Mineralogy,chemistry ans ion-exchange properties of the zeolitized tuffs from the Sheinovets caldera, Eastern Rhodopes (South Bulgaria)

摘要

Zeolitized caldera-filling ignimbrites and assiciated air-fall tuffs from the easternmost parts of the Eastern Rhodopes Paleogene volcanic area have been studied. Na-mordenite and Ca-clinopyilolite, accompanied by adularia, opal-crystobalite and montmorillonite are the main products of the cpmplete alteration of the volcanic glass. Erionite, analcime and stilbite have been also identified. Opal-crystobalite and adularia are most abundant at the base of the pyroclastic succession.Zeolite content increase upward; mordenite is prevailing in the middle part and clinoptilolite in the topmost levels of the section. The chemical analyses have shown that compared with unaltered perlite zeolitized tuffs are deplered in Na_2O, Y, Rb, Ba and Mn and enriched in CaO and Sr.C.E.C.coefficient ranges from 60.66 to94.53 meq/100g.Lowtemperature hydrothermal solutions, probably heated by the initially hot pyroclastic material is the inferred cause of the zeolite formation.