Diamond Exploration

Mining is one of Sierra Leone’s most important industries and diamond are one of the country’s main exports. In June 2003, the UN ban on the sale of Sierra Leone diamonds (introduced during the civil war) expired and was not renewed; the Government has continued to enhance its control over diamond mining.

Sierra Leone is a founder member of the Kimberley Process for diamond exports, which is promoted by the United Nations. This process brings together industry, governments and NGOs to provide certificates of origin for diamonds and to regulate exports to prevent the financing of war through the sale of ‘conflict diamonds’. Since the introduction of the Kimberley Process, Sierra Leone has seen the export of legally mined diamonds increase substantially, surging 66% in 2003 to US$76m (507,000 carats) and increasing further to US$127m in 2004 (692,000 carats). The average price achieved in 2004 was US$183 per carat.

The quality of Sierra Leonean diamonds is renowned, particularly as there have been recovered some spectacularly large stones of very high value from its alluvial deposits; the established diamond fields are concentrated in the Kono (Koidu), Kenema and Bo Districts and are mainly situated in the drainage areas of the Sewa, Bafi, Woa, Mano and Moa Rivers. Alluvial diamond concentrations occur in river-channel gravels, flood-plain gravels, terrace gravels and in gravel residues in soils and swamps.

The largest diamond ever found was the 969.8 ct ‘Star of Sierra Leone’, discovered in the Kono area in February 1972. Two stones were sold in 1996, weighing 188 ct and 283 ct that came from an unspecified location.

Sierra Leone Selection Trust (SLST) commenced alluvial diamond mining in the Kono area in 1934; its mining in the Tongo area commenced in 1954. In 1970 the government acquired a 51% interest in SLST’s assets through the National Diamond Mining Company (NDMC). Peak annual output of these two fields of over one million carats (Mct) per year was achieved in the late 1960s and early 1970s, but output steadily declined thereafter to fewer than 100,000 carats by 1985. Artisinal mining (legal and illegal) also accounted for a significant output in these areas.

Kimberlites, the primary source of diamonds, were first discovered in 1948 in the Koidu area and subsequently at Tongo and Panguma, and were tested by trenching, drilling, bulk sampling and trial mining. At Koidu, the Koidu Holdings Ltd company estimates reserves at approximately 2Mct down to a depth of 300m and further significant resources have also been delineated at the Tongo kimberlite field (a resource of up to 18.9 million carats was estimated by Rex Diamond Mining Corporation Ltd., but this is considered highly speculative - earlier reports estimated approximately 2 million carats).

Trial mining and bulk sampling programmes have been undertaken by Koidu Holdings on the No.1 kimberlite pipe at Koidu, with initial mine production of over 18,000 carats averaging a realised price of US$224 per carat. Koidu Holdings has also recently been awarded a licence over the Tongo diamondiferous kimberlite field.