Brazil has been a small but consistent source of manganese ore for world markets during the last five decades. Production both for export and for domestic use is likely to increase. Deposits can be classified into syngenetic (the primary manganese sediments in iron formation at Urucum) and epigenetic. The epigenetic deposits can be further subdivided into four classes: (a) The Queluz or Morro da Mina type, in which the manganese oxide ore has been derived by weathering processes from a manganese silicate-carbonate-sulfide protore. (b) The Lagoa Grande type, enclosed in itabirite, in which lean man-ganiferous horizons in the metamorphosed iron formation have been leached and the manganese concentrated by weathering processes. (c) Deposits in slightly manganiferous rocks of various types in which the manganese has been concentrated by weathering processes. (d) Deposits in barren rocks into which manganese oxides have been introduced from unknown sources. It is probable that the Lagoa Grande type is closely related in ultimate origin to the Urucum type, although the regional metamorphism suffered by the former obscures relations. The Urucum deposits and two deposits of the Morro da Mina type have large reserves of export-grade ore. Many deposits of the Lagoa Grande type are known and the aggregate reserves are large, although their grade makes them more suitable for domestic than for export use. Deposits of the other two types are numerous but small, and their grade seems to consign most ore from these deposits to the domestic market. © 1951 Society of Economic Geologists, Inc.