Scheelite Elemental and Isotopic Signatures : Implications for the 3 Genesis of Skarn-Type WMo Deposits in the Chizhou Area , 4 Eastern China

16 Scheelite is well developed in hydrothermal deposits, providing a window into 17 genetic processes and facilitating comparative studies, however few studies have 18 focused on characterizing scheelite in skarn-type W-Mo deposits. The primary ore 19 mineral in the Jitoushan and Baizhangyan skarn-type W-Mo deposits (Eastern China), 20 scheelite was analysed for major, trace and rare earth element (REE) abundance and 21 for Sr-Nd isotopes. The analysis revealed two unique geochemical characteristics that 22 distinguish the scheelite from skarn-type W-Mo to that from vein-type Au-W and 23 porphyry-type W-Mo deposits: higher Mo content with a negative correlation between 24 MoO3 and WO3 and a strong HREE depletion. 25 Skarn-type W-Mo scheelite mainly inherited REE signatures from ore-forming 26 fluids and the early precipitation of skarn minerals (e.g., garnet, diopside and 27 amphibole) has most likely resulted in the observed strong HREE depletion in 28 scheelite and the decoupling of LREEs and HREEs. Of the numerous substitution 29 mechanisms suggested by previous workers, 3Ca=2REE+□Ca (where □Ca is a Ca 30 site vacancy) is preferred for the substitution of REE for Ca and in this study, 31 particularly given the low salinity of ore fluids. 32 As the scheelite Eu anomalies were inherited from ore-forming fluids with 33 variable redox conditions and pH, the complex δEu/Mo correlation indicates that Mo 34 increasingly entered the scheelite under oxidizing conditions and reached a maxim at 35 δEu values of 0.8 to 1. In contrast, under reducing conditions, Mo contents in 36 scheelite decrease gradually and Mo is precipitated as molybdenite as a result of the 37 change in dominant valence state. 38 Unlike the Sr-Nd isotope compositions of scheelite from vein-type Au-(W) and 39