Total gold output rose 23% year-on-year to 602,000 ounces, while volumes of doré gold increased 6%.

Throughtput was up 43% year-on-year to 9.9Mt, at a recovery rate of 80.6%, down from 83.9% a year ago.

Polyus said the increase in processed volumes came from expanded capacity at existing operations on top of the new Natalka mill.

It said Natalka was operating at over 90% of its 10Mt per annum design capacity and it expected to complete the mill's ramp-up in the second half of 2018.

In April, Polyus obtained a licence to export antimony-rich flotation concentrate to third party offtakers, with first shipments started in May.

It said volumes of antimony contained in flotation concentration for the quarter were 6,200t.

Polyus sold an estimated $683 million worth of gold during the June quarter, up 12% on the quarter, with the estimated weighted-average gold selling price at $1,300 per ounce, down 3%.  

It has estimated net debt of $3.2 billion at the end of June, up from $3.08 billion at the end of March and $3.077 billion at the end of 2017.

Polyus CEO Pavel Grachev said the company had improved efficiency and increased gold output through its company-wide initiatives to actively grow its share of large-scale mining equipment, expand processing capacities and upgrade management and control systems.

"At Sukhoi Log, one of the world's largest gold greenfield projects, we have completed the scoping study and verification drilling, and entered the pre-feasibility stage. The results of Polyus' verification drilling support the data from historical exploration programmes," he said.

Polyus' shares were up 1.99% Tuesday at 33.35p (US43.74c).