Manganese is the twelfth most abundant element in the earth’s crust. Nevertheless it is only rarely found in concentrations high enough to form a manganese ore deposit. Among some 300 minerals containing manganese, only a dozen are of mining significance. Current estimates of world manganese reserves including low grade ore, reach several billion tons. But if only high grade ores (defined as having more than 44% Mn content) are considered then reserves are in the range of 680 million tons of ore, essentially situated in the Western World, with Australia, Brazil, Gabon and South Africa, supplying over 90% of the international market. Ghana and India, both large suppliers of the Western World in the past, are now exporting only limited quantities of low or medium grade ore. The ore mined in Mexico is mostly for internal use, but part is exported in the form of manganese nodules.
The CIS, which as the USSR was the largest supplier of manganese ore at the beginning of the century, is now left with low grade ore reserves which have to be upgraded for commercial use. Only a limited amount of these reserves is exported, in quantities that are likely to decrease. Manganese ore deposits are widely distributed in China, but there is no high grade ore, nor important reserves, and mines are generally situated far from the end-user industries: in consequence China imports high grade ores to blend with native material.
There are also large manganese reserves on deep ocean floors in the form of polymetallic nodules. Quantitative estimates vary considerably, depending on the assessment method used. Nodules contain on average 25% Mn (their main constituent) and lie in thin layers at a depth of approximately 5.000 metres. Recovery will be difficult and very expensive. During the 1970s and early 80s, these nodules were of great interest because of their nickel and copper content (each constituting approximately 1%). These nodules are now seen as potentially valuable resources for the long-term future.