Ore-forming fluid characteristics and genesis of the Liaoshang gold deposit, Jiaodong Peninsula

The Liaoshang gold deposit is situated in the mineralized district on the northeastern margin of the Jiaolai Basin. Tectonically, it lies within the northeast margin of the Jiaolai Basin, which is part of the Jiaobei Block in the North China Craton. Regional strata are dominated by the Paleoproterozoic Jingshan Group and the Cenozoic Quaternary. The mineralization of the Liaoshang gold deposit is divided into three stages: Ⅰ: pyrite-dolomite stage; Ⅱ: gold-polymetallic sulfide-dolomite stage; Ⅲ: quartz-dolomite stage. Dolomite is one of the primary gold-bearing minerals. To clarify the sources and properties of ore-forming fluids and materials, explore the mineralization process, and reveal the deposit genesis, this study conducted petrographic observations, microthermometric analyses, and laser Raman spectroscopy of fluid inclusions in gold-bearing dolomite from the main mineralization stage, along with C-O isotope analyses of gold-bearing dolomite. Fluid inclusion studies indicate that the ore-forming fluids during the main mineralization stage of the Liaoshang gold deposit belong to a CO₂-H₂O-NaCl fluid system, characterized by medium temperature (238–321℃), low salinity (3.71–10.33 wt%), low density (0.45–0.62 g/cm³), and high contents of CO₂ and H₂O. C-O isotope analyses of gold-bearing dolomite from the main mineralization stage yield δ¹³C_V-PDB values of −2.3 to −4.1 ‰ and δ¹⁸O_V-SMOW values of 8.8 to 10.7 ‰ for dolomite, suggesting that the ore-forming fluids were primarily derived from magmatic sources or deep-seated magmatic fluids. Comprehensive analysis indicates the mineralization process of the Liaoshang gold deposit as follows: During the Early Cretaceous, under the subduction of the Pacific Plate, the region transitioned from a compressional stress field to an extensional stress field. Asthenospheric materials ascended and underwent differentiation and evolution; multi-source mixed ore-forming fluids, accompanying magmatic activity, migrated upward, filled, and crystallized along early-formed fault structures. These fluids leached part of the ore-forming materials from the Jingshan Group, then enriched and precipitated at detachment structures on the basin margin, ultimately forming the Liaoshang-type pyrite-carbonate vein-type gold deposit.