| Popis |
Vesuvianite is a typical mineral for contact metamorphic and metasomatic rocks – skarns, rodingites, skarnoids. Its composition depends on several factors – bulk composition of the intrusive rock and its metasedimentary host, composi-tion of reacting fluids, and PT-conditions. Vesuvianite structure is complex and accommodates a large number of various elements – its general formula is X19Y13Z18T0-5O68W10, where X = Ca, Na, Ln3+, Pb2+, Sb3+; Y = Al, Mg, Fe3+, Fe2+, Ti4+, Mn, Cu, Zn, As3+; Z = Si; T = B; and W = OH, F, Cl, O [1,2,3]. We studied chemical (major, minor and trace elements) com-position of vesuvianite from skarns at 5 selected localities from the Bohemian Massif. VESUVIANITE COMPOSITION The studied samples are compositionally heterogeneous with variable Fe/Mg ratio, Al/R2+ ratio, and variable contents of Ti, Na and F within each locality; core-to-rim zoning was locally observed (increase of Fe, Be, B, Zn, and Sn, decrease of Al, Mg, and F). Locality-specific change of compo-sition from primary to secondary vesuvianite generations is present; while a very distinct decrease in Fe/Mg is present at Žulová, the Nedvědice sam-ples show only a slight increase of Fe/Mg, decrease of Al/R2+ and increase of Ti/R2+ ratios (Fig. 2). IMPLICATIONS: Preliminary results on vesuvianite major and trace element compositions showed that vesuvianite has a potential to record compositional changes of reacting fluids, because a) its structure is versatile enough to include a wide range of ele-ments; including light elements (Li, Be, B), REE (Y and LREE), and especially metals and semi-metals (Zn, Bi, As, Sn, Sb), and b) recrystallizes during post-magmatic hydrothermal alteration, with modified composition in contents of both major and trace elements. Vesuvianite accommodates elevated amounts of Sn whereas its contents of W and Mo are very low; we suggest this is due to incompatibility of Mo6+ and W6+ with the vesuvianite structure.
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