Mineralogical Characterization of Rare Earth Element (REE) Enrichment Within Regolith Overlying the Doradilla Tin-Skarn System, NSW, Australia

This study presents the first detailed mineralogical characterization of rare earth element (REE) enrichment (up to 1.39 wt% TREO (total rare earth oxide)) within the regolith overlying the Doradilla tin-skarn prospect, northern New South Wales, Australia. The REE mineralogy was investigated using petrography, field-emission scanning electron microscopy (FE-SEM), electron microprobe analysis (EPMA), micro-X-ray fluorescence (µ-XRF) elemental mapping, and laser Raman spectroscopy. Hydrated REE phosphate minerals are identified as the dominant REE hosts within the regolith. Raman spectroscopy confirms the presence of water in both rhabdophane and churchite. Three compositionally distinct rhabdophane populations are identified, including one La-dominant and two Y-rich groups, whereas churchite-(Y) represents the only HREE-enriched phase identified. The predominance of hydrated REE phosphates within the regolith highlights the importance of secondary phosphate minerals as major REE hosts within the Doradilla profile. This study emphasizes the need for detailed mineral characterization when studying REEs in previously undescribed settings. Furthermore, the results demonstrate that regolith developed over tin-skarn protoliths may host compositionally diverse and REE-enriched phosphate assemblages. With growing global demand for REEs, a greater understanding of REE mineralization in underexplored geological settings is increasingly important.