Figure 27. Block diagram of part of the study area

8. TYPE OF MINERALIZATION AND DISCUSSIONS

The study area has similarities with deposits in West Africa. According to Marwitz and al, 2016, there are three IRGS -type deposits in West Africa namely: the Morilla deposit in Mali , the Massawa deposit in Senegal and the Bonikro deposit in Ivory Coast. The Massawa orogenic deposit in Senegal arose from fluids that have a more magmatic origin according to Treloar et al, 2014. Indeed, the Morila mine has been qualified as an IRGS-type deposit by McFarlane et al., 2011. It is a deposit located in the south-east of Mali and hosted in greywackes and volcaniclastics . The mineralized structure is a NNE-SSW trending fold. Several intrusions of leucogranite , quartz diorite and finally muscovite-biotite granites have been identified on this deposit. ( MacFarlane and al., 2011). Bonikro deposit was described by Ouattara et al, (2015) as being of the IRGS type in which the gold has a paragenesis Au + Mo+ S + W+ (Bi + Pb +Ag) in the granodiorite. The Bonikro mine located in the center of Côte d’Ivoire represents an IRGS-type deposit according to the work of Ouattara et al. 2015 ( Ouattara and al., 2015). The mineralized rocks of this deposit consist of granodiorite with aplo-pegmatitic dykes with NS-oriented mineralized structures.
However, in the absence of mineralization dating data, the more general classification of Lang and Beker , 2001, was retained. There are three main types of mineralization related to hydrothermal alteration depending on the source of the hydrothermal fluid. Those are:
1) Mineralization linked to extrusive magmatism and volcanism, therefore to hydrothermal cells of seawater and meteoric water leading to the formation of auriferous volcanogenic massive sulphides and epithermal deposits;
2) Mineralization linked to crystallization and the liberation of magmatic fluids (porphyry, Intrusion - related gold system and skarn )
3) Mineralization related to fluids produced during deformation and metamorphism in deep zones of orogeny.
Our study area is of the second type, because it is linked to the crystallization of tonalite. The signature of gold deposits of the “Intrusion- related gold system –IRGS” type is: Au-Bi ±Te ±As ±Mo ±W (Baker, and al., 2001). This metallic signature is partly compatible with the signature of our study area which is Au-Te ±Bi ±Mo± Pb± Re. The mineralization of our study area is therefore the IRGS type.