Centerra Gold Inc.'s wholly-owned subsidiary (indirectly held), Öksüt Madencilik Sanayi ve Ticaret Anonim Sirketi (“OMAS”), is the holder of the rights to mining and exploration for the Öksüt Mine.
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Summary:
The Öksüt Mine is a high-sulphidation epithermal gold deposit within the Central Anatolian Volcanic Province, part of the Tethyan Metallogenic Belt. The belt extends from southeastern Europe across Türkiye, the Caucasus, and on into Pakistan and contains a number of important gold and porphyry copper deposits. Magmatic activity and related ore forming processes are the result of the closure of the Tethyan Ocean in response to the collision between the north-moving Arabian Plate with the Eurasian Plate that began in the late Cretaceous period and continues today.
Based on these observations, the gold mineralization at the Öksüt Project is considered to have formed as part of a high-sulphidation epithermal system, possibly overlying a porphyry system at depth. Epithermal precious metal systems may be classified as high, intermediate, and low-sulphidation styles. They are characterized by the sulphidation state of the hypogene sulphide mineral assemblage, and show general relations in volcano-tectonic setting, precious and base metal content, igneous rock association, proximal hypogene alteration, and sulphide abundance.
The Öksüt Mine gold mineralization is hosted within the Develidag Volcanic Complex, one of the numerous stratovolcanoes situated along the Central Anatolian Fault Zone. The volcanic complex is composed of Miocene basaltic-andesitic volcanic domes, pyroclastic rocks, and lava flows. Flow-banded Pliocene andesite overlies these sequences and the Öksüt Mine mineralization to the north and east.
There are several gold occurrences in the Öksüt Mine area, the most important of which is the Keltepe Deposit. The distribution of the alteration assemblages and the gold grades at the Keltepe Deposit are strongly zoned, with a central massive silica breccia having the highest gold grade. This core is surrounded by quartz-alunite altered volcanic rocks, and as the alteration intensity diminishes outwardly, the gold grade decreases.
The Keltepe Deposit has been oxidized to depth, up to 400 metres below the surface. The original copper content of the deposit has been completely leached out of the resources, however, zones of oxide copper enrichment are found deeper within the deposit, below the planned open pit. An irregular zone of supergene enrichment exists below the oxide zone, with some highgrade sulphide copper intersections. It is surmised that the oxidation of the deposit has liberated the gold allowing heap leaching at a relatively coarse crush size.
The nearby Güneytepe Deposit is significantly smaller and does not show the more straightforward zonation and continuity of alteration and gold grades as observed on the Keltepe Deposit. Silicification is intense, however, the host rocks are much less porous than those at Keltepe, and, as a result, oxidation is restricted to the upper 50 metres to 75 metres of this deposit.
Keltepe Deposit
The Keltepe Deposit is elongated NNW-SSE and is approximately 600 metres long and 350 metres wide with a minimum known vertical extent of 450 metres. Two principal rock types are present: a texturally diverse variety of polymictic breccias and a texturally uniform porphyritic andesite.
The Keltepe Deposit is strongly oxidized to a maximum known depth of up to 400 metres below surface. This unusually deep oxidation is attributed to the porous and permeable nature of the siliceous and quartz-alunite altered breccias and to the presence of a deep groundwater table controlled by the NNW-SSE and NE-SW trending fault zones that drain outwards from the topographic high beneath which the Keltepe Deposit is located.
Oxidation is not uniformly complete throughout the deposit, with patches of less oxidized or unoxidized rock enclosed by fully oxidized rocks.
Gold mineralization is believed to occur as finely disseminated particles as it was not identified during scanning electron microscope analysis. This has been confirmed by a gold deportment study that shows that the major gold mineral identified at Keltepe is native gold with an average fineness of 6.9 µm. This study also indicates that the host minerals for the gold in the sample studied are mainly quartz and other silicates and iron oxide, with minor (2% to 10%) rutile-silicate complexes and trace associations with pyrite.
Güneytepe Deposit
The Güneytepe Deposit is located approximately 600 metres to the south-southeast of the Keltepe Deposit. Gold mineralization primarily occurs along NW-SE and NE-SW trending ledges of two compositions: (1) massive to vuggy residual quartz with associated silicification, and (2) quartz-alunite plus quartz-kaolinite alteration. The location of the ledges is controlled by the intersection of NW-SE and NE-SW trending structures.
As observed at the Keltepe Deposit, gold mineralization at the Güneytepe Deposit is also considered to be controlled by NW-SE and NE-SW trending faults. The deposit is bounded to the north and south by two NE-SW trending fault zones, which confine the gold mineralization into a NE-SW trending corridor.
Oxidation in the ledges rarely exceeds 150 metres in depth and averages approximately 50 metres to 75 metres. Oxidation appears to be deeper in the massive to vuggy quartz and quartz-alunite zones as compared to those composed mainly of quartz-kaolinite.
Gold mineralization at Güneytepe is more variable than at Keltepe in both grade and lateral/vertical distribution. Higher sulphur contents are also recorded in the oxide zone due to sulphides, mostly pyrite, being encapsulated within massive silica and also in patchy silica altered rocks.