A South Korean consortium said on Monday that it has made a non-binding offer to buy Whitehaven Coal, valued at 3.5 billion Australian dollars (3.497 billion U.S. dollars).

The group consisting of Korea Resources Corp (Kores) and Daewoo International Corp said they have submitted a preliminary offer to acquire Whitehaven this month, and are examining the Sydney-based miner's books with a view to making a formal bid.

Whitehaven put itself up for sale last year. It said on Feb. 7 that short-listed parties have been invited to complete more detailed due diligence and submit binding proposals.

"Kores submitted the offer this month as leader of the consortium," a Kores spokesman said.

Whitehaven produces metallurgical coal and thermal coal from five operating mines in NSW and has expansion plans underway.

Australia is the world's largest exporter of coal with the annual export of about 252 million tonnes. The nation's coal mining assets have lately become the targets of contested takeover by companies from Asian emerging economies vying for new energy sources.