Amid speculation of a Barrick Gold-Freeport merger, Adkerson told the Wall Street Journal it was "a real challenging time" to think about strategic opportunities due to the cash flow situation as the company shifts Grasberg from an openpit to underground mine.

Freeport has estimated output from the Indonesian operation will increase to 1.7 billion pounds of copper and 1.8 million ounces of gold by 2023.

"Our company is laser-focused on completing that [Grasberg transition], so we are focused on that and not M&A opportunities," Adkerson told the paper.

"After that is complete, we would be in a position to look at a number of alternatives that could be attractive to our shareholders."

There has been a series of mega-mergers over the past year in the gold sector, led by Barrick's merger with Randgold Resources which came into effect 12 months ago.

US-focused merger and acquisition activity is set to intensify in 2020 as miners seek to capture value for shareholders, deal expert and partner at international law firm Dorsey & Whitney Nora Pincus told Mining Journal last week.

Freeport shares are trading near the upper end of a 52-week range, gaining 4.9% yesterday to close at US$13.53 as the copper price strengthened ahead of the US and China signing a phase one trade deal this week.

The company is capitalised at $19.6 billion.