Micrometric Inclusions in Platinum-Group Minerals from Gornaya Shoria, Southern Siberia, Russia: Problems and Genetic Significance

Micrometric inclusions in platinum-group minerals (PGMs) from alluvial placers carry considerable information about types of primary rocks and ores, as well as conditions of their formation and alteration. In the present contribution, we attempt to show, with concrete examples, the significance of the data on the composition and morphology of micrometric inclusions to genetic interpretations. The PGM grains from alluvial placers of the Gornaya Shoria region (Siberia, Russia) were used as the subject of our investigation. In order to determine the chemical composition of such ultrafine inclusions, high-resolution analytical methods are needed. We compare the results acquired by wavelength-dispersive spectrometry (WDS; electron microprobe) and energy-dispersive spectrometry (EDS) and scanning electron microscopy (SEM) methods. The results obtained have good convergence. The EDS method is multi-elemental and more effective for mineral diagnostics in comparison with WDS, which is its certain advantage. The possible conditions for the formation of inclusions and layers of gold, sulfoarsenides and arsenides in Pt3Fe grains, which have an original sub-graphic and layered texture pattern, are discussed. They are the result of solid solution and eutectic decompositions and are associated with the magmatic stages of grain transformation, including the result of the interaction of Pt3Fe with a sulfide melt enriched with Te and As

Platinum-Group Minerals in the Placer of the Kitoy River, East Sayan, Russia

The platinum-group minerals (PGM) in placer deposits provide important information on the types of their primary source rocks and ores and formation and alteration conditions. The article shows for the first time the results of a study of placer platinum mineralization found in the upper reaches of the Kitoy River (the southeastern part of the Eastern Sayan (SEPES)). Using modern methods of analysis (scanning electron microscopy), the authors studied the microtextural features of platinum-group minerals (PGM), their composition, texture, morphology and composition of microinclusions, rims, and other types of changes. The PGM are Os-Ir-Ru alloys with a pronounced ruthenium trend. Many of the Os-Ir-Ru grains have porous, fractured, or altered rims that contain secondary PGE sulfides, arsenides, sulfarsenides, Ir-Ni-Fe alloys, and rarer selenides, arsenoselenides, and tellurides of the PGE. The data obtained made it possible to identify the root sources of PGM in the placer and to make assumptions about the stages of transformation of primary igneous Os-Ir-Ru alloys from bedrock to placer. We assume that there are several stages of alteration of high-temperature Os-Ir-Ru alloys. The late magmatic stage is associated with the effect of fluid-saturated residual melt enriched with S, As. The post-magmatic hydrothermal stage (under conditions of changing reducing conditions to oxidative ones) is associated with the formation of telluro-selenides and oxide phases of PGE. The preservation of poorly rounded and unrounded PGM grains in the placer suggests a short transport from their primary source. The source of the platinum-group minerals from the Kitoy River placer is the rocks of the Southern ophiolite branch of SEPES and, in particular, the southern plate of the Ospa-Kitoy ophiolite complex, and primarily chromitites

Diversity and Metabolism of Microbial Communities in a Hypersaline Lake along a Geochemical Gradient

In the south of western Siberia (Russia), there are many unique and unexplored soda, saline, and freshwater lakes. In this study, the results are presented on microbial diversity, its metabolic potential, and their relation with a set of geochemical parameters for a hypersaline lake ecosystem in the Novosibirsk region (Oblast). The metagenomic approach used in this work allowed us to determine the composition and structure of a floating microbial community, the upper layer of silt, and the strata of bottom sediments in a natural saline lake via two bioinformatic approaches, whose results are in good agreement with each other. In the floating microbial community and in the upper layers of the bottom sediment, bacteria of the Proteobacteria (Gammaproteobacteria), Cyanobacteria, and Bacteroidetes phyla were found to predominate. The lower layers were dominated by Proteobacteria (mainly Deltaproteobacteria), Gemmatimonadetes, Firmicutes, and Archaea. Metabolic pathways were reconstructed to investigate the metabolic potential of the microbial communities and other hypothetical roles of the microbial communities in the biogeochemical cycle. Relations between different taxa of microorganisms were identified, as was their potential role in biogeochemical transformations of C, N, and S in a comparative structural analysis that included various ecological niches

Modeling the Process of Au Sorption by Natural Sorbents in the Conditions of the Dispersion Train of a Sulfide Tailings

Выполнено экспериментальное исследование, направленное на выявление закономерностей сорбции/осаждения Au различными природными сорбентами в кислой среде (рН=2). Эксперименты моделируют условия потока рассеяния Урского хвостохранилища (Кемеровская область, Россия), где наблюдается активное концентрирование Au природным органическим веществом в кислой среде. Установлено, что степень извлечения золота из сульфатного раствора в целом выше, чем из хлоридного. Это может говорить о большей термодинамической устойчивости хлоридных комплексов Au в кислой среде, чем сульфатных. В растворах с преобладающими содержаниями сульфат-ионов наблюдаются более высокие скорости осаждения золота. Установлен ряд активности природных веществ по степени осаждения Au (от большего к меньшему): смесь глинистых минералов (смектит + палыгорскит + мусковит) > гуминовые кислоты > каолинитThe experimental study is aimed at elucidation the laws of Au sorption/deposition by various natural sorbents in an acidic environment (pH=2). The experiments simulated the conditions of the dispersion train of the Ursk tailings (Kemerovo region, Russia), where active concentration of Au by natural organic matter in an acidic environment is observed. It was found that the degree of extraction of gold from a sulfate solution is generally higher than from chloride solution. This may indicate higher thermodynamic stability of Au chloride complexes in an acidic environment than sulfate ones. Higher deposition rates of gold are observed in solutions with a predominant content of sulfate ions. According to the degree of deposition of Au, a series was established (from larger to smaller): a mixture of clay minerals (smectite + palygorskite + muscovite) > humic acids > kaolinit

Native Gold and Unique Gold–Brannerite Nuggets from the Placer of the Kamenny Stream, Ozerninsky Ore Cluster (Western Transbakalia, Russia) and Possible Sources

We carried out a comprehensive study of native gold (morphology, composition, intergrowths, and microinclusions) from alluvial deposits of the Kamenny stream (Ozerninsky ore cluster, Western Transbaikalia, Russia). The study showed that there were four types of native gold, which differed significantly in their characteristics and probably had different primary sources from which placers were formed: gold–quartz, oxidized gold–sulfide, gold–silver, and zones of listvenites with copper–gold and gold–brannerite (Elkon-type). Particular attention was paid to the study of unique, both in size and in composition, gold–brannerite nuggets of the Kamenny stream. It was established that the gold in the gold–brannerite nuggets (GBNs) had wide variations in chemical composition and mineral features. According to them, there were five different fineness types of native gold: 750–800‰; 850–880‰; 880–920‰; 930–960‰; and 980–1000‰. The data obtained indicated a multistage, possibly polygenic, and probably polychronous formation of GBN gold–uranium mineralization. The first stage was the formation of early quartz–nasturanium–gold–W–rutile–magnetite association (Middle–Late Paleozoic age). The second was the crystallization of brannerite and the replacement of an earlier pitchblende with brannerite (Late Triassic (T3)–Early Jurassic (J1) age). The third was the formation of the hematite–barite–rutile–gold association as a result of deformation–hydrothermal processes, which was associated with the appearance of zones of alteration in brannerite in contact with native gold with 8–15 wt.% Ag. The fourth was hypergene or the low-temperature hydrothermal alteration of minerals of early stages with the development of iron hydroxides (goethite) with impurities of manganese, tellurium, arsenic, phosphorus, and other elements. The carbon isotopic composition of an organic substance indicates the involvement of a biogenic carbon source. In the OOC area, there were signs that the composition of the GBNs and the quartz–chlorite–K–feldspar-containing rocks corresponded to Elkon-type deposits

Influence of Sample Pretreatment on the Analysis of High Contents of Rare-Earth and High Field Strength Elements in Geological Samples by ICP-AES and ICP-MS (Case Study of the Tomtor Deposit)

В работе изучено влияние химической пробоподготовки на определение высоких содержаний редкоземельных (РЗЭ) и высокозарядных (ВЗЭ) элементов в геологических образцах методами атомно-эмиссионной спектрометрии с индуктивно-связанной плазмой (ИСП-АЭС) и масс-спектрометрии с индуктивно-связанной плазмой (ИСП-МС). Изучались породы и богатые руды Томторского ниобий-редкоземельного месторождения. Предложена методика сплавления с пероксидом натрия геологических образцов с высоким содержанием «упорных» минералов, при котором достигается полное вскрытие пробы. Результаты анализа методами ИСП-АЭС и ИСП-МС с химической пробоподготовкой сопоставлены с результатами, полученными методом РФА-СИ без химической пробоподготовкиInfluence of sample pretreatment on the analysis of the high contents of rare earth (REE) and high field strength (HFSE) elements in geological samples by inductively coupled plasma atomic emission spectrometry (ICP-AES) and inductively coupled plasma mass spectrometry (ICP-MS) was studied. The rocks and rich ores of the Tomtor Nb-REE deposit were explored. Complete dissolution of the geological samples with a high content of “refractory” minerals has been achieved using fusion with a sodium peroxide. The results obtained by ICP-AES and ICP-MS after chemical dissolution are comparable with the results obtained by the XRF-SR without chemical pretreatmen

Specific of Stable Carbon Isotopes Determination in Organic-Bearing Sediments

Проведено исследование изотопного состава углерода в органосодержащих донных осадках термального озера Фумарольное (кальдера Узон, Камчатка). Представлены результаты изучения изменений δ13С в донных осадках термального озера при последовательном разложении H3PO4 в течение 2 ч, 24 ч и 7 дней. На примере двух образцов показано изменение δ13С во времени и после обработки HCl и H2O2. После обработки HCl значения δ13С изменяются относительно исходных от 1 до 3 ‰, что можно учесть при интерпретации данных. При стандартной процедуре удаления карбоната перекисью водорода выявляется существенная трансформация остаточного С‑содержащего вещества в случае длительной реакции с Н3РО4 при повышенных температурахThe study of the carbon isotopic composition in organic-bearing bottom sediments of the thermal lake Fumarolnoye (Uzon caldera, Kamchatka) has been carried out. The results of studying δ13C changes in the bottom sediments of a thermal lake during the sequential extraction of H3PO4 for 2 hours, 24 hours and 7 days are presented. The change in δ13С with time and after treatment with HCl and H2O2 is shown using two samples as an example. After treatment with HCl, the δ13С values change relative to the initial ones from 1 to 3 ‰, which can be taken into account when interpreting the data. The standard procedure for removing carbonate with hydrogen peroxide reveals a significant transformation of the residual C‑containing substance in the case of a prolonged reaction with H3PO4 at elevated temperature

Determination of Ore Contents of Rare Earth Elements in Geological Samples by Atomic Emission Spectrometry with Arc Two-Jet Plasmatron

В работе приведены результаты определения рудных содержаний редкоземельных элементов (РЗЭ) в геологических образцах методом атомно-эмиссионной спектрометрии с дуговым двухструйным плазматроном, позволяющей проводить анализ твердофазных образцов в виде мелкодисперсных порошков. Изучался образец ниобий-редкоземельной руды, отобранный на участке Буранный Томторского месторождения (Арктическая Сибирь, Россия). Результаты анализа по всем РЗЭ, за исключением Tb, Ybи Lu, согласуются с данными ИСП-МС‑анализа. Показано, что использование одновременно нескольких аналитических линий при определении РЗЭ значительно повышает точность определения и достоверность результатовThe paper presents the results of determination of the ore contents of rare earth elements (REE) in geological samples by atomic emission spectrometry with arc two-jet plasmatron, which allows to analyze solid-phase samples asa fine powders. We studied a niobium-rare earth ore sampled at the Buranniy site of the Tomtor deposit (Arctic Siberia, Russia). The results for all REEs, except for Tb, Yb and Lu, are consistent with the ICP-MS data. It is shown that the use of several analytical lines at the same time in the determination of REE significantly increases the determination accuracy and reliability of the result