« Back

Abstract: The Badenian deposits from the Coştiui zone form a small sedimentary basin in the north of Maramureş depression. The Badenian is disposed discordantly over the Eocene deposits and includes dacitic tuffs having a thickness of about 250m with globigerines. Sarmatian formations represented by marls, marls-sandstone, friable sandstone and sands. In the Coştiui zone the Badenian tuffs consist of the basis of lapilic tuffs over which crystaloclastic and vitroclastic tuffs are disposed. The primary magmatic minerals are represented by plagioclase feldspars, quartz, alkaline feldspars, micas (biotite and muscovite), pyroxene, amphiboles. The volcanic glass of the Costiui tuffs shows a high degree of devritrification in glassy groundmass with formation of diagenetic minerals represented by zeolites. By using the X-ray diffraction analyses the presence of the following members from the zeolites groups has been pointed out: clinoptilolite, mordenite and heulandite. The clinoptilolite is the predominant zeolite and is characterised by an increased crystallinity degree. The celadonite and the cryptocrystalline silica appear besides the zeolites. The chemical composition of the zeolitic tuffs from the Coştiui zone emphasised a dacitic character. The average cationic exchange capacity is: Ca²⁺=62 mvali/g, Mg²⁺=6 mvali/g, Na⁺=18 mvali/g, K⁺ =24 mvali/g. The surface area varies between 12.4 – 21.9 m²/g. The density is of 1.99% g/cm3. The zeolitization of the tuffs has a pervasive character and has affected especially the volcanic glass. From the point of view of the mineralogical composition and of the physical and chemical properties the tuffs from the Coştiui zone are similar with those from the Iza zone. The deposits of zeolitic tuffs from the Coştiui zone are included in the “open system deposits” type.

Keyword: Badenian, zeolitic tuffs, clinoptilolite, cationic exchange capacity, density, zeolitization.