Circular 103 — Geology and Beryllium Mineralization near Apache Warm Springs, Socorro County, New Mexico

By Patrick D. Hillard, 1969, 16 p.

The volcanic rocks exposed southeast of Apache Warm Springs, Socorro County, New Mexico, include Tertiary pyroclastics, andesites, latites, rhyolite tuffs, and flow rhyolites. The pyroclastics, andesites, and latites are older than the Datil Formation and are propylitized. The rhyolite tuffs and flows are equivalent to lower Datil arid are altered only locally.

Quaternary Winston beds probably equivalent to the Santa Fe. Group occur along the west edge of the mapped area. They consist of locally derived sandstone, siltstone, and conglomerate.

In 1961, beryllium mineralization was discovered near the west end of Monticello Canyon and subsequently was explored by drilling. The ore mineral has been identified as bertrandite and is associated with widespread hydrothermal kaolinitization, alunitization, montmorillonitization, and silicification of the country rock. The ore mineral bertrandite is restricted to one highly faulted and brecciated zone in an altered rhyolite tuff. The mineralized breccia contains from 0.05 to 2.5 pe( cent beryllium oxide. The bertrandite occurs as light yellow-green fibrous crystals coating breccia fragments and as spheres, not more than 50 microns in diameter, disseminate(! in a clay matrix. To date, no beryllium has been commercially produced.