Page 153 - Handbook of Gold Exploration and Evaluation

Geology of gold ore deposits 131

because of the steepness of slopes and lack of vegetation. As time passes and
land surfaces are reduced in altitude, the slopes flatten until ultimately, the
topography will be so lowered in level that only a low undulating land surface
remains. The form and depth of weathering is controlled by the water table and
the permeability and chemical reactivity of the country rock. The effects of
various physical and chemical conditions at different depths of the weathering
zone are recorded by the development of gold grain morphology including
metamorphic growth, hydrothermal deposition and alteration, supergene deposi-
tion and biological change. Eluvial and colluvial gold placers, which represent
the first significant stages of lateritic placer formation are usually both formed

2.26 Schematic diagram of landmass denudation. In this model, the average
surface elevation is reduced by one-half every 15 million years. (From A.N.
Strahler, Physical Geography, Harper and Row, Publishers. Copyright by A.N.
Strahler.)