pdf № 309, September

DOI: 10.19110/geov.2020.9.1

The Vorontsovskoye gold-ore deposit (Northern Urals) generally corresponds to the Carlin-type. One of the deposit features is the presence of numerous dykes of mafic and middle chemical composition, of normal and increased alkalinity. Sm-Nd isotope studies for the first time confirmed the dykes formation age 340 ± 35 Ma. These data can be indicative of the post-collisional stage of magmatism in this area. The positive eNd values suggest a probable abyssal magmatic source of Nd.

Keywords: Sm-Nd isotopy, dykes, Vorontsovskoye gold-ore deposit, Carlin-type, Northern Urals.

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DOI: 10.19110/geov.2020.9.2

Limited data on the isotopic composition of sulfur of platinum-group minerals (PGM) are reported in the literature. The LA-ICP-MS method was used to study the S-isotopic composition of Ru-Os-Ir sulfides and sulfoarsenides forming secondary corrosion and superimposed PGM assemblages from placer deposit of the East Shishim river occurring within the Verkh-Neivinsky dunite-harzburgite massif. Sulfides from corrosion PGM assemblage (laurite, As-containing laurite) replace the grains of primary native Os and Ru minerals, forming rims on them. PGM from superimposed assemblage (laurite, irarsite, tolovkite, etc.) originated on the surface of laurite rims that form part of corrosion PGM assemblage. Variations in d³⁴S values of secondary PGM (from –4.6 to 7.6 ‰) are more pronounced than those for laurite and erlichmanite from primary PGM assemblage (i. e., 0.2—2.3 ‰). The results are consistent with a model of the ultramafic massif ascending to the surface and subsequent water metamorphism during the tectonic flow and crust-mantle interaction. At the initial stage of metamorphism, mantle sulfur is present, isotopically lightened under oxidation conditions and temperature reduction. The final stage is marked by sulfur of the metamorphic fluid formed by the involvement of isotopically-heavy sulfur derived from the host sedimentary rocks.

Keywords: platinum-group minerals, Ru-Os sulfides and sulfoarsenides, sulfur isotope composition, Verkh-Neivinsky dunite-harzburgite massif, Middle Urals.

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 DOI: 10.19110/geov.2020.9.3

Topomineralogical studies are part of mineralogenic research conducted in the Paleoproterozoic Lapland-Onega rift-related structure in Karelia. These studies are important because of the location of promising areas and the study of deposits associated with basic-hyperbasic magmatism in Paleoproterozoic rift-related structures (chromite, titanomagnetite and nickel ores with PGE and gold). The aim of mineralogenic studies is to better understand major ore and noble-metal mineral associations by microprobe and ICP-MS-analyses. It was found that chromite ores are accompanied by high-temperature associations of platinoids — arsenides, sulfo-arsenides Pt, Rh, Ir and bismutotellurides Pt (with Pd), and sulfide Cu-Ni ores — mainly Pt-Pd bismutotellurides and tellurides. Titanomagnetite ores with low-sulfide copper mineralization contain stibio-sulfoarsenides, antimonides, stannides, and more rarely sulfides of Pd, Pd-Pt, and silver-containing gold.

Keywords: noble-metal minerals, mineralogical province, Lapland-Onega, rift-related, Paleoproterozoic, Karelia.

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 DOI: 10.19110/geov.2020.9.4

Minerals of the eudialyte group from ultra-agpaitic associations are often characterized by high contents (up to the dominance) of sodium at the M2 site, which is populated with iron in eudialyte. The features of blocky isomorphism with the replacement of ^IVFe²⁺ by ^IVNa and ^VNa at the M2 micro-region are discussed. Using the methods of electron probe microanalysis, X-ray diffraction and IR spectroscopy, a potentially new mineral, ^M2Na-dominant analogue of eudialyte from the Ilimaussaq alkaline massif (Greenland), was investigated. Its crystal structure was refined to R = 5.6 % in the anisotropic approximation of atomic displacements using 1095 independent reflections with F > 3s(F). The unit-cell parameters are: a = 14.208(1), c = 30.438(1) Å, V = 5321(1) ų; the space group is R-3m. The idealized formula of the mineral is (Z = 3): (Na,H₃O)₁₅Ca₆Zr₃[Na₂Fe][Si₂₆O₇₂](OH)₂Cl∙2H₂O.

Keywords: mineral, eudialyte group, crystal structure, isomorphism, M2 key site, Ilimaussaq alkaline complex.

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 DOI: 10.19110/geov.2020.9.5

Recently various authors paid much attention to accessory minerals of clastic rocks to clarify the composition of the source area and formation conditions of terrigenous deposits. The paper describes some minerals of the heavy fraction of Triassic sandstones in the north of the Timan-Pechora oil and gas province (garnet, epidote, chromium spinels, ilmenite, etc.).

We showed that the enrichment of sandstones with various mineral grains was controlled by not only the composition of the eroded rocks, but also by the hydrodynamics of the flow, as well as the method of transfer of clastic material. We noted that the features of heavy fraction minerals could be used to reconstruct sedimentation environments, taking into account their physical and chemical properties, distribution of minerals by fractions, and their stability during transportation.

Keywords: sandstones, Charkabozh formation, natural reservoirs, accessory minerals, sedimentation environments.

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DOI: 10.19110/geov.2020.9.6

Gypsum binders are widely used in construction, mining and the oil and gas industry. The use of these binders is conditioned by stability of their technical characteristics, which is achieved by using a technological operation “artificial aging”.

The features of artificial aging are: 1) hydration of calcium sulphate hemihydrate in liquid phase deficiency; 2) the resulting dihydrate gypsum crystallizes in a limited volume of micropores of the original binder.

From the standpoint of the quataronic concept, the features of the crystallization of gypsum dihydrate in the micropores of the original gypsum binder are considered. The effect of artificial aging conditions and the degree of supersaturation on the growth mechanism and the morphology of gypsum dihydrate crystals was determined.

The use of artificial “aging” results in healing of defects in the structure of the original binder, decreasing water demand and increasing strength.

Keywords: crystallization of quataron, calcium sulfate, artificial aging, gypsum binder.

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