The Sierrita mine is a porphyry copper deposit that has oxide, secondary sulfide and primary sulfide mineralization. The predominant oxide copper minerals are malachite, azurite and chrysocolla. Chalcocite is the most important secondary copper sulfide mineral, and chalcopyrite and molybdenite are the dominant primary sulfides.

Sierrita mine has been in operation since 1959 and is an open-pit copper and molybdenum mining complex located in Pima County, Arizona, approximately 20 miles southwest of Tucson and 7 miles west of the town of Green Valley and Interstate Highway 19. The site is accessible by a paved highway and by rail.

The available mining fleet consists of twenty-four 235-metric-ton haul trucks loaded by three electric shovels with bucket sizes ranging from 34 to 56 cubic meters, which are capable of moving an average of 175,000 metric tons of material per day.

The highest bench elevation is 1,300 meters above sea level and the ultimate pit bottom is expected to be 410 meters above sea level. The Sierrita operation, including the adjacent Twin Buttes site, encompasses approximately 47,600 acres, comprising 38,700 acres of fee lands including split estate lands and 8,900 acres of unpatented mining claims held on public mineral estate.

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