Zmienność rozmieszczenia mineralizacji Zn, Pb w skałach węglanowych triasu północnego obrzeżenia GZW

Abstract

Artykuł, dotyczy przejawów mineralizacji ≥0,5% Zn, Pb w poziomie dolomitów kruszconośnych i w osadach środkowego wapienia muszlowego na obszarze północnego obrzeżenia Górnośląskiego Zagłębia Węglowego. Podstawowy materiał do badań stanowiły wyniki oznaczeń zawartości Zn i Pb w próbkach rdzeni wiertniczych z licznych otworów poszukiwawczych. Stwierdzono tendencję do kierunkowej zmienności w przestrzennym rozmieszczeniu przejawów mineralizacji kruszcowej. Zmienność ta wskazuje na związek t głównymi kierunkami zaznaczającymi się w budowie geologiczej zarówno osadów triasowych, jak i ich paleozoicznego podłoża.

VARIABILITY IN DISTRIBUTION OF Zn AND Pb MINERALIZATION IN CARBONATE TRIASSIC ROCKS IN NORTHERN MARGIN OF THE UPPER SILESIAN COAL BASIN

Geological surveys aimed at search for Zn - Pb mineralization are carried out at the northern margin of the Upper Silesian Coal Basin, from the area of Zawiercie on the east to the vicinities of Kalety on the west (Fig. 1).

In geological structure of this area may be differentiated folded older Paleozoic, Devonian and Carboniferous rocks and almost horizontally laying Permian, Triassic and Jurassic rocks overlaying the former. Disjunctive tectonics of these rocks is fairly well marked.

Traces of Zn - Pb mineralization are found throughout a large part of the profile, from the Devonian to Jurassic. The concentration is the highest and occurrences of ore minerals most common in carbonate Triassic rocks, especially in the Ore-bearing Dolomites and Middle Muschelkalk, characterized by a high variability in thickness (Figs. 2, 3).

The mineralization of rocks of the two horizons, Ore-bearing Dolomites and Middle Muschelkalk, was studied. The studies covered the areas of Zawiercie, Poręba, Marciszów, Cynków, Gołuchowice, Miotek and Kalety (Fig. 4). They were based on results of analyses of Zn and Ph content in core samples from over 750 exploratory boreholes. The results taken into account were those showing content ≥0.5% of at least of one of these metals.

In order to analyse distribution of mineralization in an the areas, there were differentiated class intervals corresponding to 5-meter sections of the profile. A relative frequency of occurrences of Zn and Ph in amounts ≥0.5% was estimated for every interval The base of the Ore-bearing Dolomites was accepted as the reference level for that horizon, and the contact of the Middle Muschelkalk and Ore-bearing Dolomites - as the reference level for the Middle Muschelkalk: horizon. The results obtained are presented in the form of graphs of dependence of relative frequency of Zn - Pb occurrences on their position in the studied profile (Figs. 5, 6).

The analysis of that frequency showed a certain trend to directional variability in vertical distribution of mineralization in the studied area. The changes are the greatest in latitudinal direction but subordinate ones may be also traced in longitudinal direction.

In eastern part of the studied area, mineralization is most intense in basal part of the Ore-bearing Dolomites. Towards the west, relative frequency of mineralization gradually but not steadily shifts upwards the profile, up to the Middle Muschelkalk beds, inclusively. This is best visible when the marginal parts of the area are compared as the maximum of mineralization coincides with basal parts of the Ore-bearing Dolomites east of Zawiercie and with the Middle Muschelkalk west of Kalety. The ratio of frequency of occurrence of metals in the Ore-bearing Dolomites and Middle Muschelkalk changes accordingly from the east westwards, i.e. from 13: 1 in the Zawiercie area to 6.5:1 at Marciszów and Cynków, 2:1 at Miotek, and 1:3 at Kalety.

The variability in. distribution of mineralization in longitudinal direction is less clear but, nevertheless, it suggests that the studied area is situated in two mineralization zones: southern (Gołuchowice, Miotek and Kalety), characterized by mineralization maximum coinciding with upper parts of the Ore-bearing Dolomites or Middle Muschelkalk, and northern (the remaining part of the area), with the maximum coincing with lower part of the Ore-bearing Dolomites.

The trends in spatial variability in distribution of mineralization are consistent with main features of geological structure of this region. This is especially the case of strike of Triassic rocks, course of longer axes of Paleozoic structures and directions of main longitudinal and transversal dislocations in both Permo-mesozoic rocks and their Paleozoic basement.

The recorded variability may be useful in prognosis of occurrence and search for Zn - Ph ores.