U-Pb dating of zircons from Gaxiuyapingdong and Hongliugoubei mafic-ultramafic intrusions on the northern margin of Qaidam Basin and its geological and prospecting significance

This paper reports two mafic-ultramafic intrusions in the Oulongbuluck microblock on the northern margin of Qaidam Basin. One is Cu-Ni-bearing Gaxiuyapingdong intrusion with LA-ICP-MS zircon U-Pb age of 408.0±1.5Ma belonging to Early Devonian; the other is Ti-Fe-bearing Hongliugoubei intrusion with SHRIMP zircon U-Pb age of 418.3±2.8Ma belonging to Late Silurian. Regional geological data show that Eastern Kunlun and North Qaidam should be in a post-orogenic extension environment during the Late Silurian -Late Devonian period. Gaxiuyapingdong intrusion and Hongliugoubei intrusion were produced by mantle-derived magmas in an extensional environment. The copper-nickel deposits and ore spots such as Niubiziliang, Binggounan, and Shitoukengde discovered in Eastern Kunlun and North Qaidam (except for Xiarihamu) were all formed in Late Silurian-Late Devonian period. Combined with regional metallogenic chronology, the authors consider that Qaidam Block as well as Olongbuluck micro-block between Eastern Kunlun orogenic belt and northern margin of Qaidam Basin and micro-ancient continental block between these two orogenic belts were favorable for the formation of magmatic Cu-Ni sulfide and Ti- Fe oxide deposits during Late Silurian-Late Devonian period.