The Mianxian-Lueyang-Ningqiang area is a significant polymetallic ore concentration region in the Southern Qinling Mountains and one of the main production areas for Sinian manganese deposits in Shaanxi Province, China. This study focuses on the Hanjiashan manganese deposit located in the central segment of the Mianxian-Lueyang suture zone. Through systematic field geological investigations, combined with petrographic, mineralogical, geochemical, and C-O isotopic analyses, the genesis, sedimentary environment, and material sources of the manganese deposit are discussed. The results indicate that the manganese-bearing series belongs to a carbonaceous fine-clastic rock - magnesium carbonate rock formation in the upper member of the Lower Sinian Doushantuo Formation, with the ore bodies occurring as stratiform and lenticular forms. Manganese deposits primarily during the sedimentary-diagenetic stage and are predominantly compsosed of rhodochrosite, manganoan dolomite and rhodochrosite, with observed framboidal pyrite. Geochemical characteristics show that the ores have low average ratios of Fe/Mn (0.10), Co/Ni (0.37), V/(V+Ni) (0.69), and Al/(Al+Fe+Mn) (0.11), but high average ratios of V/Cr (3.42), U/Th (1.17), and Y/Ho (34.47). The Post-Archean Australian Shale (PAAS)-normalized rare earth element (REE) patterns exhibit a left-leaning trend with a significant positive Y anomaly, and weak positive anomalies for both Eu (avg. 1.24) and Ce (avg. 1.33). The average δ13CPDB value is -5.46‰, which is close to values characteristic of modern seafloor hydrothermal vents and magmatic sources. Synthesizing these findings, it is concluded that the manganese deposit formed in a suboxic-to-anoxic outer shelf environment, with relatively high mineralization temperatures (avg. 106.07℃) and low salinity (avg. 1.88‰). The ore-forming materials were primarily derived from a submarine hydrothermal system, with additional contributions from seawater, classifying it as a hydrothermal sedimentary-type manganese deposit. This study confirms the dominant role of hydrothermal sedimentation in the mineralization process, deepens the understanding of manganese deposit genesis in the Mianxian-Lueyang-Ningqiang area, and provides a theoretical basis for research on regional metallogeny and prospecting exploration for manganese deposits.