Análise dos depósitos de lateritas niquelíferas do Brasil a partir do conceito de sistemas minerais holísticos

Abstract

The concept of mineral system, which interprets mineral deposits in relation to terrestrial dynamics, is currently used to interpret the genesis of deposits holistically, being an important tool for mineral research. In this sense, the present work makes an interpretation of nickel laterite according to the precepts of mineral systems and points out potential areas for further research in Brazil. One of the main sources of nickel comes from minerals formed by surface changes of ultramafic rocks submitted totropical climates and relative tectonic stability, with several potential regions in Brazil. The best protoliths that are registered in Brazil are stratiform ultramafic-mafic complexes. However, the ophiolitic complexes associated with the Precambrian mobile belts, correspond to an important geotectonic environment that can host significantdeposits. Practically all Brazilian protoliths are serpentinized, a process that supported the precipitation and accumulation of nickel dissolved in a supergenic environment. In term ofgeomorphology, the lateritizationprofile is closely related to planesurfaces. In most Brazilian nickeliferous laterites, paleobioclimatic conditions submitted the primary silicates with ultramafic nickel, exhumed by planing surfaces, to chemical weathering, andhydrolysis, forcing the precipitation of Ni-goethite (oxidized level) and subsequently to dissolution, reprecipitation and formation of 'garnieritas' (silicate level).