MANGANESE 



387 



and the Nevada production for stockpile, the latter 

 two of commercial grade, were heavily subsidized. 

 The declining production before the subsidy ended 

 clearly indicated that most known deposits were un- 

 economic even at the subsidized prices. No important 

 domestic discoveries have been made since, and 

 domestic production since 1963 has been very small, 

 largely from Montana and New Mexico. 



Much metallurgical research has been done in the 

 United States and Canada to make feasible the ex- 

 traction of manganese from the low-grade ores of 

 those countries and from slag piles from open-hearth 

 furnaces; techniques are available to do this at a 

 price two to five times the present world price for 

 manganese. 



Most manganese ore now produced in the world 

 comes from large open-pit mines ; underground mines 

 still produce in countries with low wage scales or 

 where the ore zone is thick, permitting efficient 

 underground operation, as at Molango, Mexico, and 

 in the Chiatura field in the U.S.S.R. Mining methods 

 are standard. Concentration in most areas consists of 

 relatively simple washing, screening, or jigging to 

 remove clay, sand, or other contaminants. Hand sort- 

 ing, however, still exists in some mines in South 

 Africa and India. The first pelletization plant for 

 fine ore is scheduled to begin producing in Brazil in 

 1972; heretofore such fine material has been stock- 

 piled, sintered, nodulized, or discarded, as lumpy ore 

 is needed in ferromanganese production. 



Except for the manganese carbonate mines in Mon- 

 tana and a few small mines in the Western United 

 States in which base or precious metals were co- 

 products or in which the manganese was a byproduct, 

 most manganese mines are exploited only for that 

 metal. In the future, when the mining of manganese 

 nodules from the sea floor becomes technologically 

 and economically feasible, copper, nickel, and cobalt 

 will certainly be produced as well as manganese. Ex- 

 traction of the valuable metals would probably be by 

 hydrometallurgical and electrolytic techniques. 



As in all mining operations where there is no legal 

 obligation or economic stimulus for preservation of 

 the environment, manganese mining results in mine 

 dumps, tailings piles, rapid erosion of mined-out 

 areas, and large pits. Except for increased sediment 

 load and siltation, manganese mining does not cause 

 water pollution. 



The only environment-restoration effort seen by 

 the senior author in visits to hundreds of manganese 

 mines on four continents was being carried on at the 

 enormous Nikopol open-pit mines in the U.S.S.R. 

 There the rich black topsoil of the Ukraine was care- 



fully removed, the sterile rock overburden replaced 

 after the underlying manganese bed had been ex- 

 tracted, and the topsoil replaced. After 3 to 4 years, 

 orchards or grain were planted and seemingly throve. 

 Lakes, which had been landscaped, had formed in 

 some of the older unrestored large pits. Clubhouses 

 had been built, and the lakes were used for outboard 

 motorboats, water sports, and fishing by the miners 

 and their families. Thus, the land was withdrawn 

 from productive agriculture only for about 5 or 6 

 years and theretofore-absent recreational facilities 

 were developed. Well over 100 million tons of ma- 

 terial is moved each year in these mines. The geology 

 of the Nikopol area makes such restoration rela- 

 tively easy, and the fertility of the soil makes 

 restoration economic for an integrated economy. 



The reduction of manganese ore to ferromanga- 

 nese is commonly accompanied by much air pollution 

 unless special equipment is installed to prevent this. 

 Fumes high in Mn02 are said to be very toxic and to 

 cause a high incidence of respiratory disease. 



Extraction of deep-sea nodules should cause little 

 if any significant damage to the envidonment; in 

 fact, the bottom water that is brought to the sur- 

 face in hydraulic mining is higher in nutrients and 

 will support a more numerous and broader flora and 

 fauna than the surface water. Properly planned hy- 

 drometallurgical extraction should cause no serious 

 pollution problems. 



GEOLOGIC ENVIRONMENT 



GEOCHEMISTRY AND CRUSTAL ABUNDANCE 



Manganese (Mn) constitutes about 0.1 percent of 

 the earth's crust and is the 12th most abundant ele- 

 ment. It is more abundant in mafic rocks, averaging 

 about 0.16 percent, and less abundant in granitic 

 rocks, averaging perhaps 0.06 percent. Deposits that 

 were economic at 1971 prices contained between 25 

 and 50 percent manganese; thus the element must 

 have been concentrated by natural processes 250- 

 500 times the normal background to form an eco- 

 nomic ore deposit. 



The geochemical characteristics of manganese are 

 very similar in many ways to those of iron; there- 

 fore some manganese deposits are closely related to 

 iron deposits, and some contain considerable quanti- 

 ties of iron. 



Manganese commonly occurs in nature in three 

 valence states: +2, +3, +4. The ionic radius of 

 bivalent manganese is close to that of bivalent iron 

 and calcium; manganese ions may substitute for 

 iron ions in ferrous minerals. Indeed, almost all the 



