Placer diamond mining, also known as "sand-bank mining" is used for extracting diamonds and minerals from alluvial, eluvial, and or colluvial secondary deposits, and is a derivative form of open-cast mining used to extract minerals from the surface of the earth without the use of tunneling. Excavation is accomplished using water pressure (hydraulic mining), mechanized surface excavating equipment, or hand digging (artisanal mining).
Diamonds and most gemstones are hard, highly resistant to weathering, and have a specific gravity that is higher than that of common minerals, rock or sedimentary soil, therefore, they tend to concentrate in alluvial deposits in the same way that gold placers develop. Gems are separated from waste material using various sifting and sorting techniques such as cone screens, box screens, or pans, which concentrate the heavier gems at the bottom, or sort material according to size.
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