New Mexico Mineral Symposium — Abstracts

Recent collecting activity in parts of the Central district, Grant County, and San Simon district, Hidalgo County, New Mexico, has revealed an interesting suite of wulfenite in numerous habits and associations. Specimens collected from dumps, pits, cuts, and one underground locality are suitable for micromount and thumbnail presentation. Larger hand specimens are rare.

Central district—Localities covered by this investigation in the Central district include a group of 10 prospects and mines located 1 mi west of Vanadium and 2 mi north of Bayard, Grant County, New Mexico. The area is overshadowed by the large Chino open pit copper operation at Santa Rita located 3 mi north-northeast. The workings investigated include the following mines: Betty Jo, Silver King, Home, Sweeney, Yellowdog Gulch, Lion No. 2, Lion, Tiger, Little Bobs, and the Slate. The area consists of narrow quartz veins striking generally northeast and enclosed for the most part in quartz diorite. Dark resistant altered diorite containing quartz veins is quite noticeable on the gently rolling topography. The veins contain primary sulfides at depth, and near-surface oxidation has produced wulfenite and associated vanadinite, desclozite, willemite, cerussite, smithsonite, and pyromorphite. Wulfenite crystals occur in various habits including pyramidal, square tabular, prismatic, and pseudocubic. One four-wheel drive road remains open to the col¬lecting area.

San Simon district—This district is in the central Peloncillo Mountains, just east of the Arizona border in Hidalgo County, New Mexico. The area, 5 by 10 mi in size, starts at Interstate 10 on the north and extends south to include the mines at Granite Gap. Mineral Mountain is located 2 mi west of Cedar Mountain in the northern part of the district. It is a volcanic-epithermal deposit con¬sisting of steeply dipping quartz veins. The main shaft is reported to be 200 ft deep and is now inaccessible and filled with water to within 50 ft of the surface. Vein matter on the dumps consists of altered galena pods in quartz with associated wulfenite, yellow arsenian vanadinite, zincian mottramite, aurichalcite, fraipontite, and other secondary minerals. Wulfenite forms in various habits, including square tabular, prismatic, pyramidal, acicular, and other modified forms. One mineral, essentially a Pb-Zn-Cu-As vanadate, remains unidentified after analysis using microprobe and X-ray diffraction techniques. A somewhat marginal dirt road, washed out halfway to the workings, provides access to the area.

Granite Gap is located 10 mi south of the Mineral Mountain mine at the southern end of the San Simon district east of Highway 80. The area consists of three main workings: Bob Montgomery group, World's Fair group, and the Vesley mine located on the west slope of Granite Gap Mountain. This area contains carbonate-hosted Pb-Zn replacement deposits. Wulfenite occurs un¬derground at the Bob Montgomery group as square tabular crystals associated with plattnerite. Adamite, agardite-(Y), bromargyrite, carminite, conichalcite, austinite, hemimorphite, mimetite, and other minerals can also be collected elsewhere in the mine. Wulfenite, in association with bromargyrite, has also been collected at an unnamed mine high on the east side of Granite Gap Mountain. The adit is caved, but square tabular wulfenite can be found sparingly on the dumps in gossan material. The Granite Gap mines are all located on private property, and a fee is charged for entry.

References:

1. Beyer, J., and Gibbs, R., 2002, Minerals of the Granite Gap mines, Hidalgo County, New Mexico: Rocks and Minerals, v. 77, no. 5, pp. 298-305.
2. Gillerman, E., 1958, Geology of the central Peloncillo Mountains, Hidalgo County, New Mexico and Cochise County, Arizona: New Mexico Bureau of Mines and Mineral Resources, Bulletin 57, 152 pp.
3. Lasky, S. G., 1936, Geology and ore deposits of the Bayard area, Central mining district, New Mex??ico: U. S. Geological Survey, Bulletin 870, 144 pp.
4. Northrop, S. A., 1959, Minerals of New Mexico: University of New Mexico Press, Albuquerque, 665 pp.