(ShareCast News) - Shares in Kaz Minerals surged early on Thursday, after the miner swung to an interim pre-tax profit, although lower commodity prices weighed on the company's performance.In the six months to the end of June, the miner reported a $2m pre-tax profit compared with a $104m loss in the corresponding period 2014, even though revenue declined 19.7% year-on-year to $341m.The FTSE 250 group attributed the decline in revenue to lower production levels due by maintenance work and lower copper, silver and gold prices.The improvement in results was due to a $181m loss on foreign exchange the group booked in the first half of 2014, which did not recur in the first six months of 2015.Kaz said that earnings before interest, tax, depreciation, amortisation and exceptional items more than halved to $88m.Copper production declined 3.1% year-on-year in the first half to 43,000 tonnes, although Kaz said it was on track to meet its full-year guidance of 80,000 to 85,000 tonnes, with production expected to rise in the second half once the Aktogay mine becomes operational.The miner added it expected zinc and gold production to be at the top end of its guidance range of 90,000 to 95,000 tonnes of zinc and 2.3 to 2.5m ounces of silver granules.Meanwhile, the miner added that, due to a recent fire at the site, the Bozshakol mine will not be ready by the end of the year as originally expected and it is expected to be operational in early 2016."The group continues to deliver its strategy to develop large-scale, low-cost, open-pit copper mines in Kazakhstan," the company said in a statement."Whilst lower commodity prices have affected the profitability and cash flow generation of our existing assets in the first half of 2015, we believe copper is a commodity with strong medium and long term fundamentals."Kaz Minerals shares were up 20.68% to 0840 BST on Thursday.