Assinatura geoquímica e mineralógica de uma ocorrência de elementos terras raras em argilas iônicas associadas a perfis de intemperismo granítico no sul do Ceará

Abstract

Rare Earth Element (REE) deposits of the ion-adsorption clay type are strategic sources for the energy transition, especially for Heavy REEs, which have higher added value. However, understanding the specific mineralogical controls governing the enrichment and fractionation of these elements in regolith profiles remains a scientific gap. This study investigated the hypothesis that the concentration and fractionation of REEs in weathering profiles over granites in southern Ceará are controlled by a vertical mineralogical zonation. Samples from eight drill holes were analyzed using whole-rock geochemistry, X-ray diffraction, and reflectance spectroscopy. Integration of the geochemical results with the identified clay minerals revealed that the highest concentrations of Total REEs are associated with the kaolinite+illite assemblage, while the enrichment of Heavy REEs is controlled by the presence of 2:1 clay minerals (illite and montmorillonite) in the lower parts of the profile, between the lower saprolite and saprock horizons. It is concluded that mineralogical control is key to the geochemical fractionation in the profiles, validating the initial hypothesis. Clay minerals with higher cation exchange capacity have greater potential to concentrate Heavy REEs in the basal zones, which defines these horizons as the most economically promising targets and guides future exploration strategies in the region.