What is mining and recovery?
Various mining techniques are employed worldwide to extract this most precious of metals from the earth. The oldest of these methods is called placer mining, more commonly known as panning. As a result of years of erosion the rock containing the gold disintegrated and the gold particles flowed into nearby rivers and streams. As gold resists weathering, pieces ranging from dust-size up to large nuggets were recovered by prospectors as they used their pans to wash through the silt and gravel from the river bottoms. Gold is heavier than sand so the unwanted material could be gently rinsed away leaving the particles of gold behind.
Open pit mining is another technique used when the gold is close to the earth's surface. In Brazil, for example, prospectors (garimpeiros) hand-dig open pits half a mile wide and up to 600 feet deep. After carrying 60-pound sacks of gold-bearing rock up the steep slopes the rock is pulverized and the tiny flecks of gold are separated from the gravel by use of a sluice box. This process is similar to panning, but can be accomplished on a much larger scale. Open pit mining is also employed in such major gold-producing countries as the United States and Australia, where huge quantites of rock are removed from the ground and crushed mechanically.
How deep is do you have to go?
As the surface gold is exhausted, miners are forced to go deeper in search of the metal. It is a world of shafts and tunnels, motors and drills, locomotives and air conditioning. The deepest working are about 12,000 feet below the surface with ever deeper mines being dug as technology advances. These deep shaft mines are located in the United States, South Africa, Australia, and Canada.
Mining is a difficult and expensive process. Depending on the richness of the ore, as many as 17 tons of rock need to be extracted and processed to yield one ounce of pure gold--not a simple undertaking.
How is Gold refined? After the ore is crushed, it must be chemically treated and smelted to yield pure gold. The crushed ore is ground into a fine powder which is treated with a chemical (cyanide) to dissolve the gold. It then passes through a complicated series of filters, clarifying tanks, storage tanks and precipitation plants. The result of the extraction process is a rough bar, 88% pure, containing other metals such as silver, copper, lead and zinc. The rough bars are then refined even further, up to 99.6% or 99.99% purity. Extraordinary degrees of measuring accuracy are used so that the gold content of the bars can be determined with minute precision. Each bar weighs 27.4 pounds or 400 troy ounces, which is the standard weight used for international trading.
