Author: Luis Chahua, Guillermo Barreda, Gavi Sotelo, Miguel Narva
Conference: Heap Leaching Mining Solutions
Date: October 18-20, 2016

ABSTRACT
The geotechnical design for a leach pad requires several different variables to be reviewed during the analysis of the physical stability of the structure. These variables include: 1) the material that comprises the natural foundation; 2) the potential fill material that will form the grading surface; 3) the interface shear strength between the soil liner and the geomembrane; 4) the ore that will be part of the heap; 5) the irrigation rate during the operation and 6) the placement/zoning of material within the heap leach pad.

Typically, the first three variables are controlled during the design and construction of the heap leach pad, while the last three variables are controlled by the mining company as part of their operation process. Simply, we can say that the combination of the last three variables can have a solution flow behavior along the following range: 1) free drainage, if the irrigation rate is applied at a lower enough rate compared to the ore hydraulic conductivity; and 2) pore pressure generation at areas where the irrigation rate is applied exceeding the ore hydraulic conductivity.

This paper presents an analysis of the last three variables taking into account the characteristics of two types of materials available at a mining project: 1) till material with significant fines content and medium to high plasticity; and 2) coarse ore, which corresponds to a material with a maximum size of 6” and low fines content. For the analysis, different mixtures were prepared using these materials in order to obtain the physical characteristics and  hydraulic properties to develop the geotechnical analysis and material zoning/placement within the heap configuration.

Based on the zoning recommendations, the mine developed a large scale leach test in an existing pilot cell in order to evaluate the mixing process and solution flow behavior during the implementation of the leaching process. This consisted of: 1) controlling the flow and volume (input and output); 2) recording the pore pressure readings; 3) electrical resistivity testing and 4) soils classification testing. The results of the pilot cell monitoring and testing are also presented in this document.

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