Polyphase stratabound scheelite-ferberite mineralization at Mallnock, Eastern Alps, Austria

A peculiar type of stratabound tungsten mineralization in metacarbonate rocks was discovered and explored at Mallnock (Austria) during the late 1980s. The tungsten prospect is located in the Austroalpine Drauzug-Gurktal Nappe System recording polyphase low-grade regional metamorphism. It is the only tungsten occurrence in the Eastern Alps where scheelite is associated with wolframite (96 mol% ferberite). Scheelite and ferberite occur as polyphase stockwork-like mineralization in Fe-rich magnesite in the northern ore zone (Mallnock North), while in the western ore zone (Mallnock West), only scheelite is hosted in dolomitic marbles.
LA-ICP-MS analyses of scheelite and ferberite yield low concentrations of Mo, Nb, Ta and REEs, while Na and Sr are enriched; particularly U has high concentrations of up to 200 µg/g making scheelite a suitable target for U-Pb dating. In-situ U-Pb dating of scheelite yielded Early Permian (293 ± 18 Ma) and Middle Triassic (241 ± 6 Ma) ages. A monzodioritic dyke close to Mallnock yielded an U-Pb apatite age of 282 ± 5 Ma. Raman spectroscopy of carbonaceous material yielded maximum temperatures of 296 ± 27 °C and 258 ± 27 °C, that are assigned to the Variscan and Eoalpine metamorphism, respectively.
The data are used to interpret tungsten mineralization in the geodynamic context. The new age data show that the metallogenetic model of tungsten mineralization in the Eastern Alps must also consider Permian-Triassic events and indicate that ore formation at Mallnock could be seen in the context of magnesite-siderite mineralization in the Eastern Alps.