Long Term Performance of Hydrogeochemical Riverine Mine Tailings Deposition at Freeport Indonesia

Steep terrain, intense rainfall, and seismic activity precluded use of conventional tailings storage facilities at the PT Freeport Indonesia (PTFI) copper–gold mine, in Papua, Indonesia. A controlled river tailings system was adopted as the only feasible way to manage the tailings. The tailings are transported to an engineered 230 km2 deposition area, which is bounded by levees on the east and west sides and is open on the south side to allow transport water and surges of rainfall to exit the area. We evaluated the performance of the ore-fed blending strategy for managing potential acid rock drainage formation of the tailings. Long-term leaching column tests and monitoring of deposited tailings provided insight on the reactivity, leaching behaviours, and neutralizing potential of the samples, and the ratio of acid neutralizing capacity (ANC): maximum potential acidity (MPA) that would ensure that the deposited tailings remain non-acid forming. We concluded that an ANC/MPA ratio >1.5 provides an adequate factor of safety to prevent acid generation and ensure long-term geochemical stability of the deposited tailings.