Marange diamond fields are home to an estimated 25 per cent of the world's diamonds. They first made international headlines in 2008 when they were seized by the Zimbabwean military, which used helicopter gunships to clear the area of illegal diggers when the extent of the subterranean bounty became clear. Last year, Global Witness claimed that locals were being forced to work for soldiers, then smuggle the stones over the Mozambican border to sell. Their proceeds were then returned to the military, it alleged.