Przykład zmienności litologicznej utworów wapienia muszlowego okolic Olkusza

Czesława Pastwa-Leszczyńska



Detailed examinations were made of two bore-holes (Fig. 1), in the Olkusz region (Cracow-Częstochowa Jura Chain) one of which is typical for the investigated region (B-153), whereas the second considerably differs from the typical structure (B-159). In the bore-holes studied, directly underneath the Quaternary or Keuper lies a diplopore dolomite (Middle Muschelkalk). The upper horizon of the Lower Muschelkalk is represented in bore-hole B-153 by ore-bearing dolomites, in bore-hole B-159 partly also by Gorazdów limestones (Fig. 2). Underneath lie Gogolin limestones, at their bottom bordering with dolomites of the Roth.

The diplopore dolomites as well as the Gorazdów and Gogolin limestones are assigned to the unaltered rocks, the ore-bearing dolomites to secondary rocks. The diplopore and the ore-bearing rocks differ as to their tectonic (Fig. 2), their structural (Fig. 3) and chemical features (Fig. 4). In contrast with the diplopore dolomites, the ore-bearing dolomites are mainly characterized·by a mosaic-like and, as a rule mediumgrained texture, rarely a fine-grained one, and a very different per cent content of MgO (1,12-21,42 weight per cent, Fig. 4).

The ore-bearing dolomites have been assigned to the large group of meta-somatic dolomites. 50 far it is an open question whether they were produced by dolomitization of calcareous deposits during diagenesis or by epigenetic dolomitization of calcareous rocks with the co-action of magnesium-bearing solutions.

Moreover, the fact that in both bore-holes sunk at a distance of but 240 m, different rocks appear in the same horizon fails to support any thesis of facial changes within the ore-bearing dolomite. In voids and veinlets of the ore-bearing dolomite, white coarse-crystalline dolomite was found (Table I, Fig. 9) with crystals of zincblende, galena and pyrite. This therefore is a typical epigenetic veined dolomite. It may be looked upon as the second stage of dolomitization proceeding in the consolidated ore-bearing dolomite.

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