Geological Characteristics And Genesis Of The Rare Earth Deposits In The Highlands 782 Of Mohe County,Heilongjiang Province

The sustainable exploitation and supply of rare and rare earth metals provide important guarantee for the sustainable development of economy and national defense,and it is of great significance to the study of the metallogenic characteristics and the formation process of such deposits.The rare earth deposit in the 782 highland of Mohe County,Heilongjiang province is located in the northern margin of the Erguna block.Based on petrography,geochemistry,zircon chronology and isotopic geochemistry,the following conclusions are drawn:1.Through the observation of petrology and mineralogy,it is concluded that REE mineralization in this deposit is the formation of metasomatic zircons from external fluids.The minerogenetic stage and mineral assemblage are as follows:?1?The magmatic hydrothermal period:the main minerals are zircon,albite,and quartz,and the formation of zircon is related to albite and silicification in late magmatic hydrothermal process.?2?Hydrothermal period:this phase contains chlorite,sulfide?sphalerite,galena,pyrite,etc.?and rare earth elements,forming 4 phase of different rare earth minerals.chlorite,euxenite,sulfide;chlorite,fergusonite,sulfide?appearance of,rutile?;chlorite,bastnasite,sulfide?appearance of genthelvite?;chlorite,parasite.2.The geochemical characteristics indicate that the alkali-feldspar granite and monzogranite belong to the peraluminous and calc-alkaline rock series.It is an intraplate A type granite formed in the extension setting.The value of REE tetrad effect(T_1,3)is 1.17 and 1.04 respectively,which has a weak M type REE tetrad effect and indicates a magmatic hydrothermal system.3.Zircon U-Pb dating results show that the zircon age of monzogranite is 490±5 Ma.Zircon in alkali-feldspar granite consists of two types:magmatic zircon and hydrothermal zircon.The age of magmatic zircon is 453.8±3.1Ma and the age of hydrothermal zircon is 456.5±3.2Ma.The results show that the monzogranite and alkali-feldspar granite are not evolutional relations,but formed by different magma.The oxygen isotope characteristics of zircon show that the magmatic origin of the monzogranite is different from that of the alkali-feldspar granite.The average?¹88 O of the monzogranite is 7.7‰,which tends to be a more mature crustal unit.The average?¹⁸O value of the alkali feldspar granite is 5.2‰and 5.0‰,respectively.The source of the magma may be the mantle(?¹⁸O=5.3±0.3‰).4.The magmatic zircon particles in alkali-feldspar granite are smaller?50-100?m?,colorless and transparent crystal,and CL images have obvious growth rings.They exist in quartz and potassium feldspar in the form of single minerals.There are obvious positive Ce anomalies and negative Eu anomalies in the REE distribution patterns.The hydrothermal zircon particles are larger?50-100?m?,mostly in the form of mineral aggregates,associated with snowball quartz and albite,with clear boundaries;The hydrothermal zircon color from dark brown to black,dark and unobvious growth rings in CL images,and a weak Ce positive anomalies and obvious negative Eu anomalies in the distribution diagram of rare earth elements.