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Mapping Critical Minerals from the Sky

Anjana K. Shah*, U.S. Geological Survey, DFC MS 973, P.O. Box 25046, Denver, Colorado 80225, USA, ashah@usgs.gov, ORCID:
https://orcid.org/0000-0002-3198-081X; Robert H. Morrow IV, South Carolina Dept. of Natural Resources Geological Survey, 5 Geology
Road, Columbia, South Carolina 29212, USA, morrowr@dnr.sc.gov, ORCID: https://orcid.org/0000-0001-5282-2389; Michael D. Pace,
U.S. Geological Survey, DFC MS 973, P.O. Box 25046, Denver, Colorado 80225, USA, mpace@usgs.gov, ORCID: https://orcid.org/0000
-0003-2770-5724; M. Scott Harris, 202 Calhoun Street, College of Charleston, Charleston, South Carolina 29412, USA, harriss@cofc.edu,
ORCID: https://orcid.org/0000-0002-9220-788X; and William R. Doar III, South Carolina Dept. of Natural Resources Geological Survey,
217 Ft. Johnson Road, Columbia, South Carolina 29412, USA, doarw@dnr.sc.gov, ORCID: https://orcid.org/0000-0002-9895-8422

ABSTRACT anomalies for distances of more than 100 placer deposits and subsurface faults of the
Critical mineral resources titanium, zir- km from the Santee River floodplain sug- Charleston seismic zone (Shah, 2020).
conium, and rare earth elements occur in gests that heavy minerals are delivered Placer deposits containing critical miner-
placer deposits over vast parts of the U.S. from the Piedmont to offshore areas by als titanium (Ti; used for aircraft, medical
Atlantic Coastal Plain. Key questions major rivers, transported along the coast by devices, and pigments), zirconium (Zr; used
regarding provenance, pathways of miner- the longshore current, and redeposited in ceramics, fiber-optic components, and
als to deposit sites, and relations to geologic onshore by marine processes. geothermal energy systems), and rare earth
features remain unexplained. As part of a elements (REEs; used in batteries, super-
national effort to collect data over regions INTRODUCTION magnets, solar and wind energy systems,
prospective for critical minerals, the first Technologies ranging from advanced and other advanced technology) are docu-
public high-resolution aeroradiometric sur- electronics to renewable energy and medi- mented in every continent except Antarctica.
vey over the U.S. Atlantic Coastal Plain was cal devices depend increasingly on miner- They currently supply 68% and 100% of
conducted over Quaternary sediments in als considered “critical”; i.e., materials that global Ti and Zr, respectively (Jones et al.,
South Carolina. The new data provide an are essential for the economy and its func- 2017; Woodruff et al., 2017). Prior to the
unprecedented view of potential deposits by tions, but for which there is a risk of supply 1960s they were also a primary source of
imaging Th-bearing minerals in the heavy disruption (National Research Council, REEs, but today carbonatite and ion-adsorp-
mineral assemblage. Sand ridges show the 2008; McCullough and Nassar, 2017; Schulz tion clays are generally favored, probably
highest radiometric Th values with local- et al., 2017). The need for better knowledge because they involve reduced handling of
ized, linear anomalies, especially along the of domestic critical mineral resources has thorium (Long et al., 2010; Mudd and
shoreface and in areas reworked by multiple resulted in funding for data collection over Jowitt, 2016). Placer deposits have been
processes and/or during multiple episodes. areas prospective for critical mineral depos- mined for decades in the U.S. Atlantic
Estuarine areas with finer-grained sedi- its, including 19 new airborne magnetic- Coastal Plain, where the potential resource
ments show lower, distributed Th anoma- radiometric surveys contracted through the area is vast, extending from southern New
lies. Th values averaged over geologic unit U.S. Geological Survey since 2019 (Day et Jersey to northern Florida and Alabama;
areas are similar for both environments, al., 2019; Earth MRI Acquisitions Viewer: mining is currently active in Georgia and
suggesting that heavy minerals are present https://ngmdb.usgs.gov/emri/#3/, accessed Florida (Force, 1991; Grosz and Schruben,
but have not been locally concentrated in Feb. 2021). These new data are helping 1994; Van Gosen et al., 2014; Berquist et al.,
the lower-energy estuarine environments. researchers address basic questions about 2015; Woodruff et al., 2017).
Radiometric K highlights immature miner- critical mineral deposits such as ore gen- Also referred to as heavy-mineral sand
als such as mica and potassium feldspar. esis processes and exploration approaches; deposits, placer deposits form when water
K is elevated within shallow sediments they can also have applications to other and wind concentrate unconsolidated sedi-
younger than ca. 130 ka, an attribute that fields. As part of a multidisciplinary ments according to density, size, and shape.
persists in regional data from northern effort addressing mineral resource and Minerals such as ilmenite and rutile (con-
South Carolina to northern Florida. Both K earthquake hazard studies, an airborne taining Ti), monazite and xenotime (con-
and Th are elevated over the floodplains of radiometric and magnetic survey was flown taining REEs), and zircon (containing Zr)
the Santee River and other rivers with head- over Lower Coastal Plain sediments near are relatively dense and typically become
waters in the igneous and metamorphic Charleston, South Carolina, USA, in 2019. co-located when sediments are sorted
Piedmont Terrane. The persistence of K The targets were potential critical mineral through the reworking and winnowing of

GSA Today, v. 31, https://doi.org/10.1130/GSATG512A.1. CC-BY-NC.

*Corresponding author.

4 GSA Today | November 2021