Fluid evolution of the Hub Stock, Horní Slavkov–Krásno Sn–W ore district, Bohemian Massif, Czech Republic
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Abstract
The Horní Slavkov–Krásno Sn–W ore district is hosted by strongly altered Variscan topaz–albite granite (Krudum granite body) on the northwestern margin of the Bohemian Massif. We studied the fluid inclusions on greisens, ore pockets, and ore veins from the Hub Stock, an apical expression of the Krudum granite. Fluid inclusions record almost continuously the post-magmatic cooling history of the granite body from ∼500 to <50°C. Rarely observed highest-temperature (∼500°C) highest-salinity (∼30 wt.% NaCl eq.) fluid inclusions are probably the result of secondary boiling of fluids exsolved from the crystallizing magma during pressure release which followed hydraulic brecciation of the gneissic mantle above the granite cupola. The greisenization was related to near-critical low-salinity (0–7 wt.% NaCl eq.) aqueous fluids with low amount of CO2, CH4, and N2 (≤10 mol% in total) at temperatures of ∼350–400°C and pressures of 300–530 bar. Crush-leach data display highly variable and negatively correlated I/Cl and Br/Cl values which are incompatible with both orthomagmatic and/or metamorphic origin of the fluid phase, but can be explained by infiltration of surficial and/or sedimentary fluids. Low fluid salinity indicates a substantial portion of meteoric waters in the fluid mixture that is in accordance with previous stable isotope data. The post-greisenization fluid activity associated with vein formation and argillitization is characterized by decreasing temperature (<350 to <50°C), decreasing pressure (down to ∼50–100 bar), and mostly also decreasing salinity.
Keywords
Horní Slavkov Czech Republic Greisen Sn–W mineralization Fluid inclusions HalogensNotes
Acknowledgments
The fluid inclusion study of the Horní Slavkov–Krásno deposit was supported by the project GAČR 205/09/0540. The detailed comments by two journal reviewers (A. M. van den Kerkhof and R. Thomas) and editor (B. Lehmann) helped to improve the initial draft of the manuscript. Special thank is due to R. Thomas for providing unpublished Raman data.
Supplementary material
References
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