The peculiar Co, Zn and Mn-rich chromian spinels are hosted by magnetite veins, serpentinites and chromitites of the mantle section of the Proterozoic Bou-Azzer ophiolite, Morocco. The spinel is complexly zoned either optically or chemically, and exhibits anomalously high MnO, ZnO and CoO contents (up to 22, 7.5 and 2 wt%, respectively). It has four distinct optical zones particularly in the magnetite veins and less typically in serpentinites. The highest level of these elements, probably divalent, is recorded within the ferritchromite zone and/or within the core zone if the ferritchromite zone is absent. These elements as well as Fe exhibit enrichment along grain boundaries and fractures of the altered spinels. Fe, Mn, Zn and Co were most probably supplied from olivine upon severe serpentinization during and after obduction of the ophiolite.
The enrichment of the Bou-Azzer chromian spinel in Mn, Zn and Co was governed mainly by the fluid/mineral (spinel) ratio and partition coefficient between spinel and the relevant fluid among many factors. The Co-, Zn- and Mn-rich chromian spinels can be used as an exploration guide for Co-Ni-Zn-Cu sulfide mineralization associated with serpentinized peridotites.
2007 Japan Association of Mineralogical Sciences