Trace Elements and Pb-O Isotopes of Scheelite: Metallogenic Implications for the Shimensi W-Polymetallic Deposit in South China

Abstract

The world-class Shimensi tungsten (W)-polymetallic deposit is located in Jiangnan Orogen, with an estimated reserve of 742.5 kt WO3 @ 0.195% W, 403.6 kt Cu and 28 kt Mo. In this paper, the trace elements and Pb-O isotopes of scheelite (the main ore mineral) are presented to study the ore-forming material source and ore-forming fluid evolution. The results show that the REE distribution in scheelite is mainly controlled by the substitution mechanism of 3Ca2+ = 2REE3+ + □Ca (where □Ca is the Ca-site vacancy). Oxygen isotope data indicate that the scheelite mineralization occurred under high-temperature oxygen isotope equilibrium conditions, and that the ore-forming fluid has a magmatic–hydrothermal origin. The variation in scheelite Eu anomalies and the wide range of scheelite Y/Ho ratio indicate that the ore-forming fluid evolves from reducing to oxidizing, and the early-stage and late-stage ore-forming fluid may have been relatively rich in F− and HCO3−, respectively. The significant Mo decrease in scheelite from the early to late stage that are opposite to the influence of fO2 variation may have resulted from the crystallization of molybdenite and Mo-rich scheelite. Lead isotopes of the ore minerals of scheelite, wolframite, molybdenite and chalcopyrite can be divided into three groups, similar to these of feldspars in different granites. Both the Mesozoic porphyritic and fine-grained biotite granites have Pb isotope ratios similar to the ores, which suggests that the former two are the main ore material source.