Zeolites and zeolitization of acid pyroclastic rocks from paroxysmal Paleogene volcanism, Eastern Rhodopes, Bulgaria

Abstract

An extensive bimodal volcanic suite developed in the Late Paleogene in the Eastern Rhodopes Mountains, Southern Bulgaria. Most of the widespread and thick rhyolitic tuffs and ignimbrites. erupted during two major Early Oligocene acid pha ses, were emplaced in a shallow marine environment and subsequently altered. K-rich Ca-clinoptilolite (in some places K-clinop tilolite. mordenite or analcime). clay minerals (celadonite or/and smectite). adularia (or albite) and opal-CT replace the volcanic glass. The zeolitized pyroclastic rocks are strongly depleted in MnO. Na20. K20, and enriched in CaO. Fe201. Ti02 and MgO. Regional zoning in distribution of the major glass-replacing minerals has been established: quartz+ adularia (or albite)± zeolites in the proximal to the vent area: zeolites in the medial and clay minerals in the distal area. Vertical zoning has been also recog nized because on ly the basal pyroclastic layer is transformed into adularia+ quartz whereas clinoptilolite. accompanied by opal CT and clay mineral s. prevails in the rest of the section. The zeolitized glass shards are characteristically zoned: (I) a thin rim (< 5 �m thick) of celadonite coats the shard surface retaining their original shape: (2) a 30-50 , um-thick zone. made of contiguous platy zeolite crystals. oriented perpendicular to the rim and (3) a central zone of large euhedral crystals. surrounding a central hollow area. Phenocrysts are not affected by the zeolitization and some relict glass is found in the top of the pyroclastic section. According to the semiquantitative X-ray analysis and heat of immersion test of CcLFAZ et a!. (1973) the clinoptilolite content in the zeolitized pyroclastic rocks varies from 38 to 72 wt. 'lc. The cation exchange capacity values range between 40 and 153 meq/ 100 g and show a significant positive correlation with clinoptilolite content obtained by the heat of immersion test (r = 0.71). The lateral zoning and presence of typical hydrothermal minerals such as celadotite indicate that zeolitization of the thick Eastern Rhodopes pyroclastic series results from the operation of a large low temperature hydrothermal system. The hydrothermal solu tions consist of marine water heated by the anomalous geothermal gradient of the active volcanic areas or/and by the hot pyro clastic deposits.

Use of surface modified natural zeolite (SMNZ) in pharmaceutical preparations Part 1. Mineralogical and technological characterization of some industrial zeolite-rich rocks

“…The subsequent alteration of the volcanic glass determined the crystallization of K-rich Ca-clinoptilolite, sometimes along with mordenite or analcime, clay minerals, adularia, and opal-CT. The presence of typical hydrothermal minerals such as celadonite strongly suggests that zeolitization of the thick Eastern Rhodopes pyroclastic series derives by a diffuse circulation of low temperature hydrothermal solutions consisting of marine water heated by the anomalous geothermal gradient of the active volcanic areas [33].…”

Mineralogical Contraints to the Formation of Vein-Type Zeolites From Kizari Area, Thrace Northern Greece

“…Recent studies on southeastern Rhodope zeolites in Bulgaria and Greece suggested a hydrothermal model, where the zeolitization of the volcaniclastic rocks was caused by low-temperature open hydrothermal systems in a shallow-marine environment (Raynov et al, 1997;Sheppard and Hay, 2001;Yanev et al, 2006;Marantos et al, 2007).…”

Alteration processes and products of acid pyroclastic rocks in Bulgaria and Slovakia

“…This is important because non-zeolitized glasses are often considered as the ancestor glasses of the pyroclastic rocks, and their chemical composition is used to evaluate the input-output of chemical components during the process of zeolitization. Significant K leaching and increasing of Na, Ca and Mg content is assumed from supposed hydrothermal solutions (Djourova & Aleksiev, 1983;Yanev et al, 2006). The latter fact is in contradiction with the ion-TABLE 1.…”

“…Central and Eastern Slovakia. (Own unpublished and published chemical analyses and data after Aleksiev & Djourova, 1982;Djourova & Milakovska, 1987;Ivanova et al, 2001;Yanev et al, 2006). (Cpt À clinoptilolite; Mor À mordenite; Ana À analcime; KFs À potassium feldspar; Cri À cristobalite; Q À quartz; Ad À adularia).…”

“…Raynov and coworkers correctly point out that the geoautoclave mechanism does not explain the zeolitization of both the fall-out tuffs and the matrix of epiclastic deposits, since they had been deposited as a cold material. Ivanova et al (2001) and Yanev et al (2006) supposed that the heat of the pyroclastic flows, together with abnormally high geothermal gradient in the active volcanic areas, generate hydrothermal systems circulating in the ash layers. According to our field investigations, evidence or indications of hydrothermal solution circulation in the tuff layer have not been observed.…”