Gold mineralisation at Berezitovy is present within a steeply west-southwest dipping zone of metasomatically altered and brecciated granodiorite. Mineralisation occurs in chaotic irregularsided veins, consisting of variable amounts of sulphide minerals, intergrown with a gangue of quartz and accessory minerals.

Berezitovy is located in the Sergachi Metallogenic Zone (“SMZ”), known for Au, Cu, Pb, ZN, Bi, Mo and W prospects. The SMZ is hosted by a major volcano-plutonic zone, formed in the late Permian to Cretaceous, and considered to be an Andean-type active continental margin. Magmatic complexes were intruded into Archaean and Proterozoic basement. The dominant structures of the region are the east-northeast striking Sergachinski and Khaiktinski fault zones. The other main regional structural feature is a set of northwest trending structures, less pervasively developed than the east-northeast striking fault zones. Berezitovy and several satellite occurrences of mineralisation correspond to this northwest trend.

The host rock at Berezitovy is Permian age granodiorite. Variations in texture and composite of the intrusions have been interpreted to possibly represent pulses from a Cretaceous complex.

Numerous metre-scale dioritic dykes intrude the granodiorite host rocks. The dykes have two main orientations: east-northeast striking, subvertically-dipping, or shallow northeast-dipping. The dykes exhibit a range of timing relationships with the host intrusion and faulting of the deposit.

A major feature of the Berezitovy open pit is a steeply south-southeast dipping shear zone, >8 m wide, that coincides with a swarm of mafic dykes. South of the shear zone, the mineralisation is relatively higher-grade, massive, and with a lower Ag-Au ratio. North of the shear zone, the mineralisation tends to be thinner, lower grade, a more planar structure, and higher Ag-Au ratio.

Mineralisation occurs in chaotic irregular-sided veins, consisting of variable amounts of pyrite, sphalerite, galena, lesser chalcopyrite, intergrown with a gangue of quartz ± garnet, sericite, tourmaline, biotite and chlorite. Mineralised veins do not have a strong preferred orientation. Vein geometries and textures are consistent with conditions that can occur in relatively shallow crustal levels, sub as the sub-volcanic environment.

Although pyrite is ubiquitous, higher gold grades are associated with greater contents of galena and sphalerite. Vakh et al (2016) concluded that there are two main phases of mineralisation; an earlier phase of gold-polymetallic sulphides, and a later phase of gold-quartz veins. Weathering of sulphide minerals has not occurred to substantial depths, and the depth of oxide and transitional mineralisation is typically no more than 7 m below topography.

Current mining operations at Berezitovy are focused on a single open pit with two mining areas, north and south, and a recently developed underground. Berezitovy has a well-established open pit operation, with pre-production having commenced in 2006, with the operation expanded to an underground operation in 2018.

Berezitovy is mined using conventional drill, blast, load, haul, dump and stockpile open pit mining methods utilising a top-down bench by bench approach. Truck haulage is used to convey ore to the process plant and waste to the dumps.

The deepest southern section of the pit is near completion and will be finalised in Q1 2021, with mining predominantly focused in the north for the remaining LoM in 2022. The underground mine is also planned to be finished in 2022.

Production is achieved using variants of the long-hole sub-level open stoping method, either top-down “uphole benching” with eventual backfilling, or bottom-up “Avoca” progressively backfilling each sublevel. Blastholes are drilled using dedicated electro-hydraulic long-hole drill rigs, blasted ore is removed with LHD and ore is transported to surface with ADT.

Surface is accessed through twin transport declines with 8° inclination. The declines exit the mine through a dedicated box-cut excavation.

Stability of the workings is maintained by the installation of ground support (friction anchors, mesh sheets, shotcrete), leaving supporting rib and sill pillars of ore unmined for potential later extraction, and filling mined stopes with development waste as backfill when strategically required.

Mining of the remaining ore reserves will deepen the northern workings by 40 m. There will be no deepening below the southern part of the pit surface and the workings will remain at 800 m depth upon depletion of the ore reserves. A separation distance of 15 m is maintained between the open pit and planned underground workings.

Crushing
RoM ore is screened at 750 mm on a stationary grate, with oversized broken using a rockbreaker. The primary crusher is a FLSmidth (Fuller-Traylor) 1200x1500 jaw crusher. Crushed ore is screened at 40 mm, with oversize directed to a Metso GP500 cone crusher operating in open circuit and with a nominal product size of 35 mm. Crushed ore reports to an open stockpile. The secondary crusher can be by-passed if the ore is soft, or contains a significant amount of ice or tramp metal from the mining operation.

Grinding
The first grinding stage consists of a 6.7 x 2.4 m SAG mill (1800 kW) that is closed with a 2 mm aperture screen. Screen undersize is split between two ball mills, the original 4.4 x 8.5 m (2240 kW) and the new 4.5 x 6.0 m (1800 kW) units. Each mill operates in closed circuit with a bank of Cavex 500CVX cyclones. After screening for trash removal, cyclone overflow is combined and thickened in a 24 m diameter conventional thickener ahead of cyanidation. Grinding is conducted using cyanide-containing process water to commence leaching early in the circuit.

The Berezitovy process plant treats non-refractory sulphide-hosted gold ore through a conventional carbon-in-pulp (“CIP”) circuit. Silver is present as a co-product. Lead and zinc are also present in the ore, but are at sub-economic levels.

The plant commenced production in late 2007 at a production rate of 1.2 Mtpa using mostly second-hand equipment (primary crusher, SAG and ball mill, CIP circuit). Progressive upgrades, including the addition of additional tailings filters in 2009, a second ball mill and goldroom upgrades in 2010, and a secondary crusher at a subsequent date, have resulted in an increase in plant capacity to the current figure of up to 2.0 Mtpa.

Cyanidation
The cyanidation circuit consists of eight 430 m3 mechanically agitated tanks, giving a circuit residence time of the order of 12 hours at a feed slurry density of 50% solids. Cyanide is added to the first and fifth tanks, and cyanidation addition is automatically controlled using a TAC 1 ........