EVOLUÇÃO SUPERFICIAL DAS ROCHAS MANGANESÍFERAS DE CONSELHEIRO LAFAIETE, MINAS GERAIS

ADOLPHO JOSÉ MELFI, ANDRÉ V. BITTENCOURT

Resumo


The weathering of the calc-silicate bearing manganese rocks in the humid tropical and subtropical regions is very important in the formation of manganese lateritic deposits. Samples of both the protore and the are from Morro da Mina, Conselheiro Lafaiete, MG, were studied aiming to obtain informations about the origin ot these deposits, as well as to define the conditions that control the formation of manganese oxides and hidroxide in the earth surface. The mineralogical, chemical and geochemical studies pointed out a laterization process that promotes solution and hydrolysis ofthe protore producing as a first step, manganese (III) hidroxides (manganite and groutite type). As the process goes on, these compounds give origin to manganese (IV) oxides (piroluzite and cryptomelane) through an intermediate stage characterized by the development of non stoichiometric compound, a poorly organized oxide of nsutire type.

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