(Adds full-year data, background details)
SANTIAGO, Jan 29 (Reuters) - World No. 1 copper producer Chile produced 522,674 tonnes of copper in December , a 0.5 percent decrease from a year earlier, due to lower ore grades and maintenance work at mines, the government said on Thursday.
Chile, which produces a third of the world's copper, is struggling with dwindling ore grades in many of its aging deposits, although new mines are helping to boost output.
For all of 2014, copper output reached 5.78 million tonnes, slipping a slight 0.2 percent from a year earlier. Production rose 9.4 percent in December from November.
Chile is expected to produce 6 million tonnes of the industrial metal in 2015, Chilean state copper commission Cochilco forecast on Thursday.
Production of molybdenum, a metal used to harden steel, increased 5.5 percent in December versus a year earlier to 4,343 tonnes. Full-year 2014 output jumped 27.4 percent to 48,474 tonnes. (Reporting by Anthony Esposito; Editing by Alden Bentley and Bernadette Baum)