Porphyry molybdenum deposits in the Tianshan–Xingmeng orogenic belt, northern China

Abstract

Molybdenum (Mo) exploration activity in China has increased tremendously over the past decade, and China is now known to have the largest Mo reserves in the world. The Tianshan–Xingmeng orogenic belt, the second largest Mo metallogenic belt, possesses over 8.2 Mt of Mo reserves. Porphyry Mo deposits contain 99 % of the Mo reserves in the Tianshan–Xingmeng orogenic belt; other Mo deposits contain 1 % of the Mo reserves. Five subtypes of the porphyry Mo deposits can be distinguished by deposit associations, such as Mo, Mo–Cu, Mo–W, Mo–Pb–Zn–Ag, and Cu–Mo deposits. These porphyry Mo deposits are formed at different stages: during the Ordovician, Devonian, Carboniferous, Late Permian, Triassic, Jurassic, and Cretaceous Periods. The polystage porphyry Mo mineralizations indicate that polystage tectonic–magmatic activity occurred in the orogenic belt. The Ordovician–Carboniferous porphyry Cu–Mo deposits are formed in an island-arc setting; the Late Permian porphyry Mo deposits are formed in a syn-collisional tectonic setting; and the Triassic porphyry Mo deposits are formed in a syn-collisional to post-collisional tectonic setting. The Ordovician–Triassic porphyry deposits are related to the Paleo-Asian Ocean tectonic system. The Jurassic porphyry Mo deposits are formed at the eastern margin of the Asian continent and are associated with a Paleo-Pacific plate-subduction tectonic setting. Cretaceous porphyry Mo deposits are formed in a lithospheric thinning setting and are related to the rollback of the Paleo-Pacific subduction plate.