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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 zone contains hundreds of mines and prospects, including some of the best-known historic mines of the gold-rush era. Individual gold deposits within the Mother Lode are gold-bearing quartz veins up to 15 metres (49 ft) thick and a few thousand feet long. The California Mother Lode was one of the most productive gold-producing districts in ...
Sedimentary placer deposits are known as 'leads' or 'deep leads'. Placer deposits are often worked by fossicking, and panning for gold is a popular pastime. Laterite gold deposits are formed from pre-existing gold deposits (including some placer deposits) during prolonged weathering of the bedrock. Gold is deposited within iron oxides in the ...
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.
In the most complex placer mining, groups of prospectors would divert the water from an entire river into a sluice alongside the river, and then dig for gold in the newly exposed river bottom. [15] Modern estimates by the U.S. Geological Survey are that some 12 million ounces [ 16 ] (370 t ) of gold were removed in the first five years of the ...
Orogenic gold deposits are responsible for approximately 75% of the world's gold production at over 1 billion ounces, when accounting that the origin of many gold placer deposits were orogenic in nature. [25] [46] The price of gold at a given time will have an impact on whether a deposit will be economically feasible.
Many of the entries in this list are considered Lagerstätten (sedimentary deposits that exhibits extraordinary fossils with exceptional preservation—sometimes including preserved soft tissues). Lagerstätten are indicated by a note ( [ Note 1 ] ) in the noteworthiness column.