People have mined gold for milennia.
The lure of gold attracts humans like moths to a flame. The California gold rush drew thousands of miners from all around the world. These hardy individuals and the ones who followed them devised ingenious methods to mine the precious metal.
Now modern mining technology is used to reach gold deposits ever deeper in the earth. Huge quantities of rock are drilled and crushed to extract every last bit of gold.
Placer Mining
Panning is a type of placer mining.
Different types of placer mining represent one of the oldest methods of finding gold. This method involves removing gold from river and stream sediments by washing the sediment away with water to leave the heavier gold specks and nuggets behind. Pans, sluice boxes and tables are all used to separate the gold from the river sediments.
According to Professor Richard Cowen, Senior Lecturer in the UC Davis Geology Department, the ancient Greeks washed river sediments over a wool fleece. The heavier gold particles sank deep into the wool which was then dried and burned. The molten gold droplets were then sifted out of the ashes. This method of mining gold was still used in Anatolia in the 1930s.
(See reference 1)
Mercury Amalgamation
Gold mining is causing mercury pollution in the Amazon.
A modern mining method that has its roots in the distant past is amalgamation mining. Amalgamation mining involves crushing the gold-bearing rock and mixing it with mercury. The mercury binds with the gold chemically and is then filtered out of the mix of rock and mud. Heating the mercury and gold mix causes the mercury to evaporate away leaving the gold behind.
This method of mining gold, once used in ancient Rome, is now mainly used in small mining operations in Africa and the Amazon region of South America. According to Elmer Diaz of the University of Idaho, the activity of thousands of miners using mercury amalgamation to extract gold is causing dangerous levels of mercury contamination in the Amazon. (See reference 2)
Cyanide Leaching
Modern gold mining uses cyanide to extract the ore.
The most common method of gold mining in use today is the cyanide leaching process. The ore is first blasted out of the ground with explosives and crushed. The rock is then mixed with cyanide, which dissolves the gold. The gold is then precipitated out of the cyanide by either adding a different metal to the cyanide which causes the gold to precipitate out or by inserting a charged cathode rod into the cyanide. The gold will adhere to the cathode and can be melted off and refined afterwards.
According to University of Wisconsin Department Of Engineering, cyanide leaching produces extremely hazardous waste products including acids and cyanide which have the potential to kill entire ecosystems if not managed properly.
Trenches to capture contaminated runoff water and areas set aside to allow the hazardous chemicals to degrade naturally have been successfully used to prevent pollution from gold mines to contaminate the surrounding landscape. (See reference 3)
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