Both tin beads and more sophisticated tin artifacts have been found in workings for cassiterite in Central Nigeria. It is possible that the former occurred naturally in slags produced during the smelting of lateritic iron ores containing some cassiterite. This would be by the direct (bloomery) process normally used for iron production in Africa until about 1950. The larger, more sophisticated artifacts were more likely made of straw-tin, the traditional product of the tin smelters. Cassiterite occurring as such in iron slags near Mongu is unreacted material. Iron smelting was being carried out at Bonga towards the end of the last century and the beginning of this by the Sura tribe in shaft furnaces built against a clay wall. These used lateritic ores containing cassiterite from the Ron country to the west of the Mongu dyke.