Re-Os dating of the Kalatongke Cu-Ni deposit, Altay Shan, NW China, and resulting geodynamic implications

Kalatongke is a large Cu-Ni deposit in the southern part of the Altay orogenic belt, northwestern China. Rhenium and osmium isotopic analyses of Ni- and Cu-bearing sulfide minerals from the deposit have been used to determine the timing of mineralization, the source of osimum, and, by inference, the source of ore metals. Sulfide ore samples have Os and Re concentrations varying in the ranges 0.29 to 3.07 ppb and 6.605 to 61.10 ppb, respectively. Analyses of these data yield a six-point isochron with an age of 305 15 Ma. An initial Os-187/Os-188 ratio of 0.352 +/- 0.044 (mean square of weighted deviates=2. 1) and delta S-34 values of -3.5 to +3.0%o for the ores, as well as initial Sr-17/Sr-86 ratios of metalliferous intrusions that vary from 0.70375 to 0.70504, suggest a magmatic source for the ores, with the melts dominated by mantle contributions. The intrusions clearly show island-arc geochemical signatures, such as negative anomalies for Nb, Ta, Zr and Ti and enrichment in LILE. The results indicate that the Kalatongke mafic-ultramafic intrusions, along with the Cu-Ni deposit, formed by subduction of oceanic crust in the Late Carboniferous -Early Permian. We suggest the mafic-ultramafic and associated with Ni-Cu mineralization occurred in an Alaska-type subduction zone-arc setting. (c) 2006 Elsevier B.V. All rights reserved.