Lithology and Mineral Resources最新文献

Analysis of the bulk chemical composition of fine-grained clastic/clay rocks in several objects (Ai, Prikamsk, and Trekhgornaya formations; Mukun Group and Ust-Ilya Formation, Staraya Russa, and Vasilievsky Ostrov formations; clay rocks of the lower Vindhyan and Gwalior, Bhima, Athabasca, Libby Creek groups, and others), which participate in the Proterozoic sedimentary sequences unconformably overlying the crystalline basement, showed that their initial mineral composition was close to that of most post-Archean clay rocks. The ratio of Zr, Sc, and Th in these rocks suggests that they are composed predominantly of weakly recycled material. The share of erosion products of mafic igneous rocks among the sources of their fine-grained aluminosiliciclastics was relatively small. The features of the bulk chemical composition of such clay rocks suggest that the detrital material for them was supplied mainly from rock complexes formed in collisional and/or riftogenic settings.

The structure of the Upper Jurassic reef complex of the Shalbuzdag mountainous range (southern Dagestan) is considered. It represents the western segment of the Shakhdag barrier reef separating zones with different types of sedimentation: the shallow sedimentation area of the carbonate platform of the Greater Caucasus to the north and the Dibrara trough accumulating thick carbonate and terrigenous flysch to the south. In the plan view, the reef massif has approximately a ring shape 4 km across. It includes several large reef buildups consisting of a biogenic carbonate dome-shaped core surrounded by a trail of steeply dipping sedimentary layers. There are also numerous smaller structures, bioherms, ranging in size from a few meters to the first tens of meters. Reef-forming fauna is represented by corals, gastropods, brachiopods, various types of algae, and others. The inter-reef space is filled with sedimentary rocks, which are mainly the denudation products of reef structures. These sequences frequently show gradation cyclicity. Based on the relations between biogenic and sedimentary rocks in the western margin of the massif, at least three great pulses can be distinguished in its formation. The formation of the Shalbuzdag reef complex was mainly controlled by the following factors: (1) climate changes from humid in the Middle Jurassic to arid in the Late Jurassic, (2) proximity to the transition zone between regions with different tectonic setting and sedimentation types, 3) sea level fluctuations of different orders.

Some features of ferromanganese deposits in the Izu-Bonin and Mariana Island arcs tested in cruises 1 (1977) and 5 (1978) of the R/V Vulkanolog are considered. Two types of genetic (hydrogenic and low-temperature hydrothermal) deposits have been identified. The main ore minerals in hydrogenic ferromanganese deposits are poorly crystallized structures with a low ordering of Fe-vernadite and Mn-feroxyhite, with a smaller amount of goethite and birnessite. Low-temperature hydrothermal deposits consist either primarily of birnessite along with vernadite and goethite or of hematite, goethite, and feroxyhite. Hydrogenic ferromanganese deposits are characterized by a Mn/Fe ratio of 0.84‒1.36 in the Izu-Bonin and Mariana Island arcs; low-temperature hydrothermal deposits of the Izu-Bonin arc, by 6.13‒13.9. It was found that the content of Co, Ni, and Cu is significantly higher in crusts of the Mariana arc compared with the crusts of the Izu-Bonin arc. The contents of the remaining cations of heavy and rare metals (Pb, Cd, Ba, Sr, and others) in the crusts of both arcs are close to each other. The content of most rare earth metals (REM) in hydrogenic deposits from the Izu-Bonin and Mariana arcs is comparable to each other. Low-temperature hydrothermal ferromanganese deposits in the Izu-Bonin arc differ significantly from the hydrogenic deposits by a low (1 or 2 orders of magnitude) content of nonferrous, heavy, and rare metal cations. The contents of REM cations in low-temperature hydrothermal samples from the Izu-Bonin arc are low and range from 0.24 (Tm, Lu) to 32.35 µg/g (Y). Among them, Y, Ce, and Nd are most abundant in these samples.

Kaolin weathering profiles (WP) were formed during the continental hiatuses when the relief was flattened under warm humid conditions. In the Phanerozoic, most favorable were prolonged hiatuses (with weak tectonic movements) that promoted the formation, preservation, and burial of eluvial and other correlated formations. Such periods were marked by active crust formation identified by V.P. Petrov as early as in 1967. They can be manifested repeatedly within positive structures, such as the Voronezh anteclise. Its WPs correlate rather well with the coeval rocks in other structures of the East European Platform (EEP). However, they lack such complete sections with the WP age specified as in the Voronezh anteclise. Therefore, the Voronezh section with the specified WP levels can serve as a reference section for the EEP and, possibly, for other regions in the world on the whole. A historical–mineralogical analysis concerning the chronological formation of kaolinite clay deposits in the Phanerozoic revealed that that the kaolin WPs were thin and almost lacked deposits in the pre-Middle Devonian. They started to appear as primary and secondary kaolins in the Frasnian, but did not become widespread. In the Carboniferous period, WPs served as the sources of material for the refractory and high-melting clay deposits at the margins of coal basins with abundant vegetation. The main primary and secondary kaolin deposits were formed in the Late Triassic–Early Jurassic and Early Cretaceous. In North America, the accumulation of secondary kaolins was maximal during the Late Cretaceous and Tertiary. In the Cenozoic, the scale of kaolinite accumulation reduced considerably, as compared to the Mesozoic, giving way to the formation of bauxite concentrated in the lateritic sheet of tropical countries. During that time, over 80% of all bauxites in the Earth’s history were accumulated. Kaolin rocks in the form of eluvium, secondary kaolins, and kaolinite clays were formed mainly within the lower areas of peneplains and on alluvial plains. The obtained results showed that the evolution of kaolinite accumulation, represented mainly by primary kaolins, had an interrupted-directional trend due to the geocratic stages of the Earth’s development, increase of land areas, and flattening of elevated regions. The kaolinite deposits began to form in the Late Devonian, which was facilitated by the development of plant life on land, reached the maximum in the Mesozoic during the continental hiatuses, and slowed down in the Cenozoic. The slowdown was due to the intensification of weathering with the formation of final products of hydrolysis represented by alumina and iron oxides. Vast areas were marked by the formation of laterites instead of kaolinite accumulation in the lowered areas of peneplains and alluvial plains.

The material composition of placer (alluvial) dolomite-type nephrite from the Tsipa River in the nephrite-bearing region of the Vitim Highland has been examined. Initial data on the mineral composition of both inner and outer zones of the alluvial dolomite-type nephrite pebbles have been obtained. Placer nephrite is characterized by an inherited staining rim, a small amount of accessory minerals, fine-grained texture, randomly fibrous structure, and elevated alkali content. Chemical composition features of the staining rim formed under exogenous conditions include the development of Mn–Fe hydroxides, with a significant increase in the Fe³⁺ content and elevated levels of Co and Ba. A genetic relationship has been established between the placer nephrite and its primary source (nephrite from the Kavokta deposit). Comparison between primary and placer dolomite-type nephrite promoted the identification of diagnostic characteristics for conducting expert assessments.

The Teri sands along coastal regions are distinguished by their unique red coloring. This study aims to investigate geochemical characteristics and mineralogical composition of these sediments, assess the degree of weathering in the source area, and determine the environmental factors influencing their formation. The well-sorted, finely skewed sediments reflect a fluvio-marine environment and are classified as lithic arenites or wackes. Petrographic and X-ray diffraction analyses highlight the dominance of quartz and feldspar, with accessory minerals such as rutile, ilmenite, zircon, garnet, diopside, magnetite, hematite, hypersthene, and biotite. The Chemical Index of Alteration (CIA) values suggest moderate to high weathering in the source area. The red coloration is attributed to the oxidation and leaching of iron-bearing minerals, driven by high rainfall and fluctuating groundwater levels in arid to semi-arid climates. Major oxides like SiO₂, Al₂O₃, and Fe₂O₃ are abundant, while MnO, CaO, MgO, K₂O, TiO₂, P₂O₅, and Na₂O occur in lower concentrations. Trace elements, including Cu, Cr, Ni, Zn, Sr, Ga, Rb, Ba, Y, Nb, and Pb, are present in >10 ppm, with gallium being the most concentrated. The rare earth elements (REEs) patterns show enrichment in light REEs, with a flat trend for heavy REEs, featuring a negative europium anomaly and a positive cerium anomaly. These findings suggest that the sediments originated from felsic sources, likely dating to the Post-Archean or Proterozoic era. The study provides valuable insights into the Teri sands provenance, weathering processes, and environmental conditions.

In this geochemical review, tables of average arithmetic chemical composition, mean weighted chemical composition, accumulation rates, and mass accumulation rates of chemical components are presented. They are based on the records from cruises of the International Deep Sea Drilling Project and other literature data concerning the main lithologic types of the Pacific Pleistocene sediments. These tables can be used for the comparative analysis with sediments of the same or other stratons in different oceanic basins, as well as paleoceanic sediments on the continents. The terrigenous matrix dominates in the lithogenic matter. We revealed a close resemblance between the chemical composition of volcanic sediments and hemipelagic clays. Peculiarities of hydrothermal sediments are described. Using the methods of mathematical statistics, we deciphered the main geochemical associations and principal factors determining the chemical composition of studied sediments. Masses of major oxides and several trace elements have been calculated for Pleistocene sediments. A concept about the average chemical composition of the Pacific Pleistocene is proposed.

Lithogeochemical features of the Vendian nonglacial mudrocks (Serebryanka and Sylvitsa groups) in the Middle Urals indicate that average annual temperatures in paleocatchment areas during their accumulation varied from 4 to 21°C. Such temperatures comply mainly to the temperate and temperate-warm, but less often warm climates. The calculated RW index values also suggest that paleoclimate in the Vendian catchment areas was generally temperate. At the same time, some mudrock samples of the Garevka, Kernos, and Perevalok formations, as well as the Kobylii Ostrov Member of the Chernyi Kamen Formation, have RW index values comparable to those of modern continental or subarctic climate. Variations in RW index values and reconstructed MAP values demonstrate similar cooling/warming trends for mud rocks of Vendian nonglacial intervals in the Middle Urals.

The paper reports the lithological and biostratigraphic study of the Ozerninsky Sequence, the accumulation of which is associated with the onset of the early Hercynian stage in the evolution of the Uda–Vitim structural–formational zone of the Baikal–Vitim fold system and the formation of gold–pyrite–polymetallic deposits of the Ozerninsky ore cluster. The sequence is isolated from the Lower Cambrian Oldynda Formation. It is composed predominantly of graywacke arkose and quartz graywacke and includes two subsequences. The lower subsequence is represented by the quartz–feldspar sandstone and siltstone with interlayers and lenses of polymictic conglomerate and gritstone, while the upper subsequence is composed of intercalated polymictic sandstone and siltstone, calcareous siltstone, and limestone with interlayers of clayey, clayey–siliceous, carbonaceous–clayey siltstone, and mudstone. The paleontological characteristics of the Ozerninsky Sequence determines its stratigraphic affiliation to the Lower (Emsian Stage)–Upper (Lower Frasnian Substage) Devonian. The composition, structure, and paleo-biota indicate that the sediments formed in the open shelf sea environment with a significant input of terrigenous component. The lower subsequence was accumulated in a shelf shoaling conditions at active hydrodynamic mode, while the upper subsequence was accumulated in the most submerged parts of the shelf, in areas with stagnant hydrogeological regime.

The data obtained from lithological and mineralogical study of the Upper Cambrian and Lower Ordovician terrigenous−carbonate deposits in the middle reaches of the Vilyuy River, southern Siberian Platform are discussed. The study of detrital zircon, garnet, and tourmaline in the sample from the Upper Cambrian Kholomolokh Formation and two samples from the Upper Cambrian to Lower Ordovician Balyktakh Formation revealed that the main sources for the studied minerals are acidic and intermediate igneous and metamorphic rocks, amphibolite-facies metasediments, and amphibolite to granulite-facies metamorphosed mafic−ultramafic complexes of the Precambrian Siberian Craton basement. The U−Th−Pb zircon dating from the Kholomolokh and Balyktakh Formations in the middle reaches of the Vilyuy River revealed a significant difference in the provenance areas of terrigenous material in the Late Cambrian and Ordovician. In the sample from the Upper Cambrian Kholomolokh Formation, zircon represented by a younger population is characterized by predominance of Neoproterozoic ages (peak values are 550 and 845 Ma). This indicates that rocks of the Neoproterozoic terranes of the southern margin of the Siberian Craton were the main provenance area in the Precambrian. Paleoproterozoic zircon (1880‒1890 Ma) is main population in the Early Ordovician rocks of the Balyltakh Formation (~70%). In the Early Ordovician, the most probable source of matter for the Vilyuy syneclise was an uplift of the Archean−Paleoproterozoic basement located in the central part of the Siberian Platform. Nearly complete absence of younger zircon (~500−900 Ma) in the Balyktakh Formation deposits indicates a weak effect of provenance located at the southeastern margin of the Siberian Platform in the Ordovician time.