Credit: Shutterstock photoBy Leia Michele Toovey-Exclusive to Gold Investing News
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.
Techniques
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
Alluvial Mining for Diamonds
Diamonds are a popular resource extracted through alluvial mining. Particularly prevalent in Africa, around 10 percent of the world's rough diamonds are sourced through industrial alluvial mining and 14 percent through artisanal or small-scale informal alluvial diamond digging.
On the industrial scale, when diamonds are found on the ocean shore or on riverbeds, the gravel is removed and then taken to a plant where it is washed and screened for diamonds. For offshore operations, specially constructed ships suck the gravel from the ocean floor before it is transported to land and to plants for screening. Formal alluvial diamond mining mainly takes place in Angola, Namibia and South Africa. DeBeers is currently using alluvial mining to extract diamonds.
Alluvial Mining for Gold
Like diamonds , alluvial mining is also a popular way to mine for gold in Africa. Alluvial gold is commonly found mixed with loose sediments, such as gravel. Gold is easy to separate out of these sediments due to its high density. Over the years, a variety of techniques have been utilized to separate the gold from the gravel, however, all of these methods rely on the same basic premise, water-washing of the gold-bearing gravel. Alluvial gold is commonly cemented, and in these cases, extraction is a bit more complex. Drilling and blasting is employed to remove the worthless overburden. Although unconsolidated sediments are much easier to extract, the gold concentrations in these deposits lags behind the consolidated sediments. These younger, unconsolidated sediments are the mining preference for individual miners, whereas the consolidated deposits will need the capital and force of a mining company.
Alluvial Mining for Platinum
Alluvial platinum mining was first used in the Urals, back in 1823. By the end of the 19th century the alluvial deposits of the central Urals had become the world's dominant source of platinum. The most easily accessible high-grade placer deposits, however, had largely been exhausted by the end of the 1920's and mining has since dwindled to a handful of small-scale dredging operations. Nevertheless, the Urals are currently receiving some renewed interest. Using present-day technology, explorers are examining the possibility of exploiting alluvial platinum. It is possible that a great deal of platinum, that was too fine-grained to be extracted with old technology, is still present in the region. Furthermore, the possibility remains for undiscovered sediments that were buried too deep to be found with 1920's technology.
Alluvial mining is alive and well in the Far East of Russia. Platinum group metals are currently mined from river sediments. First, bulldozers scrape out the bottom of the riverbed. The material is then made into a sluice by using hydraulic guns to break up and wash the ore. This causes the heavier particles to fall through a mesh into collectors. Then further washing is completed in stages to separate out the precious metal grains. These are collected and are passed through a final gravity concentration stage and a shaking table to separate PGM and gold concentrates. This region is known to host some very large platinum grains. The largest nugget discovered to date weighed 3.522 kg. Around three tonnes of platinum per year has been extracted from this region since 1990. It is thought that production in the range of three to four tonnes per year is sustainable for some years to come.
Alluvial Mining: Gold, Diamonds and Platinumoriginally posted ongoldinvestingnews.com
The views and opinions expressed herein are the views and opinions of the author and do not necessarily reflect those of Nasdaq, Inc.
The views and opinions expressed herein are the views and opinions of the author and do not necessarily reflect those of Nasdaq, Inc.
