Placer miningIt is technique by which the technique by which gold that has accumulated in a placer deposit is extracted. Placer deposits are composed of relatively loose material that makes tunneling difficult, and so most means of extracting it involve the use of water or dredging. There are several methods of gold prospecting: sluicing, panning, dredging, electronic metal detection and dry washing.
1.) PanningGold panning is mostly a manual technique of separating particles of greater specific gravity (especially gold) from soil or gravels by washing in a pan with water.
Panning is the principal technique of the individual prospector for recovering gold and diamonds in placer (alluvial) deposits, but is not commercially viable for extracting gold from large deposits, except where labor costs are very low or gold traces are substantial. Before large production methods are used, a new source must be identified and panning is useful to identify placer gold deposits to be evaluated for an eventual future commercial exploatation.
Gold Panning. Photo credit: media.istockphoto.com-jpeg original source: www.istockphoto.com / Creator:phuketisland(Getty Images) / CC0
2.) DredgingGold dredging is a form of hobby mining that uses a motorized vacuum to suck up the bottom of rivers and streams to look for gold. Dredging technique in gold-bearing streambeds mainly is focused upon removing the over-sized rocks (any rock which is too large to be sucked up the suction nozzle) from the work area of the dredge-hole.
A gold dredge is a placer mining machine that extracts gold from sand, gravel, and dirt using water and mechanical methods. Suction dredge (Underwater Dredge) is powerful underwater-type of vacuum cleaner. The device sucks up streambed material (rocks, sand, gravel, silt, gold and other minerals), passes it up through a suction hose, and runs it across a recovery system floating at the surface. Pieces of gold, which are very heavy, are separated from the other streambed materials and trapped, as the gravel and other material wash through the recovery system and are then washed back into the stream to fill in the hole as the dredge moves forward in the waterway. Although this method has largely been replaced by modern methods, for an amateur prospector who wants to take his hobby to the next level but doesn’t want to work in a mine, upgrading to suction dredge can be a great way to find more gold while still enjoying the great outdoors.
3.) SluicingSluicing is the use of a "sluice box" in a creek or river to separate gold from gravel. The process represents taking of river gravels and passing them through a sluice box (this acts like a concentrator). The sluice box gets rid of the lighter and worthless river material yet retains the heavier and hopefully expensive materials such as gold and platinum. Using a sluice box to extract gold from placer deposits has long been a very common practice in prospecting and small-scale mining. Larger commercial placer mining operations employ screening plants, or trommels, to remove the larger alluvial materials such as boulders and gravel, before concentrating the remainder in a sluice box or jig plant.
– Rocker box - One of the most popular tools used during gold rush times in XIX century, the rocker box (also called cradle), uses a riffles located in a high-walled box to trap gold in a similar manner to the sluice box. Rocker allow to separate gold and other heavy elements from sand and gravel by shaking and rocking the high-sided box, open on one end and top. A rocker box uses less water than a sluice box and is thus well suited for areas where water is limited. A rocking motion provides the water movement needed for the gravity separation of gold in placer material.
Trommel - Built around a rotating metal tube with a slight incline, this tool has a screen at one end and lifter bars attached to the interior. The tube is known as "the scrubber section" and ore is loaded into the top end of the standing tube. With pressurized water and a mechanical action moving the scrubber the ore is broken down separating gold which is released through the screen.
Jig plant - Simple mineral processing device using water and the force of gravity to separate a raw ore stream by particle density.
4.) Recreational mining and electronic metal detection
"Recreational Gold Prospecting”is often small-scale placer mining, that can be made into a productive task with the "Gold Rush Nugget Bucket" and some additional items. Recreational gold mining and prospecting has become a popular outdoor recreation in a number of countries, including New Zealand, Australia, South Africa, Wales, in Canada and in the United States especially in western California.
Electronic metal detection
A metal detector is an electronic instrument which detects the presence of metal nearby. Metal detectors are useful for finding gold located not very deep underground. They often consist of a handheld unit with a sensor probe which can be swept over the ground or other objects. Metal detectors find gold nuggets without spending days sifting through mountains of gravel. They are the ideal tool for an amateur gold prospector.
Impact of placer mining over the environment
Because placer mining doesn't crush rocks and doesn't usually use chemicals to extract gold, the environmental impacts are generally less than those of hardrock mining. The primary impacts of placer mining are habitat destruction and sediment release. Habitat destruction occurs as a result of river diversions, and the disruption of riverbanks and river bottoms. These activities also release large amounts of silt and sediment into downstream waterways, which can severely impact water quality.
Hard rock mining (Lode or also underground mining)Hard rock gold mining extracts gold encased in rock, rather than fragments in loose sediment, and produces most of the world's gold. Open-pit mining is method in which the waste and ore are completely removed from the sides and bottom of a pit which gradually becomes an enormous canyon like hole. Other gold mines use underground mining, where the ore is extracted through tunnels or shafts.
By product gold miningGold is also produced by mining in which it is not the principal product. Large copper mines, often recover considerable amounts of gold and other metals along with copper. The largest producing gold mine in the world, the Grasberg mine in Papua, Indonesia, is primarily a copper mine. Some small "non gold" mines, sand and gravel pits, somethimes recovers small amounts of gold in their washing operations.
Gold Cyanidation (Cyanide process or the MacArthur-Forrest process)Cyanide is used for extract of gold, either in a controlled mill environment, or more crudely on rock piles in the open. Cyanide "vat leaching" mixes finely crushed ore with a cyanide salt in water. The cyanide binds to the gold ions, and makes them soluble in water, thereby allowing separation from the rock. This process usually takes place inside a mill or other mining facility.
Gold extraction process using mercury (Mercury process)
Mercury(Hg) is a metal with special properties that give it a wide variety of applications. This element is a liquid at room temperature and standard air pressure. Just as water is an effective solvent of many substances because of its chemical composition, mercury's atomic structure makes it an effective solvent of most metals. Combination with its low boiling point, make it useful for extracting gold from ore in a process of amalgamation and distillation.
ImpactsHardrock mining have a much larger environmental scarcities that placer mining, by size of operations, the chemistry of the ore deposits, the generation of extremely large volumes of hazardous waste material, and the use of toxic chemicals. Modern commercial hardrock mines are massive complexes, that in some cases displacing and processing over 250,000 tons of gold-bearing ore per day. In addition to the direct ecological disruption of mining on this scale, much of the gold mined this way is found in sulfur-bearing rocks. These rocks, when disrupted by mining, can produce acid mine drainage. In addition, many small mines use mercury for the separation of gold, while large mines instead use cyanide (Both chemicals are very toxic, and mercury is persistent in the marine food chain).