natural mineral formations with sufficient manganese content to make economically feasible extraction of the metal or its compounds. The most important ore minerals are pyrolusite, MnO2 (63.2 percent Mn); psilomelane, m MnO.MnO2.n H2O (45-60 percent); manganite, MnO2-Mn. (OH)2 (62.5 percent); vernadite, MnO2.H2O (44-52 percent); braunite, Mn2O3 (69.5 percent); hausmannite, Mn3O4 (72 percent); rhodochrosite, MnCO3 (47.8 percent); oligonite, (Mn,Fe)CO3 (23-32 percent); manganocalcite, (Ca,Mn)CO3 (up to 20-25 percent); rhodonite, (Mn,Ca)(Si3O9) (32-41 percent); and bustamite, (Ca,Mn)(Si3O9) (12-20 percent). Iron minerals are almost always present in manganese ores.
The most important manganese deposits in terms of origin are sedimentary deposits, which are stratified and lenticular beds formed in ancient marine and lacustrine basins (Nikopol’, Chiatura, and Polunochnoe in the USSR; deposits in Morocco). These ores have the greatest industrial significance. The following principal types of ores are distinguished: (1) acidic psilome-lane-pyrolusite and manganite ores, formed at shallow depths in the zone of maximum water saturation by dissolved oxygen, containing 19-36 percent Mn in individual deposits, and (2) carbonate—primarily rhodochrosite, oligonite, and manganocalcite—ores, formed at great depths under conditions of oxygen deficiency and accompanied by hydrosulfuric fermentation, containing 16-25 percent Mn and differing from acidic ores in their increased phosphorus content.
Metamorphic deposits are formed by the change of sedimentary deposits in the earth’s interior under the action of high temperatures and pressures (the Usa deposit in Western Siberia; deposits in the Atasu region of Central Kazakhstan). They are usually represented by massive ore varieties consisting of anhydrous oxides (braunite and hausmannite) and manganese silicates (rhodonite and others). Metamorphic deposits are also characterized by the occurrence of ferromanganese ores with a manganese content of about 10 percent, which include commercial concentrations of iron minerals (magnetite, hematite, and so on).
Weathering deposits are thick ancient and modern crusts of weathering with secondary manganese concentration (deposits in India, Brazil, Ghana, and the Republic of South Africa). They are friable acidic ores in “manganese hats” composed of pyrolusite, psilomelane, and other hydroxides of manganese and iron.
Accumulations of ferromanganese concretions constituting large manganese ore deposits are located along present-day ocean floors.
REFERENCESOtsenka mestorozhdenii pri poiskakh i razvedkakh. Fasc. 14: G. A. Avaliani, Marganets. Moscow-Leningrad, 1953.
Bykhover, N. A. Ekonomika mineral’nogo syr’ia. Moscow, 1971.