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The name is from the Spanish word placer, meaning "alluvial sand". Placer mining is an important source of gold, and was the main technique used in the early years of many gold rushes, including the California Gold Rush. Types of placer deposits include alluvium, eluvium, beach placers, aeolian placers and paleo-placers. [2]
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. The metal or gemstones, having been moved by stream flow from an original source such as a vein, are ...
The origin of the gold within the Witwatersrand Basin is thought to be a combination of placer deposition and hydrothermal processes. Gold deposits are concentrated at the base of fluvial cycles within the Central Rand Group, with ancient microbial activity playing a role in the fixation of organic materials and enhancing gold concentration. [ 4 ]
For example; the medium-sized Coburn mineral sands deposit, Western Australia, is 230 million tonnes at 1.1% heavy minerals, and is 13 km long. The Tormin mine, on the Western Cape of South Africa's coastline, provides a unique ocean beach feature, which exposes the resource to wave and tidal conditions that result in a natural jigging effect.
Small amounts of gold have been found in streams draining glacial deposits in the Midwest. Gold prospecting and mining activities allowed on public lands vary with the agency and the location. Gold pans and shovels are commonly allowed, but sluice boxes and suction dredges may be prohibited in some areas.
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Drift mining methods were used extensively to mine placer deposits during the early years (1899- ) of the Nome mining district. During summer, surface deposits could be worked, but some placer deposits were buried too deeply for surface placering. In addition, water to wash the gold from the placers was not available in the winter.
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