LONDON — Mining group Anglo American posted record quarterly copper production in the three months to September, reporting a stronger than expected jump of almost a third thanks to improvements at its Collahuasi mine in Chile.

Copper accounted for just over a quarter of Anglo’s profit last year and is the second-most important contributor after iron ore, but output and revenue had been hit by troubles at Collahuasi, a venture with Glencore Xstrata, which was plagued by lower ore grades, extreme weather and accidents.

Anglo said on Friday that production at Collahuasi more than doubled in the quarter, helping the group’s third-quarter copper production rise 32% to 207,300 tonnes.

Iron ore, however, which accounted for almost half of profit last year, came in significantly below expectations, with output dropping almost a quarter compared with last year, as weaker production at unit Kumba Iron Ore’s Sishen mine was only partly offset by increased output at Kolomela.

Anglo, hit by a damaging strike at Kumba last year, said production at Sishen was hit by ongoing pit constraints and regulatory safety stoppages, working at a quarterly run rate of 8-million tonnes. Anglo plans to address pit constraints present a longer-term strategy for the mine by the end of the year.

In platinum, where Anglo is planning to cut back jobs and mothball mines to bring Anglo American Platinum (Amplats) back to profit, equivalent refined platinum production was virtually flat compared with last year at 623,000 ounces.

Amplats lost around 44,000oz as a result of a strike between the end of September and the start of October, but says it is sticking to a production target of 2.3-million platinum ounces for this year.

Export metallurgical coal, used in steel-making, increased 9%, while export thermal coal production in South Africa dipped 1% in the quarter.

Diamonds, meanwhile, saw production increase by more than a fifth to 7.7-million carats, as operations at its Jwaneng mine were fully restored after a slope collapse last year, and thanks to higher production from its Canadian mines.