(ShareCast News) - Mining giant Antofagasta lowered its annual copper production forecast for the second time this year, as it delayed the start of production at its new Antucoya project.The Chilean miner said copper output in the second quarter of 2015 grew 7.2% quarter-on-quarter to 157,000 tonnes, bringing production for the first half to 303,400 tonnes, a 12.9% decline year-on-year.The FTSE 100 group said the slowdown in output was attributable to heavy rain and protest against its operations in the first three months of the year, as well as lower throughput and grades at its Los Pelambres mine in Chile.Gold output in the first half declined 9.1% year-on-year to 112,500 tonnes, while cash costs increased 5.5% in the second quarter to $1.93 per pound.However, with the start of production at the Antucoya mine delayed until the end of the third quarter of 2015, Antofagasta warned its costs and production guidance for the full year will be negatively affected.As a result, full year copper production guidance has now been lowered from 695,000 tonnes to 665,000 tonnes, while net cash cost guidance has been updated from $1.40 per pound to $1.47 per pound.Analysts at Shore Capital described the production figure as "disappointing" and warned to expect a negative reaction in the shares.Antofagasta shares were down 1.54% to 577.00p at 0826 BST on Wednesday.