The Bashibos exploration concession is located in the SE Republic of North Macedonia. The mineralization is hosted in an extremely heterogeneous sequence of interchanging metamorphosed and ductile deformed siliciclastic, volcanic and carbonate rocks. The sedimentation of the unit initially took place in a short-lived sedimentary basin of the Early Permian Variscan foreland. The basin was formed after the main phase of the Variscan orogeny when the final amalgamation of the Pelagonian and Serbomacedonian Massifs took place. During the Middle to Late Permian, the reversal of the tectonic regime, caused by the slab rollback of the subducting Paleotethys Ocean led to a rifting in the back-arc environment, forming a back-arc basin. The sediments deposited in the basin originated from the Serbomacedonian and Pelagonian Massifs. The sedimentation took place in a distal low-energy environment. The heated hydrothermal brine from the underlying layers migrated upwards along graben-limiting faults to the seafloor where it formed the deposit. The metal chloride complexes from the hydrothermal brine were sequestered by the reduced sulphur, which was mainly produced by the bacterial sulphate reduction of the Permian seawater sulphate, leading to the formation of syngenetic sedimentary-exhalative mineralisation. During the Early Cretaceous, the Bashibos formation underwent dynamic metamorphism under the conditions of the greenschist facies, which was related to the collision and obduction of the Middle Jurassic intra-oceanic arc onto the European plate. The metamorphism led to the formation of regional foliation, asymmetric folding and formation of ductile shear zones as well as to significant hydrothermal alteration of the host rock sequence. Highly dispersed and fine-grained sedimentary-exhalative sulfides were mobilised by metasomatic fluids and precipitated in weak structural zones such as foliation planes, quartz-carbonate veins and shear zones.
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