Sudbury

Expect more earthquakes as mines dig deeper, Vale says

Mining giant Vale says seismic activity around its Sudbury-area mines is likely linked to its deep drilling operations, and that it’s a possibility that more incidents will follow.

As mines dig deeper to extract ore, more pressure builds up in rock near surface

A quake with magnitude between 2 and 3 is the lowest normally perceptible to humans. A magnitude 5 quake is considered moderate. (Associated Press)

Mining giant Vale says seismic activity around its Sudbury-area mines is likely linked to its deep drilling operations, and it's a possibility that more incidents will follow.

Natural Resources Canada recorded two earthquakes last week. 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 and all day Saturday.

According to Natural Resources Canada's website, it's unlikely that any quake that registers below 5 MN would cause damage above ground, though tremors were felt as far away 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 workers above ground.

"First and foremost, our number one priority is to get people to safe locations, as there may be unknowns right after it happens," Lamarche said. 

"Then from there in both cases, because of the magnitude of these events, employees are hoisted to surface and then we have monitoring throughout the mine that shows ground vibrations."

The blasting that likely caused the tremors at Garson were at the 5000 level, or 5200 feet below the surface, Lamarche said, while Creighton was closer to 8000 feet. 

The Garson tremor was also likely caused by "crown blasting," a large type of underground explosion. 

"We typically get a few of these a year in our operations," Lamarche said. " This is due to mining activity and in the host rock we're in, it's very, very strong host rock."

The potential for quakes start the moment drills go into the ground. The natural pressures and stresses in the rock redistribute themselves, Lamarche said. 

"If you get some faulting in the ground, which is common around these areas, there's sometimes a shift, or a sudden release of energy, which causes these [quakes.]"

Gilbert Lamarche says Vale's priority after a seismic event is to ensure all workers are accounted for and safe. (JAMES HODGINS/supplied by Vale Canada)

After the events, specialists descend to the area to see if they can detect any more vibrations in the rock.

"I've got a great team of about 20 that take care of these issues," Lamarche said. "They definitely talk to the crew members and my management to get a feeling of, and try to understand 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, and the quality of our people, our 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."

Lamarche added that teams are trying as best 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. 

"Looking at the last 10 years, we've had seismic events greater than [1.0 MN]," he said. "And ones that are noteworthy have increased through the years. But the rock bursts have decreased, meaning we've been better at controlling them and keeping damage to minimal."

ABOUT THE AUTHOR

Casey Stranges is a reporter based in Sudbury. casey.stranges@cbc.ca

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