Metallogenic Mechanism of Jinshan Gold Deposit in West Qinling Orogenic Belt: Evidence from Geochemical Characteristics of Arsenopyrite and Chlorite

Objective‌ Arsenopyrite (Apy) and chlorite (Chl) are abundant sulfide or altered minerals in hydrothermal gold deposits, which been widely used in the inversion of the physical chemical conditions of gold mineralization. The Jinshan gold deposit in Gansu Province is located in the Xiahe-Xihe-Fengxian-Huangbaiyuan metallogenic sub-belt in the eastern section of the West Qinling metallogenic belt, with superior mineralization conditions, characterized by the development of multiple generations of arsenopyrite and chlorite.

Methods In this study we take the various types of arsenopyrite and chlorite in ore samples from the Jinshan gold deposit as the research object. Based on the division of the three mineralization stages in Jinshan Gold deposit, using electron probes to determine the major elemental composition of Apy (Apy II~III) and Chl (Chl I~III) at each stage, dividing the chemical types of Chl I~III, calculating the formation temperature, oxygen fugacity (lgfO₂), sulfur fugacity (lgfS₂), and pH value of Chl I~III and Apy II~III. Furthermore, analyzing the formation environment and physicochemical conditions of Apy and Chl at each stage, and exploring the gold mineralization mechanism of the Jinshan gold deposit.

Results and Conclusion The results indicate that the diagenetic shallow metamorphic stage of Chl-I exhibits characteristics of low temperature, low lgfO₂, and low lgfS₂. During the hydrothermal mineralization stage, the temperature, lgfO₂, lgfS₂, and pH values of Chl-II and Apy II significantly increased compared to stage I, indicating the loss of a large amounts of acidic components such as CO₂ in Stage II, it is speculated that there was strong fluid mixing and boiling during the hydrothermal mineralization stage. Subsequently, during the hydrothermal mineralization stages II-III, boiling causes a significant decrease in temperature, pressure, and S content in the fluid, promoting large-scale precipitation of Au in the form of natural gold, thereby promoting the large-scale precipitation of Au in the form of natural gold. Meanwhile, under low sulfur fugacity and neutral pH value conditions, a large amount of invisible gold was formed in arsenopyrite as Au-As like substances.