Fluid inclusions of Zhunuo deposit
Description
These data suggest that the ore fluids forming the Zhunuo deposit changed from high-temperature, low-moderate salinity, CO2-bearing magmatic fluids to low-temperature, low-salinity and CO2-poor meteoritic fluids. The boiling and cooling were the important factors to cause the precipitation of the abundant chalcopyrite in the middle stage B2-subtype veins. The molybdenite mineralization was caused mainly by the decrease of pressure due to the release of CO2 , and some by the boiling of fluid in the middle stage as recorded in the B2-subtype veins. This hydrothermal ore-forming system is different from other magmatic-hydrothermal systems in GPCB, but is similar to the typical Cu-Mo porphyry systems, which were initially CO2-bearing as indicated by the presence of abundant CO2-bearing, low-moderate salinity FIs and calcite-bearing S-type FIs. Doubly polished thin sections (<0.30μm thick) were prepared from thirty six samples of drill cores for fluid inclusion petrographic studies. From them, nineteen representative thin sections were chosen for subsequent microthermometric measurements and Laser Raman spectroscopic analyses. Fluid inclusion microthermometric studies were performed using the LINKAM 94 heating-freezing stage (with temperatures ranging from -180 to 600℃) in the Key Lab of Sedimentary Basin and Oil Analysis of the Ministry of Land and Resourses. During freezing/heating runs, the freezing/heating rates were 0.5-10℃/min, and reduced to 0.5-1℃/min near the phase change points. Salinities and densities of CO2-bearing aqueous (CO2-H2O-NaCl) inclusions were calculated from the measured ice points using the program HOKIEFLINCS-H2O-NaCl (Steele-MacInnis et al., 2012). The equation of Bodnar (Bodnar et al., 1993) was used for vapor-saturated conditions (ThL-V≥Tmhalite, where ThL-V and Tmhalite are liquid-vapor homogenization temperature and dissolution temperature of halite, respectively) to calculate salinities and densities of fluid inclusions. However, the contributions of daughter minerals, which did not melt in the heating process, to salinity were ignored. Because this equation is not valid for fluid inclusions that homogenized by halite dissolution (with Tmhalite＞ThL-V), the salinities and densities of this type of FIs were calculated by using program of HOKIEFLINCS-H2O-NaCl . The compositions of single fluid inclusions, including vapor, liquid, and daughter minerals were identified by using Renishaw RM 2000 Laser Raman spectroscopy in the Key Lab of Sedimentary Basin and Oil Analysis of the Ministry of Natural Resources. Ar ion laser with a wavelength of 514.5nm and a spot size of approximately 1μm was used as a laser source at the power of 20 mW and the area of CCD detector is 20 μm2. Each spectrum was collected from 1000 to 4000 cm-1 for 10s with ten accumulations.