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Triassic sections of the Lena lower reaches (northern Yakutia) were studied. Stratigraphy and paleontology of the Triassic deposits were refined and described in detail, and their age was constrained by different fauna groups. The first detailed local Triassic biostratigraphic scheme is reported, which includes ammonoid, nautiloid, and bivalve zones and subzones and foraminifer beds. The scheme is compared with the Canadian Triassic Zonal and Standard (International) Scales.

We studied the chemical composition of rock-forming minerals in gabbroids from the Chirii outcrop and the evolutionary features of parental basic melt during the crystallization of these rocks. Results were compared with data for basanites from pipes of the North Minusa depression. The mineralogical composition and thermobarogeochemical data of the gabbroids were examined in detail, and chemical analyses of rock-forming minerals (clinopyroxene, plagioclase, amphibole, biotite, titanomagnetite, and apatite) were carried out. Based on the homogenization temperatures of primary melt inclusions, we established the minimum temperatures and sequence of mineral crystallization in the gabbroids: clinopyroxene (>1160

A unique xenolith of eclogite, 23 × 17 × 11 cm in size and 8 kg in weight, was found in the Udachnaya kimberlite pipe. One hundred twenty-four diamond crystals recovered from it were analyzed by a number of methods. The diamonds differ in morphology, internal structure, color, size, and composition of defects and impurities. The xenolith contains diamonds of octahedral and cubooctahedral habits. In cathodoluminescence, the octahedral crystals have a brightly glowing core with octahedral zones of growth and a weakly glowing rim. In the cores of these crystals the N impurity is mostly present in the B1 form (30 to 60%). At the same time, N in the rim is chiefly in the A form. The cubooctahedral crystals show a weak luminescence. The content of nitrogen and degree of its aggregation are close to those in the rim of octahedral crystals. The diversity of morphology and impurity composition of diamonds from the xenolith can be explained by their formation in two stages. At the first stage, the diamonds formed which became the cores of octahedra. After a long-time interruption, at the second stage of diamond formation crystals of cubooctahedral habit appeared and the octahedral crystals were overgrown. Wide variations in nitrogen contents in the xenolith crystals allowed their use to estimate the kinetics of aggregated nitrogen. The data obtained show that the aggregation of A centers into B1 centers in the diamonds is described by a kinetic reaction of an order of 1.5.

TEM responses in an inhomogeneous medium are modeled in 3D using the vector finite element method for induction logging in petroleum wells. The algorithm is applied to HFIL diagrams obtained in wells that tap thinly laminated formations with regard to the true position of logging tools.

Sunshading is a powerful tool for the enhancement of edges in images. Given the azimuth and elevation of a source illumination, it calculates the reflectance from a surface which is composed of the data to be interpreted. It is a standard tool used in the interpretation of geophysical potential field data. In the great Oulad Abdoun phosphate basin, inclusions of sterile hardpan - so-called

This paper deals with the behavior of fine gold particles (0.25-0.1 mm) and gold dust (<0.1 mm) during the formation of alluvial placers in denudation areas in southern West Siberia. Native gold particles with a low settling velocity, <5-10 cm/s, such as dust (<0.1 mm) and fine flat particles, are transported with a river stream beyond denudation areas. This easily migrating gold participates in the formation of lithochemical flows, which are an important indicator of gold mineralization. It occurs in the upper beds of alluvial section. Heavier fine gold particles are partly retained at the site of river activity, and the rest are partly redeposited in cooler parts of placers, being graded according to their settling velocity, as evidenced from the direct relationship between the flatness and size of gold particles. Fine gold particles do not form large accumulations in alluvial autochthonous placers. The main typomorphic features of fine gold particles and gold dust are their abundance in ore sources, compositional similarity to larger gold fractions, and high migration ability. In contrast to morphological features of gold, these ones remain stable during the river drift.

Geology and mineralogy of the Ulakhan Au-Ag epithermal deposit (northeastern Russia, Magadan Region) are considered. A four-stage scheme of mineral formation sequence is proposed. Concentrations of Au and Ag in minerals of early and late parageneses were determined. It has been established that uytenbogaardtite is associated with native gold and hypergenesis stage minerals - goethite, hydrogoethite, or limonite replacing pyrite. The compositions of uytenbogaardtite (Ag₃AuS₂), acanthite (Ag₂S), and native gold were studied. The composition of the Ulakhan uytenbogaardtite is compared with those of Au and Ag sulfides from other deposits. Thermodynamic calculations in the system H₂O-Fe-Au-Ag-S-C-Na-Cl were carried out, which simulate the interaction of native gold and silver with O₂ and CO₂-saturated surface waters (carbonaceous, sulfide-carbonaceous, and chloride-sodium-carbonaceous) in the presence and absence of acanthite and pyrite at 25

Results of study of different types of inclusions in minerals from mantle xenoliths from the Bele pipe basanites are presented. Two groups of inclusions were recognized in the host minerals according to their genesis. The first group includes single, apparently primary, fluid inclusions. They were discovered only in orthopyroxenes and consist of CO₂ (95 mol.%) and N₂ (5 mol.%). These inclusions had partly leaked. The densities of two least leaked inclusions from different xenoliths are 1.05 and 1.14 g/cm³, and their trapping pressures are estimated at >8.5 and 12 kbar, respectively. The second group includes syngenetic secondary fluid, melt, and crystalline inclusions. In composition the secondary fluid inclusions differ from the primary ones in higher concentrations of N₂ (up to 7 mol.%). Their maximum density is 0.57 g/cm³, which corresponds to 2.4-2.6 kbar and 1100-1200

The Upper Jurassic basalts (150-160 Ma) described as the Ichetui Formation over the territory of the Tugnui, Margintui, and Maly Khamar-Daban volcanic structures have been studied paleomagnetically. It is shown that natural remanent magnetization still contains a component which may reflect the geomagnetic field direction at the beginning of the Late Jurassic. This is supported by reversal and conglomerate tests. Calculation of mean paleopole gives: Plat = 63.6

A pebble of anthraxolite found in the basin of the Kendei River, a tributary of the Lena River, was examined under polarization metallographic and electron microscopes to get an insight into their structure and ontogeny. A polished section of the mineral demonstrates evident anisotropy in polarized reflected light and finely sculptured microrelief of growth and induction surfaces of spherulites on the fracture (fractograms). The morphogenetic inspection and study of ontogenetic signs of origination, growth, phase transformations, and other changes of anthraxolite revealed a growth mechanism typical of spherulitic dendrites owing to low-angle splitting of radial subindividuals. Layered gravity structures (`mineralogical levels') have been found in crystallization voids. They are composed of an ordered even-grained aggregate of spherical crystals of anthraxolite with the tactoid texture of precious opal. The tactoid mineralogical levels of anthraxolite are characterized by the block structure of microspherulite aggregates, signs of deformation, twinning and geometrical selection of blocks, and elements of recrystallization. Growth-oriented zones of regular nets with endotaxial inclusions of graphite inside the cells have been observed on induction surfaces in spherulitic dendrites. Their appearance is considered an indicator of phase transformations. Supramolecular structures and their effect on the morphology of anthraxolite are discussed in short.