Geochemistry and petrogenesis of rare-metal pegmatites: A case study of Lemera Sn ore deposits in Kivu region of Karagwe-Ankole Belt, D. R. Congo
Rub'son N'nahano-Ruhindwa HERITIER, Moïse Luemba, Huan Li, Charles Nzolang, Donat KAMPATA, Joseph Munezero Ntibahanana
Abstract
This paper reports the results from an investigation on petrogenesis and geochemistry of the Lemera granite pegmatites in Kivu region of Karagwe-Ankole Belt, D. R. Congo and the related tin ore deposits. Seven granite pegmatite samples were collected from outcrops and analyzed for bulk-rock geochemistry analysis using ICP-MS and XRF spectrometry. The analyzed samples show a relative abundance of Al2O3 over Fe2O3(T) and MgO (12.95, 0.96, and 0.16, all in wt.%, on average and respectively). The alumina saturation index ranges from 1.33 to 2.05. The abundances of some important rare metals, as well as some related key parameters, are as follows: Sn ((1–138)×10-6), Ta ((0.20–0.60)×10−6), Nb ((1–8)×10-6), Cs ((1.20–3.20)×10−6), Rb ((3–223)×10−6), Zr ((7–201)×10−6), w(K)/w(Rb) (150–272); w(K)/w(Cs) (9.06–23.3); w(Nb)/w(Ta) (3.33–14). The results indicate that the Lemera granite pegmatites crystallized from a fertile, peraluminous, and S-type granitic magma through a fractional crystallization process in a late to post-collisional setting. Mineralization of Sn and Zr of Lemera granite pegmatites is noticed.