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 is expect to finish at Dvoinoye in 2020.

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%.

The mill is designed to process ore on a two shift per day, 365 days per year schedule, at a rate of approximately 4,500 tonnes per day or 1,642,500 tonnes per year.

Ore is trucked from the mine to a stockpile and transferred to a coarse ore bin using a front end loader. From the stockpile, ore is fed via grizzly screens (bars spaced 700 mm) into a coarse ore bin of 150 tonnes. Coarse ore is then conveyed to a Birdsboro-Buchannan jaw crusher with a discharge opening of 150 mm. Crushed ore is conveyed to a crushed ore bin with 3,500 m³ capacity.

Two apron feeders are provided below the crushed ore bin to feed ore to the SAG mill feed conveyor. The first stage of grinding is wet semi-autogenous grinding in a Koppers (Metso) mill (7.0 m diameter x 3.0 m effective grinding length) in a closed circuit with a vibrating screen for 2 mm primary grind size.

Screen oversize is sent back to the SAG mill feed conveyor and screen undersize is fed to nine Krebs hydrocyclones for further size control. Hydrocyclone underflow reports to the ball mill Koppers (Metso) (5.0 m diameter x 9.2 m effective grinding length).

Hydrocyclone overflow product is at a grind size of 80% minus -0.075 mm.

A gravity gold recovery circuit is located within the grinding circuit. Slurry is pumped from hydrocyclone feed sump to two centrifugal gravity concentrators (Knelson KCXD30) equipped with a control unit to vary operation mode and flush cycle. Concentrate is further processed at a gravity table. As concentrate builds up it is refined to concentrate bars.

Hydrocyclone overflow with solid content of 15% flows by gravity to the surge tank. From the surge tank, slurry is pumped to an EIMCO deep-cone thickener equipped with an agitator drive. Flocculent is added to get a clear overflow and to enable solids sedimentation. The thickener circuit overflow is pumped to a grinding circuit to be used as process water. Underflow with solids content of 50% is pumped to a pre aeration tank. The pre-aeration tank is equipped with a covered and ventilated agitator to stir slurry. The slurry then flows by gravity into the first of six leaching tanks for gold and silver to be dissolved.

The six leaching tanks are equipped with agitators to stir slurry. All leaching tanks are covered and provided with exhaust ventilation. The design of the leaching circuit ensures that slurry flows by gravity from one tank to another due to the descending top levels of tanks. Overflow from the last leaching tank is pumped to the first CCD thickener tank. Cyanide solution is added to the first, second and third leaching tanks at an adjustable flow rate. Lime milk is added to the pre-aeration tank, and the first and third leaching tanks. Lime is required to adjust pH level, while cyanide is added based on silver and gold content. Lead nitrate is added to the pre-aeration tank, and the first and second leaching tanks.

Pregnant solution residue tails are removed in a CCD circuit in five stages. The circuit comprises five EIMCO deep-cone thickeners equipped with agitator drives. The underflow of thickener tanks at each stage is pumped to a tank and mixed with the previous stage thickener with a solid content of 50%.

Barren solution from the Merrill-Crowe circuit is pumped to a slurry/solution mix tank under the last CCD thickener tank, as a washing solution. The first thickener overflow, the pregnant solution, flows by gravity to the pregnant solution tank.

Pregnant solution is pumped to pressure leaf clarifiers to remove suspended solids. Clarified pregnant solution is transferred immediately to the de-aeration tower MerrillCrowe process. The de-aerated solution is mixed with zinc dust (for gold and silver to be precipitated) and pumped to a filter press in the refinery area. After being pressed in the filter, the barren solution is pumped to a tank to be used for washing.

When filters are caked with solids, they are taken out of operation to be cleaned. The cakes are dried, and fluxes are added before further refinement in an induction furnace to produce doré bars.

CCD thickener number 5 underflow is pumped to a hypochlorite cyanide destruction tank; from this tank the slurry flows by gravity to the tailings impoundment.