Biotite as a potential petrogenetic tracer in Eburnean granitoids: a case study from the Massigui region (southern Mali)

Biotite, a ubiquitous ferromagnesian mineral in granitoids, provides an alternative to whole-rock geochemical approaches for constraining petrogenetic processes. Its sensitivity to physicochemical parameters (T, P, fO2) allows its use where geochemical characterization is limited. This study investigates Palaeoproterozoic granitoids from the Massigui region (southern Mali), Leo–Man Shield, using biotite chemistry. The intrusions, emplaced within a structural framework controlled by the Banifing Shear Zone, include the Massigui granitoids (granodiorite to quartz monzonite), the dioritic rocks of Tiéfala–Syobougou (microdiorite to quartz monzodiorite), and the foliated granitoids of Sodioula (granodiorite and granite). Forty-nine electron microprobe analyses were used to characterize biotite crystallochemical parameters (XFe, Altot, Ti, Fe3+/Fetot). Three compositional groups are distinguished. Group 1 corresponds to an early, weakly oxidized magmatic stage. Group 2 is characterized by variable compositions, with evidence for both magmatic evolution and fluid interaction. Group 3 shows ferriferous compositions enriched in Al and Ti, consistent with advanced differentiation in an active tectonic setting. Chemical variations from Group 2 to Group 3 define a continuous trend. The coherence between biotite compositions and those of their host rocks validates their use as a petrogenetic tracer. This mineralogical approach represents a relevant strategy for preliminary investigations prior to more complex or costly methods.