Anatoly M. Sazonov

Isotope composition and magma sources of the Kresty volcanopluton in Polar Siberia

The first data are presented on the distribution of rare elements and isotope composition of neodymium and strontium in the rocks of the alkaline-ultramafitic association of the Kresty volcanoplutonic structure (one of the probable satellites of the Gulinian massif being the largest in the Maimecha-Kotui alkaline province in Polar Siberia). On the basis of the results of geochemical studies performed and formerly obtained geophysical and isotope data, a new model is proposed for the plume nature of magmatism in the region, based on the action of a single mantle source of the PREMA type and its active interaction with the matter of the Earth’s crust.

GEOCHRONOLOGY OF GRANITES, SURROUNDING SCHISTS AND ORES OF THE PANIMBA GOLD DEPOSIT (THE YENISEY RIDGE)

~ ~ ~ Data of isotope geochronological researches of zircons by U-Pb method, also results of Ar-Ar method researches of muscovites from the gold-bearing ores, surrounding schists and granites of the Panimba gold deposit in the Yenisey Ridge are presented. Regional metamorphism of the lower Riphean Kordinskaya suite terrigene sediments, containing ore bodies, took place in the interval of 996,0±32 - 889,0±26,6 Ma. The graniteforming and contact metamorphism of schists in the ore field of the mineral deposit have occurred on a boundary of 868,9±6,5 Ma. The absolute age of the quartz gold sulphide orebearing veins lies in the interval of 817,2±5,3 - 744±17 Ma (by muscovite with Ar-Ar method) and 815,0±37,6 - 762,3±33,3 Ma (by zircon from ore schists with U-Pb method). The long history of development of the Yenisei Range from Upper Archean to Upper Paleozoic was reflected in an accessory zircon of ore schists.

Formation of gold mineralization in ultramafic alkalic magmatic complexes

Study of mineral inclusions within alluvial gold particles of the Guli Complex (East Siberia) and findings of lode gold in rocks of the same intrusion have demonstrated that gold mineralization occurs in interstitions of both early high–magnesium rocks (dunite) and later alkalic and carbonatite rocks. In dunite the native gold occurs in association with Fe–Ni sulfides (monosulfide solid solution, pentlandite, and heazlewoodite). Formation of the gold-bearing alloys took place under a low oxygen potential over a broad range of temperatures: from those close to 600°C down to below 400°C.

Influence of the Phase Composition of Pyrrhotites on Gold Content in Rocks

On the basis of comprehensive analysis of the crystal structure, chemical and phase composition of natural pyrrhotites of the “Blagodatny” mine (Krasnoyarsk region), an analytical expression for calculating the concentration of point defects in nonstoichiometric minerals is obtained. Calculation of concentration of point defects in the crystal structure of natural pyrrhotites of various chemical compounds is made and compared with the gold content in samples. Concentration of point defects is calculated separately for the inclusion of defects (Co, Ni, Cu, Zn, Sb, etc.), and cation vacancies in the crystal structure. As a result of theoretical calculations and the analysis of X-ray spectra and the chemical composition, the dependence of the concentration of point defects and their ordering in the crystal structure on the gold content in the rock is established. The maximum content of gold corresponds to pyrrhotites in which vacancies are completely ordered in even (odd) basic planes of structure of type NiAs. The chemical formula for content representation of the nonstoichiometric minerals containing crystal structure of atoms, distinct from atoms of a forming matrix, is offered.

The Olivinite of the Krestovskaya Intrusion—the Product of Larnite-Normative Alkali Ultramafic Magma: Melt Inclusion Data

Olivinites of the Krestovskaya Intrusion consist of predominant amount of olivine, and minor Ti-magnetite, perovskite, and clinopyroxene (from single grain to a few vol %). Primary crystallized melt inclusions were found and studied in olivine, perovskite, and diopside of the olivinites. Daughter phases in olivine-hosted melt inclusions are monticellite, perovskite, kalsilite, phlogopite, magnetite, apatite, and garnet andradite. Perovskite-hosted melt inclusions contain such daughter phases as kalsilite, pectolite, clinopyroxene, biotite, magnetite, and apatite, while daughter phases in clinopyroxene-hosted melt inclusions are represented by kalsilite, phlogopite, magnetite, and apatite. According to melt inclusion heating experiments, olivine crystallized from above 1230°C to 1180°C. It was followed by perovskite crystallizing at ≥1200°C and clinopyroxene, at 1170°C. According to analysis of quenched glass of the melt inclusions, the chemical composition of melts hosted in the minerals corresponds to the larnite-normative alkali ultramafic (kamafugite) magma significantly enriched in incompatible elements. The high incompatible element concentrations, its distribution, and geochemical indicator ratios evidenced that the magma was derived by the partial melting of garnet-bearing undepleted mantle.

Investigation of Disordering in Natural Arsenopirite by X-Ray Powder Crystal Structure Analysis and Nuclea Gamma Resonance

The features of the FeAsS arsenopyrite crystal structure disordering occurred in geological conditions were studied by elemental analysis, X-ray diffraction and Mossbauer techniques using natural samples. There were selected and studied three practically single-phase polycrystalline samples of Blagodatnoe and Olimpiada ore deposits (Krasnoyarsk region) with the chemical composition close to stoichiometry (I), with excess sulfur (II) and arsenic (III). The Mossbauer (NGR) study detected the presence of the three forms of Fe(2+) in the substance. The first was associated with octahedral iron environment of [As3S3] type, the second with [S6] and third with [As6] forms conventionally associated with ordered arsenopyrite and FeS2, FeAs2 minerals. According to NGR data the iron atoms at 95 % were in the main form in the sample (I). Other forms were present about in equal parts. There were detected 73 % and 56 % of iron in its basic form for samples (II) and (III) respectively with FeS2, FeAs2 dominated as by-forms. X-ray powder crystal structure refinement was carried out in Space group P21/c. It was established that the iron atoms were in cationic positions of the arsenopyrite. Additional crystallographic positions of iron were not detected. The structure variation mainly occurred in the anion sublattice disordering the primary iron coordination from [FeAs3S3] to the condition described as [Fe(As3-хSx)(S3-yAsy)]. It was established that the mutual substitution of anions was accompanied by a small shift of the atomic positions due to the difference in the interatomic distances of Fe-S and Fe-As. Disordered condition admits the predominance of one of the anions. As a result, there are the set of the iron atom states with different composition and spatial configuration of the substituents in the coordination sphere in the real crystal. The disordering coordination of iron atoms obtained from X-ray diffracted data quantitatively corresponds to the data of NGR spectroscopy.

Specifics of geological composition, geochemistry and geochronology of rocks from the Kresty alkaline-ultrabasic massif (Maimecha-Kotui province, Polar Siberia)

In this work, we demonstrate new data that allows us to accurate geochronological ranges of formation of the Kresty alkaline-ultrabasic massif, which is considered to be a satellite of the Gulinian giant pluton. We also interpreted geological, geochemical and isotope-geochemical data obtained earlier for major varieties of this volcanic-plutonic association taking into account new geochronological results, as well as considered new aspects/information on matter source of alkaline-ultrabasic massifs from this province. One of the main aspects is interaction of Siberian super plume matter with hosting substrate of Siberian craton continental crust.

Effect of the Addition of Electrocorundum on Structural-Phase Transformations in the Quartz Lining of an Industrial-Frequency Crucible-Type Induction Furnace

Results are presented from studies of the phase interactions that take place between the metal, lining, slag, and gas inside the lining of an industrial-frequency crucible-type induction furnace (CIF). The lining is composed of quartzite, boric acid, and electrocorundum. The phase composition of the lining is determined. The lining lasted 295 heats in the production of ferrous-metal alloys at temperatures up to 1570°C. The chemical and phase compositions of the slag-covered layer and the sintered layer of the lining are also determined.

Weathering of Pyrrhotite to Szomolnokite

Using the method of dry synthesis in vacuum, the iron sulphides with S/Fe ratio from 1.0 upto 2.0 have been obtained. After keeping the samples under atmospheric influence in almost isothermal conditions (~25°С) for 29 years, the samples with distinct properties from the original ones have been obtained. Thus, the pyrrhotites were changed from the metastable phase into the stable one. The crystal structure and the phase structure of iron sulfides, thus obtained, were studied using the X-ray analysis method. The specimens obtained after air storage contained goethite FeO(HO), szomolnokite Fe(SO4)(H2O), pyrite FeS2, troilite FeS, and pyrrhotite with the compositions Fe0.975S and Fe0.875S. A diagram of the specimens’ phase composition with different S/Fe ratios after long-time isothermal air storage is offered. Dependence of the samples with the phase compositions Fe(SO4)(H2O) and Fe0.875S has been determined.