Characteristics Of Fluid Inclusions In Dabaiyang Gold Deposit And Erosion Preservation Of The Deposit

The Zhangxuan area is a well-known concentration area of gold deposits in the country.The geotectonic location is on the northern margin of the North China Craton,south of the Shangyi-Chongli-Chicheng deep fault.The Dabaiyang Gold Mine studied by the thesis is located in Zhangxuan Mine Concentration Area.Based on the detailed petrographic observation of fluid inclusions in Hanjiagou ore block of Dabaiyang Gold Mine in different metallogenic stages,the origin of ore-forming fluids and materials and the evolution process of ore-forming fluids are discussed by means of micro thermometry,laser Raman gas composition analysis of fluid inclusions and H-O and S-Pb isotopic data.The metallogenic mechanism and genetic types of ore deposits are analyzed.The change and preservation of ore deposits is an important research content of ore geology.In order to study the denudation and preservation of Dabaiyang Gold Mine,the method of mineral pressure gauge is used to estimate the emplacement depth of Shuiquangou alkaline complex,guzuizi,yangjiaying and qianbakou granitic rocks around Dabaiyang Gold Mine,and to discuss the uplift and denudation of the area and the denudation and preservation of Dabaiyang Gold Mine.Through the study of fluid inclusions and mineral pressure gauges,the following achievements and understandings have been achieved in this paper:?1?The type of fluid inclusions in Hanjiagou oreblock of Dabaiyang Gold Mine is simple,and they are mainly fluid rich inclusions.In the early,middle and late stages of mineralization,the fluid homogenization temperatures are 220-300?,180-220?and 140-200?respectively.The fluid salinity is low to medium salinity,and the three stages are concentrated in 12%¹8%?NaCl eq?,9%¹5%?NaCl eq?and 6%¹2%?NaCl eq?,respectively.The temperature and salinity of the fluid decreased gradually from early to late.?2?The results of fluid density calculation show that the density of ore-forming fluid is relatively stable and has little change,so it belongs to low density fluid.The density of ore-forming fluid is 0.89-0.97g/cm³,0.86-0.96g/cm³ and 0.78-0.93g/cm³in the early,middle and late stages respectively.The pressure in the main ore-forming stage is in the range of 46.3-104.6mpa.The calculated ore-forming depth is 5.40-8.45km,with an average of 6.93km.?3?The H-O isotopic study shows that the ore-forming fluid comes from the mixture of rock slurry water and atmospheric precipitation.Pb isotopic study shows that there are deep mantle source materials in the ore-forming materials,and S isotopic study shows that sulfur comes from Archean strata.The main mechanism of gold deposition is fluid boiling and fluid mixing.According to the characteristics of ore deposit geology and ore-forming fluid,dabaiyang gold deposit is considered to be a low-temperature,low salinity and CO₂ poor hydrothermal type gold deposit.?4?The estimated results of emplacement depth of several typical rock masses in Zhangxuan area are as follows:in the west section of Shuiquangou rock mass?372.7Ma?,the emplacement pressure is about 3.5kbar,and the emplacement depth is about 10.0km;in the middle section of Shuiquangou rock mass?380.5Ma?,the emplacement pressure is about 2.8kbar,and the emplacement depth is about 10.8km;in the east section of Shuiquangou rock mass?383.4Ma?,the emplacement pressure is about 3.0kbar,and the emplacement depth is about 11.1km;in guzuizi rock mass?236.0Ma?,the emplacement pressure is about 1.8kbar,and the emplacement depth is about 6.93km;the emplacement pressure of yangjiaying rock body?138.6Ma?is about 0.2kbar,and the emplacement depth is about 3.01km;the emplacement pressure of qianbakou rock body?140.2Ma?is about 0.3kbar,and the emplacement depth is about 3.13km.?5?According to the calculation results of the emplacement depth of the rock mass in Zhangxuan area and the chronological data of predecessors,the denudation rate in this area is 0.022-0.029km/Ma since Mesozoic,and the denudation amount is about 3km.However,the average emplacement depth of Dabaiyang Gold Mine in this area is 6.93km,and the denudation amount is less than the emplacement depth.Therefore,it is considered that the deposit is well preserved and has a deep prospecting prospect.