New Mexico Geological Society Annual Spring Meeting — Abstracts

The map area comprises approximately 50 square miles (75.8 square km) of the southern San Mateo Mountains in south-central Socorro County. Thick sequences of Tertiary-aged lavas, ignimbrites and associated volcaniclastic and sedimentary rock units are grouped from oldest to youngest as the Red Rock Ranch Formation (up to 1200 m thick), Rock Spring Formation (up to 1200 m thick), Nogal Canyon Cauldron sequence (300-1600 m thick), and the Turkey springs volcanic sequence (60-320 m thick). Several regional ashflow tuff units of the Mogollon-Datil volcanic field are included in the stratigraphic section.

Repeated volcanotectonic activity related to cauldron development has produced complex stratigraphic and structural relationships in the area. Gold and silver deposits of the San Jose and San Mateo Mountains mining districts occur along a broad north-east-trending fault system within cross-cutting fracture zones, breccia pipes, and veins. Mineralization is associated with late-phase intrusive rocks. Hydrothermal alteration that surrounds mineralized zones is discernible in enhanced satellite imagery.