作　　者： (郑硌）; (章永梅）; (顾雪祥）; (高海军）; (何格）; (董树义）;

机构地区： 中国地质大学地质过程与矿产资源国家重点实验室,北京100083

出　　处： 《岩石学报》 2017年第8期2633-2647,共15页

摘　　要： 安哥拉Bonga碳酸岩型铌矿床位于Parana'-Angola-Etendeka碱性岩-碳酸岩火成岩省东部,是一个孤立产出的中心式岩栓,侵入于元古宙花岗岩基底中。岩石地球化学研究表明,Bonga岩体由钙碳酸岩和少量的镁碳酸岩组成,岩体成分从钙碳酸岩向镁碳酸岩演化。矿物组合上,钙碳酸岩以方解石为主,副矿物有磷灰石、磁铁矿、烧绿石和少量稀土矿物;镁碳酸岩以白云石为主,烧绿石含量降低,稀土矿物含量增高。富钙碳酸岩(摩尔比值Ca O/Ca O+Mg O+Fe O+Mn O>0.83)中Nb含量较高,变化于148.1×10^(-6)~8394×10^(-6),平均为2127×10^(-6),∑REE变化于1441×10^(-6)~9452×10^(-6),平均为2791×10^(-6),LREE/HREE变化于16.7~58.3,平均为25.0;富镁碳酸岩(摩尔比值Ca O/Ca O+Mg O+Fe O+Mn O<0.83)Nb含量降低,变化于300.9×10^(-6)~3910×10^(-6),平均为1502×10^(-6),∑REE升高,变化于1659×10^(-6)~18849×10^(-6),平均为7111×10^(-6),轻稀土更加富集,LREE/HREE增大,变化于19.1~114,平均为57.6。铌在碳酸岩浆演化的早期富集,铌矿化主要与富钙碳酸岩有关;稀土元素的富集相对较晚,主要与富镁碳酸岩有关。对碳酸岩碳氧同位素的瑞利分馏模拟计算(RIFMS模型)结果表明,Bonga碳酸岩的铌矿化(烧绿石沉淀)主要受岩浆作用控制,其温度不低于600℃。 The Bonga carbonatite-type niobium deposit is located in the eastern part of the Parana＇-Angola-Etendeka carbonatiticalkaline province. The Bonga carbonatite is an isolated circular plug intruding Proterozoic granite basement. Study on lithogeochemistry shows the Bonga carbonatite consists of calcio-carbonatite and minor magnesio-carbonatite. There＇s a trend from calcio-carbonatite to magnesio-carbonatite during the magmatic evolution. Calcio-carbonatite is mainly composed of calcite with minor apatite,magnetite,pyrochlore and rare REE minerals; magnesio-carbonatite is mainly composed of dolomite,and differs from calcio-carbonatite in less pyrochlore and more REE minerals. Calcium-rich carbonatite（ molar ratio of Ca O/（ Ca O ＋ Mg O ＋ Fe O ＋ Mn O） 0. 83） has high niobium contents of 148. 1 × 10^-6- 8394 × 10^-6（average on 2127 × 10^-6）,∑REE contents of 1441 × 10^-6- 9452 × 10^-6（average on 2791 × 10^-6）,LREE/HREE ratios range from 16. 7 to 58. 3（average on 25. 0）; magnesium-rich carbonatite（molar ratio of Ca O/（Ca O ＋ Mg O ＋ Fe O ＋ Mn O） 0. 83） has lower Nb contents of 300. 9 × 10^-6- 3910 × 10^-6（average on 1502 × 10^-6）,higher ∑REE contents of 1659 × 10^-6- 18849 × 10^-6（average on 7111 × 10^-6）,and higher LREE/HREE ratios range from 19. 1 to 114（average on 57. 6）. Niobium enrichment occurred in early phase of magmatic evolution,mineralization is mainly associated with calcium-rich carbonatite. It was followed by later rare earth elements enrichment associated with magnesium-rich carbonatite. The result of RIFMS（Rayleigh Isotopic Fractionation from a Multicomponent Source） modeling of carbon and oxygen isotope indicates that the niobium mineralization（ pyrochlore precipitation） in the Bonga carbonatite occurred during magmatic process,with temperature approximately higher than 600℃.

关 键 词： 碳氧同位素 岩石地球化学 碳酸岩 安哥拉