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Heap leaching of gold/silver and copper ores are carried out under unsaturated flow conditions. While the
mechanics of unsaturated flow through porous media is well understood, the large diameter particles
typically present in heap leach operations present special challenges. The unsaturated flow characterisation
of these materials is one such challenge. This paper will review unsaturated flow observations in heap leach
materials under laboratory and field conditions. Specific attention will be paid to characterising the
parameters for unsaturated flow through coarse heap leach materials and its impact on the subsequent
modelling of unsaturated flow. Flow conditions during closure will also be evaluated as the drain down rate
of heap leach facilities is dependent on the heap material characteristics.
Recent observations and evaluations of the unsaturated behaviour of materials removed from dynamic (on
off pad) heap leach operations for placement in spent ore disposal areas will be presented. These materials
must be sufficiently dry to provide the shear strength and trafficability required for stacking conveyors
typically used in the spent ore disposal area. A range of geotechnical and unsaturated flow evaluations can
be used to evaluate the material behaviour.
It is concluded that 21st century designers of heap leach facilities must include full consideration of the
unsaturated behaviour of the heap leach materials, both as it relates to flow and strength of such materials.
Recommendations are made for the integrated development of heap leach projects incorporating
unsaturated material considerations.
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Integrated Heap Leach Design — Incorporating Unsaturated Material Considerations D. van Zyl
166 Rock Dumps 2008, Perth, Australia