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Why does gold collect in riverbeds and stream sediments?
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gold
The precious metal gold is a chemical element with the symbol Au. Its square on the periodic table details some of its properties, including its atomic weight, atomic number, and crystal structure.
Gold collects in riverbeds and stream sediments through the formation of placer deposits, a process driven by the effects of gravity on moving particles.1
The process occurs as follows:
- Weathering: Natural forces such as rain, wind, and temperature changes break down gold-bearing rocks, releasing gold particles from their original matrix.21
- Transport: These particles are washed downslope into streams and rivers.1
- Concentration: Because gold has a high specific gravity, it is significantly denser than the surrounding sand and gravel. As the velocity of the flowing water decreases, the heavier gold particles settle and are deposited much more quickly than lighter materials, which are winnowed away by the current.13
These accumulations, known as alluvial placers, have historically been a primary source of gold because the metal is chemically resistant to weathering and remains in its elemental form, allowing it to be easily recovered using gravity-based mining techniques.214