Osisko Mining Inc has filed the technical feasibility study report prepared by BBA Inc on its 100% owned Windfall gold deposit in the Abitibi greenstone belt, within the Eeyou Istchee James Bay region of Quebec, Canada. The project has total proven and probable mineral reserves of 12.2 Mt grading 8.06 g/t Au and 4.18 g/t Ag resulting in 3.16 Moz of gold and 1.64 Moz of silver. The expected mine life is 10 years, with peak year payable production of 374,000 oz (year 2) and average life of mine annual payable production of 294,000 oz of gold.
Production begins in mid-2025 and reaches the target production rate of 3,400 t/d in early 2029; milling throughput is maintained at approximately 3,400 t/d until 2029 using the early mine stockpile. The Lynx zone is active at project start, while the Main zone does not begin development until mid–2026. Longhole stoping provides approximately 80% of the total production with the remainder comprised of sill development.
The Windfall Project has three primary zones: Lynx (Lynx zone), Main and Underdog (Main zone). All zones trend roughly east–northeast and dip vertically between 45° to 90°. The Main zone is the western portion of the planned mining area and the Lynx zone is the eastern portion. The zones
are accessed by three ramp systems, with two surface portals for transportation and material haulage. The ramps and level accesses (up to the vent raise access) will be 5.2 m high by 5.5 m wide allowing the passage of 54 t haulage trucks as well as secondary ventilation ducting and service piping. Ore access drives towards the ore zone will be 4.5 m high by 4.3 m wide, while development in mineralized material will be 4.5 m high by 4.0 m wide.
Longitudinal longhole mining is described as suitable for the Windfall Project, where the dip of the mineralisation is 45° or greater, and the materialised zones are of sufficient width and grade that the estimated dilution does not eliminate the profitable recovery of the material. Mining will consist of an undercut level and an overcut level, each accessed from the main ramp or an access drift. Each sill will be accessed perpendicularly from the ramp or access drift, and then developed along strike of the vein to the economic extents of the mineralisation.
Once sill development is completed on each level, production holes are drilled between the sills and then blasted until the stoping panel is completed. Following cavity monitoring of the stope, the void is then prepared for backfill. Once a sufficient distance along strike (one to two stope lengths) has been extracted and backfilled, mining can progress either up–dip or down–dip and extraction can recommence opening another mining location.
To optimise material movement, 14 and 18 t capacity LHDs have been selected for mucking and truck loading activities. 14 t capacity LHDs are proposed for smaller profile development headings and stope mucking. 18 t capacity LHDs are proposed for large profile development headings and to load the 54 t trucks at the level accesses. The working schedule for the production and development crews is two shifts per day, at 12 hours per shift, 365 days per year. A utilisation of 85% was assumed for all major equipment.
The main accesses have been designed with two 15 m stockpiles per level, with many ore drives available that can serve as temporary stockpiles. During development, all larger profile headings will utilise the 18 t LHDs, while smaller profile headings will utilise the 14 t LHDs. During production, stopes will be mucked to the level access stockpiles using 14 t LHDs. Once the stockpiles are full, a dedicated 18 t LHD will conventionally load trucks until the stockpiles are empty. During this time, the stope mucking operator can continue to muck the stope to a temporary stockpile or move to an alternate level.
All mining and maintenance activities, with the exception of vertical development and concrete delivery, will be completed by a company workforce using company–owned equipment. A total of 90 units of mobile equipment will be required for the project. Apart from LHDs, trucks, personnel carriers and concrete delivery equipment, all remaining equipment will be battery electric. Battery electric equipment will charge via PTO while stationary (either working or idle).
Specifically, the fleet has an interesting mix of conventional diesel and all electric BEV units – the diesel machines include the primary LHDs and trucks – envisaging the use of initially six Epiroc 54 t MT54 trucks (rising to 10); plus two Epiroc ST14 LHDs (rising to five) and two Epiroc ST18 LHDs (rising to three).
Most of the drills and support machines will be electric – including a large planned MacLean Engineering fleet that includes at peak eight 975 EV Omnia Bolters (inc one High Reach); five MacLean EV Emulsion Chargers (three EC3 for development and two CS3 for production); five MacLean SL3-EV Scissor Lifts; plus support MacLean EV machines including a Block Holer, two Boom Trucks, two personnel carriers and two graders. Electric drills will include five Epiroc Simba ME7C-EV units and five Epiroc M20-EV two boom jumbos. Two Sandvik DL432i longhole drills will also be used.
A large fleet of Kovatera vehicles numbering over 30 units includes various Service Trucks and personnel carriers. The shotcrete machines include a SWATcrete Mobile CRF Unit and SWATcrete Sprayer which will be operated by a contractor.
Windfall will have a fuel bay located adjacent to the garage at –140 RL in the Lynx zone. Fuel will be provided from a 550 m borehole lined with steel pipe from the site’s surface fuel farm. The general fuelling strategy will be for LHDs to be fueled underground, while haulage trucks and light
vehicles to be fueled on surface, with the fuel bay used as required during the shift. The expected maximum consumption for all diesel mobile equipment is 7 million litres of diesel per year. The remainder of the mine’s equipment is proposed to be battery–electric and will require recharging
through the mine’s underground electrical distribution network.
A fibre optic network will be installed through every electrical substation, providing mine–wide network coverage. A LTE network will be installed alongside the fibre network to provide vocal communication between employees and wireless communication for the equipment. The optical fibre and LTE network will be used for gathering critical information for the control of the ventilation-on-demand system. Vehicle and cap lamp tags will allow the software to locate personnel and vehicles anywhere in the mine. Air supply can then be adjusted according to their positions.
The Windfall Project currently has two ventilation raises to surface, which will be used as exhaust raises for the Bobcat and Lynx zones, with three planned raises to surface providing exhaust for the Main zone and two F–zone satellite mining areas. These exhaust raises will be equipped with
fans and will create a pull system with fresh air being drawn down the two portal ramps.
A water management system has been designed to handle 5,200 m3/day of water. This volume includes water from infiltration and mining activities. The planned system will pump dirty water to surface for treatment before being recirculated underground for use in operations. Pumping requirements are tied directly to development and production activities, providing complete dewatering capabilities throughout the mine life.
Proposed to begin once construction is complete, paste will be pumped underground from surface through a borehole and routed to the stope level through 8–in schedule 80 and HDPE piping. Downhole stopes will be paste–filled from their overcut level while uphole stopes will be filled through a pastehole drilled from the undercut level. Pressure monitoring of the paste line will be conducted through pressure transducers located at the bottom of the surface borehole and on each level. The construction of friction loops and implementation of rupture discs are proposed for over pressure protection.