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.

The Omolon hub comprises of the Kubaka processing plant and operating mines - Tsokol, Birkachan, Olcha,Yolochka. 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.

All parts of the Omolon hub are located northeast of the Magadan region in remote and unpopulated areas covered with taiga forest, with only seasonal access. Land transportation between various parts of the Omolon hub is only possible during the winter via unpaved winter roads.

Olcha
The development of reserves at the Olcha deposit is used through the phased commissioning of production facilities: Stage I - development of reserves in the Central and Southern zones by conventional truck and shovel mining method, Stage II - development of reserves by an underground method.

Access to the underground ore bodies is carried out via East and West adits.
Sub level open stoping is utilizing for mining ore bodies with a thickness of more than 3 m and shrinkage stoping for mining ore bodies up to 3 m thick.

The ore is delivered to the stockpile, from where it is transported to the Kubaka processing plant via winter roads.

Birkachan
Mining at Birkachan open-pit was completed in Q4 2020.

Access to ore bodies at Birkachan underground carried out via adits.

Tsokol is an underground mine located near the Kubaka processing plant.

Yolochka is an open-pit mine located approximately 80 km at Kubaka processing plant which is quarried by conventional truck and shovel method via preliminary drilling and blasting operations.

Run-of-mine ore is crushed in a jaw crusher, followed by two-stage milling (SAG mill and ball mill).

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.