SRK conducted a numerical stress analysis to evaluate sill pillar stability for Tahoe Resources’ Escobal Mine located in southeast Guatemala. The Escobal mine uses LHOS methods to extract 4,500 tpd of high-grade silver ore. The mineralisation is typically wide with mining widths of up to 55m. The overall depth extends to approximately 1,200m below ground surface. Mining such large open stopes is often challenging due to the location of a major fault zone anastomosing within the hanging wall and mineralisation as well as with elevated horizontal stress conditions.
SRK developed a mine-scale FLAC3D model to evaluate mining-induced stress conditions and deformations as mining approaches a sill pillar that was left during the early stages of mining. An initial simulation was conducted incorporating the as-built mining sequence to date, allowing stress states to develop naturally within the model over time. After further calibrating the model’s input parameters to reasonably match observed ground conditions and excavation performance, different potential future mining sequences were simulated within the model. The goal was to determine the optimal sequence for shedding stresses away from each of the mining areas, long-term infrastructure and access headings.
The results of this analysis indicated that full sill extraction would be unlikely using the current mining method, extraction rate and sequence. It was also determined that rock mass disturbance (i.e. high shear strain and confinement loss) should be expected within the sill. With the results of the model, SRK was then capable of providing the mine with valuable information about the anticipated rock mass and stress conditions within the sill pillar, as well as further guidelines for developing a more suitable mining and backfilling sequence. The modelling also determined that more favourable ground conditions and increased ore recovery could be expected as a result of decreasing the mining rate within the sill area.
Mike Levy: mlevy@srk.com
John Tinucci: jtinucci@srk.com
