Two periods of magmatism in the Weishancheng ore concentration area, Henan Province: Evidences from zircon U-Pb chronology, Hf isotopes and petrogeochemistry

Abstract

The Weishancheng area of Tongbai County, Henan Province, is an important Au-Ag polymetallic ore concentration area in China, characterized by a widespread distribution of plutons and frequent magmatic activities. To investigate the genetic relationship between magmatism and the mineralization of gold and silver polymetallic deposits in the area, this study focuses on the porphyritic monzogranite of the Liangwan pluton and the biotite granite of the Taoyuan pluton in detail. The zircon U-Pb age of the Liangwan pluton is 128.5 ± 0.7 Ma, placing its intrusion age in the Early Cretaceous. Similarly, the zircon U-Pb age of the Taoyuan pluton is 431.3 ± 2.7 Ma, indicating an intrusion age in the Early Silurian. Petrogeochemical analysis reveals that both the Liangwan and Taoyuan plutons exhibit high SiO₂, Na₂O and Al₂O₃ contents, along with low MgO, Fe₂O₃ and CaO contents, indicating a (high-K) calc-alkaline series, and have the properties of peraluminous I-type granite. The total rare earth elements (REE) concentrations are low, with noticeable fractionation between light and heavy REE, and a negative Eu anomaly. High-field-strength elements (such as Nb, Ta, P, Ti) are depleted, while the large-ion lithophile elements (such as Rb, K, Pb) are enriched. The ε_Hf(t) values of the Liangwan and Taoyuan plutons range from −16.1 to −18.8 and from 11.0 to 14.6, respectively. The mean values of Hf two-stage model ages (T_DM2) are 603 Ma and 2230 Ma, respectively. These results suggest that the Liangwan pluton may have formed through partial melting of ancient crustal materials in the Palaeoproterozoic, during extensional tectonic events following the subduction of Izanagi Plate. It appears closely linked to Au-Ag mineralization in the ore concentration area. The Taoyuan pluton likely originated from the depleted mantle and experienced some degree of crustal contamination. However, it is unrelated to regional mineralization.