Türkiye Jeoloji Bülteni

Abstract: The Late Cretaceous volcanic rocks around Zigana Mountain (Gümüşhane) in the eastern Black Seametallogenic province in NE Turkey show intensive hydrothermal alteration but less weatheringalteration. The basement of the study area is formed by Late Cretaceous basalt, andesite and theirpyroclastics. These rocks are overlain by dacitic rocks of the same age, namely Dacite-I and Dacite-II.These volcanic rocks are bimodal in character and have developed in a volcanic arc environment.The volcanic rocks in the study area have been altered to the sericite/illite–chlorite facieses,and contain sericite/illite, chlorite, quartz, carbonate minerals (ankerite and calcite), iron-oxide, andrare kaolinite, smectite and epidote as the products of alteration. Sericitization/illitization is themost common type of hydrothermal alteration associated with these volcanics, and chloritization isthe most common alteration type after illitization; pyritisation is seen in all volcanics, and is the mostcommon in dacites. In some fields limonitisation is occasionally present. Epidotization is rare, andespecially seen in basalt and andesite. Isocon analysis was undertaken to estimate the mass gains andlosses of the Zigana Volcanics as a result of hydrothermal alteration. In general terms, the resultsshows that, basalt and andesite have 2-61% mass gain, Dacite-I 71% mass gain and 42 % mass loss,and Dacite-II 44% mass gain and 32% mass loss. Namely, both mass gain and mass loss occurred inthe volcanics during the hydrothermal alteration of the parent materials. From less altered rock tohighly altered rock there was an increase in illite-chlorite-kaolinite whereas there was a decrease incarbonate minerals. In the volcanics, fluids which cause sericitization and chloritization did notincrease metals like Cu, Pb and Zn and, in fact, it can be said that these fluids are poor in point ofthese metals. This also shows that the metals developed under different hydrothermal conditions. 

Abstract: SE Anatolia contains large exposed metamorphic rocks and intruded igneous rocks of variouscompositions. The study area described here includes Pütürge and Malatya metamorphites withlarge exposing in the region. Rocks of the Maden complex and local intrusion bodies constitute otherlithologies of the area.Based on petrographic studies, Pütürge metamorphites consist of mica schist/mica gneiss,garnet mica schist/garnet mica gneiss, calc-silicatic schist/ calc-silicatic gneiss, quartzo-feldspathicmica gneiss, quartz schist/quartzite, marble and amphibolite. Typical index minerals such as garnet,staurolite, kyanite, and sillimanite in these rocks characterize Barrovian zones. Mineral assemblagesof these rocks indicate that the Pütürge metamorphites were metamorphosed by the uppergreenschist and amphibolite facies conditions of the regional metamorphism. In this respect,estimates for peak temperature and pressure have been estimated as ~700 °C and 9 kbar,respectively, which implies a depth of at least 25 km. The Malatya metamorphites include mainlymarble and lesser amounts of slates, phyllites and schists. The presence of chloritoid, epidote andtremolite/actinolite minerals in the Malatya metamorphites suggest a temperature of ~500 °C and apressure of approximately 6 kbar, which coincides with a ~15 km depth.Metamorphites with progressive regional metamorphism in the study area were overprintedby products of retrograde metamorphism. The formation of the products of retrograde metamorphism has been closely related with the exhumation process of metamorphites and neo-tectonicevents in the region. 

Abstract: The Çan Geothermal Field is located on a central part of the Biga Peninsula in northwest Turkey.Volcanics are the dominant rock type in this region. Alteration zones and clay minerals are verycommon in these rocks. Sedimentary rocks, low-grade metamorphics and alluvium are othergeological units observed around Çan. These units include common fracture zones because of thetectonic activity in the region. Thermal waters have reached the surface via these fracture zones.Alluvium is the most productive aquifer in all geological units. Wells drilled in this unit yieldbetween 5-30 L/s. The transmissibility and permeability coefficients of this unit are of 50-421 m2/dayand of 1.01-16.8 m/day, respectively. In this aquifer, groundwater depth changes between 0.1 and8.3m. According to the IAH (1979) water classification, these thermal waters are of the Na-Ca-SO4type, the cold waters are of the Ca-Mg-HCO3 type and the snow samples are of a mixed water type.Geothermal waters have a meteoric origin. The mean temperature, electrical conductivity and pH ofthe thermal waters have values of 44.4C, 2941 S/cm and 6.9, respectively.Geothermometer equations were used for prediction of reservoir fluid temperatures of thegeothermal system and temperature values were obtained between 46 and 203C. δD, δT and δ18Oisotope analysis showes that thermal waters in the Çan region have a meteoric origin and are aminimum of 45-50 years old.