广西栗木花岗岩岩浆气-液分异作用与成矿作用  

Liquid-Gas Fractionation and Mineralization in the Limu Granites,Guangxi

作　　者：梁磊[1] 张玲[2] 颜自给[1] 董业才[1] 

机构地区：[1]中国有色桂林矿产地质研究院有限公司,广西桂林541004 [2]中国地质科学院岩溶地质研究所,国土资源部/广西壮族自治区岩溶动力学重点实验室,广西桂林541004

出　　处：《地质论评》2017年第1期61-74,共14页Geological Review

基　　金：全国危机矿山接替资源勘查项目“广西恭城县栗木锡矿接替资源勘查”(编号:200645091);广西区大规模地质找矿项目“广西恭城县五福锡钽铌矿普查”(编号:[2010]604)的成果~~

摘　　要：广西栗木花岗岩是华南地区具有代表性的含锡、钨、钽、铌矿的稀有金属花岗岩,发育一些紧密共生但结构有明显差异的岩石。在岩相学研究的基础上,运用热动力学原理对这些特殊地质现象进行成因分析以了解相应的岩浆演化过程,得出的结论构成了岩浆演化的动态证据链并相互印证,且与热动力学方程检验结论相吻合。研究结果表明,气—液分异是稀有金属花岗岩最重要的成岩与成矿作用机制。当富水岩浆上升侵位时,岩浆发生大规模的气—液分异作用,形成新的熔体相和大量夹带气相的气泡。新的熔体相因饱和水压尸(H_2O)的突然降低而过冷却结晶形成斑状结构岩石,气泡则上升迁移至不同部位,随后破裂再次发生气—液分异形成残余气流体和残余熔体相。残余气流体进一步交代先结晶的斑状结构岩石形成蚀变带花岗岩,或者结晶形成伟晶岩。残余气流体还是金属成矿元素迁移的主要载体,岩体内带的蚀变花岗岩型锡铌钽矿的成矿作用主要与残余气流体对花岗岩的自交代作用有关,而岩体顶上带的岩脉型钨锡矿的成矿作用主要与残余气流体在围岩裂隙中的结晶作用有关。The Limu granites in Guangxi Province, rich in tin--tungsten deposit and tantalum--niobium deposit, are typical rare-element granites in South China. There are some puzzling occurrences of silicate rocks that are intimately coexisted and show contrasting textures in the granites. On the basis of petrography study, we apply thermodynamic analysis to these abnormal phenomena to understand the evolution of magma. The results constitute the chain of evidence of magmatic evolution, verify with each other and correspond to the results of tests from thermodynamic equation. The study result illustrated that the liquid--gas fractionation is the most important mechanism in the formation of silicate rocks and deposit. As water-rich magma moves up to emplace, large scale liquid--gas fractionation takes place, the liquid separates into a new liquid phase and bubbles. Rapid reduction of P（ H2O） in the liquid system raises the solidus and liquidus temperatures abruptly, and causes the new liquid phase crystallizing quickly to form porphyritic texture rock. Some of the bubbles （vesiculation） rise to the top and upper parts of the magma chamber, and the others escape from the magma into the overlying rock, then they burst and separate into residual vapor and residual liquid phases. Later, the residual vapor can cause autometasomatism of granite, or crystallize to form pegmatite. The residual vapor is the main carrier transporting ore-forming metals too. The mineralization of altered granite-type tin--niobium--tantalum deposit is related to the autometasomatism of granite led by residual vapor, and the mineralization of veins-type tin--tungsten deposit is related to the crystallization of residual vapor in voids.

关 键 词：稀有金属花岗岩 岩相学 热动力学 岩浆演化 气-液分异 成矿作用 栗木 华南 

分 类 号：P588.121[天文地球—岩石学] P618.6[天文地球—地质学]