London shares are expected to open mixed, with the FTSE 100 index tipped to open around 8 points higher despite blockbusting results from mining titan BHP Billiton.Rocketing commodity prices meant record profits for BHP Billiton in the first half, bankrolling a huge investment programme and share buyback scheme. Profit attributable to shareholders jumped 71.5% to US$10.5bn (£6.5bn) on revenue up 39% to $34.2bn. The group announced an ambitious investment programme that's expected to top $80bn over five years, and a $10bn share buyback programme, expected to complete by the end of 2011, BG Group has announced yet another new discovery of oil in its highly prospective Santos Basin acreage, offshore Brazil but Tullow Oil has plugged and abandoned its Gharabi-1 well, located in Block 6 offshore Mauritania after poor drilling results. Full year revenue rose to $309.5m from $229.6m in 2009 as African Barrick put in a strng finish to the year. Profit before tax tripled to $104.9m from $34.4m the year before.