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Pyrite geochemistry has proven useful for tracking changes in the composition and physico-chemical conditions of hydrothermal fluids in ore-forming environments. Here, we investigated the microtextural features and chemical composition of pyrite, a main Au-bearing phase in the Akeshi and Kasuga deposits (Southern Kyushu, Japan), to better constrain the ore-forming processes in these high-sulfidation epithermal Au deposits. Despite the widespread distribution of Au-bearing pyrite in both deposits, no visible Au minerals coexist with pyrite. However, in situ laser ablation inductively coupled plasma mass spectrometry results show that Au concentrations in pyrite vary from below the detection limit to 41 ppm and are positively correlated with Cu (r = 0.4; up to 7400 ppm) and Bi concentrations (r = 0.44; up to 640 ppm). In both deposits, high Cu and Au concentrations occur in small (< 25 μm) anhedral grains of pyrite, which are interpreted to have rapidly crystallized from the ore-forming hydrothermal fluid. In addition, dissolution–reprecipitation textures and thin, concentric, Cu-rich overgrowths were identified in a number of larger (> 25 μm) pyrite grains and aggregates. These abrupt changes in the trace element compositions of pyrite grains likely record episodic metal-rich fluid inputs. We also propose that gold adsorption onto growing pyrite surfaces played a key role in the mineralization of these deposits.

The historic silver mining district of Freiberg (Germany) comprises hydrothermal vein-style mineralization of Permian and Cretaceous age. We compare sphalerite compositions with associated ore-forming fluids and constrain the behavior of critical metals such as In, Ge, and Ga in contrasting hydrothermal environments. Fluid inclusion studies reveal that the Permian veins formed due to boiling and cooling of a low-salinity (0 to 6% eq. w[NaCl]) magmatic-hydrothermal fluid at 350 to 230 °C. In contrast, Cretaceous veins formed by mixing of highly saline (17 to 24% eq. w[NaCl + CaCl2] and variable Na/(Na + Ca) ratios) brines at low temperatures (~ 120 °C). Sulfides of the Permian ore stage have a narrow range of δ34SVCDT from − 2.3 to + 0.9‰, while the sulfides of the Cretaceous stage have a large scatter and significantly more negative δ34SVCDT values (− 30.9 to − 5.5‰), supporting the different nature of the hydrothermal systems. Contrasting fluid systems and ore-forming mechanisms correspond to markedly different trace element systematics in sphalerite. Permian sphalerite is significantly enriched in In (up to 2500 μg/g In) relative to two sphalerite generations of Cretaceous veins. The latter have higher Ge (up to 2700 μg/g Ge) and Ga (up to 1000 μg/g Ga) concentrations. The observed trace element systematics of different sphalerite generations imply that In is enriched in high-temperature, low- to intermediate-salinity fluids with a significant magmatic-hydrothermal fluid component, while Ge and Ga are more concentrated in low-temperature, high-salinity crustal fluids with no obvious magmatic-hydrothermal affiliation.

It is well known that trace element sensitivity in electron probe microanalysis (EPMA) is limited by intrinsic random variation in the X-ray continuum background and weak signals at low concentrations. The continuum portion of the background is produced by deceleration of the electron beam by the Coulombic field of the specimen atoms. In addition to the continuum, the background also includes interferences from secondary emission lines, \"holes\" in the continuum from secondary Bragg diffraction, non-linear curvature of the wavelength-dispersive spectrometer (WDS) continuum and other background artifacts. Typically, the background must be characterized with sufficient precision (along with the peak intensity of the emission line of interest, to obtain the net intensity for subsequent quantification), to attain reasonable accuracy for quantification of the elements of interest. Traditionally we characterize these background intensities by measuring on either side of the emission line and interpolate the intensity underneath the peak to obtain the net intensity. Instead, by applying the mean atomic number (MAN) background calibration curve method proposed in this paper for the background intensity correction, such background measurement artifacts are avoided through identification of outliers within a set of standards. We divide the analytical uncertainty of the MAN background calibration between precision errors and accuracy errors. The precision errors of the MAN background calibration are smaller than direct background measurement, if the mean atomic number of the sample matrix is precisely known. For a simple matrix and a suitable blank standard, a high-precision blank correction can offset the accuracy component of the MAN uncertainty. Use of the blank-corrected-MAN background calibration can further improve our measurement precision for trace elements compared to traditional off-peak measurements because the background determination is not limited by continuum X-ray counting statistics. For trace element mapping of a simple matrix, the background variance due to major element heterogeneity is exceedingly small and high-precision two-dimensional background correction is possible.

The Al-rich part of the Fe-Al phase diagram between 50 and 80 at.% Al including the complex intermetallic phases Fe 5 Al 8 (ε), FeAl 2 , Fe 2 Al 5 , and Fe 4 Al 13 was re-investigated in detail. A series of 19 alloys was produced and heat-treated at temperatures in the range from 600 to 1100 °C for up to 5000 h. The obtained data were further complemented by results from a number of diffusion couples, which helped to determine the homogeneity ranges of the phases FeAl 2 , Fe 2 Al 5 , and Fe 4 Al 13 . All microstructures were inspected by scanning electron microscopy (SEM), and chemical compositions of the equilibrium phases as well as of the alloys were obtained by electron probe microanalysis (EPMA). Crystal structures and the variation of the lattice parameters were studied by x-ray diffraction (XRD) and differential thermal analysis (DTA) was applied to measure all types of transition temperatures. From these results, a revised version of the Al-rich part of the phase diagram was constructed.

The effect of thermal exposure on the microstructure and mechanical properties of Ti60 alloy was investigated in the present study. Meanwhile, the fatigue fracture microscopic appearance characteristics at elevated temperature were analyzed compared, providing the basis to further improve the performance of the series of high temperature titanium alloy. The results show that the yield strength and tensile strength were basically stable under long-term thermal exposure below 600°C, while the elongation decreased with the increase of exposure temperature. Thermal exposure below 800°C did not change the microstructure type of Ti60 alloy, but at higher temperature local β coursing occurred at the grain boundary. When the alloy was exposed above 600°C, Si was obviously concentrated in the grain boundary region, and the maximum concentration was up to 2.5%. With the increase of thermal exposure temperature, the characteristics of high-temperature fatigue fracture of Ti60 alloy change from trans-granular toughness to intergranular brittleness.

Modulated photocurrent mapping of electrical micro-junctions related to neighboring p-n zones in single or mixed phase sulphide assemblages can detect galvanic pairs which drive electrochemical reactions with overlaying fluids which is an important process for the petrophysics of geometallurgy. Understanding the role micro-junctions play in retarding or enhancing dissolution of an ore carrying sulphide requires imaging these couples near the surface and correlating them with both phase and elemental distributions. Here we apply multi-modal correlative imaging of a pyrite-sphalerite assemblage involving elemental mapping using electron and proton beam methods followed by laser beam induced current microscopy to reveal the spatial location of internal fields associated with micro-galvanic cells. This represents an important step in advancing electrochemical ore genesis models and further extends the toolkit for understanding and optimising mineral processing schemes based on specific geometallurgical footprints.

This article presents a multi-point calibration approach for electron probe microanalysis (EPMA) for the trace element analysis of indium in sphalerite (ZnS). To define a multi-point calibration curve, indium and cadmium-doped ZnS crystals in a concentration range from 0 (blank) to ~ 1500 µg / g were used. The samples were measured with two different analytical settings (25 kV acceleration voltage and 100 nA beam current as well as 7 kV and 200 nA). The figures of merit including, beam stability, lower limit of detection and limit of quantification as well as the reproducibility and precision are assessed. Equally, the line overlap of Cd and chemical shift due to non-matrix matched standards is discussed. The multi-point calibration approach results in a 2–3 times improved analytical precision compared to the classical calibration approach using only one calibration sample, and detection limits down to about 20 µg / g were achieved.

The present study was undertaken to examine the effect of iron, manganese, copper and magnesium on the microstructural characteristics of Al-11%Si-2%Cu-Mg-based alloy referred to as 396 under different working conditions. The results show that strontium (Sr) has high affinity to react with magnesium (Mg), resulting in reduced effectiveness as eutectic silicon modifier or age hardening agent. In addition, Sr alters the sequence of the precipitation of the α-AlFeMnSi phase from post-eutectic to pro-eutectic which would harden the soft α-Aluminum matrix. The mechanism is still under investigation. The interactions between iron (Fe) and Mg and Sr-Mg result in the formation of serval dissolvable intermetallics during the solutionizing treatment such as β-AlFeSi, π-AlFeMgSi and Q-AlMgSiCu phases. The study also emphasizes the role of modification and grain refining as well as intermetallics in porosity formation and hardness of samples aged in the temperature range 155–240 °C.

Wavelength dispersive analysis of tephra grains and melt inclusions by EPMA has been carried out using a focused beam of 3 µm diameter without detected loss of sodium or potassium in standard glasses, including anhydrous basalts, a slightly hydrated rhyolite and a sodium-rich intermediate composition. The ability to make analyses without chemical modification is strongly dependent upon current density at the analysis site. Analysis with narrow beams requires extremely low beam currents that are normally associated with energy dispersive analysis. Experiments indicate that a value of 0.1 nA/µm2 must not be exceeded, at least for moderately hydrated samples, if sodium loss is to be avoided. High resolution analysis without beam-induced analytical artefacts enables fully quantitative analysis of very distal and/or highly vesicular tephras and very small melt inclusions without the need to use post-analysis corrections. This development has enabled high quality analyses from crypto-tephra layers that were previously impossible to analyse, and has removed the potential for sampling bias within mixed tephra layers by making (in most cases) tephra grains accessible for analysis. The use of focused beams also increases the level of automation, and hence the cost-effectiveness of data collection. The current data suggest limits to the applicability of the beam conditions reported, and that they may lead to alkali loss in compositions most prone to beam-induced modification such as significantly hydrated and/or sodic tephras.