how to extract gold from mines

What is gold mining?

Gold mining is a mining resource that extracts gold.

How is gold mined?

Gold is extracted in four different ways. Alluvial mining, hard rock mining, by-product mining and gold ore processing.

panning

Gold prospecting is a manual technique for separating gold from other materials. Large, shallow ponds are filled with sand and gravel containing gold. The pan is immersed and shaken in the water, to sort out the pebbles, gold, and other materials. It quickly settles to the bottom of the pan because gold is denser than rock.


Wash is usually removed from the layers of the stream, often at the inner bend in the stream, or from the rock shelf of a stream, where the density of the gold allows it to concentrate, a type called a placer deposit.

gonorrhea

It has always been a very common practice for small scale prospecting and mining to use a sluice box to extract gold from placer deposits. Basically, a sluice box is a man-made channel with a riffle at the bottom. In order to allow the gold to leak out of the suspension, the guns are designed to create dead zones.


In order to direct the flow of water, the box is placed in the stream. At the top of the box a gold carrier is placed. The materials are moved by current through the volts as gold and other dense materials are deposited behind the guns. Less dense materials flow like waste out of the box.

shoveling

While this method has been largely replaced by modern methods, small miners use suction dredgers to perform some dredging. Small machines that float on water are usually operated by one or two people. The suction dredger consists of a floating supported sluice box connected to a suction hose which is controlled by an underwater miner.


State dredging permits specify a seasonal time period and area closures in many US gold dredging areas to avoid conflicts between dredging and spawning time. Some states, such as Montana, require a comprehensive licensing procedure, including US permits. Corps of Engineering, Montana Department of Environmental Quality, and local county water quality boards.

Rock box

Also called a cradle, it uses shotguns to fish for gold similar to a sluice box in a high-walled box. A swing box uses less water than a sluice box and is suitable for areas with limited water. The rocking action provides the movement of water needed to separate the gold in the placer material from gravity.

Hard rock mining

Hard rock mining extracts gold in rock rather than slivers in loose sediments, and produces most of the world's gold. Open pit mining is sometimes used, for example at the Fort Knox mine in central Alaska. Barrick Gold owns one of the largest open-pit gold mines in North America and is located at the Goldstrike Mine in northeastern Nevada.

Other gold mines use underground mining where tunnels or shafts extract the ore. South Africa has up to 3,900 meters (12,800 ft) the world's deepest solid rock gold mine. The heat is unbearable for humans at such depths, and air conditioning is essential for worker safety.

gold mining by-product

Gold is also produced through mining, as it is not the main product. Large copper mines, such as the Bingham Canyon Mine in Utah, often recover copper with significant amounts of gold and other minerals. Some sand and gravel pits, such as those around Denver, Colorado, in wash operations may recover small amounts of gold.


The largest gold-producing mine in the world, the Grasberg Mine in Papua, Indonesia, is primarily a copper mine.

gold ore processing

cyanide process

Cyanide extraction of gold can be used in areas where gold-bearing rocks are present. The sodium cyanide solution is mixed with finely ground rocks that have been shown to contain gold or silver, and then separated from the ground rocks as gold cyanide or silver cyanide solution. To precipitate the remaining minerals of zinc, silver and gold, zinc is added. The zinc is removed with sulfuric acid, leaving a silver or gold sludge that is generally melted into an ingot and then shipped to a metal refinery for final processing into 99,9999% pure metal.


In recent years, the alkali cyanide lysis technology has been greatly developed. It is particularly suitable for processing low-grade gold and silver ore (eg less than 5 ppm gold), but its use is not limited to these ores. This extraction method has several environmental hazards, largely due to the high acute toxicity of the cyanide compounds involved.


Mercury process

Historically, mercury was widely used in alluvial gold mining to form mercury-gold amalgam with smaller gold particles, thus increasing the rate of gold recovery. In the 1960s, mercury ceased to be widely used. However, in artisanal and small-scale gold mining (ASGM), mercury is still used, more often than not, in secret gold prospecting. It is estimated that 45,000 metric tons of mercury used in California for placer mining has never been recovered.


gold extraction


Removing gold-bearing rocks from the Earth is only the first step. To isolate pure gold, mining companies use a complex extraction process. The first step in this process is to break large pieces of rock into smaller pieces. In a mill, large machines known as crushers reduce the ore into pieces no larger than road gravel. The gravel-like material then enters rotating drums filled with steel balls. In these drums, the ore is ground into a fine slurry or powder.


Next, mill operators thicken the slurry with water to form pulp and run the pulp through a series of filter tanks. Leaching dissolves the gold from the ore using a chemical solvent. The most common solvent is cyanide, which must be combined with oxygen in a process known as pulping carbon. When the cyanide and oxygen react chemically, the gold in the core dissolves. When workers insert tiny grains of carbon into the tank, the gold sticks to the carbon. Filtering the pulp through a sieve separates the gold-bearing carbon.


The carbon moves to a stripping vessel where a hot caustic solution separates the gold from the carbon. Another set of screens filters carbon granules, which can be recycled for future processing. Finally, the gold-bearing solution is ready for the electroextraction process, which recovers gold from chemical leaching materials. In electroreduction, operators pour the gold-bearing solution into a special container known as a cell. The positive and negative terminals of the cell introduce a strong electric current into the solution. This causes gold to pool on the negative terminals.


Smelting, which yields nearly pure gold, involves melting the negative ends in a furnace at about 2,100°F (1,149°C). When workers add a chemical mixture known as flux to the magma, the gold separates from the metal used to make the stations. Workers pour flux, and then gold. Dies are used to convert liquid gold into solid bars called Dory bars. These low purity bars are then sent to refineries around the world for further processing.