Page 287 - Handbook of Gold Exploration and Evaluation

Sedimentation and detrital gold 253

4.33 Wandering gravel-bed placers (adapted from Desloges and Church,
1987).

in valleys. Wandering gravel-bed streams evolved under conditions typical of
present day temperate climatic conditions with densely forested drainage basins
and valley floors (Fig. 4.33).
A wandering gravel-bed stream is commonly sinuous, with large medial bars
and occasional braided reaches in which gravels are interdigitated with fine-
grained over bank and flood plain deposits (Desloges and Church, 1987).
Repeated lateral migration of wandering bed channels and the multiple reworking
of the bar platform gravels results in the development of an extensive gold-rich
basal horizon across the whole of the valley. The reworking of the Bella Coola
River, typical of the model portrayed in the above figure appears to have occurred
every 150 years since the end of the last great ice age some 10,000 years ago.