New Mexico Geological Society Annual Spring Meeting — Abstracts

The 3000 km², NW-trending area from Redrock, NM, to Clifton, AZ, is composed chiefly of mid-Tertiary volcanic rocks-which fill the wedge-shaped Blue Creek basin between basement highs at Redrock and Clifton. Calcalkaline Oligocene (35-30 m.y.) flows and tuffs are unconformably overlain by a more alkalic bimodal Miocene suite (25-18 m.y.). Composite mid-Tertiary thickness is 4⁺ km in central parts of the Blue Creek basin. Within this substantial volcanic terrain, several environments of possible economic significance have been identified. 1) The southern ring fractur.e zone of the Schoolhouse Mountain cauldron is mineralized. Other portions of the ring fracture zone could offer exploration targets, especially where ring domes intrude porous moat-facies tuffs and volcaniclastic sediments. 2) Three widespread areas of intense argillic to quartz-alunitic alteration in the Steeple Rock district probably are loci of past near-surface (venting?) geothermal activity, and could contain disseminated precious metal deposits. Much younger (Holocene) geothermal venting has deposited a fragile, well-preserved selenite-bearing sinter in Bitter Creek. 3) Preliminary geochemical studies indicate that some of the youngest Blue Creek basin felsic intrusives are well-differentiated, enriched in lithophile elements, and could potentially host porphyry molybdenum and precious metal deposits. One such intrusion contains anomalous precious metal values in a brecciated near-surface vent zone. The youngest, most highly differentiated high-silica rhyolites are approximately 18 m.y. old. Adularia associated with East Camp vein precious metal and fluorite mineralization has yielded similar ages. A causative relationship between late-stage rhyolite intrusion and some Steeple Rock district vein mineralization is suggested.