The mafic-ultramafic intrusive rock body I is the largest for Baimazhai Cu-Ni deposit distributed in the Ailaoshan-Jinshajiang tectonic zone. It is a ringlike body consisting of orebearing peridotite, mineralized pyroxenite and gabbro phase zones from the center to margin. Accordingly, the contents of SiO2,TiO2,Al2O3,CaO,Na2O and K2O are increasing gradually, and that of TFe and MgO are decreasing as well; the concentrations of ∑REEs, and LREE/HREE ratios are increasing gradually from the central phase to outer phase. Along the same direction, δEu shows negative to positive anomalies; the abundance of the large ion lithophile elements (LILE) and high field strength elements varies increasingly, but the contents of magmatophile elements have a reversal evolutive trend. The PGE distributive patterns are the PtPd type, the Pt/Pd ratios of 0.32-0.68 are between the values of enriched sulfide tholeiite (0.38) and primitive upper mantle (1.36), and the similarity of partition patterns of chondritenormalized REE, MORB-normalized trace element and primitive mantle normalized PGE for the rocks of the three phase zones, indicate the Baimazhai intrusive body I formed by the evolution, liquation, intrusion and diagenesismetallogenesis of basaltic magma. The fact that stable sedimentary succession outcropped in the deposit district, intrusive contact relationships between the sediments and the intrusion and the Zr-Y-Nb diagram of the ring rock body shows the Baimazhai intrusion body formed in an intracontinent. The lower Ti content, strongly Th positive anomaly, and the Th/Ta ratios, Th/Nb ratios, Pd/Pt ratios and the primitive mantle normalized Ir-group patterns for Baimazhai intrusive body I, which are different from those of the Emeishan basalt and typical mantle plume basalts, but similar to those of basalts from a continental rift, suggest that the Baimazhai intrusive body I are probably formed in the tectonic settings of continental rift.
