Angara-Ilim - Korshunovskoe, Rudnogorsk, Tagar, Neryunda, Kapaevskoe, Oktyabrskoe, Tatianinskoe
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The Korshunovskoe (or Korshunova) iron deposit is one of the most significant of the several tens of Angara-Ilim type iron oxide deposits found in the Angara and Ilim River Basins in the south-western part of the Siberian craton. It is located in the vicinity of Zheleznogorsk on the BAM section of the Trans-Siberian railway in Siberia, Russia, 475 km north of Irkutsk, and is the raw material source for the major steel works of the West-Siberian Steel Corporation (#Location: 56° 32"N,104° 08"E).
The Angara-Ilim type iron oxide deposits are associated with mafic igneous suites of the Permian-Triassic Siberian traps, and are represented by mineralised sub-vertical breccia pipes, likely diatreme-maars, extending for >1.5 to 2 km downward. These breccia pipes intersect tholeitic, calc-alkaline, mafic (dolerite) sills but incorporate younger basaltic dykes and stocks, which are possibly alkalic and exhibit a shoshonitic affinity. Gradual upward transition from massive basalts through porphyritic to vuggy and foamy varieties and finally to 'tuffisites' cementing explosive breccias are observed (Soloviev, 2010).
The Angara-Ilim cluster of iron oxide deposits is roughly coincident with a distinct regional extensional structural feature, expressed both in the Precambrian basement and Phanerozoic cover of the Siberian craton, part of a larger rift and related metallogenic system known as the Angara-Vilyui metallogenic belt (e.g., Odintsov et al., 1980). Individual rift troughs found within this system control variously-aged magmatic and associated mineral occurrences, including alkaline-carbonatite massifs, diamondiferous kimberlite pipes and iron oxide deposits (Soloviev, 2010). The Angara-Ilim type iron oxide deposits are interspersed with iron oxide deposits in fractures, barren explosive breccia pipes and alkaline-ultramafic intrusives with carbonatites (Soloviev, 2010).
The region is also characterised by the presence of gentle, rounded to oval-shaped domes and depressions up to 60 to 130 km across, folding Palaeozoic to Lower Triassic sedimentary rocks, and likely reflecting heterogeneity in the Precambrian basement. These structures are believed to largely control clusters of iron oxide deposits and are characterised by a larger number of mafic intrusives and dykes, uplifted Precambrian basement and dense fault networks (Strakhov, 1978; Odintsov et al., 1980). Nikulin et al. (1991) correlate these deposit clusters with inferred magmatic chambers in the upper mantle.
The Korshunovskoe deposit occurs within and adjacent to an 'explosion pipe' cutting platform cover sediments of argillites, limestones, marls, siltstones, sandstones and clays of the late Cambrian Lena, Ust'kut, Mamyr and Ordovician Bratsk groups and overlying Early Carboniferous limestone.
The 'explosion breccia' pipes are filled with tuff breccias and fragmentals composed of the surrounding country rocks which have undergone considerable metasomatic alteration. They incorporate fragments and larger blocks of sedimentary (60 to 80 vol.%; sandstones, siltstones, limestones and argillites) and igneous (10 to 40 vol.%; gabbro-dolerites, dolerites and basalts) rocks cemented by essentially chloritic material as well as by fine-grained carbonate. Its central part is characterised by intense multiple brecciation, with rock fragments in the breccias represented mostly by variably-altered dolerites. They are cemented by a finely-dispersed matrix, completely replaced by skarn, post-skarn alteration assemblages and iron oxides. Outside of this zone, intense fracturing has occurred, locally with brecciation in altered sedimentary rocks. The fractures are filled with magnetite, accompanied by chlorite and calcite. Finally, the outermost zone is characterised by weak, predominantly sub-horizontal fractures within sedimentary rocks, locally replaced by skarns. Steeply-dipping dykes of gabbro-dolerite, dolerite, dolerite-porphyry, and basalt-porphyry are present, both within and outside the breccia pipes, whilst sub-horizontal dolerite sills are found at depth (Soloviev, 2010).
The pipes are associated with Permo-Triassic Siberian Trap igneous activity, occurring locally as steeply dipping mafic dykes which strike NE to east and up to 30 m thick layered bodies of gabbro-dolerite, dolerite and dolerite porphyry. The walls of the breccia pipe dip inwards at 65 to 70°.
The orebodies are complex, occurring as: i). banded masses of metasomatic magnetite that are within, and conformable to calcareous members of the host sedimentary wall rocks (dominantly in dolomitic limestones, marls, calcareous argillites and sandstones with a calcareous or limy matrix, but only to a minor degree in sediments without a carbonate component) at a depth of some 700 to 1500 m from the surface; ii). stock-like, lensoid, layered and columnar bodies of magnetite within the altered pyroclastics of the breccia pipe; and iii). steeply dipping vein-like masses in zones of intense brecciation and replacement by skarns.
Together these mineralisation styles forms two large continuous bodies. The main deposit has the form of a sub-vertical breccia pipe with plan dimensions of approximately 2400 x 700 m. Mineralisation has been traced by drilling to a depth of 1200 m, and by geophysical data to at least 3 km below the surface (Antipov et al., 1960).
The bulk of the ore is associated with brecciation and occurs within sediments, tuffs and igneous rocks and are demonstrably due to replacement of the hosts. Massive and banded ores are less well developed. The mineralisation is mostly magnetite (~82% of iron resources), with minor magnomagnetite, hematite and martite.
The main orebody comprises vertically overlapping zones, with variable amounts of hematite and martite in the upper layers, calcite and magnetite in middle layers, and halite and magnetite in lower layers. The magnetite of the upper to middle zone is accompanied by pyroxene, chlorite and minor epidote with lesser amphibole, serpentine, calcite and garnet, and rare quartz, apatite and sphene and occurs as oolites, druses, masses and disseminations. Calcite increases downwards to 20 to 30%. In the lower part of the deposit, halite, amphibole and Mn-magnetite are more abundant. Pyrite, chalcopyrite and pyrrhotite are found throughout. Much of the magnetite is magnomagnetite which contains up to 6% MgO.
Total iron ore reserves of the Korshunovskoe deposit have been variously quoted as:
• 630 Mt @ 26% Fe to depth of 1200 m (USGS, 1996).
• 1.5 Gt of ore to a depth of 1700 m (Kommersant, 2008).
• 490 Mt @ 31.6 wt.% FeTotal (pre-production Russian B+C1+C2 reserve categories; Soloviev, 2010).
• 1.5 Gt of geological resources to 1500 m, including ~550 to 600 Mt in sub-horizontal mineralised bodies at 700 to 1500 m (Kalugin et al., 1981).
The Rudnogorsk deposit is located within 125 km to the north-west of Korshunovskoe. It comprises several sub-vertical mineralised breccia pipes, including the largest Central pipe (with dimensions of 1600 x 600 m in surface exposure), two smaller mineralised pipes (Western pipe ~350 m in diameter, Northern pipe ~450 x 200 m), and a series of smaller barren pipes. The mineralisation has been traced by drilling to a depth of 1200 m below the surface.
The mineralised pipes cut a flat lying platform cover sequence of Lower Silurian sediments comprising calcareous clays, marls, calcareous and micaceous sandstones, and dolomites, followed by a sandstone group. Distal to the deposit, these sediments are unconformably Siberian traps (Antipov et al., 1960).
The pipes are characterised by wide, funnel-like upper parts, passing downward into much narrower dyke- or veinlike roots. According to Von der Flaass et al. (1992), the upper funnel-like parts are composed of a thick tuffaceous sequence, often with massive, irregular- to rhythmiclayered textures, locally with textures indicating sliding of un-lithified sediments. Other authors (e.g., Antipov et al., 1960) suggest the funnel-like structure is composed of collapse breccia. At deeper levels, the breccias contain chaotically mixed fragments of sedimentary rocks and relatively minor dolerites, varying in size from fractions of a centimetre to a few metres across. They are cemented by fi ne-grained chloritic and carbonate matrix. The breccias were intensely altered and almost entirely converted into pyroxene and pyroxene-garnet skarns, then replaced by a calcite-serpentine-chlorite assemblage; the breccia pipes are surrounded by a thick halo of altered rocks and disseminated magnetite.
The deposit incorporates a large number of mafic dykes. Many of these occur on the periphery of the Central breccia pipe, and are composed of basalt-porphyry. These dykes have intrusive contacts with the tuffaceous rocks but are locally subjected to intense fracturing and brecciation, with a fi nely-dispersed cement of basaltic composition. The number of mafic dykes increases with depth; there are both basaltic and dolerite dykes, with the dolerite dykes apparently preceding the formation of breccia pipes.
The Central and Western breccia pipes are intersected by an east-west-trending fault zone that hosts a vein-like body of massive magnetite, or, rather, a series of sub-parallel steeply-dipping (75 to 85°, up to vertical) magnetite veins totalling some 40 m in thickness. This mineralised zone was traced for 3.8 km east-west along strike, and to 1200 m down-dip. Some individual magnetite bodies found within this zone have pillar-like shapes and are combined with sub-horizontal lodes adjoining them at depth. Subhorizontal alteration zones are some 100 to 400 m thick and incorporate massive magnetite bodies 4 to 16 m, and up to 70 m thick.
The ore at Rudnogorsk has been grouped into i). high grade 53.1% Fe, of which there was originally 66 Mt, and ii). segregated 39.8% Fe ore, originally totalling around 143 Mt. A total 'geological' resource of 850 Mt to a depth of 1200 m is quoted by Kalugin et al. (1981). Mining commenced in 1981. Mineralisation is associated with a explosive volcanic pipe, with the principal ore minerals being magnomagnetite and magnesioferrite.
This description is taken from Soloviev (2010).
Tagar occurs as a large mineralised pipe-like breccia body, with overall surface dimensions of approximately 2000 × 1000 m, that has been traced by drilling for 1000 m down plunge, with no indication that it is pinching out.
The mineralised pipes cut a platform cover sequence of Lower Cambrian carbonate rocks and Middle to Upper Cambrian and Ordovician carbonate-terrigenous sediments, which are unconformably overlain by Carboniferous terrigenous rocks away from the deposit (Antipov et al., 1960).
The contacts between the breccia body and the host carbonate rocks are sharp and dip steeply toward its centre. In cross section, the breccia body is characterised by a funnel-like shape in its upper part, and by a pipe-like form in its lower portion. The breccia contains variably-sized fragments of dolerite, carbonate and terrigenous rocks, cemented by a finely-dispersed, mostly carbonate matrix.
Large (10 to 20 m, up to 60 to 70 m across), strongly fractured blocks of dolerite are present in the central parts of the breccia body, and large (up to a 300 x 400 x 250 m) wedge-like blocks of carbonate rocks are present in the peripheries of the pipe. It is assumed that the breccia body overprints a complex shaped dolerite stock that splits into two branches to the west. The breccia body was subjected to intense alteration with the formation of prograde and retrograde skarns, followed by hydrosilicate alteration. As a result, the breccia matrix was almost entirely converted into a calcite-serpentine-chlorite aggregation, with common to abundant magnetite.
The deposit incorporates four major linear mineralised zones, which dip at 65 to 70°, often merging on depth, and are separated by weakly-mineralised breccias. The largest mineralised zones have been traced for up to 850 to 900 m along strike and down-dip, and are up to 350 to 400 m thick. These zones comprise a series of vein-like magnetite bodies, each of up to 70 m in thickness. On the periphery of the deposit, magnetite mineralisation is present in breccia-like masses, with calcite-serpentine-chlorite metasomatites replacing the carbonate matrix that cements scattered fragments of only weakly skarn-altered dolerite.
This large deposit has ore reserves of 435 Mt averaging ~30 wt.% FeTotal (Russian B+C1 reserve categories), and an additional ~200 Mt of 'geological' resources to a depth of 1200 m (Kalugin et al., 1981).
This description is taken from Soloviev (2010).
This deposit occurs as a large sub-vertical pipe-like breccia body at the intersection of east-west and roughly north-south trending faults. The breccia pipe and associated alteration halos carrying intense magnetite mineralisation, extend for more than 2.5 km along the major controlling eastwest- trending fault zone, while the associated alteration persists for more than 5 km. At surface, the thickness of the mineralised zone varies from 20 to 50 m to the west, to 200 to 400 m in the east. The breccia pipe and iron oxide mineralisation have been traced by drilling from the surface to a depth of 1200 m, and continue further down-dip. The major east-west-trending fault can be traced further to both the east and west by the presence of dolerite dyke swarms and fracture zones, although alteration and mineralisation are absent. A separate, large complex-shaped zone of skarn and magnetite veining is found to the south.
At a depth of 280 to 400 m, the sedimentary sequence hosts a thick (90 to 200 m), sub-horizontal dolerite sill. This sill is located along the discordant contact between the Lower Permian siltstone and argillite sequence and overlying Triassic tuffaceous rocks. The breccia pipe clearly intersects the sill. Outside of the pipe, the sill is altered and crosscut by magnetite veins. Sub-vertical dolerite-porphyry and basalt stocks and dykes are mostly found at greater depth, where they are 5 to 30 m thick and extend for between 10 to 20 m, up to 100 to 200 m along strike.
The deposit incorporates three large magnetite bodies. Two are sub-vertical, pillar-like in shape, and correspond to the eastern and western fl anks of the breccia body respectively. They are separated by a mass of relatively less altered and mineralised rock, essentially composed of large dolerite (remnant?) blocks. The third body is subhorizontal and occurs along the footwall of the large dolerite sill. This sub-horizontal mineralised zone was traced by drilling for 2.5 km along the southern side of the breccia pipe. To the south, it pinches out approximately 1000 m from the pipe, but remains open to the east and west. The thickness of the sub-horizontal mineralised zone ranges up to 40 m (averaging 27 m). Small sub-horizontal magnetite lenses are also present within the dolerite sill.
The deposit contains 635 Mt of ore averaging 33 wt.% FeTotal (Russian B+C1+C2 reserve categories), and a total 'geological' resource estimated to a depth of 1200 to 1500 m of some 1.2 to 1.45 Gt (Kalugin et al., 1981).
This description is taken from Soloviev (2010).
The Kapaevskoe deposit takes the form of a generally circular, steeply-dipping zone of brecciation and intense hydrothermal alteration, in which several steeply-dipping ring, radial, and flat-lying fractured and brecciation zones are distinguished . The overall diameter of this circular (possibly pipe-like) structure exceeds 1000 m, with linear, steeply-dipping zones of alteration and mineralisation that radiate out from the central structure and extend for an additional 1 to 5 km. The breccia pipe is overlain by a local cup-like depression composed of collapse breccia, in turn overlain by carbonate and terrigenous rocks. In general, this deposit is an example of a relatively small and weakly expressed breccia pipe, with several associated large linear (vein-like) mineralised zones. The breccias were replaced by skarns, with particularly abundant garnet, which were subsequently subjected to multiple brecciation, both preceding and postdating magnetite mineralisation.
The major linear mineralised zones dip steeply and strike approximately north-south and east-west. The northsouth mineralised zone extends for 4750 m along strike and varies in thickness from 4 to 70 m on its extremities, and up to 450 m in its central section (close to the central breccia structure). The mineralisation extends down-dip for 1400 m in the central part and for 50 to 200 m on its extremities. It incorporates six steeply (70 to 80°) dipping lens-shaped orebodies that are each 12 to 60 m thick, with a vertical extent of 400 to 1500 m, separated by weakly-mineralised skarns. The north-south mineralised zone hosts some 90% of the deposit resources and is mostly composed of massive ores containing 65 to 90 vol.% magnetite, up to 20 vol.% magnomagnetite, 5 to 10 vol.% hematite-martite and up to 3 vol.% hematite.
The east-west trending mineralised zone dips at 65 to 70°, has a total length of 5500 m, is 5 to 150 m thick, and has been traced for 160 to 500 m down-dip. It includes six magnetite bodies, each some 6 to 40 m thick, extending for 600 to 3000 m down-dip and separated by weaklymineralised 4 to 26 m thick skarns.
In addition, the deposit includes a large flat-lying mineralised zone in the upper part of the Ordovician sequence, which occurs along the western fl ank of the north-south, steeply-dipping, mineralised zone. Close to the central part of the deposit, the flat-lying zone is composed of five magnetite bodies, each some 8 to 100 m thick, although further to the west there are just one or two that are 30 to 60 m thick.
This deposit has ore reserves of approximately 500 Mt averaging 31.8 wt.% FeTotal (Russian B+C1+C2 reserve categories), and total 'geological' resources, estimated to a depth of 1200 m, of some 1 Gt (Kalugin et al., 1981).
This description is taken from Soloviev (2010).
This deposit is situated some 120 km from the main cluster of Angara-Ilim iron oxide deposits, and occurs as the two sub-vertical Eastern and Western breccia pipes. Local cup-like depressions occur in the uppermost part of each breccia pipe. These depressions are fi lled with intercalated thinbedded sandstones and siltstones, which overlie irregularly bedded carbonate rocks and sandstones intercalated with sulphates (anhydrite, gypsum, locally celestite) and abundant fragmental magnetite (Von der Flaass and Naumov, 1995).
The Eastern breccia pipe has an ellipsoidal-shape, with plan dimensions of approximately 1200 x 800 m, and is mostly composed of finely-fragmental (<3 cm) breccias, with a predominance of aphanitic to fine-grained dolerite, fragments of sandstone and argillite, as well as less common large sandstone blocks. Most of the breccias found in the central part of the pipe have been essentially converted into garnet skarns. No pyroxene is reported (Antipov et al., 1960). Other abundant alteration minerals include calcite, chlorite, serpentine, magnetite and hematite. Pyrite and chalcopyrite are also common, with local pyrite contents reaching 30 vol.%. The mineralised bodies are quite narrow (up to 20 m thick) and mostly steep-dipping, almost vertical, and is composed of disseminated and brecciated magnetite-hematite-calcite.
The Western breccia pipe is oval-shaped with plan dimensions of some 800 x 1000 m. It is composed of breccias with fragments of dolerite porphyry, sandstone, argillite and limestone. All of the clasts, as well as the breccia matrix, are intensely altered to a metasomatic calcite-chlorite rock, with minor garnet and amphibole. The mineralisation is represented by magnetite and hematite, occurring as narrow (~15 m thick) vein-like bodies dipping toward the centre of the breccia pipe at 35 to 40°. The surface exposure of these bodies occurs as arcuate traces along the breccia pipe walls, extending over lengths of up to 1100 m, composed of disseminated magnetite and hematite, grading into mostly brecciated magnetite at depth. In total, Oktyabrskoe differs from the other Angara-Ilim iron oxide deposit in its greater abundance of hematite and chalcopyrite.
Oktyabrskoe has ore reserves of some 240 Mt averaging 35 wt.% FeTotal (Russian C1+C2 reserve categories), and an estimated 0.8 to 1.2 Gt of total 'geological' resources to a depth of 1200 m (Kalugin et al., 1981).
This description is taken from Soloviev (2010).
Other significant deposit in this cluster include: Tatianinskoe - 80 Mt @ 34.5 wt.% FeTotal; and Krasnoyarovskoe - 172 Mt @ 28 wt.% FeTotal, including 83 Mt averaging 36.9 wt.% FeTotal.
Mineralisation and Alteration - General
Two episodes of brecciation, hydrothermal alteration and mineralisation are distinguished in Angara-Ilim type iron oxide deposits, divided by emplacement of the basaltic dykes. The first episode is expressed as brecciation of dolerites and sedimentary host rocks, followed by hydrothermal alteration of the breccias (prograde magnesian and calcic skarn to retrograde and hydrosilicate alteration) and mineralisation, including abundant magnetite. The second episode occurred after, or coeval with, the emplacement of the basaltic dykes, associated 'tuffisite' and intense 're-brecciation', and includes the formation of numerous massive magnetite (±apatite), and magnetite-calcite veins which often contain 'oolite' (concentric, spherulitic, ball-like) magnetite aggregations as well as magnetite-halite accumulations. Late weak potassic and sodic alteration episodes are also recognised.
In general, sulphides are only present in very minor amounts, and are represented mostly by pyrite, pyrrhotite, and chalcopyrite, and occasional by trace bornite, pentlandite, sphalerite, galena, etc. More intense sulphide (pyrite, chalcopyrite) mineralisation tends to occur at higher deposit levels (Vakhrushev et al., 1973; Vakhrushev and Vorontsov, 1976; Strakhov, 1978.). In particular, pyrite (up to 10 to 15 vol.%) is present in narrow fracture-controlled quartz-carbonate-sulphide zones overprinting magnetite mineralisation. According to Vakhrushev and Vorontsov (1976), some samples of pyrite from Korshunovskoe returned elevated Co (up to 0.75 wt.%) and Ni (up to 0.5 wt.%) values, with enrichment of Co in the core of pyrite crystals (up to 2 wt.%) and of Ni in their outer parts (up to 0.5 wt.%). Chalcopyrite is associated with pyrite although its content is typically less than 1 vol.%. Occasionally, minor chalcopyrite is found in microfractures and as interstitial disseminations within magnetite, garnet, pyroxene, etc. Strakhov (1978) reported local, higher chalcopyrite contents (up to 1% Cu) within magnetite ores at Oktyabrskoe. Elevated gold values are locally associated with quartz-carbonate-pyrite zones, mostly on the upper levels at Neryunda, Korshunovskoe and Rudnogorskoe (Odintsov et al., 1980; Strakhov, 1978).
Fine-grained and coarsely-crystalline specular-hematite is common and locally quite abundant, occurring as a late species in magnetite ores, less often in barren skarns and most typically in association with calcite. However, the majority of hematite was formed by replacement ('martitisation') of magnetite, a process which starts from the edge of magnetite crystals and gradually spreads inwards through the entire crystal volume. Transformation of magnetite into hematite is observed to depths of >1000 m from the surface indicating a hypogene origin for this process.
See Soloviev (2010) for more detail.
This summary is mostly based on and taken from Soloviev, 2010, with additional information from USGS 1996 and Smirnov 1977.
The most recent source geological information used to prepare this summary was dated: 2010.
Record last updated: 25/4/2016
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.
Porter T M, 2010 - Current Understanding of Iron Oxide Associated-Alkali Altered Mineralised Systems: Part II, A Review: in Porter T M, (Ed), 2010 Hydrothermal Iron Oxide Copper-Gold and Related Deposits: A Global Perspective, PGC Publishing, Adelaide v.3 pp. 33-106|
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 1 - Iron Oxide Deposits in the Angara and Ilim River Basins, South-Central Siberia: in Porter T M, (Ed), 2010 Hydrothermal Iron Oxide Copper-Gold and Related Deposits: A Global Perspective PGC Publishing, Adelaide v.4 pp. 495-514|
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