Strontium Isotope Composition of Rocks and Ores of the Porozhinsk Deposit (Yenisei Ridge, Krasnoyarsk Region).

Wide variations of 87Sr/86Sr (0.70825‒0.70924) have been established at the Porozhinsk deposit in manganese ores and carbonates ascribed to the Pod"emsk Formation. These data, together with variations in the carbon (δ13C = –14.6...2.0‰, PDB) and oxygen (δ18О = 19.4...28.3‰, SMOW) isotope composition indicate different conditions of the formation of the studied rocks. The 87Sr/86Sr values in the studied dolomites of the Porozhinsk deposit are much higher than those of carbonate rocks (dolomites, limestones) of the Pod"emsk Formation from the Chapa River section. The position of the 87Sr/86Sr values of dolomites from the Porozhinsk deposit on the secular 87Sr/86Sr variation curve for Late Proterozoic ocean (Kuznetsov et al., 2014) suggests that the carbonate rocks attributed to the Pod"emsk Formation at the Porozhinsk deposit have younger age than carbonates of the Pod"emsk Formation from the Chapa River section. The Mn/Sr values usually taken as a criterion for the degree of secondary alteration of carbonates (in interpreting 87Sr/86Sr variations and discussing the suitability of the material for chemostratigraphic constructions) are not suitable for rocks formed in manganese ore sedimentation basins. [ABSTRACT FROM AUTHOR]