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首页> 外文期刊>Contributions to Mineralogy and Petrology >Superdeep diamonds from the Juina area, Mato Grosso State, Brazil
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Superdeep diamonds from the Juina area, Mato Grosso State, Brazil

机译：来自巴西马托格罗索州Juina地区的超深钻石

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摘要

Alluvial diamonds from the Juina area in Mato Grosso, Brazil, have been characterized in terms of their morphology, syngenetic mineral inclusions, carbon isotopes and nitrogen contents. Morphologically, they are similar to other Brazilian diamonds, showing a strong predominance of rounded dodecahedral crystals. However, other characteristics of the Juina diamonds make them unique. The inclusion parageneses of Juina diamonds are dominated by ultra-high-pressure ("superdeep") phases that differ both from "traditional" syngenetic minerals associated with diamonds and, in detail, from most other superdeep assemblages. Ferropericlase is the dominant inclusion in the Juina diamonds. It coexists with ilmenite, Cr-Ti spinel, a phase with the major-element composition of olivine, and SiO2. CaSi-perovskite inclusions coexist with titanite (sphene), "olivine" and native Ni. MgSi-perovskite coexists with TAPP (tetragonal almandine-pyrope phase). Majoritic garnet occurs in one diamond, associated with CaTi-perovskite, Mn-ilmenite and an unidentified Si-Mg phase. Neither Cr-pyrope nor Mg-chromite was found as inclusions. The spinel inclusions are low in Cr and Mg, and high in Ti (Cr2O3<36.5 wt%, and TiO2Si2O4. This suite of inclusions is consistent with derivation of most of the diamonds from depths near 670 km, and adds ilmenite and relatively low-Cr, high-Ti spinel to the known phases of the superdeep paragenesis. Diamonds from the Juina area are characterized by a narrow range of carbon isotopic composition (δ13C=–7.8 to –2.5‰), except for the one majorite-bearing diamond (δ13C=–11.4‰). There are high proportions of nitrogen-free and low-nitrogen diamonds, and the aggregated B center is predominant in nitrogen-containing diamonds. These observations have practical consequences for diamond exploration: Low-Mg olivine, low-Mg and high-Mn ilmenite, and low-Cr spinel should be included in the list of diamond indicator minerals, and the role of high-Cr, low-Ti spinel as the only spinel associated with diamond, and hence as a criterion of diamond grade in kimberlites, should be reconsidered.
机译：来自巴西马托格罗索州Juina地区的冲积钻石具有形态，同生矿物包裹体，碳同位素和氮含量的特征。从形态上讲，它们与其他巴西钻石相似，显示出圆形十二面体晶体的强烈优势。但是，Juina钻石的其他特征使它们独一无二。 Juina钻石的共生共生物以超高压（“超深”）相为主导，该超高压相既不同于与钻石相关的“传统”同生矿物，又不同于大多数其他超深组合。铁菊酯酶是Juina钻石的主要成分。它与钛铁矿，Cr-Ti尖晶石（一种以橄榄石为主元素组成的相）和SiO2共存。 CaSi-钙钛矿夹杂物与钛矿（方晶），“橄榄石”和天然镍共存。 MgSi-钙钛矿与TAPP（四方Almandine-pyrope相）共存。一颗钻石中含有大铁石榴石，与钙钛矿，钙钛矿，锰钛铁矿和未识别的硅镁相有关。 Cr-pyrope或Mg-铬铁矿均未发现夹杂物。尖晶石夹杂物的铬和镁含量低，而钛含量高（Cr2 O3 <36.5 wt％，TiO2 Si2 O4 倒置。这套夹杂物与从670 km附近的深处钻出的大多数钻石是一致的，并且将钛铁矿和相对低Cr，高Ti的尖晶石添加到了超深共生的已知阶段。来自朱纳地区的钻石的特征是碳同位素组成范围狭窄（δ13 C = –7.8至–2.5‰），唯一的含一颗大粒钻石（δ13 C = –11.4‰）除外）。无氮和低氮钻石的比例很高，而聚集的B中心在含氮钻石中占主导地位。这些观察结果对钻石勘探具有实际意义：低镁橄榄石，低镁和高锰铁钛铁矿以及低铬尖晶石应列入金刚石指示剂矿物清单，以及高铬，低钛的作用尖晶石是唯一与金刚石相关的尖晶石，因此应作为金伯利岩中金刚石等级的标准来考虑。

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  • 来源
    《Contributions to Mineralogy and Petrology》 |2001年第6期|734-753|共20页
  • 作者

    F. Kaminsky; O. Zakharchenko; R. Davies; W. Griffin; G. Khachatryan-Blinova; A. Shiryaev;

  • 作者单位

    1KM Diamond Exploration 815 Evelyn Drive West Vancouver V7 T 1J1 B.C. Canada;

    Institute of Diamonds Ltd. Ste. 155–5/10 Litovskii Blvd. Moscow 117593 Russia;

    GEMOC Key Centre Department of Earth and Planetary Sciences Macquarie University Sydney 2109 Australia;

    GEMOC Key Centre Department of Earth and Planetary Sciences Macquarie University Sydney 2109 Australia;

    Institute of Diamonds Ltd. Ste. 155–5/10 Litovskii Blvd. Moscow 117593 Russia;

    Vernadsky Institute of Geochemistry and Analytical Chemistry Kosygin St. 19 Moscow 117975 Russia;

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