Mine lost power 6/11/17 at 4:45 AM & all personnel were evacuated. On 6/12/17 an electrician entered to check pump with gas detector (natural airflow of 55K CFM). 1280 ft. down the decline the EE encountered a rib fall on left side with material impeding travel, returned to sur., notified mngt. at 9:45 AM. During msha investigation est. 50-75 tons blocking 25% of decline