Sources of Ore-forming Materials and Ore-forming Model of the Jiudian Gold Deposit in Pingdu, Shandong Province

The Jiudian gold deposit in Pingdu, Shandong Province, is located in the northwestern part of the Jiaodong gold metallogenic province and the southern segment of the Zhaoping Fault Zone. It serves as a typical representative of quartz-vein type gold deposits in this region. Despite its long mining history, genetic studies of this relatively small-scale deposit have remained inadequate, constraining the understanding of regional metallogenic regularity. Based on detailed field geological investigations, this study conducted hydrogen-oxygen isotopic analyses of quartz from ore-bearing veins and sulfur isotopic analyses of pyrite from ores, aiming to elucidate ore-forming fluid and metal sources and establish a metallogenic model for the deposit. Research indicates that the mineralization process of the Jiudian gold deposit can be divided into three stages: early mineralization stage (I), main mineralization stage (II), and late mineralization stage (III). The main mineralization stage represents the primary period of gold mineralization, further subdivided into three sub-stages: medium-coarse grained pyrite stage (II₁), fine-micron fine grained pyrite stage (II₂), and polymetallic sulfide stage (II₃). Isotopic characteristics of quartz from different mineralization stages show: δ¹⁸O_H2O=2.22‰～4.64‰ and δD_V-SMOW=−90.2‰～−72.2‰ for the early stage; δ¹⁸O_H2O=1.17‰～4.36‰ and δD_V-SMOW=−84.3‰～−77.1‰ for the main stage; δ¹⁸O_H2O=−0.01‰～4.28‰ and δD_V-SMOW=−97.7‰～−87.1‰ for the late stage. The early-stage ore-forming fluids were predominantly magmatic water, with progressive mixing and increasing proportion of meteoric water during fluid evolution. Sulfur isotopic compositions of pyrite from different mineralization stages show no significant variation, with δ³⁴S values ranging from 7.65‰ to 10.10‰ (average 8.87‰), closely resembling the characteristics of Precambrian metamorphic basements and Mesozoic granites. Integrating previous research findings, a metallogenic model for the Jiudian gold deposit is proposed: During the Late Jurassic, remelting of gold-bearing ancient metamorphic basement rocks in the Jiudian area formed Linglong-type granites. In the Late Early Cretaceous, under the influence of large-scale lithospheric extension-thinning in the eastern North China Craton and asthenosphere upwelling, gold from granites and metamorphic rock relics underwent mobilization and enrichment. Driven by mixed fluids composed of magmatic water and meteoric water, gold precipitation occurred in secondary fracture structures within the footwall of the Zhaoping Fault Zone, forming the ore deposit.