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The Irokinda Mine is a producing underground room and pillar mining operation with a gravity and flotation processing plant. Flotation concentrates produced at Irokinda are transported by truck and rail to Zun-Holba for further processing. The Irokinda Mine is located in the Republic of Buryatia, Russia, 80 kilometres by road from the Baikal-Amur railroad, at the north-east end of Lake Baikal.
Gelogical Setting and Mineralization
Gold mineralization largely occurs within quartz veins hosted in Archean gneiss, which have been cut by dioritic intrusive bodies. Quartz veins are confined to three main fracture systems which are flat dipping (25-45 degrees) to the west. Individual veins have strike lengths ranging from 60 metres to 400 metres, and are generally traced down dip 300 metres or more. They pinch and swell in both the strike and dip directions with thicknesses ranging from 0.1 to 5 metres. Gold mineralization is discontinuous with local rich bonanza-type ore shoots measuring from 30 to 350 metres along strike and up to 350 metres down dip.
Gold occurs primarily in native form, mainly in quartz. Approximately 90% of gold occurs as free gold, with approximately 10% occurring in interstitials with sulphides. Gold is relatively coarse grained with gold grain sizes ranging up to 1 to 2 millimetres and in rare instances, up to 1 to 2 centimetres.
History
Gold mineralization was initially discovered at Irokinda in 1959. Between 1962 and 1974 extensive exploration of the area resulted in the discovery of over 100 gold-bearing veins. Mining operations commenced at the site around 1985. Buryatzoloto acquired the license on the Irokinda project in 1991 and became the operator of the mine in 1996, when the subcontractor's (Vitim Partners) mining contract expired. In 1995, Buryatzoloto became an open joint stock company and, shortly thereafter, 30% of the company's shares were acquired by High River via an open cash auction. High River increased its ownership in Buryatzoloto to 85% by 2005.
Mining
Since 1996, mining at Irokinda has been done using the room-and- pillar method with the rooms following the dip of the vein. Each individual vein is typically developed through the use of separate adits due to the mountainous relief and the physical distance between veins.
Plan View of the Mine Workings of the Central Tulinskaya Vein
Click to enlarge
| Operational Data |
2008 |
2007 |
| Tonnes mined |
311,000 |
302,000 |
| Tonnes milled |
291,000 |
275,000 |
| Head grade (g/t) |
8.3 |
9.0 |
| Recovery (%) |
95.5 |
94.9 |
| Gold production (oz) (100%) |
74,365 |
75,224 |
| Cash Operating Cost (US$/oz) |
511* |
367* |
*plus 6% government royalty
Processing
Ore is processed using the following flowsheet (see diagram below):
- Two crushing stages
- Two grinding stages using ball mills
- Gravity separation produces concentrates for both the gravity and flotation circuits
- Gravity circuit to recover free gold (approximately 70% of total gold production)
- Smelting to produce dore bars
- Flotation to recover finer gold particles into a flotation concentrate
- The flotation concentrate is shipped to the Zun-Holba CIP plant, via truck and rail, for further treatment
Click to enlarge
Note: numbers in above flowsheet correspond to items listed in the following table:
Exploration Potential
Known mineralization at the Irokinda Mine continues to be open along strike and at depth. The mineralization does not appear to be constrained by any major geological features. Additionally, there are currently a number of known unmined veins on which exploration is continuing (denoted in orange on the map below).
Click to enlarge
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