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In geology, a placer deposit or placer is an accumulation of valuable minerals formed by gravity separation from a specific source rock during sedimentary processes. [1] The name is from the Spanish word placer , meaning " alluvial sand".
No rocks from the Paleogene or Neogene period are known from Wisconsin; however, abundant Quaternary deposits can be found as a result of the last Ice Age. The most recent glacial cycle, the Wisconsin Glaciation, began about 31,500 years ago and receded from the state by around 7,000 years ago. During this time the Lake Michigan Lobe and the ...
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 ...
Heavy mineral sands are placer deposits formed most usually in beach environments by concentration due to the specific gravity of the mineral grains. It is equally likely that some concentrations of heavy minerals (aside from the usual gold placers) exist within streambeds, but most are of a low grade and are relatively small.
Placer gold deposits form via gravity, with the density of gold causing it to sink into trap sites within the river bed, or where water velocity drops, such as bends in rivers and behind boulders. Often placer deposits are found within sedimentary rocks and can be billions of years old, for instance the Witwatersrand deposits in South Africa ...
"Panning out" ~ Stereoscopic view of print taken by the U.S. Geological and Geographic Survey of the Territories ~ circa 1874–1879 Gold panning is a simple process. Once a suitable placer deposit is located, some alluvial deposits are scooped into a pan, where they are then wetted and loosed from attached soils by soaking, fingering, and aggressive agitation in water.
Placer mining is a method of extracting gold from alluvial deposits such as sand, gravel, and sediment. [42] [43] These are known as placer deposits which are typically found in riverbeds, stream beds, and floodplains. [44] These deposits typically contain minerals that are resistant to weathering and eroision like gold, platinum, diamonds, and ...
This process left depressions ranging from small ponds to large lakes and enclosed valleys. Water-filled kettles range in depth from 3 to 200 ft (0.9 to 60 m). The topography of this area is widely varied between the lakes and kettles and the hills of glacial deposits, which can rise up to 300 ft (90 m) from the lakes. The largest include Holy ...