Lithology and Mineral Resources最新文献

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.

We studied the geochemistry of Paleoproterozoic siliceous rocks (lydites) from the North Onega synclinorium (Karelia). The study objects are represented by 16 lydite samples taken from one stratigraphic level in the geological sections of two sites–Tetyugino and Shunga. Their structural characteristics and mineral composition were studied using a scanning electron microscope equipped with an energy-dispersion microanalyzer. The trace element composition was determined by the inductively coupled plasma mass spectrometry (ICP-MS). The contents of most trace elements are below the Clarke concentrations. The Tetyugino lydites contain mainly biophile elements (P, Co, Cu, Mo, V, Ba), while the Shunga lydites are dominated by lithophile elements (Li, Rb, Cs). The trace element composition of lydites indicates that their formation took place on the periphery of the hydrothermal system, whereas the Tetyugino site was closer to the hydrothermal discharge zone than the Shunga site. The chemical peculiarities of the lydites allow us to consider them as a raw material for very pure quartz.

For the first time, original results concerning the composition of fluids extracted from glendonite found in Japan (East) Sea continental slope bottom sediment have been obtained. We used the one-act shock-destructive extraction of volatile components from fluid inclusions and made their pyrolysis-free gas chromatography-mass spectrometry analysis, which, despite the limited amount of analytical data, are of scientific and practical interest. According to the data obtained, the fluids in glendonite represent a complex multicomponent mineral-forming system. In addition to water and carbon dioxide, representatives of 13 homologous series of organic compounds were found in the studied fluid inclusions. These include oxygen-free aliphatic and cyclic hydrocarbons (paraffins, olefins, cyclic alkanes and alkenes, arenes, polycyclic aromatic hydrocarbons-PAHs), oxygenated hydrocarbons (alcohols, ethers and esters, furans, aldehydes, ketones, carboxylic acids), nitrogen-, sulfur-, halogenated compounds. An oxidized water-carbon dioxide fluid with a reduced content of hydrocarbons and S–N–F-containing compounds 0.8 rel % is preserved in glendonite.