Page 231 - Handbook of Gold Exploration and Evaluation

202 Handbook of gold exploration and evaluation

4.5 Degradation of gold grains in samples repetitious from placer deposits in
Kasongan, Kalimantan, Indonesia.

the ice under high-pressure flow conditions; the effects upon wear of such
processes produce fluvio-glacial modifications that are not well understood.
· In shallow marine environments comminution may result from either high or
low energy conditions, depending upon exposure to the open sea and the
geological history of the shoreline.

Model experiments have done little so far to do much more than confirm facts
already indicated qualitatively by experience in the field. None has yet provided
quantitative results due to the impossibility of scaling down distributions of
small particles uniformly without significantly changing the rheological patterns
of their behaviour.

4.1.2 Shape
Shape, i.e., the gross morphology of a surface, is difficult to quantify because of
the variability of its overall form. Briggs (1977) proposes four major influences
on particle shape:

1. the original particle shape as inherited from previous cycles of erosion
2. lithological properties (e.g., mineralogy and structure) that may affect the
three-dimensional shape of material supplied by weathering
3. duration and type of weathering during transport
4. duration and type of weathering after deposition.
Indices used to describe the different shapes taken by sedimentary particles refer
either to two-dimensional shapes (roundness, angularity, sphericity), or three-