Gold Essay, Research Paper
Antwan Lucas
Gold
Gold, symbol Au , soft, dense,
bright yellow metallic element. Gold is one of the
transition elements of the periodic table (see Periodic
Law); its atomic number is 79.
Pure gold is the most malleable and ductile of all the
metals. It can easily be beaten or hammered to a
thickness of 0.000013 cm (0.000005 in), and 29 g (1.02
oz) could be drawn into a wire 100 km (62 mi) long. It
is one of the softest metals (hardness, 2.5 to 3) and is
a good conductor of heat and electricity. Gold is bright
yellow and has a high luster. Finely divided gold, like
other metallic powders, is black; colloidally suspended
gold ranges in color from ruby red to purple (see
Colloid).
Gold is extremely inactive. It is unaffected by air,
heat, moisture, and most solvents. It will, however,
dissolve in aqueous mixtures containing various halogens
such as chlorides, bromides, or some iodides. It will
also dissolve in some oxidizing mixtures, such as
cyanide ion with oxygen, and in aqua regia, a mixture of
hydrochloric and nitric acids. The chlorides and
cyanides are important compounds of gold. Gold melts at
about 1064. C (about 1947. F), boils at about 2808. C
(about 5086. F), and has a specific gravity of 19.3; its
atomic weight is 196.97.
Gold is found in nature in quartz veins and secondary
alluvial deposits as a free metal or in a combined
state. It is widely distributed although it is rare,
being 75th in order of abundance of the elements in the
crust of the earth. It is almost always associated with
varying amounts of silver; the naturally occurring
gold-silver alloy is called electrum. Gold occurs, in
chemical combination with tellurium, in the minerals
calaverite and sylvanite along with silver, and in the
mineral nagyagite along with lead, antimony, and sulfur.
It occurs with mercury as gold amalgam. It is generally
present to a small extent in iron pyrites; galena, the
lead sulfide ore that usually contains silver, sometimes
also contains appreciable amounts of gold. Gold also
occurs in seawater to the extent of 5 to 250 parts by
weight to 100 million parts of water. Although the
quantity of gold present in seawater is more than 9
billion metric tons, the cost of recovering the gold
would be far greater than the value of the gold that
could thus be recovered.
The metal has been known and highly valued from earliest
times, not only because of its beauty and resistance to
corrosion, but also because gold is easier to work than
all other metals. In addition, gold was easier to obtain
in pure form than the other metals. Because of its
relative rarity, gold became used as currency and as a
basis for international monetary transactions (see
Dollar; Gold Standard). The unit used in weighing gold
is the troy ounce; 1 troy ounce is equivalent to 31.1
grams.
The major portion of the gold produced is used in
coinage and jewelry (see Metalwork). For these purposes
it is alloyed with other metals to give it the necessary
hardness. The gold content in alloys is expressed in
carats (see Carat). Coinage gold is composed of 90 parts
gold to 10 parts silver. Green gold used in jewelry
contains copper and silver; white gold contains zinc and
nickel, or platinum metals.
Gold is also used in the form of gold leaf in the arts
of gilding and lettering. Purple of Cassius, a
precipitate of finely divided gold and stannic hydroxide
formed by the interaction of auric chloride and stannous
chloride, is used in coloring ruby glass. Chlorauric
acid is used in photography for toning silver images.
Potassium gold cyanide is used in electrogilding. Gold
is also used in dentistry. Radioisotopes of gold are
used in biological research and in the treatment of
cancer (see Isotopic Tracer).
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 center 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.
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 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,
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 Qu bec. 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 474 metric tons in 1998; 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.
In 1998, the amount of gold produced in the United
States was 366 metric tons. U.S. consumption, by major
markets, included jewelry and arts, 55 percent;
industry, 42 percent; and dental, 3 percent. Most
jewelry manufacturing in the United States is centered
in New York City and Providence, Rhode Island.
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.
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