Vanadiferous titanomagnetite (VTM) ores in mafic layered intrusions host the world's largest vanadium resources, with the Bushveld Complex representing the principal global deposit. This study examines the mineral textures and element redistributions in magnetite–ilmenite assemblages from Bushveld Upper Zone magnetites. Two main magnetite exsolution microstructures are identified: cloth textures dominated by ulvöspinel lamellae and sandwich or trellis textures characterized by ilmenite lamellae formed through ulvöspinel oxidation. In situ elemental analyses demonstrate that vanadium is concentrated in magnetite relative to ilmenite and that oxidation-driven exsolution enhances V enrichment in residual magnetite while concentrating Ti into ilmenite. The textural type strongly controls liberation potential: cloth textures exhibit pervasive fine intergrowths that hinder beneficiation, whereas sandwich and trellis textures show coarser separable lamellae. These microstructural variations have direct implications for magnetic, gravity, and flotation processing efficiency. The results highlight the necessity of textural characterization to optimize V–Ti ore beneficiation strategies.
Belmonteite (IMA 2024-040), ideally CaMn2(AsO4)2(H2O)5⋅2H2O, is a new arsenate mineral discovered in the Gambatesa mine, Graveglia Valley, Ne, Genoa Province, Liguria, Italy. It occurs as aggregates up to 0.5 mm in length, formed by thin tabular crystals, white in color, with a silky luster and white streak. A perfect {010} cleavage was observed. Associated minerals are tennantite-(Cu), calcite, and a still unidentified (Ca,Cu)-arsenate secondary phase. Calculated density is 2.677 g cm−3. The empirical chemical formula of belmonteite is (Ca0.86Mn0.11K0.01)Σ0.98(Mn1.90Cu0.08Al0.02)Σ2.00As2.01O8⋅7H2O. Unit-cell parameters are a=8.8418(9), b=23.031(2), c=13.5270(14) Å, V=2754.6(5) Å3, space group Cmce, Z=8. The crystal structure of belmonteite was refined to R1=0.0385F>4σ(F)4) groups and Ca atoms. These heteropolyhedral layers are connected along b
Fengruiite, ideally [Ag6Sb2S7][Ag9CuS2Te2], is a new mineral species of the pearceite–polybasite group discovered in the Haopinggou Ag–Pb–Zn–Au deposit, eastern Qinling, China, and approved by the IMA Commission on New Minerals, Nomenclature and Classification as IMA 2024-045. The mineral occurs as irregular grains (< 20 × 80 µm) intergrown with galena, cervelleite, and chalcopyrite in intermediate-sulfidation epithermal veins. Fengruiite is opaque, gray with a metallic luster, and brittle and has an estimated Mohs hardness of 3–4. EPMA analyses yield Ag (65.9 wt %–68.6 wt %), S (12.6 wt %–13.1 wt %), Sb (9.1 wt %–10.1 wt %), Te (6.3 wt %–7.6 wt %), and Cu (3.3 wt %–3.8 wt %), corresponding to the empirical formula [(Ag5.87Cu0.29)Σ6.16(Sb1.89As0.03)Σ1.92S7] [Ag9CuS2(Te1.28S0.63)S1.91]. Fengruiite is trigonal, space group
A novel experimental setup was developed to simulate the transport processes of Li and B and their isotopes via a fluid phase in a flux-rich pegmatitic system (1.7 % Li2O, 2.5 % B2O3). The transport capacity of the fluid was estimated by the determination of Li and B in two melt reservoirs, an Li- and B-rich source melt, and an initially Li- and B-free sink melt. These melts were physically separated by a coarse-grained (250–180 µm fraction) porous filling material containing the fluid phase that acted as the transport medium. The effectivity of Li and B transport was investigated at 100 MPa by changing various parameters in the experimental setup. The impact of the chemical composition of the filling material was tested using either quartz or zircon. Different fluid compositions containing either NaCl or CsCl were investigated with a constant Cl concentration of 0.17 mol kg−1The results of the experiments indicate that the effectivity of Li and B transport between the two melts via a fluid phase is influenced by a complex interplay of experimental duration, temperature distribution, and reactive surface area (between melt and fluid). The amount of Li and B in the sink melt generally correlates positively with experimental duration, which can be explained by a gradual mobilization of these elements from the source melt. For experiments with a temperature gradient between source and sink, higher Li and B concentrations in the sink melt were observed compared to experiments conducted under isothermal conditions. The sink melt was enriched in the heavier 7Li, which can be best explained by equilibrium isotope fractionation between silicate melt and fluid. These findings demonstrate experimentally, for the first time, the preferential partitioning of 7Li into a fluid phase compared to silicate melt. For B, possible isotope effects are smaller than our analytical uncertainty (±4.7 ‰), which is likely related to the high experimental temperature and similar bonding environments of B in melts and fluids. There is no evidence for kinetic isotope fractionation during transport of Li and B in the fluid which, expectedly, would result in an enrichment of light isotopes in the sink. Our experimental results indicate that equilibrium for Li isotopes can be established rapidly between a melt and a fluid phase. This may be important for the interpretation of isotope data in pegmatite minerals and the role of a fluid phase during their formation by disequilibrium crystallization caused by strong undercooling.
Water in the form of hydrous point defects in the crystal structure of pyroxenes from mantle xenoliths is frequently used to trace the water content in the lithospheric mantle. However, little is known about the mechanism that allows xenoliths to preserve deep hydrogen signatures and if we can avoid a complete or partial reset by reaction with the host magma during transport. In particular, it is unknown how much of the water content of xenoliths is modified during the emplacement of lava and cooling at the surface and by the eruption mode (effusive versus explosive). In this work, we attempted to address to these matters.We analysed the water content of peridotite xenoliths from two localities in the French Massif Central, Allègre and Ray Pic, using Fourier transform infrared (FTIR) spectroscopy. We performed point analyses and profile measurements in olivine (ol), clinopyroxene (cpx), and orthopyroxene (opx) crystals derived from 17 xenoliths. The two localities have different types of outcrops. In Allègre, the xenoliths are present in a frozen lava lake with a vertical structure, while in Ray Pic, xenoliths are hosted both in pyroclastic deposits and in a lava flow running over more than 20 km along a riverbed. Both studies on xenoliths in different parts of the lava flow show that the solidification and cooling of the basalt at the surface do not significantly affect the water content of pyroxenes in the xenoliths. The xenoliths do not show the presence of diffusion profiles, and the water content is independent of the location of the xenoliths within the lava bodies. However, the comparison of the water content of xenoliths from the pyroclastic deposit and within the lava flow at Ray Pic shows that the water concentrations are strongly impacted by the degree of degassing of the magma before the eruption. The concentrations of xenoliths in the degassed lava flow are much lower, by a factor of > 10 in ol and ≥ 2 in cpx and opx, compared to xenoliths from the pyroclastic deposits. Therefore, water content measured in pyroxenes can only represent minimal values, even for xenoliths hosted in rapidly cooled volcanic products (e.g. explosive eruptions). The amount of water in mantle xenoliths does not reflect the original amount of water in the lithospheric mantle. On the contrary, this study indicates that xenoliths picked up within the same lava flow, even at a few metres' distance, can exhibit pyroxenes with different spectral signatures. This suggests that the spectral signatures have been acquired before the emplacement of the lava flow and were not affected by the late degassing that occurred just before the eruption of the lava flow.
Elucidating the temperature-induced structural and crystallochemical transformations in phlogopite mineral species with a partial substitution of Fe2+
Xianhuaite-(Ce), K2CeNb5O15, is a new mineral species discovered in the Bayan Obo deposit, Inner Mongolia, China. The mineral is named in honor of Professor Xianhua Li in recognition of his outstanding contributions to research on the Bayan Obo deposit. It occurs as brownish-red to pale yellow-brown tetragonal prisms or irregular granules and exhibits a Mohs hardness of 5–6, an adamantine luster, and a calculated density of 5.23 g cm−3. Electron microprobe analysis yields the empirical formula A1(K1.30Ba0.69Sr0.02)Σ2.01A2(Ce0.39La0.31Nd0.04Pr0.02Ca0.15Na0.09)Σ1.00B(Nb4.75Fe
Located adjacent to Lappeenranta in southeastern Finland, the Ihalainen marble deposit has operated continuously since 1910. Regional metamorphism of the calcitic and dolomitic marble of the Ihalainen Formation led to wollastonite formation, well dated at 1.86 Ga. At about 1.6 Ga, the area experienced intrusion by the Wiborg batholith of anorogenic granite with a rapakivi texture. Dikes of granite, composite basic–felsic dikes, and dikelets with an aplitic texture intruded into the wollastonite deposit, now part of a roof pendant, and caused localized fluxed melting of the ore. The gaseous transfer of CaF2+ fluorite. Closer to the contact, an injection of geochemically evolved granitic melt induced anatexis of the marble. We investigated an emulsion of the two melts, one desilicated and now syenitic, the other a carbonate melt that contained dissolved silicates. The syenitic melt eventually crystallized to a sanidine solid-solution that underwent spinodal decomposition into two strained feldspars in the presence of a carbothermal fluid. A later influx of an aqueous fluid caused recrystallization of the feldspars but left intact the striking textural evidence of a once-coherent intergrowth. It also led to a bewildering array of calcic secondary minerals like pectolite, grosssular, holtstamite, and lawsomite. Three undescribed minerals in the affected rocks contain the high-field-strength elements Sn, Nb, and Ta.
The new mckelveyite group mineral bainbridgeite-(NdCe), ideally Na2Ba2NdCe(CO3)6⚫3H2O, was found at Mont Saint-Hilaire, Quebec, Canada. It occurs in two distinct environments: (1) in a “carbonate pegmatite” as pale-yellow or orange barrel-shaped short prismatic crystals up to 2 mm in size, where bainbridgeite-(NdCe) forms thin rims while the core is composed of bainbridgeite-(YCe), and (2) in a hornfels rock as white or pale-grey tabular saucer-shaped crystals up to 0.5 mm in size. It has a white streak, a vitreous lustre, and no cleavage. Dcalc−3. Bainbridgeite-(NdCe) is optically biaxial (+), α=1.577(3), β=1.592(3), γ=1.657(3), 2V (meas.) = 40(3)°, and 2V (calc.) = 52° (589 nm). The IR spectrum is reported. The composition (wt. %, average of seven analyses) is Na2O 6.85, CaO 1.16, SrO 4.83, BaO 24.02, Y2O32O32O32O32O32O32O32O32O32O3222O 5.73, total 101.17. The empirical formula of the holotype from the “carbonate pegmatite” calculated on the basis of six cations is as follows: Na2.09Ca0.19Sr0.44Ba1.48Y0.15La0.35Ce0.51Pr0.04Nd0.35Sm0.18Eu0.03Gd0.14Tb0.01Dy0.03Th0.01(CO3)5.86(H2O)3.00. The mineral is triclinic, P1, a=9.0525(3) Å, b=9.1178(2) Å, c=6.85180(19) Å, α=102.575(3)°, β=116.272(4)°, γ=59.788(4)° and V=438.23(3) Å3, and Z=1. The strongest reflections of the powder X-ray diffraction pattern [d, Å(I)(hkl)] are as follows: 6.17(50)(001,
Magmatic–hydrothermal ore deposits, such as pegmatites, are an increasingly important source of metals and critical elements for the development of green-energy resources. The geochemical processes at the magmatic–hydrothermal transition influence the degree of element enrichment in these ores. Quartz is a mineral that grows throughout the complete crystallization sequence of granitic pegmatites. Tracking the systematics of trace element incorporation into the quartz crystal structure throughout the magmatic–hydrothermal pegmatite evolution may offer unprecedented insights into pegmatite genesis.Quartz crystals from the Rosina pegmatite, Elba, Italy, and from the Misox pegmatite, Ticino, Switzerland, were mapped using scanning electron microscopy (SEM) charge contrast imaging and Fourier transform infrared (FTIR) spectroscopy to determine the distribution of OH coupled to Li, B, and Al. Trace element laser ablation inductively coupled plasma mass spectroscopy (LA-ICP-MS) spot measurements were done on the same quartz crystals, navigated by the spatial distribution of zonation observed via FTIR maps. In Rosina quartz, total Li, B, Al, and Ti mass fractions are higher in the cores of the zoned crystals when compared to the rims, whereas in Misox quartz, the total Li, B, and Al increase from core to rim. In both Rosina and Misox quartz, OH coupled to Li, B, and Al closely follows the zonation of the total trace element contents. Lithium, B, and Al coupled to OH represent 5 %–30 % of the coupled substitutions in quartz. Thus, OH-related point defects provide another tool for provenance and ore body prospecting studies. In Rosina quartz, the LiOH defect is dominant in the FTIR spectra, which is rare for quartz and only characteristic for evolved pegmatitic quartz crystals.Temperature estimates of quartz formation were constrained by Ti-in-quartz geothermometry, linking the observed geochemical processes to the pressure–temperature conditions at which they took place. Rosina quartz formed at pressures of 2.3 kbar and temperatures between 590 (core) and 330 (rim) °C, while Misox quartz formed at pressures of 5–6 kbar and temperatures between 520 (core) and 300 (rim) °C (calculated at TiO22O contents in quartz might be useful in the study of detrital quartz when prospecting for Li-rich pegmatites or other economically significant magmatic–hydrothermal ore deposits.
The coordination of boron in silicate melts has been extensively studied in synthetic industrial glasses but rarely in natural volcanic glasses or their synthetic analogues. Because coordination is a controlling factor in the boron isotope exchange between melts and coexisting phases, it is important to close this knowledge gap. We synthesized a set of boron-rich (2 wt % and 5 wt % B2O3) haplogranite glasses with water content from 0 wt % to 7 wt % and a variable alumina–alkali ratio, expressed by the aluminum saturation index (ASI), the molar ratio of Al2O3 
Yttrotungstite-(Nd), NdW2O7(OH)(H2O), is a new mineral species discovered in the Nyakabingo tungsten mine, Kigali, Rwanda. The mineral occurs in the oxidized zones of the deposit, where it forms tiny yellow-orange tabular crystals associated with anthoinite and hydrokenoelsmoreite. The crystals are transparent, reach a length of a maximum of 100 µm, and frequently form radiated groups. The dominant form is {010}, and a twinning has been observed parallel to (001). The streak of yttrotungstite-(Nd) is white, the lustre is vitreous, and the mineral is non-fluorescent. The Mohs hardness is 1; the tenacity is brittle; and observed cleavage planes are (010) perfect and (100) and (001) excellent. The calculated density is 6.25 g cm−3, and refraction indices are α= 1.90(2) and γ= 2.10(2). The mineral is optically biaxial, its optical plane is parallel to (010), and the optical orientation is X ∧ c = 6° and Z ∧ a = 9°. Pleochroism is from light yellow (X) to yellow (Z). The empirical formula of yttrotungstite-(Nd), calculated on the basis of 15 positive charges assuming 1 (OH) group and 1 H2O molecule per formula unit, corresponds to the following: (Nd0.36Sm0.13Ce0.12Pr0.08La0.06Gd0.06Y0.05Dy0.03Yb0.02Ca0.01)Σ0.92(W2.02P0.02)Σ2.04O7(OH)(H2O). The crystal structure was refined in space group P2
Bat guano deposits in caves host diverse assemblages of authigenic phosphates and sulfates. Previous field observations have proposed that some of them (e.g. brushite, gypsum, taranakite) can be subject to dehydration reactions as a response to varying environmental conditions. To evaluate the thermodynamic and kinetic constrains that regulate the dehydration reaction leading guano-derived taranakite (K3Al5(PO3OH)6(PO4)2 ⋅ 18H2O) to transform into francoanellite (K3Al5(PO3OH)6(PO4)2 ⋅ 12H2O), we conducted a multi-analytical in situ investigation consisting of temperature-resolved X-ray powder diffraction, Fourier transform infrared, and micro-Raman spectroscopy on a sample of taranakite. Thermodynamic calculations were also performed by means of the polyhedral approach to predict the phase transformation temperature at equilibrium, estimated to be 369.12 K (95.97 °C). Laboratory experiments conducted under increasing temperature conditions confirmed that the breaking of weak hydrogen bonds between interlayer water molecules and the aluminophosphate layers of taranakite is responsible for the onset of the dehydration reaction. Monitoring the evolution of the phosphate-stretching Raman peaks over time under isothermal conditions enabled us to estimate the activation energy of the process to be 7.6 ± 0.7 kJ mol−1
The new mineral piilonenite-(Nd), ideally NaNd(CO3)2⋅3H2O, was found at Mont Saint-Hilaire, Quebec, Canada, in apophyses of the Poudrette pegmatite. It occurs as thin, bladed crystals up to 600 µmDcalcg cm−3. Piilonenite-(Nd) is optically biaxial (+), α=1.546(3), β=1.616(3), γ=1.638(3), 2 V (meas.) = 56(3)°, and 2 V (calc.) = 56° (589 nm). The composition (wt. %, average of seven analyses) is Na2O 9.29, Y2O32O32O32O32O32O32O32O32O32O32O32O32O322O 16.16, total 101.48. The empirical formula of the holotype calculated on the basis of two cations is as follows: Na1.00(Nd0.48Ce0.17Sm0.13Gd0.07Pr0.06Y0.05La0.02Dy0.02)∑1.00(CO3)2(H2O)3. The IR spectrum shows IR bands of O–H-stretching and H–O–H bending vibrations of H2O molecules and C–O-stretching vibrations of CO
Argentotennantite-(Fe), Ag6(Cu4Fe2)As4S13, has been approved as a new mineral species (IMA 2023-126) by the Commission on New Minerals, Nomenclature and Classification of the International Mineralogical Association (CNMNC-IMA) using a sample of quartz gangue with argentotetrahedrite-(Zn), pyrargyrite, baryte, and siderite from the San Genaro mine, Castrovirreyna Province, Huancavelica, Peru. Argentotennantite-(Fe) occurs as anhedral grains up to 100 µmλRΣMe = 16 atoms per formula unit, is (Ag3.36Cu2.70)Σ6.06(Cu4.05Fe1.88Zn0.07)Σ6.00(As2.29Sb1.66)Σ3.95S12.82. Argentotennantite-(Fe) is cubic,
Black opal, a variety of opal pigmented by organic matter, from Volyn, western Ukrainian Shield, was investigated by means of scanning electron microscopy (SEM), electron microprobe analyses (EMPAs), μ-X-ray fluorescence (μXRF) element mapping, X-ray diffraction (XRD), and Fourier transformed infrared (FTIR) spectroscopy, and was dated by U-Pb by laser ablation (LA-ICP-SF-MS). Opal occurs as several centimeter large blocks and as cement in a breccia within pegmatites, which intruded into granites of the ca. 1.7–1.8 Ga old Korosten pluton. Opal samples were collected underground in miarolitic cavities of the pegmatites, which also host kerite, fossilized organic material (called Volyn biota). Inclusions in opal are typical pegmatitic minerals such as alkali-feldspar, Li-mica, and quartz. Buddingtonite and ammonium-bearing muscovite, as well as shape relicts of the fossils in opal, indicate interactions of organic material with the pegmatite.The XRD data indicate opal-CT with a complex pattern of the ∼ 4 Å peak. Its microstructure, as seen in SEM and back-scattered electron maps, consists of nanograins 15–35 nm in size, arranged in sphere-like structures, in some samples ∼ 5 µm-large and monodisperse, in others polydisperse with diameters of between 1 and 10 µm, and as lepispheres. Organic matter plus water makes up ∼ 10 wt %–15 wt %. The organic matter is situated within the core, in concentric zones in the sphere-like structures and in the matrix around them. Infrared (IR) spectra confirm the presence of silanol SiOH and CHn. At the contact with pegmatitic material, a pyrite-enriched zone was observed and interpreted as resulting from the infiltration of a late Fe- and Mn-bearing fluid along grain boundaries.Results of U-Pb dating yield a minimum age for opal formation of ∼ 200 Ma, and provide evidence for fluid overprint during the Jurassic (170–155 Ma) and Quaternary. These ages are much older than reported so far in opal from deposits worldwide. Furthermore, the here-reported occurrence of opal in pegmatitic rocks is unique, as all other opal deposits are either sedimentary or volcanic hosted.
Mineralogical, paragenetic, and geochemical data on sulfidic mineralization from the Cínovec Li–Sn–W greisen-type deposit (Bohemian Massif, Czech Republic) were used to refine the evolution of mineralization at this world-class deposit and to clarify the relationship between base-metal sulfides and the Li–Sn–W mineralization. Sulfides occur in three main settings: (i) quartz–zinnwaldite veins, (ii) massive greisens and greisenized granites, and (iii) late baryte–fluorite veins that locally overprint earlier types. Electron microprobe analyses and detailed BSE imaging reveal multiple mineralization stages and a surprisingly large suite of sulfide minerals. They were divided into several mineralization stages, including the greisen stage (molybdenite, arsenopyrite, safflorite), early sulfide stage (stannite–kësterite, stannoidite, sphalerite), intermediate sulfide stage (galena), and late sulfide stage (pyrite, marcasite, chalcopyrite, tennantite–tetrahedrite, enargite, lautite, Cu–Ag–Bi–Pb sulfosalts, native Bi, Cu sulfides, pearceite, cupropearceite, stromeyerite). A minor amount of sulfides was remobilized during later the fluorite–baryte stage. Distribution of sulfide mineralization at the deposit is irregular; sulfides are not strictly bound to prevalent Li–Sn–W mineralization. The dominant sphalerite-bearing assemblages (Zn–Pb–Cu) display average grades of ∼ 100–200 ppm Zn (however, Zn is partly contained in zinnwaldite), 20–50 ppm Pb, and < 50 ppm Cu in disseminated mineralization, with locally elevated In contents (≤ 0.53 wt %) in sphalerite. Progressive evolution of metal contents in the reduced sulfide-bearing hydrothermal fluid proceeds from Zn–Cu–Sn to Pb–Bi–Ag and As–Sb. Late-stage sulfate- and fluorine-bearing fluids partly altered earlier mineralization but did not deposit significant ore content.
The study of two outcrops of schists in the Padul Fault area has allowed us to corroborate the enrichment in clay minerals in the fault zone. In the case of the dark schist outcrop, the fault rocks show a reduction in mineral diversity with aluminosilicates, characteristics of the regional metamorphism losing and showing an enrichment in quartz and kaolin-group minerals. In the calc-schists, there is a clear presence of chlorite in the fault rocks, which is practically absent in the fresh rocks, as well as R1 illite/smectite and smectite. The geochemical characterization also showed differences between fresh and fault rocks, more evident in the dark schists than in the calc-schists, with an increase in SiO22O3, Fe2O3, and MgO in the fault rocks with respect to the protolith. The presence of authigenic chlorite in the fault rocks from the calc-schists allowed for the application of semi-empirical thermometric methods for the fault rocks giving predominant temperatures < 225 °C. All these data are consistent with the circulation of low-temperature fluids along the fault zone that interact with the rocks, promoting clay mineral formation. Such was also the findings in a previous study focused on the predominant rocks of the Padul Fault area, which are dolostones, affected by the dynamics of this fault. Interestingly, the circulation of fluids promoted by the existence of the Padul Fault has not been restricted to the fault rocks, given that some of these clay minerals (kaolinite and smectite) are also present in the fluid-accessible zones of the metamorphic protolith. These data highlight the importance of faults in the retrograde mineralization processes of metamorphic rocks.