New Mexico Mineral Symposium
November 29-30, 1979
Uranium Minerals and the Mineralogy of the Grants Mineral Belt
Douglas G. Brookins
The Grants Mineral Belt, New Mexico, which may contain as much as one quarter of the World's total uranium reserve, has been actively mined since the 1950's. Over one hundred minerals have been identified from the Grants Mineral Belt, about thirty of which are uranium minerals. Granger (1963) has compiled an expensive list of the minerals found to that time. Primary minerals which are found in dark, organic-rich, pyrite-bearing sandstones include both coffinite (USiO4) and lesser-amounts of pitchblende (UO2, 6). These minerals are so fine grained as to make identification difficult. Accessory minerals include vanadium-bearing clay minerals, pyrite or marcasite, selenium-bearing minerals, and jordisite (MoS2). Most of these have to be identified by petrographic means or by x-ray inspection. Secondary minerals formed by oxidation include brightly colored minerals such as uranophane, tyuyamunice, metatyuyamunice, carnotite, autunite, zellerite, etc. Not only are these minerals easy to spot in outcrop, but many are fluorescent as well. Uranium minerals found as "bloom" on mine or pit walls include soluble minerals such as zippeite, andersonite, bayleyite, uranopilite, etc. These minerals must be treated with care as they dehydrate readily when exposed to air. Secondary minerals of vanadium, selenium, and molybdenum are also common but more difficult to identify.
The common gangue minerals include various clay minerals, barite, calcite, quartz, feldspars, gypsum, and lesser amounts of many others. The clay minerals are of special importance, especially as related to ore formation, but they must be identified by x-ray or other laboratory techniques.
Field collecting is best done in groups by arranging with various mine managers to visit properties; and this can be done without too much inconvenience if enough advance notice is given.
This paper will summarize some of the research which has been conducted at UNM over the past five years on mineral deposits in the Grants Mineral Belt; some of which has been truly pioneering.
- Granger, H. C., 1963, Mineralogy: in Geology and Technology of the Grants Uranium Region: New Mexico Bureau of Mines and Mineral Resources Memoir 15 (V. C. Kelley, Editor), p. 21-37.
1st Annual New Mexico Mineral Symposium
November 29-30, 1979, Socorro, NM