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Udokan

Siberia, Russia

Main commodities: Cu Ag
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Udokan is a major sediment hosted copper deposit located in Zabaykal'skiy Kray, northeast of Lake Baikal, in the Transbaikal region of eastern Russia, and ~675 km NNE of Chita, the capital of the Krai. The deposit is ~30 km south of Chara railway station of the Baikal-Amur Mainline (BAM) loop of the Trans-Siberian Railway, and adjacent to the Chineskaya spur line (#Location: 56° 35' 15"N, 118° 26' 57"E).

It is hosted by metamorphosed terriginous, deltaic to lacustrine sediments of the Palaeoproterozoic Udokan Series, (2.3 Ga) within the intra cratonic Udokan-Kodar Trough, also known as the South Aldan Continental Rift Zone. Basement comprises Archaean granitoids and meta-sedimentary sequences.

The Udokan Succession comprises from the base (Narkelyun, et al., 1970):
Kodar Series, 1200 m thick - dark grey to black bedded shales and phyllites grading up into grey to lilac siltstones and sandstones with abundant pyrrhotite and pyrite.
Chiney Series, up to 3000 m thick - pink, green and grey sandstones with some conglomerates near the base, with intercalated but lesser siltstones and argillites, and some carbonates (marls, stromatolitic dolomites and limestone) from the middle upwards. Ripple marks, cross bedding and desiccation cracks increase from the centre towards the top. Sparse pyrite and some copper mineralisation is found in the carbonates.
Kemen Series, up to 4000 m thick - comprising the:
Sakukan Group, which exhibits cross bedding, ripple marks, desiccation cracks, mud rolls and scour structures. It has three members as follows,
- Sub ore Member, 250 m thick - grey and pinkish grey, fine and medium grained, cross bedded, quartz feldspar sandstone, with a sericite, quartz and calcite matrix. Numerous lensoid cross bedded calcareous sandstones from 0.05 to 1.5 m thick occur at 1 to 5 m intervals and characterise this unit. Extremely lean copper sulphides are present.
- Ore Member, 20 to 300 m thick - this member is characterised by its complex facies relationships. It comprises 90% grey, fine to medium and mixed grain size quartz sandstones (with a mainly quartz-sericite matrix, <10% of which has any calcareous cement); silty sandstones; siltstones; 3 to 5% argillites; and minor sandy limestones. The sandstones are commonly cross bedded in the lower sections and the siltstone laminae exhibit ripple marks and desiccation cracks. Layer and lens like orebodies are distributed in an en echelon fashion. The principal orebodies persist over strike lengths of up to 2 to 3 km. This unit contains all of the economic mineralisation.
- Supra Ore Member, 100 m thick - light grey and pinkish grey, predominantly fine grained, horizontally and wavy bedded, quartz-feldspar sandstones and less frequently siltstones. No copper is present.
Naminga Group, (1000 m thick) of dark grey to black shallow water siltstones and argillites with intercalated pink to grey sandstone. This group contains sparse magnetite.

Copper mineralisation at Udokan occupies a single 25 to 30 x 12 km outlier representing the Naminga Syncline. The rocks of the northern, eastern and western limbs dip towards the centre of the structure at from 10 to 12°, up to 35 to 40°. On the southern limb however, the fold is more complex, varying in dip from 25 to 30°S in its western section, to overturned to be 45 to 50°SSW in the central and eastern parts. In the centre of the fold, at a depth of 1.5 km the mineralised beds are flat lying. The attitude of the limbs of the fold are complicated by small second order folds as well as small concordant and discordant crush zones, faults and thrusts with displacements of 0.1 to 15 m, accompanied by zones of intense jointing. Within the syncline, the Udokan Series is cut by numerous dykes associated with various intrusive complexes. The most widespread are gabbro-dolerite dykes with thicknesses in some cases of up to 150 m or more. Adjacent to these dykes the sediments are often strongly contact metamorphosed, with Cu being upgraded and the mineralogy modified from bornite-chalcocite to bornite and to chalcopyrite as the dyke is approached (Smirnov, 1977).
Udokan
Ore and sub-ore grade copper mineralisation occupies most of the extent of the Ore Member of the Sakukan Group throughout the Naminga Syncline. Similar cupriferous units are found in the stratigraphic equivalents in adjacent areas within a radius of several hundred kilometres around Udokan. Copper mineralisation is also found at several other levels lower in the host succession in the lower Sakukan Group and the underlying Chiney Series in the Udokan area. The copper in the Chiney Series is accompanied by rare earth minerals (Narkelyun, et al., 1970; Smirnov, 1977).

The Udokan deposit comprises three separate, elongate, thick bodies, which are from 60 to 120 m thick along their central axes. These thin on their margins where they split into a series of fingers. The long axes are believed to be up to 10 km long and each is several km wide. The individual orebodies contain lenses which are continuous over strike lengths of 2 to 3 km. Dips range from flat in the core of the syncline to overturned. The reliability of the dimension figures is suspect (Smirnov, 1977).

The mineral zonation within the deposit correlates with the host lithologies. Bornite-chalcocite is usually found within coarser deltaic facies, while chalcopyrite-pyrite occurs in finer, deeper water, facies. In general there is also an upward zonation from pyrite-chalcopyrite at the base to bornite-chalcocite at the top. This vertical zonation is reversed on the overturned southern limb. Between the two associations there is usually a transitional bornite-chalcopyrite zone. The bornite-chalcocite combination is always accompanied by magnetite. The ore has been oxidised with a 'wide distribution' of malachite, azurite, covellite, chalcocite, gypsum and iron hydroxides. Oxide mineralisation accounts for approximately 5% of the ore, while mixed oxide-sulphide ore is around 60%. At a 0.6% Cu cutoff the ore grades 1.54% Cu, 12 g/t Ag. The ore contains a trace of Ag and 10 to 100 ppm Co. It also has >1% Ti and 0.1 to 1% Mn (Bakun, et al., 1966; Narkelyun, et al., 1970; Smirnov, 1977).

Where exposed, the outcrop of the copper bearing horizon is characterised by "crusts and earthy friable accumulations of a green colour, consisting of malachite, bronchantite and other minerals of the oxidation zone". Moreover ore seams have been recorded on the surface with only weakly oxidised sulphides (Smirnov, 1977).

Published JORC compliant resources (Baikal Mining Company website - published 09-May-2014) are:
    Measured resource - 344 Mt @ 1.03% Cu, 8.9 g/t Ag;
    Indicated resource - 1507 Mt @ 1.01% Cu, 11.1 g/t Ag;
    Inferred resource - 947 Mt @ 0.89% Cu, 14.3 g/t Ag;
    TOTAL resource - 2.798 Gt @ 0.97% Cu, 11.9 g/t Ag;

Note: these resources are quoted in 'tons', that are assumed to be imperial tons (2240 lbs), which have been converted above to the international metric unit 'tonnes' (1000 kg).

The most recent source geological information used to prepare this summary was dated: 1996.    
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.


Udokan

  References & Additional Information
   Selected References:
Gongalsky, B. and Krivolutskaya, N.,  2019 - The Cu-Ag-Fe Udokan Deposit: in Gongalsky, B. and Krivolutskaya, N., 2019 World-Class Mineral Deposits of Northeastern Transbaikalia, Siberia, Russia Modern Approaches in Solid Earth Sciences, Springer, Switzerland,    V.17, pp. 37-85.
Hitzman, M.W., Selley, D. and Bull, S.,  2010 - Formation of Sedimentary Rock-Hosted Stratiform Copper Deposits through Earth History : in    Econ. Geol.   v.105, pp. 627-639.
Podkovyrov, V.N., Kotov, A.B., Larin, A.M., Kotova, L.N., Kovach, V.P. and Zagornaya, N.Yu.,  2006 - Sources and Provenances of Lower Proterozoic Terrigenous Rocks of the Udokan Group, Southern Kodar-Udokan Depression: Results of Sm-Nd Isotopic Investigations: in    Doklady Earth Sciences,   v.408, pp. 518-522.
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.
Soloviev S G,  2010 - Iron Oxide Copper-Gold and Related Mineralisation of Siberian Craton, Russia 2 - Iron Oxide, Copper, Gold and Uranium Deposits of the Aldan Shield, South-Eastern Siberia: in Porter T M, (Ed),  2010 Hydrothermal Iron Oxide Copper-Gold and Related Deposits: A Global Perspective PGC Publishing, Adelaide   v.4 pp. 515-534
Zientek M L, Hayes T S and Hammarstrom J M  2013 - Overview of a New Descriptive Model for Sediment- Hosted Stratabound Copper Deposits: in Zientek M L, Hammarstrom J M and Johnson K M, 2013 Descriptive Models, Grade-Tonnage Relations, and Databases for the Assessment of Sediment-Hosted Copper Deposits - With Emphasis on Deposits in the Central African Copperbelt, Democratic Republic of the Congo and Zambia USGS Scientific Investigations,   Report 2010-5090-J pp. 2-16


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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