Kremeňovo-karbonátové žily s U-Mo-Cu mineralizáciou v permských intermediárnych až bázických vulkanitoch hronika na lokalite Kravany (Kozie chrbty, východné Slovensko)
Bulletin Mineralogie Petrologie
Historical uranium ore deposit Kravany is located in the eastern part of Kozie Chrbty Mts., approximately 9 km SW of the district town Poprad. Stratiform, infiltration U-Cu-Pb mineralization is bound to the Upper Permian clastic sediments (Kravany Beds, member of Malužiná Formation, Hronicum Unit), which are enriched in fragments of carbonized flora. Vein U-Mo-Cu mineralization was found in the Upper Permian intermediate to basic volcanics intersecting the sediments of the Kravany Beds (also
... lenses). Vein filling originated in the following development stages: I.) Quartz-pyrite (quartz, pyrite, marcasite), II.) Dolomite-pyrite (dolomite, pyrite, marcasite, galena), III.) Copper (tetrahedrite, tennantite, chalcopyrite), IV.) Uranium-molybdenum (uraninite, Pb-Mo-S phase, coffinite, quartz), and V.) Calcite (calcite, chalcopyrite). The formation of mineralization can be explained by the geological position: random emplacement of the diorite porphyrite, resp. basalt-andesite dikes, directly in the preexisting U,Mo-bearing sediments. Vein U-Mo-Cu mineralization could thus most likely have formed according to the following scenario: I.) sedimentation of Kravany Beds in the Permian riftogenic basin: formation of beds of arkoses and arkosic sandstones with abundant fragments of charred flora, II.) formation of infiltration U mineralization: reduction and accumulation of U in sediments rich in organic matter, III.) emplacement of dikes of intermediate to basic volcanics: intersection of sediments with organics and with high U and Mo content, mobilization of formation fluids, assimilation of U and Mo into intermediate-basic magma, IV.) cooling of volcanic bodies → their contraction (formation of contraction cracks) → filling of contraction cracks with quartz, carbonates and ore minerals (crystallization from residual magmatic solutions mixed with formation waters). From this point of view it is syngenetic volcanogenic vein U-Mo-Cu mineralization, originally of the Permian age, with subsequent Alpine (most probably Cretaceous) reworking (this is evidenced by the variable composition of uraninite). It belongs to the Neohercynian late- to postorogenic metallogenetic stage. The possible younger, post-Permian age of mineralization from alpine hydrothermal solutions must also be assumed, but this consideration has several inconsistencies.