Wzrost kaolinitu w „iłach witriololowych" niecki bytomskiej

Marek Michalik



Kaolinite is shown to be the major clay mineral in samples of clay and mudstone-clay karst rocks occurring in Triassic series in the Bytom Basin, Upper Silesia (so-called "vitriol clays"). It is also present but generally in much smaller amounts in unsoluble residuum of Triassic rocks, among which the described karst deposits occur.
SEM studies made it possible to state that omnipresent forms of occurrence of kaolinite include large (up to a few tenths of mm in size) crystals, book-, fan- or worm-like in outline. The mode of development of these crystals indicates that they have grown in the sediment. The in situ growth in plastic sediment is also shown by arrangement of minor plates of clay minerals along large kaolinite forms. Large kaolinite crystals are randomly distributed even in rock varieties displaying fine lamination.
"Vitriol clays" often yield even large amounts of authigenic Fe, Zn and Pb sulfides, the growth of which has been accompanying deposit-forming mineralization processes. However, any reliable data for reconstruction of time relations between the mineralization and growth of kaolinite are still not available. It may be assumed that kaolinite crystals were growing due to supply of solutions, the character of which remains difficult to decipher. The process could develop in result of either action of hydrothermal solutions responsible for low-temperature ore mineralization, or a synthesis of kaolinite. In both cases aluminasilicate minerals present in "vitriol clays" could act as the major source of substrata (Al, Si). Decay of these minerals under conditions of action of low-temperature solutions could be fairly rapid thanks to low pH ( due to action of inorganic or organic, i.e. humus or fulvic acids). The contribution of the latter in growth of kaolinite was also significant.

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