Regional Characteristics of porphyry copper deposits of the southwest

Abstract ' The largest and best studied concentration of porphyry-type deposits is the Southwest porphyry province in Arizona, southwestern New Mexico, and northern Sonora (Figure ' 1). Most of these deposits are in the 58 to 72 million-year-old range, with one 163 m.y. date and one 20 m.y. date. Several Mesozoic age porphyry copper deposits occur northwest of the main cluster, and mid-Tertiary age porphyry molybdenum and porphyry copper deposits are present in the Colorado mineral belt and at Bingham Canyon, Utah. A progressive decrease in age occurs from northwest to southeast among the Laramide age Southwest porphyries. Tertiary rocks contemporaneous with and younger than the Laramide mineralization appear to have been formed under conditions of strong deformation and crustal ex-tension. Large displacement, flat, "gravity slide " faults are present in southern Arizona together with evidence of abundant horst-graben structure and rift faulting. A correlation of rock types, structures, and intrusive and extrusive activity suggests that "basin~range"-type xtensional structures were formed throughout the Tertiar