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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 ...
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.
The word placer derives from the Spanish placer, meaning shoal or alluvial/sand deposit, from plassa (place) from Medieval Latin placea (place) the origin word for "place" and "plaza" in English. The word in Spanish is thus derived from placea and refers directly to an alluvial or glacial deposit of sand or gravel.
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 ]
This is a list of plants organized by their common names. However, the common names of plants often vary from region to region, which is why most plant encyclopedias refer to plants using their scientific names , in other words using binomials or "Latin" names.
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 ...
The list includes individual plant species identified by their common names as well as larger formal and informal botanical categories which include at least some domesticated individuals. Plants in this list are grouped by the original or primary purpose for which they were domesticated, and subsequently by botanical or culinary categories.