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.

Current mining operations at Irokinda are focused on three separate vein areas, VisokayaPoperechnaya (“Visokaya mine”), Serebryakovskaya-Sluchainaya (“Serebryakovskaya mine”) and Medvezhya-Poperechnaya-Tuluinskaya (“Tuluinskaya mine”).

Development mining is achieved using modern electro-hydraulic single and twin boom drill jumbos to drill blastholes, diesel powered load-haul-dump loaders (“LHD”) to clean the blasted rock from each blasted advance, and diesel powered articulated dump trucks (“ADT”) to haul broken rock to surface.

At SS, 70% of production is achieved using mechanised long-hole sub-level open stoping with rib and crown pillars left for support. Blastholes are drilled using electro-hydraulic long-hole drill rigs, blasted ore is removed with LHD and ore is transported to surface with ADT.

The mining method at Viso, the remaining 30% of SS and planned for Tulu is manual room and pillar mining with variants (up-dip or along strike) defined by local conditions, predominantly orebody dip. The dip in these areas varies between 25° and 35°. Hand-held pneumatic rock drills are used to drill blastholes and electric scraper winches and gravity are used to direct broken ore to millholes for removal by LHD.

Room and pillar mining generally involves 3 to 8 m wide rooms at minimum stoping widths of 1.1 m between temporary pillars and/or mine poles to achieve a recovery of approximately 85%. In steeper-dipping veins (approaching 45°) broken ore is thrown by the blast to the sublevel (sill) drift, in shallower veins (down to 25°) scrapers and slushers are required. Hydraulic props are used at the advancing face which are used to construct barricades separating the face from the back areas for vacuum cleaning.

The LHD load ADT which transport the broken rock to surface. The surface is accessed through three transport inclines with 8° inclination, one for each mine. Each transport incline reaches the surface through an adit in the slope of the steeply dipping local topography.

Stability of the workings is maintained by the installation of local ground support (including wooden split wedge point anchors, friction anchors, hydraulic props), and leaving temporary or permanent supporting pillars of ore.

Crushing
The main and third process lines have identical crushing circuits. RoM ore is screened at 350 mm on a stationary grate to remove oversize, after which it is screened using a double deck screen at 40 and 16 mm. Oversize (-350 +40 mm) is fed to the primary crusher, a Russian made SMD-109 jaw crusher. Midsize (-40 +16 mm) is fed to the secondary crusher, a Russian made KMD-1200 Gr cone crusher. Undersize (-16 mm) is fed to the grinding circuit. Product from both crushers is screened at 32 mm, with the undersize joining the -16 mm material and the oversize recycled to the cone crusher.

Grinding and Primary Gravity Separation
The two process lines in the Main Plant (lines 1 and 2) each have two stages of grinding and third process line has one. The first grinding stage is a ball mill (2.1 x 3.0 m in lines 1 and 3, 2.1 x 2.2 m in line 2, all with 200 kW motors) that is followed by a jig.

In the third process line the screw classifier reports to cyclones that further close circuit the ball mill. In the Main Plant, screw classifier sands report to cyclones that close circuit the second grinding stage. The secondary mill is a 1.5 x 3.0 m ball mill (90 kW) that is also followed by a jig and one stage of shaking table.

The target grind size for flotation is 85-90% -71 ?m.

The Irokinda process plant treats non-refractory quartz vein-hosted gold ore with associated sulphides. The Irokinda plant produces gold doré by gravity processing and a flotation concentrate generated from the gravity tailings. The flotation concentrate is transported to Nordgold’s Zun-Holba plant where it is processed a conventional CIP circuit. Silver is present as a co-product.

The plant commenced production in 1988 and has been upgraded in several stages, including the additional of the flotation circuit, duplication of the main process line and the conversion of the third production line from seasonal to year-round operation. The current plant capacity is 380 ktpa.

The Irokinda flowsheet consists of two process lines in the Main Plant, with a combined capacity of 30-35 tph, and a third process line with a capacity of 15 tph, providing a total capacity of 50 tph.

Gravity separation
Jig tailings report to a screw classifier that recycles sands ........