A rights offering by Turquoise Hill Resources has seen Rio Tinto buy nearly 511m shares in the Canadian miner in an attempt to maintain its shareholding.Rio bought the shares at a price of C$2.53 per share, totalling around C$1.29bn (£724m), buying up 50.8% of those offered under the rights offering.The rights offering took place so that Turquoise Hill could repay all amounts outstanding under the $1.8bn interim funding facility and $600m secured bridge funding facility provided by Rio Tinto.Prior to the deal, Rio already owned 511m shares, representing a 50.8% stake. Upon completion, Rio still holds a 50.8% interest in Turquoise Hill but owns 1.022m shares."Rio Tinto also has anti-dilution rights that permit it to acquire additional securities of Turquoise Hill so as to maintain its proportional equity interest in Turquoise Hill from time to time," the company said.However, the firms said that it does not currently intend to acquire additional securities of Turquoise Hill.BC