Placer mining

Placer mining recovers valuable minerals from loose sediments by using gravity, often aided by flowing water, to separate dense grains from lighter material.

Gold panning: A manual method of separating dense gold particles from sediment in a shallow pan. It is the simplest placer method: swirling water carries away lighter grains.
Placer deposit: A natural concentration of dense, durable mineral grains in unconsolidated sediment. Mining targets these naturally sorted accumulations rather than solid rock.
Alluvial gold: Gold particles found in river and stream sediments after erosion from their source rocks. It is the best-known target of placer mining.
Hydraulic mining in California: A nineteenth-century mining practice that used powerful water jets to erode gold-bearing hillsides in California. Its sediment choked rivers and caused extensive downstream damage.
Sluicing: A method that washes sediment through a channel fitted with barriers that trap dense particles. Riffles slow the flow and retain heavy minerals as lighter sediment passes downstream.
Mechanical weathering: The physical breakdown of rock into smaller pieces without changing its chemical composition. It liberates resistant mineral grains that can later accumulate in placers.
Cassiterite: A tin oxide mineral and the principal ore of tin. Its high density and durability make it a common placer mineral.
Mining tailings: Waste material left after valuable minerals are separated from mined material. Placer processing produces sediment and discarded minerals that require management.
Hydraulic mining: A mining method that uses high-pressure water jets to erode and move deposits. Water can excavate placer-bearing sediments before the material is concentrated.
Sediment transport: The movement of particles by water, wind, ice, or gravity. Transport carries liberated grains toward places where flowing water can sort them.

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