Element migration regularity during hydrothermal alteration in the Xiejiagou gold deposit, Eastern Shandong Province

The Xiejiagou gold deposit is located between the Jiaojia fault zone and the Zhaoyuan-Pingdu fault zone in northwest Jiaodong.Based on detailed field geological observations and laboratory study, the authors identified the alteration types and spatial zoning of the Xiejiagou gold deposit.In this paper, the authors systematically collected rock samples of different alteration types, and carried out geochemical analysis of rock elements.The Isocon method was used to analyze the element migration law during hydrothermal alternation and its constraint on the properties of ore-forming fluids and mineral precipitation.The alterations of the gold deposit are beresitization of steep quartz veins as well as beresitization and K-feldspathization from the center to both sides; they are K-feldspathization, beresitization, and ferritic lithology with steeply dipping quartz veins from early to late period.The K-feldspathization shows that K-feldspars and biotite replaced the plagioclases and hornblende in the Linglong biotite granite, respectively, the potassium obviously migrated in, silicon slightly migrated in, calcium and magnesium migrated out, and iron migrated slightly out.The beresitization is superimposed on the K-feldspathization, which mainly demonstrates that plagioclase, K-feldspar and biotite were destabilized in the solution containing H⁺ and HS^-, and were replaced by sericite and quartz.Iron, magnesium, and calcium moved in, potassium, sodium, and silicon moved out.From the K-feldspar stage to the beresitization stage, the fluid changed from alkaline to acidic, and the migration form of Au also gradually changed from a chloride complex to a sulfur-hydrogen complex.With the continuous evolution of the ore-forming fluid, the ore-forming fluid and the surrounding rock continuously reacted, and the chemical properties of the ore-bearing hydrothermal fluid continued to change to promote the precipitation of gold.