Bulletin 76—Molybdenum resources of New Mexico

By J. H. Schilling, 1965, 76 pp, 1 table, 7 figs., 2 plates, 1 index.

Molybdenum minerals are widely distributed in NM; 74 occurrences have been reported. Molybdenite is the most common molybdenum mineral, as it is throughout the world; wulfenite, jordisite, ferrimolybdenite, ilsemannite, powellite, and molybdian scheelite also are found in the state.

There are seven types of molybdenum deposits in NM: 1) molybdenite in pegmatite dikes, 2) molybdenite with or without other sulfide minerals in quartz veins, 3) molybdenite as disseminated grains and in quartz-stockwork veinlets in porphyry-copper deposits, 4) molybdenite as disseminated grains and in quartz-stockwork veinlets in cooper-poor porphyry-molybdenum deposits, 5) powellite, molybdenite, and/or molybdian scheelite in contact-tungsten deposits, 6) wulfenite in oxidized lead bodies, and 7) jordisite in bedded uranium deposits.

Ferrimolybdenite is present in many of the occurrences as an oxidation product of molybdenite; ilsemannite is found in the uranium deposits as an oxidation product of jordisite. Deposits of types 1-5 in nearly all instances are closely associated with granitic intrusive rocks. Nearly all the molybdenum deposits elsewhere in the world are of these same seven types and, for the world as a whole, occur in roughly similar proportions. The ore subtype that is not found in NM but is important elsewhere is the tin and/or tungsten-bearing quartz veins common in Asia.

Although production was small, NM was one of the major sources of molybdenum during the early part of this century when wulfenite was mined from the Stevenson-Bennett mine, Doña Ana County, and the Palomas Gap and Hillsboro mining districts, Sierra County. The largest, and presently the only, molybdenum producer in NM is the Santa Rita porphyry-copper mine, Grant County, from which more than 32 million pounds of molybdenite have been recovered as a by-product of copper mining. The second largest producer was the Questa molybdenum mine, Taos County, which yielded more than 20 million pounds of molybdenite from quartz veins. Although the high-grade veins have been mined out, a large low-grade porphyry-molybdenum deposit associated with the veins is now being readied for large-scale mining.

Because of its versatility and abundance, the demand for molybdenum will continue to increase rapidly. NM will remain an important producer. The Santa Rita and Questa deposits both have large reserves, and the possibility of finding other minable molybdenum deposits in the state is good. The uranium deposits of the Grants area are another potentially important source of the metal.