The Irokindinskoye deposit is comprised of quartz veins occurring in three main fracture systems which are flat dipping (25° to 45°) to the west. The veins are typical of other quartz vein deposits, with the veins pinching and swelling in both the strike and dip directions and in which, more often than not, the gold distribution is very irregular and the economic mineralization is located in shoots of varying strike lengths.

According to the Russian classification system for mineral deposits, the Irokinda deposit corresponds to a vein deposit of the third category of complexity. The third category of complexity or “Group 3 Deposits” is defined in the most recent Russian “reserve” classification guidelines dated December 11, 2006 as:

“Group 3. Deposits (subsoil areas) of complex geological structure with large and average size orebodies, having strongly dislocated bedding, characterized by very variable thickness and inner structure, sometimes immature quality of the minerals, and very uneven distribution of the basic valuable components. The peculiarities of the structure of the deposits (subsoil areas) are determined by the possibility of development of “reserves” of categories C1 and C2 in the process of exploration”

According to the recent classification of the gold deposits (Robert, F. et al, 2007), the Irokindiskoye deposit can be classified as an intrusion related, low sulphidation epithermal gold deposit. The characteristics for this deposit model are: high Au:Ag ratio and low base metal content. High grade low sulphidation gold deposits are structurally controlled and usually they are hosted within volcanic units or their basement. The hydrothermal wallrock alterations show lateral and vertical zoning and include silicification, sericitization, pyritization and propylitic alteration.

The areas containing economic mineralization within the deposit consist primarily of quartz with a low, less than 3%, content of mineralization. The mineralization is classified as a low sulphidation formation. The most abundant minerals are pyrite and galena, with rare chalcopyrite and fahlore. On rare occasions, pyrrhotite, arsenopyrite and scheelite also occur. Epigenetic units are iron hydro-oxides, malachite, azurite and jarosite, as well as others.

The inclusions of economic minerals are usually small with rare occasions where they are larger than a few millimetres, and have a mono-mineral character, although rare polymineral intergrowths occur. The mineralization in the quartz occurs as disseminated impregnations, nests, veinlets and interstitials. Weathering pits are indicative with the textures typically massive, inset and ribbed, with rare vein inset, breccia and drusy.

The deposit contains five paragenetic mineral associations corresponding to five stages of mineral generation:
1) Quartz.
2) Tourmaline-scheelite-quartz.
3) Quartz carbonate.
4) Gold-sulphide-quartz.
5) Carbonate.

Gold and silver are the primary products resulting from mining at the Irokinda mine. Gold is native (90%), mainly occurring in quartz but on rare occasions (10%) it occurs as interstitials with sulphides.

Gold in the veins occurs as spongy aggregates, plates, flakes, ambages, dendrite and falciform separations. Gold grain sizes range usually up to 1 to 2 mm, and in rare instances up to 1 to 2 cm. The colour of the gold is light yellow to bright yellow and the gold ranges in purity (fineness) from between 650 to 750 to 880 to 900.

Silver usually occurs in association with gold, galena and fahlore. The silver separations usually form a lumpy or falciform texture or appearance. The colour of the silver is silverwhite and the grain size is not larger than 1 to 2 mm.

Due to the large separations between the veins, which may reach several km, and the mountainous relief, the development of individual veins is typically conducted through one or more isolated adits. In some cases, however, a single adit provides access to more than one vein.

Development of the No. 30, No. 35 and Laguernaya veins has been incorporated into a single layout; comprised of an adit and several mine levels. In this case, the mining development included the sinking of two blind shafts to a depth of 150 m.

Since 1996, the room-and-pillar mining method has been used, with the room locations following the dip of the vein. This method is best suited for mining veins which have an extended strike length and are located in stable rock. The mining is done by extracting chambers 8 m wide, using jacklegs and stopers to drill short blast holes. Delivery of the broken material from the block to the sublevel (sill) drift is accomplished by both slushers and the initial explosive force. The mined-out space is supported by temporary pillars and, if necessary, by props.

Recently (2008) tests have been conducted on the use of a mining method that does not require leaving pillars, with faces advancing on the retreat. This system includes driving a broad face along the strike of the vein and benching along the slope or dip of the vein, with the mined-out area being left behind the current mining face. This method is best suited to areas in which the rock stability is good and to veins of any dip angle with widths up to 3 m. Extraction is accomplished by making cuts of 25 to 30 m width along the strike of the vein, with the extraction of the mineralization accomplished by taking benches of 8 to 10 m in width. The space at the face is supported using hydraulic props with screen (polymer networks) installed on the props nearest the face, in order to isolate the mined-out area for final vacuum-cleaning. After vacuum-cleaning, the mined-out area is closed off from the current mining operations and the hydraulic props are dismantled. The minimum mining width accepted for this type of stoping is 1.1 m. Although this method is being used, it is not as widely applied as the room-and-pillar method.

All of the mining methods used at Irokinda are labour intensive. Jacklegs and stopers are used to drill the blast holes. Extraction of the broken material is accomplished primarily by using slushers to move the material into the ore and waste passes. From the ore and waste passes, the broken material is loaded into rail cars either from a chute or by mucking machine (shrinkage stoping).

The metallurgical process at Irokinda involves gravity and flotation circuits with the production of both a gravity concentrate ready for smelting and a flotation concentrate which is shipped to the CIP plant at the Zun-Holba mine for further treatment by cyanidation and adsorption.

In general, the processing cycle includes trucking the run-of-mine ore, truck weighing and dumping of the ore to the coarse ore bin, followed by two-stage crushing. The crushing circuit includes a primary jaw crusher and a secondary cone crusher, and screening of the crushed material at a size of 16 to 18 mm, with manual waste rock rejection after the coarse crushing. The undersize fraction, after primary crushing, goes to the grinding circuit and the oversize material goes to the cone crusher.

Grinding is effected in two types of ball mills, operating in closed circuit with jigs and spiral classifiers. Grinding fineness is 85% passing a 0.074 mm. Concentrates from the jigs are delivered via pipelines to the gravity circuit for re-cleaning at two shaking tables. Tailings from the tables are returned for classification at the hydrocyclones. The overflow from the hydrocyclones goes to flotation and the underflow is returned to the grinding circuit.

Re-cleaning of gravity concentrates occurs at the shaking tables, with additional grinding of the products and additional re-cleaning. This allows the plant to produce a gravity concentrate with a gold grade of up to 191,000 g/t, ready for smelting. Up to 70% of the gold in the mill feed reports to the gravity concentrate.

The flotation circuit for the gravity tails includes both rougher and scavenger operations. The flotation circuit is fed by the hydrocyclone overflow, as well as by circulating loads. Reagents (butyl xanthate and foamer T-80) are added prior to flotation. The rougher flotation concentrate proceeds to re cleaning, while the rougher flotation tails go to the tailings pond. The flotation concentrates are delivered to two radial thickeners and the thickened concentrate is diverted to a drum filter. The cake from the drum filter is dried to an ultimate moisture content of 10.5 to 12.0% and the concentrate is shipped to the ZunHolba mine, via truck and rail transportation, for further treatment at the CIP plant.