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Tiris - Guelb El Rhein, Aouj, Askaf, Atomai, M Haoudat, Kedia d Idjill, Tazadit TO14, Lebtheinia |
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Mauritania |
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Fe
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Super Porphyry Cu and Au
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IOCG Deposits - 70 papers
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All papers now Open Access.
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The Tiris iron operations of the Societé Nationale Mauritanienne Industrielle et Miniere (SNIM) are centred on the mining centre of Zouerate in north western Mauritania. Zouerate is connected to the Atlantic Ocean port of Nouadhibou by a 700 km railway.
The Tiris operation is located in the northern part of the West African Craton which is exposed in two regions, i). the Man Shield to the south along the south and southwest coast of West Africa in Sierra Leone, Liberia and south-east Guinea, and ii). the Reguibat Shield, which has been stable since 1700 Ma, to the north in Mauritania and neighbouring Morrocco and Algeria.
These two shield areas are composed of: i). Cores of Archaean (3100 to 2500 Ma) crystalline rocks. The Archaean of the Man Shield is a granite-greenstone terrane, while the Reguibat Shield is predominantly composed of migmatites, gneisses, granitoids, ferruginous quartzites and banded iron formation (BIF), with charnockitic pyroxeno-amphibolites, sillimanite gneisses, marbles and feldspathic gneisses which are locally granulite terranes; and ii). Eastern blocks of Paleoproterozoic (2000 ±200 Ma) 'Eburnean/Birimian terranes', predominantly composed of intrusive granites in the west and volcanic formations in the east.
The Man and Reguibat shields are separated by the broad, shallow 'down-sag', Taoudeni Basin infilled by Neoproterozoic to Devonian continental to shallow marine sedimentary strata unconformably overlying the crystalline basement represented by the shields to the north and south. The Taoudeni Basin sequence does not exceed 5000 m in thickness, and though it varies locally, is a very homogenous lithological sequence.
The craton, including the Man and Reguibat shields and the Taoudeni Basin are bounded to the north, east and west by Pan-African (late Neoproterozoic) mobile belts, and to the west by a the superimposed Hercynian mobile belt of the Mauritanides.
The Tiris iron ore deposits, both hematite enriched and primary magnetite BIFs are within the western Archaean core of the Reguibat Shield. The Archaean basement of this shield is up to 10 km thick. The ferruginous quartzites and BIFs that characterise the western section of the Reguibat Shield are absent from the central (Archaean) and eastern (Paleoproterozoic) segments of the shield.
Two iron bearing sequences are found within the Tiris-Zouerate district, both of which formed on the Reguibat Shield, namely: (i) those of the Archaean Tiris iron formation Group and (ii) the Palaeoproterozoic Koedia-Idjill iron formation group. The deposits of the Tiris iron formation are considered to probably be a clastic sedimentary deposit derived from an Algoma-type BIF, while the deposits of the Koedia-Idjill iron formation group are Superior-type BIF.
The Tiris group is composed of amphibolites, meta-ferruginous quartzite and leptinite (medium to coarse-grained granoblastic to gneissic felsic granulites) formed from Archaean clastic protoliths. The iron ore deposits of the Tiris group consist of coarse-grained magnetite orebodies in meta-ferruginous quartzite (BIF). The ore is mainly composed of coarse-grained magnetite with average grades ranging from 35 to 42% of Fe, amenable to enrichment to 65 to 66% of Fe by magnetic separation.
The Idjill group has been thrust over the Tiris group as a large scale nappe. The nappe composed of seven leaves comprising the: El Hadej, La Breche (includes orthoquartzites containing pebbles and gravels cemented with iron oxides and silica), L'Achouil (pelitic schists), Tazadit (banded iron formation, lacking clastic rocks), Zouerate, Hamariat and M'Haoudat (basaltic schist and meta-basalt) units. The iron formations of the Idjill group are predominantly within in the Tazadit unit. These iron formations are interspersed with schists and nonferrous quartzite. This iron formation package has a thickness that ranges from 300 to 2000 m, and extends over a strike length of up to 30 km. It comprises siliceous phyllite, siliceous iron formation (35 to 45% Fe) and hematite-bearing iron formation (63 to 64% Fe) in its lower sections. The hematite-bearing ore bodies are ~150 m thick, generally with bands that are several millimetres thick. The high-grade ore is found in concentrated layers of fine-grained platy hematite with 67 to 68% Fe in the largest open pit at Tazadit over a length of ~700 m, width of 500 m and depth of 500 m.
The geology of the main deposits include:
El Rhein which is predominantly composed of magnetite, and is located 25 km northeast of Zouerate. The district around the deposit consists of meta-ferruginous quartzite (banded magnetite iron formations), meta-nonferrous quartzite, gneiss, leptinite and amphibolite of the Mesoarchaean Tiris group. The meta-ferruginous quartzite crops out as a tableland 100 to 200 m above the surrounding desert, extending over a length of 5 to 10 km and 2 to 3 km in width. The ore body comprises coarse-grained magnetite in leptinite. The ore body is ~100 m thick, with a north-south strike length of 1.2 km and has an average grade 37% Fe. The 80 to100 m thick magnetite ore zone of this deposit represents a complex, 1.5 x 1 km. north-south elongated structure characterised by intrafolial folding, with north-south trending fold axes and evidence of three deformation events. The ore is coarse grained and lumpy, mainly composed of magnetite and quartz with a little hematite and goethite. K-Ar dating of potassium feldspar and whole rock of the leptinite collected from this deposit indicate the same value of 1480±40 Ma in the Mesproterozoic), taken to represent the final phase of metamorphism.
Guelb El Aouj, includes the East and Central deposit is also predominantly of magnetite and is located 40 km northwest of Zouerate. The area around the deposit consists of meta-ferruginous quartzite, meta-white quartzite, leptinite and amphibolite of the Mesoarchaean Tiris group. Mineralisation is coarse-grained magnetite hosted by meta-ferruginous quartzite, representing a highly metamorphosed banded iron formation unit 100 to 200 m thick, in which the original bedding has been partially to completely obliterated by recrystallisation, resulting in a coarse-grained texture with aggregated magnetite grains. The deposit has a leptinite footwall and a hanging wall of amphibolitic garnetiferous gneiss, locally magnetite-rich. The magnetite-bearing quartzite defines a NE-SW-trending anticlinal structure covering a 4 x 1 km north-south elongated area. The south west limb is characterised locally by the presence of thin (mostly <6m) concordant granite intrusions within the main magnetite quartzite unit, particularly in its upper part. This unit contains occasional lenses of lower grade magnetite-bearing quartzite (QMM). Two near-vertical dolerite dykes and one large, north block down normal fault (the Central Fault) were mapped in 2003 and cross-cut the deposit. The geological sequence is overprinted by a reasonably uniform, 30 to 40 m thick weathered zone in which much of the magnetite has oxidised to hematite (as martite). The weathered zone is not included in the Mineral Resource estimate (Sphere Minerals, 2012).
Askaf North is located 35 km south of Guelb El Aouj and occurs as an east-west striking synformal structure defined by a magnetite-quartzite unit of the Mesoarchaean Tiris Group. The magnetite-quartzite ranges in true thickness from ~140 m in the western hinge zone to approximately 30 m along the eastern part of the southern limb. The synformal axis plunges at between 20 to 30° towards the east in the western part of the synform, and at about 35 to 45° towards the west at the eastern fold closure, producing a double plunging synform. A dolerite dyke has been emplaced along an east-west fault zone that displaces the northern part of the deposit in a dextral shear sense. The disruption and emplacement of the dolerite along the northern limb of the synform has not affected the quality of the mineralisation. The magnetite-quartzite unit represents a metamorphosed banded iron-formation (BIF). The precursor BIF was subjected to high-grade metamorphic conditions during the Archaean, which resulted in complete recrystallisation of the original fine-grained BIF. In most cases the primary textures have been destroyed by the recrystallisation. Coarse-grained (>1mm) magnetite-quartzite is produced as a result, with good Davis Tube liberation characteristics and concentrate grades at a relatively coarse grain size (95% passing 80 µm) (Sphere Minerals, 2012).
Atomai which is also a magnetite deposit, located in 35 km west of Zouerate. The district surrounding the deposit hosts meta-ferruginous quartzite, meta-white quartzite and leptinite of the Mesoarchaean Tiris group, with a partial intrusion of aplite. The deposit is coarse-grained magnetite hosted by meta-ferruginous quartzite. Magnetite-bearing quartzite commonly strikes east-west and dip steeply to the north. It crops out within an area of total length of 8 km and 0.5 km width.
Kedia d'Idjill deposits of Tazadit, Seyala, Rouessa and F'Derik - representing the first hematite mineralisation discovered (hosted by the Palaeoproterozoic Idjill group), occuring largely as ridges of hematite mineralisation located in 5 to 30 km south of Zouerate. The periphyry to these deposits occurs as a peneplain at approximately 300 m asl, composed of the Archaean Tiris group. These deposits occur within the Koedia-Idjill mountain range, generally at 500 to 600 m asl, although the highest peak is at 915 m, representing nappes of the Palaeoproterozoic Idjill group. These deposits are principally composed of hematite, within the Tazadit unit, one of the nappes of the Idjill group. The iron formation is predominantly composed of banded hematite-bearing quartzite, accompanied by schist and nonferrous quartzite. The thickness of the iron formation ranges from 300 to 2000 m and comprises siliceous phyllite, siliceous ironstone (60 m thick with 35 to 45% Fe) and hematite-bearing iron formation (150 m thick with 63 to 64% Fe) from the lower layer. The iron formation generally strikes east-west and develops repetitive isoclinal folds, dipping south at moderate to steep angles. Ore bodies are up to 700 x 500 m and are generally conformable with the Tazadit unit. They are lenticular, containing ~65% of Fe composed of platy hematite with goethite, with massive pocket-shaped hematite bodies of up to 68% of Fe. The iron formation comprises 1 to 2 mm thick band of fine hematite and quartz. The high grade ore with >67% Fe has a distinctively pale blue colouration. Under the microscope, hematite can be seen to replace primary magnetite. K-Ar dating of muscovite in weakly weathered muscovite schist from Guelb Hamariat located in 4 km northeast of the Rouessa deposit, shows 2407±67.7 Ma, although potassium dissolution is recognized in this sample. Other samples of muscovite and biotite retuen ages of 1754±38 Ma and 1850±50 Ma interpretted to corresponds to the last stage of Superior-type BIF formation.
M'Haoudat - occurring as a ridge containing four steeply dipping, lens-shaped direct shipping hematitic bodies located in 55 km northeast of Zouerate, hosted by the M'Haoudat unit another of the nappes of the Palaeoproterozoic Idjill group. The M'Haoudat unit comprises intercalated ferruginous quartzite, non-ferruginous quartzite and schist. The ferruginous quartzite strikes NW-SE and dips steeply to the northeast, extending within an area of 15 km in length and 200 m in width. The iron ore bodies are lenticular with pockets of >60% Fe occurring as foliated and massive hematite within the ferruginous quartzite. The principal ore body is 1200 m long and 100 m wide. Under the microscope, the banded texture is seen to be composed of quartz and hematite laminae where hematite replaces magnetite. Rb-Sr model whole rock dating of metabasalt of the Tazadit unit returns ages of 2363 to 2255 Ma.
Tazadit TO14 - in the Kedia area, also direct shipping hematite ore of the Palaeoproterozoic Idjill group;
Lebtheinia which is over 550 km to the WSW of the main Tiris mines, and only 90 km from the Atlantic Coast port of Nouadhibou. The deposit is hosted by the Mesoarchaean Lebzenea Group, exposed over a total strike length of ~24 km, occurring as less prominent topographical features in a more gentle terrain in comparison to the more rugged inselberg (guelb) terrain of the Guelb el Aouj region in the interior. Parts of the main BIF unit at Lebtheinia Centre are covered by laterite and colluvium, mostly composed of BIF fragments (detrital/canga). The lateritic cover caps the most elevated parts of the terrain. The magnetite-BIF at Lebtheinia Centre is essentially a thinly banded unit averaging ~240 m thick (locally up to 320 m). The BIF is characterised by a well defined banding pattern, with individual mesobands averaging 5 to 10 mm thick. The exposed BIF is reasonably homogeneous along the entire strike length, with mineralisation extending to depths of at least 400 m below the natural surface. Lebtheinia Centre comprises a hanging wall of (variously) quartzite, amphibolite, rhyolite, clay/saprolite (altered amphibolite) and a footwall of quartzite or amphibolite. The depth and degree of weathering (oxidation) of the BIF is variable, averaging ~50 m. In the southern part of Lebtheinia Centre, the main mineralised BIF unit splits and forms two discrete units separated by a relatively thin (~25 m) internal waste zone comprising grey quartzite and a leucocratic quartz feldspar schist/mylonite. A series of sub-vertical dolerite dykes,
striking NE-SW to NNE-SSW, crosscut the BIF (Sphere Resources, 2012).
The direct shipping Tiris hematite deposits contain 60 to 68% Fe, while the magnetite ores are 36% to 40% Fe.
The company Miferma (Mines de Fer de Mauritanie) was created in 1952 to exploit the iron ore deposits at Kedia d'Idjil. Mining commenced in 1963. Production initially concentrated on the Kedia d'Idjill hematite ores and expanded to an output of 12 Mt per annum. By 1973, as the hematite reserves were declining, focus changed to mining and upgrading the Guelb Rhein magnetite ores to the NNE of Zouerate. In 1974-5 Miferma was partially nationalised to form SNIM (78% owned by the Mauritanian government in 2000). Production commenced at M'Haoudat and TO14 hematite deposits, 50 km to the east, in 1991. By 1997, the operation had exported a cumulative total of 300 Mt of direct shipping and upgraded ore. In 2004, SNIM mined 10.7 Mt of ore and shipped 11 Mt of product, approximately 60% direct-shipping hematite, with 40% concentrates. The operation produces 0 to 90 mm and 8 to 30 mm lump ores, sinter fines and high-phosphorus concentrates.
Iron ore reserves (unspecified class of reserves) of SNIM operations (Mauritanian Office of Geological Exploration website, 2012) were:
Tazadit T014 - 170 Mt @ 67% Fe hematite ore,
M'Haoudat - tonnage not available @ 66% Fe hematite ore,
El Rhein - 342 Mt @ 37% Fe magnetite ore,
El Aouj - 287 Mt @ 40% Fe magnetite ore,
Atomai - 616 Mt @ 36% Fe magnetite ore.
Mineral Resources at 31 December, 2011, published by Sphere Minerals/Xstrata (ASX Release, Feb. 2012) were:
Guelb el Aouj East - Measured + indicated resources - 501 Mt @ 36.3% Fe, for Davis Tube Concentrate assay of 70.1% Fe,
Guelb el Aouj East - Inferred resources - 200 Mt @ 36.3% Fe, for Davis Tube Concentrate assay of 70.2% Fe,
Guelb el Aouj Centre - Inferred resources - 225 Mt @ 36% Fe, for Davis Tube Concentrate assay of 70.6% Fe,
Guelb el Askaf North - Measured + indicated resources - 291 Mt @ 35.7% Fe, for Davis Tube Concentrate assay of 70.1% Fe,
Guelb el Askaf North - Inferred resources - 104 Mt @ 35.8% Fe, for Davis Tube Concentrate assay of 70.1% Fe,
Guelb el Lebtheinia - Measured + indicated resources - 2179 Mt @ 32.3% Fe, for Davis Tube Concentrate assay of 68.6% Fe,
Guelb el Lebtheinia - Inferred resources - 354 Mt @ 32.4% Fe, for Davis Tube Concentrate assay of 68.1% Fe
Much of the information on this page is summarised from the website of the Mauritanian Office of Geological Exploration, and Sphere Minerals/Xstrata ASX Releases.
The most recent source geological information used to prepare this decription was dated: 2012.
Record last updated: 28/10/2012
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.
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Cooper, G., Lapointe, R. and Routhier, J., 2011 - The SNIM Guelb II Project in Mauritania - Process Design Challenges: in Proceedings, Iron Ore 2011 Conference, 11-13 July 2011, Perth, Western Australia, The Australasian Institute of Mining and Metallurgy, Melbourne, pp. 11-16
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