Musselwhite has a very shallow dipping orebody. Initial gold production in 1997 was trucked to surface from shallower mine depths of 500-600m. The first major expansion, which included an underground crusher and conveyor to surface from the 400m level (mL), was commissioned in 2002 as a result of deeper mining and longer haul distances to surface.
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. This requires a truck fleet of 17 45t haul trucks to transport the ore to the crusher.
Richard Blakey, project manager of the Musselwhite materials handling project, explained: “As we go deeper, we need more ventilation underground in order to accommodate the trucks, which increases costs. By bringing in more trucks, there’s more congestion on the underground road. It simply got to the point where a more economical and efficient materials handling solution was needed.”
The geographical limitations of operating a mine below a lake rule out construction of a shaft to the surface to improve transportation and ore processing capabilities. Instead, Musselwhite embarked on a C$90 million (US$69.5 million) capital project to improve materials handling by constructing a raisebore winze which will dramatically reduce truck haulage to the mine’s underground crusher.
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. Infrastructure at 1,250 mL will include a dump pocket with rockbreaker, coarse ore bin, new jaw crusher system, fine ore bin and skip loading facilities. The winze hoist will have a capacity of 5,000t/d at 100% availability (4,300t/d average). When completed, the new materials handling system will significantly reduce reliance on trucks, improve energy efficiency, reduce ventilation requirements and lower costs.
Blakey stated: “This is a state-of-the-art materials handling system that will be operated at surface. The automated rockbreaker, crusher and hoisting system will enable continuous operation between shifts, increasing efficiency and improving production levels.”
Construction commenced on the winze project in September 2016, with completion scheduled for the end of 2018. All major production equipment has been secured, including a Davey-Markham hoist previously used at the Eleonore mine.
Blakey explained: “It’s an exploration shaft hoist that was no longer being used at Eleonore. We identified this as an asset we could use at Musselwhite. It’s being refurbished now and is going to be a central part of our operation.”
A set of ore passes are currently being constructed to move materials down to the 1,170 mL truck dump level. Major drift excavations including the main decline to winze bottom, truck chute access and bottom crusher access are currently underway. Chamber and bin excavation has started in the sheave deck, hoistroom access and crusher. The first ore pass raise was pulled successfully and contractors are in the process of installing necessary safety precautions prior to completing the 1,170 mL truck dump.
The project’s main contractor, Redpath Mining, carried out most of the lateral and vertical development work, as well as the construction and installation of the new processing facilities.
Particular emphasis was placed on integrating a full team of mining contractors into Goldcorp’s safety culture, said Blakey, which was a key factor in the mine achieving a 270-day triple-zero safety performance.
The winze materials handling system is scheduled to be fully operational by the March quarter of 2019. Once up and running, the new system is expected to increase throughput, as well as generate cost savings of approximately 10% over the life of the operation.
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.
Todd White, executive vice president and chief operating officer at Goldcorp, said: “In the big scheme of things, the materials handling project is a relatively small investment for Goldcorp that could potentially result in around a 20% increase in throughput at Musselwhite mine and unlock more of the operation’s potential.”