Geology of the Tabakoto gold deposit, Kédougou-Kéniéba Inlier, West African Craton, Mali

Abstract

The Tabakoto gold deposit is part of the highly endowed west-Malian gold belt, which hosts several world-class deposits. This deposit, located in the Paleoproterozoic Kédougou-Kéniéba Inlier (KKI) of the West African Craton (WAC), is contained in Birimian metasedimentary rocks of the Kofi series that are intruded by magmatic dykes. The metasedimentary rocks are characterized by a S0/1 foliation delineated by the alternation of metagreywacke and meta-argillite. This foliation is affected by upright folds with N-S trending axial planes marked by a S2 schistosity and cross-cut by conjugate steep-dipping dextral NE-SW and sinistral NW-SE trending brittle faults. These structures record regional-scale E-W shortening, first associated with crustal thickening and then with N-S stretching, evolving from ductile to brittle deformation. The presence of the pyrrhotite-loellingite assemblage and the presence of scheelite is consistent with temperatures of upper greenshist facies (~ 430°C). Gold mineralization is found in sheared smoky quartz-pyrite veins in subvertical shear zones localized along the S2 schistosity and in S-shaped quartz-carbonate veins located in the NE-SW and NW-SE trending faults. The latter veins are marked by sodic alteration followed by carbonate (i.e., dolomite-ankerite ± calcite ± siderite) and phyllic (i.e., chlorite-muscovite-sericite) alterations. In the quartz-pyrite veins, gold occurs as inclusions in pyrite, arsenopyrite, and pyrrhotite, whereas in quartz-carbonate shear veins, gold is present in fractures cross-cutting pyrite and arsenopyrite and at the contact between pyrite and arsenopyrite or arsenopyrite and pyrrhotite. These features indicate that gold mineralization in the Tabakoto deposit results from hydrothermal fluid circulation during the Eburnean orogeny under ductile to brittle conditions, similar to other orogenic-type deposits in the WAC.