Brazilian steel maker Cia Siderurgica Nacional SA (CSN) has accepted Rio Tinto Ltd's $3.9-billion takeover offer for the Africa-focused coal miner Riversdale Mining Ltd.

Rio Tinto said late Wednesday that CSN had sold its entire 19.35 percent equity in Riversdale, which has been extended by nine days to April 29. This development leaves India's Tata Steel is Riversdale's remaining major shareholder with a 27 percent stake.

Rio Tinto now has a more than 72 percent stake in Riversdale after gaining majority control announced on April 8. Rio Tinto Energy chief executive Doug Ritchie, coal chief development officer Matt Coulter and Australia managing director David Peever were earlier this month appointed to the Riversdale board.

Riversdale operates a mine in South Africa and a 65 percent interest in a major coking coal project in Mozambique.