A new roof fall was found int he #1 entry of South Mains ""B"" return aircourse between 23 and 24 x-cut. Fall is approx. 18'wide by 8-9""high by 20-30'long. Area bolted with 8' Install III bolts with resin assisted and some floor to roof support. Cause of this fall was deterioration of the main roof due to weathering. Fall did not affect ventilation or escapeways.