Geology of the Cambrian Lemitar carbonatites, Socorro County, New Mexico: Revisited

Carbonatites are igneous rocks of magmatic origin that are composed of more than 50% carbonate minerals, less than 20% SiO2, and they can form economic deposits containing significant amounts of rare earth elements (REE), barite, fluorite, and niobium. REE are critical minerals and are essential to the functioning of information-age technologies because of their unique properties, e.g., high electric conductivity, strong magnetism, fluorescence, and luminescence. In this respect, carbonatites serve as the principal source of REE on Earth. Carbonatites in the Lemitar Mountains are light REE enriched and contain as much as ~1.1 wt.% in total. While previously described, new analytical techniques have allowed for additional and more precise description, age, and model of their origin. The age of Lemitar carbonatites has been newly established at ~515 Ma using 40Ar/39Ar and U/Pb geochronological methods. Petrographic observations combined with whole-rock geochemical and isotope data indicate the Lemitar carbonatites are mantle-derived and that their origin is related to the Cambrian-Ordovician belt of alkaline igneous rocks and carbonatites in southern Colorado and New Mexico. The Lemitar carbonatites are not economic at the present time because of small tonnage and low grades. Nevertheless, further drilling is required to determine if the carbonatites increase in REE and Nb concentrations at greater depth (1.1% total REE in a surface sample is significant). Detailed geophysical surveys are required to determine if the Lemitar Mountains could contain a larger carbonatite body emplaced in the subsurface.