Single grain Rb-Sr dating of euhedral and cataclastic pyrite from the Qiyugou gold deposit in western Henan, central China
The Rb-Sr isotopic dating of pyrite mineral from ore deposits can directly provide mineralization age. However, many geological
factors may affect the Rb-Sr isotopic system, which baffles application of this method. Employing ultra-low procedural blank
Rb-Sr method, we have dated pyrites separated from the No. 4 breccia pipe of the Qiyugou gold deposit, western Henan Province.
Single grains of euhedral pyrite crystal with few micro-cracks yield an isochron age of 126 ± 11 Ma, which represents time
of the main mineralization stage of the deposit. Pyrite grains of cataclastic type show nevertheless scattered Rb-Sr isotopic
composition and no reasonable isochron can be defined. Crystal morphology and mineral inclusion studies reveal that Rb and
Sr of pyrite mineral probably are preserved mainly in biotite, K-feldspar, and sericite mineral inclusions. The dating results
likely suggest that cataclastic pyrite is not suitable for the Rb-Sr dating due to modification of the Rb-Sr isotopic system
by later hydrothermal activity of fluid.