Szakáll Sándor - Weiszburg Tamás szerk.: A telkibányai érces terület ásványai (Topographia Mineralogica Hungariae 2. Miskolc, 1994)

Telkibánya környékének kőzetföldtani felépítése és fejlődéstörténete (Kozák Miklós)

Red rhyolite (5) is more subordinated than the former one. Predominant in its material is the pinkish-reddish volatile-rich litoidic phase. It is characterised by the nearly complete absence of microlits and slight amount of phenocrystals. Perlite (4) is one of the most characteristic rocks of industrial importance in the region, in the varied masses of which one can distinguish primary types (rhyolitic, compact, brecciated, pumiceous perlites) and secondary ones (obsidian-like, pearlstone and transitory-type perlites). Their variegation is demonstrated in Fig. 12, 13 and 15. The microscopic modal compostition of 95 thin-section samples from the Ktgat perlite area explored in detail by deep drilling is presented in Table 1. As an interesting feature, one can mention the varicoloured, mainly yellowish, greenish, vax-like and honey-coloured opals (Fig. 14) common in the environs of Kőgátbérc in the vein-like, reddish litoidic veins of the rhyolitic (spherolitic) type of perlite, appearing in the form of lenses of centimetre-decimetre size, in addition to which also appear the rarer red, white or even black opals, and manganese-dendritic variants (Kozák, 1979; Gyarmati et al. 1986). Precious opal can be found very rarely and subordinatedly, in millimetre sizes at most. Opal is the latest segregation separated along the movement planes of the volatile-rich rhyolitic phase, and frequently appear as filling materials in the residual spaces of caves lined with tridimite. Their material is frequently transgressed by micro-crevices and one can often observe on them various extents of devitrification. Very important formations in the environs of Telkibánya, evolving in genetic relationship with each other during the Sarmatian-Pannonian transition, are the pyroxene-amphibole dacite (3) and the acid, laminar pyroxene andésite (roof andésite) (2), which constitute the top region of the mountain range running South of the settlement. The dacite was exposed to stronger impacts of contamination and transvaporization, the consequences of which are pumification, enrichment in alkalis and the appearance of spherocrystals (Fig. 16). The lava from the fissure-volcanic material source of the roof andésite (Fig. 17) covered and protected the looser masses of the acid volcanites in Ósva Valley. Accompanying the dissection of the margin of the lava flow in the Pleistocene and its receding degradation, separate steep tors and extensive rock streams and stone rivers evolved. In our area the Upper Pannonian formations are represented only by remains of fluvial blanket gravel, occurring as surface ruins near Gunyakzt. On the grounds of those said above it can be stated that in the area between Telkibánya and Hollóháza, in consequence of frequent hydrothermal and transvaporisation impacts the amount of orthomagmatite is small. In Table 2 the chemical composition of the volcanites found near Telkibánya is described. Suitable for demonstration in the TAS diagram (Le Bas et al., 1986; Le Maître et al., 1989) were only 5 out of the 11 rock types and 10 from the 26 processed analyses (Fig. 18).