A former large output surface Cu-Mo-Ag-Zn-Pb-Au mine located in the SE ¼ sec. 7, the SW ¼ sec. 8, the NW ¼ sec. 17 & the NE ¼ sec. 18, T.18S., R.12E., 5½ miles WSW of Twin Buttes and 20 miles SW of Tucson, on private land. Discovered 1960. Produced initially in 1970. Owned by the Duval Sierrita Corp (subsidiary of Pennzoil) until 1986; then, owned by Cyprus Mines Co. since 1990. An open pit copper-molybdenum-rhenium mine located near Tucson. Part of the deposit is mined by solution.

Mineralization is a V-shaped ore body that is part of the Esperanza-Sierrita deposit. Ore is superficially oxidized, disseminated chalcopyrite and pyrite with copper and molybdenum sulfides in seams and fractures in a large V-shaped orebody containing Triassic to late Laramide andesite porphyry, quartz monzonite, quartz latite, quartz diorite, and quartz monzonite porphyry, as well as a breccia pipe. Ore control was the fractures and seams plus the breccia pipe. Alteration is potassic, phyllic, argillic with supergene effects, propylitic. Associated rock units are the Ruby Star Quartz Monzonite Porphyry; and the Harris Ranch Quartz Monzonite.

Local structures include fractures that strike N50-85E and N50-25W that are steeply dipping.

Workings are an open pit operation 1,524 meters long and 914.4 meters wide. Pre-mine stripping began in 1968 with initial production in 1970. Starting in 1970, production through 1972 has been some 68,000,000 tons of Cu-Mo ore. In 1980 produced 90,000 tons of ore and 135,000 tons of waste daily. Average ore grade was about 0.24% Cu, 0.03 oz. Ag/T, 0.016% MOS2, and trace amounts of Au, Pb & Zn.

The Duval/Sierrita mine was developed by the Duval Corporation, originally, the Duval Texas Sulfur Company. The company diversified into copper in 1959, when it purchased the Esperanza orebody, which had been explored, but considered too poor to develop by Kennecott Copper Company, a few years earlier. Duval received an $83 million loan to develop the low-grade (0.28 percent copper) Sierrita deposit, located near the Esperanza mine. When it opened in 1970, Sierrita had an annual capacity of 80,000 tons of metallic copper.

The Sierrita Concentrator beginning operation in 1970 at a designed capacity of 72,000 STPD (short tons per day). Subsequent additions and modifications expanded capacity to 90,000 STPD. Ore Grade 0.32% Cu., 0.030% Mo. Daily Tons Milled 90,000 STPD annual copper production 94,600 tons; annual Molybdenum production 15,000,000 lbs.; and, annual silver production of 1,135,000 Ounces. A smelter for molybdenum was operated at the Duval/Sierrita Complex.

Other Databases

Wikipedia:	https://en.wikipedia.org/wiki/Sierrita_mine
Wikidata ID:	Q16900196
Link to USGS MRDS:	10137304
Link to USGS MRDS:	10210570
Link to USGS MRDS:	10305094

Other Regions, Features and Areas containing this locality

References