Gold mineralization associated with mid-Tertiary magmatism and tectonism, Ortiz Mountains, Santa Fe County, New Mexico
Stephen R. Maynard
Since the 1820s approximately 350,000 oz of gold have been recovered from the Ortiz Mountains. Reserves of 1.17 million oz at Carache Canyon and 180,000 oz at Lukas Canyon have been delineated. Gold in the Ortiz Mountains occurs in five distinct geologic environments: breccia pipes, skulls, veins, porphyry-related stockworks and placers. Lode mineralization is associated with the latest stages of alkaline magmatism, about 28 Ma, and is concentrated along strands of the Tijeras-Canoncito fault system (TCFS). Intrusions in the Ortiz Mountains are of two petrochemical types, an older calc-alkaline suite and a younger alkaline suite. The calc-alkaline rocks are characterized by extensive andesite-porphyry sills, dikes and laccoliths. The alkaline rocks consist of a hornblende-augite monzodiorite/augite monzonite stock, a latite porphyry stock, the Ortiz diatreme (vent breccia) and trachyte dikes. K-Ar age determinations suggest the calc-alkaline suite to be 34 ± 2.2 Ma whereas the alkaline rocks range from about 30 to 28 Ma. The NE-trending TCFS passes through the southeastern Ortiz Mountains where its principal structure is the asymmetric Ortiz graben. The graben's northwest and southeast bounding faults displace stratigraphic contacts by up to 4000 and 2000 ft, respectively. Overall separation on the TCFS is left lateral and down to the north. The augite monzonite stock intrudes the Ortiz graben, therefore timing of major movement on the TCFS is constrained to 34 to 30 Ma.
- Maynard, Stephen R., 1995, Gold mineralization associated with mid-Tertiary magmatism and tectonism, Ortiz Mountains, Santa Fe County, New Mexico, in: Geology of the Sante Fe Region, Bauer, Paul W.; Kues, Barry S.; Dunbar, Nelia W.; Karlstrom, K. E.; Harrison, Bruce, New Mexico Geological Society, Guidebook, 46th Field Conference, pp. 161-166.