Talks between the two companies were ongoing yesterday, with Rio understood to be offering around A$16 a share for Mozambique-focused Riversdale.
Riversdale could instead announce a longer suspension from the stock exchange this morning if a deal is not finalised before the markets open, in accordance with Australian trading rules.
Rio entered talks with Riversdale at the start of the month, when Rio was said to have offered A$15 a share. The new offer represents a 13.5 per cent premium to Riversdale’s share price before the talks were announced.
If Rio succeeds, the purchase will boost its presence in the coking coal market, in which rival BHP Billiton already has a large holding.
Meanwhile, Rio was yesterday linked to Russian diamond miner Alrosa, with Russian media reporting that the London-listed giant was looking to spend $400m (£259.9m)?on a 49 per cent stake in the firm.
A spokesperson for Rio declined to comment on either company yesterday, while Riversdale also declined to comment. State-owned Alrosa was unavailable for comment.