As a result of analyzing the materials of hydrogenic uranium deposits formed by ground- and stratal waters enriched in uranium and accompanying elements, five types of objects have been identified. The first is distinguished from published data, while the others, from the author’s detailed studies. The main principles for typification are the occurrence and correlation between infiltration and exfiltration processes reflected in epigenetic ore-controlling zoning. The first three types—infiltration–oxidation, reduction, and exfiltration–reduction—are monochronous with a single leading geochemical barrier and primarily include small and medium-sized uranium deposits. The other two types—infiltration–exfiltration and exfiltration–infiltration have a polychronous and polygenic character with a complex combination of geochemical barriers and are represented by medium-sized and large uranium deposits. They are characterized by the presence of rich ores with uranium content >0.5% and accompanying REE and are mined by an ecological in-situ leach method, except for surficial deposits of the first type.

The Valunistoe Au–Ag deposit is the third largest among epithermal deposits in Chukotka after the Kupol and Dvoinoe. It is located at the western closing of the East Chukotka flank zone of the Okhotsk-Chukotka volcanic belt. Volcanic domes (Pravogornenskaya, Zhil’ninskaya, Shakhskaya, Valunistaya, Shalaya, and Oranzhevaya, each is 3–6 km in diameter) have the main ore-controlling significance in the area; they form a chain elongated to the northeast, along the Kanchalan fault zone. Near the deposit, Upper Cretaceous volcanics are widespread: ignimbrites, lavas and tuffs ranging from rhyolite to basaltic composition, and lenses and interbeds of sedimentary rocks, subvolcanic bodies and dikes of andesites, basalts, and dacites. The structure of the deposit is caused by its localization within the limits of the eponymous (Valunistaya) volcanic dome. Twelve ore-bearing vein zones with thicknesses ranging from several to several tens of meters have been revealed at the deposit. The Glavnaya (Main) and Novaya (New) vein zones have been studied in detail; they are traced along their strikes to a distance of more than 1500 m and consist of en echelon veins 1.0 m thick on average, with lengths varying from 100 to 400 m. Based on the sampling data, Au and Ag contents in ores are 0–474.3 and 0–3794.23 g/t, respectively. Colloform-banded structures are frequently encountered, often combined with breccia structures. The main vein minerals are quartz and adularia; calcite, chlorite, fluorite, sericite, pyrophyllite, kaolinite, montmorillonite, gypsum, and epidote are less frequent. The main ore minerals are pyrite, acanthite, chalcopyrite, galena, sphalerite; secondary ore minerals are native Au and Ag and polybasite; rare ore minerals are pearceite, magnetite, hematite, marcasite, freibergite, tetrahedrite, bournonite, hessite, matildite, and others. Ores are characterized by an Au/Ag ratio from 1 : 5 to 1 : 10 and sulfidity (0.5–5%). Ores are enriched in many elements (Au, Ag, Sb, Cd, Pb, Cu, Zn, As, Se, Mo, Te, and Cr), with enrichment factors ranging from several times (Se, Mo, Te, and Cr), to tenfold (Cd, Pb, Cu, and Zn) and hundredfold (Sb) levels, reaching an excess of tens and hundreds thousand times for Au and Ag (Fig. 7). Ores are characterized by a low total REE and demonstrate positive Eu anomalies. Geochemical features are consistent with the mineral composition of ores. Full homogenization of fluid inclusions in quartz occurs at temperatures of 203–284°C and 174–237°C in calcite, while the salt concentration in both cases is from 0.2 to 0.7 wt % NaCl equiv. Fluid density changes from 0.87 to 0.56 g/cm 3 . The results give grounds to attribute the Valunistoe deposit to the low-sulfidized epithermal class. The data provided in the article are of practical value for regional forecast–metallogenic maps and can be used in searching for and appraising epithermal Au–Ag deposits.

This paper discusses the conditions of generation for the Au–Ag epithermal mineralization in the Amguema–Kanchalan Volcanic Field (AKVF), which is situated at the western termination of the East Chukchi flank zone of the Okhotsk–Chukchi Volcanogenic Belt (OChVB). The AKVF contains the potentially large Valunistoe Au‒Ag deposit and several promising deposits and ore occurrences (Zhilnoe, Shakh, Gornoe, Ognennoe, and Osennee). Thermal and cryometric studies of fluid inclusions in quartz and calcite in epithermal veins showed that the solutions were dominated by Na and K chlorides. The epithermal mineralization was deposited by heterogeneous hydrothermal fluids with low salt concentrations (0.2–3.6 wt % equ. NaCl, under moderate temperatures 174–354°С). The fluid pressure reached values of 30–160 bars, which is proper to depths of generation of 0.1–0.6 km under hydrostatic conditions. These results classify the epithermal mineralization studied here as a low sulfide one. Meteoric waters and magma chambers of andesitic magmas are the most likely sources of ore-forming fluids. The information furnished in this paper is of practical value for regional metallogenic predictions, as well as the search for and assessment of epithermal Au–Ag deposits.

Geochemical study of water samples taken from the Malyi Mukulan and Bol’shoi Mukulan creeks and watercourses and trickling from the pile dike of tailing pond no. 3(1) of the Tyrnyauz tungsten–molybdenum plant has been carried out. Estimation of the degree of their polluting effect on the Baksan River was made.

Contrast variations in the type of REE distribution from a distinctly negative mode to a positive mode is revealed in zonal fluorites of Eastern Transbaikal, with a pronounced decrease in the Ce/Y ratios in successive zones of increasing Y accompanied by a gradual decrease in the temperature and salinity of fluid inclusions in the fluorites. It is assumed that these facts are caused by the appearance of nm-size phases of REE minerals characterized by various crystalline structures and demonstrating selective concentrations of lanthanides, i.e., exhibiting a crystal-chemical differentiation of REEs that is widespread in the processes of mineral formation. Based on this natural mechanism, the development of a procedure of selective REE extraction from the concentrates is proposed. The primary laboratory experiments resulted in the discovery of the difference in REE concentrations in the sediment and filtrate with the separation coefficient varying by a factor of 76. The results obtained allow one to expect a true separation possibility for Nd along with the medium and heavy REEs. In view of the data obtained, the crystalline-chemical separation of REEs has some advantages compared to the processes currently used, especially extraction.

The degree of concentration and REE and Zr distribution and occurrence in uranium ore samples from paleovalley deposits are considered. Various types of REE distribution in ores with variable uranium content has been revealed: the negative type with predominance of LREE in ordinary ore and the V-shaped type with significant growth of Y, MREE, and HREE contents in high-grade ore. In addition, the relationship between U, on the one hand, and MREE, HREE, Y, and Zr, on the other hand, has been established. Predominant isomorphic incorporation of these elements into various uranium constituents is suggested. The conclusion was arrived at about the most probable gain of REE and Zr along with U on various geochemical barriers from postvolcanic thermal carbonated and sulfuric-acid aqueous solutions enriched in these chemical elements. The significant enrichment of uranium ore in REE confirms the real possibility of recovery of them as a by-product from working solutions in the process of in situ uranium leaching.

Snow samples from the territory of the Setun River Valley Wildlife Sanctuary are analyzed for the content of rare-earth elements, heavy metals, and other hazardous elements by the inductively coupled plasma mass-spectrometry method. The changes in the concentrations of rare-earth elements, Pt, Pd, and indicator ratios of elements in the solid fractions of snow are revealed. A trend toward a decrease in the content of several elements northeastward of the Moscow Ring Road (MRR) is established. The level of seasonal atmospheric contamination of the area under study is assessed, and a possible source is identified.

Three groups of industrial uranium deposits that differ in the distribution of lanthanides in U oxides have been recognized. A dependence of the REE distribution type on the Yttrium content and Yttrium index YI = (La + Ce)/Y that controls the formation of REE phases capable of selective accumulation of lanthanides has been discovered. This indicates the important role of crystal–chemical fractionation in the distribution of lanthanides. Preferable accumulation of Sm–Gd by U oxides has been found to occur at relatively low contents of Y. In Proterozoic uranium deposits, the yttrium specialization of oxides predominates, while in most Phanerozoic deposits the lanthanum–cerium specialization is typical. These results extend the possibilities of using REEs in ores for purposes of study of the genesis of various uranium deposits.

Anomalous concentrations of numerous major and minor elements significantly exceeding the threshold limit values (TLV) for drinking water were registered in the area of the Tyrnyauz Tungsten–Molybdenum Combine (TTMC). The maximal excess of the TLV (by one or two orders of magnitude) were obtained for Mo (up to 11 mg/L), W (4.4 mg/L), As (1.5 mg/L), Mn (8.4 mg/L), and Tl (up to 3.3 μg/L) in water of the Bolshoi Mukulan Brook flowing through the mines and three brooks flowing out from the base of the embankment of the tailing store no. 1. They are the major pollutants for water of the Baksan River. Upon flowing out to the plain, water of the Baksan River shows significant excess of the TLVs (in summer) for Al, Fe, Mn, Be, Si, Ti, Tl, and Hg.

The decontamination of buried wastes of the Tyrnyauz Tungsten–Molybdenum Plant is complicated by the geochemical features of the waste composition: low sulfide and high carbonate content, polyelemental composition, and considerable amounts of technogenic admixtures (kerosene, oils, soda, and soluble glasses). These circumstances result in sufficient complication of the suggested technology of waste treatment, including the sulfuric-acid leaching and separate sorption recovery of hazardous and useful elements from the working solution.

The uranium deposits of Bulgaria related to the Late Alpine tectonomagmatic reactivation are subdivided into two groups: exogenic–epigenetic paleovalley deposits related to the basins filled with upper Eocene–lower Oligocene volcanic–sedimentary rocks and the hydrothermal deposits hosted in the coeval depressions. The geological and lithofacies conditions of their localization, the epigenetic alteration of rocks, mineralogy and geochemistry of uranium ore are exemplified in thoroughly studied paleovalley deposits of the Maritsa ore district. Argumentation of the genetic concepts providing insights into both sedimentation–diagenetic and exogenic–epigenetic mineralization with development of stratal oxidation zones is discussed. A new exfiltration model has been proposed to explain the origin of the aforementioned deposits on the basis of additional analysis with consideration of archival factual data and possible causes of specific ningyoite uranium ore composition.