TOKYO, July 1 (Reuters) - Sumitomo Metal Mining (SMM) , Japan's second-largest copper producer, said on Wednesday the Sierra Gorda mine in Chile that it owns jointly with Polish producer KGHM Polska Miedz began commercial production at the end of June.
The mine had been operating for more than 60 days at 65 percent of its designed capacity as of the end of last month, six months behind its schedule for establishing commercial output, the company's spokesman Hirokazu Miyauchi said.
"It took longer than expected to ramp up output as there were some technical issues, but our plan to produce 123,000 tonnes of copper ... in 2015 remains unchanged," he said.
The Sierra Gorda mine, which is 55 percent owned by KGHM, started output of copper concentrates in July 2014 and produced 11,000 tonnes of copper in 2014.
SMM aims to bring the mine's output to full capacity, processing 110,000 tonnes of copper ore a day, as soon as possible, he said.
SMM holds a 31.5 percent stake in the mine and Japanese trading house Sumitomo Corp has 13.5 percent.
The owners aim to make a final decision as early as this year on a plan to double output capacity at Sierra Gorda to 220,000 tonnes of copper a year, with expansion work to start in the April-September period of 2016, Miyauchi said.
The mine also produces molybdenum concentrate as by-product. (Reporting by Yuka Obayashi; Editing by Tom Hogue)