Valley Gold Leach Method

The valley leach method involves the preparation and placement of ore behind a retaining structure. Leaching of the ore is performed with subsequent li fts progressing up slope. The majority of ore remains in contact with leach solution during evaporation. At completion of leaching, the ore is left in place and reclaimed similar to a waste rock dump. See figure 1.6. The aspects of the valley leach method are listed below:

• Needs durable ores;
• Can be used in steep terrain;
• Requires reduced storage capacity;
• Needs high integrity liner due to hydraulic head;
• Needs to produce stable heap similar to waste rock dump;
• Needs retaining structure;
• Can operate in large range of climates;
• Can accommodate extended leach time up to several years.

The applicability of the valley leach method is dependent upon the durability of the ore and its ability to remain permeable under the stresses from subsequent ore placement. The major advantage of this method is its applicability in steep terrain and its use in a wide range of climatic conditions. The storage capacity of the pore spa ce in the ore is often used to contain pregnant solution pond. Containment of the in heap solution requires a high integrity liner system.

Typically, the liner system consists of a combination of synthetic and low permeability or amended soil material. The storage of solution behind the retaining structure requires that it functions as a dam. It is also possible to have a separate pregnant solution in the heap. Careful design of the piping and its penetration through the embankment is of special concern.

Design and construction of the valley heap to maintain a stable facility requires relatively extensive studies about topography and the ultimate height of the heap. Operating valley leaches have heights in excess of 200 ft from toe to crest.

The valley leach method is suitable for use in steep terrain. Its applicability is limited by the durability and permeability of the ore. The method is applicable in the majority of climatic environments.