Research — Mineral Resources
Alteration and Epithermal Mineralization in the Steeple Rock District, Grant County, New Mexico and Greelee County, Arizona
The Steeple Rock district in the Summit Mountains in southwestern New Mexico and southeastern Arizona offers an excellent opportunity to examine the relationship between the distribution and timing of the alteration and the formation of fissure veins in an epithermal environment. Five distinct types of epithermal veins occur in the district: base metals with gold-silver, gold-silver, copper-silver, fluorite, and manganese. These epithermal veins are structurally controlled, are hosted by Oligocene to Miocene volcanic and intrusive rocks, and are spatially associated with two types of alteration: neutral pH (alkali chloride or propylitic to argillic to sericitic) and acid sulfate (advanced argillic). Neutral pH alteration is the most pervasive type of alteration in the district and occurred in three stages: regional pre-mineralization, local syn-mineralization, and regional post-mineralization.