SRK has been developing and regularly updating a structural geological model for the Kumtor gold deposit in Kyrgyzstan, primarily to resolve geotechnical issues and aid pit design. The project, overseen by Principal Geotechnical Engineer, Neil Marshall, is being led by Dr Rob Seago, a structural geologist with 20 years experience in the oil, gas and mining industry. Rob has worked extensively in Indonesia, Pakistan, Middle East, Europe and the Far East.
The Kumtor Gold deposit is located in the southern Tien Shan Metallogenic Belt, a major suture that traverses Central Asia, from Uzbekistan in the west through Tajikistan and the Kyrgyz Republic into northwestern China, a distance of more than 1,500 kilometres. Important gold deposits occur along this belt, including Muruntau, Zarmitan, Jilau and Kumtor.
Centerra Gold Inc, based in Toronto, Canada, owns 100% of the Kumtor gold mine through its subsidiary Kumtor Gold Company. Kumtor is located in the Kyrgyz Republic, north of the border with the Peoples Republic of China. It is the largest gold mine operated in Central Asia by a Western-based company, having produced more than 5.5 million ounces of gold between 1997 and 2005. Proven and probable reserves exceeded 5 million ounces, as reported in January 2006.
The structure of Kumtor is complex, having undergone four phases of deformation. Early plate collision caused a regional schistosity and subjected the rocks to lower greenschist metamorphism. A D2 (Caledonian) thrust event produced regional scale folds and thrust faults. Mineralisation occurred during D3 (late Hercynian), with north directed thrusting and localised transpressional strike-slip tectonics. During the Himalayan event (D4), the whole region experienced NW directed thrusting, which overprinted and re-activated the pre-existing fabrics, all of which play a role in the slope stability of the pit.
In late 2004, SRK conducted a review of the geological work of the Kumtor mining department. Using Kumtor’s extensive geological database and examining drill core, SRK carried out comprehensive pit mapping with the construction of structural cross sections. These were digitised and developed into a 3D model using GEMCOM software. Gold grade from blast holes and drilling was used to determine the distribution of mineralisation associated with major fault structures. This was an important tool, as was core logging, in pinpointing incohesive faults as potential slip surfaces, as many of the faults at Kumtor are re-activated structures.
The resulting structural geological model was presented to Kumtor’s geotechnical consultants, who then produced viable pit designs to control potential slope stability in the pit. The geological structure of the area affects the stability of pit slopes and this work integrated the structural model into the geotechnical analyses.
Over the past two years SRK has been involved in developing and applying the structural geological model for the present open pit and for other adjacent prospects to significantly increase understanding of the Kumtor Gold deposit. Potential failure sites have been identified and pit walls have been modified and planned to account for these problems, leading to a safer and more cost-effective pit. The work was carried out in a professional manner with a high degree of technical ability and SRK has built a close working relationship with Kumtor staff.
