On July 29, 2022, Centerra Gold Inc. announced the closing of the previously announced global arrangement agreement with Kyrgyzaltyn JSC (“Kyrgyzaltyn”) and the Government of the Kyrgyz Republic relating to the disposition of Centerra’s ownership of the Kumtor mine and investment in the Kyrgyz Republic and the termination of Kyrgyzaltyn’s involvement with the Company (the “Transaction”).
Kyrgyzaltyn transferring to Centerra all of its Centerra Shares (the “KZN Centerra Shares”) for cancellation, representing an approximate 26.0% equity interest in the Corporation, for an aggregate purchase price of approximately C$972 million (based on the closing price of C$12.56 per Centerra Share on the TSX on April 1, 2022). In satisfaction of the purchase price for the KZN Centerra Shares, Kyrgyzaltyn will receive from Centerra the 100% equity interest in its two Kyrgyz subsidiaries, Kumtor Gold Company CJSC (“KGC”) and Kumtor Operating Company CJSC (“KOC”), and, indirectly, the Kumtor mine.
Summary:
Orogenic gold mineralization at Kumtor is structurally dependent and formed penecontemporaneous with shearing on major faults through the system. Alteration associated with gold mineralization formed during several stages and at relatively high temperatures. The deposit is present along a continental-scale, amagmatic shallow-dipping (~25°-45°) structure cutting phyllite strata along the Kumtor shear zone. This structure is situated at the margin of the Middle Tien Shan terrain near the Nikolaev line – the Kyrgyz-Kazakh micro-continental suture.
Major features of the Kumtor Deposit compare favourably with those in prominent orogenic gold deposits present in black shale flysch strata such as Muruntau (Uzbekistan), Sukhoi Log, Olympiada and Natalka (Russia). However, contrasting features with these deposits include host-rock composition and age, age and grade of host rock metamorphism, age of mineralization, and presence or absence of magmatic rock, as well as degree and composition of associated alkaline metasomatism (sodium versus potassium). Nonetheless, the main distinctive feature of the Kumtor deposit versus other orogenic gold deposits hosted by black shales is absence of anomalous arsenic (>100 ppm) in mineralized rock. Another unusual feature of Kumtor mineralization is its large quantity of CaO gains, together with sulphur and CO2. This has resulted in a major presence of abundant MnFe-carbonate minerals in mineralized rock, accompanied with a relatively reduced presence of hydrothermal quartz. All these features are striking characteristics of gold mineralization at Kumtor.
The ore-forming structure at Kumtor is confined to a continent-continent orogenic collision zone during renewal of the Middle Tien Shan terrain’s movement towards the Kyrgyz-Kazakh micro-continent. This coincided with subduction of the South Tien Shan crust under the Middle Tien Shan crust, including crustal shortening of the latter from south to north. This wedge of continental crust, thus doubly impinged, is inferred to include upwelling of the lithosphere along deeply penetrating structures that then channelled fluids associated with mineralization along the trace of throughgoing structures.
Gold mineralization is distributed with varying intensity over 12 km along the trend, and it is most intensely concentrated in the Central Deposit and less so in the Southwest and Sarytor Deposits.
CENTRAL DEPOSIT
The entire sequence of host sedimentary and metamorphic rocks composing the Central Deposit has been divided into a number of structural compositional complexes (Units) and are characterized by the following features:
- Unit 0 is present in the northern part of the Central Deposit in the Kumtor Lower Thrust and is represented by fractured rocks of varied composition — breccia, conglomerate breccia linked together by gruss-formed clay and clay aggregate.
- Unit 1 in the hanging wall of the Black Thrust and below the Kumtor Upper Thrust includes carbonaceous and graphitic rock. The unit is dominantly composed of black carbonaceous phyllite that is significantly deformed.
- Unit 2 is in the hanging wall of the Kumtor Upper Thrust and includes dark grey and black carbonaceous and carbon-containing phyllite. Its rocks are almost universally hydrothermally altered ranging from altered phyllite to quartz-feldspar-carbonate altered rock, in which there are no signs of the original primary rock left in the latter.
- Unit 3 is characteristic of the eastern part of the area and it sits above Unit 2 in the hanging wall of the Lysyi Fault. The unit is composed of phyllite and carbonate-containing phyllite of dark grey colour including interlayered strata of carbon-containing phyllite and tillite-like conglomerate.
SOUTHWEST DEPOSIT
Gold mineralization in the Southwest Deposit primarily is limited to formations assigned to Unit 2 in the hanging wall of the Kumtor Upper Fault. Boundaries of the mineralized rock are marked by a tectonic crush zone of black clay gouge at a contact with surrounding barren phyllite. Footwall contacts are generally sharp and clearly defined. In the hanging wall, the boundary is sometimes difficult to identify. Mostly due to shallow dips of bedding in mineralized rock, mineralization boundaries are somewhat contorted both in their strike and dip. In addition, distribution of mineralized rock within its envelope is very inconsistent. Though distribution of gold enrichment is depicted schematically in cross-sections along footwall and hanging wall contacts, this is not a typical presence.
SARYTOR DEPOSIT
The Sarytor Deposit structure is characterized by thrust faults of various ages. A thick thrust zone (100 to 250 m) extends through the entire deposit from east to west and has a southeast-sub-latitudinal orientation (50°/145° and 45°/180°). It is poorly defined on the surface due to the obstruction by drifts, but it can be well traced down dip in drill holes. The zone contains brecciated, mylonitised, carbonized rocks from Unit 2 with irregularly shaped and random blocks of less disturbed rocks and mineralized altered rock. It appears more commonly as a tectonic mélange with black clay matrix and large boudins of various rock types. The lower and upper contacts of the thrust zone are distinguished by shallow dipping structures with black slick surfaces including the most intensely mylonitised and crushed phyllites in the entire thrust zone. The internal structure of the thrust zone is complex and has many crushed rocks. Most of these highly deformed rocks conform consistently with the overall dip of the thrust zone.
NORHTEAST DEPOSIT
The Northeast Deposit includes several steeply dipping, narrow tabular mineralized bodies confined largely to Units 0 and 1 in the footwall of the Lysyi Thrust. The deposit includes both sulphide and oxide mineralization, the latter was known historically on the surface and was encountered at depth by recent drilling. Sulphide gold mineralization in the Northeast Deposit mostly is associated with highly sheared tectonic breccia marked by carbonaceous phyllite of Unit 1 and Unit 2 including pyrite-carbonate quartz veinlets and veins, mineralized blocks of granular quartz impregnated with carbonaceous material, rhyolite and carbonaceous-siliceous shale, as well as mineralized dolomite and limestone.
Northeast Deposit includes variably altered chlorite-sericite shale as well as. Its upper part is composed of quartz-albite-carbonate assemblages including relics of carbon-containing chlorite-sericite shale, within which there are discrete layers of hydrothermal breccia of pyrite-feldspar carbonate with gold grades as much as 1.0 to 3.0 g/t. Its lower part is the most productive and it is localized in sheared rock including well-developed pyrite-feldspar-quartz-carbonate assemblages including relics of carbonatized chlorite-sericite shale, with some scheelite and barite. Gold grades are as much as 2.0 to 6.0 g/t.
Quartz-albite-carbonate assemblages and quartz veins include bands of host rock and have 1.0 to 3.0 g/t Au.
Potential of the Kumtor District and Kumtor Gold Trend outside of the known deposits is linked primarily to inferred extensions of gold mineralization to the southwest and northeast, respectively in the Akbel – Bordoo and Petrov Lake areas. Some additional potential also could be expected in any subsidiary or subparallel mineralized trends as described below. A regional airborne electromagnetic survey conducted during 2019 yielded a number of broad target areas that warrant additional focused district-scale exploration efforts. The Kumtor trend resides in a linear northeast-trending, roughly 2.5–km wide belt of low resistivity or increased conductivity.