Lithology and Mineral Resources最新文献

This article presents results of the comprehensive study (composition, reservoir properties, geophysical parameters, and age) of altered felsic volcanic rocks (rhyolites, dacites) associated with the Permian-Triassic intermediate structural level of the West Siberian. As a result of secondary alteration, oil and gas reservoirs can form in these volcanic rocks. Taking into account their occurrence depth (more than 2 km), they are available for study only from core and geophysical data. Based on the results of core studies, 25 petrographic varieties of felsic volcanics were established. The combination of such features as 1) structural and textural features, 2) degree of secondary alteration, and 3) peculiarities of logging curves made it possible to group these numerous petrographic varieties into six key rock types. At the same time, the distinguished rock types are characterized by different reservoir properties (porosity, permeability). All 443 samples representing various rock types are characterized by similar geochemical composition, and the U-Pb ages obtained by the zircons (254 ± 2–248.2 ± 1.3 Ma) indicate that the studied felsic volcanics belong to a single tectonic-magmatic stage at the Permian-Triassic boundary. According to seismic data, it was revealed that within the Frolov megadepression (the central part of Western Siberia), the studied volcanic rocks are distributed within grabens. In particular, the boundaries of a relatively large (70 km wide and 200 km long) graben-like Rogozhnikov-Nazym structure were adjusted, and several similar, but smaller structures were identified. A comprehensive analysis of core, log and seismic data made it possible to determine the morphology and spatial relationships of volcanic bodies composed of various types of felsic volcanic rocks, providing the basis for predicting intervals of the section with the best reservoir properties.

Data on the temperature and heat flow distribution in the sedimentary cover of the Astrakhan arch in the Caspian Basin are considered. Depth temperatures in 2D and 3D models with the thermal tomography technology are carried out. Parameters for this calculation are represented by original data on the thermophysical properties of sedimentary cover rocks and the concentration of long-lived isotopes in rocks. Palinspastic reconstructions of the sedimentation history of the cover served as the basis for calculating the temperature evolution over 400 Ma.

The paper reports original data on the isotopic composition (δ¹³С, δ¹⁸О) and major and rare earth element (REE) geochemistry of manganese ores in the Rodinauli section of the Kvirila deposit (Georgia). The δ¹³С (V-PDB) and δ¹⁸О (V-SMOW) values vary from –19.6 to –6.6‰ and from 21.1 to 29.1‰, respectively, in the carbonate ores; and from ‒14.9 to ‒5.5‰ and from 21.8 to 28.4‰, respectively, in the carbonate substance of cement of oxide ores. The studied ores are characterized by the presence of negative Ce anomaly (({{{text{Ce}}} mathord{left/ {vphantom {{{text{Ce}}} {{text{Ce}}_{{{text{PAAS}}}}^{*}}}} right. kern-0em} {{text{Ce}}_{{{text{PAAS}}}}^{*}}}) up to 0.51) in majority of samples (both carbonate and oxide ores); the prominent Eu anomaly is absent. A conclusion has been made that the ores were formed both under conditions of early diagenesis of sediments and later, during catagenesis, with the participation of metal-bearing elisional solutions.

Sedimentary material sampled in the southwestern Kara Sea both directly in ice scours and on background surfaces undisturbed by ice scouring has been studied. Based on studies of the physical properties and lithomineralogical features of bottom sediments in the ice scours, the boundary of ice scouring impact (exaration contact) was identified. Based on the X-ray diffraction analysis of <0.001-mm fraction, the chlorite structure is sensitive to temperature in samples taken below this contact, in contrast to the overlying samples. Together with the results of microscopic studies of thin sections, this fact indicates the neoformation of chlorite. The presence of secondary chlorite in near-surface conditions can suggest the glaciodynamic impact (pressure) of iceberg keels on bottom sediments. Microstructures of the ice scour sediments differ both in different test sites of the study area and within the same scour, depending on the location of sampling point on the transverse profile of morphosculpture.

A new occurrence of phosphate mineralization (Shankinka) has been explored in the Fedkovskaya River mouth, Ruza district, Moscow region. The most common mineral phases are delvauxite, mitridatite, fluorapatite, and crandallite. The Fe–Ca–Al phosphate occurrences in the region are associated with the Bajocian–Bathonian paleovalleys embedded in Carboniferous rocks and partially filled with Callovian sediments. The structural features of the phosphatization zone along with its enrichment with Co, Ni, Zn, Cu, and REE indicate a possible link between the overlying Oxfordian sediments and phosphate mineralization. The epigenetic phosphate mineralization can be related to the seepage of phosphorus-rich interstitial waters released from the Oxfordian organic-rich sediments into the underlying Callovian friable rocks enriched with Fe minerals.

Dhodak concession is a part of eastern margin of Sulaiman Fold and Thrust Belt formed as a result of complex transpressional interactions during the Indian-Eurasian collision. Study area reveals the compressional structures that provide suitable hydrocarbon traps of Cretaceous age. Different lithological boundaries and structural properties are identified from 2D seismic, amplitude, and frequency derived seismic attributes. Time and depth structural mapping of the Pab Sandstone (Late Cretaceous) demonstrated an ideal doubly plunging anticlinal structure that represents four way closure for hydrocarbons accumulation in the study area. Observed relatively low-frequency anomaly confirms the hydrocarbon-bearing reservoirs. Since hydrocarbon quantity in a reservoir also depends on the generation potential of source rock, so an attempt has been made to estimate the Total Organic Carbon (TOC) of the source i.e. Sembar Formation. The latter was divided divided into three parts based on the calculated TOC using the Δ log R technique. Upper and lower parts of the Sembar Formation chiefly comprise the lower TOC values (1.90 and 2.1 wt %), whereas the middle part comprises the higher TOC values averaging 3.01 wt %.

The article presents the results of studying alteration of the hydrothermal solution composition during its percolation in the Pleistocene sediments drilled by ODP Hole 858B (38.6 m deep) in the northern segment of Middle Valley, Juan de Fuca Ridge (Dead Dog hydrothermal field), 20 m away from the hydrothermal source with a temperature 276°C. Influence of sediments in Units I, IIB, and IID from this hole on the solution composition variation during the solution–sediment interaction has been established. The greatest influence on the solution composition occurred during its interaction with sediments of Units IIB and IID under high-temperature conditions (200–350°C) expressed in enrichment of the solution with a large amount of chemical elements. A possible alteration in the solution composition is shown in the process of solution–sediment interaction during its percolation in the sedimentary cover 250–300 m thick.

The study of terrigenous rocks of the Shatak Complex, which includes rocks of the Kuz”elga and Karan subformations (Mashak Formation, Upper Riphean) revealed numerous rare-earth minerals: allanite-(Ce), monazite-(Se), monazite-(Nd), xenotime-(Y), REE-bearing epidote, and unidentified compounds. It has been established that the detrital zircon plays the role of a selective concentrator of Y, HREE, and Th during the terrigenous rock metamorphism. The comparative analysis showed that rare-earth minerals, such as monazite-(Ce) and xenotime-(Y), in the Shatak Complex differ significantly (in terms of chemical composition) from counterparts in other complexes located on the western slope of the Southern Urals by the presence of Gd in monazite, and LREE (Ce, Nd, Sm) in xenotime. In the case of similar thermobaric parameters of rock metamorphism characterizing the alteration degree of lithostructural complexes in the Southern Urals, the chemistry of mineral formation environment is among the main factors governing the compositional features of rare-earth minerals.

The paper presents the results of studying the material composition of Early–Middle Permian terrigenous rocks of the Reshetnikovo Formation in the Laoeling–Grodekovo terrane of southwestern Primorye. Studies were carried out to reconstruct paleogeodynamic environments of the accumulation of rocks and to determine the tectonic type and composition of parent rocks in sources areas. It has been established that, in terms of mineral and geochemical parameters, sandstones of the Reshetnikovo Formation are petrogenic or “first cycle” rocks. They correspond to arkoses and, only partially, subarkoses and lithite arenites. They are characterized by a fairly high maturity of clastic material. Their appearance is related to the destruction of largely weathered parent rocks in sources areas. Paleogeodynamic interpretation of the obtained data indicates that sedimentation occurred in the Early–Middle Permian in basins of a passive continental margin (intra- and intercontinental rifts and aulacogens). Sedimentation processes were governed mainly by continental sources areas: cratons and uplifted basement blocks, which were projections of the crystalline basement framed by rift zones. Mainly felsic igneous and metamorphic rocks were eroded with the participation of ancient sedimentary rocks. The U–Pb isotopic dating of detrital zircons made it possible to establish the age and possible location of magmatic complexes, whose destruction produced rocks of the Reshetnikovo Formation.

The paper considers data on the composition, age, and formation conditions of the Ulzutui and Kydzhimit sequences, which are ascribed to the Eravna Series of the Eravna Subzone of the Uda–Vitim Zone. The Eravna Series, at least 2400 m thick, is composed of tephroturbidites with a significant amount of lavas and tuffs of felsic and intermediate compositions, with which tectonic-gravitational mixtites are spatially and genetically related. The features of the structure and composition of the Eravna Series indicate the formation of sediments in an open deepening marine basin adjacent to the zone of active volcanism. Based on miospores, the time of formation of the Ulzutui Sequence was constrained, for the first time, to the Late Devonian–Early Carboniferous (late Famennian–early Tournaisian), the Kydzhimit Sequence is limited to the Early Carboniferous (Visean) age. At this time, the Kydzhimit volcanic zone was formed. The suprasubduction nature of the zone is evidenced by the following features of volcanic rocks: predominance of felsic varieties, affiliation of basalts to the tholeiitic series, and dacites and rhyodacites to the calc-alkaline series, the presence of high-K rock varieties corresponding to the K-Na alkalinity, very low MgO contents, low and moderate TiO₂ contents, high Al₂O₃ and K₂O, enrichment of the volcanogenic rocks in large-ion lithophilic elements relatively to high-field strength elements, Nb minimum, and negative εNd, their spatial association with monzonites (with suprasubduction signatures) and tephroturbidites, as well as metallogenic specialization (Cu and Zn) of the Eravna Series. We believe that the ore-bearing sequence for the pyrite–base metal Ulzutui and Ozernoe deposits is the Upper Devonian–Lower Carboniferous Eravna Series.