Gold Mining an overview
PANNING: This is a manual technique used for collection of gold. In this technique gold is separated from gravels and soil. A wide pan is used to sort gold. Gold being denser than gravels and other materials settles in the bottom of the pan from where it can be manually removed. This type of gold mining is not very profitable if there is scares deposit of gold on the surface. The rivers/streams were gold is found are known as placer deposits.
SLUICING: Sluicing is done by some small scale miners. It is done by using a sluice box. A sluice box is channel with riffles in the bottom. These riffles help in catching gold. Sluice box is placed in the water in such a way that the water flows through it. Out of the collection, the larger rocks can be removed by hand; sand and small pebbles can be washed out. Gold along with black sand and some other materials gets accumulated in front of the riffles. Gold can be separated by panning.
HYDRAULIC MINING: Hydraulic mining falls in the category of placer mining. Large amounts of gravel and sand is run through a sluice box. Gold is then separated using sluicing techniques.
CYANIDE PROCESSING: This process is used when gold is found as fine bearing in rocks. The rocks containing gold bearings are finely ground and then mixed with Sodium cyanide solution. Due to the reaction between two components gold cyanide is formed, which is removed. Gold is precipitated out by adding zinc to the gold cyanide solution. Even zinc residues are precipitated out. Zinc is removed by adding sulphuric acid. This leaves behind gold sludge that is smelted and sent to refinery for final processing.
MERCURY AMALGAMATION: This technique is used to extract gold in large-scale. The gold ore is crushed and ground to fine powder and is hydrated to form a viscous pulp that is passed over copper plates. These copper plates are coated with mercury on their upper surface. Gold has high relative density and hence it sinks through the pulp into contact with mercury and is converted into amalgam. The amalgam is scraped off plates.