull. 582.
Schrader (1917), The geologic distribution and genesis of the metals in the Santa Rita-Patagonia Mountains, Arizona, Economic Geology: 12: 237-269.
Tenney, J.B. (1927-1929) History of Mining in Arizona, Special Collection, University of Arizona Library & Arizona Bureau of Mines Library: 299-300.
Blanchard, R. & P.F. Boswell (1930), Limonite types derived from bornite and tetrahedrite, Economic Geology: 25: 557-580.
Galbraith, F.W. (1947), Minerals of Arizona, Arizona Bureau of Mines Bull. 153: 19, 23, 25.
Kirkemo, H., et al (1965), Investigations of Molybdenum Deposits in the Conterminous United States 1942-60, Contributions to Economic Geology, USGS Bull. 1182-E: E14-E16;
Kupfer, D.H. (1965) Santo Nino mine, in Kirkemo, H., Anderson, C.A., and Creasey, S.C., Investigations of molybdenum deposits in the conterminous United States, 1942-60: U.S. Geological Survey Bulletin 1182-E, p. E14-E16.
Frondel, J.W. & F.E. Wickman (1970), Molybdenite polytypes in theory and occurrence. II. Some naturally-occurring polytypes of molybdenite, American Mineralogist: 55: 1857-1875.
Simons, F.S. (1974) Geologic map and sections of the Nogales and Lochiel
quadrangles, Santa Cruz County, Arizona: U.S. Geological Survey Miscellaneous Investigations Series Map I-762, 9 p., 1 sheet, scale 1:48,000.
Kuck, P.H. (1978) The behavior of molybdenum, tungsten, and titanium in the porphyry copper environment: Tucson, University of Arizona, Ph.D. dissertation, 277 p.
Anthony, J.W., et al (1995), Mineralogy of Arizona, 3rd.ed.: 167, 302, 341, 359.
Arizona Department of Mineral Resources file data, Santo Nino Mine.
U.S. Bureau of Mines files, Santo Nino Mine.
U.S. Bureau of Mines field notes.
U.S. Bureau of Mines Coronado National Forest Study Report.
Arizona Bureau of Mines card file Santa Cruz County.
MRDS database Dep. ID file #10026908, MRDS ID #M000982; and, Dep. ID #10283632, MAS ID #0040230350.
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Map Reference: 31°21'40"N , 110°43'3"W
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