Rio Tinto Group has reached a definitive agreement to acquire all remaining shares of Turquoise Hill for $43 per share, after independent directors of the Canadian miner unanimously recommended shareholders vote in favor of the deal.

Rio’s statement on Tuesday firmed up last week’s announcement of an “in-principle” agreement, which would give Rio greater control of Mongolia’s Oyu Tolgoi -- one of the largest copper mines in the world and a key “future facing” asset for the iron ore specialist. Shareholders will vote on the deal in the fourth quarter. 

Rio already owns 51 per cent of Turquoise Hill, but more than 50 per cent of the remaining shareholders must also back the acquisition. In the meantime, the giant miner said it would provide up to US$1.1 billion in funding to Turquoise Hill, which would need to be paid back if shareholders vote against the acquisition.

Sailingstone Capital Partners, a top five shareholder with a 2.2 per cent stake, has said it will oppose the deal.

Turquoise Hill was worth considerably more than $43 per share, Sailingstone Managing Director Mackenzie Davis said in an interview on Tuesday prior to the announcement. In 2019, Rio had valued the company at around $56 a share, he said.

“We believe that Rio Tinto has created this situation, now they are trying to take advantage of it with a low-ball bid,” he said, in a reference to technical problems that have plagued the Oyu Tolgoi mine. “This is a once in a generation asset, particularly in light of long-term copper fundamentals.”

Turquoise Hill rose 1.1 per cent to $40.77 as of 12:16 p.m. on Tuesday.