Large-scale high-resolution micro-XRF analysis of histological structures in the skin of the pigeon beak

Histological analysis of biological structures in the avian beak is performed by means of large scale high-resolution micro x-ray fluorescence analysis using a Maia detector system. Element maps of S, K, Ca, Fe and Zn of square millimeter sizes show distinct cellular and subcellular tissue structures in semi-thin sections with a resolution at the (sub-)micrometer scale. Non-destructive qualitative and quantitative evaluation of the respective trace elements can be performed on the tissue samples. The elemental maps are compared with conventional differential histological stainings of parallel sections. This method is discussed as a pre-examination tool for subsequent analysis of selected structural sites by diffractive and spectroscopic X-ray nanoprobe techniques and, after additional ultrasectioning, also by transmission electron microscopy

Cu and Ni solubility in high-temperature aqueous fluids

Copper and nickel are generally associated in magmatic sulfide ores formed byimmiscibility in mafic and ultramafic magmas. In contrast, hydrothermal Cu-Ni deposits are uncommon andthese elements usually occur in separate Cu-Fe-sulfide and Ni-Co-Ag-Bi-As-S mineralizations. Among theporphyry-type deposits formed at high temperatures to about 700 °C, there are many copper but no nickeldeposits [1], pointing to a higher solubility of Cu relative to Ni in aqueous fluids at such conditions. The aim ofthis study is to measure the solubilities of Cu and Ni sulfides in high-temperature hydrothermal fluids in-situusing synchrotron-radiation micro-X-ray fluorescence spectrometry.Synthetic CuS or NiS crystals were partly dissolved in aqueous NaCl, NaCl+HCl, or CaCl2 solutions attemperatures of 400 to 600 °C and pressures between 70 and 900 MPa using a modified hydrothermaldiamond-anvil cell with a recess in one diamond [2]. Consecutive XRF spectra of the fluid in the recess werecollected in a confocal mode to exclude signal contributions from the crystals in the sample chamber [3].Equilibrium was assumed if the determined concentrations of the dissolved metals indicated that a steadystate was attained.The measured dissolved Cu concentrations ranged between 22 ppm at 70 MPa, 500 °C and 235 ppm at 306MPa, 600 °C in 0.5 to 1.6 m NaCl solutions. We observed a decrease in Cu concentration with increasingpressure at constant temperature, and for 1.6 m NaCl an increase by a factor of two along an isochore from120 MPa, 500 °C to 306 MPa, 600 °C. Higher Cu solubilities were determined in more concentrated solutions.A preliminary run with a more acidic NaCl+HCl solution (pH ~1) revealed a dramatic increase in the dissolvedCu concentration to 7898 ppm at 170 MPa, 500 °C.The measured dissolved Ni concentrations ranged between 3 ppm at 200 MPa, 500 °C in a 1 m NaCl solutionand 33 ppm at 411 MPa, 500 °C in a 0.75 m CaCl2 solution. A solubility maximum at 500 °C along anisochore was observed for both solutions. The Ni solubility increased with pressure at constant temperature.Experiments with aqueous CaCl2 solutions resulted in higher dissolved Ni concentrations compared to NaClsolutions at similar pressure-temperature conditions.Our experiments suggest that the solubility of Cu and Ni in aqueous fluids is mainly governed by fluidcomposition. For both elements, solubility increased in more chlorine-rich fluids, which could reflect metalchlorinecomplexation. Preliminary results for Cu indicate a strong dependence of the solubility on the pH ofthe fluid. A contrasting solubility behavior of Cu and Ni was observed with increasing pressure, which might beone reason for the difference in hydrothermal ore deposit formation.[1] Barnes (1979) Geochemistry of hydrothermal ore deposits, Wiley. [2] Schmidt and Rickers (2003) Am.Mineral. 88, 288-292. [3] Wilke el al. (2010) J. Synchrotron Rad. 17, 669-675

Correlative Imaging of Melanosoms with Ptychography, X-ray Fluorescence and Light Microscopy

The nature of retinal shielding pigment in the larval eyes of the midge Clunio marinus was studied by high resolution scanning X-ray fluorescence (XRF) analysis correlated with light microscopy and scanning coherent X-ray diffractive imaging (Ptychography). Clunio is known as a unique model system to decipher mechanisms underlying the complex moon-related rhythms. Shielding pigment granules within the photoreceptor cells of their primitive eyes (ocelli) have been shown to change appearance in the same rhythm [1]. The larvae are equipped with simple pigment-cup eyes (ocelli) in which the dense shielding pigment permits light access to the photosensitive rhabdomers only through a narrow pinhole resulting in a diffuse image of the environment. The pigment cup of these eyes becomes transparent during full moon [2]. Within the photoreceptor cells of the ocelli, melanin containing melanosomes form shielding pigment granules. Melanin is a nearly universally occurring pigment in different organisms and organ systems with several known functions; not only as shield against bright light (especially UV-light), but also as reservoir or sink of excessive amounts of metals, and as a component of the immune system [3]. Trace metals have been shown to be indicators of certain steps of melanogenesis. The aim of this study is to combine different non-destructive microscopy techniques to analyse the process of melanogenesis with single melanin granule-resolution

Cu solubility and complexation in high-temperature aqueous fluids

Understanding of the genesis of hydrothermal copper ore deposits requires robust knowledge of the transport properties of Cu in aqueous fluids over a wide range of pressure and temperature. The aim of this study is to combine experimental and computational techniques to investigate the Cu solubility and complexation in sulfur-bearing fluids at high temperatures and pressures. Synthetic CuS crystals were equilibrated in aqueous NaCl ± HCl solutions at 500 and 600 °C and pressures up to 650 MPa using modified hydrothermal diamond-anvil cells [2]. Dissolved Cu concentrations, determined from confocal synchrotron-radiation X-ray fluorescence (XRF) spectrometry at equilibrium conditions, ranged between 25 ppm at 500 °C, 320 MPa and 338 ppm at 600 °C, 445 MPa. Cu solubility increased with temperature along an isochore and decreased with pressure at constant temperature. Chlorine-richer fluids yielded higher dissolved Cu contents. Cu complexation was studied by in-situ X-ray near-edge absorption structure (XANES) and Raman spectroscopy at comparable conditions to the XRF experiments. The XANES spectra are in good agreement with CuCl2– complexes in solution [3], whereas the Raman spectra clearly show a different shape than expected for purely Cu–Cl bands [4]. We tentatively interpret those as mixed Cu–Cl–HS/H2S complexes, which will be verified by ab-initio molecular dynamics simulations with subsequent quasi-normal mode analysis