Temporal evolution and origin of the Yumugou Mo-W deposit, East Qinling, China: Evidence from molybdenite Re-Os age and U-Pb dating and geochemistry of titanite

Abstract

The Yumugou Mo-W deposit is an important porphyry-skarn deposit hosted in the world-class Luanchuan Mo polymetallic cluster, East Qinling, China. However, the origin and age of skarn Mo mineralization, as well as the temporal evolution, redox conditions and magmatic-hydrothermal processes of the Yumugou porphyry-skarn system remain enigmatic. Hence, we conducted molybdenite Re-Os and titanite U-Pb dating together with titanite geochemical studies on porphyry and skarn from the Yumugou deposit, with major view to resolve the life-cycle and evolution of the Yumugou deposit and to provide insights into the magmatic-hydrothermal evolution of regional Luanchuan porphyry-skarn system. Titanite U-Pb dating of Mo-hosting monzogranite yielded a lower intercept age of 145.0 Ma, consistent with reported zircon (147–141 Ma) and apatite (153–141 Ma) U-Pb ages of the Huangbeiling intrusion, interpreted as rapid post-magma cooling in response to shallow emplacement of granitic porphyries. Titanite U-Pb dating of skarns yielded titanite U-Pb lower intercept ages of 149.0–144.7 Ma, representing the timing of multiple hydrothermal events. Molybdenite Re-Os dating of Mo-hosting skarns yielded a weighted mean age of 147.2 Ma, which we interpret as the age of skarn Mo mineralization. Together with published age data of the Yumugou deposit, we suggest that the Yumugou porphyry-skarn system underwent magma emplacement at ca. 147–141 Ma, contemporaneous skarnization, Mo mineralization and rapid post-magma cooling at ca. 153–141 Ma, and multiple post-mineralization cooling and exhumation at ca. 114–58 Ma. Compiled molybdenite Re-Os isotopic data indicate crust-mantle mixed Mo source for all Mo-W deposits, and coupled with crust-mantle mixed magma and ore-forming materials of granitic porphyries and skarn-hydrothermal Pb-Zn-Ag deposits in the Luanchuan region, we propose that the Luanchuan porphyry-skarn system shares a single source. In addition, titanite textures and geochemical data suggest most titanites from the Yumugou deposit are of hydrothermal origin and mainly formed under reduced conditions. In conjuction with tectonic evolution of the East Qinling Orogen, we argue that the Yumugou Mo-W deposit formed during the tectonic transition from syn- to post-collisional settings (160–130 Ma), via multiple interactions of melt and hydrothermal fluids, Mo4+ aggregates S2– under reduced conditions to precipitate as molybdenites (MoS2) in granitic porphyries and skarns. Further, we also suggest that similar Mo enrichment processes likely occurred throughout the whole East Qinling Orogen.