placer mining


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 rapidly from moving water than the lighter siliceous materials with which it is found. Panning, used by 19th-century miners, employed a pan in which a few handfuls of the gold-bearing soil or gravel and a large amount of water were placed; by swirling the pan's contents, the miner washed the siliceous material over the side, leaving the gold and heavy materials behind. Dredging is the most important placer-mining method today. Used worldwide is the bucket-ladder dredge, with its continuous chain of buckets rotating around a rigid adjustable frame called the ladder. In sluicing, a slightly sloping wooden trough called a box sluice, or a ditch cut in hard gravel or rock called a ground sluice, is used as a channel along which gold-bearing gravel is carried by a stream of water. Riffles placed transversely along the bottom of the sluice cause the water to eddy into small basins, retarding the current so that gold may settle.

* * *

 ancient method of using water to excavate, transport, concentrate, and recover heavy minerals from alluvial or placer deposits (placer deposit). Examples of deposits mined by means of this technique are the gold-bearing sands and gravel that settle out from rapidly moving streams and rivers at points where the current slows down. Placer mining takes advantage of gold's high density, which causes it to sink more rapidly from moving water than the lighter siliceous materials with which it is found. Though the basic principles of placer mining have not altered since early times, methods have improved considerably.

       panning, used by miners during the great gold strikes of the 19th century, employed a pan in which a few handfuls of the gold-bearing soil or gravel and a large amount of water were placed. By swirling the contents of the pan, the miner washed the lighter material over the side, leaving the gold and heavy materials behind.

      An improvement over the pan was the rocker, or cradle, named for its resemblance to a child's cradle. As it was rocked, it sifted large quantities of ore. Gravel was shoveled onto a perforated iron plate, and water was poured over it, causing finer material to drop through the perforations and onto an apron that distributed it across the riffles. The apron distributed the material across riffled pieces of wood or iron perpendicular to the bottom and sides of the cradle. As the material moved through the cradle, the gold was caught on the riffles, to be removed later.

      In sluicing or hydraulicking methods, a slightly sloping wooden trough called a box sluice, or a ditch cut in hard gravel or rock called a ground sluice, is used as a channel along which gold-bearing gravel is carried by a stream of water. Riffles placed transversely along the bottom of the sluice cause the water to eddy into small basins, retarding the current so that gold may settle and be trapped.

      Early in the 20th century, dredging (dredge) became the most important method of mining placer deposits. In particular, bucket-ladder dredging, which is characterized by a continuous chain of buckets that rotate around a rigid adjustable frame called the ladder, is used worldwide. A later method known as paddock dredging allows placer deposits to be mined even when they are not adjacent to a river. In this method the dredge floats in its own pond, which is continuously extended by digging at one end while simultaneously being filled at the other end with waste, or tailings.

      Typical minerals recovered by placer mining are gold, platinum, tin, diamonds (diamond), titaniferous and ferrous iron sands, and minor amounts of chromite, scheelite, columbite, monzonite, gemstones (gemstone), and abrasives (abrasive).

William Andrew Hustrulid
 

* * *


Universalium. 2010.

Look at other dictionaries:

  • 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 …   English World dictionary

  • placer mining — noun mining valuable minerals from a placer by washing or dredging • Hypernyms: ↑mining, ↑excavation * * * noun : the process of extracting minerals from a placer especially by washing, dredging, or hydraulic mining * * * placer mining, the… …   Useful english dictionary

  • placer mining — Taking the soft earthy matter in which the particles of mineral are loosely mingled, and, by filtration, separating the one from the other. Reynolds v Iron Silver Mining Co. 116 US 687, 695, 29 L Ed 774, 777, 6 S Ct 601 …   Ballentine's law dictionary

  • 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 — 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

  • mining — /muy ning/, n. 1. the act, process, or industry of extracting ores, coal, etc., from mines. 2. the laying of explosive mines. [1250 1300; ME: undermining (walls in an attack); see MINE2, ING1] * * * I Excavation of materials from the Earth s… …   Universalium

  • Mining — This article is about the extraction of geological materials from the Earth. For the municipality in Austria, see Mining, Austria. For the siege tactic, see Mining (military). For name of the Chinese emperor, see Daoguang Emperor. Simplified… …   Wikipedia

  • Placer County, California — Coordinates: 39°04′N 120°44′W / 39.06°N 120.73°W / 39.06; 120.73 …   Wikipedia

  • Mining methods of the Klondike Gold Rush — See also: Klondike Gold Rush, Mining Contents 1 During the Klondike Gold Rush (1896 1910) 1.1 Methods of bringing out the gold 1.1.1 Underground mining …   Wikipedia


Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”

We are using cookies for the best presentation of our site. Continuing to use this site, you agree with this.