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Kachar |
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Kazakhstan |
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Fe
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Super Porphyry Cu and Au
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The Kachar, iron deposit lies within the Turgay (Turgai) iron ore province of iron ore province of Kazakhstan, ~50 km NW of Kustanay and ~270 km east of Magnitogorsk (#Location: 53° 22' 35"N, 62° 55' 53"E).
The Sarbai, Kachar and Sokolov'sk iron ore deposits, which are hosted within the Lower Carboniferous Valerianovskoe arc of northwest Kazakhstan, contain an aggregate of more than 3 billion tonnes of mineable massive magnetite. The Valerianovskoe arc lies within the broader Uralides, a 2500 km long, north-south trending mountain belt that extends from the steppes of northern Kazakhstan to the Arctic ocean, and were formed as a result of the collision of the Baltica (largely the East European craton) and Siberia-Kazakh plates during the Late Carboniferous to Early Permian period. The region hosting these giant iron deposits is located on the eastern margin of the Southern Uralides, within the tectonic domain known as the Trans-Uralian zone (Herrington et al., 2005). The Valerianovskoe arc is the possible westward extension to the South Tien Shan arc that is host to the giant Almalyk Cu-Au porphyry system in Uzbekistan. The magnetite bodies of the Turgai belt replace limestone and tuffs, and are distal to locally proximal to the contacts of gabbro-diorite-granodiorite intrusive complexes (Hawkins et al., 2010).
Kachar is the largest iron deposit of the Turgai field, masked beneath 160 to 180 m of unconsolidated cover. It is ~40 km NNW of Sarbai.
At Kachar the host sequence is described as comprising:
Lower Carboniferous Valerianovsk Group, >1000 m thick - andesitic porphyry and their pyroclastics, with bands of tuffaceous sediments and limestones, clay-carbonate rocks with bands and lenses of anhydrite near the orebodies, basalt and dacite lava flows, and plagioclase- (at the base) to pyroxene-plagioclase (at the top) porphyries and their tuffs;
Middle to late Carboniferous Kachar Group, up to 800 m thick - polymict tuffaceous sandstone, conglomerates, argillites, andesite-porphyry tuffs, basalt and andesite flows, plagioclase and pyroxene-plagioclase porphyries and their tuffs (Smirnov, 1977).
The surrounding volcano-sedimentary sequence has been cut by numerous small stock-like and irregular granitoid-porphyry intrusives which have been strongly albite and scapolite altered, and hence were emplaced before the introduction of ore, as well as rare dolerite dykes (Sokolov and Grigor'ev, 1977). Although not outcropping, geophysical interpretations infer a gabbro-diorite-granodiorite intrusion, similar to those seen near the other Turgay iron ore province deposits, but at a depth of 2 to 2.5 km from the orebodies (Smirnov, 1977). This is further supported by deep drilling that encountered significant orthomagmatic titano-magnetite mineralisation n gabbros concealed at depths of 1.3 to 1.7 km below (and exposed 18 km laterally from) the stratabound magnetite ore zone (Herrington et al., 2005).
Kachar differs from the other Turgay iron ore province deposits in this absence of an active, nearby intrusive, and by the more limited nature of the scapolite alteration, which is present, but is more restricted, being developed over widths of several hundred metres. As such, the high-temperature alteration appears to have developed in the absence of a proximal intrusion. In addition, there are broad zones of sulphide enrichment, accompanied by anhydrite and alunite alteration which are developed within and peripheral to the deposit respectively (Sledzyuk and Shiryaev 1958). The anhydrite has been variously interpreted as evaporite layers within the limestone (Belyashov and Plekhova, 1965) or as an alteration mineral related to skarn formation, where associated with the magnetite mineralisation (Sokolov and Pavlov, 1970).
The magnetite deposit is thought to have been developed on the southwestern margin of a volcano-tectonic depression known as the Koskul ring structure. A dacite porphyry, interpreted to be an extrusive facies of the host volcanosedimentary complex in the Kachar ore field, has been dated by Rb/Sr at 310±24 Ma (Sokolov and Grigor'ev, 1977).
The mineralisation at Kachar is largely hosted by altered limestone lenses and beds, enclosed within porphyritic basalts and andesites and associated intermediate tuffs, over a stratigraphic interval of up to 500 m within the Valerianovo supergroup. The iron ore zone comprises a series of stacked, stratabound, massive magnetite lenses, separated and surrounded by lower grade segregated magnetite-scapolite, with a bulk grade of up to 70% magnetite. The individual massive magnetite lenses, which have dimensions of as much as 1 × 1 km and are up to 100 m in thickness, comprise fine to coarse grained, euhedral, massive magnetite with the host rock textures having been all but obliterated. The magnetite ore is closely associated with more extensive zones of scapolite and albite alteration, in addition to other phases. Extensive scapolite (dominated by marialite) alteration, with associated sodic pyroxene, post-dates all of the intrusive phases cutting the Valerianovo supergroup in the immediate deposit area. Scapolitisation is most intensely developed in the upper part of the ore zone, decreasing markedly with depth. Associated with it are pyroxene, actinolite, tourmaline, apatite, chlorite, albite, zeolite and calcite. Pyroxene-albite products are also widely distributed, while pyroxene-garnet and garnet skarn alteration is subordinate to, and replaces scapolitised rocks. Later actinolite-chlorite rocks are also of limited distribution. Anhydrite occurs both as conformable lenses within limestone in the vicinity of the orebodies, and as metasomatic replacements as segregations, pseudomorphs after feldspar, quartz, etc., and as 'nests' and pseudomorphs after feldspars and quartz in the pre-mineralisation intrusive granitoid porphyries that are common in the magnetite ores. A halo of scapolite alteration extends for several hundred metres vertically and laterally around the deposit (Smirnov, 1977; Hawkins et al., 2010).
Orebodies are found in three fault bounded tectonic blocks. The Northern sector contains three layer like bodies of high grade ore. The upper is in scapolitised red bed conglomerates, sandstones and tuffaceous sediments; the middle is in limestones; and the lower is after skarn alteration and after anhydrite bearing volcanics, tuffs and tuffaceous sediments. Mineralisation is distributed over a strike length of 3500 m and down dip extent of 1200 m (Smirnov, 1977).
The Southern sector embraces a single, crescent shaped, layer like body which is 60 m thick and 600 m long. It is composed of massive magnetite which passes on the flanks into segregated scapolite-magnetite mineralisation. It is formed in part, directly after limestone, and in part from scapolite and pyroxene-albite rocks which have replaced quartz porphyry and related tuffs. The orebodies of the North-eastern sector are considerably smaller (Smirnov, 1977).
The overall mineral association is of magnetite (and martite in the oxidised zone), with common scapolite and albite; average to poorly distributed pyroxene, garnet, epidote, actinolite, chlorite, anhydrite, apatite, sphene, zoisite, prehnite, sericite, calcite and sulphides (pyrite, pyrrhotite, sphalerite, chalcopyrite, galena, bornite and chalcocite). The ore type assemblages include: a). uniform magnetite; b). martite in the oxidised zone; c). scapolite-magnetite; d). pyroxene-garnet-magnetite skarn; e). albite-magnetite; f). propylitic with actinolite-chlorite-zeolite-calcite-magnetite. Transitions between these types have been observed. The ores have textures which include massive, evenly and un-evenly segregated, banded, streaky, and in the zones of oxidation powdery and honeycomb (Smirnov, 1977).
In the Northern sector the high grade ore contains: 45.5% Fe, 0.5% S (increasing to 3% in the lower sections), 0.15% P, 0.03% Zn, 0.14% V2O5, 0.1 to 0.2% MnO.
The Southern sector contains: 51.2% Fe, 0.3% S, 0.3% P, 0.02% Zn, 0.12% V2O5, 0.1 to 0.2% MnO. TiO2 varies from 0.3 to 0.5%, to 0.8% in the high grade ores (Smirnov, 1977).
The total reserves as quoted by Smirnov (1977) were more than 1000 Mt @ 45% Fe, with an additional 400 Mt at a lesser reserve category.
Remaining ore reserves and mineral resources at December 31, 2012 (ENRC Annual Report, 2012), were:
Open-pit - proved + probable reserves - 792.5 Mt @ 37.8% Fe;
Open-pit - measured + indicated + inferred resources - 1415.0 Mt @ 36.8% Fe.
The most recent source geological information used to prepare this decription was dated: 2010.
Record last updated: 7/9/2013
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.
Kachar
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Selected References:
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Hawkins T, Herrington R, Smith M, Maslenikov V and Boyce A, 2010 - The Iron Skarns of the Turgai Belt, Northwestern Kazakhstan: in Porter T M, (Ed), 2010 Hydrothermal Iron Oxide Copper-Gold and Related Deposits: A Global Perspective PGC Publishing, Adelaide v.4 pp. 461-474
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Herrington R, Smith M, Maslennikov V, Belogub E and Armstrong R, 2002 - A Short Review of Palaeozoic Hydrothermal Magnetite Iron-Oxide Deposits of the South and Central Urals, and their Geological Setting: in Porter T M (Ed.), 2002 Hydrothermal Iron Oxide Copper-Gold and Related Deposits: A Global Perspective, PGC Publishing, Adelaide v.2 pp. 343-353
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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
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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, its employees and servants: i). do not warrant, or make any representation regarding the use, or results of the use of the information contained herein as to its correctness, accuracy, currency, or otherwise; and ii). expressly disclaim all liability or responsibility to any person using the information or conclusions contained herein.
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