Mineralogical,Crystal-Chemical,and Rb–Sr Isotope Data on Terrigenous Globular Phyllosilicates of the Maastakh Formation (Lower Vendian,Olenek Uplift)

Lithology and Mineral Resources - The mineralogical, structural, crystal-chemical, and isotope-geochronological data were obtained for the first time in two samples of globular phyllosilicates...     

Taxonomic composition and biostratigraphic value of the Early Riphean organic-walled microfossil association from the Ust’-Il’ya Formation of the Anabar Uplift,Northern Siberia

It is demonstrated on the basis of the first monographic study of multiple and taxonomically variable organic-walled microfossils from the Ust’-Il’ya Formation of the Anabar Uplift that both prokaryotic and eukaryotic forms are present in the composition of this microbiota. They are divided into four formal groups on the basis of the specifics of the morphological indicators of the identified taxa. The review of the data on the isotopic age of hosting deposits showed that the Ust’-Il’ya Formation is of the Early Riphean in age which are currently evaluated as 1750 ± 10–1400 Ma. Relatively large and morphologically complex eukaryotic forms present in the Ust’-Il’ya Formation served in due time as the basis for an erroneous conclusion on the Late Riphean age of the specified formation and the overlying Lower Kotuikan Subformation of the Anabar Uplift. The paper provides a global comparative analysis of the Early Riphean microbiotas, demonstrates the position of the Ust’-Il’ya and Kotuikan microbiotas amidst the microbiotas of the same age, and shows that the relatively large acanthomorphic acritarchs Tappania, Valeria, Dictiosphaera, Satka, and Shuiyousphaeridium appeared in the geological history already during the Early Riphean Erathem. Moreover, the paper discusses the recently published data on the distribution of aerobic and anaerobic conditions in the Early Riphean paleobasins and provides the conclusion on the impact of the lateral change of these conditions on the taxonomic composition of the microbiota.     

Rb–Sr Age of Riphean Glauconites of the Kamo Group (Baikit Anteclise,Siberian Craton)

Doklady Earth Sciences - A mineralogical-geochemical study of globular phyllosilicates (GPS) of the glauconite-illite series of the Dolgokta Formation from the stratigraphic well Chunkinskaya Well...     

Structural and Morphological Features of the Participation of Microorganisms in the Formation of Nb–REE–Rich Ores of the Tomtor Field (Russia)

Doklady Earth Sciences - Data indicating the important role of microorganisms in the redistribution of REEs in the weathering crust and the decisive role in the concentration of REEs during the...     

Formation Conditions of Ferromagnesian Metasomatic Carbonates in the Lower Riphean Terrigenous–Carbonate Rocks of the Southern Urals

Lithology and Mineral Resources - Ferromagnesian carbonate metasomatites in limestones of the Lower Riphean Suran Formation in the Avzyan ore region (Bashkir meganticlinorium) are represented by...     

Globular Phyllosilicates of the Glauconite–Illite Series in the Cambrian and Ordovician Rocks of the Eastern Baltica (Northern Estonia,Western Lithuania,and Western Latvia)

Lithology and Mineral Resources - The mineralogical, structural and crystal-chemical features of seven samples of globular phyllosilicates of the glauconite–illite series (GPS) from the Lower...     

A Local Source of Detritus for Rocks of the Ai Formation (Basal Level of the Lower Riphean Stratotype,Bashkir Uplift,Southern Urals): Evidence from U–Pb (LA-ICP-MS) Dating of Detrital Zircons

Doklady Earth Sciences - The results of U–Pb dating of detrital zircons extracted from rocks of the Ai Formation are presented. A provenance-signal of a local source with an age of about 2.07...     

Age and sources of the anorthosites of the Neoarchean Kolmozero-Voron’ya greenstone belt (Fennoscandian Shield)

New data are reported on U-Pb (SHRIMP-II) age (2662 ± 7 Ma), isotope (Sm-Nd) and geochemical compositions of the anorthosites of the Patchemvarek Massif and “ovoidal” anorthosite sills of the Neoarchean Kolmozero-Voron’ya greenstone belt. Mesoarchean (2938 ± 8 Ma) zircons found in the Patchemvarek anorthosite have low Th/U ratio, are overgrown by a thin rim, and may be interpreted as xenogenic crystals assimilated by primary melts of the gabbro-anorthosite massifs from host Mesoarchean tonalites during crystallization in a magmatic chamber. The “ovoidal” anorthosite sills are dated at 2730–2740 Ma on the basis of U-Pb local zircon isotope analysis. The sills of the “ovoidal” anorthosites in the Kolmozero-Voron’ya GSB represent the older (2730–2740 Ma) rock group, which differs from the Patchemvarek anorthosites in strongly depleted Nd isotope composition and some geochemical features. In terms of age and Sm-Nd isotope characteristics, the “ovoidal” anorthosites are close to the komatiites of the lower volcanogenic sequence (ε_Nd(Т) + 3.0–3.2), and metaandesites (2778 ± 5.4 Ma, U-Pb TIMS, ε_NdТ + 3.5) and metatholeiites of the upper volcanogenic sequence (ε_Nd(Т) + 3.5–3.7) of the supracrustal complex of the Kolmozero-Voron’ya GSB.     

U–Pb LA–ICP–MS Age of Detrital Zircons from the Lower Riphean and Upper Vendian Deposits of the Luga–Ladoga Monocline

The results of LA–ICP–MS U–Pb analyses of detrital zircons from the Precambrian deposits of Luga–Ladoga monocline are discussed. The age spectra of the zircons separated from the Riphean to Upper Vendian sandstones from the Shotkusa-1 well demonstrate dominance of the Paleo- and Mesoproterozoic grains while the Archaean zircons are subordinate. The Riphean debris sources were local swells of the Northern Ladoga basement. The sequence interval presumably corresponding to the Vasilieostrov Formation (Upper Vendian) has yielded not only Paleo- and Mesoproterozoic zircon ages, but Neoproterozoic as well, implying a Timanide provenance: these zircons (527 ± 9 and 516 ± 13 Ma) allow deposition of a significant part of the Shotkusa-1 sequence at the very beginning of the Cambrian.     

The Background Features and Formation of Chemical Elements of Groundwater in the Region of the Middle and Lower Reaches of the Yangtze River

The paper deals with the background features, formation and distribution of the chemical el-ements K, Na, Ca, Mg, Si, Fe, Mn, Cr, Ni,V, Co, Ti, Mo, Cu, Pb, Zn, As, Hg, Cd, Be, Li, Sr, B,F, Cl, Br and I in the groundwater in the region of the middle and lower reaches of the YangtzeRiver and their relations to the composition of the water-bearing media, properties of the overly-ing rocks and soils, redox environment, and groundwater flow condition, mineralization and pHof groundwater.     

Age of island-arc granites in the Shchuch’ya zone,Polar Urals: First U–Pb (SIMS) results

The granitic magmatism occurred at the precollisional stage of the continentalization of the mafic basement of the Shchuch’ya island arc system. The first U–Pb (SIMS, SHRIMP II) data on zircons indicate three pulses of transformation of the oceanic crust into a continental crust: in the Silurian and Middle and Late Devonian. The age of the Yanganape granite is 429 ± 4 Ma, which corresponds to the Late Wenlockian; that of the Yurmeneku massif is 385 ± 2 Ma (Givetian); and that of the Canyon Massif is 368 ± 3 Ma (Famennian). The zircons from the Yanganape granite yielded an age of 335 ± 4 Ma, which corresponds to the Early Carboniferous (Visean). Similar ages were noted in uranium-rich zircons from the Canyon Massif granite. They correlate with the collision time of the island arc with the eastern edge of the Eastern European paleocontinent, and it is possible that this event caused disturbance of the U–Pb system of zircons in the islandarc granites of the Shchuch’ya zone.     

New Data on the Early Riphean Age (U–Pb,Shrimp-II) of Acid and Basic Effusives of the Gulf of Finland (Sommers Island,Russia)

Doklady Earth Sciences - This work presents data on the age of the volcanites of Sommers Island located to the south of the submarine extension of the Vyborg massif, as potential comagmates of...     

Hydrocarbons in the Basement of the South China Sea (Vietnam) Shelf and Structural–Tectonic Model of their Formation

Geotectonics - The paper considers the origin of hydrocarbon accumulations within the Pre-Cenozoic basement of the Vietnam shelf. It is shown that the formation of hydrocarbon deposits is...     

Mineralogical–Geochemical Features,Genesis, and Age of Refractory Clays in the Shulepovo Deposit (Ryazan Region,Central European Russia)

Lithology and Mineral Resources - The Shulepovo refractory clay deposit was discovered in the 1970s. It consists of subhorizontal kaolinite lenses located at different depths (1–20 m) in a...     

Geochemical Features and Formation of the Auriferous Cherts in the Mojiang Gold Deposit,Yunnan

Auriferous cherts in the Middle Carboniferous Jinchang Formation are the dominant host rocks of auriferous quartz veins and mixed orebodies comprised of gold-bearing quartz veins and cherts in the Mojiang gold deposit.The rocks exhibit sedimentary texture and structure and are composed of hot-water deposited minerals.The FeO,Fe2O3,Au and Ag contents of the auriferous cherts are high;the Cr,Ni and Co contents are also high but significantly variable;MnO/TiO2 and TFe/TiO2 ratios are relatively higy.As viewed from a few diagrams that distinguish different chert formations,the auriferous cherts are in or near the range of hot-water deposited cherts.Because the correlation coefficients between Au contents and those of Cr, Ni of the rocks are negative,a great Au amount in the cherts might not be brought about by later hydrothermal alterations.The rare-earth elements,O and Si isotopic compositions of the auriferous cherts demonstrate that the cherts belong to hot-water deposited rocks.The later hydrothermal alterations made the petrochemical compositions of the cherts deviate from the characteristics of hot-water deposition.In general,the geological and geochemical features of the auriferous cherts demonstrate that the rocks were formed by hot water deposition.     

Rb—Sr Isotope Age of the Shangdaheyan Intrusion in the Bogda Shan Region and Its Geological Implications

The Bogda Shan orogenic belt is interpreted to be an Upper Palaeozoic continental rift, which was closed towards the end of the Carboniferous period. Intrusive activities in that belt are represented mainly by a large number of diabasic sills, dykes and stocks with sparse dioritic and granitic bodies. Determinations on a group of samples from the Shangdaheyan intrusion yielded a mineral-rock Rb-Sr isochron with an age of 298.4±0.76 Ma and an initial⁸⁷Sr/⁸⁶Sr ratio of 0.7041. In combination with field evidence, these results indicate that most of the intusions of the Bogda Shan orogenic belt were emplaced during the Hercynian cycle as a result of initial extension following rift closure, and that post-Hercynian intrusive activities are not important in that belt.     

Quartzite–Schist Sequences of the Aktau–Mointy Massif (Central Kazakhstan): Structural Position,Provenance, and Formation Stages of the Earth Crust in the Precambrian

Geotectonics - Detrital zircons from quartzite–schist sequences of the Aktau–Mointy Massif (Central Kazakhstan), which occur in various structural positions relative to the Early...     

Mineralogical and Petrographic Features of the Lower Horizon of Ferruginous Laterites and Ferriplantites of the Fouta Djallon–Mandingo Province (Guinea,West Africa)

Geology of Ore Deposits - A ferruginous laterite horizon was established for the first time as a result of the detailed study of the profile of the bauxite-bearing lateritic weathering crust in the...     

Spectroscopic Features and Formation Conditions of Sphalerite in the Lead-Zinc Deposit, Guangdong,China

Electron paramagnetic resonance spectra, absorption spectra, cathodoluminescence spectra and infrared spectra of sphalerite from the Lechang remoulded sedimentary lead-zinc deposit have been studied so as to provide microscopic evidence for the formation conditions and mineralization stages of the deposit as well as the geochemical processes of mineralization. On the basis of thermodynamic calculations, the stable fields of sphalerite from different mineralization stages were determined and are shown in logfs_2-logfo_2 diagrams; furthermore. the physico-chemical conditions of mineralization and the properties of mineralization solutions are discussed so that reliability of the genetic information provided by the spectroscopy of sphalerite may also be verified. It is suggested that the temperature and pH value of the mineralization system decrease, and so do the fugacities of O_2, S_2, H_2. and H_2S and the activities of HS~- and SO_4~(2-) from the early to late stages of minerahzation.