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How does weathering create alluvial gold deposits?

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A diagram showing the periodic table entry for gold, with the symbol Au, atomic number 79, atomic weight 196.96657, electron configuration, and labels for its properties as a solid transition metal with a face-centered cubic crystal structure. — 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.

Alluvial gold deposits, also known as stream placers, are formed through a combination of geological weathering and the mechanical action of water.12

The process begins when natural forces—such as wind, rain, and temperature fluctuations—break down gold-bearing rocks at the Earth's surface. Because gold is chemically resistant and possesses a high specific gravity, it remains intact while the surrounding rock matrix is weathered away.132

Once these gold particles are freed from their host rock, they are transported downslope by gravity and rainfall. When this material reaches streams or rivers, the flowing water acts as a sorting agent. Because the ability of water to transport sediment depends on its velocity, the current effectively "winnows" the lighter sand and gravel, allowing the much denser gold particles to settle and accumulate in riverbeds, streambeds, and floodplains. This natural concentration process creates the workable deposits that have historically been a primary source of the world's gold.2145