Genesis And Metallogenic Prediction For Songshunangou Gold Deposit In The Northern Qilian Orogenic Belt

The Songshu Nangou gold deposit is located in the southern margin of the North Qilian orogenic belt.It is a porphyry gold?copper?deposit that has made a large prospecting breakthrough in recent years.In this paper,the two ore deposits in the western and eastern sections of the Songnangou gold deposit are used as the main research objects,using detailed geological cataloging,systematic petrography,high-precision chronology and isotopic geochemical technology.We do deep researches on the geological characteristics,metallogenic evolution process and metallogenic tectonic background of the deposit.The ore-forming rules are summarized on this basis.The ore-forming model is established,and the ore-forming prediction is carried out based on the original halo characteristics and geological survey results of the deposit.It has important guiding significance for prospecting in mining areas and regional porphyry deposits.The Songshu Nangou gold deposit consists of two ore sections of the western and eastern sections.The gold ore body in the western section is generated in the internal and external contact alteration zone of the flesh-red granodiorite porphyry and the basaltic Andesite,developing potassium silicide phyllic zong?phyllic zone?propylitization alteration zone from the inner to the outer,which is the typical characteristic of the porphyry-rich gold-rich copper deposit,while gold is mainly enriched in the potassium silicification zone.The gold ore body of the eastern ore section is produced in the NW-trending fault structure,and the form of occurrence is strictly controlled by the fault structure.The alteration is mainly silicification,sericitization and pyrite mineralization.Both gold ore bodies are mainly in the form of free gold,intergranular gold and inclusion gold.The magmatism in the study area can be divided into three stages:the Neoproterozoic,the early Caledonian?Cambrian?and the late Caledonian?Ordovician-Silurian?.Specially,the late Caledonian tectonic-magmatic activity events are most closely related to mineralization activities in the study area.Through the LA-MC-ICP-MS zircon U-Pb isotope dating analysis,the age of the granodiorite porphyry with the most closely related mineralization in the western ore section is 442±1 Ma,which belongs to the Ordovician emplacement.The geochemical characteristics of the rock indicate that it has relatively rich rare earth elements and large ion lithophile elements,while the typical arc magma characteristics are relatively depleted heavy rare earth elements and high field strength elements,indicating that the ore-forming porphyry body is formed under the condition of the southward subduction of Qilian Ocean.The results of ore geochemistry and fluid inclusion geochemistry of the deposit indicate that the fluid in the main ore-forming stage of the deposit is a medium-high temperature-medium-high salinity fluid,and the H-O isotope shows that the early fluid?¹⁸OH₂O is 6.5‰⁸.8‰,and the?DH₂O value is-71.8‰.^-83.4‰;the late fluid?¹⁸O H₂O is-5.8‰³.0‰,and the?D H₂O value is-77.0‰^-96.4‰,indicating that the ore-forming fluid is mainly magmatic water,and there is mixed precipitation of atmospheric precipitation in the late stage.The sulfide?³⁴S3.1‰¹2.1‰in the mining area shows that the sulfur isotope of the Nangou gold deposit in Songshan is characterized by the mixing of deep source sulfur and crustal sulfur.The results of primary halo analysis in the western section of the mine show that the combination of frontal halo,near-mine halo and tail halo of the deposit are:As,Sb,Hg,Pb,Zn?Au,Cu,Mo?W,Bi,comprehensive research It indicates that there is still a large potential for prospecting in the deep part of the south side of the western section.On this basis,according to the latest geological survey results,the prospecting target area of pine southern ditch was optimized,and 5 prospecting targets were selected.Based on the above research and regional tectonic evolution,this paper identifies the typical porphyry-type mineralization in the Qilian orogenic belt.It is believed that the Songshu Nangou gold deposit is formed in the Andean-type active continental marginal tectonic setting,and its tectonic setting is the North Qilian Ocean.The subduction of the crust plate to the south of the Zhongjilian micro-continent is a new material for the study of regional porphyry mineralization and prospecting.