The word placer comes from the same Spanish word for “sandbar” as you can see everywhere here. In particular, it refers to alluvial deposits of debris, such as gravel, which contain particles of valuable chemical elements.
Hence, the term “gold dust” refers to gold formed on rocks that have been moved into the river bed and placed by the action of a geological force and water. Gold vein tends to erode from its source and is naturally distributed among other rocks that have been subjected to similar geological forces. This forms a secondary deposit.
Therefore the mining of alluvial deposits of gold and other precious metal deposits is called “sand mining”. Sand extraction can be carried out through several tunneling methods to the river bed. There is also open pit and hydraulic mining. In the former, sand mining is carried out in open-cast mining. In the latter, water pressure is used for excavation.
There are three sand mining methods that are used to mine gold dust.
Golden bread:
This method of using a pot is the oldest and easiest way to extract gold from soap deposits. In this method, the mined ore is placed in a large pot (plastic or metal) and filled with plenty of water. Then it is stirred. Denser gold particles settle on the bottom of the pot than other materials (e.g. mud, sand, gravel, gold are about 19 times heavier than water) and lighter materials rinse the sides.
Lock box:
This method uses the same principles as gold palms, but on a larger scale. This method uses a short lock box. The box consists of a barrier along the bottom that retains gold particles when all materials are washed with water. The lock box method is ideal for drilling to supply ore to a box using a special tool such as a shovel.
Drum:
This method uses a cylinder with a sieve to separate the materials by size (drum means “drum” in Dutch). The drum consists specifically of a slightly inclined rotating metal tube with a sieve at the discharge end. A lifting rod is attached to the inside of the metal tube. The ore is fed into the drum from its upper end. The hose and sieve section is supplied with pressurized water. Valuable minerals from ores are separated by a combination of water and mechanical action. Pieces of ore with valuable minerals pass the sieve and are further concentrated in the locks. Larger ones (which do not pass the sieve) are conveyed to the waste pile on a conveyor belt.
Today sand mining is practiced in many parts of the world as a source of precious stones and industrial metals and minerals. This also applies to countries like Sri Lanka and Myanmar. Soap mining continues in British Columbia and the Yukon Territory, particularly Alaska.