Zircon U-Pb and molybdenite Re-Os geochronology and geochemistry of the Tieling deposit in the Eastern Tianshan, NW China: Insights into the timing of mineralization and tectonic setting

Abstract

The Aqishan-Yamansu belt in the Eastern Tianshan (NW China) contains many Carboniferous granitic intrusive rocks and volcanic rocks and hosts numerous large to medium sized Fe (-Cu) deposits. The Tieling deposit consisting of 89 iron ore bodies in the Aqishan-Yamansu belt has been mined since discovered in 1970 s. Mo mineralization was newly identified in concealed rocks of the Tieling deposit, and molybdenite is extensively distributed as a disseminated phase in the biotite moyite and occurs as aggregates in quartz veins. The molybdenite Re-Os model ages (300.6 ∼ 298.7 Ma) are consistent with the zircon U-Pb age (304.5 ± 2.4 Ma) of the ore-causative biotite moyite within error, which indicating that the Tieling Mo mineralization occurred during the Late Carboniferous. The Late Carboniferous biotite moyite exhibits calc-alkaline and peraluminous characteristics, with negligible Eu anomalies, akin to I-type granites. Dominantly positive εHf(t) values (+13.6 to + 15.2), variable Mg# values (31 to 49), and limited variation in (87Sr/86Sr)i ratios (ISr = 0.70358–0.70390), and positive εNd(t) values (+4.55 to 6.39), along with the juvenile TDM2 age (548 to 697 Ma), suggest that the biotite moyite was probably originated from partial melting of the juvenile lower crust with involvement of mantle-derived magmas. Integrating published data and our work, we conclude that the Aqishan-Yamansu belt evolved from the pre- Early Carboniferous forearc basin (ca. 450–350 Ma) to the Carboniferous island arc environment (ca. 350–310 Ma) triggered by the bidirectional subduction of the Kanggur Ocean, then the extensional geodynamic setting (ca. 310–270 Ma) is conducive to the porphyry Mo mineralization of the Tieling deposit and Ni-Cu-Au deposits in the Eastern Tianshan.