Lithology and Mineral Resources最新文献

Finding of vivianite is first described in a sediment core raised from the Cambridge Strait, western Franz Josef Land. The vivianite is represented by similar spherules mainly of 200–400 µm in diameter and their rare aggregates. Distribution of vivianite grains in the core is characterized by three maxima (up to 2.7 grains/g of dry bulk sediment) within the time interval of the last 4.1 ka. Linear and flat shapes of the aggregates indicate the generation of vivianite at the sediment–water interface. It takes place in the reduced condition at sulfide sulfur deficit relative to divalent iron in the bottom water. The structure of vivianite grains varies from the cryptocrystalline porous to the fully crystalline dense variety, reflecting stages of the vivianite crystallization, likely after coagulation of the ferrous phosphate colloid formed due to the bacterial activity. Signs of vivianite microconcretions mentioned by some authors are not observed.

The work is devoted to the study of ore minerals from the surface horizon of ore-bearing sediments in the Pobeda hydrothermal cluster using the following methods: optical microscopy, scanning electron microscopy, and X-ray spectral microanalysis. It was found that ore minerals are represented by fragments of Cu–Fe sulfides (isocubanite, chalcopyrite, and pyrite), newly formed iron hydroxides, and atacamite. In addition, barite and edaphogenic material as talcified silicate clasts, sometimes with sulfide inclusions, are present. Structural-morphological types of iron hydroxides are distinguished. Based on the hydrophysical data, the location of assumed active hydrothermal vent in the Pobeda-3 ore occurrence area was updated. Distribution of the studied minerals depending on the location relative to active hydrothermal vents is described. Decrease in the size and amount of hydrothermal mineral clasts and edaphogenic material, as well as increase in the degree of sulfide replacement by iron hydroxides, were observed when moving away from the sources. Moreover, decrease in the Cu/Fe ratio in the chemical composition of Cu–Fe sulfides is also noted. An unidentified phase of Cu_3.57‒4.22Fe_1.71‒2.19S_4.99‒5.31 with the chalcopyrite lamellas was established in the surface horizon of the column at station 37L245g.

To overcome the existing uncertainty in the interpretation of kaolinite “crystallinity” indices (KCLs), such as HI (Hinckley, 1963), IK (Stoch, 1974; Stoch and Sikora, 1966), QF (Range and Weiss, 1969), AGFI (Aparicio and Galán, 1999; Aparicio et al., 2006), and WIRI (Chmielová and Weiss, 2002). Their values obtained for a representative collection of 30 kaolinite samples were compared with the results of modeling the corresponding X-ray diffraction patterns. It is shown that all the studied samples comprise a mixture of almost defect-free high-ordered kaolinite (HOK) and defective low-ordered kaolinite (LOK) phases. The HOK content shows correlation with the crystallinity index values described by different regression equations. The correlation is most prominent for HOK and the Hinckley index (HI), which is described by the quadratic equation HOK (%) = 12.236 HI² + 25.464 HI ‒ 1.2622 with the correlation factor R² = 0.993. The obtained equations can be used to find HOK and LOK concentrations in natural kaolinites. Comparison of the structural parameters of defective kaolinites obtained by modeling their XRD patterns with those of Expert System (Plançon and Zacharie, 1990) showed that the latter sometimes predicts: (1) one-phase highly defective kaolinites, whereas their diffraction pattern modeling establishes a mixture of HOK and LOK phases; and (2) in two-phase samples, the content of the low-defect phase (ldp) is greater than 100%.

The Saqez-Sardasht region (~2000) is located in the north Sanandaj-Sirjan Zone (SSZ), between longitudes of 46°00′67 00″ E to 46°30′00″ and latitudes of 36°00′00″ N to 36°30′00″, northwest Iran. The region was fully studied to recognize the promising areas for gold deposits using various methods of fuzzy fusion techniques. Accordingly, six evidential layers (i.e., lithological, tectonic, alteration, with Au, Sb, and W geochemical anomalies have been derived from three geo-data sets of geology, geochemistry, and remote sensing. A concentration–number (C–N) fractal method was used to determine the geochemical threshold values. The outcome was then combined, using the multiple indicator kriging (MIK) geochemical methods to improve the mineral potential mapping of gold deposits. In this study, four various fuzzy mineral prospectivity mapping (MPM) methods consisting of conventional VIKOR, modified VIKOR, multi-class index overlay, and Geo Fuzzy Inference System (GeoFIS) have been employed to detect the most promising areas in the Saqez-Sardasht region. The MPMs were numerically compared to each other based on the MPM efficiency index for the seven gold prospects in the study region. The Geo Fuzzy Inference System (GeoFIS) acquired 91.84% agreement, so it is selected as the superior technique to lead the prospect selection. With affiliation to the outcome of MPM maps, promising mineralized areas, controlled by shear zones, were located in the southwestern part of the Saqez region.

Illite-smectite (I-S) minerals from the Upper Jurassic oil-source shales of Denmark and the North Sea were studied by a complex of diffraction and spectroscopic methods. Detailed structures were identified to reveal the mechanism of postsedimentary transformations of these shales. Usually, oil is generated in the oil-source rocks of sedimentary basins simultaneously with the diagenetic and catagenetic I-S transformations. The results obtained demonstrate the relationship between these two reactions: NH₃ molecules released from kerogen during the maximum oil formation are fixed as NH₄ cations in smectite or vermiculite interlayers, forming mica or tobelite structural fragments. This solid-phase transformation produces the mixed-layer structures consisting of illite, tobelite, smectite, and vermiculite (I-T-S-V) layers.

The Precambrian Chernaya Rechka Formation (Igarka Uplift) hosts a high-amplitude positive carbonate carbon and dispersed organic matter δ¹³С isotope anomaly (up to +12.4‰) spanning over 500 m of the section. Variations of δ¹³С_carb and δ¹³С_org are synchronous and do not depend on local sedimentary environments, since the studied anomaly-bearing carbonates were accumulated in different zones of the carbonate ramp. The oxygen isotope composition of these carbonates and other geochemical criteria indicate an insignificant impact of postsedimentary processes on the preservation of isotope systems. Variations of trace elements in the carbonate fraction from the stratotype section of the Chernaya Rechka Formation indicate its accumulation in alternating anoxic and oxic environments that did not affect the carbon isotope composition. It is shown that the limestones, which outcrop on Plakhinskii Island and contain widespread molar-tooth structures, also belong to the Chernaya Rechka Formation in terms of the chemical and isotope composition. The profound positive δ¹³С anomaly was putatively caused by a global deficiency of ¹²С in the paleo-ocean related to the accumulation of methane hydrates and the burial of nonoxidized organic matter. Together with the geochronological and stratigraphic data, minimum ⁸⁷Sr/⁸⁶Sr values (0.7074) in the Chernaya Rechka Formation reveal the lower Ediacaran (lower Vendian) age of the unit (635–580 Ma). Among the closest stratigraphic analogues of the Chernaya Rechka Formation are the Dal’nyaya Taiga Group (Patom Basin) and coeval stratigraphic sequences in the southern Siberian Platform. The global nature of the positive δ¹³С anomaly provides its correlation with other coeval C-isotope events worldwide.

Carbonate concretions in the region of Paramushir hydroacoustic anomalies are confined to the methane seep zones controlled by deep (tectonically weakened) bottom areas. Based on the structure, as well as chemical and mineral composition, the concretions can be classified as volcanosedimentary rock consisting of the vitro-, litho-, and crystalloclasts and buried microfauna cemented with the carbonate (aragonite) cement. The details and sequence of mineral formation of carbonate concretions are considered.

The article presents results of the biostratigraphic and U–Pb geochronological (detrital zircon) studies of the volcanoterrigenous lacustrine member of the upper subformation (Lower Paleozoic Oldynda Formation), which contains polymetallic massive sulfide ores of the Ozernoe deposit (Kurba–Eravna ore district, western Transbaikalia). The first, second, and “crystalline tuff” horizons of the first ore-bearing level of the Ozernaya member were studied. It is represented by an alternation of tuffs, calcareous, siliceous, carbonaceous tuffites, pelitomorphic limestones, calcareous gravelstones with interlayers and lenses of mineralized tuffaceous conglobreccia and layers of banded siderite pyrite ores. For the first time, bryozoans, algae, and palynoflora were recorded in calcareous tuffaceous siltstones and limestones of the second and “crystalline tuff” productive horizons. These data indicate the Early Carboniferous (Tournaisian) time of sediment accumulation. Results of the U–Pb geochronological studies of detrital zircons from the mineralized tuffaceous conglobreccia of the third productive horizon suggest that the lower boundary of rock formation is not older than Late Cambrian.

The article provides an overview of various indexes/indicators (Vogt, Parker, CIA, CIW, PIA, MIA, and others) used for studying weathering profiles/crusts and reconstructing paleoclimatic environments of sedimentary sequence accumulation. Their possibilities are demonstrated with Vendian–Lower Cambrian terrigenous rocks of Podolian Transnistria (southwestern slope of the Ukrainian Shield) as example. Distribution of index ba₁ values in this section indicates the presence of material subjected to intense transformation during the chemical weathering in mudstones of the Nagoryany Formation, the lower part of the Danilovka and the middle part of the Studenitsa formations. For mudstones of the Danilovka–Zbruch interval, the HM values are close to the HM_PAAS. The HM values are slightly higher for rocks of the Yaryshev–Nagoryany interval and comparable to those inherent in hot tropical continental clays for mudstones in the lower part of the Yaryshev Formation. Average value of index SA for mudstones of the entire section is 5.6 ± 0.7. Mudstones of the Grushka–Nagoryany interval, where SA < SA_PAAS, are composed of a more weathered material. The WIP values in mudstones of the Mogilev and Yaryshev formations, as well as in the upper part of the Zbruch Formation, correspond to the interval of their values between the PAAS and average Archean granite. Clay rocks of other formations have WIP ≤ WIP_PAAS. Average CIA value (71 ± 4) for mudstones virtually corresponds to the CIA value (70), which separates the sediments of cold/arid and warm/humid climates. Variations in the index CIW value along the section are oriented similarly as CIA variation. The vast majority of mudstones are characterized by PIA > PIA_PAAS. The average CPA value is 91 ± 4, which is also typical for PAAS. These and other data suggest the following point: based on a “direct” interpretation of the values of various chemical weathering indexes inherent in the fine-grained clastic rocks, paleoclimate in Podolian Transnistria was rather moderate or warm humid in the Vendian‒Early Cambrian. Comparison of the CIA values of mudstones with the values for the particulate suspended matter in modern rivers suggests that the Vendian‒Early Cambrian climate resembled the dry and humid subtropical or dry tropical type with elements of the humid climate.

Flat spot anomalies in the Quaternary part of the section of the Nansen Basin are imaged in seismic records and are interpreted to be related to gas-rich fluid accumulations. The flat spots are mainly located above basement highs between magnetic spreading anomalies C20 (~43 Ma) and C12 (~33 Ma). The complex morphometric analysis of flat spots show that serpentinization processes identified from modelling of gravity anomalies could be original gas source. This process also makes smoothing of the basement highs amplitudes. The depth of the top of the flat spots below the seafloor has an almost constant value of ~390 m indicating the ascent of gases from variable basement depths to a common subsurface fluid trap. The depth of the anomalies below the seafloor corresponds to a theoretical thickness of gas hydrate stability zone in the studied region. Gravity modeling along the Arktika-2011-03 section showed the position of the upper mantle blocks with lower (to 2.95 g/cm³) density within the highs of the acoustic basement. The flat spot anomalies occur above basement highs, below which blocks with lower density typical of serpentinized rocks are modelled. Thus, the serpentinization of the upper mantle ultramafic rocks is considered a main geochemical process, which can explain generation and accumulation of gas in oceanic abyss at a 1–3 km thick sedimentary cover, as well as small vertical movements of the basement blocks due to density reduction and expansion of serpentinized rock.