The Mangodara district (southwestern of Burkina Faso, West African Craton) consists of a regional-scale Eburnean dome cored by granitoid-gneisses comprising rafts of migmatitic paragneisses and amphibolites of the Paleoproterozoic Birimian series. The occurrence of rare metal-bearing pegmatites in diffuse contact with these migmatitic and granitoid gneisses suggests that they originated from the segregation of a residual melt of these partially molten hosts. In this paper, we constrain the petrogenetic link between pegmatites and their hosts, and the mechanisms of rare metal fractionation in Lithium-Cesium-Tantalum (LCT) vs Niobium-Yttrium-Fluorine (NYF) petrogenetic signatures by the geochemistry of micas, apatite, columbite-group minerals, garnet, and zircon. Titanite-allanite pegmatites (containing titanite, allanite, epidote, zircon, and apatite as accessory minerals) and their evolved equivalent, apatite-zircon pegmatites (richer in apatite, lower K/Rb and Fe/Mn ratio in biotite but Li-depleted) are poorly mineralized metaluminous pegmatites. They display a continuous evolution trend in K/Rb and Fe/Mn in biotite and similar REE patterns in apatite, which favor an origin by segregation of residual melt within tonalitic-trondhjemitic gneiss in the core of the Mangodara dome. Garnet-columbite pegmatites containing REE-bearing phosphates and Zr-U-Th-bearing metamict minerals are mixed LCT + NYF pegmatites. Their micas, slightly enriched in Li, LREE-rich apatite, and Nb–Ta-U-rich garnet, are consistent with an origin by partial melting of a metasedimentary source, with dehydration of biotite (reservoir of Li, Rb, Nb) and dissolution of apatite-monazite (reservoir of REE). Apatite crystals in one garnet-columbite pegmatite reveal an inherited REE signature typical of apatite-zircon pegmatite, which suggests mingling of a LCT pegmatite-forming melt with the residual melt derived from crystallization of metaluminous pegmatites. Garnet-REE pegmatites, containing ilmenite-pyrophanite and euxenite-aeschynite), are NYF pegmatites that should originate from melt segregation within granodioritic gneiss associated with breakdown/entrainment of amphibole (reservoir of REE, Y) and LREE segregation by allanite and phosphates in the source. These data show that the LCT vs NYF signature of pegmatites of the Mangodara district results primarily from the chemical composition of the partially-molten source and the minerals involved in the partial melting reactions, which vary as a function of increasing depth (mica, phosphate, amphibole, garnet). The trace-element signature of anatectic peraluminous pegmatite-forming melt might then be affected by mingling with residual Nb-enriched metaluminous melt.

Mangodara 地区（布基纳法索西南部，西非克拉通）由一个区域尺度的 Eburnean 圆顶组成，该圆顶由花岗片麻岩组成，包括古元古代比里米系系列的混合质副片麻岩和角闪岩。与这些混合岩和花岗片麻岩分散接触的含稀有金属伟晶岩的出现表明它们起源于这些部分熔融主体的残余熔体的分离。在本文中，我们通过云母、磷灰石、磷灰石、铌铁矿、石榴石和锆石。Titanite-allanite伟晶岩（含钛矿、蓝绿石、绿帘石、锆石、和磷灰石作为辅助矿物）及其演化的等效物，磷灰石-锆石伟晶岩（磷灰石含量较高，黑云母中的 K/Rb 和 Fe/Mn 比值较低，但贫锂）是矿化程度较低的超铝伟晶岩。它们显示出黑云母中 K/Rb 和 Fe/Mn 的持续演化趋势以及磷灰石中类似的 REE 模式，这有利于 Mangodara 圆顶核心中的英云状-长花状片麻岩中残余熔体的偏析。含有含 REE 的磷酸盐和含 Zr-U-Th 的变质矿物的石榴石-铌铁伟晶岩是混合的 LCT + NYF 伟晶岩。它们的云母略微富含锂、富含 LREE 的磷灰石和富含 Nb-Ta-U 的石榴石，这与变沉积物源的部分熔融以及黑云母（Li、Rb、Nb 的储层）的脱水和磷灰石-独居石（REE 储层）的溶解。一种石榴石-铌锰矿伟晶岩中的磷灰石晶体揭示了磷灰石-锆石伟晶岩典型的遗传稀土元素特征，这表明形成 LCT 伟晶岩的熔体与来自超铝伟晶岩结晶的残余熔体混合。石榴石-REE 伟晶岩，包含钛铁矿-叶辉石和锂辉石-铁辉石），是 NYF 伟晶岩，应起源于花岗闪长片麻岩中的熔融偏析，与闪石（REE 储层，Y）的分解/夹带有关，而 LREE 在资源。这些数据表明 Mangodara 地区伟晶岩的 LCT 与 NYF 特征主要源于部分熔融源的化学成分和参与部分熔融反应的矿物，这些矿物随深度增加而变化（云母、磷酸盐、闪石，石榴石）。深熔过铝伟晶岩形成熔体的微量元素特征可能会受到与残留的富铌金属熔体混合的影响。