V. A. Koroteev

Nature and Age of Metamorphic Rocks from the Basement of the West Siberian Megabasin (according to U-Pb Isotopic Dates)

The SHRIMP-II zircon U-Pb dates for metamorphic rocks from the West Siberian basement are determined for the first time. It is established that the major protolith of the metamorphic strata from the Shaimsk-Kuznetsovsk meganticlinorium is composed of sedimentary Late- and Middle-Devonian rocks (395–398 Ma). It is likely that the greywackes, whose strata were mainly formed under erosion of ophiolitic rocks, served as a substrate for the metamorphic rocks. The metamorphic transformations of the rocks occurred under conditions of greenschist and occasionally lower amphibolite facies of metamorphism during the Late Carboniferous-Early Permian period.

The Kunashak meteorite: New data on mineralogy

Add info about the mineral composition of the Kunashak meteorite that fell in the Chelyabinsk region in 1949. It was found that the cosmic substance is composed of olivine (chrysolite), orthopyroxene (bronzite), clinopyroxene (augite), plagioclase (albite), maskelynite, chromite, magnetite, wustite, ilmenite, metals iron and nickel (kamacite and taenite), sulphides (troilite and pentlandite), chlorapatite and merrillite. This augite, ilmenite, pentlandite and chlorapatite identified in the Kunashak meteorite for the first time. For all minerals presents data on the chemical composition. Himself meteorite is an ordinary chondrite stone and belongs to petrological type L5-L6.

First Data on Early Paleozoic Granitoids in the Basement of West Siberia

1193 The investigations of the West Siberian Plate over the last 80 years have resulted in compilation of ever more specific schematic maps of its basement zoning [1–8]. The feature in common shown in all these maps is the surrounding Paleozoic fold belts and their litho� tectonic zones extending into West Siberia (in accor� dance with the strikes of these structures and general patterns of potential fields). The basement of the west� ern part of the West Siberian Plate approximately up to the Khanty Mansiisk latitude is composed of the Uralides (structural zones of the eastern segment of the Urals) [3, 4]. To the east, they are replaced by the Altaides [1], where the basement of the plate is repre� sented by rock complexes of the Siberian Platform and its folded surrounding structures [2]. Another feature in common for these maps of the basement beneath the West Siberian Plate is the presence of the block of the Kazakhstanides immediately east of the Uralides that gradually pinches out in the northern direction. These main megazones (or domains) are separated by

Platinum-Group Elements in Alpine-Type Ultramafic Rocks and Related Chromite Ores of the Main Ophiolite Belt of the Urals

On the basis of a representative collection of ultramafic rocks and chromite ores and a series of technological samples from the largest (Central and Western) deposits in the Rai-Iz massif of the Polar Urals and the Almaz-Zhemchuzhina and Poiskovy deposits in the Kempirsai massif of the southern Urals, the distribution and speciation of platinum-group elements (PGE) in various type sections of mafic-ultramafic massifs of the Main ophiolite belt of the Urals have been studied. Spectral-chemical and spectrophotometric analyses were carried out to estimate PGE in 700 samples of ultramafic rocks and chromite ores; 400 analyses of minerals from rocks, ores, and concentrates and 100 analyses of PGE minerals (PGM) in chromite ores and concentrates were performed using an electron microprobe. Near-chondritic and nonchondritic PGE patterns in chromitebearing sections have been identified. PGE mineralization has been established to occur in chromite ore from all parts of the mafic-ultramafic massifs in the Main ophiolite belt of the Urals. The PGE deposits and occurrences discovered therein are attributed to four types (Kraka, Kempirsai, Nurali-Upper Neiva, and Shandasha), which are different in mode of geological occurrence, geochemical specialization, and placer-forming capability. Fluid-bearing minerals of the pargasite-edenite series have been identified for the first time in the matrix of chromite ore of the Kempirsai massif (the Almaz-Zhemchuzhina deposit) and Voikar-Syn’ya massif (the Kershor deposit). The PGE grade in various types of chromite ore ranges from 0.1–0.2 to 1–2 g/t or higher. According to technological sampling, the average PGE grade in the largest deposits of the southeastern ore field of the Kempirsai massif is 0.5–0.7 g/t. Due to the occurrence of most PGE as PGM 10–100 mm in size and the proved feasibility of their recovery into nickel alloys, chromites of the Kempirsai massif can be considered a complex ore with elevated and locally high Os, Ir, and Ru contents. The Nurali-Upper Neiva type of ore is characterized by small-sized primary deposits, which nevertheless are the main source of large Os-Ir placers in the Miass and Nev’yansk districts of the southern and central Urals, respectively.

The meteorite Ural: New mineralogical data

New data on the mineral composition of the meteorite Ural found out near the village of Ural (Kurgan Region) in 1981 were obtained. It was established that the meteorite is composed of olivine (chrysolite), orthopyroxene (bronzite), clinopyroxene (diopside), plagioclase (albite), chromite, metals iron and nickel compounds (kamacite and taenite), sulfides (troilite and pentlandite), chlorapatite, and merrillite. Minerals such as diopside, taenite, pentlandite, chlorapatite, and merrilite were identified for the first time in the meteorite Ural. This work presents the chemical compositions of all minerals studied. The meteorite Ural is normal H5–H6 chondrite which is characterized by strong secondary changes both inside and outside, viz., development of a supergene mineral—goethite.

Suture zones of the Urals as integral prospective ore-bearing tectonic structures

Rift-related (1.2 Ga) and collision (380–240 Ma) suture zones of the Urals are described. The riftrelated suture zones comprise an ultramafic-gabbro complex with titanomagnetite mineralization, an ultramafic complex with chromite mineralization, and a complex of alkali granitoids with rare-metal (including REE) mineralization accompanied by K-feldspathites, albitites, and calcite metasomatic rocks. The collision suture zones are distinguished by early collision granitoids specialized for tungsten (scheelite) and gold, as well as by raremetal granites and such derivatives of them as pegmatite and greisen with rare-metal and colored-stone mineralization. The suture zones are characterized by long-term (up to 80 Ma or more) continuous-discontinuous periods of ore deposition; heterogeneous sources of ore matter and ore-bearing fluids; a polyelemental composition of lithogeochemical halos and an integral mineral composition of altered wall rocks; and the occurrence of mafic, intermediate, and felsic dikes at large gold deposits, as well as wide variations in PT parameters of the ore-forming process: T = 620−150°C and P = 3.2−0.6 kbar. Collision played a dual role in ore formation. On the one hand, collision led to deformation and metamorphism of precollision massive sulfide deposits and, to a lesser degree, Au-bearing Fe and Cu skarn and porphyry copper deposits, and, on the other hand, to the formation of new gold, rare-metal, quartz, colored-stone, talc, muscovite, and noble serpentine deposits. As a rule, this polygenetic mineralization differs in age and is related to collision volcanic and plutonic complexes. This diversity can be a good basis for metallogenic analysis, forecasting, and prospecting of various metallic deposits and industrial minerals. Polygenetic mineralization of various age known in suture zones is accompanied by integral lithogeochemical and metasomatic halos characterized by a continuous-discontinuous history. The complexity of ore mineralization and often nonlinear metallogeny increase the practical value of suture zones.

Zircons of Granitoids of the Yamal Peninsula Basement: Age and Composition of Inclusions

The zircons in granitoids from the basement of the Verkhnerechenskii oil exploration area (Yamal Peninsula, West Siberia) were studied. The U–Pb age of zircons was evaluated as 254.0 ± 3.0 Ma. It was found that the inclusions in zircons are represented by various minerals: fluorapatite, titanite, monazite-(Ce), albite, quartz, chamosite, and calcite. Most likely, the latter two minerals were formed separately from zircon but belonged to later secondary minerals (the rock propylitization products). In general, the accessory zircons and inclusions belonged to the “granite” association and crystallized synchronously in the Upper Permian.

Sources of Ore Substance of Carbonatite Complexes of the Ural Fold Belt: Rb–Sr and Sm–Nd Isotope Data

The results of study of the Nd and Sr isotope compositions of the Nb ore minerals (pyrochlore and aeschynite groups) and rocks from the Ilmenogorsk–Vishnevogorsk and Buldym carbonatite complexes of the Ural Fold Belt are presented. It has been established that pyrochlores of the early stages of ore formation and the IVC miaskite-carbonatite rocks have a single substance source corresponding to a mantle moderately depleted source according to isotope parameters. The crustal components, along with mantle, participate in the processes of ore formation within the Buldym complex.

The Main Factors Affecting the Distribution of Oil Fields in the West Siberian Platform

It has been found that the main oil fields in Western Siberia are attributed to Triassic rifts, because the rifts drain the upper mantle, and the deformations of the sedimentary cover are determined by the basement. On average, the thickness of the basement is 14 times greater than that of the sedimentary cover. Taking into account the mean strength (153 ± 10 MPa) of the basement rocks, the basement strength is two orders of magnitude greater than the strength of the sedimentary cover. The sialic blocks, considered as Precambrian, are composed of light granites and metamorphic rocks. They ascend to the level of the upper crust at the time of Triassic rifting and continued to emerge. As a result, antiforms were formed above the sialic blocks in the sedimentary cover; these antiforms were filled with oil.

Mineral Composition and Structure of the Sverdlovsk Meteorite (H4-5)

A fragment of the Sverdlovsk Meteorite, which was found in 1985 in the Central Urals, is studied by modern analytical methods. It belongs to H chondrites of petrologic type 4–5; shock stage of meteorite is S1-2, terrestrial weathering is W1. The composition of minerals of the meteorite is studied. It is found for the first time that the metal and sulfides are concentrated in fine veinlets of the recrystallized matrix of the chondrite and are accompanied by segregations of metal and troilite inside these veinlets. The distribution of trace elements of the metal phase of the meteorite is studied.