Diamonds were discovered in Sierra Leone in 1930. The civil war has led to a proliferation of illegal diamond mining and smuggling, depriving Sierra Leone of at least $600 million a year in foreign exchange. Apparently, most diamonds are being smuggled to Liberia. Sierra Leone produced 2.5 million carats of diamonds a year prior to the outbreak of civil war in 1992, with production in 2001 estimated at 375 000ct (officially).
DiamondWorks has invested $11 million in six mining projects. The company has a 25-year renewable lease to exploit kimberlite diamond deposits around the eastern town of Koidu, 250 km from the capital city of Freetown, and has exploration licences for other alluvial diamond properties. The Koidu property consists of a series of kimberlite dykes and pipes and has proven and probable reserves estimated at 2.6Mct and 1.9Mct from inferred reserves. DiamondWorks owns only 60% of the equity, with 30% of the equity belonging to the government while the other 10% being publicly owned. Prior to civil war breaking out, a 10 000 ton bulk sample was due to be taken. DiamondWorks are to return to the country to revive exploration and mining activities, where the focus will be on Koidu as well as other properties in the country. DiamondWorks has formed a joint venture with newly formed Magma Diamond Resources in order to develop the Koidu kimberlites where an initial capital cost of US$6.2 million is required to commence commercial production.
Rex Diamond Corporation has mining licenses at the Tongo fields and Zimmi.
De Beers recently terminated offshore exploration for marine diamonds in Sierra Leone, probably due to poor expectations. Cassierra, a Canadian group, renewed its 600 km2 exploration licence after receiving more encouraging results. 20 commercial size diamonds were found with stones reaching a maximum size of 122 carats. These are the first diamonds to be located in marine sediments in West Africa.