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.

The mining and exploration licence covers an area of 2.5 square kilometers in the Srednekansk district of the Magadan Region and is located approximately 230 kilometres from the Kubaka processing plant. Olcha mineralisation is of the conventional low-sulfide epithermal type, free milling and with very high-grade bonanza-type shoots.

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.

[http://www.minesandprojects.com/reports/annual/Polymetal_International_Omolon_geology_web_2020.jpg]

In 2019, the total ore mined was up three-fold year-on-year to 2,973 Kt due to open-pit mining recommencing at Birkachan and the start of open-pit mining at Yolochka. Underground development was 13 km and remained unchanged compared with the previous year.

Following a successful in-fill drilling campaign, open-pit mining recommenced at the Birkachan mine with a view to extending the operation of the heap leach facility and replacing the ore from the Sopka open pit, which was fully depleted in Q2 2019. Total ore mined from the open pit comprised 1,629 Kt, with average gold grade at 1.4 g/t. The underground mine delivered 169 Kt of ore mined, up 19% year-on-year, with average gold grade increased by 10% to 10.6 g/t. Underground development was flat at 5 km for the year.

Open-pit mining at Sopka was completed. Total ore mined was 418 Kt, down 33% year-on-year. The mining fleet has re-located to a new satellite deposit, Yolochka (80 km from the Kubaka mill), where mining commenced in 2019.

At Yolochka, the volume of ore mined amounted to 474 Kt, with the average gold grade at 4.5 g/t.

At Tsokol, the underground development increased by 8%, with 165 Kt of ore mined and a 29% decrease in the average gold grade to 5.2 g/t.

At Olcha, total mining volumes increased by 27% to 117 Kt, while underground development was down 9% year-onyear. The average gold grade decreased to 7.5 g/t, down 23% year-on-year.

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.