Vol CLIII, No 6 (2024)

Complex gold-iridium-osmium placer deposits are associated with the Guli massif of ultramafic, alkaline rocks and carbonatites within the Maimecha-Kotui province in the northern part of the Siberian Platform. Unlike natural Os-Ir alloys, which are genetically related to ultramafic rocks, the bedrock source of gold remains controversial. We report, for the first time, morphological and compositional features of gold mineralization from the Quaternary deposits of the Dunitovaya River in the southern part of the Guli massif. According to the morphology, gold grains are subdivided into drop-shaped-rounded, lumpy, flattened-lumpy and lamellar varieties; their main morphometric parameters, gold fineness and average statistical characteristics of the chemical composition are presented. Based on their internal structure, the studied gold grains are subdivided into homogeneous, consisting predominantly of electrum of homogeneous composition, and heterogeneous, containing (1) several minerals (e.g., electrum, tetra-auricupride, auricupride) or (2) formed by electrum with a highly variable composition (i.e., from Au-bearing silver to Ag-bearing gold). The first copper isotopic data for gold grains from various morphological types of the Dunitovaya River are characterized by similar δ⁶⁵Cu values in the range from −0.59 to 0.11‰ (δ⁶⁵Cu average = −0.30±0.23‰, n = 5), which is in favor of a primitive source of ore matter. Taking into account the geological background of the location of channel and terrace deposits of the Dunitovaya River, the insignificant character of the transfer for placer gold (4−6 km), and the similarity of gold minerals from the Dunitovaya River with gold minerals from calcite carbonatite, we propose that the main bedrock sources of the studied morphological varieties of gold were the rocks of the Maimecha-Kotui ijolite-carbonatite complex.

The paper displays review of new minerals published in 2023. Data for each one mineral include its crystal-chemical formula, unit cell parameters, principal physical properties, chemical composition, type locality, etymology of its name, reference of the first publishing about it. In total, the review includes data on 102 newly discovered minerals approved by the IMA. There are also references for publications on questions of classification and nomenclature of minerals, improvements of composition and structure of known mineral specie

In chromite ores of Central and No. 214 deposits of the Rai-Iz ultramafic massif, which is part of the Khadatinsky ophiolite belt of the Polar Urals, along with previously known platinum group minerals (PGM), native ferrous ruthenium, native ruthenium nickel (iridium-ruthenium), native platinum, new unnamed intermetallic compound (Rh,Pt)₃Zn (with Rh content of up to 88 wt %), As-rich disulfides of laurite–erlichmanite series (with As content of up to 4.2 wt %) and unnamed sulfoarsenide with stoichiometric formula (Ir,Os)(S,As) were discovered and characterized for the first time. Grains of native ruthenium with Ru content of up to 80.5 wt % were diagnosed for the first time, against the previously known Ru content of up to 36.8 wt %. The set of PGMs of massif has been expanded from 24 to 31 mineral varieties. It has been shown that diversity of PGMs depends on density of dissemination of chromite ores, degree of their cataclasis and metamorphic transformation. Solid (massive) and noticeably metamorphosed chromite ores exhibit widest and most diverse set of PGMs. The Rai-Iz massif has preserved platinum group complexes that reflect features of upper mantle deep mineral formation. Such early mantle-magmatic formations include native osmium, Ir-containing osmium, native iridium and sulfides (disulfides of the laurite-erlichmanite series, kashinite, and cuproiridsite). Formation of other specific native minerals and intermetallics of PGE, with participation of mobile metals (Ni, Cu, Zn, Mn, As) and removal of part of sulfide sulfur, is associated with cataclasis and metamorphic transformation of ore chrome spinels and primary PGM included in them. The identified secondary PGMs were formed mainly in regional-metamorphic (regressive) stage [native ruthenium, ruthenium nickel, unnamed MSS (Ru,Ni,Os,Fe), As-rich disulfides of the laurite-erlichmannite series and unnamed sulfoarsenide (Ir,Os)(S,As)] and, to lesser extent, in contact-metamorphic (progressive) stage (native ferrous ruthenium, native platinum and new intermetallic of rhodium (Rh,Pt)₃Zn).

In spodumene pegmatites, the Kolatan deposit, Nuristan province, Afghanistan, a large (about 15 mm) crystal of Cs-rich analcime was discovered for the first time in the region. The SEM-EDS and SIMS methods identified its concentric zoning. The formula (Na_0.78Cs_0.05K_0.02)_Σ0.85[(Al_0.89Si_2.12)_Σ3.01O₆]·0.65H₂O corresponds to the average composition of the mineral. The analysis of crystal zoning in two profiles by the SEM-EDS method (93 points) shows that Cs content is maximum in the core of the crystal and decrease to the rim. Contents of K, Na, and Al increase from core to rim. SIMS method (16 points) confirms the pointed profile of Cs which content decreases from 65 100 to 9200 ppm. The profile of Ca has smoother appearance. Profiles of transition metals (Mn, Fe, Ni, Cr, and V) are complex. The Rb profile is peaked and asymmetric: in the one part of the profile, Rb content varies insignificantly, in the another part it decreases from 250 ppm to 80 ppm. Water content increases from core to rim (from 48 400 ppm to 68 700 ppm). Most likely, this increasing reflects the transition to the hydrothermal stage. It is possible to assume that the formation of Cs-rich analcime marked the completion of the magmatic stage of pegmatite formation, the temperature regime of which is estimated as ~400°C. The find of such a large and gem quality crystal of extremely rare Cs-rich analcime is unique.

A collection of 120 vanadinite, pyromorphite and mimetite specimens was studied using IR spectroscopy. The features of IR spectra of phosphorus- and arsenic-bearing varieties of vanadinite are characterized in detail. It is shown that (1) the sensitivity of IR spectroscopy to the incorporation of small amounts of P in vanadinite (≥ 0.1 wt. % P₂O₅) is comparable to the sensitivity of electron microprobe analysis, and (2) phosphorus-bearing vanadinite can be reliably distinguished from intergrowths (mechanical mixture) of vanadinite and pyromorphite by P–O vibration bands position in the IR spectrum. The cause of shift of the V–O and P–O bands, including the convergence of individual components in them, in IR spectra of phosphorus-bearing vanadinite is discussed. None of the studied vanadinite specimens contain (OH)^–, (CO₃)^2–, or H₂O groups.

The effect of tellurium impurity on high-temperature transformations in the synthetic phase Pt(Bi,Te)₂, which is an analogue of the mineral insizwaite, was studied using high-temperature in-situ methods. The empirical formula of the studied compound is Pt_1.04(Bi_1.74Te_0.22)_1.96. According to the differential thermal analysis (DTA + TG) and high temperature X-ray diffraction data, two polymorphic transformations were found for the Pt(Bi,Te)₂ phase. The temperatures of phase transitions were slightly shifted compared to the values for the PtBi₂ phase. The phase transition from the cubic β-modification to the hexagonal γ-modification of Pt(Bi,Te)₂ occurs at a temperature of 523 °C, which is 100 °C higher than in the PtBi₂ phase without tellurium impurity. The γ-Pt(Bi,Te)₂ is transformed into the high-temperature δ-modification at a temperature of 626 °C, close to the temperature of a similar transition in PtBi₂. The isomorphic tellurium impurity in the structure of PtBi₂ expands stability field under the influence of high temperatures for its cubic β-modification, which is corresponding to the mineral insizwaite. On the contrary, the stability field of the γ-modification is reduced in the presence of tellurium impurity.

Information is provided about the Annual meeting of the Russian Mineralogical Society that was held on September 16–21, 2024 in the city of Apatity, Murmansk region, on the basis of the Kola Scientific Center of the Russian Academy of Sciences. The meeting was attended by more than 120 specialists from Russia, as well as from China (in person), South Africa, Germany, Tajikistan, Israel and Great Britain (in absentia). The topics of sections and reports are presented.