Located 18 miles south of Tucson near the Sierrita Mountains and organized in 1877, the Pima Mining District had humble beginnings with several small mining camps.
Deposits of copper, silver, lead, zinc and later molybdenum drew an interest to the area, including early operations conducted by the Emperor Copper Co. (1883), the Azurite Copper and Gold Co. (1897), Twin Buttes Mining and Smelting Co. (1903), Mineral Hill Consolidated Co. (1906) and ASARCO (1915).
Originally worked by the Spanish for gold and silver in the 18th century, the remains of arrastras and shallow shafts were evident during early American development. Several noteworthy operations established in the district included the Mineral Hill, San Xavier and Twin Buttes mines.
Early on, ores were treated at sites including a local smelter with a 30-ton daily capacity. The smelter operated for a year followed by other short-lived smelters, including a 150-ton smelter built by the Pioneer Smelting Co., a mile-and-a-half west of Sahuarita at Camp Corwin in 1912.
Shipments of concentrates from later mills established around Sahuarita were also sent to smelters at Hayden, El Paso and, briefly, Sasco.
Several small camps operated in the area, including one named Azurite, another called San Xavier — later changed to Olive for a nearby mine — and Twin Buttes.
Azurite, located a half-mile south of the Mineral Hill Mine, reached a population of 125 by the turn of the century. The high-grade lead-silver ores acquired from the San Xavier Mine before 1900 made it an attractive investment, having yielded a value of around $750,000.
Four miles farther south was the Twin Buttes Camp that included a cluster of buildings housing a bunkhouse, a butcher shop, a company store and a mess hall. The 10-mile Twin Buttes Railroad carried ore from the Senator Morgan Mine at Twin Buttes to the town of Sahuarita.
A line also connected Sahuarita with the Southern Pacific Railroad in Tucson. Depending on the profitability from local mines, the Twin Buttes Railroad operated from 1906 to the late 1920s, finally closing when mining in the district declined.
The Pima Mining District underwent a revival in 1950 when Banner Mining Co. bought the properties, including the Mineral Hill and Daisy mines, which were a half-mile from each other. Banner subsequently conducted mining and milling operations at the site.
The Pima Mining Co. and the Eagle-Pitcher Co. were also involved in mining ventures in the area.
The United Geophysical Co., using sensitive instrumentation, was responsible for the discovery of ore bodies that led to the establishment of open-pit mining operations at Twin Buttes in the 1960s. In 1962, the copper production from these early mines contributed to Pima County’s title of top copper producer in Arizona.
Closed in 1994, the Twin Buttes Mine was acquired in 2009 by Freeport McMoRan, which later carried out a drilling program to determine the size and quality of the deposit. The Twin Buttes Mine is estimated to contain 700 million tons of copper and molybdenum mineralization with a copper grade of 0.43 percent. Its future as an active mine depends on a sustainable high market price of copper and adequate water supply to run its operations.