延边浅成高硫化热液金矿床的成矿流体起源与演化:以杜荒岭和九三沟矿床为例

摘要

杜荒岭和九三沟矿床是延边地区两个典型的浅成热液高硫化型金矿床,两者距离不足10 km.本文运用显微测温、激光拉曼成分测试和稀有气体同位素对这两个矿床的蚀变岩和矿石中的石英内流体包裹体进行研究,以便揭示成矿流体的起源和演化过程.测温及拉曼测试结果表明:蚀变—早期矿化阶段主要气体成分为CO2、N2的两相流体包裹体,发育少量高盐度(33.4％～48.1％)高温(410～470℃)的流体包襄体,其为深部斑岩成矿系统与后期浅成矿化流体叠加的产物;主成矿阶段均一温度为90～330℃,盐度为0.4％～44.9％,成分以H2O为主,含少量的CO2;富气相、富液相及含石盐子晶多相的流体包裹体共存,表明流体发生了沸腾作用,这些流体包裹体被捕获的深度为100～500m,代表浅成矿化的主要流体.稀有气体同位素结果表明:3 He/4 He值为0.009 6～0.020 6 Ra,20Ne/22Ne、21Ne/22Ne值分别为9.734～9.987和0.030 9～0.040 6,40Ar/36Ar为1 302.4～4 433.6.上述研究结果表明,延边地区杜荒岭和九三沟金矿早期成矿流体为携带Au、Ag、Cu等成矿元素的高温、高氧化的岩浆气,主成矿阶段地壳流体的混入导致沸腾作用,晚期转以低温低盐度的大气水为主.%Less than 10 km away from each other,Duhuangling and Jiusangou deposits are two typical high-sulfidation gold deposits in Yanbian.The fluid inclusions in quartz from alteration rocks and ores were analyzed by using micro thermometry,Raman microprobe,and noble gas isotope to reveal the origin and evolution of the ore-forming fluids.The fluid inclusions in the alteration stage and the early mineralization stage are mainly gas-liquid two-phase inclusions with major gases of CO2 and N2.The occurrence of a few high-salinity (33.4％-48.1％),high-temperature (410-460℃) fluid inclusions represent the mixing of a epithermal mineralization fluids with the porphyry system at depth.The fluid inclusions indicate that the homogenization temperature of the main mineralization stage is from 90 ℃ to 330 ℃,the salinity is 0.4％-44.9％,and the composition is dominated by H2O and a small amount of CO2.The coexistence of liquid-,vapor-rich inclusions and halite-bearing multiphase inclusions suggests a boiling event.These inclusions were trapped at depth between 100 and 500 m,representing the fluids related to the epithermal mineralization at Duhuangling and Jiusangou.The fluid inclusions in pyrite are characterized by the 3 He/4 He ratio of 0.009 6-0.020 6 Ra,20Ne/22Ne ratio of 9.734-9.987,21Ne/22Ne ratio of 0.030 9-0.040 6,and 40Ar/36Ar ratio of 1 302.4-4 433.6.Combined with the stable isotope data,these ratios suggest that the early ore-forming fluid was of high temperature and high oxidized magmatic gas carrying Au,Ag,Cu and other ore-forming elements,the mixing of the fluid in the crust led to the boiling process during the main ore-forming stage,and the liquid was dominated later by low temperature and low salinity atmospheric water.