New Mexico Mineral Symposium — Abstracts

The Carnahan mine, located in the San Pedro Mountains (New Placers district) of Santa Fe County, New Mexico, has not been a major ore producer. Nonetheless, it has had a long, but intermittent, record of production of lead-silver, zinc, and manganese ores. Since 1968, the mine has been owned by the San Pedro Mining Corporation (Patrick Freeman, personal communication 1989).

The mine workings consist predominantly of an inclined tunnel (5-20°) trending N75°E to N90°E with minor drifts and some stoping. Near the end of this tunnel another north-trending inclined tunnel proceeds approximately 500 ft before intercepting the water table.

The geology and mineralogy of the Carnahan mine was looked at most extensively in 1903 (Yung and McCaffery). More recent studies have, in most cases, cited the mineralogical findings of Yung and McCaffery in reporting occurrences of specific minerals. Northrop (1959), crediting Dale Carson, cited a number of oxidized minerals including anglesite, cerussite, botryoidal hematite, limonite, possibly minium, pyrolusite, and native silver.

Since 1985, however, a number of new species have been identified from the Carnahan mine, species that were either overlooked by earlier investigators or possibly misidentified. With the help of microprobe (Paul Hlava, personal communications 1989) and x-ray diffraction/SEM (Peter Modreski, personal communications 1989) analyses, 20 species new to the Carnahan mine have been confirmed. Two of the species (adamite and hetaerolite) are the first reported occurrences of these minerals in New Mexico.

The new minerals are all secondary minerals resulting from the oxidation of primary iron, copper, zinc, and manganese sulphides. They include one native element (copper), oxides, carbonates, sulfates, arsenates, a molybdate (wulfenite), and silicates. Although galena and pyrite have been found in the oxidized zone, the predominant occurrence of primary sulphides is reputed by Atkinson (1961) to occur below the ground-water level approximately 400 ft below the surface.

Most of the secondary copper minerals were found in a very restricted zone substantially down the tunnel. The arsenates, adamite, and agardite-(Y) were found in association with cuprite octahedrons that were partially or completely altered to rosasite, malachite, and chrysocolla. Native copper commonly occurs in the cores of the less altered cuprite octahedrons. Adamite most often occurs as transparent green spheres, but crystal morphology is evident on some of the balls. This adamite is cuprian, which accounts for the green color. Some individual colorless crystals to 0.5 mm are very low in copper content (Hlava, personal communication 1989). None of the Carnahan mine adamite is fluorescent. Aurichalcite and azurite, although scarce, were also found in association. Agardite-(Y) occurs in very fine acicular sprays and tufts. Linarite occurs as sky-blue, bladed crystals about 0.1 mm long and also as fine sprays of crystals about 0.3 mm across. They are found in association with pyrite, galena, and green spheres that appear to be a mixture of malachite and brochantite (Hlava, personal communication 1989). The pyrite in some cases is coated with a dark-purple to black layer of drusy covellite that is argentiferous.

Gibbsite, opal (hyaline), and allophane are also found in the same area. Gibbsite occurs as white spheres and irregular masses often coated with hyaline opal while the allophane is in blue, transparent to opaque bands. Wulfenite is surprisingly sparse.
It was only found in a very restricted horizon near the end of the main tunnel in association with cerussite.

The uncommon zinc manganese oxide, hetaerolite, is found in many areas throughout the mine, often in fine splendant tetragonal dipyramids about 1 mm in size. Chalcophanite, cerussite, and hemimorphite are ubiquitous throughout the mine. The habit and forms of chalcophanite at the Carnahan mine are varied. It may be in lustrous black, brown, or red pseudo-hexagonal crystals that resemble hematite or goethite or more commonly as reniform, botryoidal, vermiform, or stalagtitic masses. Plattnerite is restricted in occurrence (one site) and was found on reniform chalcophanite in lustrous, black, prismatic crystals. A manganoan variety of smithsonite has been identified in association with secondary copper minerals. It has a dark-brown color and glassy luster on cleavages. The crystals have the typical rice-grain habit. Calcite is common throughout the mine and may be in papier-spath crystals or in transparent colorless rhombs, or in prisms. Botryoidal and cave-type forms are also found. As mineral investigations are continued, additional species are expected to be added to the current list.

ACCESS TO THE CARNAHAN MINE IS STRICTLY PROHIBITED AND ILLEGAL WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE SAN PEDRO MINING CORPORATION, P.O. BOX 1670, TRUTH OR CONSEQUENCES, NEW MEXICO 87901.

Suggested reading

Lasky, S. G., and Wootton, T. G., 1933, The metal resources of New Mexico and their economic features: New Mexico Bureau of Mines and Mineral Resources, Bulletin 7, 178 p.
Wells, E. G., 1918, Manganese in New Mexico: New Mexico Bureau of Mines and Mineral Resources, Bulletin 2, 85 p.

References:

1. Atkinson, W. W., Jr., 1961, Geology of the San Pedro Mountains, Santa Fe County, New Mexico: New Mexico Bureau of Mines and Mineral Resources, Bulletin 77, 50 pp.
2. Northrop, S. A., 1959, Minerals of New Mexico: University of New Mexico Press, 665 p.
3. Yung, M. B., and McCaffery, R. S., 1903, The ore deposits of the San Pedro district; in American Institute of Mining and Engineering, Transactions Volume 33, p. 350-362; abs. in Engineering and Mining Journal, v. 75, p. 297-299.