河北撒岱沟门斑岩型钼矿床流体特征对成矿过程的指示

CHARACTERISTICS OF FLUID FROM THE SADAIGOUMEN PORPHYRY MOLYBDENUM DEPOSIT IN HEBEI PROVENCE:Indication to Metallogenic Processes

撒岱沟门斑岩型钼矿床位于华北板块北缘东段,矿体产于印支期二长花岗岩中,矿化类型以细脉状、网脉状和浸染状辉钼矿为主.流体包裹体岩相学显示,成矿前期的无矿石英脉和成矿期含钼石英脉中流体包裹体形成较好,以气液两相为主,存在少量的单相包裹体和三相包裹体.流体包裹体显微测温研究结果显示,成矿前期包裹体的均一温度为196.2~390.0℃,盐度5.70%~17.52%(NaCl当量);成矿期包裹体的均一温度为161.5~340.3℃,盐度在2.06%~13.29%(NaCl当量).激光拉曼光谱测试结果显示,成矿早期以H2O为主,存在少量CO2和CO32-;而成矿期包裹体成分中有H2O和CO2的两相包裹体、含CO2的三相包裹体、SO2和CH4气体.流体特征变化指示成矿流体从成矿早期到晚期,温压条件不断降低,从氧化环境向还原环境转变.成矿流体经历了沸腾作用、流体不混溶作用,并伴随着大气降水混入形成了典型大陆碰撞体系下的浆控高温热液-斑岩型钼矿床.

The Sajigoumen porphyry molybdenum deposit is located in the eastern section of the northern margin of the North China Plate.The orebodies occur in the Indosinian monzogranite,dominated by veinlet,stockwork and disseminated molybdenite types of mineralization.Petrography study suggests that the fluid inclusions are well formed in the barren quartz veins before the mineralization stage and the Mo-bearing quartz veins during the ore-forming period,mainly in gas-liquid phase,with minor single-phase and three-phase.The results of microscopic temperature measurement for fluid inclusions show that the homogeneous temperatures in the pre-mineralization stage vary from 196.2 to 390.0℃,with salinity from 5.70%to 17.52%NaCl eq;while those in the mineralization period are from 161.5 to 340.3℃,with salinity of 2.06%-13.29%NaCl eq.The results of laser Raman spectroscopy show that the composition of fluid inclusions is mainly H2O in the early stage of mineralization,with minor CO2 and CO32-.The fluid inclusions in the ore-forming period are two-phase of H2O and CO2,three-phase plus CO2,with SO2 and CH4 gas.The change of fluid characteristics from early to later ore-forming stages indicates a continuous decreasing of temperature and pressure,with transformation from oxidation to reduction environment.The ore-forming fluid has experienced boiling and fluid immiscibility.Accompanied by atmospheric precipitation,the magma-controlled hydrothermal porphyry molybdenum deposit is formed under a typical continental collision system.