A baryte-Ce-REE-Au-Ag-Pb deposit/mine located in secs. 12 & 13, T16N, R13E, SBM, 1.5 km (0.9 miles) NE of Mountain Pass (town), immediately N of Interstate highway 15, and about 15 miles W of the Nevada state line, on private (patented) land. It was discovered in 1949. The property is comprised of 6 claims. The first production occurred in 1951. The USGS MRDS database stated accuracy for this locality is 10 meters.
Owned & operated by the Molybdenum Corporation of America (MCA) (100%) (1950-1974); Owned & operated by Molycorp, Inc. (100%) (same company - new name (1974-1977); owned by the Union Oil of California (100%) (1977); Operated by Molycorp, Inc. (100%) (1977-2005); Owned & operated by Molycorp Minerals LLC (100%), Englewood, Colorado (1983).
NOTE: The mine ceased active mining in 2002 due to environmental concerns, however the owners, Molycorp Inc., planned to return to full production in 2011. Start-up mining activities began in August 2012. In June 2015, however, Molycorp filed for bankruptcy.
The mine reopened in 2018. According to "Mineral Commodities Summary" from the USGS (2020), in the entry for Yttrium, page 1: "mined in 2019 as a primary product at the Mountain Pass Mine in California, which was restarted in the first quarter of 2018 after being put on care-and-maintenance status in the fourth quarter of 2015."[1]
Mineral occurrence model information: Model code: 24; USGS model code: 10; Deposit model name: Carbonatite. Mineralization involves vein baryte deposits with rare-earth minerals in metamorphic and igneous rocks of Precambrian age. One of the world's largest lanthanide deposits. There are environmental concerns as this mine is situated next to the Mojave National Preserve.
The carbonatite complex (1.4 BP intrusion) is intruded in Precambrian biotite-garnet-sillimanite-hornblende gneisses, biotite granitic gneisses, augen granitic gneisses (Neoproterozoic gneisses) and schists. The carbonatite complex is composed of eight 100 to 2000 meter-long plugs of alkaline intrusive rocks (from shonkinites and syenites to carbonatites) and about 200 dikes of carbonatite in NW-trending rows.
The ore body strikes N10W and dips 40W at a thickness of 75 meters, a depth-to-top of 458 meters (?? - depth-to-bottom ??), a width of 1,590 meters, a length of 750 meters and an area of 1500 HA. Ore body No. 1 is tabular; No. 2 is a fissure vein and No. 3 is a shear zone. The primary mode of origin was magmatic differentiation and the secondary mode was hydrothermal activity. Primary ore control was igneous and the secondary control was fracturing. Wallrock alteration is slight (silicification and carbonitization). Alteration also includes fenitization and hematization. The vein occurs at the contact of a dike and host rock and has an aplite dike hanging wall and a gneiss footwall. The dikes trend N30W.
Analytical data results: An ore shoot 100 feet long and 12 to 15 feet thick was said to carry $9.00 (period values) Au per ton.
Analysis of the bastnäsite-(Ce) by Hoffman et al. (1971) have confirmed the presence of plutonium-244 isotope. However, Sakamoto (1974) has suggested, that the source of this exotic isotope may be extraterrestrial.
Workings include surface and underground openings comprised of an open pit with an area of 260 ha and an overall depth of 169.16 meters. Milling method employed was flotation. Water is obtained from wells 10 km E of the mine. Power is supplied by Southern California Edison Company. The access road is paved and labor is available at the site.
An estimated production rate in the 1980s was 1,285 metric tons/day, including 1,155 metric tons/day ore and 130 metric tons/day of dilution material. The production numbers are amount of REE's in the concentrate. This is not the same as the total recovered since there is some loss in processing the concentrate. True production is somewhat less, but the loss in processing is not reported.
Reserves and resources: Type: in-situ (estimate year: 1989): Demonstrated: 28,123,000 metric tons of ore; indicated: 28,123,000 metric tons of ore. Total resources: 28,123,000 metric tons of ore. REE (Y group): 8.9 weight percent REE (1989).
For more recent information see (here).
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