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Abstract: In the Ticau Mts., (NW Transylvania, Romania) an extended level of mica-poor, quartz-feldspar gneisses (so called leptinites) occurs. In this paper, the analytical data, obtained during the exploration of the Stejera kaolin deposit for an extensive geochemical study were utilised. After a short introduction in the geological setting and in the petrography of leptinites, the authors, using the Niggli's and other discrimination diagrams, demonstrate the igneous origin of these rocks. The statistical treatise of the analytical data and the petrochemical calculations resulted, that there were two or more petrographic and genetic rock-types. These rock-types were originated from magmatic differentiation processes (i.e. between dacitic and rhyolitic ones and their pyroclastic products), from mixing up with epiclastic materials and from further (postmagmatic) transformations (loss of alkalies and residual enrichment in Al2O3). Comparing the normative minerals, which are stable in medium stage of the metamorphism with the real mineralogical composition of the leptinites, it seems to be sure, that the chemical-mineralogical equilibria was accomplished. Finally, the use of some immobile elements permits to separate the original magma types, the same ones, which were recognised by petrochemical calculations. With the immobile elements (namely Rb, Y and Nb), the geotectonic setting of these rocks determined the separation line between the syn-collisional and volcanic-arc domains.

Keyword: NW Transylvanian Crystalline Islands, Sylvanides, ticau Mts, Metaigneous Rocks, Leptinites, Chemical analyses, Trace elements, Discrimination diagrams.