1. placer mining

placer mining is often used for precious metal deposits (especially gold) and precious stones, both of which often appear in alluvial deposits-sand and gravel deposits in modern or ancient river beds, or occasional glacial deposits. Metals or precious stones are moved by water from original sources (such as veins), and usually only account for a very small part of the total deposit. Because heavy metals such as gems and gold are much denser than sand, they tend to accumulate at the bottom of sand deposits.

2. Translation

Gold panning is mainly a manual technique to separate gold from other materials. The wide and shallow plate is full of sand and gravel that may contain gold. Dip the pan in water and shake it to sort out the gold from gravel and other materials.

because the density of gold is much higher than that of rock, it will soon settle to the bottom of the pot. The elutriation material is usually taken out from the river bed, usually at the internal bend of the stream or from the bedrock frame of the stream. The density of gold enables it to concentrate, which is called placer gold deposit.

panning for gold is the most practical and quickest technology to find gold, but it is not commercially feasible to extract gold from large deposits unless the labor cost is very low or there are a lot of traces of gold. The gold rush area is often advertised as a tourist attraction in the former gold mining area. Before using large-scale production methods, new sources must be determined, and panning is helpful to determine placer gold deposits to be evaluated for commercial feasibility.

3. Flood discharge

For a long time, it has been a very common practice to use sluice boxes to extract gold from placer mines in exploration and small-scale mining. The sluice box is essentially an artificial channel with a shallow groove at the bottom. The design purpose of the shoal is to form a dead zone in the current, so that gold can be separated from the suspended state. The box is placed in the stream to guide the water flow.

the gold-containing material is placed on the top of the box. The material is carried by an electric current through a volt, in which gold and other dense materials precipitate behind the shoal. The material with lower density flows out of the box as tailings.

Large commercial placer mining operations use screening equipment or roller screen to remove large alluvial materials, such as boulders and gravels, and then concentrate the residues into a lock box or jig. These operations usually include diesel-powered earthmoving equipment, including excavators, bulldozers, wheel loaders and rock trucks.

4. Rocker box

, also known as cradle, uses grooves in high-wall boxes to capture gold in a way similar to sluice boxes. Rocker box uses less water than sluice box, which is very suitable for areas with limited water resources. The rocking motion provides the water motion needed for gravity separation of gold in placer gold materials.

5. Hard rock mining

Hard rock gold mining extracts gold wrapped in rocks instead of fragments in loose sediments, and produces most of the gold in the world. Sometimes open-pit mining is used, such as at the Fort Knox mine in central Alaska. Barrick Gold owns one of the largest open-pit gold mines in North America in the Goldstrike mining area in northeastern Nevada.

other gold mines use underground mining to extract ore through tunnels or shafts. South Africa has the deepest hard rock gold deposit in the world, with a depth of 3,9 meters (12,8 feet). At this depth, the heat is unbearable for human beings, and air conditioning is needed for the safety of workers. The first mine with air conditioning was Robinson Deep, the deepest mine of any mineral in the world at that time.

mining pollution

low-grade gold ore may contain less than 1? Ppm of gold metal; This ore is ground and mixed with sodium cyanide to dissolve gold. Cyanide is a highly toxic chemical, which can kill organisms with a small amount of exposure. Many cyanide leaks from gold mines occur in developed and developing countries, and these accidents lead to the death of aquatic life in the long rivers affected by the disaster.

environmentalists think these events are major environmental disasters. Thirty tons of used ore was dumped as waste to produce a troy ounce of gold.

Gold mines are the sources of many heavy elements, such as cadmium, lead, zinc, copper, arsenic, selenium and mercury. When sulfide-bearing minerals in these ore piles are exposed to air and water, sulfide will be converted into sulfuric acid, which will dissolve these heavy metals, thus promoting them to enter surface water and groundwater. This process is called acid mine drainage. These gold mines are long-term and highly dangerous wastes second only to nuclear waste sites.