Petrography and geochemical characterization of lithium-bearing pegmatites at Sambaru, Ikungi District, central Tanzania

The study aimed to analyze the mineralogical and elemental composition of pegmatites, classify the pegmatites, and assess the potential for lithium exploration in the Sambaru area. Various analytical techniques were employed, including petrography, XRF for major elements, LA-ICP MS for trace and rare earth elements (REEs), microwave extraction for lithium concentration, EPMA for individual minerals, and SEM+EDX for mineral composition and morphology analysis. The results indicated that Sambaru pegmatites showed imperfections in internal evolution, characterized by mineral assemblages such as quartz-K-feldspar-apatite, quartz-K-feldspar-plagioclase-lepidolite-muscovite, with accessory minerals like apatite, monazite, and garnet. The presence of trace elements (Sc, V, Co, Zn, Rb, Sr, Nb, Sn, Cs, Ta, Th, U) and minerals like Fe, Li, and Mn-rich muscovite, monazite, and columbite suggests that these pegmatites belong to the LCT family, originating from a peraluminous silica melt. The positive correlation between Fe and F contents and the presence of albite-rich feldspars indicate evolution from a highly differentiated melt. A chondrite-normalized diagram revealed a negative Eu anomaly and enrichment of MREEs (Sm, Gd, Tb), suggesting the pegmatites evolved from a fractionated plagioclase-rich melt, with Lepidolite identified as the main lithium ore mineral. The evolution of the pegmatite occurred in two stages: the primary stage involved the crystallization of key minerals like plagioclase (mainly albite), muscovite, and K-feldspar, while the secondary stage saw the formation of Li-rich muscovite. The transition between these stages was marked by the presence of accessory minerals like monazite and zircon. Most samples contained lithium concentrations above 0.016 g/t, with three samples showing significant concentrations of 2.6, 3.3, and 3.8 g/t, highlighting the potential for further lithium exploration and small-scale mining.