MINERAL RESOURCES IN THE OCEAN

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Mineral resources in the ocean
Introduction: Oceans cover 70 percent of Earth's surface, host a vast
variety of geological processes responsible for the formation and
concentration of mineral resources, and are the ultimate repository of many
materials eroded or dissolved from the land surface. Hence, oceans contain
vast quantities of materials that presently serve as major resources for
humans. Today, direct extraction of resources is limited to salt; magnesium;
placer gold, tin, titanium, and diamonds; and fresh water.
Ancient ocean deposits of sediments and evaporites now located on land
were originally deposited under marine conditions. These deposits are being
exploited on a very large scale and in preference to modern marine
resources because of the easier accessibility and lower cost of terrestrial.
These mounds of sea salt were mined from deeply buried beds deposited
when seawater evaporated in an ancient environment. The beds were
preserved by being covered and then uplifted in a modern terrestrial setting.
Mining accounts for most of the annual salt production, even though it also
can be obtained by evaporating ocean water Resources. Yet the increasing
population and the exhaustion of readily accessible terrestrial deposits
undoubtedly will lead to broader exploitation of ancient deposits and
increasing extraction directly from ocean water and ocean basins.
Principal Mineral Resources:
Resources presently extracted from the sea or areas that were formerly in
the sea range from common construction materials to high-tech metals to
water itself. Chemical analyses have demonstrated that seawater contains
about 3.5 percent dissolved solids, with more than sixty chemical elements
identified. The limitations on extraction of the dissolved elements as well as

2. the extraction of solid mineral resources are nearly always economic, but
may also be affected by geographic location (ownership and transport
distance) and hampered by technological constraints (depth of ocean
basins). The principal mineral resources presently being extracted and likely
to be extracted in the near future are briefly considered here.
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 Salt:
Salt, or sodium chloride, occurs in seawater at a concentration of about 3 percent and
hence constitutes more than 80 percent of the dissolved chemical elements in seawater.
The quantity available in all the oceans is so enormous that it could supply all human
needs for hundreds, perhaps thousands, of years. Although salt is extracted directly
from the oceans in many countries by evaporating the water and leaving the residual
salts, most of the nearly 200 million metric tons of salt produced annually is mined from
large beds of salt. These beds, now deeply buried, were left when waters from ancient
oceans evaporated in shallow seas or marginal basins, leaving residual thick beds of salt;
the beds were subsequently covered and protected from solution and destruction.
 Potassium:
Like the sodium and chlorine of salt, potassium occurs in vast quantities in
sea water, but its average concentration of about 1,300 parts per million (or
0.13 percent) is generally too low to permit direct economic extraction.
Potassium salts, however, occur in many thick evaporate sequences along
with common salt and is mined from these beds at rates of tens of millions
of metric tons per year. The potassium salts were deposited when sea water
had been evaporated down to about one-twentieth of its original volume.
 Magnesium:
Magnesium, dissolved in sea water at a concentration of about 1,000 parts
per million, is the only metal directly extracted from sea water. Presently,
approximately 60 percent of the magnesium metal and many of the
magnesium salts produced in the United States are extracted from sea water

3. electrolytically. The remaining portion of the magnesium metal and salts is
extracted from ancient ocean deposits where the salts precipitated during
evaporation or formed during digenesis. The principal minerals mined for
this purpose are magnetite (MgCO3) and dolomite (CaMg[CO 3 ] 2 ).
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 Sand and Gravel:
The ocean basins constitute the ultimate depositional site of sediments
eroded from the land, and beaches represent the largest residual deposits of
sand. Although beaches and near-shore sediments are locally extracted for
use in construction, they are generally considered too valuable as
recreational areas to permit removal for construction purposes.
Nevertheless, older beach sand deposits are abundant on the continents,
especially the coastal plains, where they are extensively mined for
construction materials, glass manufacture, and preparation of silicon metal.
Gravel deposits generally are more heterogeneous but occur in the same
manner, and are processed extensively for building materials.
 Limestone and Gypsum:
Limestones (rocks composed of calcium carbonate) are forming extensively
in the tropical to semitropical oceans of the world today as the result
of precipitation by biological organisms ranging from mollusks to corals
and plants. There is little exploitation of the modern limestone as they are
forming in the oceans. However, the continents and tropical islands contain
vast sequences of lime stones that are extensively mined; these limestone
commonly are interspersed with dolomites that formed through digenetic
alteration of limestone. Much of the limestone is used directly in cut or
crushed form, but much is also calcined (cooked) to be converted into
cement used for construction purposes. Gypsum (calcium sulfate hydrate)
forms during evaporation of sea water and thus may occur with evaporite
salts and/or with limestone. The gypsum deposits are mined and generally
converted into plaster of Paris and used for construction.

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 Manganese Nodules:
Covering huge areas of the deep sea with masses of up to 75 kilograms
per square meters, manganese nodules are lumps of minerals ranging in
size from a potato to a head of lettuce. They are composed mainly of
manganese, iron, silicates and hydroxides, and they grow around a
crystalline nucleus at a rate of only about one to 3 millimeters per
million years. The chemical elements are precipitated from seawater or
originate in the pore waters of the underlying sediments. The greatest
densities of nodules occur off the west coast of Mexico (in the Clarion-
Clipper ton Zone), in the Peru Basin, and the Indian Ocean. In the
Clarion-Clipper ton Zone the manganese nodules lie on the deep-sea
sediments covering an area of at least 9 million square kilometers – an
area the size of Europe. Their concentration in this area can probably be
attributed to an increased input of manganese-rich minerals through the
sediments released from the interior of the Earth at the East Pacific
Rise by hydrothermal activity – that is, released from within the Earth by
warm-water seeps on the sea floor and distributed over a large area by
deep ocean currents.
The sea floor contains extensive resources. They are concentrated in
certain regions depending on how they were formed.
Cross-section view of a
manganese nodule: Over millions of years, minerals are deposited around a nucleus.

5. Manganese nodules are composed primarily of manganese and iron. The
elements of economic interest, including cobalt, copper and nickel, are
present in lower concentrations and make up a total of around 3.0 per cent
by weight. In addition there are traces of other significant elements such as
platinum or tellurium that are important in industry for various high-tech
products.
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 Phosphorites:
Complex organic and inorganic processes constantly precipitate phosphate-rich
crusts and granules in shallow marine environments. These are the
analogs (comparative equivalents) of the onshore deposits being mined in
several parts of the world, and represent future potential reserves if land-based
deposits become exhausted.
 Metal Deposits Associated with Volcanism and
Seafloor Vents.
Submarine investigations of oceanic rift zones have revealed that rich
deposits of zinc and copper, with associated lead, silver, and gold, are
forming at the sites of hot hydrothermal emanations commonly called black
smokers. These metal-rich deposits, ranging from chimneyto pancake-like,
form where deeply circulating sea water has dissolved metals from the
underlying rocks and issue out onto the cold seafloor along major fractures.
The deposits forming today are not being mined because of their remote
locations, but many analogous ancient deposits are being mined throughout
the world.
 Placer Gold, Tin, Titanium, and Diamonds:
Placer deposits are accumulations of resistant and insoluble minerals that
have been eroded from their original locations of formation and deposited
along river courses or at the ocean margins. The most important of these
deposits contain gold, tin, titanium, and diamonds.

6. Today, much of the world's tin and many of the gem diamonds are
recovered by dredging near-shore ocean sediments for minerals that were
carried into the sea by rivers. Gold has been recovered in the past from such
deposits, most notably in Nome, Alaska. Large quantities of placer titanium
minerals occur in beach and near-shore sediments, but mining today is
confined generally to the beaches or onshore deposits because of the higher
costs and environmental constraints of marine mining.
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 Water:
The world's oceans, with a total volume of more than 500 million cubic
kilometers, hold more than 97 percent of all the water on Earth. However,
the 3.5-percent salt content of this water makes it unusable for most human
needs.
The extraction of fresh water from ocean water has been carried out for
many years, but provides only a very small portion of the water used, and
remains quite expensive relative to land-based water resources.
Technological advances, especially in reverse osmosis, continue to
increase the efficiency of fresh-water extraction. However, geographic
limitations and dependency on world energy costs pose major barriers to
large-scale extraction.
 OIL AND GAS:
Presently, oil and gas account for 90% of mineral value exploited from the
sea. The major offshore fields are found in the Gulf of Mexico, the Persian
Gulf and North sea, northern coast of Australia, Southern coast of California
and coast of the Artic ocean. There are still many relatively unexplored areas
of the world in the search for oil and gas. These include continental shelves
of East Asia, South Africa, East Africa, Northwest Africa, South America and
Antarctica. The recent discoveries of the giant oil active exploration along
the Gulf of Guinea (Guinea Basin)
Although the cost of drilling and equipping an off-shore well is about three to
four times greater than a similar venture in land, the large size of the
deposits allow offshore ventures to compete favorably. It is a fact that the
oil and gas potential of the deeper areas of the sea floor is still relatively

7. known, but the cost of drilling and development will continue to be the main
focus of ocean mining in the near future.
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 COAL:
Coal deposits under the sea floor are mined when the coal is present in
sufficient quantity to make the operation worthwhile. In Japan under the sea
coal deposits are reached by shafts, which stretch under the sea from the
land
 Other Solutes:
A number of materials are extracted from seawater at some 300 coastal
operations in 60 countries, including rock salt (sodium chloride),
magnesium metal, magnesium compounds, and bromine. Salt recovery
from evaporation of seawater is practiced at many places around the
Mediterranean and western France. Fresh water extracted from seawater
by desalination processes is the most critical mineral, in light of the global
need for an adequate and safe supply of water for consumption,
agriculture and industry. Desalination by reverse osmosis and other
processes is energy intensive. The oceans are the largest reservoir for
water on Earth. Production of freshwater from seawater is expected to
exceed that from all other marine minerals in importance and value as
need continues to grow and alternative energy sources for the
desalination process are developed.
CONCLUSION:
The seabed has vast potential mineral resources with oil and gas being the
most valuable. The contribution of land and gravel is notable whilst
phosphorite nodules have potentials as fertilizer. Also manganese nodules
rich in copper, nickel and Cobalt constitute resources of the future when its
status presently beclouded by disputes over international law with reference
to mining and shared technology is resolved. The discoveries of sulphide
minerals in the deep oceans show these as potential resources of the future
and it has further enhanced our knowledge on the Genesis of volcanic hosted
massive sulphide deposits.

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References:
1. www.google.com
2. www.wikipedia.com
3. MINERAL RESOURCES OF THE OCEAN
BY PROF. T. R. AJAYI
THANK YOU