KALGOORLIE, Australia (Reuters) - Gold Fields Chief Executive Chris Griffith said on Tuesday that convincing the company's shareholders to back its takeover offer for Canada's Yamana Gold was still a work in progress.

The South Africa listed miner, with assets in Australia, Africa and South America, announced plans in May to acquire Yamana in an all-share deal valuing the Canada-listed miner at $6.7 billion on May 31.

But shares of Gold Fields plunged after news of the proposed takeover. Last month the miner promised higher dividends and a Toronto Stock Exchange (TSX) listing to sweeten its takeover offer.

The market has started to understand the strategy and the timing of the deal, but is still miffed with the premium the company offered to pay, Griffith told reporters at a mining conference in Kalgoorlie, Australia.

We are trying to get them to see the massive upside that exists in this deal. So work in progress is probably the best way to describe it, he said when asked if investors and shareholders were on board with the deal.

Gold Fields shareholders will vote on the deal in the second week of October.

Griffith said the company has held a couple of road shows in recent weeks to educate shareholders.

Redwheel, one of the 10 biggest investors in Gold Fields, publicly told the miner to cancel the takeover, which it described as an expensive error with no guarantee of growth and profitability.

Gold Fields' shares tumbled 25% in the first few days after the details of the deal and the premium it was paying emerged. But the shares have made a comeback since, Griffith said.

When asked if the deal terms would be changed if there's pushback from shareholders, Griffith said: The deal structure has been locked in. We don't foresee that we will change the deal structure. But I do say that never say never.

(Reporting by Praveen Menon; Editing by Muralikumar Anantharaman)