The Xiangtan manganese ore deposit is mainly hosted in Mn-bearing black shale on the bottom of the Datangpo Formation in Neoproterozoic Nanhua system (Cryogenian), with rhodochrosite as the main ore-bearing mineral. The Xiangtan manganese ore deposit is characterized by the low Fe/Mn ratios. The ratios of redox sensitive trace elements such as Th/U, V/(V+Ni) and V/Cr indicate a sub-oxidation to exidation depositional environment, which implying that rhodochrosite was not formed by the direct precipitation of Mn²⁺ and CO₃^2-. The manganese ores are characterized by high total ΣREE content, relative middle REE enrichment compared with the light, heavy REE, and obvious positive Ce anomalies, implying that the element manganese precipitated firstly as Mn oxides or hydroxide. Meanwhile, the carbon isotopes of rhodochrosite ores display depletion of heavier C isotopes, suggesting that the organic carbon was involved in the formation of rhodochrosite. It is thus held that the metallogenic mechanism of the Xiangtan manganese ore deposit includes two processes (precipita_tion and transformation). Mn was buried under the hypoxia _condition after precipitation as Mn oxides or hydroxides from the upper oxide water, and then was reduced and transformed to Mn carbonates through the degradation of organic matter in the anoxic diagenetic environment. This ore-forming mechanism is consistent with that of several other typical Datangpo-type manganese ore deposits.