UPDATE 4-Rio Tinto, Turquoise Hill reach deal on Oyu Tolgoi expansion

(Adds analyst, updates TRQ shares)

MELBOURNE April 9 (Reuters) - Rio Tinto Ltd said on Friday it has reached a binding agreement with Turquoise Hill Resources Ltd over funding for expansion of the massive Oyu Tolgoi copper-gold mine in Mongolia.

Rio and Turquoise Hill will restructure debt payments of up to $1.4 billion with lenders and look to raise up to $500 million in supplemental debt under existing financing arrangements. (https://bit.ly/3uCfg96)

The agreement will smooth the way for the next phase of development, which has faced cost and timeline blowouts and has caused acrimony between the mining giant and its junior partner.

"It's just been such a troublesome asset, at least this takes away one of the issues - you have still got the issues with the government and the technical issues," said Andy Forster, portfolio manager at Argo Investments in Sydney.

"From a financing perspective there has been a fractured relationship there, so I guess this result is positive."

The Oyu Tolgoi mine expansion has seen costs balloon to $6.75 billion, about $1.4 billion higher than Rio's estimate in 2016, and has led to friction over funding between it and Turquoise Hill.

The new funding plan tackles the remaining estimated funding requirement of about $2.3 billion, Rio said. It will back potential shortfalls from the debt re-profiling as well as new debt up to $750 million through a co-lending facility.

Toronto-listed Turquoise Hill shares rose as much as 7.4% in Friday trading.

The Canadian miner committed to a rights offering of up to $500 million within six months of the co-lending facility becoming available to satisfy any remaining shortfall.

That is "markedly lower" than expected and is positive for Turquoise Hill investors, Bank of Nova Scotia analyst Orest Wowkodaw told clients.

Oyu Tolgoi, one of the world's largest-known copper and gold deposits, is 34%-owned by the Mongolian government with the rest held by Turquoise Hill, in which Rio owns a 50.8% stake.

The government has also sought to cancel the deal underpinning the mine's underground expansion. nL1N2KE22P]

At peak production, the operation is expected to produce an average of 480,000 tonnes of copper per year from 2028 to 2036, from the open pit and underground. By 2030 it is expected to be the fourth-largest copper mine in the world. (Reporting by Nikhil Kurian Nainan in Bengaluru and Melanie Burton in Melbourne; additional reporting by Jeff Lewis in Toronto; editing by Jason Neely, Chizu Nomiyama and Emelia Sithole-Matarise)