HYDROGEOLOGICAL ASSESSMENT OF SEEPAGE THROUGH THE ANTAMINA TAILINGS DAM - ANTAMINA COPPER/ZINC MINE, PERU, SOUTH AMERICA

摘要

The Antamina copper/zinc mine in northern Peru is expected to produce about 750 million tonnes of tailings during the mine life. A tailings dam is being progressively constructed at the confluence of two valleys in order to retain these tailings. The tailings dam will be raised in stages, reaching a potential maximum height of around 240 m. Antamina is also considering, at a conceptual level, the potential for additional raises of the dam to a height of about 285 m. To assess future seepage through the dam and bedrock abutments, a three dimensional hydrogeologic model of the study area was constructed using FEFLOW, a three-dimensional finite element numerical code. The model incorporated available geologic data, results of hydrogeologic testing, and details of various dam components and other engineered structures. Following construction, the model was successfully calibrated to measured dam seepage, tunnel inflow, and hydraulic heads measured in the dam abutments and in the tailings. Future dam seepage was then predicted for the operation and post closure periods. The assessment considered large contrasts in hydraulic conductivity (e.g. dam rockfill vs. underlying bedrock), unsaturated conditions that exist in portions of the tailings and in the dam, complex hydrostratigraphy associated with steeply dipping bedrock units, the presence of runnels under the right abutment, and changes in the location and extent of the tailings pond, tailings, and the dam throughout the mine life. Overall, long term estimates of seepage were found to be most sensitive to the hydraulic conductivity of the tailings and to the width of the tailings beach, and less sensitive to the hydraulic properties of the dam and bedrock.