Ore-forming fluid characteristics and deposit genesis of the Songjianghe gold deposit in Dunhua, Jilin Province

The Songjianghe gold deposit is located in the southeastern part of the Jiapigou–Haigou metallogenic belt, north of the North China Craton. The distribution of the ore body is governed by ductile shear zones and fractures oriented in the SN direction. The gold ore body consists of lenticular gold-bearing quartz veins. Mineralization can be divided into five stages: the quartz-oxidation stage (I), the pyrite-magnetite-quartz stage (II), the quartz-polymetallic sulfide stage (III), the telluride stage (IV), and the carbonate stage (V), with the main mineralization stages being III and IV. On the basis of lithological characteristics, three types of fluid inclusions were identified in the vein mineral assemblage: NaCl-H₂O (W-type), CO₂-H₂O (C-type), and a minor amount of pure CO₂ (pc-type). W-type and C-type inclusions coexist randomly around natural gold minerals in the same quartz grain, indicating that the mineralizing fluid is heterogeneous. The mineralizing fluids had a medium temperature and low to medium salinity based on micro temperature measurements of various inclusions. During the main mineralization phase, H-O isotope tests indicate that the mineralizing fluids are mantle-driven and mixed with atmospheric precipitation during mineralization. δ³⁴S data indicate that the mineralizing material originated from the mantle. The aforementioned characteristics suggest that Songjianghe is an orogenic gold deposit based on its dynamical background, with fluid immiscibility and sulfidation being the primary mechanisms of gold precipitation and enrichment.