Journal of

GEOsciences

  (Formerly Journal of the Czech Geological Society)

Original paper

Jan Pašava, František Veselovský, Milan Drábek, Martin Svojtka, Ondřej Pour, Josef Klomínský, Radek Škoda, Jana Ďurišová, Lukáš Ackerman, Patricie Halodová, Eva Haluzová

Molybdenite-tungstenite association in the tungsten-bearing topaz greisen at Vítkov (Krkonoše-Jizera Crystalline Complex, Bohemian Massif): indication of changes in physico-chemical conditions in mineralizing system

Journal of Geosciences, volume 60 (2015), issue 3, 149 - 161

DOI: http://doi.org/10.3190/jgeosci.197

At Vítkov, sparse molybdenite occurs within tungsten mineralization hosted by topaz greisen in orthogneiss in the envelope of the Variscan Krkonoše-Jizera granite Pluton (northern Bohemian Massif). Mineralogical study showed that sulfide mineralization started with precipitation of arsenopyrite followed by molybdenite, tungstenite, transitional Mo- and W-dominated disulfides and concluded by pyrite. Textural relationships between molybdenite and tungstenite imply that tungstenite was formed during several stages related to molybdenite bending and fracturing. Laser Ablation Inductively Coupled Mass Spectrometry (LA-ICP-MS) analyses of Re-poor (< 0.3 ppm) molybdenite showed extreme concentrations of W (up to 26 558 ppm) accompanied by Ag, As, Bi, Pb, Se, Te and other metals. Electron microprobe analyses of inclusions-free molybdenite confirmed the abundance of W (~0.5 wt. %) and tungstenite showed ~4 wt. % Mo, indicating a substitution of Mo⁴⁺ for W⁴⁺. Stability and phase relationships between molybdenite and tungstenite and locally identified transitional Mo- and W-dominated disulfidic phases suggest that tungstenite crystallization was triggered by a decrease in fO₂ below WO₂-WO₃ buffer that followed after molybdenite precipitation. Tungstenite zoning and sharp tungstenite-molybdenite contacts indicate disequilibrium during their formation.