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Unconventional Resources of Rare Elements:

The Bearing of Source and Process on the Genesis of Residual Deposits

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Table of Contents

Project Objectives
Relevance and Impact
Field Work; Stragtegy and Approach
Task 1, Economic Geology
Task 2, Soil Science Studies
Task 3, Remote Sensing Studies
Task 4, Igneous petrology and isotope geochemisty

Map showing geology and granite study areas of Southeastern USA

Image, left: Geology of the southeast United States, showing granitic suites studied: 735 Ma Striped Rock pluton, VA; 680 Ma Stewartsville pluton, VA; 305 Ma Liberty Hill pluton, NC; and Elberton-Sparta transect, GA.

Project Objectives

  1. To quantify the favorable factors for the enrichment of rare earth elements, In, Ga, and W in residual deposits associated with weathered granitoid rock suites, especially those predicted to have high heavy-rare-earth-elements
  2. To establish the behavior of the rare elements during weathering of various igneous rock suites
  3. To develop methods and models that can be used in the evaluation of the domestic potential for rare earth elements, Ga, Sn, and W and other metals in residual deposits.

Relevance and Impact

There is considerable controversy regarding rare earth elements-Ga-In-Sn-W in residual deposits.
For example (Wu et al. 1996, Sanematsu et al. 2011, Bao and Zhao 2007, Mentani et al. 2010, Long et al. 2010):

Of the established deposit types for rare earth elements, only ion adsorption clays are known to have significantly
enriched heavy rare earth elements relative to light rare earth elements. This is an important economic consideration because these deposits are relatively easy to exploit; they account for about 14% of Chinese production,
despite having very low grades (about 0.5%) of rare earth elements. Although there is a lack of models
quantifying the geochemical behavior and mineral pathways of rare metals during
weathering, advances in thermodynamic data for the rare earth elements (e.g., Gammons and others, 1996) make it possible to document these pathways.

Field Work; Stragtegy and Approach

Field work for this project will include surface sampling of granite, weathered granite, and
soil profiles in the southeastern United States, with the aim of providing a common geologic and geochemical
database for the four constituent task efforts (e.g, Foley, 2012, Bern et al., 2011, Hubbard et al., 2006, Ayuso et al., 2009). Weathering profiles will be studied at complementary field
sites (1) Robertson River batholith, Irish Creek pluton, Virginia, a peraluminous, low-P, A-type
granite of the Blue Ridge province, and 2) a to-be-determined cordierite-almandinebiotite
granite pluton of the Eastern Piedmont province, for example, the Clouds Creek, South Carolina,
or the Stumpy Point, North Carolina, pluton.
Based on a positive outcome of the 1 year's work, the proposed plan is to drill a cored
profile for detailed study at a selected site. The project will utilize state-of-the-art SEM, EMPA, XRD, LA-icpms,
TIMS, total-digest methods for analytical geochemistry, remote sensing techniques, and soil
sampling and characterization methods.
The synthesis of data will be used to develop process-based models for the genesis of rare earth element
ion adsorption clay deposits that incorporate detailed economic geology, igneous petrology,
mineralogical pathways, chemical mass balance, geochemical modeling and remote sensing
components.

Task 1, Economic Geology

Mineralogical and geochemical studies of samples will provide a basis for developing
process-based models for the genesis of REE ion adsorption clay deposits in the
southeastern United States. This task will establish source rock mineral compositions, rare earth element
mineralogy and chemical pathways for parent granite and saprolite, coordinate major and
trace element geochemistry studies, and provide overall project coordination for field site
selection, sampling, and analytical activities. In addition, the task will develop globally
applicable working models for rare earth element-clay deposits hosted by other archetypal igneous
systems. For example, studies will investigate rare element mobility in kaolins and
weathered crusts for the classic topaz-bearing leucogranite system (St. Austell pluton) of
the Cornubian batholith, Great Britain.

Task 2, Soil Science Studies

Soil science activities will incorporate site-specific and regional soil and solute sampling,
characterization and geochemistry with the goal of modeling the role of climate and
weathering mechanisms in the formation of soils enriched in sorbed rare earth elements. Focus is on the
identification of REE redistribution through transport in solution and in colloidal form and
quantification of such effects through the construction and testing of mass-balance models.

Soil science activities will incorporate site-specific and regional soil and solute sampling,
characterization and geochemistry with the goal of modeling the role of climate and
weathering mechanisms in the formation of soils enriched in sorbed rare earth elements. FY13 (1) Field
work at VA sites and submittal of samples from new and legacy sample collections and
datasets, (2) Initiate laboratory studies; (3) Compilation and analysis of currently available
datasets; (5) Potential meetings: GSA Denver 2013/Soil conference.

Task 3, Remote Sensing Studies

The proposed work will include hyperspectral methods for the identification of minerals
having essential rare earth element and rare earth element-ion adsorption clays and comparative studies of selected
regions of South China and SE United States. The initial approach will be (1)to analyze
datasets for site-specific regions of South China for spectral anomalies and use those in
concert with petrologic studies to analyze comparative areas of the SE-US; (2)
Compilation and analysis of currently available datasets; (3) Potential meeting: GSA Denver
2013/Remote sensing conference.

Task 4, Igneous petrology and isotope geochemisty

Planned studies will establish the petrologic setting and isotope geochemistry of hostrock
and mineral sources for REE and related elements in the selected granite systems. Site-specific
Sr, Nd/Sm and Pb isotope geochemistry tracer studies of granite, saprolite profiles,
and soils (colloid/solute) that comprise the weathered igneous systems will be used to
characterize and quantify the contributions of rare earth elements from diverse primary
sources (rock, mineral, altering solutions).
During 2013: (1) Field work at VA, southeastern US sites, (2) Initiate laboratory studies; (3) Compilation and
analysis of currently available datasets; (4) Field workshop: Eurogranite 2013, source rocks
correlative with the southeastern US.
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