PLANET EARTH - The Incredible Visual Guide Part 10 pps

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For thousands of years, people have mined native

metals such as gold, silver, and copper, and turned

them into tools, weapons, and ornaments. At some

point, they discovered that heating far more abundant

metal ores in a charcoal furnace separated the pure

metal, and this led to the widespread use of materials

like iron. Other minerals such as flint, building stone,

and gemstones have also been mined since prehistory.

Fuels such as coal, oil, and natural gas have been

exploited more recently. The three main techniques

are quarrying, deep shaft mining, and drilling into

the ground to tap buried oil and gas reserves.

MINING 1 STONE QUARRY

Building stone has always been a

valuable resource. Originally chipped

out and shaped using hand tools, it is

now extracted using carefully placed

explosive charges, or sliced out by

machines. The stone being quarried

here in Italy is Cararra marble, one of

the finest of all stones. It has been

used since Roman times for

prestige building

projects and

sculptures such

as the work of

Michaelangelo.

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2 STRIP MINE

Where minerals occur near the surface, they

can be extracted by digging out a deep pit, or

strip mine. The Bingham Canyon mine in Utah

has been under excavation since 1908 and is now

the largest artificial hole on Earth. The pit itself is

¾ miles (1.2 km) deep and measures

2½ miles (4 km) across.

3 HYDRAULIC MINING

Heavy metals such as gold can be extracted from

soft sediments using high-pressure hoses. The

principle is similar to panning, but it processes far

more material. The sediments are washed through

enormous sluices that retain the metal while

the waste flows away with the water. The

process can be extremely destructive,

however, sweeping away entire hills

and polluting rivers.

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4 PANNING FOR GOLD

The fact that gold exists naturally in

its native form makes it possible for

people to extract it using the most

basic methods, such as panning.

This involves swirling water through

gold-bearing sediments to carry away

the lighter particles and leave the

heavy gold. Gold is so rare, however,

that days of work by these

panners in Vietnam are

likely to yield just

a few grains of the

precious metal.

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