Placer deposits are natural concentrations of heavy minerals that are caused by the effect of gravity on moving particles. They are loose, unconsolidated, and semi-consolidated materials that form by surface weathering, erosion of primary rocks, transportation, and deposition. Placer deposits are classified into four types: stream or alluvial placers, eluvial placers, beach placers, and eolian placers. Examples of minerals found in placer deposits include gold, platinum, cassiterite, magnetite, chromite, ilmenite, rutile, native copper, zircon, monazite, and various gemstones.

In summary, placer deposits are natural concentrations of heavy minerals that form by the effect of gravity on moving particles. They are classified into four types and contain various minerals such as gold, platinum, and gemstones.