安徽铜陵朝山金矿床流体包裹体研究

Fluid inclusion studies of the Chaoshan gold deposit in Tongling,Anhui Province,China

朝山金矿床是狮子山矿田内的热液交代型金矿床,在成因上与燕山期的白芒山辉石闪长岩有关。通过采集发育在不同深度下的含金黄铁矿—石英—方解石脉样品,进行流体包裹体岩相学观察和显微测温发现,石英和方解石中均捕获了富气相、富液相的两相水溶液包裹体和含子晶的三相水溶液包裹体,以上三种类型包裹体的均一温度统计峰值分别出现于315～335℃和255～275℃,盐度的统计峰值出现于17.50%～22.50%NaCl eq.和32.50%～37.50%NaCl eq.之间。激光拉曼探针分析表明,石英中流体包裹体的气相成分以水蒸汽为主,伴有少量 CO_2,可能含有 CH_4。流体的 H、O 同位素组成具有岩浆水特征。上述研究表明,朝山金矿成矿流体经历了相态变化,发生了不均匀捕获。受燕山期岩浆作用影响,狮子山矿田内的铜、金成矿在时空上具有一定联系,成矿流体运移的过程中,主要发生了相分离、气相液化和减压沸腾作用,可能是形成铜、金矿化分带的重要原因。

Chaoshan gold deposit, which is one of the hydrothermal gold-copper deposits in Shizishan ore-field in Tangling, China, has essentially genetic links to the Baimangshan gabbroic diorite which intruded within the Yanshanian period. Based on petrographic observations of ore-bearing quartz and calcite veins collected from various depths of the deposit, we have found that the primary inclusions are generally three types： vapor （Type Ⅰ ）, brine （Type Ⅱ ）, and daughter-mineral bearing multiphase inclusions （Type Ⅲ ）. The statistics on all the measured filling temperatures of fluid inclusions reveal two evident peaks at 315 -335℃ and 255 - 275℃ respectively, while those on the salinities of fluid inclusions peak at 17. 50% - 22. 50% NaCl eq. and 32. 50% - 37.50% NaCl eq. , respectively. Raman analysis of the fluid inclusions indicates that, in the gaseous phase, water vapor is dominant with small amount of CO2 （ possibly CH4 ）. Hydrogen and Oxygen isotopic compositions are within the range of magmatic water. These results suggest that the ore-forming fluid has experienced phase changes twice, and was trapped from heterogenized fluid system. Moreover, Chaoshan gold deposit, spatially associated with Datuanshan and Donggushan copper deposits, has probably been formed from complex fluid interactions involving phase separation, vapor to liquid contraction and low-pressure boiling.