Mineralogy and geochemistry of manganese occurrences from Alto Tapajós basin, southeastern Amazonas State, Brazil

In six of almost fifty occurrences identified to now in Apuí, Novo Aripuanã and Manicoré municipalities, southeast Amazonas State, the manganese is hosted as lenses, laminations and layers in red sandstones, siltstones and mudstones, as well as in manganese lateritic crusts and colluvium accumulations. Romanechite is the main ore mineral, but manjiroite, lithiophorite, hollandite, vernardite, cryptomelane and pyrolusite are also present. There are two main geochemical associations: 1) for manganesiferous material: a) Sr, Au, U, Cu, Pb and Hg as in the Zé Julião occurrence; b) CaO, K2O, Zn, Tl, Rb, Cd, P2O5 and As in the Silva e Floresta farms occurrences; c) MnO, Ni, Mo, Be, Co, Ga and Eu, in the Beneficente, Cotovelo and Holanda occurrences; 2) for the sedimentary rocks, matrix and soil: d) Y + ETR - Eu; e) SiO2, Al2O3, TiO2, Nb, Hf, Zr, Fe2O3, Sc, Th, V. The genesis of the manganese oxy-hydroxides is related to deposition in sedimentary environment and to the subsequent processes of weathering and landscape evolution of the region.