The corrugated iron roof on a surface conveyor was damaged by stone.

The NSW Resources Regulator said it had been secured with rope.

"During high winds, the rope failed, ripping a sheet of iron from the structure," it said.

"The sheet fell to the ground. Nobody was in the area at the time."

The regulator said when plant was damaged it had to be made safe and left in a state suitable to continue operating.

"Any interim repairs must be conducted to a standard that poses no further risk," it said.