De Beers says production at its Venetia diamond mine, the largest in South Africa, should return to normal in the second half of this year, retaining its production at 2012 levels.
Of De Beers' production from South Africa last year of four million carats, three million carats were mined at the Venetia operation.
The miner decided earlier this year to invest $2.27 billion in the mine, extending it until 2042, however production has been hit by heavy rainfall.
"South Africa had the worst rain in the last 200 years and our big mine Venetia had 23 meters of water, so therefore our production was slightly lower," said Varda Shine, CEO of the Diamond Trading Company.
De Beers output last year was 27.9 million carats from its mines in Botswana, South Africa and Canada.
The company says sales in the first quarter of this year were "slightly better" than last year, boosted by Chinese New Year sales and a rebound in demand in the United States.
The firm predicts a single-digit increase in rough diamond prices this year, after a 12 percent decline in 2012.
Explaining the firm's predictions of rising prices, Shine said: "Over the last 20 years no new big (diamond) mine has been discovered, we have also seen the emergence of Asian markets like China and India."