Blake Plateau'^ 

 (averages) 



15 percent 

 11 



0.3 



0.4 



0.1 



The above figures compare with an average grade of 35-55 per cent manganese being mined from land 

 deposits in various producing countries. 



The mineralogic composition of manganese nodules is commonly a mixture manganese-oxide 

 minerals, iron hydroxide, clay minerals, and small amounts of other minerals. Copper, cobalt, nickel j 

 and other elements substitute for manganese or iron in the crystal structure of the manganese oxides. It 

 is generally beUeved that the nodules are formed by precipitation of elements from solution, most likely 

 in colloidal form, and by a process of particle agglomeration. 



Goldberg and Arrhenius'' suggest that the ocean is saturated with manganese and iron and that 

 addition of these two elements by river runoff causes precipitation of hydrated oxides in colloidal form. 

 The colloidal particles are electrically charged and while settUng down in water, tend to act as scavengers 

 and remove cobalt, nickel, copper, molybdenum, zinc, lead, and other metals from sea water. Small 

 particles of detrital minerals and organic debris settling through water could act as centers of accretion 

 and would be effective in extracting manganese and other metals from the water. 



When the colloidal particles reach the seafloor they are attracted to any protruding objects such as 

 rock fragments because such objects act as superior electric conductors in attracting the electrically 

 charged colloidal particles. Bottom currents carry a new supply of water bearing the colloids to the 

 nucleus and the nodules are in this way enlarged layer by layer by this process of particle agglomeration. 

 As long as a nodule is exposed on the sea floor it can continue to grow but once buried beneath sea floor 

 sediments it will stop growing. 



The rate of growth of nodules on the deep sea floor has been estimated from observational data and 

 radiometric observations as on the order of 0.01 to 1.0 millimeter per 1,000 years. However, nodules 

 occurring locally on continental slope areas close to continents may form more rapidly— perhaps at the 

 rate of 0.01 to 1 .0 millimeter per year.' * 



There seems to be no doubt that the gross amounts of manganese nodules on the seafloor are 

 enormous. However it is the beUef of most people in the mining business that the economic potential is 

 highly uncertain owing to: 1) the low grade compared to land sources; 2) difficulty in recovering the 

 nodules in thousands of feet of water, and 3) problems of extracting the individual fine-grained metal 

 components. Even a major breakthrough in extractive metallurgical processes might not be the answer as 

 it would bring large quantities of low grade manganese ore on land into competition with sea floor 

 nodules. It may well develop that when manganese nodule deposits are worked it will be for their 

 by-product metals cobalt, nickel, and copper and not for their manganese. 



The general outiook for manganese nodule mining is considered poor until the 1980-85 period and 

 after that fair. 



Although interest in manganese from marine sources is chiefly focused on nodules, it has been 

 pointed out by McKelvey and Chase' ^ that marine sediments hold a potential for thick high-grade 



'^John L. Mero, The Mineral Resources of the Sea (New York: Elsevier, 1965). 



'*F. T. Manheim and R. M. Piatt, Summary of Investigations Conducted in 1967, Woods Hole Oceanographic 

 Institution Ref. No. 68-32 (unpublished paper). 



"e. D. Goldberg and G. Arrhenius, "Chemistry of Pacific Pelagic Sediments," Geochimica et Cosmochimica Acta, 

 Vol. 13, 1958. 



F. T. Manheim, in "Mineral Facts and Problems," Bureau of Mines Bull. No. 630, 1965. 



V. E. McKelvey and Livingston Chase, "Selecting Areas Favorable for Subsea Prospecting," in Exploiting the 

 Ocean (Washington, D.C.: Marine Technology Society, 1966), pp. 44-60. 



VII-141 



