Petrogenesis of the Hercynian Granite in the Shuangjianzishan Super-large Ag Polymetallic Deposit, Inner Mongolia and its Metallogenic Significance: Evidence from Geochronology and Petrogeochemistry

Abstract

The Shuangjianzishan deposit is a typical magmatic-hydrothermal deposit located in the southern Great Xing'an Range. Recent investigations have identified significant copper and tin mineralization at depth within the Shuangjianzishan deposit; however, the coupling relationship between magmatic emplacement and mineralization processes remains debated. This study presents whole-rock geochemistry, zircon LA-ICP-MS U-Pb dating, and zircon Hf isotope analyses of granite from the northern Shuangjianzishan deposit. The analysis results indicate the granite crystallized between 252.3 and 257.9 Ma, corresponding to Late Permian magmatic activity. The granite displays ε_Hf(t) = 5.95–14.87, and t_DM2 = 333–900 Ma. Geochemically, the granite is rich in Si and Al, with high K, classified as a calc-alkaline, weakly peraluminous rock. LREEs are enriched, while HREEs are depleted, and a slight negative Eu anomaly, all of which are consistent with A-type granite characteristics. The Hercynian granite in the Shuangjianzishan deposit formed during the latter or post-collisional stages of the collision orogeny following the closure of the Paleo-Asian Ocean in the late Paleozoic era. The material source indicates a mixed origin, involving both crust and mantle contributions. The granite is also enriched in Cu, Pb, and Zn, suggesting its potential role as an ore-forming material source for the Shuangjianzishan deposit. This study proposes a potential link between Hercynian magmatism and mineralization at the Shuangjianzishan deposit for the first time, suggesting that multistage metallogenesis may be a response to successive magmatic events from Hercynian to Yanshanian periods in the mining area.