Thomson ReutersFebruary 13, 2013 10:15
* Ramphele to make political announcement next week
* Support seen among middle-class professionals
* ANC says ready, able to fend off challenge (Adds quotes, background on Ramphele, details on politics)
By Jon Herskovitz
JOHANNESBURG, Feb 13 (Reuters) - Respected anti-apartheid activist Mamphela Ramphele resigned as chairwoman of Gold Fields on Wednesday, intensifying speculation she is about to launch a political party to challenge the ruling African National Congress (ANC).