Rare-Earth Element Mobility During Ore-Forming Hydrothermal Alteration:A Case Study of Dongping Gold Deposit,Hebei Province,China

REE mobility during hydrothermal ore-forming processes has been extensively investi-gated in recent years and the potential of REE to provide information about ore forming processeshas commonly been recognized. The Dongping gold deposit, which is located in northwesternHebei Province, China, occurring in the inner contact zone of the Shuiquangou syenite complex,is spatially, and probably genetically, related to the syenite. The deposit was formed under themoderate to high temperature (220℃ to 320℃ ), weakly acidic to weakly alkaline, rather highfo2 (lgfo2 = - 30 ～ - 34) environment. The REE study of the host rocks, altered wall rocks,ores and gangue minerals from the deposit suggests that the REEs have been mobilized and differentiated during K-feldspathization and silicification. The extremely altered syenite envelopingauriferous quartz vein shows positive Ce anomaly and larger LREE/HREE ratio than that of theunaltered syenite. The REE concentrations and patterns of the ores are determined by the oretypes and mineral assemblages. LREE/HREE ratios in the gangue quartz and hydrothermal K-feldspars are relatively low. The most significant observation is that the gangue quartz shows sig-nificant positive Eu anomaly, whereas the hydrothermal K-feldspars show less significant or nopositive Eu anomaly at all relative to the primary feldspar in the unaltered syenite.It is evident that the REEs are mobile during K-feldspathization and silicification in the oreforming process. Weak to moderate K-feldspathization caused REE mobility without apparentdifferentiation with the exception of extreme K-feldspathization and silicification which resultedin significant depletion of HREE and Eu and relative enrichment of Ce. The REE, Y, U, Thand Au contents of the syenite decrease as the degrees of K-feldspathization and silicification of the rocks increase towards the auriferous quartz veins. As the ores were deposited under a ratheroxidized environment, Ce4 + predominated over Ce3 +. The precipitation of the former in the for