Gold Fields, the world's third largest gold producer, says it has mailed an offer document to Western Areas shareholders.

In September, the company announced its intention to purchase all the shares in Western Areas at a ratio of 35 Gold Fields shares for every 100 Western Areas shares held.

South Africa's competition authorities still need to approve the deal. "The offer will remain open for a period of at least 14 days after the requisite approvals have been obtained," said a Gold Fields announcement.