In situ SIMS U‐Th‐Pb Dating of Hydrothermal Monazite from the Large Sidaogou Deposit, Liaodong Peninsula, NE China: Insights into Early Jurassic Gold Mineralization

Abstract Recently identified hydrothermal monazite from the Sidaogou deposit in the Liaodong Peninsula, is co‐genetic with gold‐bearing ore minerals and thus can serve as ideal proxy for dating the gold‐mineralization event. Our study effectively solved the dilemma of lack of any accurate age for the Sidaogou deposit. The Sidaogou deposit is hosted mainly by Paleoproterozoic metamorphic rocks of the Liaohe Group, and hydrothermal monazite therein occurs within voids or along micro‐fractures in syn‐ore pyrite and quartz. First in situ SIMS U‐Th‐Pb isotope data on this monazite from the Sidaogou deposit yielded an inverse Concordia age of 184 ± 20 Ma, which is much younger than an 40 Ar‐ 39 Ar age of 1858.9 ± 25.4 Ma obtained on muscovite from the host rock (Gaixian Formation), thus supporting a prominent Early Jurassic gold mineralization event in the Wulong gold field, which is distinct from previously established Early Cretaceous gold mineralization, held responsible for the nearby large Wulong gold deposit. Our new findings make it possible, together with previous studies, to formulate a model for the Early Jurassic magmatic–hydrothermal gold system in the area, for which a compressional setting during the westward subduction of the Paleo‐Pacific Plate beneath the North China Craton is postulated.