Ore and rock forming ages, geochemical, mineralogical characteristics of Shuikoushan ore field and its indicating significance for Pb-Zn polymetallic mineralization, Hunan Province

We reported systematic mineralogical, geochronological, geochemical and Sr-Nd isotopic data of granodiorite and dacite porphyry in Shuikoushan ore field.The EMPA analysis result shows that the biotite in granodiorite is magnesium-rich biotite and the plagioclase is main andesine, while the plagioclase in dacite porphyry is main oligoclase-albite.Zircon U-Pb age shows that the dacite porphyry was formed at 148.8±0.5 Ma, which is about 10 Ma later than the granodiorite.However, the in situ U-Pb age of garnet shows that the deep skarn of Kangjiawan deposit was formed at 159.1±1.9 Ma, which is much closer to the formation age of granodioritie.Geochemical characteristics shows that the magmatic rocks in Shuikoushan are enriched in Al, low in Si and high in K/Na ratio, and have the affinity of subalkaline and high K calc-alkaline to shoshonite series.They are enriched in Rb, Th, U and depleted in Ba, Nb, Sr, Ti, etc.Sr-Nd isotopic characteristics show that the(⁸⁷Sr/⁸⁶Sr)_i ratios range from 0.70661 to 0.70801 and 0.71116 to 0.711156 for granodiorite and dacite porphyry, respectively.The calculated ε_Nd(t)values range from-7.4~-2.4 and-7.1 to-8.63 for granodiorite and dacite porphyry, respectively.The T_DM2 values of granodiorite range from 1.53 Ga to 1.15 Ga and of dacite porphyry are from 1.64 Ga to 1.53 Ga.It suggests that the granodiorite and dacite porphyry were derived from partial melting of Mesoproterozoic metamorphic basaltic tonalite diorite.They are formed at the different stages of magmatism and derived from distinct source regions.The evidence of formation ages, geochemical characteristics and mineralogical characteristics suggest the affinity between granodiorite and polymetallic mineralization.The Shuikoushan ore field was formed in the intracontinental extensional setting under the subduction background of paleo-Pacific plate at the late stage of early Yanshanian.