Mining 



319 



Sea Floor 



Mining 



Every cubic kilometer of sea water con- 

 tains about 40,000,000 tons of dissolved 

 solids such as sodium, calcium, magnesium, 

 bromine, iodine, copper, silver, and gold. 

 At 1940 prices these materials would have a 

 value of about a billion dollars if they could 

 be extracted (Smith, 1940). The two most 

 abundant elements in sea water, sodium 

 and chlorine, are separated as salt deposited 

 on the floors of three areas of evaporation 

 ponds in California. The largest of these is 

 at the south end of San Francisco Bay 

 where about 1,000,000 tons is produced an- 

 nually. In southern California salt is also 

 produced in salt ponds at the heads of San 

 Diego Bay and Newport Bay where the an- 

 nual production is about 80,000 and 10,000 

 tons, respectively. The chief uses of the salt 

 produced in southern California are water 

 softening, refrigeration, and stock feeding 

 (ver Planck, 1958). The third most abun- 

 dant dissolved solid in sea water is magne- 

 sium, constituting about 0.13 per cent, or 

 0.01 1 pounds per gallon. Most of the com- 

 mercial production from sea water is at 

 Freeport, Texas, where the easy availability 

 of salt, sulfur, lime, and fuel promotes cheap 

 extraction. Smaller-scale extraction of this 

 important metal has also been developed in 

 California at Moss Landing in Monterey 

 Bay. Along with the magnesium, several 

 thousand tons of bromine, the seventh most 

 abundant element in sea water, has been ex- 

 tracted (Stewart, 1934). Since 1928, iodine, 

 formerly obtained from algae, has been pro- 

 duced from oil field brines of the Los 

 Angeles Basin, the only commercial source 

 in the United States, with an annual pro- 

 duction of possibly 400 tons (ver Planck, 

 1957). 



Some mining of beaches has also been 

 done. Beaches at Redondo Beach, consist- 

 ing of sands having an average of 7 per cent 

 ilmenite, have supplied about 15,000 tons of 

 concentrates mined mostly in 1927-1928 

 (Lydon, 1957). Some beach sands, but 

 mostly dune sands, of El Segundo are mined 



and used for sand blasting and foundry 

 sand. Beach gravels between Carlsbad and 

 Encinitas (Fig. 157) were extensively mined 

 between 1915 and 1948 for grinding stones 

 and as filter aids at $65 /ton (Troxel, 1957). 



Turning to the deeper ocean floor, we 

 find two potential resources, neither of 

 which is yet mined. The first of these is 

 phosphorite which occurs in estimated 

 quantities of about 1 billion tons — on bank 

 tops, shelves, and other high areas. This 

 reserve is about 70 times the total 1954 pro- 

 duction of the United States, mostly from 

 Florida, Tennessee, Idaho, and Montana. 

 At the going price of phosphate rock 

 ($5 /ton) the sea floor phosphorite probably 

 cannot be mined for many years yet. Sim- 

 ilar submerged deposits occur off Florida 

 (Pepper, 1958). Possibly the layers and 

 nodules of manganese with their included 

 copper, nickel, and cobalt will be mined 

 from the deep sea floor before phosphorite 

 is mined from the continental borderland. 

 Comparatively negligible amounts of man- 

 ganese occur on the continental borderland. 



The second potential resource from the 

 sea floor is the basin sediment itself. This 

 is present in inexhaustible quantities, prob- 

 ably at least 3 X 10^- tons in Santa Barbara 

 Basin alone with a probable 4 per cent 

 average organic matter and other small 

 amounts of inorganic nutrients. One pos- 

 sible use for these sediments is as fertilizer 

 — to return the nutrients that have been 

 washed from the land to the sea floor dur- 

 ing past centuries. A rather simple test of 

 the value of basin sediments for growth of 

 plants was made by spreading about 10 kg 

 of it over a square meter of lawn. After the 

 salts had been leached out, the grass be- 

 came a fine dark green, appearing to be 

 healthier than the untreated surrounding 

 area. A second possible use is that of distil- 

 lation by pyrolysis. Tests showed, however, 

 that only about 0.5 per cent of oil by dry 

 weight could be produced, much less than 

 from oil shales. Whether either use will be 

 realized cannot be foretold now, but use 

 will never be prevented by insufficient sup- 

 ply of sediment. 



