Placer gold refers to gold that has been eroded from its source (such as gold-bearing quartz veins) by natural processes like water, and then concentrated in deposits known as placer deposits. Prospectors historically panned for placer gold by swirling sediment in a pan to separate gold particles from lighter material like sand and gravel. These deposits typically accumulate in stream beds, river bottoms, or beach sands due to the heavier nature of gold compared to other sediment particles.