Evolution of the Processes of Mineral Formation in Early Vendian Terrigenous Rocks of the Nepa–Botuoba Anteclise

Lithology and Mineral Resources - Main regularities in the manifestation of epigenetic processes in Lower Vendian terrigenous rocks of the Nepa–Botuoba anteclise are established. Evolution of...     

Devonian ultramafic lamprophyre in the Irkineeva–Chadobets trough in the southwest of the Siberian Platform: Age,composition, and implications for diamond potential prediction

The results of geochronological, mineralogical, petrographical, and geochemical study of the Ilbokich ultramafic lamprophyre are reported. The specific features in the mineral and chemical compositions of the studied ultramafic lamprophyre indicate that it can be regarded as a variety similar to aillikite, while other differences dominated by K-feldspar can be referred to damtjernite. According to Rb–Sr analysis, ultramafic lamprophyre dikes intruded at the turn of the Early and Middle Devonian, about 392 Ma ago. This directly proves the existence of Early Paleozoic alkali–ultramafic magmatism in the northern part of the southwest Siberian Platform. A finding of Devonian alkali–ultramafic lamprophyre is of dual predictive importance. On the one hand, it is indicative of the low probability of finding large diamond-bearing deposits in close association with aillikite. On the other hand, it can be indicative of a possible large Devonian diamond province in the studied territory, where diamondiferous kimberlite is structurally separated from aillikite.     

Gas seeps in the North Caspian water area

Seismoacoustic profiling and sonar survey of the North Caspian water area revealed in some areas signs of intense release of methane from the sedimentary sequence. This fact was also supported by submarine videorecording data. Such sites are characterized by hummocky and ridgy morphologies, which accommodate local cone-shaped bodies (up to 1.3–1.5 m high) overgrown with algae, Balanus, and shelly material. Based on dredging data, these rises are composed of hard sandstones and shells. They can cover the seafloor or make up separate interlayers in the bottom sediments down to a depth of 2.7 m. Mineralogical studies demonstrated that the coarse-grained sediments are cemented with Mg-calcite, with δ¹³C reaching ?32.6‰. They also include microcrystalline barite and globular iron sulfides. The results of investigation suggest that the local activation of authigenic mineral formation is related to gas discharge sources.     

Catagenetic transformations of gravelly–sandy rocks of the Taseeva Group in the Irkineevo–Chadobetsk riftogenic trough (southern Siberian Platform)

The stagewise optical and electron-microscopic analysis of the texture and mineralogy of the Upper Riphean–Lower Vendian gravelly–sandy rocks (Taseeva Group) in the Irkineevo–Chadobetsk riftogenic trough revealed a wide spectrum of secondary transformations: gravitational corrosion of allothigenic minerals, their plastic deformation, intense fracturing, and authigenic mineral formation. Traces of low-temperature hydrothermal processes were recorded. The multistage nature of authigenic mineral formation is attributed to the periodic resumption of tectonic dislocations owing to reactivation of fluid dynamics and thermal impulses ΔT.