The first large scale application of modern heap leach technology was in the early 1980’s at the Lo Aquirre Project in Chile. By the mid 1980’s, most new leaching operations were using modern heap leach technology. This consisted of crushed ore (sometime agglomerated), thinly stacked lifts of ore (less than 10m), irrigation of ore with a solvent to extract the identified mineral(s) and a liner system/collection system to capture the pregnant solution more efficiently. Mining companies across the globe embraced this method as an efficient way to cut production cost and increase productivity through the development of lower grade resource projects.
Over the years, heap leach technology has continued to advance, however there still remain design and environmental challenges/considerations such as: material placement, high loads on buried liner systems and solution collection systems, high temperatures in bio-leaching, slope stability and deformation, seismicity, harsh climate and terrain, etc. Additionally, improper design, incorrect material selection, poor construction and/or bad operational practices still plague the industry.
In 2004, Ausenco began an exciting assignment with Minera Escondida Ltd. at their Escondida Mine, the largest copper mine in the world. We developed both their sulfide and oxide ore heap leach facilities. Ausenco began with the development of the Sulfide Leach Project (SLP) - the largest bio-leach pad in the world (i.e. over 9.8 Mm2) which involved the development of an air injection system to promote bio-leaching. We also designed the ore placement system.
Ausenco then developed the Oxide Leach Expansion (OLE) that is a single use multilift pad that uses a shiftable conveyor and stacker system. This allows for the placement of the initial and interlift PVC liner and solution collection systems as the conveyor and stacking system retreats. This provides significant capital and sustaining capital savings along with maximizing copper recovery. This design results in zero delays in the operation of the leach pad and removes the need for a large construction crew.
Ausenco then went on to design Minera Escondida Ltd’s Oxide Leach Area Project (OLAP) that uses an on/off pad to process oxide ore using a stacking and reclaim system. This eliminated multiple lift leach pad with interlift liner systems, which saved the client additional sustaining and operating capital costs along with providing a very efficient copper oxide heap leach operation and that maximizes copper recovery.
Since our original work in 2004, we continue to provide engineering and support services for the OLE and OLAP projects that have a combined leach pad area of over 3 Mm2. Ausenco is currently working on a new heap leach expansion project for Escondida. Our new scope of services implies meeting the project’s challenging environmental conditions and mineral extraction process that includes front-end engineering to detailed engineering in the future.