Study On Ore-controlling Structure Characteristics And Metallogenic Regularity Of Zhaishang Gold Deposit In West Qinling

Zhaishang gold deposit in Gansu Province is a super large gold deposit discovered in the West Qinling Mountains in recent years.Despite the previous research work,there are still some key scientific issues that need to be further studied:For example,the observation and study of metamorphic deformation intensity and rheological cleavage superposition structure inside and outside the tectonic belt in the study area are insufficient,the identification,identification and research of ductile and brittle deformation fabric are insufficient,and there are some gaps in the research of ore-forming material sources,hydrohydrothermal alteration and enrichment mechanism.Based on the project of Zhaishang Gold Deposit Exploration in Minxian County,West Qinling,undertaken by Xi’an Mineral Resources Survey Center of China Geological Survey,this paper mainly focuses on the metallogenic geological conditions,ore-controlling structure,ore-forming fluid and ore-forming material sources of the Zhaishang Gold deposit in West Qinling,and adopts various research methods such as field investigation,section measurement,borehole cataloging,comprehensive research and mapping.The ore-controlling structure of Zhaishang gold deposit is studied systematically.The characteristics of ore-forming fluid and the source of ore-forming materials were analyzed based on the test and research of inclusions temperature measurement and isotope analysis.Based on the above research results,the metallogenic model of Zhaishang gold deposit is discussed.The main results achieved are recognized as follows:1.The ore-controlling structure of the Zhaishang gold deposit is a multistage tough-brittle shear zone and fault fracture zone in the area,and the variation of shear tectonic deformation is closely related to the degree of rock fragmentation,mineralization alteration,vein development and Au grade.The ore-controlling structure of the Zhaishang gold deposit is a joint constraint on the ore body shape and gold element enrichment.2.The Zhaishang gold deposit develops multi-stage tectonic deformation,which is accompanied by the corresponding multi-stage and multi-stage mineralization alteration,and the mineralization alteration is synchronized with the tectonic deformation period.Based on the field investigation of geological profiles and the analysis of special phenomena under microscope,the microstructures and mineralization alteration in the area can be divided into 5stages and 3 stages:（1）sedimentary-diagenetic stage;（2）Gold mineralization stage（early ductile brittle shear tectonic deformation,middle ductile brittle brittle shear tectonic deformation,middle and late superimposed brittle shear deformation）;（3）post-metallogenic stage.3.The fluid inclusion temperature test shows that the ore-forming fluid of the Zhaishanggold deposit is medium-low temperature（peak 180～260℃）,low salinity（peak1.41%～12.61%）,low density（0.66～0.96 g/cm³）,with multi-phase activity,and low ore-forming pressure（30.08～87.44 MPa）.The metallogenic depth is shallow（3.01～7.67 km）.The ore-forming fluid is similar to the fluid of epithermal deposit,and the boiling and mixing of fluid may be the important mechanism of gold mineralization.4.The iron isotope test results show that Fe isotopeδ⁵⁷Fe=-0.27‰～0.69‰,with an average value of 0.218‰;δ⁵⁶Fe=-0.15‰～0.47‰,with an average value of 0.135‰;The source of iron is mainly iron from upper crust,and a small amount of iron from upper mantle.The sulfur isotope test results show that theδ³⁴S of sulfide and sulfate in the hydrothermal stage of Zhaishang gold deposit is 0.55‰～13.23‰,with an average value of 5.39‰.The sulfur source is mixed,and the sulfur from the stratum and the magma are mixed.5.Based on the results of various studies,it is concluded that the metallogenic model of Zhaishang gold deposit is as follows:the tectonic-magmatic events of Indochine-Yanshanian period caused continuous shear action in Zhaishang area,which promoted the dissociation and migration of gold in the source layer in the area,and the ore-bearing materials such as atmospheric precipitation migrated downward and mixed with deep fluids to form ore-forming fluids.The ore-forming fluid penetrates upward along the microfissure formed by ductile and ductile brittle deformation or along the dilatant zone formed by（ductile and brittle-）brittle deformation,and continues to exchange materials with the surrounding rock.Changes in physical and chemical conditions lead to the differentiation and evolution of the mixed fluid.When it migrates to the favorable part of the structure,the ore-forming material is susaturated and precipitated with the sudden reduction of confining pressure and the boiling of the fluid.The formation of micro-disseminated alteration zone（microfissure infiltration）and vein production of each ore body in Zhahai（expansion zone penetration）.