中国钼矿中辉钼矿的稀土元素地球化学及其应用

REE characteristics of molybdenites from endogenous molybdenum deposits in China

钼矿是中国比较特殊的一个矿种，是近年来找矿突破最大的矿种之一。辉钼矿作为最具工业意义的含钼矿物，广泛分布于各种内生钼矿床中。本文尝试性地对内生独立钼矿或共伴生钼矿矿床中的辉钼矿进行了ICP—MS稀土元素分析。结果表明，各矿床辉钼矿中稀土总量在10．99～3374δg／g，集中在10．99～600μg／g。时间上，中侏罗世一早白垩世辉钼矿稀土元素含量最高：空间上，北方矿床中辉钼矿的稀土总量较南方高；矿种组合上，独立钼矿、以钼为主的多金属矿中稀土总量要大于其他伴生钼矿矿床。辉钼矿稀土元素配分曲线具有多样性，不同矿集区内矿床成矿时代、矿床类型与矿种组合对稀土元素配分模式影响不明显。辉钼矿中明显富集轻稀土，具有强烈的Eu负异常（δEu=0．01～0．80）、Ce负异常（δCe=0．24～1．06，多数δCe值〈1）和Sm正异常（6Sm=1．29～79．42）。依据辉钼矿轻稀土富集程度、Sm和Eu等稀土元素异常特征。将辉钼矿稀土元素配分模式分为6类，反映了不同辉钼矿成因或成矿流体性质的差异性：依据LREE、HREE、6Eu和δCe等特征，以及熔体／流体实验结果，推测成钼流体总体上是以富CO2、C1-（个别还富含F一）和还原性气体成分的成矿流体。内生金属矿床中辉钼矿主要形成于还原性环境，但石英脉型矿床较斑岩型矿床形成条件明显氧化性增强。

As one of special mineral species deposits in China, molybdenum deposits have got considerable prospecting breakthrough in recent years. Molybdenite, widely distributed in a variety of endogenous Mo deposits, is a molybdenum-bearing mineral with the most significant econonic significance. In this study, the authors chose molybdenite from 57 molybdenum deposits for ICP-MS REE dating. The results show that the total REE values in molybdenum deposits are between 10.99 and 3374μg/g （concentrated between 10.99 and 600μg/g）. The high R_EE amounts in molybdenite were formed in Yanshanian period （concentrated in the Middle Jurassic - Early Cretaceous）, North China has higher R_EE than South China, and independent Mo deposits or Mo polymetallic deposits have higher REE than other deposits characterized by associated Mo mineral assemblages, tLEE distribution patterns of molybdenites show diversity, but the patterns are not controlled by metallogenic ages, types and mineral assemblages in different ore concentration areas. Molybdenites are significantly enriched in LtLEE, and have strong negadve Eu anomalies （ δEu= 0.01～0.80）, negative Ce anomalies （δ Ce=0.24～1.06, Most are less than 1） and positive Sm anomalies （δSm=1.29～79.42）. According to these characteristics and distribution patterns of REE in molybdenite, 6 categories of molybdenite can be idendfied, reflecting the different geneses of molybdenite or different natures of ore-forming fluids captured in the process of molybdenite crystallization. Based on the experimental results of melt/fluid, the authors infer that molybdenum- forming fluids are usually enriched in CO2, C1- （may be also rich in F-） and some reducing gas compositions, indicating a reducing environment. The quartz vein-type deposits, however, were formed in more oxidative environment than porphyry deposits.