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Significance
In addition to gold ore mining applications, recovering tiny particles of gold from powdered ore during copper processing can yield a profitable amount of gold-filled sludge too. Purifying this gold results in the collection of commercial quantities that cover the cost of the entire refining process. Therefore, microscopic gold recovery is lucrative. More than half of the world's gold production now involves recovering microscopic gold. The chemically supported microscopic gold recovering process made Nevada the largest gold producing area in the United States during the 1960s.
Considerations
By adding chemicals like mercury and cyanide to the gold recovery process, miners can turn previously unprofitable mines into profitable ones. A mine must process roughly 100,000 ounces of ore to recover an ounce of microscopic gold. Recovering this gold with the aid of chemicals produces volumes of toxic solids and liquids.
Common Method
Cyanide leaching is a common microscopic gold recovery method. The process requires excavating, crushing and transporting gold ore to a leaching plant. Introducing a cyanide solution to the mined ore at a plant results in efficiently recovering the ore's microscopic gold content.
A controversial leaching method involves directly spraying the cyanide onto piles of the ore. This practice is called heap-leaching. The Rainforest Information Center says heap-leaching leaves "a sorry legacy of environmental disasters in countries ranging from Guyana to Kyrgyzstan and the USA."
Warning
When unsafe microscopic recovery occurs on a large scale, serious habitat degradation can result. In 2000, mining microscopic gold sent 50 to 100 tons of cyanide and heavy metals into Romania's Somes, Tisza and Danube Rivers, causing the contamination of 2.5 million people's water supply by the time the chemicals reached the Black Sea. The consequence of careless cyanide use can kill tons of fish and rob people of vital drinking water.
Expert Insight
Geological engineer Chris Van de Ven says that gold recovery operations at Homestake Mine prove that careful planning and safety measures prevent contaminating the surrounding ecosystem. He supports this position by referring to Homestake Mine's ability to produce nearly 12 tons of gold every year without negatively affecting the environment. However, a 1998 Albion Monitor report contradicts this assertion. The Cheyenne River Sioux tribe sued Homestake Mining, claiming they had dumped 100 million tons of microscopic gold mining related toxins into the waterways of South Dakota's Black Hills. Homestake Mine settled confidentially.