The containing material in an alluvial placer mine may be too loose to safely mine by tunnelling, though it is possible where the ground is permanently frozen. Placer deposits can be as young as a few years old, such as the Canadian Queen Charlotte beach gold placer deposits, or billions of years old like the Elliot Lake uranium paleoplacer within the Huronian Supergroup in Canada. Since gems and heavy metals like gold are considerably denser than sand, they tend to accumulate at the base of placer deposits.
The metal or gemstones, having been moved by stream flow from an original source such as a vein, are typically only a minuscule portion of the total deposit. Placer mining is frequently used for precious metal deposits (particularly gold) and gemstones, both of which are often found in alluvial deposits-deposits of sand and gravel in modern or ancient stream beds, or occasionally glacial deposits. This may be done by open-pit (also called open-cast mining) or by various surface excavating equipment or tunneling equipment. Placer mining ( / ˈ p l æ s ər/) is the mining of stream bed ( alluvial) deposits for minerals. JSTOR ( September 2010) ( Learn how and when to remove this template message)ġ9th-century miner pouring water into a rocker box which, when rocked back and forth, will help separate gold dust from the alluvium.Unsourced material may be challenged and removed. Please help improve this article by adding citations to reliable sources. This article needs additional citations for verification.
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