| 澳大利亚金刚石的成因类型及产地来源特征综述 |
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| 引用本文： | 莫默,丘志力,陈华,陆太进,李榴芬,邱文珺,王琦.澳大利亚金刚石的成因类型及产地来源特征综述[J].地质科学译丛,2013(3):65-74. |
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| 作者姓名： | 莫默 丘志力 陈华 陆太进 李榴芬 邱文珺 王琦 |
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| 作者单位： | [1]中山大学地球科学系,广东广州510275 [2]国土资源部珠宝玉石首饰管理中心,北京100013 |
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| 摘 要： | 对已经发表的数十篇关于澳大利亚金刚石的英文文献进行了梳理,从其金刚石的品质、颜色类型、形态及表面特征、生长结构及微量元素、包裹体、C同位素等方面探索了澳大利亚不同区域金刚石可能存在的产地来源特征.研究显示,澳大利亚金刚石可分为岩石圈地幔成因、超深地幔成因和俯冲环境来源等成因类型；大部分澳大利亚金刚石都因经历过强烈的晶格变形或熔蚀作用而晶体圆化,但不同产地来源的金刚石在颜色组合、橄榄岩型和榴辉岩型金刚石比例、C同位素组成特征等方面存在一定差异.上述结果表明,总体上,澳大利亚不同区域金刚石具有一定的产地来源个性,但无法简单确认澳大利亚金刚石“整体”的产地来源特征；只有结合成因来源进行分析,才能够较深入地理解不同区域金刚石的特征组合及其意义,从而为理解其产地来源的特殊性提供帮助.
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| 关 键 词： | 金刚石 产地特征 澳大利亚 |
Genetic Types of Australian Diamonds and Their Origin Features |
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| Authors: | MO Mo QIU Zhi-li CHEN Hua LU Tai-jin LI Liu-fen QIU Wen-jun WANG Qi |
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| Institution: | 1. Department of Earth Sdiences , Sun Yat- Sen University, Guangzhou , 510275, China; 2. National Gems ＆ Jewelry Technology Administrative Center, Beijing, 100013, China) |
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| Abstract: | Based on a series of English literature about Australian diamonds, the possible ori- gin features of Australian diamonds from different fields are discussed, such as quality, col- our, shape, surface characteristics, growth structure and trace elements, inclusions, carbon isotopes of the diamonds. Research indicates that Australian diamonds have three genetic types, namely, lithospheric mantle, super deep mantle and subduction environment related origin. First, Arygle diamonds and Ellendale diamonds from North Australian Craton pres- ent similar trace element characteristics of Mn, Ni, Cr loss and rich in Na, K, Ti, Zn, Cu, Ga, Rb, St, which indicates a lithosphere mantle origin. The diamonds from the two locali- ties can be distinguished from the following aspects. Firstly, only a small percentage of gem quality diamonds are discovered from the Argyle mine, most of which are brown and less are rare pink. However, Ellendale diamonds （60%--90%） are of gem quality, and high qualityyellow diamonds are famous. Secondly, primary inclusions of Argyle diamonds are over- whelmingly of eclogitic paragenesis （75%）, and these eclogitic diamonds, unlike the small percentage of Argyle peridotitic diamonds, show marked corrosion and deformation features, which display a certain relationship between inclusions and crystal morphology. However, the diamonds from Ellendale pipes NO. 4 and NO. 9 contain approximately equal proportions of peridotitic and eclogitic inclusions, and no relation between inclusions and crystal mor- phology is indicated. Thirdly, by carbon and nitrogen isotope features and nitrogen con- tents, diamonds from Argyle and Ellendale can be distinguished. On a plot of 13C and con tent of N, the diamonds from Argyle and Ellendale are clustered into two separate groups. Ellendale diamonds show a negative correlation of 313C and Ntot with a large range of N con- tents, whereas Argyle diamonds show no correlation of 313 C--N,o, and low N and ~13C con- tents. Furthermore, on a plot of ~5N--~13C, the Ellendale NO. 9 group is the most diffuse and overlaps the Argyle and Ellendale NO. 4 group, which are mutually distinct. Second, a- part from North Australian Craton, a small percentage of diamondiferous kimberlites are dis- covered in the Adelaide Fold Belt of Eurelia area, about 20 km north of Orroroo. Diamond placer deposits within South Australia are located in the Echunga area and the Springfield Ba- sin. Since only five diamonds from Echunga field are still known to exist, they are not in- eluded in this research. Diamonds from Springfield Basin,occur exclusively in the basal con- glomerate of Permian. The mineral inclusions ferropericlase-bearing of the diamonds from Springfield Basin are similar to the inclusions of diamonds from kimberlites at Eurelia, which suggests the part of diamonds from the two localities is of unusually deep, mantle origin. It would be hard to make a distinction between diamonds from Springfield Basin and Echunga, since they have similar crystal shapes, surface characteristics, colours and distribution of ni- trogen. However, they can be discriminated from diamonds of other fields around the world according to carbon isotope features. ~13C value of the former locates at --6%0, while ~3C values from other places in the world range mostly are from --5.0%0 to --4.0%o. Third, dia- monds occur in several alluvial diamond deposits such as Wellington, Bingara, Copeton and Airly Mountain in New South Wales, which have two distinct groups, A group and B group, according to different characteristics. Most diamonds from Wellington and Airly Mountain belong to A group, and they are similar to those found in kimberlites and lamproites globally and are thought to have formed in traditional lithospheric mantle. However, 95% diamonds from Bingara and Copeton belong to B group, all of which have undergone strong deforma- tion, being of elongated, flattened or irregular dodecahedra with corrosive and glossy sur- faces. Their carbon isotope compositions （~3C） are higher than normal values with a peak between 1.0%0 and 2.0%0. Their mineral inclusion assemblage is also unique, with rich Ca and poor Na garnet and pyroxene, termed as ＂calc-silicate＂ paragenesis and regarded as a subgroup of the eclogitic paragenesis. The origin of B group diamonds is still unknown, but it has been suggested that the diamonds formed in Phanerozoic subduction systems since they oeeured in areas of convergent-margin tectonics, without the involvement of conventional kimberlitic or lamproitic volcanism. Besides, their unusual mineral inclusions and 13C_enrich_ ment are also consistent with the subduction origin. In general, certain distinctions exist a- mong diamonds from different fields, although it＇s not easy to identify Australian diamonds as a whole. Only in combination with diamond genetic types, can we obtain deeper under-standing of diamond feature and their significance, which help to better comprehend the par- ticularity of different diamond sources. |
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| Keywords: | diamond origin feature Australia |
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