Bunker Hill Announces PFS for First Phase of Mine Restart
“The PFS for Phase 1 of our multiphase value-generation plan for the Bunker Hill mine outlines how we intend to commence profitable, sustainable, modern operations by the end of 2023,” Bunker Hill CEO Sam Ash said. “We are now focused on driving forward to a formal construction decision while maintaining momentum with ongoing restart activities.”
The PFS was prepared in accordance with National Instrument 43-101. Mine- Tech USA developed the mine infrastructure, capex and opex related portions of the PFS, as well as portions of the mine plan and operating schedules in coordination with Bunker Hill’s team, who directed Patterson & Cooke North America for the tailing backfill components, YaKum Consulting Inc for metallurgy and processing, and Barr Engineering for process design and milling.
The majority of the initial capital cost relates to construction of the processing plant at an estimated pre-contingency cost of $26.8 million and harnessing the extensive mill equipment and components from Teck’s Pend Oreille site. These costs include labor, refurbishment of equipment, costs of a new mill building, including clearance, geotechnical and foundational work, and costs of additional mechanical equipment and components to ensure all aspects of the processing plant are capable of an 1,800 short ton per day run rate.
The new plant will be located in the main yard where the Bunker Hill maintenance shop currently sits. Costs related to the purchase of the process plant from Teck are not included, nor are the costs associated with its demobilization, as this activity had been completed as of August 2022. Approximately $6.4 million has been budgeted for capital development, a moderate estimate considering the extensive, intact, pre-existing infrastructure at the mine and surface, including underground workings, surface portals and shaft access points, as well as the main mine office and adjacent surface buildings.
Bunker Hill’s long hole stoping method envisions the use of a paste backfill plant to deliver binder-added tailings product to backfill stopes. The paste plant will also deliver both binder-added and non-binder added thickened tailings to open historic mining voids throughout the mine as a means of tailings deposition. Patterson & Cooke, North America investigated several options to handle the backfill and tails placement requirements of the project. The option with the greatest amount of operational flexibility is to locate the plant on surface. The $6.2 million of capital allocated for this will include construction of a tailings thickening plant and a tailings filtration plant immediately adjacent to the building. In addition, a paste plant and pumping station will be constructed at the mine’s 5-level laydown in the Wardner yard.
Construction management (EPCM and related costs) and detailed engineering costs have been estimated at $4 million and $2.8 million respectively. Run-of-mine (ROM) ore will be fed into a mobile jaw crusher located at the surface portal in Wardner. The crushed ROM will be delivered to the secondary crushing circuit via truck haulage. Crushed ore will be fed to a fine ore storage silo ahead of the new concentrator facility.
The new concentrator facility will consist of a standard primary ball milling circuit followed by a conventional differential flotation circuit for lead and zinc. A lead concentrate will be produced first, followed by zinc concentrate in conventional flotation cells with three stages of concentrate cleaning for each product. Concentrate dewatering and loadout will take place on the north end of the concentrator to more easily accommodate the receiving and loading of concentrate trucks.
All tailings produced in the concentrator will be filtered and backfilled. No surface tailings storage facility will be required. All process water solution will be recovered and reused in the concentrator. All freshwater makeup for the concentrator will either come from mine water sources or an internally operated water treatment processes facility within the concentrator.
The zinc and lead concentrates are assumed to be transported by truck to the smelting facility owned by Teck Resources in Trail, British Columbia, with Teck exercising its option to acquire 100% of the zinc and lead concentrate production for an initial term of 5 years.