LONDON- Anglo-Australian mining company Rio Tinto PLC said Thursday it has achieved its goal of gaining a 47 percent stake in Riversdale Mining Ltd, and has come close to taking a majority stake.

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The offer has now been extended to April 20, Rio Tinto said.

Riversdale announced that three Rio Tinto executives had been appointed to its board, including Doug Ritchie, who heads Rio Tinto's energy division.

Rio Tinto said it had secured 49.53 percent of the shares by Wednesday, the original deadline for shareholders to accept a sweetened offer of 16.50 Australian dollars ($17.25) per share, up from AUS$16.00.

Rio Tinto had set the 47 percent target on March 29, when it declared the offer unconditional.

Rio Tinto shares were down 0.6 percent at 4,404 pence in morning trading on the London Stock Exchange.

Rio Tinto's holding now exceeds the combined 47 percent stake of India's Tata Steel and Brazil's CSN, which had increased their holdings since Rio first announced its $4 billion offer.

Tata has a separate 35 percent stake in Riversdale's key Benga coal mine in Mozambique, which is projected to produce 20 million tons per year of coal by 2013, and it appears more keen on protecting that interest than on supporting the Rio bid.

Riversdale owns another major project in Mozambique and controls the Zululand Anthracite operation in South Africa.