Genesis of Vanadium Ores in the Otavi Mountainland, Namibia

摘要

Zn-Cu-Pb vanadate ores (descloizite, mottramite, and vanadinite) in the Otavi Mountainland, Namibia, once were considered the greatest vanadium deposits in the world, with resources estimated at several million tons of vanadium ore. The deposits, now mostly exhausted, occurred in collapse breccias and solution cavities related to a karstic network associated with the post-Gondwana land surfaces in carbonate rocks of the Neoproterozoic Otavi Group, which already contained primary sulfide orebodies. Although a supergene, post-Damaran origin has been generally accepted, the timing and genesis of this mineralization style remains controversial. Mottramite and Cu descloizite are particularly abundant around Cu sulfide deposits (Tsumeb type), whereas descloizite occurs in the areas surrounding primary sphalerite-willemite orebodies (Berg Aukas type). The V deposits the Otavi Mountainland represent a special low-temperature, weathering-related, non-sulfide ore type, also fairly widespread in other areas of southern Africa (e.g., Zambia, Angola).