Rare Earth Element Deposits in the Southeast Mojave Desert

Science Center Objects

In an effort to better understand domestic resource potential, the USGS is investigating the genetic relationship between rare earth element deposits at Mountain Pass, California and Music Valley (Pinto Mountains, California) and extend these studies across a 130-km long belt of alkaline Proterozoic rocks in the southeast Mojave Desert. Such a combined study would significantly improve our knowledge of rare earth element deposits in this unusual extensional terrane that includes the largest rare earth element deposit in the U.S.

Clark mountain range

Clark Mountain Range, California. View northwestward.

(Credit: Kevin M. Denton, U.S. Geological Survey. Public domain.)

Science Issue and Relevance 

As a result of the increasingly high-demand for rare earth elements in emerging technologies and the reduction of rare earth element exports from China, there is a growing national focus on rare earth element deposits. In an effort to better understand domestic resource potential, the USGS is investigating the genetic relationship between rare earth element deposits at Mountain Pass, California and Music Valley (Pinto Mountains, California) and extend these studies across a 130-km long belt of alkaline Proterozoic rocks in the southeast Mojave Desert. Such a combined study would significantly improve our knowledge of rare earth element deposits in this unusual extensional terrane that includes the largest rare earth element deposit in the U.S.

Methods to Address Issue

Research focuses on understanding the geologic framework of the Nation's largest rare earth element deposits at Mountain Pass, California and its surrounding permissive Proterozoic terranes of southeast California. Our project will utilize potential-field, geology, geochemical and petrological methods. Existing data shall be collated and augmented with additional data where appropriate. Combined geophysical, geology, geochronology, and petrological data will aid in the characterization of the southeast Mojave Desert carbonatite terrane. 

gravity map Mojave Desert

Isostatic gravity map of the eastern Mojave Desert study area, California and Nevada. Black circle, gravity station; bold gray line, Mojave National Preserve. From Denton and Ponce, 2016.

(Public domain.)

Geophysical and Geologic Investigations: We will utilize gravity, magnetic, and radiometric, methods to investigate the southeast Mojave Proterozoic terrane for possible rare earth element mineralization. In particular, we plan to integrate studies of the Mountain Pass deposit (Denton and Ponce, 2018) with results from Music Valley and investigate their relationship to thermal events that encompassed the region.

Magnetotelluric Investigations: Magnetotelluric (MT) measurements are sensitive to variations in electrical resistivity and can image traces of hydrothermal alteration, providing a useful method for locating unknown resources. We will conduct a regional magnetotelluric survey across the southeast Mojave Desert carbonatite terrane to identify potential rare earth elements and other mineral deposits. 

Geochronology / Geochemistry Investigations: We will use high-resolution analytical tools (electron microprobe, SEM, SHRIMP-RG, SIMS) to determine the relationship between the alkalic intrusive suite at Mountain Pass and the Sulphide Queen carbonatite body.

Petrologic Investigations: We will conduct petrologic investigations utilizing high-resolution micro-analytical tools (e.g., electron microprobe, SEM, SHRIMP-RG) to interrogate mineral-scale archives of igneous processes underpinning the world-class Mountain Pass carbonatite deposit. Understanding the extraordinary endowment of rare earth elements hosted in the carbonatite ore body at Mountain Pass requires a thorough understanding of its genesis, including the genetic relationship between the carbonatite and ultrapotassic magmas, their mantle and crustal inputs, and relative distributions in space and time. 

Remote Sensing Investigations (completed): We used AVIRIS, HyTES and WorldView-3 in conjunction with a regional ASTER mineral map (Mars, 2014) to map carbonatites and minerals typically associated with hydrothermally-altered rocks such as alunite, kaolinite, sericite (white mica), chlorite-epidote, and hematite-goethite at Mountain Pass, Thor, and Music Valley in the southeast Mojave Desert. Spectral measurements of rare earth element-bearing minerals indicate that subtle variations in the shapes and wavelength positions of individual Lanthanide element absorptions are controlled by mineralogy (Swayze et al., 2013). Analytical results will be used to create mineral maps of rare earth element-bearing mineral phases.

Geologic Investigations - Mapping (completed): We conduced detailed geologic mapping of the Mountain Pass and surrounding area to determine the lithotectonic framework and alteration history of the region by completing the Proterozoic parts of the Mescal Range and Clark Mountain 7.5’ quadrangles. These studies were integrated with past geologic studies at the Thor deposits to derive a comprehensive geologic, structural, and alteration history of greater Ivanpah Valley region. Geologic mapping of the Music Valley and Thor rare earth element deposits were evaluated for patterns of intrusion and alteration.

 

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