Vol 16, (1980)
Vol 16, (1980)
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- Category: Vol 16, (1980)
Authors:Viktor Fiala
Full version (95,675 kB)Abstract: Coarse-grained porphyritic biotitic granite of Variscan age – Borsk granite – is the most important igneous rock of the Vítkov locality. The older rocks here are diorites and crystalline slates, these in the form of xenoliths in Bor granite. Of the younger rocks, finer-grained or non-porphyritic varieties of granite and vein rocks – lamprophyres and especially aplites – are more prominent in the locality. The petrographic characteristics of the Bor granite, which was most exposed to the action of hydrothermal solutions, always following the relevant tectogenesis, are given. The development of the altered Bor granite (and other rocks of the locality) can therefore be considered polycyclic, their current character was formed during the first, second and probably additional alteration cycles. The extensive damage of the Bor granite by hydrothermal solutions, in contrast to other rocks of the locality, can be explained by its greatly increased porosity as a result of tectonic movements. The bulk density and magnetic susceptibility values of the altered rock are variable and significantly different from the original values. Major (sericite, quartz, albite, chlorite and younger clay minerals), minor (epidote, hematite, Ti-minerals and carbonates) and facultative (adular, zeolites, organic substance (?), limonite and sulphides) alteration minerals are outlined and described. Alteration minerals in the rock were formed as pseudomorphing, freely newly formed and veined. A common phenomenon is the growth of crystals, epitaxy can also be observed in places, which can also be associated with the formation of pseudomiarols in the rock. A basic succession scheme of alteration minerals was established and individual sub-alteration processes were briefly characterized.
