Sierra Leone’s primary mineral resources are diamonds, rutile, bauxite, iron ore and gold. The mineral sector in Sierra Leone is made up of three sub-sectors:
- large-scale production of non-precious minerals – rutile, bauxite and iron ore;
- large scale production of precious minerals – diamonds; and
- artisanal and small-scale production of precious minerals – mainly diamonds, and to a much lesser extent, gold.
The Sierra Leone diamond fields cover an area of about 7,700 square miles (about one quarter of the country) in the south-eastern and eastern parts of Sierra Leone. The first diamond was found in 1930, in Kono and subsequent exploration established that there were extensive alluvial diamond fields in many parts of the region and an exceptionally rich group of deposits in the Koidu area. The diamond producing areas are concentrated in Kono, 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, gravel residues in soils and swamps.
Rutile and Ilmenite
Rutile was discovered in Sierra Leone in 1954 in the gravels of the Lanti River south of the Gbangbama region in the Southern Province. Four groups of deposits are known to be distributed around the country: The Gbangbama Deposit, the Sembehun Deposit, the Rotifunk Deposit and the Kambia Deposit. Sierra Leone has the largest natural rutile reserves in the world and was accordingly the largest producer of natural rutile worldwide, accounting for a third of the total world production.
The occurrence of bauxite in Sierra Leone was first recorded in 1920 and 1921 on the road from Falaba to Waia in northern Sierra Leone. Other bauxite occurrences include those between Moyamba and Mano (weathered dolerite sills of the Rokel River Group), the bauxite deposits of the Freetown Peninsular, the Krim-Kpaka deposits in Pujehun District, southern Sierra Leone, the Kamakwie and Makumre bauxite deposits in northern Sierra Leone. The most important bauxite discoveries were made by the Geological Survey in the Mokanji and Gbonge Hills in 1960 and by Sierra Ore and Metal Company (SIEROMCO) in Port Loko in 1972.
Iron ore was discovered in the Marampa area in 1926. In 1933, the Sierra Leone Development Company (DELCO) started iron production, continuing for over 40 years until it went into liquidation in 1975 due to worldwide economic recession. With at least 40 million tons of tailings containing 27.7% Fe after interruption of mine operations in 1975, the primary ore was estimated at 92 million tons at 37.8% Fe.
Gold was first discovered in Sierra Leone in 1926 in the Makoke River near Masumbiri, northern Sierra Leone. All greenstone belts in Sierra Leone, with the possible exception of the Marampa Group are known to contain gold. Rivers and streams draining these areas also carry gold. The established existence of gold by the Geological Survey in some localities within the granite –greenstone terrain includes: Lake Sonfon, Maranda and Yirisen (Sula Mountain area), Baomahun, Makong and Makele (Kangari Hills), Komahun (Nimini Hills), Kamakwie-Laminaia area (Loko Group), Kalangba (Kangi Hills), Sandaru (Gori Hills) and in the Kambui Hills. Small scale and generally informal mining activities, often taking place under difficult conditions, with technologically simple machinery. While irregular, artisanal mining often makes up an economically important sector in the localities.