Mineralogical and chemical characteristics of the ion adsorption type REE in West Sulawesi, Indonesia; its exploration and potential utilization implications

Abstract

This study characterizes ion adsorption-type rare earth element (REE) deposits in West Sulawesi, Indonesia, derived from the weathering of local granitoid bedrock. The investigation focuses on granite in Polewali Mandar and quartz monzonite in Mamasa as the primary host rocks. The research integrated fieldwork by systematic sampling of weathering profile zones and laboratory analyses, including petrography, XRD, XRF, and ICP-MS. The weathering profile is typical of ion-adsorption deposits, comprising four distinct layers from bottom to top: bedrock (C), saprolite (B), limonite (A), and topsoil (O). Mineralogical analysis identified key REE-bearing minerals such as monazite, xenotime, and zircon within the weathered layers, alongside associated radioactive minerals. Chemically, a high Chemical Index of Weathering (CIW: 96–98%) confirms intense weathering conditions. Results reveal significant REE enrichment, particularly in the limonit (Horizon A), with total REE+Y+Sc concentrations reaching up to 453.37 ppm in Mamasa. The deposits are characterized by a pronounced enrichment of Light REEs (LREE) over Heavy REEs (HREE), attributed to factors including the presence of biotite and the influence of Fe-Mn elements. While the total REE concentrations are approximately double those found in comparable deposits on Bangka Island (70–180 ppm), they are at the lower end of economically mined grades in China. Despite this, the LREE-enriched resources from West Sulawesi hold potential for various technological applications, including the manufacture of magnets, electric vehicles, catalysts, and batteries. This study underscores the regional potential of these deposits and provides a foundation for further exploration and utilization assessment.