Fluid Inclusion Characteristics And Ore Genesis Of The Dahu Au-Mo Deposit In Xiaoqinling Gold Field,Henan Province

The Xiaoqinling district,located on the southern margin of the North China Craton,is the second largest gold producing province in China.The Dahu Au-Mo deposit is a typical deposit on the northern margin of the Xiaoqinling terrane,and is hosted by migmatitic granites and biotite-plagioclase gneisses of the Taihua Supergroup metamorphic complex.According to the cross-cutting relationships and mineral assemblages,the ore forming process can be divided into three hydrothermal stages,including the early stage of quartz-K-feldspar-molybdenite assemblage,the middle stage of quartz-polymetallic sulfide assemblage and the late stage of quartz-calcite assemblage.The middle stage is the major stage of gold mineralization.Petrographic,fluid inclusion micro-thermometric and micro Raman spectroscopic analyses reveal three types of fluid inclusions?FIs?in quartz,i.e.,CO₂-H₂O?C-type?,pure CO₂?PC-type?and H₂O-solution?W-type?.Quartzes in the early stage mainly contain C-type,PC-type and W-type inclusions.Homogenization temperatures of C-type inclusions vary from 248°C to 385°C with NaCleqv contents of 4.3 to 14.7%and have?¹⁸O_water ranging from 7.1 to 8.9‰and?D from-93 to-54‰.Quartzes in the middle stage mainly contain C-type inclusion with small amounts of other two inclusions.Homogenization temperatures of C-type inclusions vary from 220°C to 393°C,lower than that for the early stage.The salinities of the fluids vary from 2.2 to 17.5%NaC leqv.The fluids have?¹⁸O_water vary from 3.0 to 4.5‰and?D from-90 to-50‰.Minimum trapping pressures estimated from CO₂-H₂O inclusions are 196MPa for middle stage,corresponding to the depth of 7.1km.The ore-forming fluid is characterized by meso-to hypothermal,CO₂-rich and low salinity,which are considered as the nature of metamorp hic fluids.Hydrogen and Oxygen isotope signatures indicate that the fluids originated from metamorphic devolatilization in the early stage.The reactions of metamorphic fluid with surrounding rock lead to the exchange of isotopes.Therefore,the Dahu Au-Mo deposit is an orogenic-type gold deposit and its metallogenic process is coeval with the Indosinian collisional ore genesis in the Q inling orogen.