Description of the Research Opportunity
Heavy mineral sands are an important source of critical minerals and elements such as titanium in the minerals ilmenite and rutile, and rare earth elements in minerals such as monazite, xenotime, and zircon. Additional industrial minerals, including sillimanite, kyanite, staurolite and garnet, are also often concentrated in these deposits (Van Gosen et al., 2014). Several of these minerals can be extracted as either primary commodities, or as by-products and co-products. In the Gulf and Atlantic Coastal Plains, the source of these minerals are often igneous, metamorphic, and metasedimentary rocks of the Appalachian Orogen and, in the western Gulf Coast, the Western Cordillera (Blum et al., 2017). Sediment is transported from these hinterlands by rivers and streams that carry it towards the coast, where it may ultimately be deposited in fluvial, deltaic, marginal marine, and shallow marine environments. Heavy mineral sands are found in these environments in both modern-day and ancient settings.
Sand and gravel resources are also important as industrial minerals and play a critical role in coastal erosion prevention. Over the past several decades, beach replenishment has been a multi-billion-dollar effort (Song and Shaw, 2018), and has become increasingly common in recent years. The combined effects of increased storm frequency and sea level rise due to climate change have necessitated the implementation of coastal resilience efforts along much of the mid-Atlantic coast. Thus, the origin, transport pathways, and movement of these sands within the coastal and marine environment is important for understanding how shorelines are maintained naturally, and how we might predict the fate of renourished beaches over time. To this end, studies that look at these sands from a holistic, source-to-sink perspective are useful in helping to understand their critical mineral and industrial potential. In the past several years, scientists from the USGS Geology, Energy and Minerals (GEM) Science Center have collected a large number of sand samples from the Gulf and Atlantic coastal regions and have analyzed their provenance through detrital zircon geochronology (e.g., Craddock et al., 2021; Counts et al., 2024), allowing them to reconstruct sediment pathways at both modern and geologic time scales. The extensive sample library collected during these studies forms an untapped resource from which much subsequent work may be conducted, including mineralogical and hyperspectral analyses.
As a part of the Earth Mapping Resources Initiative (EarthMRI) collaboration with state geological surveys, new high resolution geophysical and hyperspectral data surveys have been collected in several states along the Atlantic and Gulf Coast of the United States. These data include magnetic and radiometric data, which have proven invaluable in understanding the distribution of heavy minerals and critical elements along stream corridors draining to the coast (e.g., Shah et al, 2021 and references therein). Also, hyperspectral data collected in the mid-IR (MIR) or thermal infrared (TIR) region (7.0 –25.0 micrometers [μm]) is most useful for detecting quartz, other silicate, or oxide minerals in sand deposits (Van Gosen et al., 2014). These same minerals are often transparent or opaque at visible through shortwave reflected infrared wavelengths (0.4 – 2.5 μm).
We seek candidates who can employ a combination of field, laboratory, and remote sensing techniques to the study of heavy mineral sand deposits, in order to address various topics regarding the remote detectability of their critical and industrial mineral components. New mineralogical and petrographic analyses of previously collected sediment samples can be used to provide a basis for further field or ground-based geophysical and geochemical research in support of remote sensing collected magnetic, radiometric, and/or hyperspectral data. For example, areas identified as having anomalous concentrations of critical minerals (e.g., REE-bearing monazite and titanium-bearing ilmenite) based on radiometric (e.g., Shah et al., 2021) or mineralogical data (collected by the candidate) would make ideal targets for more focused field- and laboratory-based research. Such deposits will be characterized through traditional field methods (e.g., sedimentologic, stratigraphic, and environmental characterization of a site), as well as the use of portable XRF equipment for onsite geochemistry. Laboratory methods may include analyses of sediment density, grain-size distributions, and sand composition and texture using in-house instrumentation (e.g., Malvern particle size analyzer, scanning electron and optical microscopes, Raman spectroscopy, etc.). These properties can influence the spectral characteristics and geophysical properties of such deposits at various wavelengths, making them essential for accurate elemental and mineralogical characterization via remote sensing. We also welcome studies that explore the genesis of such deposits from source to sink, and that seek to integrate upstream bedrock geology with downstream fluvial, floodplain and coastal sediments where heavy mineral deposits are concentrated through other mechanisms (e.g., wind and/or longshore currents). By conducting a first-order characterization of the study region with samples collected for provenance studies, the candidate may identify areas that would benefit from additional fieldwork activities or even new airborne geophysical and/or hyperspectral data collection.
Interested applicants are strongly encouraged to contact the Research Advisor(s) early in the application process to discuss project ideas.
References
Blum, M.D., Milliken, K.T., Pecha, M.A., Snedden, J.W., Frederick, B.C. and Galloway, W.E., 2017. Detrital-zircon records of Cenomanian, Paleocene, and Oligocene Gulf of Mexico drainage integration and sediment routing: Implications for scales of basin-floor fans. Geosphere, 13(6), pp.2169-2205.
Counts, J.W., Craddock, W.H. and Gooley, J.T., 2024. Defining the hafnium isotopic signature of the Appalachian orogen through analysis of detrital zircons from modern fluvial sediments. The Journal of Geology, 131(3).
Craddock, W.H., Coleman, J.L. and Kylander‐Clark, A.R., 2021. Detrital zircon age spectra of middle and upper Eocene outcrop belts, US Gulf Coast region. Basin Research, 33(1), pp.250-269.
Shah, A.K., Morrow, R.H., Pace, M.D., Harris, M.S., and Doar, W.R., 2021. Mapping Critical Minerals from the Sky. GSA Today, v. 31, https://doi.org/10.1130/GSATG512A.1 CC-BY-NC.
Song, L. and Shaw, A., 2018. “A Never-Ending Commitment”: The High Cost of Preserving Vulnerable Beaches. ProPublica: https://www.propublica.org/article/the-high-cost-of-preserving-vulnerable-beaches.
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., http://dx.doi.org/10.3133/sir20105070L.
Proposed Duty Station(s)
Reston, Virginia
Areas of PhD
Geoscience, geology, mineralogy, geomorphology, sedimentology, planetary geology, remote sensing, or related fields (candidates holding a Ph.D. in other disciplines, but with extensive knowledge and skills relevant to the Research Opportunity may be considered).
Qualifications
Applicants must meet one of the following qualifications: Research Geologist, Research Geographer, Research Geophysicist, or Research Physical Scientist.
(This type of research is performed by those who have backgrounds for the occupations stated above. However, other titles may be applicable depending on the applicant's background, education, and research proposal. The final classification of the position will be made by the Human Resources specialist.)
