An explosion during a training exercise killed seven Marines and injured several others shortly before 10 p.m. Monday at the Hawthorne Army Depot, according to a statement issued by the 2nd Marine Division. As a result of the explosion, a ban was ordered on the use of 60 mm mortars pending completion of an investigation. The injured were transported to area hospitals for treatment. All the Marines were stationed at Camp Lejeune, and were at Pickel Meadows Mountain Warfare Training Center in addition to Hawthorne. “We send our prayers and condolences to the families of Marines involved in this tragic …