| The former study on the pegmatite type rare metal deposits in Western Sichuan is mainly concentrated in the locations of Keryin area and Jiajika area.It has achieved a good prospecting effect with the continuous investment on geological exploration in Daqianggou mine area in recent years.However,the comprehensive research data is still extremely scarce.Therefore,it is necessary for us to make a systematic study on the geological characteristics,metallogenic origin and mineralization of the deposit for discussing deposit genesis mode,which can provide the basic theoretical basis for the deep and regional rare metal prospecting.In this paper,a large number of documentliteratureare collected,and detailed study are made on field geological observation,indoor metallogeny,geochemistry and fluid inclusions.It is the first time to make the systematic analysis on the geological characteristics of the Daqianggou deposit,and the metallogenic mode of the pegmatite type rare metal ores is established to evaluate the prospecting potential of pegmatite for the deposit and the area.The following conclusions are obtained:1)Surrounding rocks of pegmatite dykes in the mining area are quartz diorite and quartz schist.The occurrence modality and intensity of dikes are significantly controlled by the Jiulong syncline,and it is filled in a series of fractured joints of its axial parts.For the regional factors,the pegmatite type consists of the micro plagioclase pegmatite,the micro plagioclase-albite pegmatite,albite pegmatite and albite-spodumene pegmatite.And the characteristics of typical zonal spatial distribution with two mica rock mass as the center are presented.The mining area is located in the C belt whose main minerals are albite-spodumene pegmatite.2)The lithium ore bodies in the mining area are mainly hosted in albitespodumene pegmatite dykes,associated with beryllium,niobium,tantalum,rubidium and tin.The ore body of 1-I is the most typical,with mineralization for the whole dyke,and it is consistent with the occurrence of pegmatite dykes.Ore minerals are mainly spodumene,lepidolite,beryl,niobium tantalum ore and cassiterite.The structures are mainly granular and metasomatic structure.The tectonics are mainly massive and disseminated.The metasomatism of ore body is strong,and tourmalinization,muscovitization(lithium),albitization and greisenization are common,with the reflection of metasomatic series for K-Na-Li.3)By comparing the geochemical characteristics of the main and trace elements and rare earth elements between the rock mass and pegmatiticin the study area,it is shown that: With the sequential order of syenite,quartz diorite,two mica granite plutons,two mica granite dykes,pegmatite dykes,the evolution direction of magma is rich in silicon,alkali(sodium instead of potassium),rare elements and volatile components,while poor in the total amount of rare earth,calcium,iron and magnesium(iron instead of magnesium).The REE distribution curves are right deviation type with light rare earth enrichment,and the trend is basically the same,which all mutually prove and reflect the process of crystallization differentiation for thehomologous magmadifferentiationandthe increasing degree of gradual evolution.4)The fluid inclusions of the ore-bearing pegmatite in the area have the characteristics of low temperature,low pressure,low salinity and shallow formation depths.The fluid composition is rich in volatile components and Na.The characteristics of the inclusion in the Daqianggou deposit belong to the characteristics of the hydrothermal phase inclusions,and is closely related to the hydrothermal metasomatism of the pegmatite melt.5)The ore-forming material of the deposit is derived from the two mica granite magma,which is the product of the multi-stages crystallization differentiation for magma activity caused by the two period tectonic movement of the Ganzi-Songpan orogenic belt.The residual magma is rich in volatile components,alkali and rare elements,and the out-migration is dominated by crystallization differentiation.Meanwhile,there occurs rare metal mineralization in the folded axial zone of surrounding rocks which are away from the rock mass by autometasomatism of the residual melt.Therefore,the genetic mode of the Daqianggou deposit is for magmatic crystallization differentiation and hydrothermal metasomatism.6)The relationship between the pegmatite and the rock mass(dyke)with tectonics,its metasomatic alteration,geochemistry and minerals can be used as the prospecting mark.The prospecting potential in the middle and south of the mining area is large.There is prospecting potential on the internal or external contact zone of granitic pluton in Jiulong West and the west side of Daqianggou mine area,as well as the north area of the mud rock mass. |
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