Flow separation—a physical process for the concentration of heavy minerals within alluvial channels

Abstract

Flow separation is a common feature within alluvial channels that occurs at abrupt changes in the bed geometry. At a wide range of scales, it is a process that can exert considerable control over the segregation and deposition of heavy mineral grains. Fluid separation generates a region of high bed shear stress that can entrain heavy minerals, and a region of low velocity that is a preferred site for the deposition of denser particles. Significant concentrations of heavy minerals, sometimes up to eight times the background value, may be formed by flow separation processes. A review of the occurrence of flow separation illustrates that it may be responsible for the accumulation of heavy mineral grains at a range of geomorphological scales.