A loud boom heard and felt in Yellowknife on Saturday was a scheduled explosion at a local mine site, not an earthquake as federal seismologists have diagnosed.

Many in the N.W.T. capital reported hearing a loud boom and feeling mild tremors at 11:08 a.m. MT.

Seismologists with Natural Resources Canada assessed the event as a small earthquake with a magnitude of 1, with the epicentre located about six kilometres south of the city.

But the loud boom actually came from the defunct Con gold mine site, where workers were levelling a rock outcrop to build a water treatment plant.

Blast delayed twice

Mine manager Scott Stringer told CBC News on Monday that Saturday's blast had been scheduled for last Thursday, but was delayed twice because of weather.

"It was a fairly large blast. We used about 15,000 kilograms of explosives," Stringer said.

Stringer said workers involved with the blast had notified the authorities a day in advance, including the mine inspector, the local airport and Natural Resources Canada.

More blasting work will take place at the site until Dec. 15. Stringer said he is looking at ways to better warn Yellowknifers in advance of the upcoming blasts.

Natural Resources Canada later updated its online report of the "earthquake" incident to say it was a blast for a water treatment plant.

Earthquakes rare around Yellowknife

Department seismologist Janet Drysdale said earlier Monday that given Yellowknife is in the middle of the North American tectonic plate, earthquakes are extremely rare in that area.

"In Yellowknife itself, they're very unusual; in fact, I think there's only been one other earthquake since the mid-1970s," she had said in an interview.

Those earthquakes from the mid-1970s had a magnitude of around 2.5 to 3, still below the minimum magnitude in which damage occurs.

"However, within Northern Canada, there's many areas that have a lot of earthquakes," she added, noting areas as far east as Baffin Bay to the Mackenzie Mountain and Beaufort Sea areas in the west."