Zircon U-Pb dating of adamellite from the Sadaigoumen porphyry molybdenum deposit in Fengning, Hebei Province, and its significance

Abstract: The Sadaigoumen molybdenum deposit lies in the Yan-Liao metallogenic belt, which is located on the north margin of North China platform. For the purpose of accurate determination of the age of ore-bearing adamellite, the authors employed the zircon LA-MC-ICP-MS dating, which yielded a concordant age of (257.4±1.1) Ma and two weighted average ages of (256.9±0.9) Ma and (247.7±1.2) Ma. Because of the cooling of the intrusion, the age of the lower part of the rock (247.7±1.2) Ma is younger than the ages of the upper part (257.4±1.1) Ma and (256.9±0.9) Ma. The inherited zircon age implies assimilation in the process of mineralization, which is consistent with the previous study result of I-type granite. Combined with the previous study, the authors investigated the metallogenic geodynamics background of the study area. North China platform was transformed from the strong squeezing stage to the post-orogenic stage around 250 Ma, which was favorable for the formation of adamellite.