Pyrite Texture, Geochemical and Isotopic Signatures of Huangjindong Gold Deposit: Implication for Ore‐Forming Process

ABSTRACT Huangjindong gold deposit, as one of the largest gold deposits in Hunan Province, its refined history of fluid evolution and the relevant gold mineralization remain unsolved. In situ trace element and sulphur isotopic compositions of pyrite types are investigated to fingerprint the ore‐forming process. Two auriferous pyrite generations are identified: G1 (Py1a and Py1b) and G2 (Py2a, Py2b, Py3). The auriferous G1, intergrown with sericite, quartz, and minor arsenopyrite, is relatively hyper‐enriched with a large number of geochemically unrelated trace elements (e.g., Ti, W, V Co, Ni, Mo, Au, and As) and shows a broader range of δ 34 S values. These features indicate G1 genesis via fluid–rock interaction. The auriferous G2 (Py2a, Py2b, Py3) mainly occurs in quartz‐sulphide veins. Py2a and Py2b are associated with arsenopyrite, whereas Py3 coexists with minor sphalerite and chalcopyrite. Py2a is characterised by hyper‐enrichment in Au, As, and Se but depletion in Co and Ni, indicating an injection of As‐Au‐rich fluid. Au, Sb, Bi, Cu, and Pb progressively decrease from Py2a to Py3, demonstrating a continued compositional variation of the hydrothermal fluids. Laminated fault‐fill G2‐bearing quartz veins, Py2a with enrichment in Au, As, Pb, Bi, Sb, and Se, Py2b with more negative δ 34 S values related to fluid oxidation, together with oscillatory zoned Py3, are indicative of G2 genesis via a fault‐valve process which likely leads to the decomposition of Au(HS) 2− complexes. In short, the variations of trace elements and sulphur isotopes of pyrite generations can provide critical information for the evolution of ore‐forming fluid and the gold depositional mechanism.