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Inclusions in anhydrite crystals from blue halite veins in the Kłodawa Salt Dome (Zechstein, Poland)

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Toboła T. T.

Geological Quarterly

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2016

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tom Vol. 60, No. 3

572--585

EN

The occurrence of both the blue and violet halites is one of the most interesting phenomena in nature. Despite numerous laboratory and field works, their origin in natural evaporitic environments has not been satisfactorily explained. In the Kłodawa Salt Dome (Zechstein, Central Po land), blue or vio let halites occur relatively frequently. Their accumulations differ in size and intensity of colours. In this paper, petrological features of anhydrite crystals derived from one of the largest outcrops of the blue halite at the Kłodawa Salt Mine are presented. Anhydrite is one of solid inclusions encountered in blue-coloured halite crystals. Special attention was paid to fluid inclusions present in this anhydrite. The microthermometric measurements showed two directions of homogenisation, i.e., towards the liquid phase (LG→L, LL→L) ortowards the gas phase (LG→G). In the former case, the temperatures ranged from 174 to 513°C, whereas in the latter one, the values from 224 to 385°C were measured. The composition of inclusions is relatively variable. We can observe transparent and opaque daughter minerals as well as CO2 in the liquid phase accompanied by a variable amount of methane or hydrogen sulphide. These features of inclusions indicate that anhydrite crystals and, thus, blue halite were formed under the influence of hydrothermal conditions. Observations in the mine workings combined with petrological studies enable to conclude that blue colouration of halite crystals is controlled by three factors: a high temperature, reducing conditions and defects in halite lattice related to tectonic stress.

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Influence of tectonics on petrological characteristics of the anhydrite and anhydrite-halite intercalations in the Oldest Halite (Na1) (Zechstein, Upper Permian) of the Bądzów area (SW Poland)

100%

Toboła T. T.

Geological Quarterly

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2014

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tom Vol. 58, No. 3

531--542

EN

The Oldest Halite (Na1) (Zechstein, Upper Permian) played a significant role in the development of geological structure of the Fore-Sudetic Monocline (SW Poland) because of its different rheological properties in comparison to the adjacent rocks. Intercalations of anhydrite and anhydrite-halite occurring within the Na1 show a lot of features of tectonically disturbed rocks. Macroscopic petrological observations revealed that anhydrite rocks represent four rock types with different structural and textural properties. On the microscopic scale, five types of crystals have been distinguished in all macroscopic types. They vary in size, shape and distribution of primary fluid inclusion assemblages. The anhydrite-halite rocks show two groups with slightly different petrological features that are apparently related to their tectonic deformation and recrystallisation processes. The main recorded directions of tectonic movements seem to be horizontal or sub-horizontal.

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Evidence of high-temperature rock salt transformations in areas of occurrence of borate minerals (Zechstein, Kłodawa salt dome, Poland)

63%

Toboła T. T. , Wachowiak J.

Geological Quarterly

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2018

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tom Vol. 62, No. 1

134--145

EN

Occurrences of borate minerals in the Zechstein salt-bearing deposits of the Kłodawa salt dome (central Poland), and the manner of their development, suggest that the minerals were formed at high temperatures, that considerably exceed the temperature estimated from the thermal gradient (~180°C). Research on rock salt and potassium-magnesium salts containing congolite and boracite, respectively, are consistent with high-temperature processes of transformations affecting the salt rocks in certain sections of the salt dome. The chemical composition of, and daughter minerals occurring in, primary fluid inclusions in halite, originating from the congolite zone, indicated a very high proportion of potassium and magnesium in the brines from which the halite crystallised. The thermal transformations observed in inclusions indicate a halite crystallisation temperature exceeding 420°C. Anhydrite crystals, co-occurring with borate minerals, represent unique features as to the distribution and composition of solid and fluid inclusions. These features indicate crystallisation or recrystallisation in conditions that differed considerably from those typical of the salt dome, with the involvement of solutions of changing chemical compositions. The crystals contain multiple solid inclusions of transparent and non-transparent minerals, among which we have focused on carnallite. The relationships of carnallite with liquid and gaseous phases indicate, as in the congolite zone, migration of very highly concentrated brines with respect to potassium and magnesium, or even transport of carnallite in the form of melt (liquid). Measurements of fluid inclusion homogenization temperatures, within the range from 197.8 to 473.8°C, supported a high-temperature origin for these minerals in hydrothermal conditions.