Charakterystyka litologiczna i drobne struktury łupków miedzionośnych monokliny przedsudeckiej

Wojciech Salski

Abstract


LITHOLOGIC DESCRIPTION AND FINE STRUCTURES OF COPPER-BEARING SHALES IN THE FORE-SUDETIC MONOCLINE

Summary

Copper-bearing shales that occur in the bottom part of the Zechstein deposits in the Fore-Sudetic monocline do not represent, as concerns lithologic-structural character, a uniform horizon. They rest on grey sandstones, referred to the Zechstein, as the so-called Weissliegendes formations. The shales are underlain in the middle part of the Fore-Sudetic monocline with a dolomite bed of various thickness, which at places are wedging out. In the vertical section of the copper-bearing shales the following horizons can be distinguished: - at the bottom are found day bituminous deposits, black in colour, strongly squeezed out and folded, known as bituminous shales. They disclose the highest content of copper and of organic carbon, and contain numerous bornite layers disturbed tectonically, - higher up occur clay-dolomitic shales characterized by platy parting and by parallel lamination. They are black or dark-grey in colour, contain chalcosine and bornite veinlets and intercalations of bituminous shales. These formations are distinguished by the most stable horizontal distribution in the total section of the copper-bearing shales. Upwards, they pass into dark-grey, massive, dolomitic-clayey rocks that show no defined parting. These formations have been distinguished as laminated, clay dolomites, and referred to the series of copper-bearing shales. Each of the horizons distinguished within the shales considered is characterized by a different chemical composition and by their structural properties. In general, from bottom to top, the contents of carbonates increase, and the amount of clay minerals and organic carbon decreases. In the horizon of bituminous shales strong mineralization of copper sulphides, and some detached blocks of Weissliegendes sandstones have been ascertained. Both the presence of sliding scratches on their surface and the orientation of these scratches prove their tectonical provenance. In these formations a folded sandstone layer has been found to occur within the adjacent shales. Most probably, the layer represents syngenetical deposit with the shales. In the copper-bearing shales secondary mineralization can distinctly be observed, represented mainly by veinlets of copper sulphides that run in accordance with the rock stratification, perpendicular to the stratification, or in an irregular manner. The character of the secondary mineralization points to certain phases in the course of these processes: the veinlets of chalcosine and bornite were formed earlier, those of calcite and chalcopyrite - in the later periods. The development of the copper-bearing shales from the middle part of the Fore-Sudetic monocline resembles rather that of the analogous formations in the Mansfeld syncline than the development in the North-Sudetic depression. This resemblance consists mainly in a considerable content of organic carbon, dolomitic nature of deposits directional change of chemical composition from bottom to top of a series, approximate thickness of shales and occurrence of distinct traces of secondary mineralization.

 


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