BHP Billiton, the world's largest mining company, may offer to help Rio Tinto raise capital as an alternative to its proposed $US19.5 billion ($26 billion) investment deal with Aluminum Corp of China (Chinalco), investment bank UBS said. The two companies may save as much as $US10 billion by combining their iron-ore assets in the Pilbara region of Western Australia through a merger or joint venture, Glyn Lawcock, a Sydney-based analyst at UBS, wrote in a report. ''BHP could propose to assist in underwriting a substantial rights offering for Rio, and in exchange propose an iron-ore joint venture in the Pilbara,'' Lawcock wrote. The combination would also have ''better control over pricing, particularly from Australia to Asia,'' he wrote. Meanwhile, the tie-up with Chinalco has been cleared by the US Committee on Foreign Investment, Rio Tinto said this morning.