Geochemistry,Chronology Of The Rongxuka Ore-bearing Granitic Pegmatites Within Daofu County,Western Sichuan Province And Their Metallogenic Implications

Rare metal minerals are essential to the development of modern industry and technology.Granite pegmatite has great potential for enriching rare metal element mineralization,which is of great significance for the study of its diagenesis and mineralization.Granite pegmatite in the Songpan-Garze Orogenic Belt is widely distributed,and it is one of the important production areas of pegmatite type rare metal minerals in China.Rongxuka pegmatite type rare metal deposit is located in the Yajiang-Barkam lithium metallogenic belt of the Songpan-Garze structural unit.At present,there is a lack of systematic petrological geochemistry,chronology and isotopic composition data of the Rongxuka ore-bearing granite pegmatite.And its connection with the largest rock body biotite quartz diorite is unclear,in the mining area.In this paper,based on the field geological survey,the research in the Rongxuka area about the petrography,petrological geochemistry,mineral chemistry,zircon U-Pb chronology of the ore-bearing granite pegmatite and the zircon U-Pb chronology of biotite quartz diorite was done to reveal the magmatic evolution,formation age,material source of the ore-bearing granite pegmatite and the connection with the genesis of biotite quartz diorite.Finally,the metallogenic significance was also discussed.Rongxuka ore-bearing granite pegmatite is distributed in a near-ring band around the core of the Rongxuka dome,and it emplaced in the low-moderate rank muddy metamorphic rocks of Triassic.The ore-bearing granitic pegmatite is composed of albite,quartz,muscovite,microcline,spodumene,garnet and other minerals.The mineralization that occurs is mainly lithium,and the ore is mainly spodumene.The ore-bearing granitic pegmatites samples show high silicon?Si O₂=72.17?79.65?and peraluminous?A/CNK=1.18?1.92?characteristics.The samples enriched in Rb,U,Nb,Hf,Y,and LREE,depleted in Ba,Sr,Ti,and HREE,and have a similar chondrite normalized chondrite-normalized rare earth elements patterns,indicating that they are comagmatic evolution.The Al₂O₃,P₂O₅ and Ca O have a clear linear relationship with Si O₂ of the samples,in the Hake diagrams,as well as a higher differentiation index?DI=90.02?96.28?and a lower crystallization temperature(t _Ti=551?651?)of the samples,indicating that the ore-bearing granitic pegmatite undergoes a high degree of crystallization differentiation.The tetrad effects of REE and the abnormality of the contrast values of Nb-Ta,Zr-Hf,and Y-Ho element pairs samples indicate that the formation of ore-bearing granitic pegmatites are related to F-rich hydrothermal fluid metasomatism.The zircon U-Pb age of ore-bearing granitic pegmatites is 205.2±4.1Ma,which was formed during the post-collision-intra-plate extension stage of the Songpan-Garze orogenic movement.The metallogenic age of ore-bearing granitic pegmatites is consistent with the diagenetic age.The ore-bearing granitic pegmatites originated from the remelting of the Mesoproterozoic crust.The emplacement age of biotite quartz diorite is 213.8±1.1 Ma,which has a similar formation age to the ore-bearing granitic pegmatites,and they were all formed in the Late Triassic.However,there is no genetic connection between the ore-bearing granitic pegmatite and biotite quartz diorite,and themineralization mother rock is a hidden granitic rock body in the core of the Rongxuka dome.The formation of pegmatite type rare metal deposits requires a relatively stable and closed tectonic environment.The continental crust remelting granitic magma diapir formed the Rongsuka dome metamorphic body,in the end of Indo-China Movement.Subsequently,the concealed granitic magma in the core of the dome crystallization differentiation into rich in volatile components melt,then,the melt intruded along structural fractures and interlayer fracture zones,and experienced a high degree of crystalline differentiation to enrich rare metal elements.The melt phase had a strong metasomatism with the exsolution rich in F,Na of fluid phase,further enriching the rare metal elements.Finally,the Rongshuka pegmatite type rare metal deposit was formed at about 205 Ma.And it is recommended to carry out prospecting and exploration of rare metals in the andalusite zone.