What is Placer Deposits ?


Chemical resistance minerals weather from a vein deposit, travel downhill via mass-wasting and are concentrated in a stream placer by running water.


Placer deposits are natural concentrations of heavy minerals that occur as a result of gravity acting on moving particles. When weathering processes remove heavy, stable minerals from their matrix, they are carried downslope into streams, which quickly winnow the lighter matrix. As a result, heavy minerals concentrate in stream, beach, and lag (residual) gravels, forming workable ore deposits. Gold, platinum, cassiterite, magnetite, chromite, ilmenite, rutile, native copper, zircon, monazite, and numerous gemstones are minerals that form placer deposits and have a high specific gravity, are chemically resistant to weathering, and are durable. 

Stream, or alluvial, placers, eluvial placers, beach placers, and eolian placers are all types of placer deposits. 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 sometimes great richness have made them the cause of some of the world’s greatest gold and diamond “rushes.” 

Stream placers depend on swiftly flowing water for their concentration. Because the ability to transport solid material varies approximately as the square of the velocity, the flow rate plays an important part; thus, where the velocity decreases, heavy minerals are deposited much more quickly than the light ones.


  • Stream placers include the rich gold deposits of Alaska and the Klondike.
  • The platinum placers of the Urals, the tin (cassiterite) deposits of Malaysia, Thailand, and Indonesia. 
  • The diamond placers of Congo (Kinshasa) and Angola.


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