RARE-EARTH ELEMENTS IN THE CRETACEOUS TO EOCENE AGE BAUXITE-KAOLIN ORES, UPPER COASTAL PLAIN, GEORGIA.

Rare-earth element (REE) potential resources are being explored in kaolin and bauxite ores from Georgia’s Upper Coastal Plain. For this study, bauxite-kaolin ore was collected from drill core over an interval of 29-79 feet below surface. The ore was hosted within sand-dominated strata. Individual samples represented 2-4 foot sections from this interval. The bauxite-kaolin ore was Cretaceous to Eocene in age and found in southern Wilkinson County, GA. The zone of bauxite was found between upper and lower kaolin zones, consistent with occurrences elsewhere in the region including Andersonville and Eufaula districts. The heavy mineral fractions of the upper and lower kaolin layers included Fe-oxides, pyrite, kaolinite, muscovite, and trace amounts of monazite, rutile, anatase, and xenotime. The heavy mineral fractions of the bauxite layer showed a more variable composition, including rutile, anatase, monazite, zircon, pyrite, and gibbsite with trace amounts of hematite, goethite and xenotime. The P₂O₅ contents remained consistent over depth through the bauxite-kaolin section and were close to concentrations found in average Upper Continental Crust (UCC, Rudnick and Gao, 2003). The kaolin zones and bauxite zone were HREE enriched (HREE, Y, Sc, Tb-Lu) relative to UCC values. Preliminary ion-exchange experiments on whole rock samples using a 0.2 M magnesium sulfate solution showed a loss of whole rock REE contents after ion-exchange. The percentages of exchangeable REE were higher for LREE in the upper and lower kaolin zones. On the other hand, ion-exchangeable HREE were highest in one sample from the bauxite zone and another sample from the upper kaolin zone. REE in these sections were primarily found as REE-bearing minerals as well as ion-sorbed REE. The occurrence of ion-sorbed REE with kaolinite minerals is often associated with extensive geochemical weathering processes. These weathering processes are hypothesized to have mobilized REE from the REE-bearing minerals, leading to their occurrences as sorbed species onto kaolin mineral surfaces. These findings were noteworthy given the critical nature of REE resources.