The phosphate-containing interlayers of the Bazhenov Formation as potential reservoirs

The possible reservoir type of the Bazhenov Formation relative to the intervals enriched in phosphates (apatite varieties) is described in this work. The phosphate rocks are characterized by a highly developed pore space; their porosity can reach up to 14%. Along with this, these rocks have explicit geochemical characteristics of oil-reservoir rocks in comparison with other rock samples in the well. As an example, the productivity index and oil-saturation index for phosphates are twice as high as the background values. The composition of such rocks can slightly vary: fluorine can be observed in phosphate minerals, while the rock is always enriched in organic matter (>8 wt %).     

Off-axis structures of spreading zones according to results of experimental modeling

The off-axis topography of spreading ridges is a result of tectonic and magmatic processes occurring in the axial zone and operating off the ridge axis during further evolution of the crust. The results of physical and numerical simulations have shown that differences in topography roughness, rift valley depth, frequency and amplitude of normal faults, and geometric stability of the rift axis are determined by (a) the rate of extension and accretion of the new crust, (b) the thickness of the brittle lithospheric layer, and (c) the temperature of the underlying asthenosphere. Under conditions of the fast spreading, the stationary axial magma chamber in the crust predetermines the existence of the thinner and weakened lithosphere. As a result, the axis jumps for a short distance and the axis geometry remains almost rectilinear. The destruction of the thin axial lithosphere with a low mechanical strength results in formation of frequent and low-amplitude normal faultings. All these factors lead to the formation of the characteristic poorly dissected topography of fast-spreading ridges. Without a stationary axial magmatic chamber in the crust of slow-spreading ridges and with a thick and strong lithosphere, a deeply dissected axial and off-axis topography arises. The axis jumps for a significant distance within the rift valley, giving rise to geometric instability of the axis and development of transform and nontransform offsets.     

Geochemical technique of organic matter research in deposits enrich in kerogene (the Bazhenov Formation,West Siberia)

The international interest in shale oil has recently provoked special attention to the Russian unconventional oil-source formations, including the Bazhenov Formation of West Siberia, domanik deposits in the Volga–Ural region, and the lower Maikop Group of the Cis-Caucasus. High contents of para-autochthonous soluble organic matter (bitumen) in clayey–carbonate, clayey–siliceous, carbonate–clayey–siliceous rocks with low filtration–capacity properties results in significant uncertainties in the identification of the generation potential of organic matter (OM). Examination of a large database on the OM of the Bazhenov Formation allowed us to propose an optimum complex technique for study of the source rock potential and assessment of the amount of produced hydrocarbons in the kerogen-rich sediments. The investigations include a combination of Rock Eval pyrolysis prior to and after extraction with different solvents, the comparison of bituminological and pyrolytic characteristics, and the determination of the group composition of soluble organic matter, as well as chromatography and chromato-mass spectrometry.     

Paleogeography of the Bazhenov Formation of Western Siberia According to the Distribution of Rare Earth Elements

Doklady Earth Sciences - The Bazhenov Formation is represented by Late Jurassic black shales. Russia is the first in the world by the reserves of shale oil, which is mostly related to the Bazhenov...     

The main types of sections of the oil-bearing Bazhenov Formation on the Northeastern Surgut Arch

The lithological study of the core samples of the Bazhenov Formation that are exposed on the northeastern Surgut arch allowed us to distinguish three types of sections, which are ascribed to the different parts of an ancient intrabasin uplift. Moving from the arch to its peripheral parts, these types demonstrate a successive change in the prevailing sedimentation type from carbonate–clayey–siliceous via siliceous to clayey–siliceous types     

Overview of some Colombian gold deposits and their development potential

Source rock gold deposits in Colombia include Proterozoic unconformity-related paleoplacers, Palaeozoic stratabound Au/Ag-Cu-Pb-V-U red bed-type ores, and Mesozoic/Tertiary hydrothermal vein systems of Cordilleran magmatic arcs. The younger metallogenic episode occurred some 8 Ma ago in the Western Cordillera. Epithermal deposits are generally small (> 10,000–1 Mt grading 5–10 g/t Au) and the precious-base metal (Cu, Zn, Fe) association was probably deposited within the temperature range 180–300 °C. Widespread palaeoplacers in Quaternary terraces with enrichment in old channels, as well as extensively dredged alluvial deposits in presently active sediments, are connected with ongoing Andean uplift and erosion. Palaeochannel and alluvial gold concentrations represent the most promising targets for future exploration. An additional output could also derive from the clastic-hosted, stratiform deposits of the shield and E Cordillera.     

An experimental approach to the palynology of cave deposits

Surface sediment, speleothems, and bat guano from two adjacent, topographically different cave sites in eastern Spain have been studied palynologically to elucidate the potential of cave sediments for palaeoenvironmental reconstruction. A cave opening with a large entrance and constant width presented far fewer problems of alteration in the pollen assemblages than a sac‐like cave opening with a constricted entrance. Pollen concentration is linked primarily to the amount of pollen input rather than to the result of post‐depositional alteration. Sampling should be undertaken away from parietal and rear areas and avoiding moisture zones. Lateral differences in the pollen spectra indicate that sampling should be on the basis of a multiple‐profile approach and selection of dry rather than wet sediments. If these procedures are followed, within‐cave sediments can realistically reflect not only local but also regional vegetation of the site. Copyright © 2000 John Wiley & Sons, Ltd.     

Organic Carbon versus Major Elements Relationship in Rocks of the Bazhenov Formation,Western Siberia

A close relation of the organic carbon (C_org) content with major has been established for rocks of the Upper Jurassic–Lower Cretaceous Bazhenov Formation. Applying the method of multiple linear regression, it has been demonstrated that the C_orgcontent in rocks of the Bazhenov Formation is stringently controlled by its bulk chemical composition. This inference is consistent with the existing ideas regarding a close interrelation between the following main components of rocks: organic carbon and authigenic quartz formed on remains of Radiolaria; pyrite formed in a highly reducing medium of C_org-rich sediments; and terrigenous clayey material diluting the authigenic siliceous–carbonaceous–pyritic matrix. These components chiefly determine the spectrum of major elements in the Bazhenov Formation. The establishment of the close relation between the C_orgcontent and the group of major elements refutes the suggestion of some authors that siliceous material was supplied to nonlithified sediments of the Bazhenov sea by hydrothermal solutions, because this mechanism would have inevitably upset geochemical relations between elements in the studied rocks.     

Formation of Strata—bound Ore Deposits in China：Studies on Fluid Inclusions

Fluid inclusion studies were made on the basis of the geological data on the strata-bound ore de-posits of China including those of Pb,Zn,Au,Ag,Sb,U,Hg,W,quartz-crystal and sparry-calcite.An attempt was made to approach the model of formation for each type of ore depos-its by considering the material sources,the migration of fluids and the conditions of mineralization.It is found that ore-forming fluids (especially H2O)originate as heated underground water reacts with the wallrocks and dissolves Na^ ,Ca^2 ,K^ ,Cl^ ,HCl^- and Mg^2 .The ore fluids are mainly of NaCl-Ca-HCO3-H2O system with salinities ranging from 4to 14wt.%.NaCl equivalent and densities ranging from 0.9 to 1.0g/cm^3.It may be concluded that the deposits were formed at temperatures ranging from 150 to 250℃ under pressures from 300 to 1000 bars.Ore deposition may have been controlled by temperature and pressure or by the mixing among different fluids.     

Models of the REE distribution in the black shale Bazhenov Formation of the West Siberian marine basin,Russia

Rare-earth elements abundance in black shales of the Upper Jurassic (Tithonian Stage)–Lower Cretaceous (Berriassian Stage) Bazhenov Formation is discussed. This formation is the principal oil source rocks of West Siberia. The deposits within the formation can be subdivided into two main marine groups: (a) moderately hemipelagic deposits (clayey-siliceous, including phosphatic and carbonate rocks) and low-density distal clayey turbidites (argillites), both are considered as normal and (b) silty argillites and clayey-silt rocks, which are channel deposits and considered as anomalous. The hemipelagic rocks of normal sections, which are enriched in the rare-earth elements (REE), accumulated under both slow rates of sedimentation (clayey-siliceous rocks) and faster rates of sedimentation (argillites). The channel deposits of anomalous sections, which are impoverished in the REE, accumulated exclusively under fast rates of sedimentation.Within the hemipelagic group the rate of sedimentation of the argillites was faster than of the clayey-siliceous rocks, but the REE concentration in the former rocks (140.4 ppm) is higher than in the latter group (97.4 ppm). The argillites are more than twice enriched in clayey material than clayey-siliceous rocks. It is likely that the clay fraction was the main carrier of REE in these rocks. In the channel group of rocks, the REE abundance in clayey-silt rocks (21.2 ppm) is lower than in the silty argillite (84.6 ppm), in which the clay content is elevated.With respect to redox potential the Bazhenov Formation rocks can be subdivided further into three groups, based on the degree of pyritization index (DOP): (1) the highly reducing clayey-siliceous rocks of normal sections, with high DOP; (2) the substantially reducing argillites and carbonate rocks of normal sections, with intermediate DOP; (3) the moderately reducing rocks of anomalous sections with low DOP. The rocks with the high DOP (group 1) are characterized by ΣLREE/Σ(M+H)REE ratios between 7.37 and 7.5, whereas the rocks with the lower DOP (group 2 and 3) are characterized by ΣLREE/Σ(M+H)REE ratios between 12.8 and 13.5. Negative Ce anomalies are either small or absent in all deposits, which is typical for reducing conditions.Thus, the Bazhenov Formation exemplifies the complex depositional conditions that influence the REE concentration in black shale. However, it is this very complexity that has contributed to the development of six separate depositional models (REE contents in ppm are given in brackets). (1) Phosphatic clayey-siliceous rocks of normal sections (367.95); (2) argillites of normal sections (130.73); (3) clayey-siliceous rocks of normal sections (85.97); (4) carbonate rocks, largely dolomites of normal sections (23.23); (5) silty argillites of anomalous sections (78.7) and (6) clayey-silt rocks of anomalous sections (19.66).     

Nickel,molybdenum, and cobalt in the black shales of the Bazhenov Formation of the West Siberian basin

It was shown that the contents of Ni, Mo, and Co in the siliceous clay black shale rocks of the normal sections of the Bazhenov Formation are several times higher than the global mean contents of these elements in black shales. These rocks have the highest contents of pyrite and organic carbon and show evidence for strongly reducing formation conditions at the slowest background rate of sedimentation of their material. A transition from the siliceous clay rocks to the mudstones of normal section, which are considered as turbidites, and further to the mudstones and clayey silt rocks of the so-called anomalous sections (deposits of submarine deltas and canyons) is accompanied by sequential depletion in pyrite and organic carbon, a decrease in indicators of the reduction level of the sedimentation environment, and an increase in sedimentation rate and clay material content. Simultaneously, the contents of the elements of interest decreases in the sequence Mo > Ni > Co. In the rocks of anomalous sections, the contents of these elements decrease to the level of their mean abundances in clays.     

The Composition and Reservoir Properties of the Deposits of the Bazhenov Formation in the Central Part of the Tundrin Depression

The section structure was characterized according to the lithological and petrophysical studies of the core from the Bazhenov Formation that has been uncovered in the central part of the Tundrin Depression. The productive oil intervals where the reservoirs of the pore and fissure-pore types occur were identified.     

Formation of mineral deposits in relation to structural developments of the kaapvaal craton

The relation between tectonics, magmatism, and mineralisation of the South African Precambrian shield is discussed. A geosynclinal and a synorogenic stage follow a long period of cratonic tectonics with associated magmatism and important mineralisation. Three different types of magma are distinguished: Primary simic magma partly of alkali character, hybrid magma of predominantly intermediate composition, and palingenetic acid magma mainly of calk-alkali character. It appears difficult to assign magmatism and mineralisation of the cratonic super-structure to any of Stille's geotectonic stages. Cratonic tectonics with considerable juvenile-basaltic as well as palingenetic magmatism characterize this stage which is associated with large mineral deposits. This stage is named cratonic.

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Zusammenfassung Die Beziehungen von Tektonik, Magmatismus und Lagerstättenbildung werden am ältesten Teil des präkambrischen südafrikanischen Schildes untersucht. Ein geosynklinales und ein synorogenes Stadium werden von einem langen Zeitraum gefolgt, der durch kratone Tektonik mit zugehörigem Magmatismus gekennzeichnet ist. Drei Magmatypen werden unterschieden: Primäres simisches Magma vorwiegend von Alkalicharakter, hybrides Magma von vorwiegend intermediärer Zusammensetzung und palingenes saures Magma vorwiegend kalk-alkalischen Charakters. Eine Zuordnung des Magmatismus und der Mineralisation des kratonen Oberbaues zu einem der geotektonischen Stadien im Sinne von H. Stille erscheint nicht möglich. Kratone Tektonik mit erheblichem juvenil-basaltischen wie auch palingenem Magmatismus charakterisieren dieses als kratonisch bezeichnete Stadium, mit dem bedeutende Lagerstättenbildung verknüpft ist.

     

Dynamics of the Formation of Globular Silica Particles according to Dynamic Light Scattering

For the first time, the dynamics of the origination and growth of monodispersion spherical silica particles is studied by dynamic light scattering in the real-time mode. Experimental changes in the particle size and intensity of scattering during their formation and growth indicate the hierarchical formation of silica globules under various mechanisms of aggregation of particles.     

丽江东部地区黑泥哨组铜矿成矿规律及潜力分析

丽江东部地区广泛分布的黑泥哨组（P₃h）是区域上一个重要的含铜层位,在该地区大公山、铜厂河、宝坪等地均发现有工业铜矿床。该地层中发现的铜矿床具有两种类型：产于火山沉积夹层中的火山沉积-热液型铜矿及产于构造破碎带中的构造热液型铜矿。主要控矿因素为二叠纪晚期古地理环境、火山活动、成矿前构造及喜山期岩浆活动。本文通过分析这些控矿因素之间的关系,总结该区域内黑泥哨组铜矿化规律,为今后的找矿工作提出一些建议。     

Formation of the strata-bound Kellhuani tin deposits,Bolivia

A magmatic-hydrothermal model of tin ore formation can best explain the geological, petrographical and geochemical data on the strata-bound Kellhuani tin district. The tin specialization of the magmatic system of the Chacaltaya porphyry stock, centered in the Kellhuani mining area, is the result of advanced fractional crystallization. The regional tin background of the least fractionated members of the Cordillera Real granite series and of their sedimentary country rocks corresponds to average crustal tin contents.Dedicated to Prof. H.-J. Schneider on the occasion of his 60th birthday     

Structure of the Zeya block of Toko Stanovik according to results of magnetotelluric sounding

The paper describes the results of magnetotelluric sounding (MTS) carried out in the Zeya block of the Stanovoi megablock, in the area of its junction with the Aldan Shield. The border between them runs along the Stanovoi fault. Based on the results of interpretation of MTS curves and the gravity, magnetic, and geological data, geological/geophysical sections have been constructed to a depth of 7 km along two ~ 20 km long profiles running across the Stanovoi fault. About 1 km thick and approximately 2 km long conductivity zone has been distinguished beneath the Okonon plateau of Quaternary basalts with electrical resistivity of < 100 Ohmm. This anomaly is associated with ore mineralization in Early Proterozoic gabbro intrusion. A 3D density modeling was performed. High-density bodies of NW strike dip to the northeast to a depth of 25 km in the area of the Okonon basalt plateau.^?Corresponding author.     

Deep structure of Kamchatka according to the results of MT sounding and seismic tomography

The key features in the distribution of geoelectric and velocity heterogeneities in the Earth’s crust and the upper mantle of Kamchatka are considered according to the data of deep magnetotelluric sounding and seismotomography. Their possible origin is discussed based on the combined analysis of electric conductivity and seismic velocity anomalies. The geoelectric model contains a crustal conducting layer at a depth of 15–35 km extending along the middle part of Kamchatka. In the Central Kamchatka volcanic belt, the layer is close to the ground surface to a depth of 15–20 km, where its conductivity considerably increases. Horizontal conducting zones with a width of up to 50 km extending into the Pacific Ocean are revealed in the lithosphere of eastern Kamchatka. The large centers of current volcanism are confined to the projections of the horizontal zones. The upper mantle contains an asthenospheric conducting layer that rises from a depth of 150 km in western Kamchatka to a depth of 70–80 km beneath the zone of current volcanism. According to the seismotographic data, the low- and high-seismic-velocity anomalies of P-waves that reflect lateral stratification, which includes the crust, the rigid part of the upper mantle, the asthenospheric layer in a depth range of ~70–130 km, and a high-velocity layer confined to a seismofocal zone, are identified on the vertical and horizontal cross sections of eastern Kamchatka. The cross sections show low-velocity anomalies, which, in the majority of cases, correspond to the high-conductivity anomalies caused by the increased porosity of rocks saturated with liquid fluids. However, there are also differences that are related to the electric conductivity of rocks depending on pore channels filled with liquid fluids making throughways for electric current. The seismic velocity depends, to a great extent, on the total porosity of the rocks, which also includes isolated and dead-end channels that can be filled with liquid fluids that do not contribute to the electric-current transfer. The data on electric conductivity and seismic velocity are used to estimate the porosity of the rocks in the anomalous zones of the Earth’s crust and the upper mantle that are characterized by high electric conductivity and low seismic velocity. This estimate serves as the basis for identifying the zones of partial melting in the lithosphere and the asthenosphere feeding the active volcanoes.