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Vol. 20 (2017 year), No. 1, DOI: 10.21443/1560-9278-2017-20-1/1

Kalinin A. A., Savchenko Ye. E.
Bismuth-silver mineralization in the Sergozerskoe gold occurrence

Bismuth-silver mineralization attendant to gold mineralization in the Sergozerskoe gold occurrence has been studied in detail. Bi-Ag mineralization is connected with diorite porphyry dykes, which cut volcanic-sedimentary Lopian complexes of the Strel'ninsky greenstone belt – hornblendite and actinolite-chlorite amphibolites, biotite and bi-micaceous gneisses. Distribution of Bi-Ag mineralization similar to gold mineralization is controlled by 80 m thick zone of silicification. Bi minerals are found in brecciated diorite porphyry. Bismuth-silver mineralization includes native metals (bismuth, electrum, silver), tellurides (hedleyite, hessite), selenides (ikunolite), sulfides and sulfosalts of Bi and Ag (matildite, lillianite, eckerite, jalpaite, prustite, acanthite, a few undiagnosed minerals). All Bi and Ag minerals associate with galena. Composition of mineralization evolved from early to late stages of development, depending on intensity of rock alteration. The earliest Bi-Ag minerals were native bismuth and hedleyite formed dissemination in galena, and electrum with 30-45 mass.% Au. Later native bismuth was partly substituted by silver and bismuth sulfosalts and bismuth sulfides. The latest minerals were low-temperature silver sulfides eckerite, jalpaite, and acanthite, which were noted only in the most intensively altered rocks. As soon as the process of formation of Bi-Ag mineralization is the same as formation of gold, findings of bismuth-silver mineralization can serve as a positive exploration sign for gold in the region.

(in Russian, стр.12, fig. 3, tables. 3, ref 15, Adobe PDF, Adobe PDF 0 Kb)

Vol. 26 (2023 year), No. 1, DOI: 10.21443/1560-9278-2023-26-1

Kalinin A. A., Kudryashov N. M., Savchenko Ye. E.
Mal'javr – the first gold prospect in the Archean conglomerates, the Kola region

A new type of prospects of gold mineralization in the Kola region is considered in the paper. The Mal'javr prospect is located in the south-western flank of the Uragubsky greenstone belt in biotite gneiss – the metamorphosed sedimentary rocks with interlayering of polymictic conglomerate, gravelite, and sandstone. Gold-bearing sulfide mineralization was found in altered rocks, which form a series of lens-shaped bodies, concentrated along a shear zone of NNE strike. The bodies of altered rocks are zonal: the central zone makes 50–80 % of the lens volume, it consists of garnet and quartz, the intermediate zone is of garnet-biotite mineral composition, and in the outer zone, which is often reduced, the main minerals are hedenbergite, hornblende, and grunerite. The metasomatic alteration is connected with an increase of iron content, decrease of Al, Si, and alkaline metals Na and K, redistribution of calcium to the outer zone of metasomatic lenses; and magnesium is inert. If compared to the unaltered gneiss, the altered rocks are depleted in Rb, Cs, Sr, Ba, Zr, Nb; and content of Cu, Zn, Mn, As, Ag, Te, W, Bi (all these elements are known to associate with gold) increases. All zones of altered rocks are rich in sulfide mineralization. Pyrrhotite and arsenopyrite are the main sulfide minerals, minor minerals are chalcopyrite, pentlandite, magnetite, tochilinite, native gold, and late pyrite and marcasite. Rock alteration and formation of sulfide mineralization happened at a high temperature > 600 °С, and the late alteration processes at ~400 °C. The arsenopyrite-gold mineralization probably formed with As and Au mobilized from the host biotite gneiss during regional metamorphism or due to pegmatite vein intrusion.

(in Russian, стр.12, fig. 8, tables. 5, ref 15, AdobePDF, AdobePDF 0 Kb)

Vol. 27 (2024 year), No. 1, DOI: 10.21443/1560-9278-2024-27-1

Goychuk O. F., Konopleva N. G., Lepekha S. V., Savchenko Ye. E., Panikorovskii T. L.
Atypical components in the composition of nepheline from rocks of the Khibiny massif according to IR spectroscopy data

Nepheline is one of the main rock-forming minerals of the rocks of the Khibiny alkaline massif. Nepheline composition changes depending on the crystallization temperature, which makes it an indicator of rock formation conditions. In addition, nepheline is one of the main concentrators of hydrocarbon gases. The study of nepheline from different rocks of the Khibiny massif by local IR spectroscopy with Fourier transformation (micro-FTIR) has revealed the presence of water and acetylene in its structure. The water content estimated according to the method of statistical quantitative determination of water in nominally anhydrous minerals varies in the range from 0 to 0.78 wt.%. The highest water content has been observed in high-temperature nepheline of early formations (foyaite of the central and outer parts of the massif), and the lowest – in relatively low-temperature nepheline of later rocks of the Main Ring Fault (urtite, apatite-nepheline rock and poikilitic (kalsilite)-nepheline syenite – rischorrite). The study reveals that water enters the structure of nepheline in the form of H2O molecules that occupy vacancies in the potassium sites. The water content in nepheline is controlled by the number of vacancies in its structure. The presence of acetylene has been determined on a qualitative level. Additional studies are required to assess its quantitative content.

(in Russian, стр.14, fig. 7, tables. 2, ref 43, AdobePDF, AdobePDF 0 Kb)