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Individual fluid inclusions with dense carbon dioxide hosted in quartz from the gold-bearing interval penetrated by the SD-3 Kola Superdeep Borehole were studied using modern techniques. The composition and density of the carbon dioxide fluid were determined by Raman spectroscopy and microthermometry. The density of the fluid is 0.37–1.14 g/cm3 and contains minor admixtures of nitrogen (0.3–1.8 mol %) and water (0.1–0.4 mol %). LA-ICP-MS data indicate that the carbon dioxide fluid inclusions contain high concentrations of Au (1–2611 ppm) and Ag (1–4389 ppm), and high-precision optical data indicate that the high-density CO2 fluid of the inclusions contains Au–Ag nanoparticles. Evidently, gold and silver were transported from the Earth's mantle to the crust by high-density carbon dioxide fluid in the form of nanoparticles. [ABSTRACT FROM AUTHOR]

An association of bismuth sulfosalts coexisting with native gold is described from a sulfide-rich copper vein in the Nistru area, Baia Mare metallogenetic district, NW Romania. This mineralization is hosted within a Neogene calc-alkaline subvolcanic porphyry quartz-micromonzodiorite stock on the southern border of the Gutâi Mountains. Cu+Au+Bi mineralization represents the inner part of a zoned vein of a type specific to the SE part of the Nistru orefield. The Pb-Zn and Au-Ag veins are located towards the external zone at the boundary of the stock with the surrounding rocks. Bismuth sulfosalts are mainly represented by bismuthinite derivatives and members of the lillianite homologous series. Cosalite, matildite and wittichenite are also present in subordinate amounts. Bi-rich members of the bismuthinite-aikinite series (from krupkaite to bismuthinite) are predominant. A phase with the empirical formula CuPbBi7S12 was also identified and could potentially be a new bismuthinite derivative. The lillianite homologous series is represented by phases with composition between Gus73 and Gus59, with a dominance of members closer to gustavite (Gus97–79) and less abundant members closer to lillianite (Gus49). Native gold and Bi-sulfosalts are closely associated with the main sulfides (pyrrhotite, pyrite, chalcopyrite) and quartz, indicating simultaneous crystallization. Fluid inclusion data for quartz indicate a temperature interval between 205 and 247 °C. The assemblage within this vein was deposited from a low-salinity fluid (0.4–2.6 wt.% NaCl equiv.) and density from 0.80 to 0.87 g/cm3. [ABSTRACT FROM AUTHOR]

Across western and northern Chukotka, a region spanning 400 000 km2, we have defined three different tectono-magmatic systems that were active during the Aptian-Albian (123–100 Ma) time span: (1) the Tytylveem post-collisional belt (123–105 Ma); (2) the Chaun province of extension-related magmatism (109–100 Ma); and (3) the earliest eruptive units (106–100 Ma) of the subduction-related Okhotsk-Chukotka volcanic belt (OCVB). The observed tectono-magmatic systems are characterized by their location and by their different chemical and isotopic compositions. The general enrichment of magma sources successively increases from the OCVB to the Tytylveem belt and then to the Chaun province. While the Tytylveem belt was active, the volcanic loci shifted northwest along the strike of the belt, perhaps because of diachronous delamination of the lithosphere of the once present, but extinct, South Anyui ocean. On the scale of the entire region of NE Asia, the tectonic re-arrangement that controlled magmatism in the Early Cretaceous was marked by the extinction of major subduction zones on the periphery of the closing Oimyakon and South Anyui oceanic basins followed by magmatic events likely caused by lithospheric delamination and/or extension. Along the Pacific margin of Asia, subduction-related volcanism was nearly continuous during the entire Cretaceous. [ABSTRACT FROM AUTHOR]

The large gold-telluride Svetlinsk deposit (~135 t Au) is considered to be a nontraditional one in the Urals and its origin is debated. A specific feature of the deposit is the abundance of various tellurides, such as tellurides of Fe, Ni, Pb, Sb, Bi, Ag, and Au. The new data of microthermometry, Raman spectroscopy, LA-ICP-MS, and crush-leach analysis (gas and ion chromatography, ICP-MS) for fluid inclusions as well as O-isotope data for quartz were obtained for the construction of PTX parameters of ore-formation and fluid sources in the deposit. Mineralisation was formed at a wide range of temperature and pressure (200-400 °C, 1-4 kbar) and from contrasting fluids with multiple sources. At the early stages, the magmatic fluid evolved during its ascent and phase separation and the fluid derived from the host rock decarbonation and dehydration were involved in the hydrothermal system. In addition, mantle-derived fluid might be involved in the ore-forming process during gold-telluride precipitation as well as heated meteoric waters during the late stages. Early fluids were rich in H2S, S0, and CH4, while the Au-Te mineralisation was formed from N2-rich fluid. [ABSTRACT FROM AUTHOR]

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 mm) 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. [ABSTRACT FROM AUTHOR]

'Barbotage' is a process of gas penetration through a layer of liquid as a flow of dispersed small gas bubbles. Barbotage is widely used in technology particularly due to its high coefficients of interphase energy and material transfer. It promotes the heat- and mass-exchange processes as well as the chemical interactions in gas-liquid systems. Upon investigation of the fluid regime at the magmatic-hydrothermal system of Darasun goldfield (Eastern Transbaikalia, Russia) we have found evidences of barbotage as an effective mechanism resulting in the formation of vein gold deposits. In spite of the fact that early associations of gold ores in the Darasun goldfield deposits were formed from a heterogeneous fluid, their histograms of fluid salinity distributions are quite different. These differences can be explained by including into the ore-forming process the stage at which the vapour phase generated by boiling rose up as a stream of small bubbles. The corresponding scheme of the formation of the Darasun goldfield hydrothermal ore-bearing system is proposed and discussed. The possibility to use gallium fractionation and the fluid salinity distribution in hydrothermal systems as the indicators of barbotage participation in hydrothermal ore-forming processes is evaluated. [ABSTRACT FROM AUTHOR]

Darasun, Teremkyn, and Talatui are neighboring deposits in the Darasun gold district of Transbaikalia (Russia) that are hosted by Middle-Late Jurassic subduction-related porphyry intrusions and dikes. Darason consists of vertically extensive, steeply dipping Au mineralized veins and zones, spatially related to a K-rich granodiorite-porphyry intrusion, within the deposit are also pipelike bodies of tourmaline sulfide hydrothermal breccias. Teremkyn consists of gently and steeply dipping veins and zones, always associated with felsic dikes comagmatic with the Darasun intrusion. Talatui consists of variably shaped mineralized zones systematically associated with dikes of different compositions and with the host Middle-Late Jurassic granite porphyry. A large proportion of both veins and mineralized zones in these deposits consists of sulfide and oxide minerals, with pyrite and arsenopyrite mostly present at Darasun and Teremkyn and pyrite, magnetite, and hematite present at Talaui. The three deposits host also a large number of sulfosalt, bismuth, oxide, and telluride minerals. Gold of variable purity occurs as free nuggets or hosted by opaque phases. The gangue mineralogy, is similar in the three deposits and includes commonly quartz, tourmaline, and calcite. Microthermometry and microchemical analyses of fluid inclusions with petrographic and compositional data on ore minerals constrain the stages of ore deposition in the district. At room temperature, the entrapped fluids are of four compositional types: (1) multiphase, with a vapor bubble, liquid, and one or more solids; (2) liquid-vapor aqueous; (3a) vapor-rich with a small proportion of liquid and rare solids, and also (3b) vapor-rich with a small proportion of aqueous liquid and carbonic liquid. Types (1) and (3) or (2) and (3) coexist within the same assemblages and are present mostly in paragenetically early quartz, whereas the type (2) fluid within later quartz, sphalerite, and calcite shows consistent phase proportions. At Darasun and Teremkyn, type (2) fluid is the main ore fluid, but all fluid types are associated with gold deposition at Talatui. Microthermometric measurements from all fluid types show a range of phase transitions that vary systematically at the deposit scale. At Darasun and Teremkyn, coexisting types (1) and (3) and types (2) and (3) homogenize into the vapor and liquid states, respectively, within the same 290° to 460°C range. The corresponding bulk salinities vary between 0.7 and 44.8 wt percent NaCl equiv. In contrast, at Talatui coexisting types (1) and (3) and types (2) and (3) homogenize into the vapor and liquid phases and show a distribution of Th(total) and bulk salinities between about 300° and 610°C and 0.9 and 48 wt % NaCl equiv, respectively, Mass spectrometric and chromatographic data from bulk samples show that the main-stage orefluid in the three deposits varies compositionally according to location within the district. In detail, Cl, Na, K, Cs, Br, Sr, Rb, Mn, and Tl are relatively enriched in the Talatui fluid, whereas CO2, CH4, HCO, Cu, Pb, Sb, Fe, Hg, and REE are enriched at Darasun and Teremkyn or show no systematic variations. Au concentrations vary within the 0.01-to 3-g/t range at Darasun and Teremkyn, whereas at Talatui values do not exceed 0.4 g/t. The salinities and homogenization temperatures of the main-stage ore fluids types (1), (2), and (3) are typical of the intrusion-related class of gold deposits. This suggests a dominant magmatic component of the ore fluid during the first stages of mineral precipitation and a magmatic derivation of gold itself in the district. Phase separation was active during the early stages of ore deposition and took place between about 600° to 400°C at Talatui and 450° to 300°C at Teremkyn and Darasun at pressures of 10 to 160 MPa (i.e., 1- to 2.5-km depth).… [ABSTRACT FROM AUTHOR]