Oil prices have sunk to fresh four-year lows, with New York crude tumbling below $US70 after the OPEC oil cartel held its collective output ceiling. At about 1610 GMT, West Texas Intermediate for January delivery struck $US69.11 per barrel -- last seen on May 25, 2010. Brent North Sea crude for January hit $US72.74, a level last witnessed on July 7, 2010. At 0804 AEDT, January delivery WTI oil was down $US4.64 at $US69.05 and Brent crude, also for January delivery, was down $US4.75 at $72.79, according to IRESS. Gold fell to the lowest level in a week as assets in the largest exchange-traded product backed by the metal shrank to the smallest in more than six years. Silver, platinum and palladium also decreased. Bullion for immediate delivery lost as much as one per cent to $US1,185.82 an ounce, the lowest since November 20, and traded at $US1,194.72 by 3.36pm in Singapore, extending Wednesday's 0.3 per cent drop, according to Bloomberg generic pricing. Gold for February delivery fell 0.3 per cent to $US1,194.50 an ounce in electronic trading on the Comex in New York. US markets are closed on Thursday for the Thanksgiving public holiday. Silver for immediate delivery retreated as much as 2.1 per cent to $US16.1688 an ounce, the biggest intraday drop since November 14, before trading at $US16.39. Spot platinum slid 0.3 per cent to $US1,225.20 an ounce, halting two days of gains. Palladium fell 0.4 per cent to $US800.50 an ounce after completing a five-day rally yesterday, the longest since October 29. Aluminium fell the most in more than a week as slumping oil prices signal lower costs to produce the energy-intensive metal. Nickel rose. While crude is not the primary source of energy for the aluminium producers, energy accounts for about 30 per cent of output costs and falling oil prices may have a deflationary impact, according to Macquarie Group Ltd. OPEC took no action to ease a global supply glut, sending Brent and West Texas Intermediate futures to the lowest in more than four years. Aluminium for delivery in three months fell 0.8 per cent to settle at $US2,044 a metric ton on the London Metal Exchange, the biggest loss since November 18. Nickel gained for the first time in three days as the Philippines moved closer to an ore export ban that could tighten supply. Prices rose less than 0.1 per cent to $US16,355 a ton. Copper for three-month delivery slipped 0.2 per cent to $US6,557.50 a ton in London. Floor trading on the Comex in New York was closed today for the Thanksgiving Day holiday. Tin, lead and zinc fell in London.