Abstract The banded iron formation (BIF) of the Saksaganska Formation within the Kryvyi Rih belt in Ukraine hosts one of the largest Fe ore resources in Europe. The multistage genesis of Fe ores involves gas-bearing fluids of complex and unresolved origins. This study aims to identify sources of these gases and their generation mechanisms within evolving fluid systems, which were responsible for Fe ore formation, upgrading, and alteration, as this is crucial for refining ore genetic models. Trace element geochemistry and stable C-N isotopes of fluid inclusion gases are used to determine multiple generations of iron oxides and associated gangue minerals, reflecting mineral transformations that fostered the development of large-scale gas-bearing fluid systems during high-temperature metamorphic and metasomatic-hydrothermal reactions. The C-N isotope compositions of quartz-hosted fluid inclusion gases from various sites within the Kryvyi Rih belt record high carbon fluxes and progressive evolution of CO2( ± N2-CH4)-bearing fluid systems during the late Paleoproterozoic. The dynamic large-scale fluid migration encompassing multiple fluid flow pulses played a pivotal role in the upgrading of Fe quartzites into high-grade hypogene Fe ores of the Saksagansk type. The δ13C(CO2) and δ15N values of fluid inclusion gases hosted in quartz within schists, ferruginous horizons, and shear zones suggest different carbon sources, including graphite-rich schists, metamorphic decarbonation reactions, devolatilization of greenstone belt sequences, metasomatic-hydrothermal decomposition of Fe carbonates, and igneous sources. Unique trace element compositions observed in specular hematite and magnetite indicate selective alteration by Nb-Ta-rare earth element + Y (REY)-bearing hydrothermal fluids likely originating from a deep alkaline magmatic source.
Sośnicka et al. (Sun,) studied this question.