Abstract Five unknown Holocene flank eruptions from the Masaya caldera are reported here. These eruptions comprise basaltic lava flows emplaced in Masaya’s northern rift zone along the Cofradía fault zone, east of Managua City. The lava flows were defined as Mosintepe, Portillo, Gorgonia, Campuzano, and Martha units. Paleosol samples were collected below each lava flow, and radiocarbon AMS analyses were performed, yielding ages of 2250 ± 30, 1610 ± 30, 1600 ± 30, 1140 ± 30, and 790 ± 30 yrs BP, respectively. Calibrated age intervals are 285–229 cal BC for Mosintepe, 496–534 cal AD for Portillo, 496–535 cal AD for Gorgonia, 914–976 cal AD for Campuzano, and 1226–1268 cal AD for Martha; all stratigraphically consistent. These eruptions emitted magma bulk volumes between 0.02 and 0.51 km3, reaching up to 8 km from their eruptive vent and 13 km from Masaya’s polygenetic system summit crater. Their mineral paragenesis, and major and trace element geochemical fingerprint reveals a common volcanic provenance from the Masaya caldera due to lateral magma draining. This study demonstrates that basaltic lava flow flank eruptions are common in the Masaya caldera along its northern volcanic rift zone. Therefore, this information should be considered in future hazard and risk assessments.

Abstract The Late Cretaceous magmatic arc of the Eastern Pontides consists of two magmatic cycles. Turonian to Santonian (93.9 to 83.6 Ma) submarine dacitic to rhyolitic rocks host major volcanogenic massive sulfide (VMS) deposits. By contrast, the degree of fertility of Campanian (83.6 to 72.1 Ma) intermediate to felsic rock sequences of the second cycle is still an open question. In particular, the nature, the absolute age, and the genetic relationship of Late Cretaceous epithermal systems with respect to the two magmatic cycles and the VMS deposits is still a matter of debate. The Yanıklı prospect, Artvin district allows us to demonstrate the fertility of the Campanian magmatism. Its intermediate-sulfidation epithermal nature is supported by its hydrothermal alteration pattern, mineral paragenesis, fluid microthermometry and stable isotope characteristics, and sphalerite chemistry. Uranium-lead zircon ages of 82.3 ± 0.4 and 81.6 ± 0.4 Ma and a 40Ar/39Ar adularia date of 78.6 ± 0.8 Ma indicate a Campanian age for both the immediate host rocks and ore formation at Yanıklı. Whole-rock geochemistry indicates that the immediate host rocks at Yanıklı belong to the second Late Cretaceous magmatic cycle of the Eastern Pontides. In this study we demonstrate a lithogeochemical, geodynamic, and metallogenic transition at ~ 83 Ma between the two Late Cretaceous magmatic cycles. The Turonian-Santonian tholeiitic to calc-alkaline magmatism in a back-arc basin setting resulted in the formation of VMS deposits, whereas the Campanian high-K calc-alkaline to shoshonitic magmatism in a continental arc environment resulted in the emplacement of epithermal-porphyry systems.

Epithermal Au–Ag and Ag Deposits of the Okhotsk Sector of the Okhotsk–Chukchi Volcanic Belt: Metallogeny, Mineral Paragenesis, and Fluid Regime

The Tambulun Prospect, Sulit Air, Solok Regency, West Sumatra, is one of the locations indicating the presence of a copper (Cu) skarn mineralization system. This study aims to identify the mineral paragenesis in the skarn system through petrographic and ore microscopic analysis. The skarn formation process is caused by the intrusion of Sulit Air granodiorite that penetrates the Tuhur Formation limestone, resulting in alteration zones in the form of exoskarn (garnet–pyroxene, garnet–pyroxene–wollastonite, pyroxene–quartz ± epidote ± chlorite) and endoskarn (pyroxene–k-feldspar–chlorite–epidote) alteration. Skarn formation is divided into four main stages, namely: (1) isochemical metamorphism, (2) prograde stage with the formation of high-temperature calc-silicate minerals, (3) retrograde stage with the emergence of lower-temperature minerals such as epidote and calcite, and (4) supergene stage. The dominant copper mineralization is chalcopyrite, bornite, covellite, and chalcocite. In the prograde phase, chalcopyrite fills fractures along with quartz veins in the garnet–pyroxene zone. The retrograde phase is characterized by the presence of bornite and chalcocite along with calcite and epidote veins that intersect the garnet–pyroxene–wollastonite alteration zone. The supergene phase shows secondary mineralization such as covellite, hematite, malachite, azurite, and chrysocola that fill fractures and pores in the rock. Understanding mineral paragenesis can explain the hydrothermal evolution of skarn systems and provide information for exploration efforts for economic metal deposits in the surrounding area.

Mineral characterization of gold-bearing metasomatites in the Khaptasynnakh ore zone of the Anabar Shield is provided in detail. The following ore formation sequence of mineral associations in the Khaptasynnakh zone was found: pyrite and pyrrhotite → gersdorffite and molybdenite → chalcopyrite, sphalerite, and galena → bornite and chalcocite → tellurides, native gold, stibnite, cinnabar, and native bismuth. Native gold is characterized by varying fineness (550 to 926‰) and Cu impurity (up to 7.87%) values. Most often, it forms symplectite intergrowths with Au telluride–calaverite. Native gold and Au tellurides showed inclusions of chalcocite, bornite, altaite, tellurobismuthite, rickardite, petzite, and clausthalite. A two-stage formation process of the examined gold is suggested: Low-fineness gold was introduced into the system during early potassium metasomatism, while higher-fineness gold related to silica metasomatism resulted from its additional mobilization by fluid during late-stage formation. The low-temperature gold–telluride association observed in the mineral paragenesis of ore-bearing rocks, as well as its inclusions in native gold, suggests epithermal gold–telluride mineralization. Mineral inclusions examined in placer gold validate a genetic relation between the examined ores and gold placers in the Khaptasynnakh ore zone.

The present study is part of the Horizon Europe-START project, which aims to recover tetrahedrite-group minerals present in mine dumps to be used as raw materials for the manufacture of thermoelectric devices. The aim of this work is to identify the mining waste facilities selected in Spain for the recovery of tetrahedrite and to outline the mineral processing operations performed on samples from each site to separate and concentrate this mineral. Ore deposits across Spain were selected based on the potential presence of tetrahedrite in their mining waste. A total of five deposits have been sampled, at which subsequent mineral separation and concentration tests have been conducted. A separation flowsheet is proposed in order to extract a high-purity tetrahedrite concentrate. Experimental results indicate two distinct options for separation approaches, depending on a key parameter that proves decisive in the processing of this mineral, which is whether the mineral paragenesis includes siderite. This study has demonstrated the technical feasibility of concentrating minerals of the tetrahedrite group through simple, cost-effective physical separation techniques—specifically magnetic and gravity separation—where the liberation size of the tetrahedrite exceeds 0.063 mm.

ABSTRACTThe Bankim area is located in the Tikar Plain, on the N50E branch of the Central Cameroon Shear Zone (CCSZ) where amphibolites occur, but their relationship with the general Pan–African metamorphism history is poorly known. The petrography, mineral chemistry, geochemistry and Sr–Nd isotope systematics of amphibolites from the Bankim area are presented in this paper in order to constrain their petrogenesis and geodynamic setting during the Pan–African orogeny. They are garnet amphibolites (GA), pyroxene amphibolites (PA) and biotite amphibolites (BA) occurring as metric flagstones showing relic of S1 foliation, lense–like, or as sheared sinistral and dextral and/or boudinaged enclaves. In GA, garnet occurs as lobate porphyroblasts (Alm54‐58Gr25‐27Pyr10‐12 ∙ Sp3‐5). It is usually surrounded by a corona made up of hornblende, plagioclase [andesite (Ab67‐59An32‐46Or0.5) to oligoclase (Ab72An27Or0.6)], quartz and ilmenite; the whole defining a kelyphitic microstructure (characterised by garnet + amphibole + plagioclase + opaques mineral (ilmenite) parageneses). In PA, clinopyroxene (diopside; Ca49‐50 Mg29‐30Fe19‐22) is mostly relic–like and displays hornblende or plagioclase (andesine (Ab65‐67An32‐34Or0.6‐0.8) to oligoclase (Ab69‐70An29‐30Or1‐1.2)) corona showing hornblende + clinopyroxene + plagioclase + opaque minerals paragenesis. Field and microstructural data indicate that these rocks recorded a polyphase prograde–peak followed by retrograde metamorphism. The metamorphic prograde phase and peak P–T conditions exceeding 5.2 kbar/789°C occurring during the D1 deformation phase (613–600 Ma) correspond to the collisional stage of the Pan–African orogeny within the granulite facies. Retrograde metamorphism occurred from the granulite facies to the amphibolite facies under P–T conditions of 1.4–5.2 kbar/789°C–513°C. These changes were synchronous with the early sinistral syn–D2 (590–580 Ma) and the late dextral syn–D3 (580–545 Ma) ductile shear deformation phases. These deformation phases, which occurred as a result of exhumation during the crustal re–equilibration related to relaxation and erosion during the post‐collisional evolution of Western Gondwana. The geochemical data indicate that the above amphibolites derived from the metamorphism of mafic protolith which represents an ancient Proterozoic crust with model ages of TDM = 1.9–1.6 Ga and initial 87Sr/86Sr600 ratios of 0.70626–0.70894. At the end of the prograde and retrograde metamorphism of this ancient crust, it was stretched, sheared, dismembered and scattered along the Pan–African mobile zone during the CCSZ reactivations.

RESUMO - As rochas ortoderivadas básicas e ultrabásicas da porção sul do Cinturão Ribeira, norte do Terreno Apiaí, no sudoeste do estado de São Paulo são definidas por anfibolitos, metabasitos, anfibólio xisto e localmente metaultrabasitos de idade meso- a neoproterozoica e encontram-se associadas às rochas da sequência metavulcanossedimentar da Formação Água Clara, Supergrupo Açungui. O metamorfismo regional progressivo é do tipo Barroviano e a paragênese mineral é constituída de pseudomorfos ígneos de piroxênios “augita” ± labradorita, associado às paragêneses metamórficas apresentando magnesiohornblenda ± oligoclásio/andesina, representando o ápice do metamorfismo regional progressivo em fácies anfibolito médio, de 579°C a 621°C de temperatura e 6,6 kbar a 7,3 kbar (±0,6). Uma paragênese mineral em fácies xisto verde baixo a médio é caracterizada pelo retrometamorfismo regional e milonítico, sendo constituída por actinolita/tremolita ± albita. Dados geoquímicos classificam as rochas como basaltos, sub alcalinos de baixo potássio a alcalinos, Fe-toleíticos a Mg-toleíticos, com leve tendência a basaltos komatiíticos. Já os dados geotectônicos, corroborados pelo comportamento dos elementos traços e dos ETRs, indicam três assinaturas principais para os grupos anfibolíticos: as rochas básicas toleíticas a komatiíticas associadas a cadeia mesoceânicas (MORB), com possível interação da crosta na fase de subducção; as rochas ultrabásicas alcalinas de ilha oceânica (OIA) e os basaltos toleíticos de arco de ilha. Portanto, os eventos magmáticos estão correlacionados ao estágio inicial de abertura de bacia ou ao início de fechamento à fase inicial de natureza toleítica de fundo oceânico, associado a basaltos alcalinos de ilha oceânica. Palavras-Chave: Metabásica; Água Clara; Supergrupo Açungui; Química Mineral; Litogeoquímica. ABSTRACT - The basic and ultrabasic orthoderived rocks in the southern portion of the Ribeira Belt, north of the Apiaí Terrain in southwestern São Paulo state, are primarily composed of amphibolites, metabasites, amphibole schists, and locally, metaultrabasalts. These rocks, dated to the Meso- to Neoproterozoic, are associated with the metavolcanic-sedimentary sequence of the Água Clara Formation within the Açungui Supergroup. The regional metamorphism is of the Barrovian type, with mineral paragenesis consisting of igneous pseudomorphs of pyroxenes ("augite") ± labradorite, associated with a metamorphic assemblage dominated by magnesiohornblende ± oligoclase/andesine. This represents the peak of progressive regional metamorphism in the medium amphibolite facies, with temperatures ranging from 579°C to 621°C and pressures between 6.6 kbar and 7.3 kbar (±0.6). Additionally, a mineral paragenesis in the low- to medium-grade greenschist facies is characterized by regional and mylonitic retrometamorphism, consisting of actinolite/tremolite ± albite. Geochemical data classify these rocks as basalts, ranging from low-potassium to alkaline sub-alkaline, with compositions transitioning from Fe-tholeiitic to Mg-tholeiitic and a slight tendency toward komatiitic basalts. Geotectonic data, supported by the behavior of trace elements and rare earth elements (REEs), indicate three main geochemical signatures among the amphibolitic groups: basic tholeiitic to komatiitic rocks associated with mid-ocean ridge basalts (MORB), possibly influenced by crustal interaction during subduction; ultrabasic alkaline rocks characteristic of oceanic islands (OIA); and tholeiitic basalts associated with island arcs. These magmatic events are therefore correlated with the initial stage of basin opening or the early phase of oceanic closure, specifically the tholeiitic nature of the ocean floor, and are associated with the alkaline basalts of an oceanic island. Keywords: Metabasic; Água Clara Formation; Açungui Supergroup; Mineral Quimic; Lithogeochemistry

Abstract Quartz chemistry is important for revealing fluid sources and evolution in hydrothermal deposits, but such information is lacking for many epithermal systems and deposit types. To investigate quartz chemistry in this system further, we collected representative samples of quartz from adularia-sericite epithermal Ag deposits in China and determined their chemical compositions. In adularia-sericite epithermal Ag-bearing systems, magmatic quartz from porphyry intrusions and host subvolcanic rocks displays SEM-CL spectral peaks at 360 and 415 nm and exhibits homogenous CL or weak zonal textures (alternating growth zones within individual quartz crystals). Trace elements in magmatic quartz have the lowest Sb concentrations (median = 0.1 ppm; n = 80). Hydrothermal quartz can be classified into type I and type II by CL false color and CL spectral peaks. Hydrothermal type I quartz has spectral peaks at 360 and 415 nm; it exhibits zonal or sector textures and is associated with base metal sulfides and minor Ag mineralization. Such hydrothermal type I quartz has low Sb concentrations (median = 4.5 ppm; n = 839), contains liquid-rich fluid inclusions, and is formed by cooling. The cooling trend is indicated by a positive correlation between the concentrations of Sb and Al, as well as between Li and Al. Hydrothermal type I quartz has an Fe center by electron spin resonance, whereas other centers are missing or weak at room temperature. In general, hydrothermal type II quartz mantles type I quartz. Hydrothermal type II quartz has an ultrahigh-intensity peak (by several orders of magnitude) at 580 nm, zonal textures, and is associated with abundant Ag mineralization. Hydrothermal type II quartz has the highest Sb concentrations (median = 71ppm; n = 185), which remain constant as Al decreases on an Sb vs. Al plot. This quartz has colloform, bladed, or zonal textures and contains coexisting liquid- and vapor-rich fluid inclusions indicative of boiling. Additionally, this quartz has a significantly higher E’1 center intensity, suggesting a high concentration of oxygen vacancies associated with rapid crystallization. The mineral paragenesis, analytical results, and geochemical models show that, in these Ag-bearing epithermal systems, hydrothermal type I quartz associated with base metal sulfides precipitated during cooling, whereas subsequent growth-zoned hydrothermal type II quartz with high Sb concentrations and Ag-minerals precipitated during boiling. These results suggest that the CL texture and spectra, trace elements, and electron spin resonance data of quartz could identify veins with potential for Ag mineralization in epithermal systems.

Abstract The region of Um Ara-Wadi Murrah is situated in Egypt's arid Southeastern Desert. The region contains a variety of tectono-stratigraphic units, with the earliest being ultramafic rocks, serpentinite, metavolcanics, metasediments, monzogranite, and syenogranite. Strong shearing, fracturing, and jointing control the high radioactivity in the anomalous areas. Uranophane, kasolite, and autunite make up the majority of visible secondary uranium mineralization. A variety of rare earth minerals, including monazite, bastnäsite, allanite, chernovite and xenotime were recorded in the study area. Betafite, ishikawaite, columbite, fergusonite and samarskite were recorded as radioactive bearing-minerals (Nb–Ta minerals). Finally; base metals represented by gold, bismite, cassiterite and wolframite. Secondary processes primarily influenced the post-magmatic addition of uranium to these granitic sites, known as uranium enrichment. We can identify the three types of ore minerals (magmatic, hydrothermal, and supergene) using a suggested paragenetic sequence. The latter comprises secondary uranium minerals and altered uranothorite. There are several ways that rare metal enrichment can happen, such as ascending hydrothermal solutions (alkaline solutions first, then acidic hydrothermal solutions) and descending acidic meteoric water during supergene enrichment processes. Changes in physicochemical conditions and the fugacity of oxygen and sulfur led to the initial precipitation of gold in mesothermal and epithermal solutions. Mineralogical and geochemical evidence confirms the different stages of mineralization. The study area has been enriched in uranium and rare earth elements (av. 3451.4, 273 ppm, respectively). The calculated values of the tetrad effect are 1.12. The chondrite-normalized REE patterns for syenogranite are M-type tetrad. The Th–U variation diagram reveals that all samples fall within the supergene enrichment field, with all Th/U ratio values being less than 0.1. Regarding the correlations between U and trace elements, we observe positive correlations with Zr, Y, and very weak to ill-defined correlations with LREEs, Nb, and F, indicating partially magmatic processes followed by post-magmatic processes.

The Nuweibi rare-metal granite is located in the Central Eastern Desert of Egypt and represents a highly evolved leucogranite pluton that intruded into Neoproterozoic basement rocks of the Arabian-Nubian Shield. It is separated by the NNE-SSW trending oblique sinistral Dabr fault into two principal granite facies: a medium-grained albite granite in the western block and a porphyritic albite granite in the eastern block. The major ore minerals among the disseminated Nb-Ta-Sn mineralization are columbite-group minerals (CGM), wodginite, microlite, and cassiterite, which follow a distinct crystallization sequence including partial dissolution and late recrystallization. These ore minerals are usually strongly zoned, exhibiting a wide range of chemical compositions. As peculiarity, cm-sized euhedral columbite crystals with thin Ta-rich rims are found in the massive quartz cap of the eastern block of the intrusion. On the basis of mineral textures and microanalysis of mineral chemistry of the Nb-Ta-Sn oxides, we propose a genetic model for the evolution of the Nuweibi granitic intrusion involving magmatic, magmatic-hydrothermal, and subsolidus ore-forming processes: 1) upward migration of a granitic melt to the level of emplacement and fractional crystallization resulting in enrichment of the residual melt in incompatible elements (e.g., Ta, Nb, Sn) and volatiles (H2O and F); 2) incipient magmatic crystallization of early Nb-rich CGM-1, albite, and snowball quartz and Ta enrichment in the melt (more incompatible than Nb); 3) onset of fluid exsolution (fluid saturation in the melt at the magmatic-hydrothermal transition), magmatic crystallization of CGM-2 with increasingly higher #Ta with co-existing fluid; 4) solidification of the quartz cap due to undercooling saturation with precipitation of columbite under hydrothermal conditions from magmatic fluids; 5) late magmatic fluid circulation, dissolution of the CGM and re-precipitation of CGM-3, followed by late-stage wodginite and microlite; 6) oblique sinistral and normal faulting after solidification of the Nuweibi granite, leading to the western block of the intrusion to move diagonally upwards resulting in today's opposing levels of exposure. As a result, the mineral paragenesis, texture, and mineral chemistry of Nb-Ta-Sn minerals prove to be remarkable tracers of the evolution from magmatic to hydrothermal conditions in rare-metal granites.

Abstract - The interesting problem in the research area based on previous research is that the rocks have been changed due to hydrothermal alteration processes and many ore mineralizations are found. This research was conducted to study alteration due to hydrothermal processes, as well as to determine the distribution of alteration zones and their relationship to metal mineralization. The research location is located in the Beruang Kanan area, Tumbang Miri District, Gunung Mas Regency, Central Kalimantan Province. Ore mineral paragenesis is a sequential stage in the formation of ore minerals from the initial phase of formation to the final phase. The stage of mineralization can be identified from the identification of ore mineral paragenesis. Identification of ore mineral paragenesis is identified using an ore microscope. The stages of metal mineral paragenesis at the research location itself are divided into 4, namely: early, middle, late, and supergene. The early to late stages are the stages of metal mineral formation hypogenely. These three stages include the process of metal mineral deposition in the magmatic to hydrothermal phases. The early stages and main mineralization are referred to as the hypogene stage.

The Gorevskoye deposit (Yenisei Ridge) is one of the largest polymetallic deposits localized in metamorphic rocks. Despite the long history of study, there is still no consensus on its genesis. Considering the important role of metamorphic transformations in recrystallisation and formation of ore appearance, assessments of the metamorphic conditions that affected the host rocks are the basis for reconstructions of the deposit genesis. Previously, such estimates were made approximately using mineral paragenesis in the rocks. This paper presents the results of studying the temperature conditions of metamorphic transformations of the host rocks of the Gorevskoye deposit using a geothermometer based on Raman spectrometry data of carbonaceous material, as well as traditional methods of mineralogical thermometry. The data obtained allowed us to estimate the peak temperature values of regional metamorphism at 490-530 °C with good convergence of the results of different methods. It is also found that the rocks were transformed by hydrothermal processes at temperatures around 345-365 °C during the post-metamorphic stage.

Abstract Laueite/stewartite epitaxy was studied using single-crystal diffraction applied to a composite crystal from Hagendorf-Süd, Bavaria. The orientation relationships between the crystals of the two minerals was facilitated by using a non-conventional B $\bar {1}$ space group setting for stewartite, giving unit cells with parallel axes and with as = 2a l , b s = b l and cs = 2 c l . Face indexing of the crystals of the two minerals confirmed the epitaxial relationship, with the {100} and {010} faces parallel. The plane of epitaxy is {010}. Refinement of laueite and stewartite datasets extracted from the composite-crystal data collection showed a significant decrease in the mean Mn-site bond distances in laueite, consistent with chemical analyses of the crystals that gave site compositions of Mn0.92Fe3+0.08 for stewartite and Mn0.66Mg0.17Fe3+0.17 for laueite. The epitaxial growth of laueite on {010} planes of stewartite appears to have been initiated by a change in solution chemistry. Possible paragenesis of the secondary phosphate minerals from primary triphylite is discussed.

Conditions of high-temperature volcano-related mineral formation are a source of the new and rare minerals and their associations; they are rather fragmentarily described for volcanic systems as a whole, except for several objects characterized in this regard. The study aim is to present the first results of the mineralogical study of atypical suprasubduction zone neoformation encountered from the Taketomi flank eruption (1933–1934) of the Alaid volcano (Kuril Islands), which has been studied through electron microprobe analyses and powder and single-crystal X-ray diffraction. The following mineral paragenesis is described: diopside, andradite, anorthite, wollastonite, esseneite, wadalite, rhönite-like mineral, fluorite, calcite, apatite, and atacamite. The parageneses of calcium silicates found in volcanic systems are usually interpreted as reworked crustal xenoliths and commonly associated with volcanoes that have a carbonate basement. However, carbonates have not been previously described at the base of the Alaid volcano. Even though the skarn nature of such a mineral paragenesis is possible, we suggest the important role of high-temperature volcanic gases along with the pyrometamorphic effect in the mineral-forming process at depth or in near-surface conditions (fumarole-like type in the form of a system of cracks and burrows). The described mineral paragenesis has not been previously documented, at least for the North Kuril Islands. A detailed mineralogical study of such formations is one of the important steps in understanding the functioning of magmatic systems, the circulation and transformation of natural matter, and mineral-forming processes.

ABSTRACTMetamorphosed pelitic and psammitic rocks with small amounts of granitic stock are found on Ozushima Island, in the Seto Inland Sea area of Yamaguchi Prefecture, Japan. The metamorphosed pelitic rocks exhibit pervasive foliation defined by the preferred orientation of muscovite, biotite, andalusite, and sillimanite. General foliation shows an E–W trend and dips to the north and south, forming upright folds. The mineral assemblages and microstructures reveal that the metamorphic rocks of Ozushima Island can be divided into the Bt zone, And zone, and Sil zone, representing three metamorphic zones and corresponding to three deformational stages. Based on field surveys, the following deformational events were identified. Stage 1 deformation resulted in S1 foliation parallel to the bedding plane (S0). The critical minerals in each metamorphic zone formed the S1 foliation. In Stage 2, the S2 foliation developed along the axial planes of the microfolding of the S1 foliation. A NW‐SE striking, NE‐dipping thrust passed through the southern part of the island. In Stage 3, S3 foliation was locally present along the thrust plane. The metamorphic conditions of the And and Sil zones were estimated using conventional geothermobarometers at 530°C, 60 MPa and 600°C–710°C, 330–400 MPa, respectively. In addition, these metamorphic conditions plot within the metamorphic field gradient of the Cretaceous Ryoke metamorphic rocks from the Yanai‐Iwakuni and Omuta areas. The detrital zircon grains separated from the psammitic rocks exhibited two age peaks at c. 1800 Ma and c. 250 Ma. A younger age indicates an older limit on the depositional age of the protoliths. These findings suggest that the metamorphic rocks of Ozushima Island originated from the Suo Belt and underwent low‐pressure and high‐temperature metamorphism, probably caused by heat supplied from the Cretaceous intrusive rocks, similar to the Ryoke metamorphic rocks.

This study analyzes the mineral paragenesis and microstructural characteristics of rocks from the Tamghas-Arkhabang section to delineate a thrust boundary and create a detailed metamorphic zonation map. A 1:25,000 scale geological map was prepared, and representative rock samples from each stratigraphic unit were systematically collected for petrographic analysis. Fourteen thin sections were examined to understand the deformation and metamorphism in the region. Field observations such as fault breccias, fault gouge, lineation, and slickensides, along with petrographic evidence of inverted and dynamic metamorphism, cataclastic deformation, and ribbon quartz, suggest the presence of a thrust equivalent to the Mahabharat Thrust (MT), a significant tectonic feature in the study area. Microstructural indicators like undulose extinction, grain boundary migration, recrystallisation, and deformation lamellae in quartz further confirm this thrust's existence. Two distinct carbonate successions were identified: the southern unit correlates with the Lesser Himalayan sequence, while the northern, more metamorphosed carbonate unit is associated with the Bhimphedi Group, part of the Jajarkot Thrust Sheet. Stratigraphic continuity is disrupted in some sections, where quartzite and schist replace the basal carbonate strata, likely due to thrusting. The thrust's propagation has impacted both footwall and hanging wall rocks, evidenced by features such as rotated garnets with spiral inclusions. Three metamorphic zones—chlorite, biotite, and garnet isograd—indicate progressive metamorphism linked to thrust tectonics, revealing an inverted metamorphic sequence in the region.

The aim of this work is to characterize the mineralogical assemblages of the rocks encountered in the Loango sector, with a view to determining the degree of metamorphism they have undergone, and to enrich and supplement the information essential for the geological mapping of the Central Kongo province. Specifically, we wanted to know whether the geological formations in the Loango area had petrographic characteristics that would enable us to classify them. We carried out a field trip and collected seven rock samples. After macroscopic and microscopic description in the CRGM laboratory, four lithofacies were determined: sericite schists, quartzophyllades, amphibolites and biotitoschists. This enabled us to classify the rocks according to metamorphic facies. The study of mineral paragenesis in the study area points to a regional metamorphism transiting from the epizone to the mesozone, characterized by the presence of sericite and biotite.

A mineralogical and geochemical study of vesuvianite from mineral aggregates sampled in the Zelentsovskaya, Nikolaje-Maximilianovskaya, Akhmatovskaya and Shishimskaya mines located at the outer contact of the Kusa-Kopan intrusion of the Southern Urals was carried out. Vesuvianite from the silicate-carbonate rock (Zelentsovskaya mine) is significantly enriched in Fe, V, Cr, Y, Zr, Th, Sn, and Cl, and the REE distribution spectrum it is close to that for garnets from the same rocks. Vesuvianite from calcite-garnet vein in chlorite schist (Nikolaje-Maximilianovskaya mine) is enriched in U, and REE distribution spectra there are significantly differentiated, which is explained by the removal of incompatible elements. Vesuvianite from rodingites (Akhmatovskaya mine) is enriched in Mn, Ni, Zn, Sr, Nb and volatile components (F and Cl), and the REE distribution spectra are conformal to each other, which testifies to a stable geochemical equilibrium in the rock. Vesuvianite from the skarn (Shishimskaya mine) is in paragenesis with garnet, so it is significantly enriched in Al, LREE and water, and depleted in impurity elements. The content of trace and rare-earth elements in all vesuvianites shows signs of contact metasomatism: the peculiarities of their composition depend on the mineral paragenesis and the influence of the frame rocks — gabbroids of the Kusa-Kopan intrusive complex.

New data are presented on the contents of major elements and trace elements, Sr-Nd-Pb isotopes in the Holocene high-potassium basic lavas of the Alaid volcano, located in the north of the Kuril island arc in the junction zone with the Kamchatka volcanic segment. According to petrochemical criteria, two groups of coeval rocks are distinguished: Ne-normative shoshonites and high-potassium subalkaline basalts, which are similar to each other in a number of geochemical characteristics. Chondrite-normalized REE distribution spectra show enrichment in LREE, with flat HREE distribution spectra, and the absence of Eu and Ce anomalies. MORB-normalized incoherent element concentrations show LILE enrichment and a well-defined negative Ta-Nb-Ti anomaly typical of suprasubduction volcanics. High K2O/Rb and Rb/Sr ratios indicate the presence of biotite and amphibole in the magmatic source, while low Sr/Y ratios and flat distribution spectra of medium and heavy lanthanides indicate the absence of garnet in the restite paragenesis. Significant variations in the contents of macro- and microcomponents at similar MgO concentrations indicate a heterogeneous magmatic source, and taking into account linear mixing trends in isotope and discrimination diagrams, experimental data, suggest the involvement in magmogenesis of not only the peridotite mantle, but also amphibole-clinopyroxene mineral paragenesis. An analysis of the literature data shows that in «cold» island arcs, manifestations of potassium alkaline magmatism are often, if not in all cases, associated with local extension zones. Since such zones are associated with the adiabatic rise of a hot and plastic asthenosphere, it can be assumed that subduction melange formed along the boundary of the slab and supra-subduction mantle, consisting of hydrated fragments of ultrabasites and metamorphosed oceanic crust transformed into amphibole-bearing pyroxenites, was involved in the melting. This mechanism makes it possible to logically explain the geochemical and isotopic features of the anomalous alkaline magmatism of the Kuril island arc and the connection with the anomalous tectonics of its northern segment. The results obtained may be important in discussing the genesis of potassium alkaline magmas manifested in subduction geodynamic settings.