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Minerals: A Nonrenewable Resource
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HOW MINERALS FOUND AND EXTRACTED
HOW MINERALS FOUND
AND EXTRACTED
Discovering Mineral
Deposits measurement is to help locate valuable minerals deposits.
Aerial or satellite photography sometimes discloses geological
formations that are associated with certain types of mineral deposits.
Aircraft and satellite instruments that measure the Earth's magnetic
field and gravity can reveal certain types of deposits. Geological
knowledge of the Earth's crust and how minerals are formed is also used
to estimate locations of possible mineral deposits. Once these sites are
identified, geologists drill or tunnel for mineral samples and analyze
their compositions.
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Seismographs, which are used to detect
earth quacks, also provide valuable clues about minerals deposits.
Deposits on the ocean floor cannot be
estimated until detailed three-dimensional maps of the sea flour
are produced, usually with the aid of depth-measuring devices.
Sophisticated computer analysis is necessary to evaluate the complex
data recorded by such devices.
Extracting Minerals
The depth of a particular deposit
determines whether it will he extracted by surface mining, in which
minerals are extracted near the Earth's surface, or subsurface
mining, in which minerals that are too deep to be removed by surface
mining are extracted. Surface mining is more common because it is
less expensive than subsurface mining. However, because even
surface mineral deposits occur in rock layers beneath the Earth's
surface, the overlying layers of soil and rock (called overburden)
must first be removed, along with the vegetation growing in the
soil. Then giant power shovels scoop the minerals out of the Earth. |
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There are two kinds of surface mining.
Iron, copper, stone, and gravel are usually extracted by open-pit
surface mining, in which a hole is dug in the Earth's surface. Large
holes that are formed by open-pit surface mining are called quarries. In
strip mining, a trench is dug to extract the minerals (sec Figure
10-5). Then a new trench is dug parallel to the old one; the overburden
from the new trench is put into the old trench, creating a hilt of loose
rock known as a spoil bank.
Subsurface mining is, which is done
underground and is more complex, may he done with a shaft mine or a
slope mine; both types. A shaft mine is a direct vertical shaft
to the vein of ore. The ore is broken apart underground and then
hoisted through the shaft to the surface in buckets. A slope mine
has a slanting passage that makes it possible to haul the broken ore
out of the mine in cars rather than hoisting it up in Kicked.
Subsurface mining disturbs the land less
than surface mining, but it is more expensive and more hazardous for
miners. There is always a risk of death or injury from explosions or
collapsing walls, and prolonged breathing of dust in subsurface mines
can result in lung disease.
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