Geochemical analyses of bauxite and associated rocks from the Arkansas bauxite region, central Arkansas

This data release compiles major and trace element analytical results of samples of bauxite (aluminum ore) and associated rocks collected from the Arkansas bauxite region, located near the center of Arkansas in Pulaski and Saline Counties. Samples were collected by the U.S. Geological Survey (USGS) in April 2018 as part of the USGS' focus on increased understanding of the United States' critical mineral resources. Mineral commodities, based on USGS studies, have been designated as critical where the United States is predominantly reliant on foreign sources (McCullough and Nassar, 2017; Fortier and others, 2018). The five primary aluminum smelters in the U.S., in 2017 and previous years, were dependent on imported bauxite as their raw material. Sources of imported bauxite from 2013 to 2016 were: 46% from Jamaica; 30% from Brazil; 21% from Guinea; 2% from Guyana; and 1% from others (Bray, 2018). Due to this foreign dependence, aluminum has been designated a critical element that requires investigation to determine feasible domestic resources. The recent increase of aluminum import tariffs (https://www.cbp.gov/trade/remedies/232-tariffs-aluminum-and-steel; last accessed 12/18/19) may induce development of domestic bauxite resources to supply the United States with alumina.    
Aluminum is manufactured from alumina derived from bauxite. The geology and exposed extent of bauxite resources in the central Arkansas region is well established (Gordon and others, 1958). Bauxite in this region formed by intense in-place weathering during the Eocene on exposed surfaces of Late Cretaceous syenite intrusions (Gordon and others, 1958). The primary USGS interest of sampling the bauxite ore was to evaluate the potential for critical elements that may be co-occurring, with aluminum in the bauxite orebodies. Particularly, this study examined the possibility of elevated concentrations of gallium and rare earth elements (REEs) in the bauxite and processed waste-material. Bauxite is the largest global source of gallium, recovered as a by-product of processing (zinc ores are the second source) (Gibson and Hayes, 2011; Frenzel and others, 2016). Bauxite can also be a potential source of REEs and scandium (Reid and others, 2017). Most intriguing are reports of significant concentrations of the highly desired heavy REEs in some bauxite and its processed residues (red muds) (Liu and others, 2014; Liu and Li, 2015). In bauxite, the REEs may be weakly sorbed on clays and (or) iron-oxide minerals, allowing extraction by reagants (Borra and others, 2015). The advancement of research on by-product recovery of critical minerals is necessary to feed our expanding technological demands (Nassar and others, 2015). 
Based on in-the-ground alumina resources and historic production, the two most significant bauxite districts in the United States are in the Arkansas bauxite region. The Arkansas bauxite deposits cover an area of about 275 miles, located about 5 miles south of Little Rock and about 25 miles southwest, respectively. Bauxite mining in the Arkansas district specifically for aluminum production began in 1898. The district mined bauxite ore continuously until 1982; production varied through the years (Arkansas Geological Survey, 2018). Bauxite production increased in this district during World War II due to a government mandate to supply aluminum for airplanes. Small quantities of bauxite are mined here today for applications in a variety of chemicals, abrasives, and proppants. The Arkansas district has produced an order of magnitude more bauxite than all other United States districts combined (Patterson, 1967). The bauxite resources that remain in the Arkansas districts dwarf the sizes of the other U.S. bauxite deposits, which are in Alabama, Georgia, Mississippi, Tennessee, and Virginia (Patterson, 1967).
This data release provides the analytical results of 59 samples from the Arkansas bauxite region, including examples of bauxite (n=19), residue remains from the processing of bauxite (n=4), clays interbedded with the bauxite (n=15), a shale layer within layered bauxite (n=1), carbonaceous shale in strata lying above the bauxite (n=4), unaltered syenite (n=12), and altered syenite (n=4). Since the bauxite formed from the extensive in-place weathering of syenite intrusions underlying the region, the syenite was sampled. This provides a comparison of the alumina source rock (syenite) and the alteration product (bauxite). The bauxite, clay, and shale samples were collected as grab samples from exposures in former open-pit bauxite mines, as well as subsurface samples of drill cuttings. The carbonaceous shales are grab samples from Eocene non-marine strata overlying layered bauxite at a former bauxite mine. The syenite samples were collected at active syenite aggregate quarries operated by Granite Mountain Quarries. The company generously provided access to the sample sites and shared valuable insights on the local geology.
All samples were analyzed by AGAT laboratories, a USGS contract laboratory, to measure concentrations of 60 elements by Inductively Coupled Plasma-Optical Emission Spectrometry (ICP-OES) and Inductively Coupled Plasma-Mass Spectrometry (ICP-MS). Additionally, samples that were rich in organics (n=5) were analyzed for carbonate carbon (inorganic carbon), organic carbon, total carbon and total sulfur using other element-specific analytical techniques (described below). Replicate splits of several samples (n=8) and analytical reference materials (n=25) were included as blind samples to evaluate the data quality of the chemical analyses.
The geology and descriptions of the bauxite deposits and mines in the two Arkansas districts are thoroughly described by Gordon and others (1958). Their comprehensive report provides the geologic context for the sample data included in this data release.
The geochemical results of this sampling study, compiled in this data release, suggest that the bauxite and associated rock types in the central Arkansas bauxite districts lack elevated concentrations of critical elements such as gallium, rare earth elements, and scandium, excluding aluminum. It was beyond the scope of this study to evaluate the bauxite resources that remain in the districts; however, the bauxite resource should be extensive considering the expansive syenite intrusive complex that underlies the mining districts and the majority of the area between. 
References cited above:
Arkansas Geological Survey, 2018, Bauxite: Arkansas Geological Survey website, at https://www.geology.arkansas.gov/minerals/industrial/bauxite.html			
Borra, C.R., Pontikes, Yiannis, Binnemans, Koen, and Van Gerven, Tom, 2015, Leaching of rare earths from bauxite reside (red mud): Minerals Engineering, v. 76, p. 20-27.
Bray, E.L., 2018, Bauxite and alumina: U.S. Geological Survey Mineral Commodity Summaries, p. 30-31. Available at  https://minerals.usgs.gov/minerals/pubs/commodity/bauxite/mcs-2018-bauxi.pdf
Fortier, S.M., Nassar, N.T., Lederer, G.W., Brainard, Jamie, Gambogi, Joseph, and McCullough, E.A., 2018, Draft critical mineral list-Summary of methodology and background information-U.S. Geological Survey technical input document in response to Secretarial Order No. 3359: U.S. Geological Survey Open-File Report 2018-1021, 15 p. Available at https://pubs.er.usgs.gov/publication/ofr20181021
Frenzel, Max, Ketris, M.P., Seifert, Thomas, and Gutzmer, Jens, 2016, On the current and future availability of gallium: Resources Policy, v. 47, p. 38-50.
Gibson, Charles, and Hayes, Tom, 2011, Indium and gallium overview: Edison Investment Research, Sector research, 10 p. Available at https://www.edisoninvestmentresearch.com/sectorreports/IndiumGalliumOverview071011.pdf
Gordon, MacKenzie, Jr., Tracey, J.I., Jr., and Ellis, M.W., 1958, Geology of the Arkansas bauxite region: U.S. Geological Survey Professional Paper 299, 268 p., 39 plates. Available at https://pubs.usgs.gov/pp/0299/report.pdf
Liu, Zhaobo, and Li, Hongxu, 2015, Metallurgical process for valuable elements recovery from red mud-A review: Hydrometallurgy, v. 155, p. 29-43.
Liu, Yanju, and Naidu, Ravi, 2014, Hidden values in bauxite residue (red mud)-Recovery of metals: Waste Management, v. 34, no. 12, p. 2662-2673.
McCullough, Erin, and Nassar, N.T., 2017, Assessment of critical minerals-Updated application of an early-warning screening methodology: Mineral Economics, v. 30, p. 257-272.
Nassar, N.T., Graedel, T.E., and Harper, E.M., 2015, By-product metals are technologically essential but have problematic supply: Science Advances, v. 1, no. 3. Available at http://advances.sciencemag.org/content/1/3/e1400180
Patterson, S.H., 1967, Bauxite reserves and potential aluminum resources of the World: U.S. Geological Survey Bulletin 1228, 175 p. Available at https://pubs.usgs.gov/bul/1228/report.pdf
Reid, Sable, Tam, Jason, Yang, Mingfan, and Azimi, Gisele, 2017, Technospheric mining of rare earth elements from bauxite residue (red mud)-Process optimization, kinetic investigation, and microwave pretreatment: Scientific Reports, v. 7, article 15252 (2017). Available at https://www.nature.com/articles/s41598-017-15457-8

Tags: aluminum, arkansas, bauxite, central-arkansas, chemical-analyses, critical-mineral-resources, economic-geology, geochemistry, geology, geology-geophysics-and-geochemistry-science-center, geoscientificinformation, gggsc, mass-spectroscopy, metallic-mineral-resources, mine, mineral-resources, mineral-resources-program, mrp, pulaski-county, saline-county, united-states-of-america, usa, usgs-5df93873e4b0cdded73b41fe
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