Lithology and Mineral Resources最新文献

Several geochemical characteristics ((La/Yb)_N, Eu/Eu*, and Th content) of gray silts of the Volga River, suspended particulate matter of the Lena River, and silt–pelite fraction of bottom sediments in the Yangtze River are analyzed. It has been established that the above parameters of the chondrite-normalized lanthanide spectra and the Th content turn out in almost all cases to be comparable with their values determined for the specially prepared (removal of nonterrigenous carriers of rare earth elements (carbonate minerals, Fe–Mn oxyhydroxides, and organic components) pelite fractions of bottom sediments deposited near the mouths of named major rivers, and are retained over thousands of kilometers upstream from their deltas/mouths. The regulation of the Volga and Yangtze flows does not have a significant impact on parameters of the suspended particulate matter and bottom sediments under consideration.

Both tectonic settings and sedimentary environments of the oil- and gas-bearing Triassic sequences in the Caspian region are examined. It is shown that the Scythian and West Turanian plates were located at an active margin of the East European continent in Triassic. A unified thick (up to 3–5 km) cover of sedimentary and volcanosedimentary (mainly tuffaceous) rocks without the characteristic features of rifting was formed. In the northern and eastern parts of the region, the Triassic is composed of variegated continental terrigenous rocks. In many areas of the region (eastern and southern parts of the Pre-Caspian Basin, Eastern Ciscaucasia, Mangyshlak, and Middle Caspian), the Lower Triassic (Olenekian) and Middle Triassic are represented by marine terrigenous–carbonate rocks. The structural features of sequences in the Pre-Caspian Basin are associated with salt tectonics. The maximum thickness (up to 4.5–5 km) of Triassic rocks within the Scythian Plate is recorded in the southwestern part of the Middle Caspian and southeastern part of the Karpinsky Ridge, where they fill up a series of NW-extending graben-shaped troughs. Their absence in the northwestern part of the region is related to the latest shear deformations, as confirmed by their discrepancy with the facies zonation of Triassic deposits. Currently, the Permian and Triassic deposits represent a pre-platform geodynamic seismic sequence unconformably overlying the pre-Kungurian deposits. Triassic deposits of the Scythian and West Turanian plates are disturbed by faults (amplitude up to 2 km) and dislocated in some areas. Folding with faults and strike-slip faults is especially intense on the Karpinsky Ridge. Increased dislocation and Late Triassic magmatism on the Scythian and West Turanian plates are associated with the processes of collision during the closure of the Paleotethys Ocean. Oil and gas prospects of the region are assessed positively.

Using a complex of analytical methods, clay minerals were studied in Pleistocene sediments from Hole ODP 1038B (120.50 m deep), drilled on the northwestern edge of the Central Hill (Escanaba Trough, Gorda Ridge) near the hydrothermal source with a temperature of 108°C, as well as in Pleistocene background terrigenous sediments from reference Hole ODP 1037B, drilled in the Escanaba Trough 5 km south of the Central Hill. The terrigenous clay mineral assemblage in sediments from Hole 1037B consists of the mixed-layer smectite-illites, smectite, chlorite, illite, and kaolinite. Sediments from Hole 1038B in the interval from the bottom surface to a depth of 5–7 m are composed of terrigenous clay minerals. In the rest of the sedimentary section, clay minerals are represented by the newly formed biotite, chlorite, and dioctahedral smectite. They were formed during the basaltic melt intrusion into the Escanaba Trough with the formation of a laccolith and the subsequent rapid cooling of its flank. The intrusion was accompanied by the ascent of high-temperature hydrothermal fluid in the central discharge channel, interacting with the adjacent sediments. As a result, the fine-dispersed biotite was formed in sediments at the high-temperature stage of this interaction due to the primary terrigenous clay minerals, K-feldspar, and amphiboles. The rapid cooling of the hydrothermal fluid to a temperature of presumably 270–330°C promoted the partial replacement of biotite by chlorite. The further rapid cooling of the hydrothermal fluid to 200°C and lower and its mixing with seawater seeping into sediments of the Central Hill fostered the formation of smectite.

The article presents the results of experimental studies of the sorption and desorption of rare-earth metal (REM) cations by the Co-bearing ferromanganese crusts of the Govorov Guyot. It has been established that the REM cations are sorbed on the CFC ore minerals (Fe-vernadite, vernadite, Mn-feroxyhite, and goethite. The crusts are characterized by high exchange capacity (1.78–3.57 mg-equiv/g, which increases in the following series: (Dy < Gd < Lu < Sm < Nd < Y, La < Eu) ( ll ) Ce. The REM cation sorption proceeds by the irreversible ion-exchange equivalent mechanism. The exchange complex of ore minerals consists of Na⁺, K⁺, Ca²⁺, and Mg²⁺ cations, which contribute 97‒98% to their total capacity. The crusts are characterized by the group sorption of REM cations from multicomponent water solutions of metal salts. The selectivity of manganese and ferruginous minerals of crusts to REM cations is significantly higher than to the main cations of ocean water. Experimental data on the desorption of sorbed REM cations with the NaCl solution suggest their irreversible sorption by ore minerals and strengthening of the chemical bond of sorbed REM cations with the main structural elements of these minerals over time. An important property of ore minerals, primarily manganese minerals, is their chemical and structural stability in aqueous electrolyte solutions, suggesting the repeated use of FMC as sorbents of REM cations.

The results of regional studies of Early Miocene deposits in Western Ciscaucasia, based on the seismic stratigraphic analysis, are presented. The spatial pattern of sediment accumulation is analyzed and the paleogeographic conditions during the Late Miocene regressive stages in Western Ciscaucasia are refined. Erosional incisions of several levels, developed during the base-level fall in the course of major regressions in the studied time interval, were identified. Based on the spatial correlation of paleoincisions using a chosen series of intersecting seismic profiles, the buried Paleo-Don and Paleo-Donets river valleys were reconstructed at the Sarmatian‒Meotian boundaries and within the Meotian‒upper Pontian interval.

This paper completes the examination of results of the study of lithogeochemical characteristics of a pilot collection of the Riphean–Vendian sandstones, siltstones, and claystones (last one based on the interpretation of results) in Belarus. Data on the age of detrital zircon published in recent years suggest that Upper Precambrian rocks of this region were sourced from the Osnitsk–Mikashevichi and the Trans-Scandinavian igneous belts, the Volyn–Brest large igneous province, rapakivi granites, as well as various rock associations of Sarmatia, Danopolonian orogen and Svecofennides. Based on the lithogeochemical characteristics, the distribution of data points of the studied clastic rocks on discriminant diagrams provides insight into the possible provenance, paleogeodynamic, paleogeographic, and paleoclimatic settings and suggests several conclusions. The considered Riphean–Vendian stratons in Belarus are composed mainly of erosion products of within-plate granitoids, as well as various island-arc and syncollisional felsic igneous rocks. The share of erosion products of mafic rocks among them generally does not exceed 30%. It is significant mainly in the Volyn Group rocks (erosion products of the Volyn–Brest large igneous province), as well as in some samples of the Nizov, Selyavy, and Kotlin formations (fragments of mafic rocks from other provenances?). The source-to-sink transport was accomplished mainly by large rivers. Paleogeodynamic settings varied from quite active to quite passive. The paleoclimate in catchment areas was most likely arid/semiarid in the Riphean. In the Vendian, it was humid and varied from subtropical in the Early Vendian (except the Glusk Formation) to tropical in the Late Vendian. The obtained results also make it possible to show some peculiarities of the known methods and techniques of paleoclimate reconstruction.

The article presents a comparative analysis of the Paleozoic and Cenozoic reef formation, mainly in terms of the position of reefs in the basins of continental and oceanic blocks. It is shown that the main formation of reefs took place in the Cenozoic directly in the oceans, including boundaries between oceans and continents, and, to an extremely limited scales, in the basins of the continental segment. In the Paleozoic, reefs were formed not only in oceans, but also in spacious basins of continental block. This is one of the manifestations of the general evolution of carbonate accumulation, when the Paleozoic carbonate sediments were formed in such shallow-water bodies that covered very significant surfaces of continents.

At the current level of research, a generalization of previously studied and new lithological-mineralogical, structural, and crystal-chemical characteristics of globular layer silicates (GLS) of the Mg-rich glauconite–illite series from Upper Proterozoic sections of eastern and northern Siberia (Uchur–Maya region, Anabar uplift) has been carried out. The classification of glauconite–illite minerals was carried out in accordance with recommendations of the International Nomenclature Committees for Mica and Clay Minerals, as well as based on the available literature and our own data. The Al index, i.e., (K_Al = ^VIAl/[^VIFe³⁺ + ^VIAl]), in minerals of the glauconite–illite series varies from 0.40 to 0.85; the content of Mg and K cations varies, respectively, from 0.51 to 0.75 and from 0.63 to 0.80 f.u. Application of the X-ray modeling method for diffraction patterns of the oriented and unoriented specimens of Upper Proterozoic GLS made it possible to determine the following properties: the content of swelling layers (4–10%), their types (mica, smectite, chlorite), the nature of the alternation (short-range order factor, R = 0), unit cell parameters c sin β, c cos β/a, and average value of parameter b (9.018–9.074 Å). The conditions of glauconite formation in the Upper Proterozoic basins are considered, and their influence on the structural and crystal-chemical features of Mg presence in hydrocarbons is discussed.

Rare earth elements (REE) of the host rocks (Fe-siliceous rocks) and manganese ores of the Nchwaning Mine (Hotazel Formation, Kalahari manganese field) were studied. An important feature of manganese ores and host rocks (Fe-silicites) is the presence of negative and positive cerium (Ce/Ce*) and europium (Eu/Eu*) anomalies. This testifies to the complex and long history of the formation of manganese ores. Initial metal-bearing (Mn, Fe) sediments of a shallow-water basin with a negative cerium anomaly (Ce/Ce*) were enriched in europium (positive Eu/Eu*) at different stages of lithogenesis both during sedimentation (underwater discharge of hydrothermal fluids), and subsequent processes of hydrothermal transformation of the ore-bearing strata. The source of manganese could be basaltic andesites of the underlying Ongeluk Formation.

The results of studies of a basaltic andesite sample (complicated by the mineralized fracture and voids, as well as fracture and gas voids filled with secondary mineralization) dredged on the submarine Esmeralda Volcano are presented. A detailed comparative study of the mineral composition of the substance lining the fracture, the near-fracture space, and the basaltic andesite part unaffected by secondary alterations made it possible to discover the presence of a mineral assemblage, which is atypical for the unaltered volcanic rocks, in the submarine Esmeralda Volcano. In the intra-fracture space and adjacent basaltic andesite zones, wide variation ranges of the plagioclase composition are recorded; isomorphism in the Fe–Ca pyroxene series is studied; REE oxides, hydroxides, and fluorohydroxides are studied; and variability in the composition of minerals of the magnetite–hematite series is shown. Tectonic movements in the previously formed basaltic andesites likely promoted the emergence of permeable zones, through which new portions of the melt leaked. In a limited space, high fluid gas saturation, temperature, and pressure fostered the extraction of metal compounds from the melt and host rocks.