Local experts say they aren’t surprised the roof of Cape Breton’s Donkin mine is subject to rock falls given the area’s geology, a week after the province shut down the operation following a collapse.
The mine was not operating when the rock fall happened Dec. 28 and no one was hurt, but the Labour Department said the incident was serious enough to warrant a closure until an acceptable safety plan is in place.
The area surrounding the mine near Glace Bay is considered geologically diverse with rock layers that vary from hard sandstone to soft clay.
Jim MacLellan, an 84-year-old retired coal miner from Glace Bay, spent more than 40 years working in Cape Breton.
He said he hasn’t been in the Donkin mine since it was built in the 1980s, but some of the collieries during his career were known for having crumbly shale roofs.
“They had good coal, but ofttimes associated with good coal is this sandstone, or hard roof. And then if you get a break in that sandstone, it sort of loses its strength and it drops,” he said.
‘You can’t work under unsupported roof’
MacLellan said the mines had geologists who would take a lot of borehole samples to determine where the roof had strengths and weaknesses, but it was still up to each miner to look out for safety.
“You can’t work under unsupported roof, or bad roof,” he said. “The first thing a miner does, he secures the roof. He secures his section, then he starts to work.”
The miners used a buddy system to look out for each other, MacLellan said.
“He’s looking over your head, and you’re looking over his. We’ve had people buried three feet from someone else. They just missed that there was a pot of stone above them and down it came.”
Deanne van Rooyen, a geology professor at Cape Breton University, said it’s no surprise the roof material would vary in strength between some mines — or even within the same mine.
Cape Breton coastline isn’t uniform
Layers of metamorphic rock are usually more uniform than sedimentary layers, she said.
“The Sydney coalfield in general is a fairly complex sedimentary environment, so some of them were deposited as rivers,” van Rooyen said.
“Some of them were continental deposits, so things like salt flats. Some of them were dunes. Some of them were swamps — that’s where we get the coal — and some of them were ocean-type rocks.”
The Cape Breton coastline isn’t uniform, she said. It has bays, rivers and outcroppings, all with different strengths of rock.
“You can walk along the Glace Bay shoreline out by Schooner Pond and … in some cases they’re so soft you can go and dig them out with a teaspoon, and in some cases you would need a hammer, and in some cases you would need dynamite.”
No clear cause of collapse
Scott Nauss, senior director of inspection and compliance with the provincial Labour Department, said Thursday the Donkin mine has been hit with a handful of roof falls in the last six months.
The latest incident was worse than the previous ones, said Nauss, and the root cause was not immediately obvious.
MacLellan didn’t want to speculate on what might have happened last week. He said he has faith in the men working underground.
“But sometimes things happen and there’s just no answer.”