ovamboite

Geier and Otteman (1970b) analysed "germanite" samples from Tsumeb by EMPA and identified several compositional varieties including one enriched in tungsten and another in molybdenum. They recognised that tungsten was substituting for iron in the germanite lattice in the W-enriched variety but made the erroneous assumption that Mo was present only as minute inclusions of molybdenite which they were able to observe in some specimens.

More than 20 years later, ovamboite (IMA 1992-039) and maikainite (IMA 1992-038) were described as the Mo and W end-members respectively of a solid solution series in the germanite group of minerals (Spiridonov 2003). Both end members occur at Tsumeb and at Maikain (in Kazakhstan) with Tsumeb having type locality status for ovamboite (and with maikainite named for its type locality in Kazakhstan). Ovamboite is named for the Ovamboland region of Namibia in which Tsumeb is located. Type material is conserved at the Fersman Museum in Moscow.

According to Spiridonov (2003) ovamboite at Tsumeb occurs "… as distinct rounded segregations and emulsion segregation in germanite aggregates and as outer zones of maikainite overgrowths on Ge-colusite [= germanocolusite]. Ovamboite is usually developed in specific sectors where germanite is actively replaced by Zn-tennantite [= tennantite-(Zn)]. Germanite associated with ovamboite contains hallite [sic. = gallite] decomposition lamellae, whereas hallite [sic. = gallite] intergrowths are absent in ovamboite. The size of ovamboite grains ranges from 1 to 20 µm (maximum 100 µm)."

Under the ore microscope ovamboite is isotropic with colour varying from whitish to pale yellow and pinkish grey. Reflectivity is lower than tennantite but higher than sphalerite or germanite; cleavage and internal reflections are absent (Spiridonov 2003). Ideally a compositional analysis is required for certain identification.

Gebhard (1999) omitted ovamboite from his list of minerals occurring at Tsumeb, despite IMA approval of the species and Tsumeb type locality in 1992. The reason for this is not known.

chalcocite; galena; gallite; germanite; germanocolusite; maikainite; molybdenite; pyrite; quartz; tennantite-(Zn)