## 2 Materials and Methods
### Geological Context of the Deposit and Mineralization  
The Guelb Moghrein IOCG mineralization, located in the West African Craton, shares several similar characteristics with other deposits around the world such as the IOCG deposits in northeastern Australia, namely the Osborne, Starra and Ernest Henry deposits, and the Salobo deposit in Brazil [1; 2; 3; 4; 5; 6; 7; 8; 9; 10; 11; 12; 13; 14; 15]. The lithostriagraphy of the supracrustal rocks in the Akjoujt area belongs to the Mauritanide greenstone series, which consists of two lithological sequences of Archean age, and is separated by an angular unconformity. The lower sequence known as the Eizxene group follows the basement rocks and is unconformably overlain by the Oumachoueima group. Detailed open pit mapping in Figure 2 shows that the main lithologies at Guelb Moghrein are metasedimentary and metavolcanic rocks of the Sainte Barbe volcanic unit and metabasalts of the Akjoujt unit. A metacarbonate (FMC) body that contains the IOCG orebody is associated with the Akjoujt meta-basalt unit. In contact with wall-rock amphibites, the FMC body is enveloped by an alteration halo up to 40 m wide, corresponding to an extent of Fe-Mg clino-amphibole alteration and consisting of biotite, actinolite, grunerite, chlorite, calcite, albite, and quartz [3; 7]. From a structural point of view, the Akjoujt area is made up of a complex set of folded and stacked thrust sheets. Five deformation events (D1 to D5) and related metamorphic overprints are distinguished [3; 46; 47]. The D1 deformation mainly affects the Eizxene group, resulting in open folds and a weak regional foliation S1. A peak metamorphic, amphibolite-facies hornblende-plagioclase paragenesis is developed parallel to the S1 foliation in the Akjoujt metabasalts. Hornblende-plagioclase thermometry indicates 580 \(\pm\) 40 \({}^{\circ}\)C for this metamorphic stage [3]. During the D2, thrusting of the Sainte Barbe volcanic unit to the NNW created a layer-parallel S2 foliation, which formed a cenulation cleavage with the S1 foliation and recumbent folds. A peak metamorphic, upper greenschist facies of garnet-biotite paragenesis is formed parallel to the S2 foliation in the Sainte Barbe volcanics. Garnet-biotite geothermobarometry records a metamorphic P-T peak of about 410 \(\pm\) 30 \({}^{\circ}\)C and 2  
Figure 1: Geographic location of the Guelb Moghrein area. to 3 Kbar for this metamorphic stage [3]. The rocks of the Akjouijt metabasalt unit were retrogressed, and a biotite-actinolite paragenesis is formed parallel to the S2 foliation. This D2 deformation event is contemporaneous with the hydrothermal mineralization and dates back to 2492 \(\pm\) 9 Ma. The main IOCG mineralization stage featured syn-D2 thrusting along NE-vergent thrust zones in the FMC body [4]. The Brecciation of siderite (FMC) during D2 was followed by a strong metasomatic overprinting with the hydrothermal transport of Fe, Mg, K, Rb, Sr, Ba, Ni, Co, Cu, Bi, Mo, As, Au and REE in the host rocks and the formation of the gold-bearing hydrothermal assemblage [2]. During the D3 deformation event, almost orthogonal fabrics were created in all units. D3 shear zones are characterized by a closely spaced S3 foliation. Coupled with hydrothermal fluid flow, this third deformation event occurred at 1742 \(\pm\) 12 Ma in the lower greenstist facies formations. It may also have been responsible for the truncation of the mineralized horizons of the Guelb Moghrein deposit [4,48]. Gentle to moderate folds with ENE-WSW trending fold axes deformed the thrust sheets during D4 and D5, which are correlated with thrusting along the sole thrust during the Westphalian [3,46,47]. D4 created a conjugate set of S4 foliations within the Guelb Moghrein deposit, and D5 is characterized by a set of NNE-SSW trending faults with minor offsets [3].