It’s the largest underground mining expansion in Canada, and one of the most challenging to date, according to SEM Hatch, the engineering and project management firm integrated with Vale and is responsible for the six year development. There are two main underground deposits at Voisey’s Bay: Reid Brook and Eastern Deeps.
At Reid Brook – the deposit closest to surface and the first to reach production later his year – ore will be transported on a decline by truck. At Eastern Deeps, where known mineralisation extends to a depth of about 1,100 m, a conveyor system will move ore to surface.Vale is learning a lot as it ramps towards the deeper ore. Following the initial blast on October 2018, managers noticed that the drill-blast cycle was stalling at the bolting phase. Overall cycle times became unacceptable. Operators needed to move faster if Voisey’s Bay was to start producing ore by its target date of mid- 2021.
Voisey’s Bay was already using Epiroc’s Boltec rigs for rock reinforcement, keeping operators safe in the rig’s cab away from the face. But still, the work was slow, cumbersome and frustrating, especially in areas where the host rock was fractured.
“Our biggest issue was assuring that the bolt actually adhered in the hole properly,” said Construction Manager Will Menheere. “We’d shoot resin cartridges in the holes, install the bolt, spin it around, mix the resin and let it sit. But we were finding on a number of occasions that the resin would creep into fractures in the rock and the bolt would pull out right away.”
In early 2020, Vale decided to try Epiroc’s pumpable resin solution that had been field tested at the Malmberget underground iron ore mine in northern Sweden and more recently adopted by Rio Tinto at the Oyu Tolgoi copper-gold mine in Mongolia. Voisey’s Bay is the first Canadian mine to implement the bolting technology. In the Voiseys Bay case, Minova’s CarboThix resin was used.
Epiroc had developed the pumpable resin system to address the very problem the Voisey’s Bay bolting operators were experiencing: inconsistent and unreliable bolt installations that often have to be redone to ensure rock reinforcement is secure, especially as mines go deeper and rocks become less competent under the added pressure.
Epiroc started working on the pumpable resin system a decade ago, when there were limited options available that could satisfy the multiple demands of easy pumpability, fast setting time, and good load bearing characteristics, said Peter Bray, Epiroc’s Global Product Manager for rock reinforcement equipment. “We didn’t want a resin that was too runny because when you pump it into the hole it runs straight back out. We wanted a resin that had a much faster setting time and a consistency more like ketchup.”
To find resin with the desired properties, Epiroc worked with a leading supplier of ground support solutions. Minova managed to modify a resin variant that was most commonly used in civil tunnelling and underground coal mining sectors for ground consolidation. The resulting resin is a mixture of two separate components that, when mixed together, provide the perfect viscosity: a substance liquid enough to easily pump into the hole, but that stays put once the pumping stops.
The solution worked well at Voisey’s Bay, significantly reducing the bolting cycle time, providing reassurance that the bolts would hold, and boosting morale. “With the new technology, the resin encapsulates the bolt entirely and we have strong confidence in all the bolts being properly installed,” said Menheere. “Operators aren’t spending 15 hours bolting a round and getting frustrated, they are doing their round in six hours. The only times we might have an issue are in areas of poorer ground.”
The self-drilling anchor (SDA) bolts that are part of the system have also been effective. Whilst the unit cost of an SDA bolt may appear high, when taking into account faster bolting times and higher quality installation, the overall cost is greatly reduced. “One shot and you’ve got it installed and you can move on to the next one,” according to Menheere.
Safety has improved as a result, adds Vale Geotechnical Engineer Brad King. “These bolts provide life-of mine-support so we wont need to go back to do as much rehab. That’s a huge safety factor for us. Another good thing is we can keep our people away from the face and under well-supported ground.”
In the meantime, Vale is saving on the volume of materials, using fewer bolts and less resin because there is less need to redrill faulty boltholes. Menheere said the technology transition was relatively painless. Vale had to upgrade the bolting rigs to install the resin carrier and injection system, alter procurement for ground support, and provide some training to the operators “but they took to it really quickly and we were off to the races.”
From the very beginning, an Epiroc technician was posted at the mine, troubleshooting and responding quickly to any first user issues that arose with the new system. Epiroc continues to work with Voisey’s Bay to ensure the Boltec rigs are configured to install multiple bolt types depending on the conditions. Menheere said Vale will gradually replace the mine’s cable bolting with extendable hollow core pumpable resin bolts.
Looking to the future, Vale is considering switching from diesel to electric equipment as part of its commitment to the Paris Climate Agreement, with trials already underway at some of its mines. Menheere doubts the existing Boltec rigs at Voisey’s Bay will be altered to incorporate battery technology, but expects any new rock reinforcement rigs to be electric.
Adopting Epiroc’s pumpable resin solution has helped Vale get closer to Voisey’s Bay’s underground orebodies at greater speed, despite COVID-19 related delays. In the process, the technology has boosted the morale of Vale’s operators and perhaps even a broader provincial audience. “The value we see in time savings and in our ability to get at the orebody quicker far outweighs the cost,” said Menheere. “In today’s industry and with the way capital projects are being developed under a tight timeline, pumpable resin is the way to go to reduce cycle times while ensuring the safety of workers.”