• The Lunshan gold deposit is a sedimentary rock-hosted epithermal deposit. • Zircon U-Pb dating precisely brackets the Lunshan gold mineralization within 105–103 Ma. • Zircon trace elements indicate Lunshan igneous suites derivate from hydrous, oxidized magmas capable of forming porphyry deposits. • Gold ore-forming fluid was exsolved from a single magma source. • Fluid boiling played a significant role in gold deposition. The Lunshan gold deposit, located in the Ningzhen district of the Middle-Lower Yangtze River Metallogenic Belt, represents the largest gold deposit in Jiangsu Province. It exhibits distinctive sedimentary rock-hosted mineralization within siltstone-shale sequences and shows transition from early Au to late Pb-Zn ore stages which are intimately linked to silicification and sericitization alteration, and are spatially associated with cryptobreccias. Despite its economic significance, the lack of robust constraints on its mineralization age, ore-forming fluid characteristics, and genetic type severely restrict the exploration and prospecting in deep and peripheral area. This study presents the first LA-ICP-MS zircon U-Pb age of pre- and post-ore igneous rocks, and precisely brackets the Lunshan gold mineralization within 105–103 Ma. This age correlates with exposed porphyry-skarn Cu-Mo-Fe deposits within the Ningzhen district. Zircon from the gold-associated dioritic dykes shows elevated Ce/ U i × T i and 10 4 × (Eu N /Eu*)Yb N ratios. These trace element signatures indicate a deep, oxidized, hydrous, and fertile magma source with potential to form porphyry deposits. Integrated fluid inclusion microthermometry and LA-ICP-MS analysis reveal that the ore-forming fluid originated from deep, single-sourced magmatic fluid. Reconstruction of the complete hydrothermal ore process reveals that gold and base metal mineralization are controlled by divergent fluid evolution pathways. Gold mineralization is primarily driven by fluid boiling linked to cryptobreccias and local carbonaceous reduction within the host strata. These processes efficiently remove H 2 S from fluids, destabilizing Au-HS complexes and eventually triggering gold precipitation. In contrast, Pb-Zn mineralization is formed mainly via fluid mixing between magmatic fluid and meteoric water, which decreases the salinity and temperature of fluids, destabilizing Pb/Zn-Cl complexes, and leads to Pb-Zn deposition. The integrated evidences suggest the Lunshan gold deposit being a distal sedimentary rock-hosted epithermal endmember of a deep-seated porphyry system. This genetic model may shed light on further gold-polymetallic mineral exploration in the Ningzhen district.
Zhang et al. (Sun,) studied this question.
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