ICE 2022


Rare Earth Elements are currently being produced at the Mountain Pass Mine, Mountain Pass, California (USA) from a carbonatite deposit. This deposit supplied an estimated 15.8% of the world’s rare-earth production in 2020 and is the only rare earth mining and processing facility in the United States. The United States hopes to construct a domestic critical mineral industry, which can prove to be a daunting task when considering the environmental, economic, and political hurdles. The paradox of wanting a carbon-free world while simultaneously preventing the industries that are required to make that future plausible. The Bear Lodge cabonatite is one of the largest rare earth deposits in the United States, with a project-wide measured and indicated resources of 10 million short tons at a grade of 3.05% total rare earth oxide. The complex displays variable weathering which in turn results in light and heavy rare-earth elemental enrichment based on weathering profiles. The deposit is zoned with weathered materials located to a depth of approximately 590 feet (180 meters) where it grades into unaltered carbonates. The Bear Lodge Mountains are considered to be a part of the Black Hills Uplift which was the result of a Tertiary-aged alkaline igneous complex towards the end of the Laramide Orogeny. The carbonate itself is expressed as a series of northwestern trending dikes intruded into the three diatreme structures. It is thought that through isotopic analysis that the carbonatitic magma responsible for the deposit was derived from the subcontinental lithospheric mantle. These deposits were further altered through chemical interactions with both hydrothermal interactions as well as meteoric waters. The carbonatite was enriched further though partial melt of a small depleted mid-ocean ridge basalt as well as an enriched mantle-1 signature suggested to be derived from subduction of the Farallon crust. Closer examinations of the complex address the questions including, can it be done economically, are there environmental safeguards in place, what are the alternatives and how can the materials be extracted responsibly. The Mountain Pass Mine remains the most viable source for the United States because of its grade, size, and simple metallurgy. The amount of research completed on the Bear Lodge complex is significant and because of this amount of work completed it provides insights into other global localities.