Challenges and Opportunities for the Geotechnical Engineering
Heap leach pads are composed of mined ore, usually crushed, disposed on drainage system to be processed with leach solutions. In the case of dynamic heap leach, after the leaching process, spent ore is transported by conveyor belts to be disposed into dumps. It is common to observe physical stability problems in these dumps, that could compromise the operation of the stacker equipment along with the operational continuity of the mine. These problems are directly associated with excessive water content present in the spent ore, due to geotechnical characteristics of these materials or to drainage problems in the leach pads. Therefore, efforts during the operation are focused on finding different ways to control moisture content in the spent ore.
Since 2007, the SRK Consulting geotechnical team has been working in several projects related with heap leach pads and spent ore dumps, working in the design and operation of this deposits. So, considering the common difficulties that we have observed during these deposits operation, it is very important to carry out a "dynamic" geotechnical design, it will updated with the different phases of ore exploitation in the pit. Therefore, it is necessary to complement the design with a permanent operational control, in such a way as to define an action plan, against the arrival of spent ore of "poor geotechnical quality" (excess of fine material with high plasticity, or materials with water content excess).
SRK's recommendations to avoid or reduce the volume of Spent ore with water content excess are as follows:
- In early stages in which metallurgical testing (like testing columns) are made or during a pilot plant implementation/execution stage, it is important to take into account geotechnical testing before to implement changes in the metallurgical process.
- During the irrigation time, identification the zones in which leach pads show water pools and/or slope sliding.
- Includes spreadsheets or databases, containing information related to the spent ore behavior in the leach pads (hazard maps) and the content of water content of spent ore before to be dumped.
- Operational controls of the spent ore after the leach pad process, are needed to obtain the particle size distribution.
- Carry out periodic maintenance of the drainage system in the heap leach pad, to ensure its correct functioning.
- Permanent control of water content of the spent ore in the dump.
- Build a temporary dump for the material with water content excess to provide additional resting time before to dispose in the final dump.
- Install piezometers in the spent ore dump to check the existence the formation of any phreatic level.
