The St. Louis-based company has not publicly released details of the mishap, except to say that the plant was damaged by a “structural failure.” Steve Earle, a United Mine Workers of America (UMWA) official in western Kentucky, blamed the incident on a beam “that gave way and the hopper came down through the floor.” Luckily, no one was injured, he said. Tests have been run on prep plant equipment to determine the cause of the accident.

The UMWA represents most hourly employees at Highland No. 9, which has a total work force of 458 people. The mine is located in both Union and Henderson counties.

At the time the mine was idled, Patriot said it anticipated full production would resume by June 30. At least limited production, however, began earlier than that after the company recalled about 120 miners earlier in June.

On June 28, Patriot spokeswoman Janine Orf said the prep plant was back operating at 50% capacity, adding all mine and prep plant employees would be back on the job by July 7. Earle said the union expected virtually all miners to be recalled around the Fourth of July holiday.

Prior to the idling, Highland No. 9, a continuous miner operation, was enjoying a good production year. The mine produced nearly 850,000 tons in the first three months of 2014, placing it well on its way to surpassing last year’s output of 2.9 million tons. The high-sulfur coal, produced from the area’s prevalent western Kentucky No. 9 seam, is loaded onto barges on the nearby Ohio River, mainly for delivery to power plants in the region.

Late last year, Patriot hired more miners to prepare for a seven-day production schedule at Highland No. 9. Some of those new employees were unemployed miners from eastern Kentucky, part of the struggling Central Appalachian coalfield.

While the outlook was brighter for Highland No. 9, the company in late June completed the layoff of approximately 75 employees at its Wells metallurgical coal and Corridor G thermal coal mining complexes in West Virginia.

Patriot had issued federal WARN Act notices to employees at the two mines in April, saying both met and thermal coal markets continued to be challenging, and the company needed to more closely align production with sales.