MAPUTO - A coal stacker has collapsed at the Mozambique port of Nacala, dealing a blow to Brazilian miner Vale, which is aiming to start coal shipments in the third quarter of this year, three sources told Reuters on Monday. The giant piece of machinery, which is used to handle coal and other bulk materials, buckled last week, according to a mining industry source with knowledge of the situation. "The contractors are investigating and an official report is expected within a couple of weeks," the source said, adding that no one was hurt in the accident.