Kuranakh - Yakokutskoye, Tshentralnoye, Porfirovoye, Severnoye

Siberia - Sakha-Yakutia, Russia

Main commodities: Au
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The Kuranakh gold operation is located in the Aldan District of the Yakutia Region in Eastern Siberia, some 400 km south of the city of Yakutsk and 40 km north of Aldan.

The Kuranakh operation comprises 11 separate orebodies, each of which comprises a series of mineralised zones, which have been evaluated over a strike length of 30 km, occurring as a series of elongate bodies within a fault bounded graben structure. Mineralisation is hosted by sandstones which vary from coarse, well sorted sands to poorly sorted clay sands.

The orebodies are host sequence is made up of Palaeozoic and Mesozoic arenaceous and argillaceous sediments up to 600 m thick covering the southeastern margin of the Siberian Platform which, in turn, is composed of highly deformed and altered Archaean gneisses, granulites and granites. The Palaeozoic sediments are interpreted to have been thrust over the Archaean basement from the east during the Late Jurassic.

The 1000 m thick Cambrian sediments are considered to have been laid down in a series of shallow ocean basins characterised by the extensive development of carbonate reef facies dolomites and limestones and shallow basinal sediments and typified by, often carbonaceous, siltstones and fine sandstones. Regional Devonian uplift and volcanism resulted in the development of deep crustal structures reflected as a series of north and northeast trending linear features, and by horst and graben structures in the underlying basement. Later volcanism related to Late Jurassic continental collision, resulted in a magmatic arc setting in the south of the Aldan Shield and associated volcanism throughout the region.

The Kuranakh orebodies are preserved within a broad linear graben, hosted by the Jurassic Yuhtinskaya Formation sandstones, immediately above their contact with the underlying Cambrian Limestone sequence. These sandstones are from 40 m to 70 m thick with the contact being represented by intermixed limestone rubble and breccia. In some areas, well developed karst sinkholes are evident in the upper surface of the limestone, which is marked by the presence of a terra rossa of variable thickness, generally varying from zero to 15 m thick at some localities, and consists of clay and weathered limestone.

Within the immediate vicinity of the ore deposits there are dykes and some plugs and sills of Mesozoic (Early Cretaceous?) vogezite, biotite-pyroxene porphyry, shonkinite, syenite-porphyry, trachyte, bostonite, microgabbro and minette. The dykes have a close spatial relationship with the gold ores and may be related to the same thermal event that gave rise to the deposits.

Several sub-horizontal, blanket- or ribbon-like ore bodies up to 50 m thick occur, mainly along and/or above, and in some places, under the contact between Cambrian calcareous footwall rocks and overlying Jurassic clastic rocks. The bulk of the ore is concentrated in the central part of the area where there appears to be a number of intersecting structures around the Yakokutskoye, Tshentralnoye and Porfirovoye orebodies. To the south of this, the orefield seems to split into a southwest and southeast limb each containing smaller orebodies. To the north, the orefield narrows. The Severnoye orebody is the most northerly of the deposits defined to 2006. It comprises a series of elongated zones of metasomatism, which are lenticular in cross section, with a preferred orientation to the northnorthwest. The orebodies are aligned parallel to the main structures and are only occasionally disrupted by cross faults.

Mineralisation is essentially restricted to the basal portion of the Jurassic sandstone, and the breccias or karst cavity fillings. The thicknesses of material grading >1 g/t Au may be up to 100 m or more. The basal sandstones have undergone hydrothermal alteration and where more intense, is mapped as a separate "metasomatite" unit. This metasomatite is an often reddish clay-potassic feldspar-quartz-bearing rock with a myriad druzy quartz veinlets and open space fillings, in places resembling jasperoids. Sandstone peripheral to metasomatites also contains quartz veinlets, and contains low-grade gold mineralisation, differing from the metasomatite mainly in the intensity of silica and adulalria flooding. The ores have a variable clay content, from a few percent to 20%. It is difficult to determine how much of this clay is due to hydrothermal alteration of feldspars in the arkosic sandstones, or is a result of weathering and oxidation since the Quaternary.

The primary gold ore contained two generations of pyrite (3 to 20%), minor marcasite, chalcopyrite, pyrrhotite, sphalerite, arsenopyrite and tellurides. Gold is closely associated with iron oxides and is represented by fine-grained native gold particles measuring from <50 to 250 µm, and rarely 4 mm, and by dispersed gold in the pyrite of the first generation. No visible gold is usually observed in the field (Rodionov et al., 2005).

The thickness of the remaining oxide orebodies varies from less than one to tens of metres and generally, but not exclusively, occurs towards the base of the sandstone sequence, near the upper contact with the weathered limestone. The clay content of the orebodies varies from less than 1% to over 40% and the extensive weathering results in no sulphides remaining. The major mineral present is quartz which makes up between 40% (Tshentralnoye) and 85% (Porphirovoye) of the total, with the clay content being inversely proportional to the quartz content. Iron hydroxides are present in varying amounts, but average 13%. Gold is fine grained, occurring as free particles of generally less than 3 µm in diameter and is associated with iron oxides (goethite) suggesting it was deposited along with pyrite prior to weathering.

Total open pit oxide resources estimated at January 1, 2006 (SRK Consulting for Polyus) was;
      Measured resource - 1.75 Mt @ 1.88 g/t Au,
      Indicated resource - 160.43 Mt @ 1.25 g/t Au,
      Inferred resource - 7.34 Mt @ 1.47 g/t Au,
      Total resource - 169.5 Mt @ 1.27 g/t Au.

Production in 2007 totalled 4.154 Mt of ore with an average grade of 1.37 g/t Au. Historic production from 1957 to 1997 amounted to around 220 t Au from 74.1 Mt @ 3.57 g/t Au (Rodionov et al., 2005).

Based in part on a report by SRK Consulting (J Arthur), 2006 for ZAO Polyus and from Rodionov et al. (2005)

Remaining JORC compliant Ore Reserves and Mineral Resources at 31 December 2017 were (Polyus Ore Reserves and Mineral Resources Update 20 March, 2018):
  Proved + Probable Ore Reserves - 141 Mt @ 1.0 g/t Au for 141 t of contained gold;
  Indicateded Mineral Resources - 153 Mt @ 1.8 g/t Au;
  Inferred Mineral Resources - 97 Mt @ 1.2 g/t Au;
  TOTAL Mineral Resources - 250 Mt @ 1.1 g/t Au for 275 t of contained gold;

The most recent source geological information used to prepare this summary was dated: 2007.    
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.

  References & Additional Information
   Selected References:
Seltmann, R., Soloviev, R., Shatov, V., Pirajno, F., Naumov, E. and Cherkasov, S.,  2010 - Metallogeny of Siberia: tectonic, geologic and metallogenic settings of selected significant deposits: in    Australian J. of Earth Sciences   v.57, pp. 655-706.

Porter GeoConsultancy Pty Ltd (PorterGeo) provides access to this database at no charge.   It is largely based on scientific papers and reports in the public domain, and was current when the sources consulted were published.   While PorterGeo endeavour to ensure the information was accurate at the time of compilation and subsequent updating, PorterGeo takes no responsibility what-so-ever for inaccurate or out of date data, information or interpretations.

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