New Mexico Mineral Symposium — Abstracts

Although New Mexico is not known for spectacular wulfenite, the state nevertheless has produced some noteworthy specimens, and this attractive mineral is more widespread than is commonly realized. A search of the literature and personal knowledge of documented specimens reveals 55 specific mines or districts that have produced wulfenite (list enclosed) in New Mexico. Most of these occurrences have been cited in the last 33 years. Schilling (1965) reports only 17 wulfenite occurrences in New Mexico.

As a secondary mineral usually derived from the oxidation of galena, wulfenite is most commonly found in arid regions. This is true in New Mexico where almost all occurrences are in the most southern, arid counties. The exceptions are two sites each in Bernalillo and Santa Fe Counties and a questionable report from a volcanic plug near El Rito in Rio Arriba County (Northrup and LaBruzza, 1996).

Before World War I, wulfenite was the most important ore mineral for molybdenum (Schilling, 1965). In that regard, the Stephenson–Bennett mine in Doña Ana County and mines in the Hillsboro and Palomas Gap (Caballo Mountains) districts of Sierra County shipped small amounts of wulfenite molybdenum ore (Schilling, 1965). Additionally, wulfenite was an important ore mineral for lead at the Stephenson–Bennett mine (Dunham, 1935). Mineral collectors today cringe at this thought.

The Stephenson–Bennett mine in Doña Ana County has arguably produced the finest and largest volume of wulfenite specimens from New Mexico. The orebody was discovered in 1847 (Dunham, 1935) with silver and lead ore production continuing well into this century. Many outstanding specimens were recovered by collectors long after the mining era was over. A fatal accident by "exploring" high-school students in the 1980s has resulted in total closure of the mine. Stephenson–Bennett wulfenite is noteworthy because of the wide variety of color and habits exhibited.

Wulfenite from the Denver shaft in the Central mining district of Grant County rivals the best of the Stephenson–Bennett specimens in quality if not quantity. Denver shaft wulfenite was discovered by Robert Eveleth and Bill Worthington during a mine evaluation in 1975. Superb yellow-orange, lustrous crystals up to 2.5 cm were found in a wet, compact fault gouge at the end of a short drift off the first level. Six fuzed rounds of dynamite were found still loaded in drill holes adjacent to the occurrence. Unfortunately, shortly after this discovery, the head frame was removed, and the poor rock dump was bulldozed over the decline. Another stellar New Mexico mineral location lost, perhaps forever.

Historically, mines such as the Ground Hog and Lucky Bill in the Central district of Grant County yielded excellent specimens. Today, however, specimens from these mines are rare to nonexistent. A sad fact is that specimens were not a priority during New Mexico's early mining history.

Many of New Mexico's current locations bring forward specimens that are best viewed with magnification, i.e., microcrystals. No less interesting or beautiful than hand-sized specimens, these microcrystals come in many habits, colors, and associations. Finding these crystals in previously unreported locations and contexts adds to the mineralogical knowledge of orebodies and should be reported or published when discovered. Perhaps with the 100th anniversary of New Mexico statehood in 2012, we will have 100 New Mexico wulfenite locations—a noble goal.

References:

1. Dunham, K. C., 1935, The geology of the Organ Mountains, with an account of the geology and mineral resources of Do??a Ana County, New Mexico: New Mexico Bureau of Mines and Mineral Resources, Bulletin 11.
2. Northrop, S. A., and LaBruzza, F. A., 1996, Minerals of New Mexico: University of New Mexico Press, third edition. Schilling, J. H., 1965, Molybdenum resources of New Mexico: New Mexico Bureau of Mines and Mineral Resources, Bulletin 76.