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Exposed Reef Mines (Saint Louis Mine), Blue Eagle and Exposed Reef group, Alum Gulch, Harshaw District, Patagonia Mts, Santa Cruz Co., Arizona, USA

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Ref.: Schrader, F.C. & J.M. Hill (1915), Mineral deposits of the Santa Rita and Patagonia Mountains, Arizona, USGS Bull. 582: 257-258.

Elsing, M.J. (1921) Report.

Moores, R.C., III (1972) The geology and ore deposits of a portion of the Harshaw district, Santa Cruz County, Arizona: Tucson, University of Arizona, M.S. thesis, 98 p.

Simons, F.S. (1972) Mesozoic stratigraphy of the Patagonia Mountains and adjoining areas, Santa Cruz County, Arizona, in Mesozoic stratigraphy in southeastern Arizona: U.S. Geological Survey Professional Paper 658-E.

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.

USGS Lochiel Quadrangle topo map.

U.S. Bureau of Mines Coronado National Forest Study Report.

U.S. Bureau of Mines - Arizona Bureau of Geology and Mineral Technology file data - Exposed Reef Mines.

Arizona Department of Mineral Resources Exposed Reef and Blue Eagle Mine file.

Arizona Bureau of Mines card file Santa Cruz County.

MRDS database Dep. ID file #10048345, MRDS ID #M899932; and, Dep. ID #10283184, MAS ID #0040230187.

A former small underground Cu-Ag-Pb-Zn-Au-Fe mine located in the SW¼NE¼ sec. 30, T22S, R16E, 4 miles S of Patagonia, between the Flux and Andes Mine groups. Located on the NE side of Alum Gulch. The Blue Eagle group is located ½ mile to the SW, on the S side of Alum Gulch. Discovered 1875. Owned by Mr. Albert De Saulles and Helen & Doris Sibold (1953); and, also included Mr. John Farley; D. Dowd; and, J.B. Shannon.

Mineralization is a vein deposit with ore occurring in veins, fissures and contacts in rhyolite, and contacts with granoporphyry and quartz diorite. Ore concentration was secondary enrichment along fault fissures and replacement of wall rock. High grade ores tended to concentrate with bands of quartz in fissure veins. Extensive surface oxidation. Associated rock units include the Mt. Wrightson Formation and the Josephine Canyon Diorite.

Ores of the Exposed Reef and Blue Eagle groups are primarily argentiferous coppers with some gold and a stromg iron content. Numerous veins occur on the property containing low-grade sulfide ores. The main vein trends NW-SE across several claims. Veins generally have very wide mineralized outcrop copper ore bodies that increase, both in size and values, with depth. Veins vary in width from 1-30 feet.

The main vein paralleled by banded iron formation-hematite dike showing some copper stain, and by several smaller parallel quartz veins. There are five principal veins on the property. The ore zone is 914.4 meters long, 9.14 meters wide, strikes W and NW and dips nearly vertically. A general structure common to regional formations is a sheeting which dips 40NNW.

Tectonic elements include the Alum Gulch Fault Block.

Workings are 95.1 meters deep and include the 312 foot deep Exposed Reef shaft; a 36 foot long tunnel and open cut on the Saint Louis claim; the 500 foot long Exposed Reef tunnel that cuts 3 veins; numerous winzes and raises extending from shafts and tunnels; a 300 foot tunnel and 112 foot shaft on the Red Fox No. 1 claim; a total of 11 tunnels, from 10 to 500 feet long. Thee are 600 feet of drifts and crosscuts.

Assay values averaged 15% Cu, 15 oz./ton Ag, and $2.00/ton Au. No records of production.

Mineral List

9 entries listed. 9 valid minerals.

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