Minerály skupiny columbitu a mikrolitu v granitovom pegmatite pri Liešťanoch: prvý výskyt vzácnoprvkovej Nb-Ta mineralizácie v Strážovských vrchoch (Slovenská republika)

Pavel Uher, Martin Števko, Sergii Kurylo
2020 Bulletin Mineralogie Petrologie  
Accessory minerals of columbite and microlite groups were identified in granitic pegmatite dike intruded into parental Carboniferous (~350 Ma) leucogranites of the crystalline basement of the Tatric Unit, Central Western Carpathians. The pegmatite is situated on E slope of Bystrý Hill near Liešťany village, the Strážovské vrchy Mts., Slovakia. Primary columbite-(Fe) forms euhedral crystal (~3 mm across) with diffuse internal zoning reflecting a relatively small compositional variations: Mn/(Mn
more » ... Fe) = 0.40 - 0.45 and Ta/(Ta + Nb) = 0.21 - 0.24. Secondary anhedral domains of Ta-rich columbite-(Fe) to tantalite-(Fe) (≤200 μm) with Mn/(Mn + Fe) = 0.45 - 0.47 and Ta/(Ta + Nb) = 0.45 - 0.62 partly replace primary columbite-(Fe) along crystal rims. Moreover, secondary subhedral crystals of microlite-group minerals (≤25 μm) form fracture fillings in columbite-(Fe). The microlites show uniform high Ta/(Ta + Nb) ratio (0.77 - 0.80) and U content (7.7 - 10.2 wt.% UO2; 0.18 - 0.21 U apfu) but different contents of F, Ca, Na and Pb: central parts locally show fluorcalciomicrolite composition (~2 wt.% F, ~9.5 wt.% CaO, 2.2 - 2.7 wt.% Na2O), whereas main microlite mass forms zero-valent-dominant microlite with inclusions (≤8 μm) of Pb-rich zero-valent-dominant microlite (16.8 - 19.7 wt.% PbO; 0.46 - 0.56 Pb apfu). Textural relationships and chemical compositions of Nb-Ta minerals indicate primary magmatic origin of columbite-(Fe) and post-magmatic (early subsolidus to late hydrothermal) formation of secondary Ta-rich columbite-(Fe) to tantalite-(Fe) and microlite-group minerals.
doi:10.46861/bmp.28.347 fatcat:o55drvtocbbbvlhz5cwvcro4xe