Massive specular hematite ores of the Congonhas district, central Minas Gerais, Brazil, are believed to have been formed by metasomatic replacement of itabirite (quartz-iron oxide rock) and associated dolomite in the central group of the Precambrian Minas series. It is suggested that heated solutions of unknown source and character were introduced along faults and replaced silica and carbonate by hematite in structurally and chemically favorable portions of the itabirite.

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