1. Key Laboratory of Ore Deposit Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550002; 2. Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640
The sulfide-bearing complex at the Baimazhai Cu-Ni deposit was a circular mafic-ultramafic one, which, intruded in the Ordovician sandstones and shales, yielded the ages of 249±32 Ma and 262±2 Ma,simultaneously with the Emeishan basalts erupting. The complex consisted of, from the core to the edge, peridotite, troctolite, pyroxenite and gabbro. The major elements showed a trend of tholeiitic fractional evolution. The REE distribution pattern showed a type of LREE-enrichment with obvious Eu anomaly. The spider diagram of trace elements showed a marked negative anomaly of elements of Ta, Nb, Ti and P. The isotopic data revealed a character of high (87Sr/86Sr)t(0.710 974~0.722 667) and low εNd(t)(-13.17~ -12.09). The evidence from the trace elements and isotopic geochemistry indicated that the magma might be derived from enriched mantle modified by subducted crustal material and contaminated by crustal material during its ascending, and the tectonic setting of the mafic-ultramafic rocks might be a post-arc extensional environment.