Invincible prospect, Blue Eagle and Exposed Reef group, Alum Gulch, Harshaw District, Patagonia Mts, Santa Cruz Co., Arizona, USA

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

Lenon, Robert (1964) Lenon’s map of Santa Cruz County.

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.

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

U.S. Bureau of Mines files, Invincible prospect.

Arizona Bureau of Mines card file Santa Cruz County.

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

MRDS database Dep. ID file #10048341, MRDS ID #M899928; and, Dep. ID #10259224, MAS ID #0040230232.

A Cu-Au-Zn-Ag-Pb prospect with undeground workings located in the NW¼SW¼ sec. 19, T22S, R16E, 2½ miles south of Patagonia, in the north foot of the Patagonia Mountains, in Alum Gulch, 2.5 miles S of Patagonia, between the Flux and Andes Mine groups, at an elevation of 4,200 feet, on National Forest land. Located on the N side of Alum Gulch. The Blue Eagle group is located to the SW and the Exposed Reef Mine is located about 1.0 mile to the S. The Invincible claim is one of 22 unpatented lode claims comprising the Blue Eagle and Exposed Reef group.
Discovered 1875. Owned/operated by the Ivanhoe Mining Co., of Minneapolis, MN. NOTE: Alternate coordinates provided: 31.49444N, 110.74806W; and, 31.4953N, 110.7483W.

Mineralization is disseminated cupriferous pyrite and minor amounts of chalcopyrite in massive porphyritic rhyolite country rock. It is cut by a series of joints dipping 25º to 30º NNW., in which there is a concentration of nearly pure iron sulphides in veinlets or bands, the widest 1½ inches wide. The ore zone is 6.1 meters wide. Ore concentration involved secondary enrichment. Surface alteration exists to unknown depths. Associated rock units are the Mt. Wrightson Formation and the Josephine Canyon Diorite.

Local structures include a general structure common to regional formations, which is sheeting that dips 40NNW. Rhyolite is cut by a series of joints dipping 25-30 NNW.

Tectonic elements include the Alum Gulch and Red Mountain Fault Blocks.

The target of the tunnel is a 20 foot wide quartz vein several hundred feet above and 500 feet from the tunnel mouth. The iron and copper sulphides it includes carry gold. Post-mining mineralization includes sulphur, alum and chalcanthite.

Workings include a 60 foot tunnel running N.25ºE., into the base of Red Mountain.

Early 1900's assay values averaged 1-3% Cu and about $1/ton Au. The deposit wall rock was tested for the manufacture of H2SO4, with concentrations averaging 33% Fe and 35-36% S.