One of the worlds largest lanthanide deposits. There are however strong environmental concerns as it is situated next to Mojave Desert National Reserve.
Mineralization involves vein baryte deposits with rare-earth minerals in metamorphic and igneous rocks of Precambrian age.
Carbonatite complex (1.4 BP intrusion) intruded in Precambrian biotite-garnet-sillimanite-hornblend gneisses, biotite granitic gneisses, augen granitic gneisses and schists. The carbonatite complex is composed of eight 100/2000 meter-long plugs of alkaline intrusive rocks (from shonkinites and syenites to carbonatites) and about 200 dikes of carbonatite in NW trendng rows.
Alteration: fenitization and hematization.
Ref.: Zadra, J.B., et al (1952), Concentration of bastnaesite and other cerium ores: US Bur. Mines Rept. Inv. 4919.
Jaffe, H.W., et al (1953), Sahamalite, a new rare earth carbonate mineral, Am.Min.: 38: 721-754.
Olson, J.C., Shawe, D.R., Pray, L.C., Sharpe, W.N., and Hewlett, D.F. (1954), Geology of the rare-earth deposits of the Mountain Pass district, San Bernardino County California, USGS PP 261.
Brobst, D.A. (1958), Barite Resources of the United States, USGS Bull. 1072-B: 108 (Table 10).
Jones, A.P. and Wyllie, P.J. (1983) Low temperature glass quenched from a synthetic rare earth carbonatite: implications for the origin of the Mountain Pass deposit, California. Economic Geology: 78: 1721-1723.
De Witt, E., Kwak, L.M., and Zartman, R.E. (1987) U-Th-Pb and 40Ar/39Ar dating of the Mountain Pass carbonatite and alkalic igneous rocks, southeastern California. Geological Society of America, Abstract of Programs: 19: 642.
Haxel, G. (2005) Ultrapotassic rocks, carbonatite and rare earth element deposit, Mountain Pass, southern California. In: Geology and Mineral Resources of the Mojava National Preserve, southern California. USGS Bulletin 2160.
http://geology.csupomona.edu/drjessey/fieldtrips/mtp/mtnpass.htm
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Map Reference: 35°20'N , 115°18'W
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