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Kochkar |
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Russia |
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Au
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Super Porphyry Cu and Au
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IOCG Deposits - 70 papers
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All papers now Open Access.
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The Kochkar gold deposit is located within the eastern Uralian Fold Belt in the Russian Federation. It is within the town of Plask, Chelyabinsk Oblast, ~90 km SSW of Chelyabinsk and 150 km NE of Magnitogorsk (#Location: 54° 22' 8"N, 60° 48' 45"E).
The Kochkar deposit and a number of others in the south central Urals are hosted by the Plast (or Plastovskiy) massif. Gneissic granitoids of this massif, dated at 341±20 Ma (Sazonov et al., 2001), were intruded into a sequence of north-south striking, steeply dipping, tightly folded and foliated, upper-greenschist to mid-amphibolite facies metavolcanic and lesser metasedimentary rocks. The youngest supracrustal unit is composed of Carboniferous limestones (Puchkov 1997). Intrusive relationships are indicated by variably sized supracrustal xenoliths within the Plast massif. The contacts between the plutonic rocks and supracrustal rocks are sharp and dip steeply outward relative to the centre of the massif (Kisters et al., 2000). The 50 x up to 10 km massif itself is elongated north-south. Its marginal zones are strongly foliated suggestive of an elongated gneiss dome.
The massif was intruded by numerous, steeply dipping mafic dykes at ~320 Ma (Sazonov et al., 2001) in an overall ENE-WSW to ESE-WNW trending radial pattern. The dykes range from a few cm to >20 m in thickness, with strike lengths that vary from several tens of metres to >1.5 km (Kisters et al., 2000). These dykes are crosscut by numerous generations of later dykes, some of which are subparallel to the mafic dykes, although the majority have northerly trends.
The Plast plagiogranite in the massif and associated Borisov granite, which was dated at 358 ±23 Ma (U-Pb zircon age), both have an adakitic character, while the mafic dykes have an arc-signature and belong to the late Devonian to early Carboniferous Valerianov Magmatic Arc.
On a district scale, economic-grade gold mineralisation is hosted by steeply-inclined, ENE-WSW trending quartz-sulphide lodes developed in a north-south 15 x 5 km corridor, widest around the town of Plast and the Kochkar deposit. The lodes are spatially associated with the northern, ENE-WSW trending mafic dykes and are mostly parallel and directly adjacent to these dykes (Kisters et al., 2000). The auriferous quartz veins are associated with mylonitised dykes, intrafolial folds and bands of shearing. All of the quartz veins exhibit recrystallisation and evidence of a dynamic regime of formation. These veins are massive and/or laminated, greyish to milky quartz, which are on average 0.2 to 1 m thick and have distinctly tabular geometries. They contain, on average, 4 to 6 g/t Au with locally high-grade ore shoots carrying ≥30 g/t Au, whereas mafic dykes and alteration zones surrounding the quartz lodes are subeconomic containing <1 g/t Au. Prominent quartz lodes can be traced along strike for over 500 m with similar subvertical extents.
Alteration mineralogy within the mafic dykes comprises biotite, actinolite, albite, K feldspar, quartz, epidote, tourmaline and sericite, with associated pyrite, arsenopyrite, chalcopyrite, sphalerite, tetrahedrite, galena, bismuthinite and gold.
Within the Plast granitoids, the equivalent alteration assemblage comprises quartz, sericite, calcite, epidote, and ore minerals.
Kolb et al. (2005) suggest fluid infiltration during hydrothermal gold mineralisation and quartz veining was promoted particularly along the contact between mafic dykes and granitoids. They suggest repeated dilation normal to dyke walls readily explains the dyke-parallel laminated or ribbon textures of gold-quartz lodes. Mafic dykes acted as weak layers during regional-scale east directed horizontal shortening related to the late Carboniferous to early Permian, regional east-west terrane amalgamation compression in the East Uralian Zone (EUZ; Kisters et al., 2000).
The Kochkar gold deposit had produced some 300 tonnes of Au at grades of 11 g/t Au to 2005.
Kochkar is part of the Uzhuralzoloto Group's Chelyabinsk region operations that also include the Bereznyaky, Svetloye, South Kurasan and West Kurasan deposits.
The most recent source geological information used to prepare this decription was dated: 2005.
Record last updated: 6/3/2020
This description is a summary from published sources, the chief of which are listed below.
© Copyright Porter GeoConsultancy Pty Ltd. Unauthorised copying, reproduction, storage or dissemination prohibited.
Kochkar
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Kolb J, Sindern S, Kisters A F M, Meyer F M, Hoernes S and Schneider J 2005 - Timing of Uralian orogenic gold mineralization at Kochkar in the evolution of the East Uralian granite-gneiss terrane: in Mineralium Deposita v40 pp 473-491
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Sazanov, V.N., van Herk, A.H. and de Boorder, H., 2001 - Spatial and Temporal Distribution of Gold Deposits in the Urals: in Econ. Geol. v.96, pp. 685-703.
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