THE LATERITIC ORE DEPOSITS OF BRAZIL

Abstract

In Brazil, the same processes responsibleforthe formation of the thick lateritic mantle, which covers nearly 65 % of its territory, are also responsible for metal accumulation which forms, under special condition, the lateritic ore deposits. In the origin ofthose accumulation. the parent rock composition and/or the convergence of the biological and morphoclimatic factors play a fundamental role. Considering this point ofview, different lateritic ore deposits are discussed in this paper. Thus, the weathering of the Banded Iron Formations (from Archean to Upper Proterozoic) gave origin to some of the biggest iron deposits in the world at Ca rajas (Para). Quudrilatero Ferrifero (Minas Gerais) and Urucum (Mato Grosso), The products o.f thc weathering of various rocks constituted very important bauxite deposits: Cretnccous nlkaline massifs in the Southeast Brazil (Minas Gcrais, Sao Paulo, Rio de Janeiro, Santa Catarina) ; Prccurnhriun metamorphic or volcanic rocks in the Central-East Brazil (Quadrilatero Fcrrifero, Atlantic coastal ridge) ; and Tertiary .continental sediments in the Amazonian Basin (Trombetas, Paragorninas, ... ). The lateritic alteration concentrated the manganese from rocks that have been previously enriched in this clement by volcanic-sedimentary processes (Arnazonia, Minas Gerais). Finally, nicke­ litcrous laterites were accumulated by the weathering of ultramafic massifs scattered all over the country, concentrated mainly in Central Brazil (Burro Alto and Niquelandia, Goias), but also occurring in the more humid regions (Atlantic Coast and Arnazonia). All this lateritic evolution of wry specific bed rocks occurred essentially in the Tertiary during periods of tectonic stability which are related with extense erosional surfaces. The influence of litho logic, climatic and morphoteetonic factors on the mechanism offormation of lateritic deposits is discussed. Laterite, Ore deposit, Bauxites, Iron, Manganese, Nickel, Brazil