Abstract

The Palaeozoic Shuiquangou complex is a major syenitic intrusion along the northern margin of the North China Craton that hosts a number of gold deposits. Despite the heterogeneity of the complex in terms of texture and modal mineralogy, mineral compositions, whole-rock chemistry as well as radiogenic isotope compositions show a well-constrained magmatic evolutionary trend. The whole-rock major element and REE trends are broadly consistent with fractional crystallization dominated by clinopyroxene, amphibole and accessory minerals. Initial Nd–Sr isotopic compositions suggest that the parent magmas to the complex were ultimately derived from an enriched mantle with relatively high initial 87Sr/86Sr ratios and negative ϵNd values. The enrichment of the mantle source was probably inherited from an older lithospheric mantle beneath the North China Craton. Sr isotopic data indicate that the Rb–Sr system was disturbed by later alteration processes, whereas Nd isotopes are essentially unaffected and exhibit a broad trend consistent with simultaneous fractional crystallization and country-rock assimilation (AFC). Quantitative modelling indicates that a very high bulk distribution coefficient for Nd and low ratios of assimilation to crystallization are needed to produce the observed Nd isotope evolutionary trend.

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