Expect more earthquakes as mines dig deeper to extract ore, Vale says

More pressure builds up in rock near-surface as mines continue…

More pressure builds up in rock near-surface as mines continue to dig for ore extraction.
Mining giant Vale says Seismic activity around its Sudbury-area mines is likely linked to its deep drilling operations, and there is the probability that more incidents will follow.
Last week, Natural Resources Canada recorded two earthquakes. A 3.6 MN (magnitude) tremor hit Creighton Mine Thursday morning, and a 3.0 MN quake forced Garson Mine to stop operations Friday night till Saturday.
According to Natural Resources Canada’s website, it’s unlikely that any quake below 5 MN could cause damage above ground, although tremors were felt as far off as lively.
Gilbert Lamarche, Vale’s head of Mines and Mills Technical Services, said inspection teams were on the scene quickly while the company brought its employees above ground.
“First And foremost, our top priority is to get people to secure locations because there could be unknowns shortly after it happens,” Lamarche said.
“Then, from there in both cases, due to the magnitude of these events, employees are hoisted to the surface, and then we have monitoring throughout the mine that shows ground vibrations.”
The blasting that likely caused the tremors at Creighton was closer to 8000 feet, while Garson was at the 5000 levels, or 5200 feet below the surface, Lamarche said.
The Garson tremor was also likely caused by “crown blasting,” a large type of underground explosion. 
“We typically get some of these a year in our Operations,” Lamarche said.” This is due to mining activity, and in the host rock we are in, it’s a very strong host rock.”
The potential for quakes begins the moment drills go into the ground. The natural pressures and stresses in the rock redistribute themselves, Lamarche explained.
“If you get some faulting in the ground, which is common around these areas, there is sometimes a sudden release of energy or a shift, which causes these [quakes.]”
After the events, experts descend to the area to find out if they can detect any more vibrations in the rock.
“I have a fantastic team of about 20 that take care of these issues,” Lamarche said. “They talk to the team members and my management to get a feeling of, and attempt to comprehend what happened, and what could have caused it.”
In both mines, Lamarche said there was only minor damage, or “a bit of rock sloughing from the walls.”
That’s something he attributes to the preparations his teams took in readying the operation. 
“It’s a good testament to the level of ground support we use in our excavations together with our experienced miners installing it.”
“When you have minor damage, that means that the ground support that our people are installing is quite effective in helping to protect themselves and our assets.”
The teams are trying as much as possible to create models that will help them predict where the next tremor could occur, as crews work at ore bodies deeper in the mines, causing more stress on the rock above, Lamarche said. 
“Looking at the last ten years, we have had seismic events greater than [1.0 MN],” he said. “And noteworthy ones have increased over the years. But the rock bursts have diminished, meaning we’ve been controlling them better and keeping damage to minimal”.

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