natural mineral formations with sufficient manganese content to make economically feasibleextraction 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); andbustamite, (Ca,Mn)(Si3O9) (12-20 percent). Iron minerals are almost always present in manganeseores.
The most important manganese deposits in terms of origin are sedimentary deposits, which arestratified and lenticular beds formed in ancient marine and lacustrine basins (Nikopol’, Chiatura, andPolunochnoe in the USSR; deposits in Morocco). These ores have the greatest industrialsignificance. 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 saturationby dissolved oxygen, containing 19-36 percent Mn in individual deposits, and (2) carbonate—primarily rhodochrosite, oligonite, and manganocalcite—ores, formed at great depths underconditions of oxygen deficiency and accompanied by hydrosulfuric fermentation, containing 16-25percent 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 interiorunder the action of high temperatures and pressures (the Usa deposit in Western Siberia; depositsin the Atasu region of Central Kazakhstan). They are usually represented by massive ore varietiesconsisting of anhydrous oxides (braunite and hausmannite) and manganese silicates (rhodonite andothers). Metamorphic deposits are also characterized by the occurrence of ferromanganese oreswith a manganese content of about 10 percent, which include commercial concentrations of ironminerals (magnetite, hematite, and so on).
Weathering deposits are thick ancient and modern crusts of weathering with secondary manganeseconcentration (deposits in India, Brazil, Ghana, and the Republic of South Africa). They are friableacidic ores in “manganese hats” composed of pyrolusite, psilomelane, and other hydroxides ofmanganese and iron.