RARE EARTH ELEMENTS (REE) IN LATE CRETACEOUS COAL BEDS IN THE SAN JUAN AND RATON BASINS, NEW MEXICO: PRELIMINARY OBSERVATIONS

Rare earth elements (REE) are increasingly becoming more important in our technological society and are used in many of our electronic devices (such as cell phones, computer monitors, wind turbines, etc.), batteries, and magnets. REE include the 15 lanthanide elements (atomic number 57-71), yttrium (Y, atomic number 39), and scandium (Sc, atomic number 21) and are lithophile elements (elements enriched in the crust) that have similar physical and chemical properties, and, therefore, occur together in nature. In New Mexico, low to moderate concentrations of REE are found in 23 coal fields in Late Cretaceous coal beds in the San Juan and Raton Basins. These rocks are being characterized as part of the DOE’s CORE-CM (Carbon Ore, REE, and Critical Minerals) program. REE can be measured in either the entire coal sample (whole rock basis) before burning or in the ash after burning (ash basis). REE are concentrated in the ash after burning, and thus ash basis REE concentrations are greater than whole rock values. Measuring REE in the ash basis approximates the REE in the fly or bottom ash remaining after coal is burned at a power plant, where REE could be leached from the coal ash. Generally, REE concentrations on ash basis are higher on average in lower ash content samples (560 ppm total REE for samples <10% ash compared to 234 ppm for samples >90% ash). Coal samples typically display relatively flat to slightly light REE enriched chondrite-normalized REE patterns. Some of the highest total REE concentrations (ash basis) are found in samples from the closed La Plata mine in the Fruitland Formation (2103 ppm total REE), the closed Metmore mine in the Gallup Formation (807 ppm), and the Crownpoint (1684 ppm), Standing Rock (523 ppm), Barker Creek (528 ppm), Mt. Taylor (696 ppm), Star Lake (795 ppm), and Monero (1026 ppm) coal fields in the San Juan Basin and in the Van Houten area of the Raton Basin (992 ppm). More chemical and mineralogical analyses are required to fully understand the distribution and origin of REE in these deposits. As the demand for REE increases because of increased need and short supplies, the dollar value per ton of ore rises, enhancing deposit economics, perhaps even from coal.