McNeill J, Pearson D G, Klein-Bendavid O, Nowell G M, Ottley C J, Chinn I
Northern Centre for Isotopic and Elemental Tracing, Department of Earth Sciences, Durham University, South Road, Durham DH1 3LE, UK.
J Phys Condens Matter. 2009 Sep 9;21(36):364207. doi: 10.1088/0953-8984/21/36/364207. Epub 2009 Aug 19.
The geochemical signature of diamond-forming fluids can be used to unravel diamond-forming processes and is of potential use in the detection of so-called 'conflict' diamonds. While fluid-rich fibrous diamonds can be analyzed by a variety of techniques, very few data have been published for fluid-poor, gem-quality diamonds because of their very low impurity levels. Here we present a new ICPMS-based (ICPMS: inductively coupled plasma mass spectrometry) method for the analysis of trace element concentrations within fluid-poor, gem-quality diamonds. The method employs a closed-system laser ablation cell. Diamonds are ablated and the products trapped for later pre-concentration into solutions that are analyzed by sector-field ICPMS. We show that our limits of quantification for a wide range of elements are at the sub-pg to low pg level. The method is applied to a suite of 10 diamonds from the Cullinan Mine (previously known as Premier), South Africa, along with other diamonds from Siberia (Mir and Udachnaya) and Venezuela. The concentrations of a wide range of elements for all the samples (expressed by weight in the solid) are very low, with rare earth elements along with Y, Nb, Cs ranging from 0.01 to 2 ppb. Large ion lithophile elements (LILE) such as Rb and Ba vary from 1 to 30 ppb. Ti ranges from ppb levels up to 2 ppm. From the combined, currently small data set we observe two kinds of diamond-forming fluids within gem diamonds. One group has enrichments in LILE over Nb, whereas a second group has normalized LILE abundances more similar to those of Nb. These two groups bear some similarity to different groups of fluid-rich diamonds, providing some supporting evidence of a link between the parental fluids for both fluid-inclusion-rich and gem diamonds.
形成钻石的流体的地球化学特征可用于揭示钻石的形成过程，并且在检测所谓的“冲突”钻石方面具有潜在用途。虽然富含流体的纤维状钻石可以通过多种技术进行分析，但由于贫流体的宝石级钻石杂质水平极低，因此针对此类钻石发表的数据非常少。在此，我们提出一种基于电感耦合等离子体质谱法（ICPMS）的新方法，用于分析贫流体的宝石级钻石中的微量元素浓度。该方法采用封闭系统激光烧蚀池。对钻石进行烧蚀，并将产物捕获，随后预浓缩到溶液中，再通过扇形场电感耦合等离子体质谱仪进行分析。我们表明，我们对多种元素的定量限处于亚皮克到低皮克水平。该方法应用于来自南非库里南矿（前称普列米尔矿）的一组10颗钻石，以及来自西伯利亚（米尔矿和乌达奇纳亚矿）和委内瑞拉的其他钻石。所有样品中多种元素的浓度（以固体中的重量表示）都非常低，稀土元素以及钇、铌、铯的含量范围为0.01至2 ppb。诸如铷和钡等大离子亲石元素（LILE）的含量在1至30 ppb之间变化。钛的含量范围从皮克水平到2 ppm。从目前合并的小数据集来看，我们在宝石级钻石中观察到两种形成钻石的流体。一组的大离子亲石元素相对于铌有富集，而另一组的大离子亲石元素丰度与铌的丰度更接近。这两组与不同组的富含流体的钻石有一些相似之处，为富含流体包裹体的钻石和宝石级钻石的母流体之间存在联系提供了一些支持性证据。
