Waste Rock and Tailings Management
Mining involves the removal of non-ore rock to access ore deposits. Because this material cannot be used to recover ore, it is called waste rock. Waste rock may contain trace amounts of metals that are naturally present in minerals, therefore it must be properly managed to reduce the risk of water pollution. Waste rock at most of our sites is placed into engineered facilities, then sloped and contoured into natural shapes, typically covered with a growth medium and vegetated – often with native grasses and shrubs. Such approaches are designed to control the amount of water than can infiltrate into the waste rock. At some sites, waste rock is returned underground or disposed of under water. Such approaches restrict the exposure of the rock mass to oxygen and inhibit minerals from oxidizing and releasing their metals or salts.
Tailings is the finely ground rock remaining after ore has been processed and the gold has been removed. Because tailings is derived from mineralized ore, it contains trace metals as well as residual process chemicals. Tailings are most often managed at Barrick’s operations by being placed in engineered storage facilities. The tailings storage facility (TSF) is managed to reduce the potential risks to the public, the environment and to the company. The TSF stores tailings solids and water in a facility which, after cessation of mining, will become part of the natural landscape. Safety is the number one priority in the design and management and ongoing monitoring of our tailings storage facilities.
The design of a modern tailings storage facility for a Barrick operation uses the best available technology, which meets the social, physiographic, climatic, biological and geochemical nature of the materials and the site. All components of the TSF design are assessed with respect to risk and risk tolerance and an independent technical review is completed. Tailing storage facilities are designed to meet regulatory requirements for safety and environmental protection, as well as meeting commitments made to communities of interest. At four operating sites, tailings material is thickened to a paste or cemented and returned to underground workings, and at three operating sites, tailings material is placed into open pits.
Barrick currently uses the Mining Association of Canada’s ‘A Guide to the Management of Tailings Facilities’ to guide the design, operation and closure of our tailings facilities. We are committed to compliance with these guidelines. The tailings facilities at active operations are inspected annually by the engineer of record or a similarly qualified professional engineer. In addition to these inspections, corporate or third-party audits are completed at many facilities each year.
At our operations where it has been determined that the waste rock and tailings have a potential for acid rock drainage, preventative management processes are implemented. Barrick is a member of the International Network for Acid Prevention which works to address this global issue.
Tailings Management at Porgera
At the Porgera Joint Venture mine, located in Papua New Guinea, tailings management methodology involves riverine tailings discharge. The mine is situated in a region subject to seismic activity where landslides are common due to extreme, sudden rainfall. Combined with these conditions, very steep, unstable terrain makes safe construction and operation of a conventional tailings facility challenging.
The Government of Papua New Guinea approved the practice of riverine tailings in 1990, recognizing the very unique operating environment and risk associated with the area. The practice of riverine tailings disposal was in place at start-up, before Barrick acquired its interest in the property as a result of the Placer Dome acquisition in 2006.
A team of experts has been engaged over the last few years to review and evaluate alternatives to improve and reduce the discharge of tailings. This extensive effort has taken into account Porgera’s unique circumstances and a full range of environmental, social, technical and regulatory considerations. Continuous improvement is being pursued in all areas, including waste management, processing and procedures.
Porgera Joint Venture operates based on a stringent, government-approved Environmental Management Program. Prior to disposal, the tailings undergo treatment. This includes neutralizing the tailings in the processing plant neutralization circuit, cyanide destruction of the carbon-in-pulp tailings, and extraction of dissolved metals through the addition of lime. The mine conducts extensive biological testing to determine the impact of the discharges on the aquatic environment. All discharges are within the water quality limits established by permit. Monitoring results are sound and the mine has never exceeded its compliance levels.