Mining giant Anglo American has agreed to purchase Oppenheimer family's 40 percent stake in diamond minor De Beers for $5.1bn in cash.

The deal with CHL Group, which represents the Oppenheimer family interest, will raise Anglo American's share in the globe's largest diamond company to up to 85 percent.

Under the current agreement Botswana, the globe's top diamond producing nation, has pre-emption rights over CHL shares and could raise its ownership to 25 percent if it wanted to exercise its rights in full.

Cynthia Carroll, CEO at Anglo American, said: “This transaction is a unique opportunity for Anglo American to consolidate control of the world's leading diamond company, De Beers. Today's announcement marks our commitment to an industry with highly attractive long term supply and demand fundamentals. Underpinned by the security of supply offered by a new 10-year sales agreement with our partner, the Government of the Republic of Botswana, this forms a compelling proposition.”

Nicky Oppenheimer noted: “This has been a momentous and difficult decision as my family has been in the diamond industry for more than 100 years and part of De Beers for over 80 years. After careful and deliberate consideration of the offer, and what is in the best interests of the family, we unanimously agreed to accept Anglo American's offer.”