A small earthquake in North Idaho near the Lucky Friday Mine temporarily slowed production Friday morning. But work resumed after an inspection determined the mine remained safe.
General Manager Clayr Alexander said he was about a mile underground when the 2.7-magnitude temblor occurred about 9:30 a.m. local time.
"There were some people that felt it underground, but I didn't personally," Alexander said Friday afternoon. "We went and looked in a couple areas. We didn't find anything unexpected or ground fall. Everybody is still underground, and everybody is still working."
There were about 50 workers in the mine at the time of the earthquake, he said. The Lucky Friday Mine produces silver and is one of the nation's deepest, reaching a mile underground.
Authorities said there were no injuries reported above or below ground from the quake the U.S. Geological Survey recorded as occurring less than a mile southwest of Mullan and a little more than a mile deep.
Lucky Friday miners are currently working about a mile north of Mullan and about a mile deep, Alexander said.
Mike Stickney, senior research geologist at the Montana Bureau of Mines and Geology based in Butte, Mont., said the quake appears to be caused by a geologic fault rather than mining activity. A smaller quake, 2.4-magnitude, occurred in roughly the same area on Thursday, he said.
"The seismic signatures of these two events is more compatible with an earthquake type source rather than a (mine) collapse type source," he said.
The area, he noted, has many old geologic faults, and it is along these faults that miners dig to collect the minerals that accumulated there as water moved through and left deposits.
"They have names for all of those faults," Stickney said. "They're well known by the miners."