The Xialei manganese deposit in Guangxi is the most important super- large sedimentary manganese deposit of the Late Devonian in South China. There are two different views on the genetic mechanism of its typical manganese carbonate ores: one is oxidation precipitation- diagenetic transformation, and the other is direct precipitation in a reduced environment. Based on previous studies, this paper systematically analyzes the mineral paragenetic association, major and trace (rare earth) elements, and C- O isotope geochemical characteristics of typical rocks and ores in the Xialei manganese deposit, revealing the synergistic control of ore- forming material sources and redox conditions on manganese ores of different grades. In the low- grade manganese ores (MnO＜25%) of the Xialei manganese deposit, rhodochrosite develops heteronuclear structures and is paragenetic with microcrystalline pyrite, indicating a direct precipitation process in a reduced (sulfidic) water environment. Meanwhile, their geochemical characteristics,including high Fe/Mn ratios, significant positive Eu anomalies (average δEu=1. 32), relatively concentrated and generally slightly positive δCe values (ranging from 0. 94 to 1. 30, with an average of 1. 12), and relatively negative δ13C values (average=5. 05‰), collectively indicate that the low- grade manganese ores are products of direct precipitation, where hydrothermal Mn2+ in deep water directly combines with dissolved CO2-3 in the sub- deep reduced water environment. In contrast, the high- grade manganese ores (MnO≥25%) exhibit systematic geochemical differences, such as insignificant positive Eu anomalies (average δEu=1. 11), significantly expanded variation range of δCe values (0. 81~1. 64), low Fe/Mn ratios, and more negative δ13C values (average=7. 72‰). Combined with evidence of residual manganese oxides reported in previous studies, it is indicated that the high- grade manganese ores underwent a phase transition process of “oxide precipitation→organic matter- driven reduction” after sufficient mixing of hydrothermal fluids and seawater. In conclusion, the formation of manganese carbonate ores with different grades in the super- large Xialei manganese deposit in Guangxi involves two distinct metallogenic mechanisms, which are jointly controlled by hydrothermal activities and the redox (sulfidic) stratified water environment. This may be genetically related to the contemporaneous intracontinental rifting- magmatic hydrothermal events and mass extinction events.