Note on the stable isotope values of vein calcite in the El-Seboah peralkaline granite (SW Egypt)

Stable isotope data for carbon (δ¹³C) and oxygen (δ¹⁸O) are used to constrain the environments of calcite formation in two veins in the El-Seboah peralkaline granite in south-western Egypt. Vein I with calcite-magnetite-goethite-hematite-quartz, and vein II with calcite-magnetite-goethite-kaolinite-hematite-quartz are texturally distinct. The calcite of each vein has characteristic δ¹³C- and δ¹⁸O-values: + 0.32 and -7.28‰ for vein I and + 1.16 and - 1.21‰ for vein II, respectively. The observed differences between the δ¹³C values of the two veins indicate that they represent two separate systems of primary dissolved inorganic carbon formed at or near equilibrium with atmospheric CO₂. The δ¹⁸O values, on the other hand, indicate calcite deposition from meteoric waters which were fresh for vein I and brackish for vein II.