江西崇义铁木里碱长花岗岩中铌和稀土元素的富集机制

华南是我国重要的战略性矿产资源基地，以花岗岩相关的稀有和稀土金属成矿作用而举世瞩目。其中，铌的成矿作用一般与过铝质高分异花岗岩有关，稀土元素则随岩浆演化程度增强而富集程度降低，而江西铁木里含黑云母碱长花岗岩体同时富集铌和稀土元素，矿化组合极具特色。本文在详细的矿物岩相学研究基础上，利用电子探针、飞秒激光电感耦合等离子质谱对铌和稀土矿物进行了矿物地球化学分析，借此对铁木里碱长花岗岩中铌和稀土元素的富集机制进行探讨。铁木里岩体由肉红色含黑云母碱长花岗岩(r-G)和灰白色含黑云母碱长花岗岩(g-G)组成，发育暗色包体。r-G中的铌矿物主要为岩浆期形成的铌铁金红石，稀土矿物包括岩浆期形成的硅钛铈矿、独居石、磷灰石和热液期形成的独居石和氟碳(钙)铈矿。g-G中的铌矿物包括岩浆期形成的铌铁金红石和热液期形成的铌铁金红石、易解石、铌铁矿，稀土矿物包括岩浆期磷灰石和热液期磷灰石、独居石、氟碳(钙)铈矿。暗色包体为岩浆混合成因，内含磷灰石、独居石和零星的硅钛铈矿、金红石。矿物组合特征显示，铁木里碱长花岗岩中的铌和稀土元素经过了岩浆和热液两个时期的富集。应用金红石、磷灰石、绿泥石等矿物成分特征约束了岩浆-...

Mechanism of Nb and REE enrichment in the Tiemuli alkali-feldspar granite, Chongyi County, Jiangxi Province

South China is an important critical metal mineral resources base,and it is remarkable for widespread granites and extensive rare and rare-earth metal metallogeny.Niobium mineralization is closly assosicated with highly differentiated peraluminous granites,while the REEs decrease as magma evolves.The Early Cretaceous Tiemuli granitic pluton,located in Chongyi County,Jiangxi Province,eastern Nanling metallogenic belt,is mainly composed of flesh red and grey metaluminous-peraluminous biotite-bearing alkali-feldspar granites(r-G and g-G in short,respectively)which are chemically distinctive with high contents of niobium and rare earth elements.In this paper,detailed mineral analyses were carried out to probe into the enrichment mechanism of Nb and REEs in this intrusion.Niobium minerals in r-G mainly compose ilmenorutile,while rare earth minerals compose magmatic chevkinite,monazite,apatite and hydrothermal monazite,bastnaesite and parasite.Niobium minerals in g-G contain magmatic ilmenorutile and hydrothermal ilmenorutile,aeschynite and columbite,while magmatic apatite and hydrothermal apatite,monazite,bastnaesite,parasite comprise the REE minerals in g-G.Enclaves in the granites were caused by mixing of mafic and acidic magmas and contain apatite,monazite,a little rutile and chevkinite.Mineral assemblage characteristics indicate that Nb and REEs of the Tiemuli alkali-feldspar granite were concentrated during the magmatic and hydrothermal stages.Physicochemical conditions of the magmatic-hydrothermal system have been constrainted by rutile,apatite,chlorite,etc.And the enrichment mechanism of Nb and REEs has been delineated.Niobium was accommodated into ilmenorutile during the magmatic crystallization at temperature of 688~500℃,and be contained by hydrothermal rutile,aeschynite and niobite during the hydrothermal stage at temperature of 500~486℃.The rare earth elements were mainly taken into apatite,monazite,chevkinite,while some were reserved into biotite during the magmatic crystallization,and then turned to be moblizied and were migrated by hydrothermal fluid.The REEs were mainly deposited at temperature of~280℃with forms of monazite,bastnaesite and parasite.The melt had high oxygen fugacity while postmagmaic hydrothermal fluid turned to be reductive.The temperature and oxygen fugacity declined following the evolution.Variation of temperature,oxygen fugacity,and composition caused by magma evolution and reaction between magma and carbonate wall rocks during the hydrothermal stage are the critical factors for the mobilization,migration and deposition of REEs.The Tiemuli alkali-feldspar granite is characterized by magmatic-hydrothermal Nb-REE mineralization,and might be comprehensivly evaluated for granite-type Nb and REEs resources.