An Adani spokesperson confirmed the appointment after Newcastle Herald questions following BHP's statement on Monday that Mr Boshoff was leaving in November to "take up another opportunity in the resources sector outside BHP".

"David is a highly experienced and successful senior mining executive who has spent his career running and building mines," the spokesperson said.

"His expertise in delivering greenfield projects will be extremely valuable as we continue to strengthen the team that will lead our project through construction and onto operations."

The spokesperson said Mr Boshoff would take up the position of chief operating officer "once the construction phase has been successfully completed".

"Construction of the Carmichael project is now well underway and we are undertaking recruitment for a number of positions."

Mr Boshoff's resignation was confirmed on Monday after three senior BHP representatives, reported to be two directors and a senior member of the Australian operations team, visited the Muswellbrook mine site on Friday.

A BHP spokesperson confirmed the visit but said it was "standard for senior people to visit any of BHP's mines".

In a statement BHP said Mr Boshoff had given "three outstanding years of service as general manager of Mount Arthur Coal".

"We wish him every success. His replacement will be the subject of a further announcement," the statement said.

Mr Boshoff worked with BHP for seven years and seven months and was a former BHP mining manager in Queensland before starting at the Muswellbrook mine in May, 2016.

Before that he worked in Queensland with Anglo American. He worked in the Johannesburg mining industry before 2010.

In June BHP reported its energy coal production for the 2019 financial year had decreased 6 per cent to 27 million tonnes.

"Production is expected to decrease to between 24 and 26 million tonnes in the 2020 financial year," a BHP financial report said.

BHP did not respond to questions about production costs at the Mount Arthur Coal site as the benchmark thermal coal price remains at a three-year low of $US62 per tonne.

The mine was reported to face unit costs of $US45 per tonne into the medium term because of geological constraints and higher strip ratios and diesel prices.

In October, 2018 BHP announced a $1.2 billion five-year contract with Thiess to expand the scope of its operations at Mount Arthur to include services as mine operator at the southern end of the mine in the Ayredale and Roxburgh pits.