Genesis and mineralization age of the quartz-vein-type scheelite deposits in Eastern Yanbian, Northeast China: Constraints on the regional tectonic setting

摘要

The Eastern Yanbian area, Northeast China is tectonically located in the easternmost margin of the Xing'an Mongolian Orogenic Belt, which is a key area for providing important evidence of mineral deposits to constrain the tectonic evolution of the Paleo-Asian Ocean. Five quartz-vein-type scheelite deposits have been identified in the eastern Yanbian area. These deposits are hosted within the late Palaeozoic metamorphic and granitic rocks and form under the identical hydrothermal mineralization. Zircon U-Pb ages and whole-rock geochemistry of the ore-hosting biotite granite and Sm-Nd ages of scheelite crystals within quartz veins are presented in this paper. Zircon U-Pb dating of the biotite granite yields a weighted mean age of 251.9 +/- 2.2Ma (mean standard weighted deviation (MSWD)=4), and Sm-Nd dating of scheelite samples yields an isochron age of 251.7 +/- 2.9Ma (MSWD=0.87), which constrains the scheelite mineralization in Eastern Yanbian to the late Permian. Our results, integrated with published geochronological data, indicate three periods of Phanerozoic W mineralization in Northeast China, (a) Cambrian, (b) late Permian (this work), and (c) Jurassic. Geochemical data reveal that the biotite granite is a calc-alkaline I-type granite, and it exhibits enrichment in large-ion lithophile and light rare earth elements and depletion in high-field-strength and heavy rare earth elements (especially in Nb and Ta), consistent with the characteristics of arc magma. The subduction-related biotite granite intrusion and quartz-vein-type scheelite mineralization together indicate that the Paleo-Asian Ocean had not closed before the late Permian in the Eastern Yanbian area, and its final closure occurred in the Early-Middle Triassic. The late Permian subduction of the Paleo-Asian Ocean induced the partial melting of the lower crust, thus forming the magmatic arc activity and related quartz-vein-type scheelite mineralization, which clearly justifies the proposed tectonic-meta