Ruby–sapphire–spinel mineralization in marble of the middle and southern Urals: Geology,mineralogy, and genesis

Ruby and spinel occurrences hosted in marble on the eastern slope of the Urals are considered. Ruby- and spinel-bearing marble is a specific rock in granite-gneiss complexes of the East Ural Megazone, which formed at the Late Paleozoic collision stage of the evolution of the Urals. Organogenic marine limestone is the protolith of the marble. No relict sedimentary bedding has been retained in the marble. The observed banding is a secondary phenomenon related to crystallization and is controlled by flow cleavage. Magnesian metasomatism of limestone with the formation of fine-grained dolomite enriched in Cr, V, Ti, Mn, Cu, Zn, Ga, and REE took place at the prograde stage of metamorphism. Dedolomitization of rocks with the formation of background calcite marble also developed at the prograde stage. Mg-calcite marble with spinel and ruby of the first type formed in the metamorphic fluid circulation zone. Magnesian metasomatism with the formation of bicarbonate marble with ruby, pink sapphire, and spinel of the second type developed at the early retrograde stage. The formation of mica-bearing mineralized zones with corundum and spinel of the third type controlled by cleavage fractures is related to the pneumatolytic–hydrothermal stage. The data on ruby-bearing marble in the Urals may be used for forecasting and prospecting of ruby and sapphire deposits hosted in marble worldwide.     

Fluid regime and origin of gold-bearing rodingites from the Karabash alpine-type ultrabasic massif,Southern Ural

The rodingites of the Karabash Massif are distinguished by the presence of native cupriferous gold. This zonal hydrothermal-metasomatic complex was formed in three stages. The inner zone of rodingite proper is made up of chlorite-andradite-diopside rocks of stage 1, which are cut by diopside veinlets of stage 2 and calcite veinlets of stage 3. The intermediate zone consists of chloritolites, which give way to the antigorite and chrysotile-lizardite serpentinites of the outer zone. Thermometric and cryometric studies and gas chromatography showed that the gold-bearing rodingites of stages 1 and 2 were formed at t = 420–470°C, P = 2–3 kbar, and \(X_{CO_2 } \) = 0.001–0.02, i.e., under conditions typical of rodingite formation. The final stage was accompanied by a decrease in P-T parameters (0.5–1.0 kbar and 230–310°C) and an increase in \(X_{CO_2 } \) up to 0.04. The rodingite-forming fluid was extremely rich in water (\(X_{H_2 O} \) = 0.942–0.981) and contained hydrogen as the major gas component (\(X_{H_2 } \) = 0.012–0.023); its composition was essentially chloride-magnesium with minor amounts of CaCl₂ and FeCl₂ and a low salinity of 2.6–8.0 wt % NaCl equiv. The rodingite minerals showed the following isotopic characteristics (‰): δ¹⁸O from 5.5 to 6.6 and δD from 42.8 to ?44.3 for chlorite, δ¹⁸0 from 2.0 to 3.8 for andradite, δ¹⁸O from 6.0 to 6.6 for diopside, and δ¹⁸O from 10.6 to 11.4 and δ¹³C from 0.1 to ?1.8 for calcite. The chloritolite is characterized by δ¹⁸O from 5.9 to 6.6 and δD from ?49.8 to ?64.4; the antigorite serpentinite shows δ¹⁸O=6.5 and δD=?65.2; and the antigoritized chrysotile-lizardite serpentinite shows δ¹⁸O from 6.8 to 6.9 and δD from ?127 to ?128. The calculated isotopic composition of fluid in equilibrium with various rocks suggested its metamorphic origin. It was formed from the water released during dehydration of oceanic serpentinites, from the components of ultrabasic and basic magmatic rocks, and, at the final stage, from marine carbon.     

Sources of Matter and Ore-Producing Fluid of the Tamunyer Gold–Sulfide Deposit (Northern Urals): Isotope Results

The Tamunyer deposit is a typical example of gold–sulfide mineralization located in the lower lithologic–stratigraphic unit (S₂–D₁) of the Auerbach volcanic–plutonic belt. The latter comprises island–arc andesitic volcano–sediments, volcanics, and comagmatic intrusive formations. Carbonates have demonstrated intermediate values of δ¹³C between marine limestone and mantle. The quartz δ¹⁸O is in the range of 15.3–17.2‰. The δ³⁴S of sulfides from the beresitized volcano-sedimentary rocks and ores varies widely from –7.5 to 12‰. The calculated isotope compositions of H₂O, CO₂, and H₂S of the ore-bearing fluid imply two major sources of matter contributing to ore genesis: local rocks and foreign fluid. The ore-bearing fluid was formed by interaction and isotope equilibration between a deep magmatic fluid and marine carbonates (W/R ~ 1), with the contribution of sulfur from the volcano-sedimentary rocks.     

Origin of Au-bearing rodingite in the Karabash massif of alpine-type ultramafic rocks in the southern Urals

The rodingite belt in the Karabash massif situated 40 km north of Miass is continuously traced for 2.5 km along its central part. Rodingites bear up to 1% sulfide disseminations and gold particles with high Cu content (up to 40 wt %) throughout the belt. The central part of the rodingite belt is especially rich in gold, which was mined at the Zolotaya Gora (Gold Mountain) deposit. The Au-bearing rodingite belt is zonal and was formed during three stages. The inner zone is composed of chlorite-andradite-diopside rock of the first stage, which is crosscut by diopside veinlets of the second stage and calcite veinlets of the third stage. The intermediate zone consists of fine-grained chloritolite of the first stage and coarse-grained chlorite veinlets of the second stage. The outer zone of the metasomatic column is occupied by antigorite and chrysotile-lizardite serpentinites. No relict rocks or minerals of the replaced protolith have been established except sporadic Cr-spinel grains. Native gold was being deposited during all periods of rodingite formation. In terms of the currently adopted concept of evolution of the Ural Foldbelt, the Sm-Nd isochron age of rodingite estimated at 369.4 ± 8.8 Ma corresponds to the period of collisional compression of Silurian-Devonian oceanic and island-arc complexes and upward pushing out of a block of the melanocratic basement underlying these complexes. A proposed model of rodingite formation is based on ore mineralogy, REE geochemistry, and thermobarogeochemical and isotopic study of minerals. It is suggested that in contrast to the barren bimetasomatic rodingite replacing dikes, the studied rodingite are considered to be fissure veins accompanied by metasomatic alteration of host serpentinite. The estimation of initial isotopic composition of fluid components indicates that the ore-bearing fluid is of metamorphic origin (δD_fl = ?4 to ?13‰ and δ¹⁸O_fl = 5.9 to 8.3‰). The fluid was formed as a product of dehydration of oceanic serpentinite at the base of melanocratic rocks and related gabbroids that moved out to the surface. These rocks were a source of gold and other components (Ca, Al, Ti, Cu, Ni, REE, P, etc.).     

Petroleum systems and the history of their formation in the northern Caspian Sea basin

This study presents the consideration of the geological history and petroleum systems in the northern Caspian Sea basin (on the basis of basin modeling using the TemisSuite2008 software package). The key patterns of the distribution of oil and gas fields and their phase composition are described. Kulaginskii Ridge and the adjacent areas are considered. The preceding data are generalized and new data are used.