Page 266 - Handbook of Gold Exploration and Evaluation

Sedimentation and detrital gold 235

4.22 Influence of different sized streambed obstructions on the free settling of
gold.

4.23). The surface of discontinuity breaks down into a large number of irregular
vortices, and fluid in regions of excess pressure will tend to move towards
adjacent regions of reduced pressure. When the bed-load of one or both of the
streams is auriferous, paystreaks will be developed along the line of discon-
tinuity. Owing to fluctuations in the flow and a fine upward grading of the
sediment load, eddies will be distributed irregularly. The final stage of
deposition is the development of an irregular, but limited medley of paystreaks
along the line of discontinuity.
Sand and gravel associated with braiding and meandering comprise the
coarsest materials of the bed-load and accumulate the most gold. Braided stream
sediments are the first particles to settle and are correspondingly coarser than
meandering stream sediments, particularly in flood plains where fine sands and
muds periodically cover the flooded areas and fill any abandoned channels and
low lying ground. In each case, the resulting mixture of gravel, sand and fines is
characteristic of the local balance between viscous and gravitational forces, local
differences in stream turbulence and depth and the settling properties of the