A peculiar composite M- and W-type REE tetrad effect: Evidence from the Shuiquangou alkaline syenite complex,Hebei Province,China

A new type of REE tetrad effect, a composite M- and W-type, was recognized in the K-feldsparthized and silicificated Shuiquangou alkaline syenites, Dongping, Hebei Province. Different analytical methods such as ICP-MS and isotopic dilution thermal ion mass spectrometer were exploited to verify the REE concentrations of the samples in three laboratories in China, France and Korea. The results are reliable and consistent within errors. In situ quantitative analysis of REE concentrations of individual zircons and apatites extracted from the very same sample has shown that fractional crystallization of magma and the superimposed hydrothermal alteration might have taken place in at least two-stage hydrothermal activities to generate the composite M- and W-type REE tetrad effect. The coexisting melt and aqueous phases, the superimposed alteration by volatile (Cl, CO₂)^– and Si, K, Al-enriched high temperature hydrothermal fluids might be the important facts for this new MW-type of REE tetrad effect. In addition, the peculiar MW-type tetrad effect might be an indicator for Au mineralization of reworked plutons.