U–Pb Ages and Whole-Rock and Zircon Geochemistry of Granitoids from the Zhireken Mo-Porphyry Deposit, Eastern Transbaikalia: New Insights into the Link to Mineralization

Abstract

The Zhireken Mo-porphyry deposit is located within the West Stanovoi terrane of the Transbaikalia sector of the Mongol–Okhotsk orogenic belt and is linked to the Middle–Late Jurassic Zhireken composite intrusion. Despite the long-term history of exploration of the deposit, many issues regarding magmatism and ore mineralization remain undetermined. In particular, the ore-producing granitoid intrusion that is genetically related to the deposit formation has not yet been identified. The study provides new U–Pb LA-ICP-MS zircon ages and geochemical whole-rock and zircon compositions obtained for igneous rocks of the Zhireken deposit. The research shows that the deposit is spatially associated with a series of high-K calc-alkaline to shoshonitic I-type granitoid intrusions that were emplaced at around 158–166 Ma at the postcollision stage of the evolution of the Mongol–Okhotsk Ocean. The sequence of the intrusive events includes biotite leucogranite (U–Pb age of ca. 164–166 Ma) → biotite–amphibole granite and granodiorite (U–Pb age of ca. 161–163 Ma) → dikes of granite-porphyry (U–Pb age of ca. 162–163 Ma), leucogranite-porphyry, and (quartz) diorite-porphyry → dikes of quartz monzonite-porphyry (U–Pb age of ca. 158 Ma). The U–Pb dates obtained and the observed geological relationships between granitoids and ore mineralization suggest that the emplacement of an ore-causative granite intrusion and the formation of porphyry-Mo stockwork system at the Zhireken deposit occurred in the interval of a. 158–161 Ma. A thorough examination employing geochemical whole-rock and mineral (zircon) fertility indicators reveals no genetic link between the studied granitoids and porphyry mineralization since they are all generated from weakly oxidized magmas. The ore-causative granitoid intrusion genetically related to Mo mineralization at the Zhireken deposit is either buried or represented by a rock type that is out of focus in both the present and previous studies.