A year ago the gap was $100 and at the peak of the deal in May, the trading gap between the two mining giants was more than $106.
In the past month, investors concerned about Rio's huge debts and the world's faltering demand for commodities have sent the company's share price down 60 per cent.
Rio shares tumbled a further $4.30 or nearly 12 per cent to $32.50 yesterday - their lowest closing price since BHP went public with its bid in November last year - amid growing concerns the miner will have trouble repaying its massive debts.
In marked contrast BHP lost only 1 per cent to $27.50.
The recent stockmarket falls have brought Rio's market capitalisation down to about $41 billion -- well below the value of BHP's offer.
BHP dropped its bid for Rio last week, on the grounds that the proposed deal was no longer in the best interests of shareholders in the face of the recent commodity price crash.
Throughout the year-long takeover battle, Rio repeatedly rejected the 3.4-for-1 all-share offer as too low.
However, most analysts argue that BHP is the better placed of the two mining giants to weather the looming global recession because of its relatively strong balance sheet.
Rio borrowed some $US40 billion from a syndicate of 27 banks in October last year to fund the $US38.1 billion acquisition of Canadian aluminium producer Alcan.
The miner originally intended to sell off non-core assets to help repay the debt but no buyer has emerged.
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