Chalcophile elementgeochemistryof the Bijigou layered intrusion,northern margin of theYangtze Block: Implications for the processes of magma evolution and sulfidesegregation.

The Bijigou layered intrusion is one of the most important-mafic.ultramaficintrusions of the Hannan complex in the northern margin of the Yangtze Block,anditiscomposed of ultra mafi crocks in the lower zone,gabbro in the middle zone and diorite in the upper zone.This study focuses on the troctolite,olivine gabbro,olivine gabbronorite in the lower zone and coarse.grained gabbro,magne titegabbro,horn blende gabbro in the middle zone.The (La/Sm) N(0.43 similar to 2.89) and (Tb/Yb) N (1.08 similar to 1.52)ratios and La/Yb.Sm/Yb diagram of the whole rock sample sindicate that the Bijigou layered intrusion was derived from spinellherzolite.The parental magma of the Bijigou intrusion is mainly high.magnesium basalt according to the Ni/Cu.Pd/Irdiagram. The simulation calculation and high S/Se ratios show similar to 5% crustalcontamination of the parental magma and the int roduction of the externalsulfur, which lead stothe prior sulfide segregation in the deep,extremely high Cu/Pd (5.21x10(3)similar to 1.67x10(6)) and low PGE contents of the parental magma.When the parental magma of the Bijigou intrusion was emplace din to the shallow chamber,these gregation of a small amoun to fsulfideinthe lower zone resultedin further depletion of the PGE,butrelatively increasing of the S and Cu contents in the residualmagma.Thus,the middle zone crystallized from the residual magma of the lower zone showed even lower PGE content and relatively higher S and Cu contents.According to the magma ticevolution and sulfidesegregation process of the Bijigou layered intrusion,it is speculated that there is potential to search for Cu.Ni.PGE deposit in thed eep and near by part of the intrusion.It is of great significance to find out its magmatic channel syste mandmag maticmigration direction of the Bijigou intrusion for ore prospecting and exploration