(Bloomberg) -- Australia’s Resolute Mining Ltd. plunged by a third after its chief executive was detained in Mali by a military government that’s seeking a greater share of resource revenues.

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Mali is among a number of West African nations putting pressure on mining companies as they seek to assert more control over mineral production. The military junta in Mali, the continent’s No. 3 gold producer, also wants to shore up revenue following a 2020 coup that triggered sanctions and cut off some aid flows.

Resolute’s CEO Terry Holohan had been in the capital, Bamako, for discussions with mining and tax authorities about the Syama gold mine it operates. The company confirmed on Sunday that he and two other employees were unexpectedly held late last week.

Mali has been steadily ramping up efforts to renegotiate existing contracts with foreign mining investors including Barrick Gold Corp., B2Gold Corp., and Allied Gold Corp. Last month, it briefly jailed four Barrick employees and said it might take back a mining concession from the world’s no. 2 gold producer. A revised law, approved last year, grants the state a bigger share in mining projects.

Resolute’s shares closed down 33% in Sydney on Monday, their biggest one-day drop since 1988, cutting its market value to A$958 million ($631 million).

“While Resolute is working toward a settlement with the government of Mali to help secure the long-term future of the Syama gold mine, the upmost priority remains the safety and wellbeing of its employees,” the company said, adding that it has followed all official processes.

Resolute previously negotiated a so-called convention for its Syama asset that runs until 2029. Mali’s military rulers have upped pressure on companies operating in the country since passing a new mining code. Their toughening stance also coincides with a 30% jump in the price of bullion this year.

“As we’re generating a lot more cash,” those running gold-rich West African countries “are looking for possibly a bigger piece of the pie,” Resolute Chief Financial Officer Chris Eger said on a recent earnings call. Resolute’s other operating mine is in neighboring Senegal.

Mali has threatened to reclaim Barrick’s Loulo mine permit when it expires in 2026, and has rejected a proposal that would give the state 55% of the economic benefits from the firm’s gold complex in the country. Barrick CEO Mark Bristow said last week that the company continues to discuss a “mutually acceptable outcome” with the nation’s leaders.