Mountain Pass

Region West, Southwest
Mineral systems
Deposit types
Critical minerals
Other minerals

Information leading to the delineation of this focus area

Basis for focus area Carbonatites Deposit type and basic geology: The southeast Mojave Desert is host to a world-class REE carbonatite deposit at Mountain Pass and to REE mineralization at Music Valley, California. Mountain Pass is about 97 km (60 mi) southwest of Las Vegas, Nevada. The magmatic Mountain Pass carbonatite is the largest light REE deposit in the U.S. The ~1.4 Ga carbonatite and associated intrusive rocks consists of (oldest to youngest): shonkinite, syenite, granite, carbonatite, numerous dikes, and include at least one late shonkinite dike and are hosted by an areally extensive 1.7 Ga gneiss.
Identified resources Identified REE resource; historical production of REE.
Production Mountain Pass (1952-2014): 614,000 short tons REO (Bair and others, 2012).
Status Past and present mining for REE: as of 2017, the Mountain Pass mine is in production by MP Mine Operations, LLC.
Estimated resources Estimated resources of 24.341 Mt grading an average of 6.68% TREO classified as Measured and Indicated mineral resources with an additional 10.446 Mt grading an average of 6.32% TREO classified as Inferred Mineral Resources (Bair and others, 2012). Barite is about 25% of the carbonatite ore material.
Geologic maps Olson and others (1954), scale 1:20,000; Hewett (1956), scale 1:125,000; Jennings and others (1977), scale 1:750,000; Miller and others (2007), scale 1:125,000; Miller and others (in prep.), scale 1:24,000.
Geophysical data Adequate aeromagnetic and aeroradiometric coverage over the Mountain Pass deposit. In the immediate vicinity of Mountain Pass, a relatively small, high-resolution, and Rank 1 airborne magnetic and radiometric survey is available (Ponce and Denton, 2018a, b, c; Ponce and Denton, 2019a, b). A Rank 1 airborne magnetic and radiometric survey is available adjacent to and on the east side the Mountain Pass (Ponce and Drenth, 2020). Gravity coverage, magnetotelluric coverage, physical property coverage, and interpretive reports are available for parts of the southeast Mojave Desert (Denton and Ponce, 2018; Peacock and others, 2019; Denton and Ponce, 2020; Denton and others, 2020). The remainder of the southeast Mojave Desert has an aeromagnetic survey of Rank 3 and aeroradiometric survey of Rank 2 and 5.
Favorable rocks and structures The Mountain Pass carbonatite, associated alkaline intrusive suite, and dikes are exposed along a NNW-trending belt 4.8 x 9.7 km (3 x 6 mi) over a 47 km2 (18 mi2) area. The original carbonatite outcrop was about 122 x 732 m (400 x 2400 ft) (Olson and others, 1954, p. 41). The 1.4 Ga carbonatite and intrusive suite are hosted by 1.7 Ga gneiss. About 25% of the carbonatite is composed of primary barite.
Deposits Mountain Pass mine (MRDS dep_id: 10212814; USMIN Site ID: CA00041).
Evidence from mineral occurrences MRDS; USMIN.
Geochemical evidence The Mountain Pass carbonatite has a wealth of geochemical and geochronological information. Typical ore consists of about 10 to 15% bastnaesite, 20-25% barite, and 65% calcite and dolomite. See Olson and others (1954), Castor and Nason (2004), and Haxel (2007).
Geophysical evidence The Mountain Pass carbonatite deposit is directly associated with a gravity anomaly, occurs along the edge of a magnetic anomaly associated with an inferred and buried granitic intrusion, and associated with radiometric anomalies.
Evidence from other sources Unknown.
Comments Mountain Pass was the leading world producer of light REE until exceeded by production in China (mostly from Bayan Obo) in about 1993 (Castor and Hedrick, 2006). In 2015, Molycorp Inc., LLC placed the Mountain Pass mine under "Care and Maintenance". As of 2017, Mountain Pass is under new ownership by MP Mine Operations, LLC and is currently in production. No barite production known.
Cover thickness and description The Sulphide Queen carbonatite body is exposed at the surface and was originally about 120-m (400-ft) wide by x 730-m (2400-ft) long (Olson and others, 1954), and based on drill hole information about 110-m (350-ft) thick (Castor, 1991). The body dips about ~40° southwest and is partly overlain by Paleoproterozoic gneiss and/or about 30 m of alluvium.
Authors David A. Ponce, Joshua M. Rosera.
New data needs Geochemistry and geochronology.
Geologic mapping and modeling needs Earth MRI Phase 1 lidar, geologic mapping, and airborne geophysical data collection currently in progress.
Geophysical survey and modeling needs A high-resolution airborne survey of the carbonatite and intrusive suite exists. Require high-resolution aeromagnetic, radiometric surveys, magnetotelluric survey, and depth-to-basement of the entire Mojave Desert, as well as 3D geophysical modeling.
Digital elevation data needs Require lidar survey of entire Mojave Desert for lineament analysis. Medium-resolution lidar survey of carbonatite and intrusive suite exist.