Mapping the distribution of calcium on apple tissue with proton-induced x-ray emission ? after application of additional pre-harvest foliar or soil calcium

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Mapping the distribution of calcium in apple tissue with proton-induced x-ray emission - after application of additional foliar or soil calcium.

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Micro-PIXE investigation of bean seeds to assist micronutrient biofortification

This study compares the distribution and concentrations of micro- and macronutrients in different bean cultivars with the aim of optimizing the biofortification, a sustainable approach towards improving dietary quality. Micro-PIXE was used to reveal the distribution of Fe, Zn, Mn, Ca, P, S in seeds of common beans (Phaseolus vulgaris) and runner beans (Phaseolus coccineus). Average concentrations of elements in different tissues were obtained using ICP-AES. The highest concentrations of Zn in the studied beans were found in the embryonic axis, but an increased concentration of this element was also detected in the provascular bundles of the cotyledons. The first layer of cells surrounding provascular bundles accumulated high concentrations of Fe, while the next cell layer had an increased concentration of Mn. The analysis showed that the provascular bundles and the first cell layers surrounding them could have a significant role in the storage of important seed micronutrients Zn, Fe, and Mn. This information has important implications for molecular biology studies aimed at seed biofortification

The Origin of the Gold and Uranium Ores of the Black Reef Formation, Transvaal Supergroup, South Africa

The Black Reef Formation is a laterally extensive sedimentary succession at the base of the Transvaal Supergroup. The quartz-pebble conglomerates host erratic concentrations of gold and uranium; however, in areas that are located spatially above the gold and uranium-bearing reefs of the Witwatersrand Supergroup, the concentrations can reach ore-grade. Although the depositional environment was similar to that of the Witwatersrand Supergroup, the processes that lead to the high gold and uranium concentrations in the Black Reef were quite different. The Black Reef experienced intense, post-depositional hydrothermal alteration by circulating aqueous and hydrocarbon fluids (oils) that deposited large volumes of native gold, uranium minerals and pyrobitumen. The gold, which is filamentous, is concentrated along As-Ni-rich surfaces of pyrite, and with uraninite in pyrobitumen. In both environments, the gold is interpreted to be the product of chemically-triggered precipitation from hydrothermal fluid(s)..

Trace element chemistry of pyrobitumen from the Tau-Tona mine in South Africa

High-grade gold and uranium mineralization in the Witwatersrand basin is intimately associated with pyrobitumen, implying that hydrocarbons may have played a role in the genesis of these ores. The nature of the pyrobitumen in the Carbon Leader Reef was therefore investigated to determine if hydrocarbons were essential to the ore-forming process. The relative proportions of trace elements in pyrobitumen seams and nodules are, in large part, similar to those of organic-rich shales located within the sedimentary succession. This indicates a strong genetic relationship between the pyrobitumen and the shales. A network of veins and veinlets filled with pyrobitumen, and the occurrence of oil inclusions in detrital and authigenic quartz grains, provide compelling evidence that the pyrobitumen was derived from a mobile (liquid hydrocarbon) precursor that circulated in the Carbon Leader Reef. Uranium, Au, Sb, Pb, Ag, Te, Th, Bi, Se and W are enriched relative to their concentrations in the shales. This is particularly the case for U and Au. The pervasive and relatively homogeneous distribution of the uranium is consistent with the presence of ubiquitous, submicroscopic uraninite in the pyrobitumen documented in an earlier study. In contrast, the distribution of the gold is heterogeneous, indicating the presence of irregularly distributed gold micrograins. These grains are concentrated mainly in the interstices between pyrobitumen nodules. Secondary minerals, such as brannerite, monazite-(Ce) and galena, are also concentrated in these interstices. On the basis of this study, we propose that intrabasinal shale units of the Witwatersrand Supergroup were the source for the pyrobitumen in the Carbon Leader Reef. These shales produced and released liquid hydrocarbons during the burial of the sedimentary succession. Phyllosilicates enriched in trace metals were transferred from the shales into the newly produced liquid hydrocarbons and were transported stratigraphically upward by the latter into the Carbon Leader Reef. During migration, the liquid hydrocarbons dissolved detrital uraninite present in the basin, adding to the uranium budget. The liquid hydrocarbons were converted into pyrobitumen in response to further burial, and precipitated uraninite nanocrystals. Post-depositional, hydrothermal fluids interacted with the hydrocarbons and deposited gold by reduction on hydrocarbon surfaces. The interaction of these fluids with the hydrocarbons may have released U, Th, REE, Pb and Ti from the hydrocarbons and triggered the formation of secondary brannerite, monazite-(Ce) and galena. The results of this study provide convincing evidence that the hydrocarbon liquids that formed the pyrobitumen seams in the Carbon Leader Reef played an essential role in the remobilization and redeposition of uranium and gold, respectively, in the Witwatersrand Supergroup