CHARACTERIZATION OF CRETACEOUS REE-BEARING HEAVY MINERAL SANDSTONES IN NEW MEXICO

Heavy mineral (beach-placer) sandstones are accumulations of high specific gravity, resistant minerals that form from mechanical concentration by waves, currents, and winds in marginal-marine environments. These sediments are enriched in critical minerals such as titanium, zirconium, and rare earth elements (REE). Cretaceous heavy mineral sandstones are found in the Colorado Plateau of northwestern New Mexico. Originally discovered by airborne radiometric surveys for uranium in the 1950s, these heavy mineral sandstones are being re-examined with modern methods as potential sources for critical minerals by the New Mexico Bureau of Geology and Mineral Resources under the DOE Carbon Ore, Rare Earths, and Critical Minerals (CORE-CM) Initiative. Selected beach-placer sandstones have been mapped with ground radiometric surveys, sampled, and analyzed with whole-rock and trace element geochemical methods. Mineralogy is being determined with optical methods, X-ray diffraction, and electron microprobe analysis. Zircon, rutile, ilmenite, and monazite are the primary heavy minerals of interest found in the studied deposits. Initial geochemical results show that the sandstones contain up to 1.4% total REE, 29.4% TiO₂, and an estimated 4.9% ZrO₂. Chondrite-normalized REE diagrams show distinct light REE and minor heavy REE enrichment, as well as pronounced negative Eu anomalies for each deposit. A simple method for the estimation of combined U and Th using a scintillation counter is demonstrated, as is a method for the estimation of Zr using Hf for samples that exceed the laboratory detection limit of Zr.