INVESTIGATION OF RESIDUAL MINERAL CONTENT OF BAUXITE STOCKPILES, SALINE MINING DISTRICT, ARKANSAS, U.S.A.

The former mining town of Bauxite is in the Saline County Mining District, in central Arkansas, approximately 40 km (25 mi) southwest of Little Rock Arkansas. This area contains extensive deposits of bauxite ore and nepheline syenite previously mined by Aluminum Company of America using open pit and subsurface mining techniques. This study incorporates five bauxite stockpiles (SP1, Clay, SP2, SP3, SP4) with varying alumina content situated on approximately 10 acres of land within an area of the former mine recognized as Section 20. Over the past several years, there has been renewed economic interest in minerals that can be derived from bauxite and related residues due to the rapid evolution in modern technologies including batteries, alloys, lasers, and much more.

One-hundred twenty-eight (128) rock samples were collected from five stockpiles and analyzed using X-ray fluorescence (XRF) and Laser Ablation – Inductively Coupled Plasma – Mass Spectrometry (LA-ICP-MS). Several samples had elements that were determined to be enriched using XRF and/or LA-ICP-MS with respect to background concentrations in the Earth’s upper continental crust and/or a NIST-698 sample (Jamaican bauxite standard), including some which are on the 2022 List of Critical Minerals. Comparing XRF and LA-ICP-MS results, Si, Ca, Rb, Sr, Zr, Nb, and Mo had very strong correlations.

Maps depicting the spatial distribution of elements (Sr, Zr, Nb, Si, Ca, and Mo) were generated using ArcGIS Pro to assess mobility by evaluating changes in element concentrations of the five stockpiles. Higher values of Sr, Zr, Nb, and Ca were noted in stockpiles with higher alumina (Al2O3) content. The hydrolysates (Zr and Nb) with the exception of Mo, mobilized around the base and slope of SP2, the tallest stockpile among the five in this study.

The chemical characteristics of each stockpile may provide understanding to elemental patterns and metal affinities within bauxite ores. The relationship between bauxite stockpile aluminum concentrations and the presence of elements associated with critical minerals could potentially lead to a future economic supply of important resources.