Bentonity i iłołupki bentonityczne w polskich Karpatach

Wacław Sikora




A quick development of chemical, metallurgical and other industry branches that use a lot  of varieties of bentonites and bentonitic clay shales is responsible for the fact that the demand for these mineral raw materials increases, and will increase in the future. Thus, the Flysch Carpathians are now area of intense prospecting works carried on by the Geological Institute to search for bentonite raw materials. Two type of bentonite raw materials have been distinguished in the Flysch Carpathians. To the first type belong Fuller’s earth 1 and proper bentonites (these latter are found in one place only – at Zagórz, near Sanok). These are rocks consisting of 90-100 per cent of pure montmorillonite. The second type represented by bentonitic clay shales, for the most part built up of illite, with an admixture of montmorillonite that may reach up to 30 per cent. Recent studies, conducted mainly by the Goelogical Institute, have shown the occurrence of pyroclastic deposits that intercalate the shale-sandstone Flysch strata. Their thickness is from several to over ten centimeters, although intercalations revealing a thickness of several metres have also been encountered. T. Wieser’s unpublished studies demonstrate that, most of the formations come from subaeral volcanic eruptions. The products of these latter have either immediately fallen down on the basin bottom, or have been redeposited from the higher parts of the sea bottom. It has also been ascertained that considerable part of the Fuller’s earth and of bentonites is, in the Carpathians, of pyroclastic origin. So, a distinct increase both in quantity and in thickness can be observed in the formations of pyroclastic provenance, from bottom to top of the stratigraphical section of the Carpathian flysch area. The greatest amassment o Fuller’s earth (bentonites consisting of Ca-montmorillonite) has been ascertained to occur in the village Polany, near Grybów (Magura nappe). The bentonites are found here in the Eocene green shales (member of variegated shales) as intercalations (0,15÷0,70 m), revealing a total thickness amounting to 2,4 m. Dip of beds ranges from 25° to 70°. Moreover, some interesting sites of Fuller’s earth are found in the Podhale flysch (vicinities of Nowy Targ) and in the Skole unit. Distribution of the Fuller’s earth and proper bentonites more than 15 cm in thickness, is illustrated on Fig. 1. Bentonitic clay shales occur in various members of the Carpathian flysch mainly, however, in two horizons regionally spread over the Carpathian flysch area. The first horizon is represented by the green shales of Cenomannian age that occur at the top of “Black Cretaceous”. The second horizon embraces the green shales found at the top part of the hieroglyphic beds or their equivalents, underlying the sub-menilite globigerina marls of Upper Eocene age. These two horizons contain siliceous rocks and manganese ores that are valuable indicators of the rocks of pyroclastic origin. Bentonitic clay shales occurring in the Carpathians can be used in production of synthetic moulding masses and their certain varieties may serve to prepare drill muds. The occurrence sites of the bentonitic clay shales that, from the industrial point ofo view, can be great value, are shown on Fig. 1. Basing on the present-day knowledge of this problem, we may assume that in the Carpathian area both the north-eastern part of the Skole unit and the marginal northern part of the Silesian unit, may be thought to represent the most promising regions in search for bentonitic clay shales.

1 Bentonite consisting of calcium montmorillonite

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