The Research Of Ore-forming Fluid And Ore Deposit Formation Mechanism In Jiangdongwan Au-sb Deposit, Western Hunan

Jiangdongwan Au-Sb deposit is one of the most important deposits of the Au-Sb-As metallogenic belt of Jiangdongwan in Western Hunan.On the basis of the field investigation of the deposit, through the research of indoor inclusion petrography observation、inclusion microthermometry、analysis of inclusions by Raman spectroscopy、carbon and oxygen isotope geochemistry、sulfur isotope geochemistry, the main results are as follows:(1) Types of fluid inclusions in Jiangdongwan Au-Sb deposit: One-phase fluid inclusions, two-phase aqueous solution, CO2-rich three-phase fluid inclusions,Daughter-mineral containing fluid inclusions, and the most of which are liquid-rich fluid inclusions. The temperature of ore-forming solutions is between 163 to 290℃; the salinity of fluids varies is from 1.73 to 15.3 wt%NaCl.; the densities of ore-fluids range is from0.81 to 1.01g/cm3; the pressure is between 13 to 40MPa; the mineralization depth is 0.5 to1.4km. All the inclusions belong to the mid-low salinity and high density.(2) In the frequency histogram of homogenization temperature of fluid, there are two peak intervals(180 to 240 ℃, 250 to 280 ℃) and they are quartz-sulfide stage and quartz-stibnite stage. Furthermore, quartz-stibnite stage( 180 to 240 ℃) is the main metallogenic temperature stage, which display the characteristic of multi staged in mineralization.(3) Raman spectroscopy shows that the main component of the liquid phase of fluid inclusions is water. Gas phase composition contains a little of CO2.(4) The calcite δ13CV-PDB of Jiangdongwan Au-Sb deposit is between-7.95‰ to-9.36‰.The narrow interval shows that the carbon in the ore-forming fluid probably come from the CO2 mixing effect of the carbonate and organic matter or from the deep. Theδ18OV- SMOW is14.53‰ to 20.87‰,and display the characteristics of the oxygen isotopic composition of sedimentary rocks and metamorphic rocks. In summary, the carbon inJiangdongwan Au-Sb deposit most probably comes from deep magma, and is obviously effected by low-temperature alteration, and some also come from sedimentary organic matter decomposition, which shows the characteristics of mixed sources.(5) The δ34S of Sulfur(arsenic) compounds mineral of Jiangdongwan Au-Sb deposit is between-9.3‰ to 0.9‰, and the characteristics of it is same with simultaneous presence of biogenic sulfide and hydrothermal sulfide.The δ34S of slate is between-2.0‰ to 8.4‰,and compared with sulfur(arsenic) compounds it is more enriched in heavy sulfur and similar to crustal sulfur. That sulfur source mainly comes from the homogenization of higher degree of deep heat source or the lower crust. From the characteristics of various sulfur source mixing, we conclude that it may belong to the sulfur which comes from crust source mixed magmatic.(6) The carbon-oxygen and sulfur isotope composition are similar to most of the deposit in Western Hunan. According to the ore-forming fluid of magmatic water,sedimentary, and metamorphic water and mixed hydrothermal, The characteristics of ore-forming materials is similar with deep magma and host wall-rock(sedimentary rock and metamorphic rock), and it shows that the deposit belongs to sedimentary- mixed hydrothermal filling metasomatic ore deposit(7) The studies of fluid inclusions in quartz indicate that the main formation mechanism of deposit is fluid mixing.