stream placer
Quick Summary
A placer deposit is a natural concentration of heavy minerals formed by gravity acting on moving particles. When rocks weather, heavy, stable minerals are released and washed into streams. The moving water winnows away lighter material, leaving the heavier minerals concentrated in stream, beach, or residual gravels, forming workable ore deposits.1
Minerals found in placer deposits are characterized by high specific gravity, resistance to weathering, and durability. Common examples include gold, platinum, cassiterite (tin ore), magnetite, chromite, ilmenite, rutile, zircon, monazite, and gemstones.12
Stream placers, formed by running water, are the most significant type and have historically yielded the most placer gold, tin, platinum, and gemstones. Mining techniques vary based on deposit characteristics, water availability, and mineral value. Methods include mechanized excavation with draglines or shovels, ground sluicing, hydraulicking, and the use of sluice boxes where riffles trap heavy minerals.123
Ask Britannica AI about this topic
Britannica doesn't have a full article on this topic, so we've curated a list of our relevant coverage.
- 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…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 
mineral depositAlluvial placersAfter 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 MoreAfter 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
miningPlacer 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…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
gold processingOres…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…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- gold processingMining 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 MoreAlluvial 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