The Zun-Holba deposit is located within a northwest trending belt of metamorphosed and tightly folded volcanic and sedimentary rocks of Proterozoic age, which contain several broadly conformable quartz-sulphide veins. Six en echelon subvertical veins contain most of the gold within a 1.3 km long mineralized zone. The width of the veins varies from 80 cm to 15 m. According to the Russian classification system for mineral deposits, the Zun-Holba deposit corresponds to a vein deposit of the third category of complexity. The third category of complexity or “Group 3 Deposits” are defined in the latest 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 the “reserves” of categories C1 and C2 in the process of exploration”.

According to the recent classifications of gold deposits, the Zun-Holba mine can be classified as an orogenic quartz-carbonate vein gold deposit (Robert, et al, 2007).

The gold deposits on the Zun-Holba Property can also be classified as intrusion related, low sulphidation epithermal gold deposits. The distinguishing characteristics for this deposit model are high Au:Ag ratios and a low base metal content. High-grade low sulphidation gold deposits are structurally controlled and usually they are hosted within volcanic units or their basement rocks. The hydrothermal wall rock alterations show lateral and vertical zoning and include silicification, sericitization, pyritization and propylitic alteration.

The gold mineralization at Zun-Holba is associated with the quartz-sulphide rocks and goldbearing altered host rocks; silicate, carbonate rocks and carbon-containing schists. The sulphide minerals amount to 8 to 9%, with pyrite the dominant mineral. Lesser amounts of galena, sphalerite and chalcopyrite are noted and arsenopyrite, fahlore, bournonite are the accessory minerals.

The metals of economic interest are gold and silver, with the average grades for the deposit being 11.0 g/t gold and 14.5 g/t silver. Gold is commonly present as very fine-grained (less than 0.07 mm), disseminated and powder-like (up to 95%) material. The gold distribution is very irregular. Arsenic and sulphur are almost absent. Graphite represents the carbon material and is 0.2 to 1.5% by volume. There is almost no oxidation of the ore.

Due to both the geotechnical factors and the geological features of the mineralized bodies within the deposit, the following mining methods are used at Zun-Holba:
- Shrinkage stoping with short blast holes (up to 6% of production).
- Timbered stoping method (up to 3% of production).
- Cut-and-fill method (up to 42% of production).
- Shrinkage stopping with backfill (up to 50%% of production)

The primary mining methods are shrinkage stoping and conventional cut-and-fill, with up to 92% of the present mining being conducted using these methods. Two different variations of the cut-and fill-method are used at Zun Holba:
- Bottom-up (overhand) cut-and-fill method.
- Top-down (underhand) cut-and-fill method.

All mining methods are labour intensive, with the use of both jacklegs and stopers 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 using either a chute (for the cut-and-fill and timbered stoping methods) or a mucking machine (shrinkage stoping).

By the time Buryatzoloto became involved with the Zun-Holba mine, in 1991, the upper portion of the deposit had already been developed with the adits spaced 40 m to 50 m apart vertically. This development included: adits # 1 and #2 (the adit entrances at an elevation of 2,256 metre above sea level (m)), adits # 3 and # 4 (2,213.8 m), adit # 4 bis (2,173 m), adit # 5 (2,134.4 ml), adit # 5 bis (2,083.4 m), adit # 11 (2,032.2 m), adit # 8 (1,820 m) and adit # 12 (1,740 m).

In the upper part of the deposit Buryatzoloto developed adits # 14 (adit entrance located at the 1,982.3 m), # 15 (1,935.0 m) and # 16 (1,883 m). Also, the 1790 m sublevel was developed between adits # 8 and # 12. “Reserves” of the deposit located below the adit # 12 level at a depth of 350 m are exposed by two vertical blind shafts. These shafts are the Glavny (Main) shaft developed from the 1790 m level and the Vspomogatelny (Secondary) shaft developed from the 1840 m level. Using a 50 m distance between active levels at the mine, the “reserves” below adit # 12 are accessed by five shaft levels, and two further shaft levels (1440 m and 1390 m) are in the process of being developed. The # 12 adit is the primary tramming level for both the upper and the lower (shaft) levels. The ore of the upper levels is transported via the ore passes to the adit # 12 level and then out of the mine. The ore from the lower levels is hoisted in the Glavny shaft to the 1790 m level where it is reloaded via the ore passes to the # 12 adit level and then transported out of the mine. The Vspomogatelny shaft is used to transport the ore and waste rock from the lower levels to the # 8 adit level, from which the waste rock is transported out of the mine and dumped to the waste rock stockpile. The ore is dumped through an ore pass to the # 12 adit level and then transported out of the mine, where it is dumped onto the ore stockpile.

Run-of-mine material is processed at the Samarta plant using the following flowsheet:
1) Two crushing stages with screening of the material after the second stage at 16 or 18 mm sizes.
2) Two grinding stages using ball mills.
3) Gravity concentration to recover the free gold.
4) Flotation of gravity tailings to recover the finer gold particles.
5) Cyanidation leaching and adsorption (CIP) of the flotation concentrate.

The final product of the process at the Zun Holba mine is doré bars which are then shipped out for further refining.

Run-of-mine material is transported by trucks to the processing plant. The trucks are weighed on a strain-gauge weigh scale before being unloaded onto one of three stockpiles located ahead the crushing circuit. The stockpiled ore is fed to the crusher using a bulldozer which blends the material from the three stockpiles. From the crushing circuit, the crushed material is transported via conveyor to the fine ore ........