Mining stocks pull FTSE down at opening

Recent bouts of profit-taking and fears of fund liquidation have stood in the way of a widely-expected break above $4,000 per tonne for the metal. BHP Billiton has come under added pressure after saying its net 2006 oil and gas production could be as much as 8% below previous guidance. Its shares are down 26p or 3.09% to 816.5p, followed by falls of 55p or 2.43% to £22.13 for Rio Tinto, while Antofagasta has dropped 39p or 2.54% to £14.98 and Anglo American has also slipped 39p or 2.35% to £16.19p. WH Smith has bucked the trend, however, and has so far seen a gain of 21p or 6% to 362....