Mountain Pass rare earth mine

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Mountain Pass Rare Earth Mine
The Mountain Pass mine surface facilities. The upper part of the open pit is seen in the background.
Mountain Pass rare earth mine is located in California
Mountain Pass rare earth mine
Mountain Pass rare earth mine
Location in California
Location Mountain Pass, San Bernardino County
State California
Country United States
Coordinates 35°29′N 115°32′W / 35.48°N 115.53°W / 35.48; -115.53Coordinates: 35°29′N 115°32′W / 35.48°N 115.53°W / 35.48; -115.53
Products Rare-earth elements
Satellite image of the Mountain Pass mine and vicinity, 2011. The mine and plant are located just north of Interstate 15. The bright green areas at left center are settling ponds for the mine's wastewater.

The Mountain Pass Rare Earth Mine is an open-pit mine of rare-earth elements (REEs) on the south flank of the Clark Mountain Range, just north of the unincorporated community of Mountain Pass, California, United States. The mine, owned by MP Materials, once supplied most of the world's rare-earth elements.


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 bastnäsite.[1] 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:[2]

Known remaining reserves were estimated to exceed 20 million tons of ore as of 2008, using a 5% cutoff grade, and averaging 8.9% rare-earth oxides.[4]

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.

The lanthanides that dissolved as a result of the acid treatment were subjected to solvent extraction, to capture the europium, and purify the other individual components of the ore. A further product included a lanthanide mix, depleted of much of the cerium, and essentially all of samarium and heavier lanthanides. The calcination of bastnäsite had driven off the carbon dioxide content, leaving an oxide-fluoride, in which the cerium content had become oxidized to the less-basic quadrivalent state. However, the high temperature of the calcination gave less-reactive oxide, and the use of hydrochloric acid, which can cause reduction of quadrivalent cerium, led to an incomplete separation of cerium and the trivalent lanthanides.


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

The Mountain Pass deposit was discovered by a uranium prospector in 1949, who noticed the anomalously high radioactivity. 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 deposit was mined in a larger scale between 1965 and 1995. During this time the mine supplied most of the worldwide rare-earth metals consumption.[4] 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.[5]

In 1998, the mine's separation plant ceased production of refined rare earth compounds; it continued to produce bastnäsite concentrate[6]. The mine closed in 2002, in response to both environmental restrictions and lower prices for REEs[7]. The mine has been mostly inactive since 2002, though processing of previously mined ore continues at the site.

In 2008, Chevron sold the mine to privately held Molycorp Minerals LLC, a company formed to revive the Mountain Pass mine. On July 29, 2010, Molycorp, Inc. became a publicly traded firm by selling 28,125,000 shares at $14 in its IPO. The shares trade under the ticker symbol MCP on the NYSE.[8]

On June 25, 2015, Molycorp filed for Chapter 11 bankruptcy. The company's shares were removed from the NYSE and as of January 2016 are traded OTC under the symbol MCPIQ. At the time of the bankruptcy, Molycorp had outstanding bonds in the amount of $US 1.4 billion.

Affiliates of two U.S. investment fund advisors, JHL Capital Group LLC and QVT Financial LP, acquired Mountain Pass in July of 2017 with the goal of reviving America’s rare earth industry. The venture does business under the name MP Materials ( MP Materials resumed mining and refining operations in January 2018

Environmental impact[edit]

In 1998, chemical processing at the mine was stopped after a series of wastewater leaks. Hundreds of thousands of gallons of water carrying radioactive waste spilled into and around Ivanpah Dry Lake.[9]

In the 1980s, the company began piping wastewater as far as 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 was shut down. 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 also passed a key county inspection in 2007.[5]

Current activity[edit]

The mine, once the world's dominant producer of rare-earth elements, was closed in large part due to competition from REEs imported from China, which in 2009 supplied more than 96% of the world's REEs. Since 2007 China has restricted exports of REEs and imposed export tariffs, both to conserve resources and to give preference to Chinese manufacturers.[10] 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 reliant on a single source.[11][12] 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."[13] 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.[14]

The mine was once owned by Molycorp Minerals LLC, a subsidiary of Molycorp Inc..[13] Molycorp planned to invest $500 million to reopen and expand the mine.[14]The money was raised through an initial public offering of stock in Molycorp Inc.[15] Full mining operations were planned to resume by the second half of 2011 as a result of increased demand for rare-earth metals.[16] In December 2010, Molycorp announced that it had secured all the environmental permits needed to begin construction of 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.[17] The company announced its resumption of operations on a start-up basis at the Mountain Pass mine on August 27, 2012.[18] As of 2015, the plant was in full production.[19]Molycorp filed for bankruptcy in June 2015. In August 2015, it was reported that the mines was to be shutdown.[20] On August 31, 2016 Molycorp Inc. emerged from chapter 11 bankruptcy as Neo Performance Materials, leaving behind the mine as Molycorp Minerals LLC in its own separate chapter 11 bankruptcy.

Affiliates of two U.S. investment fund advisors, JHL Capital Group LLC and QVT Financial LP, acquired Mountain Pass in July of 2017 with the goal of reviving America’s rare earth industry. The venture does business under the name MP Materials (  MP Materials resumed mining and refining operations in January 2018[15]


  1. ^ Gordon B. Haxel, James B. Hedrick, and Greta J. Orris, "Rare earth elements – Critical resources for high technology", US Geological Survey, Fact Sheet 087-02, 17 May 2005.
  2. ^ Geological Sciences Department (2008). "Mountain Pass Rare Earth Mine". California State Polytechnic University, Pomona. Archived from the original on 2008-10-01. Retrieved 2009-03-04.
  3. ^ Margonelli, Lisa (May 2009). "Clean Energy's Dirty Little Secret". The Atlantic. Retrieved 2009-08-05.
  4. ^ a b Castor, Stephen B. (2008). "Rare Earth Deposits of North America". Resource Geology. 58 (4): 337. doi:10.1111/j.1751-3928.2008.00068.x.
  5. ^ a b David Danelski, Expansion in works for S.B. County mine with troubled environmental past Archived 2011-07-13 at the Wayback Machine., The Biz Press, February 9, 2009.
  6. ^ "USGS Minerals Yearbook—1999" (PDF). U.S. Geological Survey. Retrieved July 27, 2018.
  7. ^ "Mineral Commodity Summaries: Rare Earths—2003" (PDF). U.S. Geological Survey. Retrieved July 27, 2018.
  8. ^ Molycorp Inc. Prospectus for Initial Public Offering
  9. ^ Lisa Margonelli, Clean Energy's Dirty Little Secret, "The Atlantic", May 2009.
  10. ^ British Geological Survey, Rare Earth Elements, PDF file, p. 25, 29.
  11. ^ Jeremy Hsu, "Shortage of rare earth minerals may cripple U.S. high-tech, scientists warn Congress", Popular Science, 17 March 2010.
  12. ^ Jeremy Hsu, "U.S. military supply of rare earth elements not secure", TechNewsDaily, 14 April 2010.
  13. ^ BRADSHER, KEITH (2010-09-24). "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 2010-11-01.
  14. ^ Amid Tension, China Blocks Crucial Exports to Japan, New York Times, 22 SEP 2010.
  15. ^ "The Californian Rare Earths Mine Caught Between Trump and China". Retrieved 2018-10-09.

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