Morro da Mina, in the Lafaiete district, Minas Gerais, Brazil, has been one of the most productive manganese deposits in the western hemisphere. The ore is residual and consists of manganese oxides formed by the weathering of silicate and carbonate basement lithologies. This protore has been called gondite (Park, 1956) and manganese silicate-carbonate protore (Dorr, Coelho, and Horen, 1956). Dorr and his coworkers state that the protores are metamorphosed sediments that formed a gradational sequence of cherts, mudstones, and manganiferous carbonates. They are in schists of Precambrian age which may be volcanic in origin. The characteristic manganiferous beds have been followed along strike for more than 60 km, and probably continue farther. The irregular distribution of most constituents in the metasediments is compatible with the present erratic distribution of manganoan carbonates in the protores. The sediments have undergone intense regional metamorphism, and locally are invaded by granitic masses and mafic and pegmatitic dikes (Guimaraes, 1935). Igneous metamorphism has been superimposed upon regional metamorphism, particularly near the northwestern part of the mine, a factor that has led observers in the past to relate the mineralization to igneous metamorphic processes. Igneous metamorphism is now thought to have developed patches of the manganoan olivine tephroite (Mn2Si04) and other silicates, mainly at the expense of manganese carbonates.

The ore at Morro ........

Morro da Mina is an open pit mining operation which is employed conventional truck and shovel method to extract medium- and low-grade silicocarbonate ores (an average content of 30% manganese grade).

Mined manganese ore is transported by truck to the Barbacena and Ouro Preto ferroalloy plants.

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