Abstract

The pegmatites in southern Akwanga occur within the reactivated belt of the basement complex of Nigeria. The pegmatites consist of dominantly albite–muscovite pegmatites (rare-metal), southern parts of the map areas and biotite-microcline pegmatites (barren) central parts of the map. The pegmatites intruded gneiss-migmatitic complex consist of metasedimentry rocks; granitic gneisses and biotite gneisses and rarely meta-igneous, amphibolites. The rare metal pegmatites are composed of quartz, albite and muscovites and tourmaline. Garnets, ilmenites and minor tin–columbite–tantalite mineralization constitute accessory minerals in contrast to the biotite-microcline pegmatites. The host rocks are composed of quartz, plagioclase (An_5–21; albites–oligoclase), microcline and muscovite. Minor constituents include biotites, cordierites and hornblendes. Ilmenite occurs as opaques. The pegmatites and their host rocks are corundum and hypersthene normative, highly peraluminous, exhibiting similar geochemical signatures; however, the rare metal pegmatites are more fractionated than the host rocks and the biotite-microcline pegmatites. The rare metal pegmatites are relatively enriched in Rb, Li, Cs, B, Be, Nb and Ta, low in K/Rb and Al/Ga ratios than the biotite–microcline–pegmatites and their host rocks. The pegmatites are products of crustal anatexis of sedimentary origin. This indicates that the rare metal pegmatites are source rock controlled (product of post-collision activities) rather than fractional crystallization.

Research highlights

• Rare metal pegmatites occur in Southern Akwanga, north central Nigeria

• Highly peraluminous and LCT pegmatites

• Sn–Nb–Ta mineralization potentials in the pegmatite

• They are related to the migmatitic-gneiss complex by anatexis

中文翻译：

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尼日利亚北部-中部地下复合体Akwanga南部伟晶岩及其宿主岩的岩石成矿特征

摘要

阿克万加南部的伟晶岩发生在尼日利亚地下复合体的活化带中。伟晶岩主要由钠长石-白云母伟晶岩（稀有金属），地图区域的南部部分和黑云母微晶伟晶岩（贫瘠）的地图中心部分组成。伟晶岩侵入的片麻岩-玛塔岩复合体由沉积岩组成。花岗片麻岩和黑云母片麻岩，很少为亚火成的角闪石。稀有金属伟晶岩由石英，钠长石，白云母和电气石组成。与黑云母微晶伟晶岩相反，石榴石，钛铁矿和少量的锡-哥伦比-钽铁矿矿化构成辅助矿物。主体岩石由石英，斜长石组成（An _5–21; 钠长石-寡糖），微斜线和白云母。次要成分包括黑云母，堇青石和角混合金属。钛铁矿以不透明的形式出现。伟晶岩及其基质岩石是刚玉和超高硫规范的，高铝质的，具有相似的地球化学特征。但是，稀有金属伟晶岩比主体岩石和黑云母微晶伟晶岩具有更高的分离度。稀有金属伟晶岩中的Rb，Li，Cs，B，Be，Nb和Ta相对丰富，其K / Rb和Al / Ga的比率低于黑云母-微晶岩-伟晶岩及其宿主岩。伟晶岩是沉积成因的地壳anatexis的产物。这表明稀有金属伟晶岩是受源岩控制的（碰撞后活动的产物），而不是分步结晶。

研究重点

• 稀有金属伟晶岩发生在尼日利亚中北部的阿克旺加南部

• 高铝质和LCT伟晶岩

• 伟晶岩中的Sn–Nb–Ta矿化潜力

• 它们与阿纳泰西斯的多片麻片岩复杂有关