Mesozoic granitic magmatism and molybdenum ore-forming processes in the Xilamulun metallogenic belt

Granitoids and molybdenum ore deposits or ore spots are well developed in the Xilamulun metallogenic belt located on the northern margin of the North China craton. The ore-bearing intrusive rocks include monozogranite, porphyritic granite, granite porphyry and rhyolite porphyry, which belong to the high-K calc-alkaline and shoshonite series. The rock-forming materials were derived from the lower crust and juvenile crust. These granitic intrusive rocks were formed in Early-Middle Triassic, Late Jurassic and Early Cretaceous. The molybdenum deposits are of porphyry, quartz vein, greisen and volcanic-subvolcanic hydrothermal types. The ore-forming ages of the molybdenum deposits are consistent with the ages of the intrusive rocks and can be divided into three stages, i. e., Early-Middle Triassic, Late Jurassic and Early Cretaceous. The Early Cretaceous porphyry molybdenum deposits are extremely well developed in the Xilamulun metallogenic belt. The Early-Middle Triassic, Late Jurassic and Early Cretaceous ore deposits were formed in a syn-collision to post-collision tectonic setting between the Siberian plate and the North China craton. Both the northwestward subduction of the Pacific plate to the East Asia continent in Jurassic period and the lithosphere thinning (extension) in East China in Mesozoic period might have provided geodynamic forces for the ore-forming processes.