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1.
The genesis and primary source of the well-known diamond placers in the Umba-Pizhma region of Timan still remain unclear. Diamonds are not associated with the typical index minerals of the ultramafic assemblage. Epigenetic rare earth aluminophosphates (florencite, goyazite, etc.) occur as individual grains or supergene coatings on the diamonds’ surfaces without any relation to the primary diamond assemblage. They are often observed over syngenetic metal films on the diamond crystals’ surfaces. These minerals also occur as secondary inclusions in pores of leucoxene from the Pizhma deposit, as well as in Brazilian carbonados. Owing to their typomorphic features, aluminophosphates may be used as the secondary index minerals of the diamonds.  相似文献   

2.
Large deposits of diamonds are associated mainly with kimberlites (and related rocks) of the cratons, but they are also known in the folded belts surrounding them. As an example is the Baltica craton and the surrounding its the Ural‐Timan (UT) folded belt. With the first object are associated diamonds of the Arkhangelsk (kimberlites and placers) provinces, and with the second one ‐ mostly placer deposits of the UT province, the probable source of which are also kimberlites. The structural position, composition and age of the potentially diamond‐bearing complexes of the Urals and Timan make it possible to propose a new petrological‐geodynamic interpretation of their formation. According to this model, during the Vendian‐Cambrian subduction of the Pechora Ocean crust, several different depth complexes have been formed, being changed in the western direction. At a shallow depth level the oceanic crust subduction is accompanied only by fluid processing, without the magmatism participation. As a result, this process leads to the formation of fluidizate‐explosive rocks of the Sertynya complex, which marks the outlet of the ancient subduction zone into the surface. At a moderately deep (up to 100–150 km) level melts are being produced, the derivatives of which are not diamond‐bearing depleted kimberlites of the Khartes (V‐Cm) complex. Apparently by the beginning of the Ordovician the active subduction of the Pechora Ocean stops. It occurs an opening of a new Ural paleoocean, and the earlier submerged the oceanic slab continues moving under the Baltica craton. At a deep (above 150 km) level the slab interaction with the mantle produces typical kimberlite magmas (from the Ordovician to the Middle Devonian) transporting diamonds to the surface of the Ural‐Timan province proper.  相似文献   

3.

The primary data are presented on gas chromatography–mass spectrometry of volatile material in diamonds from the placers in the northeast of the Siberian Platform. The new data obtained testify to the crucial role of hydrocarbons and their derivates in the processes of diamond formation within the Earth’s mantle. It was shown that the registered variations in the composition of volatile components in the treated diamonds were caused by a combination of processes including the transformation of redox conditions of the crystallization of diamonds.

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4.
Many diamond placers in the Siberian craton are heterogeneous consisting of several components that differ in origin and ages of the source. The diamonds are either kimberlite-hosted or are exotic varieties which occur mostly in the northeastern craton periphery and come from primary deposits of unknown types and ages. The two groups of diamond placers in the area represent two evolution trends: those found in Middle Paleozoic kimberlites originated in the Famennian and the exotic diamond groups became involved in sedimentation in the Carnian. The trends have been associated with successive weathering of older diamond hosts and redeposition of the minerals into younger sediments. Having joined since the Late Triassic, the two trends eventually produced a polygenetic and multistage mixture of diamond groups in placers.  相似文献   

5.
《International Geology Review》2012,54(12):1362-1366
In the southern Siberian Platform, diamonds were concentrated in placers along margins of lacustrine-alluvial plains during Jurassic tectonism and alluviation. Subsequent stages have been denudational, and the distribution of diamond deposits can be used in reconstructing pal eodrainage patterns, locating now-eroded source areas, and determining transport conditions. The Angara- Prisyan, Ilim-Nepa, Tychan-Vel'ma, Katanga, and Vilyuy diamond provinces are delineated on the basis of weight and degree of mechanical weathering of the crystals, indicating distance of travel and possible location of source area. — P. W. Wood.  相似文献   

6.
Several alternative points of view currently exist on the origin of the primary sources of diamonds from the Cenozoic Western Urals placers. Some researchers suppose that their economic diamond resource potential is related to diamonds from tuffisitic facies of the mantle kimberlites-lamproites or impact structures. Other researchers suggest that diamonds originated from the eroded sandstones of the Upper Emsian Takaty Formation of the Lower Devonian, which represents ancient (fossil) placers or intermediate reservoirs. It is assumed that these reservoirs collected diamonds from worn kimberlite bodies, which were located in the Urals or on the East European platform (EEP). This paper presents the first U-Pb (LA-ICP-MS) age of detrital zircons from quartz sandstones of the Takaty Formation, which spans a range from 1857.5 ± 53.8 to 3054.0 ± 48.0 Ma. The absence of detrital zircons younger than 1.86 Ga excludes that the structural complexes of the Uralian, Fennoscandian, and Sarmatian EEP parts were the provenance areas that supplied the clastic material to the sedimentary basin, which accumulated the Takaty Formation. The similar age of our zircons and ancient crystalline complexes of the Volga-Uralian EEP part allows consideration that it was a single provenance area. If we assume that the diamond resource potential of the Western Urals is completely or partly related to the ancient diamond placers from the Takaty Formation, then the intermediate diamond reservoirs from its structure originated due to redeposition of destruction products of primary diamond-bearing rocks of the Volga-Uralia area. Thus, within the Volga-Uralian part of the EEP basement, we may expect identification of a previously unknown stage of kimberlite formation, which is significantly older than that responsible for the diamond resource potential of the Arkhangel’sk province.  相似文献   

7.
Representative samples of diamonds from five kimberlite pipes (Lomonosovskaya, Archangel’sk, Snegurochka, XXIII Congress of the Communist Party of the Soviet Union (CPSU), and Internationalnaya) of the Arkhangelskaya and Yakutian diamond provinces in Russia have been studied. Thirty-three varieties of metal films have been identified as syngenetic associated minerals. The films consist of 15 chemical elements that occur in the form of native metals and their natural alloys. Remnants of metal films were detected within diamond crystals. The metal films coating diamonds are a worldwide phenomenon. To date, these films have been described from Europe, Asia, South America, and Africa. Native metals, their alloys, and intermetallides are actual companion minerals of diamond.  相似文献   

8.
Mosaic diamonds from the Zarnitsa kimberlite (Daldyn field, Yakutian diamondiferous province) are morphologicaly and structurally similar to dark gray mosaic diamonds of varieties V and VII found frequently in placers of the northeastern Siberian craton. However, although being similar in microstructure, the two groups of diamonds differ in formation mechanism: splitting of crystals in the case of placer diamonds (V and VII) and growth by geometric selection in the Zarnitsa kimberlite diamonds. Selective growth on originally polycrystalline substrates in the latter has produced radial micro structures with grains coarsening rimward from distinctly polycrystalline cores. Besides the formation mechanisms, diamonds of the two groups differ in origin of mineral inclusions, distribution of defects and nitrogen impurity, and carbon isotope composition. Unlike the placer diamonds of varieties V and VII, the analyzed crystals from the Zarnitsa kimberlite enclose peridotitic minerals (olivines and subcalcic Cr-bearing pyropes) and have total nitrogen contents common to natural kimberlitic diamonds (0 to 1761 ppm) and typical mantle carbon isotope compositions (-1.9 to -6.2%c 513C; -4.2%c on average). The distribution of defect centers in the Zarnitsa diamond samples fits the annealing model implying that nitrogen aggregation decreases from core to rim.  相似文献   

9.
Doklady Earth Sciences - Based on a study of diamond grains from placers of the northeastern Siberian Platform, it is shown that certain types of diamonds (rounded dodecahedroids, diamonds of the...  相似文献   

10.
Large diamond placers have been discovered in a Rhaetian basal horizon (Upper Triassic) in the north of the Sakha Republic (Yakutia) in the drainage areas of the Eekit, Nikabyt, Kelimyar, and Bur Rivers. In typomorphic features the found diamonds and indicator minerals of kimberlites are completely similar to those from Carnian basal horizons but, in contrast to them, are well sorted, and pyropes show features of mechanical wear. Analysis of the geologic evolution of the study area, morphology of diamonds and indicator minerals, and composition of the latter showed that the Rhaetian productive sediments resulted from the erosion of Carnian placers.  相似文献   

11.

The first results are presented for the synthesis of diamond at 6.5 GPa and 1600°C during migration of molten iron through a silicate matrix, which is composed of olivine crystals with interstitial graphite. The experiment shows that diamonds in the Earth’s mantle and the terrestrial planets could have formed during differentiation. Diamond crystals, which were formed during iron segregation of the Earth’s differentiation, could be centers for further crystallization of mantle diamonds.

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12.
以碳酸盐为碳源生成金刚石的实验研究   总被引：4，自引：0，他引：4  
本世纪五十年代初,在金属触媒物质的参与下,由石墨得到金刚石的成功,标志着人工合成超硬材料及高温高压技术两方面的巨大突破。三十年来的科学研究和生产实践推动着这一领域不断地向纵深发展,并提出了建立在不同理论基础上的金刚石生成方法,如爆破法、晶种法、气相生长法、常压高温法、薄膜推移法等等。  相似文献   

13.
The complex of antiquity guides testifying to the origin of diamonds from Precambrian sources is discussed. The tectonic setting of diamond placers related to Precambrian sources is characterized. It is emphasized that identification of ancient diamonds is important for the forecasting of their primary sources.  相似文献   

14.
Natural diamonds from the Ural alluvial deposits have been studied by FTIR spectroscopy. It is shown that these diamonds are similar in some typomorphic features, such as nitrogen content and aggregation state, to the diamonds of the Coromandel (Brazil) and Verkhnee Molodo (Lena region, Yakutia) placers and to the diamonds from kimberlites of the Arkhangel’sk Region but differ significantly in lower contents of hydrogen and higher contents of platelets. The high contents of hydrogen (5–20 cm–1) determined in some diamonds are due to the specific formation of their internal structure and to the presence of inclusions. The nonuniform distribution of nitrogen A- and B-centers throughout the crystal testifies to the zonal structure of diamonds. The temperature conditions of formation of the Ural diamonds have been estimated.  相似文献   

15.
The paper reports the results obtained by the detailed studying of carbonado (the first find in a gold placer in Primorie) and a collection of diamonds that was confiscated in 1937 from a poaching small digger and was kept safe at the Nezametnyi mine (near the village of Vostretsovo), which had developed this placer deposit. In the concentrate from the placer, carbonado is associated with green corundum, various ilmenite, zircon titanian amphiboles and pyroxenes, rutile, anatase, and fragments of subvolcanic biotite picrites. All of these minerals, native aluminum, and tin occur as inclusions in the diamonds. The carbonado from Primorie was determined to be practically identical to this mineral from Brazil, has a porous structure, is characterized by orange luminescence, contains inclusions of Y, Ce, La, Ba, and Sr phosphates, and has an isotopically light composition of its carbon (13C from ?25 to ?32‰). Pores of the carbonado aggregates contain clusters of diamond crystals. The collection of diamonds from an unknown source included six gem-quality transparent crystals, one rounded ballas, two cuboctahedral crystals (one of greenish and the other of silver-gray color, both with outer coats), and one black carbonado grain. The data obtained on the mineralogy of the diamonds have demonstrated that they are completely identical to this mineral from kimberlites and lamproites but bear traces of intense dissolution, fragmentation, multiple recrystallization, and graphitization at defects, which are the most widespread in the ballas. One of the crystals was determined to contain inclusions: aggregates of potassic omphacite (0.50 wt % K2O) and corundum. Ilmenite (containing up to 8 wt % MgO), titanaugite, kaersutite (4 wt % TiO2, 0.8 wt % K2O), and churchite (aqueous phosphate) were obtained from the core of the ballas. The titanaugite, kaersutite, and ilmenite were proven to be compositionally analogous to these minerals from picrites occurring near the placer. The carbon isotopic composition δ13C of the cores of the single diamond crystals varies from ?6 to ?11‰. The margins of the grains were proved to be enriched in the light carbon isotope (δ13C from ?19 to ?21‰). The gem-quality transparent diamond crystals are characterized by blue luminescence, and the color of luminescence in the carbonado varies from orange red in the bulk of the aggregate to yellowish green in its core. The aforementioned transformations of diamonds were likely caused by their transportation in pipes of micaceous picrites of the Jurassic meymechite complex. The carbonado are thought to correspond to the final stage of the metastable recrystallization (in pores, within the temperature range of the rutile-anatase transition) of the original isotopically heavy diamonds under the effect of various oxidizers (H2O, CO2, F, and others) and in the presence of catalytically acting REE, Ti, and P. The primary diamond source (kimberlite or lamproite) can be older and more distant from the study area. The complete geological analogy between the study area in Primorie, Kalimantan Island in Indonesia, and West Australia (where no sources of the placers are known) led us to consider the territory of Primorie as promising for exploration for diamondiferous placers.  相似文献   

16.
Two samplings of 65 diamond crystals divided by the intensity of a slow X-ray luminescence component are studied from the Arkhangel’skaya and Karpinskogo-1 pipes. IR and EPR spectroscopies revealed a relationship between the nitrogen A and P2 centers of the diamonds and the presence of a slow X-ray luminescence component. Its absence in most diamonds with high content of P1 (C) centers is explained by the low number of A and P2 centers.  相似文献   

17.
The objects of study are Triassic hypabyssal diamondiferous kimberlites with an age of 220-245 Ma, containing macrocrysts of unaltered olivine. The latter are close in the time of formation to the main stage of intrusion of the Siberian Trap Province (252 Ma), which lasted less than 1 Myr. A comparative high-precision analytical study of the Ti, Ca, Cr, and Al impurity patterns in about 1000 olivine macrocryst samples with a forsterite content Fo = (100Mg/(Mg + Fe)) of 78 to 93 has demonstrated the effect of traps on the lithospheric composition. A comprehensive comparative study of diamonds from northern placers and Triassic kimberlites, including determination of their carbon isotope composition, was performed. Chromatography-mass-spectroscopic analysis of submicron fluid inclusions in diamonds from northern placers and kimberlites has shown predominant hydrocarbons of a wide range of compositions and subordinate contents of N2, H2O, and CO2. These findings, together with the results of previous studies of subcalcic Cr-pyropes and diamonds found in the Lower Carboniferous gritstones of the Kyutyungde graben, lead to the conclusion that the Toluopka kimberlite field is promising for Paleozoic kimberlites. The results of comprehensive studies of diamonds and indicator minerals and U/Pb isotope dating of numerous detrital zircon samples from the basal horizon of the Carnian Stage (Upper Triassic) of the Bulkur site in the lower reaches of the Lena River suggest the presence of diamondiferous kimberlites within the northeastern Siberian Platform. The age of the probable primary diamond sources in the study area can be evaluated by an integrated U/Pb isotope dating of zircons, perovskites, and rutiles from the developed diamond placers and the basal horizon of the Carnian Stage.  相似文献   

18.
Structural defects formed as a result of plastic deformation in natural diamond crystals have been studied by EPR spectroscopy. The spectra of brown, pink-brown, black-brown, pink-purple, and gray plastically deformed diamonds of type Ia from deposits in Yakutia and the Urals were recorded. The results of EPR spectroscopy allowed us to identify various deformation centers in the structure of natural diamonds and to show that nitrogen centers were transformed under epigenetic mechanical loading. Abundant A centers, consisting of two isomorphic nitrogen atoms located in neighboring structural sites, were destroyed as a result of this process to form a series of N1, N4, W7, M2, and M3 nitrogen centers. Such centers are characterized by an anisotropic spatial distribution and a positive charge, related to the mechanism of their formation. In addition, N2 centers (probably, deformation-produced dislocations decorated by nitrogen) were formed in all plastically deformed diamonds and W10 and W35 centers (the models have not been finally ascertained) were formed in some of them. It has been established that diamonds with various types of deformation-induced color contain characteristic associations of these deformation centers. The diversity of associations of deformation centers indicates appreciable variations in conditions of disintegration of deep-seated rocks, transfer of diamonds to the Earth’s surface, and formation of kimberlitic deposits. Depending on the conditions of mechanical loading, the diamond crystals were plastically deformed by either dislocation gliding or mechanical twinning. Characteristic features of plastic deformation by dislocation gliding are the substantial prevalence of the N2 centers over other deformation centers and the occurrence of the high-spin W10 and W35 centers. The attributes of less frequent plastic deformation by mechanical twinning are unusual localization of the M2 centers and, in some cases, the N1 centers in microtwinned lamellae. Numerous data on models of deformation centers in natural diamonds, including the M2 and M3 centers, which were observed in the studied collection for the first time, are discussed.  相似文献   

19.
山东蒙阴金刚石的形成时代及地质环境   总被引：4，自引：0，他引：4  
对山东蒙阴胜利1号岩管的金刚石样品进行了CL、FTIR、RAMAN等测试。结果表明,除部分样品阴极发光显示平直的生长色带外,多数金刚石显示均一的CL颜色,说明金刚石生长过程连续,未遭受明显的溶(熔)蚀,不同于复县的多数金刚石。依据金刚石中N的聚集状态,估算了蒙阴金刚石主要形成于三个时期:1·8~1·7 ,1·3 ~1·1和0·9 ~0·6 Ga。有意义的是,这三个时期与华北克拉通三次伸展事件时间相吻合。通过金刚石中橄榄石包裹体拉曼漂移,计算出源区压力为4·6 ,5和5·5 GPa ,得出蒙阴金刚石形成的深度分别为:152 ,165和181 km,靠近岩石圈底部。上述成果为蒙阴金刚石的形成提供了时间、空间、压力等重要地质信息。  相似文献   

20.
In this paper, we consider an ontogenic model for the formation of morphological types of growth and dissolution of cubic diamonds of variety II by Yu.L. Orlov from placers of the Anabar diamondiferous region. The following ontogenic domains of crystals and corresponding evolutionary stages of growth accompanying a general decrease in supersaturation in the crystallization medium were distinguished: microblock mosaic cuboids with defects produced by the mechanism of rotational plastic deformation–cuboids with linear translation deformations–cuboids and antiskeletal growth forms of cuboids composed of octahedral growth layers–pseudocubic growth forms of a flat-faced octahedron. The crystal morphological evolution of cuboids during the bulk dissolution of individuals in fluid-bearing melt transporting them to the surface was traced. The investigation of transitional forms of cuboid diamond dissolution showed that the final form of diamond dissolution is a rounded tetrahexahedroid independent of the combination of cuboid faces with subordinate faces of octahedron, rhombododecahedron, and tetrahexahedron observed on resorbed crystals of cubic habit. It was found that the final stages of cuboid dissolution produced disk-shaped microrelief features on the diamond surface in the form of randomly distributed ideal rounded etch pits resulting from interaction with microscopic cavitation gas bubbles released during the decompression of ascending kimberlite melt.  相似文献   

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