Application of Raman spectroscopy for the identification of phosphate minerals from REE supergene deposit

Abstract

AbstractAmong critical metals, rare‐earth elements (REEs) are irreplaceable for their role in the high‐tech industry. The REE deposits commonly host REEs in fine‐grained mixtures of phosphate minerals characterized by the variable content of volatile components. However, identification of the volatile components may present challenges for laser‐ablation inductively coupled plasma mass spectrometer (LA‐ICP‐MS) and electron microprobe (EPMA) techniques. Therefore, Raman spectroscopy was applied to laterite and carbonatite samples from the Mount Weld deposit, one of the major REE deposits in Western Australia. The hydrous REE phosphate, rhabdophane, can be confidently distinguished from monazite by the presence of peaks in the region 2800–3600 cm−1. The presence of peaks at 428, 448, 579, 589, and 605 cm−1 in the Raman spectra of apatite from carbonatite allows its identification as hydroxyfluorapatite with high concentrations of F and water, and negligible Cl, SO42−, and SiO42−. The Raman spectra and composition of silcrete and carbonatite apatite are similar; thus, silcrete apatite was identified as hydroxyfluorapatite as well. The content of CO32− in both types of apatite was negligible despite the crystallization from carbonatitic magma. The aluminophosphate florencite is characterized by the presence of PO43−‐related peaks at 639, 1113, and 1609 cm−1 and H2O/OH‐related bands in the 2750–3075 cm−1 and together with rhabdophane has been identified in fine‐grained mineral mixtures. Our study demonstrates that combining Raman spectroscopy with compositional data is a powerful method for the characterization of phosphate minerals in REE deposits.