Badania petrograficzne piasków formierskich z reionu Częsłochowa-Zawiercie

Abstract

PETROGRAPHICAL EXAMINATIONS OF FOUNDRY SANDS FROM THE CZĘSTOCHOWA-ZAWIERCIE REGION

Summary

Foundry sands that fill in karst forms in the Częstochowa-Zawiercie region have been subject to granulometrical and mineralogic-petrographical examinations (Fig. 1). The granulometrical examinations have been carried out in a complex way taking into account the following features: sorting (Table 1), grain-size distribution (Table 2, Fig. 2,), spread of grains (Fig. 3), rounding degree and character of grain surface (Table 3, Fig. 4), physiography of quartz (Table 4), and mineral composition (Table 5, Fig. 6).

It ensues from the obtained results and calculated parameters that the sands in situ, both Jurassic and Cretaceous, are characterized by a worse sorting and a somewhat coarser grain that the sands filling in the karst funnels (Tables 1 and 2). In addition to this the sands in situ are slightly worse rounded (Table 3). Sands that fill in the karst funnels situated in the central part of the Częstochowa-Zawiercie region are characterized by some differentiation, as compared with the sands filling in the karst forms in the north-eastern part of the area under consideration. The differences concern both granulometrical features and mineral composition. Sands that fill in karst funnels in the central part of the area in study as a rule are a little worse sorted, coarser and better rounded than the sands from in the karst funnels in the north-eastern part. Both quartz grains and zircon from the heavy mineral association revleal a better mechanical reworking here. The rounding degree points to a longer transportation of the clastic material. Sands from the central region contain a slight admixture of glauconite, whose presence is restricted to the finest fractions only. On the other hand, in sands found in the north-eastern region the glauconite is a marked constituent occurring up to the medium fractions inclusive (Table 5). Moreover, the silty fraction of the foundry sands from the north-eastern region reveals, beside kaolinite and halloysite, also illite, and most probably montmorillonite. The presence of these minerals causes that the sands of the north-eastern, region are characterized by worse technological properties.
It results from the examinations of heavy minerals that the character of this association to some extent depends on garnets that appear in the sands of the north- eastern area. Their presence is related to the inflow of new sediments here. It should be emphasized, too, that sands that fill in the karst funnels in the central region are analogous to the Jurassic sands in situ, whereas sands that fill in the karst funnels in the north-eastern region – to the Cretaceous sands in situ. The unequivocal granulometric features and the mineral composition point to the marine conditions in sedimentation of foundry sands of different age in the Częstochowa-Zawiercie region.