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.