Placer deposits are those which are found at some location away from their original point of origin. Common placer deposits include heavy sands and gravel that contain gold, tin, diamonds, or platinum. Weathering and erosion of the original geologic structure causes the placer minerals (and host rock) to break up and move.

Alluvial deposits are a specific type of placer deposits formed by transport and deposition in streams and rivers. The mouth of a river (where it empties into a larger water body) may contain placer minerals. This is often the case for placer diamonds.

One example of where placer/alluvial deposits can be formed is on the beach. These are called beach placers where the deposits are formed on the shore. The crashing of the waves and the currents constantly moves particles of similar densities together. This leads to the consolidation of the deposit.

Gold "panning" and "sluicing" are methods which attempt to recover placer gold from stream and river sediments. In this case, the geologic formation that contained the gold is located upstream, and years of weathering and erosion has move the gold downstream.