UK-listed miner Kaz Minerals reported strong increases in copper and gold production on Thursday.
Kaz said full-year 2017 copper production was up 80% on the prior year at 259 kilotonnes (kt).
Annual gold output was also at the higher end of its forecasts.
However, the shares slid 3.5% on Thursday morning after the production update was released.
Fourth-quarter copper output actually declined over the final three months of the year versus the prior quarter, raising concerns over the outlook.
Copper output in the most recent quarter slid to 65 kt versus 75 kt in the prior period, which Kaz said reflected grade reduction at Aktogay and Bozshakol concentrator maintenance.