Geological Tectonic Evolution And Gold Mineralization In The Epithermal Mineralization Area Of Southwestern Guizhou

In tectonic,the area of southwestern Guizhou belongs to two tectonic units,that is,Yangtze Continental Block and South China fold system.In a broader sense,the study area is adjacent to the combined zone of Tethys and circum-Pacific tectonic domains.Numerous gold deposits in southwestern Guizhou are typical fine disseminated gold deposits?carlin type gold deposit?,which takes geological structure as the primary ore controlling factor,therefore,discussing the pattern of Gold mineralization from the perspective of geological structure is quite appropriate.Since the discovery of gold deposits in southwestern Guizhou,a lot of geological prospecting and research work about these gold deposits have been made by many geologists,but the comparative study about mineralogy,mineralography,ore-controlling factors,deposit geochemistry and mineralization patterns are relatively fragmented and not systematically.At the same time,there are different opinions about the genesis of these deposits,for example,carlin type gold deposit,epithermal gold deposit,structural altered rock type gold and orogenic gold deposits etc,and is in lack of specialized research from the perspective of the relationship between the tectonic evolution of southwestern Guizhou and gold mineralization.Accordingly,this paper aims at the relationship between the tectonic evolution of southwestern Guizhou and gold mineralization,try to make a systematic comparative study about mineralogy,mineralography,ore-controlling factors,deposit geochemistry and mineralization patterns of gold deposits in southwestern Guizhou,and finally establish a regional gold mineralization model,and then providing the theoretical basis for guiding deep and external gold prospecting.This paper chooses several typical gold deposits from the study area as a breakthrough point,such as Shuiyindong gold deposits,Lannigou gold deposits,Yata gold deposits and Getang gold deposits,on this basis of understanding the characteristics of regional geological features,geological tectonic evolution,geological features of mining area and geological characteristics of ore body,through using technical means such as mineralogical analysis,fluid inclusions analysis and isotope analysis,then summarizing and comparing the results of previous studies,for the purpose of disscussing the regional geological structure evolution and regional gold mineralization.Fine disseminated gold deposits in southwestern Guizhou have similar characteristics of mineralization alteration and physical and chemical conditions of mineralization,which indicates that these gold deposits have the same ore-forming material and fluid source,and under the same metallogenic geodynamic setting.Except for Shuiyindong gold deposit and Getang gold deposit are located in the southwest border of yangtz block which is adjacent to the Youjiang orogenic belts,almost all fine disseminated gold deposits are produced in Youjiang orogenic belts,which indicates that the formation of fine disseminated gold deposits in southwestern Guizhou is closely related with Youjiang basin.The main ore hosting strata of fine disseminated gold deposits in southwestern Guizhou are as follows:Longtan Formation of Upper Permian,Structure Alteration Rocks,Bianyang Formation and Xuman Formation of Middle Triassic.Among them,Shuiyindong gold deposit and Getang gold deposit are formed in Longtan Formation and Structure Alteration Rocks,Lannigou gold deposit and Yata gold deposit are formed in Xuman Formation and Bianyang Formation.Analysis of fluid inclusions data indicated that the physicochemical parameter of ore-forming fluids as follows:medium to low temperature?100²93.3??,low salinity?0.18 to 13.62 wt%?,medium to low density(0.75¹.06g/cm?3?,relatively large range in mineralization pressure?178.51⁷31.73×105 Pa,average 432.25×105Pa?.In addition,ore-forming fluids is rich in CO₂ and CH₄,partial reduction,weak acidity and low oxygen fugacity.Fine disseminated gold deposits in southwestern Guizhou is closely related with the cracking,collisional orogeny and lateral extrusion after collision,and it belongs to mesothermal and epithermal deposits which is after deposition period and related with pale-basin fluids.The formation and aggregation of ore-bearing fluids are both closely related with the formation and collision of Youjiang basin,and the ore-forming material precipitated in lateral extrusion period after collision.According to the characteristics of geological structure evolution and gold mineralization in southwestern Guizhou,the metallogenic model of fine disseminated gold deposits in southwestern Guizhou is summarized as three stages:First,the cracking to back-arc basin stage of Youjiang basin?D₂-T₁?:the forming of ore-bearing sedimentary formation;Second,foreland basin stage of Youjiang basin?T₂-J₂?:The initially formation of ore-bearing fluids;Third,collisional orogeny and lateral extrusion stage of Youjiang basin?J₃-K₁?:ore-bearing material's enrichment and the formation of deposits.