Akademik Veri Yönetim Sistemi
TURKIYE JEOLOJI BULTENI-GEOLOGICAL BULLETIN OF TURKEY, cilt.66, sa.2, ss.223-256, 2023 (ESCI)
Magnesite occurrences in Turkey are generally formed as veins and stockworks in fractures and fissures of sedimentary rocks and altered ultramafic rocks. Ophiolitic units and magnesite formations crop out in the Central Anatolia part of the Anatolian Block within the Izmir-Ankara-Erzincan Suture Belt and around Yakacik village, located 15 km northwest of Ankara.The genetical investigation of the ore-forming fluid(s) was carried out using mineralogy and petrography, XRD characteristics, geochemical investigations and C-O isotope studies of ophiolitic units and magnesite formations in this study. Magnesite mineralizations were observed in two different forms, as quartz magnesite veins and as vein-stockworks, within the serpentinites of the Kapakli member, which consists of olistostromal layers containing serpentinite, gabbro, diabase, basalt, radiolarite, and limestones around Yakacik. The vein-type magnesites show cryptocrystalline and microcrystalline structures and are accompanied by quartz, chlorite, dolomite, and serpentine minerals. Quartz, serpentine, olivine, calcite, and dolomite were determined in stockwork-type magnesite. The clay minerals were chlorite, smectite, and kaolinite.In mineralogical and Raman spectroscopic studies, both the vein-and stockwork-type mineralizations, alterations from olivine to kammererite and kammererite minerals were detected. The values obtained from the results of the geochemical analysis indicate that magnesites are associated with ultramafic rocks. In order to determine the origin of magnesites, & delta;13C (VPDB) and & delta;18O (VSMOW) stable isotope studies were carried out on magnesite and limestone. The & delta;13C and & delta;18O values are-3.07 to 9.67%o and 23.05 to 27.49%o for magnesites and 0.20 to 3.74%o and 27.05 to 28.96%o for limestones, respectively. The most important rocks that could be the main source for the C and O of magnesite formations are Jurassic limestones.In conclusion, the movement of surface waters towards the depths, the heating role of volcanism during the early-middle Miocene, the decarbonation of limestones due to the warming of the deep-flowing fluids, and the incorporation of CO2, partly from a magmatic contribution, are the main formation mechanisms of magnesite formed in the fractures of serpentinized ultramafic rocks.