At Mount Polley mine, the concept of “Dry Stacking”, an environmentally conscious and technologically advanced method for managing tailings, is being tested. Tailings are the materials left over after valuable minerals have been extracted from ore through various processing techniques. Dry Stacking refers to the process of dewatering tailings and storing them in a solid, stackable form, significantly reducing their environmental impact compared to conventional tailings storage methods.
The tailings being Dry Stacked at Mount Polley, were those deposited in the Springer Pit from August 2015 to June 2016 while the Tailings Storage Facility was being repaired. During this period the tailings were discharged over the 200-metre-high pit wall and deposited in the bottom of the Springer Pit. The maximum depth of tailings stored in the pit was 60 metres and up to 30 metres of water also stored atop the tailings in the pit. The low solids content tailings slurry segregated and settled after being deposited in the pit, and subsequently underwent self-weight consolidation from 2016 to present.
In 2022 the tailings were dewatered by pumping the surface water out of the pit, and by installing and pumping two strategically placed wells which were located on a causeway built on top of the tailings. The wells were drilled through the tailings into blasted rock on the bottom bench of the pit, and had submersible pumps installed which dewatered the tailings from below.
Mining Progress at Mount Polley in the Springer Pit
Since the recommencement of operations in 2022, mining has been ongoing in two adjacent open pits, the Cariboo and Springer pits. The area located between the two pits, referred to as a “saddle” has been successfully mined and has progressed to the point that the two pits have merged into the Springer Pit. As a result, the bottom of the Springer Pit now lies beneath the surface of the previously stored tailings. These tailings are non-acid generating and will not generate acid mine drainage. The photos below show the progress achieved in the last year.
The diagram below illustrates a cross section of the Springer Pit at Mount Polley:
The below photograph shows the mining of dewatered tailings from the 964 Bench in the Springer Pit:
Photograph of mining, in July 2023. Dry tailings being mined out of the pit:
Approximately 2.2 M m3 of tailings excavated from Springer Pit will be stored in cells atop an area used to store unmineralized rock. Dry stacking of tailings began as of May 8, 2023.
The photograph below shows a dozer spreading a lift of tailings atop the southeast rock storage area. The dry stacked tailings will be raised in 5 metre lifts to a total thickness of 20 metres.
The photograph below shows dry stacked tailings stored in cells atop the southeast rock storage area, July 2023:
The tailings being produced at the mine since the recommencement of operations last year are being stored in a traditional tailings storage facility. Dry Stacking of the tailings previously stored in the Springer Pit is a good test of this method of storing tailings, and the lessons we learn from this Dry Stacking will help us evaluate the use of this method for all our future Mount Polley mine tailings management. This test of the concept not only minimizes the environmental footprint of mining operations but also ensures the responsible stewardship of natural resources. By stacking these dewatered tailings in a secure and efficient manner, Mount Polley mine exemplifies its commitment to sustainable mining practices and contributes to a safer and more ecologically conscious mining industry.