Mountain Pass Mine in Mountain Pass, California

Rare earth elements have been in the news due to their critical role in many high-tech applications, and the Mountain Pass deposit in California was a major supplier of these elements for decades. The mine was discovered in the late 1940s and supplied much of the global demand, but its production costs soared and it shut down by 2002. The Mountain Pass deposit is located in a type of rock called carbonatite, which is a rare igneous limestone that often contains high concentrations of rare earth elements. Carbonatites are formed from magma that cools from the molten state, and they are relatively uncommon. China currently accounts for the majority of the world's rare earth mining and processing facilities, which has raised national defense concerns about dependence on a foreign supplier. Efforts to reopen the Mountain Pass Mine began in the 2010s, and after several false starts, the mine is now operating routinely. The reopening of the mine is an echo of the strategic minerals programs of the 1960s, where the US government subsidized the production of vital materials. The Mountain Pass carbonatite is slightly radioactive due to the presence of thorium, which complicates the safe extraction of rare earth elements. The radioactivity of the deposit requires special handling of waste products, which adds to the complexity of the mining operation. The discovery of the Mountain Pass deposit in 1949 was initially made by prospecting for uranium with a Geiger counter, which was a common practice at the time.