The logo of Glencore is seen in front of the company's headquarters in the Swiss town of Baar.

London - Commodities trader Glencore and Xstrata, in the final stages of a $36 billion merger, posted a drop in combined output across key metals including copper, hit by power cuts in Congo and a push to replace ageing operations.

Coal, however, provided a brighter spot for the future mining and trading giant, with production rising by more than a quarter despite a three-month Colombian strike and engineering hiccups at Xstrata's coking coal operation Australia.

Analysts are keenly awaiting pronouncements from Glencore's management on plans for the combined group - specifically spending cuts, asset sales and the acquisitive Glencore team's appetite for further deals.

But neither side gave an indication on Tuesday, leaving investors to wait until March 5, when both sides publish full earnings for the year.

However, the two companies' combined production numbers released by Glencore on Tuesday showed a 9 percent drop in total copper production, while zinc, a key metal for the combined group, dipped 1 percent.

Xstrata, the world's fourth-largest copper miner, said that mined production of the red metal hit 747,000 tonnes in 2012.

That was in line with market forecasts but down 16 percent on 2011 as the company replaces ageing operations such as the Ernest Henry open pit in Australia and moves to new projects and expansions.

Xstrata has also struggled with poor performance, bad weather and operational trouble at Collahuasi, the world's third-largest copper mine, which it owns jointly with Anglo American.

It said that annual production there would be restored to about 400,000 tonnes of copper in 2013.

Glencore, for its part, saw production at key operations in the Democratic Republic of Congo hit by power cuts, which have hobbled the industry in one of the world's most promising provinces.

Glencore's Katanga unit achieved a 2 percent increase in output over the year after power disruptions cost it 67 days of production.

Mutanda, a second Congo operation that Glencore hopes to merge with nearby Kansuki in the first half of this year, boosted production by 37 percent.

Glencore is still awaiting final regulatory approval from China for its acquisition of Xstrata but is scheduled to complete the deal next month. - Reuters