Barrick Mining appointed veteran executive Mark Hill as interim president and CEO on Monday following the sudden resignation of Mark Bristow, who led the Canadian miner for nearly seven years after its merger with Randgold Resources.

Bristow, who became CEO in 2019 when Barrick acquired Randgold, oversaw the integration of the two companies and steered the miner through a period of significant portfolio reshaping and debt reduction.

“Disappointed to see him leave, he has been a fine leader,” said Peter Letko, of the Letko Brosseau investment fund, one of Barrick’s shareholders.

Bristow indicated in May he would stay in his current role until 2028, a timeline that would have allowed him to oversee the development of the company’s Reko Diq copper and gold project in Pakistan.

The announcement was therefore “surprising,” analysts at Citi said in a note.

“One question is whether this will lead to bigger changes at Barrick,” they said. “A new CEO could bring a new strategy in Mali, at Reko Diq or for the portfolio.”

Hill, who will also continue to serve as group chief operating officer, takes charge immediately as the board begins a global search for a permanent chief executive with the help of an external firm, named by one source as Egon Zehnder.

The board has been looking at succession planning for some time, driven, according to one source with knowledge of the matter, by the business’s relative underperformance compared to competitors over the past five years.

Shares in Barrick, which owns 13 mining assets across Africa, Asia, Latin America, and North America, have lagged some rivals, rising by 37 percent since 2020 compared to a 110 percent climb in shares of fellow Canadian miner Agnico Eagle, with gold prices hitting record highs.

US-listed shares of Barrick were marginally higher in premarket trading on Monday.

MALI, REKO DIQ AMONG CHALLENGES FOR NEW CEO

The company will consider both internal and external candidates, the source said, adding it was not clear if Hill would put himself forward as permanent CEO.

Bristow’s last public appearance was earlier this month at the Denver Gold Conference, where he addressed a packed room of investors about Barrick’s future plans.

Known for his mercurial leadership style, his tenure at Barrick was focused on integrating tough assets that Barrick owned in some of the volatile regions of the world.

But his biggest test came this year when Barrick’s mine in Mali, one of its biggest gold assets in Africa, was taken over by the military government over alleged non-payment of taxes. Barrick had to write off $1 billion from its books over the dispute.

Resolving that dispute will be among the key challenges for Bristow’s successor, along with the development of Nevada gold project Fourmile and its integration with Nevada Gold Mines joint venture with Newmont, and work on Reko Diq, said Martin Pradier of Veritas Investment Research.