Wybrane procesy sedymentacyjne i diagenetyczne w skałach otaczających mineralizację cynkowo-ołowiową w Trzebionce

Jadwiga Pawłowska



The studies of higher parts of Lower Mushelkalk carbonate series were aimed at estimating the influence of original sedimentary conditions on distribution of Zn-Pb ores in certain horizons of the Triassic (i.e. in the Gorażdże, Terebratula and Karchowice Beds). Original horizontal or almost horizontal stratification of these rocks was not obscured by subsequent epigenetic dolomitization (Fig. 1). There were differentiated several types of lamination: parallel, wavy, transversal, lenticular, oblique, ripplemark and varve-like (Fig. 2). The stratification is microscopically visible only in rocks not alterated by dolomitization. When rocks are effected by dolomitization, stratification may be traced with the use of chemical analyses and detailed microscopic studies (Foig. 3). Early diagenetic rocks also display numerous erosional and deformational .structures (Figs. 4-5).
Three main sedimentary facies and two subfacies are distinguished. Tables l and 2 and Figure 6 show features of their sedimentary environments. The sediments originated in the tidal flat and mainly in the intertidal and low-tide zones not connected with land areas.
Ore-bearing dolomites originated in result of: (1) limestone metasomatosis, (2) agradational neomorphism of early diagenetic dolomites and (3) infilling of free spaces. Alterations took place mainly in result of strong diagenesis and the contribution of hot solutions was not large. Formation of the ore-bearing dolomites began at lateral and vertical facies contacts of limestones and early diagenetic dolomites.
Depositst of the Lower and some parts of Middle Mushelkalk are characterized by increased concentration of Zn and Pb. These metals were mainly absorbed by algae and other plants, animal shells and bacteria. High salinity of marine water resulted from: (1) washing of disintegrated and weathered deposits and (2) seasonal connections with Alpine basin. Diagenetic processes resulted in formation of
sulfides of the Ist generation whereas the main horizons of crust and breccia ores resulted from epigenetic processes developing in earlier formed ore-bearing dolomites.

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