STOCKWORK FRACTURING AND VEINING HISTORY OF THE RED HILLS PORPHYRY MO-CU DEPOSIT, TRANS-PECOS TEXAS

The Laramide age Red Hills porphyry Mo-Cu deposit is located at the western end of the Shafter silver mining district in Presidio County in Trans Pecos Texas. The intrusive complex was emplaced into a Permian sedimentary sequence resulting in an extensive hornfels zone with local garnet skarn. Tosca Mining Corporation conducted a drilling and evaluation program in 2012 that intersected multiple igneous phases including a biotite-rich porphyry, quartz monzonite porphyry, and quartz latite porphyry. Contorted comb quartz texture “brain rock” consisting of thin, random layering of quartz and fine grained aplitic material typically found in porphyry Mo deposits occurs in a narrow interval near the north-eastern cusp of the Mo-bearing stockwork. The igneous phases have been affected by cyclic episodes of stockwork fracturing and hydrothermal alteration. Hydrothermal solutions travelling through fractures within the deeper hypogene zone produced veining styles of molybdenite, quartz-molybdenite, and barren quartz. The upper and lateral portions of the deposit show quartz-sericite-pyrite veining cross cut by pyrite veins in the phyllic alteration zone. The thin leached cap has mm to cm wide alunite veins, and overlies a weak supergene copper zone with local high grade chalcocite typically in pyritic wall rocks. SEM-CL imaging of quartz bearing stockwork veins reveal quartz growth textures that record changes of the mineralizing hydrothermal fluids throughout ore genesis.