18 



sources, more than 1 billion tons as known "submarginal," and nearly 

 2 billion tons of inferred but undiscovered resources.^^ 



Considering the continental shelves of the world as occupying 10 

 million square miles, and assuming a 10 per cent deposit similar to that 

 of the California shelf, Mero concluded that the continental shelves of 

 the world should contain 300 billion tons of phosphorite. If 10 per 

 cent of this amount w^as economical to mine, the reserves of sea-floor 

 phosphorite would be 30 billion tons. At the rate of present world con- 

 sumption, this supply would last 1,000 years.^* 



Depending on its grade and phosphate content, phosphate rock cur- 

 rently mined on land ranges in price from $6 to $12 per ton at the mine 

 site. The value of submarine phosphorite relative to land deposits will 

 be considered later in context with technology and economics. 



MANGANESE NODULES 



Undersea deposits of manganese and iron oxides precipitate from 

 sea water in much the same way as do phosphorite nodules — the col- 

 loidal particles adhering to any grain or rock fragments and growing 

 by accretion, layer over concentric layer, to form an onion-like struc- 

 ture. Each form assumes the shape of its nucleus, sometimes forming 

 crusts on surfaces of submarine rock outcrops or coatings on animal or 

 plant remains. They range in size from half an inch to more than six 

 inches, with an overall average of two inches. 



Manganese nodules vary greatly in composition, from region to re- 

 gion as well as from nodule to nodule. The chemical constituents are 

 mostly oxides of manganese, iron, silicon, and aluminum, with calcium 

 and magnesium salts. Nodules sampled since the Challenger expedition 

 have been analyzed extensively, and numerous other elements have been 

 found. Most of the recent investigations, however, have focused the 

 attention of the mining industry on such constituents as cobalt, nickel, 

 and copper, rather than manganese alone. 



Although present knowledge of the distribution and extent of man- 

 ganese nodules in the world ocean is rudimentary, the nodules appear 

 to be almost ubiquitous. Some oceanographic expeditions have dredged 

 mananese nodules at practically every station in the Pacific, Atlantic, 

 and Indian Oceans. Manganese nodules have been found even in Lake 

 Michigan. They are known to occur particularly beyond the continental 

 shelf, in the abyssal plains and oceanic deeps such as the Mariana 

 Trench in the Pacific, deeper than 22,000 feet. Extensive research and 

 analyses have been done on nodules from numerous localities, par- 

 ticularly on their growth rates and concentrations. Accretion rates 

 in the order of 0.01 to 1 millimeter per 1,000 years are considered 

 normal growth in deep waters. In shallower waters, some samples 

 showed accretion rates close to 1 millimeter per year. 



23 Vincent E. McKelvey. "Mineral potential of the submerged parts of the continents." 

 In "Mineral Resources of the World Ocean." Proceedings of a Svmposium held at the 

 Naval War College, Newport, R.I., July 11-12, 1968. Edited by Elizabeth Keiflfer. (Uni- 

 versitv of Rhode Island, Occasional Publ. No. 4, 1968), page 34. 



McKelvey defined marginal resources as material that might be produced at prices not 

 more than fifty percent higher than those prevailing now, or with comparable advances 

 in technology. Over the longer period and with technological advances, resources recover- 

 able at costs two or three times more than those produced now may have some foreseeable 

 use and prospective value. These were termed submarginal resources. 



2* Mero, op. cit., page 73. 



