Mineralogy and genesis of the kihabe Zn-Pb-V prospect, Aha Hills, Northwest Botswana

Abstract

The Kihabe Zn-Pb-V > (Cu-Ag-Ge) prospect is located at the boundary between Namibia and Botswana (Aha Hills, Ngamiland District) in a strongly deformed Proterozoic fold belt, corresponding to the NE extension of the Namibian Damara Orogen. The Kihabe prospect contains Zn-Pb resources of 14.4 million tonnes at 2.84% zinc equivalent, Ag resources of 3.3 million ounces, and notable V-Ge amounts, still not evaluated at a resource level. The ores are represented by a mixed sulfide–nonsulfide mineralization. Sulfide minerals consist mainly of sphalerite, galena and pyrite in a metamorphic quartzwacke. Among the nonsulfide assemblage, two styles of mineralization occur in the investigated samples: A first one, characterized by hydrothermal willemite and baileychlore, and a second one consisting of supergene smithsonite, cerussite, hemimorphite, Pb-phosphates, arsenates and vanadates. Willemite is present in two generations, which postdate sulfide emplacement and may also form at their expenses. These characteristics are similar to those observed in the willemite occurrences of the nearby Otavi Mountainland, which formed through hydrothermal processes, during the final stages of the Damara Orogeny. The formation of the Kihabe willemite is likely coeval. Baileychlore is characterized by textures indicating direct precipitation from solutions and dissolution–crystallization mechanisms. Both processes are typical of hydrothermal systems, thus suggesting a hydrothermal genesis for the Kihabe Zn-chlorite as well. Baileychlore could represent an alteration halo possibly associated either with the sulfide or with willemite mineralization. The other nonsulfide minerals, smithsonite, cerussite, various Pb-phosphates and vanadates, are clearly genetically associated with late phases of supergene alteration, which overprinted both the sulfide and the willemite-and baileychlore-bearing mineralizations. Supergene alteration probably occurred in this part of Botswana from the Late Cretaceous to the Miocene.