Multi-stage tectonics and metallogeny associated with Phanerozoic evolution of the South China Block: A holistic perspective from the Youjiang Basin

The Youjiang Basin in the western part of the South China Block (SCB), preserves the records of the tectonic history from Tethyan, through Paleo-Pacific to Tibetan domains, with coeval formation of diverse types of giant metallic deposits. The prolonged tectonic evolution and its control on the genesis and spatio-temporal distribution of giant metallic deposits in the Youjiang Basin provide a window for a holistic understanding of the tectono-metalligenesis of SCB. Six tectono-metallogenic stages can be recognized in the geological evolution of the basin and their relationship to the geodynamic evolution of the surrounding tectonic units. Subsequent to the closure of the Proto-Tethyan Ocean and collision between the SCB and the Gondwana continent, a late Ordovician to early Silurian intracontinental orogeny along the southern margin of the basin resulted in the formation of Silurian Cu and W skarn deposits. During Devonian to Carboniferous, during the Paleo-Tethyan spreading, the basin experienced rifting and development of a passive continental margin, when sedimentary Mn carbonate ores were deposited in basin facies sequences in the southern part of the basin. On the northern margin, bauxite karsts formed in carbonate rocks within continental-margin sequences. In the Late Permian, the Paleo-Pacific oceanic plate was subducted below the SCB, which most likely induced migration of the coeval Emeishan mantle plume towards the plate margin. Arc volcanism resulted in voluminous ash falls on the carbonate platform and these were subsequently transformed into bauxite in the southern part of basin. Following this, Triassic intraplate shortening induced thin-skinned crustal deformation with associated formation of orogenic Au deposits throughout the basin. In the Jurassic, the Youjiang Basin experienced slab delamination, during which MVT PbZn deposits formed along the northern margin, and clusters of WSn skarns were generated at the centre of the delamination zone on the eastern margin of the basin. Subduction retreated southwards in the Cretaceous, resulting in the formation of Carlin-type Au deposits in the northern part of the basin, and Sn and Cu skarns and associated carbonate replacement PbZn deposits in the central and southern parts. Cenozoic regional denudation and climate change in response to the southeastward propagation of Tibet caused brittle deformation of pre-existing bauxite and Mn orebodies and their further enrichment. The overlap among Paleo-Tethyan, Paleo-Pacific and Tibetan tectonic regimes during the evolution of the Youjiang Basin generated a diverse range of mineral deposit types, including orogenic and Carlin-type Au deposits, both carbonate-replacement and MVT-type PbZn deposits, sedimentary Mn‑carbonate deposits and bauxite in both passive and active continental margins.