Geologic Map of the Samaniego Peak 7.5' Quadrangle, Pima County, Arizona, v. 2.0

The Sierrita Mountains are a deeply eroded Basin and Range uplift located 60 km south of Tucson, Arizona. The mountains consist of a rugged inselberg core range 300 m high flanked by a bajada surface 35 km in diameter. Bedrock geology of the core range consists of Mesozoic volcanic and sedimentary successions, a subvolcanic Mesozoic intrusive suite, and early Tertiary plutons. Porphyry copper-molybdenum mineralization of the Pima mining district has been exploited at three open-pit mines in the eastern Sierrita Mountains for nearly 50 years. This district has yielded over 18 billion pounds of copper, 290 million pounds of molybdenum, and considerable lead, zinc, and silver (Keith et al., 1983; Arizona Department of Mines and Mineral Resources file data). Most previous geological studies in the Sierrita Mountains focused on the porphyry copper deposits (e.g., Kinnison, 1966; Aiken and West, 1978; West and Aiken, 1982; Barter and Kelley, 1982; Jansen, 1982; Preece and Beane, 1982; Jensen, 1998; Herrmann, 2001). The only currently active deposit, the Sierrita-Esperanza Mine, straddles the southeast corner of the map area. Mineralization at the Sierrita-Esperanza deposit is localized along the intrusive contact between the Paleocene Ruby Star Granodiorite and a Mesozoic volcanic-plutonic complex. One map sheet, map scale 1:24,000, map plate contains cross-sections.