广西栗木水溪庙稀有金属花岗岩成因

THE GENESIS OF SHUIXIMIAO RARE METAL GRANITE LIMU, GUANGXI AUTONOMOUS REGION

本文通过对水溪庙花岗岩的综合研究,认为该花岗岩的成因及锡钽铌矿化是岩浆高度分异演化的结果,岩浆结晶于富含挥发分的环境.岩体具有富钠、贫钙、分异指数和氟锂含量高以及稀土含量很低并具强烈铕亏损等特征.钾长石的结构态研究表明,岩体中的最大微斜长石从富含挥发分的低温岩浆中晶出.石英及黄玉中熔融包裹体的始熔温度为550～600℃,均一温度为820～880℃;熔融实验结果表明花岗岩的始熔温度在压力为2000～500×10~5Pa的范围内为620～670℃,说明存在低温岩浆.随岩浆结晶而分离出的挥发分在岩浆顶部聚集成与熔体共存的超临界流体相,它的向上运移导致了花岗伟晶岩脉、长石石英脉和萤石锂云母脉的垂直分带.

Comprehensive studies show that the Shuiximiao granite and the associated Sn, Ta, Nb mineralizations are the results of high degree of magmatic differentiation and evolution. The granite crystallized from a volatile-rich magma. The granite is characterized by high Na, F, Li and low Ca and very high D. I. values. REE ale in low concentration with strong Eu depletion. The K-feldspar structural states show that the microcline crystallized from the low-solidus magma with high volatile components. The initial melting temperatures of melting inclusions in quartz and topaz are 550-600℃, and the homogenization temperatures are 820-880℃. The melting experiment of Shuiximlao granite shows that the beginning temperature of granite melting is 620-670℃ at pressure 2000-500 bars. These results indicate the possibility of existence of a low-solidus magma. The volatile deriving from magma crystallization accumulated at the top of magma and became a supercritical fluid phase coexisting with melt phase. It moved upwords leaving the vertical zonation of granite pegmatites apophyses, feldspar-quartz veins and fluorite-lepidolite stringers.