Circular 123—Mineral deposits of Nogal and Bonito mining districts

By T. B. Thompson, 1973, reprinted 1983, 29 pp., 22 figs., 3 appendices, 1 sheet.

Possible present potential for high-tonnage, low-grade copper-molybdenum "porphyry" is cited. The Nogal and Bonito mining districts have yielded approximately $1,000,000 in lead, zinc, silver, and gold. Except for small placer operations, all of the production has come from fissure veins and the Parsons breccia pipe. Today mining operations in the district are sporadic. The district has four types of mineral deposits: (1) lead-zinc-silver veins, (2) gold-copper breccia pipe deposits, (3) disseminated copper-molybdenum "porphyry" deposits, and (4) gold-bearing placers. Except the latter, hydrothermal alteration is extensive. Silicification, argillization, propylitization, and pyritization are common. The mineral deposits occur within the Sierra Blanca Volcanics of within three hypabyssal silicic stocks, the Rialto, Bonito Lake, or Three Rivers stocks. Localization of the fissure veins occur along the Bonito fault, an east-west shear zone. Disseminated mineralization is associated with fracturing, brecciation, contact features, or late-stage-intrusive phases within the stocks. Ore mineralization was consistent in the fissure veins with galena preceding sphalerite. Zinc to lead ratios show distinct zoning about the northern half of the Rialto stock. These zones are concentric to magnetite, molybdenite, and copper zones within that portion of the Rialto stock. The mineralogy and exsolution textures of sphalerite-chalcopyrite indicate mesothermal over deposition conditions. The narrow lenticular fissure veins are poor. Also the excessive cost of transporting ore to milling facilities is a significant deterrent. The district has some potential, however, for high-tonnage, low-grade copper-molybdenum "porphyry" production. The mineral deposits of the Nogal and Bonito mining districts have lain dormant for more than 30 years. This study shows the structural controls, zoning, and types of deposits present within the district. Assessment of the commercial potential is not attempted. Field work began in 1963 and continued to 1968, most of the work being done during summer and early fall. Areal geology, individual mines, and prospects were mapped. The Nogal and Bonito mining districts are located south-southeast of Carrizozo in south-central New Mexico. As considered here, is extends southward from Church Mountain to a little beyond Mon Jeau Peak. It is bounded on the east by State Highway 37, and on the west by the mountain divide of Sierra Blanca. The area, about 100 mi², is in Lincoln County, mostly in Lincoln National Forest.