The results of a comprehensive study of the morphology, composition and the internal structure of fine autigenic gold, first discovered in bedrock on the area of the Kyvvozhskoye goldfield, are presented. It has complex specific rounded-lumpy, lumpy-branched aggregate forms and a smooth growth surface without traces of mechanical wearing. X-ray studies (Debye-Scherrer method) show that reflexes in the form of dashed rings are characteristic of debyeograms of this native gold, which, according to the authors, indicates the absence of exogenous deformations of it. The internal structure of all the studied gold pieces is characterized by a relatively homogeneous inner area and a thin (~1 µm) contrasting enriched with silver low-grade rim. All the particles of the studied native gold have approximately the same average fineness (899–918‰). As a mechanism for the formation of the found autigenic gold, its crystallization is assumed by filling of the free pore space of the host sandstones. Its presence in Riphean rocks is considered as an indicator of the primary dispersion halos and is a direct search sign of the development of potentially productive gold mineralization in this part of the Middle Timan.

We present a novel study of fluid inclusions in the vein quartz of the Kyvvozh gold placer field and in the quartz of gold-quartz intergrowths from the placer (methods of homogenization, cryometry, and Raman spectroscopy were used). We determined that in vein quartz the homogenization temperature of fluid inclusions fluctuated in the range of 220–425 °C, the liquid phase was represented by aqueous solutions, predominantly sodium and magnesium chloride. The homogenization temperature of fluid inclusions in quartz of gold–quartz intergrowths is 220–330 °C, and an aqueous solution of sodium chloride predominates in the liquid phase. Mineral formation proceeded in two stages: at the first stage, the fluid was enriched with nitrogen, at the second stage — with carbon dioxide.

Fluid inclusions in quartz and lazulite (Mg,Fe2+)Al2(OH,PO4)2 were studied for the first time in the quartz‒lazulite‒hematite-tourmaline veins of Mt. Chernaya, the Nether-Polar Urals. It was found that they are very similar. Homogenization of the most inclusions occurs at 155‒220°C in lazulite and at 147‒235°C in quartz; and salinity varies between 12.5‒15.0 and 10.7‒15.7 wt % NaCl eq., respectively. The eutectic temperature of the water‒salt solution in both cases ranges within ‒31 … ‒40°C, which indicates the presence of magnesium, sodium, and iron salts in the mineral-forming fluid. The gas phase of fluid inclusions is represented by carbon dioxide and nitrogen in approximately equal proportions.

The gold deposits of the Bodaibo ore district are enclosed in a thick (several kilometers) sequence of Riphean–Vendian carbonaceous carbonate–terrigenous deposits. Gold is concentrated at several stratigraphic levels; the largest deposit in Russia, Sukhoi Log, and its counterpart, Golets Vysochaishii, are confined to terrigenous deposits of the Riphean Khomolkho Formation. The characteristic components of the Khomolkho Formation are lenticular interlayers and layered disseminations of pyrrhotite and pyrite with clearly pronounced lithological–stratigraphic control of their distribution. The Golets Vysochaishii deposit is confined to the largest thickening of sulfide layers in carbonaceous chlorite–quartz–sericite phyllite schists of the lower part of the Khomolkho Formation. The sulfide content in the ore-bearing sequence is 5 wt %; native gold is enclosed in sulfide layers. According to the data of previous researchers, based on the distribution patterns of sulfur isotopes, sulfide ore-bearing deposits of the deposit were formed by hydrothermal–sedimentary pathways. The primary gold content of sulfide sediments is assumed in analogy with the neighboring Sukhoi Log and Verna deposits. The distribution of Au, As, Ag, and carbonaceous matter in the sulfide-bearing strata of the Golets Vysochaishii deposit is substratal, reflecting their accumulation during sedimentation. The rocks were metamorphically altered under the greenschist facies conditions, during which they recrystallized and sulfides and gold were redistributed with the rocks retaining their layered structure. There are no significant differences in the contents of the rock-forming components between the ore deposit and host rocks, which indicates the absence of metasomatic alteration in rocks associated with ore formation. Metamorphic processes at the deposits of the Khomolkho Formation were accompanied by replacement of ilmenite by rutile and pyrrhotite by pyrite, as well as a change in the composition of chlorites and carbonates with increasing iron content; these processes were regulated by the fugacity of oxygen and carbon dioxide. Metamorphic alteration, based fluid inclusion study data, took place in the temperature range 230–510°C with the participation of oxidized carbon dioxide–aqueous fluids (CO2/CH4 up to 17) with a salinity of 7–12 wt % equiv. NaCl and reduced (CO2/CH4 < 0.3) methane–nitrogen fluids with a salinity of 11–13 wt % equiv. NaCl.

The results of the study of fluid inclusions in quartz from quartz–calcite veins with unique yushkinite mineralization are reported. For the first time, it was proved that their formation occurred under sharply reducing conditions. The mineral formation medium was enriched in calcium and magnesium chlorides and hydrogen sulfide. The temperature of mineral formation was ~120–150°С.

Fluid inclusions from calcite veins were studied the Astrakhanskoye gas condensate field. It was done for the identify the conditions for the formation of oil reservoirs located in bioclastic recrystallized limestones with vertically oriented fractures. Samples were selected from the core material of one studied well in interval 4215-4217 m. Two types of syngenetic inclusions were found in calcite: gas and gas-liquid inclusions. The homogenization temperature of gas inclusions is from -16.9 to 40 °C. Studying the gas phase by Raman spectroscopy show the presence of methane and hydrogen sulfide. Carbon dioxide, ethane, and propane were found in smaller quantities. The homogenization temperature is 100-130 °C of two-phase fluid inclusions. Probably, it is close to the temperature of the vein calcite aggregates. The aqueous phase of inclusions is represented by solutions of magnesium chloride. The gas-phase was not studied by Raman spectroscopy because of mobility. The total composition of inclusion gases in calcite is represented mainly by carbon dioxide, methane, and hydrogen sulfide, according to gas chromatography. Ethane, propane, and isobutane are present in smaller amounts. The concentration decreases from ethane to butane. Also, ethylene, propylene, and butylene were identified in very low concentrations. A characteristic feature of hydrocarbon gases is a decrease in concentrations from ethane to propane and from propane to butane, and it is typical for gas condensates.

—Data on gabbro-dolerite pyrite–chalcopyrite–pyrrhotite, quartz vein sphalerite–chalcopyrite, and associated early and late gold–telluride–palladium mineralization of the Krutoi ore occurrence (Pai-Khoi Ridge, Yugor Peninsula) are presented. The early (magmatic) gold–telluride–palladium mineralization is represented by minerals of the ternary system Ag–Au–Cu, palladium antimonides and stibiotellurides, and platinum arsenides, and the late (hydrothermal) one, by minerals of the binary systems Au–Ag and Au–Pd as well as mercury, lead, and silver tellurides. Sudburyite and testibiopalladite have been first found in the Krutoi ore occurrence; moreover, testibiopalladite has been first discovered in the Pai-Khoi Ridge. Their chemical compositions and Raman spectra have been examined. The results of sulfide sulfur, oxygen, and carbon isotope studies of calcium-containing minerals of chalcopyrite–quartz veinlets suggest assimilation of the material of the host deposits by the ore-forming mantle fluids. The fluid inclusions in the veinlets are divided into nitrogen–methane and carbon dioxide–nitrogen according to the composition of the gas phase. It has been established that the mineral-forming fluids were poorly saturated with gas. Magnesium and calcium salts were predominant in them. The temperature of the formation of quartz in the chalcopyrite–quartz veinlets is close to 300–490 ºC, and sphalerite–chalcopyrite and associated late gold–telluride–palladium mineralization formed at temperatures not exceeding 260 ºC.

It was studied the composition of salt-forming brines, the composition of insoluble salt residue and the sedimentation environment for the Upper Pechora evaporate basin at the halite crystallization stage in the underlying rock salt layer (Lower Permian, Kungur). The results are obtained from studying individual inclusions in halite, chemical composition of primary fluid inclusions brines, the phase composition of salts, and the homogenization temperatures of single-phase liquid inclusions in halite, by their preliminary cooling. The obtained data possible to establish the accumulation of the salt strata of the Upper Pechora potassium-magnesiums basin in shallow-water depositional environments. The brines of the basin belonged to sulfate tipe of the ocean water. The concentration of brines during the crystallization in the underlying rock salt layer was close to the stage of potassium minerals precipitation.

The results of a geological and mineralogical study of the occurrence of high-grade metamorphised carbonaceous matter in the Lower Silurian dolomites on the Kozhim River in the Subpolar Urals were presented.The forms of finding occurrence the carbon substance, chemical and isotopic compositions and the morphology of its excretions were determined.We established that the carbonaceous matter was an analogue of shungite carbon of widely known occurrences of Karelia (Shunga, Maxovo, Chebolaksha) by the composition and structural characteristics.The widespread development of shungite-like carbon in the vein mineralization and enclosing dolomites was found.In the veins of the macroscopic shungite-like carbon, there was a paragenetic connection with the calcite-dolomite mineralization.We suggested that the most favorable conditions for the formation of the shungite-like carbon had existed in the Late Permian -Early Triassic.

Условия образования месторождения Голец Высочайший

This study examines one- (gas) and two-phase (aqueous solution–gas) inclusions in the calcite of the Cheremshanskian Horizon of the Bashkirian stage at a depth of 4,215–4,217 m in the Pravoberezhnaya-1 well. Homogenizing temperature is within 100–134 °C, which is likely close to the temperature of mineral formation. Calcite vein formation involves calcium bicarbonate fluid enriched in Mg chloride. It was established the calcite inclusions contain carbon dioxide, methane, and hydrogen sulfide. The gas composition of the inclusions in limestone is distiuguished of its high carbon dioxide concentration but rather low methane and hydrogen sulfide concentration.

Hydrothermal gold deposits are known in the Subpolar Urals, which are mainly associated with sulfide-quartz veins and zones of vein-disseminated sulfide mineralization. Their investigation is very important for the development of the existing ideas about the regional patterns of ore formation. We have studied the material composition and formation conditions of gold-sulfide ores from the Sinilga deposit. As a result of the study, we have established that the gold-sulfide mineralization of this deposit is superimposed on relatively young quartz veins filling the steeply dipping fractures oriented across the foliation of the rocks. Sulfides in the ores are mainly represented by coarse-grained galena, forming nests, veins and inclusions in vein quartz. Pyrite, pyrrhotite, arsenopyrite, and chalcopyrite are present in insignificant amounts. Hypergenic minerals are widely developed: goethite, hydrogoethite, anglesite, jarosite, cerussite, and scorodite. Gold is closely associated with sulfides, mainly with galena, which is often observed in areas of development of hypergenic minerals, in fractures of vein quartz, grows on small crystals of rock crystal. The composition of gold includes an admixture of silver (up to 10 wt. %). Crystallization of quartz of gold-bearing veins occurred in hydrothermal chloride-sodium-potassium solutions with a significant proportion of carbon dioxide in the temperature range from approximately 390 degrees C to 270 degrees C. Gold-sulfide mineralization corresponds to the latest stages of mineral formation. Sulfur of galena has a predominantly heavier isotopic composition (galena delta S-34 vary from +2.9%o to +10%o and are mainly in the range of 7.3-10%), indicating its primary sedimentary origin with a subordinate value of magmatic sources. We have suggested that hydrothermal processes played the most important role in the formation of the Sinilga deposit. They were conditioned by the Late Paleozoic metamorphism of the greenschist facies.

The Mezino-Lapshinovka section is constituted by the Upper Cretaceous carbonate clayey siliceous succession. It has been studied by XRD, SEM, microprobe, and geochemical analyses in order to reconstruct the main geologic events that influenced the formation of gaizes in the NE Peri-Tethys. A new scenario for their formation proposes that open-ocean siliceous ooze might have been delivered to the active subduction zone of the African-Arabian plate and then deposited in the shallow basin of NE Peri-Tethys. The bentonite interbeds were probably formed due to diagenetic alteration of the volcanic ash. It has been suggested that the sea water during the Santonian-Campanian was characterized by the oxic conditions, while there were two short episodes of anoxia or so-called anoxic non-sulfidic conditions. The early Santonian anoxic episode can be linked to the global anoxic event OAE 3 in the NE Peri-Tethys. The Campanian Mn anomaly coupled with the simultaneous increase in delta C-13 is considered to be a manifestation the Campanian eustatic rise.

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