Abstract

Vanadium-bearing tourmaline was found in Paleozoic metacherts near Chvojnica in the Strážovské vrchy Mountains, Slovakia. The geochemistry of metacherts suggests that the protolith was deposited under anoxic conditions. Tourmaline from Chvojnica displays strong chemical zoning, with high Mg and a very low Fe content. The core has the composition of magnesio-foitite with a low V content, and is mainly controlled by alkali-deficient substitution [X□(Al,V)(NaMg)−1]. The other zones have a dravitic composition considering ordering of all Mg to the Y sites, but they may reach the composition of olenite if one proposes strong Al–Mg disorder (not proven by structural refinement). The intermediate zone is mostly enriched in V (up to 3.3 wt.% V2O3, 0.42 apfu V), and V is considered to be incorporated into the structure by VAl−1 substitution. Two rim zones were observed. Rim 1 is depleted in V but is enriched in Al. Rim 2 is similar in composition to the intermediate zone, with increased V. The increased content of trivalent cations, including Al, V and Cr in comparison to divalent Mg and Fe, suggests a deprotonation of (OH) by the proton-deficient substitution Y(Al,V)OYMg−1(OH)−1. The increase of Ca, Ti and Mg content from core to rim may be the result of several substitutions, including TiMg(Al,V)−2, CaMgOX−1(Al,V)−1(OH)−1. The increase of Ca, Ti and Mg content from core to rim may be the result of several substitutions, including TiMg(Al,V)−2, CaMgOX−1(Al,V)−1(OH)−1. The V-bearing tourmaline from Chvojnica is the result of multistage Pre-Alpine regional metamorphism. The core of the grains is a product of the lower-grade M1 metamorphic event, whereas the intermediate zone corresponds to the second metamorphic event, M2. Medium-grade metamorphism (580 < T < 600°C) remobilized V from the organic matter present in the protolith of the metacherts. Rim 1 may be the result of reheating of the host rock due to the intrusion of the Malá Magura granitic massif (M3 event). The chemical composition of rim 2 was most likely influenced by the remobilization of V from older V-bearing silicates during the M3 (M3b stage?) metamorphic event.

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