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Kholodnina, Kholodninskoye |
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Siberia, Russia |
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Zn Pb Ag
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Super Porphyry Cu and Au
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IOCG Deposits - 70 papers
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The stratabound Kholodnina or Kholodninskoye zinc-lead-silver deposit is located in Buryatia, south-central Siberia, Russia, 50 km north of Lake Baykal and 560 km NE of Irkutsk, close to the BAM, the northern alternative of the Trans-Siberian Railway (#Location: 56° 15' 11"N, 109° 53' 30"E).
Overview - A steeply dipping, stratabound ore zone has been traced for 7 km along strike. Three orebodies have been identified within this zone. A second ore type is confined to fault zones, while a third is hosted by quartzites. Ore has been divided into uniform ores with >8% Pb+Zn, rich segregations of 4 to 8% and lean segregations of 2 to 4%. The ratio of Pb:Zn is 1:4.5. The hosts are Proterozoic in age and include garnet-quartz-muscovite schists, quartz-biotite-muscovite schists, staurolite-garnet schists, carbonatised sandstones, quartz-graphite-mica schists, garnet-quartz-mica schist and micaceous quartzites. Mineralisation includes pyrite, quartz, galena, sphalerite, pyrrhotite and chalcopyrite.
Seltmann et al. (2010) quote a reserve (Russian B+C1 reserve categories) of:
300 Mt @ 4.33 wt.% Zn, 0.68 wt.% Pb, 9.4 g/t Ag and 0.1 g/t Au,
for 2.0 and 13.3 Mt of contained Pb and Zn respectively.
Geology - Kholodnina lies within the Northern Baikal-Patom Belt, bounded to the NW by the Neoproterozoic to Palaeozoic Siberian Platform cover sequence, and to the SE by the Neoproterozoic Baikal-Muya Belt which comprises and accretionary wedge and island arc terrane, characterised by volcanogenic greenstones, slate-limestone, flyschoid-greywacke and 'sequentially differentiated' volcanogenic associations (Fedotova, et al., 2014). Intrusives in this belt are exclusively of the gabbro-peridotite association. The Baikal-Patom Belt is mainly composed of sedimentary and volcano-sedimentary suites of the Neoproterozoic passive continental margin (Fedotova, et al., 2014). The Kholodnina deposit lies within a downwarp towards the northern margin of the Baikal-Patom Belt. The downwarp is a graben-like rift basin filled by carbonaceous terrigenous and carbonate-terrigenous sequences, with associated high-Mg tholeitic basalt and minor rhyolite (Seltmann et al., 2010). The marginal structures of the downwarp are characterised by black slate-carbonate associations, and finer grained, shallower water sediments, all of which have been subjected to higher grade amphibolite facies metamorphism and granitisation, in contrast to the greenschist facies of the main downwarp (Ruchkin, et al., 1976). Kholodnina appears to lie in the higher grade metamorphics of the marginal structural zone.
The late Meso- to Neoproterozoic host sequence at Kholodnina is as follows, from the base (Ruchkin, et al., 1976; Smirnov, 1977):
Avkit Suite, >500 m thick - quartz-garnet-biotite-muscovite and quartz-biotite-muscovite schist with beds of quartzite and marble.
Pereval Suite, subdivided into,
Graphitic Pelitic Schist Sub-suite, maximum thickness of 1000 m - composed of graphite bearing, mica-carbonate and quartz-mica schist, graphitic quartz-sandstone and graphitic sandy limestone. These rocks are characterised by a similar outward appearance and frequent inter layering with gradual transitions. It has been subdivided into three members, namely,
• A lower unit, 250 to 300 m thick - staurolite-garnet schist with bands of amphibolite and limestone, and intercalations of pyrrhotite;
• A middle unit, >300 m thick - interbedded graphitic quartz sandstones and quartz-graphite-mica schist, with a variable carbonate content and disseminated pyrrhotite;
• An upper unit, 400 to 500 m thick - quartz-graphite-mica schist, with intercalated pyrrhotite.
Quartzite Sub-suite,up to 550 m thick - predominantly composed of non-graphitic quartzites, quartz-sandstones and grits, and quartz-graphite-mica schist, often with garnet. The suite has been sub-divided into:
• A lower unit,>300 m thick - interbedded quartzites and graphite-bearing garnet-quartz-mica schists;
• An upper unit, >400 m thick - micaceous quartzite.
Intrusives comprise intensely metamorphosed, Neoproterozoic sill like bodies of gabbro-dolerite and serpentinised ultrabasic rocks. These are restricted to broadly conformable fault zones. Metamorphism has produced kyanite, staurolite and almandine garnet (Ruchkin, et al., 1976).
The principal structure is a complex north-easterly trending syncline, which plunges gently to the south-west. Both limbs have steep dips to the north-west. Two types of fault are evident, the first a strike slip set trending mainly north-westerly, being manifested as tectonic breccia zones with minor displacement. The second set are accompanied by intense hydrothermal alteration, control the emplacement of dykes and sills, and have greater offsets (Ruchkin, et al., 1976; Smirnov, 1977).
Mineralisation - Two styles of mineralisation are recognised, namely:
i). Stratabound mineralisation, which is formed in three specific stratigraphic positions within the graphitic-pelitic schist subsuite. The first of these, which accounts for the bulk of the mineralisation, is at the contact between the lower and middle unit of this sub-suite. This band may be traced by mapping and electrical geophysical methods over a total 11.5 km strike length. The second is 150 to 200 m higher in the sequence, while the third is in the upper unit of the same sub-suite, among the quartzites and graphite-quartz-garnet-mica schists. The second zone of mineralisation may reach a thickness of 250 m in the centre of the deposit. On the south-western and north-eastern flanks of the deposit however, the first and second ore zones converge and cumulatively result in a zone that is 300 to 400 m thick. The third is restricted to an 800 m strike length on the north-eastern flank of the orebody where it also includes veinlet ore and reaches a thickness of 15 to 20 m (Ruchkin, et al., 1976).
Overall these accumulations are sheet like, although in detail they are strongly contorted. There is usually marked thickening, by 2 to 2.5 times, in the hinges of folds, compared to the limbs (Ruchkin, et al., 1976). The ores occur as thin-layered, massive and disseminated sulphides, with major pyrite, pyrrhotite, sphalerite, galena, and chalcopyrite, and minor tennantite-tetrahedrite, arsenopyrite, magnetite. The Zn:Pb:Cu ratio is 4:1:0.3. The ores have been subjected to deformation and metamorphism resulting in intense folding, boudinage, mylonitisation as well as re-mobilization and re-deposition of sulphides into fold closures and shear zones (Ruchkin, 1984; Distanov and Kovalev, 1995).
Three mineral assemblages are represented, namely a) pyritic, composed of 60 to 100% pyrite, 0 to 20% sphalerite, and 0 to 20% galena, and including massive and banded varieties; b) chalcopyritic, made up of 25 to 100% pyrite, 0 to 30% galena, 0 to 45% sphalerite and 0 to 20% chalcopyrite, with massive, banded and brecciated textures; and c) lead-zinc pyritic, with 50 to 70% sphalerite, 15 to 30% pyrite, 5 to 25% galena, 0 to 10% chalcopyrite, and porphyritic, massive, banded and veinlet textures (Ruchkin, et al., 1976).
ii). Discordant, mineralisation, confined to the band of development of high temperature porphyroblastic metasomatites, largely along the major longitudinal faults. The composition and mineralogy comprises 35 to 60% pyrrhotite, 0 to 30% chalcopyrite, 0 to 35% sphalerite, 5 to 30% pyrite and 0 to 26% galena. The mineralisation is present as veinlets, disseminations and nests (Ruchkin, et al., 1976).
The gangue minerals are predominantly quartz, calcite, muscovite, with lesser kyanite, basic plagioclase, tourmaline, almandine garnet, gahnite and biotite. The earliest sulphides are pyrite with galena and sphalerite, forming the banded accumulations of the pyritic ore type. These, and the surrounding country rocks, are overprinted by a quartz-chalcopyrite-pyrite-galena-sphalerite suite which forms sheet like deposits, also conformable with the country rock. The next generation involves quartz-carbonate-sphalerite assemblages which form band like concentrations of "ball-ore", conformable with the country rock and stratabound ores, and as branching veins. A pyrite-galena-sphalerite-chalcopyrite-pyrrhotite association forms discordant veinlet impregnation pyritic-polymetallic ores, superimposed on all of the preceding types (Ruchkin, et al., 1976).
Smirnov (1977) indicates that there are three ore types, namely: i) uniform ores with >8% Pb+Zn; ii) rich segregations with 4 to 8% Pb+Zn and iii) lean segregated mineralisation with 2 to 4% Pb+Zn. The ratio of Pb:Zn averages 1:4.5.
Ruchkin, et al., (1976) suggest that on the basis of plunges and grade distribution, the stratabound mineralisation encountered on the two limbs of the main synform are connected across and under the keel of the structure at a depth of 1000 m to form a single 8000 x 1000 m lens.
The most recent source geological information used to prepare this decription 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.
Kholodnina
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Selected References:
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Leach D L, Bradley D C, Huston D, Pisarevsky S A, Taylor R D and Gardoll S J, 2010 - Sediment-Hosted Lead-Zinc Deposits in Earth History : in Econ. Geol. v.105 pp. 593-625
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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.
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