甘肃北山造山带南缘白石坝一带南岭型花岗岩地球化学特征与锡成矿作用浅析

白石坝一带花岗岩具高硅低铝、富钾贫钠、非常低Sr(24.9×10~(-6)~82.9×10~(-6))高Yb(2.61×10~(-6)~5.74×10~(-6))的南岭型花岗岩特征,A/CNK介于0.91~0.98之间,σ在1.92~2.22之间。明显富集Rb、Th、K等大离子不相容元素,亏损Ba、Sr、P、Ti等元素,并具有弱Nb亏损,稀土元素分布曲线呈明显的"燕式"型,其形成可能来源于下地壳底部部分熔融与地壳物质发生混合形成的产物,源区深度较浅、水含量低和氧逸度低,处于还原状态下的伸展构造背景,有利于锡矿的萃取和富集,研究其区域构造-岩浆演化,对指导区域矿产预测和评价均具有重要的理论和实际意义。

Geochemical characteristics of Nanling type granite in Baishiba area at the south rim of Beishan orogenic belt and the effect of tin mineralization

Granite in Baishiba area has characteristics of Nanling type granite which has high silicon and potas-sium content and low aluminum and sodium content,and a extremely low content of Sr (24.9×10 -6 -82.9 ×10 -6 )and high content of Yb (2.61 ×10 -6 -5.74×10 -6 ).The A/CNK value ranges from 0.91 to 0.98 and σvalue from 1.92 to 2.22.There is an obvious enrichment of large-ion incompatible elements like Rb, Th and K,and a depletion of elements like Ba,Sr,P and Ti and a slight depletion of Nb.The rare earth ele-ment distribtion curve is a typical “swallow-like”pattern.The granite is possibly a product of migmatization of the melted parts at the bottom of the lower crust with the crust materials.The source area has a shallow depth and relatively low water content and low oxygen fugacity.Extensional tectonic setting under the reducing condition is favorable for extraction and enrichment of tin ores.The study of the tetonic-magmatic evolution in the area has important theoretical and practical significance in the regional mineral occurrence prediction and assessment.