河北兴隆M111稀有金属花岗岩体地球化学和矿化特征研究

THE STUDY ON THE CHARACTERISTICS OF GEOCHEMISTRY AND MINERALIZATION OF THE M111 RARE METAL CONTAINED GRANITIC INTRUSION IN XINGLONG, HEBEI

本文研究河北兴隆一个复式小花岗岩体的岩石地球化学和矿化特征.常量氧化物、Rb-Sr同位素、稀土元素和稀有微量元素的地球化学特点综合表明,该岩体是起源较深的花岗岩浆经过较充分地分异演化的晚阶段产物.岩浆成分向着富钠富钠碱元素富挥发分的方向有规律的分异演化导致Nb,Ta,Li,Be,Rb,Cs等稀有元素富集和矿化.最晚形成的空间上位于岩体较高部位的白色似斑状铁锂云母-钠长石花岗岩,是矿化的有利地段。

:The M111 rare metal contained granitic intrusion is a composite intrusion formed by two successively intrusive events, i.e., the red fine-grained lithium ferromuscovite albite granite (γ52A) and the white fine-grained to porphyaceous alumino protolithionite zinnwaldite albite granite (γ52B). The chemical compositions of the rocks are peraluminous, rich in sodium and fluorine, somewhat alkalic. Seven fresh samples give an age of 171Ma by means of Rb-Sr isochron. The 87Sr/86Sr ratio is 0.7153. The REE content of the M111 granite, in average, is 69 ppm. The REE patterns show rich in LREE and negative Eu anomalites with Eu = 0.05-0.073. Compared with the average abundance of granite, the abundance of minor elements of the M111 granite is higher in Nb, Ta, Li, Be, Rb, Cs with abundance coefficient in 3.07-24.14 and lower in Zr, Th, Co, Ni, Cr, V, Sr, Ba with abun-dance coefficient in 0- 1. The geochemical characteristics of the major elements, minor elements, REE and Rb, Sr isotope show that the Mill granite is well fractioned by the magma from the deeper crust. The evolution of the magma trended towards the enrichments of sodium, rare-alkalic and volatile constituents led to the mineralization of rare metals, such as Nb, Ta, Li, Be, Rb, Cs. The porphyaceous zinnwaldite amazonite albite granite, which is formed at latest stage and occupied the upper part of the intrusion, is favourable to mineralization and may serve as a petrological criteria of the mineralization.