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The Sarbay (Sarbai) iron deposit is located within north-eastern Kazakhstan, ~30 km SW of Kustanay and ~300 km ESE of Magnitogorsk (#Location: 53° 03' 07"N, 63° 07' 55"E).
The Sarbai, Kachar and Sokolovsk iron ore deposits, which are hosted within the 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).
Sarbai occurs on the western limb of the NNE-trending Sokolovsk-Sarbay anticline, while Sokolov'sk (see separate record) is found 8 km to the SSE on the eastern limb.
The ore deposit occurs just to the west of the Sarbai-Sokolovsk intrusive complex which is located between the Sarbai and Sokolovsk deposits, coming to within several hundred metres of the closest magnetite orebody at Sarbai (Sokolov and Grigor’ev 1977). At Sarbai, it comprises pyroxene- and quartz-diorites and diorite porphyries, accompanied by various pre-, intra- and post-ore dyke phases, culminating in post-ore quartz-pyroxene and granite porphyries (Dymkin 1966). The Sarbai deposit is also cut by late, post-ore rhyolite to rhyodacite dykes. Preliminary geochemical data from these dykes indicate they are dominantly of granodioritic composition. Pre-ore diorite porphyry dykes follow generally north-south trending faults which dip at 65 to 70°W, while intra-ore fractures are defined by vein-like skarn partings which cross-cut bedding. Post-ore structures displace and brecciates the ore and country rock, and control the orientation of post-ore granite-porphyry dykes (Sokolov and Grigor'ev, 1977).
The ore is hosted by the lower Carboniferous Valerianovo supergroup, which is composed of the interstratified andesite porphyries and their tuffs, tuff-breccias, tuffaceous sediments, limestone, sandstone and tuffaceous sandstone, overlain by middle and upper Carboniferous hematised tuffs, as well as lavas and tuffs of basaltic composition, tuffaceous sediments and argillites. The rocks of this sequence are developed into the near north-south Sokolovsk-Sarbay anticline, with the Sarbay deposits being developed on its western limb (Smirnov, 1977).
The mineralisation replaced bituminous limestones and intercalated calcareous tuffs and tuffaceous sediments within a 350 to 400 m thick succession of those lithologies (Chuguevskaya 1969). The ore layers are conformable and appear to be bedded, passing laterally into less altered tuffaceous units and calcareous sediments. Geological relationships indicate that the host rocks and mineralisation are Early Carboniferous in age.
In the vicinity of the ore deposits there is extensive pre-, intra- and post-ore fracturing developed, with diorite porphyries having been injected along near north-south pre-ore faults, dipping at 65 to 70°W. The intra-ore fracturing is defined by the vein-like skarn-magnetite partings which cut the bedding. A system of post-ore faults has produced a block faulting pattern and crushing of the ore and skarn alteration, and in places controls the distribution of post-ore quartz-diorite porphyries and granite-porphyry dykes (Smirnov, 1977).
Alteration comprises the following stages (Sokolov and Grigor'ev, 1977):
i). pre-ore hornfelsing, mainly within the tuffs and tuffaceous sediments, decreasing in intensity away from intrusive contacts;
ii). the formation of biotite-K feldspar and sodic/albite alteration assemblages in the enclosing silicate hosts;
iii). the development of ore stage skarn alteration, comprising pyroxene-scapolite, pyroxene-garnet, scapolite-pyroxene-garnet and epidote-actinolite phases directly associated with the ore formation in the carbonate dominated hosts. The scapolite alteration is only developed after feldspar rocks, although the skarn alteration zone and other calc-silicates are formed after all preceding rocks, including hornfels and earlier alteration products. Extensive and pervasive development of chlorine-bearing sodium scapolite (marialite) is particularly characteristic of Sarbai;
iv). post-ore propylitic suites of chlorite-prehnite, calcite-quartz and zeolite which accompany zones of late tectonic disturbance. Chlorine bearing sodic scapolite is a widespread alteration product, implying NaCl metasomatism (Smirnov, 1977).
At the Eastern and South-eastern orebodies there is a zonation outwards from the intrusive contact as follows:
i). biotite-albite-scapolite over a width of 100-150 m;
ii). garnet and garnet-pyroxene skarn alteration forming a 3 to 20 m thick zone in the footwall of the Eastern and South-eastern orebodies;
iii). ore stage and skarn alteration associated ore with scapolite, 50 to 185 m thick;
iv). skarn and scapolite-pyroxene alteration from 3 to 20 m thick in the hanging wall to ore;
v). pyroxene skarn alteration with relicts of hornfels, 10 to 30 m thick;
vi). pyroxene-plagioclase hornfels, partly scapolitised and skarn altered, up to 40 m thick;
vii). hornfelsed and albitised tuffs and tuffaceous sediments up to 160 m thick (Smirnov, 1977).
In contrast, the Western orebody is within an alteration pattern, of albitised, prehnitised and zeolite altered tuffs and tuffaceous sediments, replaced by actinolite and chlorite altered pyroclastics, followed by ores and mineralised epidote-actinolite, un-mineralised epidote-actinolite, and finally a zone of variably developed epidote, actinolite, prehnite and zeolite alteration (Smirnov, 1977).
The deposit consists of three main, generally north-south trending layer like, conformable ore lenses, the Eastern, Southeastern and Western. These lenses measure approximately 1000 to 1700 m × 800 to 1700 m laterally and are 170 to 185 m thick. They are confined to a 350 to 400 m thick interval of the Visean (mid-lower Carboniferous) limestone-tuff-tuffaceous sediments sequence of the Valerianovsk Group. The host interval originally comprised dark-grey bituminous limestone, interstratified with calcareous tuffs and tuffaceous sediments. The orebodies have the shape of elongated lenses of quite well defined thickness, prior to lensing out along strike. The Eastern orebody has a length of 1700 m and thickness of 185 m, and has been traced down dip for more than 1000 m; the South-eastern orebody has a strike of 1000 m, thickness of 170 m and down-dip extent of >800 m; while the Western orebody has respective dimensions of 1400 m, 185 m and 1700 to 1800 m in its central section (Smirnov, 1977).
The orebodies at Sarbay do not come into contact with the diorite-porphyry intrusion, being separated by 25 to 150 m of barren skarn and related alteration. Ore formation appears to be connected with pre-ore fault channels, rather than the intrusive contact. The ore comprises alternating layers of uniform ores, ore bearing and non-ore skarn alteration. The orebody is around 50% uniform-massive ore with >50% Fe, and half skarn alteration associated ore with 20 to 50% Fe. Around 1% of the ore is oxidised. Magnetite is the primary ore mineral with subordinate associated pyrite, pyrrhotite-pyrite and lesser magnetite, chalcopyrite and sphalerite occurring as layers in the footwall of the magnetite ore lenses (Sokolov and Grigor’ev 1977). Sulphides can form layers in the footwall of the magnetite bodies but are currently not of commercial interest (Hawkins et al., 2010).
The uniform-massive magnetite has a banded texture, inherited from the primary calcareous tuffs and limestones. In addition to the dominant magnetite the ore contains pyroxene, scapolite, garnet, wollastonite, albite, epidote, actinolite, apatite, pyrite, calcite, quartz, and accessory idocrase and sphene. Rare pyrrhotite, arsenopyrite, sphalerite, galena and chalcocite are also recorded. The lower grade skarn altered-ores are also coarsely banded, mimicking the original banding of the sediments and tuffs. Mineralised assemblages include pyroxene-magnetite and garnet-magnetite skarn alteration; scapolite-skarn consisting of scapolite-pyroxene-garnet-magnetite; hydrosilicates of epidote-actinolite-magnetite. The skarn alteration and scapolite-skarn associations include some syn-skarn wollastonite and apatite, as well as post-skarn albite, epidote, actinolite, chlorite, sulphides, calcite, quartz and zeolite (Smirnov, 1977).
The ore contains 15 to 19% SiO2, 0.25 to 0.36% Al2O3, 5.3 to 11.1% CaO, 0.25 to 0.36% TiO2, 0.02 to 0.1% V2O5, 0.1 to 0.2% MnO, 0.03 to 0.05% Cu, 0.03 to 0.08% Zn, 0.015 to 0.02% Pb.
The higher grade reserves, with >30% Fe, as quoted in 1977, amounted to 725 Mt of ore @ 45.6% Fe, 4.05% S, 0.13% P (Sokolov and Grigor’ev 1977). The deposit was being mined from an open cut, with a potential resource of 1500 Mt at depth (Smirnov, 1977).
Remaining ore reserves and mineral resources at December 31, 2012 (ENRC Annual Report, 2012), were:
Open-pit, Main - proved + probable reserves - 56.5 Mt @ 35.2% Fe;
Open-pit, Southern - proved + probable reserves - 161.8 Mt @ 37.9% Fe;
Underground, Main - measured + indicated + inferred resources - 975.6 Mt @ 40.4% Fe;
Open-pit, Southern - measured + indicated + inferred resources - 291.5 Mt @ 45.6% Fe.
The most recent source geological information used to prepare this summary 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.
References to this deposit in the PGC Literature Collection:
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|
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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