Genesis of peculiarly zoned Co, Zn and Mn-rich chromian spinel in serpentinite of Bou-Azzer ophiolite, Anti-Atlas, Morocco

Abstract

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.

Zincian chromite inclusions in diamonds: Possibility of deep recycling origin

“…When olivine is transformed to serpentine (especially lizardite) at low temperatures, Fe is released, and this Fe forms magnetite (e.g., Sleep et al, 2004;Evans, 2010). At this stage, the magnetite possibly acts as a reservoir of Zn (cf., Gahlan and Arai, 2007). The magnetite veins in serpentinite, described by Gahlan et al (2006), show large concentrations of such Fe.…”

“…Gahlan and Arai (2007) observed the enrichment of Zn together with Fe, Mn, Co, and Ni in primary chromites in strongly serpentinized peridotites from the Proterozoic ophiolite of Bou Azzer, Morocco. This enrichment is particularly prominent in the chromites found in the magnetite veins in serpentinite (Gahlan et al, 2006).…”

“…The primary chromian spinel (or chromite) is chemically modified to various degrees in the altered/metamorphosed olivine -rich rocks (cf. Barnes, 2000;Gahlan and Arai, 2007) (Fig. 2).…”

“…The plots also show chromites low in Zn and Mn and associated with zincian chromites for altered/metamorphosed rocks. Data sources are as follows: Meyer and Boyd (1972), Stachel et al (2000), Taylor et al (2003), and Donnelly et al (2007) for diamond inclusions; Bunch et al (1970Bunch et al ( , 1972, Bunch and Keil (1971), Desnoyers et al (1985), Krot et al (1992), Ikeda et al (1997), Chikami et al (1999), Wasson et al (1999), and Fehr and Carion (2004) for meteorites; and Thayer et al (1964), Wylie et al (1987), Challis et al (1995), Weiser and Hirdes (1997), Gahlan and Arai (2007), and Johan and Ohnenstetter (2010) for low -temperature altered/metamorphosed peridotites and related rocks. Zincian chromite of possible deep recycling origin Relationships between Cr/(Cr + Al) atomic ratio and Mg#, and Cr -Al -Fe 3+ atomic ratios of zincian chromites and related spinels.…”

マントル岩起源砕屑物の解析

“…1e Okuzawa and Hisada 2008Lenaz 2008, 1992 Fig Irvine, 1965Irvine, , 1967Arai, 1992;Arai et al, 2011 Ti Mn Co Zn Ni , Gahlan andArai, 2007;Arai and Ishimaru, 20112 3 Fe Ballhaus et al, 1990Wood et al, 1990 Cr chromian spinels…”