Ahmet Yıldız

Geochemical Constraints on the Genesis of the Günyüzü Pluton, Northwest Anatolia, Turkey

The Tavsanli Zone in northwest Turkey is intruded by many Late Cretaceous to Eocene (91-45 Ma) calc-alkaline granitoids, of which the Günyüzü pluton in the Eskisehir region is the least studied. The Günyüzü rocks are high-K, calc-alkaline (I-type) intrusions, and are comprised of diorite, granodiorite, granite, and granite porphyry. Typical minerals are plagioclase, K-feldspar, quartz, biotite, hornblende and Fe-Ti oxides. Chondrite-normalized REE patterns for the Günyüzü rocks are moderately fractionated and have small negative Eu anomalies. They are enriched in LILE and LREE relative to HFSE, showing characteristics of arc-related granitoids. Low values of molar K2O/Na2O, Al2O3/(FeO+MgO+TiO2), and (Na2O+K2O)/(FeO+MgO+TiO2) ratios demonstrate that the Günyüzü magma(s) were produced from mafic lower crustal rocks.

APPLICATION OF BOX–BEHNKEN DESIGN TO MODELING THE EFFECT OF SMECTITE CONTENT ON SWELLING TO HYDROCYCLONE PROCESSING OF BENTONITES WITH VARIOUS GEOLOGIC PROPERTIES

As advances in technology have led to increased use of bentonites, more high-quality bentonite has been sought. The volume of high-quality bentonites available is shrinking and use of bentonite reserves containing impurities is inevitable. The aim of this study was to apply Box–Behnken experimental design and response surface methodology to model and optimize some operational parameters of a hydrocyclone to produce three groups of bentonite concentrates. The four significant operational parameters of hydrocyclones are feed solid ratio, inlet pressure, vortex diameter, and apex diameter, and these parameters were varied and the results evaluated using the Box–Behnken factorial design. In order to produce bentonite concentrates using a hydrocyclone, mathematical model equations were derived by computer simulation programming applying a least-squares method, using Minitab 15. Second-order response functions were produced for the swelling and to establish the quantity of smectite in the bentonite concentrates. Predicted values were found to be in good agreement with the experimental values (R2 values of between 0.829 and 0.999 for smectite and three different swelling groups for the bentonites). Although in natural states these bentonites are not suitable for industrial use, enhancements were obtained giving up to 81.45% smectite and by increasing swelling by 194% for the three bentonite groups. The swelling properties of the bentonites are improved by increasing the proportion of smectite content. The graphics were designed to relate swelling and smectite content according to the two-dimensional hydrocyclone factors, and each factor was evaluated in itself. The present study revealed that the Box–Behnken and response surface methodology can be applied efficiently to model the hydrocyclone for bentonite; the method is economical and provides the maximum amount of information in a short period of time and with the smallest numberof experiments.

Comparison of radon concentrations in soil gas and indoor environment of Afyonkarahisar Province

It is well known that radon is the main source of natural radiation exposure to the population. Indoor radon concentrations in an area are affected by ascending radon migration following the convection of groundwater and soil gas along fractures and faults in the bedrock sediments. There are various studies showing that positive radon anomalies in the soil gas are found to coincide with the locations of houses showing the highest concentrations. Moreover, soil gas radon levels and soil permeability are important factors in determining the radon potential of an area, because high permeability enables the increased migration of radon from the soil into houses. Since radon in homes originates mainly from soil gas radon, it is of public interest to study the correlation between soil gas radon and indoor radon in different geographic locations. In the present work, a correlation study was carried in conjunction with radon concentrations in soil gas and indoor environment of Afyonkarahisar Province. The provincial center was assumed to be divided into four regions according to the rock types and tectonic structure to show also the geological structure effect on radon concentrations. The indoor radon concentrations were measured in 74 dwellings using CR-39 passive nuclear track detectors, and the radon concentrations in soil gas were determined in 243 drilled holes using AlphaGUARD detector. The correlation coefficient of 0.97 was obtained between radon concentrations in soil gas and indoor environment of Afyonkarahisar Province.

SEDIMENT-HOSTED KAOLIN DEPOSIT FROM ÇAKMAKTEPE (UŞAK, TURKEY): ITS MINERALOGY, GEOCHEMISTRY, AND GENESIS

Because of their geochemical properties, the Çakmaktepe (Uşak) kaolin deposits have been considered as primary. New sedimentological, mineralogical, and geochemical data suggest that the Çakmaktepe kaolins are secondary deposits of sedimentary processes after hydrothermal alteration of the source rocks. The kaolins in the Çakmaktepe deposit were formed from the hydrothermal alteration of calcalkaline Karaboldere volcanics (KBV). The kaolinized materials were then reworked and accumulated in a lacustrine basin. The argillic alteration zones were associated with faults, and lateral zonation of minerals was observed in the KBV. Smectite was the major phyllosilicate in the ‘outer zone’. The alteration mineralogy of the ‘inner zone’ was similar to that of the Çakmaktepe kaolins and consisted mainly of kaolinite with minor amounts of smectite and alunite. The trace-element abundances in the kaolinized volcanics and the Çakmaktepe kaolins indicated hypogene conditions. The δ18O values of the Çakmaktepe kaolins ranged from 0.2 to 5.92%, which indicated that the Çakmaktepe kaolinites were formed at temperatures between 92 and 156°C, and the δD values ranged from −91.68 to −109.45‰. The irregular edge-to-face morphology, the variation in grain-size, a few broken crystals of kaolinite, the deficiency of dissolution-replacement and crystallization mechanisms, and the the low sphericity, very angular, and poorly sorted quartz crystals in the kaolins all result from transport processes. The sedimentary structures, including trough cross-lamination, tool marks, and load casts, indicate transportation by turbulent waters and deposition of kaolin layers in a shallow lake.