1. Antamina Mine Water Management Model Alan Keizur Golder Associates Roberto Manrique Arce Compañia Minera Antamina User Conference 2006 Background The Antamina mine, located at over 4,300 m elevation in the Peruvian Andes, is one of the world’s top ten producers of both copper and zinc. In 2002, a GoldSim model was developed by Golder Associates to provide Antamina with a forecasting tool to assist with water management system operations. Key Model Components Concentrator – given ore type and tonnage, the model calculates the volume of tailings slurry produced, including solids, free water, and pore water Climate – generates daily precipitation values according to the specified scenario (historical, Monte Carlo, or annual dryness condition). Lake evaporation is based on measured monthly averages, and runoff is calculated using the Australian Water Balance Model (AWBM). The input parameters for the runoff model were calibrated to match measured values in each of the major catchments. Tailings Pond – calculates volume and elevation in the tailings pond given previous values and daily inflows and outflows. Major inflows include tailings slurry (consisting of free water, pore water, and solids), runoff, direct precipitation, and inter-basin transfers. Major outflows include pumping for concentrator reclaim, transfers to polishing pond, evaporation, and seepage that is collected and (optionally) discharged. Other Storage Ponds – three other storage facilities are included in the model: Dam D (fresh water storage), Nescafe (flood control and fresh water storage), and the polishing pond (flood control and dilution or tailings pond water) Diversion Ditches – route water from one location to another Receiving Waters – calculates necessary releases to meet instream flow requirements Objectives for the Model Antamina developed the GoldSim model to meet the following objectives: Develop and confirm the water balance for the tailings basin and test under different conditions (climatic and operational). Provide useful projections of volume, elevation, and flow rate for the Tailings Dam, main upstream dams (Dam D, Polishing Pond, Nescafe Lake) downstream water systems (Tucush Creek and Ayash River) in the short, middle, and long-term. Based on the above the GoldSim model results are used to support operational decisions, such as:  Assessment for the dam raise plan (e.g. probable maximum flood (PMF) compliance) and support for dam management (e.g. tailings deposition plan, pond water volume trends).  Calculate tailings deposition rates under different concentrator operating scenarios (ore type, throughput)  Assess the impact of certain management decisions (e.g., tailings seepage return line into Tucush wetlands, replacement of batch water loads in pipeline with Dam D fresh water, etc.) Observations and Future Directions The following observations and conclusions can be drawn from the work to date: The Antamina Water Management Model is operational and adequately represents the actual site conditions. GoldSim is a very effective platform for implementing this type of model The next phase of model development may include the following: A preliminary model for an additional basin was constructed, but not maintained due to rapid site changes. This may be revised once the system stabilized. A new module may be added to simulate concentrate transfer and operations at an associated port facility. Typical Simulation Scenarios Antamina personnel run the model on a regular basis to assist with planning and operation of the water management system. Model runs are typically done deterministically based on specified scenarios, such as the following: Time Frame – typically one month to 5 years Precipitation – 100-year wet, 100-year dry (based on statistical analysis of long-duration records from nearby climate stations), or historical average precipitation (based on measured data at the site since 2000) Transfers from Tailings Pond to Polishing Pond – specify decision rules for making transfers to the polishing pond for dilution and eventual discharge. Seepage Pumpback – specify decision rules for managing collected seepage, which can be pumped back to the tailings pond, discharged directly, or pumped to a passive treatment system (wetlands) Tailings Production – various production rates and ore types can be analyzed. Release of fresh water to maintain instream flows – releases from the three fresh water storage ponds can be either specified or calculated to ensure minimum flows are maintained in the Quebrada Ayash. Water Management System Diagram