Expanding Gold Leach Pad method.

The expanding pad method involves the preparation and placement of ore on a pad. Followi ng leaching, the ore is left in place. See Figure 1.5. Subsequent releaching or washing and neutralization are done. Additional lifts to the heap or reclamation can then be performed. The factors involved in the expanding pad method are listed below:

• Needs large available areas;
• Needs relatively flat topography;
• Needs approximately net evaporation to maintain zero discharge;
• Needs larger flood/storm event capacity due to larger active areas;
• Can tolerate variable ore and leach cycle time;
• Needs relatively simple liner due to limited leach time and lo stress environment;
• Has incremental liner costs, and
• Has low initial capital cost.

The expanding pad method requires relatively large areas of suitable topography in which the pad is expanded in a staged manner. Typically, ground slope should be less than 10 percent and preferably less than 5 percent. To operate the heap with zero discharge, the climatic conditions should have an approximate balance between precipitation and evaporation or be of net evaporation.

The larger area s involved, relative to the reusable pad method, increase the influence of the hydrologic cycle. Generally, larger ponds are required to contain precipitation from storm events.

No constraints on the duration of the leach cycle exist with the expanding pad method. Ore having variable or long duration leaching characteristics can be accommodated without impacting subsequent ore production. If economical, ore can be leached in several cycles before being abandoned.

Liners for the pad are no subject to working stresses once ore is placed. Generally, membrane liner systems are installed and are designed primarily to tolerate stresses involved during initial ore placement. Low permeability natural materials or amended soils can also be applicable in this method. Some expanding pads currently operate with heap heights in excess of 100 feet.

With the staged construction of facilities, initial capital cost is relatively low. Depending upon the number of lift placed, the pad construction is a fixed cost per ton ore leached.

Thus, the expanding pad method is suited to all types of, and variable ores. It requires large, relatively flat areas and should have a net evaporation climate to maintain zero discharge criteria.