The origin of Zn-Pb-Ag ore deposit Bashibos

Raziskovalna koncesija Bašibos se nahaja v jugovzhodni Republiki Severni Makedoniji. Prikamnino rudišča predstavlja zelo heterogeno zaporedje z izmenjujočimi plastmi metamorfoziranih in duktilno deformiranih siliciklastičnih, vulkanskih in karbonatnih kamnin. Sprva je sedimentacija potekala v kratkotrajno obstoječem sedimentnem bazenu spodnjepermskega Variskičnega predgorja. Sedimentni bazen je nastal po zaključeni glavni fazi Variskične orogeneze po koliziji med Pelagonijskim in Srbskomakedonskim masivom. Zaradi spremenjenih tektonskih razmer v času srednjega in zgornjega perma, ki so nastale kot posledica vleka subducirajočega oceana Paleotetida, je prišlo do ekstenzijskih napetosti v zaločnem okolju in nastanka zaločnega bazena. V bazenu odloženi sedimenti so izvirali iz Srbskomakedonskega in Pelagonijskega masiva, sedimentacija pa je potekala v distalnem, nizkoenergijskem okolju. Vzdolž normalnih prelomov, ki so omejevali zaradi tektonike spuščene bloke kamnin, so na morsko dno pritekale hidrotermalne raztopine, iz katerih so se izločili rudni minerali. Kovinsko kloridni kompleksi iz hidrotermalnih slanic so reagirali z reduciranim žveplom, ki je nastalo z bakterijsko redukcijo sulfata iz permske morske vode, kar je vodilo do nastanka singenetske sedimentno-ekshalativne mineralizacije. V obdobju spodnje krede je bila Bašiboška formacija podvržena fazi dinamične metamorfoze do pogojev faciesa zelenega skrilavca, ki je bila povezana s kolizijo in obdukcijo srednjejurskega intraoceanskega loka na Evropsko ploščo. Metamorfoza je povzročila asimetrično gubanje, nastanek regionalne foliacije, duktilnih strižnih con ter izrazite hidrotermalne spremembe prikamnine. Metasomatski fluidi so mobilizirali razpršene ter zelo drobnozrnate sedimentno-ekshalativne sulfide, ki so se nato izločili v conah strukturnih šibkosti, kot naprimer vzdolž foliacijskih ploskev, v kremenovokarbonatnih žilah ter v strižnih conah.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