UBS lowers its earnings per share (EPS) forecast for South America-focused miner Antofagasta after the group reported lower-than-expected production figures on Wednesday.Group copper production reached just 129,800 tonnes in the first quarter, 22% below UBS's estimate of 166,500 tonnes, mainly as a result of the slower ramp up at the newly-commissioned Esperanza project in Chile's Antofagasta region.Consequently, the broker has downgraded its 2011 EPS estimate by 4.9%, but notes that there should be minimal changes going forward.The miner has now slightly reduced its full-year guidance for copper production from its Los Pelambres mine (in Chile's Coquimbo region) from 419,000 tonnes to 407,000 tonnes, and - when this is coupled with the Esperanza missing daily ore throughput estimates - the broker thinks second quarter production could disappoint further.The target price is lowered from 1,350p to 1,310p, and a 'neutral' stance is maintained.---BC