Kono District, in the Eastern Province of Sierra Leone, is the country's principal diamond-producing region and the location of the Koidu kimberlite mine and the surrounding alluvial workings. The district takes its name from the Kono ethnic group, who form the majority population in the area. Diamonds were first discovered in the Kono river systems in 1930, and the district has since been the centre of Sierra Leone's diamond industry through the colonial period, the country's independence, the civil war of 1991 to 2002, and the post-conflict recovery under the Kimberley Process Certification Scheme.

Geological setting

The Kono District lies on the West African Craton, an Archaean basement of granites and gneisses that hosts a series of Cretaceous kimberlite pipes and dykes intruded through the older crystalline rocks. The principal hard-rock occurrences are the K1 and K2 pipes at Koidu, treated separately in the related entry on Koidu. Around the kimberlites, alluvial diamond gravels have accumulated through long erosion of the pipes into the surrounding river systems, particularly the Sewa River and its tributaries, which drain the district westward toward the Atlantic. The alluvial deposits are notable for their high proportion of large, well-shaped, gem-quality stones, and Kono alluvials have produced a significant fraction of the largest historical Sierra Leonean diamonds.

History

Alluvial diamond mining in Kono began under the Sierra Leone Selection Trust from 1935 onward and has continued more or less without interruption since, although the formal sector has expanded and contracted with the country's political circumstances. During the civil war of 1991 to 2002, Kono was one of the principal areas of contestation between the Revolutionary United Front and the government, with control of the diamond fields directly funding both sides of the conflict. The trade in conflict diamonds from Kono and the broader West African region was the immediate occasion for the development of the Kimberley Process, formalised in 2003. Post-war reconstruction has restored formal mining operations at Koidu and reorganised the alluvial sector under a licensing regime, although informal artisanal mining continues throughout the district.

Notable stones

Several of the largest Sierra Leonean diamonds have been recovered from the Kono alluvials. The Star of Sierra Leone, recovered in 1972 from the Diminco mine at Yengema in Kono, weighed 968.9 carats and was the largest alluvial diamond ever found at the time. It was acquired by Harry Winston, who cut it into seventeen smaller stones, the largest of which weighs 53.96 carats. The Peace Diamond, a 706-carat rough recovered in 2017 from the Koryardu chiefdom of Kono, was sold at auction in New York for over six million US dollars, with proceeds returned to the local community under a transparency arrangement coordinated by the Sierra Leonean government. Other notable Kono stones include the Star of Yakatu and the Woyie River Diamond.

Trade relevance

Kono diamonds enter the international trade through the Sierra Leonean export channel, with stones routed via Antwerp for sorting and grading. The district's continued reputation, despite the conflict-diamond legacy, rests on the consistently high quality of its alluvial production. For Toronto retail purposes, Sierra Leonean diamonds carry the Kimberley Process Certification, and stones from large recent finds such as the Peace Diamond have been actively marketed for their provenance. Compliance documentation back to the Sierra Leonean export point is the standard requirement for stones marked Kono or Sierra Leonean origin in the Canadian and US markets.