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

This study aimed to analyse 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, X-ray fluorescence for major elements, laser ablation–inductively coupled plasma–mass spectrometry for trace and rare earth elements, microwave extraction for lithium concentration, electron probe micro-analysis for individual minerals and scanning electron microscopy with energy dispersive X-ray spectroscopy 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 such as apatite, monazite and garnet. The presence of trace elements (Sc, V, Co, Zn, Rb, Sr, Nb, Sn, Cs, Ta, Th, U) and minerals such as Fe, Li and Mn-rich muscovite, monazite and columbite suggests that these pegmatites belong to the lithium–cesium–tantalum family of pegmatites, originating from a peraluminous silica melt. The positive correlation between Fe and F contents and the presence of albite-rich feldspars indicates evolution from a highly differentiated melt. A chondrite-normalized diagram revealed a negative Eu anomaly and enrichment of medium rare earth elements (Sm, Gd, Tb), suggesting that 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 such as 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 such as monazite and zircon. Most samples contained lithium concentrations above 0.016 g t⁻¹, with three samples showing significant concentrations of 2.6, 3.3 and 3.8 g t⁻¹, highlighting the potential for further lithium exploration and small-scale mining.