New Mexico Mineral Symposium
November 11-12, 2006
Selected minerals from the Grants Uranium district
Ramon S. Demark
Interest in uranium minerals has substantially waned along with uranium mining in New Mexico during the last 25 yrs. The uranium industry was very active in New Mexico from the early 1950s until 1980 and provided much of the fuel that propelled nuclear power plant development in this country. This industrial development was also accompanied by a tremendous expansion of the study of uranium minerals, particularly in the sedimentary environments that exist in New Mexico. Thirty different uranium minerals have been reported from the Grants uranium region (comprising several districts), along with five uranium/vanadium minerals and 13 vanadium minerals. (Berglof and McLemore 1995; Brookins 1979; Granger 1963; Kittel et al. 1967; Northrop 1996; Rosenzweig 1961). Many of these minerals, particularly the unoxidized species, are black and not noteworthy as specimens. The oxidized species, however, are often brightly colored (yellow and orange) and in some cases have produced exceptional specimens. Uranophane is perhaps the most important of the specimen minerals in the region. Specimens are best developed in the Jurassic Todilto limestone. Bright yellow jackstraw crystals of uranophane in vugs to 10 cm and even larger are some of the finest examples of this mineral in North America. Tyuyamunite and, to a much lesser extent, carnotite are found in well-developed microcrystals in association with uranophane and the common gangue minerals calcite and barite. Three new vanadium minerals were first described from locations in the Grants uranium region. Goldmanite, a vanadium member of the garnet group, was described by Moench and Meyrowitz (1964), Grantsite, a hydrated sodium calcium vanadium mineral described by Weeks et al. (1964), and Santafeite, a complex hydrated vanadate described by Sun and Weber (1958).
Specimens of a bright yellow mineral on coffinite from the Jackpile mine near Laguna were commonly available in the 1970s. This mineral was generally thought to be zippeite [K4 (UO2)6(SO4)3(OH)10•4H2O]. Recent microprobe analysis (Hlava, pers. comm. 2006) has determined that this mineral does not contain potassium. Granger (1963) writes that "Most zippeite is nonfluorescent or has a weak yellow fluorescence." The material from the Jackpile mine has a strong green fluorescence. Chemistry and the strong fluorescence of the mineral suggest that it may be uranopilite [(UO2)6(SO4)(OH)10•12H2O. Positive identification awaits XRD analysis.
East Grants Ridge is a portion of the late Tertiary Mount Taylor volcanic field, which lies southwest of the main peak. Although not geologically connected with the uranium region, it is flanked by uranium districts and is thus included in this paper. The ridge is partially composed of a lithophysal rhyolite that hosts microcrystals of topaz and
spessartine. Transparent, colorless to amber-colored topaz crystals to 1 cm are abundant, and transparent, crimson-red crystals of spessartine generally less than 1 mm can be found in the vugs. Some of the spessartine crystals are coated with a drusy layer of bixbyite /hematite crystals (Hlava, pers. comm. 2006).
During the active mining years, many samples of oxidized, post-mining uranium minerals such as andersonite, bayleyite, and zippeite were collected by miners from efflorescents on the walls of the underground mines. Additionally, large numbers of specimens of uranophane, tyuyamunite, and other species were collected from the
dumps and stockpiles of Todilto limestone ore in the Poison Canyon area. Active uranium mining in this region is now over. The underground mines have been sealed, and the surface mines and pits have been bulldozed, reseeded, and reclaimed to the extent that specimens are no longer available. With the current resurgent interest in nuclear power as an energy source here in the United States and around the world, perhaps one day uranium mining will re-emerge in New Mexico and fascinating uranium minerals will once again be available.
Minerals reported from the Grants uranium region
|Uranium minerals||Vanadium minerals||Uranium/Vanadium minerals||Other minerals|
|* ID not confirmed|
- Berglof, W. R., and McLemore, V. T., 1996, Mineralogy of the Todilto uranium deposits, Grants district, New Mexico (abs.): New Mexico Geology, v. 18, no. 1, p. 19.
- Brookins, D. G., 1979, Uranium minerals and the mineralogy of the Grants mineral belt (abs.): New Mexico Minerals Symposium (unpublished).
- Granger, H. C., 1963, Mineralogy; in Kelley, V. C. (compiler), Geology and technology of the Grants uranium region: New Mexico Bureau of Mines and Mineral Resources, Memoir 15, pp. 21-37.
- Kittel, D. F., Kelley, V. C., and Melancon, P. E., 1967, Uranium deposits of the Grants region; in Trauger, F. D. (ed.), Defiance-Zuni-Mt. Taylor region, Arizona and New Mexico: New Mexico Geological Society, Guidebook 18, pp. 173-183.
- Moench, R. H., and Meyrowitz, R., 1964, Goldmanite, a vanadium garnet from Laguna, New Mexico: American Mineralogist, v. 49, pp. 644-655.
- Northrop, S. A., 1996, Minerals of New Mexico, 3rd ed., revised by F. A. LaBruzza: University of New Mexico Press, Albuquerque, 356 pp.
- Rosenzweig, A., 1961, Mineralogical notes on the uranium deposits of the Grants and Laguna districts; in Northrop, S. A. (ed.), Albuquerque country: New Mexico Geological Society, Guidebook 12, pp. 168-171.
- Sun, M.-S., and Weber, R. H., 1958, Santafeite, a new hydrated vanadate from New Mexico. American Mineralogist, v. 43, pp. 677-687.
- Weeks, A. D., Lindberg, M. L., Truesdell, A. H., and Meyrowitz, R., 1964, Grantsite, a new hydrated sodium calcium vanadate from New Mexico, Colorado and Utah: American Mineralogist, v. 49, pp. 1511-1526.
27th Annual New Mexico Mineral Symposium
November 11-12, 2006, Socorro, NM