The Study On Fluid Inclusions In Zhesang Micro-disseminated Type Gold Deposit, Funing, Yunnan

Micro-disseminated type gold deposit is one of the major gold deposit types, with great prospecting potential, good vision and important economic value, therefore, to strengthen the study of such deposit is very necessary.The Zhesang gold deposit, which located in the structural belt of Yunnan-Guizhou-Guangxi “Golden triangle”, is a typical Micro-disseminated type gold deposit. The previous studies on this deposit were mainly on the characteristics of gold carrying minerals, occurrence of gold, ore controlling conditions and the prospecting direction, lacking of studies on the ore-forming fluid and the metallogenic mechanism.In this study, we take fluid inclusions in Zhesang Micro-disseminated type Gold deposit as study object, through systematical study in fluid inclusion petrography, micro-thermometry, composition of fluid inclusions, hydrogen and oxygen isotope composition of fluid inclusions, we have analyzed the metallogenic conditions of the deposit and discussed the character and genesis of ore-forming fluid.The result of the study shows:There are three types of fluid inclusions in Zhesang Gold deposit, H2 O inclusion, H2O-CO2 inclusion, pure gas phase inclusion, and the H2 O inclusion is the main type of inclusions in the deposit.The ore forming temperature raged from 163℃to 309 ℃with an average of 231℃, and mainly concentrated in 210℃~270℃. The salinity of the ore-forming fluid ranged from 4.1%~14.8% with an average of 9.0%, which belongs to the category of low salinity. The density of the ore forming fluid ranged from 0.8% to 1.0%, which belongs to the category of low salinity, and the density of the ore-forming fluid increased gradually as the development of the mineralization. The pressure of the ore-forming fluid ranged from 16.1MPa to 33.7MPa with an average of 23.1MPa, and as the development of mineralization the pressure of the ore-forming fluid reduced gradually. The metallogenic depth ranged from 0.64 Km to 1.25 Km with an average of 0.86 Km, belonging to epithermal type.The composition analysis of fluid inclusions shows that the gas phase of the fluid inclusions are mainly H2 O and CO2 with small amount of CH4 and N2; in the liquid phase of the fluid inclusions the positive ions are mainly Ca2+、Na+、K+ with small amount of Al3+, and the negative icons are mainly Cl-. The component characteristics of fluid inclusion show that the ore-forming fluid is mainly atmosphere precipitation.The lgfO2 of the ore-forming fluid ranges from-51.3 to-62.6 with an average of-54.7; the pH of the ore-forming fluid ranges from 5.907 to 6.283 with an average of 6.04; the Eh of the ore-forming fluid ranges from-0.281 to-0.131 with an average of-0.199.The δD of fluids ranged from-70.2‰ to-46.5‰ with an average of-56.4‰. The δ18O values of quartz ranged from 6.7‰~14.6‰ with an average of 11.4‰. The δ18OH2O values are from 5.1‰~4.8‰ with an average of 1.4‰. The study of hydrogen and oxygen isotope composition in fluid inclusions shows that the ore-forming fluid are mainly from atmosphere precipitation. Preliminary analyses suggest that during the infiltration, the atmosphere precipitation was heated by geothermal gradient and magma to recycle, Au mineralization occurs in interaction process between thermal recycle and wall-rocks, and then enriches in proper space.