The Mountain Pass rare earth facility is on the south flank of the Clark Mountain Range and just north of the unincorporated community of Mountain Pass, California. Mountain Pass once supplied most of the world’s rare earth elements and is now re-emerging to, once again, become a major global supplier.
The Mountain Pass deposit is in a 1.4 billion year old Precambrian carbonatite intruded into gneiss, and contains 8% to 12% rare earth oxides, mostly contained in the mineral bastnasite. Gangue minerals include calcite, barite, and dolomite. It is a world-class rare-earth mineral deposit.
Known remaining reserves are estimated to exceed 20 million tons of ore as of 2008, using a 5% cutoff grade, and averaging 8.24% rare earth oxides.
The Mountain Pass facility dominated worldwide REE production from the 1960s to the 1980s.
The Mountain Pass deposit was discovered by a uranium prospector in 1949. The Molybdenum Corporation of America bought the mining claims, and small-scale production began in 1952. Production expanded greatly in the 1960s, to supply demand for europium used in color television screens.
The Molybdenum Corporation of America changed its name to Molycorp in 1974. The corporation was acquired by Union Oil in 1977, which in turn became part of Chevron Corporation in 2005.
The mine closed in 2002, in response to both environmental restrictions and lower prices for REEs. The mine remained inactive post 2002, though processing of previously mined ore continued at the site.
In 2008, Chevron sold the mine to privately held Molycorp Minerals LLC, a company formed to revive Mountain Pass.
In December 2010, Molycorp announced that it secured all the environmental permits needed to begin construction of Project Phoenix. Active mining at Mountain Pass recommenced in December of 2010, for the first time since 2002.
In January 2011, construction began on Phase 1 of the expansion and modernization of Mountain Pass’s facilities. Known as Project Phoenix, the redevelopment has transformed Mountain Pass and enabled environmentally superior, high volume production of rare earth materials, and it has established a new standard for the industry.