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Mines/United States

Mountain Pass

Mountain Pass, United States. Producing, open pit, mining rare earths since 1952.

Why Mountain Pass is famous

California's Mountain Pass has mined rare earths since 1952, first by Molybdenum Corporation of America, then Unocal (1977 to 1998) and Molycorp (from 2008). Operations were cold-idled in mid-2015 and MP Materials bought the site in July 2017. REO in concentrate was 50,692 t in 2025 (45,455 t in 2024).1,2

Story cards

Timeline

  1. 2002 to 2011Mountain Pass mining stops3
  2. 2012Molycorp commissions new Mountain Pass operations3

What kind of deposit

Carbonatite and alkaline intrusion

Mountain Pass today

Where rare earths is mined todayMining in United States

Where next

Mines

Same kind of depositMount WeldMountain Pass has mined rare earths since 1952. Mount Weld, a carbonatite complex, began in 2011.1ExamplesBayan OboBayan Obo, found in 1927 as an iron deposit, became China's main rare earth source.1

Events

Led toMountain Pass mining stopsRead what happened near Mountain Pass: Mountain Pass mining stops.1Led toMolycorp commissions new Mountain Pass operationsRead what happened near Mountain Pass: Molycorp commissions new Mountain Pass operations.1

Deposit types

An example ofCarbonatite and alkaline intrusionA working example of the carbonatite and alkaline intrusion type.4

Sources

  1. Form 10-K for the year ended 31 December 2025 MP Materials Corp (SEC)
  2. data/minerals/operations.csv Prospector Trails (internal)
  3. Rare-Earth Elements, Professional Paper 1802-O US Geological Survey
  4. Mineral Deposit Models (Bulletin 1693, Cox and Singer, eds., 1986) US Geological Survey

From the Prospector Trails mining history dataset: each fact links to the source it was checked against. Figures are as the source gives them, in the money of their day. Not investment advice.

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Pictures: Salar de Atacama, Chile, NASA/METI/AIST/Japan Space Systems, and U.S./Japan ASTER Science Team (Public domain (NASA media, no copyright)); Pangkalpinang. Mijn 3b. Een reeks koelies bezig met het transporteeren van grond, Europeana (Public Domain Mark 1.0).