Structural control on the Baiyinha'er gold mineralization (Southern Central Asian Orogenic belt) related to Early Paleozoic Paleo-Asian Oceanic subduction

As the largest Phanerozoic accretionary orogenic belt in the world, the Central Asian Orogenic Belt (CAOB) experienced multiple episodes of tectonic and magmatic activities in association with extensive gold mineralization during the early Paleozoic. The newly discovered Baiyinha’er gold deposit in the southwestern CAOB exemplifies a typical structure-controlled gold mineralization due tectonic compression related to oceanic–continental subduction during the closure of the Paleo-Asian Ocean. A sequence of gold-bearing quartz veins and diorite porphyry dykes are emplaced along faults and fractures in a deformed quartz diorite batholith and its host rocks. Gold mineralization is closely associated with the emplacement of quartz veins that were formed in the same stress as the diorite porphyry dykes. They are the results of continued N–S compression. Zircon U–Pb dating yielded identical ages of 433–432 Ma for the diorite porphyry dykes and their host quartz diorite batholith. Furthermore, geochemical analysis reveals that the dioritic rocks (both the batholith and the dykes) belong to a magmatic arc related to the closure of the Paleo-Asian Ocean. The tectonic–magmatic–mineralization processes in the Baiyinha’er and contiguous areas are ascribed to the prolonged oceanic-continental subduction during the closure of the Paleo-Asian Ocean in the early Silurian. Oceanic subduction beneath the Bainaimiao arc led to generation of arc magmatism, forming the quartz diorite pluton in the Baiyinha’er and contiguous areas. Subduction-related tectonic compression resulted in faulting and fracturing of the solidified diorite intrusion and subsequent emplacement of the dioritic magmas along the faults and fractures. Continued and co-axial N–S compression induced new faults and fractures that host the gold-bearing quartz veins.