GEOCHEMISTRY OF CRITICAL MINERALS IN COPPER FLAT TAILINGS, HILLSBORO DISTRICT, NEW MEXICO

Critical minerals are materials that are important for the U.S. economy and national security and have supply chains that arevulnerable to disruption. The specific critical minerals vary between countries based on the needs of the country anddecisions in government around the importance of some minerals. The U.S. has a comprehensive list of critical mineralsestablished by the USGS starting in 2018 and updated every two years. While copper is not currently a critical mineral defined by the USGS, it is considered a critical material by the DOE because it is used in energy transmission and electric components in clean energy solutions. Mine wastes, including mill tailings (the byproduct of mineral processing after ore minerals have been separated from ore), waste rock piles, and mine water, could be sources of critical minerals. The Copper Flat mine, a small porphyry copper deposit located in the Hillsboro mining district, Sierra County, NM, contains mine wastes that may contain various critical minerals. Mining ceased in 1982, but research and permitting to reopen the mine has continued. Tailings were sampled from the mine that were produced in 1981-1982, during the last mining operations. The focus of this project is to characterize the critical mineral content of the tailings at the Copper Flat mine. Critical minerals found in the Copper Flat tailings include Bi (1.3-2.3 ppm), Co (5.7-10.7ppm), Cu (346-774 ppm), Ga (18-21 ppm), Te (0.24-0.49 ppm), Zn (39-72 ppm), Zr (235-279 ppm) and total REE (135-217ppm). A shallow pit was dug into the tailings and samples collected at different depths. Initial geochemical observationsshow increasing concentrations of S and Cu (as well as Bi and Te) with depth, suggesting either the oxidation of copper sulfides and remobilization of Cu, or the dilution of tailings with cover material at the surface. In general, critical mineral concentrations in Copper Flat tailings are low, but the available tonnage of material and the fact that the material has already been finely ground may affect the economics of these commodities