Study On The Characteristics Of Ore-Forming Fluid And Ore-Body Prospecting Of Nibao Gold Deposit,Guizhou Province

The Nibao gold deposit is a large deposit in the gold deposit concentration area of southwest Guizhou province.it is composed of two types of ore bodies:“strata-controlled type”controlled by stratum and“fault-controlled type”controlled by faults.The“fault-controlled type”is the main ore body.Based on the detailed field geological survey,this paper focuses on the statistical analysis of ore grade,rock and mineral appraisal,microscopic test of fluid inclusions and primary halo test for the No.?“fault-controlled type”ore body.Combined with the data of previous research results,this paper futher discusses the characteristics ore-forming fluid,the sources of ore-forming fluid,ore-forming physicochemical conditions and ore-forming fluid evolution characteristics of two types of ore bodies in the Nibao gold deposit.Based on the comprehensive study of the structural ore-controlling features,mineralization enrichment characteristics,fluid inclusions and primary halos,the ore-prospecting target areas in the F1 fracture zone are delineated which provides a scientific basis for ore prospecting in deeper and outer of the mine The main achievements and understanding of this paper are as follows:(1)The research results of microthermometry of fluid inclusions shows that the ore-forming fluid of the“fault-controlled”ore body generally shows a decrease in temperature,pressure,x(CO2),oxygen fugacity,sulphur fugacity,while the salinity,density,PH,EH of the ore-forming fluid continue to increase from the middle(main)stage to the late stage;the general evolution law of ore-forming fluid in the strata-controlled ore body shows a decrease in temperature,salinity,sulphur fugacity,and an increase in density from the early stage to the late stage.Both of the ore-forming fluid belong to Na Cl-H₂O-CO₂±CH₄±N₂system with medium-low temperature,low salinity,medium-low density,low oxygen fugacity and low sulfur fugacity;the metallogenic environment is slightly acidic and slightly reducing-oxidizing environment.Combined with the comparative analysis of previous data,it is concluded that the source of ore-forming fluids of fault-controlled and strata-controlled ore bodies in the Nibao gold deposit have some similarities,and both of them have deep magmatic source characteristics,during the fluid migration process,a small amount of metamorphic water may be mixed,and atmospheric precipation is added when the fluid flows to the shallow region of the crust.(2)The thrust tectonic system consists of NEE-trending F1,F5,F9 thrust fault and Erlongqiangbao anticline,and the bedding fracture zone along the ore-bearing rock system beneath the lower wall of F1 thrust fault are the main ore-controlling structures in the mining area.Among them,F1 thrust fault is the main structure of the thrust tectonic system,and it is also the most important ore-conducting and ore-bearing structure in the region.The change of F1 fault occurrence from steep to slow zone is benefical to mineralization,indicating that the tectonism in the main metallogenic period in the area has the squeezing characteristics.(3)Judging from the macroscopic geological phenomena,tectonic characteristics,spatial occurrence characteristics of ore bodies and ore-rich ore bags,anomalous distribution of primary halo and Sb/Bi ratio characteristics,the spatial distribution of ore body in F1 fault in Nibao mining area has the characteristics of lanteral prostration in the direction of SW.(4)Based on the judgement of the location of the metallogenic center,the lateral direction of the ore body,the anomalous characteristics of the primary halo,and the distribution characteristics of the“hallow pockets”on the F1 fault lower wall.In F1 fracture zone,two target areas are predicted in the medium-deep part:the No.?target area is located between the 9020-9420exploration lines;the No.?target area is located between 10000-10420 exploration lines.