Page 198 - Handbook of Gold Exploration and Evaluation

Gold deposition in the weathering environment 173

3.18 Stresses imposed by mechanical weathering forces (Barlow and Newton,
1974).

due to metabolism whereby food is built up in green plants as nutriment for
animals. The nature of the vegetation and its decomposition products influences
the types of animal attracted to it. Soil fauna (earthworms, ants and other
burrowing animals) contribute to disintegration of the surface layers by forcing
individual grains apart and breaking up and mixing the rock materials. Plants
such as fungi and lichens break off tiny fragments of the rocks, absorbing them
into their own tissue.
The disintegration of rocks by physical stresses imposed upon them at or near
the Earth's surface involves mainly stresses set up by expansion and contraction
as illustrated in Fig. 3.18.

3.5 Landscape denudation
Denudation is the sum total of the combined efforts of weathering, erosion and
mass wasting involved in the lowering of the Earth's surface and transport of
sediments to the sea. The denudation cycle commences when continental crust is
elevated above sea level by tectonic processes associated with ocean floor
spreading. Uplift is rapid during the most active phase of orogeny and occurs in