四川可尔因矿田党坝稀有金属矿床中带和南带伟晶岩地球化学特征及地质意义

GEOCHEMICAL CHARACTERISTICS AND SIGNIFICANCE OF PEGMATITES IN THE MIDDLE AND SOUTH BELTS OF THE DANGBA RARE-METAL DEPOSIT IN KE'ERYIN OREFIELD,SICHUAN PROVINCE

党坝稀有金属矿床位于四川可尔因矿田东南部,是近年来新发现超大型花岗伟晶岩型稀有金属矿床,包括北带、中带和南带三段伟晶岩。前人的研究主要集中在北带的伟晶岩。本次研究以党坝稀有金属矿床中带、南带伟晶岩为研究对象,在详细的地质特征研究的基础上,开展伟晶岩主量元素、微量元素和稀土元素地球化学分析工作。结果表明,党坝矿床中带和南带伟晶岩脉具有高硅(67.43%~79.03%,平均74.97%)、高铝(13.79%~21.17%,平均16.12%)、低钙镁(0.12%~0.47%,平均0.28%和0.03%~0.06%,平均0.04%)及过铝质(A/CNK=1.35~2.22)的特征;微量元素总体富集Rb,U,Ta,Nb,Hf,Y,相对亏损Ba,Sr,Zr,Ti等元素;稀土元素总量低(ΣREE=1.34×10^(-6)~4.98×10^(-6)),轻稀土元素富集,重稀土元素亏损,具有壳源的特征。党坝矿床中带及南带的伟晶岩属于LCT(Li-Cs-Ta)型,为西康群原岩中富黏土的泥质岩低程度部分熔融的产物,与矿区西南部的白云母钠长花岗岩无直接的成因联系。伟晶岩中稀有金属富集强弱与伟晶岩浆迁移距离、演化程度和侏倭组地层中控矿裂隙的发育程度有关。

The super-large Dangba rare metal deposit of granite pegmatite type,located in the southeast of Ke'eryin ore field,Sichuan Province,consists of three pegmatite sections of north belt,middle belt and south belt.Based on the detailed geological characteristics,this study focuses on the geochemistry of major elements,trace elements and rare earth elements of pegmatite in the middle and south belt of Dangba rare metal deposit.The results show that the pegmatite dikes in the middle and south belt of the Tangba deposit have high silicon(67.43%to 79.03%,average 74.97%),high aluminum(13.79%to 21.17%,average 16.12%),low calcium and magnesium(0.12%to 0.47%,average 0.28%and 0.03%to 0.06%.average 0.04%),belonging to peraluminous rock(A/CNK=1.35-2.22).The trace elements in the rocks are generally enriched in Rb,U,Ta,Nb,Hf,'Y,and relatively depleted in Ba,Sr,Zr,Ti,etc.The total amount of rare earth elements is low(ZREE=1.34×10^(-6)-4.98×10^(-6)),light rare earth elements are enriched and heavy rare earth elements are depleted,characteristics of crust source.The pegmatite in the middle belt and south belt of Dangba deposit belongs to LCT(Li-Cs-Ta)type,which is resulted from low degree partial melting of clay-rich argillaceous rocks in the Xikang Group,and has no direct genetic relation with the muscovite albitite granite in the southwest of the mining area.The concentration of rare metals in pegmatite is related to the migration distance and evolution degree of pegmatite magma,as well as the development degree of ore-controlling fissure in the Jurassic Zhuwo Formation.