Fe, Mn and Nb variations in the hübnerite ferberite solid solution at Panasqueira reveal fluid composition and evolution

The study is part of an extensive survey of the mineralogy of the Panasqueira W–Sn–Cu deposit (Central Portugal), aimed at deciphering the main factors controlling ore deposition in space and time. Wolframite was deposited in several stages: Stages I and II correspond to the primary tungsten mineralisation in quartz-wolframite veins with tourmalinized wallrocks. In stage III, deposition of wolframite, quantitatively minor, was followed by cassiterite and sulphides. In stage IV, spectacular “collector” wolframite was deposited in tubular vugs, together with cassiterite, arsenopyrite, muscovite, and apatite. Wolframite at Panasqueira is overwhelmingly ferberitic, with Fe/(Fe + Mn) ratios predominantly between 0.81 and 0.86, but Mn-rich patches, microcracks and rims developed in Stage IV. The Fe and Mn contents of wolframite record the contributions from metamorphic, magmatic, and subsolidus interaction-derived fluids. From Stages I-II to IV, fluids evolved from dominantly Fe-rich to progressively enriched in Mn through mixing with an Mn-rich fluid end-member sourced in rare-metal granites (either magmatic fluids or a result of fluid-rock interaction). Wolframite thus provides a sensitive tracer of both the structural dynamics of the vein system and the episodic magmatic–hydrothermal contributions sustaining tungsten mineralisation at Panasqueira. Wolframite is the dominant tungsten mineral at Panasqueira, deposited in multiple generations of veins. Two main episodes of wolframite formation: early quartz–wolframite stages (I–II) and late “vug stage” (IV). Wolframite is overwhelmingly ferberitic (Fe/(Fe + Mn) = 0.81–0.86), with limited oscillatory Mn zoning. Late hydrothermal hübneritisation reflects the input of Mn-rich fluids during Stage IV, likely linked to late magmatic activity (295–300 Ma).