庙垭铌-稀土矿床的热液蚀变作用:来自碳酸岩碳-氧同位素的制约  

Hydrothermal alteration for the Miaoya Nb-REE deposit:constraints from C-O isotope composition of the carbonatite

作　　者：邱啸飞[1,2] 蔡应雄[1,2] 江拓[1,2] 卢山松[1,2] 彭练红[1,2] 赵小明[2] 彭三国[1,2] 朱江[1,2] 

机构地区：[1]中国地质调查局花岗岩成岩成矿地质研究中心 [2]中国地质调查局武汉地质调查中心,武汉430205

出　　处：《华南地质与矿产》2017年第3期275-281,共7页Geology and Mineral Resources of South China

基　　金：中国地质调查局地质调查项目"武当-桐柏-大别成矿带武当-随枣地区地质矿产调查"(编号:121201009000160902)和"中南地区基础地质综合调查与片区总结"(编号:121201004000161412)联合资助

摘　　要：对湖北省庙垭铌-稀土矿床火成碳酸岩全岩进行了碳-氧同位素分析结果显示,庙垭碳酸岩δ13C值为-5.84‰^-3.46‰,与正常地幔和初始火成碳酸岩值基本一致,δ18O值为11.3‰~13.4‰,明显高于正常地幔和初始碳酸岩值,与富CO2-H2O流体交代后的碳酸盐岩的C-O同位素结果相似。结合矿物学、岩石学和流体包裹体观察和研究结果,初步判断庙垭碳酸岩可能经历了后期热液蚀变作用改造过程。应用水-岩交换模型计算进一步获得热液蚀变温度为约400~600°C,水/岩比为10~200。通过与区域上杀熊洞碱性-碳酸岩杂岩体和内蒙古白云鄂博Nb-Fe-REE矿床中碳酸岩的C-O同位素组成进行对比,初步认为后期热液流体交代蚀变作用过程对与火成碳酸岩相关的超大型Nb-REE矿床形成可能具有重要意义。Whole-rock carbon and oxygen isotope compositions for the carbonatite of the Miaoya Nb-REE deposit in the Hubei Province were measured. The results show that δ13 C values of the carbonatite range from-5.84‰ to-3.46‰, consistent with the normal mantle δ13 C values, whereas their δ18O values vary from 11.3‰ to 13.4‰, evidently higher than the normal mantle and the primary carbonatite values. Combined with the mineralogy, petrology and fluid inclusion observations, it is suggested that the Miaoya carbonatite might have experienced alteration by post-carbonatite hydrothermal fluid. Water-rock exchange modeling further indicates that the alteration temperatures are about 400-600℃ and water/rock ratios are 10-200. Compared with the regional Shaxiongdong syenite-carbonatite complexes and the Inner Mongolia Bayan Obo Nb-Fe-REE deposit by C-O isotope compositions, we hypothesis that the post-carbonatite hydrothermal alteration could be of great significance to the carbonatite-related super-large Nb-REE deposits.

关 键 词：庙垭铌-稀土矿床 碳酸岩 碳-氧同位素 热液蚀变 矿床成因 

分 类 号：P618.7[天文地球—矿床学]