Historians believe that gold was the first metal known to man. It was love at first sight; ever since, man has desired gold for its sheer beauty and for the ease with which he can make it into beautiful objects. Because they have survived in situations where objects made of other materials have perished; gold artifacts are a source of much information about ancient civilizations. In such civilizations gold was not used only in jewelry. It gradually became a major symbol of wealth and power. It even became a standard of value, hence the expression "as good as gold." Over the centuries, gold has been used as money and in modern times, it has come to be used in industry such as dentistry, computers, electronic circuits, and even in the aerospace industry.

Egyptian wall relief's from 2300 BC show gold in various stages of refining and mechanical working. During these ancient times, gold was mined from alluvial placers-that is, particles of elemental gold found in river sands. The gold was concentrated by washing away the lighter river sands with water, leaving behind the dense gold particles, which could then be further concentrated by melting. By 2000 BC the process of purifying gold-silver alloys with salt to remove the silver was developed. The mining of alluvial deposits and, later, lode or vein deposits required crushing prior to gold extraction, and this consumed immense amount of manpower. By AD 100, up to 40,000 slaves were employed in gold mining in Spain. The advent of Christianity somewhat tempered the demand for gold until about the 10th century. The technique of amalgamation, alloying with mercury to improve the recovery of gold, was discovered at about this time.

The colonization of South and Central America that began during the 16th century resulted in the mining and refining of gold in the New World before its transferal to Europe; however, the American mines were a greater source of silver than gold. During the early to mid-18th century, large gold deposits were discovered in Brazil and on the eastern slopes of the Ural Mountains in Russia. Major alluvial deposits were found in Siberia in 1840, and gold was discovered in California in 1848. The largest gold find in history is in the Witwatersrand of South Africa. Discovered in 1886, it produced 25 % of the world's gold by 1899 and 40 % by 1985. The discovery of the Witwatersrand deposit coincided with the discovery of the cyanidation process, which made it possible to recover gold values that had escaped both gravity concentration and amalgamation. With E.B. Miller's process of refining impure gold with chlorine gas (patented in Britain in 1867) and Emil Wohlwill's Electro-refining process (introduced in Hamburg, Ger., in 1878), it became possible routinely to achieve higher purity than had been allowed by fire refining.

Silver Facts:

Silver reflects! The film coating on mirror backings is silver. Mirrors are used in telescopes, microscopes, spacecraft and solar panels, as well as bathrooms! Don't forget the silver transparent coating on double-pane thermal windows.

Silver conducts heat! Those silver ceramic lines fired into your car's rear window keep the window clear of frost and ice.

Silver conducts electricity! Silver is the metal of choice for switch contacts because it does not corrode. Every time you start your microwave, dishwasher, television set, car engine, etc., silver contacts complete the electrical circuit. The same thing happens when you tap the keys of your computer keyboard, adjust your car's power seats, or release the power trunk lock. Silver is there.

Silver kills bacteria! Silver chemically affects the cell membranes of bacteria, causing them to break down.

Bacteria do not develop resistance to silver, as they do to many antibiotics. Silver solutions are used in burn treatments. Silver gauze packs the wounds of patients during transport to medical facilities. Silver nitrate drops are used to clean the eyes of newborns. Hikers use portable silver-based water purification systems for drinking water.

Silver rings! Silver has a pure acoustic resonance and is preferred by musicians for making high quality silver bells and musical instruments.

Silver captures images! Silver salts are the basic image capture and forming materials in photography. Every picture of your sweet little darling contains silver, as well as medical/dental x-rays and your favorite movie.

Silver is pretty! Don't forget the silver in your jewelry or traditional tableware. It's a favorite medium because it is soft and malleable, and can be shaped into any form. Silver has been used in cherished heirlooms and gifts for centuries.

Gold Facts:

Gold rocks! Compact discs pressed on 24-karat gold provide the ultimate in sonic quality. Artists available on ULTRADISC II, by Mobile Fidelity Sound, include Elton John, Steve Winwood, B.B. King and Aretha Franklin.

Gold travels! The Pathfinder "robotic geologist" relies on sophisticated electronics to direct its Mars landing and movement. Its intricate gold circuitry enables new computer technology to transmit the Pathfinder's information back to Earth.

Gold communicates! Every time you type an e-mail on your computer, gold circuits relay the keyboard data to the microprocessor. Gold is essential in computer circuitry because of its electrical conductivity and because it does not degrade over time.

Gold protects! Gold-plated reflectors used on Air Force One, the U.S. President's airplane, confuse an incoming missile's heat-seeking signal so the missile's guidance system cannot focus on its target. Gold provides the highest reflectivity of heat radiation

How Gold is Mined

Exploration

The gold mining process begins with geologists discovering a deposit.

Exploration Drilling

After finding indications of gold, drill rigs are used to obtain samples from below the surface. These samples are analyzed for their gold content. If there is enough gold in the deposit to be produced economically, a mine is permitted and developed.

Open Pit Mining

The ore is mined in four steps: drilling, blasting, loading and hauling.

Blasthole Drilling

In the case of a surface mine, a pattern of holes is drilled in the pit and filled with explosives.

Blasting

The explosives are detonated in order to break up the ground so it can be loaded by large shovels or front-end loaders into haul trucks.

Underground Mining

Some orebodies are more economically mined using underground methods. In this case, a tunnel called an adit or a shaft, is dug into the earth. Sort tunnels leading from the adit or shaft, called stopes, are dug to access the ore. The surface containing the ore, called a face, is drilled and loaded with explosives. Following blasting, the broken ore is loaded into trucks and taken to the surface. Once mining is completed in a particular stope, it is backfilled with a cement compound.

Ore and Waste Haulage

The haul trucks transport the ore to various areas for processing. The grade and type of ore determine the processing method used. Higher-grade ores are taken to a mill. Lower grade ores are taken to leach pads. Some ores may be stockpiled for later processing.

Ore Processing

Heap leaching

The ore is crushed or placed directly on lined leach pads where a weak cyanide solution is applied to the surface of the heap. The solution percolates down through the ore, where it leaches the gold and flows to a central collection location. All of the solution is recovered in this closed system, preventing any infiltration into the ground below.

Milling

The ore is fed into a series of grinding mills where steel balls grind the ore to a fine slurry or powder.

Oxidization

Some types of ore require further processing before gold is recovered. In this case, the slurry is pressure-oxidized in an autoclave (shown on right) before going to the leaching tanks or a dry powder is fed through a roaster in which it is oxidized using heat before being sent to the leaching tanks as a slurry.

Leaching

The slurry is thickened and run through a series of leaching tanks. The gold in the slurry adheres to carbon in the tanks.

Stripping

The carbon is then moved into a stripping vessel where the gold is removed from the carbon by pumping a hot caustic solution through the carbon. The carbon is later recycled.

 Electro-winning

The gold-bearing solution is pumped through electro-winning cells or through a zinc precipitation circuit where the gold is recovered from the solution.

Smelting

The gold is then melted in a furnace at about 2,100°F and poured into molds, creating doré bars.

Gold Bullion

Doré bars are unrefined gold bullion bars containing anywhere from 60% to 95% gold.

Refining

The bars are sent to a refinery for further processing into pure gold.

Reclamation

To restore the landscape for future uses such as ranching, recreation or wildlife habitat protection, reclamation, including revegetation, is implemented concurrently during mining.
 

[ Back to Article Index ]