Geochemical characteristics of REE-enriched weathered anorthosite complex in Hadong district, South Korea

Abstract

The mineralogy and geochemistry of the weathered intercumulate-type anorthosite complex in the Hadong district of South Korea were investigated as a prospective area for rare earth resource exploration. In this area, gabbroic anorthosite was intruded by rare-earth elements and yttrium (REE)-bearing dioritic pegmatites (av. 242 ppm), which caused REE-enriched Fe–Ti orebody accumulation (av. 857 ppm) near the dioritic pegmatites. REE-bearing minerals, such as allanite, cerite, and xenotime, were identified from the pegmatite and orebody, which had undergone various degrees of weathering. The total REE (∑REE) in kaolin minerals-bearing clay fractions increased compared to those of the whole rocks. When treated with ammonium-salt solvents of different pH values, that is, 4.6 (NH₄Cl_(aq)), 5.0 ((NH₄)₂SO_4(aq)), and 7.8 (NH₄CO_3(aq)), 81%, 73%, and 70% of the exchangeable REE of the kaolin minerals-bearing clay fractions were recovered in the dioritic pegmatites. respectively. In contrast, in kaolin minerals-deficient clay fractions separated from the Fe–Ti ores, exchangeable REE were recovered less than 10% after treatment, regardless of the ammonium-salt solvent species. Therefore, the occurrence of REE-bearing primary minerals in the parent rock, the formation of kaolin minerals-bearing clay fractions, and the extraction rate of exchangeable REE with ammonium-salt solvents seem to be crucial to securing the ion-adsorption type REE resources.