The lithium mineralization potential of Pan-African pegmatites in Mozambique

The Pan-African rare-element pegmatites of the Alto Ligonha Pegmatite District in northern Mozambique contain abundant Li-rich micas and primary Li aluminosilicates, such as spodumene. Given the rising global demand for Li in the manufacture of Li-ion batteries, these pegmatites are viewed as potential hard rock sources of Li. In this study, five pegmatites from the Alto Ligonha region were investigated to gain a better understanding of the fractionation processes of pegmatite melts that lead to Li enrichment and to assess the economic potential of the Li mineralization. Mica, quartz, and spodumene collected from various zones within these pegmatites were analyzed. Contents of Li, Rb, Cs, Ta, and Tl in mica and of Li and Al in quartz reveal a very strong internal fractionation of the pegmatite melt with progressing crystallization. Li₂O contents in micas increase from 0.1 to 1.4 wt% in the wall zones, to 0.3–1.7 wt% in the intermediate zones, to 1.5–3.8 wt% in the core zones and up to 5.4 wt% in the core zone pockets. Using known mica/melt Li partition coefficients, the Li contents of the melt at the initial crystallization stage was calculated to be between 315 and 3910 ppm for the Li-rich pegmatites. The Li saturation of about 5000 ppm in respect to spodumene crystallization was exceeded for most pegmatites at the final core-zone crystallization. The theoretical calculations confirm field observations that spodumene occurs in pegmatite core zones only. The analyzed spodumene show low and variable bulk Li₂O contents between 1.2 and 3.0 wt%. The low Li contents in spodumene are mainly the result of kaolinization due to tropical weathering. The final deposition of the released Li, however, could not be identified. Inferred resource calculations revealed that the investigated pegmatites contain low Li₂O tonnages. However, spodumene as well as Li-rich mica might be mined selectively as a by-product of gemstone and columbite-tantalite mining.