Xiji Cobalt-Gold Deposit is a new type of cobalt-gold deposit discovered for the first time in the south of West Qinling orogenic belt.Due to its short discovery time and low degree of exploration and research,the genesis and fluid source of the deposit need to be further understood.On the basis of field geological survey,indoor petrographic study and Nano-SIMS trace element surface scanning,LA-ICP-MS in-situ micro area analysis is used to analyze the trace element characteristics of sulfide minerals related to mineralization,the results of which,combined with in-situ sulfur isotope analysis of ore-forming fluid source,provide constraints for further understanding the genesis of the deposit.The pyrite can be pided into three types: PyI occurs in the sedimentary period,mainly in the form of euhedral and hypidiomorphic structure,partly in vein distribution,almost has no As,Co,and w(Co)/w(Ni) is far less than 1,indicating sedimentary genesis; PyⅡ occurs in quartz-pyrite stage,mainly in annular belt,with high Co content,with w(Co)/w(Ni) between 0.94 and 2.21,indicating sedimentary transformation magmatic origin; PyⅢmainlyoccurs in quartz-pyrite-arsenopyrite stage,the content of As is very high,and the content of Co is muchlower than that of PyⅡ,and the w(Co)/w(Ni) is greater than 1,indicating magmatic origin.The value of δ34S increases gradually from the edge to the core of the cobalt-bearing annular pyrite,and the δ34S value shows a high degree of dispersion,indicating that the source of S is complex.The anomaly of Co element is located at the edge of zonal pyrite,and the source of S is the mixed fluid of deep magmatic rock and formation sulfur.Based on the field geological characteristics,laboratory petrography,in-situ trace sulfide and sulfur isotope analysis,this paper considers that the Xiji Cobalt-Gold Deposit is a sedimentary-hydrothermal fluid superimposition altered deposit.