Mineral Resource Assessment. Big Bend RanchState Natural Area, Presidio and Brewster Counties, Texas - Final Report

The Big Bend Ranch State Natural Area has a diverse geology reflecting nearly 600 million years of geologic evolution. Major geologic events include (1) deposition of elastic sedimentary rocks during the Paleozoic and their deformation (folding and faulting) at the end of the Paleozoic; (2) deposition of limestone and elastic rocks during the Cretaceous and their deformation during the early Tertiary; (3) intense extrusive and intrusive igneous activity during the middle Tertiary; and (4) major normal faulting during the late Tertiary. Almost all mineral potential of the area is associated with mid-Tertiary igneous activity. The only significant mineral production within the Ranch area was from the Fresno Mine in the western part of the Terlingua mercury district, one of the largest mining districts in Texas. This mine produced approximately 3500 flasks of mercury, mostly during World War II. Other production was minor and included some additional mercury from localities near the Fresno Mine, as well as silver-lead ore containing minor gold from a small mine in the Solitario.