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Tailing Storage Within a Heap Leach Facility - An Update on the Success at Yanacocha

Author: Felix E. Garcia Prado, AnaMaria Rios Pando, Thomas F. Kerr, Antonio Belmar, Miguel E. Gutierrez, Thomas Byers, John Lupo
Conference: Heap Leaching Mining Solutions
Date: October 18-20, 2016

ABSTRACT
The Yanacocha Operation is an open pit gold mine located in mountainous terrain in Northern Peru. The Operation includes one tailing storage facility (TSF) and four heap leach facilities (HLFs). Given constraints imposed by topography and permitted boundaries, the efficient use of space is a priority. As an example of a design driven by the need to use space efficiently, the existing La Quinua (LQ) TSF was constructed entirely within one of the HLFs (the LQHLF) and uses the heap leach ore to form the containing embankments for the tailings (termed mill sands at the site). The LQHLF has been in operation since the mid-1990’s and the LQTSF was commissioned in 2008. The combined facility has consistently performed within its design expectations. However, both have now been developed to their maximum heights (with the maximum height of ore above the liner at 130 meters) and due to additional mining and the existing LQTSF nearing its design capacity, there is a requirement for the mine to develop additional tailings storage capacity. To meet this demand a new TSF was designed beside the existing LQTSF in the same LQHLF. The new TSF, designated the LQTSF North Expansion, is currently under construction.

In contrast to the existing LQTSF, which was progressively developed in a basin in the LQHLF as the facility was being loaded, the LQTSF North Expansion is being built as a new excavation within the LQHLF after the ore had been placed and leached. Key design considerations included (1) stability and deformation potential of the excavation slopes under static and seismic conditions, and (2) water removal from the excavation. Both considerations were for the short term (during the construction), and the long term, thereafter.

The majority of storage will be developed in the basin excavation, but some storage in the upper LQTSF North Expansion will be developed behind a low height embankment across the north perimeter, termed the North Embankment. The embankment is being constructed as an engineered fill structure using the mine haulage fleet to place and compact it. The original intent was to use leach ore from the excavation as fill but high moisture contents in the material led to a requirement to use other borrow sources. The suitability and compaction requirements for these borrow sources were evaluated with test fills, laboratory testing, and fields density testing. Slope displacement monitoring during construction was carried out using inclinometers, conventional prism surveying, and slope monitoring radar.

The construction is on schedule with regard to timeline and cost, and operation of the facility is planned to start in late 2017.

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