Barite mineralization in the Kůzová fault zone in the Čistá-Jesenice Pluton: fluid inclusions and stable isotopes study

 

Petr Dobeš, Josef Klomínský, Bohuslava Čejková, Ivana Jačková, Zdeňka Lněničková

Geoscience Research Reports 51, 2018, pages 141–147
Map sheets: Jesenice (12-13)

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Published online: 25 September 2018

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Abstract

The discovery of barite boulders near Otěvěky and Čistá by Rakovník initiated a detailed mineral exploration in the 1980s, to assess their possible economic potential. Two barite deposits were discovered during that campaign in the Kůzová fault zone extending over 20 km, and crossing in NW-SE direction the Čistá-Jesenice Pluton (Fig. 1). They are represented by groups of hydrothermal veins with quartz containing hematite and white barite in the Čistá Granodiorite. Both deposits represent 200 kt of C2B category reserves and 800 kt of D2 category reserves of chemical barite with contents ranging from 6.6 to 80 % BaSO4.
New data on fluid inclusions in some minerals, stable isotopes and paleohydrogeology are a new contribution for understanding the tectono-thermal evolution of the major dilatation faults in the Čistá-Jesenice Pluton during the Triassic to Jurassic times.
Fluid inclusions in barite, fluorite and younger quartz revealed mostly variable liquid to vapor ratio (LVR), while only several clusters of fluid inclusions showing consistent LVR were identified and measured. Temperatures of homogenization of primary inclusions in barite with LVR 0.9 ranging between 124 and 168 °C were observed. The total salinity of aqueous solutions was varying from 1.6 to 19.5 wt. % NaCl equiv. Three types of aqueous solution were found in the studied inclusions (NaCl-H2O, MgCl2-FeCl2-NaCl-H2O, and CaCl2-NaCl-H2O). Mixing of various types of solution during different stages of the deposit evolution cannot be excluded. It could have been caused by a recurrent tectono-thermal rejuvenation of the Kůzová fault zone, and also by changes in the water-rock interaction. The temperatures of homogenization of pseudo secondary fluid inclusions with LVR 0.95 in younger quartz generation fluctuated from 118 to 136 °C. Salinity of aqueous fluids was very low, ranging from 1.2 to 2.1 wt. % NaCl equiv.
The isotopic composition of sulfur and oxygen in barites is rather homogeneous. The δ34S values for barites were found in the range from +15.6 to +27.1 ‰ (CDT). The Permian sedimentary cover was thought to have been the likely source of sulfur. Also, the values of δ18O in barites fluctuated in a narrow range from +11.5 to +13.0 ‰ (V-SMOW). The calculated δ18O values of solution ranging between +0.3 and +4.3 ‰ may indicate water of deep circulation or a mixture of waters of different origin to be the source of fluids.
 

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