Bulletin of the Mineral Research and Exploration (Nov 1996)
DISTRIBUTION AND GENESIS OF NEOFORMED MINERALS IN KOYUNAĞILI (MIHALIÇÇIK-ESKİŞEHİR) AREA
Abstract
- The study area is located at the Southwest of Koyunağılı village situated in the south margin of the BeypazarıQayirhan basin which is in the Middle Sakarya Massif. The Neogene units in the investigated area are Çoraklar, Hırka, Karadoruk, Akpınar, Bozçayır, Acısu and Kırmızıtepe Formations. The mineralogic features of the clay minerals and tha host rock samples were studied by means of petrographic, XRD, DTA-TG, SEM-EDX and IR Spectra techniques. Various effects of pH values of the environment related to evaporation and feeding of the basin from several areas, cause the formation of different mineral paragenesis. The main mineral paragenesis are; loughlinite + analcime + calcite + dolomite + feldspar, sepiolite + analcime + dolomite + illite, sepiolite + analcime + dolomite + opal-CT + feldspar, montmorillonite + analcime + dolomit + illite + feldspar + quartz + opal-CT, montmorillonite + analcime + calcite + felspar + illite and montmorillonite + dolomite + calcite + analcime + quartz + Feldspar. Montmorillonite is formed at the margin of the basin, derived from freswater and detritic materials which contain Al and Mg. Aluminum ions are generally dominant in the shallow part of the basin facies of the Bozçayır and Acısu Formations. In the Akpınar Formation, sepiolite is formed at a non-acidic environment, which is rich in Mg and Si, but poor in Al. At the center of the area (around Ocak), loughlinite is formed in a way similar to that of sepiolite by combining of Na, originated from the alteration of tuff, to the Si and Mg. As a result of the alteration, especially after the formation of montmorillonite the proportion of (Na+K)/H increases and finally analcime and feldspar are formed. At the south of the area magnesite is formed at the bottom part of the Hırka Formation, due to the high Mg and pH and low Si values. To the north, some dolomite, depending on the decreasing of Mg content, is observed. At the north, dolomite and calcite are formed interbededly, due to changes in the pH conditions controlled by evaporation and freshwater participations. Sepiolite, loughlinite, analcime, feldspar, opal-CT and a small amount of quartz are formed authigenically, in and around the altered glass pores as a result of alteration of volcanic glasses.
