Stream placer | mining | Britannica (original) (raw)
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placer deposit
In placer deposit …several varieties of placer deposits: stream, or alluvial, placers; eluvial placers; beach placers; and eolian placers. Stream placers, by far the most important, have yielded the most placer gold, cassiterite, platinum, and gemstones. Primitive mining probably began with such deposits, and their ease of mining and sometime great richness have… Read More
In mineral deposit: Alluvial placers After a mineral-bearing soil reaches the bottom of a slope, it can be moved by stream water so that stream or alluvial placers form. Alluvial placers have played an especially important historical role in the production of gold. Indeed, more than half of… Read More
In mining: Placer mining …two most economically important are stream and beach placers. Stream (or alluvial) placers are formed by running water, while beach placers are formed by the action of shore waves on preexisting or currently forming stream placers. Because of the shifting of sea and land throughout geologic time, placers can be… Read More
sources of gold
In gold processing: Ores …to gold found in riverbeds, streambeds, and floodplains. It is invariably elemental gold and usually made up of very fine particles. Alluvial gold deposits are formed through the weathering actions of wind, rain, and temperature change on rocks containing gold. They were the type most commonly mined in antiquity. Exogenetic… Read More
In gold processing: Mining and concentrating Alluvial deposits are either dredged from pond and river bottoms or sluiced from banks and floodplains with high-pressure hydraulic hoses. Alluvial deposits require little or no comminution; they are usually concentrated by gravity techniques such as jigging or tabling, in which a slurry is passed… Read More
