Anglo-Swiss mining giant Xstrata (LON:XTA) achieved record thermal coal production in the third quarter, however copper output was down 4 percent compared to a year ago.

Investors were disappointed with the production report as shares in Xstrata slipped 4 percent to 912 pence in early trade, making it one of the heaviest fallers in the FTSE 100 index.

The group added that its base metals and coal operations remain on track to deliver a stronger second half performance compared to the first half of 2011.

The group’s total consolidated coal production rose 1.7 million tonnes (Mt) in the three months to compared to the same period of 2010 to 23.6 million tonnes, a quarterly production record, as Australian thermal coal production increased by 13 percent, or 1.6 Mt.

The increase in thermal coal production was largely due to the start of operations at the Mangoola open cut mine ahead of schedule in February 2011.

While the performance of Xstrata’s coal division was strong, copper output dropped 4 percent compared to the same period last year to 223,606 tonnes.

The decline was caused by blizzard conditions, 18 days of repairs to the conveyor belt at the Collahuasi mine in Chile and lower grades at the Collahuasi, Mount Isa, Kidd and Tintaya mines.

Meanwhile, total nickel production in the third quarter was up 15 percent year on year at 26,738 tonnes, driven by successful ramp-up to exceed the planned annualised run-rate of 14,000 tonnes of nickel in ferronickel at the Falcondo operation in the Dominican Republic.

On the financial front, Xstrata said its financial position remains robust and it has maintained significant headroom within its corporate debt facilities as US$6.8 billion remains undrawn.