Stratiform U-Cu mineralization in the Lopejské Čelno valley near Podbrezová (Veporic Unit, Western Carpathians)

Abstract

The studied mineralization is located on the eastern slopes of Lopejské Čelno valley, south of the Lopej village (cadastral area of Podbrezová village, Central Slovakia). The U occurrence was described and classified as U-Cu stratiform mineralization. The mineralization is located in the Ľubietová Zone of Veporic Unit, and is bound to the arkosic sandstones containing Permian volcanoclastic material. The host rock of mineralization underwent low-grade metamorphism and limonitization. Lens shaped ore bodies are characterized by disseminated pyrite, rutile, chalcopyrite, leucoxene and metatorbernite. Small cavities and cracks in rock are also filled and/or coated by goethite, Mn oxides and malachite. Uranium is irregularly distributed within the host rock and is bound to the U-Ti oxides, brannerite and torbernite/metatorbernite. Brannerite and leucoxenized U-Ti oxides are the only one primary uranium U4+ minerals, for the first time identified in studied occurrence. Brannerite forms clusters of needle-like crystals (up to 100 μm in size). It occurs in close spatial and genetic association with U-Ti oxides, rutile, leucoxene and clay minerals. Chemical composition of brannerite and U-Ti oxides differs in ratio of U/(U + Ti): from 0.22 to 0.29 apfu for brannerite and from 0.09 to 0.22 apfu for U-Ti oxides. Metatorbernite forms light green crystals, typically occurs in small cavities and fractures in rock. It shows an unusual light green luminescence under UV radiation. The average chemical composition of metatorbernite can be expressed by empiric formula (Cu0.75Ba0.06Ca0.03K0.04Al0.02Mg0.01Fe0.01)Σ0.94 (UO2)Σ2.00 (PO4)Σ2.01 (H2O)8. Occasionally torbernite/metatorbernite directly replaces single crystals of apatite.