Iron ore explorer African Minerals said its flagship Tonkolili project in Sierra Leone contains more iron ore than previously thought. The Tonkolili project holds 12.8bn tonnes of iron ore, according to the latest resource estimate, up from 10.5bn tonnes announced in February. The update incorporates the Numbara, Simbili, Marampon and Kasafoni deposits at Tonkolili. Resources-hungry China will be a key customer of the Sierra Leone project. Spot iron ore prices have risen 43 per cent this year.