The Department of Labour has closed the Assmang plant in Cato Ridge, Durban following the death of four workers in a massive explosion on Sunday...This weekend's accident took place at a time when the plant was under inquiry for exposing workers to poisonous fumes in 2007. [Department spokesperson Zolisa ] Sigabi said the inquiry...seeks to establish [whether there had been any] negligence or flouting of occupational health and safety measures...The Assmang plant is jointly owned by Assore and African Rainbow Minerals.