江西甘坊洞上稀有金属花岗岩中铷矿化特征及成因机制

Genesis of Rb mineralization of the Dongshang rare metal granite in Jiangxi Province

江西省宜丰县甘坊地区是一个重要的稀有金属成矿区,目前在甘坊岩体内发现了一系列锂铷稀有多金属矿床(点),但其成矿机制尚不明确。选择甘坊岩体内洞上花岗岩作为研究对象,采用电子探针技术对多种花岗岩中的长石和云母类矿物进行了精细的结构和成分分析。结果表明,云母类矿物是铷的主要载体(Rb_(2)O<1.07%),长石类矿物中Rb含量低(Rb_(2)O<0.11%),尤其是在钠长石中Rb的含量几乎为0。含铷云母主要是白云母花岗岩、伟晶岩和细晶岩中的多硅白云母-铁锂云母类,其中铷可能主要通过与钠双置换云母结构中的层间钾离子存在。矿物结构特征显示,洞上花岗岩经历了明显的岩浆结晶分异和流体交代作用。结晶分异作用可能是洞上花岗岩Rb富集成矿的关键机制,而后期流体交代蚀变过程对铷的聚集作用有限。结合前人研究成果,笔者认为甘坊地区具有较好的锂、铷等稀有金属成矿潜力,后续的找矿勘查应注重与早白垩世—晚侏罗世(140~150Ma)高分异花岗岩相关的锂、铷等稀有金属矿床的找矿工作。

The Ganfang district in the Yifeng County,Jiangxi Province is an important rare metalmetallogenic area.A series of Li-Rb rare metal deposits(mineralization)have been discovered in the Ganfang intrusions,while the mineralization mechanism of rare metalsis not clear yet.The detailed mineralogy texture and composition of feldspars and micas from the Dongshang granite have beenanalyzed by electron microprobe analysis.The results show that micas are the main carriers of Rb(Rb_(2)O<1.07%),and the contents ofRb in feldspars are lower(Rb_(2)O<0.11%),particularly in albite.The Rb-bearing micas are mainly phengite to zinnwaldite frommuscovite granite,pegmatite,and granitic aplite.The substituted mechanism of Rb in micas is mainly coupled with Na for interlayercation of K.The mineral textures record both magma crystallization differentiation and fluid metasomatism for the Dongshang granites,however,the former was the key mechanism of the Rb enrichment,while the later has less role on the accumulation of Rb in granites.Together with previous publications,this paper concluded that the Ganfang intrusions have a good metallogenic potential of raremetals,and the subsequent prospecting should focus on the Li,Rb,and other rare metals related to the Early Cretaceous to Late Jurassic(140~150 Ma)highly differentiated granites.