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Mineralogical, petrographical and geochemical properties of zeolite bearing tuffs in nw Anatolia (Turkey)

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2008
Özen, Sevgi
The purpose of this study is to understand the geological, petrographical, mineralogical and geochemical characteristics of analcime-bearing tuffs in the Biga Peninsula and to determine formation process of these tuffs. The study area lies between Ayvacık and Küçükkuyu. The rock units are pre-Eocene basement rocks, Miocene Behram Volcanics (Arıklı Tuff, andesite, andesitic agglomerate), Pliocene volcanics, Miocene lacustrine sediments (Küçükkuyu Formation) and Quaternary alluvium. Analcimes which are found in Arıklı Tuff are the main objective of this study. Detailed petrographical, mineralogical and geochemical studies were caried out on the Arıklı Tuff samples by using petrographical microscope, X-ray diffractometry, scanning electron microscopy, diffrential thermal analyses inductively coupled plasma mass spectrometry and optical emission spectrometry. Fine-grained and coarse-grained analcime crystals in Arıklı Tuff were determined by their colorless, isotropic, trapezohedral and low relief. In addition to petrographic study, SEM and XRD methods also confirmed the presence of analcime. Two modes of occurrences were determined by the petrographical and mineralogical studies; coarse-grained euhedral or anhedral crystals in cavities and pumice fragments and single crystals or clusters of fine-grained analcimes embedded in the matrix. It was stated that there are two types of formation of analcime; alteration of volcanic glass and precipitation from alkaline solution based on petrographical and SEM studies. Geochemical methods, moreover, support the formation types.