INVESTIGATION OF REE MINERALIZATION FOR OFFSHORE SANDS FROM GEORGIA, SOUTH CAROLINA, AND NORTH CAROLINA, USA

Rare earth elements (REE) are used in a variety of applications, but knowledge of their presence in the environment needs to be better understood as demand for them increases. Forty-two mineral sand samples from vibracores collected offshore of North Carolina, South Carolina, and Georgia, were investigated to determine the REE concentrations and corresponding rare earth minerals. Samples were obtained within 13km (8 miles) from the coast as part of a sand resource assessment project. Geochemical analyses indicate that REE are present in very low concentrations in the samples. For example, cerium ranges from 8 ppm to 100 ppm, but it is generally less than 50 ppm in most samples, and yttrium is generally <30 ppm.

The use of QEMSCAN analysis, coupled with geochemistry and mineral chemistry, provides extremely useful data and can lead to a better understanding of the provenance of heavy minerals in the sand samples. QEMSCAN analysis identified trace amounts of monazite, zircon, apatite, Fe-oxides, rutile, and ilmenite. The morphology of monazite ranges from generally rounded in Georgia to more angular in the South Carolina, but is erratic in North Carolina. The liberation % of monazite is variable due to its low-grade mass in the samples, but illustrates its potential for gravity concentration.

Electron probe micro-analysis (EPMA) of monazite shows that Ce₂O₃, La₂O₃ and Nd₂O₃ are similar in concentration across the regions, while Y₂O₃, Gd₂O₃, and Dy₂O₃ show slightly wider variations. The average ThO₂ concentration ranges from 3.97 wt% to 5.05 wt%, and UO₂ from 0.31 wt% to 0.92 wt%, in general agreement with previously reported chemistry of monazite in the greater area. Zircon contains an average of 0.11 wt% to 0.15 wt% Y₂O₃, but REE are below the detection limit of the instrument. Laser ablation by ICP-MS analyses will be conducted to better quantify trace amounts of elements in monazite and zircon. This study provides important insight on the natural occurrence of REE in offshore sediments.