Geochemical and isotopic signatures of ultramafic-hosted magnesite deposit: a case study of the Edige region (Ankara-Central Anatolia)

The magnesite deposit of the Edige region in Ankara-Elmadağ District of Türkiye is hosted in serpentinite/serpentinized ultramafic rocks, which are mainly harzburgite and dunite. Mineralogical and petrographic studies have shown that ultramafic rocks are composed of serpentine, olivine, and pyroxene with serpentinization preceding magnesite formation. The X-ray diffraction results reveal that dolomite, quartz, calcite, and clay minerals are the main minerals in magnesite samples from serpentinite/serpentinized ultramafic units. Olivine, pyroxene, serpentine, chromite, and iron oxide minerals are also present. Scanning electron microscopy and energy dispersive spectrometry results show that magnesite in rhombohedral and cryptocrystalline forms is the dominant mineral accompanied by dolomite and quartz. The geochemical data show high MgO values between 33.3% and 37.2% and SiO₂ values between 37.3% and 42.9%, indicating peridotite characteristics. The CaO values are very low, with an average of 1.01%, and the Al₂O₃ values are between 0.2% and 1.8%. These results also suggest that peridotite rocks formed through partial melting of a depleted mantle source. Stable carbon (δ¹³C) and oxygen (δ¹⁸O) isotope data indicate magnesite formation at shallow depths through low-temperature diagenetic processes, with δ¹³C values between –13.62‰ and –10.54‰ Vienna Pee Dee Belemnite (VPDB) and δ¹⁸O values between –3.51‰ and –2.01‰ VPDB corresponding to 27.29‰ to 28.84‰ Vienna Standard Mean Ocean Water. These data suggest that the carbon came from organic-rich sediments and fluids influenced by meteoric waters.