SHARES in Rio Tinto Ltd surged above $90 for the first time this week amid speculation that BHP Billiton Ltd could take out its rival in a $122 billion-plus deal. The stock closed up more than five per cent after Citigroup analysts fuelled takeover talk about the company. Citigroup said while Rio Tinto’s strong cashflow could make it an attractive target for private equity firms, BHP Billiton was a more likely bidder given the synergies that could be generated.