Autor: |
Dumańska-Słowik M; Faculty of Geology, Geophysics, and Environmental Protection, AGH-University of Science and Technology, 30 Mickiewicz Av, 30-059, Kraków, Poland. dumanska@agh.edu.pl., Naglik B; Polish Geological Institute-National Research Institute, Upper Silesian Branch, Królowa Jadwiga str., 41-200, Sosnowiec, Poland., Toboła T; Faculty of Geology, Geophysics, and Environmental Protection, AGH-University of Science and Technology, 30 Mickiewicz Av, 30-059, Kraków, Poland., Powolny T; Faculty of Geology, Geophysics, and Environmental Protection, AGH-University of Science and Technology, 30 Mickiewicz Av, 30-059, Kraków, Poland., Huber M; Department of Geology, Soil Science and Geoinformacy, Faculty of Earth Science and Spatial Management, Maria Curie - Skłodowska University, 2d/107 Kraśnickie Rd, 20-718, Lublin, Poland., Milovska S; Earth Science Institute, Slovak Academy of Sciences, 1 Ďumbierska Str, 974 11, Banská Bystrica, Slovakia., Dobosz N; Faculty of Geology, Geophysics, and Environmental Protection, AGH-University of Science and Technology, 30 Mickiewicz Av, 30-059, Kraków, Poland., Guzik K; Geotech, 1B Chemików Str, 32-600, Oświęcim, Poland., Wesełucha-Birczyńska A; Faculty of Chemistry, Jagiellonian University, 2 Gronostajowa Str., 30-387, Kraków, Poland. |
Abstrakt: |
Light-blue barite from Jebel Ouichane in Morocco forms blade-like tabular crystals (up to ca. 10 cm) with superb transparency and lustre and represents one of the most spectacular gem-quality worldwide. The barite is hosted by iron-ore-bearing skarns, developed within Jurassic-Cretaceous limestones, and occurs in close spatial association with calcite. The crystals have their cores enriched in Sr and contain abundant monophase (liquid) fluid inclusions of primary and pseudosecondary origin. The barite probably precipitated slowly at a relatively low supersaturation and under the control of a surface reaction precipitation mechanism. However, there were some episodes during its formation with a fast growth rate and the coupled dissolution and recrystallization processes. A combination of fluid inclusion data and stable δ 18 O value for barite (+ 6.71‰ VSMOW) suggests that low-salinity barite-forming solutions resulted from the mixing of strongly-diluted meteoric waters (enriched in light oxygen isotope) with magmatic-hydrothermal fluids under low-temperature conditions (< 100 °C). Meanwhile, the mineralizing fluids must have been enriched in Ba, Sr, Ca, Mg, and other elements derived from the alteration of carbonate and silicate minerals in sedimentary and igneous rocks. The coupling between sulphur and oxygen isotope data (+ 16.39‰ VCDT and + 6.71‰ VSMOW, respectively) further suggests that barite crystallized in steam-heated environment, where SO 4 2- derived from magmatic-hydrothermal SO 2 reacted with sulphates that originate from the oxidation of H 2 S under near-surface conditions. |