Genesis of Xinli gold deposit in Jiaodong Peninsula, Shandong Province

The Xinli gold deposit in the Sanshandao-Cangshang fault zone in the northwest Jiaodong Peninsula is a typical altered-rock type gold deposit.This paper studies the geological characteristics and fluid inclusion characteristics of Xinli gold deposit, analyzes the ore-forming fluid characteristics of Xinli gold deposit, and defines the genesis of Xinli gold deposit.The hydrothermal mineralization period of Xinli gold deposit can be divided into Ⅰ beresitization stage, Ⅱ quartz-pyrite stage, Ⅲ quartz-polymetallic sulfide stage and Ⅳ quartz-calcite stage.The fluid inclusions in Xinli gold deposit can be divided into single-phase liquid inclusions(Ⅰ-l type), single-phase gas inclusions(Ⅰ-g type), two-phase liquid rich inclusions(Ⅱ-l type, V/V+L < 50%), two-phase gas rich inclusions(Ⅱ-g type, V/V+L>50%)and CO₂-H₂O three-phase inclusions(Ⅲ type, V_CO2+L_CO2+ L_H2O).In stage I, type Ⅰ-l, Ⅰ-g, Ⅱ-l, Ⅱ-g and Ⅲ fluid inclusions are developed, with homogenization temperature ranging from 201℃ to 378℃, and the salinity ranging from 3.06%NaCl.eqv. to 13.83% NaCl.eqv.. In stage Ⅱ, type Ⅰ-l, Ⅱ-l, Ⅱ-g and Ⅲ fluid inclusions are developed, with homogenization temperature ranging from 144℃ to 355℃, and the salinity ranging from 2.07%NaCl.eqv. to 13.45% NaCl.eqv.; In stage Ⅲ, type Ⅰ-l, Ⅱ-l, Ⅱ-g and Ⅲ fluid inclusions are developed, with homogenization temperature ranging from 108℃ to 299℃, and the salinity ranging from 0.35%NaCl.eqv. to 11.61% NaCl.eqv.; In stage Ⅳ, type Ⅱ-l, Ⅱ-g and Ⅲ fluid inclusions are developed, with homogenization temperature ranging from 102℃ to 236℃, and the salinity ranging from 0.35%NaCl.eqv. to 10.49% NaCl.eqv.Laser Raman spectroscopy shows that the fluid inclusions are composed of CO₂, H₂O and a small amount of CH₄.The ore-forming fluid is a medium-low temperature and low salinity NaCl-CO₂-H₂O±CH₄ fluid system.In the stage Ⅰ of Xinli gold deposit, δ¹⁸O_{water SMOW}=4.86‰~6.04‰, δD_SMOW=-72.49‰~-69.27‰, indicating that ore-forming fluids mainly come from magmatic water.The δ³⁴S_CDT values of pyrite range from 10.8‰ to 13.2‰, and the δ³⁴S_CDT values of galena is 7.7‰.The sulfur element of xinli gold deposit may be directly derived from Guojialing granite.With the decrease of ore-forming fluid temperature, the ore-forming fluid reacts with the surrounding rock and the immiscibility of the fluid leads to the phase separation of the fluid, which leads to the precipitation of gold.The genetic type is vein gold deposit related to magmatic hydrothermal solution.