Structural control and Sn-Ta-Nb mineralization potential of pegmatitic bodies in Numbi, South Kivu Eastern D.R Congo

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(...

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Bibliographic Details
Published in:	Lithos Vol. 368-369; p. 105601
Main Authors:	Oyediran, I.A., Nzolang, C., Mupenge, M.P., Idakwo, S.O.
Format:	Journal Article
Language:	English
Published:	Elsevier B.V 01-09-2020
Subjects:	Geochemical models Lithospheric mantle Numbi pegmatites Structural features Ta and Nb mineralisation Lithospheric mantle Geochemical models Ta and Nb mineralisation Sn Structural features Numbi pegmatites
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Summary:	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. •Numbi pegmatites (D.R.C) in the Kibaran belt.•High Al2O3, K2O and Na2O, indicates peraluminous and S-type pegmatite.•Trace elements consistent with indices for mineralisation.•Partial melting of lithospheric mantle sources responsible for the pegmatites.•A structurally controlled mineralisation.
ISSN:	0024-4937 1872-6143
DOI:	10.1016/j.lithos.2020.105601