Geochronology and geochemistry of magmatic rocks in the Dongzi–Changhanboluo Pb–Zn ore district in Chifeng, Inner Mongolia, and their relationship with metallogenesis

Bulk-rock elements, isotopes, and zircon U–Pb ages are reported for magmatic rocks in the Dongzi–Changhanboluo Pb–Zn ore district in Chifeng, Inner Mongolia, China. Zircon U–Pb dating identified four stages of magmatism: Late Silurian gabbroic diorite (~ 420 Ma), Middle Permian monzonite (~ 274 Ma), Late Jurassic quartz porphyry and ignimbrite, breccia tuff (153–158 Ma) and Early Cretaceous andesitic porphyrite (~ 127 Ma). Integrating field observations, geochronology, and element and isotope geochemistry indicated a complex petrogenetic history of the magmatic rocks. The gabbroic diorite may have been sourced from EM1-type mantle. The source of the monzonite may have been mantle metasomatized by melt from the subducting plate. The Jurassic volcaniclastic rocks formed in a medium-pressure, high-temperature environment, possibly in the background of crustal thickening in a syncollisional stage and an early postcollisional stage. During this process, shaly sedimentary rocks were brought into the deep crust and heated, followed by the rapid isostatic uplift of the crust, which caused partial melting of the sedimentary rocks. Quartz monzonite porphyry and quartz porphyry formed by partial melting of mantle metasomatized by subducted sediments, but the quartz porphyry experienced high-degree differentiation and evolution. The andesitic porphyrite has characteristics similar to those of Permian monzonite, indicating that its source area was also the zone of mantle metasomatized by subducted sediment. The late Silurian and Permian magmatic rocks in this area most likely formed against a continental arc background related to the subduction of the Paleo-Asian Ocean Plate beneath the North China Plate. The Late Jurassic magmatic rocks suggest that the northern margin of the North China Craton may have been in a post-collisional setting during the Late Jurassic, with no obvious crustal thinning. The Cretaceous andesitic porphyrite may have formed against the background of lithospheric extension and thinning. According to the comprehensive analysis of geological characteristics, diagenetic and metallogenic epochs, and Pb isotope data, the formation of ore bodies in the Dongzi–Changhanboluo ore district was closely related to the Jurassic quartz porphyry.