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In this article we will discuss about the classification of minerals of sea deposits.
1. Minerals of Deposits on Continental Shelves and Slopes:
Minerals of deposits on continental shelves and slopes include zircon, monazite, magnetite, gold placer, diamond, platinum, sulpher, phosphorite and several types of building materials (like sands, gravels, boulders etc.).
Monazite reserves are found in the coastal areas of India, United States of America, Brazil, Sri Lanka, Australia and New Zealand. India has the largest reserve of monazite of the world (90 per cent) in the placer deposits of Kerala coast. About 29 per cent of rutile mineral of the world is found in Australian coast areas.
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In fact, rutile is titanium dioxide and is used for coaling on welded rods. Magnetites are associated with volcanic rocks and thus these are found in those continental shelves and slopes which are characterized by valucanicity. Magnetites are, thus, found along the circum-Pacific volcanic belt i.e., along the western coastal areas of North and South America and eastern coasts of Asia. Japan coastal areas are estimated to have a magnetite reserve of 36 million tonnes.
Cassiterite is a type of tin which is separated due to weathering of granites. Maximum reserves of cassiterites are found in the coastal areas of Thailand, Malaysia and Indonesia. Gold deposits are found in the continental shelves of Alaska and Oregon (USA), Chile, South Africa and Australia but its extraction is commercially not beneficial because of extraction cost.
Phosphorites are mixed with muds and sands of continental shelves and slopes and are found in nodule form. Phosphorites are used for the manufacturing of fertilizers. Their estimated world reserves are 50 million tonnes, which are found in the continental shelves of Mexico, Peru, Australia, Japan and South Africa and their extraction at commercial level has yet to be started.
2. Minerals of Deep Ocean Bottom Deposits:
Manganese nodules are the most significant minerals to be found in the ocean bottom deposits. Pacific Ocean contains the largest deposit of manganese nodules upto the depth of4000m. It may be pointed out that manganese nodules comprise several minerals like nickel, copper, cobalt, lead, zinc, iron, silicon but there is maximum percentage of iron and manganese. Blake plateau is the second largest area of manganese nodules.
These are derived through two most prevalent techniques e.g.:
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(i) Air lift technique, and
(ii) Continuous bucket line system.
Commercial mining of manganese nodules has not developed because of very high mining cost.
3. Subsurface Minerals:
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Subsurface minerals are mostly found in the oceanic crusts of continental shelves and include mineral oil and natural gas. Many countries have already started commercial production of petroleum and natural gas. As regards the developed marine mineral resources, mineral oil and natural gas are the most developed marine mineral resources. There is great possibility of their expansion and development in future.
Mineral oil and natural gas together contribute 90 per cent of all marine mineral resources. Offshore oil fields have been developed in the continental shelves of Mexican gulf, Persial gulf, North Sea, North, Alaska, Mexico, South Californian coast, Arctic Sea, India, Brazil, Australia, Taiwan, Japan etc. Besides, offshore oilfields are being developed in Indonesia, east Africa, north-west Africa, Tasmania, East Asia etc.
Reserves of offshore mineral oil have been explored in the offshore regions of Konkan coast (Maharashtra), Gujarat coast, Malabar and Coromandal coasts, Krishna-Cauvery delta coast, Sundarban etc. From the standpoint of production, three offshore oil fields of India are most significant e.g. Bombay High, Bassein and Aliabet. Bombay (Mumbai) High offshore oil fields are located 176 km north-west of Mumbai and are spread over an area of 2,500 square kilometres.
The estimated oil reserve is 200,000,000 tonnes. Production started in 1976 and oil is drilled from the depth of 1400m. Bassein offshore oilfields are located to the south of Mumbai High, the production of which may be more than Mumbai High oilfields if fully developed. Aliabet offshore oilfields are located 45km away from Bhavnagar in the Gulf of Khambat.