Gold–silver mineralization in Northeast Asia is controlled by 9-th volcanic belts of different ages that are superimposed on cratonic, passive continental-margin, island-arc, and oceanic terranes. The brief overview of volcanic belts in Northeast Asia presented in this communication shows that the mineralogy of the epithermal gold-silver deposits in these belts depends on the metallogeny and composition of rocks in structures of the basement and, probably, the Precambrian basement.

This giant belt is 3000 km long is composed of subaerial volcanic rocks. Relative to the oceanic margin, the Okhotsk-Chukot belt is divided into the inner, outer, and perivolcanic zones. The intricate structure of terranes of the basement and the Okhotsk-Chukot belt produced a diversity of epithermal deposit types. The inner zone of the belt mainly accommodates porphyry Cu-Mo deposits. The outer and perivolcanic zones include gold-silver and silver-tin ore deposits. The gold-silver subtype is more widespread in the outer zone (Karamken, Valunisty, Kupol, and Dvoinoi). Deposits of the silver subtype (Dukat, Lunnyi, Arylakh, Golcovy and others) are confined to the volcanic rift located between the Yana Kolyma and Omolon terranes of the Okhotsk-Chukot belt.

Tsokol is a highly weathered near-surface vein deposit with almost vertical adularia-quartz veins form a continuous mineralised zone. It was first discovered in 1984. Ore shoots within the vein structure are on average 4 m wide, up to 110 m high and vary in length from 50 to 90 m. The ore is free-milling and is expected to yield gold recoveries of up to 95 per cent.

Oroch was discovered in 1979 and was extensively explored from 1980 to 2005 through diamond drilling. It is located 110 km from Kubaka and approximately 20 km from the Kubaka-Sopka winter road. Oroch is an epithermal gold-silver deposit. The ore bodies are mainly composed of quartz and carbonate. They have a steep dip and an average width of 6 m.

The Birkachan mineralisation is located in a 150 to 200 m wide zone. The mineralisation comprises two distinct types: gold-silver veins and disseminated stockwork. The individual veins generally have an average width of up to 2-8 m, extend up to 200-250 m along strike and down-dip and carry gold grades of up to 8 to 14 g/t. The stockwork comprises mineralised zones of 60 to 80 m thick extending 2.5 km along strike and 150 to 200 m down-dip from the surface and grading 1 to 3 g/t of gold.

The Omolon hub, formed in 2009, is one of the most fully realized hub concepts in our portfolio today. The hub comprises of the Kubaka processing plant, five operating mines -Tsokol, Birkachan, Olcha, Oroch, Sopka, as well as several near-mine development projects with high-grade open-pittable reserves and significant long-term potential.

At Sopka, the volume of ore mined increased by 140% to 627 Kt. The open-pit mine life at Sopka has been extended to the second half of 2019 as step-out drilling identified incremental high quality mineralisation that extends into the pit walls.

At Tsokol, the underground development decreased by 7% year-on-year with 152 Kt of ore mined and a 29% decrease in the average gold grade to 7.3 g/t. The mine is winding down ahead of expected pillar removal operations during 2019–2020.

At Oroch, open-pit mining commenced with a total of 400 Kt of ore mined, ahead of original schedule. The additional volumes will enable optimised throughput at the Kubaka mill in 2016.

Open-pit mining at Olcha started in Q3 2016, with a subsequent switch to underground mining. The ore from Olcha is processing at the Kubaka plant.

All parts of the hub are centred around the 850 Ktpa Kubaka CIP plant, which serves as the processing facility for operating mines in the area and future near-mine feedstock. In addition, the Company operates a 1 Mtpa seasonal heap leaching circuit at the Birkachan mine.

The Kubaka plant currently uses only conventional CIP cyanidation technology. Run-of-mine ore is crushed in a jaw crusher, followed by two-stage milling (SAG mill and ball mill), thickening, CIP leaching, desorption, electrolysis, carbon regeneration and doré smelting. This processing option will continue to be utilised in the long term for ores with low silver content, such as ores from the Birkachan and Tsokol mines.