Bentonity mioceńskie z Machowa

Jan Czermiński, Wacław Ryka




Several bentonite intercalations have been found to occur in the Krakowiec clays in the overburden of the sulphur mine at Machów. The intercalations are thin, their thickness amounting to 7–10 mm. Samples for the examinations discussed in this paper have been taken from two intercalations, about 14–17 m below the top of the Krakowiec clays. The distance between these two intercalations amounts to 9 cm. Beside the two closely situated intercalations, the clay overburden of the sulphur-bearing series discloses other single intercalations, too.

Within the bentonite intercalations there “rest” discoidal forms of baryte, from 25X12 to 14x6 mm in diameter. As a rule, the baryte occurs here at the top part of the bentonite layer, near the contact with the overlying clay. Although the thickness of the baryte disc is considerable (10-l2 mm), the disc as a whole sticks in the bentonite layer. Spatial distribution of the baryte discs is irregular. The distribution density of the discs resembles that shown in Table II.
The bentonite underwent chemical examinations (Tab. I), microscope analysis, X-ray examinations (Fig. 2) and thermogravimetric measurements (Fig. 3). Additionally, it was examined also under electron microscope (Tab. I, Figs. 5-10).

On the other hand, the baryte underwent chemical (Tab. II), X-ray (Fig. 4), and microscope examinations that led to the following conclusions.

The bentonite in study almost completely consists of pure calcium montmorillonite, and is characterized by a high degree of bentonitization proved by the lack of any forms of glass. As far as its chemical composition is concerned, it corresponds to the Chmielnik bentonites and to these from the vicinity of Szydłów (A. Langier-Kuźniarowa, 1967). The development of the baryte discoidal forms at the contact of bentonite and claystone is related to the liberation of barium during the decomposition of potassium feldspar (sanidine) and to its crystallization, due to the descending water rich in sulphur.
The bentonite comes from the effusion of a granite-type acid magma in the Carpathian area. According to the supposition of previous scientists working on the Miocene bentonites ascertained south of the' Świętokrzyskie Mountains, they derive from the eruption of andesites. It seems, however, that the above groups considerably differ in their mineral associations and chemical compositions so that they cannot be genetically linked together. The bentonites are rich in quartz, potassium feldspar and, oligoclase (acid andesine), whereas the andesites consist mainly of, amphibole, pyroxene, biotite and labradorite. As a consequence of this the andesites are rich in calcium, magnesium and iron (up to 10% by weight), whereas in bentonites the sum of these constituents does not exceed a half this quantity, usually being even lower. Highly analogous to bentonites are the Carpathian porphyries from Sułów, described by A. Gaweł (1958).

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