The Fluorite Vein Mineralization of the Southern Alps: Combined Application of Fluid Inclusions and Rare Earth Element (REE) Distribution

U. F. Hein*, V. Lüders and P. Dulski
FG Petrologie, Technische Universität Berlin, EB 310, Str. d. 17 Juni 135, D-1000 Berlin 12, Federal Republic of Germany
AG Geochemie, Bereich Kernchemie und Reaktor, Hahn-Meitner-Institut, Glienicker Str. 100, D-1000 Berlin, F.R.G.
*Present address: IGDL, Goldschmidtstr. 3, D-3400 Göttingen, F.R.G.

Abstract: The fluorite vein deposits of the Southern Alps (Northern Italy) exhibit similar geotectonic, paragenetic, and textural characteristics permitting useful comparison between their fluid inclusions and REE systematics. Due to differing post-crystallization deformation, primary fluid inclusions can only be observed in the northernmost deposit (Rabenstein/Corvara). Here, fluorite precipitated from highly saline H2O-NaCl-CaCl2 solutions containing appreciable H2S. During vein formation the fluids changed from low salinity (≈7 wt. % NaCl equiv.) and medium temperature (Th ≈ 230°C), corresponding to the precipitation of early quartz, towards high salinity (≈20 wt.% NaCl equiv.) and lower temperatures (Th ≈170°C during the deposition of late-stage fluorite. This was accompanied by an increase in Ca in solution.

REE distribution patterns for the northern deposits are very uniform suggesting a similar source, a large-scale homogeneous fluid system, and fluorite precipitation under reducing conditions. By comparison the southern deposits exhibit contrasting patterns documenting a more complex history, probably due to their remobilization from an earlier mineralization. None of the fluorites shows a ‘primary’ magmatic REE distribution pattern, thereby favouring a genetic model for fluorite mineralization involving the leaching of suitable rock units by formation waters.

Keywords: fluorite • vein mineralization • fluid inclusions • Alps • rare earth elements

Mineralogical Magazine; June 1990 v. 54; no. 375; p. 325-333; DOI: 10.1180/minmag.1990.054.375.18
© 1990, The Mineralogical Society
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