Thanks @Battersea. Well explained by raptureking.
It is quite common for a mine to run both a CIL plant and a Heap Leach operation in parallel. I’ve worked on a couple such . Low grade ore that would be sub-economic if treated through the process plant can be heap leached at a much lower treatment cost per tonne. The process for heap leach is much slower [ cycle times of 50-90 days versus 1 day in CIL and recovery is also lower ) but costs are minimal, and it can be a valuable additional revenue source.
One of the big challenges for a heap leach operation in the tropics is how to handle large quantities of rainfall collected by the piles during storm events. As the “heaps” can be very large, the water collected can overwhelm the circulating pond capacity. Having a CIL plant next door obviates the problem, as excess water can be sent to the mill as process make up water. A win win.Also, the pregnant solution from Heap Leach could be pumped directly to the CIL plant for gold recovery there, removing the need ( and cost) of building a separate gold recovery circuit at the Heap Leach.
The test work Tietto will be currently undertaking are laboratory scale heap leach trials. They will determine the best crush size to liberate the most gold, reagent requirements ( cyanide and lime usage) , the permeability of the ore ( critical, as the pile needs to be saturated in a reasonable time frame), cycle time , and final recovery. Not all ores are amenable to heap leaching eg . high clay content ores resist the flow of solution.
Hopefully the test results will be positive , and an additional 30 -50 000 oz per year might be obtained this way ( best guess) after Year 1 of production.
