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Guelb Moghrein, Akjoujt District

Mauritania

Main commodities: Fe Cu Au
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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).

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 belongs 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, overlain by the thick Akjoujt meta-basalt unit, which has tholeiitic to andesitic compositions and trace element patterns typical of formation in a volcanic arc setting. 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.

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.

Total remaining measured and inferred resource in 2008 were 33.4 Mt @ 1.12% Cu and 1.41 g/t Au (First Quantum website).

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.

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% Cu
T, 0.70 g/t Au (0.46% Cu Equiv. cut-off);
    Proved high grade stockpile - 3.457 Mt @ 1.19% Cu
T, 0.79 g/t Au (0.46% Cu Equiv. cut-off);
  TOTAL reserve - 29.186 Mt @ 1.05% Cu
T, 0.74 g/t Au;
    Measured + indicated sulphide resource - 28.90 Mt @ 1.14% Cu
T, 0.68 g/t Au (0.5% Cu cut-off);
    Inferred sulphide resource - 3.40 Mt @ 1.05% Cu
T, 0.65 g/t Au (0.5% Cu cut-off).
    Measured + indicated oxide resource - 0.20 Mt @ 1.77% Cu
T, 1.01 g/t Au (0.5% Cu cut-off);
    Inferred oxide resource - 4.10 Mt @ 0.90% Cu
T, 0.78 g/t Au (0.5% Cu cut-off).

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 summary 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.


  References & Additional Information
   Selected References:
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.
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
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
Martyn J, Strickland C,  2004 - Stratigraphy, structure and mineralisation of the Akjoujt area, Mauritania: in    J. of African Earth Sciences   v38 pp 489-503
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
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

   References in PGC Publishing Books: Want any of our books ? Pricelist
Strickland C, 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.),  Hydrothermal Iron Oxide Copper-Gold & Related Deposits: A Global Perspective,  v2  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 takes no responsibility what-so-ever for inaccurate or out of date data, information or interpretations.

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