Submicron-sized Inclusions Research Articles

Micro- to nanoscale constraints on metasomatic alterations of xenotime, inclusions of Th-, U- and Pb-phases and their geochronological implications (Ås pegmatite, Evje and Hornnes, S Norway)

Five crystals of pegmatitic xenotime from Ås II feldspar quarry (Evje, S Norway) were studied with comprehensive analytical methods from microscale to nanoscale with respect to fluid-mediated alterations and their geochronological implications. Xenotime crystals are strongly altered during dissolution-reprecipitation processes that resulted in the formation of (Th, U)-depleted xenotime subdomains with numerous microinclusions of (Th, U)-silicate, uraninite and minor galena. Remains of a primary xenotime (Xtm1) yielded LA-ICPMS UPb data characterized by a reverse discordance (from −10.5 to −2.6%) with a 208Pb/232Th mean age 988.4 ± 5.9 Ma (95% conf., MSWD = 0.75, n = 71), which is within uncertainty with a 207Pb/235U mean age 979.1 ± 5.0 Ma (95% conf., MSWD = 1.4, n = 22) yielded by data filtered to below ±5% discordance (i.e., from −5.0 to −2.6%). The altered xenotime domains (Xtm2) provided highly scattered dates, including 208Pb/232Th dates from 200 ± 14 to 2135 ± 120 Ma (n = 135). Discordant UPb data yielded upper intercept age 909 ± 16 Ma (MSWD = 7.9). EPMA Th-U-total Pb measurements and compositional characteristics of uraninite inclusions indicate three age populations of ca. 852–983, 594–687 and 37–101 Ma.TEM investigations revealed initial alterations within domains Xtm1, representing a primary xenotime, which progressed along parallel submicron- to nanoscale fractures. These fractures represent partially open grain boundaries, which are empty or are filled with secondary inclusions of (Th, U)-silicates, uraninite or coffinite. The submicron-sized inclusions are accompanied by subdomains of (Th, U)-depleted xenotime. Altered xenotime (Xtm2) is well crystalline in TEM imaging and electron diffraction patterns in contrast to primary unaltered xenotime domains (Xtm1) that demonstrate, in Raman spectra, moderate degree of radiation damage caused by U and Th decay. Secondary inclusions of Th and U phases are nanocrystalline or amorphous, which increases their potential for Pb-loss or accumulation of Pb in excess. Some of them contain nanoinclusions of Pb3O4 or metallic Pb, whereas <100 nm-sized inclusions of (Pb, Sb)-oxide formed in the altered xenotime.To summarize, this study provides important insights for our understanding of coupled dissolution-reprecipitation processes that affect xenotime and mobilization of released U, Th and Pb. Removal of highly mobile U in a fluid, and the presence of nanoinclusions of Pb3O4, (Pb, Sb)-oxide and metallic Pb have particular importance for xenotime dating and explain disturbance towards older ages. Nevertheless, both removal of U, Th and Pb from altered and recrystallized xenotime as well as presence of submicron- to nanoinclusions can result in age disturbance resulting in spread of dates along a concordia curve.

Ultrafast microstructure modification by pulsed electron beam to enhance surface performance

Pulsed electron beam surface treatment was used to enhance the microstructure and surface mechanical properties. After treatments with different electron beam energy densities, the microstructure and nano-structure of additively manufactured Al-Mg alloys were evaluated by scanning and transmission electron microscopy. At high Es (15 J/cm2) treatment, there is around 30–35 μm melting layer and the new second phase with complex elemental composition (Mn4.6Fe0.4Si3) in the surface modification layer. Thermal stress within different Es has a different effect on the second phase and dislocations, and the thermal stress in high Es improves the dissolution of submicron-sized inclusions presented in the initial state to form new particles. KAM (Kernel Average Misorientation) maps and calculated values prove that the electron beam irradiation increases the degree of local misorientation and surface stress. As Es is up to 15 J/cm2, the value of KAM and stress, as well as the dislocation, is the maximum. The formation of subgrains and precipitates with complex elemental composition after irradiation has comprehensive effects on the nano-hardness, wear rate and friction coefficient. It reveals that the nano-hardness and the friction coefficient of samples irradiated by 15 J/cm2 have the highest and the lowest values, respectively.

Development of nano-structure China low-activation martensitic steel for fusion reactors

Herein, we report a new castable nanostructured alloy (CNA), which was first melted in a vacuum induction furnace to introduce micron- and submicron-sized inclusions, strengthened by the multiscale secondary phases for fusion reactors. The large micron-scale inclusions are removed, whereas submicron-scale inclusions were retained during an electroslag remelting process. The ingot was subjected to heat treatment at 1050 °C for 0.5 h followed by heating at 650 °C for 1.5 h to obtain tempered martensite along with the nanosized (Ti, W) carbides. The improvement in the mechanical properties of the sample treated at 750 °C was attributed to the removal of blocky Y-rich inclusions along with the strengthening of the submicron-sized Y2O3 oxides. The performance of the sample treated at 650 °C was explained by the precipitation of the fine (Ti, W) carbides.

Development of a micro-scale Y–Zr–O oxide-dispersion-strengthened steel fabricated via vacuum induction melting and electro-slag remelting

Abstract In this paper, the CLAM steel strengthened by micro-scale Y–Zr–O was prepared by vacuum induction melting followed by electroslag remelting (VIM-ESR). Yttrium (Y) and zirconium (Zr) were easy to aggregates into massive yttrium-zirconium-rich inclusions in the steel melted by vacuum induction melting (VIM), which would interrupt the continuity of the matrix and reduce the mechanical properties of steel. Micron-sized Y–Zr–O inclusions would be produced with the removal of original blocky Y–Zr-rich inclusions and the submicron-sized inclusions smaller than 0.2 μm could be retained in the steel. The small grain size and the better refinement and distribution uniformity of Y–Zr–O inclusions after remelting would be responsible for the better yield strength and toughness. For VIM-ESR alloy, the ultimate tensile strength is 749 MPa and the yield strength is 642 MPa at room temperature, meanwhile they are 391 MPa and 367 MPa at 600 °C, respectively. Meanwhile, the ductile-brittle transition temperature (DBTT) reduced from −43 °C (VIM) to-76 °C (VIM-ESR).

LA-ICP-MS Trace-Element Analysis of Pyrite from the Huanxiangwa Gold Deposit, Xiong’ershan District, China: Implications for Ore Genesis

The Huanxiangwa deposit is a major gold deposit in the Xiong’ershan district, which is the third-largest gold-producing district in China. Pyrites from the Huanxiangwa deposit were investigated using ore microscopy and laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS). Pyrite is the dominant Au-bearing mineral in the Huanxiangwa deposit and can be divided into two types: medium- to fine-grained subhedral-anhedral pyrite (Py1) disseminated in altered rocks and coarse-grained subhedral-euhedral pyrite (Py2) hosted in auriferous quartz veins. LA-ICP-MS time-resolved depth profiles show that invisible gold occurs primarily as solid solution or as homogeneously distributed nanoparticles of native gold, electrum, or Au-Ag-Te minerals in Py1, whereas it is present mainly as nano- to submicron-sized inclusions of complex Au-Ag-Cu-Pb-Zn domains in Py2. The presented data indicate that the Huanxiangwa deposit resulted from two episodes of hydrothermal mineralization associated with two distinct source reservoirs. The first episode of mineralization was linked to the dehydration of deep-seated mafic-ultramafic metamorphic rock during the Triassic collision of the North China Craton with the Yangtze Craton. The second episode of mineralization was related to hydrothermal activity resulting from Early Cretaceous I-type granitic magmatism.

Effect of Y/Zr Ratio on Inclusions and Mechanical Properties of 9Cr-RAFM Steel Fabricated by Vacuum Melting

This study investigates the inclusions, microstructures, tensile properties, and impact toughness of reduced-activation ferritic/martensitic (RAFM) steels with different Y/Zr ratio contents. An optical microscope and a scanning electron microscope (SEM) were employed to determine the size and number of inclusions, and SEM and transmission electron microscope were employed to examine the inclusion types. The increase in Y/Zr ratio influenced the prior austenite grain size owing to the pinning effect of the inclusions. The result of this examination showed that the mechanical properties of the steel are closely related to the refinement of prior austenite grain size and as well as the fine submicron-sized inclusions. The average prior austenite grain sizes of the alloys were 14.5, 13.5, and 13.4 μm for the steels with different Y/Zr ratio contents (i.e., 1/2, 5/3, and 11/2, respectively). Moreover, the submicron-sized inclusions in the alloys achieved densities of 4.71 × 1016, 4.49 × 1016, and 3.84 × 1016/m3. The ductile-to-brittle transition temperature (DBTT) decreases when the Y/Zr ratio increases to 5/3. However, the DBTT increases when the Y/Zr ratio reaches 11/2 owing to inclusion coarsening. The RAFM steel with Y content of approximately 0.005 wt.% and Zr content of 0.002 wt.% was verified to exhibit an optimized combination of microstructures, tensile properties, and impact toughness.

TRACE ELEMENT SIGNATURE OF PYRITE FROM THE LOS COLORADOS IRON OXIDE-APATITE (IOA) DEPOSIT, CHILE: A MISSING LINK BETWEEN ANDEAN IOA AND IRON OXIDE COPPER-GOLD SYSTEMS?

Although studies have proposed that iron oxide-apatite (IOA) deposits may represent the deeper roots of some Andean iron oxide copper-gold (IOCG) systems, their genetic links remain obscure and controversial. A key question when considering an integrated genetic model is whether a magmatic-hydrothermal fluid that precipitates massive magnetite will continue transporting significant amounts of dissolved Fe, Cu, and Au after IOA precipitation. Here we provide new geochemical data for accessory pyrite from the Los Colorados IOA deposit in the Chilean iron belt that confirm the role of this sulfide as a relevant repository for economic metals in IOA deposits. Pyrite occurs at Los Colorados as disseminated grains and as veinlets associated with magnetite and actinolite that postdate the main igneous magnetite stage. Electron probe microanalysis (EPMA) data for pyrite show anomalously high Co and Ni concentrations (up ~3.9 and ~1.5 wt %, respectively) and relatively high As contents (100s of ppm to a maximum of ~2,000 ppm). When combined with results from secondary ion mass spectrometry (SIMS) spot analyses, pyrite data show significant amounts of Cu that range from sub-ppm values (~100 ppb) up to 1,000s of ppm, plus nonnegligible concentrations of Zn, Pb, Cd, Sb, Se, and Te (up to ~100 ppm). The highest contents of Cu measured (wt % level) most likely record the presence of Cu-bearing submicron-sized mineral inclusions. Contents of Au and Ag are up to ~1 and 10 ppm, respectively, with maximum concentrations that can rise up to ~800 ppm Au and ~300 ppm Ag due to the presence of submicron-sized inclusions. The high Co/Ni ratios of pyrite from Los Colorados are consistent with a magmatic-hydrothermal origin associated with a greater mafic affinity, compared to pyrite from porphyry Cu deposits. Furthermore, the geochemical signature of Los Colorados pyrite shares important similarities of composition and microtexture with the few published data for pyrite from IOCG deposits (e.g., Ernest Henry, Australia, and Manto Verde, Chile). These findings, combined with recent geochemical and isotopic studies that support an igneous origin for the dike-shaped magnetite orebodies at Los Colorados, point to a magmatic source of mafic to intermediate composition for the contained metals, and support the hypothesis that IOA systems can source Fe-Cu-Au-rich fluids. Based on experimental studies, these IOA-derived fluids may continue transporting significant amounts of metals to form IOCG mineralization at shallower levels in the crust.

Localization of submicron inclusion re-equilibration at healed fractures in host garnet

Microstructures in Permian inclusion-bearing metapegmatite garnets from the Koralpe (Eastern Alps, Austria) reveal re-equilibration by coarsening of abundant submicron-sized inclusions (1 μm–2 nm diameter) at the site of healed brittle cracks. The microstructures developed during Cretaceous eclogite-facies deformation and the related overprinting of the host–inclusion system. Trails of coarsened inclusions (1–10 μm diameter) crosscut the garnet, defining traces of former fractures with occasional en-echelon overlaps. Trails are flanked by 10- to 100-μm-wide ‘bleaching zones’ characterized by the absence of ≤1-μm-sized inclusions in optical and SE images. FEG-microprobe data show that trails and bleaching zones can form isochemically, although some trails exhibit non-isochemical coarsening. Cross-correlation-based EBSD analysis reveals garnet lattice rotation of up to 0.45°, spatially correlated with bleaching zones. The garnet lattice in the center of trails is misoriented around different axes with respect to the lattice either side of the trail. Elevated dislocation density within bleaching zones is confirmed by TEM observations. Dislocations represent a plastic wake formed by crystal plastic deformation at the crack tip. Fracture enhanced diffusion rates in the lattice adjacent to crack planes by introducing dislocations, priming these areas to behave differently to the bulk of the garnet during Cretaceous metamorphism and facilitating localized coarsening of inclusions. Diffusion within the bleaching zone was enhanced by a minimum factor of 102. The partially closed host–inclusion system records the influence of deformation mechanisms on re-equilibration and contributes to understanding of the interaction between deformation and chemical reaction during metamorphism.

Spectroscopic features of nonlinear AgGaSe2 crystals

When producing large AgGaSe2 single crystals of high optical quality, the shadow and light scattering techniques were found effective. Annealing in proper atmosphere allows one to affect the crystal composition and the state of submicron-sized inclusions and point defects. Stoichiometric crystals demonstrate mainly photoluminescence (PL) of free excitons. New PL bands, a 727/745nm doublet and a 950nm broad band, are associated with selenium vacancy, VSe, and cation antisite defect, GaAg, respectively. Using the thermoactivation spectroscopy, the traps of charge carriers were revealed in AgGaSe2: those with thermal activation energy ET>0.4eV were found responsible for photoinduced absorption on the 0.1cm−1 level.

Distinctive properties of rock-forming blue quartz: inferences from a multi-analytical study of submicron mineral inclusions

AbstractThe study discusses the mineralogical, geochemical and thermometric properties of rock-forming blue quartz from eight worldwide occurrences. Compared to non-blue quartz, blue quartz contains significant amounts of submicron-sized (1 μm—100 nm) and nanometre-sized (&lt;100 nm) inclusions. Mica, ilmenite and rutile constitute the most abundant submicron-sized inclusions, and are formed probably by syngenetic precipitation in the boundary layer between quartz and melt (entrapment model). Nanometre-sized rutile possibly originated by epigenetic exsolution of Ti from the quartz structure (exsolution model). Rayleigh scattering of light by nano-particulate inclusions best explains the origin of the blue colour. Blue quartz is generally Ti-rich (∼100—300 ppm) and formed at high temperatures (∼700°C—900°C). The large number, and high spatial density, of tiny xenocrystic inclusions of Ti-bearing minerals make calculations of crystallization temperatures using the Ti-in-quartz thermometer unreliable. The geological significance of blue quartz remains obscure.

Se, As, Mo, Ag, Cd, In, Sb, Pt, Au, Tl, Re traces in biogenic and abiogenic sulfides from Black Shales (Selwyn Basin, Yukon territories, Canada): A nuclear microprobe study

Black shales can be an important source of rare metals such as Cu, Ag, As, Mo, Se, Tl, Cd, platinum group elements (PGE) and gold (Pasava et al., Econ. Geol. 91 (1996) 63). However, especially in the case of noble metals, carriers such as discrete minerals could not be identified. This nuclear microprobe study brings new data on the partition of rare metals in Fe-, Fe (Ni)-, Ni- (Fe)-, Ni- and Zn-sulfides from the Ni-Zn-Mo-PGE mineralized marin black shales (Selwyn Basin, Yukon Territories). Sulfides are present as mineralized vestimentiferan tube-worms which are pyritized. Fluid-mineral interaction led to transformation of these biogenic Fe-sulfides successively to Fe–Ni- and Ni–Fe-sulfides which is indicated by increasing Se contents. Ni-sulfides which are interstital to the tube worms represent remobilized material, they are richest in Se. Several tens to thousands ppm of Cu, Zn, As, Se, Mo were located in the biomineralized and transformed tube worms. Antimony was located in Fe–Ni and Ni-, and Zn sulfides and Ag was present in Fe–Ni and Ni–Fe-sulfides. Pt and Au can also be related to submicron-sized inclusions in Fe–Ni sulfides. Hydrothermal fluids (at least 250 °C) precipitated silica around tube worms, intercalating submicron-sized sphalerites. Larger Zn-sulfides contain about 5000 ppm Cd and locally about 60 ppm In. Ba-rich K-feldspar contains Cl-rich Ag–Cd alloys.

Cathodoluminescence evaluation of dark spot defects in InP/InGaAsP light-emitting diodes

In this study, the formation of dark spot defects (DSD’s) in InP/InGaAsP light-emitting diodes (LED’s) is evaluated by cathodoluminescence imaging and energy dispersive x-ray spectroscopy (EDS). Defects resulting in DSD’s are shown to be located in either the p-InGaAsP contact layer, the p-InP confining layer, or the InGaAsP active layer. The presence of gold was not detected at the DSD’s using EDS. However, gold was found in the form of submicron-sized inclusions in the contact layer and confining layer of cylindrically lapped wafers using EDS. Our results strongly suggest that the migration of gold from the p contact during device processing and aging results in the formation of DSD’s in InP/InGaAsP LED’s.