Silicic vitric tuffs of the Alaçatı (Çeşme) area, west of Izmir (Turkey), are partly altered to authigenic zeolites and clay minerals. Mordenite and clinoptilolite-heulandite accompanied by smectite are the main alteration products of the tuffs. Scanning electron microscope examination indicates that mordenite forms mainly from a gel-like precursor and to a lesser degree from volcanic glass. Mordenite and clinoptilolite-heulandite have formed by the hydrolysis and dissolution of silicic vitric tuffs by thermal waters which circulated through the fracture zone into porous vitric tuffs. These thermal waters, which resulted from mixing of thermal (Na-Cl type) and groundwaters, provided the extra Na and Ca that are necessary for the formation of mordenite. Various percentages of calcite are present in the altered tuffs. The enrichment of calcite in the altered tuffs indicates that thermal waters supply Ca, sourced from dissolution of Triassic carbonate rocks.The alteration minerals in the Alaçatı (Çeşme) area do not seem to be laterally zoned. The occurrence of the zeolites seems to be related to inferred fracture zones trending NE—SW. These fracture zones are important because they provide porosity and permeability in the tuffs for zeolite formation. The large glass content and permeability of tuffs accompanied by the favorable hydrochemical condition resulted in zeolitization of the Alaçatı (Çeşme) area.
The concentrations of uranium, iron and the major constituents were determined in groundwater samples from aquifer containing uranyl phosphate minerals (meta-autunite, meta-torbernite and torbernite) in the Köprübaşı area. Groundwater samples from wells located at shallow depths (0.5-6 m) show usually near neutral pH values (6.2-7.1) and oxidizing conditions (Eh = 119-275 mV). Electrical conductivity (EC) values of samples are between 87 and 329 lS/cm -1 . They are mostly characterized by mixed cationic Ca dominating bicarbonate types. The main hydrogeochemical process is weathering of the silicates in the shallow groundwater system. All groundwater in the study area are considered undersaturated with respect to torbernite and autunite. PHREEQC predicted UO 2 (HPO 4 ) 2 2-as the unique species. The excellent positive correlation coefficient (r = 0.99) between U and PO 4 indicates the dissolved uranium in groundwater would be associated with the dissolution of uranyl phosphate minerals. The groundwater show U content in the range 1.71-70.45 lg/l but they are mostly lower than US EPA (2003) maximum contaminant level of 30 lg/l. This low U concentrations in oxic groundwater samples is attributed to the low solubility of U(VI) phosphate minerals under near neutral pH and low bicarbonate conditions. Iron closely associated with studied sediments, were also detected in groundwater. The maximum concentration of Fe in groundwater samples was 2837 lg/l, while the drinking water guidelines of Turkish (TSE 1997) andUS EPA (2003) were suggested 200 and 300 lg/l, respectively. Furthermore, iron and uranium showed a significant correlation to each other with a correlation coefficient (r) of 0.94. This high correlation is probably related to the ironrich sediments which contain also significant amounts of uranium mineralization. In addition to pH and bicarbonate controlling dissolution of uranyl phosphates, association of uranyl phosphates with iron (hydr) oxides seems to play important role in the amount of dissolved U in shallow groundwater.
The mineralogical and petrographic properties of the zeolitic tuffs around the Yenice-Saraycık, southwestern of Demirci (Manisa), were studied by using the polarizing microscope and powder X-ray diffraction (PXRD). Microscopic observations revealed that the tuffs are dominated volcanic glass however, contain small amounts of crystal and rock fragments. The crystal fragments consist mainly of quartz, k-feldspar, plagioclase and trace amounts of biotite. The glassy tuffs were altered to zeolites and other minerals.
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