MAGNESIAN REFRACTORIES 



383 



RESOURCES 



IDENTIFIED AND HYPOTHETICAL RESOURCES 



Magnesium resources in sea water are practically 

 unlimited, and those in magnesium-bearing evapor- 

 ites, dolomite, and dunite are enormous. Magnesium 

 resources contained in interior saline lakes and seas 

 must total billions of tons, and it is judged that 

 deep-well brines contain large tonnages of mag- 

 nesium salts. Identified resources in the magnesite 

 deposits of the world total 12 billion tons; those in 

 the brucite deposits of the world, several million 

 tons. 



The apparent reserve of magnesite of the United 

 States in 1970 was placed at 65 million tons (Paone, 

 1970), about equal to the national reserve in 1960 

 (Comstock, 1963). Data are not available to deter- 

 mine what fractions lie in recoverable and subeco- 

 nomic resources, but probably less than half of the 

 identified resource is commercially recoverable under 

 present prices and required grades. Hypothetical 

 resources are limited to unexplored magnesite at 

 depth below known deposits. Perhaps 20 million 

 tons of subeconomic resources seems a reasonable 

 estimate. 



Recoverable resources of magnesium chloride in 

 Great Salt Lake are said to exceed 600 million tons. 

 Resources of fresh dunite in Washington State total 

 billions of tons, and those in North Carolina total 

 more than 200 million tons. Recoverable resources 

 of brucite remaining in the Nevada deposits are 

 said to be small, probably not more than 1-2 million 

 tons. At least an additional several tens of millions 

 tons of magnesite constitutes a subeconomic re- 

 source within the magnesite-talc deposits in Ver- 

 mont. 



A recent compilation set the apparent world re- 

 serve of magnesite at 9.4 billion tons, exclusive of 

 small reserves in several countries (Paone, 1970). 

 To this should be added 300 million tons of crystal- 

 line magnesite in Brazil (Bodenlos, 1950b, 1954) ; 

 240 million tons of magnesite in the Sudan (White- 

 man, 1971) ; 100 million tons of magnesite in 

 Canada, which consist of magnesite-talc-quartz rock 

 replacing dunite ; and 2,000 million tons of talc-rich 

 magnesite at Savinsk, in eastern Siberia, the host 

 rock of which is unreported (Industrial Minerals, 

 1970). Total identified resources consist largely of 

 crystalline magnesite associated with dolomite; but 

 at least 1 billion tons consists of crystalline mag- 

 nesite replacing dunite, and perhaps more if the 

 Siberian occurrence lies in such rock. Identified re- 

 sources of bone magnesite are not well known, but 

 older compilations indicate that they are on the 

 order of several tens of millions of tons. Notwith- 



standing, bone magnesite is at present being mined 

 at a rate of more than 1 million tons per year, so it 

 is likely that past resource estimates of bone mag- 

 nesite were conservative. 



Although magnesium-bearing evaporite minerals 

 are not covered in this chapter, the tachyhydrite 

 deposits of Sergipe, Brazil, must be cited as a large 

 new resource; R. J. Hite reported that the upper 

 zone alone contains about 4 billion metric tons of 

 the mineral, equivalent to 380 million tons of mag- 

 nesium metal (U.S. Geol. Survey, 1970, p. A216; 

 Wardlaw, 1972). Similar deposits also have been 

 found in Gabon and Zaire, Africa. Tachyhydrite 

 (CaMgsCle-HsO) is so soluble, even in drilling 

 brines, that its occurrence may have been overlooked 

 in other evaporite sequences. 



SPECULATIVE RESOURCES 



Crystalline magnesite deposits are not common. 

 Areas favorable for their occurrence are carbonate 

 rocks near igneous intrusions, which in the United 

 States were thoroughly searched without success 

 during World War II. Probably nearly all deposits 

 of crystalline magnesite in Europe have been found, 

 but undiscovered deposits undoubtedly exist on 

 other continents. Because such deposits tend to be 

 large, any one discovery could add from tens to 

 hundreds of millions of tons to the world's resources. 



Crystalline and bone magnesite deposits in ultra- 

 mafic rocks are globally widespread. Bone magnesite 

 outcrops are conspicuous; therefore, most near- 

 surface deposits probably have been found, even in 

 remote areas. Ore bodies undoubtedly exist that do 

 not crop out; targets for exploration should include 

 serpentinized shear zones in relatively unaltered 

 masses of peridotite, particularly where the ser- 

 pentine is veined by chalcedony or opal. Deposits of 

 crystalline magnesite in ultramafic rocks evidently 

 are very rare, but most seem to be very large al- 

 though low in grade. Undoubtedly more will be dis- 

 covered in those parts of the world not yet fully 

 geologically mapped. 



PROBLEMS FOR RESEARCH 



Industrial technology successfully developed 

 methods to recover magnesium-bearing compounds 

 and the metal from a wide variety of natural re- 

 sources. Efforts are continuing to produce stronger 

 refractories, to increase the efficiency of recovery 

 processes, and to develop new magnesium-bearing 

 alloys. 



The geology of magnesium-bearing mineral de- 

 posits is reasonably well known. Not enough is 

 known, however, about the genesis of deep-seated 

 magnesium-rich brines. The world's resources of 



