- Placer deposit
geology, a placer deposit or placer is an accumulation of valuable minerals formed by deposition of dense mineral phases in a trap site. The name is from the Spanish word "placer", meaning "alluvial sand". Types of placer deposits include alluvium, eluvium, beach placers, and paleoplacers.
Typical locations for alluvial placer deposits are on the inside bends of
rivers and creeks, in natural hollows, at the break of slope on a stream, the base of an escarpment, waterfallor other barrier, within sand dunes, beach profiles or in gravel beds.
Alluvial placers are formed by the deposition of dense particles at a site where water velocity remains below that required to transport them further. To form a placer deposit, the particles sought after must show a marked density contrast with the
ganguematerial, which is able transported away from the trap site. Only if the deposit is winnowed in this way can the minerals be concentrated to economic levels.
Placer materials must be both dense, and resistant to
weatheringprocesses. Placer environments typically contain black sand, a conspicuous shiny black mixture of iron oxides, mostly magnetitewith variable amounts of ilmeniteand hematite. Valuable mineral components often occurring with black sands are monazite, rutile, zircon, chromite, wolframite, and cassiterite.
Exceptionally dense substances such as
goldand the platinum groupmembers will accumulate in placers, when they are present. Placer miningis an important source of gold, and was the main technique used in the early years of the California Gold Rush.
Substances commercially mined from placer deposits:
Heavy mineral sands ore deposits
* [http://www.alaskafreegold.com The Blue Ribbon Mine Alaska]
* [http://www.goldplacer.com Goldplacer]
* [http://www.arizonagoldprospectors.com Arizona Gold Prospectors]
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placer deposit — Natural concentration of heavy minerals caused by the effect of gravity on moving particles. When heavy, stable minerals are freed from their matrix by weathering processes, they are slowly washed downslope into streams that quickly winnow the… … Universalium
Placer mining — (pronounced plass er ) refers to the mining of alluvial deposits for minerals. This may be done by open pit (also called open cast mining) or by various forms of tunneling into ancient riverbeds. Excavation may be accomplished using water… … Wikipedia
placer mining — ☆ placer mining [plas′ər ] n. mining of placer deposits by washing, dredging, or other hydraulic methods * * * Oldest method of recovering gold from alluvial deposits. It takes advantage of gold s high density, which causes it to sink more… … Universalium
Placer — may refer to one of the following:*Placer deposit *Placer sheep *Placer miningGeographical names: * Placer, Masbate, Philippines * Placer, Surigao del Norte, Philippines * Placer County, California, United States … Wikipedia
deposit — /di poz it/, v.t. 1. to place for safekeeping or in trust, esp. in a bank account: He deposited his paycheck every Friday. 2. to give as security or in part payment. 3. to deliver and leave (an item): Please deposit your returned books with the… … Universalium
placer — placer1 /plas euhr/, n. Mining. 1. a surficial mineral deposit formed by the concentration of small particles of heavy minerals, as gold, rutile, or platinum, in gravel or small sands. 2. the site of a form of mining (placer mining) in which a… … Universalium
placer — I plac•er [[t]ˈplæs ər[/t]] n. 1) min mir a natural concentration of heavy metal particles, as gold or platinum, in sand or gravel deposited by rivers or glaciers 2) min the site of a form of mining(plac′er min ing)in which a placer deposit is… … From formal English to slang
Placer, Surigao del Norte — Placer is a 4th class municipality in the province of Surigao del Norte, Philippines. According to the 2000 census, it has a population of 21,542 people in 4,237 households.BarangaysPlacer is politically subdivided into 20 barangays. * Amoslog *… … Wikipedia
placer — ► NOUN ▪ a deposit of sand or gravel in the bed of a river or lake, containing particles of valuable minerals. ORIGIN Latin American Spanish, deposit, shoal … English terms dictionary
Placer — Plac er, n. [Sp.] A deposit of earth, sand, or gravel, containing valuable mineral in particles, especially by the side of a river, or in the bed of a mountain torrent. [U.S.] [1913 Webster] … The Collaborative International Dictionary of English