Sukhoi Log

Siberia, Russia

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The Sukhoi Log gold and platinum deposit is located within the Lena gold field, 120 km north of Bodaibo and 1000 km NE of the city of Irkutsk in the Irkutsk region of Siberia, Russia. The total historical placer production from the goldfield to date has been 1500 tonnes of gold (#Location: 58° 35' 31"N, 115° 15' 15"E).

The Sukhoi Log and Lena goldfleld occurs within the Patom Highlands orogenic zone which largely corresponds to the older NE-SW oriented Palaeoproterozoic (2.1 to 1.9 Ga) Akitkan Foldbelt that separates the Anabar superterrane of the main Siberian craton to the NW, from the Aldan superterrane/shield to the SE. The southern half of this orogenic zone encompases and parallels Lake Baikal. The Patom Highlands orogen, which extends over a distance of ~1500 km along the southeastern margin of the Siberian craton, has a width of 50 to 250 km, and is essentially composed of a Meso- to Neoproterozoic deformed passive margin sequence to the west, and a similar aged eastern accretionary wedge and island arc terrane. The Lena goldfleld is located in the northern part of this fold belt, within the deformed Neoproterozoic passive margin sequence that comprises a 15 to 20 km thick clastic-carbonate sequence (Large et al., 2007; Donskaya et al., 2009; Wood and Popov, 2006). This sequence also hosts the Kholodniskoe base metal deposit 400 km to the SW of Sukhoi Log.

The Meso- to Neoproterozoic sequence is underlain by high-grade Archaean rocks (the Chara units) of the Aldan shield, exposed locally to the SE, composed of gneiss, migmatite, slate and quartzite, and by a minor Palaeoproterozoic sequence unconformable overlying the Aldan shield to the SE, of slates and quartzites (Nerukan Formation), and a few Palaeo- and Mesoproterozoic spilites, keratophyres, (Medvuh'ya Formaton) in the highlands to the NW.

The Lena goldfleld occurs in a complexly folded exposed area of clastic-carbonate Proterozoic succession of the Bodaibo trough (Kuz'min et al., 2006), that is surrounded by and concealed on three sides by flat-lying Palaeozoic and younger cover of the Siberian platform. To the SE, a much thinner condensed equivalent Proterozoic sequence overlies Archaean high-grade gneiss and metasediments of the Aldan shield (Wood and Popov, 2006). The principal sequence in the Bodaibo trough is the Neoproterozoic Patom Group, representing continental margin shelf, slope, and basinal facies (Kazakevich, 1971). The Patom Group comprises three subgroups (Wood and Popov, 2006):
- the lower Ballaganakh Subgroup - a 1500 to 2800 m thick sandstone-shale sequence overlain by a thick limestone sequence;
- the middle Kadalikan Subgroup - 900 to 1500 m of black shales, siltstones and sandstones overlain by limestones and dolomites containing algal remains; and
- the upper Bodaibo Subgroup - which is >2200 m thick and is dominated by fine clastic, calcareous, and carbonaceous shales, alternating with rhyolitic molasse-type conglomerates.

Numerous intrusive complexes include many varieties of granite, and regional NE-SW trending 313±59 Ma basic dyke belt (20 km east of Sukhoi Log). Some of the granites are Palaeo- and Mesoproterozoic, others are Palaeozoic and are dated at 354 to 322 Ma.

The Kadalikan Subgroup thickens considerably northward towards Sukhoi Log, where the Khomolkho Formation is developed, a local unit of the 1500 m thick Valyukhta Fomation (Wood and Popov, 2006). Sukhoi Log is hosted by the Khomolkho Formation, a 400 to 800 m thick unit of carbonaceous shales, siltstones, and minor sandstones, in the middle Kadalikan Subgroup, (Distler, et al., 2004; Wood and Popov, 2006). The deposit occurs in a tight anticline of the Khomolkho Formation on the southern limb of a regional anticline. The Vysochaisky deposit which consists of disseminated pyrite-gold mineralisation similar to that at Sukhoi Log (Buryak and Khemelevskaia, 1997), is also hosted by the Khomolkho Formation on the northern limb of the same regional anticline.

The Khomolkho Formation is subdivided lithologically into three subformations - the Lower carbonaceous shale and siltstone with interlayers of carbonaceous limestone that is 100 to 150m thick; the Middle grey limestone with interepbeds of siltstone and carbonaceous shale that is 110 to 200 m thick; the Upper - carbonaceous shale, phyllite and siltstone that is 150 to 180 m thick and is the main ore-bearing host at Sukhoi Log.

The uppermost unit of the Kadalikan Subgroup the 500 to 700 m thick Imnyakh Formation which immediately ovelies the Khomolkho Formation, is subdivided into two subfomations: the Lower - mainly calcareous sandstone, shale and siltstone, less commonly limestone; and the Upper, of mainly limestone with interlayers of shale and dolomite. The overlying 200 to 1200 m thick Aunakit Formation of the Bodaibo Subgroup comprises polymict sandstone, sericite-quartz shale and carbonaceous shale, which hosts the sulphide-gold mineralisation of the Pervenets-Verninsky deposits. Three formations of fine to coarse clastics with an aggregate thickness of up to 3700 m overlie the Aunakit Formation (Wood and Popov, 2006).

The Patom Highland area has a distinctive regional structural pattern marked by folds in the Neoproterozoic metasedimentary units, the axes of which curve systematically from a NE trend in the west to SE in the east, forming a semi-circular pattern with the Marakan-Tungus Trough to the north and the Bodaibo Synclinorium to the south (which are the main vein-gold orebodies) Sukhoi Log lies in the anticlinorium between the two regional structures (Wood and Popov, 2006).

The Patom Group rocks were strongly folded in a major deformational phase accompanied by low-grade regional greenschist facies metamorphism which to the south is locally overprinted by metamorphic aureoles of the Palaeozoic granites (Wood and Popov, 2006).

The closest intrusive to the Sukhoi Log deposit is the small granitoid Konstantinovsky stock, 6 km to the SW, part of the Konkuder-Mamakan complex. Geophysical data indicate that the body has a steep southern contact and a gently sloping northeastern margin toward Sukhoi Log. The rock, which has been dated at 290±20 Ma, is a biotite porphyry in the centre, and is fine-grained in the contact zone, with a 100 to 250 m wide contact metamorphic aureole (Wood and Popov, 2006).

The host sedimentary rocks have been deformed into a series of south-verging folds and associated thrust faults, with the deposit occurring in the core of the very tight, south-verging Sukhoi Log anticline, located in the hanging wall of a south-verging thrust fault. This anticline plunges gently to the WNW with an axial surface that dips 20 to 30° NNE.

The gold and associated platinum group element (PGE) mineralisation at Sukhoi Log is controlled by a tectonic zone along the axis of the overturned anticline where it intersects metamorphosed carbon-bearing lithologies of the Neoproterozoic Khomolkho Formation sediments. The immediate host comprises alternating 0.1 to 3 m thick beds of carbonaceous and calcareous siltstone, argillites, shales and sandstones. Organic compounds within these sediments have been carbonatised by hydrothermal fluids.

The mineralised zone forms a gently dipping tabular body, parallel to the axial plane of the fold, extending for >2000 m along strike and 700 m down dip, forming a centro-symmetric zoning about the axis of the tight, overturned synclinorium. Structural and stratigraphic indicators suggest the deposit is generally but not strictly located along the axial surface of the south-verging anticline, with the envelope of the deposit discordant to stratigraphic units, spanning a stratigraphic interval of nearly 1000 m. In detail, the mineralisation is not uniformly distributed within the deposit-scale envelope along the axial plane of the fold. The best developed and thickest ore zones are in two black shale units (the upper and lower Khomolho subformations), reflecting a second order stratigraphic control of mineralization, while gold mineralisation also forms "wings" extending out along specific units away from the axial surface of the fold (Wood and Popov, 2006).

The central zone in the core of the fold contains abundant quartz-sulphide veinlets with complex shapes inherited from the crinkle folding of the host shales. This central zone passes out into an intermediate zone with few sulphides or quartz-sulphide veinlets, while the outer zone on the flanks of the synclinorium is characterised by disseminated fine grained pyrite, large granoblastic pyrite crystals as well as quartz-pyrite aggregates. Sulphide poor quartz veins up to 2 m thick are found in the veinlet stockwork and in the disseminated zones, while separate post-ore gold poor quartz veins are encountered at depth (300-400 m).

The major gold reserves are connected with veinlet-disseminated quartz-sulphide mineralisation and are found in three zones, namely: i). the upper outer disseminated zone; ii). the intermediate and central zone and iii). the lower outer disseminated zone.

The morphology of the gold is as follows: i). interlayers and lenticules of fine to medium grained diagenetic pyrite; ii). stratified impregnations of rounded ovoid pyrite; iii). impregnation of cleaved and foliated fine grained pyrite and pyrrhotite; iv). large zonal metacrysts of pyrite with quartz margins; v). granoblastic pyrite aggregates; and vi). stratified and cross-cutting quartz-sulphide stockwork veinlets up to 2 to 4 cm thick.

Nearly 90 minerals occur at Sukhoi Log including native metals, intermetallic alloys, sulphosalts, phosphates, tungstates, and oxides. Native gold is the main one mineral, but calaverite, hessite, petzite, and krennerite also occur. PGE mineralisation is located on the periphery of the gold zone in the form of native platinum, Pt-Cu-Fe metal alloys, sperrylite, and cooperite. The mineral assemblage also includes native Fe, Cr, Cu, Ni, Sn, W, Ti, and Te, as well as alloys of these metals.

Mineralogic, geochemical, and geophysical studies have been used to develop a three-stage model of the deposit involving: i). deposition of terrigenous and carbon-bearing terrigenous-carbonate rocks in an intraplate rift about 800 Ma ii). regional metamorphism at 520 Ma culminating in iii). the development of palingenetic granites and hydrothermal fluids transporting contrasting assemblages of elements (Cr, Ni, Ti, Pt+Pd) and (Sn, W, Mo, Zr, Au, Ag, Zn+Pb) at 320 Ma.

The total estimated resource at Sukhoi Log is 1100 tonnes of gold at an average grade of 2.45 g/t.

For details consult the reference(s) listed below.

The most recent source geological information used to prepare this summary was dated: 2009.     Record last updated: 10/10/2012
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.

Sukhoi Log

  References & Additional Information
 References to this deposit in the PGC Literature Collection:
Distler V V, Yudovskaya M A, Mitrofanov G L, Prokofev V Yu, Lishnevskii E N  2004 - Geology, composition and genesis of the Sukhoi Log noble metals deposit, Russia: in    Ore Geology Reviews   v24 pp 7-44
Large R R, Danyushevsky L, Hollit C, Maslennikov V, Meffre S, Gilbert S, Bull S, Scott R, Emsbo P, Thomas H, Singh R and Foster J,  2009 - Gold and Trace Element Zonation in Pyrite Using a Laser Imaging Technique: Implications for the Timing of Gold in Orogenic and Carlin-Style Sediment-Hosted Deposits: in    Econ. Geol.   v104 pp 635-668
Large R R, Maslennikov V V, Robert F, Danyushevsky L V and Chang Z,  2007 - Multistage Sedimentary and Metamorphic Origin of Pyrite and Gold in the Giant Sukhoi Log Deposit, Lena Gold Province, Russia: in    Econ. Geol.   v102 pp 1233-1267
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.
Wood B L and Popov N P,  2006 - The giant Sukhoi Log gold deposit: in    Russian Geology and Geophysics   v.47 pp. 315-341

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