AGE AND CHARACTERIZATION OF THE RED HILLS PORPHYRY COPPER-MOLYBDENUM DEPOSIT AND ITS RELATIONSHIP TO THE CHINATI MOUNTAINS CALDERA, PRESIDIO COUNTY, TEXAS

The Red Hills deposit in Presidio County, Texas, is the easternmost porphyry copper-molybdenum system in the southwestern United States. The Red Hills porphyry is located approximately 1 km south of the 32 Ma Chinati Mountains caldera, and it has been postulated that the two may be genetically related. The quartz-monzonite porphyry intruded upper Permian limestones, sandstones, and siltstones of the Ross Mine and Mina Grande Formations. The sericitized porphyry contains minor chalcopyrite, chalcocite, and molybdenite within stockwork quartz-pyrite veins. Garnet- and sphalerite-bearing skarn in the sedimentary rocks appear to be localized by E-W oriented faults along the periphery of the intrusion.

New U/Pb zircon and Re/Os molybdenite age data from the intrusion yield ages of 64.2 ± 0.2 Ma and 60.2 ± 0.3 Ma, respectively, indicating that the intrusion and mineralization are distinctly older than all other Tertiary magmatism (17-48 Ma) in Trans-Pecos Texas. The new ages also indicate that the Red Hills porphyry significantly predates the 32 Ma formation of the Chinati Mountains caldera. Geochemical data from the porphyry further preclude any direct relationship to the Chinati Mountains magmatism. The Laramide age for the Red Hills porphyry makes it contemporaneous with the majority of the porphyry copper systems (58-72 Ma) in Arizona, New Mexico, and northern Mexico.