Dvoinoye Zone 37 is a low sulphidation epithermal gold-silver vein deposit. The principal vein at Dvoinoye, Zone 37, strikes at 040° over a length of at least 800 m. Ore zone width ranges from a few metres to more than 30 m in the central shoot. Zone 37 has been drilled over a vertical extent of about 350 m (including sills). The vein system has a steep to subvertical dip to the southeast. There is evidence that at depth the vein system may shallow in dip, from subvertical to about 70°. There are two main thick quartz veins, within a variably wide envelope of narrower veins and veinlets (stockwork zone). The central shoot represents a blowout in width where the shoot may have a pipe-like form. The bulk of the gold in Zone 37 is in the central shoot. At depth and at the southwestern end, the mineralization forms a series of sub-parallel veins, rather than one or two wide veins. Late to post vein block faults probably disrupt vein continuity along strike, especially to the northeast where the fault-bounded granite intrusion is developed.

Mineralization at Dvoinoye Zone 37 is characterized by low total sulphide content, generally less than one percent, by variable but low gold:silver ratios (average 1:1), and by the presence of considerable free gold in parts of the deposit. The main ore minerals and related sulphides in the vein are native gold, freibergite, pyrite, chalcopyrite, galena, and sphalerite, with minor acanthite. Ore minerals are generally fine-grained. Gold occurs inter-grown with sulphides, free in quartz-illite aggregates, and in places as rare dendritic growth bands.

A wide variety of vein and mineralization textures are recognized from Zone 37 including massive vein, colloform-crustiform banded vein, breccia, and veinlet/stockwork zones. The vein mineralogy consists of quartz-chalcedony (80 to 90%), adularia (5 to 7%), carbonate (up to 5%), illite, and chlorite.

Zone 37 displays a lateral and vertical zonation in mineralization and alteration assemblages, reflecting the evolution of the system spatially and over time. Corbett (2010) describes four styles of gold mineralization that may or may not be spatially separate (Figure 8-1). From earliest to latest these are:

1. Pink quartz gold: Banded quartz veins/breccias with variable quartz textures (crystalline at depth/southwest to chalcedony in northeast), low gold grade, and silver:gold ratio less than 1:1.

2. Carbonate-base metal gold: Sulphide assemblage of pyrite-sphaleritechalcopyrite galena-silver sulphosalts, associated with carbonate (rhodochrosite). Lateral change in sphalerite colour, from red in southwest to white in northeast, indicative of fluid flow direction (hotter to cooler). Silver:gold ratio of 6:1.

3. Chalcedony-ginguro ± adularia gold-silver: Banded veins of chalcedony-opal, pink quartz, minor adularia, and black ginguro bands and spots. Dvoinoye has sparse ginguro development (compared with Kupol). Silver:gold ratio of 2:1.

4. Green quartz breccia: Quartz breccia with altered dyke clasts, contains specks of free high fineness gold, with pyrite. Gold associated with kaolinite and a silver:gold ratio of 1:1.

The chalcedony-ginguro and green quartz breccia types are the biggest volume contributors to Zone 37 mineralization.

Dvoinoye underground mining operations have used two different mining methods, transverse longhole stoping and longitudinal longhole stoping. Transverse longhole stoping has accounted for more than 90% of the historical production, but the remaining reserves will predominantly be extracted using longitudinal longhole stoping. Mining of Zone 37 and Zone 1 at Dvoinoye finished in November 2020. Currently no mining activities are in progress.

The Kupol processing plant also processes ore from Dvoinoye. The ores from the two sites are processed in batches, with Dvoinoye ore typically being processed at the start of each month.

The milling process consists of primary crushing and a semi-autogenous grinding (SAG) mill / ball mill grinding circuit, and includes conventional gravity technology followed by whole ore leaching. Merrill-Crowe precipitation is used to produce gold and silver doré bars. Countercurrent decantation (CCD) wash thickeners recover soluble gold and silver, and a cyanide destruction system is used to reduce cyanide concentrations to an acceptable level for disposal. The tailings flow by gravity through a pipeline to a conventional tailings impoundment. Doré bars are shipped to the non ferrous metals plant in Krasnoyarsk. Average mill recovery, based on both Kupol and Dvoinoye ore, is 95% for gold and 85% for silver. The mill availability is 94%.

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