Alluvial Mining

Alluvium refers to sediment that is transported and deposited by water. Alluvium is found in rivers, lakes and along coastlines. In the case of alluvium transported by an ancient stream, alluvium can also be found in a terrestrial environment. The alluvial process can transport, and concentrate, valuable minerals. Over thousands of years, minerals are eroded from their source and transported by water to a new locale. Because sediments settle out of water according to their weight, heavier, valuable minerals such as diamonds, platinum group metals, and gold will often deposit at the same time, this characteristic can lead to a concentrated deposit of valuable minerals, prime for extraction.

Alluvial mining is an ancient technology. The early gold-panners were alluvial miners. Although somewhat archaic, small scale alluvial mining operations are still common, both as a hobby and as a source of income, in areas of Africa and South America. Alluvial mining has also morphed into a big business involving cutting edge technology and a great deal of capital investment.

In the case of alluvial deposits that are “cut-off” from their water source, mining is simple. The resource can be extracted through a conventional open-pit. If the deposit is still covered by water, the mining process is a bit more complex. If the water is shallow, such as a lake or adjacent a coast-line; a wall may be built and pumps used to pump out water. The overburden (if any) is removed, and then the deposit is excavated and transported for screening. Dredging is used to remove overburden in areas with very wet ground conditions. The dredge is floated in an initial pond and then moved into the mining block where it excavates down to the mineral bearing material.

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