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

Abstract

Abstract. Stable isotope data for carbon ( 13 C) and oxygen ( 18 O) 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 calcitemagnetite-goethite-hematite-quartz, and vein II with calcite-magnetite-goethite-kaolinite-hematite-quartz are texturally distinct. The calcite of each vein has characteristic  13 C-and  18O-values: + 0.32 and -7.28‰ for vein I and + 1.16 and -1.21‰ for vein II, respectively. The observed differences between the  13 C 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  18O values, on the other hand, indicate calcite deposition from meteoric waters which were fresh for vein I and brackish for vein II.

Disentangling shallow‐water bulk carbonate carbon isotope archives with evidence for multi‐stage diagenesis: An in‐depth component‐specific petrographic and geochemical study from Oman (mid‐Cretaceous)

“…The persistently higher carbon isotope signature is not abrupt enough to consider processes related to fermentation of organic acids, CO 2 reduction or excessive evaporation (Clayton, ). Alternatively, a slight carbon isotope fractionation is here proposed, owing to lowered p CO 2 in fluids circulating at shallow depth, which is reasonable during pressure release phenomena (Shemesh et al ., ; Hassan, ). Several reports of slightly heavier δ 13 C values along late diagenetic calcite and even dolomite veins show a similar pattern (Morad et al ., ; Vandeginste et al ., ; Arndt et al ., ; Balsamo et al ., ).…”