Gold mineralization paragenesis to tectonic structures in the Birimian of the eastern Diale-Dalema Supergroup, Kedougou-Kenieba Inlier, Senegal, West African Craton

摘要

New field and petrographic data from the Birimian of the Kolia-Boboti Basin in the Kedougou-Kenieba inlier indicate two phases of gold mineralization related to Eburnean tectono-magmatic events. Syn- to late-tectonic (D-2/D-3) mineralization, controlled by stockwork sulphide-bearing quartz-chlorite and quartz-carbonate veins, is associated with fluid circulation related to magmatic intrusions. V-2 veins and disseminated assemblages are mainly composed of quartz + chlorite + pyrite and +/- gold. Haematite and arsenopyrite are added in the sediments (pelite, greywake, sandstone, quartzite, and marble) and albite in the felsic rocks (andesite, rhyolite, granodirite, and diorite). V-3 veins assemblage is composed of quartz + carbonate + pyrite + chalcopyrite and +/- gold. Pyrrhotite appears in the sediments (greywacke, quartzite, marble). Sericite, tourmaline, haematite, and magnetite are common in both V-2 and V-3 assemblages. The first sulphide-bearing quartz-chlorite assemblage is related to the hydrothermal activity of the Eburnean D-2 deformation, which was focused mostly along NW- to NNE-trending tectonic structures. The second sulphide-bearing quartz-carbonate assemblage is associated with hydrothermal activity during late Eburnean D-3 deformation, mainly located in NE- to E-W-trending tectonic structures. Gold is correlated with the abundance of sulphides (pyrite, chalcopyrite, arsenopyrite), and sulphide stockworks are more abundant in the veins sub-parallel (V-2b) or oblique (V-2c) to the N-S- to NNE-oriented S-2 foliation, as well as in the N45 degrees-N90 degrees-oriented V-3 veins. V-1 veins, which are related to D-1 Eburnean tectonics, are highly deformed (folded and boudinaged) and are poor in sulphides. The host structures of mineralization (V-2 and V-3 veins) represent the low- and medium-stress domains resulting from the Eburnean D-2 and D-3 tectonic phases, respectively. The intra-crystalline deformation of the quartz grains associated with these three vein types indicates relatively low temperatures. These different features suggest that most of the mineralization was associated with sulphides formed during the D-2 and D-3 Eburnean tectono-magmatic events dated around 2080 +/- 0.9 and 2061 +/- 15Ma, respectively.