LAUSR

Abstract The Numbi pegmatites of South Kivu Province (D.R.C) in the Kibaran belt which intruded the Mesoproterozoic Formation (1.6-0.9 Ga) was investigated to elucidate the structural imprints and geochemical characteristics related to the pegmatitic rocks associated with Sn - Nb - Ta mineralization, source(s) of the mineralisation, processes responsible for its formation and the economic viability of Tin-Niobium-Tantalum mineralisation. The structural features include: the pegmatitic veins with orientation from N150°E to N160°E characterized with direction and dip values averages of N84°E/13°SSE for horizontal veins and N138°E/73°WSW for subvertical veins. From the different stresses, the pegmatite and quartz veins occurred during the same tectonic phase. The characteristic high SiO2, Al2O3, Fe2O3 and Na2O, indicates peraluminous and S-type pegmatite, ferroan and medium to high K, characteristics of a collisional tectonic environment. The pegmatite showed an enrichment of Rb (114.70 – 1000 ppm), Ta (27.50 – 370.90 ppm), Cs (28.90 – 682.80 ppm), Sn (238 – 2451 ppm) and Nb (31.80 – 139.20 ppm) trace element, consistent with indices for mineralisation. The La/Yb vs. La and Sm/Yb vs. La/Sm diagrams established magmatic compositional heterogeneities and/or mixing in the lava suits that formed the pegmatites. Variation plots of Ta vs Ga, Ta vs Cs, Ta vs Cs + Rb and Ta vs K/Cs showed consistent trend of mineralization using their position relative to the Beus and Gordiyenkos line. These ratios - K/Ba, K/Rb, Ba/Rb, Rb/Sr and geochemical models- Y vs. Nb, (Y+Nb) vs. Rb, Zr vs. Ta/Zr, B (=Fe+Mg+Ti) vs A(=Al-(K+Na+2Ca), R1(=4Si+11(Na+K)-2(Fe+Ti)) vs R2(=6Ca+2Mg+Al) with observed tectonic markers like lineation/foliation, joints and veins suggests a structurally controlled mineralisation. The Numbi pegmatites are of partial melting of lithospheric mantle sources, relatively rich in Sn, Ta and Nb of economic value that are structurally controlled.