Bulletin-91—Geology and Mineral Resources of Rio Arriba County, New Mexico

By E. C. Bingler, 1968, 158 pp, 4 tables, 22 figs., 8 plates, 1 index.

Mineral production in Rio Arriba County since the 1880s has amounted to nearly $5 million. Sand and gravel and mica account for $3 million and $1 million of the production, respectively. Metal mining, principally gold, centered in the Hopewell and Bromide mining districts accounts for about $360,000. Crushed, dimension, and ornamental stone production represents about $250,000, and nearly $230,000 in copper and silver has been extracted from red-bed copper deposits.

The Hopewell and Bromide mining districts, most active during the late 1880s and early 1900s, include primary ore bodies in a Precambrian terrain and secondary placer deposits of Tertiary to Quaternary ages. Hydrothermal sulfide replacement veins in Precambrian schist and gneiss contain gold, silver, copper, lead, zinc, molybdenum, and a trace of fluorite. Secondary accumulations of alluvial gold in the Hopewell Lake area were the most valuable deposits of the district.

Red bed copper deposits have been exploited near Cuba and in the Coyote-Youngsville area. Chalcocite nodules and replacements of carbonaceous track in Triassic sandstone and conglomerate contain most of the copper and silver. The Petaca pegmatite district is the leading mica-producing area in NM. Mica occurs in distinct internal zones in pegmatite associated with the common pegmatite minerals, quartz, microcline, and albite, in addition to the accessory minerals, garnet, beryl, columbite-tantalite, samarskite, fluorite, monazite, bismuth, and magnetite-ilmenite.

Numerous nonmetallic commodities are scattered throughout the eastern part of the county in relatively small deposits. These include kyanite, fluorspar, kaolinite, diatomite, and bentonite. The county has very large reserves of the low-unit-value commodities, gypsum, limestone, pumice, stone, and sand and gravel.