An Isotopic (Sr, Nd and Pb) Tracer Study on the Xiaoxinancha Gold-rich Copper Deposit in Yanbian, China: Implication for the Geodynamic Model of Diagenesis and Metallogenesis

An isotopic study was systemically carried out on the granitic complex, diorite‐porphyrite, ores and ore minerals of the 103 Ma Xiaoxinancha gold‐rich copper deposit in Jilin province to determine the geodynamic model of diagenesis and metallogenesis. Results show that the initial Nd and Sr isotopic compositions of the granitic complex are in the range of 0.70425–0.70505 for (⁸⁷Sr/⁸⁶Sr)_i, 0.51243–0.51264 for I_Nd, and –1.31 to + 2.64 for ε_Nd(t); those of the diorite‐porphyrite are in the range from 0.70438–0.70448 for (⁸⁷Sr/⁸⁶Sr)_i, 0.51259–0.51261 for I_Nd, and + 1.56 to + 2.09 for ε_Nd(t). For ores and sulfides, the (⁸⁷Sr/⁸⁶Sr)_i, I_Nd, and ε_Nd(t) values are in the range from 0.70440–0.70805, 0.51259–0.51279 and +1.72 to +5.56, respectively. The Pb isotopic ratios of the granitic complex range from 18.2992–18.6636 for ²⁰⁶Pb/²⁰⁴Pb, from 15.5343–15.5660 for ²⁰⁷Pb/²⁰⁴Pb, and from 38.1640–38.5657 for ²⁰⁸Pb/²⁰⁴pb For diorite‐porphyrite, the isotopic ratios of ²⁰⁶Pb/²⁰⁴Pb, ²⁰⁷Pb/²⁰⁴Pb and ²⁰⁸Pb/²⁰⁴b are 18.3919, 15.5794 and 38.3566, respectively, whereas those of the ores and ore sulfides vary from 18.2275–18.3770 for ²⁰⁶Pb/²⁰⁴Pb, from 15.5555–15.5934 for ²⁰⁷Pb/²⁰⁴Pb and from 38.1318–38.3131 for ²⁰⁸Pb/²⁰⁴Pb. The results indicate that the mineralization was correlated to the formation and evolution of the granitic complex and the diorite‐porphyrite. Combining with the reported data in petrologic characteristics, elemental geochemistry and chronology, conclusions can be drawn that the geodynamic settings of diagenesis and metallogenesis of this deposit were consistent with the subduction of the Izanagi oceanic plate during the Early Cretaceous. The diorite‐porphyrite was formed by the emplacement of the adakitic magma triggered by partial melting of the enriched mantle, which originated from the derivative continental lithospheric mantle metasomatized by dehydration fluids from the subducting oceanic crust. The granitic complex was produced by fractional crystallization of the mixture between the adakitic magma and the high‐K calc‐alkaline acidic magma, which were generated by the remelting of the lower crust in the course of intraplate upwelling of the adakitic magma. The ore‐bearing fluid reservoir convened in a late stage of the evolution of the mixed magma chamber.