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 among three rare earth element deposits in the southeast Mojave Desert: Music Valley (Pinto Mountains, California), Thor (New York Mountains, Nevada), and the world-class rare earth element deposit at Mountain Pass, California. 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 among three rare earth element deposits in the southeast Mojave Desert: Music Valley (Pinto Mountains, California), Thor (New York Mountains, Nevada), and the world-class rare earth element deposit at Mountain Pass, California. 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.

Methodology to Address Issue

Research focuses on understanding one of the largest carbonatite deposits in the world and the search for similar deposits in the surrounding permissive Proterozoic terranes of southeast California. Knowledge gained will fill gaps in our understanding of the nature, structure, age, and genesis of these unusual rare earth element deposits. Typical studies include gravity, magnetic, electromagnetic, radiometric, possibly LiDAR, and gravity gradiometry methods. Carbonatite deposits typically have prominent geophysical signatures that include gravity, magnetic, and radiometric anomalies. In addition, geophysical studies may yield insights on through-going or possibly reactivated geologic features that might control these mineral deposits. Thus, an investigation of these unusual rare earth element deposits will likely provide new insights on their setting and genesis. These methods and techniques are applicable to the investigation of other domestic or global rare earth element deposits.

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 Investigations
    We will conduct gravity, magnetic, radiometric, and magnetotelluric investigations of the southeast Mojave Proterozoic terrane for possible rare earth element deposits. In particular, we plan to integrate studies of the Mountain Pass deposit (Ponce et al., 2013; Denton et al., 2014) with results from the Music Valley and Thor deposits and determine their relationship to hydrothermal alteration events that encompassed the region.
     
  • Geologic Investigations
    We will conduct 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 will be integrated with past geologic studies at the Thor deposits to derive a comprehensive geologic, structural, and alteration history of greater Ivanpah Valley region. We will study and integrate the geologic mapping of the Music Valley and Thor rare earth element deposits and evaluate patterns of intrusion and alteration.
     
  • Geochronology / Geochemistry Investigations
    We will use high-resolution analytical tools (electron microprobe, SEM, SHRIMP-RG, SIMS) to obtain geochemical, isotopic and geochronologic measurements within melt inclusions. Analyzing sequentially trapped melt inclusions along U-Pb dated core to rim zircon growth domains will allow reconstruction of discrete time slices in magmatic evolution that would be impossible to resolve through time-integrated whole-rock records. These new age data, trace-element characteristics, and isotopic fingerprinting can map the various stages of regional alteration and make a new geochemical template for the formation of these rare earth element deposits.
     
  • Remote Sensing Investigations
    We will use 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.