Geochemical Study On Ore-forming Fluids Of The Gongguan Hg-Sb Deposit In Xunyang Mansion, Shanxi Province

The Gongguan Hg-Sb deposit in Xunyang County,Ankang City,ShanXi Province is a medium-low temperature hydrothermal deposit which is located in the north of the Ankang fault and the north of the Zhenan-Banyanzhen fault,and it is belong to the middle zone of South Qinling Mountain.Based on the study of petrography,microthermometry and component analysis of fluid inclusions and isotopes in this deposit,the main points are as follows:The ore minerals of Gongguan Hg-Sb deposit are mainly stibnite and cinnabar,and the gangue minerals are mainly quartz and calcite,some of the ore bodies contain a small amount of pyrite and galena,and the surrounding rock is mainly dolomite.The ore-forming process can be divided into three stages.The minerals of stage I is mainly quartz and dolomite,stage?is mainly stibnite and cinnabar,which are usually mineralized together,and the crystallization time of stibnite is earlier than cinnabar.The minerals of stage?is calcite.The fluid inclusions belong to the H₂O-NaCl system,which are dominated by vapor-liquid type inclusioins.The composition of fluid inclusions is mainly H₂O,N₂ and CO₂,which is characterized by rich H₂O and poor CO₂.The results of fluid inclusions temperature measurement shows that the homogenization temperature ranges from 124³07?,the salinity ranges from0.35⁸.55%,the density is between 0.529 g/cm³ and 0.965 g/cm³,and the metallogenic presure changs from 7.50 MPa to 25.17MPa,corresponding to the depth of0.75².52km,which indicated that the ore forming fluids are characterized by the medium-low temperature,low salinity,low density and low hypabyssal features.Hydrogen and oxygen isotopes show that the?¹⁸O_H2O in Gongguan Hg-Sb deposit is 1.3¹7.5‰,and?D is-111^-63‰,which shows that the ore-forming fluid is mainly meteoric water and a small amount of metamorphic water,and the late meteoric water is involved in the mineralization.The?¹³C_PDB and?¹⁸O_SMOW values of the carbonates from the Xunyang orefield showed the decrease of?¹³C_PDB and?¹⁸O_SMOW,which indicated that there is a water–rock interaction accured in the calcite and the dolomite surrounding rock,characterized by carbonate dissolution and caused the precipitation of hydrothermal calcite.The?¹³C_PDB in the hydrothermal calcite is-0.1⁰.3‰,lower than the strata which reveals that the fluids can be sourced from the organic matter or atmospheric CO₂.