Our studies are aimed at identifying the potential for rare earth element ion-adsorption clay type deposits in weathered granite rocks of the southeastern United States. Residual deposits, including laterites, bauxites, clays, weathered crusts, and soils, are unconventional resources for many rare earth elements (REE) that are, in general, much less well-understood compared to more conventional rare element resources. REE ion-adsorption clay deposits of South China are of global economic importance because they supply virtually all heavy rare earth elements (HREE) and a significant portion of light rare earth elements (LREE) and yttrium to global markets. There is considerable ambiguity regarding the origin and global distribution of the deposit type, which is currently mined only in South China.
These resources are found in residual deposits:
The southeastern United States has extensive suites of granitic rocks that are deeply weathered and show mobility of rare earth elements (Foley et al., 2013). Plutons and prospective regolith (layer of unconsolidated rocky material covering bedrock) sites were identified based on geologic attributes, such as rock type, whole-rock chemistry, topographic setting, and acccessibility. Our research focused on two major belts of weathered igneous rocks, selected due to their whole rock chemistries and locations:
We utilized economic geology studies, petrology and isotope geochemistry, soil science studies, and remote sensing studies to accomplish the project's objectives. Econonic studies helped to develop an understanding of REE mineralization in granite-derived regolith by establishing the dominant mineralogy, mineral reactions, and REE transfer processes. Petrology and isotope geochemistry were used to identify granitic bedrock suites of the southeastern U.S. that have similar compositions and REE characteristics for comparison with Chinese REE-bearing regolith deposits. They were also used to determine the degree of fractionation of individual REE within minerals in bedrock-to-soil profiles and to relate this to the degree of weathering. Soil science was used to incorporate site-specific biogeochemistry to model the formation of soils enriched in sorbed REEs. Weathering mechanisms were modeled for improved understanding of controls on ion-exchange REE enrichment. Remote sensing used exisiting data to compare weathering minerals and abundances of exposed regolith materials in South China with those in the southeastern U.S. to establish a comparative framework for asssing a potential for similar deposits. Field and laboratory-based spectroscopic methods were developed for remote detection of REE in mineral, oxide, hydroxide, and ionic forms necessary for exploration. Our research results are in our publications.
Bern, C.R., Thompson, A., and Chadwick, O.A., 2015, Quantification of colloidal and aqueous element transfer in soils: The dual-phase mass balance model: Geochimica et Cosmochimica Acta, 151, 15 February 2015, p. 1-18. doi: 10.1016/j.gca.2014.12.008
Foley, N. and Ayuso, R., 2015. REE enrichment in granite-derived regolith deposits of the Southeastern United States: Prospective source rocks and accumulation processes. In: Simandl, G.J. and Neetz, M., (Eds.), Symposium on Strategic and Critical Materials Proceedings, November 13-14, 2015, Victoria, British Columbia, British Columbia Ministry of Energy and Mines, British Columbia Geological Survey Paper 2015-3, pp. 131-138. View Foley Symposium Paper. [PDF file, 2.9 MB]
Foley, N., Ayuso, R., Hubbard, B., Bern C., and Shah, A., 2015, Geochemical and Mineralogical Characteristics of REE in Granite-Derived Regolith of the Southeastern United States, in Proceeding of the 13th Biennial Society for Geology Applied to Ore Depoists (SGA) Meeting, 24-27 August 2015, Nancy, France; Proceedings, Vol. 2, p. 725-728. View Foley 2015 SGA extended abstract.
Foley, N.K., Ayuso, R.A., Bern, C.R., Hubbard, B.E., and Vazquez, J.A., 2014, REE Distribution and Mobility in Regolith formed on Granite Bedrock of the Southeast United States: Acta Geologica Sinica (English Edition), Special Issue: Meeting Abstracts: 14th Quadrennial International Association on the Genesis of Ore Deposits Symposium, August 19-22, 2014, Kunming, China, 88 (s2), p. 428-430. doi: 10.1111/1755-6724.12373_8
Schulte, R.F., and Foley, N.K., 2014, Compilation of gallium resource data for bauxite deposits: U.S. Geological Survey Open-File Report 2013–1272, 14 p., 3 separate tables, http://pubs.usgs.gov/of/2013/1272/.
Ayuso, R., Tucker, R., Peters, S., Foley, N., Jackson, J., Robinson, S., and Bove, M., 2013, Preliminary radiogenic isotope study on the origin of the Khanneshin carbonatite complex, Helmand Province, Afghanistan: Journal of Geochemical Exploration, 133, October 2013, p. 6-14. doi: 10.1016/j.gexplo.2013.06.012
Cosenza, A., Ayuso, R.A., Foley, N., Albanese, S., Lima, A., Messina, A., and De Vivo, B., 2012, The geogenic vs anthropogenic source of harmful element anomalies in the eastern-central sector of the Peloritani Mountains (Sicily, Italy): Rendiconti Online Della Soceità Geologica Italiana, 21(Supplement 1), p. 265-267, http://rendiconti.socgeol.it/244/fulltext.html?ida=826.
Foley, N.K. , and Ayuso, R.A., 2013, Rare earth element mobility in high-alumina altered metavolcanic deposits, South Carolina, USA: Journal of Geochemical Exploration, 133, October 2013, p. 50–67. doi: 10.1016/j.gexplo.2013.03.008
Foley, Nora, and Jaskula, Brian, 2013, Gallium—A smart metal: U.S. Geological Survey Fact Sheet 2013–3006, 2 p., http://pubs.usgs.gov/fs/2013/3006/.
Bern, C.R., and Foley, Nora, 2015, High proportions of ion-adsorbed REEs on the Liberty Hill pluton, South Carolina, a possible link to hydrothermal alteration: Geological Society of America Abstracts with Programs. Vol. 47, No. 7, p. 814. View Bern 2015 GSA abstract.
Foley, N., and Ayuso, R., 2015, Rare earth elements in clays: a domestic resource for the future?: Geological Society of America Abstracts with Programs. Vol. 47, No. 7, p. 814. View Foley 2015 GSA abstract.
Ayuso, R., and Foley, N., 2014, Weathering-related mobility of rare earth elements in high-alumina altered metavolcanic deposits, South Carolina, USA: Geological Society of America Abstracts with Programs, Vol. 46, No. 3, p. 78. View Ayuso 2014 GSA abstract.
Bern, Carleton, and Foley, N.K., 2014, Critical Zone weathering and your smartphone: Understanding how mineral decomposition and colloid redistribution can generate rare earth element deposits: American Geophysical Union 2014 Fall Meeting, 15-19 December, San Francisco, CA. View Bern 2014 AGU abstract.
Bern, C.R., and Foley, Nora, 2014, The role of topography in generating economic concentrations of ion-exchangeable rare earth elements: Geological Society of America Abstracts with Programs, Vol. 46, No. 3, p. 91. View Bern GSA 2014 abstract..
Foley, Nora, Ayuso, Robert, Bern, C.R., Hubbard, B.E., Shah, A.K., and Vazquez, J.A., 2014, REE distribution and mobility in residual deposits associated with altered granites: A review and comparison of global data-sets in the search for REE-clay deposits outside of China: Geological Society of America Abstracts with Programs, Vol. 46, No. 3, p. 91. View Foley 2014 GSA abstract.
Hubbard, B.E., and Foley, Nora, 2014, Planned remote sensing and laboratory spectral characterization of residual clay-hosted ion-adsorption type rare earth element (REE) deposits associated with deeply weathered laterite and bauxite soils: Geological Society of America Abstracts with Programs, Vol. 46, No. 3, p. 91. View Hubbard abstract.
Bern, C.R., and Shah, A.K., 2013, Geochemical and mineralogical aspects of heavy mineral sands as potential REE resources in the southeast U.S.: Geological Society of America Abstracts with Programs, Vol. 45, No. 7, p. 277. View Bern and Shah 2013 GSA abstract.
Bern, C.R., Thompson, A., and Chadwick, O.A., 2013, Physical erosion beneath the surface: quantifying colloidal gains and losses in soil: Geological Society of America Abstracts with Programs, Vol. 45, No. 7, p. 408. View Bern 2013 GSA abstract.
Cosenza, A., Ayuso, R., Foley, N., Albanese, S., Lima, A., Messina, A., and De Vivo, B., 2013, The origin of geochemical anomalies in top soils of eastern-central Peloritani Mountains (Sicily, Italy): Goldschmidt Conference 2013, Mineralogical Magazine, 77(5), p. 920. doi: 10.1180/minmag.2013.077.5.3
Foley, N.K., De Vivo, Benedetto, Salminen, Reijo, editors, 2013, Rare Earth Elements: The role of geology, exploration, and analytical geochemistry in ensuring diverse sources of supply and a globally sustainable resource: Special Issue, Journal of Geochemical Exploration, Volume 133, p. 1-214 (October 2013).
Eastern Mineral and Environmental Resources Science Center