By Fabio Teixeira

RIO DE JANEIRO Sigma Lithium on Friday said its Chief Operating Officer Brian Talbot left the company at the end of last month, confirming a Reuters report that sent the firm's shares tumbling on Thursday.

Talbot became COO last year, overseeing operations at Sigma's flagship Grota do Cirilo mine, the poster child for Brazil's budding lithium sector. He gave his resignation notice in July and his last day with the company was Sep. 29.

His exit marks at least the third shake-up of Sigma's senior management in 2023, amid a legal battle between the husband-and-wife pair who ran the company together until earlier this year.

Sigma said Talbot had resigned for health reasons.

In a statement, the miner's co-chairman Marcelo Paiva said the firm "had agreed to respect Mr. Talbot's decision regarding the timing to make his resignation public."

Talbot told Reuters that Paiva's comments were "factually incorrect as there has been no request to withhold from the investors the fact that I resigned in July."

The former COO said he was "surprised" that Sigma had disclosed his personal information, adding: "My health is excellent now and I am focused on the future."

Talbot said he is now working at his own business, R-Tek.

Sigma said it had promoted to "co-general managers" its Director of Mining Reinaldo Brandao, Director of Processing Keith Prentice, and Director of Geology and Regional Institutional Relations Iran Zan.

Those executives have been in charge of Sigma's operations on-site in Brazil for almost four months, the miner added.

Last week, Reuters reported that divorce proceedings between Sigma Chief Executive Ana Cabral-Gardner and Calvyn Gardner, her husband and former co-CEO, had triggered several lawsuits, including a dispute over some of the mineral rights where Sigma plans to build mining pits.

At the time, Sigma told Reuters the dispute would not affect its expansion plans, as it said it can develop the area via a "waste sharing agreement." It also said that efforts to attract a buyer for Sigma, which is looking for a buyout, were not affected.

Gardner left his co-CEO role in January, and Sigma announced a new chief financial officer in August.

(Reporting by Fabio Teixeira; Editing by Brad Haynes and Rosalba O'Brien)