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Controls on hydrothermal Fe oxide–Cu–Au–Co mineralization at the Guelb Moghrein deposit, Akjoujt area, Mauritania

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Abstract

The Guelb Moghrein Fe oxide–Cu–Au–Co deposit, with a total resource of 23.6 Mt at 1.88% Cu, 1.41 g/t Au, and 143 g/t Co, is hosted by an extensive metacarbonate body. However, it is restricted to up to 30-m wide tabular breccia zones developed parallel to discrete shear zones that transect the host metacarbonates. The Fe–Mg clinoamphibole–chlorite schists represent up to 1-m thick interlayer metasediments and localized viscous shearing in these shear zones. Siderite of the metacarbonate body was deformed into a breccia and was replaced by an ore and alteration assemblage comprised of Fe–Mg clinoamphibole, magnetite, pyrrhotite, chalcopyrite, graphite, Fe–Co–Ni arsenides, arsenopyrite, cobaltite, uraninite, and Bi–Au–Ag–Te minerals. In contact with wall rock amphibolites, the metacarbonate body is enveloped by an alteration halo up to 40 m wide, consisting of biotite, actinolite, grunerite, chlorite, calcite, albite, and quartz. The Guelb Moghrein ore body is structurally controlled by shear zones that developed in the footwall of a regional thrust zone. This thrust separates greenschist facies quartz–sericite schists and biotite–garnet–quartz schists of the Sainte Barbe volcanic unit in the hanging wall from amphibolite facies metavolcanic rocks, metacarbonates, and the Guelb Moghrein ore body of the Akjoujt metabasalt unit in the footwall. Peak temperatures of the latter unit are estimated by hornblende–plagioclase thermometry at 580±40°C. Thrusting was retrograde for the Akjoujt metabasalt unit, but prograde for the Sainte Barbe volcanic unit at P–T conditions of about 410±30°C and 2–3 kbar (garnet–biotite thermometry). Structural and petrological evidences suggest that the ore fluids migrated along the shear zones and reacted with the siderite in the metacarbonate. This evolution and the setting of Guelb Moghrein in the fold-and-thrust belt of the Pan-African to Variscan Mauritanides (Mauritania, West Africa) resemble Proterozoic Fe oxide–Cu–Au–Co deposits such as examples from the Tennant Creek and Mount Isa Inliers, Australia.

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Acknowledgements

The authors would like to thank Mohamed El Moctar O. M. El Hacen (Deputy General Manager, GEMAK, Nouakchott) and Aboubekrine O. A. dit Ebaye (Director MORAK, Akjoujt) for their support in Mauritania and the permission to publish the results of this study. Dr. Karsten Eden is thanked for fruitful discussions about the deposit from which this manuscript greatly benefited. A. Dziggel is thanked for comments on an earlier version of this manuscript. Thorough reviews from Y. Watanabe and M. Jébrak helped greatly to improve the manuscript. This study was made possible through grant Me 1425/6-1/2 of the Deutsche Forschungsgemeinschaft.

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  1. Institute of Mineralogy and Economic Geology, RWTH Aachen University, 52056, Aachen, Germany

    Jochen Kolb, Gregori A. Sakellaris & F. Michael Meyer

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  1. Jochen Kolb
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  2. Gregori A. Sakellaris
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Correspondence to Jochen Kolb.

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Kolb, J., Sakellaris, G.A. & Meyer, F.M. Controls on hydrothermal Fe oxide–Cu–Au–Co mineralization at the Guelb Moghrein deposit, Akjoujt area, Mauritania. Miner Deposita 41, 68–81 (2006). https://doi.org/10.1007/s00126-005-0041-7

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