Geological Characteristics And Ore-forming Fluids Of The Zhalageamu Copper Deposit,inner Mongolia

The Zhalageamu copper deposit is located on the northeastern margin of the ancient Xilinhot Block,20 kilometers south of Xilinhot in the Berwick Ranch area.The Zhalageamu copper deposit is a hydrothermal vein type deposit,240 thousand tons of copper metal.The ore body occurs in the outer contact zone of granodiorite and sandstone of the Permian Zhesi Formation.The source of ore-forming materials and the metallogenic mechanism was discussed by the characteristics of fluid inclusions and H-O isotopes in this article.The hydrothermal period can be divided into five stages according to the ore structure and vein body penetration relationship from early to late,that is the potassium stage,quartz-sericite stage,quartz-pyrite stage,quartz polymetallic sulfide stage,quartz-calcite stage.The later three stages are the main ore-forming stages.The petrographic observation indicates that the quartz-pyrite stage is characterized by liquid-rich inclusions and inclusions of irregular transparent sub-minerals with large of 9?27?m.The quartz-polymetallic sulphide stage is dominated by the gas-rich and liquid-rich fluid inclusions with large of 8?25?m.During the quartz-calcite stage,liquid-rich inclusions,inclusions of regular transparent minerals,with large of 6?18?m is common.The average temperature of inclusions ranges from early to late 300-360°C,140?230°C,and 160?220°C.The salinity varies 4.0%?16%and 36%?40%in the early stage,8%?12%and 36%?40%in the middle stage,8%?12%and 28%?32%in the late stage.The trapping pressure of the inclusions in the early and middle stages was 9?29 MPa and 7?9 MPa,indicating that the ore-forming depth was 0.7?2.8 km.The composition tests showed that the ore-forming fluids of the deposit are characterized by H₂O-rich,Ca²⁺,K⁺,SO₄^2-,and Cl^-.The p H value of the fluid is 5.86?6.25,indicating an acidic environment.The Eh value is-0.042?+0.171,the reducing ability gradually and?O₂ decreases from early to late.The Raman spectra shows that the gas phase of the inclusions show the characteristic peaks of CO₂ and the characteristic peaks of water.The results of hydrogen and oxygen stable isotope show that the?¹⁸O of quartz ranges from 8.5‰to 7.5‰and the?D of the fluid ranges from 115.5‰to 98.1‰.This data indicate that the early ore-forming fluid is magmatic water,whereas the late ore-forming fluid was mixed with meteoric water.The ore-forming fluids experienced boiling,the mixing of magmatic water with meteoric water resulted in the precipitation of ore-forming materials.