The mineralization at Musselwhite can be classified as an Iron Formation hosted gold deposit. Typically, gold in these deposits occurs in cross-cutting quartz veins and veinlets or as fine disseminations associated with pyrite, pyrrhotite, and arsenopyrite hosted in iron formations and adjacent rocks within volcanic or sedimentary sequences (McMillan 1996).

Mesothermal veins.
Mineralization is predominantly hosted within meta-chemical sediments (banded iron formations) and in particular within garnet-magnetite-grunerite facies meta-banded iron formations (locally termed the Northern Iron Formation). The location of mineralization is controlled by the intersection of shear zones and folded meta-banded iron formations. These geological controls result in mineralized shoots, which plunge at approximately 15 degrees to grid north, have a down dip extent of up to 150 metres, down plunge continuation in excess of 1.5 kilometres, and across-lithology width of up to 10 metres. Mineralized zones are characterized by abundant pyrrhotite, quartz flooding and, rarely, visible gold.

Musselwhite utilizes both conventional and modified Avoca mining methods depending on the access available for that retreat. Retreats without a secondary access are mined utilizing modified Avoca. With modified Avoca, all activities are completed from the retreat drive. The fill is placed from the retreat end and therefore, once the panel has been filled there is a requirement to remove some fill (void pull) to 1. Provide void space for the next blasting cycle and 2. Prevent fill from mixing with the ore causing dilution.

With increasing depth, blast sizes have had to be reduced to control unplanned dilution.

In a set of trials at Musselwhite mine beginning in late 2016, Goldcorp tested a new mining method to reduce dilution in its production stopes with Orica’s WebGen 100 wireless detonators.

Since the case study blast, Musselwhite has implemented the TRP method in several areas of the mine where excessive dilution is being experienced.

Temporary Rib Pillar AVOCA
The Temporary Rib Pillar (TRP) mining method was developed by Orica to take advantage of fully wireless blast initiation.

With the TRP method, a temporary pillar, located at the backfill/ore interface, as well as a slot are drilled in the next panel to be mined. The entire panel is loaded in one loading operation, the TRP is primed with WebGenTM 100 and the Mass Blast is primed with i-konTM.

The Mass Blast is fired and mucked out leaving the TRP to hold back the fill.

The TRP is fired in two distinct blasting sequences within the same blasting event. Blast 2A removes the front ring and the bottom half of the of the pillar. The muck is thrown towards the draw point. The blast is then paused for a period of time in order to let the backfill rill to its natural angle of repose. Blast 2B fires the top portion of the pillar in both directions. The muck that is thrown towards the fill lands on the top of the rill and flows down to the ore/fill interface.

The TRP concept aims to improve two key aspects of the business; safety and productivity. From a safety and asset protection perspective the benefits of the TRP method are:
• Reduced exposure to working adjacent to open holes
• In-Stope exposure time to equipment is reduced during the mucking cycle
• Lowered risk of wall sloughage damaging equipment in-stope
The productivity improvements that are projected for the TRP mining method include:
• Reduced drill and blast cycle times
• Improved fragmentation and mucking rates
• Reduced distances for remote mucking
• Reduced dilution by providing a temporary span pillar
• Reduced fill placement because of dilution reduction
• Eliminating void pulls (material re-handling)

Musselwhite Materials Handling project.
This project improves material movement from Musselwhite’s two main zones below Lake Opapimiskan. An underground shaft will hoist ore from the underground crushers, reducing haulage distances and ventilation costs. Commercial production was declared in December 2020.

The mine has now grown to a depth below 1,200m under Lake Opapimiskan with a one-way haulage distance of 7.5km to the 400mL crusher. The truck haul distance was about an hour to an hour-and-a-half round trip for the mining company's 40-tonne haul trucks. The material handling project was constructed to reduce the reliance on trucking while increasing production by 20 per cent.

The system will reduce the number of trucks operating in the mine from 17 to nine, minimising traffic congestion and associated safety risks. Less ventilation will also be required, reducing power consumption and helping lower mining costs.

The conveyor system and the material handling systems work in association to efficiently move material from deeper mine levels to the surface. Haul distances are reduced as the ore crushed at depth will be hoisted from the underground crushers to the conveyor system and brought to the surface for processing.

The project involves excavation of a winze, a vertical shaft inside the mine connecting to lower levels, which will be used exclusively to hoist ore from the 1,250 mL to the 280 mL exploration ramp level where the ore will be hauled by truck to the existing 400 mL conveyor.

In addition to the hoist room, the underground crusher installation which includes the installation of two cranes, a chute and feeder system, a jaw crusher and the conveyor system to the fine ore bin.

Process facilities include a conventional mill, which consists of a crushing and grinding circuit, carbon-in-pulp and carbon-in-leach plants, elution circuits and an electrowinning plant where the gold is recovered and smelted to produce doré. The conveyor system and the material handling project at Musselwhite reached commercial production in December 2020.

The milling facility uses two-stage crushing to reduce the ore and conventional gold extraction techniques to concentrate the gold. The tailings or residue from this process is washed with incoming tailings reclaim water in thickeners to recover cyanide. Residual cyanide is treated by an INCO SO2 cyanide destruct system prior to being pumped to the tailings thickener plant (installed in 2010) which is located in the Tailings Management Area (TMA) approximately 3 km west of the plant site.

The use of cyanide begins with the grinding area, which uses re-circulated cyanide bearing solution from the counter curre ........