New Mexico Mineral Symposium — Abstracts

The San Pedro mine in New Mexico is one of the older mines in the Southwestern USA, with the first mentioned mining by non-Indigenous people in 1839, although earlier mining had been noted since the 1500's. Of much lesser consequence is that the San Pedro was the first underground mine where the author collected minerals, beginning in 1971. Introduced to the mine by an alumni geologist of the University of New Mexico while the mine was under care and maintenance, it became the author's preferred underground collecting location, even surpassing the famous Kelly mine renown for smithsonite.

The San Pedro mine is a limestone-tactite skarn hosted Cu-Au-Ag orebody located in the San Pedro Mountains, midway between the New Mexico cities of Albuquerque and Santa Fe. The mine is best known for producing numerous Japan Law twin quartz crystals (Fig. 1) and North America's largest chalcopyrite crystals, up to 10 centimeters (cm) on an edge (Fig. 2). Limestone replaced by marble and attendant volume losses during contact metamorphism in the tactite skarn produced numerous cavities and openings. Crystals of quartz, chalcopyrite, calcite, pyrite, hematite and garnet variety andradite line the openings. Less commonly, fluorite, sceptered amethystine quartz and scheelite occur. Supergene alteration and oxidation of the chalcopyrite produced coatings of covellite, chalcocite, bornite (Fig. 3), and malachite. Of particular note are the highly aesthetic lustrous groups of fine thin wire gold specimens occurring with calcite (Fig. 4), which have been found by collectors in several areas of the San Pedro mine.

While the San Pedro mine still is capable of producing fine specimens of all of the minerals listed above, the San Pedro Mining Company still owns the mine. The Company maintains vigilance on the mining property and collecting in the mine and on the property is forbidden.