Ni Mineralization and PGE Characterization in the Kabanga and Luhuma Ni-Cu Sulfide Deposits, North West Tanzania

Abstract

Nickel mineralization in the Kabanga sulfide ores is found associated with (1) peripheral veins in the country-rock metapelites, (2) contact type massive sulfide mineralization, and (3) disseminated and vein mineralization. This work, apart from giving general highlight of the Ni mineralization (and other associated elements) in the Kabanga and Luhuma, intends to assess the PGE content in both areas. Cores (mafic-ultramafic and metasedimentary rocks as well as ore sections) from both Kabanga and Luhuma areas were sampled, cut, crushed, pulverized and analyzed for both major and trace elements. Results show that all the Iridium Platimum Group Elements (IPGEs) have very low normalized ratios in each rock and gossan samples as compared to the Paladium Platinum Group Elements (PPGEs). This can be explained by a number of contrasting reasons: (1) the effect of compatibility and incompatibility of IPGEs and PPGEs during mantle melting and fractionation, (2) the IPGEs are often associated with chromites as alloys or sulfides in dunites whilst the PPGEs are often associated with the sulfides of Fe, Ni and Cu and are found in norites, gabbros and dunites. Results also show that, in the Luhuma area lithophiles are 1.5 to 3 times more than in the Kabanga area whereas the Chalcophiles are 1.5 to 6 times more in the Kabanga than in the Luhuma. While three of the PPGE (Pt, Pd and Au) have higer concentrations in both Kabanga and Luhuma areas, they are relatively more in Kabanga than in Luhuma. The IPGE and Rh, have negligible concentrations in both areas. TiO₂ versus Fe₂O₃T, Al₂O₃ versus SiO₂, PGE
versus MgO, as well as Cu/Pd have been compared. They all indicate potentiality of the Kabanga over the Luhuma in terms of PGE. Similar positions of ores from both Luhuma and Kabanga on their TiO₂ versus Fe₂O₃T plots indicate that the Luhuma is also potential for Ni-Cu sulfide
deposits particularly on drill holes LUH05 and LUH13 where these samples were taken. In other words, if TiO2 increases then Ni-Cu sulfide increases and hence the potential for Ni-Cu mineralization.

Key words: Tanzania, Kabanga, Luhuma, PGE, Ni-Cu sulfides