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Guelb Moghrein, Akjoujt District |
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Mauritania |
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Fe Cu Au
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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 Guelb Moghrein copper-gold deposit is located 3.5 km WNW to the town of Akjoujt, and ~250 km northeast of Nouakchott, the capital of the Islamic Republic of Mauritania. It is a carbonate associated member of the Iron-oxide copper-gold (IOCG) family of deposits (#Location: 19° 45' 1"N, 14° 25' 30"W).
Copper tools and arrow heads dating from ~6000 to 4000 BCE have been found in the Akjoujt area of Mauritania where Guelb Moghrein is located. Whilst exploitable tonnages of copper were recognised in the 1930s it was not until the 1950s when serious plans for exploitation were made. In the 1970s an open pit was developed and a high temperature oxide roast metallurgical operation commenced, but had to close in 1977 due to technical difficulties and high fuel prices. Subsequently, attempts were made to recover gold, without significant success. Exploration was undertaken by a number of companies, culminating in the outlining of a resource and in November 2004, an asset sale agreement signed with the government. Site establishment and construction commenced in March 2005, and commercial production was achieved in October 2006, with 0.4 Mt of ore mined in the first and 2.3 Mt in the subsequent year. Operations were briefly suspended in both 2012 and 2014 due to protests and strikes. The mine is operated (to at least 2021) by Mauritanian Copper Mines S.A which is a subsidiary of First Quantum Minerals Ltd of Canada. In October 2009, the mining capacity was increased to 3.8 Mt of ore per annum at a strip ratio of 3:1. The processing plant was further upgraded during 2014 to a planned processing rate for 2015 of 4.0 Mt of ore per annum (First Quantum NI 43-101 Technical Report 2016). Production in 2020 totalled 3.788 Mt @ 0.85% Cu, with a Cu recovery of 89% to produce 28&nbep;491 t of Cu and 1.482 t of gold and 0.5796 Mt of magnetite concentrate (First Quantum website, 2021). Total production between 2006 and 2015 inclusive was 131.3 Mt of waste plus 29 Mt of ore averaging 1.4% Cu, of which 25.0 Mt had been processed to produce 0.3294 Mt of Cu and 17.2 t of Au (First Quantum NI 43-101 Technical Report 2016).
Guelb Moghrein is located within the Mauritanides Orogenic Belt which extends along the West African coast from Senegal to Western Sahara. The Mauritanides belt is generally interpreted to represent a pile of allochthonous terranes lying unconformably onto the western margin of the West African Craton. A thrust zone ~30 km to the NE of Akjoujt marks the boundary between the Mauritanides gneisses and granulites of the Amsaga Basement, which forms part of the ~3.5 Ga Archaean Reguibat Shield, and the Neoproterozoic to Devonian Taoudéni Basin (Villeneuve, 2005). Meyer et al. (2006) and Kolb et al. (2006) concluded that the supracrustal rocks in the Akjoujt region resemble Archaean greenstone belts that have been structurally emplaced onto the West African Carton at ~300 Ma as a result of the collision of Gondwana and Laurentia. The deposit is located within a thrust zone of strong deformation that parallels the regional WNW structural trend.
The Akjoujt area features a supracrustal stratigraphy that is currently believed to consist of two distinct lithological groups separated by an unconformity. The wall rocks to the Guelb Moghrein mineralisation belong to the Oumachoueima Group, representing the uppermost part of the stratigraphy. The oldest rocks at Guelb Moghrein, the Sainte Barbe volcanic unit, is composed of meta-rhyodacite to meta-dacite with volcanic and volcaniclastic fabrics, and minor meta-sediments, with a whole rock geochemistry suggesting an origin in a continental or island arc setting (Kolb et al., 2008). They are capped by a widespread BIF/chert marker, the Lembeitih Formation, to which the host meta-carbonate rocks of Guelb Moghrein may belong. This marker horizon is, in turn, structurally overlain by the thick Akjoujt Metabasalt unit, which has tholeiitic to andesitic compositions and trace element patterns typical of formation in a volcanic arc setting. In the pit area, a thrust zone separates the meta-rhyolitic rocks of the St. Barbe Volcanic unit from the overlying metabasaltic-andesitic unit of the Akjoujt Metabasalt unit. The supracrustal assemblage of the Akjoujt area represents a typical Archaean succession that probably formed marginal to an Archaean block that may be represented by the Reguibat Shield in the northeast (Kolb et al., 2006).
The ore is hosted by breccias in meta-carbonate and Fe-Mg clinoamphibole-chlorite schist occurring as multiple, coalescing lenses that are about 30 m wide, and broadly elongate in the direction of D2 reverse shear zones.
The dominant host rock at Guelb Moghrein is a massive, very coarse-grained, dark-grey meta-carbonate, which is mainly composed of euhedral to anhedral Fe-Mg carbonate up to 5 cm in diameter, with accessory magnetite and graphite. Locally within the meta-carbonate body, Fe-Mg clinoamphibole-chlorite schists occur as narrow, up to 1 m wide layers, which generally comprise up to 90 vol.% chlorite, with minor Fe-Mg clinoamphibole, magnetite, ilmenite, apatite, calcite, quartz, monazite and allanite. In places, the Fe-Mg clinoamphibole may dominate the mineral assemblage.
Two types of monomict breccias have been distinguished:
i). 'Jigsaw' breccias, locally, occurring as up to 5 cm wide and up to 20 cm long lenses in the Fe-Mg clinoamphibole-chlorite schist, with 50 to 200 µm diameter clasts composed of angular fragments of chlorite and Fe-Mg clinoamphibole in a massive sulphide matrix;
ii). A pebble-like breccia in the meta-carbonate, consisting of rounded, pebble-like Fe-Mg carbonate clasts within a matrix of a complex arsenide-sulphide-gold, magnetite and Fe-Mg clinoamphibole assemblage - the clast:matrix ratio and the fragment size increase systematically outward. In the central part of the breccia, massive sulphides contain <3% clasts and form a matrix-supported breccia. The Fe-Mg carbonate clasts are up to 1 cm in diameter and have a rounded to sub-rounded shape due to replacement by sulphides, magnetite and Fe-Mg clinoamphibole on their rims. Locally, the massive sulphide matrix is cut by pyrrhotite veinlets with a comb texture, implying repeated fracturing during progressive brecciation. Euhedral magnetite and Fe-Mg clinoamphibole dominate the matrix over a distance of about 0.2 to 1 m from the central massive-sulphide breccia.
The hydrothermal mineralisation is hosted by the breccias. The ore mineral assemblage comprises magnetite, pyrrhotite, chalcopyrite, Fe-Co-Ni arsenides, arsenopyrite, cobaltite and Bi-Au-Ag-Te minerals. The Fe-Mg clinoamphibole-chlorite schist locally contains breccias with an ore assemblage similar to that found in the brecciated meta-carbonate.
The Cu-Au mineralisation in the main (Occidental) deposit is hosted primarily within chalcopyrite and pyrrhotite, with Magnetite becoming abundant outside the sulphide rich zones of the ferromagnesian carbonates. This deposit extends approximately for 600 m along strike and dips to the southwest at 30 to 40°. The eastern and western flanks of the deposit are fault bounded and the deposit is open at depth.
Strickland and Martyn (2002), during advanced exploration, quoted total measured + indicated resource at 23.6 Mt @ 1.88 % Cu, 1.41 g/t Au and 143 ppm Co.
In 2007, 2.3 Mt of ore @ 1.4% Cu and 5.8 Mt of waste were mined, for 28 755 t of Cu and 3 t of Au in concentrate.
In March 2008, remaining Mineral Resources were (First Quantum NI 43-101 Technical Report 2016) were:
Measured + Indicated Resources, Sulphides - 33.02 Mt @ 1.49% Cu, 1.10 g/t Au;
Measured + Indicated Resources, Oxides - 0.37 Mt @ 2.85% Cu, 2.39 g/t Au;
TOTAL Measured + Indicated Resources - 33.39 Mt @ 1.51% Cu, 1.11 g/t Au;
TOTAL Inferred Resources - 2.45 Mt @ 1.37% Cu, 0.73 g/t Au.
Published ore reserves and mineral resources at December 31, 2012 (First Quantum website, 2013) were:
Proved reserve - 10.098 Mt @ 1.24% CuT, 0.70 g/t Au (0.46% Cu Equiv. cut-off);
Probable reserve - 15.631 Mt @ 0.93% CuT, 0.70 g/t Au (0.46% Cu Equiv. cut-off);
Proved high grade stockpile - 3.457 Mt @ 1.19% CuT, 0.79 g/t Au (0.46% Cu Equiv. cut-off);
TOTAL reserve - 29.186 Mt @ 1.05% CuT, 0.74 g/t Au;
Measured + indicated sulphide resource - 28.90 Mt @ 1.14% CuT, 0.68 g/t Au (0.5% Cu cut-off);
Inferred sulphide resource - 3.40 Mt @ 1.05% CuT, 0.65 g/t Au (0.5% Cu cut-off).
Measured + indicated oxide resource - 0.20 Mt @ 1.77% CuT, 1.01 g/t Au (0.5% Cu cut-off);
Inferred oxide resource - 4.10 Mt @ 0.90% CuT, 0.78 g/t Au (0.5% Cu cut-off).
In December 2015, remaining Mineral Resources were (First Quantum NI 43-101 Technical Report 2016) were:
Measured + Indicated Resources, Sulphides - 36.07 Mt @ 0.83% Cu, 0.68 g/t Au;
Measured + Indicated Resources, Oxides - 7.51 Mt @ 0.86% Cu, 0.74 g/t Au;
TOTAL Measured + Indicated Resources - 43.57 Mt @ 0.84% Cu, 0.69 g/t Au;
TOTAL Inferred Resources - 2.40 Mt @ 0.76% Cu, 1.95 g/t Au.
In December 2020, remaining Reserves and Resources were (First Quantum website, viewed July 2021) were:
Measured + Indicated Resources, Sulphides - 16.8 Mt @ 0.77% Cu, 0.61 g/t Au;
Measured + Indicated Resources, Oxides - 0.50 Mt @ 0.78% Cu, 0.84 g/t Au;
TOTAL Measured + Indicated Resources - 17.3 Mt @ 0.77% Cu, 0.61 g/t Au;
TOTAL Inferred Resources - 1.90 Mt @ 0.75% Cu, 1.72 g/t Au
TOTAL Proved + Probable Reserves - 7.0 Mt @ 0.50% Cu, 0.51 g/t Au.
Guelb Moghrein is the subject of papers in the monograph: "Hydrothermal Iron Oxide Copper-Gold & Related Deposits: A Global Perspective" volumes 2 and 3, published by PGC Publishing, Adelaide, Australia.
The full Abstracts of these papers can be displayed by selecting Vol 2 and Vol 3.
For detail consult these papers or other reference(s) listed below
The most recent source geological information used to prepare this decription was dated: 2002.
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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Kirschbaum, M.J. and Hitzman, M.W., 2016 - Guelb Moghrein: An Unusual Carbonate-Hosted Iron Oxide Copper-Gold Deposit in Mauritania, Northwest Africa: in Econ. Geol. v.111, pp. 763-770.
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Kolb J, Meyer F M, Vennemann T, Sindern S, Prantl S, Bottcher M E and Sakellaris G A, 2010 - Characterisation of the Hydrothermal Fluids of the Guelb Moghrein Iron Oxide-Cu-Au-Co Deposit, Mauritania: Ore Mineral Chemistry, Fluid Inclusions and Isotope Geochemistry: in Porter T M, (Ed), 2010 Hydrothermal Iron Oxide Copper-Gold and Related Deposits: A Global Perspective PGC Publishing, Adelaide v.4 pp. 553-572
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Kolb J, Sakellaris G A and Meyer F M, 2006 - Controls on hydrothermal Fe oxide Cu-Au-Co mineralization at the Guelb Moghrein deposit, Akjoujt area, Mauritania: in Mineralium Deposita v41 pp 68-81
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Kolb, J., Meyer, F.M., Vennemann, T., Hoffbauer, R., Gerdes, A. and Sakellaris, G.I., 2008 - Geological setting of the Guelb Moghrein Fe oxide-Cu-Au-Co mineralization, Akjoujt area, Mauritania: in Geological Society, London, Special Publication, 297, pp. 53-75. doi.org/10.1144/SP297.4.
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Martyn J, Strickland C, 2004 - Stratigraphy, structure and mineralisation of the Akjoujt area, Mauritania: in J. of African Earth Sciences v38 pp 489-503
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Meyer F M, Kolb J, Sakellaris G A and Gerdes A, 2006 - New ages from the Mauritanides Belt: recognition of Archean IOCG mineralization at Guelb Moghrein, Mauritania : in Terra Nova v18 pp 345-352
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Skirrow, R.G., 2021 - Iron oxide copper-gold (IOCG) deposits - a review (part 1): settings, mineralogy, ore geochemistry, and classification within the Cu-Au-Fe (±Co, REE) deposit family: in Preprint accepted Nov 2021, for Ore Geology Reviews, 71p. doi.org/10.1016/j.oregeorev.2021.104569
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Strickland C D and Martyn J E 2002 - The Guelb Moghrein Fe-Oxide Copper-Gold-Cobalt Deposit and Associated Mineral Occurrences, Mauritania: A Geological Introduction: in Porter T M (Ed.), 2002 Hydrothermal Iron Oxide Copper-Gold and Related Deposits: A Global Perspective, PGC Publishing, Adelaide v.2 pp. 275-291
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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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