* Low base of comparison, new mines, better ore grades boost * Copper output up 6.3 percent in first half of 2013 SANTIAGO, Aug 29 (Reuters) - World No. 1 copper producer Chile produced 480,440 tonnes of copper in July, a 16 percent jump from a year before, boosted by a low base of comparison, higher output from new mines and better ore grades, the government said on Thursday. Chile, which produces a third of the world's red metal, is struggling with dwindling ore grades in many of its aging deposits, although new mines have helped increase output in 2013. Esperanza, run by Chile's Antofagasta Minerals, was inaugurated in 2011. After initial woes, the mine is now on track, Antofagasta said earlier this week. However, July's copper output inched down 0.4 percent compared with June 2013. The INE national statistics agency did not provide an explanation for the difference. In the first six months of the year, copper production increased 6.3 percent to 3.257 million tonnes. The Andean country produced 5.455 million tonnes last year, a 3 percent increase compared with 2011 levels. Output of molybdenum, a metal used to harden steel, soared 20.9 percent in July versus the year earlier to 3,201 tonnes. In the January to July period, production of molybdenum jumped 16.9 percent to 21,186 tonnes.