川西扎乌龙花岗伟晶岩型稀有金属矿床白云母花岗岩岩石地球化学特征

Geochemical Features of Muscovite Granite in the Zhawulong Granitic Pegmatite Type Rare Metal Deposit,Western Sichuan

扎乌龙花岗伟晶岩型稀有金属矿床位于四川西部石渠县呷依乡,矿区出露的白云母花岗岩岩体与含稀有金属伟晶岩脉有密切的时空关系及成因联系。本文对采自扎乌龙白云母花岗岩岩体的新鲜样品进行了全岩岩石地球化学分析,结果表明,该岩体岩石富硅(Si O_2=73.49%~74.78%)、富铝(Al_2O_3=14.37%~14.83%)、高钾(K_2O/Na_2O=1.14~1.91),贫Fe、Mg、Ti,里特曼指数(σ)<3.3,铝饱和指数和Al_2O_3/Ti O_2(>100)较高。以上特征表明该岩体属高压型高钾钙碱性强过铝质花岗岩。微量元素表现出Rb、U等正异常和Ba、Sr、Zr、Ti等负异常的特征;岩石稀土总量较低,具有明显的轻稀土富集,重稀土亏损的特征,且由于较明显的负铕异常(δEu=0.36~0.53)而呈现"V"型谷状。岩石高Rb/Sr(2.08~6.51)和Rb/Ba(1.53~3.26)、低Ca O/Na_2O(<0.3)等地球化学特征,表明其来源于三叠系西康群泥质岩的脱水熔融,是同碰撞造山作用的产物。而扎乌龙式LCT型花岗伟晶岩,主要是由造山过程中变泥质岩部分熔融形成的强过铝质岩浆逐步演化而形成。

Objectives：The Zhawulong granitic pegmatite type rare metal deposit is located in Zhawulong, Shiqu County, Western Sichuan Province. There is a close spacial and genetic relations between the exposed muscovite granite pluton and the pegmatite veins containing rare metals. But no report on geochemical characteristics about muscovite granite.Methods：Based on the field work, through the microscope observation, the whole-rock geochemical analysis. Results：The Zhawulong muscovite granite has high contents of SiO2（73.49%～74.78% ） and Al2O3（14.37%～14.83%）, is riched in potassium （K2O/Na2O=1.14～1.91）, low in Fe, Mg and Ti. And the granite has high Aluminum saturation index and Al2O3/TiO2 ratio （〉100）, and its Rittmann Index（σ）〈3.3. Trace elements in the granite show positive anomalies for Rb, U and negative anomalies for Ba, Sr, Zr, Ti. The total amount of REE in the Zhawulong muscovite granite is low, which is characterized by obvious LREE enrichment and HREE loss, and has a ＂V＂ type valley shape because of the obvious negative Eu anomaly（σEu=0.36～0.53）. The muscovite granite has high Rb/Sr （2.08～6.51）, Rb/Ba （1.53～3.26） and low CaO/Na2O （〈0.3）.Conclusions： The Zhawulong muscovite granite is high-K-alkalkine and strongly peraluminous series. It is formed by dehydration melting of the Triassic Xikang Group metapelite, and it is a product of the syn-collisional orogenic processes.The LCT type granitic pegmatite from Zhawulong, mainly formed by the gradual evolution of strongly peraluminous magma, which is fomed by partial melting of metapelite during the orogenic process.