The Whole-Rock Geochemical Composition of the Wudaogou Group in Eastern Yanbian, NE China–New Clues to Its Relationship with the Gold and Tungsten Mineralization and the Evolution of the Paleo-Asian Ocean
The late Paleozoic Wudaogou Group, one of the oldest metamorphic units in the eastern Yanbian area, has important tectonic and metallogenic significance. Here, we provide new insights into their protoliths, tectonic setting of the metamorphic rocks and their relationships with the gold and tungsten mineralization, using new petrographic and whole-rock geochemical data for various lithologies within the Wudaogou Group. The protolith of the metamorphic rocks of the Wudaogou Group was intermediate–basic volcanic rocks (e.g. basaltic andesite, trachyandesite, and basalt) and sedimentary rocks including argillaceous rocks, quartz sandstone, arkose and clayish greywacke, as well as pyroclastic sedimentary rock, covering tuffaceous sandstone. Before undergoing late Paleozoic epidote–amphibolite facies regional metamorphism, these protoliths were formed during the middle–late Permian in an island arc setting within a continental margin collage zone. Combined with the regional tectonic evolution, it can be speculated that the formation and the subsequent metamorphism of the protoliths of the metamorphic rocks from the Wudaogou Group were influenced by the change from subduction to collision of the Paleo-Asian Ocean. Similarities of the rare earth element (REE) patterns and parameters among the metamorphic rocks within the Wudaogou Group, auriferous ores from the Xiaoxi'nancha gold (copper) deposit, and scheelites from the Yangjingou tungsten deposit, together with the favorable metallogenic element contents within the metamorphic rock series, imply that the Wudaogou Group could provide parts of metallic material for the gold and tungsten mineralization in the eastern Yanbian area, as exemplified by the Yangjingou deposit and Xiaoxi'nancha deposit, respectively. Further, the metamorphic sedimentary rocks, especially the metamorphic sandstones, quartz schists and quartz mica schists within the Wudaogou Group, have closer genetic relationships with the Yangjingou tungsten mineralization. However, the specific lithologies within this group which control the gold mineralization are still uncertain, and need further research.