Sulfide Re-Os and Rb-Sr isotope dating of the Kangdian IOCG metallogenic province, southwest China; implications for regional metallogenesis

The Kangdian iron oxide copper-gold (IOCG) metallogenic province contains a number of economically important Fe-Cu deposits in South China and northern Vietnam. Due to the lack of precise mineralization ages, the metallogenesis of this province has long been a matter of debate. In this study, molybdenite Re-Os, pyrite Re-Os, and Rb-Sr isotope methods are used to date the Yinachang and E'touchang Fe-Cu deposits in the central part of this province. Fine-grained (<0.1 mm) molybdenite occurs as veinlets along bandings or fractures of magnetite ores and hydrothermal veins in the Yinachang deposit. Molybdenite separates from magnetite ores have highly reproducible Re-Os model ages of 1654 + or - 7 Ma, whereas those from hydrothermal veins have a much younger Re-Os model age of 1451 + or - 6 Ma. Euhedral pyrite grains occur locally along foliations of hematite ores and their proximal alteration assemblages in the E'touchang deposit. Pyrite separates have an Re-Os isochron age of 1487 + or - 110 Ma and a single-grain Rb-Sr isochron age of 1453 + or - 28 Ma, both of which are compatible with the molybdenite Re-Os age of hydrothermal veins from the Yinachang deposit. The molybdenite age of magnetite ores is in good agreement with zircon U-Pb ages of dolerite intrusions in the region, and is considered to represent the timing of a major ore formation event at approximately 1655 Ma. The younger Re-Os and Rb-Sr ages likely record a secondary hydrothermal overprint event at approximately 1450 Ma, which has not been recognized before. The mineralization potential and implications of this event need to be investigated in future studies. Our new isotopic data set hence demonstrates that the Kangdian IOCG deposits were likely formed at approximately 1655 Ma, synchronous with the late Paleoproterozoic intracontinental rifting event of the western Yangtze block.