Origin of Pb–Zn deposits in the Hengyang Basin in the central part of the Qin-Hang metallogenic belt (South China): An example from the Yantianqiao deposit

Abstract

The metallogenesis of hydrothermal vein-type Pb–Zn deposits in the Hengyang Basin, part of the central Qin-Hang Metallogenic Belt (QHMB, South China), remains debate, with magmatic-hydrothermal and MVT models proposed. Yantianqiao (33903 t @ 3.25 % Pb and 1542 t @ 2.62 % Zn) is a representative deposit, features four distinct mineralization stages: (I) quartz-pyrite, (II) quartz-pyrite-chalcopyrite, (III) main-ore quartz-galena-sphalerite, and (IV) quartz-calcite. The limited pyrite δ³⁴S range (−5.8 to −1.7 ‰), similar ²⁰⁷Pb/²⁰⁶Pb ratios between galena (0.8483–0.8488) and the Zhaobingshan granodiorite (corrected average 0.86), and sphalerite geochemistry (Fe-In-enriched, Ga-Ge-depleted), reveal a genetic link between mineralization and the granodiorite. The low Co/Ni ratios (average 2.01) and δ³⁴S_V-CDT values (−4.0 ‰) of Stage I pyrite, commonly trapping silicate inclusions, indicate the marked fluid-rock interaction. The high Se/Te ratios (14.3) and As concentrations (median: 249 ppm), but depleted Co-Ni, of Stage II pyrite (Py-II) suggest minor meteoric fluid influx during this stage, also evidenced by the reported quartz H–O isotopes. Furthermore, low-fS₂ condition (−10.5 to −12.4) and Mn-depletion (0.869 ppm) of Stage III sphalerite (Sp-III) reflect the waning magmatism and increased meteoric fluid influx during Stage III, consistent with its low formation temperature revealed by Ni-Se-Bi-Mo depletion and SPRFT geothermometer result (119 ± 29 °C) of Sp-III. Therefore, Yantianqiao is inferred to be a magmatic-hydrothermal deposit genetically related to the Zhaobingshan granodiorite, with Pb–Zn mineralization driven by a progressively increasing meteoric fluid influx. This study advances the understanding of Pb–Zn ore genesis in the Hengyang Basin and provides insights applicable to similar sedimentary basins worldwide.