New Mexico Geological Society Annual Spring Meeting — Abstracts

The San Jose district encompasses several silver-gold "fissure type" vein occurrences hosted within the Oligocene Vicks Peak Tuff. The Vicks Peak rhyolite is a thick, densely to partially welded ash-flow tuff overlain by the Springtime Canyon Quartz Latite flow and constitutes the majority of the upper felsic volcanic sequence exposed in the southern San Mateo mountains. The majar veins infill and replace steeply dipping, northeast and northwest trending normal faults possibly related to the proposed Nogal Canyon cauldron.

Hydrothermal alteration effects contemporaneous with precious metal mineralization consist of quartz-alunite replacement alteration, pervasive intermediate argillic alteration, and pervasive and veinlet silicification related to a single hydrothermal episode. Silicification is strongly localized along fracture and breccia zones accompanied by the deposition of adularia, sericite, calcite, pyrolusite, and cryptomelane. Intermediate argillic alteration consists of montmorillinite, montmorillinite-illite mixed layer, illite, kaolinite, and pyrite systematically zoned as reaction aureoles about major structures. Argillization typically broadens beneath the Vicks Peak Tuff - Springtime Canyon Quartz Latite contact which acted as a permeability barrier to ascending hydrothermal fluids. Supergene alteration resulting primarily from hypogene pyrite oxidation locally complicates hypogene alteration patterns.

Mineralization accompanies vein-related silicification consisting of pyrite, cerargyrite. native gold, and native silver. Trace element studies
indicate the low grade mineralization locks significant base metal introduction at present exposure levels and exhibits very low arsenic and antimony signatures. Cursory fluid inclusion examinations document the presence of local boiling confined to structures which lead to the development of argillic and advanced argillic assemblages.