Concept:White settlers were attracted to South Africa mainly by rich mineral discoveries, especially gold.Explanation:The Witwatersrand region in South Africa is world-famous for its massive gold deposits.The discovery of gold there led to a mining boom and drew thousands of white settlers and miners.This made the Witwatersrand a major economic and population centre.None of the other options attracted settlers on the same scale.Answer:Gold in Witwatersrand (Option C).