Loma Prieta Mine (Commercial Mine; Copper Glance Mine; Patented claims MS 3425; Copper Hill Mine [?]; Copper Basin group [in part]), Copper Basin Mining District, Sierra Prieta Mountains, Yavapai County, Arizona, USAi

Regional Level Types
Loma Prieta Mine (Commercial Mine; Copper Glance Mine; Patented claims MS 3425; Copper Hill Mine [?]; Copper Basin group [in part])	Mine
Copper Basin Mining District	Mining District
Sierra Prieta Mountains	Mountain Range
Yavapai County	County
Arizona	State
USA	Country

A former underground Cu-Ag-Au-Pb-Mo-Zn mine located on the boundary of secs. 20 & 21 (in the SW¼ sec. 21), T.13N., R.3W., ½ mile east of the Copper Hill deposit (Wilhoit 7.5 minute topo map). Discovered in 1885 by Dan O'Carroll. Owned by Mrs. Sophia Smoot, Prescott (1943); and, the Loma Prieta Mines Co. (1916-1918 timeframe). Owned by the Phelps Dodge Corp., and under lease to F.S. Schemmer (circa 1943). Discovered 1890. Produced 1906-1968 and produced 1917-1918. Consists of patented claims: 485, 486, 487, 488, 489, 491, 510, 511, 512, 513, 514, 515, 516, and 518. Claims extend into the SE¼SE¼SE¼ of sec. 17, S½SW¼ of sec. 16, the N½ of sec. 28, and the N½NE¼NE¼ of sec. 29 & 21. Claims extend into RRC 59B.

Mineralization is a breccia pipe about 600 feet in diameter at the surface with a pipe-like, cylindrical, vertical ore body. Ore control was ore localized in breccia pipes and along late stage dikes along with disseminated ore. Alteration was sericitization and argillization. Ore concentration was oxidation and enrichment at near surface. Alteration was seritization and clay. An associated rock unit is the Copper Basin Stock.


Area structures include the Copper Basin Stock elongate NNE-SSW, faults N20-26W and N20-30E. Foliation in Precambrian rocks = N20E to N20W, with a steep dip west. Breccia around older quartz latite porphyry. The prevailing rock is fine- to medium-grained quartz diorite, deeply weathered in part and locally mineralized along joints with pyrite. Dikes of rhyolite and quartz diorite porphyry intrude the quartz diorite.

In the vicinity of the mine the quartz diorite has been brecciated, altered by hydrothermal activity, and cemented by quartz containing sulfide minerals, which are oxidized at the surface to limonite. The general elliptical horizontal outline of the breccia and the heterogeneity indicate that the mineralized breccia is part of a breccia pipe 250 feet in diameter.

The quartz cementing the breccia fragments is of two types. The more common type is white, contains coarse feldspar crystals, and has vugs lined with dolomite. The less common type of cementing quartz is dense and flinty, and its fuzzy margins against the quartz diorite suggest some replacement of the fragments. In both types of quartz sulfide minerals, pyrite and chalcopyrite, form coarse blobs and bunches that are generally confined to the center of the cementing veins. Molybdenite finely divided and forms narrow veinlets either at the margin of the veins or crosscutting the quartz. In a few places, the quartz veins are brecciated and cemented by younger, finely-divided molybdenite.

Development work occurred during the period 1916-18. The underground workings comprise the 46, 75, 150, and 400 levels and a vertical shaft 414 feet deep. Workings include shafts, adits, drifts and crosscuts, all within limits of the breccia pipe. Incomplete production records to 1955 show that more than 150,000 tons of high-silica copper ore was produced.

Other Regions, Features and Areas containing this locality

References