Diversity of critical minerals deposits in the North American Cordilleran alkaline-igneous belt in southern Colorado, New Mexico, Texas, and Mexico

Abstract

Critical minerals are nonfuel mineral commodities that are essential to the economic and national security of the United States and many other countries, mostly imported into the U.S., and are from a supply chain that is vulnerable to global and national disruption. A renewed interest in critical minerals in the U.S. and the world has become the focus of research in understanding ore formation, mineral-resource potential, and ore production of these important mineral deposits. Alkaline igneous rocks, including carbonatites, are known for their associated critical minerals deposits. The North American Cordilleran alkaline-igneous belt is one such area known for gold, molybdenum, rare earth elements (REE), and critical minerals deposits associated with Eocene-Miocene (45.6 to 22.8 Ma) alkaline igneous rocks and carbonatites. The belt extends southward from Alaska and British Columbia into New Mexico and eastern Mexico. Gold, molybdenum, and critical minerals such as REE, tellurium, fluorine, zirconium, and niobium have been found and locally exploited along this belt. In New Mexico (the focus of this paper), the belt extends southward from the Sangre de Cristo Mountains to the Cornudas Mountains, in the northern Trans-Pecos alkaline belt. The mineral deposits in the North American Cordilleran alkaline-igneous belt are controlled by composition and source of alkaline magmas, regional and local structures, and development of multiple hydrothermal systems during the transition from Laramide compression (75-40 Ma) to Rio Grande rift extension (28-5 Ma). Three predominant types of mineral deposits are found in the North American Cordilleran alkaline-igneous belt: (1) alkalic-type epithermal gold, (2) Climax-type porphyry molybdenum, and (3) magmatic REE deposits (including veins and breccia deposits in adjacent host rocks); a fourth deposit type, small alkalic porphyry copper-gold deposits, are found in a few districts. Many of the mineral deposits in this belt formed at or after peak activity of a local magmatic cycle. Magmas and sulfur were derived from melting of the lower crust to upper mantle (as indicated by isotopic data from several deposits) resulting in the diversity of mineral deposits in the southern North American Cordilleran alkaline-igneous belt. Most of the magmatic REE deposits occurred during the transitional period (40-28 Ma), whereas the Climax-type porphyry molybdenum deposits occurred mostly at the beginning of rifting (25-24 Ma). The alkali epithermal gold and small alkalic porphyry deposits occurred at the end of the Laramide orogeny and during the transitional period before rifting. Most alkalic-type epithermal gold deposits in New Mexico are found in hydrothermal breccia pipes and skarns with anomalous, but uneconomic concentrations of REE and tellurium. Alkalic-type epithermal and alkalic porphyry copper-gold deposits in New Mexico are found in the Ortiz Mountains in Santa Fe County (Carache Canyon, Lucas Canyon). Many districts in the belt have future critical minerals potential. Tellurium is found at Cripple Creek, Colorado and Organ Mountains, New Mexico. Tungsten was locally produced in the past from two of these gold deposits (Elizabethtown and White Oaks) and is found in the Ortiz Mountains deposits. The Climax-type molybdenum deposits, including the Questa deposit, contain anomalous, but uneconomic concentrations of beryllium and fluorite. The magmatic REE deposits in Laughlin Peak, Gallinas, Capitan, and Cornudas Mountains, New Mexico generally contain anomalous, but uneconomic concentrations of zircon, niobium, fluorite, and gold, and generally low tellurium, tungsten, and beryllium concentrations. The magmatic REE deposits in the Gallinas Mountains are among the highest ranked deposits for economic potential for REE in New Mexico; some samples contain as much as 8% total REE. Some samples in the Cornudas Mountains contain as much as 3110 ppm total REE, mostly in eudialyte. A mineral concentrate of the REE-bearing minerals (eudialyte, zircon, monazite, bastnäsite, calcio-catapleiite, vitusite, roumaite, xenotime) could be obtained after mining by magnetic separation and REE could be leached from that concentrate.