Lithology and Mineral Resources最新文献

The article presents the results of sorption of rare earth metal (REM) cations on samples of deep-sea base metal sulfides in the Broken Spur and TAG hydrothermal fields (Mid-Atlantic Ridge). The studied samples contain the following major minerals: marcasite, pyrrhotite, pyrite, and sphalerite in the Broken Spur field; chalcopyrite, pyrite, and marcasite in the TAG field. It has been established that these Fe–Cu–Zn sulfide minerals are natural absorbents. The exchange capacity of sulfide minerals for REM cations is 0.006‒0.061 mg-equiv/g. The exchange complex of sulfide minerals comprises the cations of alkaline, alkali-earth metals, and main cations of metals in the crystal lattice – Fe, Zn, Cu (in very limited quantities). The mechanism of the REM cation absorption is ion-exchange equivalent to the exchange cations of sulfide minerals. It was found that REM cations occur in the sulfide minerals almost completely in the sorbed form (more than 90% of the total amount). Apparently, the chemically bound form is possible only for Lu and Dy cations. The mineral composition of sulfide deposits is preserved in the exchange reaction products, and new phases do not appear.

The article discusses the main directions of lithological studies in the oil-and-gas geology, continuing and developing the ideas and researches of L.V. Pustovalov. Several such studies are coordinated closely with other geological branches (tectonics, stratigraphy, and others). A wide range of such studies is devoted to analysis of the structure and development of sedimentary basins; elucidation of the structure of the internal structure of sedimentary complexes; prediction and prospecting for non-structural oil-and-gas traps; and study of natural oil-and-gas reservoirs at different hierarchical levels.

The mineralogical, structural and crystal-chemical features of seven samples of globular phyllosilicates of the glauconite–illite series (GPS) from the Lower Cambrian sequences of Northern Estonia and Western Lithuania, from the Middle Cambrian sequences of Western Latvia, and also from the Lower Ordovician sequences of Northern Estonia and Western Latvia are considered for the first time. Based on Al index (K_Al = ^VIAl/[^VIFe³⁺ + ^VIAl]) varying from 0.27 to 0.59, the globular phyllosilicates are attributed to the glauconite–illite series, most of which are represented by glauconites (the Al index is K_Al = 0.27–0.46) and one sample, by Al-glauconite (K_Al = 0.59). The K₂O content in minerals is from 7.12 to 7.90%. The content of expandable layers (4–13%), their types (smectite, vermiculite), and the character of their alternation (R = 0, R = 2) were determined for the first time in the studied samples by simulation of experimental X-ray diffraction patterns from oriented specimens. Simulation of X-ray diffraction patterns obtained from unoriented specimens made it possible to determine the degree of three-dimensional order and mean values of the unit-cell parameter b (9.056–9.094 Å), as well as the distribution of their individual micaceous varieties. Based on these data, the microheterogeneity of the Cambrian and Ordovician GPSs was established and compared with the heterogeneity in the previously studied Riphean GPS (Drits et al., 2013). The obtained Rb-Sr и K‑Ar ages for the studied Middle Cambrian and Lower Ordovician samples, as well as the earlier published dates for the Lower Cambrian samples, are “rejuvenated” relative to age limits accepted for the Cambrian and Lower Ordovician (Gradstein et al., 2020). The relationship of the Cambrian and Lower Ordovician “rejuvenated” isotopic dates and the discovered GPS heterogeneity, as well as possible reasons for its occurrence, are discussed.

The article presents the results of studying changes in the chemical composition of Pleistocene sediments from Hole 858B (depth 38.6 m, temperature gradient 10‒11°C/m) drilled in the Middle Valley, Juan de Fuca mid-ocean ridge (Northeast Pacific) in the Dead Dog hydrothermal field 20 m away from a “black smoker” (temperature 276°C). The content of macroelements in these sediments was studied by the XRD method. For the first time, data on a large set of trace elements were obtained from this object using the ICP-MS method. The chemical composition of sediments changed in the process of solution–sediment interaction during a rapid downsection increase of temperature. In the upper part of Sequence I (1.97‒10.41 m), the sediments are commonly altered slightly at a temperature of about 17°C. Changes in the content of macro- and trace elements are prominent in the lower part of Sequence I (12.70‒25.31 m, average temperature 112‒197°C). The chemical composition of sediments is most altered in Sequences IIB and IID (25.31‒38.6 m, temperature from 112‒197 to 320‒330°С). Changes in the content of the majority of macro- and trace elements in the sediments of Sequences IIB and IID are similar, except for a stronger decrease of chemical elements in the sediments of Sequence IID, which is marked by a significantly lower content of Cu, Zn, Ga, Rb, Sr, Ag, Cd, Sb, Cs, Ba, Tl, and Bi (i.e., the majority of detected elements except U) than in background sediments. Sediments in Sequence IID, as in Sequence IIB, contain less Ca, Na, K, and P, but more Mg. A lower content of the above-listed elements in these sediments can be attributed to their evacuation during the solution–sediment interaction and concentration in the solution, whereas a higher content of these elements is likely related to their input into sediments from the solution and, accordingly, their depletion in the solution. The results of studying the chemical composition of metalliferous sediments (Sequence III, 0‒1.97 m) and sulfide layer IV (10.41‒12.70 m), as well as the chemical composition of unaltered background sediments from Holes 855A, 855C, and 855D are presented.

The article analyzes the distribution of datapoints of individual and averaged mudstones samples from almost 40 sedimentary successions of the Neoproterozoic–Ordovician (epoch lacking land plants) and the Devonian–Holocene (time of the appearance and abundance of land plants—“green epoch”) in the (La/Yb)_N–Eu/Eu*, (La/Yb)_N–(Eu/Sm)_N, and (La/Yb)_N–Th diagrams with classification fields of the silty–pelitic particulate matter in the estuary of different-category modern rivers. No fundamental differences between the “green epoch” and pre-Silurian rivers were revealed. In combination with other data, the above fact suggests the following conclusion: since the terrestrial vegetation is absent (and not only in the Neoproterozoic–Ordovician), the categories of rivers, which drained different (in area and composition) catchment areas and transported the fine-grained particulate material to the shelf zones were not fundamentally different from those at present.

New data on the C and O isotope composition in the Neoproterozoic carbonates of the Ballaganakh and Dal’nyaya Taiga regional stages (southeastern margin of the Patom paleobasin (hereafter, Basin) are presented. The negative δ¹³С anomaly, established in the upper part of the Ballaganakh regional stage, is comparable (in amplitude and stratigraphic position) to the Trezona anomaly, which preceded the Marinoan glaciation. The carbonate layers in glacial deposits of the Nichatka Formation of the Dal’nyaya Taiga regional stage have moderately positive δ¹³С values. The dolomite unit at the postglacial sequence base is characterized by moderately negative δ¹³С values that are typical for the cap carbonate sequence associated with the end-Marinoan glaciation. The lower part of the postglacial sequence (Barakun Formation) is characterized by a gradual increase of calcite in the carbonate component of rocks and a shift in the isotope composition corresponding to the difference in the fractionation coefficient of stable C and O isotopes for dolomite and calcite. This phenomenon, recorded in the postglacial sequences of Namibia and Canada as well, indicates that the carbonate mineral composition was governed by a global change in water chemistry rather than postsedimentary alteration. The overlying carbonate rocks of the Dal’nyaya Taiga regional stage in the epicontinental part of the Patom Basin (Sen Formation) are depleted in ¹³С compared to their shelf analogs in the Ura Uplift. Probably, the carbonates were accumulated asynchronously in the epicontinental and shelf facies of the Patom Basin. The reconstructed trend of variations in the carbon isotope composition for the Dal’nyaya Taiga regional stage is characterized by positive and low-amplitude negative δ¹³С anomalies similar to those in the Doushantuo Formation (China).

This paper provides the first modern day overview of fossil resin finds in western Central Asia, which is located far beyond the traditional resin-bearing regions both in Russia and in northern West Europe. Based on little-known facts and random references in the geological literature, the main locations of fossil resins were revised and described, and the level of their study is assessed. The first FTIR study of the molecular structure of fossil resins in the Aral region showed that their classification as amber (in modern understanding – succinite assigned to the group of viscous resin) is not correct. They are represented by exclusively fragile varieties (retinite and gedanite) and, therefore, have no practical significance as jewelry raw material.

Based on the lithological and gas-geochemical studies and a comprehensive interpretation of the available materials, the main factors of the formation and distribution of grain size distribution, water-physical properties, organic saturation, as well as concentrations and geochemical parameters of hydrocarbon (HC) gases in seafloor sediments of geostructures in the western part of the East Siberian Sea are summarized and analyzed. It has been established that the sediments in the northern and central parts of the studied region are represented by aleurite–pelites; in the southern part, by aleurite–pelite–psammites with the following parameters: C_org—0.6–2.0%, natural moisture content (hereafter, wetness)—18–43%, density—1.5–2.0 g/cm³, open porosity—17–33%, concentrations of methane and its homologs—0.001–5.934 and 0.00003–0.0312 cm³/kg, respectively, molecular mass of the HC fraction—16.05–22.6 g/mol, coefficients of “wetness”, “dryness”, and transformation—0.2–51, 1–1999, and 0.2–50.8%, respectively, and δ¹³С‒СН₄ varying from –82.7 to –38.4‰. Based on the values of gas-geochemical parameters, eleven types of gas sources were identified in bottom sediments. The results showed that the formation of HC anomalies in sediments is governed mainly by their reservoir properties, C_org content, sampling depths, integrated influence of geological factors, such as gas saturation of the underlying sediments, type of gas sources, fault and fold tectonics, position of geostructures, thickness of Quaternary sediments, content of coal and gas, and age of the folded basement. Anomalies of HC gases are associated to a lesser extent with the lithological composition and density parameters of sediments.

New data on the mineral composition of Lower Triassic terrigenous rocks in the northern Pechora oil- and gas-bearing basin are presented. The relevance of the study is due to the fact that the terrigenous natural reservoirs confined to this part of the section have heterogeneous structure. The purpose of the article was to identify the features of the formation and distribution of minerals that fill the void space of the reservoirs. The optical microscopic, X-ray phase, and electron microscopic study revealed diverse postsedimentary transformations of sandy reservoirs. It is shown that the most widespread are quartz regeneration, transformation of mica-group minerals, as well as the formation of calcite of various generations and authigenic clay minerals. Diagenetic changes in terrigenous rocks play a significant role in the formation of reservoir properties and promote the heterogeneity of reservoirs. The large amount of calcite in sandstone cement leads to a significant decrease in filtration and capacity parameters. The pore cement of chlorite‒smectite composition in the fine-grained sandstones also causes a decrease in the reservoir quality. The coarse- and medium-grained sandstones with a low content of cement (predominantly of the kaolinite or chlorite composition) are characterized by the higher reservoir properties. The chloritic crustification and kaolinitic pore-filling cement facilitate the formation of higher quality reservoirs.