The ordered creation of paramagnetic defects at plastic deformation of natural diamonds

The EPR-study showed that natural purple diamonds from kimberlites of Eastern Siberia (Russia) contain well known P1, P2 (in some samples), W7, and N2 centers. The EPR spectra of these centers were typical of plastically deformed diamond single crystals. Besides, several intense additional spectra of di-nitrogen centers were observed in purple diamonds. The angular dependence analysis of these spectra showed that they can be attributed to known M2 centers. Comparison of principal axis directions observed for sites of the M2 center in purple diamond crystals with theoretically predicted directions in the twin crystal revealed that these centers are allocated exclusively to the twinned lamellae. Unusual phenomenon of the ordered distribution of paramagnetic centers in natural purple diamonds confirmed that the plastic deformation in natural diamonds can be induced not only by the slip of dislocations but also by the mechanical twinning.     

辽宁瓦房店首次发现50号金伯利岩管深部隐伏矿体

<正>金刚石俗称钻石,以其高硬度和稀缺性成为世界上最珍贵的矿物之一。金刚石矿床按成因可分为原生矿床与次生矿床两大类,原生矿床又可分为金伯利岩和钾镁煌斑岩型,蛇绿岩地幔橄榄岩和铬铁矿、碱性辉长辉绿岩、超高压变质岩、火山岩、陨石及其冲积相关的岩石中均有金刚石产出,但未形成矿床(路凤香等,1998;Cartigny,2005;Gurney et al.,2010)。次生矿床主要为砂矿床。其中原生金伯利岩型金刚石是世界上金刚石矿产的主要来源(Mitchell,1991;Gurney et al.,2005)。辽宁省瓦房店地区以盛产金伯利岩型原生金刚石闻名世界,尤以50号金伯利岩管金刚石品质最好,宝石级约占70%,质量属于世界一流(任厚民,1992;宋瑞祥,2013)。     

Diamonds and eclogites of the Jericho kimberlite (Northern Canada)

We studied diamonds and barren and diamondiferous eclogite xenoliths from the Jericho kimberlite (Northern Slave craton). The majority of the diamonds are non-resorbed octahedral crystals, with moderately aggregated N (IaB < 50%, N < 300 ppm) and δ¹³C = −5 to −41‰. The diamonds belong to “eclogitic” (90% of the studied samples), “websteritic” (7%) and “peridotitic” (3%) assemblages. The Jericho diamonds differ from the majority of “eclogitic” diamonds worldwide in magnesian compositions of associated minerals and extremely light C isotopic compositions (δ¹³C = −24 to −41‰). We propose that metasomatism triggered by H₂O fluids may have been involved in the diamond formation. Multiple episodes of the metasomatism and associated melt extraction of various ages are evident in Jericho eclogite xenoliths where primary garnet and clinopyroxene have been recrystallized to more magnesian minerals with higher contents of some incompatible trace elements and to hydrous secondary phases. The model is supported by the general similarity of mineral compositions in diamondiferous eclogites to those in diamond inclusions and to secondary magnesian garnet and clinopyroxene in recrystallized barren eclogites. The ultimate products of the metasomatism could be “websteritic” diamond assemblages sourced from magnesian eclogites. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

AMT测深法在金刚石矿勘探中的应用

本文介绍了AMT(音频大地电磁测深)法在雅库特和俄罗斯的Archangelsk金刚石矿区勘探中的应用.文章描述了金伯利岩岩脉的位置和形状、电性参数、围岩和上覆岩层特性.金伯利岩矿区位于易于被AMT方法确定的参考导电层之上,或者在高阻层之上.金伯利岩岩脉发育在金伯利岩矿区良导的局部边缘地区.这些良导区与地堑构造有关,其边界与基底和厚层沉积覆盖的弯曲褶皱相一致,并具有强破裂和利于金伯利岩岩浆渗透的特点.依据AMT数据,可很好地确定局部良导区,并作为最有远景的矿脉发育区.利用AMT数据可确定断裂带和区分矿区的构造断层.金伯利岩控制的断层一般被圈闭的岩墙充填,易于被磁法资料确定,而金伯利岩的围岩断层不包含圈闭的岩墙,由磁法难以测量,因此就可较好地确定金伯利岩.本文给出了由沉积层覆盖的简单地质条件下发现岩脉的例子,也介绍了包含几种不同类型金伯利岩如导电的斑状金伯利岩、并被圈闭和厚层沉积覆盖的复杂地质条件下确定岩脉的实例.     

浅议成矿预测的有关问题：—以湖南原生金刚石矿预测为例

本文简要的介绍了成矿预测的概念、理论、准则及信息系统,以金刚石矿为例,详述了湖南原生金刚石矿小比例尺成矿预测信息系统,并用累积计分法对湘西北原生金刚石矿进行了预测,划分出长沙—安化Ⅲ级成矿带一个,石门、古丈、怀化—会同成矿区三个。     

A technique for identifying structural domain boundaries at the EKATI Diamond Mine

Over 10,000 discontinuity orientations from various sources at the EKATI Diamond Mine in northern Canada were collected and amalgamated into a common database. A new technique in which structural domains were determined in the area of three closely spaced active pits by quantitatively comparing stereonets from different regions was developed. The frequencies of discontinuity poles plotting in orientation windows on stereonets were determined and compared using a correlation coefficient to quantify the degree of similarity between different stereonets. Structural boundaries between regions were established wherever their associated stereonets display low correlation coefficients. The technique was able to determine boundaries in the vertical direction as well as radially in a number of pie-shaped zones extending around the kimberlite pipes.     

Grade-tonnage and other models for diamond kimberlite pipes

Grade-tonnage and other quantitative models help give reasonable answers to questions about diamond kimberlite pipes. Diamond kimberlite pipes are those diamondiferous kimberlite pipes that either have been worked or are expected to be worked for diamonds. These models are not applicable to kimberlite dikes and sills or to lamproite pipes. Diamond kimberlite pipes contain a median 26 million metric tons (mt); the median diamond grade is 0.25 carat/metric ton (ct/mt). Deposit-specific models suggest that the median of the average diamond size is 0.07 ct and the median percentage of diamonds that are industrial quality is 67 percent. The percentage of diamonds that are industrial quality can be predicted from deposit grade using a regression model (log[industrial diamonds (percent)]=1.9+0.2 log[grade (ct/mt)]). The largest diamond in a diamond kimberlite pipe can be predicted from deposit tonnage using a regression model (log[largest diamond (ct)]=–1.5+0.54 log[size (mt]). The median outcrop area of diamond pipes is 12 hectares (ha). Because the pipes have similar forms, the tonnage of the deposits can be predicted by the outcrop area (log[size (mt)]=6.5+1.0 log[outcrop area (ha)]). Once a kimberlite pipe is identified, the probability is approximately .005 that it can be worked for diamonds. If a newly discovered pipe is a member of a cluster that contains a known diamond kimberlite pipe, the probability that the new discovery can be mined for diamonds is 56 times that for a newly discovered kimberlite pipe in a cluster without a diamond kimberlite pipe. About 30 percent of pipes with worked residual caps at the surface will be worked at depth. Based on the number of discovered deposits and the area of stable craton rocks thought to be well explored in South Africa, about 10^–5 diamond kimberlite pipes are present per square kilometer. If this density is applicable to the South American Precambrian Shield, more than 70 undiscovered kimberlite pipes are predicted to be present.     

利用热液金刚石压腔开展扎布耶石（碳酸锂）结晶实验的研究

花岗伟晶岩一般赋存了大量富晶体包裹体,扎布耶石(碳酸锂)是锂辉石中富晶体包裹体内的主要矿物之一,因此,扎布耶石的形成机制和温压条件对富晶体包裹体的捕获条件有重要的指示意义。本文通过热液金刚石压腔(HDAC)开展Li_2CO_3-H_2O体系的结晶实验,9组实验结果表明,扎布耶石的成核温度是550(±30)℃,大约在温度降低15℃后,晶体停止快速生长,而后缓慢生长直至在400(±50)℃完全停止生长。扎布耶石的生长主要集中在550~400℃,而与压力影响不大,处于锂辉石的稳定温度范围内,这佐证了富晶体包裹体中的扎布耶石可以是捕获流体直接结晶形成的晶体。扎布耶石开始结晶后经历了快速生长,导致包裹体内部压力降低,这可能是富晶体包裹体内存在方石英的原因之一。     

Fate of carbonates within oceanic plates subducted to the lower mantle, and a possible mechanism of diamond formation

We report on high-pressure and high-temperature experiments involving carbonates and silicates at 30–80 GPa and 1,600–3,200 K, corresponding to depths within the Earth of approximately 800–2,200 km. The experiments are intended to represent the decomposition process of carbonates contained within oceanic plates subducted into the lower mantle. In basaltic composition, CaCO₃ (calcite and aragonite), the major carbonate phase in marine sediments, is altered into MgCO₃ (magnesite) via reactions with Mg-bearing silicates under conditions that are 200–300°C colder than the mantle geotherm. With increasing temperature and pressure, the magnesite decomposes into an assemblage of CO₂ + perovskite via reactions with SiO₂. Magnesite is not the only host phase for subducted carbon—solid CO₂ also carries carbon in the lower mantle. Furthermore, CO₂ itself breaks down to diamond and oxygen under geotherm conditions over 70 GPa, which might imply a possible mechanism for diamond formation in the lower mantle.     

Underground geotechnical and geological investigations at Ekati Mine–Koala North: case study

Since 1998, BHP Billiton has mined diamonds at the Ekati Diamond Mine™ near Lac de Gras in the Northwest Territories of Canada. Current operations are based on mining multiple pipes by the open-pit method, but as some pits deepen, converting to underground mining is being considered.

As a test of underground mining methods and to provide access to the lower elevations of the Panda and Koala pipes, the Koala North pipe is being developed for underground mining. Initially, the top 40 m of the pipe were mined as an open pit to provide grade information and a prepared surface for the transition to underground mining. Currently, Koala North is being developed as an open-benching, mechanized, trackless operation. Although the method was successfully used at several De Beers diamond operations in South Africa, it has never been tested in an Arctic environment.

This case study describes basic geology, mining method layout and ongoing geological and geotechnical investigation. From the beginning of underground development, geotechnical daily routines have been fully integrated within the technical services department, which supports the operation. Geotechnical, geological and structural information obtained from underground mapping and core logging is compiled, processed, reviewed and analyzed on site by the geotechnical staff. Conclusions and recommendations are implemented as part of the operations in a timely manner. This ongoing “live” process enables the operators to make the most efficient use of resources both for ground support and excavations as well as to address safety issues, which are the top priority.