Clay Mineralization Of The Neogene Aged Volcanics Of The Northeastern Sivrihisar (Mülk-Demirci)

Abstract

The Neogene lacustrine units in the Mulk-Demirci region (NE Sivrihisar) are composed of detrital- evaporitic, volcanic and pyroclastic rocks. The Miocene volcanic rocks consist of lava flows of basalt and andesite composition and pyroclastic rocks are made up of agglomerate, tuff, altered tuff and tuffitic sandstone interbed- ded with altered claystone. These volcanic units change to dolomite, dolomitic limestone, marl and gypsiferous levels to the top. Some alteration zones in tuffs such as iron oxidation, limonitization, carbonatization and argilliza- tion are very noticeable with their yellow and red colors. Smectite is the main clay mineral which was formed as a result of alteration of volcanic and pyroclastic rocks in the study area. In some samples, smectite is accompa- nied mostly by feldspar, dolomite, calcite, opal-CT, quartz and partly by illite, gypsum and analcime. In the elec- tron microscopy (SEM) studies, smectite morphology was distinguished with platy flakes that are developed as a honeycomb texture. In addition, it was also determined in SEM images that smectite mineralization mostly deve- lops in dissolution voids and along fracture and fissures of volcanic glass or on the feldspar minerals. On the basis of field and laboratory studies, formation of smectite was found to be controlled by feldspar and volcanic glass which comprises the main component of tuffaceous units. Under hot and dry climate conditions, alteration of vol- canic material in the lake water had an important role in the formation of smectite. Smectite was formed by hyd- rolysis of volcanic glass and alteration of feldspar.