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.

对取自加拿大西北地区埃卡蒂（Ekati）矿福克斯金伯利岩的11颗含显微包裹体的纤维状钻石开展主量元素、微量元素及Sr同位素组成分析，这批钻石均呈被膜状或类立方晶形。在其中9颗钻石中检出盐质成分的高密度流体（High-density fluid, HDF）显微包裹体，余下2颗则含有硅质成分的高密度流体包裹体。部分含盐质流体的钻石还包裹有其寄主橄榄岩（peridotite）围岩的显微矿物包裹体，包括橄榄石、斜方辉石、铬透辉石及铬铁矿；含硅质流体的钻石则含有绿辉石质单斜辉石显微包裹体，其寄主围岩为榴辉岩（eclogite）。盐质与硅质两类高密度流体均富集不相容元素，稀土元素配分模式均具分馏特征：Ba、U、Th及轻稀土元素（Light Rare Earth Element, LREE）含量升高，而Nb、Ta及碱金属（K、Rb、Cs）含量相对亏损。这类配分模式的分馏特征在盐质高密度流体中更为显著，且盐质流体兼具正铕异常与正锶异常；与之相对，硅质流体无铕异常，仅表现为负锶异常。盐质高密度流体的⁸⁷Sr/⁸⁶Sri比值范围为0.7039~0.7090，而含硅质流体的两颗钻石的该比值分别为0.7064与0.7111。本数据集还包含取自加拿大迪亚维克（Diavik）矿的1颗钻石的微量元素组成数据。