Composition Of Inclusions Research Articles

Composition of Non-Metallic Inclusions and Microstructure of Electric Arc Coating Formed Using the Flux-Cored Wire of Fe–C–Si–Mn–Cr–Mo System

Composition of Non-Metallic Inclusions and Microstructure of Electric Arc Coating Formed Using the Flux-Cored Wire of Fe–C–Si–Mn–Cr–Mo System

Hot isostatic pressing of laser powder-bed-fused 304L stainless steel under different temperatures

Hot isostatic pressing (HIP) is becoming a key strategic technology for post-processing metallic materials fabricated with laser powder bed fusion (LPBF), acting to eliminate the processing-induced pores and improve the mechanical properties. This paper comprehensively investigated material characteristics (porosity, residual stress, microstructures, phase composition, and inclusion), mechanical properties (microhardness, tensile properties, and fatigue properties), and deformation behaviors of LPBF 304L austenitic stainless steel (ASS) subjected to HIP process with different temperatures (965°C, 1165°C, and 1365°C). Experimental results indicated that the grain size, inclusion size, recrystallization fraction, and dimple size increased with increasing HIP temperature, which resulted in homogenized microstructure, reduced yield strength and microhardness, and significantly improved ductility. The fatigue life of HIP-treated samples after surface post-treatment was mainly influenced by porosity, inclusion, residual stress, and dislocation density. The HIP-1165°C samples with low porosity and small-sized inclusions had a higher fatigue life than HIP-965°C and HIP-1365°C samples. In addition, the evolution of crystallographic texture and inclusion composition associated with the HIP temperature were systematically revealed with the aid of orientation distribution function (ODFs) and elemental mappings. This study provides a profound understanding of the rational design of the hybrid process of LPBF and HIP.

Development of Self-Shielded Flux-Cored Wires for Arc Welding of Low-Alloy Steels

Current aspects of the developing of modern self-shielding flux-cored wires composition for arc welding of low-alloyed steels are considered. Advantages and disadvantages of flux-cored wires of carbonate-fluorite, oxide and oxide-fluoride types of are shown in comparison. The effectiveness of gas shielding of molten metal at welding with self-shielding flux-cored wires of carbonate-fluorite type is analyzed considering the thermal properties of their cores. It is shown that to improve reliability of gas shielding at welding using the wires of this type it is important not only to ensure generation of sufficiently large volume of shielding gases at thermal destruction of the wire core, but also to control this process, providing gas evolution at all stages of heating and melting of the wire. The results of complex thermal analysis of the wire core mixtures containing, for example, lithium carbonate show substantially large heat losses for heating and melting of the wire core, which are accompanied by the development of energy-intensive processes of thermal destruction of core components. It is shown that the limitation of lithium carbonate content in the wire at the level of not more than 2 wt. % allows not only to preserve welding arc burning stability at the acceptable level but also to provide effective gas shielding of molten metal and easy separation of slag crust. The control of thermochemical reactions in the core is achieved by selection of its proper composition to ensure favorable melting of flux-cored wire and electrode metal transfer to the welding pool. Results of metallographic examinations of distribution and composition of non-metallic inclusions in metal of the welds made with wires of the oxide and oxide-fluoride types are presented. Main properties of the developed self-shielding flux-cored wires and recommendations on welding are given in conjunction with prospective fields of their application.

Fluid Inclusion and Chemical Composition Characteristics of Emeralds from Rajasthan Area, India

Emerald is among the most valuable gems in the world. Over the past decade, its commercial value and geographic origin have been the focus of gemological and geological research. In this study, emerald samples from India were examined by UV-Vis-NIR, FTIR, Raman spectra analysis, EPMA, and LA-ICP-MS. Hexagonal three- and multi-phase inclusions are first reported in Indian emeralds, containing gas bubbles (CO2 or CO2 + CH4), water or liquid mixtures of H2O + CO2, and solid phases inclusions (rounded crystals of siderite and dolomite, platelets of phlogopite, and magnesite). Mineral inclusions in Indian emeralds typically included phlogopite, quartz, talc, aragonite, and albite. The representative UV-Vis-NIR spectra show a distinct Fe absorption band, and one of the more typical characteristics of Indian emeralds is that the absorption strength of Fe3+ (369 nm) and Fe2+ (851 nm) is greater than that of Cr3+ (426, 606, 635, and 680 nm). Infrared spectra show that the absorption of type II H2O is stronger than that of type I H2O. LA-ICP-MS results show that Indian emeralds contain high alkali metals (10,503–16,964 ppmw; avg. 13,942 ppmw), moderate Fe (2451–4153 ppmw; avg. 3468 ppmw), low V (37–122 ppmw; avg. 90 ppmw), and the content of Cr (106–6310 ppmw) varies in a wide range. From a greenish-white core to a medium-green rim, the content of Fe, V, Cr, Sc, Cs, Rb, and Ga gradually increases in emerald with color band.

ЦИРКОН МАГМАТИЧЕСКИХ ПОРОД КАК ИНДИКАТОР УСЛОВИЙ КРИСТАЛЛИЗАЦИИ И ИСТОЧНИКА МАТЕРИНСКИХ РАСПЛАВОВ

This review summarizes the information on the crystallomorphological features of zircon from magmatic rocks, its internal structure, the chemistry of the crystalline matrices, the composition of inclusions, and the distribution of rare-earth elements. These data allow us to reveal the discriminant features of zircon that crystallized from magmatic melts in various geodynamic settings and to distinguish crustal and mantle sources of melts. An integrated study of the above zircons may be used to determine the PT conditions of magmatic rock formation. The concentration of separate elements in zircon is significantly even in samples from the same rock. Therefore, for a reliable estimate of their distribution separate should be based on a set of analytical methods. This allows us to determine the range of variations and assess the dynamics of the distribution of individual elements in zircons of different genesis.

Mantle-Derived Noble Gas Isotopes in the Ore-Forming Fluid of Xingluokeng W-Mo Deposit, Fujian Province

China has the largest W reserves in the world, which are mainly concentrated in south China. Although previous studies have been carried out on whether mantle material is incorporated in granites associated with W deposits, the conclusions have been inconsistent. However, rare gas isotopes can be used to study the contribution of mantle-to-W mineralization. In this paper, we investigated the He and Ar isotope compositions of fluid inclusions in pyrite and wolframite from the Xingluokeng ultra-large W-Mo deposit to evaluate the origin of ore-forming fluids and discuss the contribution of the mantle-to-tungsten mineralization. The He-Ar isotopic compositions showed that the 3He/4He ratios of the ore-forming fluid of the Xingluokeng deposit ranged from 0.14 to 1.01 Ra (Ra is the 3He/4He ratio of air, 1 Ra = 1.39 × 10−6), with an average of 0.58 Ra, which is between the 3He/4He ratios of mantle fluids and crustal fluids, suggesting that the mantle-derived He was added to the mineralizing fluid, with a mean of 8.7%. The 40Ar/36Ar ratios of these samples ranged from 361 to 817, with an average of 578, between the atmospheric 40Ar/36Ar and the crustal and/or mantle 40Ar/36Ar. The results of the He-Ar isotopes from Xingluokeng W-Mo deposit showed that the ore-forming fluid of the deposit was not the product of the evolution of pure crustal melt. The upwelling mantle plays an important role in the formation of tungsten deposits.

Comment on "Discovery of davemaoite, CaSiO3-perovskite, as a mineral from the lower mantle".

Tschauner et al. (Reports, 11 November 2021, p. 891) present evidence that diamond GRR-1507 formed in the lower mantle. Instead, the data support a much shallower origin in cold, subcratonic lithospheric mantle. X-ray diffraction data are well matched to phases common in microinclusion-bearing lithospheric diamonds. The calculated bulk inclusion composition is too imprecise to uniquely confirm CaSiO3 stoichiometry and is equally consistent with inclusions observed in other lithospheric diamonds.

Study on the thermodynamic stability and evolution of inclusions in Al–Ti deoxidized steel

Abstract To investigate the thermodynamic stability and the evolution process of inclusions in the Al–Ti deoxidized steels, both laboratory experiments and thermodynamic calculations were conducted in the present work. Scanning electron microscope-energy dispersive spectrometer (SEM-EDS) and Al2O3–Ti2O3–TiO2 phase diagrams were used to investigate the composition of oxide inclusions after adding various contents of Al and Ti. The results show that the TiO x content of inclusions increases with the increase in titanium addition in steel ranging from 0.31 to 1.88%, and the typical inclusions are transferred from pure Al2O3 to multi-phase Al–Ti complex inclusions and Al2O3–TiO x complex inclusions with uniform composition. The TiO x content in the inclusions first increased and then decreased with the extension of deoxidation time in the steels with deoxidants of [% Al] = 0.055 and [% Al] = 0.71, and the content of TiO x in the inclusions is highest at 360 s of deoxidation. There is a small amount of pure titanium oxide and liquid Al2O3–TiO x composite inclusions in the steel with deoxidants of [% Al] = 0.13 and [% Ti] = 1.88 at 120 s of deoxidation, and then this part of inclusions gradually turns into the Al2O3-rich phase. The predominance diagrams of the Al–Ti–O–Fe system were obtained based on the classical thermodynamic calculation and FactSage calculation with different databases and products. The calculated results were compared with the experimental data, and the discrepancies on the stable region of oxides in the predominance diagrams were discussed. The evolution and transformation of inclusions during the solidification process were analyzed based on FactSage calculation.

Hydrocarbons in Magmatic Fluid in Phenocrysts of Eruption Products of the Men’shii Brat Volcano (Iturup Island): Data from Pyrolysis-Free Gas Chromatography–Mass Spectrometry of Melt and Fluid Inclusions

Abstract —Pyrolysis-free gas chromatography–mass spectrometry was used to determine the gas phase composition of inclusions in phenocrysts from basalts and rhyolites of the Men’shii Brat Volcano (Medvezh’ya caldera, Iturup Island). Among more than 300 compounds detected in the inclusions, hydrocarbons are predominant (52–92 rel.%). These hydrocarbons (C1–C17) are alkanes, alkenes, alcohols, polycyclic aromatic hydrocarbons, ethers and esters, aldehydes, ketones, and carboxylic acids as well as sulfonated, nitrogenated, and halogenated organic compounds. Inorganic substances, which are predominantly CO2, H2O, SO2, and N2, are present in subordinate amounts. The organic compounds are interpreted as products of abiogenic synthesis of hydrocarbons in magmatic gases. This fundamentally new information about the composition of magmatic fluid suggests that mantle and crustal magmas can transport hydrocarbon substance.

Geology, mineralogy, geochemistry and conditions of forming the Tukan gold-quartz deposit (Khudolaz trough, South Urals)

Research subject. Detailed mineralogical and geochemical studies of rocks of the Tukan gold-quartz deposit (quartz veins, dolerites, gabbro-diorites) were carried out. The deposit is one of numerous small gold-quartz occurrences in the Khudolaz trough of the West Magnitogorsk zone.Methods. The morphology and composition of native gold was studied using an Axios kop 40 A optical microscope and Tescan Vega 3 and JEOL-6390LV scanning electron microscopes. The chemical composition of rocks was determined by X-ray fluorescence (Carl Zeiss VRA-30) and atomic emission (Shimadzu ICPE-9000) analyzes. Fluid inclusions were analyzed using Linkam TMS-600 thermostage equipped with Link-System 32 DV-NC software and an Olympus BX51 optical microscope. The gas composition of fluid inclusions was examined by Raman spectroscopy (Horiba LabRam HR800 Evolution).Results. Gold-bearing quartz veins and dolerites intersect ing the gabbrodiorite intrusion of the Khudolaz complex are associated with submeridional strike-slip faults. Native gold has a various morphology and is confined to cracks in quartz veins and altered dolerites. The composition of gold is stable, with the average fineness of 871 ± 8.3‰. An analysis of fluid inclusions in a gold-bearing quartz vein showed that gold was formed at temperatures of no less than 186–230°С from a fluid with a salinity of 4–8 wt % NaCl-eq. The presence of gases СО2, N2 and CH4 was found in fluid inclusions. Dolerites and gabbrodiorites hosting gold-bearing veins contain sulfides (pyrite, pyrrhotite, chalcopyrite, pentlandite, violarite), sulfoarsenides (cobaltite and its analogs), as well as mine rals of Ag (hessite) and Pb (kuranakhite and phases similar in composition to minerals of the dugganite group and burckhardtite). Conclusions. The sustained composition of native gold and a narrow range of salinity and homogenization temperatures of fluid inclusions indicate the formation of gold during a single stage of mineralization. The main source of gold could have been the dolerite dikes of the Ulugurtau complex. The presence of CO2, N2 and CH4 gases in fluid inclusions from goldbearing quartz indicates that not only magmatic fluid, but also fluid from the host rocks took part in mineral formation. The low value of the ratio X(CO2)/X(CH4) ≤ 0.7 indicates a moderately reduced ore-forming fluid. Low Au concentrations (0.1– 0.4 ppm) in quartz veins, dolerites, and gabbro-diorites, including those containing visible gold, indicate a weak commercial potential of the deposit

Deep ore‑forming fluid characteristics of the Jiaodong gold province: Evidence from the Qianchen gold deposit in the Jiaojia gold belt

The Jiaodong gold province hosts world-class gold deposits with giant resources of >5000 t, where the Jiaojia-Xincheng fault belt and the Sanshandao-Cangshang fault belt occupy more than two-thirds of the gold deposits. Recent developments of exploration have advanced in tracking deep mineralization. The nature of the ore-forming fluid, source, and the extreme enrichment mechanism of the gold in this region remain debated. Here, we investigate the deep ore body of the Qianchen gold deposit at the southern part of the Jiaojia gold belt based on mineralogy, fluid inclusion, elemental and isotopic composition of pyrite, and the primary halo geochemistry. Natural gold is the important form of Au in this deposit with a relatively large (up to 200 μm) grain size, suggesting the prospect of mineralization at deeper domains. The accompanying PGE minerals (Hexaferrum) hint at contributions from mantle material. The ore-forming fluids of the Qianchen gold deposit are characterized by medium–low temperatures and salinities and have a general H2O–NaCl–CO2 ± CH4 composition, which indicates that the Jiaodong gold province has a unified ore-forming fluid system from shallow to deep. However, the trace elements and S isotopes of pyrite at different elevations show slight differences, suggesting the composition and properties of the fluid changed during the process of ascending, affected by ore-forming conditions such as temperature, pressure, and oxygen fugacity. Furthermore, the evidence of a decrease of salinity with depth and temperature and fluid immiscibility indicates that fluids from different sources continuously mixed during the upward migration of fluid, with the mineralization triggered possibly by phase separation. The primary halo model suggests promising prospecting potential. We formulate a comprehensive metallogenic model for the mineralization process in the Jiaodong gold province. The Au-bearing hydrous magma derived from the partial melting of the metasomatized SCLM, underwent further magmatic-hydrothermal differentiation and fluid exsolution, and thus the Au was enriched and partitioned into exsolved fluids that evolved to auriferous fluids. During the upward migration of ore-forming fluids (magmatic-hydrothermal), many factors affected mineralization, mainly including fluid-rock interaction and mixing of the metamorphic-hydrothermal and meteoric fluids. The fluid activities, multiple sources of Au in the mantle and ancient basement, together with the large fault structures resulted in the formation of the giant Jiaodong gold province.

Carbon and oxygen isotope analysis of CO2 trapped in silicate minerals

Knowledge of the carbon and oxygen isotope composition of CO2-rich inclusions in crust- or mantle-derived minerals is crucial for a more quantitative understanding of cycling of volatiles between Earth's deep and surficial reservoirs. In this study, we present a crushing method for analysis of combined carbon and oxygen stable isotope compositions of small (≤ nmole) amounts of CO2 in fluid and melt inclusions. During crushing, the released CO2 was cryo-trapped, and subsequently introduced into a Gas Bench II coupled to a Deltaplus Isotope Ratio Mass Spectrometry (IRMS). Reference standard CO2 introduced in the crusher chamber was analysed to a precision better than ~0.3 and ~ 0.4‰ (1σ) for carbon and oxygen, respectively. Analysis of previously analysed samples validates that the crushing technique can be applied to CO2-rich fluid inclusions in quartz samples as small as 0.2 to 5 mg. CO2 –rich quartz samples were analysed from the UHT-Bakhuis Granulite Belt (Suriname) and Val Nalps (Switzerland) as well as forsterite-rich olivine-hosted melt inclusions from Vulsini volcanic district (Italy). The carbon isotope compositions obtained from the quartz samples allow discrimination between different sources within the crust and mantle. In contrast, the oxygen isotopic signatures of the fluid inclusions containing water appear affected by isotopic exchange between CO2 and H2O in the inclusions, where for the free-water fluid inclusions can reflect the pristine δ18O value. Crushing of olivine grains with CO2 melt-inclusions displayed instantaneous adsorption of the released CO2, which leads to low CO2 yields, and considerable oxygen and carbon isotope fractionation, hampering reliable isotopic determinations. We conclude that the δ13C and δ18O values from CO2-rich inclusions can be used as an indicator of the CO2 source and to evaluate mantle CO2 outgassing and release from storages within Earth's crust. The method presented can be readily applied to determine carbon and oxygen isotopic compositions of CO2 (4.5−10 mol) in small amounts of fluid-inclusion bearing quartz.

Hydrocarbon Charge History of the Upper Paleozoic, Ordos Basin as Revealed by Fluid Inclusions

The petrographic characteristics of fluid inclusions of the main gas-bearing intervals of the Upper Paleozoic in the Ordos Basin are analyzed by means of plane-polarized light, fluorescence microscopy, and microthermometry. With the burial history of the basin, the charging and enrichment of natural gas in low-permeability reservoirs are also studied through a comparison of parameters such as the homogenization temperature and freezing temperature of aqueous inclusions associated with hydrocarbon inclusions. A comprehensive analysis of the assemblage characteristics, components, and temperature of fluid inclusions of the Upper Paleozoic shows that the abundance, attitude, and composition of gaseous hydrocarbon inclusions can reflect petroleum enrichment in low-permeability reservoirs. The homogenization temperature and freezing temperature of aqueous inclusions associated with gaseous hydrocarbon inclusions show no obvious discontinuities, indicating that natural gas charging was a long and continuous process since the Late Triassic to Early Cretaceous (210–100 Ma) and natural gas accumulation mainly occurred during the Early Cretaceous (125–100 Ma).

On the Chemical Composition of Non-Metallic Inclusions in Ultra-Clean Gear Steels

Abstract Fisheye failures due to non-metallic inclusions can lead to the reduced endurance fatigue limit of case-hardened, shot-peened gears. Various approaches for preventing crack initiation at non-metallic inclusions are conceivable. As one approach, steel manufacturers have invested much effort in the steelmaking process to produce ultra-clean gear steels. Such ultra-clean gear steels were investigated in a gear research project. For each steel batch, different measures were taken during steel production to avoid or bind off non-metallic inclusions in order to reduce or even suppress the harmful effect of the non-metallic inclusions. However, the influence of the measures taken on the chemical composition of non-metallic inclusions in such ultra-clean gear steels is not investigated in the gear industry in detail so far. Therefore, in the framework of this publication, the chemical composition of non-metallic inclusions in ultra-clean gear steels is investigated. Furthermore, a comparison of the chemical analysis with the crack-initiating inclusions from the experimental investigations is performed.

Impurity-impurity interaction during the growth of UMG-Si-based mc-Si

This article investigates the relationship between the chemical composition and electrophysical properties of p- and n-type multicrystalline silicon ingots based on metallurgical silicon with a purity of 99.99 at.%. In particular, the role of impurity-impurity interactions in the production of multisilicon by the Bridgman vertical method is evaluated in order to identify approaches to controlling this process effectively. The phase equilibrium calculations in the “silicon–all impurities” and “silicon-impurity-oxygen” systems were carried out based on the Gibbs energy minimization in the Selector software package. The study investigates the rank correlations of the concentrations of various impurities with each other, as well as with the specified electrical resistivity (SER) and the lifetime of nonequilibrium charge carriers (NCC) in the direction of crystal growth. Pair correlations of the element distribution profiles were considered based on the role of the main factor represented by the ratio of individual impurity solubilities in solid or liquid silicon (k0), as well as from the standpoint of direct interaction between two elements. It was found that the k0 value for two individual impurities in silicon does not automatically lead to the pair correlation of their distribution profiles in the ingot. A significant effect on the distribution profiles of impurities in multisilicon with k0→0 has the factor of binding some part of the impurity into such a form that this impurity can be incorporated easily into a growing crystal. Binding may be induced by the interaction of the impurity in the melt with the oxygen background, its segregation at the grain boundaries, and its capture by the crystallization front in the composition of the liquid inclusion. Significant correlations of impurity distribution profiles in the ingot were demonstrated by the pairs whose elements interact without the formation of chemical compounds in the 25–1413 °C temperature range. The conducted phase equilibrium calculations for the “silicon–all impurities” system revealed the possibility of forming the VB2, TiB2, ZrB2, and MgTiO4 solid phases in the melt.

Effect of petrographic composition and chemistry of aggregate on the local and general fracture response of cementitious composites

This paper concerns the results of research into the influence of the composition of rock inclusions on the fracture response of cement-based composite specimens. Specially designed specimens of the nominal dimensions 40 × 40 × 160 mm with inclusions in the shape of prisms with nominal dimensions of 8 × 8 × 40 mm were provided with an initial central edge notch with a depth of 12 mm. These specimens, which were made of fine-grained cement-based composite with different types of rock inclusion – amphibolite, basalt, granite, and marble – were tested in the three-point bending configuration. Fracture surfaces were examined via scanning electron microscopy and local response in the vicinity of rock inclusions was characterized via the nanoindentation technique. The aim of this paper is to analyse the influence of the chemical/petrographic composition of rock inclusions on the effective mechanical fracture parameters of cement-based composites, as well as on the microstructural mechanical parameters of the interfacial transition zone. The results of this research indicate the significant dependence of the effective fracture parameters on the petrographic and related chemical composition of the rock inclusions.

Experimental and Modeling Study of Deformability of Glassy CaO-(MnO)-Al2O3-SiO2 Inclusions

The occurrence of non-deformable, non-metallic inclusions is the dominant reason for failure of wire during drawing and degrades service life for some steel grades, e.g., tire cord steel. To investigate the deformability of glassy inclusions in CaO-Al2O3-SiO2 and MnO-Al2O3-SiO2 systems, experimental and numerical methods were used. Young’s modulus values of some glasses based on the CaO-Al2O3-SiO2 and MnO-Al2O3-SiO2 systems, which correspond to typical inclusions in tire cord steel, were measured with resonant ultrasound spectroscopy. The effect of basicity, defined as the ratio of mass percentage of CaO to SiO2, on Young’s modulus and Poisson’s ratio were investigated. The Young’s moduli of glasses are enhanced with increasing basicity, which could be attributed to the high field strength of calcium ions. The Poisson’s ratios of glasses also show an increase tendency with increasing basicity, which could be due to the loss of rigidity of network with introduction of calcium ions. The equations in the literature for Young’s modulus calculation were evaluated based on the present and literature data. Appen’s equation is modified by re-fitting the present and literature data to give accurate estimation of Young’s modulus with the mean deviation of 2%. The iso-Young’s modulus diagrams for CaO-Al2O3-SiO2 systems were constructed. It is proposed that the iso-Young’s modulus diagram could be combined with liquid area in CaO-Al2O3-SiO2 ternary phase diagram to optimize the inclusion composition during both hot rolling and cold drawing.

Development of a Mathematical Model and Software for Predicting the Composition and Content of Nonmetallic Oxide Inclusions in Steel in Secondary Steelmaking Processes

Development of a Mathematical Model and Software for Predicting the Composition and Content of Nonmetallic Oxide Inclusions in Steel in Secondary Steelmaking Processes

Formation of mixed paragenesis diamonds during multistage growth – Constraints from in situ δ13C–δ15N–[N] analyses of Koidu diamonds

Inclusion-bearing diamonds from the Koidu kimberlite complex, Sierra Leone (West African Craton) were analyzed in situ for carbon and nitrogen isotope compositions, nitrogen concentrations and nitrogen aggregation states. In a suite of 105 diamonds, 78% contain eclogitic mineral inclusions, 17% contain peridotitic mineral inclusions, and 5% − an unusually high proportion − contain co-occurring eclogitic and peridotitic mineral inclusions indicating a mixed paragenesis. Major and trace element compositions of mineral inclusions from two mixed paragenesis diamonds (one with omphacite + Mg-chromite, the other with eclogitic garnet + forsteritic olivine) were determined. The presence of positive Eu anomalies in centrally located omphacite and eclogitic garnet inclusions indicates derivation from subducted protoliths, formed as igneous cumulates in lower oceanic crust. Mg-chromite (Cr# 85.5; Mg# 65.2) and olivine (Mg# 94.5) inclusions, located in outer portions of the mixed paragenesis diamonds, have compositions indicative of derivation from strongly depleted cratonic peridotites. Given that the olivine Mg# of 94.5 is the highest reported to date for the West African Craton, the eclogitic and peridotitic inclusions in these mixed paragenesis diamonds cannot have precipitated during infiltration of peridotitic substrates by eclogite-derived fluids, as the consequent fluid-rock interaction should lead to Mg# lower than that for the original peridotitic diamond substrate. The different origins of eclogitic and peridotitic inclusions could be explained by physical transport of their host diamonds from eclogitic into peridotitic substrates, possibly along high-strain shear zones, before renewed diamond growth.Based on the δ13C–δ15N systematics of the entire inclusion-bearing diamond suite from Koidu, three major compositional clusters are identified. Cluster 1 (eclogitic diamond cores; δ13C = –33.2 to −14.4‰ and δ15N = −5.3 to +10.1‰) bears the isotopic signature of recycled crustal material (± a mantle component). Cluster 2 (peridotitic diamonds and including the core of a diamond containing omphacite + Mg-chromite; δ13C = −6.0 to −1.1‰ and δ15N = −4.2 to +9.7‰) likely involves mixing of carbon and nitrogen from subducted and mantle sources. Cluster 3 (rims of eclogitic diamonds and including the eclogitic garnet + olivine included diamond and the rim of the omphacite + Mg-chromite included diamond; δ13C = −7.8 to −3.6‰ and δ15N = −7.9 to −2.1‰) matches convecting mantle-derived fluids/melts. The distinct isotopic signatures of the three diamond clusters, together with differences in nitrogen aggregation and cathodoluminescence response between diamond cores and rims, suggest episodic diamond growth during multiple fluid/melt pulses.

Magmatic and Hydrothermal Evolution at Qian’echong, Central-Eastern China: Insights into Dabie-Type Porphyry Mo Mineralization

Abstract Dabie-type porphyry Mo deposits have recently been identified as a new subtype of porphyry Mo deposits, but several questions remain about the role of ore-related magmas in the formation of this type of deposit, as well as distinctions in genetic processes with the well-studied Climax-type porphyry Mo deposits. Here, mineral and melt inclusions from the giant Qian’echong deposit, Dabie orogen, central-eastern China, were studied in order to improve our understanding of the nature and the role of ore-related magmas in the genesis of Dabie-type porphyry Mo deposits. The magmatic and hydrothermal evolution of the system was reconstructed based primarily on the analysis of quartz-hosted silicate melt and mineral inclusions, in concert with field and petrographic relations as well as previously published U–Pb and Re-Os geochronology. Ore-related magmas at Qian’echong include, from early to late, quartz porphyry dikes, rhyolite porphyry dikes, granite porphyries (stock and dikes) and a newly discovered, deep-seated monzogranite porphyry stock. Based on TitaniQ thermobarometry, these lithologies were sourced from a ~16–19-km deep (500–600 MPa) magma chamber and underwent nearly isothermal decompression to ~7 km (200 MPa), at temperatures ranging from 720°C to 690°C. According to the trace element composition of melt inclusions, in combination with published whole-rock Nd isotopic compositions, the early magma evolved from quartz porphyry to rhyolite porphyry through fractionation crystallization and thus became a crystal mush. This viscous crystal mush was subsequently re-melted to produce the granite porphyries and was injected with melts from a different source to generate the monzogranite porphyry. At Qian’echong, all melt inclusions have low concentrations of Mo (2–8 ppm), >5 wt. % H2O, and little to no F (≤0.26 wt. %), arguing against the requirement for ore-related magmas to be enriched in Mo to form large porphyry Mo deposits. Rayleigh fractionation modeling shows that the concentration of Mo in the quartz and granite porphyries increased through fractionation of quartz, feldspars, biotite, magnetite, and ilmenite and that Mo was subsequently depleted in the melt through fluid exsolution, exclusively in the rhyolite and monzogranite porphyries, as a result of magma ascent and decompression. This suggests that, in addition to ore-related granite porphyry, both the rhyolite and the monzogranite porphyries also contributed to the hydrothermal mineralization. This study confirms that the formation of porphyry Mo deposits does not rely on abnormally high concentrations of Mo in ore-related magmas but instead requires efficient extraction of Mo from large volumes of magmas, with normal concentrations of Mo. Unlike the Climax-type deposits where multiple pulses of ore-forming fluids are delivered from convecting shallow magma chambers, Mo mineralization in Dabie-type deposits was achieved by the assembling of ore-forming fluids from successively emplaced, relatively deep intrusions. Although the Dabie- and Climax-type Mo deposits are respectively associated with I-type and A-type granitoids in the Dabie orogen, it is suggested that both types of magmas are derived from the partial melting of subducted Yangtze continental crust and that it is the tectonic transition from compressional to extensional settings that controlled the different styles of porphyry Mo mineralization in this orogen.