GEOCHEMICAL AND MINERALOGICAL ASPECTS OF HEAVY MINERAL SANDS AS POTENTIAL REE RESOURCES IN THE SOUTHEAST U.S

Rare earth elements (REEs) are crucial for components in many rapidly expanding technologies such as smartphones and wind turbines. Increasing demand for REEs and narrow distribution of current production is driving examination of a wide variety of potential REE deposits, including heavy mineral sands. The unconsolidated natures of sands make mining and processing less costly, plus generally unreactive spoils ease reclamation.

Heavy mineral sands become concentrated by fluvial and coastal processes that carry away and weather the finer grained, less dense and less resistant particles. Denser and more resistant phases, including REE-bearing phases such as monazite and xenotime, become concentrated. While concentrations of REE-bearing phases are often not exceptionally high, economic concentrations of other heavy minerals, especially ilmenite, rutile, and zircon can facilitate development.

To better understand how heavy mineral sands may serve as potential REE resources, we examined geochemical and mineralogical patterns at several sites in the southeastern U.S., in conjunction with geophysical surveys. Measured REE patterns in bulk material from sediments that span from Cretaceous-age to modern reflect mixtures of monazite, xenotime and zircon. Compositions of individual phases reveal their contributions to bulk material and potential chemical extractability of the different REEs. Concentrations of ion-exchange REEs were also measured, but were far below economic levels. Regional geochemical databases show that elemental compositions associated with greater heavy minerals content are concentrated at modern and paleo-shorelines and along the “Fall Line” transition from upland to coastal plain. However, likely areas of greater ilmenite, rutile, and zircon concentration do not always overlap with those having greatest concentrations of REE-bearing phases, despite all being heavy minerals. Differences in both weatherability and source rocks are likely causes. If overlap is uncommon, opportunities to maximize co-development of REE-bearing and more traditional heavy minerals from sands will be more challenging to identify. Likely co-occurrences can be identified though, and characterizing and understanding such regions will help evaluate the potential of this resource.