The Neoproterozoic Bou Azzer ophiolite in the Moroccan Anti-Atlas Panafrican belt hosts numerous chromitite orebodies within the peridotite section of the oceanic mantle. The chromitites are strongly affected by serpentinization and metamorphism, although they still preserve igneous relicts amenable for petrogenetic interpretation. The major, minor and trace element composition of unaltered chromite cores reveal two compositional groups: intermediate-Cr (Cr# = 0.60 – 0.74) and high-Cr (Cr# = 0.79 – 0.84) and estimates of parental melt compositions suggest crystallization from pulses of fore-arc basalts (FAB) and boninitic melts, respectively, that infiltrated the oceanic supra-subduction zone (SSZ) mantle. A platinum group elements (PGE) mineralization dominated by Ir-Ru-Os is recognized in the chromitites, which has its mineralogical expression in abundant inclusions of Os-Ir alloys and coexisting magmatic laurite (RuS₂) and their products of metamorphic alteration. Unusual mineral phases in chromite, not previously reported in this ophiolite, include super-reduced and/or nominally ultra-high pressure minerals moissanite (SiC), native Cu and silicates (oriented clinopyroxene lamellae), but “exotic” zircon and diaspore have also been identified. We interpret that clinopyroxene lamellae have a magmatic origin, whereas super-reduced phases originated during serpentinization processes and diaspore is linked to late circulation of low-silica fluids related to rodingitization. Zircon grains, on the other hand, with apatite and serpentine inclusions, could either have formed after the interaction of chromitite with mantle-derived melts or could represent subducted detrital sediments later incorporated into the chromitites. We offer a comparison of the Bou Azzer chromitites with other Precambrian ophiolitic chromitites worldwide, which are rather scarce in the geological record. The studied chromitites are very similar to the Neoproterozoic chromitites reported in the Arabian-Nubian shield, which are also related to the Panafrican orogeny. Thus, we conclude that the Bou Azzer chromitites formed in a subduction-initiation geodynamic setting with two-stages of evolution, with formation of FAB-derived intermediate-Cr chromitites in the early stage and formation of boninite-derived high-Cr chromitites in the late stage.

摩洛哥Anti-Atlas Panafrican带中的新元古代Bou Azzer蛇绿岩在大洋地幔橄榄岩段中拥有众多铬铁矿矿体。铬铁矿受到蛇纹石化作用和变质作用的强烈影响，尽管它们仍保留着适合于成岩解释的火成岩遗迹。未改变的铬铁矿岩心的主要，次要和微量元素组成显示出两个组成族：中铬（Cr＃= 0.60 – 0.74）和高铬（Cr＃= 0.79 – 0.84），母体熔体组成的估计表明从脉冲中结晶分别渗入海洋超俯冲带（SSZ）地幔的前弧玄武岩（FAB）和博尼尼特熔体。在铬铁矿中发现了以Ir-Ru-Os为主的铂族元素（PGE）矿化作用，_2个）及其变质改变的产物。亚铬铁矿中未曾报道过的铬铁矿中不寻常的矿物相包括超还原和/或名义上超高压的矿物莫桑石（SiC），天然铜和硅酸盐（取向的次氯环己烯薄片），但“外来的”锆石和辉绿岩也有被确定。我们解释说，clinopyroxene薄片具有岩浆成因，而蛇纹石化过程中产生的超还原相和水硬岩则与低硅化液的后期循环有关，而这些低硅化液与灵化作用有关。另一方面，带有磷灰石和蛇纹石夹杂物的锆石颗粒可能是在铬铁矿与地幔衍生的熔体相互作用后形成的，或者可能代表了后来掺入铬铁矿的俯冲碎屑沉积物。我们提供了Bou Azzer铬铁矿与全球其他前寒武纪蛇纹岩铬铁矿的比较，在地质记录中这种铬铁矿相当稀少。研究的铬铁矿与阿拉伯-努比亚盾构中报道的新元古代铬铁矿非常相似，后者也与泛非造山带有关。因此，我们得出的结论是，Bou Azzer铬铁矿形成于俯冲开始的地球动力学环境中，具有两个演化阶段，在早期阶段形成了FAB衍生的中Cr铬铁矿，而在其内部则形成了由贝宁石衍生的高Cr铬铁矿。后期。这也与Panafrican造山运动有关。因此，我们得出的结论是，Bou Azzer铬铁矿形成于俯冲开始的地球动力学环境中，具有两个演化阶段，在早期阶段形成了FAB衍生的中Cr铬铁矿，而在其内部则形成了由贝尼石衍生的高Cr铬铁矿。后期。这也与Panafrican造山运动有关。因此，我们得出的结论是，Bou Azzer铬铁矿形成于俯冲开始的地球动力学环境中，具有两个演化阶段，在早期阶段形成了FAB衍生的中Cr铬铁矿，而在其内部则形成了由贝尼石衍生的高Cr铬铁矿。后期。