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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 ...
Sedimentary placer deposits are known as 'leads' or 'deep leads'. Placer deposits are often worked by fossicking, and panning for gold is a popular pastime. Laterite gold deposits are formed from pre-existing gold deposits (including some placer deposits) during prolonged weathering of the bedrock. Gold is deposited within iron oxides in the ...
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.
"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.
In the United States, Mother Lode is most famously the name given to a long alignment of hard-rock gold deposits stretching northwest-southeast in the Sierra Nevada of California, [2] bounded on the east by the Melones Fault Zone. [3] It was discovered in the early 1850s, during the California gold rush.
The black fire opal is the official gemstone of Nevada. Most of the precious opal is partial wood replacement. The precious opal is hosted and found in situ within a subsurface horizon or zone of bentonite, which is considered a "lode" deposit. Opals which have weathered out of the in situ deposits are alluvial and considered placer deposits.
Confirmation of concentration of the placer gold deposits in relatively recent times is indicated by the bones of mastodons and elephants that were dug out of the gravels. [6] The distribution of the placer gold concentrations suggests that the common source of most of the placer gold in Confederate Gulch and White Creek was a series of quartz ...