Kumtor

Overview

Operated by Kumtor Gold Company (KGC), which is incorporated in the Kyrgyz Republic and is also a wholly-owned subsidiary of Centerra, the Kumtor open-pit gold mine's deposit was first discovered in 1978. Construction and development began in 1994 and was completed in early 1997 at a cost of about US$450 million.

Producing more than 8.4 million ounces of gold between 1997 and the end of 2011, Kumtor is the largest gold mine operated in Central Asia by a Western-based company.

The mine plays a particularly important role in the economic and political life of the Kyrgyz Republic being the largest private sector employer of Kyrgyz citizens and the largest foreign investment in the country. Ninety-four percent of Kumtor's nearly 1,600 employees are Kyrgyz nationals.

In 2011, gold production at the Kumtor mine totaled 583,000 ounces gold.

Location

The Kumtor mine is located in the southeastern part of the Kyrgyz Republic, one of the independent successor states of the former Soviet Union, some 350 kilometres to the southeast of the Kyrgyz capital of Bishkek and about 60 kilometres to the north of the international boundary with China.

The mine is remote and access is gained using rugged mountain roads. There are four crews working 14-day rotations. The pit, mill and associated buildings are located at and around 4000 meters in elevation.

Geology & Mineralization

Centerra, through its wholly owned Kyrgyz Republic subsidiary Kumtor Mountain Corporation (KMC) has exclusive rights to all minerals within an area of approximately 750 hectares of land centered on the Kumtor gold deposit until May 10, 2043. KMC is also seeking to expand its land holdings to the northeast and southwest. The extensions amount to an additional 3,651 hectares.

The Kumtor and satellite gold deposits occur in the southern Tien Shan Metallogenic Belt, a Hercynian fault and thrust belt in Central Asia that extends from Uzbekistan in the west throughTajikistan and the Kyrgyz Republic into northwestern China.

The mine geology in the Kumtor area is dominated by several major thrust slices with each thrust sheet containing older rocks than the sheet it structurally overlies. The slice hosting the gold mineralization is composed of Vendian (youngest Proterozoic or oldest Paleozoic) meta-sediments that are strongly folded and schistose. In most areas, the Kumtor Fault Zone (KFZ), a dark-grey to black, graphitic gouge zone, forms the footwall of this structural segment. The KFZ strikes northeasterly, dips to the southeast at moderate angles and has a width of up to 30 meters. The adjacent rocks in its hanging wall are strongly affected by shearing and faulting for a distance of up to several hundred meters. The rocks in the structural footwall of the KFZ are Cambro-Ordovician limestone and phyllite, thrust over Tertiary sediments of possible continental derivation that in turn rest, with apparent profound unconformity, on Carboniferous clastic sediments.Reserves

Gold mineralization occurs where the Vendian sediments have been hydrothermally altered and mineralized, an event that may have taken place in late Paleozoic time. Gold mineralization has been observed over a strike distance of more than twelve kilometers, with the Kumtor deposit being the most important accumulation. Native gold and gold bearing minerals occur as very fine inclusions in pyrite, with an average size of only 10 microns, which accounts largely for the partly refractory nature of the Kumtor ore. However, the fine grain size of the gold also renders assaying of this mineralization relatively reliable, with only a small nugget effect. Post-ore faults often carry significant quantities of graphite, and other carbonaceous components which constitute the source for the preg-robbing character of some of the mineralization. 

Mining & Operation

Mining operations at Kumtor are carried out using conventional open-pit mining methods. The Central deposit is mined in a large open pit - the overall waste to ore ratio from the open pits in 2010 was 19.2 to 1.

The ultimate pit would see mining carried out at 4,460 metres asl on top benches and at 3,618 metres in the deepest part of the deposit. The crushing plant is located at 4,050 metres in elevation. The maximum ore hauling distance of 7.8 km would be achieved starting with 2015 when mining would start in the southwestern part of the deposit.

 Waste rock is disposed in a nearby valley as it is not considered to be acid generating diue to its high carbonate content. 

Mining is based on eight-metre benches while smaller deposits would be mined on four-metre benches. Eleven rotary-percussion drill rigs are used for blasting the waste material and two DTH (down the hole) Hammers for ore blocks. Blasting uses fuel oil (ANFO) or emulsion explosives for wet holes.

In 2011, the main loading fleet includes sixteen hydraulic excavators (shovels and backhoe configuration) used for production and three front-end loaders for ore blending and cleanup. The mining fleet would be increased in the next few years in order to meet mine production schedule.

Processing

The current Kumtor plant flowsheet reflects the fine-grained nature of the gold and its intimate association with pyrite and consists of crushing, grinding, pyrite flotation and double re-grinding of the flotation concentrate. Two separate carbon-in-leach (“CIL”) circuits recover the gold from the re-ground concentrate and from the flotation tails, with final gold recovery accomplished by electrowinning and refining. The mill was originally designed with a capacity to process 4.8 million tonnes of ore per year, but the actual mill throughput in 2011 was approximately 5.7 million tonnes per year.

The ore to be milled is managed through a number of stockpiles that receive ore of different metallurgical character and of different grade ranges and thus allow blending of the mill feed. A gyratory crusher reduces the ore to minus 15-20 centimetres. The ore is then fed to a coarse ore stockpile from which it is reclaimed for grinding, first to a semi-autogenous (“SAG”) mill and then to a ball mill, which together reduce the grain size to 80% passing 140 microns. A bulk sulphide concentrate representing 7% to 11% of the original mill feed is then produced with a grade of 30 to 50 grams of gold per tonne and a gold recovery of 87% to 92% into the concentrate.

The flotation concentrate is re-ground to approximately 90% passing 20 microns. After thickening to 60% solids, it is once more re-ground to 95% to 98% passing 20 microns in an ultra-fine grinding (“ISA”) mill, re-pulped to 45% solids, pre-aerated for 40 hours and leached for 80 hours in the CIL circuit consisting of four agitated tanks in series. The ISA mill was commissioned in October 2005 and provides additional incremental liberation of the fine refractory gold (2-5 microns) enclosed in pyrite.

The flotation tailings with an average grade of 0.45 gram of gold per tonne are thickened to 50% solids and subjected to cyanidation for ten hours in a CIL circuit similar to the circuit used for the sulphide concentrate. The carbon in both CIL circuits is moved forward counter-current to the slurry flow, and the loaded carbon from the first flotation tailings CIL tank is pumped to the third concentrate CIL tank to continue loading. Loaded carbon from the first concentrate CIL tank is pumped to the gold recovery plant. The loaded carbon is stripped and the gold subsequently recovered by electro-winning. Gold recovery in the CIL circuits is generally 90% for the sulphide concentrate and 25-30% for the flotation tailings.

Concentrate CIL tailings and flotation CIL tailings are combined and discharged by gravity to the tailings disposal area through a slurry pipeline system.

Environment & Community

A number of routine static-type acid-base accounting tests were conducted to determine if rock types present at Cerro San Pedro had the potential for acid generation. As expected, limestone rocks - the major waste rock type - have substantially high neutralization potential, while porphyry rock types - the major ore bearing rock type - have the potential to produce acid.

A plan to encapsulate potentially acid generating waste rock has been incorporated into a waste rock management plan. The dump is also constructed on limestone bedrock.

To ensure protection of the biological resources of the area, particularly the three protected cactus species, MSX has rescued and protected these species - and others - prior to operations. At the end of operations, these species will be re-established at properly prepared sites.

Wildlife species, particularly birds, are being protected from any hazardous ponds by eliminating exposure to process solutions. MSX also established sources of fresh water for wildlife.