Genesis of Jiangdong Gold Deposit in Wangu Gold Field,Northeast Hunan:Constraints from Fluid Inclusions and H-O Isotope
The debate surrounding the source,properties and evolution of ore-forming fluids and the genesis of gold deposits in the Wangu area are still remains unresolved.To address this issue,the present study focuses on the Jiangdong gold deposit within the Wangu area,conducting a comprehensive analysis of quartz samples from different stages of the deposit.This analysis includes SEM-CL observation,microtemperature measurement of fluid inclusions,laser Raman spectroscopy,and H-O isotopic compositional analysis.Through examination of the relationship between the veins and the symbiotic combination between the minerals,four distinct mineralization stages have been identified.The mineralization stages at the study site are prioritized as follows:(1)quartz-scheelite stage,(2)quartz-pyrite stage,(3)quartz-pyrite-arsenopyrite-polymetallic sulfide stage,and(4)quartz-calcite stage,and the main mineralization stages are the second and third stages.Fluid inclusions within the quartz at each stage were categorized into three types,namely aqueous inclusions(TypeⅠ),aqueous and CO2 three-phase inclusions(TypeⅡ),and pure CO2 inclusions(TypeⅢ).The homogeneous temperatures of the four phases of fluid inclusions range from 264℃to 347℃,255℃to 329℃,194℃to 271℃,and 157℃to 235℃respectively,aand the salinities range from 2.82%to 8.56%NaCleqv,from 1.84%to 9.04%NaCleqv,from 2.24%to 11.23%NaCleqv,and from 1.87%to 8.71%NaCleqv.The H-O isotope analysis indicates that the ore-forming fluids in the Jiangdong gold deposit are predominantly sourced from magmatic fluids,likely associated with magmatic activities during the Yanshanian period.Fluid-rock interactions may have resulted in the early ore-forming fluids being influenced by partially metamorphic fluids.Over the course of mineralization from early to late stages,the composition of the ore-forming fluid transitioned from a medium-temperature and medium-low salinity H2O-NaCl-CO2 system to a medium-low temperature and medium-low salinity H2O-NaCl system.Gold is primarily transported in the form of Au(HS)-2 within ore-forming fluids,with fluid immiscibility and fluids-rock reaction likely serving as the primary mechanisms for gold precipitation.When considering the geological characteristics of the Jiangdong gold deposit,along with fluid inclusion studies and H-O isotope data,it can be classified as a magmatic hydrothermal deposit associated with magmatic activity.
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