When this happens, water transports the minerals downslope into streams, where they concentrate in gravel beds. Here, they’re known as alluvial deposits, and they yield high concentrations of placer gold, cassiterite, platinum, and gemstones.
Other types of placer deposits include eluvial placers, which form on hillslopes via in situ weathering. Here, instead of streams, rain and wind transport the minerals. Meanwhile, beach placers are a result of waves and currents moving heavy minerals towards the seashore, and eolian placers are formed in deserts by wind, which carries the fine mineral particles.
Key fact: The placer deposit in Witwatersrand, South Africa, is the largest gold deposit in the world, having produced over 1.5 billion ounces of gold
Placer mining techniques involve mechanical dredges, which perform large-scale sifting of alluvial deposits to recover placer gold. Other placer operations involve draglines, dozers, and backhoes to excavate the heavy minerals.
Benefits
Recovery of valuable minerals
Placer mining is less capital intensive than hard rock mining
Placer mining can be implemented on any scale
