Lithology and Mineral Resources最新文献

The article presents new information on the structure of Upper Precambrian sections in the eastern part of the Middle Tien Shan containing diamictites (tilloids). Identification of two lateral (Dzhetymtau and Akshiyrak) section types in the Vendian Dzhetym Group is substantiated. The Dzhetymtau type is characterized by the presence of rocks containing iron oxide compounds (ferruginous quartzites and hematite schists) in the section. The Akshiyrak type is marked by the presence of black shale layers with pyrite mineralization. At the same time, both types contain two (Dzhetymtau and Baikonur) regional stages (hereafter, horizons) of diamictite development. The paper presents materials indicating that the eastern part of the Middle Tien Shan includes a previously unknown (pre-Dzhetymtau) horizon of diamictite development in the Upper Riphean Boordu sequence, which is compared with the Bayisi Formation at the base of the Kurugtagh Group in northwestern China. In addition, the Kuilu–Sarydzhaz part of the Middle Tien Shan includes the Paleozoic diamictites.

Study of the internal structure of the recently described new species of sponge Gzhelistella cornigera (Davydov et al., 2023) and fusulinids from the Gzhelian stage (Moscow region) revealed numerous polymineral biomorphoses composed of mixed-layer clay minerals, goethite, chalcedony, and sanidine. A detailed structural and crystal-chemical study of clay minerals from biomorphoses and the host rock revealed a structural heterogeneity of the mixed-layer minerals. Using the X-ray diffraction pattern modeling method, it has been established that the clay material in the studied samples is represented by two authigenic mixed-layer (glauconite-nontronite) types with a contrasting relationship between the content of different layers and/or their alternation order, but identical structural and crystal-chemical characteristics of the crystallites. It is shown that such formations should be considered a single heterogeneous mixed-layer structure, with the relationship and/or alternation order of different layer types in crystals varying within certain limits. It has been established that the structural and crystal-chemical characteristics of mixed-layer minerals from brown biomorphoses and host rocks are almost indistinguishable, whereas these parameters are significantly different for green biomorphoses. It is assumed that the newly formed clay minerals from host rocks, like their brown analogs, were formed under similar physicochemical conditions. It is also obvious that during the formation of mixed-layer phases, brown biomorphoses were already deprived of the biogenic organic matter, while green biomorphoses retained it in sufficient quantity to change the environmental conditions within themselves in some places.

Based on the reports of DSDP, ODP, IODP phases of the International Deep-Sea Drilling Project and other references, the arithmetic mean chemical compositions of the main Pleistocene sediment types in the Indian, Atlantic, and Pacific oceans are compared. The mean chemical composition of different sediment types was calculated as the arithmetic mean of the chemical component concentrations, as well as the average composition of Pleistocene sediments, on the whole, for three main ocean basins. It is shown that masses of the dry sedimentary material play the leading role in the comparative analysis of the weighted mean chemical composition. The mass accumulation rates are evaluated for the major oxides in Pleistocene sediments of all oceans. Data on modern factors influencing the oceanic sedimentation, ratios of the water catchment areas with accumulation basin areas, composition of provinces, continent climate, as well as areas of the sea floor above/under the critical depth surface, and primary production of the ocean are considered. These data are compared with our results concerning the values of major oxide concentrations in Pleistocene sediments of all oceans. It has been established that the mean chemical composition of oceanic sediments is governed mainly by the level of critical depth surface and degree of geochemical differentiation.

Geomorphological analysis and age correlation of the Late Pliocene–Quaternary regional stages identified in the ARC1407A seismic section by onlapping the oceanic basement, with the age specified based on calculations of the position of theoretical linear magnetic anomalies, were carried out. Interpretation of the ARC1407A seismic time section makes it possible to use the previous seismostratigraphic correlations of glaciomarine deposits for the western Barents Sea and the northeastern part of the adjacent deep-water basin. Based on the geomorphological analysis, extended canyon systems were identified in the Nansen Basin and eastern Amundsen Basin. Significant amounts of sedimentary cover in the Nansen Basin are glaciomarine sediments deposited since the end-Late Pliocene. In the central Nansen Basin, glaciomarine sediments were deposited simultaneously from two closely located troughs (Saint Anna and Voronin). Glaciomarine sediments, transported to the central Nansen Basin cyclically, have a mixed character (underwater landslides and turbidite flows). In the Amundsen and Podvodnikov basins, glaciomarine deposits began to form in the second half of the Middle Neopleistocene.

The current study presents an integrated investigation of petrographical, mineralogical, and geochemical data from Upper Cretaceous phosphorite-bearing strata west of the Abu-Tartur Plateau in the Western Desert of Egypt. Fifty-five samples representing phosphorite and associated rocks were collected from six outcrops. Three facies are identified: phosphorites, carbonates, and siliciclastics. The mineralogy of the samples was quantified via X-ray diffraction (XRD) as follows: fluorapatite, dolomite, calcite, pyrite, quartz, and smectite species. Atomic absorption spectrophotometry (AAS) permitted the quantification of the major oxides: SiO₂, Al₂O₃, MgO, Fe₂O₃, CaO, K₂O, Na₂O, P₂O₅, and SO₃ as well as F and loss of ignition (LOI). The statistical analysis of these geochemical data revealed three significant controlling factors during and after the deposition of the studied phosphorite and associated rocks. These factors represent the effects of the diagenesis of phosphorites, argillaceous marine rocks, and alumino-silicates in descending order of their relative strength. Trends of the analyzed major elements for the study samples are documented. Phosphorite, phosphatic rocks, dolomitized rocks, and siltstone-mudstone are recognized lithologies on the basis of the chemical compositions of the analyzed major oxides. The principal diagenetic processes affecting the phosphorite-bearing rocks included dolomitization, pyritization, silicification, bone dissolution, and micritization.

To ascertain the rate of sediment accumulations and relationship to growth faulting and the formation of stratal geometries favourable to petroleum accumulation, seismic data interpretations and stratigraphic datum age-depth plot analysis as well as well-log correlations within a sequence stratigraphic framework were conducted. Biostratigraphic data show that the age of sediments penetrated by oil wells from 2280 to 3544 m depth ranged from Early Oligocene to Late Oligocene and deposition took place in inner to middle neritic environments. For 7.8 million years, the rate at which sediments accumulated over the under-compacted Akata Formation shales varied between about 144.34 and 301.54 m/Ma. The high rate of sedimentation triggered the formation of a growth fault and the nucleation and growth of other synthetic faults. The growth faults are characterised by rollover anticline and drag folds consisting of footwall anticline and hanging-wall syncline. The footwall anticlines, like the rollover anticlines, offer drilling targets. Despite strata faulting and associated complexities, principles of sequence stratigraphy was used to successfully correlate well logs across the field in both the strike and dip directions. Four third-order depositional sequences, five genetic sequences, and system tracts were identified. Highstand Systems tract (HST) and Transgressive Systems tract (TST) are well preserved in the four depositional sequences, while LSTs are primarily found in Early Oligocene deeper sequences and in downdip wells, but all generally pinch-out in updip direction. The dip-orientated stratigraphic correlation implies stepwise progradation or down-stepping stratal geometries as a result of the non-uniformed subsiding platform generated by growth faulting.

The isotopic-geochemical characteristics of boron in waters of 21 mud volcanoes in the Kerch–Taman area have been determined. Boron concentration varies from 14 to 550 mg/L, and δ¹¹B values range from +8.3 to +54.7‰ (+21‰ on average). Low δ¹¹B values (~+14‰) were also obtained in two freshwater samples collected from aquifers of Neogene–Quaternary sediments. These data reflect the high heterogeneity of boron isotopic characteristics in waters of various genesis, which are discharged on the Earth’s surface within the Kerch and Taman peninsulas. It is shown that the increase of boron concentration in the mud volcanic waters is provided by the contribution of isotopically light (δ¹¹B ~ +10‰) boron. The inverse relationship between δ¹¹B and δ¹⁸O values in water was found. It indicates common mechanisms of ¹⁰B and ¹⁸O enrichment in the mud volcanic waters. These processes are temperature-dependent. They demonstrate a significant correlation of boron concentrations ([B]) and its isotopic composition (δ¹¹B) with T(Mg-Li)-temperatures in the range from ~40 to 130^oC. Thus, the chemical ([B]) and isotopic (δ¹¹B) variations observed in the studied mud volcanic waters reflect different depths of the formation of water salt composition and, respectively, the different temperature stages of catagenetic transformation of sedimentary strata. The revealed patterns are probably related to the smectite transformation into illite, which takes place in the clayey strata of the Maikop Group and is accompanied by the release of large volumes of dehydration waters with high δ¹⁸O values (up to +14‰). The most probable source of boron with low δ¹¹B values is destructive smectites.

The field research and analysis of data from unpublished reports made it possible to identify two placer gold types within the Vagran placer cluster (northern Urals) that are indicators of the primary gold–sulfide–quartz and hypogenic-hypergenic mineralization. They are used as references for developing a digital system for predicting parameters and localizing primary placer gold sources. In the present work, the typomorphic characteristics of placer gold (grain size, roundness, sorting and fineness, as well as trace element content) are formalized as a quantitative assessment. These data were processed using the methods of multiplicative indicators, linear regression, and random regression tree algorithm, which make it possible to forecast the composition and localization of the primary mineralization with greater confidence and stability than ordinary parameters separately. Since the data needed for such an assessment are sufficient in unpublished reports on the sampling of heavy mineral concentrates, additional field and high-cost laboratory studies are optional. Analysis of the correlation matrix allowed to identify characteristic indicators for the primary gold–sulfide–quartz and hypogenic-hypergenic mineralization, as well as to propose recommendations for the prospecting and exploration of primary Au potential in the ore cluster. All three methods provide consistent results, making it possible to predict the parameters of primary Au content. The multiplicative coefficient calculation method, which yielded a more contrasting (prominent) result, seems to be the simplest and most generalized tool suitable for any set of consistent data, whereas other methods require a more in-depth analysis of input parameters. The proposed forecast estimation method promotes the efficiency and partial automatization of the determination of primary mineralization potential in regions.

Kaolin deposits of the Kachchh region in western India were investigated for their mineralogical, physicochemical, and geochemical characteristics in order to elucidate the genesis and potential for industrial applications. The sampling of kaolin deposits was carried out from all three physiographic divisions of Kachchh, which includes the Kachchh Mainland, Wagad Highland, and the Island Belt region. The geochemical characterizations of the kaolin were determined using X-ray fluorescence spectrometry (XRF). Further, mineralogical properties were assessed to identify and quantify the mineral phases using the X-ray diffraction (XRD) technique. Scanning Electron Microscopy (SEM) was used to determine the micro-morphology of kaolin minerals. Diagnostic physicochemical tests like color, brightness, whiteness, pH, and particle size distribution (PSD) were explored for several possible industrial applications. The results of geochemical indices, including the chemical index of alteration (CIA), the chemical index of weathering (CIW), and the index of compositional variability (ICV) were determined to assess the weathering conditions, type of source rock involved, and genesis of kaolin deposits. The major oxide composition of kaolin from the Kachchh region is dominated by SiO₂, Al₂O₃, Fe₂O₃, and TiO₂. Kaolinite is the major phyllosilicate present in the deposit along with accessory minerals such as quartz, goethite, muscovite, and anatase. Geochemical analysis using major, trace, and rare earth elements of kaolin samples suggests provenance and environmental conditions corresponding to formation during the Cretaceous-Tertiary period. Based on the results obtained from mineralogical, geochemical, and physical analysis, the kaolin deposits require the removal of existing impurities to optimize the grades. Further, the suitable applications could be ceramics, cosmetics, rubber, plastic, paints, and paper products. Thus, this study has a significant potential to contribute to the economic development of the kaolin industries in the region.

The geological exploration within the Lukoyanov placer district (Nizhny Novgorod region) revealed increased contents of chrome-spinel, reaching a commercial level (up to 100 kg/m³), were detected in complex coastal-marine rare metal–titanium placers, but their source is not obvious. In addition to chrome-spinels, commercial components of placers are composed of ilmenite, zircon, and rutile. Morphological features of ore minerals suggest several sources of ore material (both proximal and distal). Moderately mature mineral composition of the heavy fraction (increased amount of minerals unstable during weathering) indicates that the Permian–Jurassic deposits of this region formed without (or with weak) participation of chemical weathering crusts. During the mobilization of detrital material in the source zone and the formation of intermediate reservoirs (Permian and Early Mesozoic complexes of the sedimentary cover) in the Uralian part of the East European Platform, mechanical processes prevailed with a subordinate influence of weathering crust formation. The study of the chemical composition of chrome-spinels in the most studied and promising Itmanov placer showed that they are mostly similar to counterparts in the ophiolite association and concentric zoned Pt-bearing massifs. Against the background of general impact of regional processes on the sedimentary cover formation in the central and eastern parts of the East European Platform at the Permian–Triassic boundary of the Uralide paleo-orogen, the Puchezh–Katun ring structure, located north of the Lukoyanov dome, had a noticeable influence on the composition of the heavy fraction of sediments in the region.