Mountain Pass mine

Coordinates: 35°28′43″N 115°31′57″W / 35.47861°N 115.53250°W / 35.47861; -115.53250
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Mountain Pass Mine
Mountain Pass mine - open pit (left)
mill (right background)
Mountain Pass Mine is located in California
Mountain Pass Mine
Mountain Pass Mine
Location in California
LocationMountain Pass, San Bernardino County
CountryUnited States
Coordinates35°28′43″N 115°31′57″W / 35.47861°N 115.53250°W / 35.47861; -115.53250
ProductsRare-earth elements in concentrates
Production38,000 tonnes[1]
Financial year2020
Active1952–2002, 2007–2015, 2017–
CompanyMP Materials Corp.
WebsiteMountain Pass Mine
Year of acquisition2017

The Mountain Pass Rare Earth Mine and Processing Facility, owned by MP Materials, is an open-pit mine of rare-earth elements on the south flank of the Clark Mountain Range in California, 53 miles (85 km) southwest of Las Vegas, Nevada. In 2020 the mine supplied 15.8% of the world's rare-earth production. It is the only rare-earth mining and processing facility in the United States.[1][2]

As of 2022, work is ongoing to restore processing capabilities for domestic light rare-earth elements (LREEs) and work has been funded by the United States Department of Defense to restore processing capabilities for heavy rare-earth metals (HREEs) to alleviate supply chain risk. [3]


The Mountain Pass deposit is in a 1.4 billion-year-old Precambrian carbonatite intruded into gneiss. It contains 8% to 12% rare-earth oxides, mostly contained in the mineral bastnäsite.[4] Gangue minerals include calcite, barite, and dolomite. It is regarded as a world-class rare-earth mineral deposit. The metals that can be extracted from it include:[5] cerium, lanthanum, neodymium,[6] and europium.

At 1 July 2020, Proven and Probable Reserves, using a 3.83% total rare-earth oxide (REO) cutoff grade, were 18.9 million tonnes of ore containing 1.36 million tonnes of REO at an average grade of 7.06% REO.[7]

Ore processing[edit]

To process bastnäsite ore, it is finely ground and subjected to froth flotation to separate the bulk of the bastnäsite from the accompanying barite, calcite, and dolomite. Marketable products include each of the major intermediates of the ore dressing process: flotation concentrate, acid-washed flotation concentrate, calcined acid-washed bastnäsite, and finally a cerium concentrate, which was the insoluble residue left after the calcined bastnäsite had been leached with hydrochloric acid.[citation needed]

The lanthanides that dissolve as a result of the acid treatment are subjected to solvent extraction to capture the europium and purify the other individual components of the ore. A further product includes a lanthanide mix, depleted of much of the cerium, and essentially all of samarium and heavier lanthanides. The calcination of bastnäsite drives off the carbon dioxide content, leaving an oxide-fluoride, in which the cerium content oxidizes to the less-basic quadrivalent state. However, the high temperature of the calcination gives less-reactive oxide, and the use of hydrochloric acid, which can cause reduction of quadrivalent cerium, leads to an incomplete separation of cerium and the trivalent lanthanides.[citation needed]


The Mountain Pass mine dominated worldwide REE production from the 1960s to the 1980s (USGS).

The Mountain Pass deposit was discovered in 1949 by Herbert S. Woodward, Clarence Watkins and P. A. Simon, who noticed anomalously high radioactivity.[8] Molybdenum Corporation of America bought most[9] of the mining claims, and began small-scale production in 1952.

Mountain Pass mine, mill, shop & offices in 2010

Production expanded greatly in the 1960s, to supply demand for europium used in color television screens. Between 1965 and 1995, the mine supplied most of the worldwide rare-earth metals consumption.[10]

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.[11]

In 1998, the mine's separation plant ceased production of refined rare-earth compounds; it continued to produce bastnäsite concentrate.[12]

The mine closed in 2002 after a toxic waste spill[13] and wasn't reopened due to competition from Chinese suppliers, though processing of previously mined ore continued.[14]

In 2008, Chevron sold the mine to privately-held Molycorp Minerals LLC, a company formed to revive the Mountain Pass mine. Molycorp announced plans to spend $500 million to reopen and expand the mine, and on July 29, 2010, it raised about $400 million through an initial public offering, selling 28,125,000 shares at $14 under the ticker symbol MCP on the New York Stock Exchange.[15]

In December 2010, Molycorp announced that it had secured all the environmental permits needed to build a new ore processing plant at the mine; construction would begin in January 2011, and was expected to be completed by the end of 2012. On August 27, 2012, the company announced that mining had restarted.

The processing plant was in full production on June 25, 2015, when Molycorp filed for Chapter 11 bankruptcy with outstanding bonds in the amount of $US 1.4 billion. The company's shares were removed from the NYSE.

In August 2015, it was reported that the mine was to be shut down.

On August 31, 2016, Molycorp Inc. emerged from bankruptcy as Neo Performance Materials, leaving behind the mine as Molycorp Minerals LLC in its own separate Chapter 11 bankruptcy. As of January 2016, its shares were traded OTC under the symbol MCPIQ.

Mountain Pass was acquired out of bankruptcy in July 2017 with the goal of reviving America's rare-earth industry.[16][17][18][19] MP Materials resumed mining and refining operations in January 2018.[2]

Current ownership[edit]

MP Materials is 51.8%-owned by US hedge funds JHL Capital Group (and its CEO James Litinsky) and QVT Financial LP, while Shenghe Resources Holding Co. Ltd., a partially state-owned enterprise of the Government of China, holds an 8.0% stake. Apart from institutions, the public owns 18%.[20][21]

Environmental impact[edit]

Satellite image of the Mountain Pass mine and vicinity (2011)

In the 1980s, the company began piping wastewater up to 14 miles to evaporation ponds on or near Ivanpah Dry Lake, east of Interstate 15 near Nevada. This pipeline repeatedly ruptured during cleaning operations to remove mineral deposits called scale. The scale is radioactive because of the presence of thorium and radium, which occur naturally in the rare-earth ore. A federal investigation later found that some 60 spills—some unreported—occurred between 1984 and 1998, when the pipeline and chemical processing at the mine were shut down.[22] In all, about 600,000 gallons of radioactive and other hazardous waste flowed onto the desert floor, according to federal authorities. By the end of the 1990s, Unocal was served with a cleanup order and a San Bernardino County district attorney's lawsuit. The company paid more than $1.4 million in fines and settlements. After preparing a cleanup plan and completing an extensive environmental study, Unocal in 2004 won approval of a county permit that allowed the mine to operate for another 30 years. The mine passed a key county inspection in 2007.[11]

Current activity[edit]

Mountain Pass mine in 2022

Since 2007, China has restricted exports of REEs (rare-earth elements) and imposed export tariffs, both to conserve resources and to give preference to Chinese manufacturers.[23] In 2009, China supplied more than 96% of the world's REEs. Some outside China are concerned that because rare-earths are essential to some high-tech, renewable-energy, and defense-related technologies, the world should not be so reliant on a single supplier country[24][25]

On September 22, 2010, China quietly enacted a ban on exports of rare-earths to Japan, a move suspected to be in retaliation for the Japanese arrest of a Chinese trawler captain in a territorial dispute. Because Japan and China are the only current sources for rare-earth magnetic material used in the US, a permanent disruption of Chinese rare-earth supply to Japan would leave China as the sole source. Jeff Green, a rare-earth lobbyist, said, "We are going to be 100 percent reliant on the Chinese to make the components for the defense supply chain."[26] The House Committee on Science and Technology scheduled on September 23, 2010, the review of a detailed bill to subsidize the revival of the American rare-earths industry, including the reopening of the Mountain Pass mine.[27]

After China doubled import duties on rare-earth concentrates to 25% as a result of the US-China trade war, MP Materials said, in May 2019, it will start its own partial processing operation in the United States, though full processing operations without Shenghe Resources have been delayed. [28] According to Bloomberg, China in 2019 established a plan for restricting U.S. access to Chinese heavy rare earth elements, should the punitive step be deemed necessary.[29] In 2022, the company announced that it had secured Department of Defense grants to support both light rare-earth elements (LREEs) and heavy rare earth elements (HREEs).[3] The facility plans to begin separating NdPr oxide in early 2023.[30]


  1. ^ a b Gambogi, Joseph (January 29, 2021). "Rare Earths". Mineral Commodity Summaries (PDF). Reston, Virginia: U.S. Geological Survey. pp. 132–133. ISBN 978-1-4113-4398-6. Retrieved February 27, 2021.
  2. ^ a b "The Californian Rare Earths Mine Caught Between Trump and China". Bloomberg News. September 26, 2018. Archived from the original on October 9, 2018. Retrieved November 7, 2018.
  3. ^ a b "MP Materials secures heavy rare-earth processing contract with the U.S. Department of Defense". Kitco. February 22, 2022.
  4. ^ Haxel, Gordon B.; Hedrick, James B.; Orris, Greta J. (May 17, 2005). Rare earth elements – Critical resources for high technology. {{cite book}}: |work= ignored (help)
  5. ^ "Mountain Pass Rare Earth Mine". Geological Sciences Department. California State Polytechnic University, Pomona. 2008. Archived from the original on October 1, 2008. Retrieved March 4, 2009.
  6. ^ Margonelli, Lisa (May 2009). "Clean Energy's Dirty Little Secret". The Atlantic. Retrieved August 5, 2009.
  7. ^ "Prospectus" (PDF). f MP Materials Corp. December 28, 2020. p. 4. Retrieved March 1, 2021.
  8. ^ Olson, J.C.; Shawe, D.R.; Pray, L.C.; Sharp, W.N. (1954). "Rare-Earth Mineral Deposits of the Mountain Pass District, San Bernardino County, California" (PDF). U.S. Geological Survey Professional Paper. 119 (261): 325–326. doi:10.3133/pp261. PMID 17754332. Retrieved October 11, 2020.
  9. ^ "Pele Mountain enters agreement to acquire rare earth mining claims surrounded by Molycorp, 1800 metres from the Mountain Pass Mine". Glacier Media. March 6, 2012. Retrieved October 11, 2020.
  10. ^ Castor, Stephen B. (2008). "Rare Earth Deposits of North America". Resource Geology. 58 (4): 337. doi:10.1111/j.1751-3928.2008.00068.x.
  11. ^ a b Danelski, David (February 9, 2009). "Expansion in works for S.B. County mine with troubled environmental past". The Biz Press. Archived from the original on July 13, 2011.
  12. ^ "USGS Minerals Yearbook—1999" (PDF). U.S. Geological Survey. Retrieved July 27, 2018.
  13. ^ Hansen, Tobin (March 2020). "Securing U.S. Access to Rare Earth Elements" (PDF). Defense 360°. p. 4.
  14. ^ "Mineral Commodity Summaries: Rare Earths" (PDF). U.S. Geological Survey. 2003. Retrieved July 27, 2018.
  15. ^ "Prospectus for Initial Public Offering". Molycorp Inc.
  16. ^ Peg Brickley (June 23, 2017). "Mountain Pass Mine Approved for Sale to JHL, QVT, Shenghe". The Wall Street Journal. ISSN 0099-9660. Wikidata Q114387011. Retrieved October 3, 2022.
  17. ^ "Mountain Pass sells for $20.5 million |". June 16, 2017. Retrieved November 7, 2018.
  18. ^ Xie, John (December 31, 2020). "California Mine Becomes Key Part of Push to Revive US Rare Earths Processing". Voice of America. Archived from the original on December 31, 2020. Retrieved December 31, 2020.
  19. ^ Hui, Mary (February 5, 2021). "The US is taking steps towards breaking China's rare earths monopoly". Quartz. Archived from the original on February 10, 2021. Retrieved February 13, 2021.
  20. ^ "MP Materials Corp. (MP)". Market Screener. Annecy, France: Surperperformance. Retrieved February 28, 2021.
  21. ^ "Shenghe Resources Holding Co. Ltd: Shareholders Board Members Managers and Company Profile". MarketScreener. Retrieved February 14, 2021.
  22. ^ Margonelli, Lisa (May 2009). "Clean Energy's Dirty Little Secret". The Atlantic.
  23. ^ "Rare Earth Elements". British Geological Survey. pp. 25, 29.
  24. ^ Hsu, Jeremy (March 17, 2010). "Shortage of rare earth minerals may cripple U.S. high-tech, scientists warn Congress". Popular Science.
  25. ^ Hsu, Jeremy (April 14, 2010). "U.S. military supply of rare earth elements not secure". TechNewsDaily.
  26. ^ BRADSHER, KEITH (September 24, 2010). "China halts exports of minerals crucial to Japanese industry HONG: Customs officers at ports stop rare earth elements amid fishe". International Herald Tribune, Hong Kong. thejakartapost. Retrieved November 1, 2010.
  27. ^ Bradsher, Keith (September 22, 2010). "Amid Tension, China Blocks Crucial Exports to Japan". New York Times.
  28. ^ "Caught Between Trump and its biggest market, America's sole rare earths mine is an unusual victim in the US- China trade war". South China Morning Press. May 26, 2019. (published 05-26-2019)
  29. ^ "China Has Rare Earths Plan Ready to Go If Trade War Deepens". Bloomberg News. May 30, 2019. Retrieved February 4, 2021.
  30. ^ Stone, Maddie (June 29, 2023). "A once-shuttered California mine is trying to transform the rare earth industry". Fast Company. Grist.

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