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What are placer deposits of gold?

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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.

Placer deposits are natural concentrations of heavy minerals, such as gold, formed by the effect of gravity on moving particles. When gold is released from its host rock through weathering, its high specific gravity and chemical resistance allow it to be separated from lighter materials by natural forces.12

These deposits are categorized by the agent that concentrates the gold:

Stream (Alluvial) Placers: The most significant type, where flowing water winnows away lighter particles, leaving gold concentrated in riverbeds and floodplains.12
Eluvial Placers: Formed on hillslopes where rain and wind remove lighter debris, acting as an intermediate stage before material reaches streams.1
Beach Placers: Created by wave action and shore currents that shift materials, concentrating heavy gold particles along seashores.1
Eolian Placers: Found in arid regions where wind removes fine, lighter dross, leaving heavier gold behind.1

Because of their accessibility and potential richness, placer deposits have historically been the primary source for many of the world’s major gold rushes.1