Bulletin 83—Mineral deposits of western Grant County, New Mexico

By E. Gillerman, 1964, reprinted 1976, 213 pp., 3 tables, 34 figs., 11 plates, 11 photos, 1 index.

Grant County has produced more than a billion dollars worth of metals and minerals since 1880. Most of this has come from the eastern part of the county, but important amounts of copper, gold, silver, fluorspar, and turquoise were mined from the western half. Lesser amounts of zinc, lead, and manganese and small amounts of tungsten, uranium, perlite, and ricolite have also been produced. Concentrations of other commodities present include nickel, cobalt, bismuth, molybdenum, and rare earths.

Mineral deposits occur in the Precambrian igneous and metamorphic rocks and in the Tertiary volcanic rocks that occupy most of the western part of the county. They are associated with northwest and northeast-to-east fractures and with intruded stocks and plugs. Major districts are at the intersection of the structural trends.

The largest and most productive mineral deposits are in the Big Burro Mountains. The supergene-enriched copper deposits at Tyrone have accounted for most of the copper produced, and the outlook for future production is excellent. Copper also occurs elsewhere in the mountains, and numerous deposits have been exploited. Fluorspar and turquoise have been mined, and large amounts of fluorspar still remain. In the White Signal subdistrict, gold, copper, and uranium deposits are numerous. Mining here essentially has been confined to the oxidized zone, and only small amounts of gold, radium, and uranium have been produced.

In the Steeple rock district, gold and silver were the major commodities produced in the early days of mining, but in recent years lead, zinc, and copper have been extracted in significant amounts. In the Bullard Peak district, silver was produced from veins that contain native silver, nickel, cobalt, and uranium.

Other major districts include Gold Hill, Gila, Redrock, Malone, Little Burro Mountains, and Soldier's Farewell. Excluding perlite, diatomite, clay, and dimension stone, most of the mineral deposits are hydrothermal in origin, but oxidation and supergene enrichment have been important in concentrating the low-grade ores into deposits of economic worth. A few small deposits in the Redrock area were formed by metamorphic processes. Rare-earth-bearing pegmatites are in the Big Burro Mountains and Gold Hill.