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

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.