REE characteristics of molybdenites from endogenous molybdenum deposits in China

Abstract：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 REE amounts in molybdenite were formed in Yanshanian period (concentrated in the Middle Jurassic - Early Cretaceous), North China has higher REE than South China, and independent Mo deposits or Mo polymetallic deposits have higher REE than other deposits characterized by associated Mo mineral assemblages. REE 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 LREE, and have strong negative Eu anomalies (δEu= 0.01~0.80), negative Ce anomalies (δCe=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 identified, 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, Cl- (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.