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Rare-earth elements (REE) are an essential component of numerous advanced technology applications including high efficiency batteries, emerging energy technologies, and key defense systems. The goal of this study was to assist in the evaluation of the distribution of rare earth element deposits in the southeastern U.S., with a focus on sediment-hosted resources. Minerals housed in sedimentary environments are much easier to extract than those hosted in intrusions, and thus provide a potentially important U.S. resource. Various studies have indicated the presence of such resources in the southeastern U.S. in the form of placer, phosphoritic, and residual (soil/clay) environments, but many questions remain regarding the nature and amount of these resources and how they vary geographically over this large area (Overstreet, 1967; Pirkle et al., 1989; Grosz and Schruben, 1994; Long et al., 2010; Cross and Lasseter, 2011; Foley, 2012). Geophysical, geochemical, and mineralogical approaches were developed and applied using data available at the national scale complemented by targeted field studies at specific sites.
Geophysical data analyses provide a means of remotely sensing mineral concentrations of interest and mapping their probable spatial extent. When combined with geochemical and mineralogical ground-truth data, they form a powerful tool. We examined how and under what conditions geophysical and geochemical methods can be used for the detection and evaluation of rare earth element mineral deposits in sediment-hosted environments, with an emphasis on using data available at the national scale. The results of this study revealed key information regarding the distribution and composition of heavy mineral sand (placer) deposits in the southeastern U.S. Results were analyzed to determine how these deposits relate to the surrounding geology (especially sedimentary provenance) and have implications for the relative roles of erosion, alluvial processes, and coastal processes. Synthesis efforts contributed to our broader understanding of the processes associated with genesis and evolution of these deposit types.
Objectives were to develop geophysical approaches to rare earth element evaluation, including the analysis and synthesis of existing and new relevant data to evaluate links between geophysical and geochemical properties, rare earth element content and local geologic processes. Regional radiometric and magnetic data are publically available over the southeastern U.S.; several studies have shown that these methods can highlight certain mineral concentrations in sedimentary environments (Force et al., 1982; Grosz, 1983; Peterson et al., 1986; Grosz et al., 1989; Grosz and Schruben, 1994; Shah et al., 2012; Shah and Harris, 2012).
Objectives were to conduct geochemical and mineralogical analyses of heavy mineral sand samples from both archives and field efforts. Analysis of new and existing data on the samples was performed to evaluate links between geophysical properties, rare earth element content and local geologic processes. Soil and stream sediment samples have also been collected over much of the region, with analyses performed as part of other USGS research efforts. In some areas rare earth element components have been measured, but in others only proxies were available, suggesting a benefit from further geochemical and mineralogical analysis.
Objectives were to synthesize geophysical, geochemical and geological data using statistics and/or other quantitative approaches, and to relate results to geological processes acting on a regional scale. The results provided insights into the formation and preservation of placer deposits that may or may not host rare earth elements.
Bern, C.R., Shah, A.K., Benzel, W.M., and Lowers, H.A., 2016, The distribution and composition of REE-bearing minerals in placers of the Atlantic and Gulf coastal plains, USA: Journal of Geochemical Exploration, 162, p. 50-61. doi:10.1016/j.gexplo.2015.12.011
Berquist, C.R., Shah, A.K., and Karst, A., 2015, Placer deposits of the Atlantic Coastal Plain: stratigraphy, sedimentology, mineral resources, mining and reclamation: Cove Point, Maryland, Williamsburg and Stony Creek, Virginia, Society of Economic Geology Guidebook, 50, 48 p. Information online at: http://www.segweb.org/store/detail.aspx?id=EDOCGB50.
Ellefsen, K.J., Van Gosen, B.S., Fey, D.L., Budahn, J.R., Smith, S.M., and Shah, A.K., 2015, First steps of integrated spatial modeling of titanium, zirconium, and rare earth element resources within the Coastal Plain sediments of the southeastern United States: U.S. Geological Survey Open-File Report 2015–1111, 40 p., https://doi.org/10.3133/ofr20151111.
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.
Shah, A.K., Bern, C.R., Van Gosen, B.S., Daniels, D.L., Benzel, W.M., Budahn, J.R., Ellefsen, K.J., Karst, A., and Davis, R., 2017, Rare earth mineral potential in the southeastern U.S. Coastal Plain from integrated geophysical, geochemical, and geological approaches: Geological Society of America Bulletin, First published online May 11, 2017, doi:10.1130/B31481.1.
Van Gosen, B.S., Bleiwas, D.I., Bedinger, G.M., Ellefsen, K.J., and Shah, A.K., 2016, Coastal deposits of heavy mineral sands; Global significance and US resources: Mining Engineering, 68(10), p. 36-43. View article preview.
Van Gosen, B.S., Fey, D.L., Shah, A.K., Verplanck, P.L., and Hoefen, T.M., 2014, Deposit model for heavy-mineral sands in coastal environments: U.S. Geological Survey Scientific Investigations Report 2010–5070–L, 51 p., https://doi.org/10.3133/sir20105070L.
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 2013 GSA abstract.
Bern, C.R., Shah, A.K., Benzel, W.M., and Lowers, H.A., 2015, The distribution and composition of REE-phosphates in the Atlantic and Gulf coastal plains, USA: Geological Society of America Abstracts with Programs. Vol. 47, No. 7, p. 520. View Bern 2015 GSA 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.
Foley, N., Bern, C., Ayuso, R., Hubbard, B., and Shah, A.K., 2015, Geochemical and mineralogical characteristics of REE in granite-derived regolith: a model for the southeastern United States: Society for Geology Applied to Mineral Deposits (SGA) Biennial Meeting, Nancy, France, 24-27 August 2015.
Shah, A.K., Bern, C.R., Ellefsen, K.J., Burton, B.L., Van Gosen, B.L., and Karst, A., 2013, Geophysical approaches to evaluating sediment-hosted rare earth element potential in the southeastern U.S.: Geological Society of America Abstracts with Programs. Vol. 45, No. 7, p. 277. View Shah 2013 GSA abstract.
Shah, A.K., Bern, C.R., Ellefsen, K.J., Van Gosen, B.S., Budahn, J.R., Benzel, W.F., Daniels, D.F., Karst, A., and Davis, R.B., 2015, Geophysical and geochemical approaches to evaluating placer rare-earth element resources in the southeastern U.S. coastal plain: Geological Society of America Abstracts with Programs. Vol. 47, No. 7, p. 814. View Shah 2015 GSA abstract.
Shah, A.K., Bern, C.R., Ellefsen, K.J., Van Gosen, B.S., and Karst, A., 2014, Geophysical imaging of REE-bearing minerals hosted in southeastern U.S. placer deposits: Geological Society of America Abstracts with Programs. Vol. 46, No. 3, p. 91. View Shah 2014 GSA abstract.
Van Gosen, B.S., and Shah, A.K., 2013, Heavy-mineral sands as sources of rare earth elements: Monazite in the southeastern United States: Geological Society of America Abstracts with Programs. Vol. 45, No. 7, p. 849. View Van Gosen 2013 GSA abstract.
Cross, A. and Lassetter, W.L. 2011, Stratigraphic modeling for concealed phosphate deposits in Virginia’s Coastal Plain: U.S. Geological Survey Mineral Resources External Research Program Final Technical Report for Agreement G10AP00054. Available at http://minerals.usgs.gov/mrerp/reports.html.
Duval, J.S., Carson, J.M., Holman, P.B., and Darnley, A.G., 2005, Terrestrial radioactivity and gamma-ray exposure in the United States and Canada: U.S. Geological Survey Open-File Report 2005-1413, https://pubs.usgs.gov/of/2005/1413/.
Foley, N., 2012, Behavior of REE in high-alumina alteration zones formed by weathering of felsic volcanic rocks [abs]: The 22nd V.M. Goldschmidt Conference, Montreal, Canada: Mineralogical Magazine, 76(6) 1712. Available at https://goldschmidtabstracts.info//abstracts/abstractView?id=2012001192.
Force, E.R., Grosz, A.E., Loferski, P.J., and Maybin, A.H., 1982, Aeroradioactivity maps in heavy-mineral exploration—Charleston, South Carolina, area: U.S. Geological Survey Professional Paper 1218, 19 p., 2 plates, https://pubs.er.usgs.gov/publication/pp1218.
Grosz, A.E., 1983, Application of total count aeroradiometric maps to the exploration for heavy-mineral deposits in the coastal plain of Virginia: U.S. Geological Survey Professional Paper 1263, scale 1:250,000, 20 p., https://pubs.er.usgs.gov/publication/pp1263.
Grosz, A.E., Cathcart, J.B., Macke, D.L., Knapp, M.S., Schmidt, Walter, and Scott, T.M., 1989, Geologic interpretation of the gamma-ray aeroradiometric maps of central and northern Florida: U.S. Geological Survey Professional Paper 1461, 48 p. Available at http://pubs.er.usgs.gov/publication/pp1461.
Grosz, A.E., and Schruben, P.G., 1994, NURE Geochemical and geophysical surveys - defining prospective terranes for United States placer exploration: U.S. Geological Survey Bulletin 2097, 9 p., https://pubs.er.usgs.gov/publication/b2097.
Long, K.R., Van Gosen, B.S., Foley, N.K., and Cordier, Daniel, 2010, The principal rare earth elements deposits of the United States—A summary of domestic deposits and a global perspective: U.S. Geological Survey Scientific Investigations Report 2010-5220, 96 p., https://pubs.usgs.gov/sir/2010/5220/.
Overstreet, W.C., 1967, The Geologic Occurrence of Monazite: U.S. Geological Survey Professional Paper 530, 327 p., https://pubs.er.usgs.gov/publication/pp530.
Peterson, C.D., Komar, P.D., and Scheidegger, K.F., 1986, Distribution, geometry, and origin of heavy mineral placer deposits on Oregon beaches: Journal of Sedimentary Petrology, 56 (1), p. 67-77, doi:10.1306/212F8882-2B24-11D7-8648000102C1865D.
Pirkle, F.L., Pirkle, E.C., Pirkle, W.A., Dicks, S.E., Jones, D.S., and Mallard, E.A., 1989, Altama heavy mineral deposits in southeastern Georgia: Economic Geology, 84 (2), p. 425-433, doi:10.2113/gsecongeo.84.2.425.
Shah, A.K., Vogt, P., Rosenbaum, J.G., Newell, W., Cronin, T.M., Willard, D.A., Hagen, R.A., Brozena, J., and Hofstra, A., 2012, Shipboard magnetic field "noise" reveals shallow heavy mineral sediment concentrations in Chesapeake Bay: Marine Geology, Volumes 303–306, 15 March 2012, p. 26-41, doi:10.1016/j.margeo.2012.02.006.
Shah, A.K., and Harris, M.S., 2012, Shipboard surveys track magnetic sources in marine sediments—Geophysical studies of the Stono and North Edisto Inlets near Charleston, South Carolina: U.S. Geological Survey Open-File Report 2012–1112, 1 poster, https://pubs.usgs.gov/of/2012/1112/.
U.S. Geological Survey, 2004, The National Geochemical Survey: Database and Documentation: U.S. Geological Survey Open-File Report 2004-1001, https://pubs.usgs.gov/of/2004/1001/.
Crustal Geophysics and Geochemistry Science Center