No injuries to persons/no miners exposed. Incident occurred overnight, no one was underground. Accident investigation is ongoing to determine cause, including if there was a pillar failure. Area affected by the fall included NW corner of M29&S37 to the NE corner of M29&S49 to the SE corner of S49&M47 to the SW corner of M47&S37 and back N to M29&S37. No equipment involved.