394 



UNITED STATES MINERAL RESOURCES 



percent Mn, underlying the supergene oxide ores in 

 Ghana, Brazil, and elsewhere are considered as con- 

 ditional resources. Figui-es on the size of such bodies 

 are very gross estimates indeed, for none have been 

 explored to depth. Low-grade bodies of manganifer- 

 ous rocks such as those at Artillery Peak, Ariz., and 

 Aroostook County, Maine, are here included, al- 

 though they probably will never be used. Also in- 

 cluded are the Tambao deposits in Upper Volta, 

 constituting 9 million tons of 50 percent Mn oxide 

 ore plus possibly a greater amount of high-grade 

 manganese carbonate, now without transportation 

 facilities. 



HYPOTHETICAL RESOURCES 



Included as hypothetical resources are some de- 

 posits about which too little is known to include 

 them as identified resources, such as some reported 

 in eastern Bolivia and western Brazil; that such 

 deposits exist is known, but details of size and grade 

 ar6 not accurate enough to include the resource as 

 identified. Similarly, a large area of the southern 

 Ukraine is underlain by manganese deposits like 

 those mined at Nikopol ; their presence is said to be 

 indicated by widely scattered drilling, but the possi- 

 ble extent and grade of the whole resource are un- 

 known, and given the enormous known reserve, there 

 is no incentive to establish those facts. Clearly, esti- 

 mates of such resources can be scarcely more than 

 informed guesses — and not very well informed at 

 that. 



The assumptions on which these estimates are 

 based are : ( 1 ) sedimentary manganese deposits laid 

 down in a shelf or platform environment may be very 

 extensive, and (2) the possible extent may be judged 

 from the continuity of the geologic environment as 

 witnessed by the associated rocks, even though the 

 manganiferous layer (s) are buried beneath younger 

 rocks. Thus the Molango manganiferous zone is 

 known for some 80 kilometers along strike, although 

 it is below present ore grade for most of that dis- 

 tance. Who can say what might be revealed by 

 exploration back from the outcrop, which is a for- 

 tuitous sample of a much more extensive mangani- 

 ferous zone. 



Sedimentary deposits in small tectonic basins, 

 such as some of the Moroccan deposits, cannot be 

 thus extrapolated, nor can the spotty and relatively 

 small hypogene or volcanogene deposits. Similarly, 

 although small deposits of manganese oxide formed 

 by the weathering of manganiferous dolomite or 

 limestone, such as those along the west foot of the 

 Blue Ridge in the Appalachians, remain to be discov- 

 ered, what will be the cost and the expectable eco- 



nomic return? Such small deposits are not here 

 included. Some districts with residual ore of this 

 type, such as the Postmasburg district in South 

 Africa, have produced millions of tons although 

 known reserves probably never exceeded half a mil- 

 lion tons and are here included on the basis of past 

 productivity. 



The sea-floor nodules, of course, will represent a 

 great resource of manganese and some other metals 

 when problems of extraction, metallurgical treat- 

 ment, and legal status have been solved. The true 

 extent of this resource is not yet even approximatly 

 known, but exploration is continuing, and the re- 

 source may well eventually reach billions to tens of 

 billions of minable tons. Resource data on nodules 

 given in table 76 are subject to gross modification. 



Table 77 gives details of resources and grade of 

 known significant deposits of manganiferous rock 



Table 77. — Major identified manganese resources ' of the 

 United States 



[In millions of long tons. Data slightly modified from Pavlides, (in Hewett 

 and others, 1956, p. 214)] 



Average 

 Raw grade Contained 



District material (percent Mn 



Mn) 



Cuyuna Range, Minn 460 6 22.5 



Aroostook County, Maine 280 9 25.2 



Chamberlain, S. Dak 69 15.5 10.7 



Artillery Peak, Ariz 156 4 6.2 



Pioche, Nev 3 10 0.3 



Leadville, Colo 3 15 0.5 



Total 961 6.8 66.4 



1 Specific, identified mineral deposits that may or may not be evaluated 

 as to extent and grade, and whose contained minerals may or may not be 

 profitably recoverable with existing technology and economic conditions. 



that have been considered as potential sources of 

 manganese in the United States. These deposits are 

 included in the identified rsources shown in table 76. 

 Brooks (1966, p. 70-92) ably discussed the tech- 

 nical and economic problems involved in developing 

 these domestic deposits ; to the authors' knowledge, 

 no breakthroughs have been made in the metallurgi- 

 cal problems since Brooks' analysis was made. Be- 

 cause capacity of the high-grade ore producers in 

 Brazil, Gabon, South Africa, and Australia was being 

 greatly increased in 1971-72, it is doubtful that the 

 world price of manganese in constant dollars will rise 

 significantly in the near future; the price is lower 

 now in constant dollars than for many years. Ac- 

 cordingly, there is now little stimulus to search for 

 and develop the hypothetical resources here discussed 

 or the speculative resources discussed below. 



SPECULATIVE RESOURCES 



Speculative resources are impossible to quantify. 

 Manganese deposits of usable mineralogy, size, and 

 grade are too sporadically distributed to permit 



