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Location: 59 km SW from Sikasso, Mali
Rue 50, porte 901 BadalabougouBamakoMaliB.P. 1939
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Specifically, the Nampala deposit can be classified as a turbidite-hosted structurally controlled orogenic (mesothermal) lode-gold system.Gold mineralization is primarily hosted in competent coarse-grained sedimentary rock where brittle fracturation, openings and veining occurred. Gold is associated to structurally controlled tension quartz vein systems and stockworks developed in the brittle fractures and in areas of increased porosity as a result of the deformation of the more competent coarse-grained greywacke, siliciceous sandstone and sandstone. Shear zones are developed in the more ductile adjacent (or locally intercalated) shales (particularly the graphitic shale) and are commonly barren. Some narrow NNE-trending subvertical shear corridors are exposed in the pit from north to south and have been traced nearly continuously to the southernmost drill hole of the 2017-2018 drilling program.Some anomalous gold values can also be found locally in the chill margins or along the contact of the intermediate intrusives. Local brittle deformation seems to have created space for tension quartz veins to penetrate the fringe of the stock and this seems to be confirmed by resistivity and conductivity geophysical maps which display what seem to be a slight NE/SW and NW/SE fracture pattern. This corresponds to the general orientation of the mineralization in the mine where mineralized domains are oriented 020°N and are controlled laterally by subvertical structures and stratigraphy. Within these delineations, as many as five generations of veins are observed and there seems to be a global plunge of 25-30° to the SW as well as the SE where flatter undulating quartz veins are noted. The mineralization type found at the Main and East zones is structurally controlled sediment-hosted orogenic gold affected by late intrusives. In both zones, the mineralized quartz veins have propagated into the more competent coarsegrained wakes, sandstones and arenites affected by brittle deformation. Through rheological contrasts between the different sediments, the plastic planar shear slipping along the ductile and less permeable siltstones and mudstones resulted in the propagation of interplanar shear bands, the brittle fracturing of arenitic rocks, the opening of tension jogs and the formation of dilation joints. As a result, quartz vein propagation and hydrothermal alteration of the protolith was favourable in the more porous sandstones and arenitic rocks. Hydrothermal alteration and quartz vein development patterns follow the structural corridors, filling extension gashes and jogs along shear corridors in the sediments and along the intrusives. The dominant hydrothermal alteration in both zones is characterized by pervasive carbonatization-silicification and pyrite- arsenopyrite disseminations accompanied by chlorite and clay minerals (kaolinitization). The hydrothermal alteration displays outward zonation around quartz veins. The bulk of the sulphides occur as widespread disseminations of fine (submillimetre) pyrite and arsenopyrite. They are found within silicate-carbonate alteration rims in the wall rock around individual quartz veins, within quartz-carbonate veins. The degree of silicification and arsenopyrite concentrations appear to be slightly higher in the East Zone than in the Main Zone.
