GABARONE, Oct 20, 2007 (AFP) - The world's richest diamond mine, which produces up to 15 million carats a year, celebrated its silver jubilee in Botswana on Friday, october 19th amid concerns about the growing cost of diamond mining.

A hydraulic shovel is loading freshly blasted kimberlite on a truck at the diamond mine in Jwaneng - Photo : Alexander Joe/AFP

"When these gemstones are cut and polished, they produce eight million pieces of jewellery in a year. This means over the last 25 years Jwaneng mine's diamonds have been worn by over 100 million customers all over the world", said Gareth Penny, chief executive of De Beers, the world's biggest mining company.

But Penny said growing costs of mining diamonds in Botswana presented a new challenge to Jwaneng, which was scheduled to move to underground mining in 2012.

"We continue to do more explorations in search of the new Jwaneng," Penny said.

Botswana is one of the world's top diamond producers, and President Festus Mogae told those attending the celebrations it had been the largest contributor to the country's gross domestic product since 1982.

"We can thus factually state that since Jwaneng Mine entered into operation, this country was catapulted to the top of the international arena of diamond players," Mogae said.

Known for its blue diamonds, Jwaneng accounts for up to 70 percent of the annual earnings from all the four diamond mines owned by Debswana, a 50/50 partnership between the government of Botswana and De Beers.

The Debswana mines produce a cumulative 30 million carats a year, about 22 per cent of the world's diamond output.