British platinum miner Lonmin says chief executive Ian Farmer, off work since August due to a "serious illness", is stepping down permanently from his role at the troubled group.
Simon Scott will continue as interim head until a permanent successor is found, the world's third-largest platinum producer said in a statement on Friday. Scott would eventually revert to being chief financial officer, it added.
Friday's announcement follows a turbulent end to the year for Lonmin, whose shareholders last month approved a rights issue to boost its finances after violent strikes disrupted work at its Marikana platinum mine in South Africa.
"Lonmin plc announces that Ian Farmer, who is being treated for a serious illness, has informed the board of his request to step down as chief executive officer (CEO) and as a director of Lonmin with immediate effect," the company said.
"The board has appointed an executive search agent to pursue the selection and engagement of Ian's successor as CEO. In the meantime, Simon Scott will continue in his role as acting CEO with the full support of the Lonmin board.
"Simon has requested that he should not be considered as a candidate for the role of CEO. Following the appointment of a new CEO, Simon will dedicate his time fully to his role as chief financial officer."
Farmer, 50, was chief executive for four years at the end of a career with Lonmin lasting more than a quarter of a century.
Lonmin chairman Roger Phillimore said Farmer's ability, commitment and drive would be missed.
"He has been CEO for the last four years and the consistent improvement in Lonmin's operating performance over that period owes much to his leadership," he said.
The end of Farmer's tenure was overshadowed by the violence at Marikana that left 46 people dead, including 34 who were killed by police gunfire on August 16.
The recently announced rights issue, worth $US817 million ($A790.94 million), was aimed at reducing Lonmin's level of debt and increasing its financial strength in the wake of the violence.
Major shareholder, Swiss commodities giant Xstrata has called for a management shake-up at Lonmin, citing serious financial problems at the mining group.