Ore fluid characteristics and genesis of the Shuangmiaoguan gold deposit,Dabie orogen
The Shuangmiaoguan gold deposit in the Macheng City,Hubei Province,is a newly discovered Au polymetallic deposit located in the central part of the Dabie orogenic belt.However,its origin is still unclear.Through the detailed field geological survey and indoor petrological and mineralogical studies,in this paper,4 stages of the mineralization process have been identified,with respective mineral assemblages of quartz+K-feldspar±pyrite(S1),quartz+pyrite±chalcopyrite(S2),quartz+pyrite+chalcopyrite±gold and silver telluride(S3),and quartz+carbonate(S4).Especially,Stage S3 is the main mineralization stage of the deposit.Four types of fluid inclusions developed in quartz.They include fluid-rich two-phase fluid inclusions(Type WL),gas-rich two-phase fluid inclusions(Type WV),CO2-bearing three-phase fluid inclusions(Type C)and daughter-mineral-bearing multiphase fluid inclusions(Type S).They have homogeneous temperatures of 226～445,234～422,258～392 and 152～215 ℃,and salinities of 2.8％～17.6％,2.9％～11.9％,1.9％～14.2％and 1.2％～9.1％NaCleqv,respectively,indicating that the ore-forming fluid is mainly the medium-low temperature,medium-low salinity and low density H2O-CO2-NaCl system fluid.δDV-SMOW and δ18OH2O values of inclusion fluids in quartz of Stage S3 vary from-89.30‰ to-75.9‰ and 4.77‰ to 8.0 1‰,respectively.In situ sulfur isotopic data of pyrites of Stage S2 and Stage S3 show that their δ34S values vary from-3.‰ to 1.6‰,indicating that the ore-forming fluid has characteristics of deeply sourced magmatic fluid.Comprehensive analysis suggests that the ore-forming fluid of the Shuangmiaoguan gold deposit is mainly derived from magmatic hydrothermal fluids.The fluid immiscibility is an important factor caused the gold precipitation in the ore-forming process.
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