ST. PAUL, Minn. (AP) — A report says sparks produced during maintenance probably caused last month’s fire at Soudan Underground Mine State Park near Tower.

The state fire marshal says the fire began in the shaft where the work was happening and didn’t spread beyond it. It’s considered accidental.

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Damage to the mine was limited to charred timbers and melted PVC pipes and electrical wiring. The University of Minnesota physics laboratory was unharmed.

Park staff was replacing degraded steel sheeting in the lowest 600 feet of the mine shaft. The fire started after grinding tools caused pieces of wood to smolder.

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Experts will visit the mine in coming weeks to determine costs of repair and cleanup.

The park’s above-ground facilities have reopened, but public tours of the underground mine likely won’t be offered this season.

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