Nb–Ta mineralization in Ti-oxide minerals from the Bagolyhegy Metarhyolite Formation (Bükk Mountains, NE Hungary)

Abstract The foliated low-grade metamorphic rocks of the Triassic Bagolyhegy Metarhyolite Formation, mainly pyroclastic origin, host post-metamorphic quartz-albite veins containing abundant tourmaline and occasionally rutile/ilmenite. study Ti-oxide-mineralized with SEM-EDX revealed an unusual mineral assemblage comprising fine-grained Nb–Ta-bearing oxides (columbite-tantalite series, fluorcalciomicrolite other Nb–Ti–Y–Fe-REE-oxide minerals) intergrown Nb-rich polymorphs TiO 2 (anatase, rutile), ilmenite zircon enriched hafnium. This high field strength elements (HFSE)-bearing paragenesis is unexpected in this lithology, was not described from any formation Paleozoic-Mesozoic rock suite Bükk Mountains (NE Hungary) before. metavolcanics are significantly depleted all HFSE compared to typical concentrations felsic volcanics mineralized have even lower Ti–Nb–Ta concentration than rock, so mineralization does mean enrichment. From proximal outcrops Szentistvánhegy Metavolcanics, potassic metasomatized lenses albite-quartz vein fillings rutile/ilmenite known. We studied them for comparison, but they only contain REE (allanite-monazite-xenotime); Nb–Ta-content Ti-oxide minerals undetectably low. LA-ICP-MS measurements U–Pb dating Hf-rich Nb–Ta-rich gave 71.5 ± 5.9 Ma as intercept age while allanite 113 11 age. REE-bearing formed during a separate phase Early Cretaceous, Nb–Ta by alkaline fluids Late Cretaceous., controlled fault zones fractures.