Geochemistry of hydrothermally altered rocks in Klisura occurrence, Sofia district

Klisoura occurence is located close to Klisoura Village, about 6 km west of the town of Bankya. Host rocks are Upper Cretaceous andesite pyroclastics, some andesite bodies and veins that form the core of Radui anticline – part of Viskyar-Vitosha synclinorium. The hydrothermallly altered rocks cover an area of about 2 km² and are exposed around the intersection center of several fault systems. Кунов et al. (2000) described the occurence as epithermal, of acid-sulfate type. 
   The main aim of the present study is to trace the behaviour of rare elements in the process of advanced argillic alteration that lead to the formation of secondary quartzites in the occurrence. The conclusion are based on the distribution of rare elements in different alteration types – from less to more intensively altered varieties. Here, the term "zone" is used as a synonim of "hydrothermally altered rock type" since the latter forms the zones of hydrothermal alterations.
   Samples from all alteration types were collected during the field studies. Materails from drillhole No3 (drilled in 1974) were also analyzed. The main components and 18 rare elements were analyzed by X-ray fluorescence and atomic absorption.