Home – Home – Jornals – Russian Geology and Geophysics 2018 number Неопубликованное

Using a model sample of pyrite ore collected at the Degdekan gold deposit (North East Russia), we demonstrate the use of different variants of the IСP-MS method to determine the ratio of surficial-bound and structural-bound forms of trace elements (TE) in pyrite. Despite the difference in the physicochemical nature of the analysis methods involving the decomposition of crystals of different sizes (analytical data selections for single crystals - ADSSC) and direct determination by scanning the surface with a laser beam of different power (LA-IСP-MS), it has been shown that a number of elements tend to enrich the surface layer of pyrite crystals. The ratio of TE contents in the surface layer and in the volume (structure) of the crystal is defined as the selectivity (S) of surficial phases in the uptake of a given element. According to ICP MS – ADSSC data, the selectivity was 3.9 (Mn), 3.3 (Ag), 6.4 (Pd), 6.4 (La), 0.3 (Pr), 0.8 (Tb), 2.6 (Ho), 0.5 (Er), 1.0 (Lu), according to the results of LA-ICP-MS 3.9 (Mn), 1.4 (Co), 6.2 (Ni), 1.6 (Cu), 0.9 (Sb), 0.2 (Au), 0.3 (As), 6.8 (Ag), 18 (La), 46 (Ce), 5.2 (Pr), 11 (Nd), 1 (Eu), 0.6 (Dy). A comparison with experimental data for S Mn, Pd, and Ag reveals comparable results. However, it is concluded that LA-IСP-MS should be more representative in order to enable criterion-based statistical sampling (CBSS) according to a principle similar to ADSSC for more accurate discrimination of the structural component of TE concentration. Otherwise, significant errors are possible due to the influence of microinclusions of autonomous phases, in this case galena, which concentrates As, Au and Sb due to heterovalent isomorphism, resulting in S<1 for these elements. Most of the studied TEs show a direct correlation between selectivity and the difference in the ionic radii of the element and Fe, which confirms the relationship between S and the level of incompatibility of the impurity element in FeS₂. High correlation coefficients between light REEs in the surface and the absence or negative correlations between light and heavy REEs are noted. This may reflect differences in the species of heavy and light lanthanides and requires more detailed study using LA-ICP-MS surface analysis and the application of the CBSS procedure. Despite the preliminary nature of the results, they deserve attention in practical terms as a justification for the development of technology for the extraction of critically important REEs as by-products in the processing and enrichment of pyrite ores and concentrates. They also justify the importance of the surface accumulation effect of REEs and the need to take it into account in meta-analysis and statistical processing of the results of analytical determinations of element content.

This paper describes a system for monitoring seismicity in specific volcanic areas of Kamchatka (Russia, Kamchatka Peninsula) based on estimates of the seismicity level according to the SESL’09 (Statistical Estimation of Seismicity Level) methodology. The application of the SESL’09 method to studying the preparation of volcanic activations is a promising approach for monitoring volcano state. We present the results of identifying seismically active source volumes for 10 active Kamchatka volcanoes. Nomograms were constructed for these volumes, allowing for the estimation of the seismicity level for any given time interval based on the seismic energy released within it. Examples of variations in the seismicity level of the volcanic areas, which are associated with the preparation for an eruption, are provided and support this conclusion.

At the end of the Pleistocene, two large-scale volcanic eruptions, associated with the formation of the Lvinaya Past caldera, occurred in the southern part of Iturup Island (Southern Kurils). These eruptions resulted in the formation of the largest partially submerged caldera in the Kuril Island arc, measuring 7×9 km, with a rim area of ~50 km² and a volume of ~25 km³ (including a submarine part of 12.26 km³). Comprehensive geological and geochronological studies established that the caldera formation was associated with two successive, very powerful explosive eruptions (LP-I and LP-II), separated by a repose period of several hundred years. The age of the first eruption (LP-I) is likely about 13,500 cal yr BP. The age of the second eruption (LP-II), determined from a series of radiocarbon dates, is estimated at ~12,300 cal yr BP. The eruptions were of Plinian type and involved the massive ejection of silicic pyroclastic material, represented by pyroclastic flow deposits and tephra. Based on silica and total alkali contents, the pumice from the caldera-forming eruption corresponds to low-alkali dacites and rhyodacites (SiO₂ 63.4–69.95 wt.%, total alkalis 3.9–5.5 wt.%), with less frequent andesitic (SiO₂ 58.3 wt.%, total alkalis 3 wt.%) and rhyolitic compositions (SiO₂ ~74 wt.%, total alkalis 5.6 wt.%). The total volume of erupted material from both events is preliminarily estimated at 80–100 km³ (DRE 35–45 km³), with the LP-II eruption being 30–40% more powerful than LP-I. It is suggested that the LP-I and LP-II eruptions, occurring only a few hundred years apart, could have impacted the natural environment on a regional and possibly global scale.

When conducting seismic surveys on the ground, it is usually not possible to place receivers with a uniform sufficiently frequent step over the area of observation. Interpolation (regularization) is an effective tool for generating additional seismic records without changing the spectral composition of data over time and with expansion of the spectral composition over space. This paper considers the optimization of a regularization algorithm based on iterative application of discrete Fourier transform (DPF) over a space known as ALFT (Anti-leakage Fourier transform). The proposed modification of ALFT is a way to reduce the set of test wave numbers when performing DPF. The effectiveness of the proposed algorithm was confirmed by processing both synthetic and field data. The calculation time has been reduced by several times compared to the original algorithm, and the results of recovery of skipped routes have not deteriorated. The results are valuable from a practical point of view and can be applied in future to the processing of ground-based seismic data on an industrial scale.

New data on the composition and distribution of polycyclic aromatic hydrocarbons (PAHС) in thermal waters and host rocks in Baikal Rift Zone were obtained. It was shown that the total content of all identified individual compounds is 0.17-1.15 μg/L in the thermal springs and is 0.021-1.19 μg/kg in the rock. Naphthalene, phenanthrene, and dibenzo[a,h]anthracene dominate in the water. Phenanthrene, fluoranthene, and dibenzo[a,h]anthracene are predominant in the rock. The total PAHC content increased with TDS of water and with N₂ and He growth in escaped gases. The calculated coefficients of technogenic load showed a low level of pollution for all studied sources. According to indicator ratios, the PAHC origin was determined. On the one hand, PAHC in thermal waters had petrogenic origin and were formed due to geochemical transformations of organic matter under high temperatures and pressures and microbial activity, entered with aqueous and gas along faults and fractures. On the other hand, some compounds have a natural pyrogenic origin, where pyrolysis products enter springs either at near-surface conditions or when mixing. The results let to characterize the composition of thermal waters in more detail and to describe a conceptual model the thermal waters composition formation in the studied region.