Formation and age of granites and molybdenum in Shuangyangshu, NE China: Insights from UPb and ReOs geochronology geochemistry, and Hf isotopes

Abstract

Recent research indicates that the magmatic–metallogenic events in Northeast China were mainly influenced by the tectonic regimes of the Paleo–Asian Ocean and the Paleo–Pacific Ocean. Nonetheless, significant challenges remain in comprehending the petrogenesis and source regions of the mineralizing magmas for metallogenic event. This study examines the geological chronology and geochemical data of ore–bearing granites and molybdenite from the Shuangyangshu molybdenum deposit in central Jilin. The objective is to ascertain their petrogenetic and metallogenic ages, petrogenesis, magmatic activity, and their implications for the geodynamic evolution of central Jilin. LA–ICP–MS zircon UPb dating reveals that the Shuangyangshu K–feldspar granite has an age of 179 Ma, and the monzogranite has an age of 178 Ma, indicating that they are synchronous phase change granites. ReOs isotopic analysis of molybdenite indicates a metallogenic age of 176.3 Ma for the Shuangyangshu molybdenum deposit, which is closely associated with K–feldspar granite diagenesis. The Re content ranges from 9.4 to 17.8 μg/g, suggesting that the metallogenic source is predominantly crustal with a minor mantle–derived component. Petrological geochemical data classify the Shuangyangshu granites as high–potassium calc–alkaline series highly fractionated I–type granites. The εHf (t) values are positive, ranging from 7.1 to 9.1 and 6.2 to 8.9, respectively. The two–stage model ages (tDM2) range from 477 to 560 Ma and 558 to 697 Ma, indicating that the granite source is the partial melting of the Neoproterozoic high–potassium basaltic crust caused by the underplating of mantle–derived magma. Subsequently, the magma experienced extensive crystallization of plagioclase, K–feldspar, titanium–bearing minerals, monazite, apatite and allanite. Tectonic discrimination diagrams based on trace elements and their characteristic ratios suggest that Shuangyangshu granites formed during the subduction of the Paleo–Pacific Ocean. This implies that the Paleo–Pacific Ocean had already subducted in the early Jurassic, leading to the formation of numerous endogenic metal deposits. The subduction of the ancient Pacific Ocean plate led to regional compression, which was conducive to the accumulation of a large amount of magma in the deep, and finally formed a large molybdenum deposit.