The petrographic observations made in the field and by microscopy enabled us to distinguish 3 main granitic facies. These are the granite with two (2) micas intrusive in the central part of the belt with a NE-SW elongation over several kilometers, the Dougoulogo pluton intrusive in the northern part of the belt and the Folonzo granitic intrusions in the southern part.

1) Two-mica granite

The dominant facies are the two-mica granites ( Figure 3 ), an elongated batholith running NE-SW. Its NE limit is at Banfora in Burkina Faso and it extends for hundreds of kilometers into Côte d’Ivoire, where it is known as the Ferké granite (Arnould, 1960; Yobou, 1993; Ouattara, 1998). At outcrop ( Figure 3(a) ), the rock is leucocratic, medium- to coarse-grained. It is very often foliated and/or cataclased. Polarizing microscopy ( Figure 3(b) ) shows that it consists of biotite (10%), muscovite (7%), plagioclase (25%), potassium feldspar (25%) and quartz (30%). Accessory minerals (sphene, zircons, opaques, etc.) occupy around 1% of the volume of the rock. There is a notable presence of minerals such as damourite, sericite, chlorite, calcite and oxides (2%), which are minerals resulting from the partial alteration of certain primary minerals.

2) Dougoulogo quartz monzonite

At outcrop, quartz monzonite is a highly weathered rock with a pinkish-grey to reddish patina ( Figure 4(a) ). The texture is grainy, heterogranular and medium-grained. In a few places it contains comagmatic enclaves. The elliptical pluton is elongated in a N-S direction for around 40 km in the same direction as the volcanosedimentary belt and is 3.5 km wide. In microscopy ( Figure 4(b) ), the main minerals observed are hornblende (10%), biotite (25%), plagioclases sometimes zoned and altered to white micas (25%), microperthitic potassium feldspars (20%) and quartz in limpid patches (10%). A few accessory minerals (zircon and apatite) and minerals resulting from the alteration of primary minerals (damourite, sericite, chlorite and opaques) are also sometimes observed.

3) Folonzo granite

The entire pluton is elliptical in shape with a long axis running NW-SE for about 33 km and a short axis averaging 4.5 km. It cuts through the volcanic sequences on the eastern side of the Greenville-Ferkessédougou-Bobo-Dioulasso shear. At outcrop, the patina is light grey and the texture is coarse-grained ( Figure 5(a) ). The rock is foliated and in places contains enclaves of basic rock. Microscopically ( Figure 5(b) ), the mineralogical composition is as follows: amphiboles (0 - 10%), biotite (20%), plagioclases (20%), potassium feldspars (15%) and quartz (25%). Accessory minerals and certain minerals resulting from the alteration of primary minerals (epidote, chlorite, apatite, zircon and opaque minerals) are also observed.

The majors of fourteen (14) granitic rock samples ( Table 1 ) show that SiO₂ contents range from 54.2% to 75.1%. Al₂O₃ ranged from 14.3% to 18.3%, TiO₂ from 0 to 0.99%, Fe₂O₃ from 0.68% to 9.12%, MgO from 0.1% to 6.27%, CaO from 0.16% to 6.02%, Na₂O from 2.38% to 6.29%, K₂O from 1.71% to 5.04%, MnO from 0 to 0.19% and P₂O₅ from 0.11% to 0.49%.

The Chemical Alteration Index (CIA) of [25] was used to assess the degree of alteration of the rocks. The CIA was determined on the basis of molar proportions: Al₂O₃/(Al₂O₃ + CaO + Na₂O + K₂O). If the AIC values obtained are greater

than 92, the rocks are highly weathered, if the AIC values are between 60 and 80, they are weathered, and if the AIC is less than 60, the rocks are sound [26] . Thus, 6 rock samples have AIC values below 60, i.e. unaltered, and 8 samples have AIC values between 60 and 80, which shows that these rocks have undergone atmospheric alteration, i.e. virtually unaltered [27] . All the rocks studied do not show a high degree of alteration, which allows a good petrogenetic study.

In the [28] TAS diagram, Ferké two-mica granites are mainly found in the compositional fields of syenitic-trending quartz granites and monzonites ( Figure 6(a) ). They are mainly peraluminous, with values for the ratio (Al₂O₃/(CaO + Na₂O + K₂O)) ranging from 1.44 to 2.14 [29] and the ratio (Al₂O₃/(CaO + Na₂O + K₂O)) > 1.1. According to the classification of [30] , these granitoids are of the “S” type and are calcoalkaline [31] ( Figure 6(b) and Figure 6(c) ).

In the TAS diagram ( Figure 6(a) ) by [28] , the samples from the Dougoulogo quartz monzonite are positioned, one in the monzodiorite range and the other at the boundary between the granodiorite and quartz monzonite compositional ranges. On the same diagram, the Folonzo granite samples are one in the granodiorite range and the other at the boundary between the granodiorite and quartz monzonite compositional ranges. According to the classification of [31] , these rocks are all of calc-alkaline affinity ( Figure 4(b) ). Plotted in the [32] diagram ( Figure 6(c) ), the quartz monzonite of Dougoulogo and the Folonzo granite show a peraluminous character.

These plutonic rocks maintain the same peraluminous trend in the molecular Na₂O-Al₂O₃-K₂O diagram ( Figure 6(d) ). In addition, the ratio (Al₂O₃/(CaO + Na₂O + K₂O)) of these samples is > 1.1 [29] . According to the classification of [30] , these granitoids are also of the “S” type. Which could mean that all of the intrusive granitoids of the Banfora belt come from the same magmatic source.

The rare earth content (∑REE) of all the granites studied varies from 12.67 to 183.02 ppm ( Table 1 ). Rare earth spectra normalized to the primitive mantle [33] show that the Ferké two-mica granite exhibits light rare earth enrichment relative to heavy rare earths. The rate of fractionation is moderate to high with ratios (La/Yb) N = 6.00 to 52.67 and (La/Sm) N = 1.85 to 5.24. The spectra show the

existence of two subfacies in the Ferké pluton ( Figure 7 ). Some of the samples of the two (2) mica granite of Ferké (subfacies 1), on average richer in REE, do not show a Europium anomaly while the others (subfacies 2), poorer in REE, present a more or less marked negative Europium anomaly (Eu/Eu* = 0.23 to 1.13).

The spectra of Rare Earth Elements (REEs) normalized to the primitive mantle [33] of the Dougoulogo and Folonzo granitoids are similar to those of the first group (subfacies 1) of the two (2) mica granite of Ferké ( Figure 7 ). These granitoids have remarkable rare earth contents (∑REE = 112.37 to 187.97 ppm) with a (La/Yb)N ratio varying between 10.59 and 20.84, reflecting a strong fractionation. The Eu/Eu* ratio is 0.83 to 0.95, which shows a slight or almost no negative anomaly in europium.

From the point of view of the geodynamic context, the R2 versus R1 diagrams of [34] and [35] , inform us about the geotectonic relationships of these granitoids. The data projected in the diagram of [34] , indicate that the majority of the two (2)

mica granites of Ferké are located in the syn-collisional field (Syn-COLG) with the exception of one sample which is in the field of anorogenic granites; all the Dougoulogo granitoids and a Folonzo sample show a post-collision signature. The other sample of the Folonzo granite is located in the field of the fractional mantle ( Figure 8 ). The Rb versus (Y + Nb) diagram of [35] ( Figure 9(a) ), indicates that the majority of the two-mica granites (2) of Ferké are located in the syn-collisional field (Syn-COLG) and another in the intraplate granite field (WPG), which corresponds to an enrichment in Nb and Y.

All the Dougoulogo and Folonzo granitoids fall into the volcanic arc field (VAG). In the Nb versus Y diagram ( Figure 9(b) ), all the samples are in the field of volcanic (VAG) and syn-collisional (Syn-COLG) arcs.