document: INVESTORS are being asked to provide money for a diamond mine near the River Limpopo in Zimbabwe , which De Beers , the South African group that dominates the diamond business , discovered but then let get away . The mine is River Ranch , 12km upstream from Beitbridge on the southern border of Zimbabwe . De Beers found diamonds there in 1975 but decided to concentrate instead on another site 60km away and , importantly , given the heat generated by the politics of the region , across the border in South Africa . After an investment of Dollars 500m that site went into production as Venetia , one of the world 's biggest diamond mines . The South African group eventually gave up its rights to River Ranch in 1991 after it failed to reach agreement with the Zimbabwe government about marketing the diamonds . The government insists that all minerals are sold through its state-controlled Minerals Marketing Corporation . Mr Robin Baxter-Brown , chairman of Redaurum Red Lake Mines , one of the new joint owners of River Ranch , said yesterday that De Beers bulldozed the site before leaving . Also , all documentation about the deposit has mysteriously disappeared from the Zimbabwe Ministry of Mines . -LRB- A De Beers official said equipment would usually be removed from a site before it was abandoned but he could neither confirm nor deny that River Ranch had been bulldozed . -RRB- Mr Baxter-Brown is a South African geologist who started his career with De Beers and has 36 years of diamond exploration experience . He helped Auridiam , an Australian-quoted company that he co-founded and where he was once chairman , win the mining rights to River Ranch when they were put up for tender by the Zimbabwe government in 1991 . The deposit is estimated by the joint venturers to have resources of 17.5 m tonnes containing 5m carats of diamonds , and since mining started in March last year it has produced 43,000 carats of diamonds , 60 per cent of them of gem quality , Mr Baxter-Brown said . Redaurum , which is quoted in Toronto , is raising CDollars 1.5 m -LRB- Pounds 780,000 -RRB- net of expenses via a placing by London stockbrokers Carr Kitcatt & Aitken to help boost annual output from the present rate of 50,000 carats to 330,000 carats . The increase will be reached in two phases . The first , costing USDollars 2.1 m , will raise output to 180,000 carats next year , while the second will cost Dollars 8.7 m . The partners have spent about Dollars 850,000 to buy and move a heavy minerals separation plant recently decommissioned at the RTZ Corporation 's diamond mine near Mafikeng , 500km away . The joint venturers have exclusive exploration rights to 13,474 hectares of ground around the mine and Mr Baxter-Brown suggested the chances of finding another diamond deposit were good . While most of River Ranch 's gem diamonds are small , typically under half a carat , the mine has yielded some big stones , the biggest so far being 29.6 carats . A 28-carat stone was sold for Dollars 110,000 or Dollars 4,000 a carat , and one of 17 carats for Dollars 95,000 -LRB- Dollars 6,000 a carat -RRB- . Diamonds are being sold directly to the market in Antwerp , Belgium , and not through De Beers ' Central Selling Organisation , which controls about 80 per cent of the world rough -LRB- uncut -RRB- diamond trade . But as Mr Baxter-Brown pointed out : ' 330,000 carats a year is no threat to De Beers . '
extractive_keyphrases: diamond business diamond mines zimbabwe government diamond exploration experience joint venturers exclusive exploration rights central selling organisation diamond trade diamond deposit river ranch south african group