Longhua, the first five-element (Ni-Co-As-Ag-Bi) hydrothermal vein deposit in China: Constraints from mineral characteristics and fluid evolution

• Published in: Journal of Asian earth sciences Vol. 292; p. 106712
• Main Authors: Huang, Xinshuo, Cao, Mingjian, Zhang, Baolin, Evans, Noreen J., Li, Zengsheng, Zou, Xinyu, Wang, Shuo, Shan, Pengfei, Li, Junyu, Li, Guangming, Qin, Kezhang
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.10.2025
• Subjects: Arsenides-sulfarsenides-sulfides; Five-element vein; Fluid inclusions; Reduction; The Longhua deposit; Five-element vein; Reduction; The Longhua deposit; Arsenides-sulfarsenides-sulfides; Fluid inclusions
• ISSN: 1367-9120
• DOI: 10.1016/j.jseaes.2025.106712

•Longhua has a Ni-Co-As-Ag-Bi assemblage with fern-like and spherical textures.•Longhua shows mineral and element sequence: arsenide → sulfarsenide → sulfide; Ni → Co → Fe; As → S.•CH4-rich, medium–low temp fluids from black shales affect Longhua’s mineral sequence.•Longhua is China’s first five-element vein deposit with a rare late Ni-Co sulfidic stage. The Longhua deposit is a vein-type Ni-Co deposit in South China, known for its ultrahigh grades of Ni (6.48 %) and Co (0.44 %), which has attracted considerable attention. However, the classification of the deposit remains disputed, presenting challenges for comprehensive metallogenic studies. This study primarily investigates the mineral characteristics and fluid evolution of the deposit, which is characterized by the following features: (1) It hosts a Ni-Co-As-Ag-Bi assemblage within steeply dipping quartz-calcite veins; (2) It contains Ni-Co-Fe arsenides, sulfarsenides, sulfides and native Bi with special fern-like and spherical textures; (3) The ore minerals precipitate from the stage of arsenide (monoarsenide → diarsenide → triarsenide), to sulfarsenide, and ultimately to sulfide, aligning with the elemental sequence of Ni → Co → Fe in each stage and overall transition from As to S; (4) The ore-forming fluids are characterized by medium-to-low temperatures (230 − 90 °C) and are enriched in CH4. Together, these findings indicate that the deposit could be classified as a five-element (Ni-Co-As-Ag-Bi) hydrothermal vein deposit. The reduction of the ore-forming fluid, attributed to the oxygen fugacity buffering effect of CH4-organic carbon derived from the thermal decomposition of the host black shales, probably plays a significant role in generating the mineral sequence. The final sulfide stage formed at a higher oxygen fugacity, likely due to the consumption of the black shales, which reduced the overall reducing capacity. The Longhua deposit is the first five-element hydrothermal vein deposit in China, and provides an excellent example for investigating the complete formation processes.