U-Pb Zircon And Re-Os Molybdenite Geochronology Of The W-Mo Mineralized Region Of South Qinling, China, And Their Tectonic Implications

A W-Mo mineralized region is located along the northern margin of the South Qinling tectonic belt of China. W-Mo mineralization occurs mainly in Cambrian-Ordovician clastic and carbonate rocks, and the ore bodies are structurally controlled by NW-SE- and NNE-SSW-striking faults. Evidence for magmatism in the area is widespread and is dominated by intermediate-felsic intrusives or apophyses, such as the Dongjiangkou, Yanzhiba, Lanbandeng, and Sihaiping granitic bodies. Quartz-vein-type mineralization and fault-controlled skarn-type mineralization dominate the ore systems, with additional enrichment in residual deposits. At present, there are few or insufficient studies on (1) the age of mineralization, (2) the relationship between intermediate-felsic granite and W-Mo mineralization, (3) the source of ore-forming materials, and (4) the metallogenic and tectonic setting of the mineralized area. In this paper, we present geochronology results for numerous intrusive granitic bodies in the South Qinling tectonic belt. U-Pb zircon geochronology of the Lanbandeng monzogranite and Wangjiaping biotite monzogranite yields ages of 222.7 +/- 2.3 and 201.9 +/- 1.8 Ma, respectively. In contrast to the Late Triassic age of the Lanbandeng monzogranite, the age of the newly discovered Wangjiaping biotite monzogranite places it at the Triassic-Jurassic boundary. Re-Os molybdenite geochronology on the Qipangou W-Mo deposit yielded a model age of 199.7 +/- 3.9 Ma, indicating the deposit formed in the early Yanshanian period of the Early Jurassic. Granitoid intrusions in the mineralized area are characterized by composite granite bodies that crystallized at ca. 240-190 Ma. While there were multiple stages of intrusion, most occurred at 210-220 Ma, with waning magmatic activity at 200-190 Ma. The Re-Os age of molybdenite in the region is ca. 200-190 Ma, which may represent a newly discovered period of W-Mo metallogenesis that occurred during the final stages of magmatism. The heat associated with this magmatism drove ore formation and might have provided additional ore-forming components for metallogenesis (represented by the Wangjiaping biotite monzogranite). Ore materials in the mineralized area were derived from mixed crustal and mantle sources. Enrichment of the region occurred during intracontinental orogenesis in the late Indosinian-Yanshanian, subsequent to the main Indosinian collision. At this time, the tectonic environment was dominated by extension and strike-slip motion.