Yanshanian Magmatism In Jinchangyu And Its Relationship With Gold Mineralization

Jinchangyu Gold Deposit is located in Eastern Hebei Province,which is the largest gold deposit in the area.The geological exploration and research of Jinchangyu Gold Deposit started in 1965.The understanding of the genesis of the deposit has experienced different views,such as ductile shear zone type,magmatic hydrothermal type and composite type.At present,most scholars agree that it is a magmatic hydrothermal deposit.The magmatic hydrothermal gold deposits in Eastern Hebei are all related to the magmatic activities during the formation of the deposits(such as Yu'erya gold deposit,Dushan gold deposit,etc.),but there is no evidence of direct correlation between the Jinchangyu Gold Deposit and the adjacent Qingshankou complex rock mass.Based on petrology,mineralogy,isotope geochemistry and petrochemistry,the origin and evolution of Qingshankou granite complex and its surrounding dikes are systematically studied in this paper.The lithology and stratigraphic stages are determined by field investigation;Stable isotope geochemistry is used to trace the source of fluids;LA-ICP-MS zircon U-Pb dating was used to determine the formation age of the pluton and divide the formation stages of the pluton;The source and enrichment process of minerals were studied by geochemical tracing of major and trace elements.Through the above research,the main achievements are as follows(1)The main lithology of Qingshankou granite complex is granite,followed by syenite,diorite,syenite and fine-grained rock.(2)Zircon U-Pb dating and inference by LA-ICP-MS,the formation of Qingshankou granite complex can be divided into four stages: the first stage was formed at 220 Ma,the second stage was formed at 201.1 Ma,the third stage was formed at 190 Ma and the fourth stage was formed at 187 ma.The dikes around the Qingshankou complex rock mass were formed in three stages: 2521.0 MA in the first stage,193 MA in the second stage and 186 MA in the third stage,which is consistent with the formation time of the third and fourth stages of the Qingshankou complex rock mass.(3)The Qingshankou complex and its surrounding dikes are characterized by Atype granite.The geochemical characteristics are characterized by high silicon,aluminum,potassium,low calcium,phosphorus and mafic composition.The REE pattern is LREE enriched.(4)Based on in-situ zircon Hf isotopic measurements of the Qingshankou granite complex,the results show that the monzogranite in the Qingshankou granite complex is derived from the Mesoproterozoic crustal rock remelting.The biotite quartz syenite material may be derived from the Neoproterozoic crustal rock remelting material.The subrhyolite porphyry material is derived from Neoarchean mantle-derived rocks or from the inner crust remelting of mantle-derived rocks.(5)Through the discussion of the relationship between the Qingshankou compound intrusion and the Jinchangyu gold deposit in terms of time,space and genesis,the Qingshankou compound intrusion provides a source of heat and part of the oreforming material for the formation of the deposit.