The role of hydrothermal enrichment in the Pratápolis sedimentary phosphorite deposit, Minas Gerais, Brazil

1 Abstract The Pratápolis sedimentary phosphate deposit, located southwestern Minas Gerais, is a relatively recent discovery that began production in 2016. Its development has had a major impact on regional agribusiness, driven by the growing demand for phosphate fertilizers. This study aims to understand the geological processes responsible for the mineralization and its implications for sedimentary phosphate exploration, particularly within Brazil’s Bambuí Group. The deposit is situated in the geological context of the Passos Nappe, within the southern, structurally complex portion of the Brasília Fold Belt. Field descriptions, field data and whole-rock lithogeochemical analyses reveal the ore is a metasedimentary sequence hosted mainly in metasiltstones, tectonic breccias, and alterites. These lithologies were enriched in phosphate by hydrothermal fluids that circulated through zones of discontinuity. The ore content ranges from 4.64 to 38.1% P 2 O 5 , with an average of 9.25%. The metasiltstones, in particular, are believed to have been hydrothermally enriched over a zone of primary mineralization, allowing them to partially retain a geochemical signature (ΣREY and Sr anomalies) that is distinct from the other lithologies. Based on petrographic, X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), and Cathodoluminescence (CL) analyses, a mineral succession scheme was developed. These analyses also identified fluorapatite as the sole ore mineral, which occurs in four main textural types. This study suggests that the phosphate rocks are associated with the Bambuí Group. This conclusion is consistent with the established Neoproterozoic metallogenic period of phosphatization, though their exact stratigraphic position remains uncertain.