The Discovery And Its Significance Of Fluid-Crystal Assemblages In Talnakh Cu-Ni Deposits,Russia

The Ni-Cu-PGE deposit of Noril'sk Region in Russia is one of the most important magmatic sulfide deposits in the world,in which the Talnakh intrusion plays an important part.The source of the deposit and the intrusion is commonly related to their nearby Siberian Flood Trap.However,the transportation process and the next emplacement of the sulfide melt is always in dispute.Recent researches show that the vast fluid activity contributes a lot to the formation of Cu-Ni deposit.According to the new model “Magmatic Conduit Metallogenic System”,the degassing process at the late period of magma evolution results in the emplacement.Thus we can invert the evolution of magma by using the assemblage of fluid-crystals.The assemblage of fluid-crystals is the combination of crystals which come from fluid phase directly,whose analyze is well applied many times.The rock types of Talnakh deposit are bulk sulfide,sulfide drops bearing olivine gabbro and gabbro from bottom to top,and the bulk sulfide contacts with the country rock anhydrock.Analyzes are completed with samples of the rocks above by using electronic microprobe and LA-ICM-MS.The results and explanations are given below.(1)Fluid-crystals are found in the Talnakh deposits,and the assemblage in host rock is albite + apatite + tremolite + augite + ilmenite + chalcopyrite,whereas is anhydrite + chalcopyrite + Huite + electrum in bulk sulfide.The finds prove that there are large amount of fluids contained in bulk sulfide during its migration and invasion,just as the rock is.(2)The special minors characters of silicate minerals in olivine gabbro divide pyrite and plagioclase into two types,one is rich in LILEs such as Rb,Sr and LREEs,while the another is not.Harker diagrams reveals different directions of magma evolution too.This contrast suggests that fluids are added into the system after the beginning of silicate crystallization.(3)The metamorphism that leads the serpentinization,uralitization,chloritization of dark minerals,the albitization of plagioclase,and the appearance of star-like pyrite,is thought to be connected with extrinsic anhydrite byusing thermodynamics methods.In conclusion,we reconstruct the formation process of Talnakh deposit.The fluids get into the chamber just after the very first appearance of silicate crystals,which causes the special minor characters in silicate crystals,the being of fluid-crystals and the invasion of silicate melt and bulk sulfide.When the fluid-melt flow advances near the earth's surface,the fluids in it dissipate into the igneous rock and generate a vast metamorphism aureole.The whole process fits in the “Magmatic Conduit Metallogenic System” model very well,and approves the model conversely.