O porfirycie z Huty Starej koło Siewierza

Wacław Ryka, Hubert Sylwestrzak



The bore-hole of Huta Stara (northeastern periphery of the Upper Silesian Basin) encountered at the depths of 302.5-305.3m. and 313,5-319.0 m. two porphyrite dykes appearing amidst Carboniferous siltstones and argillaceous shales.

Exogenic changes in the surrounding the dykes are but feeble. The endogenic contact is well developed at the top of the lower dyke. Siltstone fragments embedded in the porphyrite are surrounded by contact aureoles. The fragments of this breccia are separated by zones of injecting porphyrite.

Texture and composition of the upper dyke resemble the middle part of the lower dyke. The lower dykes texture changes, depending on the distance from the contact pIane with the sedimentary rocks. Here may be observed a felsitie-streaky texture, coarse-feIsitic, fine- and coarse-microlithic.

Phenocrysts are developed irrespective of the type of texture. They are feldspars belonging to oligoclase and anorthoclase. In lesser quantities occur biotite and quartz. Numerous are pseudomorphoses after amphiboles filled by hydrobiotite, epidote, chlorite, calcite and ore minerals.

The porphyrite has undergone conspicuous metamorphoses. The successive stages of these changes are: albitation, hydration, calcitation and beresitation.

The authors carried out three chemical analyses (TabIe 1). They interpreted these analyses on the basis of the C. I. P., W. mineral standards and of A. Zawaricki's method of index computations (Table 3). Lt appears from these analyses that the porphyrite represents a granodiorite magma; a slightly different composition discloses the upper dyke.

The differences in composition between lower and upper dyke, as well as the absence of zones of glass formation in the upper dyke, seem to indicate a somewhat later formation of the upper dyke. Presumably it was formed by technic movements which made possible the escape of plastic masses from the lower dyke before it bad fully congealed.

Finally, the authors compared this porphyrite with the neighboring magmatie rocks occurring at Mrzygłód.

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