ALBERT

Description: The origin of yellow cathodoluminescence (CL) in quartz has been investigated by a combination of CL microscopy and spectroscopy, electron paramagnetic resonance (EPR) spectroscopy, and spatially resolved trace-element analysis by laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS). The study shows that the appearance of a ~570 nm (2.17 eV) emission band can be attributed to high oxygen deficiency and local structural disorder in quartz. A proposed luminescence center model implies self-trapped exciton (STE) emission from localized amorphized regions in quartz. Although the high-intensity emission at 570 nm is in general consistent with high concentrations of E ' 1 defects detected by EPR spectroscopy, CL studies with different electron beam parameters and annealing experiments up to 600 °C show a temperature and irradiation dependence of the luminescence related defects excluding the role of E ' 1 centers as direct luminescence activators for the 570 nm emission. The evaluation of geochemical data shows that quartz with yellow CL occurs in low-temperature hydrothermal environment (mostly 〈250 °C) and is related to fast crystallization in an environment with oxygen deficiency.

Description: A systematic investigation of agates from different occurrences in Europe, Northern and Southern America reveals that macrocrystalline quartz and chalcedony within them have an unusually high uranium content. Whereas agates may contain 〉70 ppm of U, quartz from magmatic and metamorphic rocks as well as pegmatite quartz commonly exhibit U concentrations at sub-ppm levels. Spatially resolved trace-element analyses by laser ablation inductively coupled plasma mass spectrometry show that the distribution of U within the agate samples is heterogeneous and coincides with the structural banding. The results indicate that U is incorporated into agate as uranyl ions. These ions, which are bound to the silica surface, are interpreted to originate from the parallel accumulation of Si and U by alteration processes of surrounding host rocks during agate formation. The uranyl ion is the cause of greenish photoluminescence (PL) in agate, which can only be excited by short wavelengths (〈300 nm). The green PL is due to the electron transition from an excited to a ground state of the uranyl ion and is shown by a typical emission line at ~500 nm accompanied by several equidistant lines. These are due to the harmonic vibration of oxygen atoms along the uranyl axis. Luminescence can be detected in samples with a U content down to the 1 ppm level.

Description: Growth and regrowth textures, trace element and oxygen isotope compositions, and water content or species have been studied in alkali feldspars from the late Archaean Closepet igneous bodies. Feldspar crystals grew from mixed magmas that are characterized by a high degree of homogenization. The 3D depiction of trace element distribution indicates that the crystallization process was followed by interaction with fluids. The magmatic system involved in feldspar formation shows non-linear dynamics. The interaction with fluids is also deterministic, but in contrast to magmatic crystallization, it shows an increasing persistency in element behaviour. The degree of persistency of the element activities in both processes has been calculated using the Hurst exponent. The recrystallization (regrowth) process induced by fluids proceeded along crystal fractures and cleavages, causing selective enrichment in large ion lithophile elements (light rare earth elements), Pb, Y, and in various water species. It did not change the feldspar oxygen isotope signature. In turn, the incorporation of hydrogen species into feldspar domains reduced Al–O – –Al defect densities in the structure, decreasing their luminescence. Water speciation shows persistent behaviour during heating, the process being reversible at least up to 600°C. Carbonate crystals with a mantle isotope signature are associated with the re-equilibrated feldspar domains. The feldspar compositions, the abundance of water species in them and the refractory nature of the residuum after heating, the unchanged oxygen isotopes and the mantle signature of co-precipitated carbonates testify that the observed recrystallization has taken place at temperatures above 600°C with H 2 O–CO 2 fertile, mantle-derived fluids. The paper draws special attention to some methodological aspects of the problem. The multi-method approach used here (major element, trace element and isotope geochemistry, infra-red, cathodoluminescence, 3D depiction of geochemical data and fractal statistics) may help to recognize and separate the various processes throughout the alteration history of the pluton.

Description: 〈p〉The chemical composition of different rocks as well as volatile-bearing and volatile-free minerals has been used to assess the presence of fluids in the Closepet batholith and to estimate the intensity of the fluid–rock interactions. The data were processed using polytopic vector analysis (PVA). Additional data include measurements of water content in the structure of volatile-free minerals and an examination of growth textures. The composition of mineral domains indicated formation/transformation processes with common fluid–mineral interactions. In general, the results suggested that the processes occurred in a ternary system. Two end-members were likely magmas and the third was enriched in fluids. In contrast, analysis of the apatite domains indicated that they likely formed/transformed in a more complex, four-component system. This system was fluid-rich and included hybrid magma with a large mafic component. PVA implies that the fluids do not appear to come from one source, given their close affinity and partial association with mantle-derived fluids. A dynamic tectonic setting promoting heat influx and redistribution, and interaction of fluids suggests that the formation/transformation processes of minerals and rocks occurred in a hot-spot like environment.〈/p〉 〈p〉〈b〉Supplementary material:〈/b〉 〈a href="https://doi.org/10.6084/m9.figshare.c.4356926"〉Fig. S1 (〈b〉a〈/b〉) Representative raw-, (〈b〉b〈/b〉) fitted- and (〈b〉c〈/b〉) deconvolved-IR spectrum; 〈inter-ref locator="https://doi.org/10.6084/m9.figshare.c.4356926" locator-type="url"〉Table S1〈/inter-ref〉 Whole rock analyses of Closepet granite available at 〈inter-ref locator="https://doi.org/10.6084/m9.figshare.c.4356926" locator-type="url"〉https://doi.org/10.6084/m9.figshare.c.4356926〈/inter-ref〉〈/a〉〈/p〉

Description: Radiation-induced damage in quartz from the overlying Athabasca Supergroup sandstones and the basement host rocks at the Arrow uranium deposit in the southwestern margin of the Athabasca basin, Saskatchewan, has been investigated by electron paramagnetic resonance (EPR) spectroscopy as well as cathodoluminescence (CL) imaging and spectroscopy. Powder EPR spectra confirm that quartz from the Arrow deposit contains a suite of radiation-induced defects, including characteristic silicon vacancy hole centers formed from bombardment of α particles emitted from the radioactive decay of U, Th, and their daughter isotopes. The EPR intensity distribution of α particle-induced defects in detrital quartz close to the sandstone–basement unconformity suggests that uranium-bearing fluids at Arrow are restricted to areas directly above the basement-hosted mineralization. Pink quartz in the basement, which occurs as veins and breccias in spatial association with uranium mineralization, is characterized by elevated, homogeneously distributed radiation-induced defects, suggesting its crystallization from uranium-bearing fluids most likely linked to the main mineralization event. Smoky quartz in veins and cavities often exhibits characteristic α particle-induced CL rims, which crosscut the growth zoning and apparently record late uranium remobilization. Abundant radiation-induced defects in the basement at the Arrow deposit are restricted to quartz within ~7 m from uranium mineralization, confirming structurally controlled fluid flows. These results highlight the application of radiation-induced defects in quartz for determining the loci of uranium-bearing fluids.

Description: Silicified Agathoxylon -type wood of Late Palaeozoic age was characterized by means of cathodoluminescence (CL) and LA-ICP-MS of the quartz mass, which was found to contain wakefieldite, characterized by electron-microprobe (EMP) analysis, Raman microspectroscopy and X-ray diffraction. Although former organic matter is almost absent, plant anatomy served as the template for the quartz mass texture. Two generations of quartz mass were distinguished; the large proportion of the silicified wood consisting of brownish α-quartz with a dark reddish CL emission, and the minor portion of whitish ‘leached’ wood with a short-lived (transient) blue CL. On the outer edge, a silicified texture of formerly slightly humified wood also emits a dark reddish CL. Likely the wood specimen has been fossilized and diagenetically altered in several steps. The marginal part had been humified (reductively degraded) before the initial stages of silicification. The LA-ICP-MS analyses revealed chemical differences in all three distinct parts. The quartz mass relatively enriched in REEs and As and giving the dark reddish CL is interpreted as a primary diagenetic mineral mass. Whitish zones relatively depleted in U and V, and enriched in Al, Li, Rb, Cu, and Sr producing the blue CL would then be a secondary diagenetic overprint. An EMP/WDS analysis identified As-rich xenotime-(Y) and a solid solution of wakefieldite–(Ce) and wakefieldite–(Y), which locally enclose individual silicified tracheids. Wakefieldite, identified in silicified plant tissue for the first time, was most likely formed as a secondary mineral during post-depositional diagenesis. The mineral diagenesis did not erase the original anatomy of the wood.