Rock-and Ore-Controlling Regularity For Tectonic Stress Field And Fluid Inclusion Characteristics Of The Huanghaping Cu-Sn Polymetallic Deposit,Southern Hunan Province And Their Implications For The Deep Extension Of Ore Bodies

Huangshaping Cu-Sn polymetallic deposit is located in Qianlishan-Qitianling ore concentration area in southern Hunan.It is a typical representative of magmatic hydrothermal polymetallic metallogenic system under the background of superimposed structure of Qinzhou-Hangzhou tungsten-copper metallogenic belt and Nanling tungsten-tin metallogenic belt.The Cu-Sn polymetallic ore body is closely related to quartz porphyry and granite porphyry in the area.In this paper,based on a large number of actual field geological characteristics and the summary of previous research results,two aspects of ore-controlling tectonic stress field and fluid inclusion geochemistry are studied.The study of ore-controlling tectonic stress field mainly uses the theory and method of ore field geological mechanics and the numerical simulation technology of ore-controlling tectonic stress field to discuss the ore-controlling mechanism of tectonic stress field from the aspects of rock-controlling and ore-controlling structural types,metallogenic structural system and ore-controlling tectonic stress field.Geochemistry of fluid inclusions,using mineral petrography,fluid inclusion petrography,combined with laser Raman spectroscopy and other research,to explore the composition of oreforming fluid,temperature,salinity,pressure and other physical and chemical conditions and metallogenic depth,and finally combined with structural and fluid research results to explore the prospecting direction of the deposit.The main research results are as follows :(1)Combined with the previous study of ore field tectonic combination and tectonic system,the tectonic evolution of the third stage of Pingbao ore field is further deepened : SN tectonic belt in the early metallogenic period(Indosinian),NE tectonic belt in the metallogenic period(early and middle Yanshanian),NW tectonic belt after mineralization(late Yanshanian).(2)Through the large-scale structural-altered lithofacies mapping of deposit structure and the fine analysis of tectonic mechanical properties,it is considered that the structure obviously controls the formation and spatial-temporal distribution of the deposit.Based on the actual structural characteristics before and during mineralization,the tectonic stress field simulation of Pingbao ore field and Huangshaping deposit is carried out by using ANSYS Workbench software.The distribution characteristics and evolution characteristics of maximum principal stress,maximum shear stress,strain energy and maximum principal strain are basically consistent with the actual field geological characteristics.The SN tectonic belt is generated by the near EW compression in the early mineralization.Its associated EW fault strain energy is low,which provides favorable conditions for magmatic emplacement.The high value zone of NW-trending maximum shear stress provides favorable conditions for large-scale emplacement of magma in this area,and further migrates to the shallow along the EWtrending faults.Due to the restriction of fluid migration in the high strain energy area around the mining area,it can continuously accumulate and precipitate mineralization in the low strain energy area.The thermal-mechanical coupling analysis of the geological section of the deposit shows that the thermal expansion and thermal stress of the magma itself enable the ore-forming fluid to flow to the outer expansion space,and finally form precipitation mineralization on the contact zone and far away from the rock mass.(3)Through the study of fluid inclusion geochemistry,it is considered that the Huangshaping Cu-Sn polymetallic deposit is a typical magmatic hydrothermal metallogenic system.The metallogenic process of the deposit can be divided into four stages :(I)Anhydrous skarn stage,(II)Hydrous skarn stage,(III)Polymetallic sulfide stage,(IV)Calcite stage.Based on the petrographic study of fluid inclusions,six types of inclusions were identified : pure liquid inclusions;liquid-rich gas-liquid two-phase inclusions;gas-rich gas-liquid two-phase inclusions;pure gas inclusions;c O2-rich three-phase inclusions;three-phase inclusions containing daughter crystals.In the metallogenic process,the fluid shows the evolution process from high temperature,high salinity to low temperature,low salinity.The results of inclusion lithofacies research and temperature measurement at different stages show that the main mechanism of polymetallic mineralization is the multiple fluid boiling,strong material exchange and the mixing of atmospheric precipitation at late stage.(4)Based on the numerical simulation of tectonic stress field and the geochemical study of fluid inclusions,the tectonic-fluid coupling ore-controlling law of Huangshaping deposit is summarized and the metallogenic model is established.Based on the temperature measurement results of mineral fluid inclusions at different elevations,the fluid inclusion index indicating the depth of the ore body is established,and the deep ore body is predicted.