document: The Office of Fair Trading said Tuesday it was investigating a complaint alleging anti-competitive practices by a London-based diamond cartel controlled by South Africa 's giant De Beers diamond organization . The watchdog body said De Beers `` appeared to have '' a monopoly on diamond trading in London and it was interested in establishing whether there had been an abuse of the monopoly . Consolidated Gold Fields PLC , a British mining concern with no diamond interests , acknowledged that it filed the complaint as a defensive move against a stalled takeover bid by Luxembourg-based Minorco SA . Minorco is 60.1 percent owned by Anglo American Corp. of South Africa Ltd. and De Beers Consolidated Mines Ltd. , the gold and diamond mining interests controlled by the Oppenheimer family of South Africa . The British government is expected to rule in the next few weeks whether to allow Minorco to proceed with its 2.9 billion-pound -LRB- about $ 5.1 billion -RRB- bid for Consolidated Gold following an investigation by the Monopolies and Mergers Commission . A Consolidated Gold spokesman , commenting on condition he was not identified , said the company wanted to point up the `` monopolistic tendencies '' of South Africa 's Anglo-American group of companies . De Beers ' Central Selling Organization , which controls 80 percent of world diamond trading , has been based in London for 60 years . As well as selling the stones mined by De Beers and other South African companies , the organization trades on behalf of diamond producers including Zaire , Australia , Botswana and the Soviet Union . The Office of Fair Trading said it would first have to establish whether it had jurisdiction over the Central Selling Organization because although it is based in London , De Beers is a South African company . There is no time limit on the office 's investigation . After it is completed , the Office of Fair Trading may decide to refer the complaint to the Monopolies and Mergers Commission . A spokesman for the Central Selling Organization said the Office of Fair Trading notified the organization about the inquiry but had n't yet requested any information . `` It 's still early '' in the investigation , said the spokesman , commenting on condition he was not identified . De Beers 's shares were unchanged Tuesday on the London Stock Exchange at $ 12 -LRB- U.S. -RRB- .
extractive_keyphrases: de beers diamond organization fair trading south africa world diamond trading defensive move central selling organization investigation
abstractive_keyphrases: anti-competitive practices london-based diamond cartel luxembourg-based minorco sa