Genesis of Sulfide and Platinum-Metal Mineralization of the Khudolaz Complex (Southern Urals)

Doklady Earth Sciences - Mineralogical and geochemical studies of sulfide–platinum metal assemblages of the Khudolaz complex made it possible for the first time to substantiate their...     

First Finds of Platinum and Palladium Minerals in Sulfide Ores of the Khudolaz Intrusive Complex (Southern Urals)

Forms of occurrence of platinum (sperrilite, moncheite) and palladium (Sb-michenerite, Pd–Bi phase) minerals in intrusive rocks of the Khudolaz differentiated complex have been studied. Platinum minerals were identified in disseminated Cu–Ni sulfide ores from ultramafic olivine–hornblende rocks of the Khudolaz complex, whereas palladium minerals were found in ores from olivine–hornblende gabbroids. The structural arrangement of grains as inclusions in sulfides of the primary magmatic association testifies that they were formed as a result of segregation of platinum group elements, which partitioned into the composition of sulfides during low-temperature mineral formation process at the late-magmatic stage.     

PGE Mineralization of Massive Chromitites of the Iov Dunite Body (Northern Urals)

This work presents the results of the first comprehensive study of PGE mineralization from massive chromitites of the Iov dunite body (Northern Urals). The chromitites are composed of chromespinelides with a higher content of Cr₂O₃ with respect to those from other zonal clinopyroxenite–dunite massifs of the Urals. However, the composition of chromespinelides fits the trend that is characteristic of the dunite–clinopyroxenite–gabbro formation. PGE minerals, in particular Pt–Fe solid solutions, were identified in chromitites and in chromespinelides in the form of crystals and aggregates of a complex non-crystallographic habit and less often of an idiomorphic cubic habit. In terms of stoichiometry, Pt–Fe minerals correspond to ferroplatinum (Pt₂Fe) and isoferroplatinum (Pt₃Fe). The minerals of the isomorphic tetraferroplatinum–tulameenite–nickelferroplatinum series are widely distributed. Thus, the PGE mineralization of the Iov dunite body has features that are characteristic of clinopyroxenite–dunite massifs of the Urals.     

Zirconology of rutile eclogites of the Maksutov Complex (Southern Urals)

The age data (U–Pb, SHRIMP II) of zircons from rutile eclogites of the Maksutov Complex (MC) (village Shubino, Southern Urals) were subdivided into three age groups. The Neoproterozoic zircons (561 ± 10 Ma) recorded the formation stage of eclogites, the protolith of which was diabase and gabbro-diabase bodies. The Neoarchean ancient zircons (2884 ± 36 Ma) belong to the mantle substratum, which was repeatedly transformed (2303 ± 12, 2008 ± 18, 1626 ± 59 Ma). Zircons of early Ordovician–early Silurian age (433–477 ± 6 Ma; 340 ± 40 Ma) recorded superimposed processes, corresponding to high-pressure metamorphism.

     

Garnet-pyroxene and lawsonite-bearing rocks of the Maksyutov Complex (Southern Urals)

The new petrological and geochrological data are used to constrain the nature of garnet-clinopyroxene and lawsonite-bearing rocks, which contain a rare variety of Fe-Ca-rich garnets. These rocks associated with antigorite serpentinites have no equivalents in the other units of the Maksyutov eclogite-glaucophane schist complex and, thus, can be regarded as a separate “mafic-ultramafic” unit. Based on their mineral and chemical composition, the garnet-clinopyroxene and lawsonite-bearing rocks can be interpreted as HP associations formed within a deep continental rifting setting. They experienced a series of metasomatic alterations during decompression exhumation and were accreted to the Maksyutov Complex as a result of the arc-continent collision. The U–Pb zircon data indicate that a Late Riphean–Lower Paleozoic age (824 and 440–470 Ma) was a crystallization age of garnet-clinopyroxene rocks and Ar–Ar white mica age (341 ± 2 Ma) represents the timing of the final accretion of all structural unit to the Maksyutov Complex.     

Geochemical signatures for eclogite protolith from the Maksyutov Complex, South Urals

We conducted a geochemical study of eclogites (40 samples) from a boudin of the Lower Unit of the Maksyutov Complex in the South Urals in order to determine their protolith nature. The eclogites have major element compositions corresponding to quartz-bearing hypersthene basalts. Trace-element characteristics of the eclogites further suggest that they resemble enriched-type of tholeiites such as E-MORB. The compositional variation of eclogites was likely caused by fractional crystallization of parental melt under hypabyssal conditions, during its intrusion in thinned continental crust shortly before subduction. The high-pressure metamorphism has not affected significantly the major- and trace-element signatures of the protoliths. The compositions of co-existing minerals from the distinguished rock groups do not show significant distinctions. The considerable scatter of P–T estimates of metamorphic conditions does not depend on whole-rock composition. Therefore, the eclogitization was preceded by a chemical differentiation of an initial magmatic source, which is responsible for co-existence of rocks of variable composition in the same boudin. Dikes or sills of tholeiite basalts having geochemical characteristics of E-MORB could be the protoliths for the Maksyutov eclogites.     

Nickel-sulfide ores in ultrabasites of Khabarnyy massif (South Urals)

The mineralized area (fig. 1) lies inside a large dunitic body. The sulfides are small phenocrysts of pentlandite (with chalcopyrite and pyrrhotite); chromite is generally present and metasomatic magnetite is locally abundant, as replacer of the sulfides. A genetic connection of the sulfides with the dunites is indicated. There is no evidence of any epigenetic segregation of the ore minerals and hence no reason to expect presence of economic ores in this particular part of the massif. — V.P. Sokoloff     

Listvenite-related gold deposits of the South Urals (Russia): A review

The Urals is a complex fold belt, which underwent long geological evolution. The formation of most gold deposits in the Urals is related to the collision stage. In this paper, we review some relatively small listvenite-related gold deposits, which are confined to the large Main Uralian fault zone and some smaller faults within the Magnitogorsk zone. The Mechnikovskoe, Altyn-Tash, and Ganeevskoe deposits are studied in detail in this contribution. They comprise the ore clusters along with other numerous small gold deposits, and constituted the sources for the gold placers exploited in historical time. The gold is hosted by metasomatites (listvenites, beresites) and quartz veins with economic gold grades (up to 20 g/t Au). Listvenites are developed after serpentinites and composed of quartz, fuchsite, and carbonates (magnesite, dolomite) ± albite. Volcanic and volcanoclastic rocks are altered to beresites, consisting of sericite, carbonates (dolomite, ankerite), quartz and albite. Pyrite and chalcopyrite are major ore minerals associated with gold; pyrrhotite, Ni sulfides, galena, sphalerite, arsenopyrite and Au-Ag tellurides are subordinate and rare. Gold in these deposits is mostly high-fineness (>900‰). The lower fineness (∼800‰) is typical of gold in assemblage with polymetallic sulfides and tellurides. The ores have been formed from the NaCl–CO₂–H₂O ± CH₄ fluids of low (∼2 wt% NaCl-equiv.) to moderate (8–16 wt% NaCl-equiv.) salinity at temperatures of 210–330 °C. The oxygen isotopic composition of quartz (δ¹⁸O) varies from 14.7 to 15.4‰ (Mechnikovskoe deposit), 13.2 to 13.6‰ (Altyn-Tash deposit) and 12.0 to 12.7‰ (Ganeevskoe deposit). The oxygen isotopic composition of albite from altered rocks of the Ganeevskoe deposit is 10.1‰. The calculated δ¹⁸O_H2O values of the fluid in equilibrium with quartz are in a range of 5.7–6.3, 4.2–4.6 and 6.3–6.7‰ respectively, and most likely indicate a magmatic fluid source.     

Tellurium-Bearing Mineralization in Clastic Ores at the Yubileynoe Copper Massive Sulfide Deposit (Southern Urals)

At the well-preserved Yubileynoe VMS deposit (Southern Urals), sulfide breccias and turbidites host abundant tellurides represented by hessite, coloradoite, altaite, volynskite, stützite, petzite, and calaverite, as well as phases of the intermediate tellurobismuthite → rucklidgeite solid solution. Three telluride generations were highlighted: (1) primary hydrothermal tellurides in fragments of chalcopyrite and sphalerite of chalcopyrite-rich black smoker chimneys; (2) authigenic tellurides in pseudomorphic chalcopyrite and chalcopyrite veins after fragments of colloform and granular pyrite; and (3) authigenic tellurides in pyrite nodules. Authigenic tellurides are widespread in pyrite-chalcopyrite turbidites. Primary hydrothermal and authigenic tellurides are less common in sulfide turbidites and gritstones with fragments of sphalerite-pyrite, pyrite-sphalerite paleosmoker chimneys and clasts of colloform and fine-grained seafloor hydrothermal crusts. Siliceous siltstones intercalated with sulfide turbidites contain pyrite nodules, whose peripheral parts contain inclusions of epigenetic tellurides. It is assumed that Te for authigenic tellurides originated from fragments of colloform pyrite and hydrothermal chalcopyrite of pyrite-chalcopyrite chimneys, which dissolved during the postsedimentation processes. The main Te concentrators in clastic ores include pseudomorphic chalcopyrite, which inherits high Te, Bi, Au, Ag, Co, Ni, and As contents from the substituted colloform pyrite, and varieties of granular pyrite containing microinclusions of tellurobismuthite (Bi, Te), petzite (Au, Ag, Te), altaite (Pb, Te), coloradoite, and hessite (Ag, Te).

     

Evolution of the Vagran Gold-Bearing Placer Cluster (Northern Urals) and Prospects for Revealing Bedrock Mineralization

Geology of Ore Deposits - Abstract—More than 10 t of gold have been mined within the Vagran placer cluster (Northern Urals), and the identified primary sources are limited to single...     

The Geochemical Characteristics of the Early Riphean Navysh Volcanic Complex (Southern Urals)

The Navysh volcanic complex, which is an integral part of the Ai Formation (Lower Riphean), overlies Archean–Early Proterozoic formations of the Taratash metamorphic complex. It is represented mainly by trachybasalts, as well as by dacites and metasomatic bostonites. The Navysh complex is subdivided for the first time here into several volcanic series, which differ in their contents of TiO₂ and several incompatible elements. The metasomatic nature of the bostonites has been proven. Reasons are given for excluding dacites from the composition of the Navysh complex.     

Multi-Stage Mineralization of the Early Yanshanian Granites from the Central Nanling Region, South China: Implications from REE Geochemistry

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New data on geology of the Shatak Complex (western slope of the Southern Urals)

The comprehensive study of sections of the Shatak Complex has revealed that conglomerates at the base of Middle Riphean rocks are not basal but intraformational rocks. Previously described angular unconformities between shales of the Sukhin Subformation (Yusha Formation, R₁) and conglomerates of the Kuz”elga Subformation (Mashak Formation, R₂) are related to late tectonic movements. Magmatic rocks developed at the base of the Middle Riphean section are represented by sheet intrusions formed in the course of emplacement of a fluid-saturated magmatic melt into partially or completely lithified terrigenous rocks at the graben formation stage during the origination of synkinematic faults that served as magma conduits. It is inferred that distribution of provenances of clastic materials and sedimentation basins in the Burzyanian and Yurmatian should be scrutinized in the study region, because the normal regressive sequence of rocks from the uppermost Yusha Formation to the lowermost Mashak Formation, which was established in the Shatak Ridge, eliminates a clear boundary distinguished between them at present. The idea about an older age of the Mashak conglomerates is substantiated.     

New iron resources of the South Urals

An area with brick-red loose and viscous sandy-clayey rocks and brown ores with an average Fe content of 19.84% and possible resources of 1 billion tons of metal was determined. Mn and Ti are the main alloying components; Ni, Co, Cr, V, and Zr are additional; and goethite (FeOOH) is an ore mineral.