The Study On Mineralogical Characteristics Of Olivine From Dashihe,Jilin

The Dashihe olivine deposit in Jilin Province is located in the southeast margin of the ring craton Xingmeng orogenic belt.The peridotite xenoliths record the geochemical evolution of the mantle of the ring craton lithosphere.In this paper,the spinel lherzolite in the Dashihe olivine mining area is studied.The mineralogical characteristics of the spinel olivine in the Dashihe olivine mining area are studied by naked eye observation,gemstone microscope and super depth of field microscope,and by means of polarizing microscope,electron probe analysis and laser Raman spectroscopy,The genesis of olivine in this area is discussed.The main achievements of this paper are as follows:The olivine of Dashihe is forsterite in Jilin Province.It is light green,yellow green,transparent,glass luster,granular production and incomplete crystal shape;The results show that the system is inert in the long and short wave ultraviolet light;The hardness of Morse is 6.36,which is lower than the standard value;The relative density is 3.33-3.36,which is affected by fractures and inclusions;The infrared spectrum shows that the pyroxene is a typical spectrum.The Raman spectrum shows that the chromite inclusions in olivine are contained in olivine,pyroxene is a symbiotic mineral.There are two types of Si-O bonds in pyroxene,bridged bond and non bridged bond.The displacement at 1011cm^-1 is caused by Si-O^-1 non bridged bond.Petrological analysis shows that the peridotite inclusions are spinel lherzolites,and no garnet facies peridotite is found.The inclusions are ellipsoidal spherical or irregular,yellow green,medium to coarse grain.The results of quantitative chemical analysis by electron probe show that the MgO content of olivine in peridotite inclusions is 48.20-50.55wt.%,FeO content is 8.41-9.70wt.%,Fo value is 90.31-91.40,olivine CaO content is lower than 0.10wt.%,NiO average is0.35wt.%,which is close to the typical value of Fo90Fa10 mantle olivine of 0.40wt.%.The chemical composition of forsterite in Dashihe river is consistent with that of Fo90Fa10,which is the typical characteristic of olivine in other regions of the world.Pyroxene is mainly tenacious pyroxene and diopside,and spinel is low chromium spinel.The temperature and pressure calculation shows that the pressure range of lherzolite formation in Dashihe area is 17-23kbar and the formation temperature is 951-1060℃.The formation depth is approximately 56km to 76km.The main mineral elements were analyzed by mapping（olivine Fo value spinel Cr^#value,etc.）and the partial melting degree of lherzolite in Dashihe is less than 10%.According to the above conclusions,it is suggested that the origin of olivine in Dashihe may be the basalt magma formed by the melting and melting of mantle fluid,which will bring the peridotite inclusions out of the surface through deep fault zone.Compared with the composition of olivine in foreign mining areas,the maximum of large grains olivine fo produced in the zapat valley of Pakistan is 94,indicating that the mineralization is different from that of olivine produced by mantle in this study area,but may be related to hydrothermal formation of Eocene pale granite.