Source of the mineralizing fuids in ultramafc related magnesite in the Eskişehir area, northwest Turkey, along the İzmir Ankara Suture: a stable isotope study 1, 2

Abstract

The Eskişehir magnesite deposits (Süleymaniye, Margı, and Tutluca) are located in the western part of the İzmir AnkaraSuture Zone, northwestern Turkey. Tese vein and stockwork type magnesite deposits, which occur along major and minor faultsystems, are hosted by Alpine-type ultramafc rocks. Te purpose of this study was to understand the origin of the hydrothermalwaters responsible and the source of carbon dioxide, and to compare these deposits with similar magnesite occurrences in Turkey andelsewhere. Petrographic and XRD analyses indicate that magnesite was the major carbonate mineral formed. Deposits are predominantlymicritic and locally microsparitic, but some also contain secondary calcite and dolomite. Te δ 13C (V-PDB) values of the Süleymaniyemagnesites ( 2.7 to 7.7 ), the Margı magnesites ( 7.6 to 11.2 ), and the Tutluca magnesites ( 8.7 to 10.4 ) indicatethat sources of carbon may include atmospheric carbon, dissolved inorganic carbon, freshwater carbonate, and mantle derived CO 2.Te δ 18O (SMOW) compositions of the magnesite range from 27.4 to 30.8 and show that the oxygen was derived from marinelimestone and metamorphic rocks. Te Süleymaniye magnesites have heavier carbon isotopic values than the others because of thegreater contribution of mantle sourced CO 2, while oxygen isotopic values were similar to those of other altered ultramafc relatedmagnesites in Europe (Former Yugoslavia, Greece). Te Margı and the Tutluca magnesite deposits have carbon and oxygen isotopicvalues similar to those of other ultramafc-related magnesite deposits. Based on isotopic data, we argue that the magnesite deposits inthe Eskişehir area formed in a near surface environment at low pressure and temperature. Te estimated temperature, using average δ 18Ovalues, suggests that magnesite was precipitated from water at 37 °C.