Palaeoproterozoic Chibaisong mafic intrusion and mineralization (Northeast China), the oldest Cu-Ni sulphide deposit in China: evidence from Re-Os dating of pyrrhotite

摘要

The Chibaisong magmatic Cu-Ni sulphide deposit is located in Tonghua City, Jilin Province, in the eastern part of the northern margin of the North China Craton. The geological characteristics of the deposit have been investigated, and pyrrhotite Re-Os isotope dating has been utilized to constrain the age. Five pyrrhotite samples separated from the Chibaisong Cu-Ni sulphide deposit yielded a Re-Os isotopic isochron age of 2237 ± 62 Ma (mean squared weighted deviation = 1.13, n = 5), indicating that the only Palaeoproterozoic magmatic Cu-Ni sulphide deposit in China is the Chibaisong Cu-Ni sulphide deposit. The geodynamic setting during ore formation was related to the Liaoning-Jilin Palaeoproterozoic rift split. The Re-Os isotope analyses showed an initial ~(187)Os/~(188)Os ratio of 0.778 ± 0.033, and (~(187)0s/~(188)0s), and γOs(t) values ranged from 0.7531 to 0.8013 (average 0.7734) and from 574 to 617 (average 592), respectively, indicating that abundant crustal material (5-10%) was mixed with the Cu-Ni sulphide ore system during magma ascent and ore formation.