17 



rock is composed mainly of calcium phosphate, and more than half of 

 what is mined on land goes primarily for the manufacture of agricul- 

 tural fertilizers. A smaller percentage is used in the manufacture of 

 organic and inorganic chemical compounds of phosphorus. 



Phosphorite is formed by the precipitation of phosphates from 

 sea water. These dissolved phosphates have probably come from de- 

 cayed phosphatic matter in regions where sudden and extreme en- 

 vironmental changes result in massive kills of marine organisms. In 

 its circulation through the oceanic domain, the phosphate-rich water 

 passes through regions where little or no detrital sedimentation is 

 taking place. In these regions of depositional quiescence the dissolved 

 phosphates begin to precipitate from sea water and accumulate on 

 the ocean floor. ^° 



Submarine phosphates are deposited in the form of irregular accre- 

 tionary nocluies, tiat slabs, and coatmgs on sand grains and rock frag- 

 ments. They vary in shape and size, some weighing between 150 and 

 250 pounds. Large areas of the ocean floor are blanketed with modular 

 phosphorite. Occurrences are known from closely near shore to more 

 than 200 miles offshore, in depths ranging from 60 feet to more than 

 11,000 feet.^^ Sampling and preliminary exploration around the world 

 indicate the presence of phosphate rock on the east and west coasts of 

 North and South America, off South Africa, northwest Africa, and 

 Equatorial West Africa. In places where oceanographic data were suc- 

 cessful in locating seawater upwelling and detecting phospha,te-rich 

 waters, the prospects are considered good that phosphate rock is pres- 

 ent. Examples of such upweilmg areas include northwestern Aus- 

 tralia, the Timor Sea, the eastern Araf ura Sea, the Coral Sea, and the 

 Tasman Sea. 



Although there has been no production of submarine phosphate rock 

 on a commercial scale, some deposits have been surveyed and current 

 investigations reflect the increasing interest of mining companies 

 in these offshore minerals. The most extensive of these investigations 

 have been offshore southern California, U.S.A., and Baja California, 

 Mexico. Phosphorite nodules were first discovered off the coast of 

 southern California in 1937. Extensive sampling and exploration has 

 been conducted since, the most recent being the investigations of the 

 sand deposits offshore Baja California, Mexico, by Bruno d'Anglejan 

 (Ph. D. Thesis, 1964) and by the Global Marine Company in 1966. 



John L. Mero (1965) estimated that the California deposits cover 

 about 10 per cent of the potentially workable area of 36,000 square 

 miles. The concentration averages about 22 pounds of phosphorite 

 nodules for every square foot of sea floor, and the deposits available for 

 mining exceed one billion tons.-^ More recently, the California deposits 

 were estimated at 100 million tons classed as known "marginal' re- 



2» The phenomenon of upwelling of ocean waters appears to be the most accepted theory 

 for the origin of submarine phosphates. The knowledge of the processes forming phosphate 

 rock and its depositional environment is essential to the successful exploration for, and 

 locating, these deposits. 



a During the oceanographic expedition of the British corvette H.M.S. Challenger (1872- 

 1876) phosphorite nodules were recovered from a depth of 11,400 feet on the Agulhas 

 Bank off South Africa. 



22 John L. Mero, "The Mineral Resources of the Sea." (New York, Elsevier, 1965), page 71. 



