Lithology and Mineral Resources最新文献

Based on lithogeochemical data related to the fine-grained clastic rocks of the Volyn, Valdai, and Baltic groups in the western part of the East European Platform (Belarus and Volyn, partly Lithuania), categories of rivers that transported the fine-grained aluminosiliciclastics to the sinks were reconstructed. It is concluded that the formation of Vendian and Lower Cambrian sedimentary sequences in this area was controlled mainly by river systems similar to modern large rivers (catchment area >100 000 km²) and rivers draining sedimentary rocks (catchment area <100 000 km²). The fine-grained aluminosiliciclastics transported by them was delivered mainly from areas composed of rocks of the platform crystalline basement and, in part, sedimentary rocks. The distribution of data points of Vendian–Lower Cambrian mudstones on the (La/Yb)_N–Eu/Eu* and (La/Yb)_N–Th diagrams with fields of the pelitic and silty–pelitic sediments at the mouths of modern different-category rivers shows that mafic rocks of the Volyn–Brest large igneous province, apparently, were not suppliers of the fine-grained aluminosiliciclastics in the indicated time intervals.

New results of the lithological structural–textural observations and petrographic study of rocks of the Uryuk Formation (sandstones and gravelstone-sandstones with the subordinate mudstone interlayers) exposed in the Malyi Tolpar River basin in the Bashkir meganticlinorium. For the first time, a wide development of synsedimentary underwater landslide folds (varying from the first tens of centimeters to the first meters in size) has been established in the Uryuk deposits. The sandstones demonstrate the oblique, wavy, flaser, and horizontal (with paired thin clay lamina) stratification, as well as massive layers. Signs of shallow wave ripples have been established. The rocks are characterized by mechanoglyphs and textures similar to Arumberia banksi, which presumably represent the lithified textures of bacterial mats that existed under shallow-marine environments with sandy–clayey sedimentation. Despite the absence of direct lithological signs of diamictites, the Uryuk deposits likely form a single sedimentary sequence with the underlying Tolparovo–Suirovo marine glacial deposits, in which a shallow-sea sedimentation regime was established by the end of the Uryuk time. It is shown that the presence of ferruginous minerals in the sandstone cement is secondary in nature and is associated with their epigenetic transformations. It is concluded that the red color of rocks of the Uryuk Formation cannot be used for the stratification of its sections and reconstruction of sedimentation conditions in the Uryuk time.

The first results of the U–Th–Pb isotope dating of detrital zircons (dZr, N = 130, n = 91) from the middle Danian sandstones (63.9–65.3 Ma) of the Cretaceous–Eocene Novorossiisk–Anapa flysch widely developed in the Sochi synclinorium (southern slope of the Western Caucasus) are presented. The maximum and minimum dZr age is 2973 ± 12 Ma and 318 ± 3 Ma, respectively; weighted average age of the four youngest dZr is ~322 ± 7 Ma. There are no signs of erosion products of the Jurassic magmatites involved in the structure of the Greater Caucasus and Crimean Mountains into the sedimentary basin, where the Novorossiisk–Anapa flysch was formed. The results have revealed a high degree of similarity between the provenance signals of the Danian sandstones from the Novorossiisk–Anapa flysch, some Paleogene–Neogene and Early Quaternary (Early Pleistocene) sandstones of the Western Caucasus and Western Cis-Caucasia, red-colored Upper Permian and Lower Triassic sandstones of the Moscow syneclise, as well as Late Quaternary alluvium at lower reaches of the Don and Volga rivers draining vast expanses of the Russian Plate. These facts suggest: (1) the absence of eroded mountain structures of the Greater Caucasus and Crimea in the middle Danian; (2) the main volume of detrital material composing the Novorossiisk–Anapa flysch was formed due to the recycling of Permian–Triassic and younger sequences of the Russian Plate.

In two marginal depressions of the East European Platform (Pechora Syneclise and Caspian Basin), reef structures are widespread, but their stratigraphic intervals are far from similar. The reef formation began in the Caradocian in the Pechorian Ural, in the second half of the Llandoverian in the Pechora Syneclise, reached the maximum in the Frasnian, and gave way to the development of reef mounds in the Famennian. The structures are represented both as asymmetric reefs framing shallow zones at their boundary with the relatively deep paleobasins and as solitary structures within the latter. Reefs of the next global maximums (late Visean–Serpukhovian and Lower Permian) are confined to some places at the boundary with the Ural paleocean and its relict (Cis-Ural foredeep). The Caspian Basin accommodates reefs of all three global maximums of development—both asymmetric reef systems framing the shelf edges and symmetric intra-basin isolated structures. Such difference is due to the different paleogeomorphological type of basins. The Caspian Basin was sharply differentiated in depth throughout the Middle and Late Paleozoic, resulting in the formation of reefs rising above the bottom of these basins. In the Pechora Syneclise, depth differentiation of the basins occurred only in the Late Devonian. The Visean–Serpukhovian and early Permian shallow seas were generally weakly dissected and did not provide conditions for the formation of thick reefs protruding above the seafloor. Such reefs were formed only on the Ural paleocean edge in the Visean–Serpukhovian and on the Cis-Ural foredeep edge in the Permian.

For Upper Jurassic–Lower Cretaceous rocks of the Bazhenov Formation, a significant positive linear correlation of the content of Th, Hf, Sc, and La with the Al₂O₃ content was revealed, and their terrigenous genesis was confirmed. It has been determined that the samples, in which the distribution of Sc/Al₂O₃ and La/Al₂O₃ values does not satisfy the linear correlation, represent the mixed clayey–siliceous rocks (with P₂O₅ > 1 wt %) or the substantially pyritized rocks (with the pyrite content exceeding the OM content and C/S ≤ 1), as well as siliceous mudstones (with the SiO₂ content > 70 wt %). It is concluded that, in addition to carbonatized rocks, rocks of the above-mentioned types, as well as rocks subjected to the late diagenetic kaolinization, should be excluded before analyzing the geochemical indicators for reconstructing the formation conditions of the Bazhenov Formation. The formation conditions of these rocks were reconstructed based on the analysis of values of several geochemical modules and indicators. Based on the study of CIA and CIW variations, it was confirmed that the Late Jurassic–Early Cretaceous climate in the West Siberian sedimentary basin was warm and semiarid, and it did not change significantly during the entire period under consideration. For rocks of the Bazhenov Formation, several indicators, such as (La/Yb)_N and Eu/Eu*, as well as the distribution of trace elements in the Th‒La‒Sc triangular diagram, suggest that rocks of the Bazhenov Formation were deposited in the central and southeastern regions, with the dominant impact of source areas of mafic rocks.

The results of experimental studies of the sorption properties of ferromanganese crusts on the Kocebu Guyot relative to rare-earth metal (REM) cations are presented. It is established that the crusts are a natural, highly selective sorbent of REM cations. The REM cations are adsorbed on ore minerals (Fe-vernadite, vernadite, Mn-feroxyhyte, and goethite). The crusts are characterized by a high exchange capacity (1.67‒3.28 mg-equiv/g), which increases in the series: Lu < Gd < Dy < La, Sm < Nd < Y < Eu ( ll ) Ce. The REM cations are adsorbed by the ion-exchange equivalent mechanism—in the case of Ce³⁺ cations, according to the superequivalent mechanism with respect to cations of the exchange complex of ore minerals—Na⁺, K⁺, Ca²⁺, Mg²⁺, Mn²⁺, and Ni²⁺, which contribute 95–98% to the total capacity of minerals.

The Nagengkancherer (“Nageng”) silver deposit is the only independent silver mine in Qinghai Province, China. Here, the results of LA–ICP–MS U–Pb dating of apatite and zircon in quartz veins in this area are reported for the first time. The apatite is homogeneous and bright, with characteristics typical of unaltered magmatic apatite that has been unaffected by fluid. The zircons display oscillatory zonation typical of a magmatic origin. Apatite and zircon ages of the Paleoproterozoic Jinshuikou Group are older than those of the Triassic Erashan Formation, with apatite lower-intercept ages of 409.0 ± 3.7 and 376.2 ± 5.6 Ma, respectively, consistent with ²⁰⁷Pb-corrected ages and representing the two formation ages of apatite minerals. The zircon weighted-mean ²⁰⁶Pb/²³⁸U age is 425.2 ± 1.8 Ma, with ages of 425–408 Ma being consistent those of late Silurian outcrops on the periphery of the mining area. This indicates the occurrence of a major tectonothermal event in the late Silurian–Early Devonian, revealing the existence of concealed rock at depth in the mining area and providing new information concerning the geological characteristics of the mining area. The age of 376 Ma is reported here for the first time and provides new constraints on the regional tectonic evolution. One sample from the Erashan Formation contained magmatic zircons with a U–Pb age of 220 ± 0.62 Ma, which represents the age of the country rocks (Erashan rhyolite) captured during the ascent of ore-forming hydrothermal fluids.

Generalization of the grain size analyses of the basal Neopleistocene moraines from the sections of coastal outcrops and boreholes in the vast European Subarctic region of Russia and in more southern areas of the Timan–Pechora–Vychegda region showed that the moraines are typical mixed, almost unsorted rocks with similar contents of the gravel–sand, silt, and clay fractions, serving as one of the arguments in favor of their glacial genesis. Their grain size composition is related to the peculiarities of rocks in the glacier bed. It is formed during the crushing, abrasion, and mixing of the glacier-rafted, assimilated, and transported material during its transportation and deposition, which determines variability of the grain size composition of moraines. Consequently, the grain size composition of moraines in combination with other lithological data reflects the pathway and dynamics of the glacier movement.

A model of the gold-bearing placer formation in platform areas is proposed for the first time. Placers on the platforms are formed mainly due to the Precambrian ore sources spatially confined to the basement outcrops, and, locally, Mesozoic sources formed during the tectonomagmatic activation in the paleorift and deep fault zones. Placers related to the Precambrian sources are characterized by the presence of fine and thin gold (size 0.1‒0.25 mm) and, as a rule, are not of commercial interest. They make up alluvial bar and coastal-marine allochthonous placers. They are considered as complex (mainly rare metal–titanium) placers, where gold occurs as associated component). Placers related to sources of the Mesozoic ore formation stage are assigned to the class of small and medium reserves (gold size ranging from the dust-size to 0.2‒0.25 mm or more) and are usually mined by prospectors' teams. Placers on the platforms do not make up sheet deposits, since they are formed mainly due to sources that do not generate placers. The presence of such placers indicates the proximity of ore occurrence, whose type and location can be determined based on the study of mineralogical-geochemical features of the placer gold.

The article presents the results of studies of postsedimentary processes in Silurian carbonate rocks of the central part of the Chernyshev Ridge. A complex combination of secondary transformations in carbonate reservoir is shown. The sedimentary sequences show manifestations of regional and superimposed lithogenesis. In addition to stagewise catagenetic changes, the sediments were also subjected to regressive infiltration catagenesis (epigenesis), which was accompanied by leaching and dolomitization of limestone. All this significantly affected the filtration–capacitive properties. The obtained data can contribute to the identification of new objects for exploration drilling and optimization of exploration works in complex regions.