Application of lithogeochemistry to exploration for Ni-Cu sulfide deposits in the Kabanga area, NW Tanzania

The Kabanga Ni-Cu sulfide deposits and the Luhuma Ni-Cu sulfide prospect are located in NW Tanzania roughly 200 km SW of Lake Victoria. Both areas are within the Meso-Proterozoic Karagwe-Ankolean tectonic domain, which consists of medium grade metasedimentary rocks, that are intruded by mafic to ultramafic intrusions, late syn- and post-orogenic granites. The two Ni-Cu sulfide deposits found in the Kabanga area are Kabanga Main and Kabanga North deposits; both of these deposits are associated with ultramafic rocks. The ore zones are classified into (1) those located within ultramafic rocks, (2) those detached from ultramafic rocks and located within metasedimentary rocks and (3) those located at the contact between ultramafic rocks and metasedimentary rocks. This paper focuses on the identification of element ratios (or lithogeochemical vectors) which could be used for target generation and prediction of mineralized zone(s) from the surface in order to avoid missing of ore targets due to complexities of leaching and trace element mobilization in soils. To do this, drill cores from Kabanga North and from Kabanga Main Ni-Cu sulfide ores were sampled. Core samples from the drill holes were selected in such a way that, at least each ore interval and associated lithologic units (ultramafic/metasedimentary rocks) were well represented. Core sampling was also undertaken in the Luhuma prospect. Soil sample lines were established in proximity of the sampled drill cores from Kabanga ore deposits and Luhuma prospect. Soil samples were taken and analyzed for trace elements. The most useful element ratios are (Pd/V) x 1000 and [(Pd/V)/(Cu/Cr)] x 100; V, Cr and Cu are in ppm and Pd is in ppb. These ratios were derived based on element variations in detached and contact ores. The results were corroborated by the Principal Component analytical data, which groups elements into clusters reflecting their host minerals, e.g. (1) Cr, V and Mo for oxides, (2) Ni, Cu and Pb for sulfides, etc. (C) 2011 Elsevier Ltd. All rights reserved.