A broadly in-line production update from Antofagasta underwhelmed investors on Wednesday with Westhouse Securities dampening sentiment by downgrading the stock from 'add' to 'neutral'.Chile-based miner Antofagasta reported a sequential increase in gold and copper output in the second quarter, while molybdenum production fell. The group said it is on track to hit its full-year guidance.However, Westhouse said it has lowered its rating in response to the recent share-price movement - the stock had risen 12% over the last month as of Tuesday - with Antofagasta starting to look "fully valued" against others in the sector.It also highlighted a "marginal" growth outlook and an uncertain future for copper prices."This was a reasonable set of results for Antofagasta and with numbers in line with our forecasts for 2014, we retain our 885p target price. "However, consensus appeared to be that the company would beat its full-year guidance, so these results might be viewed as slightly negative by the market." Antofagasta's shares were down 2.4% at 834.5p by 11:14.BC