Cathodoluminescence Characteristics Research Articles

Origin of hydrothermal dolomitization in the Huize Zn–Pb ore district, SW China: Insights from in situ U–Pb dating, fluid inclusion, and C–O–Sr–Mg isotope analyses

The temporal and genetic association between Mississippi Valley-type (MVT) Zn–Pb mineralization and hydrothermal dolomitization remains controversial. To determine the origin of hydrothermal dolomite and its genetic links with the MVT ore deposit, detailed petrographic observations and geochemical analyses were conducted on various carbonates from the giant Huize MVT Zn–Pb ore district in SW China. The following paragenetic sequence of the carbonates (from the early to late stages) was established: host limestone (ML), early diagenetic micritic dolostone (D1), late diagenetic or pre-ore fine- to medium-grained ferroan dolostone (D2) and medium- to coarse-crystalline non-ferroan dolostone (D3), pre-ore reworked D3 dolomite (D3o), ore-related void-filling dolomite cement (DC), and calcite cement (CC) related to sulfide mineralization. D2, D3, DC, and CC exhibit higher homogenization temperatures for fluid inclusion than the burial temperature, indicating a hydrothermal origin. Geochemical data indicate that D2, D3, D3o, DC, and CC display oxygen isotope depletion and radiogenic Sr isotope enrichment signatures relative to D1. Their parent fluids have more positive δ18O values and similar or lower δ26Mg values relative to those of D1 and seawater. These geochemical proxies indicate that the pre-ore hydrothermal dolomites (D2 and D3) formed from modified seawater circulated in the underlying sandstone aquifers through fault-related thermal convection. DC and CC, related to Zn–Pb mineralization, were formed by the dissolution and reprecipitation of preexisting carbonates. Sphalerite shows higher temperatures and salinities compared with D2 and D3 dolostones, indicating that the ore-forming fluid, different from the hydrothermal dolomitizing fluid, originated from a deep-sourced brine. In situ U–Pb dating of D3o reveals that the pre-ore hydrothermal dolomitization occurred at 253.7 ± 8.7 Ma, and a late-stage hydrothermal imprint occurred at 203 ± 11 Ma, likely related to tectono-thermal events, including the Emeishan large igneous province and Indosinian Orogeny, respectively. These findings imply that the hydrothermal dolomitization and Zn–Pb mineralization in the Huize ore district are likely associated with the multistage basin and basement fluid flows driven by elevated geothermal gradient and tectonic compression, respectively. The void-filling DC and CC and their cathodoluminescence characteristics are useful indicators for MVT Zn–Pb ore exploration.

Diagenetic archives of the deeply-buried Cambrian Xiaoerbulake Formation microbialite reservoirs, Bachu-Tazhong area, Tarim Basin, China

The deep-burial Cambrian Xiaoerbulake Formation microbialites reservoir hosts significant hydrocarbon in the Tarim Basin. However, limited understandings of fluid-rock interactions from deposition to deep-burial regimes hamper petroleum exploration. Here, petrological observations, in-situ elemental contents and porosity-permeability analyses were performed to understand the complex interactions and the microbialites performance. Dolo-mudstone, crystalline dolostone, and four kinds of microbialites are distinguished as dolostones types. In the depositional stage, microbialites are characterized by (evaporated) seawater dolomitization with the mediation of microbial activity. The dolostone matrix shows seawater-like δ13C, δ18O and REY patterns. Thrombolitic and foam spongy dolostones from high-energy subtidal to intertidal zones show large framework pores compared to stratiform stromatolitic dolostones from low-energy intertidal zones. In near-surface settings, meteoric diagenesis generates secondary pores, while fine-crystalline dolomite cements partially fill pores. During the shallow to intermediate burial regimes, medium-to coarse-crystalline dolomite cements yield negative δ18O values and slightly flat REY patterns. The precipitation of this dolomite phase further decreases reservoir porosity. In deep burial settings, one type of saddle dolomite is likely to be formed by replacement from carbonate precursors, while the second type might be directly precipitated from hydrothermal fluids. These two types of saddle dolomites show different cathodoluminescent characteristics and geochemical data. Subsequently, two types of calcite cements are formed by the calcification of dolomite and yield significant negative δ13C values due to thermochemical sulfate reduction. Finally, the third calcite phase is likely to be a direct precipitate from burial brines. Hydrothermal activity and thermochemical sulfate reduction generate and/or re-distribute secondary pores. Based on the plethora of depositional environments and fluid-rock interactions, thrombolitic dolostone generally yields higher porosity-permeability than other types of microbialites. Thrombolite reservoir has high potential for petroleum exploration and is significant for those concerned with microbialite hydrocarbon fields.

Crystallization processes of quartz in a granitic magma: Implications for the magma chamber processes of Okueyama granite, Kyushu, Japan

Cathodoluminescence (CL) characterization combined with titanium concentration of quartz crystals in granite is a prevalent tool for elucidating the crystal growth of quartz in granitic magmas. The CL pattern yields to the internal structure, and the titanium concentration allows crystallization temperature determination based on TitaniQ geothermometry. Using two approaches, 1) observations of quartz crystals using thin sections and 2) observations based on multiple sections of separated quartz, we identified the overall characteristics of quartz crystals within a magma chamber and the 3D internal structure and growth characteristics of quartz grains. Thin section observations allow for the characterization of quartz containing zircon inclusions, indicating that zircon crystallization was followed by quartz crystallization; therefore, the onset of quartz crystallization occurred later than the onset of zircon crystallization in the cooling magma chamber. Such petrological restrictions permit allow for suitable geothermometer use and appropriate TiO2 activity estimation, and thus, accurate quartz crystallization temperature determination. Observations using multiple sections of separated quartz crystals provide 3D internal structures and true onset parts within the grains. Progressive variation in local activities of TiO2 in the concentration boundary layer at the growing quartz crystal interface in the magma chamber can be evaluated using a combination of the crystallization temperature and variations in titanium concentration within the grain, yielding a sequential crystallization model of oscillatory zoning quartz with local activities of TiO2 in the cooling magma chamber. The difference in CL characteristics and crystallization temperature among the lithofacies in granite contributes to clarifying the spatiotemporal magma chamber processes.

Analysis of Nanowire pn-Junction with Combined Current-Voltage, Electron-Beam-Induced Current, Cathodoluminescence, and Electron Holography Characterization.

We present the characterization of a pn-junction GaAs nanowire. For the characterization, current-voltage, electron-beam-induced current, cathodoluminescence, and electron holography measurements are used. We show that by combining information from these four methods, in combination with drift-diffusion modelling, we obtain a detailed picture of how the nanowire pn-junction is configured and how the recombination lifetime varies axially in the nanowire. We find (i) a constant doping concentration and 600 ps recombination lifetime in the n segment at the top part of the nanowire; (ii) a 200-300 nm long gradient in the p doping next to the pn-junction; and (iii) a strong gradient in the recombination lifetime on the p side, with 600 ps lifetime at the pn-junction, which drops to 10 ps at the bottom of the p segment closest to the substrate. We recommend such complementary characterization with multiple methods for nanowire-based optoelectronic devices.

Genesis of the Tiemuli skarn W–Fe deposit in the Nanling region, South China: Constrains from multi-mineral U-Pb geochronology and scheelite geochemistry

The Tiemuli scheelite-magnetite (W-Fe) deposit is located in the central part of the Nanling region, South China and contains five skarn-type ore bodies that are associated with the Tiemuli porphyritic granite. The mineralization process of this deposit can be divided into three stages: the prograde skarn, the retrograde skarn, and the quartz-sulfide-calcite stages. Zircon grains from the porphyritic granite yielded a U-Pb age of 138±1 Ma. The vesuvianite and garnet grains from the prograde skarn stage yielded a weighted mean 206Pb/238U age range of 139–136 Ma. The apatite and cassiterite from the retrograde stage exhibited a weighted mean 206Pb/238U age range from 138 to 136 Ma. These U-Pb ages suggest that the Tiemuli granite emplacement and W–Fe skarn mineralization occurred during the Early Cretaceous period. Based on the cathodoluminescence (CL) characteristics, two generations of scheelite were identified. Sch-I showed homogeneous luminescence, whereas Sch-II exhibited a complex core-mantle-rim texture. REE was incorporated into scheelite following the substitution mechanism of 3Ca2+ = (2REE)3+ + □Ca, allowing the scheelite to effectively reflect the REE features of the ore-forming fluids. The Mo concentration and Eu anomaly in the scheelite reflected fluctuation in the fluid conditions during the scheelite crystallization. While transiting from the prograde to retrograde skarn stage, the hydrothermal fluid shifted from a relatively reducing environment to a relatively oxidizing environment. The Tiemuli deposit is characterized by the reductive skarn mineralization that occurred during the Early Cretaceous lithospheric expansion. Variations in the physicochemical characteristics of the fluids and fluid-rock interaction played crucial roles in the W–Fe mineralization of the Tiemuli deposit. Thus, this deposit serves as a unique example of a W–Fe mineralization event in the Nanling region of South China during the Early Cretaceous.

Cathodoluminescence and geochemical characteristics of Apatite: Implications for mineral exploration in the Xiongcun District, Tibet, China

Apatite grains from the No. 2 porphyry Cu–Au deposit in the Xiongcun district of Tibet, China, have a range of physical and compositional features. This study investigates the potential use of apatite associated with hydrothermal alteration as a tool for mineral exploration. In situ textural, cathodoluminescence (CL), and chemical analyses were performed on thin sections containing apatite from various alteration zones in the deposit. No clear variation was seen in apatite from rocks of the potassic, sodic–calcic, chlorite–sericite, phyllic, and propylitic alteration zones using visible light and scanning electron microscopy; however, distinct variations were observed in optical cathodoluminescence (OP-CL) (dark yellow to green, orange to green, yellow–brown to green, yellow-orange to brown, and light yellow–brown to green luminescence for the respective zones). The alteration-related differences in luminescence were a result of the interaction between Fe and Mn; the Na and Cl contents; and depletion in total heavy rare earth elements (ΣHREE) and Y. The variations in the REE contents of apatite from different types of altered rock record reactions with Cl- and F-rich fluids. The partitioning behavior of Cl between apatite and hydrothermal fluids is influenced by pressure, temperature, pH, and fluid composition, whereas the partitioning of F between apatite and fluids is dependent on the fluid composition and not the temperature. At high temperatures, Eu3+ is reduced to Eu2+, which results in negative Eu anomalies in apatite from the potassic-altered rocks and propylitic-altered rocks. Apatite grains in the sodic–calcic-altered rocks and chlorite–sericite-altered rocks show a similar enrichment in light REEs (LREEs) that resulted from REE and Y incorporation as follows: Na+ + (Y + REE)3+ = 2Ca2+. Apatite grains in the phyllic-altered rocks are enriched in the middle REEs. This study confirms that the luminescence, chemical composition (including Fe, Mn, Na, Cl, ΣHREE, and Y contents), and REE patterns of apatite can be affected by hydrothermal alteration; therefore, these results may be used to constrain the evolution of ore-forming hydrothermal fluids and may offer an effective tool for mineral exploration.

White luminescent emissions from HfO2 and HfO2:Al3+ layers deposited by ultrasonic spray pyrolysis technique

Polycrystalline HfO2 and HfO2:Al3+ coatings were synthesized by the spray pyrolysis technique. The photoluminescence and cathodoluminescence characteristics of the coatings were studied as a function of the synthesis parameters; the temperature of deposition and the dopant content (Al3+ions). A blue, bluish-white and warm white emission was found in the coatings, depending on the substrate temperature, doping concentration and excitation wavelength. The photoluminescence emission was enhanced with the increment of the deposition temperature and a quenching effect was also observed with the dopant concentration. The CIE chromatic coordinates: (0.3067, 0.3462), (0.3091, 0.3502) and (0.3073, 0.3498), were close to the ideal white emission. CCT values for some of the coatings make them potentially useful in white lighting systems. The structural characterization was also carried out by X-ray diffraction, SEM, HRTEM and EDS elemental composition.

Application of blocky calcite vein LA-MC-ICP-MS U–Pb dating and geochemical analysis to the study of tectonic–fault–fluid evolutionary history of the Tabei Uplift, Tarim Basin

In this work, blocky calcite veins in drilling cores were studied by integrating petrography, in-situ laser ablation multiple collector inductively coupled plasma mass spectrometry U–Pb dating and trace element analysis to investigate whether calcites without obvious syn-kinematic features can constrain the timing of local fault/fracture activity and far-field tectonic movement. On this basis, a synergistic ‘tectonic–fault–fluid’ evolution model in the Tabei Uplift, Tarim Basin was developed. Cathodoluminescence characteristics, rare earth elements and U–Pb ages allow the subdivision of calcite veins into three categories. The much shorter timescales for sealing the studied calcite vein than the uncertainties of current carbonate U–Pb dating (<5 %) attest to a temporal link between calcite precipitation and fracture activity. The consistency between calcite U–Pb ages and the timing of terminal collisions of the Tarim Craton with surrounding terranes demonstrates the potential of blocky calcites to record far-field tectonics. The information on the origin of fluids and the timing of fracture activity revealed by the calcite veins is placed within the established tectonic evolutionary history of the study area, allowing the tectonic–fracture–fluid evolutionary history of the study area to be recovered. From ~466 Ma to ~454 Ma, accompanying the formation of strike-slip faults under compressional stresses resulting from the closure of the Kudi Ocean, seawater and formation fluids seeped down into the carbonate strata and eventually precipitated along the fracture walls. From ~383 Ma to ~366 Ma, continued northward subduction of the eastern Kunlun–Altyn Tagh terrane caused tectonic uplift and fault reactivation. Circulating meteoric fluid and downward seeping seawater transported by advection eventually precipitated blocky calcites. From ~287 Ma to ~232 Ma, activation of the early faults along with the closure of the Paleo-Asian Ocean promoted the formation fluids buffered by the host limestones to flow into open fractures and precipitated. This work, in a practical geological context, confirms that centimeter-scale blocky calcite veins have the potential to constrain the timing of fault slip and associated fracturing, which further boost confidence in the applicability of calcite U–Pb geochronology in dating of brittle faulting episodes.

Cathodoluminescence Characterization of Point Defects Generated through Ion Implantations in 4H-SiC

The high quality of crystal growth and advanced fabrication technology of silicon carbide (SiC) in power electronics enables the control of optically active defects in SiC, such as silicon vacancies (VSi). In this paper, VSi are generated in hexagonal SiC (4H) samples through ion implantation of nitrogen or (and) aluminum, respectively the n- and p-type dopants for SiC. The presence of silicon vacancies within the samples is studied using cathodoluminescence at 80K. For 4H-SiC samples, the ZPL (zero phonon line) of the V1′ center of VSi is more intense than the one for the V1 center before annealing. The opposite is true after 900 °C annealing. ZPLs of the divacancy defect (VCVSi) are also visible after annealing.

Heavy rare earth element and crustal-derived silicon enrichment in Huayangchuan carbonatites, Qinling orogenic belt

The Huayangchuan carbonatite is found in the North Qinling orogenic belt. It is distinguished from most carbonatites worldwide by its abundance of quartz and high heavy rare earth element (HREE) content. The origin of Si supersaturation and HREE enrichment in carbonatite is still unknown. Here, we conducted a detailed mineralogical investigation and in situ geochemical analyses on a suite of drill-core samples obtained from Huayangchuan carbonatite. In situ titanite and monazite UPb dating yielded ages of 212.3 ± 6.4 Ma and 211.8 ± 5.0 Ma, respectively, corresponding to the post-collision stage of the Qinling orogeny. Clinopyroxene and amphibole in the carbonatite are commonly intergrowth with quartz grains and trapped by quartz as mineral inclusions. The mineralogical textures and compositions indicate that quartz crystallized simultaneously with the mafic minerals from a Si supersaturation magma. The high Si activity during clinopyroxene formation may be related to Si assimilation from the wall-rocks. In situ Nd isotopic compositions of apatite and titanite show consistent εNd(t) ranging from −4.8 to −9.0, similar to the values of the whole-rocks and calcites. This indicates that the REE were derived from carbonatite magma without an external source. Two types of calcites were identified based on their cathodoluminescence characteristics, and they have variable chondrite-normalized REE patterns (La/Yb(CN) ranging from <0.01 to 19) but similar HREE contents. This implies that the carbonatite underwent strong crystal fractionation of early LREE-rich minerals, which may be essential for HREE enrichment. Therefore, we proposed that Si supersaturation in the carbonatite was probably caused by wall-rock assimilation, and fractional crystallization yielded primary HREE enrichment in the residual melts. Moreover, HREE enrichment in highly evolved carbonatites is further aided by high Si and alkaline activities.

Hyperspectral cathodoluminescence, trace element, and U-Pb geochronological characterization of apatite from the Ernest Henry iron oxide copper-gold (IOCG) deposit, Cloncurry district, Queensland

Hyperspectral cathodoluminescence (CL), geochemical, and geochronological characterization of a series of apatite-bearing samples from within and around the Ernest Henry IOCG deposit, NW Queensland, Australia, have revealed complex mineral parageneses and a spectrum of U-Pb ages that point to the effects of multiple geological processes. No two samples are identical, either in geochemistry or texture, despite their relative proximity to one another (all samples within 5 km from Ernest Henry). Hyperspectral CL maps reveal diverse internal textures and emissions ranging from near infrared (NIR) to near ultraviolet (UV) with a complex series of spectra in all samples, requiring the fitting more than 40 individual peaks (both sharp and broad) to capture the observed variability. Imaging analyses via LA-ICPMS show that apatite from the Ernest Henry district is enriched above background in a variety of trace elements, including Na, Mg, Al, Si, V, Mn, As, Sr, Y, the rare Earth elements (REEs), Pb, Th, and U. Samples outside the ore zone display chondrite-normalized REE profiles that are consistent with either a magmatic or hydrothermal origin, whereas ore zone apatite exhibits profiles that are decidedly hydrothermal in nature. Moreover, specific zones within ore zone apatite grains are very As-rich (up to 7 wt% As2O5), and the effect of such high As on the hyperspectral CL signature of these zones is a pronounced dampening of CL emission, regardless of REE concentrations. Uranium-Pb dating of the same samples (via LA-ICPMS) has yielded a diverse array of overlapping Mesoproterozoic ages ranging from 1,580 ± 34 Ma to 1,533 ± 61 Ma. These results correlate to published ages that constrain hydrothermal alteration in the Ernest Henry area, both before and during Cu-Au mineralization. Collectively, these data highlight the complexity of apatite studies at Ernest Henry, the broader Cloncurry district, and probably analogous terranes elsewhere. A combination of micro-scale methods such as those used in this study are shown to be essential for accurately deciphering geological information contained within petrogenetic indicator minerals.

Structural and Luminescent Peculiarities of Spark Plasma Sintered Transparent MgAl2O4 Spinel Ceramics Doped with Cerium Ions

In the present study, the concentration series of MgAl2O4:Ce3+ ceramics have been fabricated by the Spark Plasma Sintering (SPS) method. Cerium-doping concentration was varied within a range of 0.1–5 wt.%. The prepared ceramics have been tested using the various experimental techniques: X-ray diffraction (XRD), scanning electron microscopy, as well as optical and cathodoluminescence spectroscopy. According to XRD, all synthesized samples are biphasic with structural impurities. The cerium ion concentration effect on the cathodoluminescent characteristics of MgAl2O4:Ce3+ ceramics has been studied in terms of emission intensity and decay time. Before annealing the concentration, quenching is observed. The optimal doping Ce3+ concentration was determined to be 5 wt.% after temperature annealing at 1300 °C. The successfully prepared spinel ceramics could be potentially applying for high-energy electrons detection.

Seeking new, ultra-narrow-band blue emitting phosphors with high color purity for wide color gamut displays

Ultra-narrow-band phosphors have gained widespread applications in lighting and displays to enhance brightness and improve color saturation. Typical phosphor designs employ UCr4C4-type compounds and designing new narrow-band phosphors with high color purity is a major challenge. Here, we explored a Eu2+-doped Ba5GeO4Br6 phosphor, showing a narrow-band blue emission (λem = 436 nm) excitation at the near-ultraviolet light with a full width at half maximum of 30.7 nm and high color purity of 96.6%. In addition, attractive cathodoluminescence characteristics were systematically analyzed by varying filament current (30–70 mA) and accelerating voltage (3–7 eV). Robust anti-degradation behavior and color point stability under continuous electron beam bombardment were confirmed. Given its excellent performance in photoluminescence and cathodoluminescence, application in wide color gamut displays appears promising. Using commercial phosphors β-SiAlON:Eu2+ and K2SiF6:Mn4+ as green and red light converters respectively, and the title phosphor as the blue light converters, the fabricated w-LED exhibits a wide color gamut of 82% NTSC.

The Marinoan cap carbonate of Svalbard: Syngenetic marine dolomite with 17O‐anomalous carbonate‐associated sulphate

AbstractTwo cap carbonates overlying Cryogenian panglacial deposits are found in North‐East Svalbard of which the younger (635 Ma) forms the base of the Ediacaran Period. It is represented by a transgressive succession in which laminated dolostone, typically around 20 m thick (Member D1), is succeeded transitionally by a similar thickness of impure carbonates (Member D2). In Spitsbergen, there is evidence of microbially influenced sediment stabilisation and carbonate precipitation in the lower part of D1, whilst the upper part of D1 and D2 show centimetre‐decimetre‐scale graded units with undulatory lamination interpreted as evidence of storm activity. Carbonate originated as possible freshwater whitings, as well as microbial precipitates. Exhumed and eroded hardgrounds display replacive 10–30 μm dolomite crystals with cathodoluminescence characteristics consistent with early diagenetic manganese and iron reduction. Regionally, carbon isotope values consistently decrease by around 2‰ from around −3‰ over 30 m of section which is both a temporal and a bathymetric signal, but not a global one. An exponential decline in carbonate production predicted by box models is fitted by a semi‐quantitative sedimentation model. A mass‐anomalous 17O depletion in carbonate‐associated sulphate in dolomite, inherited from precursor calcite, decreases from −0.6 to −0.3‰ in the basal 15 m of section and then approaches background values. The post‐glacial anomalous 17O depletion in carbonate‐associated sulphate and barite elsewhere has been interpreted in terms of ultra‐high pCO2 at the onset of deglaciation. Such anomalies, with larger amplitude, have been reported in Svalbard from underlying lacustrine and tufaceous limestones representing a hyperarid glacial environment. The anomalous sulphate could be produced contemporarily, or the internally drained landscape may have continued to release 17O‐anomalous sulphate as it was transgressed during cap carbonate deposition. The late Cryogenian to earliest Ediacaran record in Svalbard provides the most complete record of the basal 17O‐depletion event in the world.

Role of Temperature in Arsenic-Induced Antisurfactant Growth of GaN Microrods

Due to the antisurfactant properties of arsenic atoms, the self-induced dodecagonal GaN microrods can be grown by molecular beam epitaxy (MBE) in Ga-rich conditions. Since temperature is a key parameter in MBE growth, the role of temperature in the growth of GaN microrods is investigated. The optimal growth temperature window for the formation of GaN microrods is observed to be between 760 and 800 °C. Lowering the temperature to 720 °C did not change the growth mechanism, but the population of irregular and amorphous microrods increased. On the other hand, increasing the growth temperature up to 880 °C interrupts the growth of GaN microrods, due to the re-evaporation of the gallium from the surface. The incorporation of As in GaN microrods is negligible, which is confirmed by X-ray diffraction and transmission electron microscopy. Moreover, the photoluminescence and cathodoluminescence characteristics typical for GaN are observed for individual GaN microrods, which additionally confirms that arsenic is not incorporated inside microrods. When the growth temperature is increased, the emission related to the band gap decreases in favor of the defect-related emission. This is typical for bulk GaN and attributed to an increase in the point defect concentration for GaN microrods grown at lower temperatures.

Prolonged grain boundary sliding in naturally deformed calcite marble at the middle crustal level

It is generally accepted that grain boundary sliding (GBS) is the dominant deformation mechanism in fine-grained strain localization zones. However, the lifetime of GBS during deformation in monomineralic rocks is hotly debated, as grain growth may inhibit the operation of GBS. In this contribution, recrystallized matrix grains in calcite marbles from the Jinzhou detachment fault zone at the middle crustal level, Liaodong Peninsula, Northeast China, show clear evidence of GBS, e.g., 1) fine grains with sizes of 5–30 μm, nearly equant grain shapes and slightly curved grain boundaries, 2) rare evidence for intracrystalline deformation, 3) existence of four-grain junctions and aligned straight grain boundaries, and 4) weak crystallographic preferred orientations. The existence of high misorientation zones along the margins of the matrix grains, especially at their triple junctions, and differences in cathodoluminescence (CL) characteristics between rims and cores of the grains indicate simultaneous accommodation of GBS by dislocation motion and grain boundary diffusion. The different CL characteristics between rims and cores of calcite matrix grains and the presence of calcite-filled cracks imply fluid activity during deformation. Fluids could dramatically enhance GBS by promoting dislocation motion and grain boundary diffusion. Additionally, the nucleation of fine grains by dynamic recrystallization and cavitation-sealing processes during GBS guaranteed the maintenance of GBS. At the same time, the occurrence of micropores and the existence of second phases also inhibit grain growth. These features make GBS the dominant deformation mechanism in naturally deformed marbles in the middle-upper crust.

Tungsten mineralization process and oxygen fugacity evolution in the Weijia W deposit, South China: Constraints from the microstructures, geochemistry, and oxygen isotopes of scheelite, garnet, and calcite

Scheelite is a major (W)-bearing mineral enriched in rare earth elements (REEs) and is widely used to investigate the mineralization process, fluid source and redox environment of W deposits. In the Weijia skarn-type W deposit in South China, scheelite was formed during the greisen, retrograde skarn, oxidation, and sulfide-quartz vein stages. Various characteristics of cathodoluminescence (CL) images of scheelite grains (e.g., light to dark color, core-rim texture and oscillatory zonation) have recorded their detailed crystallization process. Scheelite grains formed in the greisen and retrograde skarn stages have similar LREE patterns, and the gradual fractionation in HREEs may be a result of the precipitation of garnet (And38-70Gr29-52Pr1-3) in the prograde skarn stage. In addition, the similar REE patterns of scheelite from the greisen stage and the granite porphyry pluton suggest a genetic relationship. The oxygen isotopic compositions of scheelite and quartz are all plotted near the edge of the magmatic fluid field, confirming their derivation from the same magmatic hydrothermal fluid. Elemental mapping and spot analyses using an electron probe microanalyzer indicated that extensive isomorphic substitution of W by molybdenum (Mo) occurs in scheelite, and the darker color in the CL images corresponds to a higher Mo content and lower W content. The Mo content of scheelite gradually increased from the greisen stage (mean = 0.46%), through the retrograde stage (mean = 2.89%), to the oxidation stage (mean = 19.8%), and then dropped sharply in the sulfide-quartz vein stage (mean = 0.20%), indicating a change in oxygen fugacity. Moreover, scheelite formed in the sulfide-quartz vein stage has an oscillating Mo content, thus implying a slight or periodical change in oxygen fugacity during the same mineralization stage.

Formation and optical characteristics of GaN:Eu/GaN core–shell nanowires grown by organometallic vapor phase epitaxy

We report on the formation and optical characteristics of Eu-doped GaN (GaN:Eu)/GaN core–shell nanowires (NWs) grown by organometallic vapor phase epitaxy. A moderate V/III ratio and growth temperature enable the incorporation of Eu3+ ions into the GaN shells on GaN core NWs, resulting in red luminescence at room temperature whose peak intensity is more than 20 times larger than for a GaN:Eu film on planar GaN. The cathodoluminescence characterization corroborates that the observed enhanced Eu luminescence originates from the predominant formation of highly efficient Eu centers in the sidewalls of the GaN:Eu/GaN core–shell NWs.

Novel Dy incorporated Ca3Y2B4O12 phosphor: Insights into the structure, broadband emission, photoluminescence and cathodoluminescence characteristics

This study reports cathodoluminescence (CL) and photoluminescence (PL) properties of undoped borate Ca3Y2B4O12 and Ca3Y2B4O12:x Dy3+ (x = 0.5, 1, 2, 3, 5, and 7) synthesized by gel combustion method. Micro-X-Ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), CL and PL under electron beam and 359 nm pulse laser excitation, respectively were used to investigate characterization and luminescence studies of synthesized samples in the visible wavelength. As-prepared samples match the standard Ca3Y2BO4 phase that belongs to the orthorhombic system with space group Pnma (62) based on XRD results. Under electron beam excitation, this borate host shows a broad band emission from about 250 to 450 nm, peaked at 370 nm which is attributed to NBHOC. All as-prepared phosphors exhibited the characteristic PL and CL emissions of Dy3+ ions corresponding to 4F9/2→6HJ transitions when excited with laser at 359 nm. The CL emission spectra of phosphors were identical to those of the PL spectra. Concentration quenching occurred when the doping concentration was 1 mol% in both the CL and PL spectra. The underlying reason for the concentration quenching phenomena observed in the discrete orange-yellow emission peaked at 574 nm of Dy3+ ion-doped Ca3Y2B4O12 phosphor is also discussed. According to these data, we can infer that this new borate can be used as a yellow emitting phosphor in solid-state illumination.

Cathodoluminescent, chemical and strontium isotopic characteristics of apatite from Lanniping Fe-Cu deposit, southwestern China: Implications for fluid evolution in IOCG systems

Apatite occurs in diverse types of hydrothermal mineral deposits and has been widely used to constrain the nature and evolution of ore-forming fluid. The origin of ore fluids responsible for formation of iron oxide-copper–gold (IOCG) deposits remains controversial. Here we combine textural observations from optical microscopic cathodoluminescence (OM-CL) and backscattered electron (BSE) images with in situ chemical and strontium isotopic analyses of apatite in the Lanniping Fe-Cu deposit in Kangdian metallogenic province, SW China, to reconstruct the hydrothermal evolution history of this deposit. Paragenetic sequences of the deposit include pre-ore Na-alteration (stage I) of predominant albite, stage II iron-oxide mineralization with the associated Ca-Fe alteration characterized by magnetite and minor apatite, stage III Cu-Fe sulfides and the associated K-Fe alteration, and final stage IV Ca-Mg alteration. Three types of apatite at different paragenetic stages were identified in this deposit. The pristine Type 1 apatite are intergrown with stage II magnetite and show blue colors under OM-CL images. The Type 2 apatite, which are darker than Type 1 apatite under BSE images, show dark yellow CL colors. They commonly occur as metasomatized domains of Type 1 apatite and can contain chalcopyrite mineral inclusions, indicating that they are coeval products during stage III. The Type 3 apatite show bright yellow CL colors, and occur as overgrowth rims of both Type 1 and 2 apatite. The Type 1 apatite have highest REY contents (5342 to 12983 ppm) and primitive 87Sr/86Sr ratios ranging from 0.70630 to 0.71093, which overlap the associated igneous intrusions. In contrast, the Type 2 and Type 3 apatite have gradually lower REY contents (866 to 4255 ppm and 142 to 635 ppm, respectively) but higher 87Sr/86Sr ratios (0.71009 to 0.71698 and 0.71904 to 0.72602, respectively). Our data hence suggest that the ore-forming fluids were mainly magmatic-hydrothermal origin and were gradually enriched in radiogenic Sr isotope by mixing with external fluid. Our case study highlights that texturally constrained apatite could be utilized to effectively trace fluid evolution of IOCG mineralization, and by reference, other hydrothermal mineralizing systems.