Foran Mining Corporation recently filed an independent NI 43-101 technical report for the Pre-feasibility Study (PFS) on the company’s McIlvenna Bay zinc-copper-gold-silver project in eastern Saskatchewan. The report was authored by byAGP Mining Consultants Inc (AGP). McIlvenna Bay is the largest undeveloped VMS deposit in the region. This prolific metallogenic belt is host to 29 past and present producing mines, including Hudbay Minerals Inc’s 777 and Lalor operations.
The mining method selected for the McIlvenna Bay deposit is a combination of transverse longhole stoping and Avoca longitudinal stoping. The orebody will be accessed by a decline, with trucks being used to haul ore to surface initially and a vertical conveyor to be commissioned later in the third year of production to transport ore to surface.
McIlvenna Bay will be an early adopter of Battery Electric Vehicles (BEV) haul trucks. The report states: “At the time of writing, these trucks are a proven technology currently under use in at least two underground mines in Ontario with many companies investing in the technology.” Because the mine will be an early adopter the PFS includes a ‘BEV factor’ of 30% which has been applied to the truck requirement calculations to account for any learnings that would result in lower productivity than indicated by the manufacturer. Years three and four will see the greatest truck need with a requirement up to seven BEV trucks.
The nominal production rate will be 3,600 t of polymetallic ore per day, which is slightly lower than would be suggested by Taylor’s Law due to the narrow nature of the orebody. Backfill will be achieved with paste backfill utilising filtered tailings. In the interest of minimising stope cycle time, all transverse stopes are scheduled to be backfilled with paste, however, secondaries could potentially be backfilled with development waste to reduce cement cost. Avoca stopes will be backfilled with development waste.
Lateral development will be achieved using conventional jumbo drill and blast methods. Typical ramp dimensions will be 5.0 m wide by 5.5 m high to accommodate the 50 t haul trucks. The round length will be 4 m. The blasted material from development rounds will be mucked using LHDs and standard ground support will be installed using mechanised bolters. The company currently envisages the potential use of 7 Sandvik LH517i LHDs and 11 Artisan Vehicles (Sandvik) Z50 battery electric trucks.
During year three, an underground crushing station and vertical conveying system will be installed and commissioned to allow transfer of ore directly to surface. Once commissioned, trucks will be able to dump ore into a coarse ore bin at level 0 m AMSL. The coarse ore bin will be protected with a static grizzly and hydraulic rockbreaker for the handling of grizzly oversize material. This bin will be discharged in a controlled manner by a heavy duty vibrating grizzly feeder which feeds oversize (+125 mm) material into the jaw crusher and bypasses undersize material onto the jaw crusher product conveyor. Material discharged from the crusher, together with material passing through the vibrating grizzly feeder will be transferred a short distance into the fine ore bin by a heavy duty conveyor, equipped with a self cleaning tramp removal magnet and oversized drive.
The fine ore bin will be discharged in a controlled manner by a pair of heavy duty “brute force” pan feeders via lined chute work onto a transfer conveyor equipped with a static tramp metal magnet. The transfer conveyor will discharge crushed material onto the tail end of the vertical conveyor. The vertical conveyor will reduce the number of required haul trucks, and therefore ramp congestion. The capital cost of the vertical conveyor is significantly less than the cost of additional haul trucks that would be required to sustain production from deeper levels in the mine as well.
Once the vertical conveyor is commissioned in year 3, trucks will dump at the underground crusher in preference to hauling to surface, although surface crushing facilities will remain available for periods in which the underground crushing system is unavailable. The BEV trucks will be equipped with the ability to self-change batteries, so extensive infrastructure such as a crane is not required. This also allows battery charging stations to be moved as needed.
During the first three years of the minelife all the batteries will be charged on surface. There will be two batteries for each truck and the charge time is less than the battery life so the trucks can dump the ore or waste at an appropriate location on surface and change batteries before heading back underground. Once the vertical conveyor is commissioned, the charging stations will need to be relocated as required. These can be located in remuck bays that are no longer in use. Haulage Productivity Simulation data was provided by Sandvik based on the productivity for a single truck based on the longest haul distance (hauling waste from the bottom of the mine to surface).
The McIlvenna Bay ventilation system is designed as a pull system with total airflow requirements of 200 m3/s. There will be two 2‐fan exhaust fan systems installed over two perimeter located exhaust raises. The decline will be the primary intake route and will include a propane heater system located at the portal. In addition, a minimal amount of intake air will also enter the mine via the egress system. Regulators will be used on production levels to control the flow of air across the levels between the intake ramp level accesses and the exhaust raises. Ramp, level development and stope ventilation when required will rely on auxiliary ventilation by way of auxiliary fans and either lay flat or hard plastic duct to distribute the air.
Production ventilation airflows will be regulated across each level using ‘drop-board’ type regulators. These regulators will be located at each end of the level and set to regulate the flow based on the activities taking place on the level. Normally for a mucking sequence this flow will be set to approximately 20 m3/s. This will allow for a 50 t BEV truck and LH517i LHD to operate in this area. Truck loading will take place in the truck turn‐a‐round. Lesser amounts of air would be required for drilling or screening activities, once again these would be regulated based on the location of the activities on the level. Ore accesses and captive development on these levels longer than 25 m in length will require the use of auxiliary fans and ducting.