Re–Os pseudo-isochron of disseminated ore from the Kalatongke Cu–Ni sulfide deposit, Xinjiang, Northwest China: Implications for Re–Os dating of magmatic Cu–Ni sulfide deposits

Re–Os dating of disseminated ore from the Kalatongke Cu–Ni sulfide mineral deposit, Xinjiang, Northwest (NW) China, yields an apparent isochron age of 433 ± 31 Ma with an apparent initial 187Os/188Os (433 Ma) ratio of 0.197 ± 0.027. This apparent age is older than not only the zircon U–Pb age of the host intrusion (287 ± 5 Ma, Han et al., 2004) but also the stratigraphic age of the intruded country rock. Thus, the regression line is a pseudo-isochron. However, previous Re–Os dating of massive ores of the same deposit yielded an age that is consistent, within analytical uncertainty, with the zircon U–Pb age (Zhang et al., 2008). This relationship is similar to that observed in the Jinchuan deposit, NW China. Therefore, we suggested that the same mechanism, post-segregation diffusion of Os (Yang et al., 2008), is applicable to the Kalatongke deposit. isotopic studies of Kalatongke, Jinchuan and representative magmatic Cu–Ni sulfide deposits suggest that the massive ores of mafic–ultramafic-rock-associated Cu–Ni sulfide deposits would yield geologically meaningful Re–Os age, whereas a pseudo-isochron would be obtained for the disseminated ores. Therefore, to obtain a geologically meaningful Re–Os age, the type of the deposit, the type of the ore and the ore-forming process should be taken into account.