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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.
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   

9.
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   

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   

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