Stope stabilisation with self-levelling cemented paste backfill

The use of self-levelling cemented fills has gained widespread use for the rehabilitation and stabilisation of abandoned mines. This paper documents the use of this method for stabilising stopes subject to uncontrolled cave in an active mining area. OZ Minerals is the owner and operator of the Pedra Branca copper-gold mine in Pará State, Brazil. The mine produces roughly 0.8 million tonnes per annum of high-grade copper ore from underground operations. Mining is accomplished via longhole stoping on 30 m levels. Stopes are then backfilled with cemented rockfill. In 2023 the mine experienced an uncontrolled cave in two adjacent stopes on the 1035 m sublevel, creating a void of roughly 40,000 m3. After a review of the available options for backfilling the void, OZ Minerals selected hydraulic filling with re-slurried tailings as the best alternative. One challenge faced at the mine was a lack of tailings as the mill is located 75 km away. The mine was also constrained to the use of available resources and had a lack of equipment for the drilling of boreholes. This paper documents the many challenges and successes faced in implementing this temporary fill system, including the paste mix designs and the reliance on admixtures to ensure a flowable paste product.