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).