New Mexico Geology

In situ recovery (ISR) operations have been proposed to recover uranium from sandstone-hosted uranium deposits in New Mexico. ISR (also known as in situ leaching, solution mining, solution-leach mining, leach mining) is conducted by wells that circulate native groundwater, amended with oxygen (or other forms of oxidant) to dissolve the uranium and gaseous carbon dioxide (or some form of sodium bicarbonate) to complex the uranium in order to keep it in solution through the ore zone. This amended groundwater is commonly referred to as lixiviant. The lixiviant dissolves uranium as it is drawn from injection wells through the uranium-bearing host rock by pumps in nearby extraction wells, and is subsequently piped to a processing plant where the uranium is extracted from the solution. The groundwater is then refortified and sent back to the ore zone through the injection wells to recover additional uranium. The cycle continues until the desired uranium extraction is complete. Thereafter groundwater restoration is conducted. Several technical and regulatory criteria must be met in order for ISR to be successful. To comply with post-mining restoration criteria dictated by state and federal regulations, the groundwater in the mined areas is restored to baseline or other agreed upon water quality standards. This is usually accomplished by circulating clean groundwater through the mined zones to remove the lixiviant. Since groundwater is the fundamental leaching agent, the uranium deposit must be hosted within permeable sandstone below the water table and generally confined by less permeable strata for proper hydrodynamic wellfield control. The mineralized portion of the aquifer must qualify for an “Exemption” from the EPA (U.S. Environmental Protection Administration) from being an underground source of drinking water. A number of ISR test and pilot operations have been conducted in New Mexico in the past (Mobil, Crownpoint; UNC-Teton, Section 23; Grace Nuclear, Hook’s Ranch, Seboyeta, Church Rock; Anaconda, Windwhip). Also, analogous to the ISR process, United Nuclear and Kerr-McGee (later Quivira Mining Co., Rio Algom) successfully produced uranium from mine-water recovery (recirculated mine water) from underground mines in the Ambrosia Lake area during the mid-1960s to 2002. Potential ISR site locations in the U.S., including in New Mexico, require careful aquifer characterization and project operational design and monitoring. With such proper site characterization and design, ISR is a viable alternative mining technology to provide future uranium recovery from many of New Mexico’s known uranium deposits. This initial investigation suggests that a significant portion of deposits in the Grants uranium district may be amenable to ISR production.