Vol CLIII, No 2 (2024)

Morphology and compositions of minerals in metamorphized Early Proterozoic gabbroids of the Northern Ladoga area were studied with the purpose to identify criteria of their magmatic or metamorphic origin. These rock-forming minerals of the Kaalamsky complex are stable in the wide range of temperatures and pressure. To solve the problem, together with comparison with minerals from non-metamorphized rocks of the Potudan intrusion (Volga-Don orogen), there were used the data of petrographic study in as well as the data of mineral compositions and thermodynamic modeling. It was concluded that it is possible to distinguish groups of magmatic and metamorphic rock-forming minerals with help of morphogenetic, geochemical, and thermobarometric criteria, as well as criteria based on revealing the concordance between observed and modeled mineral compositions. Combined application of these criteria has allowed determining that rocks of Kaalamsky complex contain olivine, clinopyroxenes, amphiboles, plagioclases of magmatic origin, and also their metamorphic analogues.

Fluid inclusions have been studied in vein quartz with gold sulfide mineralization from metamorphosed sandstones of the Eekite series and metarhyolites of the Early Proterozoic, in quartz breccia from the zone of overlapping gold mineralization on the Early and Middle Permian sandstones, as well as in the gold quartz intergrowths from the Sololi River placer. It has been revealed that formation of quartz breccias occurred within a wide temperature interval from 230 to 425 ºC, with predominance of carbon dioxide and nitrogen in the vapor phase. It is suggested that the increased nitrogen content may be associated with a chemical reaction between the fluid and ammonium-containing silicates of host rocks, in which nitrogen in the form of NH⁴⁺ isomorphically replaces potassium at the regressive stage of metamorphism. At the same time, it is possible that mantle nitrogen, which was transported along the Anabar-Eekite deep fault, participated in formation of the studied breccias. The close homogenization temperatures and similar nature of the water-salt composition for the fluid inclusions of quartz veins that inject the Eekite series meta-rocks and meta-rhyolites indicate the synchronism of their formation and attribute them to the common stage of ore formation. Quartz veins with gold sulfide mineralization were the primary sources of pebbles with gold-quartz intergrowths from the Sololi River, this is evidenced by similarity of principal characteristics of fluid inclusions. Oxidizing conditions of the mineralization serve as favorable factor for the Au deposition, it is indicated by the predominant CO₂ content in fluid inclusions, keeping role of a geochemical barrier and leading to an elevated gold content in quartz veins.

The article presents a review of current knowledge about the first finds of fossil resins in the Arctic territories of Denmark, Canada, the USA and Norway. The history of their study is briefly given on the base of little-known and fragmentary multilingual documents, the primacy of researchers who mentioned fossil resins is noted, location of their occurrences and varieties of fossil resins are given, and the level of their study is assessed. M.D. Levashov is the author of the first written mention of fossil resins in the territory of the foreign Arctic. Information about the findings of fossil resins in the foreign Arctic allows expanding the existing database on resins, and an in-depth study of their physic-chemical characteristics and formation conditions will help clarify the classification features of fossil resins.

Raman spectra of lucasite-(Ce), La-analogue of lucasite, kassite and cafetite are significantly different. Most evident differences were revealed in the position of bands corresponding to vibrational modes for bands assigned to symmetrical v₁(Ti-O) and asymmetrical v₃(O-Ti-O) stretching vibrations, as well as the bands determined by asymmetrical bending vibrations v₄(transTiO₆) and asymmetrical v₃(O-Ti-O) stretching vibrations. Raman spectra of lucasite-(Ce) and La-analogue of lucasite are published for the first time. The presented data are valuable for the identification of cafetite and kassite group minerals using Raman spectroscopy.

Stillwellite-(Ce) and some its synthetic analogues tend to undergo phase transition from polar (ferroelectric) to nonpolar (paraelectric) modification on heating. However, the reasons for the transition and phase stability remain the subject of scientific debate. Here we present detail studies (scanning electron microscopy, energy-dispersive X-ray spectroscopy, Raman spectroscopy and single-crystal X-ray diffraction (SCXRD)) of hydrothermally grown BaBPO₅ isostructural with stillwellite-(Ce). Its thermal behavior was studied by an in situ low- (from –173 to +25 °C) and high-temperature (HT; 25–800 °C) SCXRD. Fully ordered crystal structure of BaBPO₅ (at T = 25 °C: trigonal, P3₂21, a = 7.1166(1) Å, c = 7.0011(1) Å, V = 307.07(1) ų, R1 = 1.42 %) does not exhibit any change of symmetry upon cooling / heating unlike natural stillwellite-(Ce). Thermal expansion of BaBPO₅ is almost isotropic (α_min = 8.4, α_max = 8.7⋅10^-6 °C^-1) despite the chain nature of borophosphate anion. The comparative crystal chemical analysis of HT behavior of cationic polyhedra in the stillwellite-family members is presented.

Lednevite, ideally Cu[PO₃(OH)]·H₂O, is a new mineral discovered at the 255 m level of the Murzinskoe Au deposit, Krasnoshchyokovskiy District, Altai Krai, Western Siberia, Russia. It forms spherulites up to 0.1 mm in diameter, composed of very thin fibers and grouped in aggregates up to 1.5 mm across. Lednevite overgrows philipsburgite crystals on a matrix of epidote-andradite skarn and quartz and associates with malachite, chrysocolla, kaolinite, goethite and P-bearing cornubite. The new mineral is transparent, has sky blue color, very pale blue streak and vitreous lustre. Cleavage is not observed. The Mohs’ hardness is ~3. D_meas = 3.18(2) g cm^–3, D_calc = 3.196 g cm^–3. The chemical composition of lednevite is (electron microprobe, wt.%; H₂O by stoichiometry): CuO 40.20, ZnO 3.92, P₂O₅ 36.29, As₂O₅ 4.80, H₂O 14.98, total 100.15. The empirical formula calculated on the basis of 3 H and 5 O apfu is (Cu_0.91Zn_0.09)_Σ1.00[(P_0.92As_0.08)_Σ1.00O₃(OH)]·H₂O. The crystal structure was refined by the Rietveld method to R_p = 0.0042, R_wp = 0.0061, R_obs = 0.0354. Lednevite is monoclinic, space group P2₁/a, with a = 8.6459(6), b = 6.3951(4), c = 6.8210(5) A, β = 93.866(2)°, V = 376.28(4) A³ and Z = 4. The strongest lines of the powder X-ray diffraction pattern [d, A (I, %) (hkl)] are: 5.135 (100) (110), 4.648 (33) (011), 3.241 (28) (21-1), 3.095 (49) (211), 2.891 (27) (11-2), 2.775 (53) (112), 2.568 (29) (220). The new mineral is isotypic to the synthetic CuHPO₄·H₂O. Some optical and spectroscopic data, which could not be obtained on natural sample, were obtained from the synthesized material. The crystal structure of the synthetic analogue of lednevite was solved from single-crystal X-ray diffraction data and refined to R₁ = 0.0173 for 1159 independent reflections with I > 2σ(I). All positions of H atoms were determined. Lednevite is named for Vladimir Sergeevich Lednev, amateur mineralogist from Barnaul (Altai Krai) who collected the sample with the new mineral.

Number of members and the activities of the Russian Mineralogical Society in 2022–2023 are reported