High-density fluid microinclusions in diamonds from the Ekati mine and the Diavik Mine (Canada)

Eleven microinclusion-bearing fibrous diamonds from the Fox kimberlite, Ekati mine, Northwest Territories, with either coated or cubic-like morphologies were analyzed for their major and trace element and Sr isotopic compositions. High-density fluid (HDF) microinclusions of saline compositions were found in 9 of the diamonds and silicic compositions in 2 diamonds. Some of the saline diamonds encapsulate also micro-mineral inclusions of their peridotite host rock (olivine, orthopyroxene, Cr-diopside and chromite); the silicic diamonds contain microinclusions of omphacitic clinopyroxene and are related to eclogite host. Both saline and silicic HDFs are enriched in incompatible elements; they have fractionated REE patterns with elevated Ba, U, Th and LREE but depleted Nb, Ta and alkalis (K, Rb, and Cs). The fractionated nature of these patterns are more pronounced in the saline HDFs, which are also characterized with positive Eu- and Sr-anomalies versus no Eu anomaly and negative Sr anomalies in the silicic fluids. 87Sr/86Sri in the saline HDFs are 0.7039-0.7090 compared to 0.7064 and 0.7111 in the two diamonds with silicic fluids. Also provided, the trace element composition of one diamonds from the Diavik mine, Canada.

对来自加拿大西北地区Ekati矿区的Fox金伯利岩中的十一颗含微包裹体的纤维状金刚石进行了分析，这些金刚石具有涂层或立方体状形态。在九颗金刚石中发现了高密度盐水（HDF）微包裹体，而在两颗金刚石中发现了酸性（硅质）微包裹体。部分盐水金刚石包裹了其辉长岩母岩（橄榄石、斜方辉石、铬透辉石和铬铁矿）的微矿物包裹体；硅质金刚石含有斜方辉石微包裹体，与生态岩母岩有关。盐水和硅质HDFs均富含不兼容元素；它们表现出分馏的稀土元素（REE）模式，具有增高的钡（Ba）、铀（U）、钍（Th）和轻稀土元素（LREE），但铌（Nb）、钽（Ta）和碱金属（钾K、铷Rb和铯Cs）含量减少。这些模式的分馏性质在盐水HDFs中更为显著，盐水HDFs还表现出正Eu异常和正Sr异常，而硅质流体中则没有Eu异常和负Sr异常。盐水HDFs中的87Sr/86Sri比值为0.7039-0.7090，而含有硅质流体的两颗金刚石中的比值分别为0.7064和0.7111。此外，还提供了来自加拿大Diavik矿的一颗金刚石的微量元素组成。