New Mexico Geological Society Annual Spring Meeting — Abstracts

The Steeple Rock mining district is located in western New Mexico near Duncan, Arizona. More specifically, it occupies the southwestern portion of the Blue Creek Basin, which contains the Schoolhouse Mountain cauldron. The district lies in a transition zone between the Datil-Mogollon volcanic field to the northeast and the Basin and Range Province to the west.

Tertiary volcanic rocks cover the majority of the Steeple Rock district, with only small exposures by hypabyssal rocks in the western portion of the area. The three main units are the Virden Dacite (34.7 m.y.; host to most of the mineralization in the district), a younger Amygdaloidal Andesite, and the Brown Andesite Porphyry.

The ore deposits of the district are veins which occupy northwest to west-northwest trending normal faults. The main structural pattern is linear, but there are numerous vein intersections, warped fault planes, bifurcations and cymoid loops. All of these features occur at both large and small scales and in horizontal as well as vertical planes.

Mineralization is in epithermal silica veins that contain gold, silver, copper, lead and zinc. Production from the district to 1975 is as follows: gold - 140,700 ounces; silver - 3,140,500 ounces; and significant amounts of base metals.

The paragenesis consists of at least three stages, but has received limited attention district-wide. The precious metals were deposited in the third stage. Selected large areas of the district have been very intensely silicified and/or argillically altered. This alteration is interpreted to be the result of hydrothermal solutions flowing along open structures during the mineralizing event in the Steeple Rock mining district.