Experimental studies of channel incision reveal that heavy minerals are concentrated on the bedrock floor of valleys by reworking of valleyfill sediments. Inner channels formed by scour into bedrock are especially favorable locations. These deeper parts of the valley floor are located at both the inside and outside of valley bends, depending on the nature of the sediment load. Pauses in deposition and renewed scour permit heavy mineral concentrations to form within the valley-fill.

Arid alluvial fans rarely contain economic concentrations of heavy minerals, and yet the large fluvial fans of Ghana and South Africa contain important gold concentrations. During experimental studies of the growth of a fluvial or wet fan under conditions of perennial flow, fan-head trenching occurred repeatedly, and this reworking of the fan-head deposits plus rejuvenation of the source area streams remobilized and concentrated heavy minerals in the fan head and mid-fan. This process was not influenced by external variables but rather it reflected the natural morphologic and sedimentologic development of a fluvial fan.

Valley-fill, bedrock and fluvial fan placers may in many instances reflect the behavior of a complex geomorphic system, rather than the influence of external variables.