Small-scale manganese deposits in the Midwest of Brazil: geochemistry, Nd, Sr, and Pb isotopes, and a potential source of high-technology elements

In the Midwest of Brazil, several small manganese (Mn) deposits are located within the metavolcano-sedimentary rocks of the Paleoproterozoic Araí Group and the metasedimentary rocks of the Mesoproterozoic Paranoá Group. Mn occurs as layers, lamellae, fractures-filling, pocket-type, and blocks at the surface. For this study, 23 Mn ore samples from 12 small Mn-deposits were analysed using XRD, SEM, EPMA, and whole-rock geochemistry. This research aimed to identify the mineral and geochemical characteristics of these small Mn deposits, focusing on the geochemical associations, geological environment, source, and mineralization style of the Mn ores. This information facilitates the exploration of the influence of the Araí and Paranoá Groups as a potential source of Mn and critical and rare high-technology elements. Several stages of Mn mobilization were identified based on their geochemical differences, host geological units, and types of Mn occurrence. The Araí Group Mn deposit is characterized by hausmannite, cryptomelane, pyrolusite, and hollandite paragenesis, low P2O5 contents, high Sr, Tl, and U concentrations, positive Eu/Eu* anomalies, high (La/Yb)N, and low Co/Zn ratios. These features suggest that the Mn deposit in the Araí Group had a metamorphic and hydrothermal overprint. The Paranoá Group Mn deposits are characterized by romanechite, lithiophorite, hollandite, cryptomelane, and pyrolusite paragenesis, high Al2O3, Ba, Co, Cu, and Ni concentrations, high Co/Zn ratios, and LREE UCC depletion. These features indicate an interplay of older sources, tectonic deformation, and surficial weathering. Moreover, the high content of Ba, Co, Cu, Ni, Sr, Tl, U, Y, and REE in the Mn deposits makes them suppliers of critical and rare high-technology elements.