Gold is processed by cyanide milling, a chemical procedure that separates 95 to 98 percent of the gold from raw mined ore. It is then refined to the gold standard purity, according to Mineweb. Heap leaching is a less expensive method of gold extraction, but it is a longer process and it recovers less gold than the cyanide milling process.
Gold mining teams include geologists who analyze rock structure to guide mining explorations, engineers who plan extraction and blasting strategies, and miners who do the work of removing the ore from the mines. For the cyanide milling process, the large chunks of raw ore are broken down into sand-size grains, and then they are made into a muddy slurry by adding a weak cyanide solution. The cyanide dissolves the gold without acting on the other rock and metal components of the ore. The liquid containing the dissolved gold is drawn off and treated again to release the gold in preparation for refinement. At the smelter, the gold is combined with flux and heated to 1,600 degrees Celsius to free it from any impurities. Secondary refinement produces liquid gold of 99.9 percent purity that is molded into standard bars of bullion.