The Pima mining district, Arizona--a geochronologic update
— M. Shafiqullah and J. D. Langlois

The Pima mining district, one of the largest porphyry cop-per districts in the United States, is located south-southwest of Tucson, along the eastern pediment of the Sierrita Mountains in Pima County, Arizona (fig. 1). The mining district has produced 4.6 billion pounds of copper, 183 million pounds of molybdenum, 87 million pounds of lead, 233 million pounds of zinc, 40 million ounces of silver and 58,000 ounces of gold through 1975 (Keith, pers. commun.). Mineralization, related to Laramide igneous activity, occurs in Paleozoic sedimentary rocks, Mesozoic sedimentary and volcanic sequences, and in Paleocene igneous rocks. Post-mineralization, coarse-grained alluvial-clastic deposits rest in fault contact with Precambrian to Paleocene rocks. Stratigraphic and structural studies by Cooper (1960, 1973), Lacy (1959), Lacy and Titley (1962), Lynch (1968), Titley and Lynch (1968), Weaver (1971) along with geochronologic studies by Creasey and Kistler (1962), Damon and Bikerman (1964), Damon and Mauger (1966) and Marvin and others (1973) have indicated that the geologic complexities of the mining district are far from understood. The eight new K-Ar ages reported here (Table 1) provide additional temporal and spatial constraints on the interpretation of this complex geology. Previously reported K-Ar ages (Table 2) recalculated using constants recommended by Steiger and Jager (1977) are also included for comparison.