Magmatic oxygen fugacities of porphyry Mo deposits in the East Xing’an-Mongolian Orogenic Belt (NE China) with metallogenic implications

Abstract

The East Xing’an–Mongolian Orogenic Belt (EXOB) in China hosts numerous porphyry Mo deposits that are associated with calc-alkaline granitic intrusions. Here we report the trace-element compositions of zircon grains from 11 intrusions collected from 8 porphyry Mo deposits in the EXOB: the superlarge-sized Daheishan and Luming deposits; the large-sized Aolunhua deposit; the medium-sized Kulitu and Yangchang deposits; and the small-sized Erbadi, Hashitu, and Longtoushan deposits. The results show a positive correlation between the Mo tonnage of each deposit and the zircon Ce4+/Ce3+ ratio of the ore-related intrusions. In addition, the Ce4+/Ce3+ ratio of zircon in ore-related intrusions is much higher than that of the associated barren rocks. The Ce4+/Ce3+ ratios of 300, 200 and 100 of zircon seem to separate the intrusions into superlarge-sized, large-sized, medium-sized and small-sized porphyry Mo deposits, respectively. Oxygen fugacity values of ΔFMQ +2 of ore-related intrusions discriminate the medium-sized to superlarge-sized Mo deposits from the small-sized deposits. The relationship between the scale of mineralization and oxygen fugacity suggests that the oxidation condition of the source magma played a critical role in the development of large-sized and superlarge-sized Mo porphyry systems in the EXOB. The zircon Ce4+/Ce3+ ratios of ore-related intrusions of the EXOB are similar to those of porphyry Cu deposits in the Central Asian Orogenic Belt and the Yulong copper belt, but much lower than those of the Chuquicamata porphyry Cu deposit in Chile.