Caracterização geoquímica e avaliação do potencial para depósitos de terras raras em perfis regolíticos da região de Três Braços, Bahia

Abstract

Rare Earth Elements (REE) play a crucial role in advanced technologies and sustainable solutions. The increasing demand for these commodities in a global market currently dominated by China has driven the search for mineral deposits in other parts of the world. The Três Braços region in Bahia, within the context of the Jequié Block in the São Francisco Craton, offers favorable conditions for the development of ion adsorption deposits (IAD) in regolith profiles developed over the lithologies of the Volta do Rio Plutonic Suite. Currently, there is a lack of studies characterizing the regolith in the Jequié Block, and no such work has been conducted in the Três Braços region. This study utilized descriptions of the regolith zones and geochemical data from soil sampling and mechanized auger drilling to characterize geochemical signatures, parental lithologies, and assess the potential of the Três Braços region for REE mineralization. Simplified tactile-visual descriptions of the regolith zones, application of mass balance methods, chemical weathering indices, and other prospective geochemical methodologies allowed to advance the understanding of the area's regolith profile. Two macro geochemical signatures were characterized, along with interpretations of their parental lithologies and possible REE-bearing mineral phases. Macro Geochemical Signature I features intermediate to high Total Rare Earth Oxides (TREO) concentrations along with high Th and U, associated with felsic saprolites developed from granodiorites and monzogranites of the Volta do Rio Plutonic Suite, favorable for the development of IAD with supergene enrichment patterns analogous to proposed models for Chinese deposits. Macro Geochemical Signature II features high TREO concentrations with high Fe₂O₃, TiO₂, P₂O₅, Y, V, and Nb, associated with mafic saprolites correlated to the mafic-ultramafic and cumulatic rocks of the Volta do Rio Plutonic Suite. This signature indicates potential for residual xenotime concentration deposits or primary mineralization due to the possible occurrence of significant subsurface bodies of these lithologies, with associated concentrations of a mineral from the chevkinite-perrierite group. Finally, a simplified classification based on Th and Ti concentrations was proposed to delineate zones of predominance for each parental lithology across the study area. The results highlight the high potential of the Três Braços area, as well as the portion of the Jequié Block within the São Francisco Craton, for REE mineralization.