Ilaste skały kaolinitowe (paratonsteiny) ze złoża węgla brunatnego Bełchatów

Abstract

 W serii węglowej kopalni węgla brunatnego Bełchatów stwierdzono poziomy skał zasobnych w kaolinit, o typie genetycznym tonsteinów. Określono skład mineralny tych skał, identyfikując wiele elementów materiału piroklastycznego. Dokonano korelacji najmłodszych poziomów skał kaolinitowych z poziomem tufitowym w złożach rejonu Konina oraz z horyzontem tufitu bocheńskiego, który jest szeroko rozprzestrzeniony w utworach mioceńskich i badeńskich środkowej Europy.

CLAY KAOLINITE (PARATONSTEIN) ROCKS FROM THE BEŁCHATÓW BROWN COAL

DEPOSIT

Four horizons of clay rocks of the genetic type of kaolinite-rich tonsteins are present in coal series of the Bełchatów brown coal deposit. The youngest two of the horizons (I and II) have been found in Upper Miocene group of brown coal seams (A) and the two others – among rocks or the coal seam group B and C which are supposed to be of the Middle Miocene age (Fig. 1). Kaolinite rocks form layer-like concentrations 0.05 to 0.3 m in thickness and marked lateral extent.

Rocks of the above mentioned horizons are weakly coherent. This feature differs them from typical tonsteins from black coal deposits and it justifies the use of term paratonsteins for them.

The Bełchatów paratonsteins appear similar in composition. The major components include kaolinite and volcanic glass, and the subordinate ones – feldspars (sanidine and orthoclase), biotite, chlorites, zircon, apatite and clay minerals: illite and intergrowths of the illite-montmorillonite type (Figs. 2 and 3). The other characteristic component of these rocks is coal matter fragments of stems, leaves and roots of higher plants, built of textinite, ulminite and cutinite.

Kaloinite occurs in the form of columnar and cementating clay aggregates (Fig. 5). Moreover, it impregnates the preserved fragments of plant tissue. It is a secondary mineral, formed in result of processes of degradation of some alumnosilicates such as feldspars, biotite and presumably a part of volcanic glass. Chlorites represent by-products of these processes.

Volcanic glass is the major component of groundmass in paratonsteins. It is also present in the form of grains, morphological outline of which indicates airborne transport (Fig. 6). Low (below 1.54) coefficient of light refraction suggests origin of the glass from acid igneous source.

Mineral composition shows that paratonsteins from Bełchatów originated in result of alteration of material of pyroclastic origin and detrital (tuffite) one. The material was sedimenting in acid environment (pH below 7), with local concentration of ions Al³⁺, Si³⁺ and Ca²⁺, and well-drained.

Attempt was made to correlate paratonstein horizons from Bełchatów and widely distributed tuffite

and benthonite horizons dated at the Miocene. Taking into account mineral composition of pyrogenic material, chemistry and morphological-granulometric characteristics of volcanic glass, and the type of secondary alterations of these components it is concluded that the two youngest paratonstein horizons from Bełchatów may be correlated with tuffite horizon widely distributed in central Europe and best known from the Badenian (Bochenian) Spiralis Clays in the Carpathian Foredeep in Poland, Romania, Czechoslovakia and the USSR. The horizon of these rocks is also known from the Konin area (Middle Tortonian), southern foreland of the Góry Świętokrzyskie Mts and a part of the Upper Silesian Coal Basin (Fig; 7).

The third paratonstein horizon (HI) from Bełchatów seems to represent an equivalent of tuffite known from chemical sediments of the Badenian in the Carpathian Foredeep, and the fourth, the oldest

(IV) appears correlable with tuffite horizons from the Baranów or Kłodnice Beds in the foredeep.