Cost overrun of Oyu Tolgo copper and gold mine or poor management of Rio Tinto

According to the report, a panel of experts examined the cause of a $1.4 billion overrun at a Mongolian mine operated by Rio Tinto, saying it was due to the miner's mismanagement.

The cost of expanding the Oyu Tolgoi mine, Rio's largest copper growth project, has surged to $6.75 billion from Rio's initial budget of $5.3 billion in 2016, creating a funding conflict with Turquoise Hill.

Rio owns 50.8 per cent of Turquoise Hill, while Turquoise Hill owns 66 per cent of Oyu Tolgoi, with the rest held by the Mongolian government. Oyu Tolgoi is one of the most famous copper and gold deposits in the world.

According to related reports, the report, commissioned by the owner of the copper project, said the cost overrun was not caused by unfavorable rock conditions blamed by one of the world's largest miners.

Rio Tinto said the confidential report would be reviewed by the OT (Oyu Tolgoi) board and would contact the OT board as soon as it had the opportunity to review the report in detail.

There is no evidence that the rock quality and general ground conditions are significantly different from the mine owners' forecasts in 2016, the report said.

It is reported that the US Securities and Exchange Commission and British regulators are investigating the matter.

Turquoise Hill Resources could not be reached for comment.