Tectonic setting of Mesozoic magmatism and associated metallogenesis in Beishan area

Abstract: The Central Asian Orogenic Belts (CAOB) resulted from evolution and final closure of the Plaeo-Asian Ocean(s). Located in the central segment of the southern portion of the CAOB, the Beishan area, which refers to the conjunction region of Inner Mongolia, Gansu and Xinjiang, is one of the most important metallogenic belts in China, with abundant Cu, Mo, Au, Fe and base metal deposits. Two collisional events took place in the Beishan area during Late Paleozoic-Early Mesozoic: one occurred at the end of Late Paleozoic, which was related to the final closure of the CAOB, and the other took place in Early Mesozoic, resulting from the closure of the Carboniferous-Permian rifts in southern Beishan. As a consequence, the Beishan area was involved, in terms of temporal relations, in a collision to post-collision stage in Indosinian epoch of Mesozoic period, during which large-scale ductile shear zones and intensive magmatism as well as associated metallic mineralization occurred. The Mesozoic magmatism, which is predominated by intermediate-felsic intrusions locally with minor basic ones, is characterized by plutonic intrusive facies, without extrusive counterpart. Petrogenically, S-, I-and A-type granites have been delineated in the area. Types of Mesozoic mineral deposits in the area mainly include porphyry-type Mo mineralization, which is associated with I-and/or A-type granites, W (Sn) deposits associated with S-type granites, skarn-type Au-Ag-Cu polymetallic deposits associated with intermediate-felsic intrusions, and Au deposits related to granitic intrusions and controlled by ductile shear zones. Indosinian epoch is the latest period of major magmatism and metallic mineralization in the area, to which more attentions should be paid since the Indosinian granitoid intrusions and associated mineral deposits may be much more extensive and abundant than recognized presently.