Pressure was coming from "parts of the US government," chair Dominic Barton said.

The due diligence period on the offer ends May 11.

Barrick CEO Mark Bristow is refusing to shut the door on accepting new investment from state-controlled Chinese companies, and questioned the move by Canada and the US to clamp down on such investment.

Argyle Rose features one of the last diamonds to be mined from the iconic Argyle mine in the East Kimberley, Western Australia.

World's biggest miners are inviting expressions of interest from technology providers, equipment manufacturers, reagent suppliers, startups and research groups across the globe.

“We’re certainly learning from it and watching how that progresses,” said Mark Bristow.

Miner said it will need to look at ways to address lost capacity should its Malaysian plant be shut indefinitely.

Wood Mackenzie estimates a greener world will be short about six million tonnes of copper by next decade.