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Placer mining (/ ˈ p l æ s ər /) [1] is the mining of stream bed deposits for minerals. [2] This may be done by open-pit mining or by various surface excavating equipment or tunneling equipment.
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]
"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.
The basic concept of retrieving gold via placer mining has not changed since antiquity. The concept is that the gold in sand or soil will settle to the bottom because gold is heavy/dense, and dirt, sand and rock will wash away, leaving the gold behind. The original methods to perform placer mining involved gold panning, sluice boxes, and ...
Loss of mercury in the amalgamation process was a source of environmental contamination. [25] Eventually, hard-rock mining wound up becoming the single largest source of gold produced in the Gold Country. [17] [26] The total production of gold in California from then until now is estimated at 118 million ounces (3700 t). [27]
The reason was that the mine itself was closed after the discovery that most of the gold was unrecoverable, and the investors in the project only made $80,000 after investing over $1,000,000 into the mine and associated engineering works. After the closure of the mine, local residents reused the timber. [3]
A favorite design consists essentially of a combination washing box and screen, a canvas or carpet apron under the screen, a short sluice with two or more riffles, and rockers under the sluice. The bottom of the washing box consists of sheet metal with holes about a half an inch in diameter punched in it, or a half-inch mesh screen can be used.
A miner using a hydraulic jet to mine for gold in California, from The Century Magazine January 1883. Hydraulic mining is a form of mining that uses high-pressure jets of water to dislodge rock material or move sediment. [1] In the placer mining of gold or tin, the resulting water-sediment slurry is directed through sluice boxes to