The simplest process used for mining gold is panning,
using a circular dish often with a small pocket at the bottom. The
prospector fills the dish with gold-bearing sand or gravel, holds it
under a gentle stream of water, and swirls it. The lighter parts of
the gravel are gradually washed off and the gold particles are left
near the centre of the pan or in the pocket.
As gold mining developed, more elaborate methods were introduced and
hydraulic mining was invented. The hydraulic method consists of
directing a powerful stream of water against the gold-bearing gravel
or sand. This operation breaks down the material and washes it away
through specially constructed
sluices in which the gold settles, while
the lighter gravel is floated off. For mining on rivers, elevator
dredges are generally used. The elevator dredge is a flat-bottomed
boat that uses an endless chain of small buckets to scoop up the
material from the river bottom and empty it on the dredge into a
trommel (a container built of screening). The material is rotated
in the trommel as water is played on it. The gold-bearing sand sinks
through perforations in the trommel and drops onto shaking tables, on
which it is further concentrated. Dredging can also be used in dry
beds of ancient rivers if ample water is within a reasonable distance.
A pit is dug, and the dredge is moved in and floated on water pumped
from the adjacent source.
Extensive underground deposits of gold-bearing rocks are often
discovered by a small outcrop on the surface. Shafts are sunk, as in
coal mining, and the ore is brought to the surface. It is then
crushed in special machines.
Gold is extracted from gravel or from crushed rock by dissolving it
either in mercury (the
amalgam process) or in
cyanide solutions (the
cyanide process). Some
ores, especially those in which the gold
is chemically combined with tellurium, must be roasted before
extraction. The gold is recovered from the solution and melted into
ingots. Gold-bearing rock with as little as 1 part of gold to 300,000
parts of worthless material can be worked at a profit.
The rarest form of gold is a nugget. The largest known nugget, the
Welcome Stranger, weighing 2,284 troy oz (equivalent to 59.0 kg/130.1
pounds), was turned up accidentally, just below the surface of the
ground, by a wagon wheel in Victoria, Australia, in 1869.
Gold Production
Gold production dates from the Etruscan, Minoan, Assyrian, and
Egyptian civilizations, when placer gold was derived from alluvial
sands and gravels by simple processes of washing or panning. Gold was
produced in this manner at an early period in India, central Asia, the
southern Ural Mountains and in the regions bordering the eastern
Mediterranean. With progress in mining technique, primary auriferous
(gold-bearing) veins were exploited; this type of gold mining attained
some importance before the Christian era. During the Middle Ages
little progress was made in gold production and mining.
At the time of the discovery of the Americas the value of the total
gold stock of Europe was probably less than $225 million. During the
succeeding 350 years, from the end of the 15th century to about 1850,
the world gold output totaled about 4,665,000 kg (about 150 million
troy oz). South America and Mexico became large producers of gold
during this period. Spain's domination in South America resulted, in
the 16th century, in a large increase in gold produced in the New
World; some resulted from simple seizure of gold from the Native
Americans, who had long mined the metal. In the same century Mexico
contributed about 9 percent of the total world production. Gold was
discovered in Australia in February 1851, and rich fields were found
there.
By the middle of the 19th century the United States produced a
considerable percentage of the world gold production. In the United
States gold has been produced in two regions: the eastern region along
the Appalachian Mountains, and the western region along the Rocky
Mountains and the Sierra Nevada, Coast, and Cascade ranges. Gold has
been found in numerous places on the eastern slope of the Appalachians
from Newfoundland and Labrador, Canada, to Alabama, although workable
deposits occur only in Nova Scotia and in the southern United States.
In the South the auriferous belt, ranging up to 120 km (75 mi) in
width, extends from Virginia through North Carolina, South Carolina,
and Georgia into Alabama. Both veins and surface deposits have been
worked; some pockets of ore were exceptionally rich. The first gold
shipped to the United States Mint for coinage from the southern states
was from North Carolina in 1804. For the next 20 years the value of
the annual output of North Carolina amounted to less than $2,500. In
1829 Virginia and South Carolina, in 1830 Georgia, in 1831 Alabama and
Tennessee, and in 1868 Maryland shipped gold to the mint for coinage.
The western gold fields extend in the Cordilleran region from Alaska
to Mexico. Gold was discovered first in this region in California on
January 24, 1848, during excavation for a sawmill on land settled by
the American pioneer John Sutter. During the next five years gold
valued at more than $285 million, an amount 21 times greater than the
value of the total previous production of the entire country, was
produced in California. The gold rush took place at this time, when
people from all parts of the world rushed to the new gold district (see
Forty-niners). The discovery furnished the incentive for the
exploration and development of the whole far-western section of the
United States. The Comstock Lode, a famous discovery made in 1859, is
situated on an eastern spur of the Sierras, extending into Nevada.
Placers and veins similar to those of the Sierras are found also in
Oregon and Washington. The Rocky Mountains and the outlying ranges,
which were first prospected in the early 1860s, include an immense
area of gold-bearing territory. Rich gravels have been worked at the
following locales: near Leadville, Fairplay, and in San Miguel County,
Colorado; near Helena and Butte, Montana; along the Snake and Salmon
rivers, Idaho; near Deadwood, South Dakota; at Santa Fe, New Mexico;
and in Alaska.
Placer deposits of gold were discovered on the Yukon River in
Canada and Alaska in 1869. The discovery in 1896 of a rich deposit in
the Bonanza Creek, a headwater of the Klondike River, which in turn is
a tributary of the Yukon, led to another gold rush. In 1910
discoveries were made on Bitter Creek, near Stewart, British Columbia.
In 1911 gold was also discovered in Alaska, some 30 km (some 20 mi)
from the Canadian boundary at the source of the Sixty Mile River,
which rises in Alaska and flows into the Yukon River. Since 1911 the
production of gold in Ontario, in the Porcupine and Kirkland lake
districts, has gone ahead rapidly. Important discoveries of gold mixed
with copper were made in northwestern Québec. The gold production of
Australia has been famous since 1851; the chief centers of production
are in Western Australia and Victoria.
South Africa is the world's leading supplier of gold, producing 376
metric tons in 2003; its most important gold mines are in the
Witwatersrand region. Some 70 other countries produce gold in
commercial quantities, but two thirds of the total worldwide
production now comes from South Africa, the United States, Australia,
China, Canada, and Russia.
On December 31, 1974, the U.S. federal government lifted a 41-year
ban on the private ownership of gold. Around that time gold was
being traded on the London bullion market at record highs approaching
$200 an ounce. After subsequent sharp decreases, prices rose to a high
of $850 in January 1980. They then dropped considerably and in the
early 1990s settled at about $370 an ounce.
