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 Os-187/(OS)-O-188 (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. Re-Os 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. (C) 2012 Elsevier B.V. All rights reserved.