maikainite

Geier and Ottemann (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. For the Mo-rich variety, however, they observed minute inclusions of molybdenite and made the erroneous assumption that the molybdenum content was solely attributable to such inclusions.

More than 20 years later, maikainite (IMA 1992-038) and ovamboite (IMA 1992-039) were described as the Mo and W endmembers 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 the latter assigned type locality status for maikainite, and with Tsumeb as type locality for ovamboite.

At Tsumeb, maikainite occurs in germanium-enriched massive sulphide ores "… as rounded segregations and emulsion dissemination, which are distinctly separated from germanite". It also occurs as overgrowths on germanocolusite. Zoned crystals are noted, with maikainite cores giving way to outer zones of ovamboite. Maikainite grains are typically in the 3 µm to 40 µm range, with a maximum recorded size of 150 µm (Spiridonov 2003).

Under the ore microscope maikainite is isotropic with colour varying from bright yellow to greyish- yellow. Reflectivity is lower than tennantite but higher than sphalerite or germanite; cleavage and internal reflections are absent (Spiridonov 2003). A compositional analysis is required for certain identification.

germanocolusite; molybdenite; ovamboite