4.2 Analysis of structural field data

4.2.1 Sedimentary structures

On the field, the original bedding or stratification (S0) is underlined by alternating beds with different sizes of minerals or grading of rock elements. In short, these various syn - sedimentary structures demonstrate the instability tectonic of the basin. This bedding is sometimes quite well preserved in the metasediments (Figure 11, 12). This bedding strikes N020 and dips steeply 76° towards the SE then secondarily towards the NW (Figure 13).

4.2.2 Tectonic structures

The Birimian rocks in the study area are affected by various types of tectonic structures. These structures were identified and characterized in the field through trenching campaigns and core drilling. They have been grouped according to their nature and their geometric and chronological relationships, into Eburnean deformation structures D1, D2 and D3. The quartz veins associated with these deformations are respectively of three types V1, V2 and V3.

4.2.2.1 Deformation D1

To the bedding (S0) often transposes a poorly preserved S1 shearing foliation in metasediments such as sandstones and argillites. It often appears in competent lithologies, as sinistral shear at the contact between Ferkessedougou granite and metasediments (Figure 14). The origin of the S1 shearing foliation is discussed. Could it be linked to peribatholitic deformations (Max et al,. 1996). S1 shearing foliation strikes N003 and dips steeply 83° towards the E (Figure 15). V1 quartz veins are well preserved in the S0 bedding. These V1 veins are laminated bedding veins and strikes N016 and dips gently 58° towards the SE. (Figure 16).

4.2.2.2 Deformation D2

The S2 shearing foliation is well marked in the metasediment units. It is caused by the intrusion of tonalite into the metasediment basement complex (Figure 17). S2 shearing foliation strikes N022 and dips steeply 76 towards the SE then secondarily towards the NW (Figure 18). The types of V2 veins associated with the D2 deformation are of two sets V2a and V2b. The V2a quartz veins are en echelon veins and display a consistent trend of N020 to N040 and the V2b quartz veins strikes between N070 to N090. V2b quartz veins are isolated type veins and sometimes appear as stockworks. The dip of these two sets of veins is 44° towards the NW then secondarily towards SE (Figure 19).