A New Look at the Occurrences of the Rare-Earth Elements in the Georgia Kaolins

Abstract

AbstractThe high-density siliciclastic minerals (e.g. zircon) in the coarse fractions (>44 mm, informally known as grit) of the mined Georgia kaolins are potential and significant sources of the rare-earth elements (REE). The abundances and provenance of the REE signature have not been studied extensively for the Georgia kaolins. The objective of the present study was, therefore, to define the contribution of these heavy minerals (e.g. zircon) to the REE inventory of the coarse fractions of Georgia kaolins. Heavy-mineral subfractions separated from the coarse fractions contained 1647 mg/kg REE from the Jeffersonville Member of the Lower Tertiary Huber Formation and 5012 mg/kg REE from the Buffalo Creek Kaolin Member of the Upper Cretaceous Galliard Formation, respectively. These heavy-mineral subfractions were enriched 10–100 times in the heavy rare-earth elements (HREE, Gd—Lu,), Hf, and Zr relative to the concentrations of these elements in Upper Continental Crust. The heavy-mineral subfractions comprised 5% of the coarse fractions (grit) of these two kaolin-producing formations. The heavy-mineral subfractions consisted of zircon, anatase, rutile, kaolinite, and minor amounts of muscovite, trace ilmenite, and staurolite. The large concentrations of REE were obtained by separating the dense heavy minerals from the coarse fraction (grit) obtained during the typical production of kaolin-group minerals (kaolinite) from kaolin ore. The amount of zircon (estimated from the 6–11 wt.% Zr) and the absence of monazite did not explain the high concentrations of REE in the heavy-mineral subfractions. The large amounts of REE could have resulted from the sorption of REE released during weathering reactions, or from the presence of small amounts (0.025 wt.%) each of monazite and xenotime in addition to the presence of zircon. This heavymineral subfraction represented a novel domestic resource of extractable REE, especially the HREE, of a grade as high as 0.50 wt.% total REE.