Offshore mineral resources
F. B.
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When the ninth year had passed over, Kalevala- |
Minerals under the sea come in several forms:
Loose deposits come from three sources. Some are detrital, like sand or gravel, or consist of “placer” deposits containing tin, titanium, gold, rare earths, zirconium and diamonds. Others are of biological origin, such as shells of marine creatures which have turned into sand. A third category originates from elements suspended in water, yielding chemical deposits which produce, for example, barytes or metal-rich sediments.
Rock deposits, which are the undersea extension of seams of coal, tin, iron and other minerals.
Deposits dissolved in sea water, such as sodium chloride, magnesium and iodine.
Offshore mineral extraction has grown to the point that it now involves, or soon will, almost two-thirds of the 103 chemical elements identified in 1869 by the Russian chemist Mendeleyev. Mineral sands, also known as beach sand, come from the bedrock of continents worn away by the weather and the passage of the seasons, especially in tropical latitudes. The minerals are freed and carried away by rivers, first to beaches and then to the seabed of the continental shelf.
Extracting these minerals is important because they have become indispensable to modern technology, which depends heavily on titanium, zirconium and rare earths (which include nine heavy minerals—radioactive thorium, and eight lighter ones). Titanium, considered a strategic metal, provides a white colouring for paper and plastic, and plays an important role in the aeronautical industry and in manufacturing golf clubs and tennis rackets. Zirconium’s refractory qualities make it useful in the thrust nozzles of jet aircraft. Rare earths, which contain quartz or rutile (titanium dioxide), supply state-of-the-art technologies such as the red colour in television pictures or the catalysis of engine exhaust gases. Rutile has an amazing resistance. It does not wear out and cannot be corroded by other chemicals. But deposits of it are scarce and unevenly distributed. The biggest are in Australia, Madagascar, Cameroon, Ghana and Sierra Leone.
Beach sand is mined using huge, super-powerful dredges which can scoop up as much as 2,500 tonnes an hour. Between 90 and 98 per cent of the dredged material is waste which, after the minerals have been separated out by gravity, is put back where it came from. The most conscientious mining companies try to leave the landscape as they found it. They set aside topsoil, and later replace, fertilize and replant it.