Mamphela Ramphele has resigned as chairwoman of Gold Fields, the top bullion producer said on Wednesday, amid speculation she will start a South African political party to rival the ruling ANC.
"Dr Ramphele has decided to retire as Chair to further her socio-economic and political work," the world's number four producer said in a statement.
"She has resigned from most of her private sector directorships and will relinquish all other remaining private sector directorships."
Ramphele -- a former World Bank official and close confident of black empowerment leader Steve Biko -- is expected to announce her political plans in Johannesburg on Monday.
Commentators speculate Ramphele, a medical doctor and respected activist against white minority rule, could be a rallying point for opposition against the ruling African National Congress (ANC).
But her involvement with Gold Fields was seen as a potential Achilles heel of her political ambitions.
Violent strikes shut down the miner's operations last year, as unrest swept across the industry.
The firm sacked 8,500 people amid the strikes, but later reinstated most of them.