The company reported 14% lower copper production year-on-year at 864 million pounds as the giant Grasberg mine in Indonesia continues to transition to underground, and a disappointing performance at Cerro Verde impacted output.

The Phoenix, Arizona-based company reported a net loss of US$131 million, or 9c per share for the period, after earnings of $556 million, or 38c per share, in the year-earlier period.

Adjusted to exclude $123 million in special items, the company reported a loss of 1c per share, lower than Wall Street analyst forecasts calling for breakeven.

Revenue fell 33% year-on-year to $3.308 billion, which was also below the consensus average of $3.53 billion.

Freeport said copper sales of 795Mlb were 4% below its July forecast, and it tracked 24% below the year-earlier figure. Gold output at 333,000oz was 6% higher than the July estimate but 71% lower year-on-year, mainly owing to the lower milling and ore grades at Grasberg.

Freeport reiterated its full-year guidance for 3.3Blb of copper sales, 874,000oz gold and 92Mlb molybdenum.

"We are effectively executing our plans to establish large-scale production from our significant high-grade, low-cost and -lived underground ore bodies at Grasberg; advance the Lone Star project in Arizona as a new cornerstone asset in the US; and progress our innovation initiatives to enhance productivity and grow our Americas operations with low capital intensity," CEO Richard Adkerson said.

Company shares (NYSE:FCX) closed 2% or 20c higher at $10.13, which gives it a market capitalisation of $10.13 billion.