MANGANESE 



397 



by interruption, either political or military, of the 

 supply of this essential raw material, all of which is 

 now imported. 



2. From the viewpoint of raw-materials supply, 

 the most promising development would be the suc- 

 cessful winning of nodules from the sea floor and 

 extraction of the contained metals. This would in- 

 sure not only a greatly increased resource of man- 

 ganese but also a significant increment in the supply 

 of nickel, cobalt, and copper — also metals for which 

 the United States is dependent on imports. Large 

 investments are needed to bridge the gap between 

 promising research and pilot-plant operations and 

 industrial-scale application, but the legal status of 

 deep-sea mining must be resolved before large-scale 

 private investment can be secure. 



3. Should a decision be reached to attempt to make 

 this country more self-sufficient in manganese sup- 

 ply from conventional sources, greatly expanded 

 metallurgical research would be necessary to tap 

 known submarginal identified resources as well as 

 geological research to locate the hypothetical and 

 speculative resources already discussed. 



4. Continuing research into the geological habi- 

 tat of manganese, causes of concentration into large 

 economic deposits, and the geochemistry of the ele- 

 ment can only make the search for conventional and 

 nonconventional sources more fruitful and increase 

 the supply available to our industry and civilization. 

 Because most of the large-scale concentrations and 

 all of the high-grade concentrations of economic 

 size are outside the United States, much of the 

 needed research must be carried out overseas. Judg- 

 ing from past successes and their impact on the 

 supply situation during the last two decades, invest- 

 ment in such research is sound. Specifically, thor- 

 ough subsurface investigations of at least one of 

 the large carbonate sedimentary bodies, such as 

 Nsuta, Ghana, or Serra do Navio, Brazil, should be 

 undertaken to establish the geological habits and 

 expectable reserves of this type of manganese ore. 

 Such a study probably would have to be subsidized ; 

 at present there is little economic justification for 

 a company to undertake research of this type inde- 

 pendently because of the abundance of high-grade 

 oxide ores in the world. Results must be published. 



NEEDS FOR NEW PROSPECTING TECHNIQUES 



Because manganese oxide is very resistant to 

 weathering and usually crops out or is found as 

 concretionary or detrital pebbles or boulders in 

 residual soils overlying significant bodies, prospect- 

 ing in areas of residual soils is relatively simple. 

 In areas of transported soils or debris and in areas 



of glacial moraine, loess, or other transported sur- 

 ficial material, or under unconformities, there may 

 be no surface sign of underlying bodies. Geochemical 

 prospecting is much handicapped by the widespread 

 presence of manganese in the earth's crust and the 

 ease with which it is precipitated from solutions 

 under near-surface conditions; positive anomalies 

 are, accordingly, much more common than ore de- 

 posits and, by themselves, are relatively meaningless. 



Except for a rare magnetic mineral, manganese 

 oxide deposits have no particularly distinguishing 

 geophysical characteristics that would selectively 

 locate concentrations. Manganese minerals have 

 relatively high specific gravity, but many near- 

 surface secondary deposits have so many voids that 

 gravimetric techniques would have only moderate 

 chance of success, although in certain environments 

 the technique has been successfully used (Rowston, 

 1965). Carbonate-facies sedimentary manganese 

 deposits are in most places closely associated with 

 a high free-carbon content in the wallrocks, and 

 this can be detected under slight or moderate cover 

 by certain electrical methods of prospecting. Unfor- 

 tunately, many carbonaceous rocks are not associated 

 with manganese deposits, and unless positive indi- 

 cation of the presence of manganese at depth is 

 available, the method is nondiagnostic. In drift- 

 covered areas a combination of geochemical pros- 

 pecting followed by geophysical investigation in the 

 neighborhood of major anomalies might help locate 

 large bodies of manganese carbonate, but to the 

 authors' knowledge this dual approach has not been 

 attempted and may not be practical. Large man- 

 ganese carbonate sedimentary bodies are known in 

 many tropical shield areas and may be present but 

 undiscovered in shield areas in northern latitudes. 

 These bodies have hitherto not been exploration 

 targets for economic reasons ; the oxide is the pre- 

 ferred ore. 



In South Africa, Australia, and the Eastern 

 United States, certain plants have been shown to 

 concentrate manganese in their leaves and (or) 

 twigs. To the authors' knowledge, no extensive re- 

 search has been done on the general applicability 

 of biogeochemical prospecting to manganese-ore 

 finding; and therefore this is a promising avenue 

 for future systematic research, to determine whether 

 variation in manganese content of plants is a func- 

 tion of generic type, climate, or soil environment. 



A better understanding of the exact sedimentary 

 conditions and environment causing large-scale 

 deposition of relative pure manganese minerals in 

 the specific spots in which they are found seems 

 prerequisite to evolving new prospecting techniques. 



