This profile originally appeared in the September 2020 issue of International Mining.
To improve on filling rate and to produce a consistent, high quality backfill, Hudbay Minerals looked to install a new paste backfill plant at their Lalor zinc, gold and copper mine, located in Snow Lake, Manitoba. Paste backfill plants are not new to Hudbay, in fact, the company operated one of the earliest facilities at their Flin Flon operation, also located in Manitoba. The Lalor Paste Backfill Plant is one of the newest plants in Canada featuring state of the art process control technology that allows the facility to run with minimal operator intervention. The plant was commissioned in the spring and early summer of 2018 and by late summer, was in full operation.
There are some unique features to this backfill plant. This includes the delivery of tailings from the Stall Mill which is located 16km away from the Lalor mine. A booster station situated adjacent to the tailings management area (TMA) was designed to intercept the tailings and pump them 13.5 km to the paste backfill plant. Since there were no disposal or treatment options at the mine, excess water from dewatering of the tailings needed to be pumped back 13.5 km to the TMA in a parallel return line. The booster station was also designed to deal with large swings in tailings flow rates, and future increases in production.
A fibre optic cable was laid down along the remote booster station line that provided communications back to the paste plant. Multiple leak detection stations were also set up along the pipeline at critical locations and monitored through the fibre optic network. Environmental monitoring and compliance were a key consideration during the design phase.
The Lalor Paste Backfill Plant has the unique ability to store four days worth of tailings from the mill through the use of two large agitated filter feed tanks. This serves to both decouple paste production from mill tailings delivery by using the stored tailings and effectively allows the paste backfill plant to pour at a sustained higher rate than the mill tailings feed rate when it is coupled. The paste plant design includes a high rate thickener, large agitated tailings storage tanks, 3.8 m diameter disc filter, belt conveyor, cement silos with a loss in weight feeder, multiple cement screw conveyors, and a twin shaft mixer.
Paste is delivered to the underground mine via twin boreholes (standby and operating) located in the paste plant. The surface location of the paste backfill plant allows for gravity flow of paste to the stopes for backfilling. The plant is designed to operate on a continuous basis with sufficient redundancy, surge capacity and provisions for emergency power to warrant an optimal, safe and reliable operation.
Lalor was discovered in 2007 on 100% owned land using Hudbay’s innovative exploration techniques and it is the largest VMS deposit found in the Snow Lake region to date. In February 2020, Hudbay announced increased mineral reserves and resources for the Lalor mine and nearby satellite deposits, and a new mine plan that includes the processing of gold and copper-gold ore at the company’s New Britannia mill.