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摘要
As one of several known magmatic sulfide deposits that formed in the Neoproterozoic in China, the magmatic evolution and tectonic setting of the ore-forming plutons in the Baotan area of northern Guangxi are highly debated. The study carried out an integrated analysis of petrography, zircon U-Pb dating, geochemistry for the Disu ultramafic-mafic complex. The results show that the complex developed three magmatic pulsations: pyroxenite, pyroxene peridotite-olivine pyroxenite-pyroxenite-grabbo and diorite, and the sulfide ore occurs at the bottom of the former two pulsations. Zircon U-Pb age 857±8 Ma of diorite constrains the ore-forming time to the Early Neoproterozoic; Mg# of the complex is 71.91~80.07, with an m/f ratio of 2.56~4.02, and content of MgO is negatively correlated to Al2O3 and CaO. The rare earth elements (REE) patterns show enriched light rare earth elements (LREE) and flat heavy rare earth elements (LREE). The complex is characterized by enrichment in large ion lithophile elements (LILE, such as Rb, Th, U) and pronounced depletion in high field strength elements (HFSE, such as Nb, Ta, Ti), which are similar to that of subalkaline continental arc basalt. And δ34S values of sulfide range from 2.3‰ to 3.8‰, obviously different from the value (-1.57‰ to +0.60‰) of MORB. Rock assemblages and geochemical characteristics indicate that primitive magma of the Disu mafic-ultramafic complex sourced from partially melted lithosphere mantle which has been modified by crustal contamination and fluid metasomatism. Thus, the Cu-Ni deposits in the Baotan area formed in a subduction setting. Crustal contamination and fractional crystallization during the magmatic emplacement were the main factors to promote sulphur saturation and sulfide segregation of mafic-ultramafic magma in the Baotan area of northern Guangxi. ? 2019, Science Press. All right reserved.
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单位中国地质科学院; 桂林理工大学
