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Blue sapphire of gem quality was recently discovered in spinel–chlorite–muscovite rock within meta-ultramafites near the Ilmenogorsky alkaline complex in the Ilmen Mountains of the South Urals. More than 20 minerals were found in the assemblage with the blue sapphire. These sapphire-bearing rocks are enriched in LREE and depleted in HREE (with the negative Eu anomalies) with REE distribution similar to those in miascites (nepheline syenite) of the Ilmenogorsky alkaline complex. 87Sr/86Sr ratios in the sapphire-bearing rocks varied from 0.7088 ± 0.000004 (2σ) to 0.7106 ± 0.000006 (2σ): epsilon notation εNd is −7.8. The Rb-Sr isochrone age of 289 ± 9 Ma was yielded for the sapphire-bearing rocks and associated muscovite. The blue sapphires are translucent to transparent and they have substantial colorless zones. They occur in a matrix of clinochlore-muscovite as concentric aggregates within spinel-gahnite coronas. Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry (LA-ICP-MS) analyses showed values with trace elements typical for “metamorphic” blue sapphires, with Ga/Mg < 2.7, Fe/Mg < 74, Cr/Ga > 1.5 (when Cr is detectable), and Fe/Ti < 9. Sapphires overlap “metasomatic” at “sapphires in alkali basalts” field on the FeO–Cr2O3–MgO–V2O3 versus FeO + TiO2 + Ga2O3 discriminant diagram. The sapphires formed together with the spinel-chlorite-muscovite rock during metasomatism at a contact of orthopyroxenites. Metasomatic fluids were enriched with Al, HSFE, and LILE and genetically linked to the miascite intrusions of Ilmenogorsky complex. The temperature required for the formation of sapphire–spinel–chlorite–muscovite rock was 700–750 °C and a pressure of 1.8–3.5 kbar.

The porous fine grained to microcrystalline copper-zinc ore of the Semenov 2 hydrothermal field, a site in the Semenov hydrothermal cluster discovered in 2007 (13°31′N, MAR), is anomalously enriched in Au (22-188 ppm) and Ag (127-1787 ppm). Chalcopyrite, isocubanite, würtzite, and opal are major minerals; sphalerite, marcasite, pyrite, and covellite are auxiliary; and galena, pyrrhotite, native gold, silver telluride, barite, and aragonite are sporadic. Gold containing 0.31 to 23.07 wt % Ag occurs as up to 9 μm sized subhedral, dendritelike, and elongated grains mostly hosted in opal and less frequently in sphalerite and in pores within isocubanite-chalcopyrite aggregate. An elongated grain (2 × 4 μm in size) of the Ag-Te phase was found in a pore. So far only basalts have been dredged from the Semenov 2 field, but anomalous gold and silver concentrations suggest the influence of ultramafic rocks; the latter were found 1.5 km westward, in the Semenov 1 hydrothermal field. Mineral assemblage and morphology of gold parti cles indicate its primary origin in contrast to the hydrothermal fields hosted in basalts, where gold is a product of remobilization. Zonal gold grains, found on oceanic floor for the first time, are characterized by low Ag content in the cores and high Ag content in the outer rims, reflecting variation in formation conditions.

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