Research subject. The composition, properties, and connection of the lattice defects in the disordered s tructure of quartz with the conditions of its formation. Materials and methods. The quartz of the gold deposits of the Darasun ore field – Darasun, Teremkinskoye, and Talatuy – were studied. For the purpose of comparative analysis, gold-ore quartz from the deposits of Northern Kazakhstan was used. Registration of centers in quartz samples was carried out by the EPR method. When interpreting the obtained results, genetic information consisting in the distribution of substitutional Ge and Ti impurities in quartz was used. Results. Two groups of paramagnetic centers were identified in the quartz under study. One of them is associated with substitutional Al, Ti, and Ge impurities in quartz zones with an ordered crystal structure, while the other is associated with the lattice defects localized in the disordered crystal structure of quartz. The latter group includes several types of E'-centers formed in quartz glass and Al-X-centers caused by Al3+ ions associated with oxygen vacancies. In the case of stable thermodynamic conditions of mineral formation, a linear relationship was established between the concentrations of Al-X-centers (CAl-X) and E'-centers (CEs). Under a change in thermodynamic conditions, a deviation of the points from the CEs(CAl-X) dependence was observed. Conclusions. The type of CEs(CAl-X) dependence is determined by the thermodynamic conditions of mineral formation and can be used to identify cases of non-equilibrium solidification of quartz.

The results of a comprehensive detailed study of the vein structure, mineral zoning of veins, and mineral typomorphism of the Shakhtama deposit obtained on the basis of new samples from poorly studied horizons are given. The results obtained show that the Mo resources of the deposit are far from being exhausted, and the typomorphic features of ore minerals indicate that base metal mineralization associated with Au (Ag), also continues to a depth, along with Mo. The presence of rare Sr mineral, svanbergite, in the Shakhtamа deposit and the typomorphic properties of ore minerals testify in favor of the near-surface origin of the exposed mineralization. The succession of mineral formation has been established. Based on the study of ore and metasomatic zonality, fluid inclusions and isotopic data, as well as the composition of structural impurities in molybdenite, conclusions were made of the formation conditions of ore mineralization in a porphyry ore-forming system.

The results of a comprehensive detailed study of the vein structure, mineral zoning of veins, and mineral typomorphism of the Shakhtama deposit obtained on the basis of new samples from poorly studied horizons are given. The results obtained show that the Mo resources of the deposit are far from being exhausted, and the typomorphic features of ore minerals indicate that base metal mineralization associated with Au (Ag), also continues to a depth, along with Mo. The presence of rare Sr mineral, svanbergite, in the Shakhtamа deposit and the typomorphic properties of ore minerals testify in favor of the near-surface origin of the exposed mineralization. The succession of mineral formation has been established. Based on the study of ore and metasomatic zonality, fluid inclusions and isotopic data, as well as the composition of structural impurities in molybdenite, conclusions were made of the formation conditions of ore mineralization in a porphyry ore-forming system.

In the second part of this study, we analyze how crystallization differentiation can affect concentrations of elements and their ratios in melt inclusions and glasses of rocks in major geodynamic environments. The paper presents analysis of experimental data on the partition coefficient of elements between minerals (olivine, pyroxenes, garnet, amphibole, biotite, sulfide, apatite, spinel, ilmenite, rutile, and zircon) and silicate melts, which were discussed in the first part of this study. It is demonstrated that the crystallization of major minerals only insignificantly affects the ratios of incompatible elements. The partition coefficients of some elements between accessory minerals and melts can be very high, but the effects of crystallization differentiation cannot be significant because of the small amounts of the crystallizing phases. These effects are the most significant for chalcophile elements (Cu, Ni, and others), at the separation of sulfides, and for Nb and Ta, at the crystallization of rutile. Differences in concentrations of various elements and their ratios to Cs concentrations are discussed with reference to various geodynamic environments. The maximum values of the ratios of practically all elements to Cs were found in melts in mid-oceanic ridges. The melts of oceanic islands and backarc basins are characterized by relatively low ratios, without any significant anomalies. The lowest ratios of elements to Cs were found in melts of continental and marginal environments. These melts are also characterized by clearly seen geochemical anomalies that are typical of rocks of the corresponding environments (negative Ta–Nb, positive Pb, and other anomalies).

Published data on the composition of mineral-hosted inclusions and quenched glasses of rocks were used to estimate the mean concentrations of 45 volatile, trace, and ore elements in silicate igneous melts from the main geodynamic settings of the Earth and in natural fluids. The following geodynamic settings were distinguished according to the conditions of formation and evolution of the igneous melts: (I) oceanic spreading zones (mid-oceanic ridges), (II) oceanic mantle-plume zones (oceanic islands and lava plateaus); (III and IV) subduction-related settings (III is island-arc zones, and IV is active continental margins); (V) continental rifts and hotspot zones; and (VI) backarc spreading basins related to subduction. The contents of the elements in basic and felsic melts were compared in settings III, IV and V. It was shown that differences in the enrichment factors of ore elements between the geodynamic settings could be caused by variations in the contribution of fluids to element transport and accumulation. Ratios of element contents in each of the geodynamic environments to the global mean values were calculated.

Tungstenite of unusual shapes (spheroids, rings, threads, spirals, etc.) was found in scheelite of gold-bearing quartz–carbonate–pyrite–chalcopyrite veins. It is crystallized in the veins in the final part of mineral deposition, after crystallization of sulfides, sulfosalts, and scheelite of several generations against the background of decreasing activity of sulfur. The issue concerning the type of the strong reducing agent of the W6+ → W4+reaction rarely occurring in nature is crucial for the formation of tungstenite. There are no traces of reducing agents, which could be solid or liquid hydrocarbons, in the veins. The unusual shapes of tungstenite aggregates similar to biomorphosеs may be evidence of the existence of microorganisms in the fractured anisotropic medium in scheelite at the boundary of the transition of the quartz part of the vein to the substantially carbonate part. The occurrence of the biomorphоsеs only in scheelite suggests that microorganisms have a W-dependent metabolism, which is observed in extremophiles of the Archaea domain producing a strong reducing agent H2; methanogens producing CH4 coexist in symbiosis with them.

Рассмотрены первые результаты изучения (методы минераграфии, катодолюминесценции (CL), рентгеноспектрального микроанализа (EPMA) и масс-спектрометрии с индуктивно-связанной плазмой и лазерным пробоотбором (LA-ICPMS)) шеелита из кварц-молибденитовой и кварц-карбонат-сульфидной жильно-прожилковой (порфировый тип), а также кварц-магнетит-сульфидной гнездово-вкрапленной (скарновый тип) минерализаций скарново-порфирового Cu-Au-Fe-месторождения Быстринское (Восточное Забайкалье) – одного из наиболее крупных золотомедных порфировых объектов России. Установлено, что шеелит, не являясь главным минералом руд месторождения, встречается практически повсеместно, что дает возможность выявлять его ключевые признаки, отражающие специфику генезиса, как разнотипной минерализации, так и месторождения в целом. Показано, что шеелит из разных типов рудной минерализации обладает четко детерминированными индивидуальными характеристиками, отчетливо различаясь распространенностью, ансамблями ассоциированных минералов, цветом катодолюминесценции и флуоресценции в УФ-свете, составом и концентрациями макро- и микроэлементов, а также характером спектров РЗЭ. Эти отличительные особенности свидетельствуют о существенном несходстве условий формирования изученных типов руд и обнаруживают зависимость от физико-химических и композиционных параметров минералообразующей среды, что позволяет рассматривать шеелит как принципиально важный генетический индикатор эволюции обстановок минералообразования. Ключевое значение при этом имеют концентрации в шеелите Mo, тип и форма РЗЭ-спектров, которые в целом определяются как унаследованием химизма минералообразующих флюидов и особенностями изоморфного вхождения РЗЭ в структуру минерала, так и вариациями окислительно-восстановительных свойств минералообразующего флюида.

The first results of the study (methods of mineragraphy, cathodoluminescence (CL), electron-probe microanalysis (EPMA) and laser-ablation inductively-coupled plasma-mass spectrometry (LA-ICPMS)) of scheelite from quartz-molybdenite and quartz-carbonate-sulfide vein-veinlet (porphyry type) are considered, as well as the magnetite-sulfide massive, veinlets and disseminated (skarn type) mineralization of the skarn-porphyry Cu-Au-Fe deposit of Bystrinskoye (East Transbaikalia) one of the largest gold-copper porphyry ore-fields in Russia. It has been established that scheelite, being not the main mineral of the deposit ores, is found almost everywhere, which makes it possible to identify its key features reflecting the specific features of the genesis, both of different types of mineralization and the deposit as a whole. It is shown that scheelite from different types of ore mineralization has clearly determined individual characteristics, differing in prevalence, ensembles of associated minerals, color of CL and fluorescence in the UV-light, composition and concentrations of macro- and microelements, as well as the nature of REE-spectra. These distinctive features testify to a significant difference in the conditions for the formation of the studied ore types and reveal the dependence on the physicochemical and compositional parameters of the mineral-forming medium, which makes it possible to consider scheelite as a fundamentally important genetic indicator of the evolution of mineral formation patterns. Concentrations of Mo in scheelite, the type and form of REE-spectra, which are generally, determined both by the inheritance of the mineral-forming fluid chemistry and the peculiarities of isomorphic occurrence of REE in the structure of the mineral, and variations in the redox properties of the mineral-forming fluid, are of key importance.

The paper presents pioneering data on the composition, texture, and crystal structure of molybdenite from various types of molybdenum mineralization at the Bystrinsky Cu–Au–Fe porphyry–skarn deposit in the eastern Transbaikal region, Russia. The data were obtained using electron microprobe analysis (EMPA), laser ablation–inductively coupled plasma mass spectrometry (LA-ICP-MS), and high-resolution transmission electron microscopy (HRTEM). Molybdenite found at the deposit in skarn, sulfide-poor quartz veins, and quartz–feldspar alteration markedly differs in the concentrations of trace elements determined by their species in the mineral, as well as in its structural features. Molybdenite-2H from skarn associated with phyllosilicates occurs as ultrafine crystals with uniform shape and texture; no dislocations or inclusions were found but amorphous silica was. The molybdenite composition is highly contrasting in the content and distribution of both structure-related (Re, W, and Se) and other (Mn, Co, Ni, Cu, Zn, As, Ag, Cd, Sb, Te, Ag, Pd, Au, Hg, Pb, and Bi) metals. In the sulfide-poor quartz veins, highly structurally heterogeneous (2H + 3R) molybdenite microcrystals with abundant defects (dislocations and volumetrically distributed inclusions) are associated with illite, goethite, and barite. Some single crystals are unique three-phase (2H + 3R polytypes + amorphous MoS2). The mineral has a low concentration of all trace elements, which are uniformly distributed. However, individual domains with uniquely high Pd, Te, Ni, Hg, and W concentrations caused by mineral inclusions are found in some grains. Molybdenite from quartz–feldspar alteration is characterized by low concentrations of all trace elements except for Re and Se, which enrich some domains of the grains. Our data indicate that the compositional and structural heterogeneity of molybdenite from the Bystrinsky deposit are its crucial features, which obviously correlate with the types of Mo mineralization.

Different forms of abundant silica (e. g., quartz and chalcedony) are closely associated with many types of ore deposits in igneous, metamorphic, and sedimentary environments. Occurrence of quartz and metal-bearing minerals together strongly indicates that silica is an important component in hydrothermal fluids transporting and concentrating economic metals to the ore grade, however chemical and physical characteristics of such ore-forming media remain debated. Understanding of the environment in which chalcedony forms is largely hampered by the lack of chalcedony-hosted fluid inclusions. Our study reports for the first time fortuitously preserved, large-sized (up to 150 mu m) fluid inclusions in chalcedony from the Gonchak deposit of optical calcite in the Early Triassic basalts belonging to the Siberian large igneous province. The application of microthermometric methods, scanning electron microscopy with cathodoluminescence, and laser Raman spectroscopy to the fluid inclusions and their host chalcedony recognized the formation of chalcedony from a colloidal suspension. The fluid inclusions represent a gel-like saline aqueous fluid that is residual after precipitation of spherulitic chalcedony aggregates with numerous H2O-bearing and H2O-poor layers. We propose that the colloidal nature of fluids forming chalcedony lends strong support to the natural existence of experimentally predicted "silicothermal fluids". Such fluids can be instrumental in mobilizing and transporting large quantities of both silica and nano-and micro-particles of ore minerals, followed by efficient separation of the latter from coagulating silica gel into ore-rich zones and bodies.

The Bystrinskoe skarn-porphyry Cu–Au–Fe deposit (Eastern Trans-Baikal Region) is confined to skarn zones, which were formed along the contact of granitoids referred to the Shakhtama intrusive complex (J2–3), with terrigenous–carbonate sedimentary rocks. Commercial (Cu–Au–Fe ± W, Mo) mineralization was formed due to the regional postcollision development involving the intrusion of porphyritic granitoids, the derivatives of oxidized adakite highly magnesian magmas enriched in water, sulfur, and metals, which could develop under melting of garnet-bearing amphibolite in the mafic lower crustal arc.

Based on intergration of the published data on composition of inclusions in minerals and quenched glasses, the mean concentrations of 24 ore elements have been calculated for magmatic silicate melts formed in main geodynamic settings of the Earth and in natural fluids. The mean glass compositions normalized to the primitive mantle correlate with the partition coefficient between olivine and the basic melt. It is established that the degree of enrichment in ore elements depending on geodynamic setting is controlled by various contribution of fluids to the element transfer and accumulation. The ratios of element contents in each geodynamic setting to the mean concentrations of elements over all settings in the Earth have been calculated.

This paper reports the newly obtained petrologic, geochemical and isotope data on the ore forming system of the Bystrinskoe Cu-Au-Fe skarn-porphyry deposit that is related to adakite and produced in relation to postcollisional magmatism.

Crystal inclusions (plagioclase, biotite, magnetite) and melt inclusions were studied in minerals of the Laleaua Albă dacite (Baia Sprie, Romania). Electron microprobe analysis of 29 melt inclusions in the plagioclase, K-feldspar, and quartz confirm that crystallization of these minerals took place from typical silicic melts enriched in potassium relative to sodium (K2O/Na2O = 1.5). The sum of the petrogenic components is 92–99 wt%. This points to a possible change in water content from 8 to 1 wt% during crystallization of phenocrysts. According to ion microprobe analysis of 11 melt inclusions, the minimum water content is 0.5 wt%, and the maximum water content is 6.1 wt%. The presence of high-density water fluid segregation in one of the melt inclusions suggests that the primary water content in the melt could reach 8.4 wt%. Ion microprobe data revealed a high concentration of Cu (up to 1260 ppm) as well as higher U content (from 5.0 to 14.3 ppm; average 11.5 ppm) in some melt inclusions as compared to the average U contents in silicic melts (2.7 ppm in island-arc settings and 7.9 ppm in continental rift settings). Chondrite-normalized trace-element patterns in melt inclusions suggest a complex genesis of the studied magmatic melts. Contents of some elements (for instance Sr and Ba) are close to those in island-arc melts, while others (for instance Th, U, and Eu) resemble those in melts of continental settings.