Kursk Magnetic Anomaly, KMA - Yakovlevsk, Mikhailovsk, Lebedinsky


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The iron rich region known as the Kursk Magnetic Anomaly (KMA) includes a number of major iron ore mines, including Lebedinsky (#Location: 51° 17' 02"N, 37° 37' 34"E) near Stary Oskol, YakovIevsk (#Location: 50° 51' 43"N, 36° 25' 08"E), at Yakovlevo, which is 35 km north of Belgorod and Mikhailovsk (#Location: 52° 18' 43"N, 35° 25' 16"E) which is near Zheleznogorsk, 100 km NW of Kursk.

The region comprises two separate bands of gravimetric-magnetic anomalies, the most intense of which reflect steeply dipping magnetite-quartzites. The north-east band consists of the Stary Oskol and Novy Oskol iron-ore regions. The south-west band includes the anomalies of the Belgorod and lgov-Mikhailovsky regions. The Belgorod region comprises a linear NW trending 150 x 80 to 100 km zone of crystalline rocks, largely covered by 350 to 750 m of Mezozoic and Palaeozoic sedimentary rocks. The Precambrian rocks form the base of the Russian Platform and are composed of two structural stages, separated by a 2600 ±100 Ma boundary. The lower stage comprises structurally complex sedimentary-volcanogenic sequences, composed of ortho- and paragneisses, quartz-mica schists and amphibolites which have been granitised locally and 'magnetised'. The upper, mainly Palaeoproterozoic stage, is predominantly of less deformed sedimentary-volcanogenic rocks, mainly quartzites, phyllites and ferruginous quartzites of the Kursk Series, which comprises three units, namely: i). a lower, primarily sand-shale group, metamorphosed to arkosic meta-sandstones and black phyllitic sericite-biotite schists; ii). a middle iron-ore group (hosting the main deposits); and iii). an upper slate sequence.

Three facies have been recognised in the iron formations of the Belgorod region, namely:

Volcanogenic cherty-iron formation - restricted in occurrence, these rocks include chlorite and biotite-chlorite slates to stilpnomelane-magnetite slates and quartzites.

Slate cherty-iron formation - which is part of the Kursk Series and reflects continental deposition in a shallow sea (slightly ferruginous, coarse-banded, silicate rocks) grading into deep-sea facies (finely banded magnetite and mica-iron quartzites). Stratigraphic division of these ferruginous quartzites in the YakovIevo and Gostishchevo deposits, indicate up to seven horizons of quartzites. The odd-numbered quartzite units correspond to martite (magnetite)-hydrohematite rocks and ferriferous silicates; even-numbered ones to martite (magnetite) rocks with mica-iron facies. The thickness of the mica-iron facies decreases and locally one or more primary oxide facies are absent. Ferrous, ferrous carbonate and silicate (magnetite, silicate quartzites and ferruginous silicate slates) facies prevail.

Clastogenic cherty-iron formation - which is part of the Oskol Series and is more widespread. These rocks repesent metamorphosed, re-deposited sediments (detrital ores) of the slate cherty-iron formation and are composed of conglomerates, gritstones, debris of ferruginous quartzites, metasandstones and slates. Along strike these rocks grade into cherty-iron rocks locally called 'conglomeratic' or 'nodular' quartzites. Martite mica-iron quartzites average about 50 m in thickness, 'nodular' ones being up to 30 m thick. In contrast to the quartzites of the other two facies, the ore bands of coarse martite mica-iron quartzites of this facies commonly have sand-like structure. The sandy appearance is due to oval and octahedral martite grains of about 1.5 mm in flaky bands of hematite. Semi-ore bands are mainly, composed of oval, lenticular and round jasper debris of brick-red and pink colour averaging 2-3 mm occasionally 8 mm. Flaky, specular hematite is commonly interstitial and does not form separate bands, as it may be seen in the quartzites of the slate cherty-iron formation. Occasionally jasper debris occupies 25 to 40% of rock volume. The rocks are composed of iron hydroxides evenly dispersed or in patches. 'Conglomeratic' quartzites have lenticular en echelon like lenses debris of hornfels in silicate cherty-iron rocks. Conglomerates and gritstones grading into metasandstones, metasiltstones and slates are abundant in sections of the clastogenic cherty-iron formation. The bands of conglomerates range from 5 to 30 m in thickness. When the conglomerate is a product of Kursk quartzite erosion, they consist of quartzite debris (mainly semi-ore rocks) cemented by quartz, hydromica and ferruginous material.

The YakovIevsky Deposit is one of the largest in the KMA region, located 35 km north of Belgorod, on the southwestern margin if the KMA. It is hosted in Precambrian complexes of the base of the Russian Platform and is overlain by a 490 - 550 m thick sequence of Carboniferous and younger platform cover sediments.

The sediments and iron formations of the middle Kursk Series have been folded into a deep, 320° trending compressed syncline, overturned to the northeast, so that these sediments are represented in plan by two parallel belts, the Western (Yakovlevsk proper) and Eastern (the Pokrovsk). The limbs of the fold which persists for 70 km, dip at 60 to 70° NW, with a keel at a depth of >2 km. Superimposed folding and faulting has produced cross folding and faulting and brecciation.

The deposits of the Yakovlevsk limb can be traced for 50 km over widths of 200 to 400 m. The greatest thicknesses of the individual supergene enriched ore bodies are from 40 to 160 m and in places extend to depths of 300 to >600 m before wedging out.

The deposits of the Pokrovsk limb are also linear in nature and include enriched ores which are friable or weakly lithified and finely porous. In the near surface zone the ores have been cemented by late carbonates and chlorites and have undergone compaction.

The seven horizons of the 'slate cherty-iron formation' are both thinly- or thickly-bedded, with red, blue and grey bands and are composed principally of martite, specularite, hydrohematite and gangue minerals.

The initially mined section of the deposit is almost completely within a deep zone of oxidation, so that oxidised iron-ore minerals and hypergene gangue minerals (ferruginous chlorites, clay minerals, etc.) predominate.

Five types of rich ore have been recognised: i). blue specularite and specularite-martite; ii). blue-red martite-hydrogoethite iii). red hydrohematite-hydrogoethite; iv). carbonatised (siderite-specularite and siderite-specularite-martite); v). chloritic ore. Types i)., ii)., and iii). are supergene products formed from the magnetite quartzites while the remaining two types represent the addition of supergene cements and subsequent compaction.

The enriched ores comprise an assemblage of martite, relict specularite, dispersed and earthy hematite, hydrohematite, goethite, hydrogoethite, relict magnetite, clay minerals (kaolinite, montmorillonite, etc.), chlorite, calcite, and relict quartz. The compact cemented ores contain in addition, siderite and ferruginous chlorite. Subordinate hypergene pyrite, marcasite, hypergene magnetite and galena are also present.

Clastogenic cherty-iron formation (conglomeratic ore) is also present, having been distributed in depressions in a palaeo-surface at some distance from the main orebodies. They consist of 1 - 3 cm diameter clasts of rich ores of various types, and less frequently slates and quartz in a matrix of sand-clay which has been unevenly carbonatised and chloritised.

The central high grade core of the Yakovlevsk deposit is characterised by grades of 56 to 63% (average 60.5%) Fe; 0.14 to 0.31% Fe; and 0.05 to 0.11% S.

The proven reserves of the Yakovlevsk deposit in 1977 were 1.8 Gt, plus substantial resources.
The known resources at the Yakovlevsk deposit is of th eorder of 9.6 Gt @ 61.7% Fe (Wikipedia record).

The Mikhailovsky Deposit is located near Zheleznogorsk, 100 km NW of Kursk. The mineralised Mikhailovsk Series, which is up to 3000 m thick, rests unconformably on Archaean basement (as described previously) and consists mainly of amphibolites with subordinate quartzites and metasandstones, talc-carbonate rocks, meta-dolerites and serpentinites. At Mikhailovsk, the overlying Kursk Series comprises the 500 to 1000 m thick lower sand-shale group; the 500 to 600 m thick middle iron-ore group, containing specularite-magnetite, magnetite, and lean-ore quartzites; and the upper 700 m thick group of quart-sericite phyllitic and carbonaceous slates with seams of dolomite. These are followed by the 1000 m thick Kurbakinsk Group, of metamorphosed quartz porphyries, their tuffs, tuffites, sandstones and sedimentary breccias.

The Mikhailovsk deposit is restricted to a large block of ferruginous quartzites on the western limb of the Mikhailovsk Syncline where the quartzite layers have been deformed into a series of folds with steep 60 to 80°E dipping axial planes.

The overlying platformal sediments are of Devonian, Jurassic, Cretaceous, Palaeogene, and Quaternary age and comprise clays, limestones, sands and loams and are thinnest in the central section of the deposit where they are only 35 to 40 m thick while the greatest thickness is100 to 114 m on the margins of the deposit.

Two zones of supergene enriched ores have been identified, the Vereteninsk and Ostapovsk orebodies, with areas of 8.6 and 1.7 sq. km respectively, and average thicknesses of 13 and 9.5 m, below 90 to 109 m of cover. Both are distinguished by sinuous outlines pinch-outs along strike.

The compact enriched ores contain 45 to 46.4% Fe; 0.7 to 0.9% S; 0.06 to 0.08% P; while the friable enriched ores contain 52 to 58.5% Fe; 0.24 to 0.32% S; and 0.03 to 0.05% P.   In 1977, the reserves of supergene enriched ores to a depth of as much as 280 to 330 M was 340 Mt.

Underlying hypogene ferruginous quartzites cover an area of 14.8 sq. km and contain 37.5 to 39% Fe; 40 to 42% SiO2;0.01 to 0.07% S; and 0.01 to 0.06% P.   In 1977, the resource of hypogene ferruginaous quartzite to a depth of as much as 280 to 330 m was 3.7 Gt. and 340 million tonnes of rich iron ores have been proved in the deposit.

The Lebedinsky deposit in the Stary Oskol district exploited supergene enriched ores averaging 68.5% Fe with very low P and S, but now largely enriches low grade hypogene iron formation averaging around 32% Fe to produce 2.5 Mt of 70% Fe pellets from 15 to 18 Mt of ore per annum (in 1994). Archaean basement is overlain by Mikhailovsk Kursk Series rocks as descriobed for the Mikhailovsk deposit area above. The iron formation in the Kursk Series is around 70 m thick, but has been complexly and tightly folded in the pit to form a thicker more compact mass. The enriched zone has an irregular upper siderite rich zone above an interval characterised by martite. which grades downwards via a very irregular base to hypogene iron formation.

The Metalloinvest Annual report, 2012, states JORC compliant proven + probable reserves as follows:
    Lebedinsky - 4.2 Gt of ore at an unspecified grade;
    Mikhailovsky Deposit - 10.7 Gt of ore at an unspecified grade.

The most recent source geological information used to prepare this summary was dated: 1994.    
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 & Additional Information
   Selected References:
Alexandrov E A,  1973 - The Precambrian banded iron formations of the Soviet Union: in    Econ. Geol.   v68 pp 1035-1062

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 takes no responsibility what-so-ever for inaccurate or out of date data, information or interpretations.

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