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Simandou Range - Simandou South (Pic de Fon, Oueleba), Simandou North, Zogota |
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Guinea |
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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.
Available as Full Text for direct download or on request. |
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The Pic de Fon and Ouéléba iron deposits comprise the Simandou South project and are located at the southern end of the 110 km long Simandou Range in south-eastern Guinea, approximately 550 km ESE of Guinea's capital Conakry. The similar Simandou North project deposits are ~70 km north of Simandou South.
(#Location: Pic de Fon 8° 31' 35"N, 8° 54' 2"W).
Significant iron deposits within the Simandou Range are distributed between four title blocks namely Blocks 1 and 2 (Simandou North) and Blocks 3 and 4 (Simandou South). Following initial investigations, Rio Tinto was granted exploration licenses over all four blocks in 1997, covering an area of 1488 km2. The four exploration licenses were renewed in 2000 with a reduced total area of 738 km2. Subsequently, the presence of large high-grade iron ore resources within these blocks was confirmed in 2002. Rio Tinto secured mining concession over deposits in all four blocks in 2006. However, in 2008, it was stripped of the mining rights over Blocks 1 and 2 by the Government of Guinea and the rights transferred to BSG Resources (BSGR), a company owned by Israeli interests. In 2010, the Brazilian company Vale entered into a joint venture agreement with BSGR to acquire a 51% interest in Simandou North. In July 2010, Rio Tinto entered into a joint venture partnership with the Chinese state-owned Chinalco for the development of Simandou South. In December 2010, a newly elected government in Guinea scrutinised past mining agreements for corruption and irregularities. Rio Tinto retained Blocks 3 and 4 under a settlement agreement in 2011. Vale decided to withdraw from Simandou North and after various investigations and court actions BSGR relinquished the Simandou North mining rights. However, it retained the right to mine the smaller Zogota deposit, to the south of Simandou South, and export iron ore via a Liberian rail line route and port under a settlement agreement finalised in February 2019. The Guinea Government launched an international tender for Blocks 1 and 2 in July 2019 and later in the same year awarded the titles to The Société Minière de Boké-Winning (SMB-Winning) a consortium of the Singapore-based shipping company Winning International Group, Chinese aluminum producer China Hongqiao Group, Guinea-based integrated logistics company UMS and China-based Yantai Port Group. In addition, the Republic of Guinea holds a 10% interest in the project.
The north-south trending Simandou South Pic de Fon and Oueleba deposits are 7.5 and 8.5 km in length respectively, up to 1 km wide, and are separated by ~4 km in a north south direction along the Simandou range. At both deposits, the banded iron formations (BISs, also referred to as itabirites) have been enriched to form hematite and hematite-goethite mineralisation.
Little detail of the Simandou North deposit has been encountered.
The iron deposits of the Simandou Range are located in the southern domain of the West African Craton which is exposed in two regions,
i). the Man Shield to the south along the south coast of West Africa in Sierra Leone, Liberia and south-east Guinea, and
ii). the Reguibat Shield to the north in Mauritania and neighbouring Morrocco and Algeria.
These two shield areas are composed of:
i). Cores of Meso to Neoarchaean (3100 to 2500 Ma) crystalline rocks. The Archaean of the Man Shield is a granite-greenstone terrane, which comprises 85% granitoid basement of overall granodiorite composition, but ranging from diorite through tonalite to granite, occurring as granitic gneisses and migmatites, mostly quartz-feldspar-biotite and amphibole bearing, metamorphosed to amphibolite and granulite facies. The greenstones occur as linear infolded, north to NE trending remnants of ultramafic lavas and sills, now serpentinites and chloritic schists, with intercalated amphibolites and altered metasediments; 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, particularly in Ghana, Cote d'Ivoire and Mali on the Man Shield.
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 rocks within the Man Shield are composed of three main components (Egal et al.., 2002):
• an Archaean granitic gneiss basement with Late Neoarchaean to Palaeoproterozoic supracrustal sequences (including the Simandou Group);
• Palaeoproterozoic metasediments and metavolcanics forming the Siguiri Basin in the north; and
• a Palaeoproterozoic plutonic belt, which appears to surround the Arcahaean terranes.
Several large dolerite-gabbro bodies found within the shield have been dated to ~200 Ma, and are possibly related to the initial opening of the Atlantic Ocean (Deckart, Feraud and Bertrand, 1997).
The supracrustal sequences regionally overlying the Archaean domain, which include the Simandou Group, are volcano-sedimentary successions (Billa et al.., 1999) which have been metamorphosed to greenschist to amphibolite facies (Rocci, Bronner and Deschamps, 1991), resting unconformably on crystalline basement (Obermuller and Rocques, 1946; Billa et al., 1999). From bottom to top they comprise, a series of amphibolites, ferruginuous quartzites, cherts, shales and banded iron formations (Rocci, Bronner and Deschamps, 1991; Egal et al., 2002). From SE to NW, supracrustal belts increase in overall thickness although the proportion of banded iron formation and the metamorphic grade both decrease (Rocci, Bronner and Deschamps, 1991). The regional structural fabric rotates from NE trending in the south of the shield to NNW aligned in the north (Rocci, Bronner and Deschamps, 1991). Two phases of deformation dominate, producing subvertical to steeply NW dipping fold axes (Rocci, Bronner and Deschamps, 1991; Billa et al., 1999). Both phases resulted in infolding of Simandou Group rocks into the crystalline basement. D1, produced recumbent isoclinal folding with local transposition of bedding into an S1 foliation and possible thrusting. D2, resulted in upright, open to isoclinal NNE trending folds in a regional sinistral transpressive shear regime. D2 produced the present-day form of the Simandou Range and the marked strain heterogeneity at the deposit scale. Itabirites and shales have been metamorphosed to staurolite-grade itabirite and phyllite respectively, at and near Pic de Fon, and as indicated by a quartz-mica-staurolite schist observed 10 km north of the deposit (Marten, 2000).
On a more local scale, the Simandou Range is composed of metamorphosed supracrustal rocks of the Simandou Group that comprises basal quartzites, ferruginous quartzites, cherts, shales to phyllites and banded iron formations or itabirites. The maximum age of this succession is estimated at 2871 to 2711 Ma based on detrital zircons from a quartzite near the base of the sequence (Thieblemont et al., 1999), although the minimum age is unconstrained by geochronology. However, the rocks are interpreted to have been deformed by the 'Eburnean/Birimian' Orogeny, suggesting they are older than ~2250 Ma (Billa et al., 1999).
The Pic de Fon deposit is composed of selectively enriched iron formation/itabirite, located along a ridge of intensely deformed and strongly weathered Simandou Group rocks, which overlie a biotite granite-gneiss basement. Although stratigraphic relationships have been obscured by polyphase deformation, the sequence appears to comprise a lower phyllite (with minor quartzite) unit, a transitional phyllite-iron formation suite and three overlying itabirite units. In more detail, the stratigraphic succession is, from bottom to top (after: Cope et al., 2005):
• Basal Phyllite - a very fine-grained, dark greenish-grey pelite, with minor intercalations of quartzite, chert and itabirite, and a structural fabric broadly conformable to that of the basement;
• Phyllite - medium to pale greenish-grey, very fine-grained phyllite, locally containing deformed quartz bands/veins;
• Banded phyllite and iron oxide, representing a transition from dominantly medium to dark brownish-red phyllite to itabirite, with thin intercalated bands of iron oxide within phyllite;
• Lower Itabirite - well-defined thin, 0.1 to 3 cm, brown, grey and white bands of phyllite, goethite and silica;
• Middle Itabirite - well-defined thick, 0.6 to 5 cm, grey and white bands of hematite/magnetite and silica;
• Upper Itabirite - poorly-defined to diffuse, thin 0.1 to 1 cm grey and white bands of hematite/magnetite and silica.
Several sub-metre to metre-scale beds of phyllite are interleaved with the itabirite units with sheared contacts, giving the appearance of having been structurally emplaced. The overall thickness of the itabirite package is estimated to be not less than 250 m, and apparently lack any carbonate-bearing lithologies in the Pic de Fon area, nor are any intrusive bodies evident within the deposit itself. The flanks of the ridge on which the Pic de Fon deposit is exposed is flanked to the east and west by significant recent debris flows/talus or 'canga', comprising material derived from the iron formation. These 'canga' accumulations form plateaux of cemented enriched itabirite and represent secondary iron oxide deposits.
The 7.5 x 0.5 to 1 km Pic de Fon deposit has been sub-divided into the three contiguous Northern, Central and Southern ore zones. These higher grade hematite zones are predominantly controlled by, and localised within, deep NNE trending D2 synforms. Enrichment apparently shallowly transgresses stratigraphy, such that ore grade zones form stratabound bodies within the D2 synformal keels. At Pic de Fon, the Middle and Upper Itabirite units have been locally enriched from ~30 to 35% Fe iron formation, to hematite-rich mineralisation with >65% Fe and low deleterious elements. Although the Lower Itabirite unit has also been enriched in the ore zones, it has formed a lower grade goethite-hematite product, possibly due to the greater abundance of phyllite in the protolith. The enrichment of itabirite units is transitional downwards, from >65% Fe hematite-rich, through siliceous hematite rocks to partially- and un-enriched itabirite with <50% Fe. This transition typically occurs over an interval of 10 to 20 m, but may be as much as 50 m.
Where the Lower Itabirite unit is exposed on the flanks of the main ridge, it is capped by a blanket-like hematite-goethite mineralised zone that appears to reflect topography. At surface, a 0.5 to 2 m thick hard cap of weathered goethite-rich carapace caps all of the iron formations, often preserving textural features of the underlying rocks. This carapace is underlain by a 10 to 20 m thick zone with local clay and limonite weathering horizons. This underlying weathered zone may extend to greater depths in fault zones.
Pic de Fon is predominantly composed of high grade haematite with >62% Fe, while Ouéléba has a hematite-goethite mineralogy.
The ore is composed of a variety of hematite textures, which include recrystallised trellis, interlobate and granoblastic hematite after magnetite. In addition, fine-grained bladed to acicular microplaty hematite appears to both replace itabirite banding and to infill porosity. Field relationships indicate that the microplaty hematite development is structurally controlled. Geochemical and related studies indicate that the enrichment of primary itabirite to ore grade mineralisation has resulted from a loss of SiO2 with negligible addition of iron, accompanied by a gradual increase in K, Mg, Na, and lesser Ca and Al (Flis, 2008).
The mineralisation at Pic de Fon is characterised by friable hematite with discrete hard hematite bodies developed within the sheared and deformed sequence of itabirite, phyllite and quartzite. The mineralogy is dominated by hematite, magnetite, goethite and silica, with itabirite protoliths either magnetite- or hematite-rich that have been enriched in the ore zones to an assemblage of hematite and silica. Four main types of hematite ore are differentiated, as follows (after Cole et al, 2005):
• Medium hard hematite - usually banded, will scratch, but cannot be broken by hand. It consists of interbanded martite (i.e., hematite after magnetite) and fine-grained microplaty hematite. The martite and microplaty hematite bands are sharply defined and are thought to reflect the composition of precursor itabirite bands, with microplaty hematite replacing bands of gangue minerals (dominantly silica)
• Hard hematite - which is massive, banded or brecciated, and is apparently the result of the addition of microplaty hematite to the existing intra- and inter-grain porosity of medium-hard hematite.
• Friable biscuity hematite - strongly banded, easily scratched bands that snap but do not rub away between the fingers. This type is martite dominated, but has been cemented by overgrowths of granoblastic hematite which part along discrete microplaty laminae to form biscuits.
• Friable powdery hematite - which usually has weak or no banding that, when present, will rub away between fingers. Like the friable biscuity hematite, this type is also dominated by martite. However, when the biscuits contain less granoblastic hematite then they will disintegrate more readily to powder. The granoblastic hematite generally does not have strained textures or a preferred grain orientation, although where it does, it is apparently axial planar to D2.
Published (Minerals World, Jan 2005) Indicated + Inferred Mineral Resource estimates from the three mining zones outlined at Pic de Fon include:
South Zone - 216 Mt @ 66.96% Fe, 1.18% Al2O3, 1.84% SiO2, 1.13% LOI, 0.021% P.
Central Zone - 296 Mt @ 67.18% Fe, 0.99% Al2O3, 1.92% SiO2, 0.99% LOI, 0.027% P.
North Zone - 490 Mt @ 66.16% Fe, 1.35% Al2O3, 2.77% SiO2, 1.29% LOI, 0.036% P.
Total - 1002 Mt @ 66.63% Fe, 1.21% Al2O3, 2.32% SiO2,1.17% LOI, 0.030% P
Published Mineral Resources for the Simandou South deposits in May 2008 (Rio Tinto, 2008) were:
Pic de Fon
Indicated resource: 320 Mt @ 67.2% Fe,
Inferred resource: 252 Mt @ 66.2% Fe,
Total: 572 Mt @ 66.8% Fe.
Ouéléba
Indicated resource: 980 Mt @ 65.6% Fe,
Inferred resource: 703 Mt @ 65.8% Fe,
Total: 1682 Mt @ 65.7% Fe.
Published Mineral Resources for Simandou South (Blocks 3 and 4 which include Pic de Fon and Ouéléba) at 31 December, 2019 (Rio Tinto Annual Report, 2019) were:
Measured + Indicated + Inferred Mineral Resource: 2.757 Gt @ 65.5% Fe,
No Ore Reserves are quoted as there was no production to that date.
As at 1 January 2020, Simandou South was owned by Simfer S.A., a joint venture between Rio Tinto (45.05%), Aluminum Corporation of China (Chinalco 39.95%) and the Government of Guinea (15%).
Simandou North, Blocks 1 and 2 with resources additional to those quoted above was held as of January 2020, by The Société Minière de Boké-Winning (SMB-Winning) consortium.
Blocks 1 and 2 are estimated to contain an additional ~2 Gt @ 63.5% Fe.
The most recent source geological information used to prepare this decription was dated: 2008.
Record last updated: 8/3/2020
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.
Simandou
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Cope, I.L., Wilkinson, J.J., Boyce, A.J. , Chapman, J.B., Herrington, R.J. and Harris, C.J., 2008 - Genesis of the Pic de Fon iron oxide deposit, Simandou Range, Republic of Guinea, West Africa: in Banded iron formation-related high-grade iron ore. Reviews in economic geology, 15, Society of Economic Geology, pp. 339-360.
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Cope, I.L., Wilkinson, J.J., Herrington, R.J. and Harris, C.J., 2005 - Geology and Mineralogy of the Pic de Fon Iron Oxide Deposit, Simandou Range, Republic of Guinea,West Africa: in Proceedings, Iron Ore 2005 Conference, Perth, WA, September 19-20, 2005, The AusIMM, Melbourne, Publication Series 8, pp. 1-6.
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Flis, M.F., 2008 - Advances in geophysics applied to the search for banded iron formation-related, high-grade hematite iron ore: in Hagemann S, Rosiere C, Gutzmer J and Beukes N J, (eds.), 2008 Banded Iron Formation-Related High-Grade Iron Ore, Reviews in Economic Geology, v.15 pp. 381-391
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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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