N'Djamena - Ten people were killed in clashes at a gold mine in the Tibesti Mountains in northern Chad, pitting locals against outsiders in search of riches, a security source told AFP.The violence erupted early on Tuesday when local residents told gold miners who had flocked to the central Sahara mountain region from other parts of Chad to leave, the source said on condition of anonymity."A fight broke out and the outsiders killed three locals," he said. "The locals then ambushed the outsiders, who ended up leaving the area ... but seven gold miners were killed while the others got away." The discovery of gold in Tibesti in 2012-2013 drew miners from all over Chad, and also from neighbouring Sudan.But their arrival has triggered clashes against locals who have seen their livelihoods threatened. "Gold miners dig pastures for livestock, use water resources - which are also rare - occupy wells and use products like mercury, a heavy pollutant," Jerome Tubiana of the NGO Small Arms Survey told French radio RFI.Trafficking is also rife in the lawless, sparsely populated desert region, which borders Libya, Niger and Sudan.