MINERALOGICAL CONSIDERATIONS FOR SOLUTION MINING OF URANIUM IN NEW MEXICAN DEPOSITS

In a volatile uranium market, it is essential to have as thorough an understanding of a deposit as possible. This, on a fundamental level, is the mineralogical makeup of the ore and gangue. Solution mining for uranium (compared to processes where the ore is excavated) is a subtle process where the deposit mineralogy may confound leaching efforts. Also, in-situ leaching processes may liberate environmentally hazardous metals (e.g., molybdenum) into groundwater. These considerations are largely determined by the deposit’s inherent geochemistry. Despite this, there are some significant deposits which have little known of their mineralogy, but well-constrained structure and lithology.

In light of this, we evaluated the mineralogical makeup of material from two deposits within the Grants Uranium Region in northwestern New Mexico. The samples encompass two distinct systems in the Jurassic Morrison Formation: the primary (tabular-type) St. Anthony deposit, and redistributed-type Borrego Pass deposit. Methods included X-ray powder diffraction, thin section microscopy, infrared spectroscopy, and electron microprobe analysis.

Generally, uranium mineralization in the samples is interstitial to feldspathic sandstones. The St. Anthony samples’ uranium was predominantly in the form of organo-uranium complexes, also containing uraninite, various uranyl sulfates, phosphates and vanadates. Though higher organic matter content (as encountered in tabular-type uranium deposits) may prevent the adequate recovery of uranium under most leaching methods, significant amounts of uranium were historically extracted from unaugmented mine water in deposits north of St. Anthony. The Borrego Pass samples were lower in organic matter and higher in uraninite, which is readily available to typical in-situ leach lixiviants. The Borrego Pass deposit resources (approximately 8 million lbs uranium oxide), though never exploited, were considered for in-situ recovery in the 1980s.

This study is a stepping stone to comprehensive kinetic studies which link behavior under leaching conditions to mineralogy.