Diamonds were discovered in Sierra Leone in 1930, and in 1934 sole mining rights were granted to the Sierra Leone Selection Trust (SLST), a subsidiary of the London-based Consolidated African Selection Trust, part of De Beers empire. In 1956, partly to restrict the increasingly prevalent illicit mining, and partly for political reasons, SLST opened part of its lease to mining by licensed miners under the Alluvial Diamond Mining Scheme (ADMS). The Sierra Leone government took over 51 per cent of the SLST shares in 1970, and a new company, the National Diamond Mining Company (NDMC), was formed. In 1980 SLST sold out to British Petroleum and left Sierra Leone.