The Grants Uranium District, New Mexico: Update on Source, Deposition, and Exploration 1 VIRGINIA T. M cLEMORE 2 1. Manuscript received September 2, 2010; Accepted November 28, 2010 2. NM Bureau of Geology and Mineral Resources, New Mexico Institute of Mining and Technology, Socorro, NM, 87801;
[email protected] ABSTRACT More than 340 million pounds (lbs) of U 3O8 have been produced from the Grants uranium deposits in New Mexico between 1948 and 2002, and at least 403 million lbs of U 3O8 remain as unmined resources. The Grants district is one of the largest uranium provinces in the world. The Grants district extends from east of Laguna to west of Gallup in the San Juan Basin of New Mexico. Three types of sandstone uranium deposits are recognized: tabular, redistributed (roll-front, fault- related), and remnant-primary. The tabular deposits formed during the Jurassic Westwater Canyon time. Subsequently, oxidizing solutions moved downdip, modifying tabular deposits into redistributed roll- front and fault-related deposits. Evidence, including age dates and geochemistry of the uranium deposits, suggests that redistributed deposits could have been formed shortly after deposition in the early Creta - ceous and from a second oxidation front during the mid-Tertiary. The source of uranium is important in understanding how the Grants deposits formed. Two possible sources exist: 1) the Zuni Mountains, which lie south of the district and consist of a Proterozoic granitic highland enriched in uranium with as much as 11 parts per million, and with high heat flow; and 2) vol - canic rocks erupted from a Jurassic arc volcanism, which formed southwest of the San Juan Basin, and deposited ash over much of the region.