The state Department of Natural Resources has not determined a cause for a blaze in the main shaft of the Soudan Underground Mine State Park in northeastern Minnesota.
The fire was spotted Thursday night by Park staff who saw smoke coming up the shaft. The mine was a working iron mine from 1884-1962. It's been a State Park since 1963 -- one of two mines in the United States that provides public tours. About 37,000 people a year take the tour, which started in 1965.
Officials now say the fire likely started in wood in the mine shaft between the 25th and 27th levels.
After the fire was reported, park officials feared they could lose the retired iron mine, park manager Jim Essig said. The fire created multiple problems, including the loss of power the turned off pumps on several levels, allowing water to begin filling the mine.
Officials haven't declared the fire out, but suspect 70,000 gallons of firefighting foam have doused the fire. Department spokesman Mark Wurdeman said crews are first concentrating on restarting pumps that keep the retired iron mine from flooding.
"At this point in time we're focused on the pumps, getting the communications in there, getting all that up and going, then making sure the air is clear enough so that we can access that," Wurdeman said. "Then an investigation will ensue as to pinpointing where that fire started."
As of Monday, power had been restored to pumps on two levels. Officials now expect little if any smoke or water damage to a $60 million University of Minnesota physics laboratory on the mine's lower level.
Essig said the fire retardant foam workers dumped down the shaft on Friday and Saturday filled the lower level, outside the sealed doors of U of M's lab on the 27th level. Crews restarted pumps to drain the water.
Laboratory supervisor Bill Miller said the lab's main experiment, receiving a neutrino beam from the Fermi National Laboratory near Chicago, was deactivated before the fire because of an equipment failure.
Miller said the Soudan laboratory should be back in service before April, when the experiment is to resume. The laboratory also conducts six or seven additional experiments, including a search for dark matter.
"We have not been into the lab yet," Miller said Monday. "It may be even a few days. We don't really know how long it will be until we get a chance to look into there, but all indications are that the lab is just sealed off from the rest of the mine."
The mine also is home to thousands of bats that hibernate there during winter. They are expected to survive, as they hibernate closer to mine air intakes, which were a quarter to a half mile from the shaft. Air in the mine comes in the intakes and goes up the shaft, as did the smoke.
A relieved Essig said Monday that the mine appears to have survived the blaze.
"There's a lot of challenges ahead; don't get me wrong," he said. "But where we were Friday compared to where we are right now, we're going to get her back."