Fluid inclusions of Zhunuo deposit

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.

这些数据表明，形成朱诺（Zhunuo）矿床的成矿流体经历了从富含CO₂的高温、中低盐度岩浆流体，向贫CO₂的低温低盐度大气降水流体的转变。沸腾与冷却作用是导致B2亚型脉体中期阶段大量黄铜矿沉淀的关键因素。辉钼矿矿化主要由CO₂逸出引发的压力降低所致，部分则由B2亚型脉体中记录的流体沸腾作用形成。这套热液成矿系统与GPCB（冈底斯斑岩铜矿带）内其他岩浆热液系统存在差异，但与典型的Cu-Mo斑岩系统相似——后者以大量含CO₂的中低盐度流体包裹体（Fluid Inclusion, FI）及含方解石的S型流体包裹体为标志，初始流体富含CO₂。

本次研究从36件岩芯样品中制备了厚度小于0.30μm的双面抛光薄片，用于流体包裹体岩相学研究。从中选取19件具有代表性的薄片，开展后续的流体包裹体显微测温实验与激光拉曼光谱分析。流体包裹体显微测温实验依托国土资源部沉积盆地与油气资源重点实验室的LINKAM 94冷热台（温度范围-180~600℃）完成。升降温过程中，速率设置为0.5~10℃/min，在相变点附近则降至0.5~1℃/min。对于含CO₂的水溶液（CO₂-H₂O-NaCl）包裹体，其盐度与密度通过程序HOKIEFLINCS-H₂O-NaCl（Steele-MacInnis等，2012），由实测的冰点数据计算得到。对于蒸汽饱和条件（ThL-V ≥ Tmhalite，其中ThL-V为液相-气相均一温度，Tmhalite为盐粒溶解温度），采用Bodnar等（1993）提出的公式计算流体包裹体的盐度与密度，但未考虑加热过程中未熔融的子矿物对盐度的贡献。由于该公式不适用于通过盐粒溶解实现均一的流体包裹体（Tmhalite＞ThL-V），此类流体包裹体的盐度与密度通过程序HOKIEFLINCS-H₂O-NaCl计算得到。单颗流体包裹体（包括气相、液相及子矿物）的成分通过Renishaw RM 2000激光拉曼光谱仪完成测试，实验依托自然资源部沉积盆地与油气资源重点实验室进行。实验采用波长514.5nm、光斑直径约1μm的氩离子激光器作为光源，激光功率为20mW，CCD探测器有效面积为20μm²。每个光谱的采集范围为1000~4000cm⁻¹，积分时间10s，累计扫描10次。