Hydrothermal and diagenetic barites from colloform and clastic pyrite-rich ores from the weakly metamorphic Saf'yanovka volcanogenic massive sulfide deposit (Devonian, Central Urals) were studied in comparison with barite from similar modern seafloor deposits from the mid-Atlantic Ridge (Semenov-1 and Semenov-3 hydrothermal fields). Hydrothermal barites from all the studied deposits exhibit similar morphology: they occur as tabular crystals or their aggregates. In contrast, diagenetic barite from clastic ores of the Saf'yanovka deposit occur as compact aggregates of deformed, broken, or slightly curved tabular crystals with stylolite boundaries. The variable Sr contents in the studied barites show no relationship with the genetic types. The average δ 34 S values of hydrothermal barite from both ancient and modern colloform sulfides (+22.9 ‰, Saf'yanovka deposit; +21.2‰, Semenov-1 field) match those of Silurian-Devonian and contemporary seawater, respectively. The lower δ 34 S of hydrothermal barite from clastic sulfides of the Semenov-3 field (+19.6 ‰), which is associated with high-Se, high-temperature chalcopyrite, indicates light sulfur contribution from oxidation of fluid H 2 S. The higher average δ 34 S of diagenetic barite from clastic
An overview of a geological structure of Nurali massif is presented. Compositional data of ultramafic rocks from mantle section and transitional mantle-crust assemblages, and chemistry of accessory and ore-forming Cr spinels are examined. We showed that ultramafic rocks from mantle section (spinel a spinel-plagioclase peridotites, harzburgites, dunites) are the tectonites. They have a strong predominantly optical orientation of rock-forming olivine due to a plastic flow of rocks. We presented different points of view on the mantle-crust assemblage origin, which composed by wehrlites, clinopyroxenites, vebsterites, dunites and melanocratic gneiss-like gabbro, and described two PGE-occurrences in the chromitites of this ophiolite section unit. This paper is based on a guidebook of an International field trip to Nurali massif as a part of conference "Magmatism of the Earth and related deposits of strategic metals" held in 2017 August.
Research subject. Quartz veins of the Svetlorechenskoye, Karayan, Gora Khrustalnaya and Tolstikha quartz deposits in the Southern Urals.Methods. An optical study of quartz was performed using an Olympus BX51 optical microscope. A fluid inclusion study was performed using a thermostage TMS-600 (Linkam) equipped with the LinkSys V-2.39 software and an Olympus BX51 optical microscope (South Urals State University, Miass). The fluid composition in the inclusions was estimated from eutectic temperatures. Fluid salinity was calculated based on the melting temperatures of crystalline pha ses. Registration of infrared spectra was carried out using an infrared Fourier spectrometer Nicolet-6700 Thermo Scientific (SU FRC MG UB RAS, Miass). The spectra were processed using the OMNIC Thermo Nicolet software package and the Peakfit program. The extinction coefficients for calculating the concentration of molecular water and OH-groups were used from.Results. The veins are composed of coarse-grained milky-white quartz. The fluid inclusion data shows that the quartz veins were deposited from similar in composition NaCl-H2O fluids with salinities of 3–9 wt % NaCl eq. and at temperatures ranging from 100 to 280°C. Quartz in the Tolstikha deposit was deposited at the highest temperatures. According to IR spectroscopy data, quartz in the studied deposits is characterized by high contents of molecular water and average concentrations of Al-OH groups. According to the content of OH-groups, quartz in the Tolstikha deposit approaches industrial granulated quartz used in the production of high-purity quartz concentrates.Conclusions. Quartz veins in the studied deposits formed at temperatures ranging from 100 to 280°C. The salinity of inclusions in quartz ranged from 10 to 3.5 wt % NaCl eq. Mineral-forming fluids were of Na-chloride or Na-K-chloride composition, which indicates quartz crystallization during the post-diagenetic (metamorphic) transformation of rocks. Quartz in the studied deposits is characterized by a specific ratio of water and Al-OH, which is associated with the conditions of deposit formation and incompleteness of quartz metamorphism processes therein.
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