Geochemical charateristics of platinum-group elements of Jijie alkaline-ultrabasic rocks, Yunnan Province
云南鸡街碱性超基性岩铂族元素地球化学特征

This paper reports the geochemical characteristics of platinum-group elements (PGE) of Jijie alkaline-ultrabasic intrusive rock complex, in the southern part of Panxi rift, Yunnan Province, Southwest of China. Trace PGE concentrations in melteigite,ijolites and urtites were measured by ID-ICP-MS coupled with a modified Carius tube digestion. The significant fractionation between PPGE and IPGE of these alkaline-ultrabasic rocks, suggest that Pt and Pd are incompatible while Ir, Ru and Rh are compatible during low degree partial melting. The negative Ru anomalies on primitive mantle-normalized PGE patterns of all these samples indicate the removal of olivine during the magma ascent. Pd show more incompatible than Pt during crystal fractionation. Most of the Cu/Pd ratios are much higher than prime mantle, suggesting the parent magma may reach partial sulfide saturation and then segregation due to the change of pressure and crystal fractionation. The characteristics of the prime magma source and magma evolvement were discussed by comparison with the PGE characteristics of typical kimberlites, lamprophyres and alkaline basalts.