Research subject. Neoproterozoic and Early Paleozoic igneous and metamorphic complexes of the Ural mobile belt and their minerageny.

   Aim. To identify the geochemical features of igneous and metamorphic rocks characteristic of different geodynamic regimes in the Timanide and Uralide cycles.

   Methods. A comprehensive review of a large volume of literature and original data on the behavior of trace elements and their ratios in igneous and metamorphic systems of the Urals. A comparative analysis of the key geochemical parameters that characterize the crust of ancient (Uralian and
other) and modern oceans.

   Results. The geodynamic evolution of the Ural mobile belt was characterized by the successive opening of paleooceans within the same geological domain along the margin of the Baltica continent. The oceanic crust of both the Riphean–Vendian (Y/Nb = 20–50) and Paleozoic (Y/Nb = 20–30) Ural paleooceans exhibits a distinctive geochemical signature marked by pronounced Nb depletion. In this respect, it differs significantly from the crust of modern oceans as well as from that of other ancient oceanic systems, including the Paleoasian and Iapetus oceans.

   Conclusions. The distinct composition of the Ural oceanic formations reflects the “anomalous” compositional features of its Riphean–Vendian–Paleozoic mantle. A suggestion is made that the pronounced Nb depletion of the crust, formed during successive stages of Ural paleoocean development, resulted from the preferential extraction of Nb from an already Nb-depleted mantle by rift- and spreading-related magmatism, which exceeded its replenishment by plume-derived material. It is concluded that the presence of an “anomalous” mantle and a distinctive fluid regime (high activity of chlorine and sulfur, as well as water and carbon-containing phases) were the main factors determining the “femicity” of the Ural ore potential (Cr, Pt, Pd, Fe, V, Ti, Cu, Zn, Au). In addition, the unique tectonic evolution of the region (“soft” collisional regime), promoted the preservation, inheritance, and concentration of ore deposits within a narrow geological belt along the margin of the ancient craton.

   Research subject. The study presents new geological, geophysical, and mineralogical data on the prospects for identifying massifs of ultrabasic alkaline rocks and carbonatites within the Udzha Province (northwestern Yakutia).

   Materials and methods. Modern approaches to the interpretation of geological and geophysical datasets, combined with new mineralogical results, were applied to substantiate the prediction of new ultramafic alkaline–carbonatite (UAC) complexes.

   Results. Analysis of geophysical anomalies allowed the dimensions of the predicted Buolkalakh-1, Buolkalakh-2, and Chyuempe massifs to be constrained. These are comparable in size to the Tomtor and Bogdo massifs, whereas the Uele massif significantly exceeds them in extent. The Buolkalakh-1, Buolkalakh-2, and Chyuempe massifs are promising in terms of Nb and REE mineralization, with their ore potential potentially comparable to that of the Tomtor deposit. In addition to Nb–REE mineralization, the Uele massif, similar to the Guli massif in the Maymecha-Kotuy province of the UAC, is also prospective for gold and platinum group metals (PGM). The forecast is supported by the presence of extensive gold and PGM halos with distinctive indicator characteristics in the alluvial deposits of the Anabara–Olenyok interfluve. Microprobe analyses of silicate inclusions in PGE-bearing grains, as well as their volume proportions, indicate affinities with meltteigite from the Tomtor massif, suggesting a genetic relationship with UAC magmatism.

   Conclusions. Integrated geophysical data and mineralogical-geochemical characteristics of PGE-bearing minerals (MPG) from alluvial deposits of the Anabar–Olenyok interfluve provide a basis for predicting previously unrecognized UAC massifs in Northwestern Yakutia that are prospective for Nb–REE and noble metal mineralization.

   Research subject. The Salma metamorphic rock association (Belomorian Eclogite Province (BEP), Fennoscandian Shield, East European Craton) represents a manifestation of a single Meso-Neoarchean subduction-accretion complex of the active continental margin of the Kola paleocontinent.

   Aim. To investigate genetic relationships between eclogites, metaperidotites, products of eclogite melting in the subduction zone, as well as the tonalite-trondhjemite-granodiorite (TTG) gneisses that host these rocks.

   Key points. Information on the rocks of the Meso-Neoarchean oceanic paleosubduction zone beneath the active continental margin of the Kola paleocontinent is reviewed and generalized. The work compiles both published and new petrological and geochemical data. Eclogites. Salma subduction eclogites of Salma in the BEP are localized within TTG gneisses and have variable protolith compositions of oceanic crust ranging from N-MORB to E-MORB. The eclogites preserve a record of prograde evolution of the oceanic crust, from formation in a slow-spreading center and low-temperature seafloor alteration to subduction into the mantle to depths >70 km. Adakites and andesites. Adakitic leucosomes in eclogites and adakitic gneisses indicate partial melting of relatively young eclogitized oceanic crust in the subduction zone at depths > 70 km and temperatures > 750 °C. Large volumes of andesitic magmas probably originated from the melting of the mantle wedge metasomatized by supra-subduction fluids. Both adakitic and andesitic supra-subduction magmatism contributed to the growth of the continental margin.

   Metaperidotites. The eclogites contain magnesian ultramafic rocks, including serpentinites, talc schists, carbonate-bearing chlorite harzburgites with layers and veins of garnet pyroxenites. Metaperidotites formed by low-temperature hydration of abyssal mantle peridotites in a slow-spreading oceanic ridge or in the plate-bending zone near a deep-sea trench, which transformed them into serpentinites. Large serpentinite fragments were tectonically incorporated into the subducting plate. Chlorite harzburgites resulted from partial dehydration of serpentinites at depths >30 km and temperatures of ≈ 650 °C. At depths > 70 km and temperatures > 750°C, mantle rocks interacted with slab-derived melts, forming layers and veins of garnet pyroxenites of websteritic composition.

   Conclusions. The rocks studied in the Belomorian Eclogite Province record a complete cycle of oceanic lithosphere evolution (crust and mantle) in an Archean subduction zone and the synchronous formation of an active margin of the Kola paleocontinent. The rocks described in the paper reflect key stages of this process.

   Research subject. The ultramafic-mafic association of the Kurtushiba Range (the Altai–Sayan Segment of the Central Asian Mobile Belt), conventionally regarded as a single ophiolitic association composed of dunites, harzburgites, pyroxenites, gabbroic rocks, diabases, and basalts.

   Aim. To demonstrate the heterogeneous nature of this association, to substantiate the distinction of independent Ordovician “late” gabbroids that were previously included in the ophiolite assemblage, as well as to clarify their role in the overall scheme of Caledonian magmatism in the Western Sayan.

   Materials and methods. Field observations and rock sampling, petrographic study, whole-rock petrogeochemical analysis, Sm–Nd isotope geochemistry, and amphibole ⁴⁰Ar/³⁹Ar geochronology; comparison of the data obtained with those published on the Kurtushibinsky ophiolites and gabbroic rocks from adjacent areas.

   Results. The ultramafic-mafic association of the Kurtushibinsky Range was shown to comprise two complexes of different ages: Vendian suprasubduction-zone ophiolites and Ordovician syn-collisional gabbroids (amphibole ⁴⁰Ar/³⁹Ar age of 487 ± 7 Ma for the Verkhneozhinsky massif) that intruded the ophiolites and are accompanied by narrow near-contact zones of serpentinite polymict mélanges. The “late” gabbroids are characterized by an N-MORB-like geochemical affinity and display two levels of REE depletion (ΣREE = 2.9–7.1 and 24–44 ppm) with εNd(T) values of +6.8 and +8.7, respectively, indicating a juvenile DMM source with no significant subduction-related component.

   Conclusions. The ultramafic-mafic association of the Kurtushibinsky Range is heterogeneous. Thus, Vendian ophiolites are associated with Ordovician gabbroic intrusions formed by renewed partial melting of depleted mantle during the collisional stage of Caledonian evolution in the Western Sayan, most likely in a setting of syn-collisional transtensional deformation. Recognition of the “late” gabbroids as distinct from the ophiolite assemblage refines the accepted model of Caledonian magmatic evolution of the region and may provide a basis for revising other ultramafic-mafic associations conventionally regarded as exclusively ophiolitic.

   Research subject. The Tsaginsky and Achinsky gabbro–anorthosite massifs of the Keivy structure (Kola region).

   Aim. To develop a model of the Archean anorthosite magnetism formation based on new isotopic geochemical and geochronological characteristics.

   Methods. U–Pb dating of zircon (ID TIMS and SHRIMP-RG), Sm–Nd (whole-rock) determination of isotopic characteristics, determination of the geochemical composition of rocks, study of the zircon internal structure in back-scattered electrons and cathode luminescence, determination of REE contents in zircon.

   Results. Zircon from the gabbro–anorthosites and gabbronorite of the Tsaginsky massif crystallized at 2672 ± 10 and 2667 ± 2 Ma, correspondingly. For subalkaline granites cutting through the gabbro–anorthosites of the Tsaginsky massif, the analysis of magmatic zircon established the crystallization age of 2671 ± 2 Ma. The crystallization age of zircon from the gabbro–anorthosites of the Achinsky massif was estimated to be 2675 ± 10 Ma. The Sm–Nd isotopic data for the gabbro–anorthosites of the Tsaginsky and Achinsky massifs indicate that the parental melts were formed from a mantle source with εNd from +0.1 to +3.1. The Sm–Nd isotopic values for alkaline and subalkaline granites of the Keivy structure with εNd from +0.2 to +1.9 also showed mantle characteristics without significant addition of crustal material.

   Conclusions. The Neoarchean gabbro–anorthosites, subalkaline, and alkaline granites of the Keivy structure were formed over a relatively short time interval (2.75–2.67 Ga) as a result of partial melting of a metasomatized mantle source, plume-related uplift in an extensional setting during the post-collisional evolution of the structure, and subsequent differentiation of magmatic melts from basaltic to alkali-granitic compositions, with early-stage plagioclase accumulation. The apparent predominance of felsic over mafic magmatic products within the Keivy structure is likely related to the present erosional level. The studied gabbro–anorthosite massifs, associated with regional faults in the marginal parts of the Keivy structure, may represent only the upper parts of larger, deeper-seated basaltic bodies.

Research subject. Mineral assemblages of sulfides, iron-titanium oxides and amphibole from titanomagnetite-copper-sulfide ores of the Volkovsky massif, Middle Urals. Aim. Identification of the physicochemical conditions for the formation of titanomagnetite-copper-sulfide ores based on a comprehensive study of sulfide assemblages, iron-titanium oxides and amphibole using mineralogical-geochemical and isotopic analytical methods.

Methods. The chemical composition of amphibole, sulfides and iron-titanium oxides was studied using a CAMECA SX 100 electron probe microanalyzer at the Institute of Geology and Geochemistry, UB RAS. Sulfur isotope data for sulfide samples (22 analyses) were obtained using a laser femtosecond ablation system (NWR Femtosecond UC with Pharos 2mJ-200-PP laser and harmonics module HE-4Hi-A) and a MAT-253 mass spectrometer (Thermo Fisher Scientific, Germany) at the Far East Geological Institute, Far Eastern Branch of the Russian Academy of Sciences (Vladivostok).

Results and conclusions. It has been established that the early magmatic stage occurred under closed-system conditions (Т_ox ≈ 657 ± 17°C, Т_amp ≈ 845 ± 30°C) at oxygen fugacity (logfO₂) values controlled by the FMQ buffer. Disseminated sulfide mineralization is represented by an assemblage of chalcopyrite (from –0.3 to –0.7‰), consistent with a mantle sulfur source, and subordinate bornite showing initial signs of fractionation (δ³⁴S from –1.3 to –2.0‰). The halogen profile is characterized by the dominance of fluorine (F/Cl = 2.4). The transitional stage records the onset of fluid-driven destabilization and a shift in the halogen regime (F/Cl drops to 0.5). Iron-titanium oxides are characterized by a wide range of formation parameters (Т = 516–704°C, mean 590 ± 50°C) and logfO₂instability (±3.2 orders relative to FMQ), indicating non-equilibrium conditions in an open system. A stabilization of the bornite isotopic composition (δ³⁴S = –1.1‰) is observed while mantle signatures are preserved in chalcopyrite, along with the appearance of sperrylite (PtAs₂) associated with cobaltite.  The fluid-metasomatic stage is associated with intensive high-temperature (604 ± 22°C) chloride metasomatism  (F/Cl = 0.2). Under high oxidizing potential (consistently above FMQ), the removal of iron from the sulfide composition  and a sharp negative sulfur isotope shift were recorded: from –2.1 to –2.2‰ in bornite and down to –2.9‰ in chalcocite. Myrmekitic textures of chalcocite and Cu-excess bornite (Сu_5.16Fe_0.96s₄) containing inclusions of merenskyite (PdTe₂) were formed by the exsolution of a high-temperature bornite solid solution (Bn_ss). This process occurred under the influence of oxidized chloride fluids. The established correlation between the decrease in the F/Cl ratio in amphiboles, the increase in copper content in bornite, and the negative δ³⁴S shift can serve as a prospecting criterion for identifying rich PGE-copper-sulfide ores in analogous massifs.

   Research subject. Small taxitic gabbro intrusions that are widespread within the Khudolaz differentiated complex of the Southern Urals. This study is the first to investigate intrusions located outside the Khudolaz Trough.

   Aim. To reconstruct the petrogenetic conditions of taxitic gabbro formation, to identify the causes of their petrographic heterogeneity, and to determine their ore specialization.

   Methods. The bulk chemical composition of hand-selected samples collected from natural outcrops and drill core was determined by X-ray fluorescence analysis and inductively coupled plasma mass spectrometry. Sr and Nd isotopic compositions were measured by thermal ionization mass spectrometry using the isotope dilution method. Mineral compositions were studied using a scanning electron microscope and microprobes with wavelength-dispersive spectroscopy. Comagmat 3.75 software was used to reconstruct the parental melt, and FC- AFC- FCA and a mixing modeler were used to calculate the degree of crustal contamination.

   Results and conclusions. Based on petrographic characteristics, three types of taxitic gabbros were distinguished: (1) patchy, including schlieren varieties; (2) patchy-banded; and (3) hybrid. These types are virtually similar in mineral composition and bulk geochemistry, indicating a common melt source. The development of taxitic textures was largely associated with the water saturation of the initial melt and the dynamics of its emplacement along faults during strike-slip tectonics. The heterogeneous distribution of melanocratic and leucocratic segregations occurred during repeated melt inputs into a limited-sized intrusive chamber, creating domains with varying degrees of viscosity and crystallization. The bulk geochemical characteristics of the rocks, together with the isotopic composition of Sr (0.70319–0.70396) and Nd (εNd(330) from +4.59 to +6.72), indicate a mantle source of mixed origin between the primitive mantle and the suprasubduction wedge mantle. Calculations showed that the melt underwent up to 7 % contamination by host rocks of the Magnitogorsk island-arc terrane, a level insufficient to distort the crystallization conditions of the primary magma. The reconstruction of the primary melt and hornblende thermobarometry indicate crystallization at temperatures of approximately 1200–900 °C and pressures of 2–5 kbar with an initial water content exceeding 0.5 wt %. The taxitic gabbros of the Khudolaz complex exhibit limited ore potential with a specialization in Ti–Fe mineralization. This contrasts with the earlier homogeneous ultramafic–mafic rocks of the complex, which are prospective for sulfide Cu–Ni–PGE mineralization.

Research object. The izrandites of the Alexandrovsky metamorphic complex (Southern Urals) are massive, melanocratic plagioclase–olivine clinopyroxenites, characterized by high density (3.27–3.33 g/cm³), specific paragenesis (65–70% clinopyroxene, 10–16% olivine, 5–8% plagioclase, 3–8% amphibole), and Proterozoic–Archean ages.

Research subject.  Isotopic and geochemical patterns of the ¹⁴⁷Sm–¹⁴³Nd isotopic systematics obtained by ID–TIMS for izrandites and monomineralic fractions of plagioclase and clinopyroxene from the Alexandrovsky metamorphic complex.

Objectives. To determine the timeframes of metamorphic events related to the evolution of the complex; to reconstruct the isotopic evolution of the source material based on calculations of ε_Nd(T) and Nd model ages (T_DM); to compare the ¹⁴⁷Sm–¹⁴³Nd signature with the results of previously applied K–Ar, Rb–Sr, and U–Pb methods; to verify two petrogenetic hypotheses: (a) orthocumulate genesis resulting from fractional crystallization in a layered intrusion; (b) mantle-restite origin with subsequent metasomatic and metamorphic overprinting.

Materials and methods. The research was conducted by integrating modern analytical methods (ID–TIMS) to a representative series of geological samples. Data interpretation was performed using current geochronological models, taking into account previously published petrological, mineralogical, and isotopic data for the region.

Results. Ages (in million years) of two metamorphic events were established: 2014 ± 130 (whole-rock isochron for four samples, MSWD = 1.8) interpreted as the time of protolith rehomogenization; 1127 ± 84 (Pl+Wr+Cpx isochron, MSWD = 1.7, ε_Nd = +7.5), an event corresponding to amphibolite-facies metamorphism. The calculated ε_Nd(T) values demonstrate an anomalously high degree of isotopic depletion. While ε_Nd(1127) = +7.5 is practically identical to ε_DM = +7.6 for the mineral isochron of 1127 Ma, the rocks are characterized by ε_Nd(T) significantly exceeding the model value for ε_DM(2014)=+5.7. T_DM ages ranging from 1788 to 2308 Ma indicate that the material basis of izrandites separated from the mantle reservoir during the Archean–early Paleoproterozoic era.

Conclusions. Using ¹⁴⁷Sm– ¹⁴³Nd  ID-TIMS isochron dating, two metamorphic events were distinguished: a Paleoproterozoic event (~2.01 Ga), corresponding to a high-temperature stage, and a Mesoproterozoic event (~1.13 Ga), corresponding to amphibolite-facies metamorphism. The affiliation of the izrandite protolith to an ancient depleted mantle reservoir was confirmed. The high ε_Nd(1127) value of +7.5, the anomalously high ε_Nd(2014) values (>> +5.7), and T_DM ages in the range of 2.3–1.8 Ga indicate that the initial material was formed in the Archean–Early Paleoproterozoic as a result of multiple episodes of melting and melt extraction, which confirms the presence of a relict restitic mantle. A fundamental petrogenetic paradox between mineralogical and textural features indicative of a magmatogenic-cumulate genesis and a ¹⁴⁷Sm–¹⁴³Nd signature characteristic of mantle restites was identified and conceptually resolved. The most plausible model suggests that the izrandites represent fragments of highly depleted Archean mantle that underwent autochthonous partial melting during the Paleoproterozoic (~2.01 Ga). Subsequent in situ crystallization of the generated melt led to the development of the observed cumulate textures.

   Research subject. Alkaline and nepheline ore-bearing syenites of the Burpala massif (Western Baikal).

   Aim. To experimentally model crystallizing much–melt interactions during the early magmatic stages of syenite body formation in the Burpala massif to identify ore concentration mechanisms.

   Materials and methods. Experimental modeling of interactions between a crystallizing mush (alkaline syenite of the Burpala massif) and an interstitial, volatile-rich, alkali-saturated melt (in the form of glass obtained by preliminary melting of ore-bearing nepheline syenite from the Burpala massif) was carried out in hydrothermal autoclaves equipped with a rapid-quench system at 750 °C and 200 MPa. The starting materials and experimental products were analyzed using SEM and LA–ICP–MS methods.

   Results. Experimental runs at 750 °C and 200 MPa revealed intensive recrystallization of clinopyroxenes and localized reworking of K-feldspar at crystal–melt interfaces in alkaline syenites. The melt produced as a result of glass melting interacts with the syenite and changes its composition, retaining an alkaline (agpaitic) character although with a lower agpaitic index. From this melt, a discrete assemblage of HFSE–REE phases crystallizes, including zircon, Zr-titanite, and sorosilicates of the chevkinite–perrierite group. A sharp enrichment of clinopyroxene rim zones in Mn, Sr, LREE, Y, and Nb is observed, while the feldspar composition shows relatively minor changes, highlighting the role of clinopyroxene as the main temporary “buffer” for rare elements at the early reaction stage.

   Conclusions. The results support the model of local redistribution of Zr–Ti-Nb–REE in the intercrystalline melt at the crystal–melt interface, which allows the formation of ore mineralization before the participation of later hydrothermal processes and can be directly applied to the interpretation of ore-bearing syenites of the Burpala massif.

   Research subject. Ultramafic rocks from mantle sections of the Kraka (Southern Urals) and Syum-Keu (Polar Urals) ophiolite massifs.

   Methods. Electron backscatter diffraction (EBSD) was the primary method used to study olivine microstructures. Mineral compositions were determined by energy-dispersive microanalysis (SEM/EDS). EBSD data were processed using the HKL Channel 5 and MTEX software packages.

   Results. The mineralogical, geochemical, and microstructural characteristics of lherzolite, harzburgite, and dunite samples from these massifs were studied. Olivine from the Kraka ultramafic rocks exhibits a crystallographic fabric controlled by slip systems (010)[100], (001)[100], and {0kl} [100]. In addition, multiple-slip deformation is most strongly developed in dunites. The microstructure of olivine from the Syum-Keu ultramafic rocks records two stages of ductile deformation: early (upper mantle) and late (lower crustal). The former corresponds to a higher-temperature flow according to the {0kl}[100] system, while the latter corresponds to a lower-temperature flow according to the {110}[001] system.

   Conclusions. Olivine in the Kraka peridotites preserves mantle-stage microstructures, where most low-angle boundaries are relatively straightforward and correspond to kink-band types. In the Syum-Keu peridotites, these microstructures are partially or completely transformed by superimposed static recrystallization (annealing). Elevated temperatures and pressures, together with the observed olivine fabric, indicate the formation of the Kraka ultramafic rocks at the spinel/plagioclase facies boundary in the upper mantle. Conversely, the Syum-Keu ultramafic rocks record lower P–T conditions, likely corresponding to lower crustal environments. These results generally support the previously developed concept suggesting a longer evolution of mantle ultramafic rocks in the Syum-Keu massif relative to the Kraka massif, and they are consistent with a suprasubduction origin of both complexes.

   Research subject. Amphiboles from the Kaalamo metamorphosed multiphase clinopyroxenite-gabbronorite-diorite complex in the Northern Ladoga region.

   Aim. To elucidate the genesis of all amphibole rock types in the complex.

   Methods. Amphibole morphology was analyzed using optical (Olimpus BX53) and electron microscopy (JEOL JSM- 6510LA). The chemical composition of minerals was analyzed using a JEOL JED-2200 energy-dispersive spectrometer. Mineral parageneses were modeled by Gibbs energy minimization using the MAGEMin software.

   Results. In the rocks of the Kaalamo complex, amphiboles of igneous and metamorphic origin were identified. The presence of magmatic amphiboles (magnesiohastingsites and magnesioferrigornblendites) in phase 1 pyroxenites and phase 2 gabbrodiorites was revealed. These amphiboles are characterized by elevated titanium contents and crystallization temper-
atures higher than the regional metamorphic temperature. Some of the amphiboles in the pyroxenites gabbro, and gabbrodiorites, as well as all the amphiboles in phase 3 diorites and tonalites, are metamorphic and could have formed either through the replacement of pyroxenes or from earlier magmatic amphibole. Discrimination diagrams with projections of the petrochemical parameters of amphiboles (content of titanium, magnesium number et al.) are suitable for a preliminary assessment of their nature; however, they should not be relied upon solely due to the overlapping compositions of minerals of different origins.

   Conclusions. The metamorphosed rocks of the Kaalamo complex contain not only metamorphic but also igneous amphiboles, indicating the saturation of the parental magma with water.

   Research subject. The mafic–ultramafic massifs of Ikchuka (~16 km²) and Dukaly (~30 km²) located in the Central Sikhote-Alin (Khabarovsk Krai) formed under accretion–collision tectonic conditions.

   Aim. To compare the mineralogical and geochemical characteristics of the massifs, determine their formational affiliation, and identify factors controlling the formation of different types of ore mineralization.

   Materials and methods. Over 4600 lithogeochemical samples were analyzed (ICP–MS/AES after four-acid digestion). Microscopy, X-ray diffraction, FTIR spectroscopy, and scanning electron microscopy with EDS were carried out. Nonparametric statistical tests (Mann–Whitney), discriminant and factor analyses (Statistica), and geothermobarometry based on antigorite composition were applied.

   Results. The ultramafic part of the Ikchuka massif represents a tectonic slab of mantle restite exhumed to the surface during accretion–collision events. In contrast, the Dukaly massif formed as a product of magmatic differentiation, where local hybridization of ultramafic and gabbroic melts in contact zones triggered sulfide liquid immiscibility and primary PGE concentration. Epigenetic Ni–Bi–Pb mineralization (parkerite, maucherite, cobaltite) against the background of Cu–Fe sulfides dominates in Ikchuka, whereas Dukaly hosts low-sulfide PGE assemblages (cabriite, irarsite, tomamaeite, potarite, tatianaite, stannopalladinite, sperrylite). In PGE-enriched zones of the Dukaly massif, Cr/Ni = 4.16–5.0 and Pt/Pd = 1.94–2.25, indicating hybridization between ultramafic and gabbroic melts in contact zones. The formation of PGE-bearing assemblages occurred via a two-stage process: (1) extraction of platinum-group elements from a highly evolved basaltic melt at
T ~ 1000–1200°C and P = 3–20 kbar; and (2) their redeposition during a pneumatolytic–hydrothermal stage as temperatures decreased from 480–650 °C to ~250 °C. The critical involvement of Cl-bearing fluids (Cl-apatite, phlogopite, chlorite) is demonstrated.

   Conclusions. The massifs represent two geochemically distinct systems. The Dukaly massif exhibits the highest ore potential, as its low-sulfide PGE mineralization is genetically linked to contact plagioperidotites and followed by pneumatolytic–hydrothermal reworking.