Ore-forming granites from Jurassic porphyry Mo deposits, east–central Jilin Province, China: geochemistry, geochronology, and petrogenesis

Abstract

<p>The east–central part of Jilin Province, NE China, hosts an important polymetallic metallogenic district that contains more than 10 recently discovered large-, medium-, and small-scale Mo deposits. The Mo deposits in this area include porphyry-, skarn-, and quartz vein-type mineralization, of which the porphyry-type deposits dominate. Few studies of these mineralization-related granitoids have been undertaken. Here, we present the results of a systematic regional survey of the geochemistry and geochronology of Mo mineralization-related granites in this area. Zircon U–Pb dating of the Fuanpu, Jidetun, Shuangshan, and Jiapigou granites, all of which are associated with Mo mineralization, yielded weighted mean ²⁰⁶Pb<i>/</i>²³⁸U ages of 167.05 ± 0.81, 170.91 ± 0.83, 183.8 ± 1.1, and 182.3 ± 2.2 Ma, respectively, indicating that these plutons were emplaced during the Early–Middle Jurassic. They have SiO₂ = 62.59–73.5 wt.%, Al₂O₃ = 13.74–16.19 wt.%, and K₂O/Na₂O = 0.8–2.18. Chemically, they are metaluminous to peraluminous and belong to the high-K calc-alkaline to shoshonitic series. Moreover, they are enriched in large ion lithophile elements and light rare earth elements, and are depleted in high field strength elements, which are characteristics of I type granite. Whole rock Sr–Nd–Pb isotopic compositions of these granitoids are similar (initial ⁸⁷Sr/⁸⁶Sr = 0.70404 to 0.70554; <i>ε</i>Nd(<i>t</i>) = –0.9 to 2.4; (²⁰⁶Pb/²⁰⁴Pb)<i>_t</i> = 15.549–15.567, (²⁰⁷Pb/²⁰⁴Pb)<i>_t</i> = 18.035–18.530, ⁽²⁰⁸Pb/²⁰⁴Pb)<i>_t</i> = 37.966–38.229) and altogether suggest that the magmas from which the Mo deposits were generated originated from the mantle or juvenile crust. Combining our results with regional Jurassic tectonic setting, we conclude that the mineralization of these granitoids reflected Pacific plate subduction which induced magma underplating and promoted the remelting of the juvenile crust, resulting in voluminous granitic magma.</p