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]

The Kedon marginal volcanic belt formed on the continental crust in the Middle Paleozoic during a period of 30-35 Ma. Relicts of this volcanic belt are retained as fragments in the Omolon cratonic terraine. The belt is composed of differentiated subaerial red-colored volcanic rocks coupled with compositionally similar subvolcanic and hypabyssal intrusions. The volcanic rocks belong to the calc-alkaline series. There are two types of epithermal volcanic mineralization in the Kedon volcanic belt. Gold mineralization (Au/Ag=1:1-1:5) is developed in the Kubaka, Birkachan, and Elochka deposits. Whereas the gold-silver mineralization (Au/Ag=1:10-1:50) is developed in the Sedoi, Yunyi and Ol'cha deposits. The large Kubaka and Birkachan deposits are characterized by a low content of sulfides (<0.1 and 0.1-0.5%, respectively). The ores are mainly composed of gold, electrum, and pyrite.

Following a successful in-fill drilling campaign, open-pit mining recommenced at the Birkachan mine (Omolon) with a view to extending the operation of the heap leach facility.

Kubaka mill processed larger volumes of higher grade ore from the Birkachan and Olcha underground mines.

The hub comprises of the Kubaka processing plant, three operating mines - Tsokol, Birkachan, Olcha as well as several near-mine development projects with high-grade open-pittable reserves and significant long-term potential. 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.