Petro-Structural Study of the Paleoproterozoic Formations of the Faboula Gold Deposit (Bougouni-Kékoro Basin, Leo-Man Shield)

Résumé

Recent petro-structural investigations on the Faboula gold deposit located in
the Bougouni-Kékoro basin, in southern Mali, north-west of the Leo-Man
Shield, have provided new data on the nature and spatial organization of the
lithostratigraphic units as well as their deformation style. The deposit is covered
by a thick lateritic layer and is hosted by a metavolcano-sedimentary sequence
of Paleoproterozoic age intersected by intrusive bodies and filled
fractures of various shapes and types. The lithostratigraphic units consist of
metagreywackes, metasiltstones, meta-argillites, slates and schists. Metagreywackes
and metasiltstones are generally feldspathic, both may contain biotite
and locally amphibole, just as slates may contain andalusite which is locally
stretched. Plutonic units most often occur as stocks or as dikes on the drill
core, up to 1 m. The metavolcano-sedimentary rocks are schistose and deformed
under greenschist facies conditions, and locally they reach the epidote-
amphibolite facies. The structural study revealed that the deposit is affected
by several stages of deformation evolving from a ductile type to a brittle
type via a ductile-brittle type. The dominant ductile and brittle-ductile deformations
show a combination of isoclinal folding and strike-slip faults. Both
the isoclinal folding and the strike-slip faults whose sigmoidal en-echelon tension
gashes indicate a dextral movement in the NNE-SSW direction are the
result of the same ENE-WSW regional shortening. Consequently, they highlight
a transpressive deformation. This deformation noted here D2Fb, could be
equivalent to the regional D2 or D3 deformations identified at the scale of the
Leo-Man Shield if we refer to the style of deformation. There is an abundance of quartz veins networks. Their relation within the structural features indicates
that the mineralization is structurally controlled during a hydrothermal
event linked certainly to the circulations of fluids during the transpressive
event D2Fb.

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