Petrogenesis Of The Shibaogou Granitoid Pluton And Evaluation Of Metallogenic Potential,western Henan Province

Late Mesozoic granitoids are well developed in western Henan Province, and some of them are closely related to the Mo polymetallic mineralization,such as Nannihu, Huoshenmiao, Leimengou etc..The Shibaogou granitoid pluton occurs in Luanchuan ore field in western Henan province, located between the Luanchuan Fault and Machaoying Fault,intruded into the Neoproterozoic Luanchuan Group. The mafic microgranular enclaves(MMEs) are well developed in this granitoid pluton.Researchers have discovered orphyry–skarn deposits, located near the Shibaogou granitoid pluton. The study of petrogenesis of the Shibaogou granitoid pluton and evaluation of metallogenic potential is helpful to improve and summarize petrogenesis and metallogenic potential of granites in western Henan Province.This pluton consists of mid-fine-grained porphyritic monzogranites, mid-fine-grained porphyritic granites, mid-coarse-grained porphyritic monzogranites, mid-coarse-grained porphyritic granites. The pluton contains quartz syenite porphyry dykes and porphyritic biotite granites dyke.The mafic microgranular enclaves(MMEs) are developed in mid-fine-grainedgranites, and the type of rock is biotite quartz-diorites.According to the previous age data,mid-fine-grained granitoids formed at158 Ma,the mid-coarse-grained granitoids formed at 145 Ma.The mid-fine-grained granitoids and the mid-coarse-grained granitoids and MMEs are similar in mineral compositions,including alkali feldspar,feldspar, quartz, biotite, hornblende, accessory mineral assemblage include apatite, sphene, zircon and magnetite.But the MMEs have more biotite and hornblende.The ocellar hornblende-mantled quartz in the mid-coarse-grained and the cicular apatite in MMEs are evidences of magma mixing.The mid-fine-grained granitoids and the mid-coarse-grained granitoids have similar whole-rock geochemistry and Sr-Nd isotopic compositions.They were derived from crust,which should be the remelting of the crust of the Yangtze Block.In Harker diagram and diagram of Rb/Sr-Rb etc.,the plot of mid-coarse-grained granitoids perform a trend of magma mixing. The mid-fine-grained granitoids’ geochemical data also suggest magma mixing had happened.But the petrography does not support this point. The whole-rock geochemistry of MMEs indicate that they were not derived from crust,and the ratio of Nb/Ta,Ce/Nb,Yb/Ta etc. suggest they were derived from mantle. Whole rock Sr-Nd isotopic compositions of MMEs are similar with the host rock,it’s the result of magma mixing.The Shibaogou granitoid pluton have similar age,whole-rock geochemistry and isotopic compositions with the other ore-bearing granitoid plutons in uanchuan ore field.Together with the high oxygen fugacity,medium-high water content and magma mixing,the Shibaogou granitoid pluton is under a favourable circumstance of mineralization,especially the mid-coarse-grained granitoids.