* Chile January copper output up 8.6 percent * World No.1 copper miner produces 474,496 tonnes in Jan SANTIAGO, Feb 28 (Reuters) - Chile produced 474,496 tonnes of copper in January, an 8.6 percent expansion from a year earlier, on higher ore grades and improved productive capacity at some deposits, the government said on Thursday. But compared with December, output slipped 7.6 percent. The INE statistics agency did not give an explanation for the drop. World No. 1 copper producer Chile is seeking to propel output in many of the its tired, ageing mines. But analysts warn accidents, extreme weather and energy woes threaten to curb forecast production jumps. The Sonami mining association sees Chile attracting $100 billion in mining investment in the next 10 to 12 years, a slightly longer time frame than previously forecast, as regulatory uncertainty and energy woes loom as key risks.The Andean country's output of the red metal jumped by 3 percent to 5.455 million tonnes during all of 2012, boosted by better grades, new mines and a low base of comparison. Chile's molybdenum output grew 7.1 percent year-on-year to 2,447 tonnes in January, the INE added.