Concordant ages for the giant Kipushi base metal deposit (DR Congo) from direct Rb-Sr and Re-Os dating of sulfides

摘要

We report concordant ages of 451.1 + - 6.0 and 450.5 + - 3.4 Ma from direct Rb-Sr and Re-Os isochron dating, respectively, of ore-stage Zn-Cu-Ge sulfides, including sphalerite for the giant carbonate-hosted Kipushi base metal (+Ge) deposit in the Neoproterozoic Lufilian Arc, DR Congo. This is the first example of a world-class sulfide deposit being directly dated by two independent isotopic methods. The 451 Ma age for Kipushi suggests that the ore-forming solutions did not evolve from metamorphogenic fluids mobilized syntectonically during the Pan-African-Lufilian orogeny but rather were generated in a Late Ordovician postorogenic, extensional setting. The homogeneous Pb isotopic composition of the sulfides indicates that both Cu-Ge- and Zn-rich orebodies of the Kipushi deposit formed contemporaneously from the same fluid system. The sulfide Pb isotope signatures in combination with initial ~(87)Sr/~(86)Sr and ~(187)Os/~(188)Os ratios defined by the isochrons point to metal sources located in the (upper) crust. The concordant Re-Os and Rb-Sr ages obtained in this study provide independent proof of the geological significance of direct Rb-Sr dating of sphalerite.