Late-Pan-African granitic pegmatites in Malawi host gem mineralization (tourmaline, beryl/aquamarine/heliodor). We use major and trace element chemistry of mica and tourmaline as proxies to describe the geochemical characteristics and to analyze the evolution of the pegmatite-forming melts. Trace element contents and ratios of pegmatitic micas and tourmalines show characteristic fractionation trends. Mica from highly fractionated pegmatite typically shows high Rb, Cs, Zn, Nb, Ta, F, and Li concentrations but low Ni, Co, V, Ti and Sc concentrations. In their less fractionated counterparts, these compositional patterns are largely reversed. Exceptions in these element patterns are related to the presence or absence of other phases that may fractionate specific elements more strongly than mica. Tourmaline shows similar fractionation trends in major and trace elements. The observed patterns indicate fractional crystallization as the dominant process of melt evolution. A near exponential decrease of alkali element ratios, such as K/Rb and K/Cs, and an increase in Rb, Cs and Li in white mica from the less to the more strongly differentiated zones suggest Rayleigh fractional crystallization. The modelling of these element ratios shows that in different pegmatite bodies the least differentiated zone formed at a fractionation coefficient of F = 0.35–0.5. Zones of intermediate fractionation show F = 0.85–0.9. Gem mineralization is associated with the most highly fractionated pegmatites or pegmatite zones (F = ~ 0.99). These highly fractionated pegmatites show strong enrichment of Li, Rb and Cs in mica and tourmaline forming from melts rich in incompatible elements. The crystallization of gem phases depended on this highly enriched environment.

马拉维的晚期泛非花岗岩伟晶岩孕育着宝石矿化（电气石、绿柱石/海蓝宝石/金矿石）。我们使用云母和电气石的主量和微量元素化学作为代理来描述地球化学特征并分析伟晶岩形成熔体的演化。伟晶云母和电气石的微量元素含量和比例显示出特征的分馏趋势。来自高度分馏伟晶岩的云母通常表现出较高的 Rb、Cs、Zn、Nb、Ta、F 和 Li 浓度，但 Ni、Co、V、Ti 和 Sc 浓度较低。在其较少细分的对应物中，这些组成模式在很大程度上是相反的。这些元素模式的例外情况与其他相的存在或不存在有关，这些相可能比云母更强烈地分馏特定元素。电气石在主量元素和微量元素中表现出相似的分馏趋势。观察到的模式表明分步结晶是熔体演化的主要过程。白云母中碱金属元素比率（例如 K/Rb 和 K/Cs）的近指数下降，以及白云母中 Rb、Cs 和 Li 的增加，从差异较小的区域到差异较大的区域，表明存在瑞利分级结晶。这些元素比例的模拟表明，在不同的伟晶岩体中，分异系数最小的区域为 F = 0.35–0.5。中间分馏区显示 F = 0.85–0.9。宝石矿化与分馏程度最高的伟晶岩或伟晶岩带有关 (F = ~ 0.99)。这些高度分异的伟晶岩表现出云母和电气石中锂、铷和铯的强烈富集，而电气石是由富含不相容元素的熔体形成的。宝石相的结晶依赖于这种高度富集的环境。